UTILIZATION OF AN ACTIVE-CLAMP CIRCUIT TO ACHIEVE SOFT-SWITCHING IN FLYBACK CONVERTERS

Flyback derived topologies are attractive because of their relative si mplicity when compared with other topologies used in low power applica tions, Incorporation of active-clamp circuitry into the flyback topolo gy serves to recycle transformer leakage energy while minimizing switc h voltage stress, The addition of the activef-clamp circuit also provi des a mechanism for achieving zero-voltage-switching (ZVS) of both the primary and auxiliary switches, ZVS also limits the turn-off di/dt of the output rectifier, reducing rectifier switching losses, and switch ing noise due to diode reverse recovery. This paper analyzes the behav ior of the ZVS active-clamp flyback operating with unidirectional magn etizing current and presents design equations based on this analysis. Experimental results are then given for a 500 W prototype circuit illu strating the soft-switching characteristics and improved efficiency of the converter, Results from the application of the active-clamp circu it as a low-loss turn-off snubber for IGBT switches is also presented.