Constant current dimming circuit and dimming method thereof

Abstract

This invention relates to the field of dimming power supply technology, and discloses a constant current dimming circuit and dimming method. The circuit includes a main power supply circuit, a constant current control circuit, a peak current control circuit, and an MCU control circuit. The input terminal of the main power supply circuit is connected to AC mains power to convert AC mains power into stable DC power. The input terminal of the constant current control circuit is connected to the main power supply circuit to convert the stable DC power into a constant current DC power. The input terminal of the peak current control circuit is connected to the constant current control circuit, and its output terminal is connected to the lamp load to convert the constant current DC power into a dimming current with a constant peak current. The MCU control circuit adjusts the magnitude of the constant current DC power through a first control signal; and outputs a second control signal to the peak current control circuit according to an external dimming signal to achieve dimming of the lamp load. This constant current dimming circuit can adjust the brightness of the lamp load with a constant current without color temperature drift.

Description

Technical Field

[0001] This invention relates to the field of dimming power supply technology, specifically to a constant current dimming circuit and its dimming method. Background Technology

[0002] With the rapid development of the LED lighting industry, LED lighting has become the preferred choice for indoor and outdoor lighting in many households, and users' requirements for LED power supplies are also increasing. Currently, most LED constant current dimming power supplies on the market achieve constant current dimming of LEDs by adjusting the output current. However, when the output current of an LED constant current dimming power supply decreases, it usually causes a change in the color temperature of the LED chips. For example, the color temperature of white LEDs will shift towards a lower color temperature (warmer), causing the color temperature of the LED lamp to drift with brightness adjustments. Furthermore, existing constant current dimming circuits can only output one current specification, which cannot adapt to various lamp specifications, increasing customers' circuit storage costs. Therefore, a new, highly adaptable constant current dimming solution without color temperature drift is needed. Summary of the Invention

[0003] In order to overcome the shortcomings of the prior art, the purpose of this invention is to provide a constant current dimming circuit and dimming method, which can avoid the color temperature drift of the lamp during the dimming process and adjust the output current specification to adapt to lamps of different specifications, thereby reducing the circuit storage pressure for customers.

[0004] To solve the above problems, the technical solution adopted by the present invention is as follows: a constant current dimming circuit, comprising: a main power supply circuit, the input terminal of which is connected to AC mains power and is used to convert AC mains power into stable DC power; a constant current control circuit, the input terminal of which is connected to the main power supply circuit and is used to convert the stable DC power into constant current DC power with a constant current; a peak current control circuit, the input terminal of which is connected to the constant current control circuit and the output terminal of which is connected to the lamp load, and is used to convert the constant current DC power into a dimming current with a constant peak current; and an MCU control circuit, which is used to output a first control signal to the constant current control circuit according to the rated current of the lamp or the color temperature value in the external dimming signal to adjust the current magnitude of the constant current DC power; and to output a second control signal to the peak current control circuit according to the brightness value in the external dimming signal to adjust the average current magnitude of the dimming current, thereby realizing dimming of the lamp load.

[0005] The constant current dimming circuit described above includes a main power supply circuit comprising a rectifier and filter circuit and a DC voltage regulator circuit. The input terminal of the rectifier and filter circuit is connected to the AC mains power supply, the output terminal of the rectifier and filter circuit is connected to the input terminal of the DC voltage regulator circuit, and the output terminal of the DC voltage regulator circuit is connected to the input terminal of the constant current control circuit.

[0006] In the aforementioned constant current dimming circuit, the positive terminal of the output of the DC voltage regulator circuit is connected to the anode of diode D1, the cathode of diode D1 is connected to the input of the constant current control circuit, the cathode of diode D1 is also connected to the positive terminal of electrolytic capacitor EC1, the negative terminal of electrolytic capacitor EC1 is connected to ground, and the negative terminal of the output of the DC voltage regulator circuit is grounded.

[0007] In the aforementioned constant current dimming circuit, the constant current control circuit is a loop constant current control circuit. The first input terminal of the constant current control circuit is used to sample the output current of the main power supply circuit. The second input terminal of the constant current control circuit is connected to the MCU control circuit. The feedback terminal of the constant current control circuit is connected to the feedback control terminal of the main power supply circuit. The output terminal of the main power supply circuit serves as the output terminal of the constant current control circuit and is connected to the input terminal of the peak current control circuit.

[0008] The constant current dimming circuit described above includes a constant current control circuit comprising a current sampling resistor R1, an operational amplifier U1B, an optocoupler U1, a capacitor C1, and several resistors. The current sampling resistor R1 is connected in series between the negative terminal of the output of the main power supply circuit and the negative terminal of the input of the peak current control circuit. The inverting input of the operational amplifier U1B is connected to the end of the current sampling resistor R1 facing away from the main power supply circuit via a resistor R2. The non-inverting input of the operational amplifier U1B is connected to the MCU control circuit via a resistor R3. The non-inverting input of the operational amplifier U1B is also grounded via a resistor R4. The capacitor C1 is connected in parallel across the two ends of the resistor R4. The output of the operational amplifier U1B is connected to the negative terminal of the input of the optocoupler U1. The positive terminal of the input of the optocoupler U1 is connected to a first voltage. The output of the optocoupler U1 is connected to the feedback control terminal of the main power supply circuit.

[0009] The constant current dimming circuit described above uses a chip-based constant current control circuit.

[0010] The aforementioned constant current dimming circuit includes a constant current control circuit comprising a power supply chip U2 and an external circuit consisting of a MOSFET Q1, a capacitor C2, an inductor L1, a resistor R6, a diode D3, and an electrolytic capacitor EC2. The power supply input pin of the power supply chip U2 and the first terminal of the resistor R6 are both connected to the positive terminal of the main power supply circuit's output. The sampling pin of the power supply chip U2 is connected to the second terminal of the resistor R6. The second terminal of the resistor R6 serves as the positive terminal of the constant current control circuit's output and is connected to the positive terminal of the peak current control circuit's input. The second terminal of the resistor R6 is also connected to the positive terminal of the electrolytic capacitor EC2. The negative terminal of capacitor EC2 is connected to the negative terminal of the output of the constant current control circuit and the negative terminal of the input of the peak current control circuit. The drive pin of power chip U2 is connected to the gate of MOSFET Q1. The source of MOSFET Q1 is grounded. The drain of MOSFET Q1 is connected to the negative terminal of electrolytic capacitor EC2 through inductor L1. The drain of MOSFET Q1 is also connected to the anode of diode D3. The cathode of diode D3 is connected to the positive terminal of the output of the main power supply circuit. The power supply output pin of power chip U2 is grounded through capacitor C2. The control signal input pin of power chip U2 is connected to the MCU control circuit.

[0011] The constant current dimming circuit described above includes a peak current control circuit comprising a MOSFET Q2 and a gate drive circuit. The source of the MOSFET Q2 is connected to the negative terminal of the output of the constant current control circuit, the drain of the MOSFET Q2 is connected to the negative terminal of the lamp load, the gate of the MOSFET Q2 is connected to the output of the gate drive circuit, the input of the gate drive circuit is connected to the MCU control circuit, and a resistor R7 is provided between the drain and the gate of the MOSFET Q2.

[0012] The constant current dimming circuit described above includes an NMOS transistor Q4, a PMOS transistor Q3, and several resistors. The gate of the NMOS transistor Q4 is connected to the MCU control circuit through a resistor R9. The drain of the NMOS transistor Q4 is grounded. A resistor R8 is provided between the drain and gate of the NMOS transistor Q4. The source of the NMOS transistor Q4 is connected to the gate of the PMOS transistor Q3. The source of the PMOS transistor Q3 is connected to a second voltage. A resistor R10 is provided between the source and gate of the PMOS transistor Q3. The drain of the PMOS transistor Q3 is connected to the gate of the MOS transistor Q2.

[0013] A constant current dimming method for the above-mentioned constant current dimming circuit, characterized in that it includes: The output current Iout of the constant current control circuit is calculated based on the first control signal. The average current Iavg of the peak current control circuit is calculated based on the output current Iout and the brightness value in the external dimming signal. Calculate the duty cycle of the second control signal as Iavg / Iout; The second control signal in the form of a corresponding PWM signal is generated based on the calculated duty cycle, and the second control signal is sent to the peak current control circuit.

[0014] Compared to existing technologies, the advantages of this invention are as follows: The constant current dimming circuit of this embodiment first controls the current value output to the peak current control circuit to remain constant through a constant current control circuit. Then, it controls the peak current control circuit to convert the constant DC current into a dimming current with a constant peak current but a variable average current. Therefore, while adjusting the brightness of the lamp, because the peak value of the dimming current remains constant, the color temperature of the lamp can be prevented from drifting with brightness adjustment. The output of the constant current dimming circuit can be adjusted by a first control signal, thereby adjusting the peak current output of the circuit to adapt to products with different current specifications. Furthermore, the first control signal can be calculated based on the required color temperature, thereby achieving independent adjustment of the color temperature and brightness of the lamp, and ensuring that the color temperature does not drift with brightness adjustment at each color temperature.

[0015] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0016] Figure 1 This is a block diagram illustrating the principle of the constant current dimming circuit in an embodiment of the present invention.

[0017] Figure 2 This is a schematic diagram of the constant current control circuit according to the first embodiment of the present invention.

[0018] Figure 3 This is a schematic diagram of the constant current control circuit according to the second embodiment of the present invention.

[0019] Figure 4 This is a schematic diagram of the peak current control circuit according to an embodiment of the present invention. Detailed Implementation

[0020] The embodiments of the present invention are described in detail below, with reference to... Figure 1This invention provides a constant current dimming circuit, including a main power supply circuit, a constant current control circuit, a peak current control circuit, and an MCU control circuit. The input terminal of the main power supply circuit is connected to AC mains power, and the output terminal is connected to the constant current control circuit to convert the AC mains power into stable DC power. The output terminal of the constant current control circuit is connected to the peak current control circuit to convert the stable DC power into constant current DC power. The input terminal of the peak current control circuit is connected to the output terminal of the constant current control circuit, and the output terminal is connected to the lamp load to convert the constant current DC power into a dimming current with a constant peak value. Both the constant current control circuit and the peak current control circuit are controlled by the MCU control circuit. The MCU control circuit outputs a first control signal to the constant current control circuit to adjust the magnitude of the constant current DC power, and outputs a second control signal to the peak current control circuit based on the brightness value in the external dimming signal to adjust the average current magnitude of the dimming current, thereby achieving dimming of the lamp load.

[0021] In practice, under otherwise constant conditions, the color temperature of LED chips is affected by the driving current. A higher driving current results in a higher proportion of blue light in the emitted light, making the light cooler and the color temperature higher. Conversely, a lower driving current results in a warmer light and a lower color temperature. In other words, the color temperature of an LED lamp is affected by changes in the peak current. Therefore, in the constant current dimming circuit of this embodiment, since the peak current of the final output dimming current is constant, the color temperature of the lamp load will not shift, thus preventing the color temperature of the lamp load from drifting with brightness adjustments. The first control signal can be preset according to the rated current of the lamp load, allowing a single circuit to adapt to various lamp loads with different current specifications, improving the circuit's applicability and avoiding customers needing to stock multiple circuits of different specifications for different lamp loads, reducing customer warehousing pressure and inventory costs. The first control signal can also be calculated based on the user's desired color temperature, thereby achieving color temperature adjustment of the lamp load and preventing the value of each color temperature from drifting with brightness adjustments, achieving decoupled control of color temperature and brightness.

[0022] Reference Figure 2 and Figure 3It is understood that the main power supply circuit typically consists of a rectifier and filter circuit and a DC voltage regulator circuit. The input terminal of the rectifier and filter circuit is connected to the AC mains power, and its output terminal is connected to the input terminal of the DC voltage regulator circuit. The output terminal of the DC voltage regulator circuit is connected to the input terminal of the constant current control circuit. In this embodiment, to further improve the power supply quality of the main power supply circuit and prevent damage from backflow voltage, the output terminal of the DC voltage regulator circuit is equipped with a backflow-preventing diode D1 and an electrolytic capacitor EC1 for further filtering the output voltage of the DC voltage regulator circuit. The positive terminal of the output terminal of the DC voltage regulator circuit is connected to the anode of diode D1, the cathode of diode D1 is connected to the input terminal of the constant current control circuit, the cathode of diode D1 is also connected to the positive terminal of electrolytic capacitor EC1, the negative terminal of electrolytic capacitor EC1 is connected to ground, and the negative terminal of the output terminal of the DC voltage regulator circuit is grounded.

[0023] It is understandable that a constant current dimming circuit can be a loop constant current control circuit that samples the output current of the main power supply circuit and uses the sampled output current as a feedback signal to the feedback control terminal of the DC voltage regulator circuit. This allows the DC voltage regulator circuit to adjust its output based on the feedback output current, so that the stable DC power output from the main power supply circuit can be considered a constant current DC power with a constant current value. Alternatively, a constant current dimming circuit can be a chip-based constant current control circuit controlled by the power supply chip, modulating the stable DC power into a constant current DC power.

[0024] Reference Figure 2In some embodiments, the constant current control circuit includes a current sampling resistor R1, an operational amplifier U1B, an optocoupler U1, a capacitor C1, and several resistors. The current sampling resistor R1 is connected in series between the negative terminal of the output of the DC voltage regulator circuit and the negative terminal of the input of the peak current control circuit. The inverting input of the operational amplifier U1B is connected to the end of the current sampling resistor R1 facing away from the DC voltage regulator circuit via resistor R2, and the non-inverting input is connected to the MCU control circuit via resistor R3. The non-inverting input of the operational amplifier U1B is also grounded via resistor R4. The capacitor C1 is connected in parallel across resistor R4. The output of the operational amplifier U1B is connected to the negative terminal of the input of the optocoupler U1, the positive terminal of the input of the optocoupler U1 is connected to the first voltage Vcc, and the output of the optocoupler U1 is connected to the feedback control terminal of the main power supply circuit. The control voltage input to the MCU control circuit is divided by resistors and filtered by capacitors before entering the non-inverting input of operational amplifier U1B. It is compared with the voltage signal generated by the current output from the main power supply circuit flowing through the current sampling resistor R1. Based on the comparison result between the voltage signal output by the MCU control circuit and the voltage signal corresponding to the current output by the main power supply circuit, the optocoupler U1 is controlled to be turned on or off. The output of optocoupler U1 transmits the signal to the main power supply circuit, thereby adjusting the current value output by the main power supply circuit to adapt to different types of lamp loads, or adjusting the peak current output to the lamp load so that the lamp load emits light with the color temperature required by the user.

[0025] Reference Figure 3In some embodiments, the constant current control circuit may also include a power supply chip U2 and an external circuit consisting of a MOSFET Q1, a capacitor C2, an inductor L1, a resistor R6, a diode D3, and an electrolytic capacitor EC2. The power supply input pin 1 of the power supply chip U2 and the first end of the resistor R6 are both connected to the cathode of the diode D1, and the sampling pin 2 is connected to the second end of the resistor R6. The second end of the resistor R6 serves as the positive terminal of the output of the constant current control circuit and is connected to the positive terminal of the input of the peak current control circuit. The second end of the resistor R6 is also connected to the positive terminal of the electrolytic capacitor EC2. The negative terminal of the electrolytic capacitor EC2 serves as the negative terminal of the output of the constant current control circuit and is connected to the negative terminal of the input of the peak current control circuit. The drive pin 5 of the power supply chip U2 is connected to the gate of the MOSFET Q1. The source of the MOSFET Q1 is grounded, and the drain of the MOSFET Q1 is connected to the negative terminal of the electrolytic capacitor EC2 through the inductor L1. The drain of the MOSFET Q1 is also connected to the anode of the diode D3. The cathode of diode D3 is connected to the positive terminal of the main power supply circuit output. Power supply output pin 6 of power chip U2 is grounded through capacitor C2. Control signal input pin 3 of power chip U2 is connected to the MCU control circuit, and grounding pin 4 is grounded. Power chip U2 adjusts the conduction angle of MOSFET Q1 according to the control signal input from the MCU control circuit, thereby regulating the output current. When MOSFET Q1 is on, the current output from the main power supply circuit starts from the positive terminal of the main power supply circuit output, passes through resistor R6, the peak current control circuit, inductor L1, and MOSFET Q1, and returns to the negative terminal of the main power supply circuit output, forming a loop. When MOSFET Q1 is off, inductor L1 generates a reverse electromotive force to maintain a constant current, thus forming a loop with inductor L1, freewheeling diode D3, resistor R6, and the peak current control circuit. When current flows through resistor R6, a voltage difference is generated across resistor R6. The power chip adjusts the switching on and off of MOSFET Q1 based on the voltage across resistor R6, thereby maintaining the stability of the current flowing through R6. Finally, the output current is filtered by electrolytic capacitor EC2 and becomes a constant DC current with a constant current value.

[0026] Understandably, the peak current control circuit can use a PWM signal to control the switching device connected in series between the output of the constant current control circuit and the lamp load to periodically turn on and off, forming a PWM waveform dimming current. This allows for the adjustment of the average current output to the lamp load while maintaining a constant peak current, thereby regulating the brightness of the lamp load. (Refer to...) Figure 4In this embodiment, the switching device can be a MOSFET, and the peak current control circuit can include a MOSFET Q2 and a gate drive circuit. The source of MOSFET Q2 is connected to the negative terminal of the output of the constant current control circuit, the drain is connected to the negative terminal of the lamp load, and the gate is connected to the output of the gate drive circuit. The input of the gate drive circuit is connected to the MCU control circuit, and a resistor R7 is provided between the drain and gate of MOSFET Q2. The gate drive circuit receives the second control signal output by the MCU control circuit and converts it into a corresponding PWM drive signal, driving MOSFET Q2 to periodically turn on and off, converting the constant DC current into a PWM waveform dimming current.

[0027] In this embodiment, refer to Figure 4 The gate drive circuit includes an NMOS transistor Q4, a PMOS transistor Q3, and several resistors. The gate of the NMOS transistor Q4 is connected to the MCU control circuit through a resistor R9. The drain of the NMOS transistor Q4 is grounded, and a resistor R8 is placed between the drain and gate of the NMOS transistor Q4. The source of the NMOS transistor Q4 is connected to the gate of the PMOS transistor Q3. The source of the PMOS transistor Q3 is connected to a second voltage of 12V, and a resistor R10 is placed between the source and gate of the PMOS transistor Q3. The drain of the PMOS transistor Q3 is connected to the gate of the MOS transistor Q2. The MCU control circuit controls the peak current control circuit through a second control signal in PWM form. When the second control signal is high, NMOS transistor Q4 is turned on, pulling down the gate voltage of PMOS transistor Q3, causing PMOS transistor Q3 to also turn on. The 12V second voltage is output through PMOS transistor Q3 to the gate of MOS transistor Q2, causing MOS transistor Q2 to turn on. At this time, the constant current control circuit and the lamp load form a closed loop, and the constant current control circuit outputs Iout to the lamp load. Conversely, when the signal is low, both NMOS transistor Q4 and PMOS transistor Q3 are turned off, the 12V second voltage cannot be applied to the gate of MOS transistor Q2, MOS transistor Q2 is turned off, the constant current control circuit is disconnected from the lamp load, and the current flowing through the lamp load is zero. If the duty cycle of the second control signal is D2, then the average current flowing through the lamp load is Iavg = Iout * D2. Thus, the required average current can be calculated based on the required brightness, and the duty cycle of the second control signal can be calculated based on the required average current. The MCU control circuit generates the corresponding second control signal based on the calculated duty cycle and sends it to the peak current control circuit, so that the required brightness can be adjusted without affecting the color temperature of the lamp load.

[0028] It is understandable that MCU control circuits are typically composed of MCU control chips and their peripheral circuits. The specific structures of rectifier filter circuits and DC voltage regulator circuits are common knowledge in this field, and their specific circuits will not be described in detail here.

[0029] Based on the same inventive concept, the constant current dimming circuit of this invention can adjust the brightness of the lamp load through the following dimming method: First, the output current Iout of the constant current control circuit is calculated based on the first control signal. The value of Iout can be set according to the color temperature required by the user or the rated current of the lamp load. In some embodiments, the MCU control circuit can calculate the required output current Iout based on the color temperature value in the external dimming signal, and calculate the duty cycle or voltage value of the first control signal based on the required output current Iout. Then, the average current Iavg of the peak current control circuit is calculated based on the output current Iout and the brightness value in the external dimming signal. Since the brightness and current of an LED chip are typically approximately linearly related, if 20% brightness is required, Iavg can be 20% * Iout. Next, the duty cycle of the second control signal is calculated as Iavg / Iout. Finally, the MCU control circuit generates a corresponding PWM signal form of the second control signal based on the calculated duty cycle and sends the second control signal to the peak current control circuit, thereby adjusting the brightness of the lamp load without color temperature drift.

[0030] It should be noted that in the description of this invention, any descriptions of orientation, such as up, down, front, back, left, right, etc., indicating orientation or positional relationships, are based on the orientation or positional relationships shown in the accompanying drawings. They are only for the purpose of facilitating the description of this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed or operated in a specific orientation, and should not be construed as a limitation of this invention.

[0031] In the description of this invention, "several" means one or more, "more than" means two or more, "greater than," "less than," "exceeding," etc. are understood to exclude the stated number, while "above," "below," "within," etc. are understood to include the stated number. If "first" or "second" is mentioned, it is only for the purpose of distinguishing technical features and should not be construed as indicating or implying relative importance, or implicitly indicating the number of indicated technical features, or implicitly indicating the order of the indicated technical features.

[0032] In the description of this invention, unless otherwise explicitly defined, terms such as "set up," "install," and "connect" should be interpreted broadly, and those skilled in the art can reasonably determine the specific meaning of the above terms in this invention in conjunction with the specific content of the technical solution.

[0033] The above embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention shall fall within the scope of protection claimed by the present invention.

Claims

1. A constant current dimming circuit, characterized in that, include: The main power supply circuit has an input terminal for connecting to AC mains power, which is used to convert AC mains power into stable DC power. A constant current control circuit, with its input terminal connected to the main power supply circuit, is used to convert the stable DC power into a constant current DC power with a constant current. The peak current control circuit has its input terminal connected to the constant current control circuit and its output terminal connected to the lamp load. It is used to convert the constant current DC power into a dimming current with a constant peak current. The MCU control circuit is used to output a first control signal to the constant current control circuit according to the rated current of the lamp or the color temperature value in the external dimming signal, so as to adjust the current of the constant current DC power supply. The system outputs a second control signal to the peak current control circuit based on the brightness value in the external dimming signal, thereby adjusting the average current of the dimming current and achieving dimming of the lamp load.

2. The constant current dimming circuit according to claim 1, characterized in that, The main power supply circuit includes a rectifier and filter circuit and a DC voltage regulator circuit. The input terminal of the rectifier and filter circuit is connected to the AC mains power, the output terminal of the rectifier and filter circuit is connected to the input terminal of the DC voltage regulator circuit, and the output terminal of the DC voltage regulator circuit is connected to the input terminal of the constant current control circuit.

3. The constant current dimming circuit according to claim 2, characterized in that, The positive terminal of the output of the DC voltage regulator circuit is connected to the anode of diode D1, the cathode of diode D1 is connected to the input of the constant current control circuit, the cathode of diode D1 is also connected to the positive terminal of electrolytic capacitor EC1, the negative terminal of electrolytic capacitor EC1 is connected to ground, and the negative terminal of the output of the DC voltage regulator circuit is grounded.

4. The constant current dimming circuit according to claim 1, characterized in that, The constant current control circuit is a loop constant current control circuit. The first input terminal of the constant current control circuit is used to sample the output current of the main power supply circuit. The second input terminal of the constant current control circuit is connected to the MCU control circuit. The feedback terminal of the constant current control circuit is connected to the feedback control terminal of the main power supply circuit. The output terminal of the main power supply circuit is used as the output terminal of the constant current control circuit and is connected to the input terminal of the peak current control circuit.

5. The constant current dimming circuit according to claim 4, characterized in that, The constant current control circuit includes a current sampling resistor R1, an operational amplifier U1B, an optocoupler U1, a capacitor C1, and several resistors. The current sampling resistor R1 is connected in series between the negative terminal of the output of the main power supply circuit and the negative terminal of the input of the peak current control circuit. The inverting input of the operational amplifier U1B is connected to the end of the current sampling resistor R1 facing away from the main power supply circuit through a resistor R2. The non-inverting input of the operational amplifier U1B is connected to the MCU control circuit through a resistor R3. The non-inverting input of the operational amplifier U1B is also grounded through a resistor R4. The capacitor C1 is connected in parallel across the two ends of the resistor R4. The output of the operational amplifier U1B is connected to the negative terminal of the input of the optocoupler U1. The positive terminal of the input of the optocoupler U1 is connected to a first voltage. The output of the optocoupler U1 is connected to the feedback control terminal of the main power supply circuit.

6. The constant current dimming circuit according to claim 1, characterized in that, The constant current control circuit is a chip-based constant current control circuit.

7. The constant current dimming circuit according to claim 6, characterized in that, The constant current control circuit includes a power supply chip U2 and an external circuit consisting of a MOSFET Q1, a capacitor C2, an inductor L1, a resistor R6, a diode D3, and an electrolytic capacitor EC2. The power supply input pin of the power supply chip U2 and the first terminal of the resistor R6 are both connected to the positive terminal of the main power supply circuit's output. The sampling pin of the power supply chip U2 is connected to the second terminal of the resistor R6. The second terminal of the resistor R6 serves as the positive terminal of the constant current control circuit's output and is connected to the positive terminal of the peak current control circuit's input. The second terminal of the resistor R6 is also connected to the positive terminal of the electrolytic capacitor EC2. The negative terminal of the power supply chip U2 is connected to the negative terminal of the output of the constant current control circuit and the negative terminal of the input of the peak current control circuit. The drive pin of the power supply chip U2 is connected to the gate of the MOSFET Q1. The source of the MOSFET Q1 is grounded. The drain of the MOSFET Q1 is connected to the negative terminal of the electrolytic capacitor EC2 through the inductor L1. The drain of the MOSFET Q1 is also connected to the anode of the diode D3. The cathode of the diode D3 is connected to the positive terminal of the output of the main power supply circuit. The power supply output pin of the power supply chip U2 is grounded through the capacitor C2. The control signal input pin of the power supply chip U2 is connected to the MCU control circuit.

8. The constant current dimming circuit according to claim 1, characterized in that, The peak current control circuit includes a MOSFET Q2 and a gate drive circuit. The source of the MOSFET Q2 is connected to the negative terminal of the output of the constant current control circuit, the drain of the MOSFET Q2 is connected to the negative terminal of the lamp load, and the gate of the MOSFET Q2 is connected to the output of the gate drive circuit. The input of the gate drive circuit is connected to the MCU control circuit, and a resistor R7 is provided between the drain and the gate of the MOSFET Q2.

9. The constant current dimming circuit according to claim 8, characterized in that, The gate drive circuit includes an NMOS transistor Q4, a PMOS transistor Q3, and several resistors. The gate of the NMOS transistor Q4 is connected to the MCU control circuit through a resistor R9. The drain of the NMOS transistor Q4 is grounded. A resistor R8 is provided between the drain and gate of the NMOS transistor Q4. The source of the NMOS transistor Q4 is connected to the gate of the PMOS transistor Q3. The source of the PMOS transistor Q3 is connected to a second voltage. A resistor R10 is provided between the source and gate of the PMOS transistor Q3. The drain of the PMOS transistor Q3 is connected to the gate of the MOS transistor Q2.

10. A constant current dimming method for a constant current dimming circuit according to any one of claims 1 to 9, characterized in that, include: The output current Iout of the constant current control circuit is calculated based on the first control signal. The average current Iavg of the peak current control circuit is calculated based on the output current Iout and the brightness value in the external dimming signal. Calculate the duty cycle of the second control signal as Iavg / Iout; The second control signal in the form of a corresponding PWM signal is generated based on the calculated duty cycle, and the second control signal is sent to the peak current control circuit.

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