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(11) | EP 3 589 080 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | LED LINEAR DRIVING CIRCUIT |
| (57) The disclosure relates to an LED linear driving circuit, which is used for driving
sequentially series-connection n LED loads, wherein the anode of a first LED load
is connected with the anode of a direct current (DC) voltage, and the cathode of an
(n-1)-th LED load is connected with the anode of an n-th LED load; the n is greater
than or equal to 2; and the LED linear driving circuit is characterized by comprising
an input voltage sampling circuit, an error amplifying circuit, an adder circuit,
a current detecting circuit and a load switching circuit. The LED linear driving circuit
may help the waveform of the input current to basically follow the waveform of the
input voltage to show a waveform of the sine wave; in the LED linear driving circuit,
MOS tubes utilize discrete devices and are arranged on a PCB in parallel, so that
the arrangement positions of the MOS tubes are flexible, and excellent heat dissipation
performance and reliability are achieved; additionally, one or a plurality of LED
loads can be randomly utilized according to system efficiency requirements, and the
more the utilized LED loads are, the higher the efficiency is. |
TECHNICAL FIELD
[0001] The present disclosure relates to the field of driving circuits, and in particular to an LED linear driving circuit.
BACKGROUND
[0002] In the existing LED linear driving circuit solution, the input current of the LED linear driving circuit is mostly formed by superimposing 3 to 5 rectangular wave currents so that the power factor of the LED linear driving circuit is relatively lower and the harmonic wave is hard to pass the existing standard. Moreover, in the existing LED linear driving circuit solution, it mostly utilizes chip package, integrates power MOS tubes and utilizes the constant number of LED loads so that the power MOS tubes are hard to dissipate heat, or it needs a plurality of chips to be arranged in parallel, wherein the number of the LED loads is constant, so that the design is not enough flexible and the efficiency is not high.
SUMMARY
[0003] A technical problem to be solved by the present disclosure is to provide an LED linear driving circuit by aiming at the prior art above.
[0004] In order to solve the technical problem above, a technical solution adopted by the present disclosure is as follows: an LED linear driving circuit is used for driving sequentially series-connection n LED loads, the anode of a first LED load is connected with the anode of a direct current (DC) voltage, and the cathode of an (n-1)-th LED load is connected with the anode of an n-th LED load; the n is greater than or equal to 2; and the LED linear driving circuit is characterized by comprising an input voltage sampling circuit, an error amplifying circuit, an adder circuit, a current detecting circuit and a load switching circuit; wherein:
a first input end of the input voltage sampling circuit is connected with the anode or the cathode of the first LED load, a first output end of the input voltage sampling circuit is connected with a first input end of the error amplifying circuit, and a second output end of the input voltage sampling circuit is grounded;
a second input end of the error amplifying circuit is connected with a first output end of the adder circuit, and a first output end of the error amplifying circuit is connected with a first input end of the load switching circuit;
a first input end of the adder circuit is connected with a first output end of the current detecting circuit, and a second input end of the adder circuit is connected with the cathode of the n-th LED load;
a first input end of the current detecting circuit is connected with a first output end of the load switching circuit, and a second output end of the current detecting circuit is grounded; and
an n-th input end of the load switching circuit is connected with the cathode of the (n-1)-th LED load.
[0005] Preferably, in the LED linear driving circuit, the input voltage sampling circuit comprises: a fourth resistor and a fifth resistor; a first end of the fourth resistor is connected with the first input end of the input voltage sampling circuit, and a second end of the fourth resistor is connected with the first output end of the input voltage sampling circuit; and a first end of the fifth resistor is connected with the first output end of the input voltage sampling circuit, and a second end of the fifth resistor is grounded.
[0006] Preferably, in the LED linear driving circuit, the error amplifying circuit comprises: a first triode and a second triode; the first triode is an PNP type triode, the base of the first triode is connected with the collect of the second triode, the emitter of the first triode is connected with the first output end of the error amplifying circuit, and the collect of the first triode is grounded; and
the second triode is an NPN type triode, the base of the second triode is connected with the second input end of the error amplifying circuit, and the emitter of the second triode is connected with the first input end of the error amplifying circuit.
[0007] Preferably, in the LED linear driving circuit, the adder circuit comprises: a sixth resistor and a seventh resistor; a first end of the sixth resistor is connected with the first input end of the adder circuit, and a second end of the sixth resistor is connected with the first output end of the adder circuit; and
a first end of the seventh resistor is connected with the second input end of the adder circuit, and a second end of the seventh resistor is connected with the first output end of the adder circuit.
[0008] Preferably, in the LED linear driving circuit, the current detecting circuit comprises: a fourth diode, an eighth resistor and a ninth resistor; and the fourth diode and the ninth resistor are connected in parallel, the anode of the fourth diode is connected with the first input end of the current detecting circuit, the cathode of the fourth diode is connected with a first end of the eighth resistor, and a second end of the eighth resistor is grounded.
[0009] More preferably, in the LED linear driving circuit, the load switching circuit comprises: a first switching circuit and a second switching circuit; wherein:
a first input end of the first switching circuit is connected with a third input end of the load switching circuit, a second input end of the first switching circuit is connected with the first input end of the load switching circuit, a third input end of the first switching circuit is connected with a second input end of the load switching circuit, and a first output end of the first switching circuit is connected with the first output end of the load switching circuit; and
a first input end of the second switching circuit is connected with a fourth input end of the load switching circuit, a second input end of the second switching circuit is connected with the first input end of the load switching circuit, a third input end of the second switching circuit is connected with a third input end of the load switching circuit, and a first output end of the second switching circuit is connected with the first output end of the load switching circuit.
[0010] Furthermore, in the LED linear driving circuit, the x-th switching circuit comprises: an x-th resistor Rx, an x-th diode Dx, an x-th MOS tube Mx and an x-th controllable switch Sx, and the x is greater than or equal to 2; wherein:
a first end of the x-th resistor Rx is connected with the grid of the x-th MOS tube Mx, and a second end of the x-th resistor Rx is connected with the drain of the x-th MOS tube Mx;
the anode of the x-th diode Dx is connected with the grid of the x-th MOS tube Mx, and the cathode of the x-th diode Dx is connected with a second input end of the x-th switching circuit;
the grid of the x-th MOS tube Mx is connected with one end of the x-th controllable switch Sx, the drain of the x-th MOS tube Mx is connected with a third input end of the x-th switching circuit, and the source of the x-th MOS tube Mx is connected with a first output end of the x-th switching circuit; and
the other end of the x-th controllable switch Sx is connected with the first output end of the x-th switching circuit, the positive electrode of a switch control end of the x-th controllable switch Sx is connected with a first input end of the x-th switching circuit, and the negative electrode of the switch control end of the x-th controllable switch Sx is connected with the first output end of the x-th switching circuit.
[0011] Compared with the prior art, the present disclosure has the advantages:
firstly, the LED linear driving circuit provided by the present disclosure may help the waveform of the input current to basically follow the waveform of the input voltage to show the waveform of the sine wave so that the waveform of the input current in the circuit may more easily pass the existing standard;
secondly, in the LED linear driving circuit provided by the present disclosure, the MOS tubes utilize discrete devices, and the MOS tubes are arranged on a PCB in parallel, so that the arrangement positions of the MOS tubes are more flexible, and the heat dissipation performance and the reliability of the MOS tubes are effectively improved;
thirdly, in the LED linear driving circuit provided by the present disclosure, the current detecting circuit comprises the fourth diode, the eighth resistor and the ninth resistor, the fourth diode is configured to counteract BE junction voltage of the triode Q2 of the error amplifying circuit so that the waveform of the current is closer to the waveform of the output voltage of the input voltage sampling circuit; and the ninth resistor is configured to further regulate the waveform of the current to be closer to the waveform of the output voltage of the input voltage sampling circuit; therefore, high power factor (PF) and low harmonic wave of the circuit is achieved; and
finally, the LED linear driving circuit provided by the present disclosure may randomly utilize one or a plurality of LED loads according to system efficiency requirements, wherein the more the utilized LED loads are, the higher the obtained efficiency is.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012]
FIG. 1 is a schematic diagram illustrating an LED linear driving circuit in an embodiment.
FIG. 2 is a schematic diagram illustrating an input voltage sampling circuit in the embodiment.
FIG. 3 is a schematic diagram illustrating an error amplifying circuit in the embodiment.
FIG. 4 is a schematic diagram illustrating an adder circuit in the embodiment.
FIG. 5 is a schematic diagram illustrating a current detecting circuit in the embodiment.
FIG. 6 is a schematic diagram illustrating a load switching circuit in the embodiment.
DESCRIPTION OF THE EMBODIMENTS
[0013] The present disclosure is described in further detail below in conjunction with accompanying drawings and embodiments.
[0014] As shown in FIG. 1, an LED linear driving circuit in an embodiment is used for driving sequentially series-connection n LED loads, wherein the n LED loads are respectively LED 1, LED 2, LED 3 and LED n; the n is greater than or equal to 2; and an AC power supply and a rectifier bridge circuit are marked as 11, and an LED load circuit is marked as 12. The LED linear driving circuit 10 comprises: an input voltage sampling circuit 101, an error amplifying circuit 102, an adder circuit 103, a current detecting circuit 104 and a load switching circuit 105; wherein,
a first input end of the input voltage sampling circuit 101 is connected with the anode or the cathode of the load LED 1, a first output end of the input voltage sampling circuit 101 is connected with a first input end of the error amplifying circuit 102, and a second output end of the input voltage sampling circuit 101 is grounded; therefore, the waveform and the size of an input voltage are obtained, and a reverse input end of the error amplifying circuit 102 is achieved;
a second input end of the error amplifying circuit 102 is connected with a first output end of the adder circuit 103, and a first output end of the error amplifying circuit 102 is connected with a first input end of the load switching circuit 105; therefore, the size and the waveform of the current of LED loads are controlled to obtain an input current with a certain value and a waveform similar to the waveform of the sine wave;
a first input end of the adder circuit 103 is connected with a first output end of the current detecting circuit 104, and a second input end of the adder circuit 103 is connected with the cathode of the load LED n; therefore, a voltage, including the sum of the size of the current of the LED loads and the size of the input voltage, is generated to counteract input power variation caused by input voltage variation, and the constant input power or input current is basically achieved;
a first input end of the current detecting circuit 104 is connected with a first output end of the load switching circuit 105, and a second output end of the current detecting circuit 104 is grounded; therefore, the current of the LED loads is transformed into a voltage signal with a certain ratio;
a second input end of the load switching circuit 105 is connected with the cathode of the load LED 1, a third input end of the load switching circuit 105 is connected with the cathode of the load LED 2, and by that analogy, an n-th input end of the load switching circuit 105 is connected with the cathode of the load LED n; therefore, the number of the LED loads is switched to ensure that there are enough LEDs to be lightened under a certain condition, so relatively higher efficiency of a power supply is obtained.
[0015] The voltage of the commercial power generates an absolute value waveform of one sine wave after passing through the rectifier bridge circuit 11, such waveform passes through the input voltage sampling circuit 101, an absolute value waveform of a sine wave with a certain value is generated at the first output end of the input voltage sampling circuit 101, and the error amplifying circuit 102 reverses a reference voltage.
[0016] When the voltage gradually increases from 0 V to a value larger than the turn-on voltage of the load LED 1, an internal control circuit of the load switching circuit 105 controls an MOS tube between the second input end and the first output end of the load switching circuit 105 to be turned on, the MOS tube may also be turned on before the voltage reaches the turn-on voltage of the load LED 1, at this time the load LED 1 generates a current, the current flows through the current detecting circuit 104 and then returns a ground wire, a voltage with a certain value is generated at the first output end of the current detecting circuit 104, and the generated voltage reaches the second input end of the error amplifying circuit 102 after passing through the adder circuit 103; if the generated voltage is larger than the output voltage of the input voltage sampling circuit 101, the grid voltage of the MOS tube in the load switching circuit 105 is pulled down by the first output end of the error amplifying circuit 102; and otherwise, the grid voltage of the MOS tube in the load switching circuit 105 is pulled up; therefore, the circuit may ensure the consistency of the waveform of the current flowing through the LED loads and the waveform of the input voltage;
when the voltage continuously increases to be larger than the sum of the voltage of the load LED 1 and the voltage of the LED 2, the load switching circuit 105 helps a MOS tube between the third input end and the first output end of the load switching circuit 105 to be turned on, and meanwhile, the MOS tube between the second input end and the first output end of the load switching circuit 105 is turned off; it is tested that the load LED 1 and the load LED 2 generate the current, and the waveform of the current is under the control like the foregoing; by that analogy, the load LED n is turned on; and
when the input voltage drops, the LED loads are sequentially turned off from the load LED n to the load LED 1, and at this time, a work cycle is complete.
[0017] When the effective value of the input voltage increases, the voltage outputted by the input voltage sampling circuit 101 also increases, and if the voltage is not to be controlled, the input power also increases, so a compensating circuit needs to be additionally configured. Specifically, the control on the voltage outputted by the input voltage sampling circuit 101 is implemented by the adder circuit 103. In the embodiment, the second input end of the adder circuit 103 is connected with the cathode of the load LED n, and the second input end of the adder circuit 103 may also be connected with any nodes capable of showing variation of the effective value of the input voltage. When the effective value of the input voltage increases, the effective value of the cathode voltage of the load LED n also increases, so that the voltage of the second input end of the adder circuit 103 also increases, the voltage of the first output end of the adder circuit 103 also increases, and then the voltage (forward) of the second input end of the error amplifying circuit 102 increases; for the error amplifying circuit 102, if its forward voltage and backward voltage increase the same amplitude, the output voltage is changeless, that is, the current of the LED load is changeless; and if the increased amplitude of its forward voltage is greater than the increased amplitude of its backward voltage, the output current of the LED load is to be small, so the circuit may be in the constant current or constant power state by reasonably regulating the increased amplitudes of its forward voltage and backward voltage.
[0018] FIG. 2 is a schematic diagram illustrating the input voltage sampling circuit 101 in the embodiment. As shown in FIG. 2, a first end of a resistor R4 is connected with the first input end of the input voltage sampling circuit 101, and a second end of the resistor R4 is connected with the first output end of the input voltage sampling circuit 101; and a first end of the resistor R5 is connected with the first output end of the input voltage sampling circuit 101, and a second end of the resistor R5 is grounded. An input voltage with a certain value is obtained based on voltage division of the resistor R4 and the resistor R5, the reference waveform of the current is provided, and the reference amplitude of the current is also provided.
[0019] FIG. 3 is a schematic diagram illustrating the error amplifying circuit 102 in the embodiment. As shown in FIG 3, the error amplifying circuit 102 comprises a triode Q1 and a triode Q2, the triode Q1 is an PNP type triode, the base of the triode Q1 is connected with the collect of the triode Q2, the emitter of the triode Q1 is connected with the first output end of the error amplifying circuit 102, and the collect of the triode Q1 is grounded; and the triode Q2 is an NPN type triode, the base of the triode Q2 is connected with the second input end of the error amplifying circuit 102, and the emitter of the triode Q2is connected with the first input end of the error amplifying circuit 102.
[0020] When the LED output current is greater than a preset value, the driving current of the BE electrode of the triode Q2 increases, the current is amplified by the triode Q2 and is used for driving the BE electrode of the triode Q1, and at this time, the current of the collect of the triode Q1 also increases, so that the driving voltage of the MOS tube in the load switching circuit 105 drops, and the LED output current drops; and vice versa. Finally, the LED output current is consistent with the sampling voltage of the voltage sampling circuit 101.
[0021] FIG. 4 is a schematic diagram illustrating the adder circuit 103 in the embodiment. As shown in FIG 4, the adder circuit 103 comprises a resistor R6 and a resistor R7; a first end of the resistor R6 is connected with the first input end of the adder circuit 103, and a second end of the resistor R6 is connected with the first output end of the adder circuit 103; and a first end of the resistor R7 is connected with the second input end of the adder circuit 103, and a second end of the resistor R7 is connected with the first output end of the adder circuit 103.
[0022] Because the resistance of the resistor R6 and the resistance of the resistor R7 are much larger than the internal resistance of the current detecting circuit 104, the output voltage of the current detecting circuit 104 may be approximated to be as a voltage source, and the output voltage of an adder may be approximated to the sum of the output voltage of the current detecting circuit 104 and a certain ratio of the cathode voltage of the load LED n, wherein the ratio is R6/(R6+R7).
[0023] FIG. 5 is a schematic diagram illustrating the current detecting circuit 104 in the embodiment. As shown in FIG 5, the current detecting circuit 104 comprises a fourth diode D4, an eighth resistor R8 and a ninth resistor R9; and the fourth diode D4 and the ninth resistor R9 are connected in parallel;
the anode of the fourth diode D4 is connected with the first input end of the current detecting circuit 104, and the cathode of the fourth diode D4 is connected with a first end of the resistor R8; and a second end of the resistor R8 is grounded.
[0024] The resistor R8 is a current sampling resistor, and the fourth diode D4 is used for counteracting the BE junction voltage of the triode Q2 in the error amplifying circuit 102 so that the waveform of the current is closer to the output voltage of the input voltage sampling circuit 101; and the resistor R9 is auxiliary to further regulate the waveform of the current to be closer to the output voltage of the input voltage sampling circuit 101, so that high PF and low harmonic wave of the circuit are achieved.
[0025] FIG. 6 is a schematic diagram illustrating the load switching circuit 105 in the embodiment. The load switching circuit 105 comprises: a first switching circuit 1051, a second switching circuit 1052, a third switching circuit 1053, and by that analogy, an n-th switching circuit 105n; the n is the number of the needed switching circuits, and the more the number is, the higher the system efficiency is; wherein:
a first input end of the first switching circuit 1051 is connected with a third input end of the load switching circuit 105, a second input end of the first switching circuit 1051 is connected with the first input end of the load switching circuit 105, a third input end of the first switching circuit 1051 is connected with a second input end of the load switching circuit 105, and a first output end of the first switching circuit 1051 is connected with the first output end of the load switching circuit 105; and
a first input end of the second switching circuit 1052 is connected with a fourth input end of the load switching circuit 105, a second input end of the second switching circuit 1052 is connected with the first input end of the load switching circuit 105, a third input end of the second switching circuit 1052 is connected with a third input end of the load switching circuit 105, and a first output end of the second switching circuit 1052 is connected with the first output end of the load switching circuit 105; a connection manner of the third switching circuit 1053 is analogized; and a first input end of the n-th switching circuit 105n is connected with an n-th input end of the load switching circuit 105, a second input end of the n-th switching circuit 105n is connected with the first input end of the load switching circuit 105, a third input end of the n-th switching circuit 105n is connected with an n-th input end of the load switching circuit 105, and a first output end of the n-th switching circuit 105n is connected with the first output end of the load switching circuit 105.
[0026] For any one switching circuit 105x ranged from the first switching circuit 1051 to the n-th switching circuit 105n, the n-th switching circuit 105n comprises: an x-th resistor Rx, an x-th diode Dx, an x-th MOS tube Mx and an x-th controllable switch Sx. For convenient expression, the x represents the x-th switching circuit 105x (the x is greater than or equal to 1 and smaller than or equal to n).
[0027] One end of the x-th resistor Rx is connected with the grid of the x-th MOS tube Mx, and the other end of the x-th resistor Rx is connected with the drain of the x-th MOS tube Mx; the anode of the x-th diode Dx is connected with the grid of the x-th MOS tube Mx, and the cathode of the x-th diode Dx is connected with a second input end of the x-th switching circuit 105x; and
the grid of the x-th MOS tube Mx is connected with one end of the x-th controllable switch Sx, the drain of the x-th MOS tube Mx is connected with a third input end of the x-th switching circuit 105x, and the source of the x-th MOS tube Mx is connected with a first output end of the x-th switching circuit 105x; and the other end of the x-th controllable switch Sx is connected with the first output end of the x-th switching circuit 105x, the positive electrode of a switch control end of the x-th controllable switch Sx is connected with a first input end of the x-th switching circuit 105x, and the negative electrode of the switch control end of the x-th controllable switch Sx is connected with the first output end of the x-th switching circuit 105x.
[0028] The x-th resistor Rx is used for providing a voltage for turning on the x-th MOS tube Mx, the voltage needs to be provided while or before the drain of the x-th MOS tube Mx generates the voltage, that is, while or before the input voltage is equal to the sum of forward voltages of LED 1, LED 2 and LED n, the x-th MOS tube Mx is in an on state; and its power supply connection position is not limited to the drain of the x-th MOS tube Mx, it may be the drain of the x-th MOS tube Mx or any other nodes with the voltage higher than the voltage of the drain of the x-th MOS tube Mx. Meanwhile, the voltage of the grid of the (x-1)-th MOS tube is pulled down by the controllable switch S(x-1) when the drain of the x-th MOS tube Mx generates the voltage, that is, the (x-1)-th MOS tube is turned off; and because the grid of each MOS tube is connected with the same node through the diode Dx, the pulling down of the voltage of the grid of the MOS tubes in the same path does not influence the turning on of the other MOS tubes. Therefore, the LED loads may be switched when the voltage increases, so that there are sufficient more LED loads to be turned on, that is, the system efficiency is improved; and when the voltage drops, the switching circuit 105x operates reversely.
[0029] A control signal of each controllable switch Sx obtains a signal from the drain of the MOS tube M(x+1), but the last controllable switch Sn obtains the signal from the MOS tube Mn, wherein the signal is not used for switching the LED loads, but is used for implementing over-voltage protection of the input voltage to help the circuit in a protection state when the input voltage is over high, that is, the MOS tube Mn is turned off, and the whole circuit does not output.
[0030] Although the foregoing describes preferable embodiments of the present disclosure in detail, it should be clearly understood that the present disclosure may have various changes and variations for those skilled in the art. Any modification, equivalent replacement and improvement made without departing from the spirit and principle of the present disclosure shall fall within the protection scope of the present disclosure.
a first input end of the input voltage sampling circuit is connected with the anode or the cathode of the first LED load, a first output end of the input voltage sampling circuit is connected with a first input end of the error amplifying circuit, and a second output end of the input voltage sampling circuit is grounded;
a second input end of the error amplifying circuit is connected with a first output end of the adder circuit, and a first output end of the error amplifying circuit is connected with a first input end of the load switching circuit;
a first input end of the adder circuit is connected with a first output end of the current detecting circuit, and a second input end of the adder circuit is connected with the cathode of the n-th LED load;
a first input end of the current detecting circuit is connected with a first output end of the load switching circuit, and a second output end of the current detecting circuit is grounded; and
an n-th input end of the load switching circuit is connected with the cathode of the (n-1)-th LED load.
the second triode is an NPN type triode, the base of the second triode is connected with the second input end of the error amplifying circuit, and the emitter of the second triode is connected with the first input end of the error amplifying circuit.
a first end of the seventh resistor is connected with the second input end of the adder circuit, and a second end of the seventh resistor is connected with the first output end of the adder circuit.
a first input end of the first switching circuit is connected with a third input end of the load switching circuit, a second input end of the first switching circuit is connected with the first input end of the load switching circuit, a third input end of the first switching circuit is connected with a second input end of the load switching circuit, and a first output end of the first switching circuit is connected with the first output end of the load switching circuit; and
a first input end of the second switching circuit is connected with a fourth input end of the load switching circuit, a second input end of the second switching circuit is connected with the first input end of the load switching circuit, a third input end of the second switching circuit is connected with a third input end of the load switching circuit, and a first output end of the second switching circuit is connected with the first output end of the load switching circuit.
a first end of the x-th resistor Rx is connected with the grid of the x-th MOS tube Mx, and a second end of the x-th resistor Rx is connected with the drain of the x-th MOS tube Mx;
the anode of the x-th diode Dx is connected with the grid of the x-th MOS tube Mx, and the cathode of the x-th diode Dx is connected with a second input end of the x-th switching circuit;
the grid of the x-th MOS tube Mx is connected with one end of the x-th controllable switch Sx, the drain of the x-th MOS tube Mx is connected with a third input end of the x-th switching circuit, and the source of the x-th MOS tube Mx is connected with a first output end of the x-th switching circuit; and
the other end of the x-th controllable switch Sx is connected with the first output end of the x-th switching circuit, the positive electrode of a switch control end of the x-th controllable switch Sx is connected with a first input end of the x-th switching circuit, and the negative electrode of the switch control end of the x-th controllable switch Sx is connected with the first output end of the x-th switching circuit.