Zero voltage switching DC converter for high-input voltage and high-load current applications

A new DC/DC pulse-width modulation (PWM) converter with the functions of zero voltage switching (ZVS) for power switches and zero current switching (ZCS) for rectifier diodes is presented for high-input voltage and high-load current applications. Three-level PWM circuit with two clamped diodes and one flying capacitor is adopted to achieve ZVS turn-on for all power switches, to balance two input capacitor voltages and to limit the voltage rating of each switch at one-half of input voltage. Two three-level PWM circuits with the same power switches are used to share the load current for medium power applications. Series-parallel resonant converter or LLC (L_r, L_m and C_r) converter is adopted to achieve ZCS turn-off for rectifier diodes. Thus, the switching losses of power switches are reduced and the reverse recovery losses of rectifier diodes are eliminated. In order to high load current application, four centre-tapped rectifiers are connected in parallel to reduce the current rating of rectifier diodes and transformer windings. Experiments are provided to verify the effectiveness of the proposed converter.