A Novel Control Scheme for High PF Buck LED Driver With Reduced Compensation Capacitance

Abstract

A novel control scheme for high power factor (PF) Buck LED driver with reduced compensation capacitor is proposed in this paper. The proposed control scheme is composed of a novel output current estimation circuit based on an accumulator and a novel adaptive compensation circuit with a half-line-cycle step control. The proposed output current estimation circuit can achieve the information of the average output current by using the accumulator so that the capacitance of the capacitor in the RC filter can be reduced greatly. Meanwhile, the proposed adaptive half-line-cycle step control can further reduce the compensation capacitance greatly and increase the closed-loop bandwidth of the system under low input voltages. In this way, the control circuit can be fully integrated into a single chip with saved I/O pins and the dynamic response of the converter can be also improved. Detailed theoretical analysis has been presented and an 80V/240mA laboratory prototype of High PF Buck LED driver was built up to verify the feasibility of proposed control scheme.