Overcurrent detection and protection circuit applied to three-phase full-bridge inverter
By introducing a circuit structure of UVW module and optocoupler output module into a three-phase full-bridge inverter, real-time monitoring of switching transistor current and dual overcurrent protection are achieved, solving the problems of space limitation, high cost and low reliability in the existing technology, and improving the reliability and flexibility of the inverter.
Patent Information
- Application Number
- CN202422027283.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-08-20
- Publication Date
- 2025-12-12
- Estimated Expiration
- 2034-08-20
AI Technical Summary
Existing overcurrent detection and protection circuits for three-phase full-bridge inverters suffer from space limitations, high costs, low reliability, and poor anti-interference capabilities in high-density designs, making it difficult to achieve dual protection compatibility.
The circuit structure consists of a UVW module, an optocoupler output module, a six-channel blocking drive PWM module, and a microprocessor MCU. By parallel setting of the UL lower bridge drive unit, Vce current detection unit, and protection output unit in the UVW module, combined with the real-time detection and blocking drive of the optocoupler output module and the microprocessor MCU, the current status monitoring and dual overcurrent protection of each switching transistor can be realized.
This circuit achieves high compatibility, high reliability, strong anti-interference capability, rapid response to overcurrent conditions, small footprint, low cost, and improves product reliability and flexibility.
Smart Images
Figure CN223666021U_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The utility model belongs to electronic circuit technical field especially relates to a kind of overcurrent detection and protection circuit applied to three-phase full-bridge inverter. BACKGROUND
[0002] Servo, variable-frequency drive controller main power core device will pursue high reliability, high density, low cost overcurrent protection drive scheme, with double protection main power MOS, IGBT, some conflict contradictions, time detection, high response will select good brand drive optocoupler with Vce protection, in some high-density PCB board design, space is limited, leading to structure space needs to design relatively large, and the cost requirement is relatively strict, reliability requirement is very high, when selecting overcurrent protection scheme, double protection, overcurrent protection response is fast, not easy to compatible do trade-off.
[0003] The overcurrent detection and protection methods commonly used in the industry at present are as follows: 1) bridge arm internal short circuit protection, which detects the Vce voltage drop of IGBT as the standard for judging whether to trigger protection, Vce optocoupler overcurrent protection has high cost, realizes with peripheral circuit, large size, not conducive to high density; 2) Hall element detects current, when the current reaches the set overcurrent point, the overcurrent protection is triggered, the current is large in size, the peripheral circuit is more expensive; 3) bus stringing resistor shunt, the detected voltage signal is amplified by an operational amplifier, and then compared with the set overcurrent reference point, as the basis for whether to trigger overcurrent protection, overcurrent point setting is flexible, and the anti-interference ability is poor; 4) use the current detection circuit in IPM module as overcurrent protection circuit, high cost, low flexibility;
[0004] The application site is different, the power density is different, and the cost scheme is different, and the current application implementation is as follows: 1) commonly used bus stringing resistor shunt, detects bus input current, cost, space can be, application is more; 2) use the current detection circuit in IPM module as overcurrent protection circuit for small power, high cost, protection is single, 3) select Hall element to detect current and add optocoupler Vce voltage drop detection for large power, high cost. UTILITY MODEL CONTENTS
[0005] The utility model aims at providing a kind of overcurrent detection and protection circuit applied to three-phase full-bridge inverter, to solve the above technical problems.
[0006] The utility model discloses a kind of overcurrent detection and protection circuit applied to three-phase full-bridge inverter, the overcurrent detection and protection circuit applied to three-phase full-bridge inverter includes UVW module, opto-coupler output module, lock six-way drive PWM module, microprocessor MCU and power supply module, the output of the UVW module is connected with the input of the opto-coupler output module, the output of the opto-coupler output module is respectively connected with the input of the lock six-way drive PWM module and the input of microprocessor MCU, the output of the microprocessor MCU is connected with the input of the lock six-way drive PWM module, the output of the lock six-way drive PWM module is connected with the input of the UVW module, the power supply module is electrically connected with the UVW module, opto-coupler output module, lock six-way drive PWM module and microprocessor MCU respectively.
[0007] Further technical solutions of the utility model are: the UVW module includes UL lower bridge drive unit, Vce current detection unit and protection output unit, and the UL lower bridge drive unit, Vce current detection unit and protection output unit are arranged in parallel.
[0008] Further technical solutions of the utility model are: the UL lower bridge drive unit includes diode D2, resistance R4, diode D3, resistance R7, inductance L1, resistance R5, capacitor C1, capacitor C3, resistance R6, diode Q1, capacitor C2 and diode D1, the cathode of diode D2 is connected with U_UCE, the anode of diode D2 is connected with one end of inductance L1 and the cathode of diode D3 respectively through resistance R4, the anode of diode D3 is connected with one end of resistance R7, the other end of resistance R7 is connected with LIN_DRV_UL, the other end of inductance L1 is connected with one end of resistance R5 and one end of capacitor C3 respectively, the other end of resistance R5 is connected with one end of capacitor C1, one end of resistance R6 and the base of triode Q1 respectively, the collector of triode Q1 is connected with the cathode of diode D1 and one end of capacitor C2 respectively, the anode of diode D1 is connected with FAIL, the other end of capacitor C3, the other end of capacitor C1, one end of resistance R6, the emitter of triode Q1 and the other end of capacitor C2 are connected with BUS_N respectively.
[0009] The further technical scheme of the utility model discloses: the Vce current detection unit includes diode D5, resistance R3, diode D6, resistance R10, inductance L2, resistance R8, electric capacity C6, electric capacity C4, resistance R9, triode Q2, electric capacity C5 and diode D4, the negative pole of diode D5 is connected V_VCE, the anode of diode D5 is connected the one end of inductance L2 and the negative pole of diode D6 respectively through resistance R3, the anode of diode D6 is connected LIN_DRV_VL through resistance R10, the other end of inductance L2 is connected the one end of resistance R8 and the one end of electric capacity C6 respectively, the other end of resistance R8 is connected the one end of electric capacity C4, the one end of resistance R9 and the base of triode Q2 respectively, the collector of triode Q2 is connected the negative pole of diode D4 and the one end of electric capacity C5 respectively, the anode of diode D4 is connected FAIL, the other end of electric capacity C6, the other end of electric capacity C4, the other end of resistance R9, the emitter of triode Q2 and the other end of electric capacity C5 are connected BUS_N respectively.
[0010] The further technical scheme of the utility model discloses: the protection output unit includes diode D8, resistance R11, diode D9, resistance R14, inductance L3, resistance R12, electric capacity C9, electric capacity C7, resistance R13, triode Q3, electric capacity C8 and diode D7, the negative pole of diode D8 is connected W_WCE, the anode of diode D8 is connected the one end of inductance L3 and the negative pole of diode D9 respectively through resistance R11, the anode of diode D9 is connected LIN_DRV_WL through resistance R14, the other end of inductance L3 is connected the one end of resistance R12 and the one end of electric capacity C9 respectively, the other end of resistance R12 is connected the one end of electric capacity C7, the one end of resistance R13 and the base of triode Q3 respectively, the collector of triode Q3 is connected the one end of electric capacity C8 and the negative pole of diode D7 respectively, the anode of diode D7 is connected FAIL, the other end of electric capacity C9, the other end of electric capacity C7, the other end of resistance R13, the emitter of triode Q3 and the other end of electric capacity C8 are connected BUS_N respectively.
[0011] The further technical scheme of the utility model discloses: the light coupling output module includes resistance R15, capacitor C10, operational amplifier U1, capacitor C11, resistance R16, resistance R17, triode Q4, resistance R18, resistance R20, light coupling U2, resistance R19, capacitor C12 and capacitor C13, the bottom 2 feet of operational amplifier U1 are connected with one end of resistance R15, one end of capacitor C10 and FAIL respectively, the other end of resistance R15 is connected with 5VCC_BUS_N, the 5th foot of operational amplifier U1 is connected with 5VCC_BUS_N and one end of capacitor C11 respectively, the 4th foot of operational amplifier U1 is connected with one end of resistance R17 and the base of triode Q4 through resistance R16 respectively, the collector of triode Q4 is connected with one end of resistance R20 and the bottom 2 feet of light coupling U2 respectively, the 1st foot of light coupling U2 is connected with the other end of resistance R20 and one end of resistance R18 respectively, the other end of resistance R18 is connected with 5VCC_BUS_N, the 4th foot of light coupling U2 is connected with one end of capacitor C13, one end of resistance R19 and OC respectively, the 5th foot of light coupling U2 is connected with the other end of resistance R19, one end of capacitor C12 and power supply 3.3V respectively, the other end of capacitor C12, the other end of capacitor C13 and the 3rd foot of light coupling U2 are grounded respectively, the other end of capacitor C10, the 3rd foot of operational amplifier U1, the other end of capacitor C11, the other end of resistance R17 and the emitter of triode Q4 are connected with BNS_N respectively.
[0012] The utility model discloses the beneficial effect is: the circuit compatibility is big, and the reliability is high, and the anti -interference is strong, and the current state that each switch tube passes through is detected in real time, and the response is fast when overcurrent, and 7us is locked in drive, and the cost is extremely low, and the product increases the reliability and double overcurrent protection, and the circuit is simple, and the device power consumption is small, and the package is small, and the function circuit wiring is convenient, and the pcb space is small, and the product optimization increases the convenience, and the product size is small and the miniaturization is favorable. BRIEF DESCRIPTION OF DRAWINGS
[0013] Figure 1 It is the principle block diagram of overcurrent detection and protection circuit applied to three-phase full bridge inverter that the utility model embodiment provides.
[0014] Figure 2 It is the principle circuit diagram of UL lower bridge drive unit that the utility model embodiment provides.
[0015] Figure 3 It is the principle circuit diagram of Vce current detection unit that the utility model embodiment provides.
[0016] Figure 4 It is the principle circuit diagram of protection output unit that the utility model embodiment provides.
[0017] Figure 5 is a principle circuit diagram of the optical coupling output module provided by the embodiment of the present application.
[0018] Figure 6 is a principle circuit diagram of the six-way drive PWM module provided by the embodiment of the present application. DETAILED DESCRIPTION
[0019] LIN_DRV_UL: the driving signal of the lower bridge U-phase power tube, flowing into the front end of the driving resistor;
[0020] U_UCE: the collector of the lower bridge U-phase power tube;
[0021] FAIL: the fault output signal;
[0022] BUS_N: the reference ground and bus of the signal;
[0023] 5VCC_BUS_N: 5V power supply voltage;
[0024] OC: the overcurrent signal;
[0025] The embodiments of the present application are described in detail below, and examples of the embodiments are shown in the drawings, wherein the same or similar reference signs represent the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by referring to the drawings are exemplary and are intended to explain the present application, and cannot be understood as a limitation of the present application.
[0026] In the description of the present application, it should be understood that the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation of the present application. In addition, in the description of the present application, the meaning of "a plurality of" is two or more, unless otherwise specifically limited.
[0027] Each switch cycle current detection signal is compared with reference voltage, when detected Vce tube voltage drop exceeds set threshold, overcurrent signal outputs blocking drive signal, main power switch tube IGBT or MOS exits from on state to become cut-off, protects driver, and overcurrent signal is sent to MCU to stop machine failure indication, scheme detection, comparison, failure output is simple, stable and reliable, system is small, as follows bridge U V W is applied, three-way Vce respectively detects each switch current signal, protection output can be connected together, and feedback is given to control end MCU through isolated output of optocoupler.
[0028] As shown in Figures 1-6 The overcurrent detection and protection circuit applied to the three-phase full-bridge inverter provided by the utility model, the overcurrent detection and protection circuit applied to the three-phase full-bridge inverter includes a UVW module, an optocoupler output module, a blocking six-way drive PWM module, a microprocessor MCU and a power supply module, the output end of the UVW module is connected with the input end of the optocoupler output module, the output end of the optocoupler output module is respectively connected with the input end of the blocking six-way drive PWM module and the input end of the microprocessor MCU, the output end of the microprocessor MCU is connected with the input end of the blocking six-way drive PWM module, the output end of the blocking six-way drive PWM module is connected with the input end of the UVW module, and the power supply module is electrically connected with the UVW module, the optocoupler output module, the blocking six-way drive PWM module and the microprocessor MCU respectively.
[0029] The microprocessor MCU accurately sends six-way PWM waves to six power tubes through a drive isolation amplification circuit, and the six power tubes are accurately switched in rhythm, so that DC voltage is converted into AC voltage, the U V W module controls the speed and torque of a motor, the lower bridge drive power tube is turned on, the Vce tube voltage drop of the power tube is detected, the optocoupler output pulse signal is used to block the six-way PWM drive when overcurrent occurs, the power tube is cut off, and the microprocessor MCU is informed of overcurrent to make corresponding processing.
[0030] The UVW module includes a UL lower bridge drive unit, a Vce current detection unit and a protection output unit, and the UL lower bridge drive unit, the Vce current detection unit and the protection output unit are arranged in parallel.
[0031] The UL lower bridge driving unit includes a diode D2, a resistor R4, a diode D3, a resistor R7, an inductor L1, a resistor R5, a capacitor C1, a capacitor C3, a resistor R6, a diode Q1, a capacitor C2, and a diode D1, a cathode of the diode D2 is connected to U_UCE, an anode of the diode D2 is connected to one end of the inductor L1 and a cathode of the diode D3 through the resistor R4, an anode of the diode D3 is connected to one end of the resistor R7, the other end of the resistor R7 is connected to LIN_DRV_UL, the other end of the inductor L1 is connected to one end of the resistor R5 and one end of the capacitor C3, the other end of the resistor R5 is connected to one end of the capacitor C1, one end of the resistor R6, and a base of the diode Q1, a collector of the diode Q1 is connected to a cathode of the diode D1 and one end of the capacitor C2, an anode of the diode D1 is connected to FAIL, the other end of the capacitor C3, the other end of the capacitor C1, one end of the resistor R6, an emitter of the diode Q1, and the other end of the capacitor C2 are connected to BUS_N.
[0032] The Vce current detection unit includes a diode D5, a resistor R3, a diode D6, a resistor R10, an inductor L2, a resistor R8, a capacitor C6, a capacitor C4, a resistor R9, a diode Q2, a capacitor C5, and a diode D4, a cathode of the diode D5 is connected to V_VCE, an anode of the diode D5 is connected to one end of the inductor L2 and a cathode of the diode D6 through the resistor R3, an anode of the diode D6 is connected to LIN_DRV_VL through the resistor R10, the other end of the inductor L2 is connected to one end of the resistor R8 and one end of the capacitor C6, the other end of the resistor R8 is connected to one end of the capacitor C4, one end of the resistor R9, and a base of the diode Q2, a collector of the diode Q2 is connected to a cathode of the diode D4 and one end of the capacitor C5, an anode of the diode D4 is connected to FAIL, the other end of the capacitor C6, the other end of the capacitor C4, the other end of the resistor R9, an emitter of the diode Q2, and the other end of the capacitor C5 are connected to BUS_N.
[0033] The protection output unit includes diode D8, resistor R11, diode D9, resistor R14, inductor L3, resistor R12, capacitor C9, capacitor C7, resistor R13, triode Q3, capacitor C8 and diode D7, the cathode of diode D8 is connected with W_WCE, the anode of diode D8 is connected with one end of inductor L3 and the cathode of diode D9 through resistor R11, the anode of diode D9 is connected with LIN_DRV_WL through resistor R14, the other end of inductor L3 is connected with one end of resistor R12 and one end of capacitor C9, the other end of resistor R12 is connected with one end of capacitor C7, one end of resistor R13 and the base of triode Q3, the collector of triode Q3 is connected with one end of capacitor C8 and the cathode of diode D7, the anode of diode D7 is connected with FAIL, the other end of capacitor C9, the other end of capacitor C7, the other end of resistor R13, the emitter of triode Q3 and the other end of capacitor C8 are connected with BUS_N.
[0034] The optical coupling output module includes resistor R15, capacitor C10, operational amplifier U1, capacitor C11, resistor R16, resistor R17, triode Q4, resistor R18, resistor R20, optical coupling U2, resistor R19, capacitor C12 and capacitor C13, the second pin of operational amplifier U1 is connected with one end of resistor R15, one end of capacitor C10 and FAIL, the other end of resistor R15 is connected with 5VCC_BUS_N, the fifth pin of operational amplifier U1 is connected with 5VCC_BUS_N and one end of capacitor C11, the fourth pin of operational amplifier U1 is connected with one end of resistor R17 and the base of triode Q4 through resistor R16, the collector of triode Q4 is connected with one end of resistor R20 and the second pin of optical coupling U2, the first pin of optical coupling U2 is connected with the other end of resistor R20 and one end of resistor R18, the other end of resistor R18 is connected with 5VCC_BUS_N, the fourth pin of optical coupling U2 is connected with one end of capacitor C13, one end of resistor R19 and OC, the fifth pin of optical coupling U2 is connected with the other end of resistor R19, one end of capacitor C12 and power supply 3.3V, the other end of capacitor C12, the other end of capacitor C13 and the third pin of optical coupling U2 are grounded, the other end of capacitor C10, the third pin of operational amplifier U1, the other end of capacitor C11, the other end of resistor R17 and the emitter of triode Q4 are connected with BNS_N.
[0035] The microprocessor MCU adopts STM32H723ZET6 type chip or STM32H723VGH type chip or STM32H750XBH6 type chip.
[0036] Working principle: when the power tube is turned on, the current flows through the power tube body (the internal resistance is equivalent to a resistor), and as the current changes, the voltage on the internal resistance changes, and the Vce voltage also changes.
[0037] When the LIN_DRV_UL signal is high, the voltage is sent to the transistor Q1 through R7, D3, L1, R5 and R6, and the voltage of the other branch is detected through R7, D3, R4 and D2. At this time, the Uce tube voltage drop is in the normal range, Q1 is not turned on, D1 FAIL signal is high, Q4 is not turned on, the optocoupler U2 is not turned on, and the OC is high, no overcurrent signal; when the Uce tube voltage drop increases, the voltage on R6 also increases, Q1 is turned on, D1 is pulled low, C2 is discharged, the FAIL fault signal is low, and the U1 output is high, which is divided by R16 and R17, Q4 is turned on, the high-speed optocoupler U2 is turned on, the OC level is pulled low, and the overcurrent fault output is obtained.
[0038] The V-phase LIN_DRV_VL and V_VCE, and the W-phase LIN_DRV_WL and W_WCE have the same principles, the fault signals FAIL are connected in parallel, and the OC is reported when overcurrent occurs.
[0039] The above is only a preferred embodiment of the present application, and is not intended to limit the present application. Any modification, equivalent replacement and improvement within the spirit and principles of the present application shall be included in the protection scope of the present application.
Claims
1. An over-current detection and protection circuit applied to a three-phase full-bridge inverter, characterized in that, The over-current detection and protection circuit applied to the three-phase full-bridge inverter comprises a UVW module, a photocoupler output module, a blocking six-way driving PWM module, a microprocessor MCU and a power supply module, the output end of the UVW module is connected with the input end of the photocoupler output module, the output end of the photocoupler output module is respectively connected with the input end of the blocking six-way driving PWM module and the input end of the microprocessor MCU, the output end of the microprocessor MCU is connected with the input end of the blocking six-way driving PWM module, the output end of the blocking six-way driving PWM module is connected with the input end of the UVW module, and the power supply module is electrically connected with the UVW module, the photocoupler output module, the blocking six-way driving PWM module and the microprocessor MCU respectively.
2. The over-current detection and protection circuit applied to a three-phase full-bridge inverter according to claim 1, characterized in that, The UVW module comprises a UL lower bridge driving unit, a Vce current detection unit and a protection output unit, and the UL lower bridge driving unit, the Vce current detection unit and the protection output unit are arranged in parallel.
3. The over-current detection and protection circuit applied to a three-phase full-bridge inverter according to claim 2, characterized in that, The UL lower bridge driving unit comprises a diode D2, a resistor R4, a diode D3, a resistor R7, an inductor L1, a resistor R5, a capacitor C1, a capacitor C3, a resistor R6, a diode Q1, a capacitor C2 and a diode D1, the cathode of the diode D2 is connected with U_UCE, the anode of the diode D2 is respectively connected with one end of the inductor L1 and the cathode of the diode D3 through the resistor R4, the anode of the diode D3 is connected with one end of the resistor R7, the other end of the resistor R7 is connected with LIN_DRV_UL, the other end of the inductor L1 is respectively connected with one end of the resistor R5 and one end of the capacitor C3, the other end of the resistor R5 is respectively connected with one end of the capacitor C1, one end of the resistor R6 and the base of the triode Q1, the collector of the triode Q1 is respectively connected with the cathode of the diode D1 and one end of the capacitor C2, the anode of the diode D1 is connected with FAIL, and the other end of the capacitor C3, the other end of the capacitor C1, one end of the resistor R6, the emitter of the triode Q1 and the other end of the capacitor C2 are respectively connected with BUS_N.
4. The over-current detection and protection circuit for a three-phase full-bridge inverter according to claim 3, characterized in that, The Vce current detection unit includes a diode D5, a resistor R3, a diode D6, a resistor R10, an inductor L2, a resistor R8, a capacitor C6, a capacitor C4, a resistor R9, a transistor Q2, a capacitor C5, and a diode D4, a cathode of the diode D5 is connected to V_VCE, an anode of the diode D5 is connected to one end of the inductor L2 and a cathode of the diode D6 through the resistor R3 respectively, an anode of the diode D6 is connected to LIN_DRV_VL through the resistor R10, the other end of the inductor L2 is connected to one end of the resistor R8 and one end of the capacitor C6 respectively, the other end of the resistor R8 is connected to one end of the capacitor C4, one end of the resistor R9, and a base of the transistor Q2 respectively, a collector of the transistor Q2 is connected to one end of the capacitor C5 and a cathode of the diode D4 respectively, an anode of the diode D4 is connected to FAIL, the other end of the capacitor C6, the other end of the capacitor C4, the other end of the resistor R9, the emitter of the transistor Q2, and the other end of the capacitor C5 are connected to BUS_N respectively.
5. The over-current detection and protection circuit for a three-phase full-bridge inverter according to claim 4, wherein, The protection output unit includes a diode D8, a resistor R11, a diode D9, a resistor R14, an inductor L3, a resistor R12, a capacitor C9, a capacitor C7, a resistor R13, a transistor Q3, a capacitor C8, and a diode D7, a cathode of the diode D8 is connected to W_WCE, an anode of the diode D8 is connected to one end of the inductor L3 and a cathode of the diode D9 through the resistor R11 respectively, an anode of the diode D9 is connected to LIN_DRV_WL through the resistor R14, the other end of the inductor L3 is connected to one end of the resistor R12 and one end of the capacitor C9 respectively, the other end of the resistor R12 is connected to one end of the capacitor C7, one end of the resistor R13, and a base of the transistor Q3 respectively, a collector of the transistor Q3 is connected to one end of the capacitor C8 and a cathode of the diode D7 respectively, an anode of the diode D7 is connected to FAIL, the other end of the capacitor C9, the other end of the capacitor C7, the other end of the resistor R13, the emitter of the transistor Q3, and the other end of the capacitor C8 are connected to BUS_N respectively.
6. The over-current detection and protection circuit applied to a three-phase full-bridge inverter according to any one of claims 1-5, characterized in that, The light coupling output module includes resistance R15, capacitor C10, operational amplifier U1, capacitor C11, resistance R16, resistance R17, triode Q4, resistance R18, resistance R20, light coupling U2, resistance R19, capacitor C12 and capacitor C13, the bottom 2 feet of the operational amplifier U1 are connected with one end of the resistance R15, one end of the capacitor C10 and FAIL respectively, the other end of the resistance R15 is connected with 5VCC_BUS_N, the 5th foot of the operational amplifier U1 is connected with 5VCC_BUS_N and one end of the capacitor C11 respectively, the 4th foot of the operational amplifier U1 is connected with one end of the resistance R17 and the base of the triode Q4 through the resistance R16 respectively, the collector of the triode Q4 is connected with one end of the resistance R20 and the bottom 2 feet of the light coupling U2 respectively, the 1st foot of the light coupling U2 is connected with the other end of the resistance R20 and one end of the resistance R18 respectively, the other end of the resistance R18 is connected with 5VCC_BUS_N, the 4th foot of the light coupling U2 is connected with one end of the capacitor C13, one end of the resistance R19 and OC respectively, the 5th foot of the light coupling U2 is connected with the other end of the resistance R19, one end of the capacitor C12 and power supply 3.3V respectively, the other end of the capacitor C12, the other end of the capacitor C13 and the 3rd foot of the light coupling U2 are grounded respectively, the other end of the capacitor C10, the 3rd foot of the operational amplifier U1, the other end of the capacitor C11, the other end of the resistance R17 and the emitter of the triode Q4 are connected with BNS_N respectively.