A Hardware-Simplified Soft-Start Scheme for Current-Fed Full-Bridge DC-DC Converter

At present, the current-fed full-bridge DC-DC converter still faces two inherent defects, namely, the soft-start issue during the start-up process and the voltage spike issue in normal working conditions. In existing research, a large number of attempts have been reported to overcome these two inherent issues. However, the existing solutions are all based on both redundant soft-start circuits and snubber circuits, and two different circuits are required. As a result, the cost of the current-fed full-bridge DC-DC converter is high, especially because the soft-start circuits are only used during the start-up process. So, to reduce device redundancy, a hardware-simplified soft-start scheme is proposed in this paper. In the proposed scheme, the snubber circuit is reused for the soft-start process based on topology reconfiguration, avoiding additional soft-start circuits to reduce the cost of this DC-DC converter. In this proposed method, the current-fed full-bridge DC-DC converter is operated as the voltage-fed full-bridge DC-DC converter by always turning on the snubber switch during the start-up process. Then, the output capacitor can be charged by slowly increasing the output voltage of the H bridge. Then, when the output voltage is high enough, the current-fed full-bridge DC-DC converter is again operated in the current-fed mode to boost the voltage. Subsequently, the converter characters and control strategy were examined and analyzed. The experimental results verify the feasibility of the proposed hardware-simplified soft-start scheme for the current-fed full-bridge DC-DC converter.