Overcurrent protection circuit and working method thereof

Abstract

The invention discloses an overcurrent protection circuit and a working method thereof. A voltage stabilizing circuit unit is used for stabilizing an input voltage to a fixed value to supply power to a current sensor; the current detection circuit unit is used for completing a current detection function and processing a voltage value converted by the current sensor; the over-current detection circuit unit is used for judging whether the circuit is over-current or not according to the voltage value output by the current detection circuit and uploading an over-current signal to the controller; and the control circuit unit is used for controlling the on-off of the MOSFET tube through a control signal of the controller so as to control the output voltage. According to the invention, a power supply overcurrent protection function is completed by combining software and hardware, so that the system is more stable and reliable; according to the invention, the MCU is used for controlling the on and off of the MOS tube switch, and the output voltage of the overcurrent protection circuit can realize a self-recovery function when the circuit is subjected to light and heavy load switching.

Description

Technical Field

[0001] The invention relates to an overcurrent protection circuit and a working method thereof, belonging to the technical field of power supply protection. Background Art

[0002] During the use of electronic equipment, power supply plays a vital role, but overcurrent problems may occur due to line short circuits or other reasons, so an overcurrent protection circuit needs to be designed.

[0003] Traditional overcurrent protection circuits are mainly designed with resettable fuses. Although the design principle is simple, the fuse has a long melting time, which leads to a slow response of the overcurrent protection device in an emergency, and may cause the equipment to overheat and be damaged. In particular, high-power devices in the circuit system, such as MOSFET and IGBT, have poor short-term overcurrent tolerance and are easily damaged. In addition, the resettable fuse is easily affected by external environmental factors during operation and has poor reliability, which may cause the overcurrent protection device to fail to work, affecting equipment safety. Summary of the invention

[0004] Purpose: In order to overcome the deficiencies of the conventional overcurrent protection circuit in the prior art, the present invention provides an overcurrent protection circuit and a working method thereof.

[0005] Technical solution: To solve the above technical problems, the technical solution adopted by the present invention is:

[0006] In a first aspect, an overcurrent protection circuit includes: a voltage stabilizing circuit unit, a current detection circuit unit, an overcurrent detection circuit unit, a control circuit unit and a controller.

[0007] The voltage stabilizing circuit unit is used to stabilize the input voltage to a fixed value to supply power to the current sensor.

[0008] The current detection circuit unit is used to complete the current detection function and process the voltage value converted by the current sensor.

[0009] The overcurrent detection circuit unit is used to determine whether the circuit has overcurrent according to the voltage value output by the current detection circuit, and to upload the overcurrent signal to the controller.

[0010] The control circuit unit is used to control the on and off of the MOSFET tube through the control signal of the controller to control the output voltage.

[0011] As a preferred solution, the voltage stabilizing circuit unit includes a resistor R11, a capacitor C25, a voltage reference V7 and an NPN transistor V6. The resistor R11, one end of the capacitor C25 and the voltage input pin of the voltage reference V7 at the 1-end intersect at a point and are connected to the base of the NPN transistor V6. The other end of the resistor R11 and the collector of the NPN transistor V6 intersect at a point and are connected to the positive electrode of the power supply. The other end of the capacitor C25 and the voltage output pin of the voltage reference V7 at the 2-end intersect at a point and are connected to the negative electrode of the power supply. The emitter of the NPN transistor V6 is connected to the VCC pin of the 8-end of the current sensor N2.

[0012] As a preferred solution, a transformer L9 is further included, the positive pole of the power supply is connected to the positive pole of the power supply of the secondary side of the transformer L9, and the negative pole of the power supply is connected to the negative pole of the power supply of the secondary side of the transformer L9.

[0013] As a preferred solution, the current detection circuit unit includes a resistor R12, a resistor R13, a capacitor C27, a capacitor C28, a capacitor C29 and a current sensor N2, one end of the resistor R12, the resistor R13 and the capacitor C29 intersect at a point and are connected to the voltage input pin of the reference source V8 at the 1 end, the other end of the resistor R12 and one end of the capacitor C28 intersect at a point and are connected to the OUT pin of the 7 end of the current sensor N2, the two ends of the capacitor C27 are respectively connected to the VCC pin of the 8 end of the current sensor N2 and the negative pole of the power supply, the other ends of the resistor R13, the capacitor C29 and the capacitor C28 intersect at a point and are connected to the negative pole of the power supply, the IP+ pin of the 1 end and the IP+ pin of the 2 end of the current sensor N2 are respectively the positive poles of the power supply, and the IP- pin of the 3 end and the IP- pin of the 4 end of the current sensor N2 are respectively connected to the source of the P-MOS tube Q3.

[0014] As a preferred solution, it also includes a capacitor C23 and a capacitor C24, and the capacitor C23 and the capacitor C24 are respectively connected in parallel between the positive electrode and the negative electrode of the power supply.

[0015] As a preferred solution, the overcurrent detection circuit unit includes a resistor R16, a resistor R17, a resistor R18, a reference source V8, and an optocoupler E2, one end of the resistor R16 is connected to the source of the P-MOS tube Q3, one end of the resistor R17 is connected to the negative electrode of the power supply, the other ends of the resistors R16 and R17 intersect at a point and are connected to the Anode end of the optocoupler E2, one end of the resistor R18 is connected to the controller power supply, the other end of the resistor R18 is connected to the I / O1 pin of the controller and the Collector end of the optocoupler E2, the Emitter end of the optocoupler E2 is connected to the controller power supply ground, the 3-terminal voltage output pin of the reference source V8 is connected to the Cathode end of the optocoupler E2, and the 2-terminal ground pin of the reference source V8 is connected to the negative electrode of the power supply and then connected to the negative end of the power supply output.

[0016] As a preferred solution, the control circuit unit includes a resistor R14, a resistor R15, a resistor R19, a resistor R20, a voltage stabilizing diode V9, an NPN transistor V10, a P-MOS tube Q3, and an optical coupler E9. One end of the resistor R14 and the negative electrode of the voltage stabilizing diode V9 intersect at one point and are connected to the source of the P-MOS tube Q3. The other end of the resistor R14, one end of the resistor R15, and the positive electrode of the voltage stabilizing diode V9 intersect at one point and are connected to the gate of the P-MOS tube Q3. The other end of the resistor R15 is connected to the Colle of the optical coupler E9. ctor end, the Emitter end of the optocoupler E9 is connected to the negative pole of the power supply, the drain of the P-MOS tube Q3 is connected to the positive end of the power supply output, the two ends of the resistor R19 are respectively connected to the controller power supply and the Anode end of the optocoupler E9, the collector of the NPN transistor V10 is connected to the Cathode end of the optocoupler E9, the emitter of the NPN transistor V10 is connected to the controller power supply ground, the base of the NPN transistor V10 is connected to one end of the resistor R20, and the other end of the resistor R20 is connected to the I / O2 pin of the controller.

[0017] As a preferred solution, the controller includes an MCU, a crystal oscillator XT1, a resistor and a capacitor. The 24-port I / O1 pin of the MCU is connected to the Collector end of the optical coupler E2, and the 25-port I / O2 pin is connected to the other end of the resistor R20.

[0018] In a second aspect, a working method of an overcurrent protection circuit comprises the following steps:

[0019] When the overcurrent protection circuit is working, the voltage of the secondary side of the transformer L9 is used as the input voltage, and the output current of the drain of the P-MOS tube Q3 is used as the maximum output current.

[0020] The input voltage generates a stable voltage through the voltage reference V7 to power the current detection circuit through the NPN transistor.

[0021] When the output current of the overcurrent protection circuit is less than the maximum output current and the circuit works normally, the current detected by the current sensor N2 is converted into a voltage, filtered by the capacitor C28, and then divided by the resistors R12 and R13 to obtain a voltage value.

[0022] When the voltage divided by resistors R12 and R13 is less than the conduction threshold of reference source V8, reference source V8 is not turned on, so optocoupler E2 does not work, the I / O1 pin of the controller detects a high level, the I / O2 pin of the controller sends a high level control signal, transistor V10 is turned on, and the P-MOS tube Q3 is turned on through optocoupler E9 isolation control, and the power supply is output normally.

[0023] As a preferred solution, it also includes: when the output current of the overcurrent protection circuit is greater than the maximum output current and the overcurrent protection circuit is in overcurrent operation, the current detected by the current sensor N2 is converted into a voltage, filtered by the capacitor C28, and then divided by the resistors R12 and R13 to obtain a divided voltage value.

[0024] When the voltage divided by resistors R12 and R13 is greater than the turn-on threshold of reference source V8, reference source V8 is turned on, and the power supply generates a voltage after voltage division by resistors R16 and R17 to turn on the light-emitting diode in optocoupler E2, thereby turning on the transistor in optocoupler E2, and the I / O1 pin of the controller detects a low level. When the I / O1 pin of the controller detects a low level k times, the I / O2 pin of the controller sends a low-level control signal, the transistor V10 is not turned on, the optocoupler E9 is not turned on, the P-MOS tube Q3 is not turned on, and the power supply has no output, thereby achieving an overcurrent protection function.

[0025] Beneficial effects: Compared with the prior art, the overcurrent protection circuit and the working method thereof provided by the present invention have the following advantages:

[0026] 1. The present invention uses a combination of software and hardware to complete the power overcurrent protection function, making the system more stable and reliable;

[0027] 2. The present invention uses MCU to control the closing and opening of the MOS tube switch. When the circuit switches between light and heavy loads, the output voltage of the overcurrent protection circuit can achieve a self-recovery function. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a structural schematic diagram of the overcurrent protection circuit of the present invention.

[0029] Figure 2 The schematic diagram of the structure of the controller of the present invention is a STM32 series single chip microcomputer.

[0030] Figure 3 It is a waveform diagram of the overcurrent protection circuit of the present invention when it is working. DETAILED DESCRIPTION

[0031] The following is a clear and complete description of the technical solutions in the examples of the present invention in conjunction with the accompanying drawings in the examples of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the protection scope of the present invention.

[0032] The present invention will be further described below in conjunction with specific embodiments.

[0033] Embodiment 1:

[0034] This embodiment introduces an overcurrent protection circuit. Figure 1 As shown, it includes: a voltage stabilizing circuit unit, a current detection circuit unit, an overcurrent detection circuit unit, a control circuit unit and a controller.

[0035] The voltage stabilizing circuit unit is used to stabilize the input voltage to a fixed value to supply power to the current sensor.

[0036] The current detection circuit unit is used to complete the current detection function and process the voltage value converted by the current sensor.

[0037] The overcurrent detection circuit unit is used to determine whether the circuit has overcurrent according to the voltage value output by the current detection circuit, and to upload the overcurrent signal to the controller.

[0038] The control circuit unit is used to control the on and off of the MOSFET tube through the control signal of the controller to control the output voltage.

[0039] In one embodiment, the voltage stabilizing circuit unit includes a resistor R11, a capacitor C25, a voltage reference V7 and an NPN transistor V6, wherein the resistor R11, one end of the capacitor C25 and a voltage input pin of the voltage reference V7 at terminal 1 intersect at a point and are connected to the base of the NPN transistor V6, the other end of the resistor R11 and the collector of the NPN transistor V6 intersect at a point and are connected to the positive electrode of the power supply, the other end of the capacitor C25 and a voltage output pin of the voltage reference V7 at terminal 2 intersect at a point and are connected to the negative electrode of the power supply, and the emitter of the NPN transistor V6 is connected to the VCC pin of the current sensor N2 at terminal 8.

[0040] Furthermore, a transformer L9 is included, wherein the positive pole of the power supply is connected to the positive pole of the power supply of the secondary side of the transformer L9, and the negative pole of the power supply is connected to the negative pole of the power supply of the secondary side of the transformer L9.

[0041] In one embodiment, the current detection circuit unit includes a resistor R12, a resistor R13, a capacitor C27, a capacitor C28, a capacitor C29 and a current sensor N2, one end of the resistor R12, the resistor R13 and the capacitor C29 intersect at a point and are connected to the voltage input pin of the reference source V8 at the 1 end, the other end of the resistor R12 and one end of the capacitor C28 intersect at a point and are connected to the OUT pin of the 7 end of the current sensor N2, the two ends of the capacitor C27 are respectively connected to the VCC pin of the 8 end of the current sensor N2 and the negative pole of the power supply, the other ends of the resistor R13, the capacitor C29 and the capacitor C28 intersect at a point and are connected to the negative pole of the power supply, the IP+ pin of the 1 end and the IP+ pin of the 2 end of the current sensor N2 are respectively the positive poles of the power supply, and the IP- pin of the 3 end and the IP- pin of the 4 end of the current sensor N2 are respectively connected to the source of the P-MOS tube Q3.

[0042] Furthermore, it also includes a capacitor C23 and a capacitor C24, and the capacitor C23 and the capacitor C24 are respectively connected in parallel between the positive electrode and the negative electrode of the power supply.

[0043] In one embodiment, the overcurrent detection circuit unit includes a resistor R16, a resistor R17, a resistor R18, a reference source V8, and an optocoupler E2, one end of the resistor R16 is connected to the source of the P-MOS tube Q3, one end of the resistor R17 is connected to the negative electrode of the power supply, the other ends of the resistors R16 and R17 intersect at a point and are connected to the Anode end of the optocoupler E2, one end of the resistor R18 is connected to the controller power supply, the other end of the resistor R18 is connected to the I / O1 pin of the controller and the Collector end of the optocoupler E2, the Emitter end of the optocoupler E2 is connected to the controller power supply ground, the 3-terminal voltage output pin of the reference source V8 is connected to the Cathode end of the optocoupler E2, and the 2-terminal ground pin of the reference source V8 is connected to the negative electrode of the power supply and then to the negative end of the power output.

[0044] In one embodiment, the control circuit unit includes a resistor R14, a resistor R15, a resistor R19, a resistor R20, a voltage stabilizing diode V9, an NPN transistor V10, a P-MOS transistor Q3, and an optical coupler E9, one end of the resistor R14 and the cathode of the voltage stabilizing diode V9 intersect at one point and are connected to the source of the P-MOS transistor Q3, the other end of the resistor R14, one end of the resistor R15, and the anode of the voltage stabilizing diode V9 intersect at one point and are connected to the gate of the P-MOS transistor Q3, and the other end of the resistor R15 is connected to the Collec of the optical coupler E9. tor terminal, the Emitter terminal of the optocoupler E9 is connected to the negative electrode of the power supply, the drain of the P-MOS tube Q3 is connected to the positive terminal of the power supply output, the two ends of the resistor R19 are respectively connected to the controller power supply and the Anode terminal of the optocoupler E9, the collector of the NPN transistor V10 is connected to the Cathode terminal of the optocoupler E9, the emitter of the NPN transistor V10 is connected to the controller power supply ground, the base of the NPN transistor V10 is connected to one end of the resistor R20, and the other end of the resistor R20 is connected to the I / O2 pin of the controller.

[0045] An embodiment, such as Figure 2 As shown, the controller includes an MCU, a crystal oscillator XT1, a resistor, and a capacitor. The 24-port I / O1 pin of the MCU is connected to the Collector end of the optical coupler E2, and the 25-port I / O2 pin is connected to the other end of the resistor R20.

[0046] In one embodiment, the MCU is a STM32F103 single-chip microcomputer.

[0047] Embodiment 2:

[0048] This embodiment introduces a working method of an overcurrent protection circuit. Figure 2As shown, when the overcurrent protection circuit is working, the voltage of the secondary side of the transformer L9 is used as the input voltage, the output current of the drain of the P-MOS tube Q3 is used as the maximum output current, and the input voltage generates a stable voltage through the voltage reference V7 to power the current detection circuit through the NPN transistor.

[0049] In one embodiment, an input voltage of 28V and a maximum output current of 5A are taken as an example.

[0050] When the overcurrent protection circuit operates normally with an output current less than 5A, the current detected by the current sensor N2 is converted into a voltage, filtered by the capacitor C28, and then divided by the resistors R12 and R13 to obtain a divided voltage value.

[0051] When the voltage divided by resistors R12 and R13 is less than the conduction threshold of reference source V8, reference source V8 is not turned on, so optocoupler E2 does not work, the I / O1 pin of the controller detects a high level, the I / O2 pin of the controller sends a high level control signal, transistor V10 is turned on, and the P-MOS tube Q3 is turned on through optocoupler E9 isolation control, and the power supply is output normally.

[0052] When the overcurrent protection circuit is in overcurrent operation with an output current greater than 5A, the current detected by the current sensor N2 is converted into a voltage, filtered by the capacitor C28, and then divided by the resistors R12 and R13 to obtain a voltage division value.

[0053] When the voltage divided by resistors R12 and R13 is greater than the turn-on threshold of reference source V8, reference source V8 is turned on, and the power supply generates a voltage after voltage division by resistors R16 and R17 to turn on the light-emitting diode in optocoupler E2, thereby turning on the transistor in optocoupler E2, and the I / O1 pin of the controller detects a low level. When the I / O1 pin of the controller detects k times (k=3) of low level, the I / O2 pin of the controller sends a low level control signal, the transistor V10 is not turned on, the optocoupler E9 is not turned on, the P-MOS tube Q3 is not turned on, and the power supply has no output, thereby achieving an overcurrent protection function.

[0054] like Figure 3 As shown in the figure, it is a waveform diagram of the overcurrent protection control circuit when it is working. In the overcurrent state, when the I / O1 pin of the controller detects a low level k times, the control power supply has no output, and then the controller re-detects the state of the I / O1 pin. It is a cyclic process. There is a certain delay in the program detection operation. Therefore, when the power supply has no output in the overcurrent state, there is a spike less than the output voltage.

[0055] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. An overcurrent protection circuit, characterized in that: include: A voltage stabilizing circuit unit, a current detecting circuit unit, an overcurrent detecting circuit unit, a control circuit unit and a controller; The voltage stabilizing circuit unit is used to stabilize the input voltage to a fixed value to supply power to the current sensor; The current detection circuit unit is used to complete the current detection function and process the voltage value converted by the current sensor; The overcurrent detection circuit unit is used to determine whether the circuit has overcurrent according to the voltage value output by the current detection circuit, and upload the overcurrent signal to the controller; The control circuit unit is used to control the on and off of the MOSFET tube through the control signal of the controller to control the output voltage.

2. An overcurrent protection circuit according to claim 1, characterized in that: The voltage stabilizing circuit unit includes a resistor R11, a capacitor C25, a voltage reference V7 and an NPN transistor V6. The resistor R11, one end of the capacitor C25 and a voltage input pin of the voltage reference V7 intersect at one point and are connected to the base of the NPN transistor V6. The other end of the resistor R11 and the collector of the NPN transistor V6 intersect at one point and are connected to the positive electrode of the power supply. The other end of the capacitor C25 and the voltage output pins of the voltage reference V7 intersect at one point and are connected to the negative electrode of the power supply. The emitter of the NPN transistor V6 is connected to the VCC pin of the current sensor N2.

3. An overcurrent protection circuit according to claim 2, characterized in that: It also includes a transformer L9, the positive pole of the power supply is connected to the positive pole of the power supply of the secondary side of the transformer L9, and the negative pole of the power supply is connected to the negative pole of the power supply of the secondary side of the transformer L9.

4. The overcurrent protection circuit according to claim 1, characterized in that: The current detection circuit unit comprises a resistor R12, a resistor R13, a capacitor C27, a capacitor C28, a capacitor C29 and a current sensor N2. One ends of the resistor R12, the resistor R13 and the capacitor C29 intersect at one point and are connected to a voltage input pin at the 1 end of a reference source V8. The other end of the resistor R12 and one end of the capacitor C28 intersect at one point and are connected to an OUT pin at the 7 end of the current sensor N2. Two ends of the capacitor C27 are respectively connected to a VCC pin at the 8 end of the current sensor N2 and a negative electrode of a power supply. The other ends of the resistor R13, the capacitor C29 and the capacitor C28 intersect at one point and are connected to the negative electrode of the power supply. The IP+ pin at the 1 end and the IP+ pin at the 2 end of the current sensor N2 are respectively positive electrodes of the power supply. The IP- pin at the 3 end and the IP- pin at the 4 end of the current sensor N2 are respectively connected to the source of the P-MOS tube Q3.

5. An overcurrent protection circuit according to claim 4, characterized in that: The device also includes a capacitor C23 and a capacitor C24, wherein the capacitor C23 and the capacitor C24 are connected in parallel between the positive electrode and the negative electrode of the power supply, respectively.

6. The overcurrent protection circuit according to claim 1, characterized in that: The overcurrent detection circuit unit includes a resistor R16, a resistor R17, a resistor R18, a reference source V8, and an optical coupler E2. One end of the resistor R16 is connected to the source of the P-MOS tube Q3, one end of the resistor R17 is connected to the negative electrode of the power supply, the other ends of the resistors R16 and R17 intersect at a point and are connected to the Anode end of the optical coupler E2, one end of the resistor R18 is connected to the controller power supply, the other end of the resistor R18 is connected to the I / O1 pin of the controller and the Collector end of the optical coupler E2, the Emitter end of the optical coupler E2 is connected to the controller power supply ground, the 3-terminal voltage output pin of the reference source V8 is connected to the Cathode end of the optical coupler E2, and the 2-terminal grounding pin of the reference source V8 is connected to the negative electrode of the power supply and then connected to the negative end of the power supply output.

7. The overcurrent protection circuit according to claim 1, characterized in that: The control circuit unit includes a resistor R14, a resistor R15, a resistor R19, a resistor R20, a voltage stabilizing diode V9, an NPN transistor V10, a P-MOS tube Q3, and an optical coupler E9. One end of the resistor R14 and the negative electrode of the voltage stabilizing diode V9 intersect at one point and are connected to the source of the P-MOS tube Q3. The other end of the resistor R14, one end of the resistor R15, and the positive electrode of the voltage stabilizing diode V9 intersect at one point and are connected to the gate of the P-MOS tube Q3. The other end of the resistor R15 is connected to the collector of the optical coupler E9. The emitter end of the optocoupler E9 is connected to the negative electrode of the power supply, the drain of the P-MOS tube Q3 is connected to the positive end of the power supply output, the two ends of the resistor R19 are respectively connected to the controller power supply and the Anode end of the optocoupler E9, the collector of the NPN transistor V10 is connected to the Cathode end of the optocoupler E9, the emitter of the NPN transistor V10 is connected to the controller power supply ground, the base of the NPN transistor V10 is connected to one end of the resistor R20, and the other end of the resistor R20 is connected to the I / O2 pin of the controller.

8. The overcurrent protection circuit according to claim 1, characterized in that: The controller includes an MCU, a crystal oscillator XT1, a resistor and a capacitor. The 24-port I / O1 pin of the MCU is connected to the Collector end of the optical coupler E2, and the 25-port I / O2 pin is connected to the other end of the resistor R20.

9. A working method of an overcurrent protection circuit according to any one of claims 1 to 8, characterized in that: The steps include: When the overcurrent protection circuit is working, the voltage of the secondary side of the transformer L9 is used as the input voltage, and the output current of the drain of the P-MOS tube Q3 is used as the maximum output current; The input voltage generates a stable voltage through the voltage reference V7 to power the current detection circuit through the NPN transistor; When the output current of the overcurrent protection circuit is less than the maximum output current and the circuit is operating normally, the current detected by the current sensor N2 is converted into a voltage, filtered by the capacitor C28, and then divided by the resistors R12 and R13 to obtain a voltage value; When the voltage divided by resistors R12 and R13 is less than the conduction threshold of reference source V8, reference source V8 is not turned on, so optocoupler E2 does not work, the I / O1 pin of the controller detects a high level, the I / O2 pin of the controller sends a high level control signal, transistor V10 is turned on, and the P-MOS tube Q3 is turned on through optocoupler E9 isolation control, and the power supply is output normally.

10. The working method of an overcurrent protection circuit according to claim 9, characterized in that: Also includes: When the output current of the overcurrent protection circuit is greater than the maximum output current and the overcurrent protection circuit is in operation, the current detected by the current sensor N2 is converted into a voltage, filtered by the capacitor C28, and then divided by the resistors R12 and R13 to obtain a voltage value; When the voltage divided by resistors R12 and R13 is greater than the turn-on threshold of reference source V8, reference source V8 is turned on, and the power supply generates a voltage after voltage division by resistors R16 and R17 to turn on the light-emitting diode in optocoupler E2, thereby turning on the transistor in optocoupler E2, and the I / O1 pin of the controller detects a low level. When the I / O1 pin of the controller detects a low level k times, the I / O2 pin of the controller sends a low-level control signal, the transistor V10 is not turned on, the optocoupler E9 is not turned on, the P-MOS tube Q3 is not turned on, and the power supply has no output, thereby achieving an overcurrent protection function.

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