CN218243340U - Switching power supply circuit - Google Patents

Abstract

The embodiment of the utility model discloses switching power supply circuit. The circuit comprises a power-on starting power supply circuit and a rectifying and filtering circuit; the power-on starting power supply circuit comprises: the circuit comprises a first resistor, a second resistor, a third resistor, a first voltage regulator tube and a triode; the first end of a second winding of the transformer is grounded, the second end of the second winding of the transformer is connected with the anode of a first diode, and the cathode of the first diode is connected with the first end of at least one third capacitor and then connected with a seventh pin of the PWM chip; the first end of the third capacitor is also connected with the emitter of the triode, and the second end of the third capacitor is grounded. The technical scheme of the utility model can improve switching power supply power-on start supply circuit's reliability, reduce starting resistance's calorific capacity and energy consumption, have very high price/performance ratio.

Description

Switching power supply circuit

Technical Field

The embodiment of the utility model provides a relate to switching power supply technical field, especially relate to a switching power supply circuit.

Background

With the development of national economy, electronic products have gone into thousands of households, each electronic product cannot leave a power supply part, particularly an electronic product powered by a power grid, and the electronic product is large in size and has high requirements on the reliability and stability of the product. Among them, the most common and critical is that the quality of the switching power supply part directly determines the quality of the product; the main reason is that starting power is directly provided for a PWM chip by a starting resistor on direct current after alternating current rectification in the market, and the starting resistor always works after starting is completed, so that the starting resistor generates heat seriously and has high energy consumption.

SUMMERY OF THE UTILITY MODEL

The utility model provides a switching power supply circuit improves switching power supply power-on start supply circuit's reliability, reduces the calorific capacity and the energy consumption of starting resistance, has very high price/performance ratio.

According to an aspect of the utility model provides a switching power supply circuit, this circuit includes: a power-on starting power supply circuit and a rectification filter circuit;

the power-on starting power supply circuit comprises: the circuit comprises a first resistor, a second resistor, a third resistor, a first voltage regulator tube and a triode; the first end of the first resistor is connected with the output end of the rectifying and filtering circuit, the second end of the first resistor is connected with the first end of the first voltage-regulator tube, the second end of the first voltage-regulator tube is grounded, the first end of the second resistor is connected with the first end of the first voltage-regulator tube, the second end of the second resistor is connected with the base electrode of the triode, the collector electrode of the triode is connected with the second end of the third resistor, and the first end of the third resistor is connected with the first end of the first resistor;

the first end of a second winding of the transformer is grounded, the second end of the second winding of the transformer is connected with the anode of a first diode, and the cathode of the first diode is connected with the first end of at least one third capacitor and then connected with a seventh pin of the PWM chip; the first end of the third capacitor is further connected with the emitter of the triode, and the second end of the third capacitor is grounded.

Optionally, the switching power supply circuit further includes a fourth resistor, a fifth capacitor, a fifth resistor, and a second diode; the first end of the first winding of the transformer is connected with the first end of the third resistor after being connected with the first ends of the fourth resistor and the fifth capacitor respectively, the second end of the fourth resistor and the second end of the fifth capacitor are connected with the first end of the fifth resistor, the second end of the fifth resistor is connected with the negative electrode of the second diode, and the positive electrode of the second diode is connected with the second end of the first winding of the transformer.

Optionally, the rectifying and filtering circuit includes: the first input end, the second input end, the first rectifier diode, the second rectifier diode, the third rectifier diode, the fourth rectifier diode, the first capacitor and the second capacitor;

the first input end is respectively connected with the cathode of the first rectifier diode and the anode of the third rectifier diode, the second input end is respectively connected with the cathode of the second rectifier diode and the anode of the fourth rectifier diode, the anode of the first rectifier diode is connected with the anode of the second rectifier diode and then grounded, the cathode of the third rectifier diode is connected with the cathode of the fourth rectifier diode and then respectively connected with the first ends of the first capacitor and the second capacitor, and the second ends of the first capacitor and the second capacitor are respectively grounded;

the switching power supply circuit further comprises a safety capacitor, the first end of the safety capacitor is connected with the first end of the first winding of the transformer, and the second end of the safety capacitor is grounded.

Optionally, the switching power supply circuit further includes a third diode, a sixth capacitor, a seventh capacitor, and a sixth resistor; a first end of a third winding of the transformer is connected with an anode of a third diode, a cathode of the third diode is respectively connected with first ends of the sixth capacitor, the seventh capacitor and the sixth resistor, and second ends of the sixth capacitor, the seventh capacitor and the sixth resistor are connected with a second end of the third winding of the transformer; the second end of the sixth resistor is grounded, and the first end of the sixth resistor is used as a voltage output end to output.

Optionally, the switching power supply circuit further includes a seventh resistor, an eighth resistor, a ninth resistor, and a switching tube; a sixth pin of the PWM chip is connected to a first end of the seventh resistor, a second end of the seventh resistor is connected to a gate of the switching tube, a drain of the switching tube is connected to an anode of the second diode, a first end of the eighth resistor is connected to the gate of the switching tube, a second end of the eighth resistor is connected to the drain of the switching tube, the drain of the switching tube is connected to a first end of the ninth resistor, and a second end of the ninth resistor is grounded.

Optionally, an eighth pin of the PWM chip is output as a reference voltage output terminal, and a fifth pin of the PWM chip is grounded.

Optionally, the switching power supply circuit further includes an optocoupler, a tenth resistor, a second voltage regulator tube, an eighth capacitor, an eleventh resistor, and a twelfth resistor; the optocoupler comprises a phototriode and a light-emitting diode, the negative electrode of the light-emitting diode is grounded, the positive electrode of the light-emitting diode is connected with the first end of the tenth resistor, the second end of the tenth resistor is connected with the positive electrode of the second voltage-stabilizing tube, and the negative electrode of the second voltage-stabilizing tube is connected with the voltage output end;

a collector of the phototriode is connected with a first end of the eighth capacitor and then connected with the reference voltage output end, a second end of the eighth capacitor is grounded, an emitter of the phototriode is connected with a first end of the eleventh resistor, and a second end of the eleventh resistor is grounded; and an emitter of the phototriode is connected with a first end of the twelfth resistor, and a second end of the twelfth resistor is connected with a second pin of the PWM chip.

Optionally, the switching power supply circuit further includes a thirteenth resistor and a ninth capacitor; and a first pin of the PWM chip is respectively connected with the thirteenth resistor and a first end of the ninth capacitor, and a second end of the thirteenth resistor and a second end of the ninth capacitor are connected with a second pin of the PWM chip.

Optionally, the switching power supply circuit further includes a tenth capacitor and a fourteenth resistor; a third pin of the PWM chip is connected to a first end of the tenth capacitor, a second end of the tenth capacitor is grounded, a first end of the tenth capacitor is connected to a first end of the fourteenth resistor, and a second end of the fourteenth resistor is connected to the ninth resistor.

Optionally, the switching power supply circuit further includes an eleventh capacitor and a fifteenth resistor; a fourth pin of the PWM chip is connected to the eleventh capacitor and a first end of the fifteenth resistor, a second end of the eleventh capacitor is grounded, and a second end of the fifteenth resistor is connected to the reference voltage output terminal.

According to the technical scheme of the embodiment, the power supply control circuit for the power-on starting of the switching power supply is formed by utilizing the two resistors, the voltage stabilizing tube and the triode, the problems of low reliability, serious heating and high energy consumption of the power supply circuit for the power-on starting in the prior art are solved, the reliability of the power supply circuit for the power-on starting of the switching power supply is improved, the heating amount and the energy consumption of the starting resistors are reduced, and the high cost performance is achieved.

It should be understood that the statements herein are not intended to identify key or critical features of any embodiment of the present invention, nor are they intended to limit the scope of the invention. Other features of the present invention will become apparent from the following description.

Drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the description of the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without creative efforts.

Fig. 1 is a schematic circuit diagram of a switching power supply circuit according to an embodiment of the present invention;

fig. 2 is a schematic circuit diagram of another switching power supply circuit provided according to an embodiment of the present invention;

fig. 3 is a schematic circuit diagram of another switching power supply circuit according to an embodiment of the present invention.

Detailed Description

In order to make the technical solutions of the present invention better understood, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments in the present invention, all other embodiments obtained by a person skilled in the art without creative efforts shall belong to the protection scope of the present invention.

It should be noted that the terms "first," "second," and the like in the description and claims of the present invention and in the drawings described above are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used is interchangeable under appropriate circumstances such that the embodiments of the invention described herein are capable of operation in sequences other than those illustrated or otherwise described herein. Furthermore, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed, but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.

Fig. 1 is a schematic circuit diagram of a switching power supply circuit according to the embodiment of the present invention, referring to fig. 1, the embodiment of the present invention provides a switching power supply circuit, which includes: a power-on starting power supply circuit 10 and a rectification filter circuit 20; the power-on startup power supply circuit 10 includes: the circuit comprises a first resistor R4, a second resistor R3, a third resistor R2, a first voltage regulator tube Z2 and a triode Q3; the first end of a first resistor R4 is connected with the output end of the rectification filter circuit 20, the second end of the first resistor R4 is connected with the first end of a first voltage-regulator tube Z2, the second end of the first voltage-regulator tube Z2 is grounded, the first end of a second resistor R3 is connected with the first end of the first voltage-regulator tube Z2, the second end of the second resistor R3 is connected with the base electrode of a triode Q3, the collector electrode of the triode Q3 is connected with the second end of a third resistor R2, and the first end of the third resistor R2 is connected with the first end of the first resistor R4; the transformer 30 and the PWM chip U1 are further included, a first end of a second winding N2 of the transformer 30 is grounded, a second end of the second winding N2 of the transformer 30 is connected with an anode of a first diode D3, and a cathode of the first diode D3 is connected with a first end of at least one third capacitor C7 and then connected with a seventh pin 7 of the PWM chip U1; the first end of the third capacitor C7 is further connected to the emitter of the transistor Q3, and the second end of the third capacitor C7 is grounded.

Specifically, the ac power is rectified by a rectifier bridge in the rectifier and filter circuit 20, filtered by a filter capacitor, and then output as the dc power through the output terminal. The positive electrode of the direct current output by the output end of the rectifying and filtering circuit 20 reaches the collector electrode of the triode Q3 through the third resistor R2, the positive electrode voltage 12V of the first voltage-regulator tube Z2 reaches the negative electrode of the direct current through the first resistor R4-12V voltage-regulator tube Z2, the positive electrode voltage 12V of the first voltage-regulator tube Z2 reaches the base electrode of the triode Q3 through the second resistor R3, the emitter electrode of the triode Q3 is 0V when the power-on is carried out, the base electrode voltage of the triode Q3 is greater than the collector electrode voltage by 0.6V, the collector electrode and the emitter electrode of the triode Q3 are conducted, the emitter electrode of the triode Q3 supplies 11.4V power to the seventh pin 7 of the PWM chip U1, and the PWM chip U1 starts to work.

The third resistor R2 is a starting resistor, the first resistor R4 is a current-limiting resistor, the first voltage-stabilizing tube Z2 is a 12V voltage-stabilizing tube, the PWM chip U1 is of a model UC3842 and is provided with 8 pins, and the seventh pin of the PWM chip U1 is a power pin.

After the PWM chip U1 normally works, the second end of the second winding N2 of the transformer 30 is rectified by the first diode D3, and after being filtered by the third capacitor C7 and the fourth capacitor C8, a voltage of 15V is obtained, and the seventh pin 7 of the PWM chip U1 is continuously supplied with power; at this time, the voltage of the emitting electrode of the triode Q3 is 15V, the voltage of the base electrode of the triode Q3 is 12V, the voltage of the base electrode of the triode Q3 is smaller than the voltage of the emitting electrode, the collecting electrode and the emitting electrode of the triode Q3 are not conducted, and no current flows through the third resistor R2, so that the starting resistor does not generate heat, the energy consumption can be reduced, and the power-on starting of the switching power supply is completed.

Fig. 1 exemplarily shows a case where the third capacitor C7 and the fourth capacitor C8 coexist, a first terminal of the fourth capacitor C8 is connected to a first terminal of the third capacitor C7 and then connected to an emitter of the transistor Q3, and a second terminal of the fourth capacitor C8 is connected to a second terminal of the third capacitor C7 and then grounded. The third capacitor C7 and the fourth capacitor C8 are both filter capacitors, and continuously provide stable voltage for the seventh pin 7 of the PWM chip U1.

According to the technical scheme of the embodiment, the power supply control circuit for the power-on starting of the switching power supply is formed by utilizing the two resistors, the voltage stabilizing tube and the triode, the problems of low reliability, serious heating and high energy consumption of the power supply circuit for the power-on starting in the prior art are solved, the reliability of the power supply circuit for the power-on starting of the switching power supply is improved, the heating amount and the energy consumption of the starting resistors are reduced, and the high cost performance is achieved.

With continued reference to fig. 1, optionally, the switching power supply circuit further includes a fourth resistor R1, a fifth capacitor C3, a fifth resistor R16, and a second diode D2; a first end of a first winding N1 of the transformer 30 is connected to first ends of a fourth resistor R1 and a fifth capacitor C3 respectively and then to a first end of a third resistor R2, second ends of the fourth resistor R1 and the fifth capacitor C3 are connected to a first end of a fifth resistor R16, a second end of the fifth resistor R16 is connected to a cathode of a second diode D2, and an anode of the second diode D2 is connected to a second end of the first winding N1 of the transformer 30.

Specifically, the fifth capacitor C3 is a voltage stabilizing capacitor, and the fourth resistor R1 and the fifth resistor R16 are voltage dividing resistors.

Fig. 2 is a schematic circuit diagram of another switching power supply circuit provided in accordance with an embodiment of the present invention, and referring to fig. 2, optionally, the rectifying and filtering circuit 20 includes: the circuit comprises a first input end L, a second input end N, a first rectifying diode VD1, a second rectifying diode VD2, a third rectifying diode VD3, a fourth rectifying diode VD4, a first capacitor C1 and a second capacitor C2; the first input end L is respectively connected with the cathode of the first rectifying diode VD1 and the anode of the third rectifying diode VD3, the second input end N is respectively connected with the cathode of the second rectifying diode VD2 and the anode of the fourth rectifying diode VD4, the anode of the first rectifying diode VD1 is connected with the anode of the second rectifying diode VD2 and then grounded, the cathode of the third rectifying diode VD3 is connected with the cathode of the fourth rectifying diode VD4 and then respectively connected with the first ends of the first capacitor C1 and the second capacitor C2, and the second ends of the first capacitor C1 and the second capacitor C2 are respectively grounded; the switching power supply circuit further comprises a safety regulation capacitor CY1, wherein a first end of the safety regulation capacitor CY1 is connected with a first end of a first winding N1 of the transformer 30, and a second end of the safety regulation capacitor CY1 is grounded.

Specifically, alternating current enters from a first input end L and a second input end N, is rectified by a rectifier bridge, and becomes direct current after being filtered by a first capacitor C1 and a second capacitor C2. The rectifier bridge is composed of a first rectifier diode VD1, a second rectifier diode VD2, a third rectifier diode VD3 and a fourth rectifier diode VD4, and the rectifier bridge is used for converting alternating current into unidirectional pulsating direct current. The first capacitor C1 and the second capacitor C2 are both filter capacitors for filtering out ac components, so that the output dc power is smoother. The filter capacitor reduces alternating current components in pulsating direct current voltage as much as possible, and keeps direct current components thereof, so that the ripple factor of the output voltage is reduced, and the waveform becomes smoother. First ends of the first capacitor C1 and the second capacitor are connected to serve as an output end of the rectifying and filtering circuit 20. The safety capacitor CY1 is a Y capacitor and can filter common-mode interference signals.

With continued reference to fig. 2, optionally, the switching power supply circuit further includes a third diode D1, a sixth capacitor C6, a seventh capacitor C4, and a sixth resistor R5; a first end of a third winding N3 of the transformer 30 is connected with an anode of a third diode D1, a cathode of the third diode D1 is respectively connected with first ends of a sixth capacitor C6, a seventh capacitor C4 and a sixth resistor R5, and second ends of the sixth capacitor C6, the seventh capacitor C4 and the sixth resistor R5 are connected with a second end of the third winding N3 of the transformer 30; the second end of the sixth resistor R5 is grounded, and the first end of the sixth resistor R5 is output as the voltage output terminal VCC.

Specifically, a first end of the third winding N3 of the transformer 30 forms a direct current through the third diode D1, the sixth capacitor C6, the seventh capacitor C4, and the sixth resistor R5, and outputs the direct current through the voltage output terminal VCC. The third diode D1 is a rectifier diode, the sixth capacitor C6 and the seventh capacitor C4 are filter capacitors, and the sixth resistor R5 is a voltage dividing resistor.

Fig. 3 is a schematic circuit diagram of another switching power supply circuit provided in accordance with an embodiment of the present invention, and referring to fig. 3, optionally, the switching power supply circuit further includes a seventh resistor R8, an eighth resistor R10, a ninth resistor R12, and a switching tube Q2; the sixth pin 6 of the PWM chip U1 is connected to the first end of the seventh resistor R8, the second end of the seventh resistor R8 is connected to the gate of the switching tube Q2, the drain of the switching tube Q2 is connected to the anode of the second diode D2, the first end of the eighth resistor R10 is connected to the gate of the switching tube Q2, the second end of the eighth resistor R10 is connected to the drain of the switching tube Q2, the drain of the switching tube Q2 is connected to the first end of the ninth resistor R12, and the second end of the ninth resistor R12 is grounded.

Specifically, the sixth pin 6 of the PWM chip U1 is used to drive the switching tube Q2, the sixth pin 6 of the PWM chip U1 outputs a square wave to the gate of the switching tube Q2 through the seventh resistor R8 to turn on the switching tube Q2, the drain of the switching tube Q2 passes through the first winding N1 of the transformer 30 to the positive electrode of the direct current, the source of the switching tube Q2 passes through the ninth resistor R12 to the negative electrode of the direct current, and the ninth resistor R12 is a current sampling resistor. A current signal flowing through the switching tube Q2 is fed back to a third pin 3 of the PWM chip U1 through a fourteenth resistor R11 and a tenth capacitor C12, and the third pin 3 is a current feedback input pin; and when the voltage of the current feedback input pin of the PWM chip U1 exceeds the threshold value inside the PWM chip U1, closing the sixth pin 6 of the PWM chip U1 and stopping outputting the square wave. Otherwise, the sixth pin 6 of the PWM chip U1 is not turned off, and the square wave continues to be output. When the sixth pin 6 of the PWM chip U1 outputs a square wave to control the on and off of the switching tube Q2 through the seventh resistor R8, the second winding N2 of the transformer 30 forms a direct current after being rectified by the first diode D3 and filtered by the third capacitor C7 and the fourth capacitor C8 to provide a stable power supply voltage to the seventh pin 7 of the PWM chip U1.

With continued reference to fig. 3, optionally, the eighth pin 8 of the PWM chip U1 is output as the reference voltage output REF, and the fifth pin 5 of the PWM chip U1 is grounded.

Specifically, the eighth pin 8 of the PWM chip U1 outputs a 5V reference voltage, and the reference voltage output terminal REF is configured to provide a charging current to the eleventh capacitor C11 through the fifteenth resistor R9. The fifth pin 5 of the PWM chip U1 is a common ground. The fifteenth resistor R9 is a timing resistor, and the capacitor C11 is an oscillator timing capacitor.

With continued reference to fig. 3, optionally, the switching power supply circuit further includes an optocoupler U2, a tenth resistor R13, a second voltage regulator tube Z1, an eighth capacitor C9, an eleventh resistor R15, and a twelfth resistor R14; the optocoupler U2 comprises a phototriode Q1 and a light emitting diode LED, the cathode of the light emitting diode LED is grounded, the anode of the light emitting diode LED is connected with the first end of a tenth resistor R13, the second end of the tenth resistor R13 is connected with the anode of a second voltage-regulator tube Z1, and the cathode of the second voltage-regulator tube Z1 is connected with a voltage output end VCC; a collector of the phototriode Q1 is connected with a first end of an eighth capacitor C9 and then connected with a reference voltage output end REF, a second end of the eighth capacitor C9 is grounded, an emitter of the phototriode Q1 is connected with a first end of an eleventh resistor R15, and a second end of the eleventh resistor R15 is grounded; an emitter of the phototransistor Q1 is connected to a first end of a twelfth resistor R14, and a second end of the twelfth resistor R14 is connected to a second pin 2 of the PWM chip U1.

Specifically, direct current formed by the third diode D1, the sixth capacitor C6, the seventh capacitor C4 and the sixth resistor R5 reaches the light emitting diode LED in the optocoupler U2 through the second voltage regulator tube Z1 and the tenth resistor R13. When the direct current output by the voltage output end VCC is larger than the voltage stabilizing value of the second voltage stabilizing tube Z1, the light emitting diode LED in the optocoupler U2 is conducted to emit light, and the phototriode Q1 is conducted after receiving the light. The collector of the phototriode Q1 is connected with a reference voltage output end REF of an eighth pin 8 of the PWM chip U1, and the emitting end of the optocoupler U2 is connected to the negative electrode of the direct current through an eleventh resistor R15.

When a phototriode Q1 in the optocoupler U2 receives light, a collector and an emitter of the phototriode Q1 are conducted, a high level voltage on an eleventh resistor R15 passes through a twelfth resistor R14 to a second pin 2 of the PWM chip U1, the second pin 2 is a voltage feedback input pin, a PI ring of a voltage feedback loop is formed by a thirteenth resistor R7 and a ninth capacitor C10 to the first pin 1 of the PWM chip U1, and square wave output of a sixth pin 6 of the PWM chip U1 is closed; when the direct current output by the voltage output end VCC is lower than the voltage stabilization value of the second voltage-stabilizing tube Z1, the voltage feedback loop of the PWM chip U1 can not close the square wave output of the sixth pin 6 of the PWM chip U1.

With continued reference to fig. 3, optionally, the switching power supply circuit further includes a thirteenth resistor R7 and a ninth capacitor C10; the first pin 1 of the PWM chip U1 is connected to the first ends of the thirteenth resistor R7 and the ninth capacitor C10, and the second ends of the thirteenth resistor R7 and the ninth capacitor C10 are connected to the second pin 2 of the PWM chip U1.

Specifically, a first pin 1 of the PWM chip U1 is an output pin of the error amplifier, and an external resistor-capacitor element is used to improve the gain and frequency characteristics of the error amplifier; the second pin 2 of the PWM chip U1 is a feedback voltage input pin, and the voltage of this pin is compared with the 2.5V reference voltage at the non-inverting terminal of the error amplifier to generate an error voltage, thereby controlling the pulse width.

With continued reference to fig. 3, optionally, the switching power supply circuit further includes a tenth capacitor C12 and a fourteenth resistor R11; the third pin 3 of the PWM chip U1 is connected to the first end of the tenth capacitor C12, the second end of the tenth capacitor C12 is grounded, the first end of the tenth capacitor C12 is connected to the first end of the fourteenth resistor R11, and the second end of the fourteenth resistor R11 is connected to the ninth resistor R13.

Specifically, the third pin 3 of the PWM chip U1 is a current sensing pin of the first winding N1 of the transformer 30, and when the detected voltage exceeds 1V, the pulse width can be reduced to make the switching power supply in an intermittent operation state. The in-phase input end of a comparator in the PWM chip U1 is compared with a signal of an output signal of the error amplifier after voltage division through a diode and a resistor, and the PWM latch is controlled to output a low level to close the MOS transistor. A current sensing resistor is connected in series with the pin to the ground, so that the current can be converted into voltage, and the PWM chip U1 works in a voltage mode control state.

With continued reference to fig. 3, optionally, the switching power supply circuit further includes an eleventh capacitor C11 and a fifteenth resistor R9; the fourth pin 4 of the PWM chip U1 is connected to the eleventh capacitor C11 and the first end of the fifteenth resistor R9, the second end of the eleventh capacitor C11 is grounded, and the second end of the fifteenth resistor R9 is connected to the reference voltage output terminal REF.

Specifically, the fifteenth resistor R9 is a timing resistor, and the eleventh capacitor C11 is a timing capacitor. The fourth pin 4 of the PWM chip U1 is an oscillator fixed frequency setting pin. By setting the charging and discharging time of the fifteenth resistor R9 or the eleventh capacitor C11, the frequency of the clock signal generated by the oscillator inside the PWM chip U1 can be changed.

It should be noted that the electrical nodes with the same labels are electrically connected, such as VCC. AGND is analog ground and GND is reference ground.

The above detailed description does not limit the scope of the present invention. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions may be made in accordance with design requirements and other factors. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (10)

1. A switching power supply circuit, comprising: a power-on starting power supply circuit and a rectification filter circuit;

the power-on starting power supply circuit comprises: the circuit comprises a first resistor, a second resistor, a third resistor, a first voltage regulator tube and a triode; the first end of the first resistor is connected with the output end of the rectifying and filtering circuit, the second end of the first resistor is connected with the first end of the first voltage-regulator tube, the second end of the first voltage-regulator tube is grounded, the first end of the second resistor is connected with the first end of the first voltage-regulator tube, the second end of the second resistor is connected with the base electrode of the triode, the collector electrode of the triode is connected with the second end of the third resistor, and the first end of the third resistor is connected with the first end of the first resistor;

the first end of a second winding of the transformer is grounded, a second end of the second winding of the transformer is connected with the anode of a first diode, and the cathode of the first diode is connected with the first end of at least one third capacitor and then connected with a seventh pin of the PWM chip; the first end of the third capacitor is also connected with the emitter of the triode, and the second end of the third capacitor is grounded.

2. The switching power supply circuit according to claim 1, further comprising a fourth resistor, a fifth capacitor, a fifth resistor, and a second diode; the first end of the first winding of the transformer is connected with the first end of the third resistor after being connected with the first ends of the fourth resistor and the fifth capacitor respectively, the second end of the fourth resistor and the second end of the fifth capacitor are connected with the first end of the fifth resistor, the second end of the fifth resistor is connected with the negative electrode of the second diode, and the positive electrode of the second diode is connected with the second end of the first winding of the transformer.

3. The switching power supply circuit according to claim 2, wherein the rectifying and filtering circuit comprises: the first input end, the second input end, the first rectifying diode, the second rectifying diode, the third rectifying diode, the fourth rectifying diode, the first capacitor and the second capacitor;

the first input end is respectively connected with the cathode of the first rectifier diode and the anode of the third rectifier diode, the second input end is respectively connected with the cathode of the second rectifier diode and the anode of the fourth rectifier diode, the anode of the first rectifier diode is connected with the anode of the second rectifier diode and then grounded, the cathode of the third rectifier diode is connected with the cathode of the fourth rectifier diode and then respectively connected with the first ends of the first capacitor and the second capacitor, and the second ends of the first capacitor and the second capacitor are respectively grounded;

the transformer further comprises a safety capacitor, the first end of the safety capacitor is connected with the first end of the first winding of the transformer, and the second end of the safety capacitor is grounded.

4. The switching power supply circuit according to claim 3, further comprising a third diode, a sixth capacitor, a seventh capacitor, and a sixth resistor; a first end of a third winding of the transformer is connected with an anode of a third diode, a cathode of the third diode is respectively connected with first ends of the sixth capacitor, the seventh capacitor and the sixth resistor, and second ends of the sixth capacitor, the seventh capacitor and the sixth resistor are connected with a second end of the third winding of the transformer; the second end of the sixth resistor is grounded, and the first end of the sixth resistor is used as a voltage output end to output.

5. The switching power supply circuit according to claim 4, further comprising a seventh resistor, an eighth resistor, a ninth resistor and a switching tube; a sixth pin of the PWM chip is connected to a first end of the seventh resistor, a second end of the seventh resistor is connected to a gate of the switching tube, a drain of the switching tube is connected to an anode of the second diode, a first end of the eighth resistor is connected to the gate of the switching tube, a second end of the eighth resistor is connected to the drain of the switching tube, the drain of the switching tube is connected to a first end of the ninth resistor, and a second end of the ninth resistor is grounded.

6. The switching power supply circuit according to claim 5, wherein the eighth pin of the PWM chip is output as a reference voltage output terminal, and the fifth pin of the PWM chip is grounded.

7. The switching power supply circuit according to claim 6, further comprising an optocoupler, a tenth resistor, a second voltage regulator tube, an eighth capacitor, an eleventh resistor, and a twelfth resistor; the optocoupler comprises a phototriode and a light-emitting diode, the negative electrode of the light-emitting diode is grounded, the positive electrode of the light-emitting diode is connected with the first end of the tenth resistor, the second end of the tenth resistor is connected with the positive electrode of the second voltage-stabilizing tube, and the negative electrode of the second voltage-stabilizing tube is connected with the voltage output end;

a collector of the phototriode is connected with a first end of the eighth capacitor and then connected with the reference voltage output end, a second end of the eighth capacitor is grounded, an emitter of the phototriode is connected with a first end of the eleventh resistor, and a second end of the eleventh resistor is grounded; and an emitter of the phototriode is connected with a first end of the twelfth resistor, and a second end of the twelfth resistor is connected with a second pin of the PWM chip.

8. The switching power supply circuit according to claim 7, further comprising a thirteenth resistor and a ninth capacitor; and a first pin of the PWM chip is respectively connected with the thirteenth resistor and a first end of the ninth capacitor, and a second end of the thirteenth resistor and a second end of the ninth capacitor are connected with a second pin of the PWM chip.

9. The switching power supply circuit according to claim 8, further comprising a tenth capacitor and a fourteenth resistor; a third pin of the PWM chip is connected to a first end of the tenth capacitor, a second end of the tenth capacitor is grounded, a first end of the tenth capacitor is connected to a first end of the fourteenth resistor, and a second end of the fourteenth resistor is connected to the ninth resistor.

10. The switching power supply circuit according to claim 9, further comprising an eleventh capacitor and a fifteenth resistor; a fourth pin of the PWM chip is connected to the eleventh capacitor and a first end of the fifteenth resistor, a second end of the eleventh capacitor is grounded, and a second end of the fifteenth resistor is connected to the reference voltage output terminal.

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