Study On Full-Bridge Phase-Shift Soft Switching Converters

High frequency soft-switching conversion is an important subject of power electronics . It is a powerful approach of minimization of size and weight for power supplies. And the quick development of modern communication technology requires such more excellent power supplies as higher efficiency , more small volume and more light weight. DC/DC full-bridge converters is widely used under the situation which needs middle and high power supplies, so the investigation into its soft-switching technologies is very significant.Firstly, the basic theory of full-bridge phase-shift ZVS PWM converters are expatiated and another three kinds of circuits of full-bridge phase-shift ZVS PWM converters are discussed. There are four kinds of problems which are emphasized: how to expand the ZVS range; how to reduce the circulation in the primary side of the transformer in order to minimize the on state losses; how to decrease the loss of effective duty circle and how to eliminate the parasitic oscillation of the output rectifiers.Secondly, the specific circuit effects in the phase-shift PWM converter and their impact on the converter dynamics are analyzed. The small-signal model is derived incorporating the effects of phase-shift control. The design of control stage of the converter are optimized based on the small-signal model theoretically.In the end we have made a 50V/10A full-bridge PWM DC/DC converters based on an improved circuit topology of full bridge phase shift ZVS PWM converter. It can achieve ZVS from no load to full load in virtue of an assistant commutation inductor. By virtue of the small-signal model the control stage is optimized and the integrated circuit UC3875 is used to complete the control stage.