A novel dimmable LED driver with soft-start and UVLO circuits  

作　　者：江金光 谭高建 张泽宇 周细凤 

机构地区：[1]GNSS Research Center, Wuhan University [2]School of Physics and Technology, Wuhan University [3]Suzhou Institute, Wuhan University [4]School of Electronic Information and Electrical Engineering, Shanghai Jiao Tong University

出　　处：《Journal of Semiconductors》2015年第2期135-143,共9页半导体学报（英文版）

基　　金：Project supported by the National Natural Science Foundation of China(No.41274047);the Natural Science Foundation of Jiangsu Province(No.BK2012639);the Changzhou Science and Technology Support(Industrial)Project(No.CE20120074)

摘　　要：A fully integrated LED driver based on a current mode PWM boost DC-DC converter with constant output current is proposed. In order to suppress the inrush of current and the overshoot voltage at the start up state, a soft-start circuit is adopted. Additionally, to adjust the LED brightness without color variation over the full dimming range and achieve high efficiency, a PWM dimming circuit is presented. Furthermore, to keep the loop stability of the LED driver, an internal slope compensation network is designed to avoid the sub-harmonic oscillation when the duty cycle exceeds 50%. Finally, a UVLO circuit is adopted to improve the reliability of the LED driver against the input voltage changing. The LED driver has been fabricated with a standard 0.5/xm CMOS process, and only occupies 1.21 × 0.76 mm^2. Experimental results show that the brightness of the LED can be adjusted by an off- chip PWM signal with a wide adjusting range. The inductor current and output current increase smoothly over the whole load range. The chip is in the UVLO condition when the input voltage is below 2.18 V and has achieved about 137 μs typical start-up time.A fully integrated LED driver based on a current mode PWM boost DC-DC converter with constant output current is proposed. In order to suppress the inrush of current and the overshoot voltage at the start up state, a soft-start circuit is adopted. Additionally, to adjust the LED brightness without color variation over the full dimming range and achieve high efficiency, a PWM dimming circuit is presented. Furthermore, to keep the loop stability of the LED driver, an internal slope compensation network is designed to avoid the sub-harmonic oscillation when the duty cycle exceeds 50%. Finally, a UVLO circuit is adopted to improve the reliability of the LED driver against the input voltage changing. The LED driver has been fabricated with a standard 0.5/xm CMOS process, and only occupies 1.21 × 0.76 mm^2. Experimental results show that the brightness of the LED can be adjusted by an off- chip PWM signal with a wide adjusting range. The inductor current and output current increase smoothly over the whole load range. The chip is in the UVLO condition when the input voltage is below 2.18 V and has achieved about 137 μs typical start-up time.

关 键 词：LED driver DC-DC converter UVLO soft-start PWM dimming 

分 类 号：TN312.8[电子电信—物理电子学] TN949.7