A PWM full-bridge converter with load independent soft-switching capability

Abstract

Although the zero-voltage switched (ZVS) pulsewidth modulated (PWM) full-bridge (FB) converter can operate with soft-switching and fixed frequency control it loses its ZVS capability under light-load conditions. This paper examines the use of auxiliary circuits attached to the bottom switches of the standard ZVS-PWM-FB converter as a means of extending the ZVS range. The auxiliary circuits, each consisting of an active switch and passive components, operate for only a small portion of the switching cycle, and handle very little power. The basic operating principles of these type of modified ZVS-PWM-FB converters are explained in detail in the paper, and general guidelines for their design are given. A design procedure is derived and demonstrated on an example converter. The feasibility of this converter is shown with results obtained from an experimental prototype.