A Two-Phase High-Step-Down DC-DC Converter with Zero-Voltage Switching and Automatic Current Sharing

This paper proposes a two-phase high-step-down converter with zero-voltage switching (ZVS) and automatic current sharing, which is suitable for power conversion systems requiring a high step-down voltage conversion ratio. The proposed structure consists of three power switches, two energy-transferring capacitors, two freewheeling diodes, and one differential-mode transformer. This structure is compared with the conventional two-phase series-capacitor buck converter, which requires two independent inductors at the output side and thereby limits the power density. Therefore, in this paper, the dual-inductor structure with a differential-mode transformer is presented. The turns ratio of the differential-mode transformer is designed as one, enabling the two phases to achieve good symmetry. This design not only effectively improves the overall power density, but also realizes current sharing between the two-phase output currents by means of the differential-mode transformer. In addition, due to the leakage inductance continuity of the differential-mode transformer and the discharge path of the energy-transferring capacitors, the power switches can achieve zero-voltage switching during switching transitions, thereby significantly reducing switching losses. On the other hand, the voltage-dividing characteristic of the series capacitors can effectively reduce the voltage stress on the power switches. According to the above features, the proposed converter not only significantly improves the overall conversion efficiency, but also enhances the operational stability and reliability of the system. In this study, the operating principle of the proposed circuit is first analyzed, with some experimental results to verify effectiveness.