CN216672849U - Switching power supply circuit with protection function - Google Patents

Abstract

The application relates to a switch power supply circuit with protection function, which comprises an input rectification filter circuit, a transformer and a control circuit, the power switch circuit, feedback regulation circuit and output rectification filter circuit, the primary first end of transformer is coupled in inputting rectification filter circuit, the secondary of transformer is coupled in outputting rectification filter circuit's input, output rectification filter circuit's output exports mains voltage, feedback regulation circuit's input is coupled in outputting rectification filter circuit's output, power switch circuit's output is coupled in the primary first end of transformer, control circuit includes the chip U1 that the model is PN8275, the power input end of chip U1 is coupled in the primary second end of transformer, the input of chip U1 is coupled in the output of feedback regulation circuit, the output of chip U1 is coupled in power switch circuit's input. The application has the effect of preventing the switch power supply from being damaged.

Description

Switching power supply circuit with protection function

Technical Field

The application relates to the technical field of switching power supply circuit design, in particular to a switching power supply circuit with a protection function.

Background

With the high-speed development of power electronic technology, the relationship between power electronic equipment and the work and life of people is increasingly close, the electronic equipment can not be powered by a reliable power supply, a switching power supply enters the fields of various electronic and electrical equipment, the switching power supply is widely used for a program controlled switch, a communication, an electronic detection equipment power supply, a control equipment power supply and the like, and the rapid development of the switching power supply technology is promoted.

Common switching power supplies are all voltage control type, the traditional voltage control type pulse width modulation technology has the defects of slow dynamic response, poor regulation performance and the like, and a switching tube used for pulse width modulation in a circuit is often damaged due to a voltage spike signal caused by input voltage surge. In addition, the existing switching power supply lacks current-limiting protection and overcurrent protection, so that the switching power supply is easy to damage, and certain improvement space exists.

SUMMERY OF THE UTILITY MODEL

In order to make switching power supply circuit have intelligent protection switching power supply function when operating condition, prevent that switching power supply from damaging, this application provides a switching power supply circuit with protect function.

The application provides a switching power supply circuit with protect function adopts following technical scheme:

a switch power supply circuit with protection function comprises an input rectification filter circuit, a transformer, a control circuit, a power switch circuit, a feedback regulation circuit and an output rectification filter circuit, the first end of the primary side of the transformer is coupled with the input rectifying filter circuit, the secondary side of the transformer is coupled with the input end of the output rectifying filter circuit, the output end of the output rectifying filter circuit outputs power supply voltage, the input end of the feedback regulating circuit is coupled with the output end of the output rectifying filter circuit, the output end of the power switch circuit is coupled to the first end of the primary side of the transformer, the control circuit comprises a chip U1 with the model number of PN8275, the power input terminal of the chip U1 is coupled to the second terminal of the primary side of the transformer, the input terminal of the chip U1 is coupled to the output terminal of the feedback regulation circuit, and the output terminal of the chip U1 is coupled to the input terminal of the power switch circuit.

By adopting the technical scheme, the alternating voltage is input into the input rectifying and filtering circuit to be filtered and rectified, stable high-voltage direct current voltage is formed and output to the primary side of the transformer, the voltage is converted into required voltage current of +24V/2A through the transformer and is output along with the output rectifying and filtering circuit; meanwhile, the feedback adjusting circuit receives the current output by the output rectifying and filtering circuit, the feedback adjusting circuit detects the magnitude of the output current and outputs a detection signal to the chip U1 of the control circuit, the power input end of the chip U1 inputs starting voltage through the primary second end of the transformer, the chip U1 is electrified to work, the output end of the chip U1 outputs a control signal to the power switch circuit to control the on-off of the power switch circuit and adjust the duty ratio of the primary output of the transformer, so that the aim of adjusting the output voltage and the output current is fulfilled, and when the output voltage or the output load output by the output rectifying and filtering circuit is overhigh, the chip U1 of the control circuit outputs a control signal to adjust so as to perform overvoltage protection on the power supply; when the voltage output by the output rectifying and filtering circuit is too low, the chip U1 outputs a control signal to perform undervoltage protection on the power supply, so that the intelligent protection switch power supply circuit is realized, and the switch power supply is prevented from being damaged.

Optionally, the protection circuit further comprises an electromagnetic filter circuit and a protection circuit, wherein an input end of the protection circuit is coupled to the alternating current power supply, an output end of the protection circuit is coupled to an input end of the electromagnetic filter circuit, and an output end of the electromagnetic filter circuit is coupled to an input end of the input rectification filter circuit.

By adopting the technical scheme, the protection circuit and the electromagnetic filter circuit are coupled between the input rectifying filter circuit and the alternating current power supply, so that the alternating current voltage input to the input rectifying filter circuit is more stable and safer, and the function of protecting the circuit of the switching power supply is realized.

Optionally, the protection circuit includes fuse F1, piezo-resistor RV1, first capacitor C1, adjustable resistor RT, first resistor R1 and second resistor R2, one end of piezo-resistor RV1 is coupled in series with fuse F1 and then is coupled in the live wire end of ac power supply, the other end of piezo-resistor RV1 is coupled in series with adjustable resistor RT and then is coupled in the zero line end of ac power supply, first capacitor C1 is connected in parallel at the both ends of piezo-resistor RV1, first resistor R1 and second resistor R2 are connected in series and then are all connected in parallel at the both ends of first capacitor C1.

By adopting the technical scheme, when the input alternating voltage is too high, the fuse F1 can be blown by the alternating current power supply output alternating voltage value protection circuit, so that the protection circuit is in a disconnection state, and the function of protecting the switching power supply circuit to prevent the input of the too high alternating voltage is realized.

Optionally, the electromagnetic filter circuit includes a second capacitor C2, a common-mode filter inductor L, a first zener diode D1 and a second zener diode D2, two input terminals of the common-mode filter inductor L are both coupled to the protection circuit, two output terminals of the common-mode filter inductor L are coupled to two ends of the second capacitor C2, an anode of the first zener diode D1 is coupled to one end of the second capacitor C2, a cathode of the first zener diode D1 is coupled to a cathode of the second zener diode D2, and an anode of the second zener diode D2 is coupled to the other end of the second capacitor C2.

By adopting the technical scheme, the electromagnetic demagnetization function is performed on the alternating-current voltage by arranging the second capacitor C2, the common-mode filter inductor L, the first voltage stabilizing diode D1 and the second voltage stabilizing diode D2, so that the electromagnetic interference of the alternating-current voltage input to the switching power supply circuit is reduced.

Optionally, the feedback adjusting circuit includes a detection module, a comparison module and a photoelectric coupling module, an input end of the detection module is coupled to an output end of the output rectifying and filtering circuit to receive the output voltage and the output current, an input end of the comparison module is coupled to an output end of the detection module, an output end of the comparison module is coupled to an input end of the photoelectric coupling module, and an output end of the photoelectric coupling module is coupled to an input end of the chip U1.

By adopting the technical scheme, the detection module receives the current and voltage output by the output rectifying and filtering module and outputs the current and voltage to the comparison module, the comparison module receives the current and voltage output by the detection module and compares the current and voltage to output a comparison signal, and the photoelectric coupling module outputs a feedback detection signal to the chip U1 of the control circuit when receiving the comparison signal, so that the feedback detection function of the switching power supply circuit is realized.

Optionally, the detection module includes a third resistor R3 and a fourth resistor R4, the comparison module includes a fifth resistor R5 and a third zener diode D3, the photocoupling module includes a light emitting diode D and a photoelectric switching tube Q, one end of the third resistor R3 is coupled to the output end of the output rectifying and filtering circuit, the other end of the third resistor R3 is coupled to the fourth resistor R4, the other end of the fourth resistor R4 is coupled to the fifth resistor R5, the other end of the fifth resistor R5 is grounded, a connection node between the fourth resistor R4 and the fifth resistor R5 is coupled to the reference electrode of a third zener diode D3, the anode of the third zener diode D3 is coupled to the fifth resistor R5, the cathode of the third zener diode D3 is coupled to the cathode of the light emitting diode D, the anode of the light emitting diode D is coupled to the output end of the rectifying and filtering circuit, the photo-switch tube Q is coupled to the light emitting diode D, a collector of the photo-switch tube Q is coupled to the input end of the chip U1, and an emitter of the photo-switch tube Q is grounded.

By adopting the technical scheme, the output rectifying and filtering circuit outputs the power supply current to the detection module, the detection module outputs the voltage and the current to the comparison module, the third voltage stabilizing diode D3 is conducted after receiving the voltage and the current, the light emitting diode D is conducted, the light emitting diode D emits a light signal to the photoelectric switch tube Q, the photoelectric switch tube Q is conducted after receiving the light signal output by the light emitting diode D, and the input end of the chip U1 in the control circuit receives a feedback detection signal to realize the feedback detection function.

Optionally, a clamping circuit is disposed between the input rectifying filter circuit and the transformer, an input end of the clamping circuit is coupled to an output end of the input rectifying filter circuit, and an output end of the clamping circuit is coupled to a first primary end of the transformer.

By adopting the technical scheme, the clamping circuit is used for absorbing the peak voltage of the power switch circuit, reducing the power loss of the switch power supply circuit and improving the conversion efficiency of the switch power supply circuit.

Optionally, the clamp circuit includes a fourth zener diode D4, a sixth resistor R6, a third capacitor C3, a seventh resistor R7 and a diode D5, an anode of the fourth zener diode D4 is coupled to the output end of the input rectification filter circuit, a cathode of the fourth zener diode D4 is coupled to the sixth resistor R6, the other end of the sixth resistor R6 is coupled to an anode of the fourth zener diode D4, the third capacitor C3 is connected in parallel to two ends of the sixth resistor R6, one end of the seventh resistor R7 is coupled to the third capacitor C3, the other end of the seventh resistor R7 is coupled to a cathode of the diode D5, and an anode of the diode D5 is coupled to the first end of the primary side of the transformer.

By adopting the technical scheme, the peak voltage of the power switching circuit is absorbed through the sixth resistor R6, the third capacitor C3, the seventh resistor R7 and the diode D5, so that the conversion loss of the switching power supply circuit is reduced, and the voltage conversion rate of the switching power supply circuit is improved.

In summary, the present application includes at least one of the following beneficial technical effects:

1. a chip U1 of the control circuit outputs a control signal for adjustment, and overvoltage protection is carried out on a power supply; when the voltage output by the output rectifying and filtering circuit is too low, the chip U1 outputs a control signal to perform undervoltage protection on a power supply, so that the intelligent protection of a switching power supply circuit is realized, and the switching power supply is prevented from being damaged;

2. a protection circuit and an electromagnetic filter circuit are coupled between the input rectifying filter circuit and the alternating current power supply, so that the alternating current voltage input to the input rectifying filter circuit is more stable and safer, and the switching power supply circuit is further protected;

3. the clamping circuit is used for absorbing the peak voltage of the power switch circuit, reducing the power loss of the switch power supply circuit and improving the conversion efficiency of the switch power supply circuit.

Drawings

Fig. 1 is a block diagram of a switching power supply circuit having a protection function according to an embodiment of the present application.

Fig. 2 is a circuit diagram of a first part of a switching power supply circuit with a protection function according to an embodiment of the present application.

Fig. 3 is a circuit diagram of a second part of a switching power supply circuit with a protection function according to an embodiment of the present application.

Fig. 4 is a circuit diagram of a third part of a switching power supply circuit with a protection function according to an embodiment of the present application.

Description of reference numerals: 1. an input rectifying filter circuit; 2. a transformer; 3. an output rectifying filter circuit; 4. a control circuit; 5. a power switching circuit; 6. a feedback regulation circuit; 61. a detection module; 62. a comparison module; 63. a photoelectric coupling module; 7. a protection circuit; 8. an electromagnetic filter circuit; 9. a clamping circuit.

Detailed Description

The present application is described in further detail below with reference to figures 1-3.

The embodiment of the application discloses a switching power supply circuit with a protection function.

Referring to fig. 1, a switching power supply circuit having a protection function includes a protection circuit 7, an electromagnetic filter circuit 8, an input rectifying filter circuit 1, a clamp circuit 9, a transformer 2, a control circuit 4, a power switch circuit 5, a feedback regulation circuit 6, and an output rectifying filter circuit 3.

The input end of the protection circuit 7 is coupled to an alternating current power supply, the output end of the protection circuit 7 is coupled to the electromagnetic filter circuit 8, the output end of the electromagnetic filter circuit 8 is coupled to the input end of the input rectifying filter circuit 1, the output end of the input rectifying filter circuit 1 is coupled to the clamping circuit 9, the output end of the clamping circuit 9 is coupled to the primary first end of the transformer 2, the secondary end of the transformer 2 is coupled to the output rectifying filter circuit 3, the output end of the output rectifying filter circuit 3 is coupled to the feedback adjusting circuit 6, the output end of the feedback adjusting circuit 6 is coupled to the input end of the control circuit 4, the primary second end of the transformer 2 is coupled to the power supply input end of the control circuit 4, the output end of the control circuit 4 is coupled to the power switch circuit 5, and the output end of the power switch circuit 5 is coupled to the primary first end of the transformer 2.

Referring to fig. 2, the protection circuit 7 includes a fuse F1, a voltage dependent resistor RV1, a first capacitor C1, an adjustable resistor RT, a first resistor R1 and a second resistor R2, one end of the voltage dependent resistor RV1 is coupled to a live wire end of the ac power source after being connected in series with the fuse F1, the other end of the voltage dependent resistor RV1 is coupled to a neutral wire end of the ac power source after being connected in series with the adjustable resistor RT, the first capacitor C1 is connected in parallel to two ends of the voltage dependent resistor RV1, one end of the first resistor R1 is coupled to the first capacitor C1, the other end of the first resistor R1 is coupled to the second resistor R2, and the other end of the second resistor R2 is coupled to the first capacitor C1.

The electromagnetic filter circuit 8 includes a second capacitor C2, a common-mode filter inductor L, a first zener diode D1 and a second zener diode D2, the common-mode filter inductor L includes a first input end and a second input end, the first input end of the common-mode filter inductor L is coupled to a connection node between the first resistor R1 and the first capacitor C1, the second input end of the common-mode filter inductor L is coupled to a connection node between the second resistor R2 and the first capacitor C1, an output end of the common-mode filter inductor L is connected in series with the second capacitor C2, an anode of the first zener diode D1 is coupled to a connection node between the common-mode filter inductor L and the second capacitor C2, a cathode of the first zener diode D1 is coupled to a cathode of the second zener diode D2, and an anode of the second zener diode D2 is coupled to a connection node between the common-mode filter inductor L and the second capacitor C2.

The input rectifying and filtering circuit 1 includes a diode D6, a diode D7, a diode D8, a diode D9, and a fourth capacitor C4, wherein a cathode of the diode D6 is coupled to an anode of the diode D7, a cathode of the diode D7 is coupled to a cathode of the diode D8, an anode of the diode D8 is coupled to a cathode of the diode D9, an anode of the diode D9 is coupled to an anode of the diode D6, a connection node between the diode D6 and the diode D7 is coupled to an anode of the first zener diode D1, a connection node between the diode D8 and the diode D9 is coupled to an anode of the second zener diode D2, a connection node between the diode D7 and the diode D8 is coupled to one end of the fourth capacitor C4, and the other end of the fourth capacitor C4 is coupled to a connection node between the diode D6 and the diode D9.

Referring to fig. 3, the clamp circuit 9 includes a fourth zener diode D4, a sixth resistor R6, a third capacitor C3, a seventh resistor R7 and a diode D5, an anode of the fourth zener diode D4 is coupled to the fourth capacitor C4 and a connection node between the diode D7 and the diode D8, a cathode of the fourth zener diode D4 is coupled to the seventh resistor R7, the other end of the seventh resistor R7 is coupled to a cathode of the diode D5, an anode of the diode D5 is coupled to the first end of the primary winding of the transformer 2, the sixth resistor R6 is connected across the fourth zener diode D4 in parallel, and the third capacitor C3 is connected across the sixth resistor R6 in parallel.

The control circuit 4 comprises a chip U1 with the model number PN8275, the chip U1 comprises eight pins, and the sixth pin of the chip U1 is a power input terminal. The sixth pin of the chip U1 is coupled to the second terminal of the primary of the transformer 2. The second pin of the chip U1 is an input terminal, and the fifth pin of the chip U1 is an output terminal. The first pin of the chip U1 is coupled to a fifth capacitor C5, and the other end of the fifth capacitor C5 is coupled to the second end of the primary side of the transformer 2. An eighth resistor R8 is connected in parallel to two ends of the fifth capacitor C5, a sixth capacitor C6 is coupled to one end of the eighth resistor R8, the other end of the sixth capacitor C6 is coupled to the sixth pin of the chip U1, a seventh capacitor C7 is coupled to a connection node between the sixth capacitor C6 and the eighth resistor R8, the other end of the seventh capacitor C7 is coupled to a connection node between the sixth capacitor C6 and the sixth pin of the chip U1, one end of a connection node between the seventh capacitor C7 and the sixth capacitor C6 is coupled to the second end of the primary of the transformer 2, a diode D10 is coupled to the other end of the connection node between the seventh capacitor C7 and the sixth capacitor C6, an eighth resistor R8 is connected in series to an anode of the diode D10, the other end of the eighth resistor R8 is coupled to the second end of the primary of the transformer 2, a ninth resistor R9 is coupled to a connection node between the eighth resistor R8 and the second end of the second terminal of the primary of the transformer 2, and the ninth resistor R1 is coupled to the chip U1. The fifth pin of the chip U1 is coupled to the power switch circuit 5. The second pin of the chip U1 is connected in series with an eleventh resistor R11 and then coupled to the feedback regulation circuit 6, one end of the eleventh resistor R11 is coupled to the eighth capacitor C8, and the other end of the eighth capacitor C8 is grounded. A ninth capacitor C9 is coupled to a third pin of the chip U1, the other end of the ninth capacitor C9 is grounded, a twelfth resistor R12 is coupled to a connection node between the third pin of the chip U1 and the ninth capacitor C9, a thirteenth resistor R13 is coupled to the other end of the twelfth resistor R12, a fourteenth resistor R14 is connected to two ends of the thirteenth resistor R13 in parallel, and a fifteenth resistor R15 is connected to two ends of the fourteenth resistor R14 in parallel. The fourth pin of chip U1 is connected to ground. The eighth pin of the chip U1 is coupled to a sixteenth resistor R16, and the other end of the sixteenth resistor R16 is coupled to a connection node between the first zener diode D1 and the second zener diode D2.

The power switch circuit 5 includes a MOS transistor Q1, a seventeenth resistor R17, an eighteenth resistor R18, a nineteenth resistor R19 and a diode D11, a G pole of the MOS transistor Q1 is coupled to the eighteenth resistor R18, the other end of the eighteenth resistor R18 is coupled to the nineteenth resistor R19, the other end of the nineteenth resistor R19 is coupled to the fifth pin of the chip U1, an anode of the diode D11 is coupled to the G pole of the MOS transistor, a cathode of the diode D11 is coupled to a connection node between the eighteenth resistor R18 and the nineteenth resistor R19, an S pole of the MOS transistor Q1 is coupled to the seventeenth resistor R17, the other end of the seventeenth resistor R17 is coupled to the eighteenth resistor R18, a connection node between the S pole of the MOS transistor Q1 and the seventeenth resistor R17 is coupled to the fifteenth resistor R15, and a D pole of the MOS transistor Q1 is coupled to a first end of the primary winding of the transformer 2.

A tenth capacitor C10 is coupled to a first end of the primary side of the transformer 2, an eleventh capacitor C11 is coupled to the other end of the tenth capacitor C10, and the other end of the eleventh capacitor C11 is coupled to the secondary side of the transformer 2.

Referring to fig. 4, the output rectifying and filtering circuit 3 includes a schottky diode D12, an anode of the schottky diode D12 is coupled to the secondary side of the transformer 2, an anode of the schottky diode D12 is further coupled with a twentieth resistor R20, the other end of the twentieth resistor R20 is coupled with a twelfth capacitor C12, the other end of the twelfth capacitor C12 is coupled to a cathode of the schottky diode D12, and two ends of the twentieth resistor R20 are connected in parallel with a twenty-first resistor R21. The cathode of the schottky diode D12 is further coupled to an inductor L1, the other end of the inductor L1 is coupled to a twenty-second resistor R22, the other end of the twenty-second resistor R22 is coupled to the secondary side of the transformer 2, a connecting node between the cathode of the schottky diode D12 and the inductor L1 is coupled to a thirteenth capacitor C13, the other end of the thirteenth capacitor C13 is coupled to the secondary side of the transformer 2, a connecting node between the inductor L1 and the twenty-second resistor R22 is coupled to a fourteenth capacitor C14, the other end of the fourteenth capacitor C14 is coupled to the secondary side of the transformer 2, and a fifteenth capacitor C15 is connected in parallel to two ends of the fourteenth capacitor C14. The cathode of the schottky diode D12 outputs a +24V/2A voltage current.

The feedback regulating circuit 6 comprises a detection module 61, a comparison module 62 and a photoelectric coupling module 63, wherein the input end of the detection module 61 is coupled to the output end of the output rectifying and filtering circuit 3, the input end of the comparison module 62 is coupled to the output end of the detection module 61, the output end of the comparison module 62 is coupled to the input end of the photoelectric coupling module 63, and the output end of the photoelectric coupling module 63 is coupled to the input end of a chip U1 of the control circuit 4.

The detection module 61 includes a third resistor R3 and a fourth resistor R4, the comparison module 62 includes a fifth resistor R5 and a third zener diode D3, the photocoupling module 63 includes a light emitting diode D and a photo switch Q, one end of the third resistor R3 is coupled to a connection node between a fourteenth capacitor C14 and a fifteenth capacitor C15, the other end of the third resistor R3 is coupled to the fourth resistor R4, the other end of the fourth resistor R4 is coupled to the fifth resistor R5, the other end of the fifth resistor R5 is coupled to an anode of the third zener diode D3, a connection node between the fourth resistor R4 and the fifth resistor R5 is coupled to a reference electrode of the third zener diode D3, a cathode of the third zener diode D3 is coupled to a cathode of the light emitting diode D, an anode of the light emitting diode D is coupled to a twenty-fifth resistor R25, and the other end of the twenty-fifth resistor R25 is coupled to a connection node between the schottky diode D12 and the thirteenth capacitor C13. A twenty-fourth resistor R24 is connected in parallel to two ends of the led D, a sixteenth capacitor C16 is coupled to a connection node between the third zener diode D3 and the led D, a twenty-third resistor R23 is coupled to the other end of the sixteenth capacitor C16, and the other end of the twenty-third resistor R23 is coupled to a reference electrode of the third zener diode D3.

The implementation principle of the switching power supply circuit with the protection function in the embodiment of the application is as follows:

the alternating voltage is input into the input rectifying and filtering circuit 1 for filtering and rectifying to form stable high-voltage direct voltage which is output to the primary side of the transformer 2, converted into the required voltage current of +24V/2A through the transformer 2 and output along with the output rectifying and filtering circuit 3; meanwhile, the detection module 61 of the feedback regulation circuit 6 receives the current output by the output rectifying and filtering circuit 3 and outputs the current to the comparison module 62, the comparison module 62 outputs a comparison signal to the photoelectric coupling module 63, when the photoelectric coupling module 63 receives the comparison signal, the light emitting diode D emits a light signal to the photoelectric switching tube Q, the photoelectric switching tube Q is turned on, the second pin of the chip U1 receives a feedback detection signal, the feedback regulation circuit 6 detects the magnitude of the output current and outputs a detection signal to the chip U1 of the control circuit 4, the sixth pin of the chip U1 inputs a starting voltage through the second end of the primary side of the transformer 2, the chip U1 is powered on to work, the fifth pin of the chip U1 outputs a control signal to the power switching circuit 5 to control the on-off of the MOS tube Q1 and regulate the duty ratio of the primary output of the transformer 2, so as to achieve the purpose of regulating the output voltage and current, when the voltage output by the output rectifying and filtering circuit 3 or the output load is too high, a control signal is output by a chip U1 of the control circuit 4 for adjustment, and overvoltage protection is carried out on the power supply; when the voltage output by the output rectifying and filtering circuit 3 is too low, the chip U1 outputs a control signal to perform undervoltage protection on the power supply, so that the intelligent protection switch power supply circuit is realized, and the switch power supply is prevented from being damaged.

When the alternating voltage input into the switching power supply circuit is too large, the fuse in the protection circuit 7 is cut off in time, so that the input of the alternating voltage is cut off, and the switching power supply circuit is prevented from being damaged.

The above are preferred embodiments of the present application, and the scope of protection of the present application is not limited thereto, so: equivalent changes in structure, shape and principle of the present application shall be covered by the protection scope of the present application.

Claims (8)

1. A switching power supply circuit with a protection function is characterized in that: including input rectifier filter circuit (1), transformer (2), control circuit (4), power switch circuit (5), feedback regulating circuit (6) and output rectifier filter circuit (3), the elementary first end of transformer (2) is coupled in input rectifier filter circuit (1), the secondary of transformer (2) is coupled in the input of output rectifier filter circuit (3), the output of output rectifier filter circuit (3) exports mains voltage, the input of feedback regulating circuit (6) is coupled in the output of output rectifier filter circuit (3), the output of power switch circuit (5) is coupled in the elementary first end of transformer (2), control circuit (4) includes the chip U1 that the model is PN8275, the power input end of chip U1 is coupled in the elementary second end of transformer (2), the input end of the chip U1 is coupled to the output end of the feedback adjusting circuit (6), and the output end of the chip U1 is coupled to the input end of the power switch circuit (5).

2. A switching power supply circuit having a protection function according to claim 1, characterized in that: still include electromagnetic filter circuit (8) and protection circuit (7), the input of protection circuit (7) is coupled in alternating current power supply, the output of protection circuit (7) is coupled in the input of electromagnetic filter circuit (8), the output of electromagnetic filter circuit (8) is coupled in the input of input rectification filter circuit (1).

3. A switching power supply circuit having a protection function according to claim 2, characterized in that: the protection circuit (7) comprises a fuse F1, a voltage dependent resistor RV1, a first capacitor C1, an adjustable resistor RT, a first resistor R1 and a second resistor R2, one end of the voltage dependent resistor RV1 is coupled to a live wire end of an alternating current power supply after being connected with the fuse F1 in series, the other end of the voltage dependent resistor RV1 is coupled to a zero line end of the alternating current power supply after being connected with the adjustable resistor RT in series, the first capacitor C1 is connected to two ends of the voltage dependent resistor RV1 in parallel, and the first resistor R1 and the second resistor R2 are connected with each other in parallel to two ends of the first capacitor C1 after being connected with each other in series.

4. A switching power supply circuit having a protection function according to claim 2, characterized in that: the electromagnetic filter circuit (8) comprises a second capacitor C2, a common-mode filter inductor L, a first zener diode D1 and a second zener diode D2, wherein two input ends of the common-mode filter inductor L are both coupled to the protection circuit (7), two output ends of the common-mode filter inductor L are coupled to two ends of the second capacitor C2, an anode of the first zener diode D1 is coupled to one end of the second capacitor C2, a cathode of the first zener diode D1 is coupled to a cathode of the second zener diode D2, and an anode of the second zener diode D2 is coupled to the other end of the second capacitor C2.

5. A switching power supply circuit having a protection function according to claim 1, characterized in that: the feedback adjusting circuit (6) comprises a detection module (61), a comparison module (62) and a photoelectric coupling module (63), wherein the input end of the detection module (61) is coupled to the output end of the output rectifying and filtering circuit (3) to receive output voltage and current, the input end of the comparison module (62) is coupled to the output end of the detection module (61), the output end of the comparison module (62) is coupled to the input end of the photoelectric coupling module (63), and the output end of the photoelectric coupling module (63) is coupled to the input end of a chip U1.

6. The switching power supply circuit with a protection function according to claim 5, characterized in that: the detection module (61) comprises a third resistor R3 and a fourth resistor R4, the comparison module (62) comprises a fifth resistor R5 and a third zener diode D3, the optical coupling module (63) comprises a light emitting diode D and an optical switch Q, one end of the third resistor R3 is coupled to the output end of the output rectifying and filtering circuit (3), the other end of the third resistor R3 is coupled to the fourth resistor R4, the other end of the fourth resistor R4 is coupled to the fifth resistor R5, the other end of the fifth resistor R5 is grounded, the connection node between the fourth resistor R4 and the fifth resistor R5 is coupled to the reference electrode of the third zener diode D3, the anode of the third zener diode D3 is coupled to the fifth resistor R5, the cathode of the third zener diode D3 is coupled to the cathode of the light emitting diode D, the anode of the light emitting diode D is coupled to the output end of the output rectifying and filtering circuit (3), the photo-switch Q is coupled to the light emitting diode D, a collector of the photo-switch Q is coupled to an input terminal of the chip U1, and an emitter of the photo-switch Q is grounded.

7. A switching power supply circuit having a protection function according to claim 1, characterized in that: a clamping circuit (9) is arranged between the input rectifying filter circuit (1) and the transformer (2), the input end of the clamping circuit (9) is coupled to the output end of the input rectifying filter circuit (1), and the output end of the clamping circuit (9) is coupled to the primary first end of the transformer (2).

8. A switching power supply circuit having a protection function according to claim 7, wherein: the clamping circuit (9) includes a fourth zener diode D4, a sixth resistor R6, a third capacitor C3, a seventh resistor R7 and a diode D5, an anode of the fourth zener diode D4 is coupled to the output end of the input rectifying filter circuit (1), a cathode of the fourth zener diode D4 is coupled to the sixth resistor R6, the other end of the sixth resistor R6 is coupled to an anode of the fourth zener diode D4, the third capacitor C3 is connected in parallel to two ends of the sixth resistor R6, one end of the seventh resistor R7 is coupled to the third capacitor C3, the other end of the seventh resistor R7 is coupled to a cathode of the diode D5, and an anode of the diode D5 is coupled to the first end of the primary side of the transformer (2).

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