TWI461108B - Light-emitting diode lamp driving device - Google Patents

Description

Light-emitting diode lamp driving device

The present invention relates to a light source driving device, and more particularly to a light-emitting diode (LED) lamp driving device that can be used for a liquid crystal display product.

1 is a block diagram of a power supply system of a conventional liquid crystal display product. Referring to FIG. 1, an alternating current to direct current (AC-DC) converter 11 and a direct current to direct current (DC-DC) boost converter 12 in a power supply system are provided. The LED tube 13 constitutes an LED tube driving device, wherein the AC-DC converter 11 is, for example, an external power adapter. The commercial AC power supply Vac is input to the AC-DC converter 11, and is converted to generate a DC voltage Vdc1 of 12V to 19V. The DC voltage Vdc1 is input to the DC-DC boost converter 12, and is converted and boosted to generate a DC voltage Vdc2 that can supply the operating voltage of the LED lamp 13. The DC voltage Vdc2 is input to the input end of each LED string in the LED tube 13, and the output of each LED string is fed back to the DC-DC boost converter 12 to ensure that each The LED string operates in a constant current state.

The DC voltage Vdc1 is also input to the DC-DC buck converter 14, which is converted to generate a 5V DC voltage Vdc3 for supplying power to the image processing circuit 15 and the liquid crystal panel drive circuit 16. The main function of the image processing circuit 15 is to convert the input video signal into a Low-Voltage Differential Signaling (LVDS) to the liquid crystal panel driving circuit 16. The control circuit 151 in the image processing circuit 15 can output a switching signal ON/OFF to the DC-DC boost converter 12 so that the liquid crystal display product can turn off the DC-DC boost converter 12 in the standby state for energy saving purposes. The control circuit 151 can also output a Pulse-Width Modulation (PWM) dimming signal DIM to the DC-DC boost converter 12 to control the average brightness of the LED tube 13. The control circuit 151 is, for example, a Micro Control Unit (MCU) or a scaler integrated with the MCU.

The LED lamp driving device of the existing liquid crystal display product is not an optimal design in terms of design cost. For example, the electromagnetic noise generated in the power transistor and the boost rectifier diode in the DC-DC boost converter 12 is large, resulting in design difficulty and cost of the electromagnetic interference suppression circuit in the AC-DC converter 11. increase. Moreover, the PWM control chip for controlling power transistor switching in the DC-DC boost converter 12 has a weak antistatic discharge (ESD) capability, which easily leads to a liquid crystal display product using the LED lamp driving device. There is a certain percentage of badness in the factory and in the market.

In view of this, the object of the present invention is to provide an LED lamp driving device, which can reduce electromagnetic noise generated, reduce the design difficulty and cost of the required electromagnetic interference suppression circuit, and reduce the liquid crystal display using the LED lamp driving device. The poor ratio of products in the factory and in the market, while reducing the design cost of the power supply of liquid crystal display products.

To achieve the above object or other objects, the present invention provides an LED lamp driving device, including an AC-DC converter, an LED lamp, a constant current control circuit, a protection circuit, a control circuit, and a dimming circuit, wherein the LED tube includes n LED string, where n is a positive integer. The AC-DC converter receives the commercial AC power and converts the commercial AC power to generate the first DC voltage. Each LED string has an input end and an output end, and an input end thereof is coupled to the AC-DC converter to receive the power supply of the first DC voltage. The constant current control circuit is coupled to the output end of each LED string, and when enabled, causes each LED string to have a current flowing through it and controls the current flowing through each LED string to be constant and is disabled. When there is no current flowing through each LED string. The protection circuit is coupled to the output end of each LED string, and outputs a protection signal when detecting that the output voltage of any LED string exceeds a critical value. The control circuit is coupled to the protection circuit and outputs a PWM dimming signal, wherein each period of the PWM dimming signal includes an enable period and a disable period, and the control circuit does not determine whether to receive the protection signal during the disable period, but is enabled During the period, it is also judged whether the protection signal is received, and once the protection signal is received, the remaining time of the current enabling period is changed to the inactive period. The dimming circuit is coupled to the control circuit and the constant current control circuit, receives the PWM dimming signal, enables the constant current control circuit during the enable period, and disables the constant current control circuit during the disable period. In addition, the LED lamp driving device may further include a DC-DC buck converter coupled to the dimming circuit, receiving the first DC voltage, and converting the first DC voltage to generate a second DC voltage, wherein the dimming circuit is The constant current control circuit can be enabled by transmitting a second DC voltage to supply power, and the second DC voltage is stopped during the disable period to stop the power supply and the constant current control circuit is disabled.

The invention overcomes the output of the DC voltage of each LED string in the LED tube by directly outputting from the AC-DC converter, and overcomes the DC voltage of the existing AC-DC converter after outputting the DC voltage. The DC boost converter generates a higher DC voltage to provide LED string operation, which reduces electromagnetic noise generated, reduces the design difficulty and cost of the required electromagnetic interference suppression circuit, and reduces the liquid crystal using the LED lamp driving device. Shows the poor ratio of products in the factory and on the market, as well as the design cost of reducing the power supply of liquid crystal display products. In addition, since the existing DC-DC boost converter is not used, the present invention further adopts a constant current control circuit to ensure that each LED string operates in a constant current state, and by controlling the enabling and disabling of the constant current control circuit. To control the average brightness provided by the LED tube, and disable the constant current control circuit to turn off the LED tube for protection purposes when the LED tube is working and it is detected that the output voltage is greater than the threshold.

The above and other objects, features and advantages of the present invention will become more apparent and understood.

2 is a block diagram of a power supply system of a liquid crystal display product according to an embodiment of the present invention. Referring to FIG. 2, an AC-DC converter 21, an LED lamp 23, a DC-DC buck converter 24, a control circuit 251, a constant current control circuit 27, a protection circuit 28, and a dimming circuit 29 in the power supply system constitute an LED. The lamp driving device, wherein the AC-DC converter 21 is, for example, an external power adapter. The AC-DC converter 21 receives the commercial AC power supply Vac and converts the commercial AC power supply Vac to generate a first DC voltage Vd1 that can supply the operating voltage of the LED lamp 23. The LED tube 23 includes n LED strings 231 to 23n, where n is a positive integer. Each LED string 23i has an input end and an output end Pi, and for example, a plurality of LEDs are coupled in series between the input end and the output end Pi, where i is any positive integer from 1 to n. The input end of each LED string 23i is coupled to the AC-DC converter 21 to receive the power of the first DC voltage Vd1.

The constant current control circuit 27 is coupled to the output terminal Pi of each LED light string 23i. The constant current control circuit 27, when enabled, causes a current to flow through each of the LED strings 23i and controls the magnitude of the current flowing through each of the LED strings 23i to be constant, thereby ensuring that each LED string 23i is in operation. Constant current state. When the constant current control circuit 27 is disabled, no current flows through each of the LED strings 23i, that is, the LED strings 231 to 23n are turned off. The protection circuit 28 is coupled to the output terminal Pi of each LED light string 23i. When the first DC voltage Vd1 rises abnormally or a LED in the LED lamp tube is short-circuited, the LED lamp strings 231 to 23n are all or at least one of the LED lamp strings has an abnormally high output voltage, so the LED can be detected. The output voltages of the strings 231 to 23n are used to determine whether it is necessary to activate the protection mechanism to turn off the LED tubes 23, that is, to turn off the LED strings 231 to 23n. When the protection circuit 28 detects that the output voltage of any of the LED strings exceeds a critical value, the protection signal DET is output to activate the protection mechanism to turn off the LED tube 23.

The DC-DC buck converter 24 is coupled to the AC-DC converter 21, the image processing circuit 25, the liquid crystal panel driving circuit 26, and the dimming circuit 29, and receives the first DC voltage Vd1 output by the AC-DC converter 21, and The first DC voltage Vd1 is converted to generate a second DC voltage Vd2, which is output to the image processing circuit 25, the liquid crystal panel drive circuit 26, and the dimming circuit 29. The main function of the image processing circuit 25 is to process the input video signal into an LVDS to the liquid crystal panel driving circuit 26. The control circuit 251 in the image processing circuit 25 is, for example, an MCU or a scaler integrated with the MCU.

The control circuit 251 is coupled to the protection circuit 28, and the dimming circuit 29 is coupled to the DC-DC buck converter 24, the control circuit 251, and the constant current control circuit 27. The control circuit 251 outputs the PWM dimming signal DIM to the dimming circuit 29, wherein each period of the PWM dimming signal DIM includes an enabling period and an inactive period. The dimming circuit 29 allows the second DC voltage Vd2 to be transmitted during the enable period, and enables the constant current control circuit 27 to receive the power supply of the second DC voltage Vd2' transmitted by the dimming circuit 29, thereby enabling the LED string 231. ~23n work and glow. The dimming circuit 29 does not allow the second DC voltage Vd2 to be transmitted during the disable period, so that the constant current control circuit 27 is no longer receiving the power supply of the second DC voltage Vd2', and is disabled, thereby causing the LED light strings 231 to 23n to be turned off. Not bright. Therefore, the dimming circuit 29 alternately enables and disables the constant current control circuit 27 according to the PWM dimming signal DIM, so that the LED light strings 231 to 23n alternately emit light (bright) and no light (dark), if the light and dark are switched. When the frequency is above 150 Hz, the human eye will not feel the change of light and dark due to the influence of persistence of vision. Only the average value of this change can be felt, that is, the human eye can only feel the average brightness and the average brightness is bright and dark. The ratio is proportional, so the duty ratio of the enabling and disabling of the constant current control circuit 27 can be adjusted by adjusting the duty cycle of the PWM dimming signal DIM to adjust the average brightness of the LED strings 231 to 23n. The dimming effect is called PWM dimming or burst mode dimming.

The control circuit 251 does not need to start the protection mechanism of the LED lamp 23 during the disable period because the LED lamp strings 231 to 23n are not operated, so the control circuit 251 does not need to judge whether or not the protection signal DET is received. The control circuit 251 may need to activate the protection mechanism of the LED lamp 23 during operation due to the operation of the LED lamp strings 231 to 23n. Therefore, the control circuit 251 also determines whether the protection signal DET is received during the enablement, and once received. The protection signal DET changes the remaining time of the current enable period to the disable period, that is, the remaining time during the current enable period disables the constant current control circuit 27 through the dimming circuit 29 to turn off the LED string 231~ 23n, at this time, the constant current control circuit 27 is enabled through the dimming circuit 29 until the next enable period to enable the LED lamp strings 231 to 23n to operate normally.

Since the AC-DC converter 21, the LED tube 23, the DC-DC buck converter 24, the image processing circuit 25, and the liquid crystal panel driving circuit 26 are known in the prior art, they will not be described in detail herein. The flow control circuit 27, the protection circuit 28, and the dimming circuit 29 will be described in detail.

FIG. 3 is a circuit diagram of an embodiment of the constant current control circuit 27 shown in FIG. 2. 2 and FIG. 3, the constant current control circuit 27 includes a constant voltage source 271, a first transistor Q1, a first resistor R1, and m×n second transistors Q11 to Q1m, Q21 to Q2m, . Qn1 to Qnm (hereinafter referred to as Q11 to Qnm), m×n second resistors R11 to R1m, R21 to R2m, ..., Rn1 to Rnm (hereinafter referred to as R11 to Rnm) and third resistor R3, Where m is a positive integer. The first transistor Q1 is matched with the second transistors Q11-Qnm and has a first end, a second end and a control end. In this embodiment, the first transistor Q1 and the second transistor Q11-Qnm are both NPN transistors, and the first end, the second end and the control end are respectively a collector terminal, an emitter terminal and a base terminal.

The constant voltage source 271 is coupled to the dimming circuit 29, and outputs a constant reference voltage Vref due to receiving the power supply of the second DC voltage Vd2' transmitted by the dimming circuit 29 during the enable period, and is disabled during the disable period. The power supply of the second DC voltage Vd2' is received again and the reference voltage Vref is no longer output. In this embodiment, the constant voltage source 271 includes a three-terminal regulator U1, an NPN transistor Q4 and a resistor R4, wherein the three-terminal regulator U1 has an anode terminal A, a cathode terminal K and a reference terminal R, which are existing Mature techniques are known and will not be described in detail herein. If the three-terminal regulator U1 uses the integrated circuit of the type TL431, a very stable reference voltage Vref of 2.5V is outputted to the reference terminal R during the enable period.

The first end of the first transistor Q1 is coupled to the control end of the first transistor Q1 and the first end of the third resistor R3. The second end of the third resistor R3 is coupled to the constant voltage source 271 to receive the reference voltage Vref. The second end of the first transistor Q1 is coupled to the first end of the first resistor R1. The second end of the first resistor R1 is coupled to the ground. Each m second transistor is a set of second transistors. For example, the second transistors Q11 to Q1m are the first group of second transistors, the second transistors Q21 to Q2m are the second group of second transistors, ..., and the second transistors Qn1 to Qnm are the nth group of the second group. Crystal. The first ends of all the second transistors in each of the second transistors are coupled to the output ends of the corresponding LED strings, and the second ends of all the second transistors are respectively coupled to the corresponding second resistors. The first end, the control end of all the second transistors are coupled to the control end of the first transistor and the second ends of all the second resistors are coupled to the ground. For example, the first ends of all the second transistors Q11-Q1m in the first group of the second transistor are coupled to the output end P1 of the LED string 231, and the second ends of all the second transistors Q11-Q1m are respectively coupled. The first ends of the second resistors R11-R1m, the control ends of all the second transistors Q11-Q1m are coupled to the control end of the first transistor Q1 and the second ends of all the second resistors R11-R1m are Coupling to ground.

Since the first transistor Q1 is matched with the second transistor Q11-Qnm, the voltage between the base terminal and the emitter terminal of the first transistor Q1 and the second transistor Q11-Qnm is the same (assuming Vbe) and The current between the extreme and the emitter is the same (assuming Ibe). Therefore, it is possible to obtain Vref - I3 × R3 - Vbe - I1 × R1 = 0, I3 = I1 + m × n × Ibe, I1 × R1 = I11 × R11, where I1 is the current flowing through the first resistor R1, I11 For the current flowing through the second resistor R11, I3 is the current flowing through the third resistor R3. Further, when the second resistors R11 to Rnm are matched, the operating current output from the output terminal Pi of each of the LED lamp strings 23i is m × I11. Therefore, the current values I1, I11, and I3 can be adjusted by adjusting the resistance values of the first resistor R1, the second resistor R11, and the third resistor R3 to design a required LED string operating current (m× I11).

4 is a circuit diagram of another embodiment of the constant current control circuit 27 shown in FIG. 2. Referring to FIG. 2, FIG. 3 and FIG. 4 simultaneously, compared with the constant current control circuit 27 shown in FIG. 3, the constant current control circuit 27' shown in FIG. 4 further includes a third transistor Q3, so that the first transistor The first end of Q1 is no longer directly coupled to the control terminal of the first transistor Q1. The third transistor Q3 has a first end, a second end and a control end, and the first end of the first transistor Q1 is coupled to the control end of the third transistor Q3. The second end of the third transistor Q3 is coupled to the control end of the first transistor Q1. The first end of the third transistor Q3 is coupled to the constant voltage source 271 to receive the reference voltage Vref.

Since the first transistor Q1 matches the second transistor Q11-Qnm and matches the third transistor Q3, the base terminal of the first transistor Q1, the second transistor Q11-Qnm and the third transistor Q3 The magnitude of the voltage between the extremes is the same (assumed to be Vbe) and the magnitude of the current between the base and the emitter is the same (assuming Ibe). Therefore, the current flowing through the first resistor R1, I1 = I3 = (Vref - 2 × Vbe) / (R1 + R3), and the current flowing through the second resistor R11, I11 = I1 × R1/R11, where I3 is obtained Is the current flowing through the third resistor R3. Further, when the second resistors R11 to Rnm are matched, the operating current output from the output terminal Pi of each of the LED lamp strings 23i is m × I11. Therefore, the currents I1 and I11 can be adjusted by adjusting the resistance values of the first resistor R1, the second resistor R11 and the third resistor R3 to design a required LED string operating current (m×I11). .

FIG. 5 is a circuit diagram of an embodiment of the protection circuit 28 of FIG. 2. 2 and FIG. 5, when n is greater than 1, the LED tube 23 includes a plurality of LED strings 231 to 23n, and the protection circuit 28 includes a plurality of diodes D1 to Dn and a first Zener diode. ZD1, first voltage dividing resistor Rd1, second voltage dividing resistor Rd2, capacitor C1 and second Zener diode ZD2. The anode ends of each of the diodes are respectively coupled to the output ends of the corresponding LED strings. For example, the anode end of the diode D1 is coupled to the output terminal P1 of the LED string 231, and the anode end of the diode D2 is coupled to the output terminal P2 of the LED string 232. The cathode end of each of the diodes is coupled to the cathode end of the first Zener diode ZD1, that is, the cathode ends of all of the diodes D1 to Dn are coupled to the cathode terminal of the first Zener diode ZD1. The anode end of the first Zener diode ZD1 is coupled to the first end of the first voltage dividing resistor Rd1. The second end of the first voltage dividing resistor Rd1 is coupled to the first end of the second voltage dividing resistor Rd2, the first end of the capacitor C1, and the cathode end of the second Zener diode ZD2. The second end of the second voltage dividing resistor Rd2, the second end of the capacitor C1 and the anode end of the second Zener diode ZD2 are both coupled to ground. The second end of the first voltage dividing resistor Rd1 is also coupled to the control circuit 251 to output the protection signal DET when the voltage at the output of any of the LED strings exceeds a threshold.

When the LED lamp tube 23 is working normally, and when the output voltage of any one of the LED lamp strings 231 to 23n (taking the LED lamp string 231 as an example) exceeds a critical value, the first Zener diode ZD1 collapses. When the voltage of the output terminal P1 of the LED string 231 is subtracted from the forward bias of the diode D1 and the breakdown voltage of the first Zener diode ZD1, the voltage drop will fall on the first voltage dividing resistor Rd1 and the first The bistatic resistor Rd2 is designed such that the divided voltage falling on the second voltage dividing resistor Rd2 reaches a comparative reference voltage set by the internal software of the control circuit 251 (MCU or scaler), and the control circuit 251 will The decision protection circuit 28 outputs a high level signal (i.e., indicates an output protection signal DET). When the output voltage of the LED string of any one of the LED strings 231 to 23n does not exceed the critical value and the first Zener diode ZD1 cannot be collapsed, there is no voltage drop falling on the first voltage dividing resistor Rd1 and the second. The voltage dividing resistor Rd2, the divided voltage falling on the second voltage dividing resistor Rd2 is smaller than the comparison reference voltage set by the software inside the control circuit 251, and the control circuit 251 determines that the protection circuit 28 outputs a low level signal (ie, Indicates that the protection signal DET is not output. Therefore, the threshold value can be designed by using the first Zener diode ZD1 of different breakdown voltages, that is, the protection signal DET is output when how many LEDs in the LED string are short-circuited.

In addition, when the transistors Q11 to Qnm are turned on for normal operation, the on-voltage of each of the corresponding light-emitting diodes 231 to 23n is, for example, about Vf(on) = 3.0V to 3.2V; and in the transistor Q11~. When Qnm is turned off, each of the corresponding light-emitting diodes 231 to 23n has a critical collapse conduction voltage of, for example, about Vf(off) = 2.0V to 2.4V. Assuming that each light-emitting diode has Vf(on) = 3.2V and Vf(off) = 2.0V, each LED light string is composed of 14 light-emitting diodes in series, and the LED light string falls on the LED when it works. The voltage of the string VLED(on) = 3.2V×14 = 44.8V; when the LED string does not work, the voltage falling on the LED string VLED(off) = 2V×14 = 28V, that is, when the LED string is not working , at least ΔV = 44.8V - 28V = 16.8V or more voltage falls between the collector terminal and the emitter terminal of the transistor Q11 ~ Qnm and between the anode terminal of the diode D1 ~ Dn to the ground, forcing the first Qi The nano-diode ZD1 is turned on, so that the protection circuit 28 outputs a high-level signal. In order to prevent the high level signal voltage outputted by the protection circuit 28 from being too high or even higher than the control circuit 251 (such as an MCU or a scaler) for receiving when the LED string is not working, the output is detected by the side protection circuit 28. The maximum withstand voltage of the detection pin of the high or low level signal may cause the control circuit 251 to be damaged. Therefore, the second Zener diode ZD2 needs to be added as the voltage clamp of the detection pin to ensure the protection circuit. The high-level signal voltage of the 28 output does not exceed the upper limit of the withstand voltage specification of the control circuit 251.

In another embodiment, when n is 1, that is, the LED tube 23 includes only one LED string 231, and the diodes D1 to Dn of the protection circuit 28 can be removed by the first Zener diode. The cathode end of the body ZD1 is coupled to the output terminal P1 of the unique LED string 231.

FIG. 6 is a circuit diagram of an embodiment of the dimming circuit 29 of FIG. 2. 2 and FIG. 6, the dimming circuit 29 includes an NPN transistor Q5, a PNP transistor Q6, and resistors R5 and R6. The first end (set terminal) of the NPN transistor Q5 is coupled to the first end of the resistor R5 and the control end (base terminal) of the PNP transistor Q6, and the second end (the emitter end) of the NPN transistor Q5 is coupled to The control terminal (base terminal) of the NPN transistor Q5 is coupled to the first end of the resistor R6. The second end of the resistor R6 is coupled to the control circuit 251 to receive the PWM dimming signal DIM. The first end (emitter end) of the PNP transistor Q6 is coupled to the second end of the resistor R5 and the DC-DC buck converter 24 to receive the second DC voltage Vd2, the second end of the PNP transistor Q6 (set extreme ) is coupled to the constant current control circuit 27 to output a second DC voltage Vd2'.

In the present embodiment, the PWM dimming signal received by the dimming circuit 29 is at a high level during the enable period and a low level signal during the disable period. During the enable period, the NPN transistor Q5 is turned on, and the PNP transistor Q6 is turned on, so the dimming circuit 29 allows the second DC voltage Vd2 to be transmitted, so that the constant current control circuit 27 receives the second DC voltage Vd2', wherein the second DC voltage Vd2' is the second DC voltage Vd2 minus the voltage drop between the emitter and collector terminals when the PNP transistor Q6 is turned on. During the disable period, the NPN transistor Q5 is turned off and the PNP transistor Q6 is turned off, so that the dimming circuit 29 does not allow the second DC voltage Vd2 to be transmitted, so that the constant current control circuit 27 no longer receives the second DC voltage Vd2'.

While the present invention has been described above in terms of the preferred embodiments thereof, it is not intended to limit the invention, and the present invention may be modified and modified without departing from the spirit and scope of the invention. The scope of protection is subject to the definition of the scope of the patent application.

11, 21. . . AC-DC converter

12. . . DC-DC boost converter

13,23. . . LED tube

231~23n. . . LED light string

P1~Pn. . . LED light string output

14, 24. . . DC-DC Buck Converter

15,25. . . Image processing circuit

151, 251. . . Control circuit

16, 26. . . LCD panel driver circuit

27, 27’. . . Constant current control circuit

271. . . Constant voltage source

28. . . protect the circuit

29. . . Dimming circuit

C1. . . Capacitor

D1~Dn. . . Dipole

Q1. . . First transistor

Q11~Qnm. . . Second transistor

Q3. . . Third transistor

Q4, Q5. . . NPN transistor

Q6. . . PNP transistor

R1. . . First resistor

R11~Rnm. . . Second resistor

R3. . . Third resistor

R4~R6. . . Resistor

Rd1. . . First voltage dividing resistor

Rd2. . . Second voltage dividing resistor

U1. . . Three-terminal regulator

A. . . Anode end of a three-terminal regulator

K. . . Cathode terminal of a three-terminal regulator

R. . . Reference end of three-terminal regulator

ZD1. . . First Zener diode

ZD2. . . Second Zener diode

I1, I11, I3. . . Current

Vac. . . City AC power supply

Vdc1~Vdc3. . . DC voltage

Vd1. . . First DC voltage

Vd2, Vd2’. . . Second DC voltage

Vref. . . Reference voltage

DIM. . . PWM dimming signal

DET. . . Protection signal

1 is a block diagram of a power supply system of a conventional liquid crystal display product.

2 is a block diagram of a power supply system of a liquid crystal display product according to an embodiment of the present invention.

3 is a circuit diagram of an embodiment of the constant current control circuit shown in FIG. 2.

4 is a circuit diagram of another embodiment of the constant current control circuit shown in FIG. 2.

Figure 5 is a circuit diagram of an embodiment of the protection circuit of Figure 2.

Figure 6 is a circuit diagram of an embodiment of the dimming circuit of Figure 2.

twenty one. . . AC-DC converter

twenty three. . . LED tube

231~23n. . . LED light string

P1~Pn. . . LED light string output

twenty four. . . DC-DC Buck Converter

25. . . Image processing circuit

251. . . Control circuit

26. . . LCD panel driver circuit

27. . . Constant current control circuit

28. . . protect the circuit

29. . . Dimming circuit

Vac. . . City AC power supply

Vd1. . . First DC voltage

Vd2, Vd2’. . . Second DC voltage

DIM. . . PWM dimming signal

DET. . . Protection signal

Claims (4)

A light-emitting diode lamp driving device comprises: an AC to DC converter, receiving a commercial AC power source, and converting the city AC power source to generate a first DC voltage; and a light emitting diode lamp, including n light-emitting diode strings, wherein n is a positive integer, wherein each light-emitting diode string has an input end and an output end, and the input end is coupled to the AC-to-DC converter to receive the first a DC voltage supply; a constant current control circuit coupled to the output end of each of the LED strings, when enabled, causes current to flow through each of the LED strings and control each illumination The current flowing through the diode string is constant, and when the ban is disabled, no current flows through each of the LED strings; a protection circuit is coupled to the output of each LED string And outputting a protection signal when detecting that the output voltage of any of the LED strings exceeds a threshold; a control circuit is coupled to the protection circuit to output a pulse width modulation dimming signal, wherein the pulse width Each period of the modulated dimming signal includes one During the energy period and during the disable period, the control circuit does not judge whether the protection signal is received during the disable period, and determines whether the protection signal is received during the enabling period, and once the protection signal is received, the control signal is received. The remaining time of the energy period is changed to the disable period; a dimming circuit is coupled to the control circuit and the constant current control circuit to receive the pulse width modulation dimming signal, and enable the constant current control during the enabling period a circuit, and disabling the constant current control circuit during the disable period; and flowing to the DC buck converter, coupled to the dimming circuit, receiving Depressing the first DC voltage to generate a second DC voltage, wherein the dimming circuit transmits the second DC voltage during the enabling to supply the constant current control circuit, and Stopping the second DC voltage during the disable period to stop the power supply and disabling the constant current control circuit; wherein the constant current control circuit includes a certain voltage source, a first transistor, a first resistor, and m×n a second transistor, m×n second resistors and a third resistor, wherein m is a positive integer, the constant voltage source is coupled to the dimming circuit and is configured to receive power from the second DC voltage And outputting a reference voltage of a constant size, the first transistor is matched with the second transistors, and each has a first end, a second end, and a control end, and the first end of the first transistor is coupled To the control end of the first transistor and the first end of the third resistor, the second end of the third resistor is coupled to the constant voltage source to receive the reference voltage, the second of the first transistor The end is coupled to the first end of the first resistor, the first resistor The two ends are coupled to the ground, each m second transistors are a set of second transistors, and the first ends of all the second transistors in each set of the second transistors are coupled to a corresponding light emitting diode The output end of the light string, the second ends of all the second transistors are respectively coupled to the first end of a corresponding second resistor, and the control ends of all the second transistors are coupled to the control of the first transistor And the second ends of all the second resistors are coupled to the ground. The illuminating diode lamp driving device of claim 1, wherein the constant current control circuit further comprises a third transistor having a first end, a second end and a control end, wherein the The first end of the first transistor is coupled to the control end of the third transistor, and the second end of the third transistor is coupled to the control end of the first transistor, the first end of the third transistor The voltage source is coupled to the constant voltage source to receive the reference voltage. The illuminating diode lamp driving device of claim 1, wherein when n is greater than 1, the protection circuit comprises a plurality of diodes, a first Zener diode, and a first partial pressure. a resistor, a second voltage dividing resistor, a capacitor and a second Zener diode, wherein the anode ends of each of the diodes are respectively coupled to the output ends of a corresponding LED string, each a cathode end of the diode is coupled to the cathode end of the first Zener diode, and an anode end of the first Zener diode is coupled to the first end of the first voltage dividing resistor. a second end of the voltage dividing resistor is coupled to the first end of the second voltage dividing resistor, the first end of the capacitor, the cathode end of the second Zener diode, and the second voltage dividing resistor The second end of the capacitor, the second end of the capacitor and the anode end of the second Zener diode are both coupled to ground, and the second end of the first voltage dividing resistor is further coupled to the control circuit for The protection signal is output when the output terminal voltage of the LED string exceeds the threshold. The illuminating diode lamp driving device of claim 1, wherein when n is 1, the protection circuit comprises a first Zener diode, a first voltage dividing resistor, and a second a voltage dividing resistor, a capacitor and a second Zener diode, wherein a cathode end of the first Zener diode is coupled to an output end of a corresponding LED string, the first Zener The anode end of the diode is coupled to the first end of the first voltage dividing resistor, and the second end of the first voltage dividing resistor is coupled to the first end of the second voltage dividing resistor, the capacitor a first end, a cathode end of the second Zener diode, a second end of the second voltage dividing resistor, a second end of the capacitor, and an anode end of the second Zener diode are coupled to The second end of the first voltage dividing resistor is further coupled to the control circuit to output the protection signal when the output voltage of any of the LED strings exceeds the threshold.