Functional circuit conforming to starting of large capacitive load

By designing power conversion, PWM control, and sampling feedback circuits, the problem of the power supply of the distribution automation remote terminal unit (DTU/FTU) being unable to quickly respond to large capacitive loads after AC power failure was solved, short-circuit protection was achieved, and the safety and fast response capability of the power supply were improved.

CN223729633UActive Publication Date: 2025-12-26WUHAN CINTONLE POWER SUPPLY TECH
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Patent Information

Application Number
CN202423093570.8
Authority / Receiving Office
CN · China
Patent Type
Utility models(China)
Current Assignee / Owner
Filing Date
2024-12-16
Publication Date
2025-12-26
Estimated Expiration
2034-12-16

AI Technical Summary

Technical Problem

In the existing technology, the battery or capacitor-charged switching power supply of the distribution automation remote terminal unit (DTU/FTU) cannot respond quickly to large capacitive loads after AC power failure, resulting in a prolonged output voltage rise time, which may lead to short-circuit high current output and damage to the power supply.

Method used

Design a functional circuit that includes a power conversion circuit, a PWM control circuit, a sampling feedback circuit, and an output rectification and filtering circuit. The sampling feedback circuit collects voltage information, and the PWM control circuit adjusts the power conversion process to achieve short-circuit protection when a large capacitive load starts up.

Benefits of technology

It achieves short-circuit protection during startup of large capacitive loads, simplifies circuit structure, reduces costs, and improves the safety, reliability, and fast response capability of the power supply.

✦ Generated by Eureka AI based on patent content.

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Abstract

The utility model provides a functional circuit conforming to starting of a large capacitive load, and relates to the field of switching power supplies, and the circuit comprises a power conversion circuit, a PWM control circuit, a sampling feedback circuit and an output rectification filter circuit. The power conversion circuit is electrically connected with the PWM control circuit; the PWM control circuit is electrically connected with the sampling feedback circuit; the sampling feedback circuit is electrically connected with the output rectification filter circuit. The output rectification filter circuit is electrically connected with the power conversion circuit; the sampling feedback circuit is used for collecting voltage information of the output rectification filter circuit; and the PWM control circuit is used for adjusting the power conversion process of the power conversion circuit according to the voltage information, so that short-circuit protection during starting when the output is connected with a large capacitive load is realized. According to the utility model, short-circuit protection can be realized when the output is connected with a large capacitive load, and strict safety and reliability of the power supply can be satisfied.
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Description

TECHNICAL FIELD

[0001] The present application relates to the field of switching power supply, in particular to a functional circuit meeting the starting of large-capacity load. BACKGROUND

[0002] At present, the battery or capacitor charging type switching power supply of power distribution automation remote terminal DTU / FTU needs to have the ability to independently operate the switch to ensure that the output instantaneous large load drives the switch to remotely open and close the line when the power distribution line is under maintenance or fault, and when the AC power is lost, the super capacitor as the main backup power source can seamlessly switch to supply power to the supporting system of the power distribution automation remote terminal, ensuring that the power distribution terminal can also operate stably for a long time after the AC power is lost, realizing a series of intelligent management functions such as remote fault diagnosis, positioning, isolation, and self-recovery power supply. Since the backup super capacitor starts charging from 0V and needs tens of minutes or even hours to be fully charged, the input may be lost when the line fault occurs, and at this time, the backup super capacitor cannot maintain the normal operation and switch opening of the DTU / FTU terminal if it is not fully charged.

[0003] At present, the battery or capacitor charging type switching power supply of power distribution automation remote terminal DTU / FTU needs to have the ability to independently operate the switch to ensure that the output instantaneous large load drives the switch to remotely open and close the line when the power distribution line is under maintenance or fault, and when the AC power is lost, the super capacitor as the main backup power source can seamlessly switch to supply power to the supporting system of the power distribution automation remote terminal, ensuring that the power distribution terminal can also operate stably for a long time after the AC power is lost, realizing a series of intelligent management functions such as remote fault diagnosis, positioning, isolation, and self-recovery power supply. Since the backup super capacitor starts charging from 0V and needs tens of minutes or even hours to be fully charged, the input may be lost when the line fault occurs, and at this time, the backup super capacitor cannot maintain the normal operation and switch opening of the DTU / FTU terminal if it is not fully charged.

[0004] However, the addition of a large-capacity capacitor at the output port of the power supply will cause the output voltage rise time to be longer when the power supply starts, and when a short circuit fault occurs at the output, the long starting process will cause the power supply to be in a long-term short-circuit large-current output state, which cannot be protected immediately, and in severe cases, the power supply will overheat and be damaged.

[0005] At present, the industry adopts increasing the overcurrent capacity and heat dissipation capacity of power devices, but these solutions do not solve the problem of long-term short-circuit large-current output of the power supply, which cannot be protected immediately and damages the power supply. CONTENT OF THE UTILITY MODEL

[0006] The present application aims to solve the problem of long-term short-circuit large-current output of the power supply, which cannot be protected immediately and damages the power supply in the prior art, and provides a functional circuit meeting the starting of large-capacity load.

[0007] The above-mentioned purpose of the present application is realized by the following technical scheme:

[0008] The circuit comprises a power conversion circuit, a PWM control circuit, a sampling feedback circuit, and an output rectification and filtering circuit.

[0009] The power conversion circuit is electrically connected with the PWM control circuit; the PWM control circuit is electrically connected with the sampling feedback circuit; the sampling feedback circuit is electrically connected with the output rectification and filtering circuit; and the output rectification and filtering circuit is electrically connected with the power conversion circuit.

[0010] The sampling feedback circuit is used for collecting voltage information of the output rectification and filtering circuit.

[0011] The PWM control circuit is used for adjusting the power conversion process of the power conversion circuit according to the voltage information, so as to realize short circuit protection when the output is connected with a large capacitive load.

[0012] Optionally, the power conversion circuit comprises a transformer T1, an alternating current input end, a bridge rectifier circuit BD1, a capacitor C1, a capacitor C2, a capacitor C3, a resistor R1, a resistor R2, a resistor R3, a resistor R4, a diode D1, a diode D2 and a MOS field effect transistor Q1.

[0013] Optionally, the alternating current input end is connected with the bridge rectifier circuit BD1, and the bridge rectifier circuit BD1 is connected with the capacitor C1.

[0014] The negative electrode of the capacitor C1 is grounded, and the positive electrode of the capacitor C1 is connected with one end of the resistor R1, one end of the capacitor C2 and one end of a first coil of the transformer T1.

[0015] The negative electrode of the diode D1 is connected with the other end of the resistor R1 and the other end of the capacitor C2, and the positive electrode of the diode D1 is connected with the other end of the first coil of the transformer T1 and the drain of the MOS field effect transistor Q1.

[0016] The gate of the MOS field effect transistor Q1 is connected with one end of the resistor R4 and one end of the resistor R3.

[0017] The source of the MOS field effect transistor Q1 is connected with one end of the resistor R2, and the other end of the resistor R2 is grounded.

[0018] The positive electrode of the diode D2 is connected with one end of a second coil of the transformer T1.

[0019] The negative electrode of the diode D2 is connected with the positive electrode of a capacitor C3, and the negative electrode of the capacitor C3 is connected with the other end of the second coil of the transformer T1; and the negative electrode of the capacitor C3 is grounded.

[0020] Optionally, the output rectification and filtering circuit comprises a resistor R5, a capacitor C4, a capacitor C5, an inductor L1, a voltage output end and a diode D3.

[0021] The positive electrode of the diode D3 is connected with one end of a third coil of the transformer T1.

[0022] The other end of the third coil of the transformer T1 is connected to the negative pole of the capacitor C4, the negative pole of the capacitor C5 and the resistor R5;

[0023] The positive pole of the capacitor C4 is connected to the negative pole of the diode D3;

[0024] One end of the inductor L1 is connected to the negative pole of the diode D3, and the other end is connected to the positive pole of the capacitor C5, the other end of the resistor R5 and the voltage output end.

[0025] Optionally, the PWM control circuit comprises a reference voltage terminal Vref, an optocoupler U2, an optocoupler U3, an input voltage terminal UD+, a PWM control chip U1, a resistor R6, a resistor R7, a resistor R8, a resistor R9, a capacitor C6, a capacitor C7, a capacitor C8, a capacitor C9, a capacitor C10, a capacitor C11 and a diode D6;

[0026] The model of the PWM control chip U1 is UC3844;

[0027] The model of the optocoupler is PC817B.

[0028] Optionally, one end of the resistor R7 is connected to the source of the MOS field effect transistor Q1 in the power conversion circuit, and the other end is connected to the 3rd pin of the PWM control chip U1 and one end of the capacitor C7;

[0029] The other end of the capacitor C7, the 5th pin of the PWM control chip U1, the 2nd pin of the PWM control chip U1, one end of the capacitor C8, one end of the capacitor C9, one end of the capacitor C10 and the negative pole of the capacitor C11 are all grounded;

[0030] The 6th pin of the PWM control chip U1 is connected to the other end of the resistor R4 in the power conversion circuit;

[0031] The 7th pin of the PWM control chip U1 is connected to one end of the resistor R6, one end of the capacitor C6 and the positive pole of the capacitor C3 in the power conversion circuit; the other end of the capacitor C6 is grounded;

[0032] The other end of the capacitor C8 is connected to the 8th pin of the PWM control chip U1;

[0033] The other end of the capacitor C9 is connected to the 4th pin of the PWM control chip U1 and one end of the capacitor R9;

[0034] The other end of the capacitor C10 is connected to the 1st pin of the PWM control chip U1, the 4th pin of the optocoupler U2 and the 4th pin of the optocoupler U3;

[0035] The positive pole of the capacitor C11 is connected to the positive pole of the diode D6 and the 3rd pin of the optocoupler U3;

[0036] The other end of the resistor R8, the other end of the resistor R9, the negative pole of the diode D6 and the No. 8 pin of the PWM control chip U1 are all connected with the reference voltage terminal Vref.

[0037] The No. 3 pin of the optocoupler U2 is grounded, and the other end of the resistor R6 is connected with the input voltage terminal UD+.

[0038] Optionally, the sampling feedback circuit comprises a resistor R10, a resistor R11, a resistor R12, a resistor R13, a resistor R14, a resistor R15, a resistor R16, a capacitor C12, a stabilizing diode D7 and a stabilizing diode U4.

[0039] Optionally, one end of the resistor R10 is connected with the No. 2 pin of the optocoupler U2, and the other end of the resistor R10 is connected with one end of the resistor R11, one end of the resistor R12 and the cathode of the stabilizing diode U4.

[0040] The other end of the resistor R11 is connected with the No. 1 pin of the optocoupler U2 and the cathode of the diode D3 in the output rectification filtering circuit.

[0041] The other end of the resistor R12 is connected with one end of the capacitor C12.

[0042] The other end of the capacitor C12 is connected with one end of the resistor R13, the regulating end of the stabilizing diode U4 and one end of the resistor R14.

[0043] The other end of the resistor R14 and the anode of the stabilizing diode U4 are grounded.

[0044] The other end of the resistor R13 is connected with one end of the resistor R15 and the output voltage terminal of the output rectification filtering circuit.

[0045] The other end of the resistor R15 is connected with one end of the resistor R16 and the No. 1 pin of the optocoupler U3.

[0046] The No. 2 pin of the optocoupler U3 is connected with the other end of the resistor R16 and the cathode of the stabilizing diode D7.

[0047] The anode of the stabilizing diode D7 is grounded.

[0048] The technical scheme provided by the application has the following beneficial effects:

[0049] By using the electronic components such as the triode, the optocoupler, the resistor, the capacitor and the diode, the sampling feedback circuit and the output rectification filtering circuit are constructed, the short circuit protection when the output is connected with the large capacitive load is realized, the circuit is simple, the cost is low, and the safety and reliability of the special power supply for the power distribution terminal can be met. BRIEF DESCRIPTION OF DRAWINGS

[0050] The application will be further described below in connection with the drawings and embodiments, in which:

[0051] Figure 1 is a structural diagram of a functional circuit in accordance with the large-capacitive load starting machine in the embodiment of the application;

[0052] Figure 2 is a circuit schematic diagram of a functional circuit in accordance with the large-capacitive load starting machine in the embodiment of the application. DETAILED DESCRIPTION

[0053] In order to have a clearer understanding of the technical features, objects and effects of the application, the specific embodiments of the application will be described in detail with reference to the drawings.

[0054] The embodiment of the application provides a functional circuit in accordance with the large-capacitive load starting machine.

[0055] Please refer to Figure 1 , Figure 1 is a structural diagram of a functional circuit in accordance with the large-capacitive load starting machine in the embodiment of the application, and specifically comprises:

[0056] The circuit comprises a power conversion circuit, a PWM control circuit, a sampling feedback circuit and an output rectification and filtering circuit;

[0057] The power conversion circuit is electrically connected with the PWM control circuit; the PWM control circuit is electrically connected with the sampling feedback circuit; the sampling feedback circuit is electrically connected with the output rectification and filtering circuit; and the output rectification and filtering circuit is electrically connected with the power conversion circuit;

[0058] The sampling feedback circuit is used for collecting voltage information of the output rectification and filtering circuit;

[0059] The PWM control circuit is used for adjusting the power conversion process of the power conversion circuit according to the voltage information, so as to realize short-circuit protection when the output is connected with the large-capacitive load starting machine.

[0060] The power conversion circuit comprises a transformer T1, an alternating current input end, a bridge rectifier circuit BD1, a capacitor C1, a capacitor C2, a capacitor C3, a resistor R1, a resistor R2, a resistor R3, a resistor R4, a diode D1, a diode D2 and a MOS field effect transistor Q1.

[0061] The alternating current input end is connected with the bridge rectifier circuit BD1, and the bridge rectifier circuit BD1 is connected with the capacitor C1;

[0062] The negative electrode of the capacitor C1 is grounded, and the positive electrode of the capacitor C1 is connected with one end of the resistor R1, one end of the capacitor C2 and one end of the first coil of the transformer T1;

[0063] The negative pole of the diode D1 is connected with the other end of the resistor R1 and the other end of the capacitor C2, and the positive pole of the diode D1 is connected with the other end of the first coil of the transformer T1 and the drain of the MOS field effect transistor Q1;

[0064] The gate of the MOS field effect transistor Q1 is connected with one end of the resistor R4 and one end of the resistor R3;

[0065] The source of the MOS field effect transistor Q1 is connected with one end of the resistor R2, and the other end of the resistor R2 is grounded;

[0066] The positive pole of the diode D2 is connected with one end of the second coil of the transformer T1;

[0067] The negative pole of the diode D2 is connected with the positive pole of the capacitor C3, and the negative pole of the capacitor C3 is connected with the other end of the second coil of the transformer T1, and the negative pole of the capacitor C3 is grounded.

[0068] The output rectification filter circuit comprises a resistor R5, a capacitor C4, a capacitor C5, an inductor L1, a voltage output end and a diode D3;

[0069] The positive pole of the diode D3 is connected with one end of the third coil of the transformer T1;

[0070] The other end of the third coil of the transformer T1 is connected with the negative pole of the capacitor C4, the negative pole of the capacitor C5 and the resistor R5;

[0071] The positive pole of the capacitor C4 is connected with the negative pole of the diode D3;

[0072] One end of the inductor L1 is connected with the negative pole of the diode D3, and the other end of the inductor L1 is connected with the positive pole of the capacitor C5, the other end of the resistor R5 and the voltage output end.

[0073] The PWM control circuit comprises a reference voltage terminal Vref, an optocoupler U2, an optocoupler U3, an input voltage terminal UD+, a PWM control chip U1, a resistor R6, a resistor R7, a resistor R8, a resistor R9, a capacitor C6, a capacitor C7, a capacitor C8, a capacitor C9, a capacitor C10, a capacitor C11 and a diode D6;

[0074] The model of the PWM control chip U1 is UC3844;

[0075] The model of the optocoupler is PC817B.

[0076] One end of the resistor R7 is connected with the source of the MOS field effect transistor Q1 in the power conversion circuit, and the other end of the resistor R7 is connected with the No. 3 pin of the PWM control chip U1 and one end of the capacitor C7;

[0077] The other end of capacitor C7, pin 5 of PWM control chip U1, pin 2 of PWM control chip U1, one end of capacitor C8, one end of capacitor C9, one end of capacitor C10, and the negative terminal of capacitor C11 are all grounded.

[0078] Pin 6 of the PWM control chip U1 is connected to the other end of resistor R4 in the power conversion circuit;

[0079] Pin 7 of the PWM control chip U1 is connected to one end of resistor R6, one end of capacitor C6, and the positive terminal of capacitor C3 in the power conversion circuit; the other end of capacitor C6 is grounded.

[0080] The other end of capacitor C8 is connected to pin 8 of PWM control chip U1;

[0081] The other end of capacitor C9 is connected to pin 4 of PWM control chip U1 and one end of capacitor R9;

[0082] The other end of capacitor C10 is connected to pin 1 of PWM control chip U1, pin 4 of optocoupler U2, and pin 4 of optocoupler U3.

[0083] The positive terminal of capacitor C11 is connected to the positive terminal of diode D6 and pin 3 of optocoupler U3;

[0084] The other end of resistor R8, the other end of resistor R9, the cathode of diode D6, and pin 8 of PWM control chip U1 are all connected to the reference voltage terminal Vref;

[0085] Pin 3 of optocoupler U2 is grounded; the other end of resistor R6 is connected to the input voltage terminal UD+.

[0086] The sampling feedback circuit includes: resistors R10, R11, R12, R13, R14, R15, and R16, capacitor C12, Zener diode D7, and Zener diode U4.

[0087] One end of resistor R10 is connected to pin 2 of optocoupler U2, and the other end of resistor R10 is connected to one end of resistor R11, one end of resistor R12, and the cathode of Zener diode U4.

[0088] The other end of resistor R11 is connected to pin 1 of coupler U2 and the cathode of diode D3 in the output rectifier filter circuit;

[0089] The other end of resistor R12 is connected to one end of capacitor C12;

[0090] The other end of capacitor C12 is connected to one end of resistor R13, the adjustment terminal of Zener diode U4, and one end of resistor R14;

[0091] The other end of resistor R14 and the anode of Zener diode U4 are grounded;

[0092] The other end of resistor R13 is connected to one end of resistor R15 and the output voltage terminal of the output rectifier and filter circuit.

[0093] The other end of resistor R15 is connected to one end of resistor R16 and pin 1 of optocoupler U3;

[0094] Pin 2 of optocoupler U3 is connected to the other end of resistor R16 and the cathode of Zener diode D7;

[0095] The anode of Zener diode D7 is grounded.

[0096] As one embodiment, the circuit schematic of the functional circuit of this application is shown in Figure 2.

[0097] In one embodiment, when there is power input, the input voltage charges the VCC capacitor C6 of the PWM control chip U1 through the high-voltage start-up resistor R6. When the voltage reaches the start-up voltage of the control chip, the PWM control chip starts to work, and the output voltage begins to build up slowly. Due to the presence of C10, the voltage at pin 1 (COMP) of the control chip rises slowly, and the duty cycle of the PWM control chip output increases slowly, achieving the purpose of soft start. When C10 is fully charged, the voltage at the COMP pin reaches its maximum, and the controller continues to output at the maximum duty cycle, and the output voltage begins to rise.

[0098] In one embodiment, when the output voltage rises above the voltage of the Zener diode D7, the optocoupler U3 is turned on. The COMP pin of the PWM control chip charges the capacitor C11 through pins 3 and 4 of U3, causing the voltage at the COMP pin of the PWM control chip to enter the process of rising from low to high again, entering a working state where the duty cycle increases slowly. This prevents the controller from continuously outputting at the maximum duty cycle and stops working in the open-loop state until the output capacitor is fully charged and the output voltage rises to the normal value. This reduces the long-term open-loop operation of the power supply caused by the long output start-up time.

[0099] As one example, by adjusting the voltage regulation value of Zener diode D7 and the capacitance value of capacitor C11 according to the value of the external output capacitor, the large current when the large output capacitor starts up can be limited to a considerable range, which greatly improves the safety of the power supply when starting up with a large capacitor.

[0100] In the above embodiments, the descriptions of each embodiment have different focuses. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions in other embodiments.

[0101] The above merely is an exemplary embodiment of the present disclosure, and cannot limit the scope of the present disclosure. That is, equivalent changes and modifications made according to the teachings of the present disclosure are still within the scope of the present disclosure.

[0102] This application is intended to cover any variations, uses, or adaptations of the present disclosure following, in general, the principles of the present disclosure and including such departures from the present disclosure that come within known or customary practice within the art to which the present disclosure pertains. The specification and drawings should be considered in an illustrative rather than a restrictive sense, the scope of the present disclosure being defined by the claims.

Claims

1. A functional circuit in compliance with a function of starting a large-capacity load, characterized by comprising: The circuit comprises a power conversion circuit, a PWM control circuit, a sampling feedback circuit and an output rectification filter circuit; The power conversion circuit is electrically connected with the PWM control circuit; the PWM control circuit is electrically connected with the sampling feedback circuit; the sampling feedback circuit is electrically connected with the output rectification filter circuit; and the output rectification filter circuit is electrically connected with the power conversion circuit; The sampling feedback circuit is used for collecting voltage information of the output rectification filter circuit; The PWM control circuit is used for adjusting the power conversion process of the power conversion circuit according to the voltage information, so as to realize short circuit protection when a large capacitive load is connected to the output.

2. A functional circuit according to claim 1, wherein The power conversion circuit comprises a transformer T1, an AC input end, a bridge rectifier circuit BD1, a capacitor C1, a capacitor C2, a capacitor C3, a resistor R1, a resistor R2, a resistor R3, a resistor R4, a diode D1, a diode D2 and a MOS field effect transistor Q1.

3. A functional circuit according to claim 2, wherein The AC input end is connected with the bridge rectifier circuit BD1, and the bridge rectifier circuit BD1 is connected with the capacitor C1; The negative electrode of the capacitor C1 is grounded, and the positive electrode of the capacitor C1 is connected with one end of the resistor R1, one end of the capacitor C2 and one end of a first coil of the transformer T1; The negative electrode of the diode D1 is connected with the other end of the resistor R1 and the other end of the capacitor C2, and the positive electrode of the diode D1 is connected with the other end of the first coil of the transformer T1 and the drain of the MOS field effect transistor Q1; The gate of the MOS field effect transistor Q1 is connected with one end of the resistor R4 and one end of the resistor R3; The source of the MOS field effect transistor Q1 is connected with one end of the resistor R2, and the other end of the resistor R2 is grounded; The positive electrode of the diode D2 is connected with one end of a second coil of the transformer T1; The negative electrode of the diode D2 is connected with the positive electrode of a capacitor C3, and the negative electrode of the capacitor C3 is connected with the other end of the second coil of the transformer T1; and the negative electrode of the capacitor C3 is grounded.

4. The functional circuit according to claim 2, wherein The output rectification filter circuit comprises a resistor R5, a capacitor C4, a capacitor C5, an inductor L1, a voltage output end and a diode D3; The positive electrode of the diode D3 is connected with one end of a third coil of the transformer T1; The other end of the third coil of the transformer T1 is connected with the negative electrode of the capacitor C4, the negative electrode of the capacitor C5 and the resistor R5; The positive electrode of the capacitor C4 is connected with the negative electrode of the diode D3; One end of the inductor L1 is connected with the negative electrode of the diode D3, and the other end of the inductor L1 is connected with the positive electrode of the capacitor C5, the other end of the resistor R5 and the voltage output end.

5. A functional circuit according to claim 4, wherein The PWM control circuit comprises a reference voltage terminal Vref, an optical coupler U2, an optical coupler U3, an input voltage terminal UD+, a PWM control chip U1, a resistor R6, a resistor R7, a resistor R8, a resistor R9, a capacitor C6, a capacitor C7, a capacitor C8, a capacitor C9, a capacitor C10, a capacitor C11 and a diode D6; The model of the PWM control chip U1 is UC3844; The model of the optical coupler is PC817B.

6. A functional circuit according to claim 5, wherein One end of the resistor R7 is connected with the source of the MOS field effect transistor Q1 in the power conversion circuit, and the other end of the resistor R7 is connected with pin 3 of the PWM control chip U1 and one end of the capacitor C7; The other end of the capacitor C7, the No. 5 pin of the PWM control chip U1, the No. 2 pin of the PWM control chip U1, the one end of the capacitor C8, the one end of the capacitor C9, the one end of the capacitor C10 and the negative pole of the capacitor C11 are all grounded; The No. 6 pin of the PWM control chip U1 is connected with the other end of the resistor R4 in the power conversion circuit; The No. 7 pin of the PWM control chip U1 is connected with the one end of the resistor R6, the one end of the capacitor C6 and the positive pole of the capacitor C3 in the power conversion circuit; the other end of the capacitor C6 is grounded; The other end of the capacitor C8 is connected with the No. 8 pin of the PWM control chip U1; The other end of the capacitor C9 is connected with the No. 4 pin of the PWM control chip U1 and the one end of the capacitor R9; The other end of the capacitor C10 is connected with the No. 1 pin of the PWM control chip U1, the No. 4 pin of the photo-coupler U2 and the No. 4 pin of the photo-coupler U3; The positive pole of the capacitor C11 is connected with the positive pole of the diode D6 and the No. 3 pin of the photo-coupler U3; The other end of the resistor R8, the other end of the resistor R9, the negative pole of the diode D6 and the No. 8 pin of the PWM control chip U1 are all connected with the reference voltage terminal Vref; The No. 3 pin of the photo-coupler U2 is grounded; the other end of the resistor R6 is connected with the input voltage terminal UD+.

7. The functional circuit according to claim 5, wherein The sampling feedback circuit comprises the resistor R10, the resistor R11, the resistor R12, the resistor R13, the resistor R14, the resistor R15, the resistor R16, the capacitor C12, the stabilizing diode D7 and the stabilizing diode U4.

8. A functional circuit according to claim 7, wherein One end of the resistor R10 is connected with the No. 2 pin of the photo-coupler U2; the other end of the resistor R10 is connected with the one end of the resistor R11, the one end of the resistor R12 and the cathode of the stabilizing diode U4; The other end of the resistor R11 is connected with the No. 1 pin of the photo-coupler U2 and the cathode of the diode D3 in the output rectification filter circuit; The other end of the resistor R12 is connected with the one end of the capacitor C12; The other end of the capacitor C12 is connected with the one end of the resistor R13, the regulating end of the stabilizing diode U4 and the one end of the resistor R14; The other end of the resistor R14 and the anode of the stabilizing diode U4 are grounded; The other end of the resistor R13 is connected with the one end of the resistor R15 and the output voltage terminal of the output rectification filter circuit; The other end of the resistor R15 is connected with the one end of the resistor R16 and the No. 1 pin of the photo-coupler U3; The No. 2 pin of the photo-coupler U3 is connected with the other end of the resistor R16 and the cathode of the stabilizing diode D7; The anode of the stabilizing diode D7 is grounded.