High-Efficiency Active-Clamp Forward Converter With Transient Current Build-Up (TCB) ZVS Technique

In this paper, an active-clamp forward converter with transient current build-up zero-voltage switching (ZVS) technique is proposed. The proposed converter is suitable for the low-voltage and high-current applications. The structure of the proposed converter is the same as that of the conventional active-clamp forward converter. However, since it controls the secondary synchronous switch to build up the primary current during the very short period of time, the ZVS operation is easily achieved without any additional conduction losses of magnetizing current in the transformer and clamp circuit. Furthermore, there are no additional circuits required for the ZVS operation of power switches. Therefore, the proposed converter can achieve the high efficiency and low electromagnetic-interference noise resulting from the soft switching without any additional conduction losses and shows the high power density resulting from the high efficiency and no additional components added. The operational principle and design example are presented. Experimental results demonstrate that the proposed converter can achieve an excellent ZVS performance throughout all load conditions and a significant improvement in the efficiency for the 100-W (5 V, 20 A) prototype converter