Digital variable frequency control for zero voltage switching and interleaving of synchronous buck converters

When a synchronous buck converter is operated with zero voltage switching (ZVS) and fixed frequency, the direction of the current in the output inductor is alternated each switching period. Thus the output current ripple of the converter is high to ensure zero voltage switching operation at maximum load. With interleaved outputs this leads to high circulating currents at low loads. In this paper, to minimize circulating currents at low loads, solutions for digital control of ZVS with variable switching frequency and interleaving control for bidirectional power flow are presented. The methods have been implemented in a DSP and verified by measurements.