Capacitively-aided switching technique for high-frequency isolated bus converters

This paper presents a new capacitively-aided zero voltage switching (ZVS) technique for isolated bus converters. The proposed technique helps to achieve ZVS conditions for both inverter and rectifier switches with the aid of magnetizing current of the transformer and capacitors interconnecting primary and secondary side switching nodes. With the proposed topology, the ZVS conditions for inverter and rectifier switches occur at the same time, and (ideally) maintain constant required dead time independent of the load level of the converter. These features are particularly advantageous especially for designs operating at high frequencies where timing control becomes critical. The proposed approach is demonstrated in a 1.4 MHz prototype converter which operates from 36 Vdc and supplies a 12 Vdc output load (i.e., fixed input voltage and fixed voltage transformation ratio, 3 : 1 ) at a 36 W rating. Experimental results show ZVS operation of all devices independent of the load level, and the prototype converter achieves 94% peak efficiency with 300 W/ in3 power density.