LLC resonant DC transformer (DCX) with parallel PWM output tight regulation

This paper proposes a parallel output regulation method for isolated resonant DC transformer (DCX). With an auxiliary transformer in series with the main transformer at primary side and independent at secondary side, the DCX creates an additional output which feeds the cascaded PWM DC-DC converter. Because the output of the DC-DC converter is parallel with main output, the output voltage is regulated by the duty cycle of DC-DC stage. With the proposed topology, the major part power is delivered to load through the main transformer of DCX, and only small portion of power is converted by two-stage, DCX with cascaded DC-DC. Therefore, the output voltage is tightly regulated by PWM DC-DC stage and the conversion efficiency is almost as high as conventional LLC resonant DCX. The steady state operating principle of the proposed converter is analyzed, and a prototype with an LLC-DCX and an auxiliary Buck DC-DC stage is built-up based on the theoretical analysis.