Design of High Step-Down Ratio Isolated Three-Level Half-Bridge DC-DC Converter With Balanced Voltage on Flying Capacitor

A high step-down ratio three-level half-bridge (TLHB) dc-dc converter with a current-doubler rectifier is presented for power conversion from a 48-to-60-V input to a 0.5-to-1-V output. The proposed TLHB topology and operation employed on the primary side improve the power-conversion efficiency by reducing the switching loss while minimizing the turn ratio of the transformer by converting the input voltage down to one quarter on the primary side. Moreover, it reduces the voltage stress on switches by half, thereby enabling the converter to be implemented with Si transistors with low breakdown voltage. The designed TLHB gate-driver IC minimizes the delay mismatches in gate drivers and mitigates the effect of the leakage inductance of the transformer, reducing the voltage imbalance on the flying capacitor without any balancing scheme in the controller. The proposed dc-dc converter implemented with 40-V Si transistors for the primary-side switches achieves 92.8% peak efficiency while supporting the maximum load current of 60 A and the maximum input voltage of 60 V. The converter with the proposed TLHB gate driver IC shows less than 0.8% voltage imbalance on the flying capacitor.