High Step-Down Ripple-Free Resonant DC/DC Converter Using Stacked T-Type Half-Bridge

This article presents a high step-down ripple-free resonant dc/dc converter. By incorporating the stacked T-type half-bridge and center-tapped rectifier structure, it achieved high step-down capability without using a high-turns ratio transformer. By using voltage fluctuation across a T-type half-bridge circuit, hard-switched components are turned off with nearly zero-voltage-switching. Soft-switching capability realizes high switching frequency operation, which brings down the size of the magnetic components. The interleaved active-clamped circuit and corresponding switching modulation with a duty ratio fixed at 0.5 generate ripple-free output current. This aspect ensures no use of extra filter inductor. The use of secondary-side switching hinders the magnetizing current from flowing through the resonant inductor; the core size of the resonant external inductor can remain compact. As a result, the proposed converter features high-voltage step-down, high efficiency, and ripple-free characteristic. To confirm the viability of the design concept, a 1-kW laboratory built prototype is implemented with the input voltage of 400-600 V and the output voltage of 48 V.