Series-Capacitor Buck Converter with Soft Turn-On

The Series-Capacitor Buck (SCB) converter lowers the switching loss, doubles the duty ratio, and equalizes the current between two phases. A Resonant Series-Capacitor Buck (RSCB) converter is realized by adding a parallel resonant tank next to the series-capacitor C-s. All switches turn on into zero-voltage (ZVOn) and the low-side switches turn off from zero-current (ZCOff). The voltage gain is still linearly proportional to the off-time of the low-side switches. The resonant tank generates additional loss and increases the voltage stress of the low-side switches. A 2-MHz prototype with a full load efficiency of 97.3%, 48 V at the input, and 7 V, 20 A at the output, was built to verify the design.