LED short circuit protection circuit

Abstract

The utility model provides a kind of LED short circuit protection circuit, it includes: LED lamp string, its input end is connected with first power supply;Power tube Q1, its first connecting end is connected with the output end of LED lamp string, its second connecting end ground, its control end receives PWM drive signal;Short circuit detection unit, it includes first detection end, second detection end and detection output end, first detection end is connected with the output end of LED lamp string, its second detection end receives PWM drive signal, short circuit detection unit is based on the voltage of the output end of LED lamp string and PWM drive signal detects whether LED lamp string is short-circuited;Short circuit protection unit, its input end is connected with detection output end, its output end is connected with the control end of power tube Q1, when short circuit detection unit detects that LED is in short-circuit state, short circuit protection unit drives power tube Q1 to shut down by its output end.Compared with prior art, the utility model saves the cost of shunt resistance, reduces heat generation and improves the efficiency of product.

Description

TECHNICAL FIELD

[0001] The utility model relates to circuit design technical field, especially relates to a LED short circuit protection circuit. BACKGROUND

[0002] LED has small volume, high brightness, long life and other advantages, is widely used in the field of automobile and industrial market, along with the technical development of LED, the short circuit protection of LED power loop is more and more important.The LED short circuit protection on the market mainly detects the current on the resistance on the LED power loop, and the cost is high and the resistance heating is relatively large.

[0003] Therefore, it is necessary to provide a new technical scheme to solve the above problems. UTILITY MODEL CONTENTS

[0004] One of the purposes of the utility model is to provide a kind of LED short circuit protection circuit, it is built by discrete device, and circuit is simple and reliable, and it judges whether LED is in short circuit state by detecting the negative voltage of LED, if LED is in short circuit state, then it will trigger the short circuit protection of LED.This way, the utility model saves the cost of shunt resistance, reduces the heat and improves the efficiency of product.

[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 first 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 on and off;Short circuit detection unit, 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 short circuit detection unit detects whether the LED lamp string is short-circuited based on the voltage of the output end of the LED lamp string and the PWM drive signal, and the detection signal indicating whether short-circuited is output through the detection output end C;Short circuit protection unit, its input end is connected with the detection output end C, and its output end D is connected with the control end of the power tube Q1, when the short circuit detection unit detects that the LED is in short circuit state, the short circuit protection unit drives the power tube Q1 off through its output end D.

[0006] Further, the LED short circuit protection circuit further includes resistance R1, one end of the resistance R1 is connected with the PWM drive signal, and the other end is connected with the control end of the power tube Q1.

[0007] Further, the short-circuit detection unit comprises a diode D1, a diode D2, a resistor R3, a resistor R4, a resistor R5, a resistor R6, a resistor R9, a switching device Q2 and a switching device Q3, a negative electrode of the diode D1 is connected with the first detection end A of the short-circuit detection unit, and a positive electrode thereof is connected with a node E; a negative electrode of the diode D2 is connected with the second detection end B of the short-circuit detection unit, and a positive electrode thereof is connected with the node E; one end of the resistor R3 is connected with the second detection end B of the short-circuit detection unit, and the other end thereof is grounded; one end of the resistor R4 is connected with the second power supply VCC, and the other end thereof is connected with the node E; a first connection end of the switching device Q2 is connected with the second power supply VCC, a second connection end thereof is connected with the detection output end C, and a control end thereof is connected with a first connection end of the switching device Q3 through the resistor R6; one end of the resistor R5 is connected with the first connection end of the switching device Q2, and the other end thereof is connected with the first connection end of the switching device Q3; the control end of the switching device Q3 is connected with the node E, and the second connection end thereof is grounded.

[0008] Further, when the short-circuit detection unit detects that the PWM driving signal is the first logic level and the voltage of the output end of the LED lamp string is a high level, the switching device Q2 and the switching device Q3 are turned on, the detection signal output by the detection output end C of the short-circuit detection unit is the first logic level, indicating that the LED lamp string is in a short-circuit state, so as to make the short-circuit protection unit work, thereby controlling the power tube Q1 to be turned off; otherwise, the switching device Q2 and the switching device Q3 are turned off, the detection signal output by the detection output end C of the short-circuit detection unit is the second logic level, indicating that the LED lamp string is in a non-short-circuit state, so as to make the short-circuit protection unit not work, 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.

[0009] Further, the short-circuit protection unit comprises a resistor R2, a resistor R7, a resistor R8, a resistor R10, a diode D3 and a switching device Q4, one end of the resistor R2 is connected with the output end D of the short-circuit protection unit, and the other end thereof is connected with a node F; a first connection end of the switching device Q4 is connected with the node F, a second connection end thereof is grounded, and a control end thereof is grounded through the resistor R10; one end of the resistor R7 is connected with the detection output end C of the short-circuit detection unit, and the other end thereof is connected with the control end of the switching device Q4; a positive electrode of the diode D3 is connected with the detection output end C of the short-circuit detection unit, and a negative electrode thereof is connected with the node F through the resistor R8.

[0010] Further, when the detection signal outputted by the detection output end C of the short-circuit detection unit is the second logic level, the switch device Q4 is turned off, so that the short-circuit protection unit does not work; when the detection signal outputted by the detection output end C of the short-circuit detection unit is the first logic level, the switch device Q4 is turned on, so that the short-circuit protection unit drives the power tube Q1 to be turned off through the output end D.

[0011] 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 switch device Q2 is a PNP type triode, the first connection end, the second connection end and the control end of the switch device Q2 are the emitter, the collector and the base of the PNP type triode respectively; the switch device Q3 is an NPN type triode, the first connection end, the second connection end and the control end of the switch device Q3 are the collector, the emitter and the base of the NPN type triode respectively; the switch device Q4 is an NPN type triode, 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 type triode respectively.

[0012] Further, the resistance values of the resistance R7 and the resistance R10 are selected to satisfy that when the switch device Q2 and the switch device Q3 are turned on, the voltage division voltage value on the resistance R10 is greater than the turn-on voltage threshold of the switch device Q4, so that the switch device Q4 is in the turn-on state.

[0013] Compared with the prior art, the utility model discloses by discrete device builds, and the circuit is simple and reliable, and it determines whether the LED is in the short circuit state through the detection of the negative pole voltage of the LED, and if the LED is in the short circuit state, the short circuit protection of the LED will be triggered. In this way, the utility model saves the cost of shunt resistance, reduces the heat generation and improves the efficiency of the product. BRIEF DESCRIPTION OF DRAWINGS

[0014] In order to more clearly illustrate the technical scheme of the embodiments of the utility model, the drawings needed to be used in the embodiment description will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the utility model, and other drawings can be obtained according to these drawings without the creative labor of the ordinary skilled in the art. Among them:

[0015] Figure 1 It is the circuit schematic diagram of the LED short-circuit protection circuit in an embodiment of the utility model. DETAILED DESCRIPTION

[0016] To make the above-mentioned objectives, features and advantages of this utility model more apparent and understandable, the utility model will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0017] The term "an embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that excludes other embodiments. Unless otherwise specified, the terms coupling, connection, linking, and interconnection used herein to indicate electrical connection mean direct or indirect connection. For example, A being connected to B includes both a direct electrical connection between A and B and a connection between A and B via electrical components or circuits.

[0018] In the description of this utility model, it should be understood that the terms "upper", "lower", "front", "back", "positive", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this utility model and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this utility model.

[0019] Please refer to Figure 1 As shown, it is a circuit diagram of an LED short-circuit protection circuit in one embodiment of the present invention. Figure 1 The LED short-circuit protection circuit shown includes an LED string LED1, a power transistor (MetalOxide Semiconductor Field Effect Transistor, MOSFET) Q1, a short-circuit detection unit 110, and a short-circuit protection unit 120.

[0020] In this configuration, the input terminal (or positive terminal) of LED1 in the LED string is connected to the first power supply Vbat; the first connection terminal of power transistor Q1 is connected to the output terminal (or negative terminal) of LED1 in the LED string, and its second connection terminal is grounded. Its control terminal receives a PWM drive signal, which is used to drive power transistor Q1 to periodically turn on and off. The PWM (Pulse Width Modulation) drive signal is a periodic high and low level square wave signal. By changing the duty cycle of the PWM drive signal, power transistor Q1 can be controlled, thereby adjusting the brightness of LED1 in the LED string.

[0021] The short-circuit detection unit 110 includes a first detection end A, a second detection end B and a detection output end C. The first detection end A is connected to the output end (or negative electrode) of the LED lamp string LED1, and the second detection end B receives the PWM driving signal. The short-circuit detection unit 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 the LED lamp string LED1 is short-circuited through the detection output end C.

[0022] The input end of the short-circuit protection unit 120 is connected to the detection output end C, and the output end D is connected to the control end of the power tube Q1. When the short-circuit detection unit 110 detects that the LED lamp string LED1 is in a short-circuit state, the short-circuit protection unit 120 drives the power tube Q1 to be turned off through the output end D, so as to protect the power tube Q1 from being damaged due to overheating.

[0023] Figure 1 The LED short-circuit protection circuit shown also includes a resistor R1. One end of the resistor R1 is connected to the PWM driving signal, and the other end is connected to the control end of the power tube Q1. In other words, the PWM driving signal, the resistor R1, the power tube Q1, the LED lamp string LED1 and the first power supply Vbat constitute a main power loop of the Mosfet. In normal times, this loop realizes the dimming function of the LED.

[0024] The short-circuit detection unit 110 includes a diode D1, a diode D2, a resistor R3, a resistor R4, a resistor R5, a resistor R6, a resistor R9, a switching device Q2 and a switching device Q3. The negative electrode of the diode D1 is connected to the first detection end A of the short-circuit detection unit 110, and the positive electrode is connected to a node E. The negative electrode of the diode D2 is connected to the second detection end B of the short-circuit detection unit 110, and the positive electrode is connected to the node E. One end of the resistor R3 is connected to the second detection end B of the short-circuit detection unit 110, and the other end is grounded. One end of the resistor R4 is connected to the second power supply VCC, and the other end is connected to the node E. The first connection end of the switching device Q2 is connected to the second power supply VCC, and the second connection end is connected to the detection output end C. The control end of the switching device Q2 is connected to the first connection end of the switching device Q3 through the resistor R6. One end of the resistor R5 is connected to the first connection end of the switching device Q2, and the other end is connected to the first connection end of the switching device Q3. The control end of the switching device Q3 is connected to the node E, and the second connection end is grounded.

[0025] When the short-circuit detection unit 110 detects that the PWM drive signal is at the first logic level and the voltage at the output terminal (or negative terminal) of the LED string LED1 is high, switching devices Q2 and Q3 are turned on. The detection output terminal C of the short-circuit detection unit 110 outputs a detection signal at the first logic level, indicating that the LED string LED1 is in a short-circuit state, thereby enabling the short-circuit protection unit 120 to operate and control the power transistor Q1 to turn off. Otherwise, switching devices Q2 and Q3 are turned off, and the detection output terminal C of the short-circuit detection unit 110 outputs a detection signal at the second logic level, indicating that the LED string LED1 is in a non-short-circuit state, thereby enabling the short-circuit protection unit 120 to not operate. The first logic level of the PWM drive signal is used to drive the power transistor Q1 to turn on; the second logic level of the PWM drive signal is used to drive the power transistor Q1 to turn off.

[0026] The short-circuit protection unit 120 includes resistors R2, R7, R8, and R10, diode D3, and switching device Q4. One end of resistor R2 is connected to the output terminal D of the short-circuit protection unit 120, and the other end is connected to node F. The first connection terminal of switching device Q4 is connected to node F, its second connection terminal is grounded, and its control terminal is grounded via resistor R10. One end of resistor R7 is connected to the detection output terminal C of the short-circuit detection unit 110, and the other end is connected to the control terminal of switching device Q4. The anode of diode D3 is connected to the detection output terminal C of the short-circuit detection unit 110, and its cathode is connected to node F via resistor R8.

[0027] When the detection signal output from the detection output terminal C of the short-circuit detection unit 110 is at the second logic level (indicating that the LED string LED1 is in a non-short-circuit state), the switching device Q4 is turned off, and the short-circuit protection unit 120 does not work; when the detection signal output from the detection output terminal C of the short-circuit detection unit 110 is at the first logic level (indicating that the LED string LED1 is in a short-circuit state), the switching device Q4 is turned on, and the short-circuit protection unit 120 drives the power transistor Q1 to turn off through its output terminal D.

[0028] 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 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 Q3 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 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.

[0029] The resistance values of the resistance R7 and the resistance R10 are selected to satisfy: when the switch device Q2 and the switch device Q3 are turned on, the voltage value of the voltage division on the resistance R10 is greater than the turn-on voltage threshold of the switch device Q4, so that the switch device Q4 is in the turn-on state.

[0030] The working principle of the LED short circuit protection circuit is specifically introduced as follows. Figure 1 The working principle of the LED short circuit protection circuit is specifically introduced as follows.

[0031] 1. When the system is in normal operation (or the LED lamp string LED1 is not in short circuit), the PWM drive signal drives the power tube Q1 to be turned on and turned off continuously, so that the brightness of the LED lamp string LED1 can be adjusted according to the different duty cycle.

[0032] 2. When the system is in normal operation (or the LED lamp string LED1 is not in short circuit), when the PWM drive signal is high (which can be referred to as the first logic level of the PWM drive signal), the power tube Q1 is an NMOS tube, the power tube Q1 is turned on, and the drain of the power tube Q1 is pulled down to 0V. Due to the clamping effect of the diode D1, the base voltage of the switch device Q3 is clamped to about 0.3V. Due to the unidirectional conductivity of the diode D2 and the clamping effect of the diode D1, even if the PWM drive signal is high, the base voltage of the switch device Q3 will not be affected. Because the switch device Q3 is an NPN transistor, and the base voltage of the switch device Q3 is about 0.3V, the switch device Q3 is in the off state (i.e., the switch device Q3 is turned off). The switch device Q2 is a PNP transistor, the switch device Q3 is in the off state, and the emitter and base levels of the switch device Q2 are consistent, so the switch device Q2 is also in the off state (i.e., the switch device Q2 is turned off). The voltage on the resistance R9 is not affected by the second power supply VCC and the switch device Q2, and the resistance R9 is pulled down to GND, that is, the detection output end C of the short circuit detection unit 110 outputs a low level (which can be referred to as the second logic level of the detection signal, indicating that the LED lamp string LED1 is in a non-short circuit state), so the base of the switch device Q4 is also low. Since the switch device Q4 is an NPN transistor, the switch device Q4 is in the off state (i.e., the switch device Q4 is turned off). Due to the unidirectional conductivity of the diode D3, the short circuit protection unit 120 will not affect the driving control of the power tube Q1 by the PWM drive signal. When the PWM drive signal is low (which can be referred to as the second logic level of the PWM drive signal), the power tube Q1 is in the off state, the cathode of the diode D2 is low, and the base of the switch device Q3 is also clamped to 0.3V by the diode D2. Like when the PWM drive signal is high, the short circuit detection unit 110 and the short circuit protection unit 120 will not affect the driving control of the power tube Q1 by the PWM drive signal.

[0033] 3. When the LED string LED1 appears short circuit, before the LED string LED1 appears short circuit, when the PWM drive signal is high level, the negative pole of the diode D2 is high level, the negative pole of the diode D1 is pulled to 0V, the base of the switching device Q3 is clamped to 0.3V by the diode, so the switching device Q3 will not be turned on, the short circuit detection unit 110 and the short circuit protection unit 120 will not work. When the LED string LED1 suddenly appears short circuit, the output end (or the negative pole) of the LED string LED1 will be high level, so the negative poles of the diodes D1 and D2 are high level, the base of the switching device Q3 will be saturated and turned on through the loop of the resistance R4 and the second power supply VCC, the collector of the switching device Q3 will be pulled to 0V, the switching device Q2 is a PNP triode, the switching device Q2 will also be turned on, so the collector of the switching device Q2 is also the voltage of the second power supply VCC, so that the voltage on the resistance R9 is also high level, that is, the detection output end C of the short circuit detection unit 110 outputs high level (which can be called the first logic level of the detection signal, indicating that the LED string LED1 is in a short circuit state), through the voltage division of the resistances R7 and R10, the voltage value of the voltage division on the resistance R10 (which is equal to the voltage between the base and the emitter of the NPN triode Q4) is greater than the turn-on voltage threshold of the NPN triode Q4 (or the PN junction voltage of the NPN triode Q4), which meets the saturation turn-on condition, the switching device Q4 is turned on, the collector of the switching device Q4 is pulled to 0V, the gate of the power tube Q1 is clamped to 0V by the switching device Q4, the power tube Q1 is an NMOS tube, when the gate of the power tube Q1 is at 0V, the power tube Q1 will be turned off, so as to achieve the function of detecting the LED short circuit state and triggering the LED short circuit protection.

[0034] In summary, the LED short circuit protection circuit has the following beneficial effects:

[0035] 1. The LED short circuit protection circuit is built by discrete devices, and the circuit is simple and reliable, which determines whether the LED is in a short circuit state by detecting the negative pole voltage of the LED, and if the LED is in a short circuit state, the short circuit protection of the LED will be triggered.

[0036] 2. The LED short circuit protection circuit does not need to detect the short circuit of the LED through a shunt resistor, which reduces the cost, reduces the heat generation of the shunt resistor and improves the efficiency of the product.

[0037] It should be pointed out that any modification made by the skilled person to the specific embodiments of the utility model does not deviate from the scope of the claims of the utility model. Correspondingly, 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 first 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; Short circuit detection unit, which comprises 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 light string, and the second detection end B receives the PWM drive signal, and the short circuit detection unit 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 detection signal indicating whether short-circuited through the detection output end C; Short circuit protection unit, its input end is connected with the detection output end C, its output end D is connected with the control end of the power tube Q1, when the short circuit detection unit detects that the LED is in short-circuit state, the short circuit protection unit drives the power tube Q1 to be turned off through its output end D.

2. The LED short protection circuit of claim 1, wherein, It further comprises resistance R1, One end of the resistance R1 is connected with the PWM drive signal, 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, characterized in that The short circuit detection unit comprises diode D1, diode D2, resistance R3, resistance R4, resistance R5, resistance R6, resistance R9, switching device Q2 and switching device Q3, The negative electrode of the diode D1 is connected with the first detection end A of the short circuit detection unit, and the positive electrode is connected with node E; the negative electrode of the diode D2 is connected with the second detection end B of the short circuit detection unit, and the positive electrode is connected with the node E; one end of the resistance R3 is connected with the second detection end B of the short circuit detection unit, and the other end is grounded; one end of the resistance R4 is connected with the second power supply VCC, and the other end is connected with the node E; the first connection end of the switching device Q2 is connected with the second power supply VCC, the second connection end is connected with the detection output end C, and the control end is connected with the first connection end of the switching device Q3 through the resistance R6; one end of the resistance R5 is connected with the first connection end of the switching device Q2, and the other end is connected with the first connection end of the switching device Q3; the control end of the switching device Q3 is connected with the node E, and the second connection end is grounded.

4. The LED short-circuit protection circuit according to claim 3, characterized in that When the short-circuit detection unit 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, the switch device Q2 and the switch device Q3 are turned on, the detection signal output by the detection output end C of the short-circuit detection unit is the first logic level, indicating that the LED lamp string is in a short-circuit state, so as to make the short-circuit protection unit work, thereby controlling the power tube Q1 to be turned off; otherwise, the switch device Q2 and the switch device Q3 are turned off, the detection signal output by the detection output end C of the short-circuit detection unit is the second logic level, indicating that the LED lamp string is in a non-short-circuit state, so as to make the short-circuit protection unit not work, 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.

5. The LED short-circuit protection circuit according to claim 4, characterized in that, the short-circuit protection unit comprises a resistor R2, a resistor R7, a resistor R8, a resistor R10, a diode D3 and a switch device Q4, one end of the resistor R2 is connected with the output end D of the short-circuit protection unit, the other end thereof is connected with a node F, the first connection end of the switch device Q4 is connected with the node F, the second connection end thereof is grounded, and the control end thereof is grounded through the resistor R10; one end of the resistor R7 is connected with the detection output end C of the short-circuit detection unit, the other end thereof is connected with the control end of the switch device Q4; the anode of the diode D3 is connected with the detection output end C of the short-circuit detection unit, and the cathode thereof is connected with the node F through the resistor R8.

6. The LED short-circuit protection circuit according to claim 5, characterized in that, when the detection signal output by the detection output end C of the short-circuit detection unit is the second logic level, the switch device Q4 is turned off, so that the short-circuit protection unit does not work; when the detection signal output by the detection output end C of the short-circuit detection unit is the first logic level, the switch device Q4 is turned on, so that the short-circuit protection unit drives the power tube Q1 to be turned off through the output end D thereof.

7. The LED short-circuit protection circuit according to claim 6, characterized in that, 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 switch device Q2 is a PNP type triode, the first connection end, the second connection end and the control end of the switch device Q2 are the emitter, the collector and the base of the PNP type triode respectively; the switch device Q3 is an NPN type triode, the first connection end, the second connection end and the control end of the switch device Q3 are the collector, the emitter and the base of the NPN type triode respectively; the switch device Q4 is an NPN type triode, 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 type triode respectively.

8. The LED short-circuit protection circuit according to claim 6, characterized in that, The resistance values of the resistors R7 and R10 are selected to satisfy: when the switch devices Q2 and Q3 are turned on, the voltage value of the voltage division on the resistor R10 is greater than the turn-on voltage threshold of the switch device Q4, so that the switch device Q4 is in the turn-on state.

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