Three-path output switching power supply circuit

Abstract

The utility model relates to a three-path output switching power supply circuit, which comprises an electromagnetic interference suppression circuit, a rectification filter circuit, a power supply control circuit, a power conversion circuit, a power supply output circuit and a feedback circuit which are electrically connected, the electromagnetic interference suppression circuit is electrically connected with the input end of the rectification filter circuit. The rectification filter circuit is electrically connected with the input end of the power conversion circuit and the input end of the power supply control circuit. The power control circuit is electrically connected with the input end of the power conversion circuit, the power conversion circuit is electrically connected with the input end of the power output circuit, the power output circuit is electrically connected with the input end of the feedback circuit, and the feedback circuit is electrically connected with the input end of the power control circuit. The device is reasonable in design, compact in structure and convenient to use.

Description

Technical Field

[0001] The utility model relates to a switch power supply circuit with three outputs. Background Art

[0002] At present, most single-phase smart energy meters on the market are powered by linear power supply circuits. With the development of the meter industry, higher requirements are put forward for the anti-interference ability, power supply voltage range, power efficiency, etc. of the meter. With the increasing application of switching power supplies in meters, various switching power supply circuits are uneven, and most of them are realized in the form of one power output, and different load circuits are not isolated.

[0003] Switching power supplies are becoming more and more the mainstream of electronic equipment. With the development of smart energy meters, the trend of single-phase smart energy meters changing from linear power supplies to switching power supplies is becoming more and more obvious. The application environment of electric meter products is relatively harsh and has high requirements for power supply quality. At the same time, electric meters also have very strict requirements for electrical isolation, so switching power supplies are increasingly widely used in electric meters. However, in actual applications, most flyback circuits have only one power output, and have problems such as poor anti-interference ability, low stability, and low output efficiency. Utility Model Content

[0004] In order to solve the above problems, the utility model provides a three-way output flyback switching power supply circuit, which improves the power utilization efficiency by converting the AC power supply into a DC power supply and then outputting the DC power supply through three channels, and can effectively isolate and drive different loads. The utility model has a wide power input range, high stability, strong anti-interference ability, high working efficiency, and can achieve electrical isolation between each load.

[0005] In order to solve the above problems, the technical solution adopted by the utility model is:

[0006] In order to realize reasonable output power, a three-way output switching power supply circuit includes an electromagnetic interference suppression circuit, a rectifier filter circuit, a power control circuit, a power conversion circuit, a power output circuit and a feedback circuit that are electrically connected;

[0007] The electromagnetic interference suppression circuit is electrically connected to the input end of the rectifier and filter circuit, and the rectifier and filter circuit are electrically connected to the input end of the power conversion circuit and the input end of the power control circuit respectively; the power control circuit is electrically connected to the input end of the power conversion circuit, the power conversion circuit is electrically connected to the input end of the power output circuit, the power output circuit is electrically connected to the input end of the feedback circuit, and the feedback circuit is electrically connected to the input end of the power control circuit.

[0008] As a further improvement of the above technical solution:

[0009] In order to suppress electromagnetic interference, the electromagnetic interference suppression circuit includes a varistor RN1, a differential mode inductor LN1, a safety capacitor CN1 and a composite thermistor RN2;

[0010] The varistor RN1 is connected across the live wire UN and the neutral wire of the AC power supply. After the live wire UN passes through the differential mode inductor LN1, the safety capacitor CN1 is connected across the output end of the neutral wire connected in series with the differential mode inductor LN1 and the neutral wire. After the live wire UN passes through the neutral wire connected in series with the differential mode inductor LN1 and the safety capacitor CN1, it is connected to the composite thermistor RN2.

[0011] The rectifier and filter circuit includes a rectifier bridge DN1, an electrolytic capacitor EN1, an electrolytic capacitor EN2, voltage-equalizing resistors RN3-RN6, and a voltage-dividing resistor RN7;

[0012] The output end of the electromagnetic interference suppression circuit is electrically connected to the input end of the rectifier bridge DN1, and the output end of the rectifier bridge DN1 is a power supply POWER+;

[0013] The voltage-equalizing resistors RN3 and RN4 are connected in series and in parallel with the electrolytic capacitor EN1;

[0014] The voltage-equalizing resistors RN5 and RN6 are connected in series with the voltage-dividing resistor RN7 and then connected in parallel with the electrolytic capacitor EN2; the parallel-connected electrolytic capacitor EN1 is connected in series with the parallel-connected EN2;

[0015] The power supply POWER+ is grounded through the series-connected electrolytic capacitor EN1 and the parallel-connected EN2.

[0016] In order to achieve reasonable power optimization, the power conversion circuit includes a high-frequency transformer T1, a diode DN3, a capacitor CN2, a resistor RN8, and a resistor RN9;

[0017] The high frequency transformer T1 includes an inductive primary winding N1, an auxiliary winding N2, and output windings N3, N4, and N5;

[0018] The power source POWER+ is connected to the primary winding N1. The primary winding N1 is connected in series with the diode DN3 and then connected in parallel with the capacitor CN2 and the series-connected resistors RN8 and RN9.

[0019] In order to realize the electronic control optimization control, the power control circuit includes a power control chip UN1, an electrolytic capacitor EN3, capacitors CN3, CN4, CN5, CN7, resistors RN10, RN12, RN13, RN14 and a diode DN4;

[0020] Pin 1 and pin 2 are connected to PGND; pin 3 is the chip power supply pin, electrolytic capacitor EN3 and capacitor CN7 are connected in parallel between pin 3 and PGND, resistor RN12 and diode DN4 are connected in series between pin 3 and auxiliary winding N2; resistor RN10 is connected between pin 4 and PGND, capacitor CN4 is electrically connected between pin 1 and pin 4; capacitor CN5 is connected between pin 5 and PGND; pin 6 is connected to the feedback circuit through line FB;

[0021] Pin 7 and pin 8 are connected to PGND; resistors RN13 and RN14 are connected between pin 9 and PGND; pin 13 is left floating, and capacitor CN3 is connected between pin 14 and pin 9.

[0022] In order to achieve reasonable circuit output, the power supply output circuit includes a first output connected to the output winding N5, a second output connected to the output winding N4, and a third output connected to the output winding N3;

[0023] The first output includes diode DN7, electrolytic capacitor EN6, capacitors CN19 and CN18, and dummy load RN18;

[0024] The output end of the output winding N5 passes through the diode DN7, and is electrically connected to the parallel filtering circuit of the electrolytic capacitor EN6, the capacitors CN19 and CN18, and then the output end is connected to the dummy load RN18 for output;

[0025] The second output includes diode DN6, electrolytic capacitor EN5 and capacitor CN10;

[0026] The output end of the output winding N4 passes through the diode DN6 and is electrically connected to the parallel electrolytic capacitor EN5 and the capacitor CN10 output;

[0027] The third output includes a diode DN5 electrically connected to the output winding N3 and an electrolytic capacitor EN5 electrically connected to the diode DN5.

[0028] In order to achieve the optimization of the feedback circuit, the feedback circuit includes an optocoupler DN8, resistors RN20-R25, capacitors CN13, CN13 and a reference voltage chip UN2;

[0029] The primary side of the optocoupler DN8 is connected in parallel with the resistor RN21, one end of the parallel resistor RN21 is connected in series with the resistor RN20, and the resistor RN20 outputs the first power supply;

[0030] The other end of the parallel resistor RN21 is connected to the input end of the reference voltage chip UN2 and the resistor RN24 respectively;

[0031] The output end of the reference voltage chip UN2 is connected to GND; the resistor RN24 is connected in series with the capacitor CN14, and the capacitor CN14 is electrically connected to the resistor R23, the resistor R25 and the reference end of the reference voltage chip UN2 respectively; the resistor R25 is connected to GND; the resistors R23 and R22 are connected in series and then connected to the first power supply.

[0032] The utility model has the following beneficial effects: 1. The utility model adopts the HF920GS power control chip of Xinyuan Company, the switching power frequency is adjustable, has overvoltage protection function, and has the advantage of frequency jitter, which greatly reduces the noise level and effectively suppresses electromagnetic interference. 2. The utility model has three independent power outputs, the power supply has high working efficiency, and each output is electrically isolated, effectively drives different loads, and has a wider range of applications. 3. A filter capacitor is connected across pins 14 and 9 of the power control circuit UN1 of the utility model to reduce the noise generated during switching, effectively suppress electromagnetic interference, and improve the quality of power supply. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a block diagram of the connection between the various circuits of the utility model.

[0034] Figure 2 This is a schematic diagram of a three-way output switching power supply circuit of the utility model.

[0035] Figure 3 for Figure 2 The local circuit schematic at point A.

[0036] Figure 4 for Figure 2 Schematic diagram of the local circuit at point B.

[0037] Figure 5 for Figure 2 Schematic diagram of the local circuit at C. DETAILED DESCRIPTION

[0038] like Figure 1-5 As shown, the three-way output switching power supply circuit of this embodiment,

[0039] See also Figure 1 , this embodiment includes an electromagnetic interference suppression circuit, a rectifier and filter circuit, a power control circuit, a power conversion circuit, a power output circuit and a feedback circuit that are electrically connected;

[0040] The electromagnetic interference suppression circuit is electrically connected to the input end of the rectifier and filter circuit, and the rectifier and filter circuit are electrically connected to the input end of the power conversion circuit and the input end of the power control circuit respectively; the power control circuit is electrically connected to the input end of the power conversion circuit, the power conversion circuit is electrically connected to the input end of the power output circuit, the power output circuit is electrically connected to the input end of the feedback circuit, and the feedback circuit is electrically connected to the input end of the power control circuit;

[0041] The mains electricity passes through the electromagnetic interference suppression circuit, the rectifier filter circuit, and then the power control circuit controls the conversion circuit to the power output circuit. The feedback circuit adjusts the output voltage of the power output circuit and feeds back to the power control circuit.

[0042] The electromagnetic interference suppression circuit includes a varistor RN1, a differential mode inductor LN1, a safety capacitor CN1 and a composite thermistor RN2;

[0043] In the electromagnetic interference suppression circuit, the varistor RN1 is connected across the live wire UN and the neutral wire of the mains. After the live wire UN passes through the differential mode inductor LN1, the safety capacitor CN1 is connected across the output end of the neutral wire connected in series with the differential mode inductor LN1 and the neutral wire. After the live wire UN passes through the neutral wire connected in series with the differential mode inductor LN1 and the safety capacitor CN1, it is connected to the composite thermistor RN2.

[0044] The rectifier and filter circuit includes a rectifier bridge DN1, an electrolytic capacitor EN1, an electrolytic capacitor EN2, voltage-equalizing resistors RN3-RN6, and a voltage-dividing resistor RN7;

[0045] In the rectifier filter circuit, the output end of the electromagnetic interference suppression circuit is electrically connected to the input end of the rectifier bridge DN1, and the output end of the rectifier bridge DN1 is the power supply POWER+;

[0046] The voltage-equalizing resistors RN3 and RN4 are connected in series and in parallel with the electrolytic capacitor EN1;

[0047] The voltage-equalizing resistors RN5 and RN6 are connected in series with the voltage-dividing resistor RN7 and then connected in parallel with the electrolytic capacitor EN2; the parallel-connected electrolytic capacitor EN1 is connected in series with the parallel-connected electrolytic capacitor EN2;

[0048] The power supply POWER+ is connected to ground through the series-connected electrolytic capacitor EN1 and the parallel-connected electrolytic capacitor EN2;

[0049] The power conversion circuit includes a high-frequency transformer T1, a diode DN3, a capacitor CN2, a resistor RN8, and a resistor RN9;

[0050] The high frequency transformer T1 includes an inductive primary winding N1, an auxiliary winding N2, and output windings N3, N4, and N5;

[0051] In the power conversion circuit, the power source POWER+ is connected to the primary winding N1, the primary winding N1 is connected in series with the diode DN3, and then connected in parallel with the capacitor CN2 and the series resistors RN8 and RN9.

[0052] The power control circuit includes a power control chip UN1, an electrolytic capacitor EN3, capacitors CN3, CN4, CN5, CN7, resistors RN10, RN12, RN13, RN14 and a diode DN4;

[0053] In the power control chip UN1, pins 1 and 2 are connected to PGND; pin 3 is the chip power supply pin, electrolytic capacitor EN3 and capacitor CN7 are connected in parallel between pin 3 and PGND, and resistor RN12 and diode DN4 are connected in series between pin 3 and auxiliary winding N2; resistor RN10 is connected between pin 4 and PGND, and capacitor CN4 is electrically connected between pin 1 and pin 4; capacitor CN5 is connected between pin 5 and PGND; pin 6 is connected to the feedback circuit through line FB;

[0054] Pin 7 and pin 8 are connected to PGND; resistors RN13 and RN14 are connected between pin 9 and PGND; pin 13 is left floating, and capacitor CN3 is connected between pin 14 and pin 9;

[0055] In the power control circuit, the power control chip UN1 completes the control. The power control chip UN1 uses the HF920GS chip of Xinyuan Company. In the power control circuit, the power control chip uses the HF920 chip of Xinyuan. The parallel capacitor CN3 between pin 14 and pin 9 effectively suppresses the switching noise and reduces the electromagnetic interference;

[0056] The power output circuit includes a first output connected to the output winding N5, a second output connected to the output winding N4, and a third output connected to the output winding N3;

[0057] The first output includes diode DN7, electrolytic capacitor EN6, capacitors CN19 and CN18, and dummy load RN18;

[0058] The output end of the output winding N5 passes through the diode DN7, and is electrically connected to the parallel filtering circuit of the electrolytic capacitor EN6, the capacitors CN19 and CN18, and then the output end is connected to the dummy load RN18 for output;

[0059] The output signal of the output winding N5 is rectified by the diode DN7 and then filtered by the electrolytic capacitor EN6 and the capacitors CN19 and CN18. The output end is connected to the dummy load RN18 to ensure stable voltage output.

[0060] The second output includes diode DN6, electrolytic capacitor EN5 and capacitor CN10;

[0061] The output end of the output winding N4 is electrically connected to the parallel electrolytic capacitor EN5 and the capacitor CN10 after passing through the diode DN6.

[0062] The output winding N4 is rectified by the diode DN6 and then filtered by the electrolytic capacitor EN5 and the capacitor CN10 to stabilize the output.

[0063] The third output includes a diode DN5 electrically connected to the output winding N3 and an electrolytic capacitor EN5 electrically connected to the diode DN5;

[0064] The output winding N3 is rectified by diode DN5 and then filtered and stabilized by electrolytic capacitor EN5.

[0065] Three-way output switching power supply circuit, the control chip UN1 in the power supply control circuit is HF920.

[0066] The three-way output power supply achieves electrical isolation, drives different loads, and improves reliability and safety.

[0067] The feedback circuit includes an optocoupler DN8, resistors RN20-R25, capacitors CN13, CN13 and a reference voltage chip UN2;

[0068] The primary side of the optocoupler DN8 is connected in parallel with the resistor RN21, one end of the parallel-connected resistor RN21 is connected in series with the resistor RN20, and the resistor RN20 is connected to the first power output.

[0069] The other end of the parallel resistor RN21 is connected to the input end of the reference voltage chip UN2 and the resistor RN24 respectively;

[0070] The output end of the reference voltage chip UN2 is connected to GND; the resistor RN24 is connected in series with the capacitor CN14, and the capacitor CN14 is electrically connected to the resistor R23, the resistor R25 and the reference end of the reference voltage chip UN2 respectively; the resistor R25 is connected to GND. The resistors R23 and R22 are connected in series and then connected to the first power output.

[0071] See also Figure 2-5 After the AC power passes through the varistor RN1, it is filtered out through the differential mode inductor LN1 to remove the differential mode interference, passes through the safety capacitor CN1 and then connects to the composite thermistor RN2, and is rectified by the rectifier bridge DN1 and filtered by the electrolytic capacitors EN1 and EN2 to output a stable DC power. RN3, RN4, RN5 and RN6 are equalizing resistors, and the voltages at both ends of the electrolytic capacitors EN1 and EN2 are basically the same. RN7 is a voltage divider resistor connected to the power control chip UN1 to ensure that the chip is self-protected when the circuit is over-voltage.

[0072] The power control chip UN1 uses HF920 from Xinyuan Company. HF920 is a high-reliability power control chip with an integrated 900V withstand voltage switch MOS tube. It has a wide voltage input range of 85V~420V. The programmable switching frequency supports up to 150kHz. In addition to the programmable frequency, HF920 uses frequency jitter, which greatly reduces the noise level and the cost of EMI filters. HF920 uses peak current mode control to provide good transient response and simple loop compensation. When the output power is lower than a given level, the regulator enters burst mode. The consumption of the integrated circuit is also specially optimized. Therefore, HF920 achieves very low power consumption under standby conditions. HF920 has the functions of over-temperature protection, over-voltage protection, overload protection, and short-circuit protection.

[0073] Pins 1, 2, 7, and 8 of UN1 are grounded, and pin 5 is filtered by capacitor CN5 connected to the ground, and connected to the rectifier resistor to monitor whether it is overvoltage. Pin 4 is filtered by capacitor CN4 connected to the ground, and resistor RN10 is used to set the switching frequency of UN1 according to different resistance values. Pin 14 is the drain of the built-in MOS tube connected to the primary winding N1 of the high-frequency transformer T1 of the power conversion circuit, and connected to capacitor CN3 with pin 9, which is the source of the built-in MOS tube, to suppress the noise generated by the switch and reduce electromagnetic interference. Sampling resistors RN13 and RN14 are connected between pin 9 and ground to monitor the current of the primary winding N1 to adjust the switching duty cycle. Pin 3 is the power supply pin of UN1, connected to the auxiliary winding N2 of the high-frequency transformer T1 of the power conversion circuit. The output of the auxiliary winding N2 is rectified by diode DN4 and then passes through the current limiting resistor RN12, and then filtered by electrolytic capacitor EN3 and capacitor CN7 to power UN1.

[0074] The primary winding N1 of the high-frequency transformer T1 of the power conversion circuit is connected to the diode DN3, the capacitor CN2, the resistor RN8 and the resistor RN9 to form an RCD absorption circuit. The function of the RCD absorption circuit is to suppress the resonant voltage spike, leave a voltage margin for the MOS tube withstand voltage, avoid damage to the MOS tube or affect the service life of the MOS tube. In addition, the RCD absorption circuit suppresses the resonant voltage oscillation and can suppress electromagnetic interference.

[0075] The power supply output circuit includes three outputs, the first output winding N5, the second output winding N4, and the third output winding N3. The first output is rectified by diode DN7 and then filtered by electrolytic capacitor EN6, capacitors CN19 and CN18. The output end is connected to a dummy load RN18 to ensure stable voltage output. The second output winding N4 is rectified by diode DN6 and then filtered by electrolytic capacitor EN5 and capacitor CN10 for stable output. The third output winding N3 is rectified by diode DN5 and then filtered by electrolytic EN5 for voltage stabilization.

[0076] The feedback circuit monitors the first voltage output and transmits the feedback signal to the pin 6 of UN2 through the reference voltage chip UN2 via the optocoupler DN8 for isolation, and then adjusts it through the power control chip.

[0077] The present invention is fully described for a clearer disclosure, and the prior art will not be listed one by one.

[0078] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the utility model, rather than to limit it; although the utility model is described in detail with reference to the above embodiments, ordinary technicians in this field should understand that they can still modify the technical solutions recorded in the above embodiments, or replace some of the technical features therein with equivalents; it is obvious for those skilled in the art to combine multiple technical solutions of the utility model. However, these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the utility model.

Claims

1. A three-way output switching power supply circuit, characterized in that: It includes an electromagnetic interference suppression circuit, a rectifier filter circuit, a power control circuit, a power conversion circuit, a power output circuit and a feedback circuit that are electrically connected; The electromagnetic interference suppression circuit is electrically connected to the input end of the rectifier and filter circuit, and the rectifier and filter circuit are electrically connected to the input end of the power conversion circuit and the input end of the power supply control circuit respectively; The power control circuit is electrically connected to the input end of the power conversion circuit, the power conversion circuit is electrically connected to the input end of the power output circuit, the power output circuit is electrically connected to the input end of the feedback circuit, and the feedback circuit is electrically connected to the input end of the power control circuit.

2. The three-way output switching power supply circuit according to claim 1, characterized in that: The electromagnetic interference suppression circuit includes a varistor RN1, a differential mode inductor LN1, a safety capacitor CN1 and a composite thermistor RN2; The varistor RN1 is connected across the live wire UN and the neutral wire of the AC power supply. After the live wire UN passes through the differential mode inductor LN1, the safety capacitor CN1 is connected across the output end of the neutral wire connected in series with the differential mode inductor LN1 and the neutral wire. After the live wire UN passes through the neutral wire connected in series with the differential mode inductor LN1 and the safety capacitor CN1, it is connected to the composite thermistor RN2.

3. The three-way output switching power supply circuit according to claim 1, characterized in that: The rectifier and filter circuit includes a rectifier bridge DN1, electrolytic capacitors EN1 and EN2, voltage-equalizing resistors RN3-RN6, and a voltage-dividing resistor RN7; The output end of the electromagnetic interference suppression circuit is electrically connected to the input end of the rectifier bridge DN1, and the power switch POWER+ at the output end of the rectifier bridge DN1; The voltage-equalizing resistors RN3 and RN4 are connected in series and in parallel with the electrolytic capacitor EN1; The voltage-equalizing resistors RN5 and RN6 are connected in series with the voltage-dividing resistor RN7 and then connected in parallel with the electrolytic capacitor EN2; the parallel-connected electrolytic capacitor EN1 is connected in series with the parallel-connected EN2; The power switch POWER+ is grounded through the series-connected electrolytic capacitor EN1 and the parallel-connected EN2.

4. The three-way output switching power supply circuit according to claim 1, characterized in that: The power conversion circuit includes a high-frequency transformer T1, a diode DN3, a capacitor CN2, a resistor RN8, and a resistor RN9; The high frequency transformer T1 includes an inductive primary winding N1, an auxiliary winding N2, and output windings N3, N4, and N5; The power switch POWER+ is connected to the primary winding N1, and the primary winding N1 is connected in series with the diode DN3 and then connected in parallel with the capacitor CN2 and the series resistors RN8 and RN9.

5. The three-way output switching power supply circuit according to any one of claims 1 to 4, characterized in that: The power control circuit includes a power control chip UN1, an electrolytic capacitor EN3, capacitors CN3, CN4, CN5, CN7, resistors RN10, RN12, RN13, RN14 and a diode DN4; Pin 1 and pin 2 are connected to PGND; pin 3 is the chip power supply pin, electrolytic capacitor EN3 and capacitor CN7 are connected in parallel between pin 3 and PGND, resistor RN12 and diode DN4 are connected in series between pin 3 and auxiliary winding N2; resistor RN10 is connected between pin 4 and PGND, capacitor CN4 is electrically connected between pin 1 and pin 4; capacitor CN5 is connected between pin 5 and PGND; pin 6 is connected to the feedback circuit through line FB; Pin 7 and pin 8 are connected to PGND; resistors RN13 and RN14 are connected between pin 9 and PGND; pin 13 is left floating, and capacitor CN3 is connected between pin 14 and pin 9.

6. The three-way output switching power supply circuit according to claim 5, characterized in that: The power output circuit includes a first output connected to the output winding N5, a second output connected to the output winding N4, and a third output connected to the output winding N3; The first output includes diode DN7, electrolytic capacitor EN6, capacitors CN19 and CN18, and dummy load RN18; The output end of the output winding N5 passes through the diode DN7, and is electrically connected to the parallel filtering circuit of the electrolytic capacitor EN6, the capacitors CN19, and CN18, and then the output end is connected to the dummy load RN18 for output; The second output includes diode DN6, electrolytic capacitor EN5 and capacitor CN10; The output end of the output winding N4 passes through the diode DN6 and is electrically connected to the parallel electrolytic capacitor EN5 and the capacitor CN10 output; The third output includes a diode DN5 electrically connected to the output winding N3 and an electrolytic capacitor EN5 electrically connected to the diode DN5.

7. The three-way output switching power supply circuit according to claim 6, characterized in that: The feedback circuit includes an optocoupler DN8, resistors RN20-R25, capacitors CN13, CN13 and a reference voltage chip UN2; The primary side of the optocoupler DN8 is connected in parallel with the resistor RN21, one end of the parallel resistor RN21 is connected in series with the resistor RN20, and the resistor RN20 outputs the first power supply; The other end of the parallel resistor RN21 is connected to the input end of the reference voltage chip UN2 and the resistor RN24 respectively; The output end of the reference voltage chip UN2 is connected to GND; the resistor RN24 is connected in series with the capacitor CN14, and the capacitor CN14 is electrically connected to the resistor R23, the resistor R25 and the reference end of the reference voltage chip UN2 respectively; the resistor R25 is connected to GND; the resistors R23 and R22 are connected in series and then connected to the first power supply.

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