To overcome the limitation that the battery sourcing stepup dcdc converters can not possess the merits of hicgh efficiency and highdc gain both in the application of backup mode for online uninterrupted power supply (UPS) systems, a novel stepup pushpull type isolated inductorinductorcapacitor (LLC) series resonant dcdc converter was proposed. This converter possessed the softswitching advantage for all power semiconductors. When operated under Boost mode, the proposed converter obtained a high dc gain, which reduced the transformers turnratio to improve conversion efficiency. The inside lowside gate driving circuit was also simplified because of inherit of the pushpull topology. Therefore, the proposed converter is quite suitable for the stepup conversion under battery souring mode in UPS systems. The detail operation principles,characteristics and topdogy variations of the conveter were presented. the validity and applicability were also verified by a 600 V·A dual outputs prototype．
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