Lamp lighting control circuit

Abstract

 In a lamp lighting control circuit according to claim 1 for lighting a lamp (5) with an AC voltage output from an electric generator (2) which rotates in conjunction with an engine, a switching device (SCR2) is connected between the electric generator (2) and the lamp (5) and the switching device (SCR2) is turned on after a delay (Td) from a point of time (T1) when either one of positive and negative half-waves of said AC voltage begins to be generated from said electric generator (2). Preferably, the control circuit may further comprise a lamp effective voltage monitoring circuit (7a) for monitoring an effective voltage of the lamp (5), wherein said lamp effective voltage monitoring circuit (7a) prevents the turning on of the thyristor when it detects an overvoltage of said lamp (5).

Description

TECHNICAL FIELD

[0001] The present invention relates to a lamp lighting control circuit that conducts lighting of a lamp by using a voltage regulation circuit connected to an electric generator which rotates in conjunction with an engine.

BACKGROUND OF THE INVENTION

[0002] Conventionally, in some motorcycles for example, an AC voltage is generated by an electric generator rotating in conjunction with an engine, and the AC voltage is used to charge a battery as well as to light a lamp such as a headlight.

[0003] Figure 3 shows an example of a control circuit for controlling the battery charging and lamp lighting. In the shown circuit, an end tap (output terminal) of a coil 2 of a magneto-generator is connected to a power source terminal CH of the control circuit 11, while a battery 3 and a DC load 4 representing various electric equipment are connected to an output terminal BT of the control circuit 11.

[0004] In the control circuit 11, a battery charge control thyristor SCR1 is provided on a power line extending between the terminals CH and BT for transmitting positive waves of the AC voltage input to the power source terminal CH to the output terminal BT. The battery charge control thyristor SCR1 is controlled by a battery voltage detecting and controlling circuit 6 for detecting the voltage at the output voltage BT and preventing overcharge of the battery.

[0005] A lamp (headlight) 5 is connected to a lamp terminal LA of the control circuit 11. Between the power source terminal CH and the lamp terminal LA of the control circuit 11 is connected a lamp control thyristor SCR2 for transmitting negative waves of the AC voltage to the lamp 5. Further, a lamp voltage detecting circuit 12 is provided for keeping the lamp control thyristor SCR2 in an off state when it detects that an effective (or root mean square value of) voltage of the lamp exceeds a limit value (for example, 13V), to thereby protect the lamp 5.

[0006] Figure 4 is a waveform diagram showing lamp current control in the above circuit. The electric generator 2 provides an AC voltage having a sine waveform as shown in an upper part of Figure 4. As mentioned above, the lamp 5 is supplied only with the negative voltage waves, of which amplitude and hence the lamp effective voltage increases with the engine speed. Thus, as shown in the lower waveform in Figure 4, when the lamp effective voltage exceeds a limit value during one negative voltage half-wave, because consecutive voltage supply (phantom line in the drawing) could cause an overvoltage, the next negative voltage half-wave is prevented from being supplied to the lamp (solid line in the drawing) so that a so-called intermittent voltage supply control is conducted.

[0007] However, this may have a problem that in a low engine speed range, the intermittent voltage supply control can result in detectable flickering of the lamp. Further, in the above lamp lighting control circuit, since the lamp voltage may have a substantially the same peak (absolute) value as that of the AC generator voltage, there may be a problem that the increase in the generator voltage amplitude with the engine speed will cause an undesirable increase in the peak value of the lamp voltage, leading to a shorter operable period of time of the lamp.

BRIEF SUMMARY OF THE INVENTION

[0008] In view of such problems of the prior art and the recognition by the inventors, a primary object of the present invention is to provide a lamp lighting control circuit for a motor vehicle utilizing an electric generator which rotates in conjunction with an engine to generate an AC voltage that can suppress the lamp voltage so as to increase the operable period of time of the lamp.

[0009] A second object of the present invention is to provide a lamp lighting control circuit for a motor vehicle utilizing an electric generator which rotates in conjunction with an engine to generate an AC voltage that can prevent detectable flickering of the lamp as well as prevent overvoltage of the lamp.

[0010] A third object of the present invention is to provide a lamp lighting control circuit for a motor vehicle utilizing an electric generator which rotates in conjunction with an engine to generate an AC voltage that can reduce the electric power that the electric generator has to produce.

[0011] A fourth object of the present invention is to provide such a lamp lighting control circuit in a simple configuration with minimum modification to the conventional circuit and at low cost.

[0012] According to the present invention, these and other objects can be accomplished by providing a lamp lighting control circuit for lighting a lamp (5) with an AC voltage output from an electric generator (2) which rotates in conjunction with an engine, comprising: means (SCR2, 7b) for conducting either one of alternate positive and negative voltage half-waves of the AC voltage from the electric generator (2) to the lamp (5), wherein said means (SCR2, 7b) for conducting reduces a size of said voltage half-wave conducted to the lamp (5).

[0013] In this way, although the generated electricity increases with the engine speed, the reduction in the size of the voltage half-wave can achieve a reduced peak value of the lamp voltage for a given engine speed and accordingly, the engine speed at which the generated AC voltage reaches the rate voltage of the lamp can be shifted to a higher engine speed. This can lead to an extended operable period of time of the lamp.

[0014] The reduction of the size of the voltage half-wave conducted to the lamp (5) may be achieved by controlling an amplitude of said voltage half-wave or by delaying start of conduction of said voltage half-wave to the lamp (5).

[0015] According to an preferred embodiment of the invention, there is provided a lamp lighting control circuit for lighting a lamp (5) with an AC voltage output from an electric generator (2) which rotates in conjunction with an engine, comprising: a switching device (SCR2) connected between the electric generator (2) and the lamp (5); and a drive circuit (7b) for generating an activation signal for turning on said switching device (SCR2) when either one of positive and negative voltage half-waves of said AC voltage is generated from said electric generator (2), wherein said drive circuit (7b) turns on said switching device (SCR2) after a prescribed delay (Td) from a point of time (T1) when said either one of said positive and negative half-waves of said AC voltage begins to be generated from said electric generator (2).

[0016] Preferably, said drive circuit (7b) may comprise a delay circuit, which can be embodied by a CR time constant circuit (R3, C3). According to a preferred embodiment of the invention, said switching device consists of a thyristor (SCR2).

[0017] Thus, by delaying the turning on of the thyristor (SCR2) connected between the lamp (5) and the electric generator (2), it is possible to preferably reduce the size of the half-wave voltage provided to the lamp (5) and hence reduce the effective lamp voltage, without an undesirable dissipation of the generated electric power as heat.

[0018] The lamp lighting control circuit may further comprise a lamp effective voltage monitoring circuit (7a) for monitoring an effective voltage of the lamp (5), wherein said lamp effective voltage monitoring circuit (7a) prevents an operation of said drive circuit (7b) when it detects an overvoltage of said lamp (5).

[0019] Such a lamp effective monitoring circuit (7a) can conduct the intermittent voltage supply control to protect the lamp (5) from an overvoltage. At low engine speed where the intermittent voltage supply control would cause a detectable flickering of the lamp (5), however, since the lamp voltage control is preferably achieved by delaying the turning on of the thyristor (SCR2), the intermittent voltage supply control may be avoided.

[0020] Other and further objects, features and advantages of the invention will appear more fully from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Now the present invention is described in the following with reference to the appended drawings, in which:

Figure 1 is a schematic circuit diagram showing a lamp voltage regulation circuit (or lamp lighting control circuit) to which the present invention is applied;

Figure 2 is a waveform diagram for showing lamp lighting control according to the present invention;

Figure 3 is a schematic control circuit diagram for showing conventional lamp lighting control; and

Figure 4 is a waveform diagram for showing conventional lamp lighting control.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] Figure 1 is a schematic circuit diagram for showing a lamp voltage regulation circuit according to the present invention. In the drawing, similar parts to those in the conventional embodiment are denoted with the same reference numerals and the detailed explanation thereof is omitted.

[0023] As shown in Figure 1, a control circuit 1 comprises the terminals CH, BT and LA to which the battery 3, DC load, and lamp 5 are connected, respectively, in a similar fashion to the conventional embodiment. In the control circuit 1, the battery charge control thyristor SCR1, lamp control thyristor SCR2 and battery voltage detecting circuit 6 are provided also in a similar fashion to the conventional embodiment. Further, to the lamp lighting control circuit 7 for controlling a gate of the lamp control thyristor SCR2 is connected a generator output voltage detecting block 8. Thus, the lamp control thyristor SCR2, lamp lighting control circuit 7 and generator output voltage detecting block 8 constitute a lamp voltage regulation circuit.

[0024] Next, an inner configuration of the lamp lighting control circuit 7 is explained. A transistor Q1 is connected to the gate of the lamp control thyristor SCR2. The transistor Q1 is adapted to be turned on when another transistor Q2 is turned on. A diode D1 is connected to the power source terminal CH so as to permit an electric current only toward the power source terminal CH, and via the diode D1, the transistor Q2 and a transistor Q3 for on/off controlling the transistor Q2 are connected to the terminal CH. A base of the transistor Q2 is connected to ground via a resistor R1.

[0025] Between the diode D1 and the generator output voltage detecting block 8 is provided a lamp voltage detection block 7a serving as a lamp effective voltage monitoring circuit. The above transistor Q3 constitutes an output stage of the lamp voltage detection block 7a so that turning on of the transistor Q3 causes the transistor Q2 to be turned off. A transistor Q4 that is turned on while an electric current is flowing through the lamp 5 is connected to the generator voltage detecting block 8.

[0026] Further, a noise absorbing circuit comprising a capacitor C2 and a resistor R2 is provided between the base and emitter of the transistor Q1. Similarly, between the base and emitter of the transistor Q2 are provided a capacitor C3 and a resistor R3 connected in parallel for constituting a CR time constant circuit serving as a delay circuit 9, which may also function as a noise absorbing circuit. Thus, as shown in Figure 1, the delay circuit 9 and the transistors Q1, Q2 constitute a drive circuit 7b.

[0027] The lamp voltage detection block 7a in the control circuit 1 detects the lamp effective voltage based on charging and discharging of a capacitor C1 provided in a base circuit of the transistor Q3. The capacitor C1 is charged by an electric current flowing through the transistor Q4 and the generator output voltage detecting block 8 so that the capacitor C1 is charged only while and an electric current is flowing through the lamp 5 and discharged through a resister connected thereto in parallel during other period of time. Further, a zener diode ZD1 is provided between the capacitor C1 and the base of the transistor Q3 so that a limit value of the lamp effective voltage for prohibiting the turning on of the thyristor SCR2 is set by a breakdown voltage of the zener diode ZD1, as described more in detail later.

[0028] An operation of the control circuit 1 constructed as above is explained hereinafter. When a negative voltage is generated from the electric generator 2, an electric current first flows to the capacitor C3 in the delay circuit 9 via the resistor R1 so as to charge the capacitor C3, and after a prescribed delay time defined by the delay circuit 9 (or after a time required for fully charging the capacitor C3) from the generation of the negative voltage from the electric generator 2, a base current flows to the base of the transistor Q2 to turn it on. The turning on of the transistor Q2 causes the transistor Q1 to turn on so that a gate voltage is applied to the lamp control thyristor SCR2. This turns on the thyristor SCR2, whereby the lamp 5 is lighted.

[0029] In this way, as shown in Figure 2, the lamp voltage (lower waveform) is generated after a delay time Td has passed from a negative voltage generation timing T1 in the AC voltage (upper waveform). It should be noted that the delay time Td is determined so that the magnitude (absolute value) of the AC voltage begins to decrease when the magnitude of the lamp voltage is still increasing. This results in the lamp voltage having a smaller peak value (or amplitude) VL_max than a peak value VG_max of the AC voltage (VL_max<VG_max). Also, the period of time during which the voltage is applied to the lamp 5 (or duration time) is reduced due to the delay time Td. Thus, by delaying the turning on of the thyristor SCR2 from the negative voltage generation timing T1, a size (amplitude and duration time) of the voltage half-wave provided to the lamp 5 can be reduced and accordingly the effective voltage of the lamp 5 can be preferably reduced.

[0030] According to the reduction in size of the voltage half-wave provided to the lamp 5, the amount of electric charge stored in the capacitor C1 in the lamp voltage detection block 7a by a single wave (a negative wave for lighting the lamp) is also reduced with respect to the case where the lamp lighting is started without the delay time Td (phantom line in Figure 2). Thus, at low engine speed where the intermittent voltage supply control would cause a detectable flickering of the lamp 5a, the voltage of the capacitor C1 does not reach the breakdown voltage of the zener diode ZD1 and thus, the intermittent voltage supply control can be avoided at such low engine speed.

[0031] As the engine speed increases higher, the peak value VG_max of the AC voltage from the electric generator 2 increases, which in turn increases the peak value VL_max of the lamp voltage having the delay time Td relative to the generator voltage. And at a certain high engine speed, the voltage of the capacitor C1 reaches the breakdown voltage of the zener diode ZD1 so that the transistor Q3 is turned on. This prevents the turning on of the transistor Q2 which in turn prevents the thyristor SCR2 from turning on. Thus, in the control circuit 1 also, the intermittent voltage supply to the lamp 5 can take place as in the conventional circuit. However, in the control circuit 1 of the present invention, the intermittent voltage supply control takes place only at a sufficiently high engine speed range where the frequency of the AC voltage from the electric generator 2 is sufficiently high and the intermittent voltage supply control would not cause a detectable flickering of the lamp 5.

[0032] Since the engine speed at which the peak lamp voltage VL_max reaches the rated maximum voltage of the lamp 5 is relatively high, the number of occasions that the lamp 5 is applied with its rated maximum voltage can be reduced whereby an extended operable period of time of the lamp 5 is achieved. Further, since the delay circuit 9 can also function as a noise absorbing circuit for the transistor Q3 and thus no additional circuit is required, a simple control circuit can be achieved with a reduced manufacturing cost.

[0033] As described above, according to the present invention, the turning on of the thyristor SCR2 is controlled by the drive circuit 7b so that the size of the voltage half-wave (or the amount of electricity) conducted to the lamp 5 is reduced with respect to the case where the generated electricity, which increases with the engine speed, is supplied to the lamp 5 directly without delay. This can reduce the peak value of the lamp voltage for a given engine speed, and the engine speed at which the AC voltage reaches the rated lamp voltage is shifted to a higher engine speed side, whereby an extended operable period of time of the lamp 5 is preferably achieved. Further, the reduction in size of the voltage half-wave conducted to the lamp 5 can reduce the effective lamp voltage without conducting intermittent voltage supply control. Although the intermittent voltage supply control to the lamp could take place to protect the lamp 5 from an excessive generated electric power, such intermittent lamp voltage supply control will take place only in a high engine speed range where the frequency of the AC voltage is sufficiently high and the lamp flickering due to the intermittent lamp voltage supply control can be inconspicuous. Therefore, it is possible to prevent flickering of the lamp at low engine speed and at the same time to prevent overvoltage of the lamp at high engine speed.

[0034] The control of the amplitude of the half-wave supplied to the lamp 5 may be achievable by connecting a resister between the electric generator 2 and the lamp 5. However, in such a case, an electric power would be dissipated as heat at the resister and this would be undesirable in view of minimizing the electric power that the electric generator 2 has to produce. In the control circuit according to the invention, the lamp voltage control can be preferably achieved by delaying the turning on of the thyristor SCR2 connected between the lamp 5 and the generator 2 without causing an undesirable dissipation of the generated electric power.

[0035] Although the present invention has been described in terms of preferred embodiments thereof, it is obvious to a person skilled in the art that various alterations and modifications are possible without departing from the scope of the present invention which is set forth in the appended claims. For example, although in the above shown embodiment a negative voltage of the AC voltage was used in lighting the lamp, it may be possible to reverse the polarity of the voltages and obtain the same effects.

Claims

1. A lamp lighting control circuit for lighting a lamp (5) with an AC voltage output from an electric generator (2) which rotates in conjunction with an engine, comprising:

means (SCR2, 7b) for conducting either one of alternate positive and negative voltage half-waves of the AC voltage from the electric generator (2) to the lamp (5),
wherein said means (SCR2, 7b) for conducting reduces a size of said voltage half-wave conducted to the lamp (5).

2. A lamp lighting control circuit according to claim 1, wherein said reduction of the size of said voltage half-wave is achieved by controlling an amplitude of said voltage half-wave.

3. A lamp lighting control circuit according to claim 1, wherein said reduction of the size of said voltage half-wave is achieved by delaying start of conduction of said voltage half-wave to the lamp (5).

4. A lamp lighting control circuit for lighting a lamp (5) with an AC voltage output from an electric generator (2) which rotates in conjunction with an engine, comprising:

a switching device (SCR2) connected between the electric generator (2) and the lamp (5); and

a drive circuit (7b) for turning on said switching device (SCR2) when either one of positive and negative voltage half-waves of said AC voltage is generated from said electric generator (2),
wherein said drive circuit (7b) turns on said switching device (SCR2) after a prescribed delay (Td) from a point of time (T1) when said either one of said positive and negative half-waves of said AC voltage begins to be generated from said electric generator (2).

5. A lamp lighting control circuit according to claim 4, wherein said drive circuit (7b) comprises a delay circuit (R3, C3).

6. A lamp lighting control circuit according to claim 5, wherein said delay circuit consists of a CR time constant circuit (R3, C3).

7. A lamp lighting control circuit according to claim 4, wherein said switching device consists of a thyristor (SCR2).

8. A lamp lighting control circuit according to claim 4, further comprising a lamp effective voltage monitoring circuit (7a) for monitoring an effective voltage of the lamp (5), wherein said lamp effective voltage monitoring circuit (7a) prevents an operation of said drive circuit (7b) when it detects an overvoltage of said lamp (5).

Drawing