ZVS Resonant Converter With Series-Connected Transformers

This paper presents a new series-resonant converter with series-connected transformers in order to realize zero voltage switching (ZVS) for power switches, zero current switching (ZCS) for rectifier diodes at full load, less transformer secondary winding with a full-wave rectifier, and load current sharing. Two series-resonant converters using the same switches are operated with interleaved half switching cycle. The secondary windings of transformers are connected in series in order to ensure that the primary side currents are balanced to share load current. Thus, the sizes of the transformer core and bobbin are reduced. The full-wave diode rectifier is adopted on the output side such that the voltage stress of the rectifier diodes is equal to the output voltage, rather than being two times the output voltage as in a conventional center-tapped rectifier topology. Based on the resonant behavior, all switches are turned on at ZVS, and rectifier diodes are turned off at ZCS if the switching frequency is less than the series resonant frequency. The proposed converter can be applied for the power supply unit of all-in-one PCs, liquid crystal display (LCD) TVs and servers, and dc-dc converters for fuel-cell power system. Laboratory experiments with a 1000-W prototype, verifying the effectiveness of the proposed converter, are described.