Design of an off-line AC/DC controller based on Skip Cycle Modulation

This paper analyses the principles of SCM (skip cycle modulation) in switching converters. A controller for AC/DC flyback converter based on SCM is proposed. Four key building blocks, namely the oscillator, skip cycle comparator, digital control and two control loops are used to achieve skipping cycle control. This circuit is designed in CSMC 0.5 ¿m BCD process and verified by Hspice simulation. The simulation results show that the switching efficiency of the converter is not affected by the change of the load. It solves the problem of low efficiency at light loads in PWM mode.