Soft switched PWM DC/DC converter with synchronous rectifiers

In this paper, a low DC voltage output, soft-switched PWM DC/DC converter with two different synchronous rectification (SR) schemes (self-driven and external-driven) is presented. The operating principle of the circuit is discussed briefly. Power losses in the two synchronous rectifiers for different implementations have been analytically estimated. The commutation overlap interval of the rectifiers significantly increases power loss in the self-driven scheme and this could be eliminated (or substantially reduced) through an external-driven scheme. The 'fully' external-driven scheme was, however, found to be difficult to implement due to accurate gate timing requirements. A 'partially' external driven SR scheme is proposed for such soft-switched converters derived from half-bridge topology. This scheme is relatively simple and robust. It has reduced losses during the commutation overlap intervals; also, being external-driven, it allows optimum choice of gate voltage for low losses. Various efficiency results from an experimental prototype using self-driven end 'partially' external-driven SR schemes as well as Schottky rectifiers are provided to show the anticipated good performance of the proposed SR scheme.