Zero-crossing distortion analysis in one cycle controlled boost PFC for Low THD

A low-power low THD boost PFC with one cycle control is discussed. Two novel structures, the periodic self-starting timer and feedforward current control block, are introduced to reduce the zero-crossing distortion. The improved boost PFC could regulate the switch turn-on time timely according to the ac input line voltage, and reduce the distortion near the input voltage zero-crossing points significantly. The experimental THD is only 3.8%, the power factor is 0.998, the load adjust rate is 3%, the linear adjust rate is less than 1%, and the efficiency is 96.9%. Both theoretical and practical results reveal that the improved PFC meets the demands for low-power and low THD.