LED illumination constant-current driving system with automatic dimming function

Abstract

The invention relates to an automatic dimming LED illumination constant-current driving system, and the system comprises a direct-current power module which is connected with a power supply circuit and a constant-current driving circuit, and provides direct current for the power supply circuit and the constant-current driving circuit; the power supply circuit is connected with the PWM dimming control circuit and converts the direct current provided by the direct current power supply module into a low-voltage power supply required by the PWM dimming control circuit; the PWM dimming control circuit is connected with the constant-current driving circuit, automatically generates a PWM signal with a variable duty ratio according to the environment illumination intensity and outputs the PWM signal to the constant-current driving circuit; and the constant current driving circuit is connected with the LED lamp bead string, adjusts output current based on the received PWM signal, and provides constant current for the LED lamp bead string. The automatic dimming LED illumination constant-current driving system can adaptively adjust the brightness of the LED, is energy-saving and efficient, ensures the constant current of the LED lamp bead, prolongs the service life of the LED lamp bead, provides a stable illumination effect, and meets different illumination requirements.

Description

Technical Field

[0001] The present application relates to the fields of electronic engineering and semiconductor lighting technology, and in particular to an automatic dimming LED lighting constant current drive system. Background Art

[0002] With the rapid development of LED technology, its advantages such as high efficiency and energy saving, long life, and stable light quality have gradually made it become the mainstream light source in the lighting field. However, the performance of the LED driving circuit directly affects the overall quality and life of LED lamps. In the current market, some LED driving circuits have problems such as inaccurate constant current control and poor adaptability. In particular, some driving methods are still based on constant voltage, which can easily lead to an increase in LED junction temperature, causing the current to be out of control, and ultimately reduce the luminous efficiency and life. At the same time, problems such as complex driving circuit design, many components, and easy damage further limit the reliability and cost advantages of LED lamps in large-scale applications.

[0003] The demand for dimming of LED lighting is gradually increasing with the popularization of intelligent and energy-saving concepts, but the current dimming technology still has obvious shortcomings. The traditional analog dimming method achieves brightness adjustment by changing the LED current, but this method will cause the color temperature and luminous wavelength of the LED to change, affecting the light quality. In contrast, PWM dimming uses high-frequency switching to control the average current of the LED, which can ensure that the instantaneous current flowing through the LED is stable in the most suitable range, thereby maintaining the best luminous effect and avoiding color deviation. However, existing PWM dimming circuits often have problems such as complex design, high cost or the need for software programming, and are not suitable for the popularization of economical LED lamps. Therefore, the development of PWM dimming drive circuits with simple structure, stable performance and easy implementation has become an important development direction of LED lighting technology.

[0004] In addition, existing dimming mainly relies on manual brightness adjustment and cannot automatically adjust the brightness of the light source according to the ambient light intensity, causing inconvenience in operation and failing to effectively optimize energy efficiency. Summary of the invention

[0005] In order to solve the above technical problems, the present application provides an automatic dimming LED lighting constant current drive system, the system comprising:

[0006] A DC power supply module is connected to the power supply circuit and the constant current drive circuit to provide DC power to the power supply circuit and the constant current drive circuit;

[0007] A power supply circuit, connected to the PWM dimming control circuit, converts the DC power provided by the DC power supply module into a low-voltage power supply required by the PWM dimming control circuit;

[0008] A PWM dimming control circuit is connected to the constant current drive circuit, automatically generates a PWM signal with a variable duty cycle according to the ambient light intensity and outputs it to the constant current drive circuit;

[0009] The constant current driving circuit is connected to the LED lamp bead string, and adjusts the output current based on the received PWM signal to provide a constant current for the LED lamp bead string.

[0010] Optionally, the constant current driving circuit includes:

[0011] The LM3402HV chip comprises an internally integrated diode and an N-channel MOS tube, wherein the drain of the N-channel MOS tube is connected to the VIN pin of the LM3402HV chip, and the source is connected to the SW pin of the LM3402HV chip; the anode of the internally integrated diode is connected to the VCC pin of the LM3402HV chip, and the cathode is connected to the BOOT pin of the LM3402HV chip;

[0012] An inductor L1, one end of which is connected to the SW pin of the LM3402HV chip, and the other end of which is connected to the positive end of the LED lamp bead string;

[0013] a diode D1, wherein a cathode of the diode D1 is connected to the SW pin and an anode of the diode D1 is grounded;

[0014] Capacitor C B , the capacitor C B One end is connected to the BOOT pin of the LM3402HV chip, and the other end is connected to the SW pin;

[0015] A resistor RSNS, one end of the resistor RSNS is connected to the CS pin of the LM3402HV chip, and the other end is grounded; the CS pin is also connected to the negative end of the LED lamp bead string.

[0016] Optionally, the constant current driving circuit further includes:

[0017] A diode D2, wherein the cathode of the diode D2 is connected to the DIM pin of the LM3402HV chip, the anode of the diode D2 is connected to the DIM port, and the diode D2 is connected to the PWM dimming control circuit through the DIM port to receive the PWM signal;

[0018] Resistor R7 and resistor R8, the VCC pin of the LM3402HV chip is grounded through the resistor R7 and resistor R8 connected in series; the VCC pin is also grounded through the capacitor CF;

[0019] A switch S1 , one end of which is connected to the DIM pin, and the other end of which is connected between the resistor R7 and the resistor R8 .

[0020] Optionally, the constant current driving circuit further includes:

[0021] A capacitor CIN, one end of the capacitor CIN is connected to the VIN pin of the LM3402HV chip, the other end is grounded, and the VIN pin is also connected to the positive electrode of the DC power supply module;

[0022] A resistor RON, one end of which is connected to the VIN pin, and the other end of which is connected to the RON pin of the LM3402HV chip. The RON pin is also connected to port.

[0023] Optionally, the PWM dimming control circuit includes:

[0024] A TL494 chip, wherein the +IN1 pin of the TL494 chip is connected to the -IN1 pin of the TL494 chip, and the +IN2 pin of the TL494 chip is connected to the -IN2 pin of the TL494 chip; the REF OUT pin of the TL494 chip is connected to the FB pin of the TL494 chip through an adjustable resistor RP1 and a resistor R3 connected in series in sequence; the FB pin is also grounded through a resistor R4, and the resistor R4 is a photoresistor.

[0025] Optionally, the PWM dimming control circuit further includes:

[0026] A voltage stabilizing diode VZ2 , wherein a cathode of the voltage stabilizing diode VZ2 is connected to the FB pin, and an anode of the voltage stabilizing diode VZ2 is grounded.

[0027] Optionally, the PWM dimming control circuit further includes:

[0028] A capacitor C1, one end of the capacitor C1 is connected to the CT pin of the TL494 chip, and the other end is grounded;

[0029] Resistor R6, one end of the resistor R6 is connected to the RT pin of the TL494 chip, and the other end is grounded.

[0030] Optionally, the VCC pin of the TL494 chip is connected to the C1 pin of the TL494 chip and the C2 pin of the TL494 chip;

[0031] The E1 pin of the TL494 chip is connected to the E2 pin of the TL494 chip, and the E1 pin and the E2 pin are connected to the DIM port through a resistor R5 to output a PWM signal;

[0032] The OUT CON pin and DT CON pin of the TL494 chip are grounded.

[0033] Optionally, the power supply circuit includes:

[0034] A voltage zener diode DZ1, wherein the cathode of the voltage zener diode DZ1 is connected to the DC power supply module via a resistor R1, and the anode of the voltage zener diode DZ1 is grounded;

[0035] Transistor Q1, the base of the transistor Q1 is connected to the DC power supply module through a resistor R1, the collector is connected to the DC power supply module through a resistor R2, and the emitter is connected to the PWM dimming control circuit to supply power to the PWM dimming control circuit.

[0036] Optionally, when the switch S1 is closed, the DIM pin is fixed at a high level and is not affected by a PWM signal; when the switch S1 is open, the DIM pin adjusts the current through a PWM signal.

[0037] The automatic dimming LED lighting constant current drive system provided in the present application can effectively realize constant current drive and dimming control of LED lamp beads through the coordinated work of DC power supply module, power supply circuit, PWM dimming control circuit and constant current drive circuit. The DC power supply module provides stable DC input, and the power supply circuit converts the DC voltage into a low-voltage power supply suitable for the PWM dimming control circuit to ensure the stability of system operation. The PWM dimming control circuit automatically generates a PWM signal with an adjustable duty cycle according to the ambient light intensity, and combines the constant current drive circuit to accurately control the current of the LED lamp beads, so that the LED lamp can achieve efficient and stable brightness adjustment under different lighting requirements, while avoiding the problems of reduced light efficiency and shortened life due to unstable current.

[0038] Furthermore, the constant current drive circuit in the technical solution of the present application adopts the LM3402HV chip, combined with peripheral components such as the inductor L1, the diode D1, and the resistor RSNS, to form an efficient Buck circuit structure, which can provide a stable constant current output within a wide input voltage range, while accurately setting the conduction time of the internal MOS tube, thereby improving the drive efficiency and reducing the energy consumption of the system. In addition, the PWM dimming control circuit is designed based on the TL494 chip, and the adaptive adjustment of the ambient light is achieved by introducing the photoresistor R4, and the maximum voltage on the FB pin of the TL494 chip is limited by the voltage regulator diode VZ2 to protect the chip. The overall design makes this system not only energy-efficient, but also takes into account the light quality and service life, which is suitable for the needs of intelligent LED lighting. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 A system block diagram of an automatic dimming LED lighting constant current drive system according to an embodiment of the present application is shown;

[0040] Figure 24 shows a circuit diagram of a constant current driving circuit 400 according to an embodiment of the present application;

[0041] Figure 3 1 shows a circuit diagram of a PWM dimming control circuit 300 according to an embodiment of the present application;

[0042] Figure 4 FIG. 4 shows a circuit diagram of a power supply circuit 200 according to an embodiment of the present application. DETAILED DESCRIPTION

[0043] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are described in detail below in conjunction with the accompanying drawings. It is to be understood that the specific embodiments described herein are only used to explain the present application, rather than to limit the present application. It should also be noted that, for ease of description, only some structures related to the present application are shown in the accompanying drawings, rather than all structures. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0044] The terms "including" and "having" and any variations thereof in this application are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device comprising a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to these processes, methods, products or devices.

[0045] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0046] Figure 1 FIG. 1 shows a system block diagram of an automatic dimming LED lighting constant current drive system according to an embodiment of the present application. Figure 1 As shown, the automatic dimming LED lighting constant current drive system includes:

[0047] The DC power supply module 100 is connected to the power supply circuit 200 and the constant current drive circuit 400 to provide DC power to the power supply circuit 200 and the constant current drive circuit 400.

[0048] The DC power supply module 100 is the energy basis of the entire system. It mainly provides DC power for the system and transmits electrical energy to the power supply circuit 200 and the constant current drive circuit 400, providing reliable energy support for subsequent modules. During system operation, the output of this module is directly related to the voltage stabilization effect of the power supply circuit 200 and the working stability of the constant current drive circuit 400. By providing a stable DC voltage, the DC power supply module 100 can ensure that the subsequent circuits operate under efficient and stable conditions.

[0049] The power supply circuit 200 is connected to the PWM dimming control circuit 300 , and converts the DC power provided by the DC power supply module 100 into a low-voltage power required by the PWM dimming control circuit 300 .

[0050] The power supply circuit 200 is located between the DC power supply module 100 and the PWM dimming control circuit 300. Its function is to step down and stabilize the high-voltage DC power provided by the DC power supply module 100, converting it into low-voltage DC power to meet the voltage requirements of the PWM dimming control circuit 300. The design of the power supply circuit 200 not only protects the PWM control chip from high-voltage damage, but also reduces the energy loss of the system by optimizing the step-down efficiency. This module works closely with the DC power supply module 100 and the PWM dimming control circuit 300 to form a stable energy chain, providing reliable support for subsequent dimming and constant current driving.

[0051] The PWM dimming control circuit 300 is connected to the constant current driving circuit 400 , and automatically generates a PWM signal with a variable duty cycle according to the ambient light intensity and outputs it to the constant current driving circuit 400 .

[0052] The PWM dimming control circuit 300 receives the low-voltage direct current provided by the power supply circuit 200 as a power source, automatically generates a PWM signal with an adjustable duty cycle through the internal PWM control chip and according to the ambient light intensity, and outputs the signal to the DIM pin of the constant current drive circuit 400 to control the brightness adjustment of the LED lamp beads. In the specific working process, the PWM dimming control circuit 300 will dynamically adjust the duty cycle of the PWM signal according to the ambient light intensity or user settings. The duty cycle determines the working time of the Buck circuit in the constant current drive circuit 400 within a dimming cycle, thereby changing the time of the current flowing through the LED lamp bead string within a dimming cycle to achieve the purpose of adjusting the brightness.

[0053] The PWM signal generated by the PWM dimming control circuit 300 can accurately control the working current of the LED, which not only maintains the luminous efficiency and stability of the LED lamp beads, but also effectively avoids the color deviation or light efficiency reduction caused by directly changing the current. In addition, the PWM technology can ensure that the LED works in the ideal conduction current range, prolong the service life of the LED lamp, and realize energy saving and intelligent lighting through dimming.

[0054] The constant current driving circuit 400 is connected to the LED lamp bead string 500, and adjusts the output current based on the received PWM signal to provide a constant current for the LED lamp bead string 500.

[0055] The constant current drive circuit 400 is the core part of the system that provides constant current for the LED lamp bead string 500. The constant current drive circuit 400 receives the high voltage DC power provided by the DC power supply module 100 as input, and receives the PWM signal from the PWM dimming control circuit 300 at the same time, and can convert the input voltage into a stable constant current output suitable for the LED lamp bead string 500. Through the adjustment of the constant current drive circuit 400, the current flowing through the LED lamp bead always remains constant, and the working state of the LED will not be affected by the fluctuation of the supply voltage or the change of the load. This constant current drive mode not only ensures the brightness consistency of the LED, but also effectively avoids the overheating caused by excessive current, thereby extending the service life of the LED. In addition, the efficient energy conversion design of the constant current drive circuit 400 greatly reduces the energy loss in the operation of the system and improves the overall performance of the system. The coordinated work of the constant current drive circuit 400 and the PWM dimming control circuit 300 not only realizes the dynamic adjustment of the brightness, but also further optimizes the energy saving effect of the system.

[0056] According to the above embodiments, the automatic dimming LED lighting constant current drive system provided by the present application can effectively realize constant current drive and dimming control of the LED lamp bead string 500 through the coordinated work of the DC power supply module 100, the power supply circuit 200, the PWM dimming control circuit 300 and the constant current drive circuit 400. The DC power supply module 100 provides a stable DC input, and the power supply circuit 200 converts the DC voltage into a low-voltage power supply suitable for the PWM dimming control circuit 300 to ensure the stability of the system operation. The PWM dimming control circuit 300 automatically generates a PWM signal with an adjustable duty cycle according to the ambient light intensity, and combines the constant current drive circuit 400 to accurately control the current of the LED lamp beads, so that the LED lamp can automatically achieve efficient and stable brightness adjustment under different lighting requirements, while avoiding the problem of reduced light efficiency and shortened life due to unstable current.

[0057] In some embodiments, the DC power supply module 100 provides DC power through an external power supply, such as a 48V DC power supply. In addition, a 48V battery can also be used for power supply, and the voltage of the 48V battery is about 59V when fully charged. In this application, the power supply voltage can be selected according to the LED lamp bead string 500, but the power supply voltage cannot exceed the maximum allowable power supply voltage of the chip LM3402HV, which is 75.0V.

[0058] Figure 2 FIG. 4 shows a circuit diagram of a constant current driving circuit 400 according to an embodiment of the present application. Figure 2 As shown, the constant current driving circuit 400 includes:

[0059] The LM3402HV chip includes an internally integrated diode and an N-channel MOS tube, wherein the drain of the N-channel MOS tube is connected to the VIN pin of the LM3402HV chip, and the source is connected to the SW pin of the LM3402HV chip; the anode of the internally integrated diode is connected to the VCC pin of the LM3402HV chip, and the cathode is connected to the BOOT pin of the LM3402HV chip.

[0060] The drain of the N-channel MOS tube is connected to the VIN pin of the LM3402HV chip to receive the DC input voltage; the source is connected to the SW pin to control the output switching of the current. One end of the diode inside the LM3402HV chip is connected to the VCC pin of the LM3402HV chip, and the other end is connected to the BOOT pin. The internal diode and capacitor C B Together they form a bootstrap circuit to provide driving voltage for the MOS tube.

[0061] The LM3402HV chip is the core control unit. It forms an efficient Buck step-down constant current circuit through the synergy of the internally integrated N-channel MOS tube and external inductor L1, diode D1 and other components. When the PWM signal is input to the DIM pin, the chip controls the working time of the Buck circuit in a dimming cycle according to the duty cycle of the signal, thereby changing the time of the current flowing through the load (LED lamp string) in a dimming cycle. The diode and capacitor C inside the chip B When the MOS tube inside the chip is disconnected, the VCC pin connects to the capacitor C through the internal diode. B When the MOS tube is turned on, the diode inside the chip is reverse biased, and the capacitor C B It provides driving voltage for the MOS tube.

[0062] The supply voltage range of the LM3402HV chip is 6.0V to 75.0V, and it can withstand a maximum input voltage of 75V, which is higher than the LM3402 chip. Therefore, the LM3402HV chip is selected to adapt to a wider range of applications, and the supply voltage and output voltage can reach higher levels to meet a variety of power supply conditions. At the same time, key components are integrated inside the chip, reducing the use of external devices, simplifying circuit design, and improving reliability. The MOS tube integrated inside the LM3402HV chip has excellent conduction and shutdown characteristics, reducing energy loss and improving system efficiency.

[0063] Inductor L1, one end of the inductor L1 is connected to the SW pin of the LM3402HV chip, and the other end is connected to the positive end of the LED lamp bead string 500.

[0064] Inductor L1 is one of the key components of the Buck circuit. When the MOS tube is turned on, the inductor stores energy; when the MOS tube is turned off, the inductor releases energy to the load through the freewheeling diode D1. The energy storage and release characteristics of the inductor determine the current waveform and stability of the LED lamp bead. By limiting the current change rate, the inductor L1 avoids the problem of unstable brightness of the LED lamp bead caused by instantaneous current fluctuations. In addition, the selection of L1 takes into account the current ripple and load requirements. Selecting a suitable value can optimize the balance between current ripple and efficiency, such as 1.36mH.

[0065] Diode D1, the cathode of diode D1 is connected to the SW pin and the anode is grounded.

[0066] Diode D1 plays a freewheeling role when the MOS tube is turned off. When the MOS tube is turned off, the energy stored in the inductor L1 is released to the LED load through the diode D1 to maintain the continuity of the load current. Diode D1 generally uses a Schottky diode, which has fast recovery characteristics and low forward voltage drop, reduces switching losses, and improves efficiency. Diode D1 can also protect the circuit to prevent the backwash current of the inductor energy storage from damaging the chip.

[0067] Capacitor C B , capacitor C B One end is connected to the BOOT pin of the LM3402HV chip, and the other end is connected to the SW pin.

[0068] Capacitor C B Cooperating with the internal diode, it provides the startup voltage for the high-side drive circuit of the MOS tube. It charges and provides voltage to the BOOT pin in each switching cycle to ensure that the MOS tube can be turned on normally. B The existence of enables the MOS tube to work stably on the high-voltage side, avoiding failure due to insufficient drive. B The capacitance is usually selected as 10nF, which can reduce the interference of parasitic effects on the circuit while ensuring stability.

[0069] Resistor RSNS, one end of the resistor RSNS is connected to the CS pin of the LM3402HV chip, and the other end is grounded; the CS pin is also connected to the negative end of the LED lamp bead string 500.

[0070] The resistor RSNS is a key component for detecting the load current. When the current in the LED lamp string 500 passes through the resistor RSNS, a voltage is generated across the resistor RSNS, and the voltage is compared with the reference voltage inside the chip. When the detection voltage is lower than the reference voltage, the internal MOS tube is turned on.

[0071] refer to Figure 2The DC power module 100 supplies power to the LM3402HV chip through the VIN pin; the inductor L1, the resistor RSNS and the LED lamp string 500 form a core current loop at the output end; the diode D1 and the capacitor C B The freewheeling and high-side driving functions are completed respectively. All components together form a stable Buck constant current circuit. The positive end of the LED lamp bead string 500 is connected to L1, and the negative end passes through RSNS and is grounded. When the system starts, the LM3402HV chip receives the DC input voltage, and the PWM signal controls the operation of the Buck circuit through the DIM pin. When the MOS tube is turned on, the inductor L1 stores energy, and the LED lamp bead string 500 forms a loop through the MOS tube and receives a constant current; when the MOS tube is turned off, the energy stored in the inductor L1 is released to the LED lamp bead string 500 through the diode D1 to continue to power it. The CS pin detects the voltage on RSNS to feedback the current in real time to ensure that the current is stable at the preset value, thereby realizing constant current drive for the LED lamp beads.

[0072] This application adopts an optimized Buck circuit structure, which significantly improves energy conversion efficiency, reduces heat loss, and is suitable for long-term stable operation. By smoothing current fluctuations through inductor L1, ensuring the continuity of freewheeling through diode D1, and achieving precise current control through RSNS, the system can provide highly stable constant current output and ensure the reliability of LED lamps. In addition, the LM3402HV chip supports a wide input voltage range of 6 to 75V, adapts to a variety of power supply environments, and meets different brightness requirements through duty cycle adjustment of PWM signals. Accurate constant current control not only avoids damage to LED lamp beads due to overheating or overcurrent, but also effectively improves the luminous efficiency and service life of the LED.

[0073] In some embodiments, reference Figure 2 , the constant current driving circuit 400 further includes:

[0074] The diode D2 has a cathode connected to the DIM pin of the LM3402HV chip, an anode connected to the DIM port, and is connected to the PWM dimming control circuit 300 through the DIM port to receive a PWM signal.

[0075] As a unidirectional conducting element, the diode D2 ensures that the DIM pin can only receive the PWM signal from the PWM dimming control circuit 300, and will not output in reverse or be interfered by the external circuit. The diode D2 can provide isolation in the direction of signal transmission, enhance the anti-interference ability of the system, ensure the purity of the DIM pin signal, and facilitate accurate PWM dimming control. In addition, the simple structure of the diode D2 makes the circuit design more reliable and low-cost.

[0076] Resistor R7 and resistor R8, the VCC pin of the LM3402HV chip is grounded through the resistor R7 and resistor R8 connected in series; the VCC pin is also grounded through the capacitor CF.

[0077] Resistors R7 and R8 are connected in series to form a voltage divider network, which is designed to limit the voltage of the chip DIM pin to prevent it from exceeding the safe operating range. At the same time, the resistance of these two resistors should be large enough to ensure that the VCC pin only needs to provide a small current to stably drive the voltage divider network.

[0078] Switch S1, one end of the switch S1 is connected to the DIM pin, and the other end of the switch S1 is connected between the resistor R7 and the resistor R8.

[0079] In some embodiments, when the switch S1 is closed, the DIM pin is fixed at a high level and is not affected by the PWM signal. At this time, the constant current drive circuit 400 outputs a constant drive current, and the LED lamp maintains a fixed maximum brightness. When the switch S1 is open, the DIM pin adjusts the current through the PWM signal, changes the duty cycle, and thus adjusts the brightness of the LED.

[0080] By setting switch S1, two working modes, manual control and automatic dimming, are provided, which increases the flexibility of the system. In some scenarios, the maximum output brightness can be manually forced to be fixed, which is convenient for debugging or responding to emergencies.

[0081] Capacitor CIN, one end of the capacitor CIN is connected to the VIN pin of the LM3402HV chip, and the other end is grounded. The VIN pin is also connected to the positive electrode of the DC power module 100.

[0082] Capacitor CIN is used as an input decoupling capacitor to stabilize the power input voltage of the VIN pin. It stores electrical energy and releases energy when the voltage fluctuates or the instantaneous current changes, preventing the voltage drop from affecting the chip. Capacitor CIN can reduce the ripple and noise in the input voltage to ensure the stable operation of the LM3402HV chip. In addition, capacitor CIN can also alleviate the impact of instantaneous current changes on the chip at the power supply end and extend the life of the chip. Selecting the appropriate capacitance can improve the circuit's anti-interference ability and adapt to complex power supply environments.

[0083] Resistor RON, one end of the resistor RON is connected to the VIN pin, and the other end is connected to the RON pin of the LM3402HV chip. The RON pin is also connected to port.

[0084] The resistor RON is connected between the VIN pin and the RON pin of the LM3402HV chip. Its resistance directly determines the on-time of the MOS tube inside the chip. The on-time is an important parameter for controlling the switching frequency and also affects the current waveform flowing through the LED. The chip calculates and sets the on-time of the MOS tube through the resistance value of the resistor RON. The larger the value of the resistor RON, the shorter the on-time of the MOS tube; conversely, the smaller the resistance of the resistor RON, the longer the on-time. This adjustment ensures that the MOS tube turns on and off at the set time in each working cycle, thereby achieving precise control of the current and generating a constant current waveform suitable for the operation of the LED lamp beads. The resistor RON is also related to The chip is connected to a port, and through the control of this port, the chip can dynamically adjust the conduction time. The coordination of the port and the resistor RON can further optimize the switching timing of the MOS tube, ensuring that the ideal switching frequency and current waveform can be maintained according to circuit requirements in actual work.

[0085] Figure 3 FIG. 4 shows a circuit diagram of a PWM dimming control circuit 300 according to an embodiment of the present application.

[0086] like Figure 3 As shown, the PWM dimming control circuit 300 includes:

[0087] TL494 chip, the +IN1 pin of the TL494 chip is connected to the -IN1 pin of the TL494 chip, the +IN2 pin of the TL494 chip is connected to the -IN2 pin of the TL494 chip; the REF OUT pin of the TL494 chip is connected to the FB pin of the TL494 chip through the adjustable resistor RP1 and the resistor R3 connected in series in sequence; the FB pin is also grounded through the resistor R4, and the resistor R4 is a photoresistor.

[0088] The +IN1 pin and -IN1 pin of the TL494 chip are connected for the first error amplifier; the +IN2 pin and -IN2 pin are connected for the second error amplifier. The inputs of the two error amplifiers are short-circuited so that their outputs are both zero, indicating that the function of the error amplifier is fixed by the internal logic for a specific mode to avoid interfering with the PWM signal generation.

[0089] The REF OUT pin of the TL494 chip outputs a fixed 5V reference voltage, which passes through the series-connected adjustable resistor RP1 and resistor R3, and then is grounded through the photoresistor R4 to form a stable voltage divider network. The adjustable resistor RP1 is used to manually adjust the initial value of the feedback voltage to adapt to different LED light brightness requirements. The resistance of the photoresistor R4 dynamically adjusts the feedback voltage as the light intensity of the external environment changes. When the light is enhanced, the resistance of R4 decreases, resulting in a decrease in the voltage at the divider point; when the light is weakened, the resistance of R4 increases, and the voltage at the divider point increases. The voltage at the divider point is input into the TL494 chip through the FB pin as the main control signal for adjusting the duty cycle. The internal oscillator of the TL494 dynamically adjusts the duty cycle of the PWM signal according to the voltage of the FB pin. A higher feedback voltage corresponds to a smaller duty cycle to reduce the brightness; a lower feedback voltage corresponds to a larger duty cycle to increase the brightness. According to the feedback voltage of the FB pin and the modulation of the internal oscillator of the TL494, a PWM signal corresponding to the duty cycle is generated. This signal is used to drive the subsequent constant current circuit, thereby controlling the current and brightness of the LED lamp to achieve intelligent dimming.

[0090] The PWM dimming control circuit 300 is based on the TL494 chip, integrating an error amplifier, an oscillator, and a PWM generation circuit, simplifying the design, reducing costs, and improving stability. It supports multiple dimming modes through a precise 5V reference voltage. The RP1 adjustability of the voltage divider feedback network flexibly sets the initial brightness value, and the photoresistor R4 dynamically senses the ambient light intensity to achieve intelligent automatic dimming. The system can quickly respond to light changes, optimize the PWM duty cycle, save energy and extend the life of the LED while being environmentally friendly. It is a stable, efficient, and adaptable dimming solution.

[0091] In some embodiments, reference Figure 2 , the PWM dimming control circuit 300 further includes:

[0092] The cathode of the Zener diode VZ2 is connected to the FB pin, and the anode of the Zener diode VZ2 is grounded.

[0093] The voltage zener diode VZ2 is used to protect the FB pin from high voltage. When the voltage of the FB pin exceeds the voltage stabilization value of VZ2, the excess voltage will be discharged to the ground through the voltage zener diode to prevent the chip from being damaged by excessive voltage. At the same time, the existence of the voltage zener diode VZ2 limits the maximum voltage of the FB pin, thereby avoiding damage to the chip.

[0094] Capacitor C1, one end of capacitor C1 is connected to the CT pin of the TL494 chip, and the other end is grounded.

[0095] Capacitor C1 is connected to the CT pin to determine the charge and discharge time of the oscillator. The voltage of the CT pin changes with the charge and discharge cycle of capacitor C1, thereby controlling the frequency generation of the internal oscillator. The frequency of the oscillator directly affects the period of the PWM signal output by the TL494 chip.

[0096] Resistor R6, one end of the resistor R6 is connected to the RT pin of the TL494 chip, and the other end is grounded.

[0097] Resistor R6 is connected to the RT pin and cooperates with the CT pin to determine the oscillation frequency of the internal oscillator of TL494. The larger the resistance of resistor R6, the longer the charge and discharge time, the lower the oscillation frequency, and vice versa. This design provides flexibility for the frequency setting of PWM dimming.

[0098] The frequency of the PWM dimming signal should be at least one order of magnitude lower than the operating frequency of the Buck converter in the constant current drive circuit to avoid interference with the constant current output. However, generally, the PWM dimming frequency should not be lower than 200Hz to prevent the human eye from noticing flicker. The recommended PWM dimming frequency range is 200Hz to 500Hz.

[0099] In some embodiments, the VCC pin of the TL494 chip is connected to the C1 pin of the TL494 chip and the C2 pin of the TL494 chip.

[0100] The E1 pin of the TL494 chip is connected to the E2 pin of the TL494 chip, and the PWM signal passing through the internal power amplifier is output. The E1 pin and the E2 pin are connected to the DIM port through the resistor R5 to provide the PWM signal for dimming for the constant current drive circuit.

[0101] The OUT CON pin and DT CON pin of the TL494 chip are grounded.

[0102] Connecting the DT CON pin to ground ensures that the TL494 chip can output PWM signals normally. At the same time, connecting the OUT CON pin to ground makes the two transistor outputs (E1 and E2) inside the TL494 chip consistent, and the maximum duty cycle is not less than 96%.

[0103] Figure 4 FIG. 2 shows a circuit diagram of a power supply circuit 200 according to an embodiment of the present application. Figure 4 As shown, the power supply circuit 200 includes:

[0104] The voltage zener diode DZ1 has a cathode connected to the DC power supply module 100 through a resistor R1 and an anode grounded.

[0105] Transistor Q1, the base of transistor Q1 is connected to the DC power module 100 through resistor R1, the collector is connected to the DC power module 100 through resistor R2, and the emitter is connected to the PWM dimming control circuit 300 to supply power to the PWM dimming control circuit 300.

[0106] The base of transistor Q1 is connected to the positive electrode of DC power module 100 through resistor R1, and appropriate base current is provided through resistor R1. The emitter of transistor Q1 is connected to PWM dimming control circuit 300, and the collector is connected to the positive electrode of DC power module 100 through resistor R2. When Q1 is working, it is equivalent to an emitter follower, and the voltage on the emitter follows the voltage on the voltage regulator DZ1, providing a stable voltage output to PWM dimming control circuit 300 to ensure its normal operation.

[0107] The PWM dimming control circuit 300 obtains power through the emitter of Q1. The stable power supply ensures that the PWM dimming control circuit 300 can adjust the duty cycle of the PWM signal according to the change of ambient light to achieve precise dimming control. Through the power supply design of the combination of voltage regulator diode and transistor, the whole system can obtain a stable and reliable power supply. Regardless of the fluctuation of the input voltage, the PWM dimming control circuit 300 can work stably and achieve precise dimming control. This design improves the robustness of the system, so that the LED lighting system can provide consistent performance under different power supply conditions.

[0108] According to the above embodiments, the technical solution of the present application provides an efficient and stable LED lighting constant current drive system, which is mainly composed of a DC power supply module 100, a power supply circuit 200, a PWM dimming control circuit 300 and a constant current drive circuit 400. The system provides stable power to each circuit through the DC power supply module 100, and the power supply circuit 200 adopts a combination of a voltage regulator diode and a transistor to ensure the stable power supply of the PWM dimming control circuit 300. The PWM dimming control circuit 300 generates a PWM signal based on the TL494 chip, and automatically adjusts the dimming PWM signal duty cycle by sensing the ambient light changes through a photoresistor, thereby adjusting the brightness of the LED lamp beads. The constant current drive circuit 400 uses the LM3402HV chip, combined with inductors, capacitors and resistors to achieve precise constant current control, ensuring that the LED lamp beads work at a constant current, avoiding overcurrent or overheating, and extending the service life of the LED. The overall system achieves efficient energy saving, stable operation and flexible dimming through PWM signal adjustment, which can adapt to different lighting requirements and improve energy efficiency.

[0109] The automatic dimming LED lighting constant current drive system of the present application is further explained below with a specific implementation process.

[0110] refer to Figure 2, the system is first powered by a DC power input, and the current sensing resistor RSNS is used to detect the current flowing through the LED. The voltage value of RSNS is compared with the 200mV reference voltage inside the chip LM3402HV. When the voltage of RSNS is lower than 200mV, the MOS tube inside the chip starts to conduct and allows current to flow to the LED string. The resistance value of the resistor RON sets the conduction time of the MOS tube. The duration that determines the conduction of the MOS tube inside the chip can be calculated by the following formula:

[0111]

[0112] Among them, t on The duration of the internal MOS tube conduction, R ON is the resistance value of resistor RON, U in Input voltage for the DC power supply.

[0113] After the MOS tube conduction time ends, the MOS tube inside the chip is turned off and remains in the off state for 300ns to ensure stable operation. The minimum off time (t offmin ) is 300ns, which provides a necessary interval between each switch to prevent the MOS tube from overheating or overcurrent. When the voltage on RSNS is lower than 200mV again, the MOS tube will turn on again, and the whole process will continue to cycle to maintain a constant current.

[0114] In actual use, the number of LEDs in series is determined according to actual needs. The system can calculate the maximum output voltage based on the input voltage Uin, and then combine the voltage drop of a single LED lamp bead to determine the maximum number of LED lamp beads that the system can connect in series. The maximum output voltage calculation formula is as follows:

[0115]

[0116] Among them, U Omax is the maximum output voltage, D max is the maximum duty cycle, U in is the power supply input voltage, t on The duration of the internal MOS tube conduction, t offmin It is the minimum disconnection time of LM3402HV chip.

[0117] The design in this embodiment is to drive 12 1W LED lamp beads in a string of 500, and the target driving current is 350mA. The current is set by the resistor RSNS, and the LM3402HV chip continuously adjusts the current to ensure a constant output current.

[0118] One of the main functions of the inductor L1 is to smooth the current fluctuation during the current conversion process. In the constant current drive circuit 400, the current of the LED light string should be kept constant as much as possible to ensure stable brightness. By selecting an appropriate inductor, the peak-to-valley fluctuation of the current can be reduced, ensuring that the current flowing through the LED is stable and avoiding overcurrent or undercurrent, thereby extending the life of the LED and improving efficiency. The minimum value of the inductor L1 is calculated by the following formula:

[0119]

[0120] Among them, L min is the minimum value of inductance L1, U inmax is the maximum value of the input voltage, U O is the output voltage, t on is the duration of the internal MOS tube conduction. ΔiL is the difference between the maximum current and the minimum current on the LED, that is, the peak-to-valley current difference. This difference helps to control the operation of the inductor so that the system can effectively maintain a constant current output. In this embodiment, 0.6 times the desired constant current value, 210mA, is taken. According to the above formula and the set parameters, the value of the inductor L1 in this embodiment is selected as 1.36mH, which can ensure that the current fluctuation is minimal under load conditions and the system works stably.

[0121] The selection of RSNS resistor is based on the delay time t of the current sensing comparator. SNS (take 200nS) and LED drive current (350mA) to calculate, the specific calculation formula is as follows:

[0122]

[0123] Among them, R SNS is the resistance of RSNS resistor. L is the inductance of inductor L1. L is the current flowing through the LED string, i.e. the driving current. SNS is the delay time of the current sensing comparator, which is 200nS in this embodiment. In this embodiment, the RSNS resistor is selected to be 0.56Ω, ensuring that the current is maintained at the target value of 350mA during the entire working process.

[0124] In the designed Buck circuit, the switching frequency of the MOS tube inside the chip is calculated to be 200kHz. This frequency matches the changing cycle of the inductance and current, ensuring the constant output of current. The specific calculation formula for the switching frequency of the internal MOS tube is as follows:

[0125]

[0126] In this embodiment, R ON The resistance value is 16kΩ.

[0127] When switch S1 is closed, the voltage of the DIM pin is high. At this time, the output current of the constant current drive circuit 400 is not affected by the PWM signal of the PWM dimming control circuit 300, but drives the LED light string at a constant current according to the designed current (e.g., 350mA). The output on the VCC pin is a stable 7V, which is connected to the DIM pin through switch S1 after voltage division by R7 and R8. The voltage division on R8 needs to be higher than 2.2V, so that the DIM pin is always high when switch S1 is closed. Diode D2 ensures that the high level of the DIM pin is not affected by the PWM dimming control circuit 300 when S1 is closed.

[0128] When the switch S1 is turned off, the current of the constant current driving circuit 400 is affected by the PWM dimming control circuit 300, and the dimming circuit controls the brightness of the LED by adjusting the duty cycle of the PWM signal. The DIM pin receives the PWM signal from the PWM dimming control circuit 300, and according to the duty cycle of the signal, the constant current driving circuit 400 adjusts the current of the LED string to achieve dimming.

[0129] Figure 2 The rated current of D1 is determined according to the output constant current. In this embodiment, D1 selects a Schottky diode with a current of not less than 500mA. The capacitor CF is 0.1μF, and the capacitor C B The value is 10nF. In addition, Figure 2 In When the port is grounded, When the port is below 0.3V logic level, the chip is placed in low power shutdown state. When the chip is working normally, The port is open.

[0130] refer to Figure 3 The system detects the ambient light intensity through the photoresistor R4 and dynamically adjusts the PWM duty cycle according to the change of light intensity. When the light is strong, the resistance of R4 decreases, the voltage of the FB pin is low, the duty cycle of the PWM signal is small, and the brightness of the LED decreases; when the light is weak, the resistance of R4 increases, the voltage of the FB pin increases, the duty cycle of the PWM signal is large, and the brightness of the LED increases.

[0131] In this embodiment, the voltage stabilization value of DZ1 is selected according to the working voltage range of the chip TL494 and the power consumption of the power supply circuit 200. The maximum allowable power supply voltage of the chip TL494 is 42V, and the voltage stabilization value of the zener diode 1N4754 is 39V. The resistance value of R2 and the rated current of Q1 are determined according to the output power of the PWM dimming control circuit 300. In this embodiment, the resistance value of R2 is 18Ω and the power is 1.5W. Q1 uses a transistor of model BSR52 with a rated current of 1A and a voltage of 80V.

[0132] In this embodiment, the photoresistor R4 is selected as model GL5528, whose bright resistance is about 10kΩ and dark resistance is greater than 1MΩ. The voltage regulator diode VZ2 is selected as model 1N4730, and the voltage regulation value is 3.9V. The resistance of the photoresistor R4 changes with the ambient light intensity. When the ambient light is strong, the resistance of R4 decreases, and the voltage on the FB pin decreases accordingly, approaching zero. At this time, the duty cycle of the PWM signal output by the PWM dimming control circuit 300 to the constant current drive circuit 400 is also very small, and the brightness of the LED lamp bead is low; on the contrary, when the ambient light is weak, the resistance of R4 increases, and the voltage on the FB pin increases accordingly, and the PWM duty cycle output by the PWM dimming control circuit 300 also increases, resulting in an increase in the brightness of the LED lamp bead. In this way, the system can automatically adjust the LED brightness according to the ambient light intensity to achieve the effect of adaptive dimming.

[0133] It is worth noting that the photoresistor needs to be installed in a place where the LED light string cannot reach so that it can receive changes in the surrounding light.

[0134] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0135] The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the attached claims.

Claims

1. An automatic dimming LED lighting constant current drive system, characterized in that: The system comprises: A DC power supply module is connected to the power supply circuit and the constant current drive circuit to provide DC power to the power supply circuit and the constant current drive circuit; A power supply circuit, connected to the PWM dimming control circuit, converts the DC power provided by the DC power supply module into a low-voltage power supply required by the PWM dimming control circuit; A PWM dimming control circuit is connected to the constant current drive circuit, automatically generates a PWM signal with a variable duty cycle according to the ambient light intensity and outputs it to the constant current drive circuit; The constant current driving circuit is connected to the LED lamp bead string, and adjusts the output current based on the received PWM signal to provide a constant current for the LED lamp bead string.

2. The automatic dimming LED lighting constant current drive system according to claim 1, characterized in that: The constant current driving circuit comprises: The LM3402HV chip comprises an internally integrated diode and an N-channel MOS tube, wherein the drain of the N-channel MOS tube is connected to the VIN pin of the LM3402HV chip, and the source is connected to the SW pin of the LM3402HV chip; the anode of the internally integrated diode is connected to the VCC pin of the LM3402HV chip, and the cathode is connected to the BOOT pin of the LM3402HV chip; An inductor L1, one end of which is connected to the SW pin of the LM3402HV chip, and the other end of which is connected to the positive end of the LED lamp bead string; a diode D1, wherein a cathode of the diode D1 is connected to the SW pin and an anode of the diode D1 is grounded; Capacitor C B , the capacitor C B One end is connected to the BOOT pin of the LM3402HV chip, and the other end is connected to the SW pin; A resistor RSNS, one end of the resistor RSNS is connected to the CS pin of the LM3402HV chip, and the other end is grounded; the CS pin is also connected to the negative end of the LED lamp bead string.

3. The automatic dimming LED lighting constant current drive system according to claim 2, characterized in that: The constant current driving circuit also includes: A diode D2, wherein the cathode of the diode D2 is connected to the DIM pin of the LM3402HV chip, the anode of the diode D2 is connected to the DIM port, and the diode D2 is connected to the PWM dimming control circuit through the DIM port to receive the PWM signal; Resistor R7 and resistor R8, the VCC pin of the LM3402HV chip is grounded through the resistor R7 and resistor R8 connected in series; the VCC pin is also grounded through the capacitor CF; A switch S1 , one end of which is connected to the DIM pin, and the other end of which is connected between the resistor R7 and the resistor R8 .

4. The automatic dimming LED lighting constant current drive system according to claim 2, characterized in that: The constant current driving circuit also includes: A capacitor CIN, one end of the capacitor CIN is connected to the VIN pin of the LM3402HV chip, the other end is grounded, and the VIN pin is also connected to the positive electrode of the DC power supply module; A resistor RON, one end of which is connected to the VIN pin, and the other end of which is connected to the RON pin of the LM3402HV chip. The RON pin is also connected to port.

5. The automatic dimming LED lighting constant current drive system according to claim 1, characterized in that: The PWM dimming control circuit comprises: A TL494 chip, wherein the +IN1 pin of the TL494 chip is connected to the -IN1 pin of the TL494 chip, and the +IN2 pin of the TL494 chip is connected to the -IN2 pin of the TL494 chip; the REF OUT pin of the TL494 chip is connected to the FB pin of the TL494 chip through an adjustable resistor RP1 and a resistor R3 connected in series in sequence; the FB pin is also grounded through a resistor R4, and the resistor R4 is a photoresistor.

6. The automatic dimming LED lighting constant current drive system according to claim 5, characterized in that: The PWM dimming control circuit also includes: A voltage stabilizing diode VZ2 , wherein a cathode of the voltage stabilizing diode VZ2 is connected to the FB pin, and an anode of the voltage stabilizing diode VZ2 is grounded.

7. The automatic dimming LED lighting constant current drive system according to claim 5, characterized in that: The PWM dimming control circuit also includes: A capacitor C1, one end of the capacitor C1 is connected to the CT pin of the TL494 chip, and the other end is grounded; Resistor R6, one end of the resistor R6 is connected to the RT pin of the TL494 chip, and the other end is grounded.

8. The automatic dimming LED lighting constant current drive system according to claim 5, characterized in that: The VCC pin of the TL494 chip is connected to the C1 pin of the TL494 chip and the C2 pin of the TL494 chip; The E1 pin of the TL494 chip is connected to the E2 pin of the TL494 chip, and the E1 pin and the E2 pin are connected to the DIM port through a resistor R5 to output a PWM signal; The OUT CON pin and DT CON pin of the TL494 chip are grounded.

9. The automatic dimming LED lighting constant current drive system according to claim 1, characterized in that: The power supply circuit comprises: A voltage zener diode DZ1, wherein the cathode of the voltage zener diode DZ1 is connected to the DC power supply module via a resistor R1, and the anode of the voltage zener diode DZ1 is grounded; Transistor Q1, the base of the transistor Q1 is connected to the DC power supply module through a resistor R1, the collector is connected to the DC power supply module through a resistor R2, and the emitter is connected to the PWM dimming control circuit to supply power to the PWM dimming control circuit.

10. The automatic dimming LED lighting constant current drive system according to claim 3, characterized in that: When the switch S1 is closed, the DIM pin is fixed at a high level and is not affected by the PWM signal; when the switch S1 is open, the DIM pin adjusts the current through the PWM signal.

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