99.7% Efficient 800 V ZVS Partial Power Switched Capacitor Buck Converter with 650 V GaN HEMTs

This letter presents a highly efficient synchronous buck converter based on a partial power processing switched capacitor topology with two 650 V gallium nitride (GaN) transistors and a diode-based resonant circuit. In this topology, only the output voltage is switched, which allows an extended input voltage range up to 800 V, beyond the 650 V blocking voltage of the semiconductors (for output voltages of at least half the input voltage). A hysteretic current control ensures zero-voltage switching over the complete voltage range. A hardware demonstrator is characterized for three cases targeting battery charging applications: 1 A constant input current operation (CC, at 450 V input) sweeping from 250 V to 425 V output is 99% to 99.7% efficient. Constant voltage operation (CV, 450 V to 400 V) sweeping from 0.2 A to 1 A input is 99.3% to 99.7% efficient. Finally, the input voltage is further swept from 470 V to 800 V (CC, 1 A input, 450 V output), and this 99.7% to 99% efficient operation proves that the converter is efficiently functional at input voltages exceeding the semiconductor blocking voltage.