LED short circuit protection circuit
By building an LED hardware short-circuit protection circuit using discrete components, the problems of high cost and unstable supply of integrated chips are solved, achieving low-cost and reliable LED short-circuit protection.
Patent Information
- Application Number
- CN202423154071.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-19
- Publication Date
- 2025-11-25
- Estimated Expiration
- 2034-12-19
AI Technical Summary
When LED lights are short-circuited, integrated chips are commonly used for protection. However, this method is costly, susceptible to chip shortages, and has few available chips, making it difficult to change product solutions.
A hardware short-circuit protection circuit for LEDs is built using discrete components. The LED detection circuit and the driver shutdown circuit detect the short-circuit state of the LED and shut down the power transistor to prevent damage.
It reduced costs, improved device substitutability, avoided disruptions caused by semiconductor market supply, and protected the power transistor from damage.
Smart Images
Figure CN223600070U_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The utility model relates to circuit design technical field, especially relates to a LED short circuit protection circuit.
BACKGROUND
[0002] The LED lamp on the market is extremely easy to have LED short circuit when using, and the current technology is basically through integrated chip to do LED short circuit protection, and the integrated chip needs to set sampling resistance in the power loop of LED, and the cost is high, and the optional short circuit protection chip is few, and the product scheme change problem is very easy to appear due to chip shortage.
[0003] Therefore, it is necessary to provide a new technical scheme to solve the above problems.
UTILIT Y MODEL CONTENTS
[0004] One of the purposes of the utility model is to provide a kind of LED short circuit protection circuit, and the LED hardware short circuit protection circuit is built by discrete device, and cost is low and device substitution is strong, and it will not be affected by semiconductor market supply.
[0005] According to one aspect of the utility model, the utility model provides a kind of LED short circuit protection circuit, it includes: LED lamp string, its input end is connected with power supply Vbat;Power tube Q1, its first connection end is connected with the output end of the LED lamp string, its second connection end is grounded, and its control end receives PWM drive signal, and the PWM drive signal is used to drive the power tube Q1 periodically conduction and shut down;LED detection circuit, it includes first detection end A, second detection end B and detection output end C, the first detection end A is connected with the output end of the LED lamp string, and its second detection end B receives the PWM drive signal, and the LED detection circuit is based on the voltage of the output end of the LED lamp string and the PWM drive signal detects whether the LED lamp string is short-circuited, and the detection signal indicating whether short-circuit is output through the detection output end C;Drive-off circuit, it includes first input end D, second input end E and drive output end F, the first input end D is connected with the output end of the LED lamp string, and its second input end E is connected with the detection output end C, and its drive output end F is connected with the control end of the power tube Q1, and the drive-off circuit is based on the voltage of the output end of the LED lamp string and the detection signal output by the detection output end C to determine whether the power tube Q1 is turned off through its drive output end F.
[0006] Further, the LED short circuit protection circuit further comprises a resistor R1 and a resistor R2, one end of the resistor R1 is connected with the PWM driving signal, and the other end thereof is connected with the driving output end F of the driving off circuit; one end of the resistor R2 is connected with the driving output end F of the driving off circuit, and the other end thereof is connected with the control end of the power tube Q1.
[0007] Further, the LED detection circuit comprises a diode D3, a diode D4, a resistor R4, a resistor R5, a resistor R6, a resistor R9, a resistor R10, a switching device Q3 and a switching device Q4, the negative electrode of the diode D3 is connected with the first detection end A of the LED detection circuit, and the positive electrode thereof is connected with the first connection end of the switching device Q3; the negative electrode of the diode D4 is connected with the second detection end B of the LED detection circuit, and the positive electrode thereof is connected with the first connection end of the switching device Q3; the first connection end of the switching device Q3 is connected with the control end thereof through the resistor R4, and the second connection end thereof is connected with the detection output end C of the LED detection circuit; one end of the resistor R5 is connected with the first connection end of the switching device Q3, and the other end thereof is connected with the second detection end B of the LED detection circuit; the first connection end of the switching device Q4 is connected with the control end of the switching device Q3 through the resistor R6, the control end thereof is connected with the second detection end B of the LED detection circuit through the resistor R9, and the second connection end thereof is grounded; one end of the resistor R10 is connected with the control end of the switching device Q4, and the other end thereof is grounded.
[0008] Further, the LED detection circuit further comprises a capacitor C1, one end of the capacitor C1 is connected with the control end of the switching device Q4, and the other end thereof is grounded.
[0009] Further, when the LED detection circuit detects that the PWM driving signal is the first logic level and the voltage of the output end of the LED lamp string is high level, the switch Q3 and the switch Q4 are turned on, the detection signal output by the detection output end C of the LED detection circuit is the first logic level, indicating that the LED lamp string is in a short circuit state; when the LED detection circuit detects that the PWM driving signal is the first logic level and the voltage of the output end of the LED lamp string is low level, the switch Q3 is turned off and the switch Q4 is turned on, the detection signal output by the detection output end C of the LED detection circuit is the second logic level, indicating that the LED lamp string is in a non-short circuit state; when the LED detection circuit detects that the PWM driving signal is the second logic level and the voltage of the output end of the LED lamp string is high level, the switch Q3 is turned off and the switch Q4 is turned off, the detection signal output by the detection output end C of the LED detection circuit is the second logic level, indicating that the LED lamp string is in a non-short circuit state, wherein the first logic level of the PWM driving signal is used to drive the power tube Q1 to be turned on; the second logic level of the PWM driving signal is used to drive the power tube Q1 to be turned off.
[0010] Further, the driving-off circuit comprises a diode D1, a diode D2, a resistor R3, a resistor R7, a resistor R8 and a switch Q2, the positive electrode of the diode D2 is connected with the first input end D of the driving-off circuit, and the negative electrode thereof is connected with the first connection end of the switch Q2 through the resistor R3; the positive electrode of the diode D1 is connected with the driving output end F of the driving-off circuit, and the negative electrode thereof is connected with the first connection end of the switch Q2; the control end of the switch Q2 is connected with the detection output end C of the LED detection circuit through the resistor R7, and the second connection end thereof is grounded; one end of the resistor R8 is connected with the control end of the switch Q2, and the other end thereof is grounded.
[0011] Further, when the detection signal output by the detection output end C of the LED detection circuit is the first logic level and the voltage of the output end of the LED lamp string is high level, the switch Q2 is turned on, so that the driving-off circuit drives the power tube Q1 to be turned off through the driving output end F thereof; otherwise, the switch Q2 is turned off, so that the driving-off circuit does not work.
[0012] Further, the power tube Q1 is an NMOS tube, the first connection end, the second connection end and the control end of the power tube Q1 are the drain, the source and the gate of the NMOS tube respectively; the switching device Q2 is an NPN type triode, the first connection end, the second connection end and the control end of the switching device Q2 are the collector, the emitter and the base of the NPN type triode respectively; the switching device Q3 is a PNP type triode, the first connection end, the second connection end and the control end of the switching device Q3 are the emitter, the collector and the base of the PNP type triode respectively; the switching device Q4 is an NPN type triode, the first connection end, the second connection end and the control end of the switching device Q4 are the collector, the emitter and the base of the NPN type triode respectively.
[0013] Further, the resistance values of the resistance R7 and the resistance R8 are selected to satisfy: when the switching device Q3 and the switching device Q4 are turned on, the voltage value of the voltage division on the resistance R8 is greater than the turn-on voltage threshold of the switching device Q2, so that the switching device Q2 is in the turn-on state; the resistance values of the resistance R4 and the resistance R6 are selected to satisfy: when the power tube Q1 and the switching device Q4 are turned on, and the voltage of the output end of the LED lamp string is a high level, the voltage value of the voltage division on the resistance R4 is greater than the turn-on voltage threshold of the switching device Q3, so that the switching device Q3 is in the turn-on state.
[0014] Compared with the prior art, the utility model discloses a discrete device builds LED hardware short circuit protection circuit, and the cost is low and the device replacement is strong, and will not be influenced by semiconductor market supply. BRIEF DESCRIPTION OF DRAWINGS
[0015] In order to more clearly illustrate the technical scheme of the embodiments of the utility model, the drawings needed in the embodiment description will be briefly introduced, and obviously, the drawings in the following description are only some embodiments of the utility model, and for those skilled in the art, other drawings can be obtained according to these drawings without the creative labor, wherein:
[0016] Figure 1 It is the circuit schematic diagram of the LED short circuit protection circuit in an embodiment of the utility model. DETAILED DESCRIPTION
[0017] In order to make the above purpose, features and advantages of the utility model more apparent and easy to understand, the utility model will be further explained in detail in the following with the drawings and specific embodiments.
[0018] As used herein, the term "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one implementation of the technology. The appearances of the phrase "in one embodiment" or "in an embodiment" in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. The terms coupled, connected, linked, or the like, as used in the specification, are intended to mean either a direct electrical connection between elements or an indirect electrical connection between elements in which an electrical current associates with the coupled, connected, or linked elements.
[0019] In the description of the present application, it is to be understood that the terms "upper", "lower", "front", "rear", "right", "left", "vertical", "horizontal", "top", "bottom", "inner", "outer", and the like, indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application.
[0020] Please refer to Figure 1 As shown in the figure, it is a circuit schematic diagram of the LED short circuit protection circuit in one embodiment of the present application. Figure 1 The LED short circuit protection circuit shown in the figure includes an LED lamp string LED1, a power tube (Metal Oxide Semiconductor Field Effect Transistor, Mosfet) Q1, an LED detection circuit 110, and a driving-off circuit 120.
[0021] Among them, the input end (or anode) of the LED lamp string LED1 is connected with the power supply Vbat; the first connection end of the power tube Q1 is connected with the output end (or cathode) of the LED lamp string LED1, the second connection end thereof is grounded, and the control end thereof receives a PWM driving signal, which is used to drive the power tube Q1 to be periodically turned on and turned off. Among them, the PWM (Pulse Width Modulation) driving signal is a periodic high-low square wave signal, and by changing the duty cycle of the PWM driving signal, the power tube Q1 can be controlled, so as to adjust the luminous brightness of the LED lamp string LED1.
[0022] The LED detection circuit 110 comprises a first detection end A, a second detection end B and a detection output end C, the first detection end A is connected with the output end (or negative electrode) of the LED lamp string LED1, the second detection end B receives the PWM driving signal, the LED detection circuit 110 detects whether the LED lamp string LED1 is short-circuited based on the voltage of the output end (or negative electrode) of the LED lamp string LED1 and the PWM driving signal, and outputs a detection signal indicating whether short-circuited through the detection output end C.
[0023] The drive-off circuit 120 comprises a first input end D, a second input end E and a drive output end F, the first input end D is connected with the output end (or negative electrode) of the LED lamp string LED1, the second input end E is connected with the detection output end C, and the drive output end F is connected with the control end of the power tube Q1, the drive-off circuit 120 determines whether to turn off the power tube Q1 through the drive output end F based on the voltage of the output end of the LED lamp string LED1 and the detection signal output by the detection output end C.
[0024] Figure 1 The LED short-circuit protection circuit shown further comprises a resistor R1 and a resistor R2, one end of the resistor R1 is connected with the PWM driving signal, and the other end thereof is connected with the drive output end F of the drive-off circuit 120;
[0025] One end of the resistor R2 is connected with the drive output end F of the drive-off circuit 120, and the other end thereof is connected with the control end of the power tube Q1. In other words, the PWM driving signal, the resistor R1, the resistor R2, the power tube Q1, the LED lamp string LED1 and the power supply Vbat constitute a main power loop of the Mosfet, and the loop realizes the dimming function of the LED in normal time.
[0026] The LED detection circuit 110 comprises a diode D3, a diode D4, a resistor R4, a resistor R5, a resistor R6, a resistor R9, a resistor R10, a switching device Q3 and a switching device Q4. The negative electrode of the diode D3 is connected with the first detection end A of the LED detection circuit 110 (or the output end of the LED lamp string LED1), and the positive electrode thereof is connected with the first connection end of the switching device Q3; the negative electrode of the diode D4 is connected with the second detection end B of the LED detection circuit 110, and the positive electrode thereof is connected with the first connection end of the switching device Q3; the first connection end of the switching device Q3 is connected with the control end thereof through the resistor R4, and the second connection end thereof is connected with the detection output end C of the LED detection circuit 110; one end of the resistor R5 is connected with the first connection end of the switching device Q3, and the other end thereof is connected with the second detection end B of the LED detection circuit 110; the first connection end of the switching device Q4 is connected with the control end of the switching device Q3 through the resistor R6, the control end thereof is connected with the second detection end B of the LED detection circuit 110 through the resistor R9, and the second connection end thereof is grounded; one end of the resistor R10 is connected with the control end of the switching device Q4, and the other end thereof is grounded. Figure 1 In the embodiment shown, the LED detection circuit 110 further comprises a capacitor C1, one end of the capacitor C1 is connected with the control end of the switching device Q4, and the other end thereof is grounded.
[0027] When the LED detection circuit 110 detects that the PWM driving signal is the first logic level (for example, high level) and the voltage of the output end of the LED lamp string LED1 is high level, the switching device Q3 and the switching device Q4 are turned on, the detection signal outputted by the detection output end C of the LED detection circuit 110 is the first logic level (for example, high level), which indicates that the LED lamp string LED1 is in the short circuit state; when the LED detection circuit 110 detects that the PWM driving signal is the first logic level (for example, high level) and the voltage of the output end of the LED lamp string LED1 is low level, the switching device Q3 is turned off and the switching device Q4 is turned on, the detection signal outputted by the detection output end C of the LED detection circuit 110 is the second logic level (for example, low level), which indicates that the LED lamp string LED1 is in the non-short circuit state; when the LED detection circuit 110 detects that the PWM driving signal is the second logic level (for example, low level) and the voltage of the output end of the LED lamp string LED1 is high level, the switching device Q3 is turned off and the switching device Q4 is turned off, the detection signal outputted by the detection output end C of the LED detection circuit 110 is the second logic level (for example, low level), which indicates that the LED lamp string LED1 is in the non-short circuit state. The first logic level of the PWM driving signal is used to drive the power tube Q1 to be turned on, and the second logic level of the PWM driving signal is used to drive the power tube Q1 to be turned off.
[0028] The drive-off circuit 120 includes diodes D1 and D2, resistors R3, R7, and R8, and a switching device Q2. The anode of diode D2 is connected to the first input terminal D of the drive-off circuit 120 (or the output terminal of the LED string LED1), and its cathode is connected to the first connection terminal of the switching device Q2 via resistor R3. The anode of diode D1 is connected to the drive output terminal F of the drive-off circuit 120, and its cathode is connected to the first connection terminal of the switching device Q2. The control terminal of the switching device Q2 is connected to the second input terminal E of the drive-off circuit 120 (or the detection output terminal C of the LED detection circuit 110) via resistor R7, and its second connection terminal is grounded. One end of resistor R8 is connected to the control terminal of the switching device Q2, and the other end is grounded.
[0029] When the detection signal output by the detection output terminal C of the LED detection circuit 110 is at the first logic level (e.g., high level) and the voltage at the output terminal of the LED string LED1 is high level, the switching device Q2 is turned on, thereby driving the shutdown circuit 120 to drive the power transistor Q1 to turn off through its drive output terminal F; otherwise, the switching device Q2 is turned off, thereby driving the shutdown circuit 120 to not work.
[0030] exist Figure 1 In the specific embodiment shown, power transistor Q1 is an NMOS transistor, and its first connection terminal, second connection terminal, and control terminal are the drain, source, and gate of the NMOS transistor, respectively; switching device Q2 is an NPN transistor, and its first connection terminal, second connection terminal, and control terminal are the collector, emitter, and base of the NPN transistor, respectively; switching device Q3 is a PNP transistor, and its first connection terminal, second connection terminal, and control terminal are the emitter, collector, and base of the PNP transistor, respectively; switching device Q4 is an NPN transistor, and its first connection terminal, second connection terminal, and control terminal are the collector, emitter, and base of the NPN transistor, respectively.
[0031] The values of resistors R7 and R8 are chosen to satisfy the following condition: when switching devices Q3 and Q4 are turned on, the voltage across resistor R8 is greater than the turn-on voltage threshold of switching device Q2, thus ensuring that switching device Q2 is turned on. The values of resistors R4 and R6 are chosen to satisfy the following condition: when power transistor Q1 and switching device Q4 are turned on, and the output voltage of LED1 in the LED string is high, the voltage across resistor R4 is greater than the turn-on voltage threshold of switching device Q3, thus ensuring that switching device Q3 is turned on.
[0032] The following is a detailed introduction Figure 1 The working principle of the LED short-circuit protection circuit shown.
[0033] 1、System normal work time (or LED light string LED1 does not appear short circuit), when PWM drive signal is high (it can be called the first logic level of PWM drive signal), through resistance R1 and resistance R2 to the gate of power tube Q1, drive power tube Q1 conduction, power tube Q1 drain voltage is 0V, because PWM drive signal is high, switch device Q4 is NPN triode, switch device Q4 will also be saturated conduction, switch device Q4 collector is also pulled low to 0V, because the negative of diode D3 is connected to the drain of power tube Q1, power tube Q1 drain voltage is 0V, due to the clamping effect of diode, switch device Q3 emitter will be clamped to about 0.3V, switch device Q3 is a PNP triode, when switch device Q4 saturated conduction, switch device Q3 emitter voltage through resistance R4, resistance R6 voltage division does not meet the saturation conduction condition of switch device Q3, so switch device Q3 is off state (or off state), switch device Q3 collector is connected to ground through resistance R7 and R8, so switch device Q3 collector and switch device Q2 base are 0V, that is, the detection output end C of LED detection circuit 110 is low (it can be called the second logic level of detection signal), so that NPN triode Q2 is also in the off state (or off state), because D1 and D2 are diodes, diode has unidirectional conductivity, and switch device Q2 is in the off state, so the system works normally and the PWM drive signal is high, LED detection circuit 110 and drive off circuit 120 will not work, will not affect the drive of power tube Q1.
[0034] 2、System normal work time, when PWM drive signal is low, through resistance R1 and resistance R2 to the gate of power tube Q1, power tube Q1 is NMOS tube, power tube Q1 will not be turned on, power tube Q1 drain voltage is the voltage of power supply Vbat, switch device Q4 is a NPN triode, switch device Q4 will not be turned on, resistance R5 is also connected to PWM drive signal, D3 is a diode, diode has unidirectional conductivity, switch device Q3 emitter is also 0V, because switch device Q4 is in the off state, switch device Q3 is also in the off state, so switch device Q3 collector and Q2 base are also 0V, that is, the detection output end C of LED detection circuit 110 is low (it can be called the second logic level of detection signal), so that NPN triode Q2 is also in the off state (or off state), because D1 and D2 are diodes, diode has unidirectional conductivity, and switch device Q2 is in the off state, so the system works normally and the PWM drive signal is low, LED detection circuit 110 and drive off circuit 120 will not work, will not affect the drive of power tube Q1.
[0035] 3、When the PWM drive signal is high, and the LED string LED1 is short-circuited, the negative electrode of the diode D3 will rise from 0V to the voltage value of the power supply Vbat instantaneously, because the switch device Q4 is turned on when the PWM drive signal is high, and the negative electrode of the diode D3 becomes the voltage value of the power supply Vbat suddenly, the diode D3 loses the clamping effect, and the positive electrode voltage of the diode D3 is close to the voltage of the high level of the PWM drive signal, after being divided by the resistors R4 and R6, the PNP triode Q3 meets the turn-on condition, and the collector voltage of the switch device Q3 is also the high level voltage of the PWM drive signal, that is, the detection output end C of the LED detection circuit 110 is high (which can be called the first logic level of the detection signal)
[0036] Because the collector of the switch device Q3 is connected to the base of the switch device Q2 through the resistor R7, the switch device Q2 is saturated and turned on, and the collector of the switch device Q2 is pulled down to 0V, and the negative electrode of the diode D1 is connected to the collector of the switch device Q2, so that the clamping effect of the diode clamps the positive electrode voltage of the diode D1 to about 0.3V (that is, the voltage of the drive output end F of the drive-off circuit 120 is about 0.3V), and the power tube Q1 is an NMOS tube, which is turned off when the gate voltage is 0.3V, so that the power tube Q1 is protected from being damaged by the large current caused by the short circuit of the LED string LED1.
[0037] In summary, the LED short-circuit protection circuit has the following beneficial effects:
[0038] 1、The utility model discloses a simple and reliable circuit built by discrete devices, which determines whether the LED is in a short-circuit state by detecting the negative electrode voltage of the LED, and turns off the power drive (that is, turns off the power tube Q1) if the LED is in a short-circuit state, thereby protecting the power tube Q1 from being damaged in a very short time.
[0039] 2、The utility model discloses a short-circuit detection of the LED without the need for a shunt resistor, thereby reducing the cost, reducing the heat generation of the shunt resistor, and improving the efficiency of the product.
[0040] Compared with the prior art, the utility model discloses a low-cost and strong device replacement LED hardware short-circuit protection circuit built by discrete devices, which is not affected by the semiconductor market.
[0041] It should be pointed out that any modification made by a person skilled in the art to the specific embodiments of the utility model does not deviate from the scope of the claims of the utility model. Accordingly, the scope of the claims of the utility model is not limited to the foregoing specific embodiments.
Claims
1. An LED short circuit protection circuit, characterized by, It comprises: LED light string, its input end is connected with power supply Vbat; Power tube Q1, its first connection end is connected with the output end of the LED light string, its second connection end is grounded, and its control end receives PWM drive signal, and the PWM drive signal is used for driving the power tube Q1 to be periodically turned on and turned off; LED detection circuit, which comprises a first detection end A, a second detection end B and a detection output end C, the first detection end A is connected with the output end of the LED light string, and the second detection end B receives the PWM drive signal, and the LED detection circuit detects whether the LED light string is short-circuited based on the voltage of the output end of the LED light string and the PWM drive signal, and outputs a detection signal indicating whether short-circuit through the detection output end C; Drive-off circuit, which comprises a first input end D, a second input end E and a drive output end F, the first input end D is connected with the output end of the LED light string, the second input end E is connected with the detection output end C, and the drive output end F is connected with the control end of the power tube Q1, and the drive-off circuit determines whether to turn off the power tube Q1 through its drive output end F based on the voltage of the output end of the LED light string and the detection signal output by the detection output end C.
2. The LED short protection circuit of claim 1, wherein, It further comprises resistance R1 and resistance R2, One end of the resistance R1 is connected with the PWM drive signal, and the other end is connected with the drive output end F of the drive-off circuit; One end of the resistance R2 is connected with the drive output end F of the drive-off circuit, and the other end is connected with the control end of the power tube Q1.
3. The LED short-circuit protection circuit according to claim 1 or 2, wherein The LED detection circuit comprises diode D3, diode D4, resistance R4, resistance R5, resistance R6, resistance R9, resistance R10, switching device Q3 and switching device Q4, The negative electrode of the diode D3 is connected with the first detection end A of the LED detection circuit, and the positive electrode is connected with the first connection end of the switching device Q3; the negative electrode of the diode D4 is connected with the second detection end B of the LED detection circuit, and the positive electrode is connected with the first connection end of the switching device Q3; the first connection end of the switching device Q3 is connected with its control end through the resistance R4, and the second connection end is connected with the detection output end C of the LED detection circuit; one end of the resistance R5 is connected with the first connection end of the switching device Q3, and the other end is connected with the second detection end B of the LED detection circuit; the first connection end of the switching device Q4 is connected with the control end of the switching device Q3 through the resistance R6, the control end is connected with the second detection end B of the LED detection circuit through the resistance R9, and the second connection end is grounded; one end of the resistance R10 is connected with the control end of the switching device Q4, and the other end is grounded.
4. The LED short-circuit protection circuit according to claim 3, wherein The LED detection circuit further comprises capacitor C1, One end of the capacitor C1 is connected to the control end of the switch device Q4, and the other end is grounded.
5. The LED short-circuit protection circuit according to claim 3, wherein, when the LED detection circuit detects that the PWM driving signal is the first logic level and the voltage at the output end of the LED lamp string is high, the switch device Q3 and the switch device Q4 are turned on, and the detection signal output by the detection output end C of the LED detection circuit is the first logic level, indicating that the LED lamp string is in a short-circuit state; when the LED detection circuit detects that the PWM driving signal is the first logic level and the voltage at the output end of the LED lamp string is low, the switch device Q3 is turned off, the switch device Q4 is turned on, and the detection signal output by the detection output end C of the LED detection circuit is the second logic level, indicating that the LED lamp string is in a non-short-circuit state; when the LED detection circuit detects that the PWM driving signal is the second logic level and the voltage at the output end of the LED lamp string is high, the switch device Q3 is turned off, the switch device Q4 is turned off, and the detection signal output by the detection output end C of the LED detection circuit is the second logic level, indicating that the LED lamp string is in a non-short-circuit state, wherein the first logic level of the PWM driving signal is used to drive the power tube Q1 to be turned on, and the second logic level of the PWM driving signal is used to drive the power tube Q1 to be turned off.
6. The LED short-circuit protection circuit according to claim 5, wherein, the driving-off circuit comprises a diode D1, a diode D2, a resistor R3, a resistor R7, a resistor R8, and a switch device Q2, the anode of the diode D2 is connected to the first input end D of the driving-off circuit, and the cathode thereof is connected to the first connection end of the switch device Q2 through the resistor R3; the anode of the diode D1 is connected to the driving output end F of the driving-off circuit, and the cathode thereof is connected to the first connection end of the switch device Q2; the control end of the switch device Q2 is connected to the detection output end C of the LED detection circuit through the resistor R7, and the second connection end thereof is grounded; one end of the resistor R8 is connected to the control end of the switch device Q2, and the other end is grounded.
7. The LED short-circuit protection circuit according to claim 6, wherein, when the detection signal output by the detection output end C of the LED detection circuit is the first logic level and the voltage at the output end of the LED lamp string is high, the switch device Q2 is turned on, so that the driving-off circuit drives the power tube Q1 to be turned off through the driving output end F thereof; otherwise, the switch device Q2 is turned off, so that the driving-off circuit does not work.
8. The LED short-circuit protection circuit according to claim 7, wherein, the power tube Q1 is an NMOS tube, and the first connection end, the second connection end, and the control end of the power tube Q1 are the drain, the source, and the gate of the NMOS tube, respectively. The switch device Q2 is an NPN triode, and the first connection end, the second connection end and the control end of the switch device Q2 are the collector, the emitter and the base of the NPN triode respectively; The switch device Q3 is a PNP triode, and the first connection end, the second connection end and the control end of the switch device Q3 are the emitter, the collector and the base of the PNP triode respectively; The switch device Q4 is an NPN triode, and the first connection end, the second connection end and the control end of the switch device Q4 are the collector, the emitter and the base of the NPN triode respectively.
9. The LED short circuit protection circuit according to claim 7, characterized in that, The resistance values of the resistors R7 and R8 are selected to satisfy that when the switch device Q3 and the switch device Q4 are turned on, the voltage value of the voltage division on the resistor R8 is greater than the turn-on voltage threshold of the switch device Q2, so that the switch device Q2 is in the turn-on state; The resistance values of the resistors R4 and R6 are selected to satisfy that when the power tube Q1 and the switch device Q4 are turned on, and the voltage of the output end of the LED lamp string is high level, the voltage value of the voltage division on the resistor R4 is greater than the turn-on voltage threshold of the switch device Q3, so that the switch device Q3 is in the turn-on state.