Research And Design Of A High-precision Constantcurrent LED Driver With Hysteresis Control

With the rapid development of semiconductor technology,LED is widely used in the field of lighting and display because of its high efficiency,energy saving,green and environmental protection,and is gradually replacing the traditional lighting methods.As an important part of the LED lighting system,the performance of LED driver chips directly affects the performance of the whole system.Therefore,it is of great value and significance to research and design high performance LED driver chips.Aiming at the application of medium and small power AC-DC LED lighting,this paper firstly studies the LED lighting principle and driving mode,the working principle and control mode of DC-DC driver,the constant current control principle of LED driver and the current sampling principle.Secondly,a high precision constant current LED driver is designed based on the new constant current control mode of adaptive off-time.Based on the hysteresis current control mode,a new type of adaptive off-time control loop is adopted in this driver instead of valley detection feedback loop,which converts the control of the inductor current valley to an adaptive control of the off-time.This constant current control method avoids the error caused by the fixed off-time,and improves the constant current accuracy of the system.In addition,this constant current control method based on adaptive off-time does not need to detect the valley of the inductor current,only need to sample the current in the switch-on phase,so the loss on the sampling resistor is reduced and the conversion efficiency of the LED drive system is improved.The whole driving circuit includes power management,logic control,constant current control,leading edge blanking and system protection.In this paper,TSMC 0.18?m 70 V BCD process is used to complete the circuit design,and the simulation verification is completed based on Cadence Spectre platform.The simulation results show that: under typical conditions,the sampling resistor is 3.3 ?,the ideal output current is 60.61 m A,the actual output current is 60.45 m A,the off-time is 8.7?s,and the constant current accuracy is 0.26%;in the output current range of 20?125m A,the maximum constant current error is not more than 0.8%;in the output voltage range of 20?100V,the maximum change rate of output current does not exceed 1%.In the whole load range,the maximum working frequency of the system is 100 k Hz,and the peak conversion efficiency of the system is 92.6%.It is suitable for high precision LED lighting applications.