A New Family of ZCT-PWM Isolated DC-DC Converters with the Optimized Control Strategy ZCT Cell On Secondary Side

To overcome the complicated strategy and circuit implementation issue for control of the conventional ZCS converter to derive the driving signal for the auxiliary switch, a novel ZCT cell which greatly simplifiers the control strategy by directly extending the duty duration to be the whole off-time of the primary switch is proposed in this paper, where the control circuit is implemented only by a logic inverter and two sets of RC combinations with the same parameters. When preferably placed on the secondary side, the proposed ZCT cell can not only help the converter to achieve ZCS for the primary switches and the ZCT for auxiliary switch wherein itself but also soften the communication of the secondary rectifiers. In addition, the behavior of ZCS has no interaction with primary side ZVS process, therefore a fully soft-switching (ZVS on and ZCS off) converter can be easily obtained. The detail operation principles and design considerations, as well as the family of the new ZCS converters, were presented. A prototype with the fully soft-switching dual switch active-clamped forward topology suitable for being the front-end dc-dc converter in the server system, whose highest conversion efficiency is 95.5%, was built to verify the validity and applicability of this proposed ZCT cell.