A Regulated 36V-60V-Input VIN-Insensitive Resonant Switched-Capacitor Converter with Large Voltage Conversion Ratio

This paper presents an input-voltage-insensitive regulated resonant switched-capacitor converter for converting 36 V-60 V to 3.3 V or 5 V. By introducing a regulating stage to decouple input voltage from resonant tanks, the resonant capacitor voltages are determined solely by the fixed output voltage. This design avoids resonant frequency variation caused by input voltage changes when applying Class II capacitors that offer higher capacitance but suffer significant capacitance derating due to voltage bias. Meanwhile, the voltage difference between two resonant capacitors is greatly reduced, resulting in only 4% capacitance derating difference, which ensures a better match between the resonant tanks. Unlike using Class I ceramic capacitors that have stable capacitance but lower energy density, this approach achieves higher power density. Compared with the conventional two-stage architecture (a switched tank converter and a regulated buck converter), this converter realizes a larger voltage conversion ratio without adding more passive components. A prototype using only Class II capacitors was designed with a constant resonant frequency of 340 kHz, immune to input voltage or capacitance derating. Measurement results show that the converter achieves a peak efficiency of 92.6% for 36 V-to-5 V conversion and a power density of 567 W/in³.