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

• Published in: Journal of semiconductors Vol. 36; no. 2; pp. 135 - 143
• Main Author: 江金光 谭高建 张泽宇 周细凤
• Format: Journal Article
• Language: English
• Published: 01.02.2015
• Subjects: Adjustment; Brightness; Circuits; CMOS工艺; DC-DC转换器; Dimming; Electric potential; LED驱动器; Pulse duration modulation; PWM信号; Semiconductors; Voltage; 可调光; 电流模式; 软启动电路; 输出电流
• ISSN: 1674-4926
• DOI: 10.1088/1674-4926/36/2/025004

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.