Operation of a Split-Capacitor Push-Pull Parallel Resonant Converter in Buck Mode

This paper describes a technique for operating split- capacitor push-pull resonant converters (SCPPRC) in buck mode with zero voltage switching (ZVS). The technique, which also allows for both normal (conventional) and boost modes, operates the converter at a variable switching frequency to provide a lower and variable output voltage than that would result in the conventional normal mode. In the buck mode, the variable switching frequency is essentially lower than the damped resonant frequency for any given load, and is generated by modulating a variable phase-shift into the damped resonant frequency. A model and theoretical analysis are presented to show the difficulty in obtaining a closed form analytical solution for the performance in the buck mode. Measured performance of a prototype 150 W converter is compared with simulated results to show the validity of the proposed concept.