High Density Fractional Ratio Switched Capacitor Converter

In modern power distribution systems, the conversion from a 48V bus to the point-of-load (POL) voltage is commonly implemented in two stages. Intermediate bus converters (IBCs) often employ resonant LLC topologies that typically step the bus voltage down to approximately 12V. In these converters, the transformer size is largely dictated by the output voltage, and zero-voltage switching (ZVS) is achieved through the transformer's magnetizing inductance. Conversely, resonant switched capacitor converter (SCC) derivatives generally operate with zero-current switching (ZCS), which limits switching frequency flexibility and increases sensitivity to component tolerances.This work presents a novel unregulated Fractional Switched Capacitor (FSC) converter, derived from Dickson-based topologies, capable of delivering flexible non-integer conversion ratios (e.g., 3.25:1, 3.5:1) while maintaining ZVS across all MOSFETs. The proposed FSC integrates an autotransformer, removing the need for additional inductors to provide both ZVS and resonant operation, thereby enhancing power density. A 1kW prototype, derived from a 3:1 Dickson configuration, is presented in this work. It achieves a compact footprint (23.5mm×19mm) and a peak efficiency exceeding 98.5%. Experimental results confirm symmetrical ZVS operation and robust performance, even in the presence of component tolerances and under non-optimal switching frequency conditions.