Design optimization of soft-switched insulated DC/DC converters with active voltage clamp

The use of an active voltage clamp in insulated DC/DC converters allows a limitation of the voltage stress due to transformer leakage inductance, a reduction of the commutation losses, and an increase of the switching frequency. It is therefore important to ensure soft switching in the whole operating range; the penalty is a considerable worsening of converter efficiency and electromagnetic noise generation. In this paper a design approach of insulated converters with active voltage clamp is presented, which allows soft switching from no load to full load. The approach is described for the case of a flyback converter but is valid also for Sepic and Cuk topologies. Experimental results of a 100 W-300 kHz converter demonstrate the excellent performances obtained according to the proposed design procedure: switch overvoltage less than 20% of the nominal value in any operating condition and overall converter efficiency above 83% from 50% to 100% of rated load