UC Berkeley

By operating resonant switched-capacitor converters at resonance, zero current switching (ZCS) can be achieved to eliminate voltage-current overlap losses. Previous literature has shown that zero voltage switching (ZVS) can also be achieved to further reduce switching losses and attain a higher peak efficiency by recovering the charge stored in the parasitic output capacitance of the switches. Contrary to ZCS operation, ZVS timing is highly dependent on load current even with ideal primary passive components. This paper proposes a novel digital control technique that can dynamically track the optimum ZVS timing across a wide range of load current, through passive component and voltage variations. The proposed concept is validated in a 48-V-to-24-V resonant switched-capacitor (ReSC) converter prototype, demonstrating over 10% power loss reduction compared with the conventional open-loop ZVS, and approximately 30% power loss reduction compared with ZCS.