CN215646629U

CN215646629U - Constant voltage dimming circuit and switching power supply

Info

Publication number: CN215646629U
Application number: CN202121018640.7U
Authority: CN
Inventors: 刘政
Original assignee: SHENZHEN LONGYUN LIGHTING ELECTRIC APPLIANCES CO Ltd
Current assignee: SHENZHEN LONGYUN LIGHTING ELECTRIC APPLIANCES CO Ltd
Priority date: 2021-05-13
Filing date: 2021-05-13
Publication date: 2022-01-25
Anticipated expiration: 2031-05-13

Abstract

The utility model provides a constant-voltage dimming circuit and a switching power supply, wherein the circuit comprises an EMI filter circuit, a pump type power factor correction circuit, a smoothing processing circuit, a self-oscillation circuit, an output processing circuit and an LLC controller; the EMI filter circuit is connected with a first alternating current voltage for electromagnetic interference processing and then outputs the first alternating current voltage to the pump type power factor correction circuit, the first alternating current voltage is rectified into a first direct current voltage, and then the first direct current voltage is pumped to the smoothing processing circuit; the smoothing circuit smoothes the first direct-current voltage to obtain a second direct-current voltage and outputs the second direct-current voltage to the self-excited oscillation circuit; the LLC controller provides starting pulses for the self-oscillation circuit, and the self-oscillation circuit converts the second direct-current voltage into high-frequency alternating-current voltage and outputs the high-frequency alternating-current voltage to the output circuit to be output and processed so as to supply power for the LED. The pump type power factor correction circuit, the smoothing circuit and the self-excited oscillation circuit are combined to enable the output voltage of the power supply to be smooth, and the problem of light source stroboscopic is effectively restrained.

Description

Constant voltage dimming circuit and switching power supply

Technical Field

The utility model relates to the field of switching power supplies and dimming, in particular to a constant-voltage dimming circuit and a switching power supply.

Background

Most of power supply parts of common constant-voltage dimming power supplies in the market are flyback switching power supplies, and the flyback switching power supplies have the advantages of being simple in circuit and having cost advantages, but have the defects of low working efficiency, large voltage and current output pulse coefficients and the like.

Because the market in the present stage pays more and more attention to the problems of product efficiency, light source stroboscopic and the like, the flyback switching power supply is additionally provided with a primary active power factor correction circuit for solving the problem of the light source stroboscopic caused by output ripples, the circuit can better solve the problem of the light source stroboscopic caused by poor output characteristics of the flyback switching power supply, but the product cost is increased and the efficiency is further reduced.

Thus, the prior art has yet to be improved and enhanced.

SUMMERY OF THE UTILITY MODEL

In view of the above-mentioned shortcomings of the prior art, the present invention aims to provide a constant voltage dimming circuit and a switching power supply, which combine a pump type power factor correction circuit, a smoothing circuit and a self-oscillation circuit to make the output voltage of the power supply smooth, thereby effectively suppressing the problem of stroboflash of the light source.

In order to achieve the purpose, the utility model adopts the following technical scheme:

the present invention provides a constant voltage dimming circuit, including: the device comprises an EMI filter circuit, a pump type power factor correction circuit, a smoothing processing circuit, a self-excited oscillation circuit, an output processing circuit and an LLC controller; the EMI filter circuit is connected with a first alternating voltage, and outputs the first alternating voltage to the pump type power factor correction circuit after suppressing interference signals generated in a power grid; rectifying the first alternating current voltage into a first direct current voltage by the pump type power factor correction circuit, and pumping the first direct current voltage to the smoothing circuit; the smoothing circuit is used for smoothing the first direct-current voltage to obtain a second direct-current voltage and outputting the second direct-current voltage to the self-oscillation circuit; the LLC controller provides a starting pulse for the self-oscillation circuit, and the self-oscillation circuit converts the second direct-current voltage into high-frequency alternating-current voltage and outputs the high-frequency alternating-current voltage to the output circuit; the output circuit performs output processing and supplies power to the LED.

The pump type power factor correction circuit comprises a first diode, a second diode, a third diode, a fourth diode, a fifth diode, a sixth diode, a seventh diode, an eighth diode, a first capacitor, a second capacitor, a third capacitor, a fourth capacitor and a fifth capacitor; the input end of the first diode is connected with the input end of the second diode, the output end of the third diode, one end of a first capacitor and one end of a second capacitor, the input end of the third diode is connected with the input end of the fourth diode, one end of a third capacitor, a smoothing processing circuit and a self-oscillation circuit, the other end of the second capacitor is connected with the output end of the fifth diode, the output end of the sixth diode, the smoothing processing circuit and the self-oscillation circuit, the output end of the first diode is connected with the EMI filtering circuit, one end of the fourth capacitor, the input end of the fifth diode and the output end of a seventh diode, the output end of the second diode is connected with the EMI filtering circuit, the input end of the sixth diode and the output end of an eighth diode, the input end of the seventh diode is connected with one end of the fifth capacitor, one end of the seventh diode, The output end of the fourth diode, the input end of the eighth diode and the other end of the third capacitor are connected, and the other end of the first capacitor, the other end of the fourth capacitor and the other end of the fifth capacitor are all grounded.

The smoothing circuit comprises a first resistor, a second resistor, a third resistor, a fourth resistor, a first electrolytic capacitor and a second electrolytic capacitor; one end of the first resistor is connected with the output end of the fifth diode, the output end of the sixth diode, one end of the second capacitor and the anode of the first electrolytic capacitor, the other end of the first resistor is connected with one end of the second resistor, the other end of the second resistor is connected with one end of the third resistor, the cathode of the first electrolytic capacitor and the anode of the second electrolytic capacitor, the other end of the third resistor is connected with one end of the fourth resistor, and the other end of the fourth resistor is connected with the cathode of the second electrolytic capacitor, one end of the third capacitor, the input end of the fourth diode and the self-excited oscillation circuit; the first electrolytic capacitor and the second electrolytic capacitor also supply power to the LLC controller through the first voltage division unit.

The self-oscillation circuit comprises a first transformer, a fifth resistor, a sixth capacitor, a seventh capacitor, an eighth capacitor, a first triode, a second triode, a ninth diode and a twelfth diode; a first end of a primary first winding of the first transformer is connected with an input end of the ninth diode, one end of a seventh capacitor, an output end of a twelfth diode and an output processing circuit, a second end of the primary first winding of the first transformer is connected with an output end of the first triode, an input end of the second triode, one end of a sixth capacitor and a first end of a secondary first winding of the first transformer, a first end of a primary second winding of the first transformer is connected with a first pulse output end of the LLC controller, a second end of the primary second winding of the first transformer is connected with a second pulse output end of the LLC controller, a second end of the secondary first winding of the first transformer is connected with one end of the fifth resistor, and the other end of the fifth resistor is connected with the other end of the sixth capacitor and a base electrode of the first triode, the first end of the secondary second winding of the first transformer is connected with one end of the sixth resistor, the second end of the secondary second winding of the first transformer is connected with one end of the eighth capacitor and the base electrode of the second triode, the other end of the eighth capacitor, the other end of the sixth resistor, the output end of the second triode, the other end of the seventh capacitor and the input end of the twelfth triode are connected with the negative electrode of the second electrolytic capacitor, the other end of the fourth resistor, one end of the third capacitor, the input end of the fourth diode and the input end of the third diode, and the output end of the ninth diode and the input end of the first triode are connected with the positive electrode of the first electrolytic capacitor, one end of the first resistor, the output end of the fifth diode, the output end of the sixth diode, one end of the second capacitor and the first voltage division unit.

The output processing circuit comprises a second transformer, an eleventh diode, a twelfth diode, a thirteenth diode, a third electrolytic capacitor and a fourth electrolytic capacitor; a first end of a primary first winding of the second transformer is connected with an input end of the ninth diode, an output end of the twelfth diode, one end of a seventh capacitor and a first end of a primary first winding of the first transformer through a first inductor, a second end of the primary first winding of the second transformer is connected with a CS pin of the LLC controller through an overcurrent protection unit, a first end of a primary second winding of the second transformer is connected with an input end of the eleventh diode, an output end of the eleventh diode is connected with a power supply end of the LLC controller, a first end of a secondary first winding of the second transformer is connected with an input end of the twelfth diode, a second end of a secondary first winding of the second transformer is connected with an input end of the thirteenth diode, and a center tap of the secondary first winding of the second transformer is connected with the EMI filter circuit and the pump-type power factor correction circuit through a ninth capacitor, and a center tap of a secondary first winding of the second transformer is also connected with a cathode of the third electrolytic capacitor and a cathode of the fourth electrolytic capacitor and grounded, and an output end of the twelfth diode and an output end of the thirteenth diode are both connected with an anode of the third electrolytic capacitor and an anode of the fourth electrolytic capacitor and output power supply voltage to supply power for the LED.

The first voltage division unit comprises a seventh resistor, an eighth resistor, a ninth resistor and a tenth resistor; one end of the seventh resistor is connected with the output end of the ninth diode, the input end of the first triode, the anode of the first electrolytic capacitor, one end of the first resistor, the output end of the sixth diode, the output end of the fifth diode and one end of the second capacitor, and the other end of the seventh resistor is connected with the power pin of the LLC controller sequentially through the eighth resistor, the ninth resistor and the tenth resistor.

The over-current protection unit comprises an eleventh resistor, a twelfth resistor, a thirteenth resistor, a fourteenth resistor, a fifteenth resistor and a sixteenth resistor; one end of the eleventh resistor, one end of the twelfth resistor, one end of the thirteenth resistor, one end of the fourteenth resistor, one end of the fifteenth resistor and one end of the sixteenth resistor are all connected with the second end of the primary first winding of the second transformer, and the other end of the eleventh resistor, the other end of the twelfth resistor, the other end of the thirteenth resistor, the other end of the fourteenth resistor, one end of the fifteenth resistor and the other end of the sixteenth resistor are all grounded.

The constant-voltage dimming circuit also comprises a feedback circuit for sampling the power supply voltage output by the output processing circuit and sending the power supply voltage to the LLC controller; the feedback circuit comprises a seventeenth resistor, an eighteenth resistor, a nineteenth resistor, a twentieth resistor, a twenty-first resistor, a twenty-second resistor, a tenth capacitor, an eleventh capacitor, a controllable precision voltage-stabilizing source and a first optical coupler (the type is not limited to PC 817B); one end of the seventeenth resistor, one end of the eighteenth resistor, one end of the tenth capacitor and the secondary input end of the first optocoupler are all connected with the output end of the output processing circuit, the other end of the tenth capacitor is connected with the other end of the seventeenth resistor and one end of the nineteenth resistor, the secondary output end of the first optocoupler is connected with one end of the twentieth resistor, the other ends of the eighteenth resistor and the twentieth resistor are connected with one end of the twenty-first resistor and the output end of the controllable precise voltage-stabilizing source, the other end of the twenty-first resistor is connected with one end of the eleventh capacitor, the other end of the eleventh capacitor is connected with the other end of the nineteenth resistor, one end of the twenty-second resistor and a control end of the controllable precision voltage-stabilizing source, the input end of the controllable precise voltage-stabilizing source is connected with the other end of the twenty-second resistor and grounded; the primary input end of the first optical coupler is connected with the first end of the primary second winding of the second transformer, and the primary output end of the first optical coupler is connected with the feedback pin of the LLC controller.

The constant-voltage dimming circuit further comprises a dimming circuit for adjusting the brightness of the LED, and the dimming circuit comprises a third triode, a fourth triode, a twenty-third resistor, a twenty-fourth resistor, a twenty-fifth resistor, a twenty-sixth resistor, a twenty-seventh resistor, a twenty-eighth resistor, a twenty-ninth resistor, a thirty-fifth resistor, a thirty-eleventh resistor, a thirty-second resistor, a thirty-third resistor, a twelfth capacitor, a thirteenth capacitor, a fourteenth capacitor, a fifteenth capacitor, a fifth electrolytic capacitor, a sixth electrolytic capacitor, a fourteenth diode, a first voltage regulator tube, a programmable unijunction transistor, a second optocoupler and a dual operational amplifier; an input end of the fourteenth diode is connected with a first end of a secondary second winding of the second transformer, an output end of the fourteenth diode is connected with an anode of the fifth electrolytic capacitor, one end of a twenty-third resistor and an input end of a third triode, a base of the third triode is connected with the other end of the twenty-third resistor and an output end of the first voltage regulator tube, an output end of the third triode is connected with an anode of the sixth electrolytic capacitor, one end of a twenty-fourth resistor, one end of a twenty-fifth resistor, one end of a twelfth capacitor, one end of a twenty-sixth resistor, a power pin of the double operational amplifier and one end of a thirteenth capacitor, the other end of the twenty-fourth resistor is connected with a control end of the programmable unijunction transistor and one end of a twenty-seventh resistor, and the other end of the twenty-fifth resistor is connected with an input end of the programmable unijunction transistor, a first end of the second winding of the programmable unijunction transistor, a second end of the second resistor, a base of the third triode, a base of the second triode, a third triode, a fourth resistor, a third triode, a fourth resistor, a third resistor, a fourth resistor, a second resistor, a third resistor, a fourth resistor, a third resistor, a second resistor, a fourth resistor, a third resistor, a fourth resistor, a, One end of a fourteenth capacitor is connected with the first positive phase input end and the second positive phase input end of the dual operational amplifier, the other end of the twelfth capacitor is connected with one end of a twenty-eighth resistor, one end of a fifteenth capacitor and the first reverse phase input end and the second reverse phase input end of the dual operational amplifier, the other end of a twenty-sixth resistor and the other end of a twenty-eighth resistor are connected with the positive electrode input end of the DIM, the first output end and the second output end of the dual operational amplifier are both connected with one end of a twenty-ninth resistor, the other end of the twenty-ninth resistor is connected with the primary input end of the second optocoupler, the secondary input end of the second optocoupler is connected with one end of a thirty resistor, one end of a thirty-first resistor and the base of a fourth triode, and the input end of the thirty-second resistor is connected with the input end of the fourth triode, One end of a thirty-third resistor is connected with the grid electrode of the first MOS tube, the secondary output end of the second optocoupler, the other end of the thirty-first resistor, the output end of the fourth triode, the other end of the thirty-third resistor and the source electrode of the first MOS tube are all grounded, the drain electrode of the first MOS tube is connected with the cathode end of the LED, the other end of the thirty-second resistor and the other end of the thirty-third resistor are both connected with the anode end of the LED, the primary output end of the second optocoupler, the other end of the thirteenth capacitor, the grounding end of the double operational amplifier, the other end of the fifteenth capacitor, the other end of the fourteenth capacitor, the output end of the programmable unijunction transistor, the other end of the twenty-seventh resistor, the cathode of the sixth electrolytic capacitor, the input end of the first voltage regulator tube, the cathode of the fifth electrolytic capacitor and the second end of the secondary second winding of the second transformer are connected with the cathode input end of the DIM.

Based on the constant voltage dimming circuit, the utility model also provides a switching power supply which comprises a power supply body, wherein the constant voltage dimming circuit is arranged in the power supply body.

Compared with the prior art, the constant-voltage dimming circuit and the switching power supply provided by the utility model comprise: the device comprises an EMI filter circuit, a pump type power factor correction circuit, a smoothing processing circuit, a self-excited oscillation circuit, an output processing circuit and an LLC controller; the EMI filter circuit is connected with the first alternating voltage, and outputs the first alternating voltage to the pump type power factor correction circuit after suppressing interference signals in the power grid; the pump type power factor correction circuit rectifies the first alternating current voltage into a first direct current voltage and sends the first direct current voltage to the smoothing processing circuit; the smoothing circuit smoothes the first direct-current voltage to obtain a second direct-current voltage and outputs the second direct-current voltage to the self-excited oscillation circuit; the LLC controller provides starting pulses for the self-oscillation circuit, and the self-oscillation circuit converts the second direct-current voltage into high-frequency alternating-current voltage and outputs the high-frequency alternating-current voltage to the output circuit to be output and processed so as to supply power for the LED. The pump type power factor correction circuit, the smoothing circuit and the self-excited oscillation circuit are combined to enable the output voltage of the power supply to be smooth, and the problem of light source stroboscopic is effectively restrained.

Drawings

Fig. 1 is a block diagram of a constant voltage dimming circuit according to the present invention (fig. 1 is modified);

fig. 2 is a circuit diagram of a power supply portion of the constant voltage dimming circuit provided in the present invention;

fig. 3 is a circuit diagram of a dimming circuit of the constant voltage dimming circuit according to the present invention.

Detailed Description

The utility model provides a constant-voltage dimming circuit and a switching power supply, which enable the output voltage of the power supply to be smooth by combining a pump type power factor correction circuit, a smoothing processing circuit and a self-oscillation circuit, and effectively inhibit the problem of stroboflash of a light source.

The embodiments of the present invention are intended to explain technical concepts of the present invention, technical problems to be solved, technical features constituting technical solutions, and technical effects to be brought about in more detail. The embodiments are explained below, but the scope of the present invention is not limited thereto. Further, the technical features of the embodiments described below may be combined with each other as long as they do not conflict with each other.

Referring to fig. 1, the present invention provides a constant voltage dimming circuit, including: EMI filter circuit 100, pump type power factor correction circuit 200, smoothing processing circuit 300, self-excited oscillation circuit 400, output processing circuit 500 and LLC controller; the EMI filter circuit 100 is connected to a first ac voltage, and outputs the first ac voltage to the pump-type pfc circuit 200 after suppressing an interference signal generated in the power grid; rectifying the first ac voltage into a first dc voltage by the pump pfc circuit 200, and pumping the first dc voltage to the smoothing circuit 300; the smoothing circuit 300 smoothes the first dc voltage to obtain a second dc voltage, and outputs the second dc voltage to the self-oscillation circuit 400; the LLC controller IC1 provides a start pulse for the self-oscillation circuit 400, and the self-oscillation circuit 400 converts the second dc voltage into a high-frequency ac voltage and outputs the high-frequency ac voltage to the output circuit; the output circuit performs output processing and supplies power to the LED. In specific implementation, the pump-type power factor correction circuit 200, the smoothing circuit 300 and the self-excited oscillation circuit 400 are combined to enable the output voltage of the power supply to be smooth, so that the problem of stroboflash of the light source is effectively suppressed.

Specifically, referring to fig. 2, the pump-type pfc circuit 200 includes a first diode D1, a second diode D2, a third diode D3, a fourth diode D4, a fifth diode D5, a sixth diode D6, a seventh diode D7, an eighth diode D8, a first capacitor C1, a second capacitor C2, a third capacitor C3, a fourth capacitor C4, and a fifth capacitor C5; an input end of the first diode D1 is connected to an input end of the second diode D2, an output end of the third diode D3, one end of the first capacitor C1 and one end of the second capacitor C2, an input end of the third diode D3 is connected to an input end of the fourth diode D4, one end of the third capacitor C3, the smoothing circuit 300 and the self-oscillation circuit 400, another end of the second capacitor C2 is connected to an output end of the fifth diode D5, an output end of the sixth diode D6, the smoothing circuit 300 and the self-oscillation circuit 400, an output end of the first diode D1 is connected to one end of the EMI filter circuit 100, the fourth capacitor C4, an input end of the fifth diode D5 and an output end of the seventh diode D7, an output end of the second diode D2 is connected to an input end of the EMI filter circuit 100, an input end of the sixth diode D6 and an output end of the eighth diode D8, an input end of the seventh diode D7 is connected to one end of the fifth capacitor C5, an output end of the fourth diode D4, an input end of the eighth diode D8, and the other end of the third capacitor C3, and the other ends of the first capacitor C1, the fourth capacitor C4, and the fifth capacitor C5 are all grounded.

In specific implementation, in this embodiment, after the EMI filter circuit 100 filters out the electromagnetic interference, the fifth diode D5, the sixth diode D6, the seventh diode D7, and the eighth diode D8 in the pump-type power factor correction circuit 200 constitute a rectification circuit to rectify the first ac voltage into a pulsating first dc voltage, and at the same time, the whole circuit performs power factor correction, and the ac switching current flowing through the first inductor, the primary first winding of the second transformer T2, the first capacitor C1, the fourth capacitor C4, and the fifth capacitor C5 is alternately conducted through the first diode D1, the second diode D2, the third diode D3, the fourth diode D4, the seventh diode D7, and the eighth diode D8 to pump the current to the smoothing circuit 300, and the voltage of the smoothing circuit 300 is raised to realize control of the power factor and the harmonic.

Specifically, with reference to fig. 2, the smoothing circuit 300 includes a first resistor R1, a second resistor R2, a third resistor R3, a fourth resistor R4, a first electrolytic capacitor CS1 and a second electrolytic capacitor CS 2; one end of the first resistor R1 is connected to the output end of the fifth diode D5, the output end of the sixth diode D6, one end of the second capacitor C2, and the anode of the first electrolytic capacitor CS1, the other end of the first resistor R1 is connected to one end of the second resistor R2, the other end of the second resistor R2 is connected to one end of the third resistor R3, the cathode of the first electrolytic capacitor CS1, and the anode of the second electrolytic capacitor CS2, the other end of the third resistor R3 is connected to one end of the fourth resistor R4, and the other end of the fourth resistor R4 is connected to the cathode of the second electrolytic capacitor CS2, one end of the third capacitor C3, the input end of the fourth diode D4, and the self-excited oscillation circuit 400; the first electrolytic capacitor CS1 and the second electrolytic capacitor CS2 also supply power to the LLC controller IC1 through the first voltage dividing unit 900.

In specific implementation, in this embodiment, the first electrolytic capacitor CS2 and the second electrolytic capacitor CS2 are both bus capacitors, which convert the pulsating first dc voltage into a smoother second dc voltage and provide energy to the subsequent stage. Furthermore, the first resistor R1, the second resistor R2, the third resistor R3 and the fourth resistor R4 are all voltage-sharing resistors, so that voltage-withstand breakdown caused by uneven voltage division due to large internal resistance difference between the first electrolytic capacitor CS1 and the second electrolytic capacitor CS2 is avoided.

Specifically, as shown in fig. 2, the self-oscillation circuit 400 includes a first transformer T1, a fifth resistor R5, a sixth resistor R6, a sixth capacitor C6, a seventh capacitor C7, an eighth capacitor C8, a first triode, a second triode, a ninth diode D9, and a twelfth diode D10; a first end of a primary first winding of the first transformer T1 is connected to an input end of the ninth diode D9, one end of a seventh capacitor C7, an output end of a twelfth diode D10, and the output processing circuit 500, a second end of the primary first winding of the first transformer T1 is connected to an output end of the first triode, an input end of the second triode, one end of a sixth capacitor C6, and a first end of a secondary first winding of the first transformer T1, a first end of a primary second winding of the first transformer T1 is connected to a first pulse output end of the LLC controller IC1, a second end of a primary second winding of the first transformer T1 is connected to a second pulse output end of the LLC controller IC1, a second end of a secondary first winding of the first transformer T1 is connected to one end of a fifth resistor R5, and the other end of the fifth resistor R5 is connected to the other end of the sixth capacitor C6 and a base of the first diode D5, a first end of the secondary second winding of the first transformer T1 is connected to one end of the sixth resistor R6, a second end of the secondary second winding of the first transformer T1 is connected to one end of the eighth capacitor C8 and the base of the second transistor, the other end of the eighth capacitor C8, the other end of the sixth resistor R6, the output end of the second triode, the other end of the seventh capacitor C7 and the input end of the twelfth diode D10 are all connected with the cathode of the second electrolytic capacitor CS2, the other end of the fourth resistor R4, one end of the third capacitor C3, the input end of the fourth diode D4 and the input end of the third diode D3, an output end of the ninth diode D9 and an input end of the first triode are connected to the anode of the first electrolytic capacitor CS1, one end of the first resistor R1, an output end of the fifth diode D5, an output end of the sixth diode D6, one end of the second capacitor C2, and the first voltage division unit 900.

In specific implementation, in this embodiment, the LCC controller provides the start pulse required by the self-oscillation circuit 400, and the LLC controller IC1 is powered by the smoothing circuit 300 through the first voltage dividing unit 900. Specifically, the LCC controller provides a start pulse to the first transformer T1 in the first two cycles to start oscillation of the oscillation circuit, and then the windings of the first transformer T1 are coupled with each other to provide base driving currents for the first triode and the second triode to keep the circuit oscillating, the first triode and the second triode convert the second dc voltage into high-frequency ac voltage through alternate conduction, the sixth capacitor C6 and the eighth capacitor C8 are respectively connected in parallel between the base and the emitter of the first triode and the second triode, so as to shunt the base currents flowing into the first triode and the second triode in the transient state, the ninth diode D9 and the twelfth diode D10 are connected in parallel between the collector and the emitter of the first triode and the second triode, and mainly reduce the switching loss of the first triode and the second triode.

The output processing circuit 500 comprises a second transformer T2, an eleventh diode D11, a twelfth diode D12, a thirteenth diode D13, a third electrolytic capacitor CS3 and a fourth electrolytic capacitor CS 4; a first end of a primary first winding of the second transformer T2 is connected to an input end of the ninth diode D9, an output end of the twelfth diode D10, an end of the seventh capacitor C7, and a first end of a primary first winding of the first transformer T1 through a first inductor, a second end of the primary first winding of the second transformer T2 is connected to the CS pin of the LLC controller IC1 through the overcurrent protection unit 800, a first end of a primary second winding of the second transformer T2 is connected to an input end of the eleventh diode D11, an output end of the eleventh diode D11 is connected to a power supply end of the LLC controller IC1, a first end of a secondary first winding of the second transformer T2 is connected to an input end of the twelfth diode D12, a second end of a secondary first winding of the second transformer T2 is connected to an input end of the thirteenth diode D13, the center tap of the secondary first winding of the second transformer T2 is connected to the EMI filter circuit 100 and the pump-type power factor correction circuit 200 through a ninth capacitor C9C9, the center tap of the secondary first winding of the second transformer T2 is further connected to the cathode of the third electrolytic capacitor CS3 and the cathode of the fourth electrolytic capacitor CS4 and grounded, and the output end of the twelfth diode D12 and the output end of the thirteenth diode D13 are both connected to the anode of the third electrolytic capacitor CS3 and the anode of the fourth electrolytic capacitor CS4 and output a supply voltage to supply power to the LED.

In specific implementation, in this embodiment, the second transformer T2 converts the second dc voltage into a power supply voltage suitable for the LED, and outputs the power supply voltage to the anode of the LED to supply power to the LED.

Specifically, with reference to fig. 2, the first voltage divider 900 includes a seventh resistor R7, an eighth resistor R8, a ninth resistor R9, and a tenth resistor R10; one end of the seventh resistor R7 is connected to the output end of the ninth diode D9, the input end of the first triode, the anode of the first electrolytic capacitor CS1, one end of the first resistor R1, the output end of the sixth diode D6, the output end of the fifth diode D5, and one end of the second capacitor C2, and the other end of the seventh resistor R7 is connected to the power pin of the LLC controller IC1 sequentially through the eighth resistor R8, the ninth resistor R9, and the tenth resistor R10.

In specific implementation, in this embodiment, the seventh resistor R7 obtains a voltage from the smoothing circuit 300, and obtains a working voltage of the LLC controller IC1 after voltage division is performed sequentially by the seventh resistor R7, the eighth resistor R8, the ninth resistor R9, and the tenth resistor R10, so that the LLC controller IC1 is started.

Specifically, with reference to fig. 2, the over-current protection unit 800 includes an eleventh resistor R11R11, a twelfth resistor R12R12, a thirteenth resistor R13R13, a fourteenth resistor R14R14, a fifteenth resistor R15R15, and a sixteenth resistor R16R 16; one end of the eleventh resistor R11R11, one end of the twelfth resistor R12R12, one end of the thirteenth resistor R13R13, one end of the fourteenth resistor R14R14, one end of the fifteenth resistor R15R15 and one end of the sixteenth resistor R16R16 are all connected to the second end of the primary first winding of the second transformer T2, and the other end of the eleventh resistor R11R11, the other end of the twelfth resistor R12R12, the other end of the thirteenth resistor R13R13, the other end of the fourteenth resistor R14R14, one end of the fifteenth resistor R15R15 and the other end of the sixteenth resistor R16R16 are all grounded.

In specific implementation, in this embodiment, the eleventh resistor R11R11, the twelfth resistor R12R12, the thirteenth resistor R13R13, the fourteenth resistor R14R14, the fifteenth resistor R15R15 and the sixteenth resistor R16R16 are connected in series to the second end of the primary first winding of the second transformer T2, so as to sample the current output from the second end of the primary first winding of the second transformer T2, output the current to the CS pin of the LLC controller IC1, and control the output current of the oscillation circuit thereof through the LLC controller IC1, thereby achieving the effect of overcurrent protection.

Specifically, with continued reference to fig. 2, the constant voltage dimming circuit further includes a feedback circuit 600 for sampling the supply voltage output by the output processing circuit 500 to the LLC controller IC 1; the feedback circuit 600 comprises a seventeenth resistor R17, an eighteenth resistor R18, a nineteenth resistor R19, a twentieth resistor R20, a twenty-first resistor R21, a twenty-second resistor R22, a tenth capacitor C10, an eleventh capacitor C11, a controllable precision voltage-stabilizing source Z1 and a first optical coupler; one end of a seventeenth resistor R17, one end of an eighteenth resistor R18, one end of a tenth capacitor C10 and an input end of a secondary OP1B of the first optocoupler are all connected with an output end of the output processing circuit 500, the other end of the tenth capacitor C10 is connected with the other end of the seventeenth resistor R17 and one end of a nineteenth resistor R19, an output end of the secondary OP1B of the first optocoupler is connected with one end of the twentieth resistor R20, the other ends of the eighteenth resistor R18 and the twentieth resistor R20 are connected with one end of the twenty-first resistor R21 and an output end of a controllable precision voltage-stabilizing source Z1, the other end of the twenty-first resistor R21 is connected with one end of the eleventh capacitor C11, the other end of the eleventh capacitor C11 is connected with the other end of the nineteenth resistor R19, one end of the twenty-second resistor R22 and a control end of the controllable precision voltage-stabilizing source Z1, the input end of the controllable precise voltage-stabilizing source Z1 is connected with the other end of the twenty-second resistor R22 and is grounded; the input end of a primary OP1A of the first optical coupler is connected with the first end of a primary second winding of the second transformer T2, and the output end of a primary OP1A of the first optical coupler is connected with a feedback pin of the LLC controller IC 1.

In specific implementation, in this embodiment, the LLC controller IC1 is of a model RED2543, but is not limited to this model, and other devices that can achieve the same or corresponding functions may be used instead. The power pin obtains the working voltage through the first voltage division unit 900 of the resistor to output the starting pulse of the first two cycles to the self-oscillation circuit 400, specifically, when the voltage of the power pin of the LLC controller IC1 reaches 3.6V, the IC1 starts to start, when the output voltage rises, the output voltage is rectified by the eleventh diode D11 through the primary second winding of the second transformer T2, and the VDD pin is supplied with power after being filtered by the sixteenth capacitor C16, at this time, the LLC controller IC1 enters a working mode, and the voltage of the VDD pin is clamped at about 3.45V by the internal voltage stabilizing diode of the LLC controller IC 1.

Further, a voltage signal fed back by the first optical coupler is received by a feedback pin of the LLC controller IC1, is divided by a thirty-fifth resistor R35 and a thirty-seventh resistor R37, is filtered by an eighteenth capacitor C18, and is compared with an internal comparator reference voltage, and then the output voltage is calibrated by changing the operating frequency.

Specifically, referring to fig. 3, the constant voltage dimming circuit further includes a dimming circuit 700 for adjusting the LED brightness, where the dimming circuit 700 includes a third triode Q3, a fourth triode Q4, a twenty-third resistor R23, a twenty-fourth resistor R24, a twenty-fifth resistor R25, a twenty-sixth resistor R26, a twenty-seventh resistor R27, a twenty-eighth resistor R28, a twenty-ninth resistor R29, a thirty-third resistor R30, a thirty-eleventh resistor R31, a thirty-second resistor R32, a thirty-third resistor R33, a twelfth capacitor C12, a thirteenth capacitor C13, a fourteenth capacitor C14, a fifteenth capacitor C15, a fifth electrolytic capacitor CS5, a sixth electrolytic capacitor CS6, a fourteenth diode D14, a first voltage regulator ZD1, a programmable single junction transistor Z2, a second optical coupler OP2, and a dual optical coupler IC 2; an input end of the fourteenth diode D14 is connected to a first end of the secondary second winding of the second transformer T2, an output end of the fourteenth diode D14 is connected to an anode of the fifth electrolytic capacitor CS5, one end of a twenty-third resistor R23 and an input end of a third triode, a base of the third triode is connected to the other end of the twenty-third resistor R23 and an output end of a first voltage regulator ZD1, an output end of the third triode is connected to an anode of the sixth electrolytic capacitor CS6, one end of a twenty-fourth resistor R24, one end of a twenty-fifth resistor R25, one end of a twelfth capacitor C12, one end of a twenty-sixth resistor R26, a power pin of the dual operational amplifier IC2 and one end of a thirteenth capacitor C13, and the other end of the twenty-fourth resistor R24 is connected to a control end of the programmable unijunction transistor Z2 and one end of a twenty-seventh resistor R27, the other end of the twenty-fifth resistor R25 is connected to the input end of the programmable unijunction transistor Z2, one end of a fourteenth capacitor C14, and the first and second non-inverting input ends of the dual operational amplifier IC2, the other end of the twelfth capacitor C12 is connected to one end of the twenty-eighth resistor R28, one end of the fifteenth capacitor C15, and the first and second inverting input ends of the dual operational amplifier IC2, the other end of the twenty-sixth resistor R26 and the other end of the twenty-eighth resistor R28 are connected to the DIM positive input end, the first and second output ends of the dual operational amplifier IC2 are connected to one end of the twenty-ninth resistor R29, the other end of the twenty-ninth resistor R29 is connected to the primary OP2A input end of the second optical coupler, the secondary OP2B input end of the second optical coupler is connected to one end of the thirty-resistor R30, and the first and second non-inverting input ends of the dual operational amplifier IC 3535 are connected to the first and second positive input ends of the second optical coupler, One end of a thirty-first resistor R31 is connected with a base electrode of a fourth triode, an input end of the fourth triode is connected with one end of a thirty-second resistor R32, one end of a thirty-third resistor R33 and a grid electrode of a first MOS (metal oxide semiconductor) QT1, an output end of a second optocoupler secondary OP2B, the other end of a thirty-first resistor R31, an output end of a fourth triode, the other end of a thirty-third resistor R33 and a source electrode of the first MOS QT1 are all grounded, a drain electrode of the first MOS QT1 is connected with a negative electrode end of the LED, the other end of the thirty-second resistor R30 and the other end of the thirty-second resistor R32 are all connected with a positive electrode end of the LED, an output end of a primary OP2A of the second optocoupler, the other end of a thirteenth capacitor C13, a ground end of a double operational amplifier IC2, the other end of a fifteenth capacitor C15, the other end of a fourteenth capacitor C14, the output end of a unijunction transistor Z2, The other end of the twenty-seventh resistor R27, the cathode of the sixth electrolytic capacitor CS6, the input end of the first voltage regulator tube ZD1, the cathode of the fifth electrolytic capacitor CS5 and the second end of the secondary second winding of the second transformer T2 are all connected with the DIM cathode input end.

In specific implementation, in this embodiment, a fourteenth diode D14, a fifth electrolytic capacitor CS5, a sixth electrolytic capacitor CS6, a twenty-third resistor R23, a third triode, and a first voltage regulator ZD1 form a series voltage limiting power supply, a voltage of a secondary second winding of the second transformer T2 is rectified by the fourteenth diode D14 and then reaches the fifth electrolytic capacitor CS5 to obtain a relatively smooth dc voltage, the twenty-third resistor R23 limits the current of the first voltage regulator ZD1, and according to the operating characteristics of the third triode, the voltage of the sixth electrolytic capacitor CS6 does not exceed the reverse breakdown voltage of the first voltage regulator ZD1 and provides a relatively stable power supply for a subsequent circuit.

Furthermore, the twenty-fourth resistor R24, the twenty-fifth resistor R25, the twenty-seventh resistor R27, the fourteenth capacitor C14 and the programmable unijunction transistor Z2 (the type is not limited to 2N6027) form a triangular wave generating circuit, the twenty-fourth resistor R24 and the twenty-seventh resistor R27 form a resistor divider to apply a voltage to the gate of the programmable unijunction transistor Z2 (i.e. the control end of the programmable unijunction transistor Z2), the voltage on the sixth electrolytic capacitor CS6 is limited by the twenty-fifth resistor R25 and then slowly charges the fourteenth capacitor C14, so that the voltage on the fourteenth capacitor C14 has a slope rising trend, when the voltage on the fourteenth capacitor C14 reaches the sum of the peak point voltage (i.e. the gate voltage) and the positive voltage drop of the PN junction in the programmable unijunction transistor Z2, the programmable unijunction transistor Z2 is turned on, the voltage on the fourteenth capacitor C14 has a slope falling, and when the voltage on the valley of the fourteenth capacitor C14 falls to a point which is less than the voltage on the programmable unijunction transistor Z2, the programmable unijunction transistor Z2 is turned off, so that the fourteenth capacitor C14 is charged and discharged repeatedly, and the voltage thereof is in a triangular wave state.

The 3 rd pin (IN1+) and the 5 th pin (IN2+) of the dual operational amplifier IC2 (the model is not limited to LM358) are non-inverting input terminals of the operational amplifier, the voltage on the fourteenth capacitor C14 is input to the 3 rd pin and the 5 th pin of the dual operational amplifier IC2 as a reference voltage, and the 2 nd pin (IN1-) and the 6 th pin (IN1-) of the dual operational amplifier IC2 are inverting input terminals of the operational amplifier. The voltage on the sixth electrolytic capacitor CS6 is applied to the non-inverting input terminal (i.e., DIM +) of the dimmer via a twenty-sixth resistor R26, and the terminal voltage is applied to

pins

2 and 6 of the dual operational amplifier IC2 as a comparison voltage via a twenty-eighth resistor R28. When the voltage of the positive phase input end of the dual operational amplifier IC2 is greater than that of the negative phase input end, the 1 st pin and the 7 th pin of the dual operational amplifier IC2 output high levels, and when the voltage of the positive phase input end of the dual operational amplifier IC2 is less than that of the negative phase input end, the 1 st pin and the 7 th pin of the dual operational amplifier IC2 output low levels, so that the output voltages of the 1 st pin and the 7 th pin of the dual operational amplifier IC2 are in a square wave state, and the output voltages of the 1 st pin and the 7 th pin of the dual operational amplifier IC2 are square waves with different duty ratios along with different voltage of a dimmer end. The 8 th pin of the dual operational amplifier IC2 is a power pin, and the sixth electrolytic capacitor CS6 supplies power for the operation of the dual operational amplifier IC 2. Pin 4 of the dual operational amplifier IC2 is the chip reference ground.

Furthermore, the output voltage signals of the 1 st pin and the 7 th pin of the dual operational amplifier IC2 are transmitted to the output end of the second optical coupler through the twenty-ninth resistor R29 to the input end of the second optical coupler (the model is not limited to PC817B), so that the conduction state of the fourth triode is opposite to the duty ratio of the output square wave of the 1 st pin and the 7 th pin of the dual operational amplifier IC2, the collector (input end) of the fourth triode is connected to the gate of the first MOS transistor QT1, the conduction state of the first MOS transistor QT1 is opposite to the conduction state of the fourth triode, and thus the conduction state of the first MOS transistor QT1 is consistent to the duty ratio of the output square wave of the 1 st pin and the 7 th pin of the dual operational amplifier IC2, and the purpose of controlling the power output current and further dimming the LED light source is achieved.

Based on the constant voltage dimming circuit, the utility model also provides a switching power supply which comprises a power supply body, wherein the constant voltage dimming circuit is arranged in the power supply body. Since the constant voltage dimming circuit has been described in detail above, it is not described in detail here.

In summary, the present invention provides a constant voltage dimming circuit and a switching power supply, including: the device comprises an EMI filter circuit, a pump type power factor correction circuit, a smoothing processing circuit, a self-excited oscillation circuit, an output processing circuit and an LLC controller; the EMI filter circuit is connected with the first alternating voltage, and outputs the first alternating voltage to the pump type power factor correction circuit after suppressing interference signals in the power grid; the pump type power factor correction circuit rectifies the first alternating current voltage into a first direct current voltage and sends the first direct current voltage to the smoothing processing circuit; the smoothing circuit smoothes the first direct-current voltage to obtain a second direct-current voltage and outputs the second direct-current voltage to the self-excited oscillation circuit; the LLC controller provides starting pulses for the self-oscillation circuit, and the self-oscillation circuit converts the second direct-current voltage into high-frequency alternating-current voltage and outputs the high-frequency alternating-current voltage to the output circuit to be output and processed so as to supply power for the LED. The pump type power factor correction circuit, the smoothing circuit and the self-excited oscillation circuit are combined to enable the output voltage of the power supply to be smooth, and the problem of light source stroboscopic is effectively restrained.

It should be understood that the technical solutions and the inventive concepts according to the present invention may be equally replaced or changed by those skilled in the art, and all such changes or substitutions should fall within the protection scope of the appended claims.

Claims

1. A constant voltage dimming circuit, comprising: the device comprises an EMI filter circuit, a pump type power factor correction circuit, a smoothing processing circuit, a self-excited oscillation circuit, an output processing circuit and an LLC controller;

the EMI filter circuit is connected with a first alternating voltage, and outputs the first alternating voltage to the pump type power factor correction circuit after suppressing interference signals generated in a power grid; rectifying the first alternating current voltage into a first direct current voltage by the pump type power factor correction circuit, and pumping the first direct current voltage to the smoothing circuit; the smoothing circuit is used for smoothing the first direct-current voltage to obtain a second direct-current voltage and outputting the second direct-current voltage to the self-oscillation circuit; the LLC controller provides a starting pulse for the self-oscillation circuit, and the self-oscillation circuit converts the second direct-current voltage into high-frequency alternating-current voltage and outputs the high-frequency alternating-current voltage to the output circuit; the output circuit performs output processing and supplies power to the LED.

2. The constant-voltage dimming circuit according to claim 1, wherein the pump power factor correction circuit comprises a first diode, a second diode, a third diode, a fourth diode, a fifth diode, a sixth diode, a seventh diode, an eighth diode, a first capacitor, a second capacitor, a third capacitor, a fourth capacitor, and a fifth capacitor;

the input end of the first diode is connected with the input end of the second diode, the output end of the third diode, one end of a first capacitor and one end of a second capacitor, the input end of the third diode is connected with the input end of the fourth diode, one end of a third capacitor, a smoothing processing circuit and a self-oscillation circuit, the other end of the second capacitor is connected with the output end of the fifth diode, the output end of the sixth diode, the smoothing processing circuit and the self-oscillation circuit, the output end of the first diode is connected with the EMI filtering circuit, one end of the fourth capacitor, the input end of the fifth diode and the output end of a seventh diode, the output end of the second diode is connected with the EMI filtering circuit, the input end of the sixth diode and the output end of an eighth diode, the input end of the seventh diode is connected with one end of the fifth capacitor, one end of the seventh diode, The output end of the fourth diode, the input end of the eighth diode and the other end of the third capacitor are connected, and the other end of the first capacitor, the other end of the fourth capacitor and the other end of the fifth capacitor are all grounded.

3. The constant-voltage dimming circuit according to claim 2, wherein the smoothing circuit includes a first resistor, a second resistor, a third resistor, a fourth resistor, a first electrolytic capacitor, and a second electrolytic capacitor;

one end of the first resistor is connected with the output end of the fifth diode, the output end of the sixth diode, one end of the second capacitor and the anode of the first electrolytic capacitor, the other end of the first resistor is connected with one end of the second resistor, the other end of the second resistor is connected with one end of the third resistor, the cathode of the first electrolytic capacitor and the anode of the second electrolytic capacitor, the other end of the third resistor is connected with one end of the fourth resistor, and the other end of the fourth resistor is connected with the cathode of the second electrolytic capacitor, one end of the third capacitor, the input end of the fourth diode and the self-excited oscillation circuit;

the first electrolytic capacitor and the second electrolytic capacitor also supply power to the LLC controller through the first voltage division unit.

4. The constant-voltage dimming circuit according to claim 3, wherein the self-oscillation circuit comprises a first transformer, a fifth resistor, a sixth capacitor, a seventh capacitor, an eighth capacitor, a first transistor, a second transistor, a ninth diode, and a twelfth diode;

a first end of a primary first winding of the first transformer is connected with an input end of the ninth diode, one end of a seventh capacitor, an output end of a twelfth diode and an output processing circuit, a second end of the primary first winding of the first transformer is connected with an output end of the first triode, an input end of the second triode, one end of a sixth capacitor and a first end of a secondary first winding of the first transformer, a first end of a primary second winding of the first transformer is connected with a first pulse output end of the LLC controller, a second end of the primary second winding of the first transformer is connected with a second pulse output end of the LLC controller, a second end of the secondary first winding of the first transformer is connected with one end of the fifth resistor, and the other end of the fifth resistor is connected with the other end of the sixth capacitor and a base electrode of the first triode, the first end of the secondary second winding of the first transformer is connected with one end of the sixth resistor, the second end of the secondary second winding of the first transformer is connected with one end of the eighth capacitor and the base electrode of the second triode, the other end of the eighth capacitor, the other end of the sixth resistor, the output end of the second triode, the other end of the seventh capacitor and the input end of the twelfth triode are connected with the negative electrode of the second electrolytic capacitor, the other end of the fourth resistor, one end of the third capacitor, the input end of the fourth diode and the input end of the third diode, and the output end of the ninth diode and the input end of the first triode are connected with the positive electrode of the first electrolytic capacitor, one end of the first resistor, the output end of the fifth diode, the output end of the sixth diode, one end of the second capacitor and the first voltage division unit.

5. The constant-voltage dimming circuit according to claim 4, wherein the output processing circuit comprises a second transformer, an eleventh diode, a twelfth diode, a thirteenth diode, a third electrolytic capacitor, and a fourth electrolytic capacitor;

a first end of a primary first winding of the second transformer is connected with an input end of the ninth diode, an output end of the twelfth diode, one end of a seventh capacitor and a first end of a primary first winding of the first transformer through a first inductor, a second end of the primary first winding of the second transformer is connected with a CS pin of the LLC controller through an overcurrent protection unit, a first end of a primary second winding of the second transformer is connected with an input end of the eleventh diode, an output end of the eleventh diode is connected with a power supply end of the LLC controller, a first end of a secondary first winding of the second transformer is connected with an input end of the twelfth diode, a second end of a secondary first winding of the second transformer is connected with an input end of the thirteenth diode, and a center tap of the secondary first winding of the second transformer is connected with the EMI filter circuit and the pump-type power factor correction circuit through a ninth capacitor, and a center tap of a secondary first winding of the second transformer is also connected with a cathode of the third electrolytic capacitor and a cathode of the fourth electrolytic capacitor and grounded, and an output end of the twelfth diode and an output end of the thirteenth diode are both connected with an anode of the third electrolytic capacitor and an anode of the fourth electrolytic capacitor and output power supply voltage to supply power for the LED.

6. The constant-voltage dimming circuit according to claim 3, wherein the first voltage division unit includes a seventh resistor, an eighth resistor, a ninth resistor, and a tenth resistor;

one end of the seventh resistor is connected with the output end of the ninth diode, the input end of the first triode, the anode of the first electrolytic capacitor, one end of the first resistor, the output end of the sixth diode, the output end of the fifth diode and one end of the second capacitor, and the other end of the seventh resistor is connected with the power pin of the LLC controller sequentially through the eighth resistor, the ninth resistor and the tenth resistor.

7. The constant-voltage dimming circuit according to claim 5, wherein the overcurrent protection unit includes an eleventh resistor, a twelfth resistor, a thirteenth resistor, a fourteenth resistor, a fifteenth resistor, and a sixteenth resistor;

one end of the eleventh resistor, one end of the twelfth resistor, one end of the thirteenth resistor, one end of the fourteenth resistor, one end of the fifteenth resistor and one end of the sixteenth resistor are all connected with the second end of the primary first winding of the second transformer, and the other end of the eleventh resistor, the other end of the twelfth resistor, the other end of the thirteenth resistor, the other end of the fourteenth resistor, one end of the fifteenth resistor and the other end of the sixteenth resistor are all grounded.

8. The constant-voltage dimming circuit according to claim 1, further comprising a feedback circuit for sampling the supply voltage output by the output processing circuit and transmitting the sampled supply voltage to the LLC controller; the feedback circuit comprises a seventeenth resistor, an eighteenth resistor, a nineteenth resistor, a twentieth resistor, a twenty-first resistor, a twenty-second resistor, a tenth capacitor, an eleventh capacitor, a controllable precision voltage-stabilizing source and a first optical coupler;

one end of the seventeenth resistor, one end of the eighteenth resistor, one end of the tenth capacitor and the secondary input end of the first optocoupler are all connected with the output end of the output processing circuit, the other end of the tenth capacitor is connected with the other end of the seventeenth resistor and one end of the nineteenth resistor, the secondary output end of the first optocoupler is connected with one end of the twentieth resistor, the other ends of the eighteenth resistor and the twentieth resistor are connected with one end of the twenty-first resistor and the output end of the controllable precise voltage-stabilizing source, the other end of the twenty-first resistor is connected with one end of the eleventh capacitor, the other end of the eleventh capacitor is connected with the other end of the nineteenth resistor, one end of the twenty-second resistor and a control end of the controllable precision voltage-stabilizing source, the input end of the controllable precise voltage-stabilizing source is connected with the other end of the twenty-second resistor and grounded;

the primary input end of the first optical coupler is connected with the first end of the primary second winding of the second transformer, and the primary output end of the first optical coupler is connected with the feedback pin of the LLC controller.

9. The constant-voltage dimming circuit according to claim 5, further comprising a dimming circuit for adjusting the brightness of the LED, wherein the dimming circuit comprises a third triode, a fourth triode, a twenty-third resistor, a twenty-fourth resistor, a twenty-fifth resistor, a twenty-sixth resistor, a twenty-seventh resistor, a twenty-eighth resistor, a twenty-ninth resistor, a thirty-fifth resistor, a thirty-eleventh resistor, a thirty-second resistor, a thirty-third resistor, a twelfth capacitor, a thirteenth capacitor, a fourteenth capacitor, a fifteenth capacitor, a fifth electrolytic capacitor, a sixth electrolytic capacitor, a fourteenth diode, a first voltage regulator, a programmable unijunction transistor, a second optocoupler, and a dual operational amplifier;

an input end of the fourteenth diode is connected with a first end of a secondary second winding of the second transformer, an output end of the fourteenth diode is connected with an anode of the fifth electrolytic capacitor, one end of a twenty-third resistor and an input end of a third triode, a base of the third triode is connected with the other end of the twenty-third resistor and an output end of the first voltage regulator tube, an output end of the third triode is connected with an anode of the sixth electrolytic capacitor, one end of a twenty-fourth resistor, one end of a twenty-fifth resistor, one end of a twelfth capacitor, one end of a twenty-sixth resistor, a power pin of the double operational amplifier and one end of a thirteenth capacitor, the other end of the twenty-fourth resistor is connected with a control end of the programmable unijunction transistor and one end of a twenty-seventh resistor, and the other end of the twenty-fifth resistor is connected with an input end of the programmable unijunction transistor, a first end of the second winding of the programmable unijunction transistor, a second end of the second resistor, a base of the third triode, a base of the second triode, a third triode, a fourth resistor, a third triode, a fourth resistor, a third resistor, a fourth resistor, a second resistor, a third resistor, a fourth resistor, a third resistor, a second resistor, a fourth resistor, a third resistor, a fourth resistor, a, One end of a fourteenth capacitor is connected with the first positive phase input end and the second positive phase input end of the dual operational amplifier, the other end of the twelfth capacitor is connected with one end of a twenty-eighth resistor, one end of a fifteenth capacitor and the first reverse phase input end and the second reverse phase input end of the dual operational amplifier, the other end of a twenty-sixth resistor and the other end of a twenty-eighth resistor are connected with the positive electrode input end of the DIM, the first output end and the second output end of the dual operational amplifier are both connected with one end of a twenty-ninth resistor, the other end of the twenty-ninth resistor is connected with the primary input end of the second optocoupler, the secondary input end of the second optocoupler is connected with one end of a thirty resistor, one end of a thirty-first resistor and the base of a fourth triode, and the input end of the thirty-second resistor is connected with the input end of the fourth triode, One end of a thirty-third resistor is connected with the grid electrode of the first MOS tube, the secondary output end of the second optocoupler, the other end of the thirty-first resistor, the output end of the fourth triode, the other end of the thirty-third resistor and the source electrode of the first MOS tube are all grounded, the drain electrode of the first MOS tube is connected with the cathode end of the LED, the other end of the thirty-second resistor and the other end of the thirty-third resistor are both connected with the anode end of the LED, the primary output end of the second optocoupler, the other end of the thirteenth capacitor, the grounding end of the double operational amplifier, the other end of the fifteenth capacitor, the other end of the fourteenth capacitor, the output end of the programmable unijunction transistor, the other end of the twenty-seventh resistor, the cathode of the sixth electrolytic capacitor, the input end of the first voltage regulator tube, the cathode of the fifth electrolytic capacitor and the second end of the secondary second winding of the second transformer are connected with the cathode input end of the DIM.

10. A switching power supply comprising a power supply body in which the constant voltage dimming circuit according to any one of claims 1 to 9 is provided.