CN210927071U

CN210927071U - Overcurrent protection circuit

Info

Publication number: CN210927071U
Application number: CN201922098971.5U
Authority: CN
Inventors: 王庆; 陈友坚
Original assignee: Jianfeng Electronic Technology Co ltd
Current assignee: Jianfeng Electronic Technology Co ltd
Priority date: 2019-11-29
Filing date: 2019-11-29
Publication date: 2020-07-03
Anticipated expiration: 2029-11-29

Abstract

The utility model relates to an overcurrent protection circuit, include: the device comprises a bridge rectifier circuit, a motor load interface circuit, an MOS (metal oxide semiconductor) tube output and current sampling circuit, a sampling high-voltage isolation circuit, an MOS tube driving and protecting circuit, an overcurrent protection comparison circuit, an MCU (microprogrammed control unit) control circuit, an overcurrent protection reference circuit, an optical coupling isolation circuit I, an optical coupling isolation circuit II and an optical coupling isolation circuit III. The utility model can realize power-driven overcurrent protection, combines the advantages of hardware circuit and software control, has the advantages of quick response and reliable action of the hardware circuit, flexible software control and adjustable parameters; PWM signals and overcurrent protection signals between the MCU control circuit and the MOS tube driving and protecting circuit are isolated by optical couplers, no electric interference exists, and stable work of the MCU circuit is guaranteed.

Description

Overcurrent protection circuit

Technical Field

The utility model relates to a protection circuit technical field especially relates to an overcurrent protection circuit.

Background

In the aspect of power electronic technology, a novel semiconductor power device is widely applied due to high power, high speed, small volume and simple control. However, semiconductor devices have inherent disadvantages, namely, poor overload capability, insufficient shock resistance, and susceptibility to damage by slight overvoltage or overcurrent. The overcurrent protection is the key point, and the technical difficulty is also large. The general overcurrent protection circuit has a hardware circuit and also has a circuit of hardware and software. The hardware protection circuit has the advantages of good real-time performance and high response speed, but has simple function and is generally current-limiting protection. The hardware plus software protection circuit has better protection function due to the participation of software control, but has slightly poor real-time performance and inferior overall reliability to the hardware circuit. Therefore, it is very necessary to design an overcurrent protection circuit.

SUMMERY OF THE UTILITY MODEL

The utility model aims to overcome the defects and provides an overcurrent protection circuit, which can realize power-driven overcurrent protection, combines the advantages of hardware circuits and software control, has the advantages of quick response and reliable action of the hardware circuits, flexible software control and adjustable parameters; PWM signals and overcurrent protection signals between the MCU control circuit and the MOS tube driving and protecting circuit are isolated by optical couplers, no electric interference exists, and stable work of the MCU circuit is guaranteed.

The utility model discloses a reach above-mentioned purpose through following technical scheme: an overcurrent protection circuit comprising: the device comprises a bridge rectifier circuit, a motor load interface circuit, an MOS (metal oxide semiconductor) tube output and current sampling circuit, a sampling high-voltage isolation circuit, an MOS tube driving and protecting circuit, an overcurrent protection comparison circuit, an MCU (microprogrammed control unit) control circuit, an overcurrent protection reference circuit, an optical coupling isolation circuit I, an optical coupling isolation circuit II and an optical coupling isolation circuit III; the bridge rectifier circuit is connected with alternating current and is input into the motor load interface circuit after being rectified by the bridge rectifier circuit; the motor load interface circuit is respectively connected with the sampling high-voltage isolation circuit and the MOS tube output and current sampling circuit; the MOS tube driving and protecting circuit is respectively connected with the sampling high-voltage isolating circuit, the MOS tube output and current sampling circuit, the overcurrent protection comparison circuit and the optical coupling isolating circuit I; the overcurrent protection comparison circuit, the optical coupling isolation circuit III and the MCU control circuit are sequentially connected; the MCU control circuit, the optical coupling isolation circuit II, the overcurrent protection reference circuit and the overcurrent protection comparison circuit are sequentially connected; the MCU control circuit is connected with the MOS tube driving and protecting circuit through the optical coupling isolating circuit I.

Preferably, the bridge rectifier circuit comprises a fuse F1, a piezoresistor ZR1, an EMC capacitor C1 and a rectifier bridge stack D1; one end of the piezoresistor ZR1, one end of the EMC capacitor C1 and one end of the rectifier bridge stack D1 are respectively connected with an AC live wire interface through a protective tube F1, and the other end of the piezoresistor ZR1, the other end of the EMC capacitor C1 and the other end of the rectifier bridge stack D1 are respectively connected with an AC zero wire interface; the piezoresistor ZR1, the EMC capacitor C1 and the rectifier bridge stack D1 are connected in parallel; the fuse F1 plays a role in short-circuit protection, and the piezoresistor ZR1 and the EMC capacitor C14 are used for enhancing the electromagnetic compatibility of the circuit; the bridge rectifier D1 is used to convert ac power to dc power.

Preferably, the motor load interface circuit comprises a relay J1, a relay J2, an RS1M diode D2, an S14L diode D3, and an S14L diode D4; the relay J1 and the relay J2 control the positive and negative rotation and stop of the motor; diodes D2 and D3 of RS1M and S14L and D4 of S14L are freewheeling diodes, diode D2 of RS1M continues current for the externally connected direct current motor, diode D3 of S14L and diode D4 of S14L respectively continue current for the relay J1 and the relay J2, and a reverse current path is provided when the inductive load is turned off.

Preferably, the MOS transistor output and current sampling circuit comprises a MOS transistor Q6, a voltage regulator D7, a capacitor C4, a resistor R19, and a resistor R90; the drain electrode of the MOS tube Q6 is connected with the capacitor C4 and the output end OUT, the grid electrode of the MOS tube Q6 is connected with the voltage-regulator tube D7 and the resistor R19, and the source electrode of the MOS tube Q6 is connected with the resistor R90; the voltage regulator tube D7 is used for clamping the grid voltage of the MOS tube Q6 and ensuring that the driving voltage is not higher than 18V; the capacitor C4 is a switch buffer capacitor of the drain electrode of the MOS transistor Q6; the resistor R90 is a main sampling resistor, the MOS tube Q6 is an auxiliary sampling circuit, and a sampling signal is output from an OUT end.

Preferably, the sampling high-voltage isolation circuit comprises a diode D6 and a resistor R10; the diode D6 and the resistor R10 are connected to each other.

Preferably, the MOS transistor driving and protecting circuit comprises a C8050 triode Q8, a C8050 triode Q9, a C8050 triode Q10, a C8050 triode Q11, a C8050 triode Q3, a C8550 triode Q12, a resistor R9, a resistor R37, a resistor R83, a resistor R11 and a resistor R14; the resistor R17 is connected with the base electrode of the C8050 triode Q8, and the collector electrode of the C8050 triode Q8 is respectively connected with the resistor R9, the resistor R37 and the resistor R83; the resistor R37 is also connected with the base of a C8050 triode Q9, the collector of the C8050 triode Q9 is respectively connected with a resistor R10, a resistor R24 and a diode D6, wherein the resistor R24 is connected to the positive input end of the over-current protection comparison circuit, and the diode D6 is connected to the collector of the MOS tube Q6; the resistor R83 is also connected with the base electrode of a C8050 triode Q10, and the collector electrode of the C8050 triode Q10 is respectively connected with a resistor R11, a C8050 triode Q11, a C8050 triode Q3 and a C8050 triode Q12; the base electrode of the C8050 triode Q11 is connected with an output end resistor R25 of the overcurrent protection comparison circuit; the C8050 triode Q3 and the C8050 triode Q12 form a push-pull circuit, and the push-pull circuit is output to the grid electrode of the MOS transistor Q6 through a resistor R14.

Preferably, the overcurrent protection comparison circuit comprises a comparator IC4A, a resistor R24, a resistor R25 and a capacitor C7; the negative input end of the comparator IC4A is connected with a capacitor C6 of the overcurrent protection reference circuit, the positive input end of the IC4A is respectively connected with a capacitor C7 and a resistor R24, and the output end of the IC4A is connected with a resistor R25.

Preferably, the MCU control circuit includes an MCU chip IC6, a crystal oscillator Y1, a capacitor C9, a capacitor C17, a capacitor C18, a capacitor C39, a capacitor C40, a capacitor C37, a capacitor C38, a capacitor C21, and a resistor R36; a capacitor C9, a capacitor C18, a capacitor C39 and a capacitor C40 are filter capacitors of a power supply pin of the MCU chip IC6, and a capacitor C17 is a filter capacitor of reference voltage inside the MCU chip IC 6; the crystal oscillator Y1 is a quartz crystal oscillator; the capacitor C37 and the capacitor C38 are load capacitors of the oscillator and are used for providing stable clock frequency for the MCU chip IC 6; the resistor R36 and the capacitor C21 are reset circuits of the MCU chip IC 6. The MCU control circuit is used for generating a driving signal M-PWM and an overcurrent protection reference signal C-PWM and reading an overcurrent protection state signal.

Preferably, the optical coupling isolation circuit I comprises an optical coupling IC2, a resistor R16, a resistor R20 and a resistor R17, and the optical coupling isolation circuit I is used for isolating and transmitting M-PWM signals; the optical coupling isolation circuit II comprises an optical coupling IC8, a resistor R28 and a resistor R31, and is used for isolating and transmitting a C-PWM signal; the optical coupling isolation circuit III comprises an optical coupling IC5, a resistor R29, a resistor R26 and a capacitor C42; and the optical coupling isolation circuit III is used for transmitting overcurrent protection state signals.

Preferably, the overcurrent protection reference circuit comprises a transistor Q14, a transistor Q15, a resistor R27, a resistor R32, a resistor R30, a capacitor C5 and a capacitor C6; the C-PWM signal input by the optical coupling isolation circuit II is subjected to push-pull driving of a triode Q14 and a triode Q15, then is divided by a resistor R27 and a resistor R32 to become a PWM signal, and then is input into a low-pass filter circuit consisting of a capacitor C5, a resistor R30 and a capacitor C6 to be processed to become smooth direct-current voltage; the voltage is a reference voltage of overcurrent protection and is used for comparing with an effective overcurrent protection signal, and the comparison result determines whether the circuit enters an overcurrent protection state or not.

The beneficial effects of the utility model reside in that: the utility model can realize power-driven overcurrent protection, combines the advantages of hardware circuit and software control, has the advantages of quick response and reliable action of the hardware circuit, flexible software control and adjustable parameters; PWM signals and overcurrent protection signals between the MCU control circuit and the MOS tube driving and protecting circuit are isolated by optical couplers, no electric interference exists, and stable work of the MCU circuit is guaranteed.

Drawings

Fig. 1 is a schematic structural diagram of the present invention;

fig. 2 is a schematic circuit diagram of the present invention.

Detailed Description

The invention will be further described with reference to specific examples, but the scope of protection of the invention is not limited thereto:

example (b): as shown in fig. 1, an overcurrent protection circuit is composed of a bridge rectifier circuit, a motor load interface circuit, an MOS transistor output and current sampling circuit, a sampling high-voltage isolation circuit, an MOS transistor drive and protection circuit, an overcurrent protection comparison circuit, an MCU control circuit, an overcurrent protection reference circuit, an optical coupling isolation circuit I, an optical coupling isolation circuit II, and an optical coupling isolation circuit III. The bridge rectifier circuit is connected with alternating current and is input into the motor load interface circuit after being rectified by the bridge rectifier circuit; the motor load interface circuit is respectively connected with the sampling high-voltage isolation circuit and the MOS tube output and current sampling circuit; the MOS tube driving and protecting circuit is respectively connected with the sampling high-voltage isolating circuit, the MOS tube output and current sampling circuit, the overcurrent protection comparison circuit and the optical coupling isolating circuit I; the overcurrent protection comparison circuit, the optical coupling isolation circuit III and the MCU control circuit are sequentially connected; the MCU control circuit, the optical coupling isolation circuit II, the overcurrent protection reference circuit and the overcurrent protection comparison circuit are sequentially connected; the MCU control circuit is connected with the MOS tube driving and protecting circuit through the optical coupling isolating circuit I.

Fig. 2 is a schematic circuit diagram of the present invention, wherein the bridge rectifier circuit is composed of a fuse F1, a varistor ZR1, an EMC capacitor C1, and a rectifier bridge D1; AC-L is an AC live wire interface, and AC-N is an AC zero line interface; one end of a piezoresistor ZR1, one end of an EMC capacitor C1 and one end of a rectifier bridge stack D1 are respectively connected with an AC live wire interface through a protective tube F1, and the other end of the piezoresistor ZR1, the other end of the EMC capacitor C1 and the other end of the rectifier bridge stack D1 are respectively connected with an AC zero wire interface; the piezoresistor ZR1, the EMC capacitor C1 and the rectifier bridge stack D1 are connected in parallel; the fuse F1 plays a role in short-circuit protection, and the piezoresistor ZR1 and the EMC capacitor C14 are used for enhancing the electromagnetic compatibility of the circuit and preventing the EMC interference from causing the circuit to fail; the bridge rectifier D1 is used to convert ac power to dc power. The circuit is not connected with a large-capacity filter capacitor, due to the specific application and cost consideration, because the load is a direct current motor and can normally work under a pulsating direct current power supply, the large filter capacitor is omitted, and the cost and the volume are favorably reduced.

The motor load interface circuit comprises a relay J1, a relay J2, an RS1M diode D2, an S14L diode D3, and an S14L diode D4; the MOTOR + and the MOTOR-are respectively connected with the anode and the cathode of the direct current MOTOR. The 310V direct current voltage is connected with the direct current motor through the relays J1 and J2, and the LOAD is connected with the output end of the power tube. The relay J1 and the relay J2 control the positive and negative rotation and stop of the motor; diodes D2 and D3 of RS1M and S14L and D4 of S14L are freewheeling diodes, diode D2 of RS1M continues current for the externally connected direct current motor, diode D3 of S14L and diode D4 of S14L respectively continue current for the relay J1 and the relay J2, and a reverse current path is provided when the inductive load is turned off.

The MOS tube output and current sampling circuit comprises an MOS tube Q6, a voltage regulator tube D7, a capacitor C4, a resistor R19 and a resistor R90; the drain electrode of the MOS tube Q6 is connected with the capacitor C4 and the output end OUT, the grid electrode of the MOS tube Q6 is connected with the voltage-regulator tube D7 and the resistor R19, and the source electrode of the MOS tube Q6 is connected with the resistor R90; the voltage regulator tube D7 is used for clamping the grid voltage of the MOS tube Q6 and ensuring that the driving voltage is not higher than 18V; the capacitor C4 is a switch buffer capacitor of the drain electrode of the MOS transistor Q6, and reduces voltage and current impact of Q6 during switching. And OUT is the output end of the power book and is connected with the negative electrode of the motor load interface circuit. The resistor R90 is a main sampling resistor, the MOS transistor Q6 is an auxiliary sampling circuit, and a sampling signal is output from the OUT terminal. The Q6 mainly plays a positive feedback role in the sampling circuit, when the Q6 is conducted, the conduction resistor of the Q6 is connected with the R90 in series to play a role of a current sampling resistor together, when the overcurrent protector works, the Q6 is closed, so that a sampling signal keeps high voltage, and the high sampling voltage enables the circuit to be in an overcurrent protection state continuously, and the function of positive feedback is realized. Once overcurrent protection occurs, the circuit is always in a protection state until the power supply voltage is reduced to zero or the MOS drive output is closed by software, and the circuit can not recover the working state.

The sampling high-voltage isolation circuit consists of a diode D6 and a resistor R10; the diode D6 and the resistor R10 are connected to each other. When the circuit is in an overcurrent protection state, the protection output signal is close to 300V, the high voltage is isolated due to the reverse bias of D6, and the positive pole of D6 is connected with 15V through a pull-up resistor R10. So in the overcurrent protection state, the output of the protection signal is 15V. When the circuit is in a normal operating state and the Q6 is turned on, the voltage drop of the output terminal OUT is the sum of the on-resistance of the operating current in the Q6 and the voltage drop of the operating current in the R90, the voltage is usually very small, and is only about 1-2V, at this time, the D6 is turned on, the voltage of the positive electrode of the D6 is pulled low, and at this time, the signal of the positive electrode of the D6 is an effective current sampling signal.

The MOS tube driving and protecting circuit consists of a C8050 triode Q8, a C8050 triode Q9, a C8050 triode Q10, a C8050 triode Q11, a C8050 triode Q3, a C8550 triode Q12, a resistor R9, a resistor R37, a resistor R83, a resistor R11 and a resistor R14. The resistor R17 is connected with the base of the C8050 triode Q8, the collector of the C8050 triode Q8 is respectively connected with the resistor R9, the resistor R37 and the resistor R83, wherein R9 is pulled up to 15V; the resistor R37 is also connected with the base electrode of a C8050 triode Q9, the collector electrode of the C8050 triode Q9 is respectively connected with a resistor R10, a resistor R24 and a diode D6, wherein R10 is pulled up to 15V; the resistor R24 is connected to the positive input end of the over-current protection comparison circuit, and the diode D6 is connected to the collector of the MOS transistor Q6; the resistor R83 is also connected with the base electrode of a C8050 triode Q10, the collector electrode of the C8050 triode Q10 is respectively connected with a resistor R11, a C8050 triode Q11, a C8050 triode Q3 and a C8050 triode Q12, wherein the R11 is pulled up to 15V; the base electrode of the C8050 triode Q11 is connected with an output end resistor R25 of the overcurrent protection comparison circuit; the C8050 triode Q3 and the C8050 triode Q12 form a push-pull circuit, and the push-pull circuit is output to the grid electrode of the MOS transistor Q6 through a resistor R14. When an M-PWM driving signal enters Q8 from the opto-coupler IC2 through R17 and R20, Q8 drives Q9 and Q10 simultaneously. Q9 is used as synchronous selection control, when Q6 is turned on, an effective current sampling signal is led to the comparator IC4, when Q6 is turned off, an ineffective high-voltage signal is reversely isolated through D6 and is turned on and short-circuited with Q9, and the comparator is forbidden to output an alarm signal. When the Q6 is conducted and overcurrent protection occurs again, the Q11 is conducted to forcibly pull down the grid voltage of the Q6, so that the Q6 is turned off, the overcurrent protection signal continuously exists due to the fact that the sampling signal is at the drain of the Q6, the circuit is in an overcurrent protection state all the time, and the overcurrent protection state is not exited until the software turns off the driving signal or the power supply voltage is reduced to 0V. The driving signal output by the Q10 is amplified by the Q3 and the Q12, and then passes through the gate from the R14 to the Q6 to control the on and off of the MOS transistor Q6.

The overcurrent protection comparison circuit consists of a comparator IC4A, a resistor R24, a resistor R25 and a capacitor C7. The negative input end of the comparator IC4A is connected with a capacitor C6 of the overcurrent protection reference circuit, the positive input end of the IC4A is respectively connected with a capacitor C7 and a resistor R24, the output end of the IC4A is connected with a resistor R25, and the R25 is connected with the Q11 and is a hardware protection output. The output end of the IC4A is also connected with a resistor R29 of the optical coupling isolation circuit III; when the voltage of the C7 is less than the voltage of the C6, the output level of the comparator IC4A is low, the Q11 is cut off, and the MOS tube driving signal normally passes through the driving circuit. When the voltage of the C7 is larger than the voltage of the C6, the comparator IC4A outputs high level, the Q11 is conducted, the driving signal of the MOS tube is forced to be grounded, and the MOS tube is in a cut-off state.

The MCU control circuit comprises an MCU chip IC6, a crystal oscillator Y1, a capacitor C9, a capacitor C17, a capacitor C18, a capacitor C39, a capacitor C40, a capacitor C37, a capacitor C38, a capacitor C21 and a resistor R36; a capacitor C9, a capacitor C18, a capacitor C39 and a capacitor C40 are filter capacitors of a power supply pin of the MCU chip IC6, and a capacitor C17 is a filter capacitor of reference voltage inside the MCU chip IC 6; the crystal oscillator Y1 is a quartz crystal oscillator; the capacitor C37 and the capacitor C38 are load capacitors of the oscillator and are used for providing stable clock frequency for the MCU chip IC 6; the resistor R36 and the capacitor C21 are reset circuits of the MCU chip IC 6. The MCU control circuit mainly plays an auxiliary control role in the circuit and is used for generating a driving signal M-PWM and an overcurrent protection reference signal C-PWM and reading an overcurrent protection state signal.

The optical coupling isolation circuit I comprises an optical coupling IC2, a resistor R16, a resistor R20 and a resistor R17; the optical coupling isolation circuit I is used for isolating and transmitting the M-PWM signal; the optical coupling isolation circuit II comprises an optical coupling IC8, a resistor R28 and a resistor R31, and is used for isolating and transmitting the C-PWM signals; the optical coupling isolation circuit III comprises an optical coupling IC5, a resistor R29, a resistor R26 and a capacitor C42; and the optical coupling isolation circuit III is used for transmitting overcurrent protection state signals. The M-PWM signal and the C-PWM signal are transmitted to the MOS tube driving circuit by the MCU, and the over-current protection state signal is transmitted to the MCU by the MOS tube driving circuit.

The overcurrent protection reference circuit comprises a triode Q14, a triode Q15, a resistor R27, a resistor R32, a resistor R30, a capacitor C5 and a capacitor C6; C-PWM signals (the amplitude is 15V) input by the optical coupling isolation circuit II are subjected to push-pull driving of a triode Q14 and a triode Q15, then are subjected to voltage division by a resistor R27 and a resistor R32 to become PWM signals with the amplitude of about 7.5V, and then are input into a low-pass filter circuit consisting of a capacitor C5, a resistor R30 and a capacitor C6 to be processed to become smooth direct-current voltage; the voltage is a reference voltage of overcurrent protection and is used for comparing with an effective overcurrent protection signal, and the comparison result determines whether the circuit enters an overcurrent protection state or not.

The utility model discloses the during operation, alternating current power supply becomes direct current pulsating voltage through bridge rectifier circuit, and direct current motor load is supplied with to rethread motor load interface circuit, and motor load interface circuit can control the rotation direction of motor, and motor load interface circuit's negative pole connects the output of MOS pipe. The source electrode of the MOS tube is grounded through the current sampling resistor to form a loop of power current, and the output end of the MOS tube is also used as the output of a current sampling signal. The optical coupling isolation circuit I is controlled by an output signal of the MCU control circuit, can generate an M-PWM signal and is used for soft start control and speed regulation control of the motor. The M-PWM signal is isolated by the optocoupler IC2 and then is connected to the grid of the MOS transistor Q through the MOS transistor driving and protecting circuit to control the on and off of the MOS transistor. A sampling high-voltage isolation circuit (D6, R10) is also connected into the MOS tube driving and protecting circuit, so that the normal work of the driving circuit is prevented from being influenced by the high voltage when the MOS tube is cut off. The output of the MOS tube driving and protecting circuit is also controlled by the output of the over-current protection comparison circuit, and when over-current protection occurs, the MOS tube is forcibly closed by a hardware circuit, so that the circuit is prevented from being further damaged. The optical coupling isolation circuit II is also controlled by the MCU control circuit to generate a C-PWM signal for generating the reference voltage of the overcurrent protection comparison circuit. The overcurrent protection signal is compared with the reference signal to generate a control signal to the MOS tube driving circuit, the MOS tube can be forcibly closed to be turned off when overcurrent protection occurs, and meanwhile, a signal output by the overcurrent protection comparison circuit is input to the MCU control circuit through the optical coupling isolation circuit III to inform the MCU of closing the M-PWM signal. The overcurrent protection is directly responded by a hardware circuit, and is quick and reliable. The MCU control circuit can modify the parameters of overcurrent protection, and is convenient and flexible. The circuit combines the respective advantages of a hardware circuit and a software control.

The foregoing is directed to embodiments of the present invention and other technical principles, and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.

Claims

1. An overcurrent protection circuit, comprising: the device comprises a bridge rectifier circuit, a motor load interface circuit, an MOS (metal oxide semiconductor) tube output and current sampling circuit, a sampling high-voltage isolation circuit, an MOS tube driving and protecting circuit, an overcurrent protection comparison circuit, an MCU (microprogrammed control unit) control circuit, an overcurrent protection reference circuit, an optical coupling isolation circuit I, an optical coupling isolation circuit II and an optical coupling isolation circuit III; the bridge rectifier circuit is connected with alternating current and is input into the motor load interface circuit after being rectified by the bridge rectifier circuit; the motor load interface circuit is respectively connected with the sampling high-voltage isolation circuit and the MOS tube output and current sampling circuit; the MOS tube driving and protecting circuit is respectively connected with the sampling high-voltage isolating circuit, the MOS tube output and current sampling circuit, the overcurrent protection comparison circuit and the optical coupling isolating circuit I; the overcurrent protection comparison circuit, the optical coupling isolation circuit III and the MCU control circuit are sequentially connected; the MCU control circuit, the optical coupling isolation circuit II, the overcurrent protection reference circuit and the overcurrent protection comparison circuit are sequentially connected; the MCU control circuit is connected with the MOS tube driving and protecting circuit through the optical coupling isolating circuit I.

2. An overcurrent protection circuit according to claim 1, wherein: the bridge rectifier circuit comprises a fuse F1, a piezoresistor ZR1, an EMC capacitor C1 and a rectifier bridge stack D1; one end of the piezoresistor ZR1, one end of the EMC capacitor C1 and one end of the rectifier bridge stack D1 are respectively connected with an AC live wire interface through a protective tube F1, and the other end of the piezoresistor ZR1, the other end of the EMC capacitor C1 and the other end of the rectifier bridge stack D1 are respectively connected with an AC zero wire interface; the piezoresistor ZR1, the EMC capacitor C1 and the rectifier bridge stack D1 are connected in parallel; the fuse F1 plays a role in short-circuit protection, and the piezoresistor ZR1 and the EMC capacitor C14 are used for enhancing the electromagnetic compatibility of the circuit; the bridge rectifier D1 is used to convert ac power to dc power.

3. An overcurrent protection circuit according to claim 1, wherein: the motor load interface circuit comprises a relay J1, a relay J2, an RS1M diode D2, an S14L diode D3 and an S14L diode D4; the relay J1 and the relay J2 control the positive and negative rotation and stop of the motor; diodes D2 and D3 of RS1M and S14L and D4 of S14L are freewheeling diodes, diode D2 of RS1M continues current for the externally connected direct current motor, diode D3 of S14L and diode D4 of S14L respectively continue current for the relay J1 and the relay J2, and a reverse current path is provided when the inductive load is turned off.

4. An overcurrent protection circuit according to claim 1, wherein: the MOS tube output and current sampling circuit comprises an MOS tube Q6, a voltage regulator tube D7, a capacitor C4, a resistor R19 and a resistor R90; the drain electrode of the MOS tube Q6 is connected with the capacitor C4 and the output end OUT, the grid electrode of the MOS tube Q6 is connected with the voltage-regulator tube D7 and the resistor R19, and the source electrode of the MOS tube Q6 is connected with the resistor R90; the voltage regulator tube D7 is used for clamping the grid voltage of the MOS tube Q6 and ensuring that the driving voltage is not higher than 18V; the capacitor C4 is a switch buffer capacitor of the drain electrode of the MOS transistor Q6; the resistor R90 is a main sampling resistor, the MOS tube Q6 is an auxiliary sampling circuit, and a sampling signal is output from an OUT end.

5. An overcurrent protection circuit according to claim 1, wherein: the sampling high-voltage isolation circuit comprises a diode D6 and a resistor R10; the diode D6 and the resistor R10 are connected to each other.

6. An overcurrent protection circuit according to claim 1, wherein: the MOS tube driving and protecting circuit comprises a C8050 triode Q8, a C8050 triode Q9, a C8050 triode Q10, a C8050 triode Q11, a C8050 triode Q3, a C8550 triode Q12, a resistor R9, a resistor R37, a resistor R83, a resistor R11 and a resistor R14; the resistor R17 is connected with the base electrode of the C8050 triode Q8, and the collector electrode of the C8050 triode Q8 is respectively connected with the resistor R9, the resistor R37 and the resistor R83; the resistor R37 is also connected with the base of a C8050 triode Q9, the collector of the C8050 triode Q9 is respectively connected with a resistor R10, a resistor R24 and a diode D6, wherein the resistor R24 is connected to the positive input end of the over-current protection comparison circuit, and the diode D6 is connected to the collector of the MOS tube Q6; the resistor R83 is also connected with the base electrode of a C8050 triode Q10, and the collector electrode of the C8050 triode Q10 is respectively connected with a resistor R11, a C8050 triode Q11, a C8050 triode Q3 and a C8050 triode Q12; the base electrode of the C8050 triode Q11 is connected with an output end resistor R25 of the overcurrent protection comparison circuit; the C8050 triode Q3 and the C8050 triode Q12 form a push-pull circuit, and the push-pull circuit is output to the grid electrode of the MOS transistor Q6 through a resistor R14.

7. An overcurrent protection circuit according to claim 1, wherein: the over-current protection comparison circuit comprises a comparator IC4A, a resistor R24, a resistor R25 and a capacitor C7; the negative input end of the comparator IC4A is connected with a capacitor C6 of the overcurrent protection reference circuit, the positive input end of the IC4A is respectively connected with a capacitor C7 and a resistor R24, and the output end of the IC4A is connected with a resistor R25.

8. An overcurrent protection circuit according to claim 1, wherein: the MCU control circuit comprises an MCU chip IC6, a crystal oscillator Y1, a capacitor C9, a capacitor C17, a capacitor C18, a capacitor C39, a capacitor C40, a capacitor C37, a capacitor C38, a capacitor C21 and a resistor R36; a capacitor C9, a capacitor C18, a capacitor C39 and a capacitor C40 are filter capacitors of a power supply pin of the MCU chip IC6, and a capacitor C17 is a filter capacitor of reference voltage inside the MCU chip IC 6; the crystal oscillator Y1 is a quartz crystal oscillator; the capacitor C37 and the capacitor C38 are load capacitors of the oscillator and are used for providing stable clock frequency for the MCU chip IC 6; the resistor R36 and the capacitor C21 are reset circuits of the MCU chip IC 6; the MCU control circuit is used for generating a driving signal M-PWM and an overcurrent protection reference signal C-PWM and reading an overcurrent protection state signal.

9. An overcurrent protection circuit according to claim 1, wherein: the optical coupling isolation circuit I comprises an optical coupling IC2, a resistor R16, a resistor R20 and a resistor R17, and is used for isolation transmission of M-PWM signals;

the optical coupling isolation circuit II comprises an optical coupling IC8, a resistor R28 and a resistor R31, and is used for isolating and transmitting a C-PWM signal;

the optical coupling isolation circuit III comprises an optical coupling IC5, a resistor R29, a resistor R26 and a capacitor C42; and the optical coupling isolation circuit III is used for transmitting overcurrent protection state signals.

10. An overcurrent protection circuit according to claim 1, wherein: the over-current protection reference circuit comprises a triode Q14, a triode Q15, a resistor R27, a resistor R32, a resistor R30, a capacitor C5 and a capacitor C6; the C-PWM signal input by the optical coupling isolation circuit II is subjected to push-pull driving of a triode Q14 and a triode Q15, then is divided by a resistor R27 and a resistor R32 to become a PWM signal, and then is input into a low-pass filter circuit consisting of a capacitor C5, a resistor R30 and a capacitor C6 to be processed to become smooth direct-current voltage; the voltage is a reference voltage of overcurrent protection and is used for comparing with an effective overcurrent protection signal, and the comparison result determines whether the circuit enters an overcurrent protection state or not.