A 40-W Flyback Converter with Dual-Operation Modes for Improved Light Load Efficiency

Abstract

A flyback converter operates with either pulse width modulation (PWM) or pulse frequency modulation (PFM) control scheme depending on the load current. At light load condition, PFM control is employed to reduce the switching frequency and thereby minimize the switching power loss. For heavier load, PWM control is used to regulate the output voltage of the flyback converter. The flyback controller has been implemented in a 0.35 mu m BCDMOS process and applied to a 40-W flyback converter. The light-load power efficiency of the flyback converter is improved up to 5.7-% comparing with the one operating with a fixed switching frequency.