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

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 co...

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Veröffentlicht in:Journal of semiconductors 2015-02, Vol.36 (2), p.135-143, Article 025004
1. Verfasser: 江金光 谭高建 张泽宇 周细凤
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Sprache:eng
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Zusammenfassung: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.
ISSN:1674-4926
DOI:10.1088/1674-4926/36/2/025004