Design Of A High-efficiency Brightness Adjustable LED Driver Circuit

As the rapid development of consumer portable electronic devices,switching power supply products have been widely used in many fields for its advantages as high power density,high conversion efficiency,small size and so on,LED lamps have long operating life and consume low electricity,it has been development trend of energy saving,high efficiency LED driver circuit is becomeing even more important.The thesis analysed and designed a high efficiency dimmable LED driver base on current mode Boost DC-DC converter.The thesis analyzed familiar topological structures’ work principle,modulation modes and feedback mechanism,then choose the current model Pulse-Width-Modulation Boost DC-DC converter according to application requirements,and after that it analysed the stability and compensation of the converter using average state space method,finalized the compensation method and performance criteria of key modules,and built a Matlab/Simulink model to test the credible of the circuit system;the mechanism of the subharmonic oscillation which remained the major stability problem in current mode,compensation methods and compensation’s influence on the system are intensive studied,then proposed the thought of segmented slope compensation to slove current loop’s stability problem and the influence on response performance of over-compensation;finally,it designed a high-efficiency dimmable LED driver circuit base on current mode Boost DC-DC converter baseing on the analysis of the system model,the chip integrated bandgap circuit,oscillator and slope compensation circuit,PWM control logic circuit,error amplifier,ramp voltage signal generator,voltage level shift circuit,hysteretic thermal-shutdown circuit and LED dimming circuit based on current sink circuit and so on;the thesis proposed a multi-functions error amplifier which integrated soft start,mode switch in PWM and Sleep mode,peak current limiting in the design,the error amplifier circuit is of simple structure,easy to design.The circuit is designed in CMSC 0.5um 25 V BCD process,and simulated under Cadence Spectre environment.The result shows that on condition that the input voltage is 4Vand the output voltage is 15 V,the output voltage ripple is less than 25 mV,the maximum load current achieved 200 mA,the chip can drive 4 parallel LED lamps,the number of every row of lamps reachs 4,the line regulation of the chip is 1%,the load regulation of the chip is 3.34%,the efficiency achieved 92% under heavy load,and it realized analog and PWM light-dimming,the chip has response characteristic,good load regulation and line regulation.