Line voltage compensation technology for AC-direct multiple-string LED drivers

Abstract

An AC-mains voltage compensation technology for variable load multiple-string LED drivers is presented. By forming a closed loop control of the multiple reference voltages and by introducing an external compensation resistor, the output luminance is well compensated in case of line voltage variations. The proposed technology along with the accompanied AC-direct multiple-string LED driver were integrated in an 1 µm trenchisolated BCD process and tested with a three-string prototype. With very few external components used, the line regulation character of the LED driver is highly optimized by the proposed technology. The experimental results show that within 15% AC-mains voltage tolerance, the output luminance deviation is restrained to 2.0% (1.5%) under 10 W, 110 V/AC (220 V/AC), 50 Hz conditions.