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(11) | EP 1 041 862 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
| published in accordance with Art. 158(3) EPC |
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| (54) | APPARATUS FOR LIGHTING DISCHARGE LAMP |
| (57) A discharge lamp lighting device for lighting a discharge lamp (5c) within a discharge
lamp load circuit (5) by converting a direct current supplied from a direct current
power source (1) into a high frequency current by an inverter circuit (2) and using
the high frequency current, comprising a current detecting circuit (6) for detecting
a current supplied to the discharge lamp load circuit (5), a reference voltage circuit
(14) for outputting a plurality of different reference voltages, an error amplifier
(9) for producing a control signal based on an output from the current detecting circuit
(6) and an output from the reference voltage circuit (14), an inverter driving circuit
(3) for controlling the inverter circuit (2), based on the control signal from the
error amplifier (9), to regulate the current to be supplied to the discharge lamp
load circuit (5), and reference voltage selecting means (19) for selecting a reference
voltage output from the reference voltage circuit (14). The discharge lamp lighting
device is applicable to the discharge lamp having a plurality of different rated values. |
Technical Field
[0001] This invention relates to a discharge lamp lighting device for lighting a discharge lamp by high frequency electric power from an inverter circuit.
Related Art
[0002] Fig. 24 shows a circuit diagram of a conventional discharge lamp lighting device. In the figure, reference numeral 1 denotes a direct current power source which provides the direct current by rectifying and smoothing the alternating current from the commercial power supply. Reference numeral 2 denotes an inverter circuit consisting of the switching elements 2a and 2b such as MOS FET. Reference numeral 3 denotes an inverter driving circuit for driving the inverter circuit 2. Reference numeral 4 denotes a coupling capacitor which is connected to the output side of the inverter circuit 2. Reference numeral 5 denotes a discharge lamp load circuit consisting of a choke coil 5a and a starting capacitor 5b and a discharge lamp 5c. Reference numeral 6 denotes a current detecting circuit for detecting the net current to be supplied to the discharge lamp load circuit 5, the current detecting circuit being comprised of a detecting resistor 7 and an integrating circuit 8 (high-pass filter) having a resistor 8a and a capacitor 8b. Reference numeral 9 denotes an error amplifier. Reference numerals 10a and 10b denote an integrating resistor and an integrating capacitor in the error amplifier 9, respectively. At the inverted input end of the error amplifier 9, an output voltage of the integrating circuit 8 is input, and at the non-inverted input end, a reference voltage is input from a reference voltage circuit 14 having a stabilized direct current power source for reference voltage 11 and the dividing resistors 12, 13. A difference between these two voltages is amplified by the error amplifier 9, and fed back as a control signal to the inverter driving circuit 3.
[0003] A configuration example of the direct current power source 1 for providing the direct current from the commercial power supply is shown in Fig. 25. As shown in the figure, the alternating current output from a commercial power supply 1a is full-wave rectified by a diode bridge 1b, then smoothed by a smoothing capacitor 1c, and output to the load circuit as the direct current.
[0004] The operation of the conventional discharge lamp lighting device as shown in Fig. 24 will be described below. In the figure, if the inverter circuit 2 is driven by the inverter driving circuit 3, a direct current supplied from the direct current power source 1 is converted into a high frequency electric current, which is then supplied to the discharge lamp load circuit 5 to light the discharge lamp 5c. Since the coupling capacitor 4 is connected to the discharge lamp load circuit 5, an alternating current flows through the detecting resistor 7 in a forward or reverse direction (regenerative direction) when the switching elements 2a, 2b are turned on and off. If the circuit loss is ignored, this effective component (sum of current in the forward and reverse directions, hereinafter referred to as a net current) is consumed as electric power by the discharge lamp 5c.
[0005] On the other hand, an electric current is detected by the detecting resistor 7, and integrated as the sum of the current (net current) in the forward and reverse directions by the integrating circuit 8. A corresponding voltage is input into the inversion-input end of the error amplifier 9. At the non-inversion input end of the error amplifier 9, a reference voltage is input from the reference voltage circuit 14, the reference voltage being generated by dividing the voltage of the direct current power source 11 for reference voltage in the reference voltage circuit 14 by the dividing resistors 12 and 13. In the error amplifier 9, a difference between this reference voltage and an output voltage from the integrating circuit 8 is amplified, integrated by the resistor 10a and the capacitor 10b for integration, and fed back as a control signal to the inverter driving circuit 3. The inverter driving circuit 3 controls the switching frequency of the inverter circuit 2 to adjust the high frequency current to be supplied from the direct current power source 1 to the discharge lamp load circuit 5. Thus, the high frequency current to be supplied to the discharge lamp load circuit 5 is controlled by the switching frequency of the inverter circuit 2. The switching frequency of the inverter circuit 2 is controlled so that the output voltage of the integrating circuit 8 may be held to be equal to the reference voltage. When the output voltage of the direct current power source 1 is constant, the electric power to be supplied to the discharge lamp 5c can be maintained at a fixed value.
[0006] However, in the conventional discharge lamp lighting device as shown in Fig. 24, the reference voltage output from the reference voltage circuit 14 was predetermined for each lighting device. For this reason, in order to cope with discharge lamp having different rated values, it was necessary to prepare several kinds of parts for the choke coil 5a or starting capacitor 5b to change the circuit constants in accordance with the rated value of a discharge lamp 5c attached. Or, when the group of products is lined up, it was necessary to prepare for several kinds of discharge lamp lighting devices in accordance with the rated values of the discharge lamps 5c. As a result, there was a problem that the parts management at the time of production or the inventory control of products becomes troublesome, leading to a problem of higher management cost.
[0007] After installation of a discharge lamp lighting device, when the discharge lamp was changed to a discharge lamp having a different rated value for the purpose of increasing the illumination or saving the power, it was required to change or install the discharge lamp lighting device newly, leading to a problem of higher purchasing cost or increased operating cost owing to the change of the discharge lamp lighting device.
[0008] This invention has been achieved to resolve the above-mentioned problems, and a first object of this invention is to provide a discharge lamp lighting device which is applicable to a plurality of discharge lamps having different rated values, wherein the management cost including the parts management at the time of production can be reduced.
[0009] A second object of this invention is to provide a discharge lamp lighting device which can cope with changing the rated value of a discharge lamp even after installation.
[0010] A third object of this invention is to provide a discharge lamp lighting device which allows the rated value of a discharge lamp to be easily changed.
[0011] A fourth object of this invention is to provide a discharge lamp lighting device for automatically changing the rated value of a discharge lamp to facilitate changing the rated value of the discharge lamp, wherein the rated value can be securely changed, even without sufficient knowledge of electricity, to prevent an excessive current beyond the rated value from flowing through the discharge lamp to impair the discharge lamp.
[0012] A fifth object of this invention is to provide a discharge lamp lighting device which can be adapted to a discharge lamp per se having different rated values.
[0013] Further, a sixth object of this invention is to provide a discharge lamp lighting device which is superior in respect of comfortable sense when in use, while suppressing the abrupt fluctuation of brightness (light output) caused by change of the rated value.
Disclosure of the Invention
[0014] A discharge lamp lighting device according to this invention comprises a direct current power source, an inverter circuit for converting a direct current supplied from the direct current power source into high frequency current, a discharge lamp load circuit for lighting a discharge lamp by high frequency current from the inverter circuit, a current detecting circuit for detecting an electric current supplied from the inverter circuit to the discharge lamp load circuit, a reference voltage circuit for generating a plurality of different reference voltages, an error amplifier for producing a control signal based on an output from the current detecting circuit and a reference voltage output from the reference voltage circuit, an inverter driving circuit for driving the inverter circuit based on the control signal from the error amplifier in such a way as to adjust the electric current supplied to the discharge lamp load circuit to a current value corresponding to the reference voltage output from the reference voltage circuit, and reference voltage selecting means for selecting the reference voltage to be output from the reference voltage circuit.
[0015] Also, the discharge lamp lighting device according to this invention is configured such that the reference voltage selecting means selects a reference voltage to be output from the reference voltage circuit by manual operation.
[0016] Also, the discharge lamp lighting device according to this invention is configured such that the reference voltage circuit comprises a reference voltage generator for generating a plurality of different reference voltages corresponding to the preset rated values of a discharge lamp, the reference voltage generator having a direct current power source for reference voltage and the dividing resistors for dividing a voltage from the direct current power source for reference voltage, wherein the reference voltage selecting means selects a reference voltage for output from among the plurality of reference voltages generated by the reference voltage generator.
[0017] Also, the discharge lamp lighting device according to this invention is configured such that the reference voltage circuit comprises a direct current power source for reference voltage, dividing resistors for dividing a voltage from the direct current power source for reference voltage, and reference voltage selecting means connected in parallel with the dividing resistors, wherein the reference voltage selecting means selects a reference voltage output from the reference voltage circuit by choosing the dividing resistors to be bypassed.
[0018] The discharge lamp lighting device according to this invention uses a jumper wire as the reference voltage selecting means.
[0019] The discharge lamp lighting device according to this invention is configured such that the jumper wire is provided on a circuit board with the error amplifier packaged therein, and a work hole is drilled on the circuit board with the jumper wire mounted to allow the confirmation of the set conditions of the jumper wire and the cutting thereof through the work hole.
[0020] The discharge lamp lighting device according to this invention is configured such that a reference voltage circuit is provided on the circuit board with the error amplifier packaged therein.
[0021] The discharge lamp lighting device according to this invention is configured such that the circuit board with the reference voltage selecting means mounted therein is contained within a metallic case having an opening portion formed to allow the confirmation of the set conditions of the reference voltage selecting means and the alteration of settings through the opening portion.
[0022] The discharge lamp lighting device according to this invention is configured such that the operation parts of reference voltage selecting means are arranged in the order of reference voltages.
[0023] The discharge lamp lighting device according to this invention is configured such that the reference voltage selecting means automatically select a reference voltage adapted to a rated value of a discharge lamp attached in the discharge lamp load circuit by discriminating this rated value, the reference voltage being output from the reference voltage circuit.
[0024] The discharge lamp lighting device according to this invention is configured such that initial frequency setting means for setting a switching frequency of the inverter circuit is provided, and the reference voltage selecting means discriminates the rated value of a discharge lamp attached in the discharge lamp load circuit, based on an output from the current detecting circuit, when operated at the switching frequency set by the initial frequency setting means.
[0025] The discharge lamp lighting device according to this invention is configured such that the reference voltage selecting means comprises a switch control portion having an A/D converter for converting an output of the current detecting circuit into digital data, a storing circuit for storing a current value of a discharge lamp corresponding to the switching frequency set by the initial frequency setting means, and an operation circuit for discriminating the rated value of the discharge lamp attached by comparison between digital data detected by the A/D converter and the current value stored in the storing circuit to output a control signal, and a switch unit for selecting a reference voltage output from the reference voltage circuit in accordance with the control signal from the operation circuit.
[0026] The discharge lamp lighting device according to this invention is configured such that frequency detecting means for detecting a switching frequency of the inverter circuit is provided, and the reference voltage selecting means discriminates the rated value of a discharge lamp attached in the discharge lamp load circuit, based on the switching frequency output from the frequency detecting means.
[0027] The discharge lamp lighting device according to this invention is configured such that the reference voltage selecting means discriminates the rated value of a discharge lamp attached in the discharge lamp load circuit, based on the switching frequency output from the frequency detecting means and the current value output from the current detecting circuit and supplied to the discharge lamp load circuit.
[0028] The discharge lamp lighting device according to this invention is configured such that the reference voltage selecting means discriminates the rated value of a discharge lamp attached in the discharge lamp load circuit, based on the reference voltage to be output from the reference voltage circuit and the switching frequency output from the frequency detecting means.
[0029] The discharge lamp lighting device according to this invention is configured such that the reference voltage selecting means comprises a switch control portion having an A/D converter for converting an output of the frequency detecting circuit into digital data, a storing circuit for storing a switching frequency of the inverter circuit, and an operation circuit for discriminating the rated value of a discharge lamp attached by comparison between digital data detected by the A/D converter and the switching frequency stored in the storing circuit to output a control signal, and a switch unit for selecting the reference voltage output from the reference voltage circuit in accordance with the control signal from the operation circuit.
[0030] The discharge lamp lighting device according to this invention is configured such that at the initiation of the discharge lamp lighting device, the reference voltage selecting means selects a reference voltage corresponding to a minimum current value from among the reference voltages which can be output from the reference voltage circuit.
[0031] The discharge lamp lighting device according to this invention is configured such that in changing the reference voltage, the reference voltage selecting means selects a reference voltage in the order of the reference voltages closer to that selected at the time of change.
[0032] The discharge lamp lighting device according to this invention is configured such that the reference voltage selecting means is provided with external setting means for manually setting a reference voltage to be output from the reference voltage circuit.
[0033] The discharge lamp lighting device according to this invention is configured such that there is provided a buffer circuit for continuously changing the reference voltage for input into the error amplifier between the reference voltage circuit and the error amplifier.
[0034] Also, the discharge lamp lighting device according to this invention is configured such that the reference voltage circuit comprises a reference voltage generator for generating a plurality of different reference voltages corresponding to the preset rated values of a discharge lamp, the reference voltage generator having a direct current power source for reference voltage and the dividing resistors for dividing a voltage from the direct current power source for reference voltage, wherein the reference voltage selecting means comprises a switch unit for selecting a reference voltage for output from among the plurality of reference voltages generated by the reference voltage generator.
[0035] Also, the discharge lamp lighting device according to this invention is configured such that the reference voltage circuit comprises a direct current power source for reference voltage, the dividing resistors for dividing a voltage from the direct current power source for reference voltage, and a switch unit consisting of the switches connected in parallel with the dividing resistors, wherein the reference voltage selecting means selects a reference voltage to be output from the reference voltage generator by choosing the switches within the switch unit and the dividing resistors for bypass.
[0036] Also, the discharge lamp lighting device according to this invention is configured such that the reference voltage circuit is provided on a circuit board with the error amplifier packaged therein, and the circuit board with the reference voltage circuit and the error amplifier packaged therein is contained within a metallic case.
Brief Description of the Drawings
[0037]
Fig. 1 is a circuit diagram showing the configuration of a circuit according to an embodiment 1 of this invention.
Fig. 2 is a circuit diagram showing the configuration of a circuit according to an embodiment 2 of this invention.
Fig. 3 is a circuit diagram showing the configuration of a circuit according to an embodiment 3 of this invention.
Fig. 4 is a schematic view showing the mounting state on a circuit board according to the embodiment 3 of this invention.
Fig. 5 is a schematic view showing another mounting state on a circuit board according to the embodiment 3 of this invention.
Fig. 6 is a circuit diagram showing the configuration of a circuit according to an embodiment 4 of this invention.
Fig. 7 is a flowchart showing the operation according to the embodiment 4 of this invention.
Fig. 8 is an explanatory view showing a method of discriminating the rated value of discharge lamp according to the embodiment 4 of this invention.
Fig. 9 is a characteristic curve showing the relation between the reference voltage and the consumption power according to the embodiment 4 of this invention.
Fig. 10 is a circuit diagram showing the configuration of a circuit according to an embodiment 5 of this invention.
Fig. 11 is a flowchart showing the operation according to the embodiment 5 of this invention.
Fig. 12 is a circuit diagram showing the configuration of a circuit according to an embodiment 6 of this invention.
Fig. 13 is a circuit diagram showing the configuration of a circuit according to an embodiment 7 of this invention.
Fig. 14 is a circuit diagram showing the configuration of a circuit according to an embodiment 8 of this invention.
Fig. 15 is a circuit diagram showing the configuration of a circuit according to an embodiment 9 of this invention.
Fig. 16 is a flowchart showing the operation according to the embodiment 9 of this invention.
Fig. 17 is an explanatory view showing a method of discriminating the rated value of discharge lamp according to the embodiment 9 of this invention.
Fig. 18 is a characteristic chart showing the relation between the reference voltage and the consumption power according to the embodiment 9 of this invention.
Fig. 19 is a circuit diagram showing the configuration of a circuit according to an embodiment 10 of this invention.
Fig. 20 is an explanatory view showing a method of discriminating the rated value of discharge lamp according to the embodiment 10 of this invention.
Fig. 21 is a circuit diagram showing the configuration of a circuit according to an embodiment 11 of this invention.
Fig. 22 is a circuit diagram showing the configuration of a circuit according to an embodiment 12 of this invention.
Fig. 23 is a circuit diagram showing the configuration of a circuit according to an embodiment 13 of this invention.
Fig. 24 is a circuit diagram showing the configuration of a conventional discharge lamp lighting device.
Fig. 25 is a circuit diagram showing the configuration of a direct current power source in the conventional discharge lamp lighting device.
Fig. 26 is a waveform chart of the current flowing through a detecting resistor in the conventional discharge lamp lighting device.
Best Mode for Carrying Out the Invention
[0038] The embodiments of the present invention will be described below with reference to the accompanying drawings.
Embodiment 1
[0039] Fig. 1 is a circuit diagram showing the configuration of a discharge lamp lighting device according to an embodiment 1 of this invention. In the figure, reference numeral 1 denotes a direct current power source which provides the direct current by rectifying and smoothing the alternating current from the commercial power supply. Reference numeral 2 denotes an inverter circuit consisting of the switching elements 2a, 2b such as MOS FET. Reference numeral 3 denotes an inverter driving circuit for driving the inverter circuit 2, the inverter driving circuit comprising a voltage-controlled oscillation circuit (hereinafter designated as "VCO") and a driver. Reference numeral 4 denotes a coupling capacitor which is connected to the output side of the inverter circuit 2. Reference numeral 5 denotes a discharge lamp load circuit consisting of a choke coil 5a, a starting capacitor 5b and a discharge lamp 5c. Reference numeral 6 denotes a current detecting circuit for detecting the net current flowing through the discharge lamp load circuit 5, the current detecting circuit being comprised of a detecting resistor 7 and an integrating circuit 8 (high-pass filter) having a resistor 8a and a capacitor 8b. Reference numeral 9 denotes an error amplifier. Reference numerals 10a and 10b denote a resistor and a capacitor, respectively, which are used for integration in the error amplifier 9. At the inversion input end of the error amplifier 9, an output voltage of the integrating circuit 8 is input, and at the non-inversion input end, a reference voltage is input from a reference voltage circuit 14. A difference between these two voltages is amplified by the error amplifier 9, and fed back as a control signal to the inverter driving circuit 3.
[0040] In this embodiment 1, the reference voltage circuit 14 comprises a reference voltage generator 15 for generating three preset reference voltages corresponding to the rated values (e.g., 32W, 40W, 45W) of the discharge lamp 5c by dividing a voltage of a stabilized direct current power source for reference voltage 11 by the dividing resistors 12a, 12b, 12c and 13, and a switch 20 which is reference voltage selecting means 19 for selecting a reference voltage adapted to a rated value of the discharge lamp 5c from among three reference voltages generated by the reference voltage generator 15 to input it into the error amplifier 9.
[0041] The operation of this embodiment 1 will be described below. In the figure, if the inverter circuit 2 is driven by the inverter driving circuit 3, a direct current supplied from the direct current power source 1 is converted into a high frequency electric current, which is then supplied to the discharge lamp load circuit 5 to light the discharge lamp 5c.
Since the coupling capacitor 4 is connected to the discharge lamp load circuit 5, an alternating current flows through the discharge lamp load circuit 5 in a forward direction (from the direct current power source 1 to switching element 2a to coupling capacitor 4 to discharge lamp load circuit 5 to detecting resistor 7 to direct current power source 1) or a reverse direction (from the coupling capacitor 4 to switching element 2b to discharge lamp load circuit 5 to coupling capacitor 4) when the switching elements 2a and 2b are turned on and off.
[0042] On the other hand, an alternating current flows through the detecting resistor 7, as in Fig. 26, and integrated as the sum of the current (net current) in the forward and reverse directions by the integrating circuit 8. A corresponding voltage is input into the inversion-input end of the error amplifier 9. If the circuit loss is ignored, an effective component (net current) of this alternating current is consumed as electric power in the discharge lamp 5c, as in the conventional example.
[0043] At the non-inversion input end of the error amplifier 9, a voltage is input (an uppermost switch being on in Fig. 1), a reference voltage corresponding to the rated value of the discharge lamp 5c attached being selected by the switch 20 from among three reference voltages generated by the reference voltage generator 15 in the reference voltage circuit 14. In the error amplifier 9, a difference between this reference voltage and an output voltage from the integrating circuit 8 is amplified, integrated by the resistor 10a and the capacitor 10b for integration, and fed back as a control signal to the inverter driving circuit 3. The inverter driving circuit 3 controls the switching frequency of the inverter circuit 2 so that the output voltage of the integrating circuit 8 be equal to the reference voltage. Then, a high frequency current (net current) adapted to the rated value of the discharge lamp 5c is supplied from the direct current power source 1 to the discharge lamp load circuit 5 and maintained at a fixed value.
[0044] According to this embodiment 1, a net current flowing through the discharge lamp load circuit 5 can be controlled by the reference voltage input from the reference voltage circuit 14. A plurality of different reference voltages can be output from the reference voltage circuit 14 by switching the switch 20. The net current supplied to the discharge lamp load circuit 5 can be maintained substantially at a constant value adapted to the rated value of the discharge lamp 5c. By switching the switch 20, the same discharge lamp lighting device can be applied to a discharge lamp having different rated values. With this, there is no need of preparing for various kinds of parts or discharge lamp lighting devices, leading to reduction in the management cost including the parts management at the time of production.
[0045] The discharge lamp lighting device can be adapted to the discharge lamp having different rated values by switching the switch 20, even after installing it. Therefore, there is no need of changing or installing the discharge lamp lighting device newly, leading to reduction in the purchasing expense or operation cost.
[0046] Further, the reference voltages generated by the reference voltage generator 15 are set corresponding to the preset rated values (e.g., 32W, 40W, 45W) of the discharge lamp 5c. Therefore, there is no need of adjusting the reference voltage. And the switch 20 is used as the reference voltage selecting means. Hence, it is possible to provide a discharge lamp lighting device which is easy to change the rated value. Also, the reference voltage can be changed as many times as desired by means of the switch 20. Therefore, the discharge lamp lighting device is usable over the long term and superior in the resource efficiency.
Embodiment 2
[0047] Fig. 2 shows an embodiment 2 of this invention in which the switch 20 is connected in parallel with the dividing resistors 12a, 12b, 12c. In the figure, reference numeral 16 denotes a dividing resistor connected in series to the dividing resistors 12a, 12b, 12c and a dividing resistor 13. In this embodiment 2, the switch 20 is connected in parallel with the dividing resistors 12a, 12b, 12c. By turning on or off each switch point of the switch 20, each of the dividing resistors 12a, 12b, 12c is bypassed, so that the division ratio of the dividing resistors across an output end of the reference voltage connected to the error amplifier 9 may be varied to change the reference voltage. Note that the same or like parts as in Fig. 1 are indicated by the like numerals, and are not described. Also, the operation is exactly the same as that in the embodiment 1, and is not described.
[0048] According to the embodiment 2, in addition to the effects of the embodiment 1, there are the following effects. Since the input impedance of the error amplifier 9 is typically very large, a minute current will continuously flow over the long term through each contact of the switch 20 in the embodiment 1. In order to maintain the value of reference voltage stable over the long term under such conditions, it is required to suppress the resistance at each contact as completely as possible against a secular change. For this purpose, the use of an expensive switch plated with gold at the contact was required. However, since the switch is connected in parallel with the dividing resistors 12a, 12b, 12c, according to this embodiment 2, a current from the direct current power source for reference voltage 11 through the dividing resistors will flow through the switch 20. Therefore, it is possible to have a current value necessary to be stable against the secular change. The switch 20 which is relatively cheap can be used. In addition to an advantage in the respect of cost, the reliability is increased owing to high endurance against the secular change.
[0049] In Fig. 2, each switch point of the switch 20 is provided in parallel between the upstream side of the dividing resistor 12a, 12b, 12c and the ground side. But each switch point of the switch 20 may be connected to bypass the dividing resistor 12a, 12b, 12c. In this case, various kinds of division ratios can be attained by changing over each switch point. As a result, it is possible to provide a discharge lamp lighting device capable of coping with more rated values with a smaller number of dividing resistors.
Embodiment 3
[0050] Fig. 3 shows an embodiment 3 in which the reference voltage selecting means 19 is constructed using a conducting wire (jumper wire) 21. In the figure, reference numeral 21 denotes the conducting wire (jumper wire), in which by connecting the error generator 9 at each output end of the reference voltage generator 15 via the conducting wire (jumper wire) 21, a reference voltage adapted to a rated value of the discharge lamp 5c attached therein can be selected from among three reference voltages generated by the reference voltage generator 15 and input into the error amplifier 9. Note that the same or like parts as in Fig. 1 are indicated by the like numerals, and are not described. Also, the operation is exactly the same as in the embodiment 1, and is not described.
[0051] Figs. 4A and 4B are a cross sectional view and a plan view showing a state where the conducting wire 21 is specifically mounted to the circuit board 22 in the embodiment 3. In the figure, reference numeral 21 denotes the conducting wire. Reference numeral 22 denotes the circuit board onto which the conducting wire 21 is mounted. Reference numeral 23 denotes a work hole which is drilled in a region of the circuit board 22 where the conducting wire 21 is mounted. By virtue of this work hole 23, it is possible to visually check and cut off the conducting wire 21 from the back (opposite side of a mounting face) of the circuit board 22. In this embodiment 3, a reference voltage circuit 14 consisting of the conducting wire 21 and the reference voltage generator 15 is mounted on the same circuit board 22 as the error amplifier 9. This circuit board 22 is accommodated within a case 24 made of metal.
[0052] According to this embodiment 3 of the invention, in addition to the effects of the embodiment 1, there are the following effects. As already indicated in the embodiment 2, a minute current continues to flow through each contact of the switch 2 over the long term in the embodiment 1. In order to maintain a stable operation against the secular change under such conditions, it was required to use an expensive switch plated with gold at each contact. However, according to this embodiment 3, the cheap jumper wire 21 can be substituted for it. Therefore, there is not only an advantage in the respect of cost, but also an effect that the reliability is enhanced owing to high endurance against the secular change.
[0053] Since the reference voltage circuit 14 including the reference voltage selecting means 19 such as the jumper wire 21 is mounted on the same circuit board 22 having the error amplifier packaged, a minute current flowing through the conducting wire 21 is prevented from fluctuating under the influence of disturbance or noise to make the output of the discharge lamp 5c unstable. Thereby, there is an advantage that the noise measures expense can be less than when the reference voltage selecting means 19 is mounted on another board.
[0054] Further, since the circuit board 22 is accommodated within the case 24, there is less risk that the circuit board 22 may be damaged when exchanging the discharge lamp 5c. Also, if the case 24 is formed of the metal, the noise influence due to discharging of the discharge lamp 5c can be further reduced.
[0055] In this embodiment 3, since the work hole 23 is drilled in the region of the circuit board 22 where the conducting wire is mounted, it is possible to visually check the arrangement of the conducting wire 21 and the selected state of the reference voltage, even after a component face of the circuit board 22 is covered with the case 24 and without removing the case 24. If needed, the conducting wire 21 can be cut off through the work hole 23 to change over to a rated value of the discharge lamp 5c adaptable.
[0056] In Fig. 4, the conducting wire 24 is visually checked through the work hole 23 drilled in the circuit board 22. However, an opening portion 25 may be provided in a region corresponding to the mounting position of the conducting wire 21 as shown in Fig. 5. In this case, the selected state of the reference voltage can be visually checked or the reference voltage can be changed with the case 24 covered, even if the switch 20 is used as the reference voltage selecting means 19. Also, the opening portion 25 may be provided at another position to manipulate the switch 20 by use of a cord or the like.
[0057] In the embodiments 1 to 3, the reference voltage selecting means 19 is the switch 20 or the conducting wire (jumper wire) 21. But a semiconductor switch may be used. Further, at least one of the dividing resistors 12a, 12b, 12c and 13 may be constituted of a variable resistor and the reference voltage output from the reference voltage circuit 14 may be changed by altering the resistance of this variable resistor.
[0058] Also, the arrangement of operation parts of the reference voltage selecting means 19 such as the switch 20 (including a rotary switch or the like) or the conducting wire (jumper wire) 21 (viz., arrangement of the operation parts of the switch 20 or the jumper wire 21) may be made in the order of rated values for the discharge lamp to be adapted. Thereby, there is lesser failure in operating the switch 20 or the conducting wire 21.
[0059] In the embodiments 1 and 2, if the switch 20 is mounted on the circuit board 22 having the error amplifier 9 packaged, the noise-proof can be enhanced, resulting in the same effect as in the embodiment 3.
Embodiment 4
[0060] Fig. 6 shows a circuit diagram representing the configuration of a discharge lamp lighting device according to an embodiment 4 of this invention. This embodiment 4 has the features that the rated value of a discharge lamp 5c attached in the discharge lamp load circuit 5 can be automatically discriminated, and the reference voltage to be output from the reference voltage circuit 14 is automatically set to a voltage corresponding to this rated value.
[0061] In Fig. 6, reference numeral 1 denotes a direct current power source which provides the direct current by rectifying and smoothing the alternating current from the commercial power supply. Reference numeral 2 denotes an inverter circuit consisting of the switching elements 2a, 2b such as MOS FET. Reference numeral 3 denotes an inverter driving circuit for driving the inverter circuit 2, the inverter driving circuit internally comprising a voltage-controlled oscillation circuit 3a (hereinafter designated as "VCO") in which the switching frequency is controlled by the voltage and a driver 3b. Reference numeral 4 denotes a coupling capacitor which is connected to the output side of the inverter circuit 2. Reference numeral 5 denotes a discharge lamp load circuit consisting of a choke coil 5a, a starting capacitor 5b and a discharge lamp 5c. Reference numeral 6 denotes a current detecting circuit for detecting the net current to be supplied to the discharge lamp load circuit 5, the current detecting circuit being comprised of a detecting resistor 7 and an integrating circuit 8 (high-pass filter) having a resistor 8a and a capacitor 8b. Reference numeral 9 denotes an error amplifier. Reference numerals 10a and 10b denote a resistor and a capacitor, respectively, which are used for integration in the error amplifier 9. At the inversion input end of the error amplifier 9, an output voltage of the integrating circuit 8 is input, and at the non-inversion input end, a reference voltage is input from a reference voltage circuit 14. A difference between these two voltages is amplified by the error amplifier 9, and fed back as a control signal to the inverter driving circuit 3.
[0062] In this embodiment 4, the inverter driving circuit 3 is connected to initial frequency setting means 31 comprising a ROM 31a for storing a switching frequency of the inverter circuit 2 at the time of initiating this discharge lamp lighting device, and a control portion 31b for controlling the inverter driving circuit 3 to drive the inverter circuit 2 at the switching frequency stored in the ROM 31a for a fixed time period from the initiation.
[0063] The reference voltage circuit 14 comprises a reference voltage generator 15 for generating three preset reference voltages corresponding to the rated values (e.g., 32W, 40W, 45W) of the discharge lamp 5c by dividing a voltage of the stabilized direct current power source for reference voltage 11 by the dividing resistors 12a, 12b, 12c and 13, a switch unit 20 consisting of three switches 20a, 20b, 20c for selecting a reference voltage from among three reference voltages generated by the reference voltage generator 15 to input it into the error amplifier 9, and a switch control portion 32, connected to the current detecting circuit 6, for automatically controlling each switch of the switch unit 20 by detecting the rated value of the discharge lamp 5c attached in the discharge lamp load circuit 5 based on the switching frequency at the time of initiation which has been set by the initial frequency setting means 31 and an output from the current detecting circuit 6. Also, this switch control portion 32 and the switch unit 20 constitute the reference voltage selecting means 19 as a whole.
[0064] Further, the specific configuration of this switch control portion 32 comprises an A/D converter 32a for converting the output of the current detecting circuit 6 into digital form, a storing circuit 32b for storing the relation between the switching frequency of the inverter circuit 2 and the net current value flowing through the discharge lamp load circuit 5, and an operation circuit 32c for discriminating the rated value of the discharge lamp 5c attached in the discharge lamp load circuit 5 based on the output from the A/D converter 32a and the current data saved in the storing circuit 32b to issue an on/off signal to the switch unit 20, as shown in Fig. 6.
[0065] In this embodiment 4, the switch control portion 32 is a microcomputer having an A/D conversion function and containing an internal memory, and the switch unit 20 is a semiconductor switch.
[0066] The operation of this embodiment 4 will be described below with reference to a block diagram of Fig. 6 and a flowchart of Fig. 7. If the discharge lamp lighting device is initiated, a control signal is sent from the initial frequency setting means 31 to the inverter driving circuit 3 at step S1. Then, the voltage-controlled oscillation circuit 3a within the inverter driving circuit 3 oscillates at a frequency stored in the ROM 31a within the initial frequency setting means 31. This signal is amplified by the driver 3b to drive the inverter circuit 2. Thereby, a direct current from the direct current power source 1 is converted into a high frequency current, which is then supplied to the discharge lamp load circuit 5 to light the discharge lamp 5c.
[0067] Since the coupling capacitor 4 is connected to the discharge lamp load circuit 5, an alternating current flows through the discharge lamp load circuit 5 alternately in a clockwise direction (from the direct current power source 1 to switching element 2a to coupling capacitor 4 to discharge lamp load circuit 5 to detecting resistor 7 to direct current power source 1) or a counterclockwise direction (from the coupling capacitor 4 to switching element 2b to discharge lamp load circuit 5 to coupling capacitor 4) when the switching elements 2a and 2b are turned on and off. Consequently, an alternating current flows through the detecting resistor 7, as in Fig. 26, and integrated as the sum (net current) of the alternating current in the clockwise and counterclockwise directions by the integrating circuit 8. A signal of net current being supplied to the discharge lamp load circuit 5 is input into the switch control portion 32 connected to the integrating circuit 8.
[0068] In this way, if the inverter circuit 2 is driven at a fixed frequency (f1) which has been preset by the initial frequency setting means 31, after initiating the discharge lamp lighting device, a net current corresponding to this switching frequency is supplied to the discharge lamp load circuit 5. In the meantime, in the switch control portion 32, the A/D converter 32a detects a net current (ID) input from the current detecting circuit 6 at step S2. The operation circuit 32c determines whether or not the current value has been stable, that is, whether or not the operation transfers to a steady operation state, at step S3. After transferring to the steady state, a comparison is made between the detected current data and the data representing the relation between the switching frequency and the net current as shown in Fig. 8 which has been stored in the storing circuit 32b, at step S4. As a result, the rated value of the discharge lamp 5c attached in the discharge lamp load circuit 5 is discriminated.
[0069] At steps S5 and S6, the operation circuit 32c controls the switch unit 20, based on this resulted rated value, to select a reference voltage adapted to the rated value of the discharge lamp 5c attached from among three reference voltages generated by the reference voltage generator 15. This reference voltage is input into the error amplifier 9. On the other hand, at step S7, the elapsed time since the initiation is supervised. If a preset fixed time has elapsed, the operation transfers to step S8 to stop the control by the initial frequency setting means 31 which functions at the time of initiation and thereafter change over to the control by the error amplifier 9.
[0070] Using a circuit characteristic curve which represents the relation between the switching frequency and the net current as shown in Fig. 8, a method of discriminating the rated value of the discharge lamp 5c from the relation between the net current and the switching frequency will be described below. In the figure, the switching frequency of the inverter circuit 2 is indicated along the horizontal axis, and the net current value in driving the discharge lamp 5c at the switching frequency is indicated along the longitudinal axis. The lines represented by discharge lamp A and discharge lamp B are characteristic curves for two discharge lamps having different rated powers WLA and WLB (WLA>WLB), respectively.
[0071] As shown in Fig. 6, a circuit system consisting of the coupling capacitor 4 and the discharge lamp load circuit 5 constitutes a resonance system consisting of an LCR. Therefore, the internally flowing current varies as shown in Fig. 8 by changing the switching frequency. Also, when the discharge lamps with the rated powers WLA>WLB are lighted at the same frequency f1, the net current IDA of a discharge lamp A having a larger rated power is greater than the net current IDB of a discharge lamp B having a smaller rated power, owing to a difference between the impedances. Thus, the rated value of the discharge lamp 5c attached can be discriminated by judging whether the net current value ID obtained by A/D converting a signal from the current detecting circuit 6 is closer to the current value IDA or IDB of each discharge lamp at the switching frequency f1 which has been set by the initial frequency setting means 31. In Fig. 8, the relation between the switching frequency and the net current is represented by a characteristic curve. However, because the switching frequency f1 at the time of initiation is predetermined in a practical discharge lamp lighting device, it is only required to store the net currents IDA and IDB corresponding to the preset switching frequency in the storing circuit 32b, and compare them with a net current value output from the current detecting circuit 6.
[0072] Fig. 9 shows a characteristic curve representing the relation between the reference voltage input into the error amplifier 9 and the electric power consumed in the discharge lamp load circuit 5. After a reference voltage adapted to the rated value is selected, the switching frequency of the inverter circuit 2 is controlled so that the output voltage of the current detecting circuit 6 be equal to the reference voltage. A high frequency current (net current) adapted to the rated value of the discharge lamp 5c is supplied from the direct current power source 1 to the discharge lamp load circuit 5. If the circuit loss is ignored, a fixed electric power corresponding to this net current is consumed in the discharge lamp 5c, exactly in the same way as in the conventional example.
[0073] According to this embodiment 4, the net current to be supplied to the discharge lamp load circuit 5 is controlled by the reference voltage input from the reference voltage circuit 14. The rated value of the discharge lamp 5c attached in the discharge lamp load circuit 5 is detected by the switch control portion 32. The reference voltage to be output from the reference voltage circuit 14 is automatically switched by the switch unit 20, so that the net current adapted to the rated value of the discharge lamp 5c attached is supplied into the discharge lamp load circuit 5. Therefore, a discharge lamp lighting device can be obtained which is applicable to the discharge lamp having different rated values. As a result, there is no need of preparing for various kinds of parts or discharge lamp lighting devices, leading to reduction in the management cost for the parts management at the production and so on. Also, since the reference voltage is changed automatically in accordance with the rated value of the discharge lamp 5c, there is no need of setting the rated value by manual operation of the switch when the products are shipped.
[0074] In a case where the rated value of the discharge lamp 5c is changed to increase the illuminance after installing the discharge lamp lighting device, the reference voltage is automatically switched in accordance with the rated value of the discharge lamp 5c. Therefore, it is possible to use the discharge lamp having different rated values in the same discharge lamp lighting device. There is no need of exchanging or installing the discharge lamp lighting device newly, leading to reduction in the purchasing cost or the operating expense. Also, since the reference voltage can be changed at any time, a discharge lamp lighting device which is usable over the long term and superior in the respect of resource efficiency can be provided.
[0075] Further, the reference voltage selecting means 19 consisting of the switch control portion 32 and the switch unit 20 judges the rated value of the discharge lamp 5c attached, and switches automatically the reference voltage, so that a net current adapted to the rated value of the discharge lamp 5c may be supplied. Hence, without the knowledge of electricity, the net current adapted to the rated value of the discharge lamp 5c can be flowed at any time. When exchanging the discharge lamp 5c, the discharge lamp 5c is protected from an excessive current passing through it to impair the discharge lamp 5c due to failure in selecting the discharge lamp 5c or setting the switch unit.
[0076] Also, the inverter circuit 2 is driven at the switching frequency f1 which has been set by the initial frequency setting means 31, and the rated value of the discharge lamp 5c attached in the discharge lamp load circuit 5 is detected by the switch control portion 32, based on the data of the net current from the current detecting circuit 6 at this time. Therefore, by appropriately setting the switching frequency f1 at the time of initiation, the discharge lamp 5c is protected from a current beyond the rated value passing through it to impair the discharge lamp 5c, before discriminating the rated value of the discharge lamp 5c.
[0077] The reference voltage circuit 14 is comprised of the reference voltage generator 15, having the direct current power source for reference voltage 11 and the dividing resistors 12a, 12b, 12c and 13, for generating a plurality of different reference voltages corresponding to the preset rated values of the discharge lamp, and a switch unit 20 for selecting automatically a reference voltage generated by the reference voltage generator 15. Therefore, a circuit configuration is simpler than a method in which the dividing resistors are made by the variable resistors, and the division ratio of voltage is varied by changing the resistance of the variable resistors, for example. In addition, an inexpensive reference voltage circuit can be provided. And the reference voltage can be easily set up.
[0078] Also, the switch control portion 32 is comprised of the A/D converter 32a, the storing circuit 32b and the operation circuit 32c. The A/D converter 32a converts the output of the current detecting circuit 6 into digital data. And the operation circuit 32c allows this digital data to be compared with the current data stored in the storing circuit 32c to discriminate the rated value of the discharge lamp 5c attached. The switch unit 20 is controlled so that a reference voltage corresponding to this rated value may be output from the reference voltage circuit 14. Therefore, it is possible to provide a discharge lamp lighting device which can cope with a variety of kinds of discharge lamps only by changing the data stored in the storing circuit 32b, and has the excellent flexibility in a wide range of applications.
[0079] Since the switch control portion 32 is a microcomputer and the switch unit 20 is a semiconductor switch, the circuit of the reference voltage selecting means 19 can be integrated, leading to reduction in the size of the device.
[0080] In this embodiment 4, the discharge lamp lighting device is initially driven at a switching frequency which has been set by the initial frequency setting means 31 and meanwhile a reference voltage is selected in an initiation procedure. However, the discharge lamp 5c may be initially lighted at a reference voltage corresponding to the minimum net current by the reference voltage circuit 14 and the error amplifier 9, and then the discharge lamp lighting device may be driven at a switching frequency which has been set by the initial frequency setting means 31, while the reference voltage may be changed by discriminating the rated value.
[0081] In the embodiment 4, as a way of getting the net current, a signal to be output from the current detecting circuit 6 to the error amplifier 9 is branched into the switch control portion 32. However, a current detecting circuit may be provided apart from the current detecting circuit 6 above to input the current into the switch control portion 32.
[0082] Also, in this embodiment 4, the inverter circuit 3 is constituted of the voltage-controlled oscillation circuit 3a and the driver 3b. However, a current-controlled oscillation circuit may be applied instead of the voltage-controlled oscillation circuit 3a, in which there is the same effect as above described.
[0083] Further, as reference voltage selecting means 19, the switch control portion 32 is a microcomputer and the switch unit 20 is a semiconductor switch. However, a relay circuit having a combination of the relays which are turned on or off at different voltages may be made, in which each contact point of the switch 20a, 20b, 20c is turned on or off in accordance with an output voltage from the current detecting circuit 6, to enable the analog processing. Or the dividing resistor may be a variable resistor to change the division ratio of the voltage.
[0084] Also, in this embodiment 4, a net current to be supplied to the discharge lamp load circuit 5 is detected by the A/D converter 32a, and supervised by the operation circuit 32c to judge the transfer to a steady operation state. However, the net current may be detected after waiting for a fixed time, with a timer contained within the microcomputer 32. Or instead of presetting the time for transferring the control from the initial frequency setting means 31 to the error amplifier 9, a signal may be issued from the switch control portion 32 to the initial frequency selecting means 31, after selecting the reference voltage, to stop the control with the initial frequency selecting means 31. In this case, since the steady state is judged by supervising the value of net current, there is no need of having a tolerance in the waiting time, leading to quick operation from the initiation to the selection of reference voltage.
Embodiment 5
[0085] Fig. 10 shows a circuit diagram representing the configuration of a discharge lamp lighting device according to an embodiment 5 of this invention. In this embodiment 5, the inverter driving circuit 3 is comprised of a current-controlled oscillation circuit 3c (designated by "CCO" in the figure) in which the oscillation frequency is controlled by the current, and a driver 3b. Further, initial frequency setting means 31 for setting the switching frequency in initiating the discharge lamp lighting device has a frequency setting resistor 34 connected between the inverter driving circuit 3 and the ground, and a diode 35 connected between the inverter driving circuit 3 and the error amplifier 9. Note that the same or like parts as in Fig. 6 are indicated by the like numerals, and are not described.
[0086] The operation of this embodiment 5 will be described below regarding a difference between the voltage-controlled oscillation circuit 3a and the current-controlled oscillation circuit 3c, and an operation of the frequency setting resistor 34 and the diode 35, with reference to a block diagram of Fig. 10 and a flowchart of Fig. 11. In Fig. 10, the current-controlled oscillation circuit 3c is an oscillation circuit having the oscillation frequency controlled by the current value flowing out of an internal power source (not shown) contained within the current-controlled oscillation circuit 3c. In this case, the oscillation frequency of the current-controlled oscillation circuit 3c is controlled by the sum of a current flowing from the internal power source via the frequency setting resistor 34 to the ground and a current drawn from the diode 35 into the error amplifier 9.
[0087] Firstly, at step S11 of Fig. 11, before initiating this discharge lamp lighting device, a switch 20c corresponding to the highest reference voltage among the switches 20a, 20b, 20c in the switch unit 20 is turned on, and other switches 20a, 20b are turned off. This is made to prevent a current flowing from the current-controlled oscillation circuit 3c into the error amplifier 9, due to the presence of the diode 35, by setting the potential at the output side of the error amplifier 9 above the potential at the upstream side of the frequency setting resistor 34. As a result, for a fixed time period after the initiation, the switching frequency is retained at a constant frequency set by the frequency setting resistor 34, by maintaining constant a current flowing out of the current-controlled oscillation circuit 3c.
[0088] At step S12, if the discharge lamp lighting device is initiated in the above state, the current-controlled oscillation circuit 3c is oscillated at a fixed frequency corresponding to a current flowing through the frequency setting resistor 34 into the ground. This signal is amplified by the driver 3b and the inverter circuit 2 is driven, so that a direct current supplied from the direct current power source 1 is converted into a high frequency current, which is then supplied to the discharge lamp load circuit 5 to light the discharge lamp 5c.
[0089] If the current begins to flow through the discharge lamp load circuit 5, an alternating current, as in Fig. 26, flows through the detecting resistor 7, and integrated by the integrating circuit 8 to have a sum of the current (net current) in the forward and backward directions of the alternating current. A signal corresponding to a net current to be supplied to the discharge lamp load circuit 5 is input into the inversion input end of the error amplifier 9, and into the switch control portion 32 within the reference voltage selecting means 19.
[0090] If the switching frequency set by the frequency setting resistor 34 and the reference voltage at the initiation are appropriately selected as described above, a current can be prevented from flowing from the current-controlled oscillation circuit 3c into the error amplifier 9. As a result, the inverter circuit 2 can be switched at a fixed frequency set by the frequency setting resistor 34, after initiating the discharge lamp lighting device. A steady net current corresponding to a switching frequency set by the frequency setting resistor 34 can be supplied to the discharge lamp load circuit 5.
[0091] In this way, in the switch control portion 32, the A/D converter 32a detects a net current value (ID) from the signal of net current passed from the current detecting circuit 6 at step S13. Subsequently, it is determined whether or not the current value is stabilized at step S14. After the steady state, the operation circuit 32c makes a comparison between this current data and the data of net current stored in the storing circuit 32b at step S15. Thereby, the rated value of the discharge lamp 5c attached in the discharge lamp load circuit 5 can be discriminated.
[0092] And the switch unit 20 selects a reference voltage adapted to a rated value of the discharge lamp 5c attached, based on this result, at step S16 or S17. Consequently, the potential of the diode 35 at the side of the error amplifier 9 is lower, so that a current is drawn from the inverter driving circuit 3 into the error amplifier 9. From step S18 and beyond, the current-controlled oscillation circuit 3c within the inverter driving circuit 3 is controlled by both the current flowing through the frequency setting resistor 34 and the current drawn into the error amplifier 9, so that the net current to be supplied to the discharge lamp load circuit 5 may be adjusted.
[0093] According to this embodiment 5, there are exactly the same effects as the embodiment 4. Because of the frequency setting resistor 34, which is provided as the initial frequency setting means 31 for setting the switching frequency in initiating the discharge lamp lighting device, the switching frequency at the initiation can be set by a simple circuit comprised of the frequency setting resistor 34 and the diode 35. Consequently, there is no need of providing another control circuit for controlling the inverter driving circuit 3, unlike the embodiment 4, leading to the reduced cost.
[0094] As will be clear from the above description, the voltage-controlled oscillation circuit may be applied instead of the current-controlled oscillation circuit 3c in this embodiment 5, resulting in the same effects.
Embodiment 6
[0095] Fig. 12 shows a circuit diagram of a discharge lamp lighting device according to an embodiment 6 of this invention. This invention has been achieved to resolve such a problem that in a case where one discharge lamp having a plurality of rated values such as an Hf fluorescent discharge lamp (type FHF32EX) manufactured by Mitsubishi Electric Oslum (with two rated values of 32W and 45W in the case of FHF32EX) is driven in the discharge lamp lighting device as shown in the embodiment 4, it is not possible for the switch control portion 32 singly to determine whether this discharge lamp is operated at 32W or 45W because there is only one characteristic curve representing the output ID of net current from the current detecting circuit 6 for a switching frequency f1, in spite of a plurality of rated values.
[0096] The configuration and operation of this embodiment 6 will be described below with reference to, Fig. 12. In Fig. 12, reference numeral 36 denotes external setting means for manually setting the rated value of the discharge lamp 5c from the outside, which is provided in the switch control portion 32. In this embodiment, this is an external setting switch which is able to change over three modes of "automatic mode", "32W mode" and "45W mode". Note that the same or like parts as in Fig. 6 are indicated by the like numerals, and are not described.
[0097] The operation of this embodiment 6 will be described below. In Fig. 12, if this discharge lamp is initiated, the inverter circuit 2 is first driven at a switching frequency set by the initial frequency setting means 31. The discharge lamp 5c is lighted with a power corresponding to this frequency. On the other hand, in the switch control portion 32, for a certain period of being operative at this switching frequency, the setting condition of the external setting switch 36 is first detected. When it is set at an "automatic mode", the rated value of the discharge lamp 5c attached is automatically discriminated in accordance with the same procedure as in the embodiment 4, and after a fixed time period, the switching over to a reference voltage adapted to this rated value occurs. Also, when the external setting switch 36 is set at a "32W mode" or a "45W mode", the switch unit 20 is switched to light the discharge lamp 5c at a rated value set by this external setting switch 36, without the automatic discrimination.
[0098] Thus, according to this embodiment 6, in addition to the effects as attained in the embodiment 4, there is an effect that the discharge lamp lighting device capable of coping with the discharge lamp having a plurality of rated values can be provided, owing to the external setting means 36 capable of manually setting the rated value in the switch control portion 32.
[0099] In the embodiment 6 as described above, the setting condition of the external setting switch 36 is detected, the switch control portion 32 controls the process corresponding to the "automatic mode", the "32W mode" or the "45W mode" to be performed in accordance with this setting condition. However, in a case where the characteristic curve for the switching frequency and the net current of the discharge lamp having a plurality of rated values is known, it may be first determined whether or not the discharge lamp has the plurality of rated values from the relation between the switching frequency and the net current. For the plurality of rated values, the setting condition of the external setting switch 36 may be checked. In this case, the rated value is automatically discriminated for the discharge lamp not having the plurality of rated values, in the same way as in the embodiment 4.
[0100] In the above embodiment 6, the external setting switch 36 has two modes of "32W mode" and "45W mode", besides the "automatic mode" If the number of contacts for the external setting switch 36 is increased, it is possible to deal with three or more rated values.
Embodiment 7
[0101] Fig. 13 shows a circuit diagram of a discharge lamp lighting device which can change continuously the brightness of a discharge lamp 5c as the reference voltage is changed, according to an embodiment 7 of this invention. In the figure, reference numerals 37a, 37b and 38 denote a buffer resistor, a buffer capacitor and a resistor, respectively. The buffer resistor 37a and the buffer capacitor 37b constitute a buffer integrating circuit 37 as a whole. Note that the same or like parts as in Fig. 6 are indicated by the like numerals, and are not described.
[0102] Thus, in this embodiment 7, in a case where the switches in the switch unit 20 for selecting the reference voltage are changed from the state where a switch 20a is on to the state where a switch 20b is on, the amount of variation in the voltage is integrated in the buffer integrating circuit 37. Therefore, the reference voltage input into the error amplifier 9 is continuously changed along with the integration constant of the buffer integrating circuit 37. If this integration constant is appropriately chosen, the reference voltage can be gradually changed, so that the light output can be changed smoothly.
[0103] According to this embodiment 7 described above, in addition to the effects of the embodiment 4, there is the following effect. Since the buffer integrating circuit 37 which is a buffer circuit is provided between the input end of the error amplifier 9 and the reference voltage circuit 14, to buffer the stepwise variations in the output of the reference voltage circuit 14 as the reference voltage is changed, and the signal input into the error amplifier 9 is changed gradually and continuously, it is possible to suppress the abrupt stepwise variations in the light output (brightness) of the discharge lamp 5c which may occur when automatically changed to a reference voltage adapted to a rated value of the discharge lamp 5c from the switching frequency at the initiation. Therefore, the light output can be changed smoothly from the initiation to the steady state, leading to less sense of incompatibility or discomfort for the user. Consequently, there is provided a discharge lamp lighting device which is very agreeable.
[0104] In this way, in the discharge lamp lighting device for discriminating the rated value of the discharge lamp 5c at every initiation, the reference voltage is automatically selected by switching the switch unit 20. In this case, the brightness of the discharge lamp 5c is varied at every initiation of the device. An abrupt change in the brightness at every initiation may be significantly less comfortable for the user. The discharge lamp lighting device in the embodiment 7 which can change the light output smoothly is very advantageous in practice.
[0105] Further, when changing the switching frequency at the initiation to the 45W rating, for example, the switch control portion 32 controls the switching to be made step by step in the order of 32W, 40W and 45W, but not directly changing over to a reference voltage at the 45W rating. Thereby, besides the effect of the buffer integrating circuit 37, the light output can be continuously changed, resulting in a more grateful discharge lamp lighting device.
[0106] In the embodiment 7, the buffer circuit 37 for input into the error amplifier 9 is the buffer integrating circuit 37 comprised of the buffer resistor 37a and the buffer capacitor 37b. Other configurations having the same function may be used, such as an integrating circuit with an operational amplifier.
Embodiment 8
[0107] Fig. 14 shows a circuit diagram of a discharge lamp lighting device according to an embodiment 8 of the invention. In the embodiments 4 to 7, the switch unit 20 is placed between the reference voltage generator 15 and the error amplifier 9, wherein a reference voltage for input into the error amplifier 9 is selected from among a plurality of reference voltages generated by the reference voltage generator 15 by the switch unit 20. In the embodiment 8 as shown in Fig. 14, however, each switch 20a, 20b, 20c of the switch unit 20 is connected in parallel with each dividing resistor 12a, 12b, 12c. Each switch 20a, 20b, 20c of the switch unit 20 is turned on or off to bypass each dividing resistor 12a, 12b, 12c to vary the division ratio of the dividing resistors across the output end of the reference voltage connected to the error amplifier 9.
[0108] In Fig. 14, reference numeral 16 denotes a dividing resistor connected in series to the dividing resistors 12a, 12b, 12c and 13. Note that the same or like parts as in Fig. 6 are indicated by the like numerals, and are not described. Further, the operation is exactly the same as in the embodiment 4, and is not described.
[0109] Thus, according to the embodiment 8, in addition to the effects of the embodiment 4, there is the following effect. Since the input impedance of the error amplifier 9 is typically very large, a minute current continues to flow through each contact of the switch unit 20 over the long term in the embodiment 4. Under such conditions, it was quite difficult to maintain the value of the reference voltage stable over the long term. However, in this embodiment 8, the switch unit 20 is connected in parallel with the dividing resistors 12a, 12b, 12c. Therefore, a current through the dividing resistors from the direct current power source for reference voltage 11 will flow through the switch unit 20. A current value necessary to be stable against a secular change can be passed. As a result, there is an effect that a discharge lamp lighting device which is endurable against the secular change and highly reliable can be provided.
[0110] In Fig. 14, each switch 20a, 20b, 20c of the switch unit 20 is connected in parallel between the upstream side of each dividing resistor 12a, 12b, 12c and the ground. However, each switch 20a, 20b, 20c of the switch unit 20 may be connected to bypass each dividing resistor 12a, 12b, 12c. In this case, a variety of division ratios can be obtained by switching each switch. A discharge lamp lighting device capable of dealing with more rated values with a smaller number of dividing resistors can be provided.
Embodiment 9
[0111] Fig. 15 shows a circuit diagram representing the configuration of a discharge lamp lighting device according to an embodiment 9 of this invention. In the figure, reference numeral 1 denotes a direct current power source which provides the direct current by rectifying and smoothing the alternating current from the commercial power supply. Reference numeral 2 denotes an inverter circuit consisting of the switching elements 2a, 2b such as MOS FET. Reference numeral 3 denotes an inverter driving circuit for driving the inverter circuit 2, the inverter driving circuit internally comprising a voltage-controlled oscillation circuit 3a (hereinafter designated as "VCO") in which the switching frequency is controlled by the voltage and a driver 3b. Reference numeral 4 denotes a coupling capacitor which is connected to the output side of the inverter circuit 2. Reference numeral 5 denotes a discharge lamp load circuit consisting of a choke coil 5a, a starting capacitor 5b and a discharge lamp 5c. Reference numeral 6 denotes a current detecting circuit for detecting the net current to be supplied to the discharge lamp load circuit 5, the current detecting circuit being comprised of a detecting resistor 7 and an integrating circuit 8 (high-pass filter) having a resistor 8a and a capacitor 8b. Reference numeral 9 denotes an error amplifier. Reference numerals 10a and 10b denote a resistor and a capacitor, respectively, which are used for integration in the error amplifier 9. At the inversion input end of the error amplifier 9, an output voltage of the integrating circuit 8 is input, and at the non-inversion input end, a reference voltage is input from a reference voltage circuit 14. A difference between these two voltages is amplified by the error amplifier 9, and fed back as a control signal to the inverter driving circuit 3.
[0112] In this embodiment 9, the inverter driving circuit 3 is provided with a frequency output terminal 41a for outputting the oscillation frequency of the voltage-controlled oscillation circuit 3a, viz., the switching frequency of the inverter driving circuit 3, to the outside. Frequency detecting means 41 comprised of the frequency output terminal 41a and a connecting line 41b provides the information as to this switching frequency into the switch control portion 32 within the reference voltage circuit 14.
[0113] The reference voltage circuit 14 comprises a reference voltage generator 15 for generating three preset reference voltages corresponding to the rated values (e.g., 32W, 40W, 45W) of the discharge lamp 5c by dividing the voltage of the stabilized direct current power source for reference voltage 11 by the dividing resistors 12a, 12b, 12c and 13, and reference voltage selecting means 19 for selecting a reference voltage adapted to a rated value of the discharge lamp 5c attached from among three reference voltages generated by the reference voltage generator 15 to input it into the error amplifier 9. This reference voltage selecting means 19 comprises a switch unit 20 consisting of three switches 20a, 20b, 20c, and a switch control portion 32 for automatically controlling each switch of the switch unit 20 by discriminating the rated value of the discharge lamp 5c attached in the discharge lamp load circuit 5 based on the switching frequency of the inverter driving circuit 3 input via the connecting line 41b from the frequency output terminal 41a.
[0114] Further, the specific configuration of this switch control portion 32 comprises an A/D converter 32a for converting the output of the frequency output terminal 41a into digital form, a storing circuit 32b for storing the relation between the reference voltage output from the reference voltage circuit 14 and the switching frequency of the inverter driving circuit 3, and an operation circuit 32c for discriminating a rated value of the discharge lamp 5c attached in the discharge lamp load circuit 5 based on the output from the A/D converter 32a and the frequency data saved in the storing circuit 32b to issue an on/off signal to the switch unit 20, as shown in Fig. 15. In this embodiment 9, the switch control portion 32 is a microcomputer having an A/D conversion function and containing an internal memory, and the switch unit 20 is a semiconductor switch.
[0115] The operation of this embodiment 9 will be described below with reference to a block diagram of Fig. 15 and a flowchart of Fig. 16. Firstly, when the discharge lamp lighting device is initiated, at step S21 of Fig. 16, the switch control portion 32 controls a switch 20c corresponding to a reference voltage producing the lowest net current among the switches 20a, 20b, 20c in the switch unit 20 to be turned on, and other switches 20a, 20b to be turned off. If the discharge lamp lighting device is initiated in this state, the error amplifier 9 has a reference voltage corresponding to the minimum net current from the reference voltage circuit 14. Hence, the error amplifier 9 amplifies a difference between this reference voltage and a signal from the current detecting circuit 6. This difference is input into the inverter driving circuit 3. The voltage-controlled oscillation circuit 3a within the inverter driving circuit 3 is oscillated at a switching frequency corresponding to this voltage. The inverter circuit 2 is driven by the driver 3b, so that the direct current supplied from the direct current power source 1 is converted into high frequency current and supplied to the discharge lamp load circuit 5 to light the discharge lamp 5c.
[0116] At this time, because of the coupling capacitor 4 connected to the discharge lamp load circuit 5, when the switching elements 2a and 2b are turned on and off, an alternating current will flow through the discharge lamp load circuit 5 alternately in a clockwise direction from the direct current power source 1 to the switching element 2a to the coupling capacitor 4 to the discharge lamp lighting device 5 to the detecting resistor 7 to the direct current power source 1, and in a counterclockwise direction from the coupling capacitor 4 to the switching element 2b to the discharge lamp lighting device 5 to the coupling capacitor 4. As a result, an alternating current flows through the detecting resistor 7, as in Fig. 26, and integrated by the integrating circuit 8 to have a sum of the current (net current) in the forward and backward directions of the alternating current. A corresponding voltage is input into the inversion-input end of the error amplifier 9.
[0117] On the other hand, a reference voltage from the reference voltage circuit 14 is input at the non-inversion-input end of the error amplifier 9. Hence, after initiating the discharge lamp lighting device, a difference between the output of the integrating circuit 8 and the reference voltage is fed back via the error amplifier 8 into the inverter driving circuit 3. Thereby, the switching frequency of the inverter circuit 2 is adjusted till the net current supplied to the discharge lamp load circuit 5 is equal to a present value by the reference voltage circuit 14. As a result, a power corresponding to this minimum net current is consumed in the discharge lamp 5c, in the same way as in the conventional example.
[0118] After the initiation, the discharge lamp lighting device is operated at a reference voltage corresponding to the minimum net current for a fixed time period at step S22. When the net current to be supplied to the discharge lamp load circuit 5 becomes invariable at a current value corresponding to the reference voltage, the operation transfers to step S23, where the A/D converter 32a within the switch control portion 32 detects a switching frequency (fD) output from the frequency output terminal 41a. Subsequently, this data is compared with the data stored in the storing circuit 32b by the operation circuit 32c and representing the relation between the reference voltage and the switching frequency as shown in Fig. 17 at step S24. Thereby the rated value of the discharge lamp 5c attached in the discharge lamp load circuit 5 is discriminated.
[0119] Based on this discrimination result, a reference voltage adapted to the rated value of the discharge lamp 5c attached is selected from among three reference voltages generated by the reference voltage generator 15 by the operation circuit 32c at step S25 or S26. A switch 20a initially set is automatically changed by the switch unit 20. Thereafter, the error amplifier 9 controls the inverter driving circuit 3, based on a new reference voltage, so that a net current adapted to the rated value of the discharge lamp 5c is supplied to the discharge lamp load circuit 5.
[0120] Using a circuit characteristic curve which represents the relation between the reference voltage and the switching frequency as shown in Fig. 17, a method of discriminating the rated value of the discharge lamp 5c attached from the relation between the reference voltage and the switching frequency will be described below in detail. In the figure, the reference voltage output from the reference voltage circuit 14 is indicated along the horizontal axis, and the switching frequency of the inverter driving circuit 3 is indicated along the longitudinal axis. The lines represented by discharge lamp A and discharge lamp B are characteristic curves for two discharge lamps having different rated powers WLA and WLB (WLA>WLB), respectively.
[0121] As described above, in this discharge lamp lighting device, the error amplifier 9 controls the switching frequency of the inverter driving circuit 3 so that the output from the integrating circuit 8 be equal to the reference voltage output from the reference voltage circuit 14. If the reference voltage output from the reference voltage circuit 14 is decided, the net current corresponding to this reference voltage and the switching frequency at which this net current is supplied can be uniquely decided in a steady state. Thus, if the reference voltage is changed for the same discharge lamp, the switching frequency and the net current are changed along with this. Consequently, the characteristic curve as shown in Fig. 17 can be obtained.
[0122] On the other hand, a circuit system consisting of the coupling capacitor 4 and the discharge lamp load circuit 5 constitutes a resonance system consisting of an LCR. Therefore, the switching frequency for supplying a same net current (i.e., reference voltage) is changed, due to a difference in the impedance of the discharge lamp 5c, to give a different characteristic curve. For example, in Fig. 17, in a case where the discharge lamps A and B having the rated powers (WLA>WLB) are driven at a same reference voltage (VREF), the switching frequency fDA of a discharge lamp A having a larger rated power is greater than the switching frequency fDB of a discharge lamp B having a smaller rated power. Thus, while the discharge lamp lighting device is being operated in a state having a reference voltage to give a minimum net current, a signal output from the frequency detecting means 41 is converted from analog to digital form, and a switching frequency fD is detected. The rated value of the discharge lamp 5c attached can be discriminated by judging whether this switching frequency is closer to a switching frequency fDA or fDB for each discharge lamp corresponding to this reference voltage (VREF).
[0123] In Fig. 17, the relation between the reference voltage and the switching frequency is represented by the characteristic curve. In the actual discharge lamp lighting device, however, the reference voltage (VREF) at the initiation has been decided. Therefore, the switching frequencies fDA and fDB corresponding to a preset reference voltage are only stored in the storing circuit 32b. The rated value of the discharge lamp can be discriminated only by comparing the switching frequency output from the frequency detecting means 41 with them. In this case, there is no need of providing means for detecting the reference voltage.
[0124] Fig. 18 shows a characteristic curve representing the relation between the reference voltage input into the error amplifier 9 and the electric power consumed in the discharge lamp load circuit 5. After a reference voltage adapted to the rated value is selected, the switching frequency of the inverter circuit 2 is controlled by the error amplifier 9 and the inverter driving circuit 3 so that the output voltage of the current detecting circuit 6 be equal to a new reference voltage. A high frequency current (net current) adapted to the rated value of the discharge lamp 5c is supplied from the direct current power source 1 to the discharge lamp load circuit 5. If the circuit loss is ignored, a fixed electric power (WLA in Fig. 17) corresponding to this net current is consumed in the discharge lamp 5c.
[0125] According to this embodiment 9, the net current to be supplied to the discharge lamp load circuit 5 is controlled by the reference voltage output from the reference voltage circuit 14. The switching frequency fD of the inverter circuit 2, when operated at a predetermined reference voltage, viz., when supplied with a predetermined net current, is detected in terms of the frequency detecting means 41. Thereby, the rated value of the discharge lamp 5c attached in the discharge lamp load circuit 5 is discriminated by the switch control portion 32. The reference voltage to be output from the reference voltage circuit 14 is automatically switched by the switch unit 20, so that a net current adapted to the rated value of the discharge lamp 5c attached is supplied into the discharge lamp load circuit 5. Therefore, a discharge lamp lighting device, which is applicable to the discharge lamps having different rated values, can be provided. As a result, there is no need of preparing for various kinds of parts or discharge lamp lighting devices, leading to reduction in the management cost for the parts management at the production and so on. Also, since the reference voltage is changed automatically in accordance with the rated value of the discharge lamp 5c, there is no need of setting the rated value by manually operating the switch at the shipment of products.
[0126] In a case where the rated value of the discharge lamp 5c is changed to increase the illuminance after installing the discharge lamp lighting device, the reference voltage is automatically switched in accordance with the rated value of the discharge lamp 5c. Therefore, it is possible to use the discharge lamps having different rated values in the same discharge lamp lighting device. There is no need of exchanging or installing the discharge lamp lighting device newly, leading to reduction in the purchasing cost or the operating expense. Also, a discharge lamp lighting device, which is usable over the long term and superior in the respect of resource efficiency, can be provided.
[0127] Further, the reference voltage selecting means 19 consisting of the switch control portion 32 and the switch unit 20 judges the rated value of the discharge lamp 5c attached, and switches automatically the reference voltage, so that a net current adapted to the rated value of the discharge lamp 5c may be supplied. Hence, without the knowledge of electricity, the net current adapted to the rated value of the discharge lamp 5c can be flowed at any time. When exchanging the discharge lamp 5c, the discharge lamp 5c is protected from an excessive current flowing through it to impair the discharge lamp 5c due to failure in selecting the discharge lamp 5c or setting the switch.
[0128] Also, the reference voltage circuit 14 is comprised of the reference voltage generator 15, having the direct current power source for reference voltage 11 and the dividing resistors 12a, 12b, 12c and 13, for generating a plurality of different reference voltages corresponding to the preset rated values of the discharge lamps, and reference voltage selecting means 19 for automatically selecting a reference voltage generated by the reference voltage generator 15. A circuit configuration is simpler, and an inexpensive reference voltage circuit can be provided. The reference voltage can be set more easily than a method in which the dividing resistors 12 are made by the variable resistor, and the division ratio of voltage is varied by changing the resistance of the variable resistor, for example.
[0129] Also, the switch control portion 32 is comprised of the A/D converter 32a, the storing circuit 32b and the operation circuit 32c. The A/D converter 32a converts the output of the current detecting circuit 6 into digital data. And the operation circuit 32c allows this digital data to be compared with the frequency data stored in the storing circuit 32c to discriminate the rated value of the discharge lamp 5c attached. The switch unit 20 is controlled so that a reference voltage corresponding to this rated value may be output from the reference voltage circuit 14. Therefore, it is possible to provide a discharge lamp lighting device which can cope with a variety of kinds of discharge lamps only by changing the data stored in the storing circuit 32b, and has the excellent flexibility in a wide range of applications.
[0130] Since the switch control portion 32 is a microcomputer and the switch unit 20 is a semiconductor switch, the circuit of the reference voltage selecting means 19 can be integrated, leading to reduction in the size of the device.
[0131] In this embodiment 9, the reference voltage to be output when initiating the discharge lamp lighting device is set to a reference voltage corresponding to the minimum net current. The discharge lamp 5c is protected from an excessive current flowing through the discharge lamp with small rated value to impair the discharge lamp 5c.
[0132] Also, the frequency detecting means is configured to get a signal of the switching frequency through the frequency output terminal 41a within the inverter driving circuit 3. Therefore, the switching frequency can be obtained with a quick response and correctly.
[0133] In this embodiment 9, the switching frequency is detected after waiting for a fixed time till the net current to be supplied to the discharge lamp load circuit 5 and the switching frequency get to a steady state. However, from the time of initiation, the switching frequency is repeatedly detected by the frequency detecting means 41 and the switch control portion 32. When the switching frequency becomes constant, it is determined that the steady state is reached. Then, the rated value of the discharge lamp 5c is discriminated. In this case, there is no need of having a tolerance till the steady state. Therefore, the rated value can be changed quickly.
[0134] In the above embodiment 9, the switching frequency is detected in a state where the switch 20a is on. However, the switching frequency may be detected in a state where other switches are on. Further, in a case where the characteristic curve as shown in Fig. 17 is stored in the storing circuit 32b, an arbitrary switch may be turned on for the initiation, and the settings of the switch unit 20 may be detected by the operation circuit 32c. The rated value of the discharge lamp 5c may be discriminated from a reference voltage and a switching frequency corresponding to this settings of the switch unit 20.
[0135] Further, as reference voltage selecting means 19,the switch control portion 32 is a microcomputer and the switch unit 20 is a semiconductor switch. However, a relay circuit having a combination of the relays which are turned on or off at different voltages may be made, for example, in which a contact point of each switch 20a, 20b, 20c is turned on or off in accordance with an output voltage from the frequency detecting means 41, to enable the analog processing. Or the dividing resistor may be a variable resistor to change the division ratio of the voltage.
[0136] Further, in Fig. 15, the frequency detecting means 41 is configured to detect the switching frequency from the frequency output terminal 41a of the inverter driving circuit 3. For example, a current flowing through the inverter circuit 2 or the discharge lamp load circuit 5 or a voltage waveform may be input into the switch control portion 32, and converted into digital form by the A/D converter 32a within the switch control portion 32. Then, the switching frequency may be detected through the Fourier transform by the operation circuit 32c.
[0137] In this embodiment 9, the inverter driving circuit 3 is comprised of the voltage-controlled oscillation circuit 3a and the driver 3b. However, a current-controlled oscillation circuit may be used instead of the voltage-controlled oscillation circuit 3a, resulting in the same effect as above.
Embodiment 10
[0138] Fig. 19 shows a circuit diagram representing the configuration of a discharge lamp lighting device according to an embodiment 10 of this invention. In this embodiment 10, the inverter driving circuit 3 is comprised of a current-controlled oscillation circuit 3c (designated by "CCO" in the figure) in which the oscillation frequency is controlled by the current, and the driver 3b. Further, a frequency setting resistor 34 is connected between the inverter driving circuit 3 and the ground, and a diode 35 is connected between the inverter driving circuit 3 and the error amplifier 9. A switching frequency is input from the frequency output terminal 41a of the inverter driving circuit 3 via the connecting line 41b into the switch control portion 32 within the reference voltage circuit 14. Further, an output corresponding to a net current to be supplied to the discharge lamp load circuit 5 via the connecting line 39 is input from the current detecting circuit 6. Note that the same or like parts as in Fig. 15 are indicated by the like numerals, and are not described.
[0139] The operation of this embodiment 10 will be described below with regard to a difference in operation between the voltage-controlled oscillation circuit 3a and the current-controlled oscillation circuit 3c, and a way of utilizing the net current data to be output from the current detecting circuit 6. In Fig. 19, the current-controlled oscillation circuit 3c is an oscillation circuit having the oscillation frequency controlled by the current value flowing out of an internal power source (not shown) contained within the current-controlled oscillation circuit 3c. In this case, the oscillation frequency of the current-controlled oscillation circuit 3c is controlled by the sum of a current flowing from the internal power source via the frequency setting resistor 34 to the ground and a current drawn from the diode 35 into the error amplifier 9.
[0140] Firstly, when initiating this discharge lamp lighting device, a switch 20c corresponding to the minimum net current among the switches 20a, 20b, 20c in the switch unit 20 is turned on, and other switches 20a, 20b are turned off. If the discharge lamp lighting device is operated in this state, a current flows from the internal power source (not shown) of the current-controlled oscillation circuit 3c via the frequency setting resistor 34 into the ground. Since the potential of the error amplifier 9 is lower than the upstream side of the frequency setting resistor 34, the current flows through the diode 35 into the error amplifier 9. Thus, the current-controlled oscillation circuit 3c is oscillated at an oscillation frequency corresponding to the sum of a current flowing from the internal power source through the frequency setting resistor 34 into the ground and a current drawn from the diode 35 into the error amplifier 9. This signal is amplified by the driver 3b and the inverter circuit 2 is driven, so that a direct current supplied from the direct current power source 1 is converted into a high frequency current, which is then supplied to the discharge lamp load circuit 5 to light the discharge lamp 5c.
[0141] On the other hand, if a current begins to flow through the discharge lamp load circuit 5, an alternating current, as in Fig. 26, flows through the detecting resistor 7, and integrated by the integrating circuit 8 to have a sum of the current (net current) in the forward and backward directions of the alternating current. This signal is input into the inversion-input end of the error amplifier 9. A difference from the reference voltage input into the non-inversion input end is amplified by the error amplifier 9, and output to cause the potential on the downstream side of the diode 35 to be changed. As a result, the current amount flowing from the current-controlled oscillation circuit 3c into the error amplifier 9 is varied to regulate the oscillation frequency of the current-controlled oscillation circuit 3c. The switching frequency is controlled so that the output from the current detecting circuit 6 may be equal to the reference voltage. The operation transfers to a steady state.
[0142] Also in this embodiment 10, if the switch unit 20 selects a reference voltage corresponding to the minimum net current, the error amplifier 9 controls the switching frequency of the inverter driving circuit 3 so that the net current to be supplied to the discharge lamp lighting device 5 may be equal to a current value corresponding to the selected reference voltage. In the steady state, there is a one-to-one correspondence between the reference voltage, the net current and the switching frequency, as in the embodiment 9. Accordingly, the relation between the reference voltage and the switching frequency as in Fig. 17 is stored in the storing circuit 32b. Thereby, it is possible to discriminate the rated value of the discharge lamp 5c attached from the switching frequency detected by the frequency detecting means 41. The operation circuit 32c and the switch unit 20 can effect an automatic switching to a reference voltage adapted to this rated value.
[0143] However, in this embodiment 10, a more precise discrimination of rated value can be effected in accordance with the following configuration and operation. As described above, in this embodiment 10, the current-controlled oscillation circuit 3c is controlled by the sum of current flowing into the frequency setting resistor 34 and the error amplifier 9. Therefore, if there is any variation in the resistance of the frequency setting resistor 34 in spite of setting the reference voltage output from the reference voltage circuit 14, the current value flowing out of the current-controlled oscillation circuit 3c may be varied. As a result, there occurs some variation in the switching frequency of the inverter circuit 3 corresponding to a predetermined reference voltage. Hence, it is difficult to discriminate the rated value precisely.
[0144] Thus, in this embodiment 10, the rated value of the discharge lamp 5c is discriminated directly from the relation between the net current value and the switching frequency as illustrated in Fig. 20, but not from the relation between the reference voltage and the switching frequency. More specifically, a signal of switching frequency from the frequency detecting means 41 and a signal of net current from the current detecting circuit 6 are input into the switch control portion 32. The switching frequency and the net current value are detected in the A/D converter 32a of the switch control portion 32. And the rated value of the discharge lamp 5c is discriminated directly from the data regarding the net current value and the switching frequency stored in the storing circuit 32b. The operation circuit 32c and the switch unit 20 effect an automatic switching to a reference voltage adapted to this rated value.
[0145] As described above, the reference voltage, the net current and the switching frequency are in the one-to-one relation in the steady state. Hence, the rated value of the discharge lamp 5c can be also discriminated from the net current and the switching frequency. In particular, the relation between the net current value and the switching frequency is determined only by the characteristics of the inverter circuit 2 and the discharge lamp load circuit 5. By adopting such a discrimination method, the rated value of the discharge lamp 5c can be always discriminated precisely without being affected by variation in the resistance of the frequency setting resistor 34.
[0146] As described above, this embodiment 10 has exactly the same effects as the embodiment 9 previously described. The rated value of the discharge lamp 5c is discriminated directly from the data of the net current output from the current detecting circuit 6 and the data of the switching frequency from the frequency detecting means 41. Thereby, a reference voltage is selected. With this, the rated value can be discriminated more precisely without being affected by the variation in the resistance of the frequency setting resistor 34.
[0147] As will be clear from the above description, the current-controlled oscillation circuit 3c in this embodiment 10 may be constituted by the voltage-controlled oscillation circuit. With this, the rated value can be discriminated from the relation between the net current and the switching frequency. There is exactly the same effect. Also in this embodiment 10, a way of getting the value of net current is to branch a signal output from the current detecting circuit 6 to the error amplifier 9 and input it into the switch control portion 32. Apart from the current detecting circuit 6 as described above, a current detecting circuit may be provided to input it into the switch control portion 32.
[0148] Further, in Fig. 19, a switching frequency is detected from the frequency output terminal 41a of the inverter driving circuit 3. In a case where a signal of net current output from the current detecting circuit 6 is not fully smoothed and contains a switching frequency component, this signal may be converted into digital form by the A/D converter 32a, and subjected to the Fourier transform by the operation circuit 32c to detect the switching frequency. In this case, there is no need of connecting to the frequency output terminal 41a, leading to a simpler configuration of the circuit.
Embodiment 11
[0149] Fig. 21 shows a circuit diagram of a discharge lamp lighting device according to an embodiment 11 of this invention. This invention has been achieved to resolve such a problem that in a case where one discharge lamp having a plurality of rated values such as an Hf fluorescent discharge lamp (type FHF32EX) manufactured by Mitsubishi Electric Oslum (with two rated values of 32W and 45W in the case of FHF32EX) is driven by the discharge lamp lighting device as shown in the embodiment 9, it is not possible for the switch control portion 32 singly to determine whether this discharge lamp is operated at 32W or 45W because there is only one characteristic curve representing the switching frequency fD for the reference voltage VREF.
[0150] The configuration and operation of this embodiment 11 will be described below with reference to Fig. 21. In Fig. 21, reference numeral 36 denotes external setting means for manually setting the rated value of the discharge lamp 5c from the outside, which is provided in the switch control portion 32. In this embodiment, this is an external setting switch which is able to change over three modes of "automatic mode", "32W mode" and "45W mode". Note that the same or like parts as in Fig. 15 are indicated by the like numerals, and are not described.
[0151] The operation of this embodiment 11 will be described below. In Fig. 21, if this discharge lamp is initiated, a reference voltage corresponding to the minimum net current is output from the reference voltage circuit 14. The error amplifier 9 sends a control signal to the inverter driving circuit 3 to control the switching frequency of the inverter circuit 2. A current to be supplied to the discharge lamp load circuit 5 is adjusted so that the output from the current detecting circuit 6 may be equal to the reference voltage. On the other hand, in the switch control portion 32 for a certain period of operation at this switching frequency, the setting condition of the external setting switch 36 is first detected. When it is set at an "automatic mode", the rated value of the discharge lamp 5c attached is automatically discriminated in accordance with the same procedure as in the embodiment 9, and after a fixed time period, the switching over to a reference voltage adapted to this rated value occurs. Also, when the external setting switch 36 is set at a "32W mode" or a "45W mode", the switch unit 20 is switched to light the discharge lamp 5c at a rated value set by this external setting switch 36, without the automatic discrimination.
[0152] Thus, according to this embodiment 11, in addition to the effects of the embodiment 9, there is an effect that the discharge lamp lighting device capable of coping with the discharge lamps having a plurality of rated values can be provided, owing to the external setting means 36 capable of manually setting the rated value which is appended in the switch control portion 32.
[0153] In the embodiment 11 as described above, the setting condition of the external setting switch 36 is first detected, and the switch control portion 32 controls the process corresponding to the "automatic mode", the "32W mode" or the "45W mode" to be performed in accordance with this setting condition. However, in a case where the characteristic curve for the reference voltage and the switching frequency of the discharge lamp having a plurality of rated values is known, it is first determined whether or not the discharge lamp has the plurality of rated values from the relation between the reference voltage and the switching frequency at the initiation. For the plurality of rated values, the setting condition of the external setting switch 36 may be checked. In this case, the rated value is automatically discriminated for the discharge lamps not having the plurality of rated values, in the same way as in the embodiment 9.
[0154] In the above embodiment 9, the external setting switch 36 has two modes of "32W mode" and "45W mode", besides the "automatic mode". If the number of contacts for the external setting switch 36 is increased, it is possible to deal with three or more rated values.
Embodiment 12
[0155] Fig. 22 shows a circuit diagram of a discharge lamp lighting device which can change continuously the brightness of the discharge lamp 5c as the reference voltage is changed, according to an embodiment 12 of this invention. In the figure, reference numerals 37a, 37b and 38 denote a buffer resistor, a buffer capacitor and a resistor, respectively. The buffer resistor 37a and the buffer capacitor 37b constitute a buffer integrating circuit 37 as a whole. Note that the same or like parts as in Fig. 15 are indicated by the like numerals, and are not described.
[0156] Thus, in this embodiment 12, in a case where the switches in the switch unit 20 for selecting the reference voltage are changed from the state where a switch 20a is on to the state where a switch 20b is on, the amount of variation in the voltage is integrated by the buffer integrating circuit 37. Therefore, the reference voltage input into the error amplifier 9 is continuously changed along with the integration constant of the buffer integrating circuit 37. If this integration constant is appropriately chosen, the reference voltage can be gradually changed, so that the light output can be changed smoothly.
[0157] According to this embodiment 12 described above, in addition to the effects of the embodiment 9, there is the following effect. Since the buffer integrating circuit 37 which is a buffer circuit is provided between the input end of the error amplifier 9 and the reference voltage circuit 14, to buffer the stepwise variations in the output of the reference voltage circuit 14 as the reference voltage is changed, and the signal input into the error amplifier 9 is changed gradually and continuously, it is possible to suppress the abrupt stepwise variations in the light output (brightness) of the discharge lamp 5c which may occur when automatically changed to a reference voltage adapted to a rated value of the discharge lamp 5c from the switching frequency at the initiation. Therefore, the user can relieve the sense of incompatibility or discomfort. Consequently, there is provided a discharge lamp lighting device which is very agreeable.
[0158] In this way, in the discharge lamp lighting device for automatically selecting the reference voltage by discriminating the rated value of the discharge lamp 5c at every initiation and switching the switch unit 20, the brightness of the discharge lamp 5c is varied at every initiation of the device. An abrupt change in the brightness at every initiation may be significantly less comfortable for the user. The discharge lamp lighting device in the embodiment 12 which can change the light output smoothly is very advantageous in practice.
[0159] Further, when switching from the reference voltage at the initiation to the 45W rating, for example, the switch control portion 32 controls the switching to be made step by step in the order of 32W, 40W and 45W, but not directly changing to a reference voltage at the 45W rating. Thereby, besides the effect of the buffer integrating circuit 37, the light output can be continuously changed, resulting in a more grateful discharge lamp lighting device.
[0160] In the embodiment 12, the buffer circuit 37 for input into the error amplifier 9 is the buffer integrating circuit 37 comprised of the buffer resistor 37a and the buffer capacitor 37b. Other configurations having the same function may be used, such as an integrating circuit with an operational amplifier.
Embodiment 13
[0161] Fig. 23 shows a circuit diagram of a discharge lamp lighting device according to an embodiment 9 of the invention. In the embodiments 9 to 12, the switch unit 20 is placed between the reference voltage generator 15 and the error amplifier 9, wherein a reference voltage for input into the error amplifier 9 is selected from among a plurality of reference voltages generated by the reference voltage generator 15 by the switch unit 20. In the embodiment 13 as shown in Fig. 23, however, each switch 20a, 20b, 20c of the switch unit 20 is connected in parallel with each dividing resistor 12a, 12b, 12c. Each switch 20a, 20b, 20c of the switch unit 20 is turned on or off to bypass each dividing resistor 12a, 12b, 12c. Thereby, the division ratio of the dividing resistors across the output end of the reference voltage connected to the error amplifier 9 is varied, so that the reference voltage is changed.
[0162] In Fig. 23, reference numeral 16 denotes a dividing resistor connected in series to the dividing resistors 12a, 12b, 12c and 13. Note that the same or like parts as in Fig. 15 are indicated by the like numerals, and are not described. Further, the operation is exactly the same as in the embodiment 9, and is not described.
[0163] Thus, according to the embodiment 13, in addition to the effects of the embodiment 9, there is the following effect. Since the switch unit 20 is connected in parallel with the dividing resistors 12a, 12b, 12c, a current through the dividing resistors from the direct current power source for reference voltage 11 will flow through the switch unit 20. A current value necessary to be stable against a secular change can be passed. Consequently, there is an effect that a discharge lamp lighting device which is endurable against the secular change and highly reliable can be provided.
[0164] In Fig. 23, each switch 20a, 20b, 20c of the switch unit 20 is connected in parallel between the upstream side of each dividing resistor 12a, 12b, 12c and the ground. However, each switch 20a, 20b, 20c of the switch unit 20 may be connected to bypass each dividing resistor 12a, 12b, 12c. In this case, a variety of division ratios can be obtained by switching each switch. A discharge lamp lighting device capable of dealing with more rated values with a smaller number of dividing resistors can be provided.
Embodiment 14
[0165] In the embodiments 4 to 13 as described previously, the reference voltage circuit 14 comprising the reference voltage generator 15 and the switch unit 20 may be mounted on a same circuit board as the error amplifier 9. A minute current flowing through the reference voltage generator 15 or the switch unit 20 can be prevented from fluctuating under the influence of the disturbance noise caused by discharging of the discharge lamp 5c to make the output of the discharge lamp 5c unstable. There is an advantage that the noise measures expense can be less than when the switch unit is installed in another circuit board.
Embodiment 15
[0166] Moreover, the circuit board may be accommodated within the case 24, as shown in Figs. 4 and 5, leading to less risk of damaging the circuit board when replacing the discharge lamp 5c. And if this case is made of metal, the noise caused by discharging of the discharge lamp 5c may be reduced.
[0167] In the embodiments 1 to 13, the integrating capacitor 10b is added to the error amplifier 9. However, if the integration constant for the integration circuit 8 is appropriately selected, there is no need of providing the integration function for the error amplifier 9. The capacitor 10b can be replaced with a resistor for amplification. Also, the function of the integration circuit 8 may be provided integrally within the error amplifier 9.
[0168] Also, in the embodiments 1 to 13, the number of reference voltages to be input into the error amplifier 9 is three. However, this number may be two or four. Thereby, the same effect can be obtained. Further, the discharge lamp load circuit 5 is for one discharge lamp. But it may be applied to two or more discharge lamps having the same rated value. The direct current power source for reference voltage 11 may use the stabilized DC voltage to be supplied from the direct current power source 1. With this, the power source can be commonly used, leading to reduction in the number of parts or cost.
[0169] The oscillation circuit within the inverter driving circuit 3 may be constituted of the current-controlled oscillation circuit (CCO) or the voltage-controlled oscillation circuit (VCO), so that the same effect can be expected, as described above.
[0171] A current supplied from the inverter circuit to the discharge lamp load circuit is controlled by the reference voltage output from the reference voltage circuit. And a plurality of different reference voltages can be output from the reference voltage circuit. Therefore, a discharge lamp lighting device capable of coping with the discharge lamp having different rated values can be provided.
[0172] The reference voltage circuit is provided with a reference voltage generator for generating a plurality of reference voltages which have been preset for the rated values of a discharge lamp, having a direct current power source for reference voltage and the dividing resistors. Therefore, there is no need of adjusting the reference voltage. As a result, a discharge lamp lighting device, which is easy to change the rated value, can be provided.
[0173] The reference voltage circuit is provided with a direct current power source for reference voltage and the dividing resistors, and reference voltage selecting means for selecting the reference voltage to be output from the reference voltage circuit is connected in parallel with the dividing resistors. Therefore, a discharge lamp lighting device which can operate stably against a secular change and is highly reliable can be provided.
[0174] The reference voltage selecting means may be a jumper wire. Therefore, a discharge lamp lighting device which has less degradation of the contacts due to minute current, can operate stably against a secular change, and is highly stable can be provided.
[0175] Also, the jumper wire is placed on a circuit board with the error amplifier packaged, and a work hole is drilled in the circuit board having the jumper wire mounted. The jumper wire can be checked for the setting condition or cut off through the work hole. The arrangement of the jumper wire, and the selection of the reference voltage can be checked. Or the rated value of the discharge lamp to be adapted can be altered from the back of the circuit board. After the component face of the circuit board is covered with a case or the like, the user can work without removing the case.
[0176] The reference voltage circuit is provided on the circuit board with the error amplifier packaged. Therefore, the discharge lamp can be prevented from being unstable in the output due to influence of disturbance noise. Additionally, the noise measures cost can be less than when installed on another circuit board.
[0177] Also, the circuit board with the reference voltage selecting means mounted may be accommodated within a metallic case, and an opening portion may be provided in the case. Therefore, the influence of disturbance noise can be reduced, and the circuit board can be protected from being damaged. Further, it is possible to check the setting condition of the reference voltage selecting means or change the setting of the reference voltage selecting means, without removing the case from the opening portion.
[0178] The operation parts of the reference voltage selecting means are arranged in the order of reference voltages. Therefore, it is possible to reduce the mistake in selecting the reference voltage by the reference voltage selecting means.
[0179] Also, the reference voltage selecting means discriminates the rated value of a discharge lamp attached in the discharge lamp load circuit, and automatically selects a reference voltage adapted to this rated value as the reference voltage output from the reference voltage circuit. The setting of the reference voltage is facilitated, leading to less failure in selecting the discharge lamp or setting the reference voltage.
[0180] Initial frequency setting means for setting a switching frequency of the inverter circuit is provided, and the reference voltage selecting means discriminates the rated value of a discharge lamp attached in the discharge lamp load circuit based on the output from the current detecting circuit when operated at the switching frequency set by the initial frequency setting means. Therefore, by appropriately setting the switching frequency at the initiation, the discharge lamp can be protected from a current beyond the rated value flowing to impair the discharge lamp, before discriminating the rated value.
[0181] Also, the reference voltage selecting means comprises a switch control portion having an A/D converter for converting the output of the current detecting circuit into digital data, a storing circuit for storing a current value of a discharge lamp corresponding to a switching frequency set by the initial frequency setting means, and an operation circuit for discriminating the rated value of the discharge lamp attached by comparing the digital data detected by the A/D converter and the current value stored in the storing circuit to output a control signal, and a switch unit for selecting a reference voltage to be output from the reference voltage circuit in accordance with the control signal from the operation circuit. Therefore, it is possible to cope with a variety of kinds of discharge lamps only by changing the data within the storing circuit. As a result, a discharge lamp lighting device, which has a wide range of applications, can be provided.
[0182] Frequency detecting means for detecting a switching frequency of the inverter circuit is provided, and the reference voltage selecting means discriminates the rated value of a discharge lamp attached in the discharge lamp load circuit, based on the switching frequency output from the frequency detecting means and the current value output from the current detecting circuit and supplied to the discharge lamp load circuit. Therefore, it is possible to discriminate the rated value of the discharge lamp correctly.
[0183] Also, the reference voltage selecting means comprises a switch control portion having an A/D converter for converting the output of frequency detecting means into digital data, a storing circuit for storing a switching frequency of the inverter circuit, and an operation circuit for discriminating the rated value of a discharge lamp attached by comparing the digital data detected by the A/D converter and the switching frequency stored in the storing circuit to output a control signal, and a switch unit for selecting a reference voltage to be output from the reference voltage circuit in accordance with the control signal from the operation circuit. Therefore, it is possible to cope with a variety of kinds of discharge lamps only by changing the data within the storing circuit. As a result, a discharge lamp lighting device, which has a wide range of applications, can be provided.
[0184] When the discharge lamp lighting device is initiated, the reference voltage selecting means selects a reference voltage corresponding to the minimum current from among the reference voltages which can be output from the reference voltage circuit. Therefore, the discharge lamp can be protected from an excessive current flowing through the discharge lamp having a small rated value to impair the discharge lamp.
[0185] In changing the reference voltage, the reference voltage selecting means selects a reference voltage in the order of the reference voltages closer to a selected reference voltage at the time of change. Therefore, the amount of variation in light output along with the change of reference voltage can be reduced. As a result, a discharge lamp lighting device which is more grateful can be provided.
[0186] Also, the reference voltage selecting means is provided with external setting means for manually setting the reference voltage output from the reference voltage circuit. Therefore, a discharge lamp lighting device capable of coping with the discharge lamp having a plurality of rated values can be provided.
[0187] Between the reference voltage circuit and the error amplifier, a buffer circuit for varying continuously the reference voltage input into the error amplifier is provided. Therefore, it is possible to suppress abrupt changes in light output of the discharge lamp along with the change of the reference voltage, so that the light output can be changed smoothly. As a result, it is possible to relieve the sense of incompatibility or discomfort of the user. A discharge lamp lighting device, which is agreeable to the user, can be provided.
Industrial Applicability
1. A discharge lamp lighting device comprising:
a direct current power source;
an inverter circuit for converting the direct current supplied from said direct current power source into high frequency current;
a discharge lamp load circuit for lighting a discharge lamp due to high frequency current from said inverter circuit;
a current detecting circuit for detecting the electric current supplied from said inverter circuit to said discharge lamp load circuit;
a reference voltage circuit which can output a plurality of different reference voltages;
an error amplifier for producing a control signal based on an output from said current detecting circuit and a reference voltage output from said reference voltage circuit;
an inverter driving circuit for driving said inverter circuit based on the control signal from said error amplifier to adjust the electric current supplied to said discharge lamp load circuit to a current value corresponding to a reference voltage output from said reference voltage circuit; and
reference voltage selecting means for selecting the reference voltage to be output from said reference voltage circuit.
2. The discharge lamp lighting device according to claim 1, wherein said reference voltage
selecting means selects a reference voltage to be output from said reference voltage
circuit by manual operation.
3. The discharge lamp lighting device according to claim 2, wherein said reference voltage
circuit comprises a reference voltage generator for generating a plurality of different
reference voltages corresponding to the preset rated values of a discharge lamp, said
reference voltage generator having a direct current power source for reference voltage
and the dividing resistors for dividing the voltage from said direct current power
source for reference voltage, and said reference voltage selecting means selects a
reference voltage for output from among the plurality of reference voltages generated
by said reference voltage generator.
4. The discharge lamp lighting device according to claim 2, wherein said reference voltage
circuit comprises a direct current power source for reference voltage, the dividing
resistors for dividing the voltage of said direct current power source for reference
voltage, and the reference voltage selecting means connected in parallel with the
dividing resistors, and said reference voltage selecting means selects the dividing
resistors for bypass to choose a reference voltage output from said reference voltage
circuit.
5. The discharge lamp lighting device according to claim 3, wherein a jumper wire is
used as said reference voltage selecting means.
6. The discharge lamp lighting device according to claim 5, wherein said jumper wire
is mounted on a circuit board with said error amplifier packaged therein, a work hole
is drilled on said circuit board with the jumper wire mounted to allow the confirmation
of the set conditions of said jumper wire and the cutting thereof through said work
hole.
7. The discharge lamp lighting device according to claim 2, wherein said reference voltage
circuit is provided on the circuit board with said error amplifier packaged therein.
8. The discharge lamp lighting device according to claim 2, wherein the circuit board
with said reference voltage selecting means mounted therein is contained within a
metallic case having an opening portion formed to allow the confirmation of the set
conditions of said reference voltage selecting means and the alteration of setting
through said opening portion.
9. The discharge lamp lighting device according to claim 2, wherein the operation parts
of said reference voltage selecting means are arranged in the order of reference voltages.
10. The discharge lamp lighting device according to claim 1, wherein said reference voltage
selecting means automatically selects a reference voltage adapted to a rated value
as the reference voltage to be output from said reference voltage circuit by discriminating
the rated value of a discharge lamp attached in said discharge lamp load circuit.
11. The discharge lamp lighting device according to claim 10, wherein initial frequency
setting means for setting the switching frequency of said inverter circuit is provided,
and said reference voltage selecting means discriminates the rated value of a discharge
lamp attached in said discharge lamp load circuit, based on an output from said current
detecting circuit when operated at a switching frequency set by said initial frequency
setting means.
12. The discharge lamp lighting device according to claim 11, wherein said reference voltage
selecting means comprises a switch control portion having an A/D converter for converting
the output of said current detecting circuit into digital form, a storing circuit
for storing a current value of a discharge lamp corresponding to a switching frequency
which has been set by said initial frequency setting means, and an operation circuit
for discriminating the rated value of the discharge lamp attached by comparison between
digital data detected by said A/D converter and the current value stored in said storing
circuit to output a control signal, and a switch unit for selecting a reference voltage
output from said reference voltage circuit in accordance with the control signal from
said operation circuit.
13. The discharge lamp lighting device according to claim 10, wherein frequency detecting
means for detecting a switching frequency of said inverter circuit is provided, and
said reference voltage selecting means discriminates the rated value of a discharge
lamp attached in said discharge lamp load circuit, based on the switching frequency
output from said frequency detecting means.
14. The discharge lamp lighting device according to claim 13, wherein said reference voltage
selecting means discriminates the rated value of a discharge lamp attached in said
discharge lamp load circuit, based on a switching frequency output from said frequency
detecting means and a current value output from said current detecting circuit and
supplied to said discharge lamp load circuit.
15. The discharge lamp lighting device according to claim 13, wherein said reference voltage
selecting means discriminates the rated value of a discharge lamp attached in said
discharge lamp load circuit, based on a reference voltage to be output from said reference
voltage circuit and a switching frequency output from said frequency detecting means.
16. The discharge lamp lighting device according to claim 13, wherein said reference voltage
selecting means comprises a switch control portion having an A/D converter for converting
an output of said frequency detecting means into digital data, a storing circuit for
storing a switching frequency of said inverter circuit, and an operation circuit for
discriminating the rated value of a discharge lamp attached by comparison between
digital data detected by said A/D converter and the switching frequency stored in
said storing circuit to output a control signal, and a switch unit for selecting a
reference voltage output from said reference voltage circuit in accordance with the
control signal from said operation circuit.
17. The discharge lamp lighting device according to claim 13, wherein when initiating
said discharge lamp lighting device, said reference voltage selecting means selects
a reference voltage corresponding to the minimum current value from among the reference
voltages which can be output from said reference voltage circuit.
18. The discharge lamp lighting device according to claim 10, wherein when changing the
reference voltage, said reference voltage selecting means selects a reference voltage
in the order of the reference voltages closer to that selected at the time of change.
19. The discharge lamp lighting device according to claim 10, wherein said reference voltage
selecting means is provided with external setting means for manually setting the reference
voltage output from said reference voltage circuit.
20. The discharge lamp lighting device according to claim 20, wherein there is provided
a buffer circuit for continuously changing the reference voltage for input into said
error amplifier between said reference voltage circuit and said error amplifier.
21. The discharge lamp lighting device according to claim 10, wherein said reference voltage
circuit comprises a reference voltage generator for generating a plurality of different
reference voltages corresponding to the preset rated values of a discharge lamp, said
reference voltage generator having a direct current power source for reference voltage
and the dividing resistors for dividing the voltage from said direct current power
source for reference voltage, and said reference voltage selecting means comprises
a switch unit for selecting a reference voltage for output from among the plurality
of reference voltages generated by said reference voltage generator.
22. The discharge lamp lighting device according to claim 10, wherein said reference voltage
circuit comprises a direct current power source for reference voltage, the dividing
resistor for dividing the voltage from said direct current power source for reference
voltage, and a switch unit consisting of the switches connected in parallel with said
dividing resistors, and said reference voltage selecting means selects a reference
voltage for output from said reference voltage circuit by choosing a switch within
said switch unit and the dividing resistors for bypass.
23. The discharge lamp lighting device according to claim 10, wherein said reference voltage
circuit is provided on a circuit board with said error amplifier packaged therein,
and said circuit board with said reference voltage circuit and said error amplifier
packaged therein is contained within a metallic case.