Design of compensation circuits for quasi-resonant PWM controllers

The quasi-resonant converters can significantly reduce the turn-on losses, but the line voltage feed-forward characteristics are sacrificed in order to get the good transient response in current mode quasi-resonant converters. In this paper, a voltage feed-forward compensation circuit is proposed which effectually resolved above-mentioned problem. Simultaneity, to prevent the possible unstable operation at the large load conditions, an internal synchronized slop compensation circuit is added to the current loop to ensure system stable operation. Based on 1 ¿m 40 V BCD process, the voltage feed-forward compensation and adaptive slop compensation circuits were designed, the excellent transient response and system stability are obtained eventually. When the output system is 12 V/30 W, the voltage regulation can be reduced to 0.17% from 0.5% (without voltage feed-forward compensation) and the load regulation is 7.5 mV/A with these modules in chip in the same power supply system.