Research On High Power LED Driver Circuit In PCCM Based On GaN EHEMT

LED(Light Emitting Diode)was invented and developed since 1962.Due to its advantages of energy saving,safety,low heat,high luminous efficiency and long service life,LED lighting is popularized in various application scenarios,and the requirements for LED drive circuits are also It is getting higher and higher,and the requirements for the brightness of LEDs in different scenarios are also different.Especially for short-distance lighting devices such as smart phones,the color and brightness of light are extremely high.Therefore,the development trend of LED drive circuits is more precise and wider dimming.At present,the low-power drive circuit of LED is relatively mature,while the high-power drive circuit has restricted its development due to factors such as conversion efficiency,cost,and volume,and cannot replace the traditional high-intensity lighting system.At present,the research on high-power LED drive circuits is increasing at home and abroad,especially in terms of improving integration and efficiency.The single-inductor multi-output(SIMO)circuit structure is commonly used,which can not only achieve the independence of multiple LED strings Drive,and can time-multiplex the power circuit to achieve the purpose of reducing the size.However,there are still many worth studying in the design of the drive circuit structure and the more flexible and larger range of dimming circuit.This article will conduct research from these two aspects.In this paper,through the research of LED dimming technology and PCCM BUCK circuit,a LED drive circuit based on GaN eHEMT is designed.The PCCM BUCK circuit with SIMO structure is used.The input voltage is 50 V and the output voltage is 36 V.The circuit is independently powered,the maximum output power of the circuit is 48 W,the operating frequency of the main switch is 1 MHz,the operating frequency of the branch switch is 33.3 kHz,and the operating frequency of the dimming switch is 333 Hz.In order to realize the independent driving of the three LED strings,the power supply of the three branches adopts the time division multiplexing strategy.The dimmable LED drive circuit designed in this paper uses PWM dimming at a lower dimming ratio,and combines the reference voltage of the feedback compensation network with the dimming ratio voltage at a larger dimming ratio to achieve the PWM dimming direction.Analog dimming switching.This article uses GaN eHEMT switch tube to increase the circuit switching frequency,reduce the size of the circuit components,compared to the traditional board-level BUCK circuit is smaller.The BUCK circuit is a non-isolated DC-DC circuit.The main power inductor has a large current ripple during operation,and in the case of high frequency and high power,a large voltage ripple is likely to occur at the switching point,causing electromagnetic interference(EMI),the circuit designed in this paper works in the PCCM mode,which can reduce the current ripple of the main power inductor and suppress the mutual interference between parallel branches.At the same time,when designing the circuit,several measures are taken to reduce the impact of voltage ripple.In order to achieve the above goals,the main research contents of this article are:(1)consult the data to study the development status of high-power LED drive circuit,analyze the future development direction of LED drive circuit and dimming technology;(2)based on input and output voltage and work For the frequency target,calculate the parameters of the main components in the circuit,such as the parameters of the main power inductance and the output filter capacitor.The state space method is used to model the BUCK circuit working in PCCM(pseudo continuous conduction mode),analyze the frequency characteristics of the system transfer function and design the compensation network;(3)analyze the timing relationship between each control switch The generating circuit of each signal,at the same time,in order to make the circuit realize the function of PWM-DC dimming switching,the switching circuit is designed in combination with the working principle of the compensation network and the dimming module.(4)Build a simulation platform on the Orcad PSPICE platform,and verify the function of the designed circuit through the simulation results.Then use Altium Designer 16 to draw the PCB board,complete the welding of various components,and use the oscilloscope,DC power supply and signal generator to verify the circuit function.Compare the circuit test results with the simulation results to verify that the LED drive circuit designed in this paper can work in the PCCM mode to drive the LED,and achieve PWM dimming at low dimming ratio,and from PWM dimming to high dimming ratio.DC dimming switch.