Dimming circuit

By setting up isolation components in the LED dimming circuit, the current harmonic problem caused by the constant voltage output module participating in the charging and discharging of the dimming module is solved, and the current harmonic suppression and circuit efficiency are achieved.

CN222564004UActive Publication Date: 2025-03-04SUZHOU OPPLE LIGHTING +1
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Patent Information

Application Number
CN202421193780.1
Authority / Receiving Office
CN · China
Patent Type
Utility models(China)
Current Assignee / Owner
Filing Date
2024-05-29
Publication Date
2025-03-04
Estimated Expiration
2034-05-29

AI Technical Summary

Technical Problem

In the existing LED dimming circuit, the constant voltage output module participates in the charging and discharging process of the dimming module, resulting in a large current harmonic value and uncontrollable.

Method used

Isolation elements are arranged between the rectifier module and the flyback constant voltage isolation module to prevent the voltage of the flyback constant voltage isolation module from flowing back to the rectifier module, so that the flyback constant voltage isolation module does not participate in the charging and discharging process of the non-isolated dimming module.

Benefits of technology

Through the setting of the isolation element, current harmonics are suppressed, making them meet the specification requirements, and the efficiency and stability of the circuit are improved.

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Abstract

The utility model provides a dimming circuit. The dimming circuit comprises a rectification module, a flyback constant voltage isolation module, an MCU module, a non-isolation dimming module, an optocoupler module and an isolation element. Wherein the rectifier module is used for converting alternating current commercial power into direct current; the flyback constant voltage isolation module is connected with the rectifier module and converts the direct current into constant voltage; the MCU module is connected with the flyback constant-voltage isolation module and is used for receiving the constant voltage output by the flyback constant-voltage isolation module and outputting a PWM (Pulse Width Modulation) signal; one end of the non-isolated dimming module is connected with the rectifier module and receives the direct current output by the rectifier module, the other end of the non-isolated dimming module is connected with an external lamp and the MCU module, and dimming is carried out on the external lamp by receiving a PWM signal output by the MCU module; the optocoupler module is connected between the MCU module and the non-isolated dimming module and is used for coupling the PWM signal output by the MCU module to the non-isolated dimming module; and the isolation element is arranged between the rectification module and the flyback constant-voltage isolation module and is used for isolating the direct current output by the rectification module and then inputting the direct current to the flyback constant-voltage isolation module so as to prevent the voltage of the flyback constant-voltage isolation module from flowing back to the rectification module. Compared with the prior art, the dimming circuit provided by the utility model is provided with the isolation element between the rectification module and the flyback constant-voltage isolation module so as to further suppress current harmonics and enable the current harmonics to meet standard requirements.
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Description

Technical Field

[0001] The utility model relates to a dimming circuit and belongs to the technical field of electronics. Background Art

[0002] With the rapid development of electronic technology, LED lighting products have gradually become intelligent. In order to achieve the goals of power saving and lighting control effects, LED lamps with dimming functions are being used more and more widely.

[0003] At present, a widely used LED dimming technology is PWM (Pulse Width Modulation) technology, which adjusts the lighting time of the LED light source by adjusting the duty cycle of the PWM signal. However, in the current lighting industry, the rectifier module and the constant voltage output module of the lamp are directly connected, which will make the constant voltage output module participate in the charging and discharging process of the dimming module, resulting in a large value of current harmonics that cannot be controlled.

[0004] In view of this, it is indeed necessary to improve the existing dimming circuit to solve the above problems. Utility Model Content

[0005] The utility model aims to provide a dimming circuit which can suppress current harmonics to meet the specification requirements.

[0006] To achieve the above object, the utility model provides a dimming circuit, comprising:

[0007] Rectifier module, used to convert AC mains power into DC power;

[0008] A flyback constant voltage isolation module is connected to the rectifier module and converts direct current into constant voltage electricity;

[0009] An MCU module is connected to the flyback constant voltage isolation module, and is used to receive the constant voltage output by the flyback constant voltage isolation module and output a PWM signal;

[0010] A non-isolated dimming module, one end of which is connected to the rectifier module and receives the direct current output by the rectifier module, and the other end of which is respectively connected to the external lamp and the MCU module, and dims the external lamp by receiving the PWM signal output by the MCU module;

[0011] an optical coupling module, connected between the MCU module and the non-isolated dimming module, and used for coupling the PWM signal output by the MCU module to the non-isolated dimming module; and

[0012] The isolation element is arranged between the rectifier module and the flyback constant voltage isolation module, and is used to isolate the direct current output by the rectifier module and then input it into the flyback constant voltage isolation module to prevent the voltage of the flyback constant voltage isolation module from flowing back to the rectifier module.

[0013] As a further improvement of the present invention, the isolation element is a diode D1, the anode of the diode D1 is connected to the rectifier module, and the cathode of the diode D1 is connected to the flyback constant voltage isolation module.

[0014] As a further improvement of the utility model, the flyback constant voltage isolation module includes a first filtering unit connected to the isolation element, a constant voltage controller U2 connected to the first filtering unit, and a transformer connecting the constant voltage controller U2 and the MCU module, and a first voltage dividing resistor R13, a second voltage dividing resistor R16 and a third voltage dividing resistor R20 connected in series are connected between the power input end of the constant voltage controller U2 and the first filtering unit to output a starting voltage for providing the constant voltage controller U2 to work.

[0015] As a further improvement of the present utility model, the flyback constant voltage isolation module also includes a peak absorption unit connected to the first filtering unit and the transformer, the peak absorption unit includes a capacitor C1, a diode D2, a first resistor group and a second resistor group, the cathode of the diode D2 is respectively connected to one end of the first resistor group and one end of the capacitor C1, the anode of the diode D2 is connected to one end of the second resistor group, the other end of the first resistor group and the other end of the capacitor C1 are connected to pin 1 of the primary winding of the transformer, and the other end of the second resistor group is connected to pin 3 of the primary winding of the transformer.

[0016] As a further improvement of the present utility model, the flyback constant voltage isolation module also includes a driving unit, which includes a resistor R17, a resistor R18, a diode D3 and a switch Q1, one end of the resistor R17 is connected to the driving end of the constant voltage controller U2, and the other end is connected to one end of the resistor R18 and the cathode of the diode D3, the other end of the resistor R18 and the anode of the diode D3 are both connected to the gate of the switch Q1, the drain of the switch Q1 is connected to pin 3 of the primary winding of the transformer, and the source of the switch Q1 is grounded.

[0017] As a further improvement of the present invention, a fourth voltage-dividing resistor R21, a fifth voltage-dividing resistor R22, a sixth voltage-dividing resistor R23 and a seventh voltage-dividing resistor R24 ​​are also connected between the source of the switch Q1 and the ground. The fourth voltage-dividing resistor R21, the fifth voltage-dividing resistor R22, the sixth voltage-dividing resistor R23 and the seventh voltage-dividing resistor R24 ​​are connected in parallel to each other to divide the voltage output from the source of the switch Q1.

[0018] As a further improvement of the present utility model, the flyback constant voltage isolation module also includes a detection circuit, which includes a resistor R27 and a capacitor C5, one end of the resistor R27 is connected to the CS pin of the constant voltage controller U2, and the other end is connected to one end of the capacitor C5, and the other end of the capacitor C5 is connected to pin 3 of the primary winding of the transformer.

[0019] As a further improvement of the present invention, the flyback constant voltage isolation module also includes a voltage-stabilized power supply unit, one end of which is connected to pin 5 of the auxiliary winding of the transformer, and the other end is connected to the power input end of the constant voltage controller U2 to provide a working voltage to the constant voltage controller U2.

[0020] As a further improvement of the present invention, the optocoupler module includes an optocoupler U3 and a resistor R35, pin 1 of the optocoupler U3 is connected to one end of the resistor R35, the other end of the resistor R35 is connected to the MCU module, and pin 2 of the optocoupler U3 is grounded.

[0021] As a further improvement of the present invention, the non-isolated dimming module includes a second filter unit, a dimming controller U4 and a BUCK circuit. One end of the second filter unit is connected to the rectifier module, and the other end is connected to the voltage input end of the dimming controller U4. The dimming controller U4 is connected to the external lamp through the BUCK circuit to dim the external lamp.

[0022] The beneficial effect of the utility model is that the dimming circuit of the utility model sets an isolation element between the rectifier module and the flyback constant voltage isolation module, so that the flyback constant voltage isolation module does not participate in the charging and discharging process of the non-isolated dimming module, so as to further suppress the current harmonics and meet the specification requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a dimming circuit diagram that conforms to the preferred embodiment of the utility model.

[0024] Figure 2 yes Figure 1 Enlarged view of the rectifier module.

[0025] Figure 3 yes Figure 1Enlarged view of the flyback constant voltage isolation module.

[0026] Figure 4 yes Figure 1 An enlarged view of the MCU module.

[0027] Figure 5 yes Figure 1 Enlarged view of the optocoupler module.

[0028] Figure 6 yes Figure 1 A magnified image of the isolated dimming module in Africa.

[0029] Figure 7 yes Figure 1 Magnified view of the isolation element. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0031] See also Figure 1 As shown, the utility model discloses a dimming circuit 100, including a rectifier module 1, a flyback constant voltage isolation module 2, an MCU module 3, a non-isolated dimming module 4, an optical coupling module 5 and an isolation element 6.

[0032] In this embodiment, the rectifier module 1 is connected to the external mains power and converts the external AC mains power into DC power, that is, converts the AC mains power sinusoidal wave signal into a steamed bun wave; the flyback constant voltage isolation module 2 is connected to the rectifier module 1 and converts the DC power into constant voltage power; the MCU module 3 is connected to the flyback constant voltage isolation module 2, for receiving the constant voltage power output by the flyback constant voltage isolation module 2, and outputting a PWM signal; one end of the non-isolated dimming module 4 is connected to the rectifier module 1 and receives the DC power output by the rectifier module 1, and the other end is respectively connected to the external lamp and the MCU module 3, and the external lamp is dimmed by receiving the PWM signal output by the MCU module 3; the optocoupler module 5 is connected between the MCU module 3 and the non-isolated dimming module 4, for coupling the PWM signal output by the MCU module 3 to the non-isolated dimming module 4.

[0033] In other words, the flyback constant voltage isolation module 2 outputs constant voltage electricity and supplies power to the MCU module 3, and then the PWM signal is coupled to the non-isolated dimming module 4 through the MCU module 3 and the optical coupling module 5 to perform dimming control on the external lamp. In this embodiment, the optical coupling module 5 transmits the PWM signal through photoelectric conversion, and isolates the MCU module 3 and the non-isolated dimming module 4 to ensure the safety of the circuit.

[0034] Please combine Figure 2 As shown, the rectifier module 1 includes a fuse F1 and a rectifier bridge 11 composed of a plurality of rectifier diodes, and the rectifier bridge 11 is respectively connected to one end of the isolation element 6 and one end of the non-isolated dimming module 4 to simultaneously transmit the rectified DC power to the isolation element 6 and the non-isolated dimming module 4. Preferably, there are four rectifier diodes, namely, diode BD1, diode BD2, diode BD3 and diode BD4.

[0035] Please combine Figure 7 As shown, the isolation element 6 is provided between the rectifier module 1 and the flyback constant voltage isolation module 2, and is used to isolate the DC power output by the rectifier module 1 and then input it into the flyback constant voltage isolation module 2, so as to prevent the voltage of the flyback constant voltage isolation module 2 from flowing back to the rectifier module 1. In other words, by providing the isolation element 6, the DC power output from the rectifier module 1 can only enter the flyback constant voltage isolation module 2 after passing through the isolation element 6, and will not participate in the charging and discharging process of the non-isolated dimming module 4. In this way, the current harmonics can be further suppressed and meet the regulatory requirements.

[0036] Preferably, the isolation element 6 is a diode D1 , the anode of the diode D1 is connected to the rectifier module 1 , and the cathode of the diode D1 is connected to the flyback constant voltage isolation module 2 .

[0037] Please combine Figure 3 As shown, the flyback constant voltage isolation module 2 includes a first filtering unit 21 connected to the isolation element 6, a constant voltage controller U2 connected to the first filtering unit 21, and a transformer 22 connecting the constant voltage controller U2 and the MCU module 3, and the first filtering unit 21 is respectively connected to the transformer 22 and the constant voltage controller U2.

[0038] The first filtering unit 21 includes an electrolytic capacitor EC3, an electrolytic capacitor EC4, a capacitor C4 and an inductor L1, the positive electrode of the electrolytic capacitor EC4 is connected to pin 1 of the inductor L1, and the negative electrode of the electrolytic capacitor EC4 is grounded; the positive electrode of the electrolytic capacitor EC3 and one end of the capacitor C4 are connected to pin 2 of the inductor L1, and the negative electrode of the electrolytic capacitor EC3 and the other end of the capacitor C4 are grounded.

[0039] Preferably, a first voltage-dividing resistor R13, a second voltage-dividing resistor R16 and a third voltage-dividing resistor R20 connected in series are connected between the power input terminal (i.e., the VDD pin) of the constant voltage controller U2 and the first filtering unit 21, so that a starting voltage for providing the operation of the constant voltage controller U2 can be output.

[0040] The flyback constant voltage isolation module 2 also includes a driving unit, which includes a resistor R17, a resistor R18, a diode D3 and a switch Q1. One end of the resistor R17 is connected to the driving end (i.e., the GATE pin) of the constant voltage controller U2, and the other end is connected to one end of the resistor R18 and the cathode of the diode D3. The switch Q1 is preferably a MOS tube. The other end of the resistor R18 and the anode of the diode D3 are both connected to the gate of the switch Q1. The drain of the switch Q1 is connected to pin 3 of the primary winding of the transformer 22, and the source of the switch Q1 is grounded.

[0041] A fourth voltage-dividing resistor R21, a fifth voltage-dividing resistor R22, a sixth voltage-dividing resistor R23 and a seventh voltage-dividing resistor R24 ​​are also connected between the source of the switch Q1 and the ground. The fourth voltage-dividing resistor R21, the fifth voltage-dividing resistor R22, the sixth voltage-dividing resistor R23 and the seventh voltage-dividing resistor R24 ​​are connected in parallel to each other to divide the voltage output from the source of the switch Q1.

[0042] In this embodiment, the driving end of the constant voltage controller U2 controls the on and off of the switch Q1. When the switch Q1 is connected, the voltage is output from the 3rd pin of the primary winding of the transformer 22, and then passes through the drain of the switch Q1 to the source ground; when the switch Q1 is disconnected, the residual voltage in the switch Q1 flows from the diode D3 to the resistor R17 and then discharges.

[0043] The flyback constant voltage isolation module 2 also includes a detection unit, which includes a resistor R27 and a capacitor C5. The resistor R27 and the capacitor C5 form an RC filter circuit. One end of the resistor R27 is connected to the CS pin of the constant voltage controller U2, and the other end is connected to one end of the capacitor C5. The other end of the capacitor C5 is connected to the 3rd pin of the primary winding of the transformer 22. In other words, the voltage of the primary winding of the transformer 22 is detected to determine whether it reaches a preset value. When the preset value is reached, the switch Q1 is controlled to be connected or disconnected through the driving end of the constant voltage controller U2.

[0044] The flyback constant voltage isolation module 2 also includes a voltage stabilizing power supply unit 23, one end of which is connected to pin 5 of the auxiliary winding of the transformer 22, and the other end is connected to the power input end of the constant voltage controller U2 to provide a working voltage to the constant voltage controller U2.

[0045] In this embodiment, the voltage-stabilized power supply unit 23 includes a power supply VCC1 for providing voltage to the constant voltage controller U2. When the auxiliary winding of the transformer 22 is in operation, the voltage-stabilized power supply unit 23 transmits a voltage that meets the requirements to the power input terminal of the constant voltage controller U2 to provide the working voltage required for the normal operation of the constant voltage controller U2. In other words, the power input terminal of the constant voltage controller U2 will receive two input voltages, one as the starting voltage of the constant voltage controller U2, and the other as the working voltage of the constant voltage controller U2.

[0046] In addition, the flyback constant voltage isolation module 2 also includes a peak absorption unit 24 connected to the first filtering unit 21 and the transformer 22, and the peak absorption unit 24 includes a capacitor C1, a diode D2, a first resistor group and a second resistor group, the cathode of the diode D2 is respectively connected to one end of the first resistor group and one end of the capacitor C1, the anode of the diode D2 is connected to one end of the second resistor group, the other end of the first resistor group and the other end of the capacitor C1 are connected to pin 1 of the primary winding of the transformer 22, and the other end of the second resistor group is connected to pin 3 of the primary winding of the transformer 22.

[0047] In this embodiment, the first resistor group is used for discharging the capacitor C1, and includes a resistor R1, a resistor R2, a resistor R3, a resistor R7, a resistor R8, and a resistor R9. One end of the resistor R1, the resistor R2, and the resistor R3 is connected to the pin 1 of the primary winding of the transformer 22, and the other end is connected to one end of the resistor R7, the resistor R8, and the resistor R9, and the other end of the resistor R7, the resistor R8, and the resistor R9 is connected to the cathode of the diode D2. The resistor R1, the resistor R2, and the resistor R3 are connected in parallel to each other, and the resistor R7, the resistor R8, and the resistor R9 are also connected in parallel to each other.

[0048] The second resistor group includes resistor R4, resistor R5, resistor R10, resistor R11, resistor R14 and resistor R15. One end of the resistor R4, resistor R10 and resistor R14 is connected to the positive electrode of the diode D2, and the other end is connected to one end of the resistor R5, resistor R11 and resistor R15, and the other end of the resistor R5, resistor R11 and resistor R15 is connected to pin 3 of the primary winding of the transformer 22. The resistor R4, resistor R10 and resistor R14 are connected in parallel with each other, and the resistor R5, resistor R11 and resistor R15 are also connected in parallel with each other.

[0049] Preferably, the peak absorption unit 24 is used to suppress the resonance voltage spike, leaving at least 20% voltage margin for the withstand voltage of the switch Q1 (ie, MOS tube), thereby avoiding damage to the switch Q1 or affecting the service life of the switch Q1. At the same time, the peak absorption unit 24 also suppresses the resonance voltage oscillation.

[0050] The transformer 22 also includes a secondary winding, and a third filter unit 25 is connected between the secondary winding and the MCU module 3, so as to ensure that the flyback constant voltage isolation module 2 outputs constant voltage electricity through the third filter unit 25. In this embodiment, the constant voltage electricity is 5V / 2A.

[0051] Please combine Figure 4 As shown, the MCU module 3 includes an MCU controller U1 and a capacitor C6 connected in parallel with the MCU controller U1. The output end of the third filtering unit 25 is connected to the power input end of the MCU controller U1 to power the MCU controller U1, and the capacitor C6 filters high frequencies.

[0052] The MCU module 3 also includes a PWM signal terminal (i.e., P1.1 / PWM1 pin) and a ground terminal (i.e., GND pin), the PWM signal is output from the PWM signal terminal, and the ground terminal is grounded. Of course, the MCU module 3 can also integrate other control methods, which are not fully described in this embodiment and can be integrated according to actual conditions, without limitation.

[0053] Please combine Figure 5 As shown, the optical coupling module 5 includes an optical coupler U3 and a resistor R35, wherein the pin 1 of the optical coupler U3 is connected to one end of the resistor R35, the other end of the resistor R35 is connected to the MCU module 3, and the pin 2 of the optical coupler U3 is grounded. The optical coupler U3 is configured to perform photoelectric conversion on the PWM signal so as to couple it to the non-isolated dimming module 4.

[0054] Please combine Figure 6 As shown, the non-isolated dimming module 4 includes a second filtering unit 41, a dimming controller U4 and a BUCK circuit 42. One end of the second filtering unit 41 is connected to the rectifier module 1, and the other end is connected to the voltage input end (i.e., the HV end) of the dimming controller U4 through a series-connected resistor R32 to provide a starting voltage to the dimming controller U4. The dimming controller U4 is connected to an external lamp through the BUCK circuit 42 to dim the external lamp.

[0055] The second filtering unit 41 includes capacitor C12, capacitor C13, electrolytic capacitor EC8 and inductor L2, one end of the capacitor C12 is connected to pin 1 of the inductor L2, and the other end is grounded, one end of the capacitor C13 and the positive electrode of the electrolytic capacitor EC8 are connected to pin 2 of the inductor L2, and the other end of the capacitor C13 and the negative electrode of the electrolytic capacitor EC8 are grounded.

[0056] Of course, the dimming controller U4 is also provided with a PWM terminal for receiving the PWM signal converted by the optocoupler module 5. The non-isolated dimming module 4 also includes a switch Q3 connected between the PWM terminal of the dimming controller U4 and the optocoupler U3. The switch Q3 is used to make the waveform of the voltage flowing through it PWM-shaped.

[0057] The dimming controller U4 also integrates a switch for controlling the BUCK circuit 42, so as to connect an external lamp through the BUCK circuit 42 and perform dimming control on the external lamp. The BUCK circuit 42 is conventional technology, and will not be described in detail.

[0058] To sum up, the dimming circuit 100 of the present invention sets an isolation element 6 between the rectifier module 1 and the flyback constant voltage isolation module 2, so that the flyback constant voltage isolation module 2 does not participate in the charging and discharging process of the non-isolated dimming module 4, so as to further suppress the current harmonics and meet the regulatory requirements.

[0059] The above embodiments are only used to illustrate the technical solution of the utility model rather than to limit it. Although the utility model is described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the utility model can be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the utility model.

Claims

1. A dimming circuit, characterized in that: include: A rectifier module (1) is used to convert AC mains power into DC power; A flyback constant voltage isolation module (2) is connected to the rectifier module (1) and converts direct current into constant voltage electricity; An MCU module (3) is connected to the flyback constant voltage isolation module (2), and is used to receive the constant voltage output by the flyback constant voltage isolation module (2), and output a PWM signal; A non-isolated dimming module (4), one end of which is connected to the rectifier module (1) and receives the direct current output by the rectifier module (1), and the other end of which is respectively connected to the external lamp and the MCU module (3), and dims the external lamp by receiving the PWM signal output by the MCU module (3); an optical coupling module (5), connected between the MCU module (3) and the non-isolated dimming module (4), and used for coupling the PWM signal output by the MCU module (3) to the non-isolated dimming module (4); and An isolation element (6) is provided between the rectifier module (1) and the flyback constant voltage isolation module (2) and is used to isolate the direct current output by the rectifier module (1) and then input it into the flyback constant voltage isolation module (2) to prevent the voltage of the flyback constant voltage isolation module (2) from flowing back to the rectifier module (1).

2. The dimming circuit according to claim 1, characterized in that: The isolation element (6) is a diode D1, the anode of the diode D1 is connected to the rectifier module (1), and the cathode of the diode D1 is connected to the flyback constant voltage isolation module (2).

3. The dimming circuit according to claim 1, characterized in that: The flyback constant voltage isolation module (2) comprises a first filtering unit (21) connected to the isolation element (6), a constant voltage controller U2 connected to the first filtering unit (21), and a transformer (22) connecting the constant voltage controller U2 and the MCU module (3); a first voltage dividing resistor R13, a second voltage dividing resistor R16, and a third voltage dividing resistor R20 connected in series are connected between the power input end of the constant voltage controller U2 and the first filtering unit (21) to output a start-up voltage for providing the constant voltage controller U2 to operate.

4. The dimming circuit according to claim 3, characterized in that: The flyback constant voltage isolation module (2) further comprises a peak absorption unit (24) connected to the first filtering unit (21) and the transformer (22); the peak absorption unit (24) comprises a capacitor C1, a diode D2, a first resistor group and a second resistor group; the cathode of the diode D2 is respectively connected to one end of the first resistor group and one end of the capacitor C1; the anode of the diode D2 is connected to one end of the second resistor group; the other end of the first resistor group and the other end of the capacitor C1 are connected to pin 1 of the primary winding of the transformer (22); and the other end of the second resistor group is connected to pin 3 of the primary winding of the transformer (22).

5. The dimming circuit according to claim 3, characterized in that: The flyback constant voltage isolation module (2) also includes a driving unit, which includes a resistor R17, a resistor R18, a diode D3 and a switch Q1, one end of the resistor R17 is connected to the driving end of the constant voltage controller U2, and the other end is connected to one end of the resistor R18 and the cathode of the diode D3, the other end of the resistor R18 and the anode of the diode D3 are both connected to the gate of the switch Q1, the drain of the switch Q1 is connected to pin 3 of the primary winding of the transformer (22), and the source of the switch Q1 is grounded.

6. The dimming circuit according to claim 5, characterized in that: A fourth voltage-dividing resistor R21, a fifth voltage-dividing resistor R22, a sixth voltage-dividing resistor R23 and a seventh voltage-dividing resistor R24 ​​are also connected between the source of the switch Q1 and the ground. The fourth voltage-dividing resistor R21, the fifth voltage-dividing resistor R22, the sixth voltage-dividing resistor R23 and the seventh voltage-dividing resistor R24 ​​are connected in parallel to each other to divide the voltage output from the source of the switch Q1.

7. The dimming circuit according to claim 3, characterized in that: The flyback constant voltage isolation module (2) also includes a detection unit, which includes a resistor R27 and a capacitor C5, one end of the resistor R27 is connected to the CS pin of the constant voltage controller U2, and the other end is connected to one end of the capacitor C5, and the other end of the capacitor C5 is connected to pin 3 of the primary winding of the transformer (22).

8. The dimming circuit according to claim 3, characterized in that: The flyback constant voltage isolation module (2) further comprises a voltage stabilizing power supply unit (23), one end of the voltage stabilizing power supply unit (23) being connected to pin 5 of the auxiliary winding of the transformer (22), and the other end being connected to the power input end of the constant voltage controller U2, so as to provide an operating voltage to the constant voltage controller U2.

9. The dimming circuit according to claim 1, characterized in that: The optical coupling module (5) comprises an optical coupler U3 and a resistor R35, wherein pin 1 of the optical coupler U3 is connected to one end of the resistor R35, the other end of the resistor R35 is connected to the MCU module (3), and pin 2 of the optical coupler U3 is grounded.

10. The dimming circuit according to claim 1, characterized in that: The non-isolated dimming module (4) comprises a second filtering unit (41), a dimming controller U4 and a BUCK circuit (42); one end of the second filtering unit (41) is connected to the rectifier module (1), and the other end is connected to the voltage input end of the dimming controller U4; the dimming controller U4 is connected to an external lamp via the BUCK circuit (42) to dim the external lamp.