A new concept of high input voltage to low load voltage (1500 V – 48V) DC-DC conversion with hybrid ZVS-ZCS and asymmetrical voltage distribution

A new dc-dc converter with asymmetrical voltage distribution between two primary switch pairs is proposed. It allows an implementation with popularly used MOSFETs for the low-voltage switch pair and IGBTs for the high-voltage switch pair, giving the optimal option for a particular class of high-voltage applications. A new hybrid zero-voltage-switching (ZVS)-zero-current-switching (ZCS) technique, which is different from the ZVZCS solution, is proposed. A secondary-side snubber is used to achieve ZCS of all IGBTs in the IGBT pair; its resonant energy is fully released to the load. The energy used for achieving ZVS for the upper MOSFET in the low-voltage switch pair at the transition from the freewheeling to energy transfer stage is provided by the primary-side input capacitor and dc-blocking capacitor. All IGBTs and MOSFETs in the proposed structure are soft-switched from very light load to full load. The duty cycle of the upper switch in each pair determines the voltage distribution between the switch pairs. It is controlled by a simple PWM. A 2kW, 1500/48V experimental prototype has been built and evaluated. The experimental results confirmed the theoretical predictions.