ZVS Resonant Converter With Parallel–Series Transformer Connection

A new series resonant converter with a parallel-series transformer connection is proposed in order to achieve zero voltage switching (ZVS) for all power switching, zero current switching (ZCS) for rectifier diodes at a full load, and less transformer secondary winding with a full-wave rectifier. For high-output-voltage applications, the primary windings of two transformers are connected in parallel in order to share the input current and reduce the root-mean-square rms current on the primary windings such that the copper losses on the transformers are reduced. The secondary windings of the two transformers are connected in series in order to ensure that the primary side currents are balanced and the secondary winding turns are also reduced. Thus, the sizes of the transformer core and bobbin are reduced. The full-wave diode rectifier is used on the output side. Thus, the voltage stress of the rectifier diode is equal to the output voltage rather than being two times the output voltage as that in a center-tapped rectifier topology. Based on the resonant behavior, all switches are turned on at the ZVS, and the rectifier diodes are turned off at the ZCS if the operating switching frequency is less than the series resonant frequency. The laboratory experiments with a 660-W prototype, verifying the effectiveness of the proposed converter, are described.