Isolated, High-Conversion Ratio, Flying-Capacitor-based Quasi-Resonant Step-Up Converter

An isolated, soft-switching step-up converter with voltage conversion ratio approaching 100x, while maintaining high efficiency for sub-1W applications is introduced. This is achieved by resonantly charging and discharging a small flying capacitor on the secondary side through a specific control scheme, and strategically incorporating a charge pump. Key features of the introduced converter are: (a) load-independent soft-switching for all the switches on the secondary side, (b) voltage rating of the devices and transformer are lowered, (c) operation of the converter is independent of load and input-to-output voltage conversion ratio. With significant reduction in switching losses and voltage stress, the converter is well suited for low-power applications, and on-chip implementation on process-nodes much lower than the output voltage. The operation of the converter is experimentally verified using a discrete prototype with an input voltage of 3 V, output voltages up to 300 V, and output power as low as 50 mW.