Flyback converter with hybrid clamp

This paper presents a flyback converter with a hybrid clamp, i.e., a combined passive RCD and active clamp, and a corresponding power management circuit that substantially optimizes the performance of the flyback converter in the entire line and load ranges. By sensing the operating conditions, the power management circuit configures the clamp circuit either as a passive clamp or as an active clamp. In the passive-clamp configuration, the clamp switch is kept turned off and the main switch turns on with valley switching, whereas, in the active-clamp configuration, the clamp switch operates with pulse-width modulation (PWM) which enables zero-voltage-switching (ZVS) turn-on of the main switch. Performance of the flyback converter with the hybrid clamp is evaluated on a laboratory prototype of a 65-W (19.5-V, 3.33-A) universal-line-voltage-range (90-264 Vrms) adapter.