Combination switch with zero-cross detection circuit

Abstract

The utility model discloses a combination switch with a zero-cross detection circuit, and relates to the technical field of combination switch circuits. The circuit comprises an amplitude limiting circuit, an operational amplifier circuit, an under-voltage protection circuit, a zero-crossing comparison circuit and an MCU. The amplitude limiting circuit is respectively connected with the three-phase power and the operational amplifier circuit and is used for protecting the operational amplifier circuit; the under-voltage protection circuit is connected with the amplitude limiting circuit and is used for avoiding line damage caused by circuit overload; the operational amplifier circuit is connected with the zero-crossing comparison circuit and is used for amplifying the signal; and the zero-crossing comparison circuit is connected with the MCU and is used for judging a zero-crossing threshold value, so that the moment when the zero-crossing signal is generated is matched with a zero-crossing point. According to the utility model, the problems of phase error and signal distortion of a zero-crossing comparator formed by an operational amplifier are reduced, the traditional zero-crossing detection is interfered by various factors such as temperature, and the problem of high-speed conversion is also considered while the stability of the circuit is improved, so that the accuracy is greatly improved.

Description

Technical Field

[0001] The utility model relates to the technical field of composite switch circuits, in particular to a composite switch with a zero-crossing detection circuit. Background Art

[0002] The composite switch can suppress inrush current and avoid arcing. During use, the three-phase electricity is detected through the zero-crossing detection circuit, and the zero-point signal is transmitted to the single-chip microcomputer for processing. Then the single-chip microcomputer performs transient switching on the thyristor. At the same time, due to the coordinated use of the thyristor and the magnetic latching relay, it has the characteristics of low power consumption during use, and does not need to be equipped with a bulky radiator and cooling fan. The zero-crossing pulse signal is used as a trigger signal for the on and off of the switching device, which can realize the zero-crossing on and off of the switching device, effectively reduce the switching loss of the power electronic device, reduce the harmonics generated by the on and off of the electronic device, and thus reduce the device cost and the impact of the device on the power grid. The thyristor switch is responsible for controlling the input and removal of the capacitor, and the magnetic latching relay is responsible for the conduction of the subsequent power supply circuit. After the magnetic latching relay is put into use, the thyristor is turned on by the magnetic latching relay, so that the current passing through the two ends of the thyristor is zero, thereby turning off the on-state of the thyristor, thus avoiding the problem of thyristor heating for a long time.

[0003] However, due to factors such as grid voltage fluctuations and noise, zero-crossing detection leads to multiple zero-crossing phenomena and large errors between the actual fundamental zero point and the extracted zero point. The operational amplifier in the circuit has a major influencing factor. Therefore, the zero-point phase given is actually not accurate. If switching is performed near the zero point, inrush current will be generated. Utility Model Content

[0004] The purpose of the utility model is to provide a composite switch with a zero-crossing detection circuit to solve the problems raised in the above background technology.

[0005] In order to solve the above technical problems, the utility model provides the following technical solutions:

[0006] A composite switch with a zero-crossing detection circuit includes a limiter circuit, an operational amplifier circuit, an undervoltage protection circuit, a zero-crossing comparison circuit and an MCU.

[0007] The limiting circuit is connected to the three-phase power and the operational amplifier circuit respectively;

[0008] The undervoltage protection circuit is connected to the amplitude limiting circuit;

[0009] The operational amplifier circuit is connected to the zero-crossing comparison circuit;

[0010] The zero-crossing comparison circuit is connected to the MCU.

[0011] Preferably, the limiting circuit includes a plurality of resistors and diodes, two adjacent resistors are connected in series, and the diodes are connected in parallel with the resistors. The resistors and diodes are used to prevent the operational amplifier from being damaged due to excessive differential mode voltage, and when the input voltage is reduced, the output voltage of the positive and negative power supply voltages will not be distorted within a limited power supply range, and the top and bottom of the signal are cut off without affecting the detection of the zero crossing point.

[0012] Preferably, the amplitude limiting circuit comprises a resistor RA1, a resistor RA2, a resistor RA3, a resistor RA4, a diode DA1 and a diode DA2, wherein the resistor RA1, the resistor RA2, the resistor RA3 and the resistor RA4 are sequentially connected in series, and an end of the resistor RA1 away from the resistor RA2 is connected to the UA_in end;

[0013] The amplitude limiting circuit further includes a resistor RB1, a resistor RB2, a resistor RB3, a resistor RB4, a diode DB1 and a diode DB2. The resistor RB1, the resistor RB2, the resistor RB3 and the resistor RB4 are connected in series in sequence. The end of the resistor RB1 away from the resistor RB2 is connected to the UB_in end.

[0014] The amplitude limiting circuit further includes a resistor RC1, a resistor RC2, a resistor RC3, a resistor RC4, a diode DC1 and a diode DC2. The resistor RA1, the resistor RC2, the resistor RC3 and the resistor RC4 are connected in series in sequence. The end of the resistor RC1 away from the resistor RC2 is connected to the UC_in end.

[0015] Preferably, the operational amplifier circuit includes an operational amplifier LF353-A1, an operational amplifier LF353-A2, an operational amplifier LF353-B1, an operational amplifier LF353-B2, an operational amplifier LF353-C1, and an operational amplifier LF353-C2; a LF353 two-stage operational amplifier is used to perform two-stage amplification of the signal, and LF353 has the characteristics of high gain, high common mode rejection ratio, stable operation, and simple compensation;

[0016] The operational amplifier LF353-A1 is connected in series with the operational amplifier LF353-A2, and the operational amplifier LF353-A1 is connected in series with the resistor RA4 through the INPUT (+) pin. The diode DA1 and the diode DA2 are respectively connected between the INPUT (+) pin of the operational amplifier LF353-A1 and the resistor RA4, and the diode DA1 and the diode DA2 are grounded;

[0017] The operational amplifier LF353-B1 is connected in series with the operational amplifier LF353-B2, and the operational amplifier LF353-B1 is connected in series with the resistor RB4 through the INPUT (+) pin. The diode DB1 and the diode DB2 are respectively connected between the INPUT (+) pin of the operational amplifier LF353-B1 and the resistor RB4, and the diode DB1 and the diode DB2 are grounded;

[0018] The operational amplifier LF353-C1 is connected in series with the operational amplifier LF353-C2, and the operational amplifier LF353-C1 is connected in series with the resistor RC4 through the INPUT (+) pin. The diode DC1 and the diode DC2 are respectively connected between the INPUT (+) pin of the operational amplifier LF353-C1 and the resistor RC4, and the diode DC1 and the diode DC2 are both grounded.

[0019] Preferably, the zero-crossing comparison circuit includes comparator LM311-A, comparator LM311-B, and comparator LM311-C; the LM311 comparator is used, which can make the threshold for judging zero crossing very small, so that the time when the zero-crossing signal is generated is more consistent with the zero-crossing point. The device has low open-loop gain, small offset voltage, low power consumption, high cost performance, can accept large differential input signals, fast response speed, only 200ns, short transmission delay time, and thus can effectively improve the accuracy of zero-crossing detection;

[0020] The OUTPUT pin of the operational amplifier LF353-A2 is connected to the INPUT (+) pin of the comparator LM311-A, and the OUTPUT pin of the comparator LM311-A is connected to the MCU;

[0021] The OUTPUT pin of the operational amplifier LF353-B2 is connected to the INPUT (+) pin of the comparator LM311-B, and the OUTPUT pin of the comparator LM311-B is connected to the MCU;

[0022] The OUTPUT pin of the operational amplifier LF353-C2 is connected to the INPUT (+) pin of the comparator LM311-C, and the OUTPUT pin of the comparator LM311-C is connected to the MCU.

[0023] Preferably, the undervoltage protection circuit includes a photocoupler K1, a resistor RQ1, a resistor RQ2, a resistor RQ3, a resistor RQ4, a capacitor C1, a capacitor C2, a Schmitt trigger CD4016BM-1, a Schmitt trigger CD4016BM-2; a bidirectional TVS diode; when the voltage is reduced, the circuit damage caused by circuit overload can be avoided;

[0024] The 3 interface of the photocoupler K1, the Schmitt trigger CD4016BM-1, the diode D3, the Schmitt trigger CD4016BM-2 and the MCU are connected in series in sequence, the 3 interface of the photocoupler K1 and the Schmitt trigger CD4016BM-1 are externally connected with a resistor RQ3, the resistor RQ3 is connected to the 5V terminal, the 4 interface of the photocoupler K1 is grounded, the 1 interface of the photocoupler K1, the resistor RQ1, the diode D1 and the 2 interface of the photocoupler K1 are connected in series in sequence, the UB_in terminal is externally connected between the resistor RQ1 and the diode D1, the resistor RQ2 is externally connected between the diode D1 and the 2 interface of the photocoupler K1, and the resistor RQ2 is connected to the UC_in terminal through a bidirectional TVS diode;

[0025] An external capacitor C1 is connected between the diode D3 and the Schmitt trigger CD4016BM-2, and the capacitor C1 is grounded. A capacitor C2 and a resistor RQ4 are connected in parallel to the outside of the capacitor C1, and the capacitor C2 and the resistor RQ4 are connected in parallel.

[0026] Compared with the prior art, the beneficial effects achieved by the utility model are:

[0027] The utility model includes a limiting circuit, an operational amplifier circuit, an undervoltage protection circuit, a zero-crossing comparison circuit and an MCU; the limiting circuit is respectively connected to the three-phase power and the operational amplifier circuit to protect the operational amplifier circuit; the undervoltage protection circuit is connected to the limiting circuit to avoid line damage due to circuit overload; the operational amplifier circuit is connected to the zero-crossing comparison circuit to amplify the signal; the zero-crossing comparison circuit is connected to the MCU to determine the zero-crossing threshold so that the moment when the zero-crossing signal is generated coincides with the zero-crossing point. The utility model reduces the problem of phase error in the zero-crossing comparator composed of the operational amplifier, and reduces the problem of signal distortion. At the same time, the traditional zero-crossing detection will be interfered by various factors such as temperature. The design can improve the circuit stability while taking into account the problem of high-speed conversion, so the accuracy is greatly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0029] Figure 1 It is a schematic diagram of the modules of the circuit connection in the utility model;

[0030] Figure 2 It is a circuit principle diagram of the circuit connection in the utility model. DETAILED DESCRIPTION

[0031] The following will be combined with the drawings in the embodiments of the utility model to clearly and completely describe the technical solutions in the embodiments of the utility model. Obviously, the described embodiments are only part of the embodiments of the utility model, not all of the embodiments. Based on the embodiments in the utility model, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the utility model.

[0032] refer to Figure 1-Figure 2 The utility model provides a technical solution: a composite switch with a zero-crossing detection circuit, including a limiter circuit, an operational amplifier circuit, an undervoltage protection circuit, a zero-crossing comparison circuit and an MCU.

[0033] The limiting circuit is connected to the three-phase power and the operational amplifier circuit respectively;

[0034] The undervoltage protection circuit is connected to the amplitude limiting circuit;

[0035] The operational amplifier circuit is connected to the zero-crossing comparison circuit;

[0036] The zero-crossing comparison circuit is connected to the MCU;

[0037] The operational amplifier circuit is used to increase the slope of the rising edge of the electrical signal, so that the error time is reduced. The zero-crossing comparison circuit reduces the threshold for judging zero crossing, so that the time when the zero signal is generated is more consistent with the zero-crossing point. The undervoltage protection circuit is used to protect against overload caused by a significant drop in voltage.

[0038] The limiting circuit includes a plurality of resistors and diodes, two adjacent resistors are connected in series, and the diodes are connected in parallel with the resistors. The resistors and diodes are used to prevent the operational amplifier from being damaged due to excessive differential mode voltage, and when the input voltage is reduced, the output voltage of the positive and negative power supply voltages will not be distorted within a limited power supply range, and the top and bottom of the signal are cut off without affecting the detection of the zero crossing point.

[0039] In the limiting circuit, after the A phase is connected, it is connected in series with four resistors of the same size, and is connected to two reverse parallel diodes. While using the series resistors for circuit protection, two reverse diodes are also used to ensure that after the input voltage becomes smaller, the positive and negative power supply voltages can output voltages within a limited power supply range without distortion, and the top and bottom of the signal are cut off without affecting the detection of the zero crossing point; the limiting circuit includes a resistor RA1, a resistor RA2, a resistor RA3, a resistor RA4, a diode DA1 and a diode DA2, and the resistors RA1, RA2, RA3 and RA4 are connected in series in sequence, and the end of the resistor RA1 away from the resistor RA2 is connected to the UA_in end;

[0040] The amplitude limiting circuit further includes a resistor RB1, a resistor RB2, a resistor RB3, a resistor RB4, a diode DB1 and a diode DB2. The resistor RB1, the resistor RB2, the resistor RB3 and the resistor RB4 are connected in series in sequence. The end of the resistor RB1 away from the resistor RB2 is connected to the UB_in end.

[0041] The amplitude limiting circuit further includes a resistor RC1, a resistor RC2, a resistor RC3, a resistor RC4, a diode DC1 and a diode DC2. The resistor RA1, the resistor RC2, the resistor RC3 and the resistor RC4 are connected in series in sequence. The end of the resistor RC1 away from the resistor RC2 is connected to the UC_in end.

[0042] The LF353 operational amplifier used in the operational amplifier circuit has the characteristics of high gain, high common mode rejection ratio, stable operation, simple compensation, etc. Compared with the error caused by the dead zone of the amplifier in ordinary zero detection, the error caused by the dead zone of the circuit designed after the signal is amplified by 10,000 times, when the voltage amplitude Δx of the operational amplifier dead zone is equal and the original signal frequency is not changed, the slope of the rising edge of the signal is increased, and the error of the latter is obviously lower than that of the former; the operational amplifier circuit includes operational amplifier LF353-A1, operational amplifier LF353-A2, operational amplifier LF353-B1, operational amplifier LF353-B2, operational amplifier LF353-C1, operational amplifier LF353-C2; LF353 two-stage operational amplifier is used to perform two-stage amplification of the signal. LF353 has the characteristics of high gain, high common mode rejection ratio, stable operation, and simple compensation;

[0043] The operational amplifier LF353-A1 is connected in series with the operational amplifier LF353-A2, and the operational amplifier LF353-A1 is connected in series with the resistor RA4 through the INPUT (+) pin. The diode DA1 and the diode DA2 are respectively connected between the INPUT (+) pin of the operational amplifier LF353-A1 and the resistor RA4, and the diode DA1 and the diode DA2 are grounded;

[0044] The operational amplifier LF353-B1 is connected in series with the operational amplifier LF353-B2, and the operational amplifier LF353-B1 is connected in series with the resistor RB4 through the INPUT (+) pin. The diode DB1 and the diode DB2 are respectively connected between the INPUT (+) pin of the operational amplifier LF353-B1 and the resistor RB4, and the diode DB1 and the diode DB2 are grounded;

[0045] The operational amplifier LF353-C1 is connected in series with the operational amplifier LF353-C2, and the operational amplifier LF353-C1 is connected in series with the resistor RC4 through the INPUT (+) pin. The diode DC1 and the diode DC2 are respectively connected between the INPUT (+) pin of the operational amplifier LF353-C1 and the resistor RC4, and the diode DC1 and the diode DC2 are both grounded.

[0046] The zero-crossing comparison circuit can make a more accurate judgment of the small threshold value by taking the output signal of the amplifying circuit. This circuit uses the LM311 device, which has low open-loop gain, small offset voltage, low power consumption, and high cost performance; it can accept larger differential input signals; it has a fast response speed of only 200ns, and a short transmission delay time, so it can effectively improve the accuracy of zero-crossing detection; the zero-crossing comparison circuit includes comparator LM311-A, comparator LM311-B, and comparator LM311-C; the LM311 comparator is used, which can make the threshold for judging zero crossing very small, so that the moment when the zero-crossing signal is generated is more consistent with the zero-crossing point. The device has low open-loop gain, small offset voltage, low power consumption, and high cost performance. It can accept larger differential input signals, has a fast response speed of only 200ns, and a short transmission delay time, so it can effectively improve the accuracy of zero-crossing detection;

[0047] The OUTPUT pin of the operational amplifier LF353-A2 is connected to the INPUT (+) pin of the comparator LM311-A, and the OUTPUT pin of the comparator LM311-A is connected to the MCU;

[0048] The OUTPUT pin of the operational amplifier LF353-B2 is connected to the INPUT (+) pin of the comparator LM311-B, and the OUTPUT pin of the comparator LM311-B is connected to the MCU;

[0049] The OUTPUT pin of the operational amplifier LF353-C2 is connected to the INPUT (+) pin of the comparator LM311-C, and the OUTPUT pin of the comparator LM311-C is connected to the MCU.

[0050] The undervoltage protection circuit includes a photocoupler K1, a resistor RQ1, a resistor RQ2, a resistor RQ3, a resistor RQ4, a capacitor C1, a capacitor C2, a Schmitt trigger CD4016BM-1, and a Schmitt trigger CD4016BM-2; a bidirectional TVS diode; wherein the photocoupler is electrically connected to the B phase and the C phase at the same time to perform electrical-optical-electrical conversion, and then connected to two Schmitt triggers and a parallel RC circuit. This circuit can prevent line damage caused by circuit overload when the voltage is reduced;

[0051] The 3 interface of the photocoupler K1, the Schmitt trigger CD4016BM-1, the diode D3, the Schmitt trigger CD4016BM-2 and the MCU are connected in series in sequence, the 3 interface of the photocoupler K1 and the Schmitt trigger CD4016BM-1 are externally connected with a resistor RQ3, the resistor RQ3 is connected to the 5V terminal, the 4 interface of the photocoupler K1 is grounded, the 1 interface of the photocoupler K1, the resistor RQ1, the diode D1 and the 2 interface of the photocoupler K1 are connected in series in sequence, the UB_in terminal is externally connected between the resistor RQ1 and the diode D1, the resistor RQ2 is externally connected between the diode D1 and the 2 interface of the photocoupler K1, and the resistor RQ2 is connected to the UC_in terminal through a bidirectional TVS diode;

[0052] An external capacitor C1 is connected between the diode D3 and the Schmitt trigger CD4016BM-2, and the capacitor C1 is grounded. A capacitor C2 and a resistor RQ4 are connected in parallel to the outside of the capacitor C1, and the capacitor C2 and the resistor RQ4 are connected in parallel.

[0053] Specific working principle: The working process of the utility model is roughly divided into the following parts: first, the power supply is divided to prevent the zero-crossing detection circuit from being damaged due to excessive differential mode voltage; second, two operational amplifiers are used to amplify the signal, which is conducive to the circuit's judgment accuracy of the zero-crossing point; third, the use of the LM311 device can reduce the threshold value of the zero-crossing detection, thereby effectively improving the accuracy of the zero-crossing detection; at the same time, in order to protect the zero-crossing detection circuit, an undervoltage protection circuit is set to prevent the circuit from being overloaded;

[0054] At the beginning, the limiting circuit first divides the power supply (three-phase electricity) so that the zero-crossing detection circuit will not be damaged due to excessive differential mode voltage, and through two reverse diodes, after the input voltage becomes smaller, the positive and negative power supply voltages can output voltages within a limited power supply range without distortion, and the top and bottom of the signal are cut off and do not affect the detection of the zero-crossing point; after the limiting circuit is processed, it is transmitted to the operational amplifier circuit, and the operational amplifier circuit amplifies the signal to reduce the error of the signal waveform, and then transmitted to the zero-crossing comparison circuit. After being processed by the zero-crossing comparator, it can be sent to the MCU for processing; while the zero-crossing detection circuit is working, the undervoltage protection circuit is also protecting its safe operation; while improving the circuit stability, the problem of high-speed conversion is also considered, and the accuracy is greatly improved.

[0055] Finally, it should be noted that the above description is only a preferred embodiment of the utility model and is not intended to limit the utility model. Although the utility model is described in detail with reference to the above embodiments, those skilled in the art can still modify the technical solutions recorded in the above embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the utility model shall be included in the protection scope of the utility model.

Claims

1. A composite switch with a zero-crossing detection circuit, comprising a limiter circuit, an operational amplifier circuit, an undervoltage protection circuit, a zero-crossing comparison circuit and an MCU, characterized in that: The limiting circuit is connected to the three-phase power and the operational amplifier circuit respectively; The undervoltage protection circuit is connected to the amplitude limiting circuit; The operational amplifier circuit is connected to the zero-crossing comparison circuit; The zero-crossing comparison circuit is connected to the MCU.

2. A composite switch with a zero-crossing detection circuit according to claim 1, characterized in that: The amplitude limiting circuit includes a plurality of resistors and diodes, two adjacent resistors are connected in series, and the diodes are connected in parallel with the resistors.

3. A composite switch with a zero-crossing detection circuit according to claim 2, characterized in that: The amplitude limiting circuit includes a resistor RA1, a resistor RA2, a resistor RA3, a resistor RA4, a diode DA1 and a diode DA2. The resistor RA1, the resistor RA2, the resistor RA3 and the resistor RA4 are connected in series in sequence. The end of the resistor RA1 away from the resistor RA2 is connected to the UA_in end. The amplitude limiting circuit further includes a resistor RB1, a resistor RB2, a resistor RB3, a resistor RB4, a diode DB1 and a diode DB2. The resistor RB1, the resistor RB2, the resistor RB3 and the resistor RB4 are connected in series in sequence. The end of the resistor RB1 away from the resistor RB2 is connected to the UB_in end. The amplitude limiting circuit further includes a resistor RC1, a resistor RC2, a resistor RC3, a resistor RC4, a diode DC1 and a diode DC2. The resistor RA1, the resistor RC2, the resistor RC3 and the resistor RC4 are connected in series in sequence. The end of the resistor RC1 away from the resistor RC2 is connected to the UC_in end.

4. A composite switch with a zero-crossing detection circuit according to claim 3, characterized in that: The operational amplifier circuit includes an operational amplifier LF353-A1, an operational amplifier LF353-A2, an operational amplifier LF353-B1, an operational amplifier LF353-B2, an operational amplifier LF353-C1, and an operational amplifier LF353-C2; The operational amplifier LF353-A1 is connected in series with the operational amplifier LF353-A2, and the operational amplifier LF353-A1 is connected in series with the resistor RA4 through the INPUT (+) pin. The diode DA1 and the diode DA2 are respectively connected between the INPUT (+) pin of the operational amplifier LF353-A1 and the resistor RA4, and the diode DA1 and the diode DA2 are grounded; The operational amplifier LF353-B1 is connected in series with the operational amplifier LF353-B2, and the operational amplifier LF353-B1 is connected in series with the resistor RB4 through the INPUT (+) pin. The diode DB1 and the diode DB2 are respectively connected between the INPUT (+) pin of the operational amplifier LF353-B1 and the resistor RB4, and the diode DB1 and the diode DB2 are grounded; The operational amplifier LF353-C1 is connected in series with the operational amplifier LF353-C2, and the operational amplifier LF353-C1 is connected in series with the resistor RC4 through the INPUT (+) pin. The diode DC1 and the diode DC2 are respectively connected between the INPUT (+) pin of the operational amplifier LF353-C1 and the resistor RC4, and the diode DC1 and the diode DC2 are both grounded.

5. A composite switch with a zero-crossing detection circuit according to claim 4, characterized in that: The zero-crossing comparison circuit includes a comparator LM311-A, a comparator LM311-B, and a comparator LM311-C; The OUTPUT pin of the operational amplifier LF353-A2 is connected to the INPUT (+) pin of the comparator LM311-A, and the OUTPUT pin of the comparator LM311-A is connected to the MCU; The OUTPUT pin of the operational amplifier LF353-B2 is connected to the INPUT (+) pin of the comparator LM311-B, and the OUTPUT pin of the comparator LM311-B is connected to the MCU; The OUTPUT pin of the operational amplifier LF353-C2 is connected to the INPUT (+) pin of the comparator LM311-C, and the OUTPUT pin of the comparator LM311-C is connected to the MCU.

6. A composite switch with a zero-crossing detection circuit according to claim 5, characterized in that: The undervoltage protection circuit includes a photocoupler K1, a resistor RQ1, a resistor RQ2, a resistor RQ3, a resistor RQ4, a capacitor C1, a capacitor C2, a Schmitt trigger CD4016BM-1, a Schmitt trigger CD4016BM-2; a bidirectional TVS diode; The 3 interface of the photocoupler K1, the Schmitt trigger CD4016BM-1, the diode D3, the Schmitt trigger CD4016BM-2 and the MCU are connected in series in sequence, the 3 interface of the photocoupler K1 and the Schmitt trigger CD4016BM-1 are externally connected with a resistor RQ3, the resistor RQ3 is connected to the 5V terminal, the 4 interface of the photocoupler K1 is grounded, the 1 interface of the photocoupler K1, the resistor RQ1, the diode D1 and the 2 interface of the photocoupler K1 are connected in series in sequence, the UB_in terminal is externally connected between the resistor RQ1 and the diode D1, the resistor RQ2 is externally connected between the diode D1 and the 2 interface of the photocoupler K1, and the resistor RQ2 is connected to the UC_in terminal through a bidirectional TVS diode; An external capacitor C1 is connected between the diode D3 and the Schmitt trigger CD4016BM-2, and the capacitor C1 is grounded. A capacitor C2 and a resistor RQ4 are connected in parallel to the outside of the capacitor C1, and the capacitor C2 and the resistor RQ4 are connected in parallel.

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