High Step-Down Converter Integrating Switched Capacitor Converter and PWM Synchronous Buck Converter

Traditional non-isolated PWM buck converters for high step-down voltage conversion applications suffer from duty cycle limitation issues, such as higher device stresses and increased switching losses. In this paper, a high step-down converter integrating a switched capacitor converter (SCC) and PWM synchronous buck converter is proposed to mitigate such duty cycle limitation issues. The input voltage is divided by the SCC, whereupon the divided voltage is converted and regulated to a desired level by the synchronous buck converter. A fundamental operation analysis as well as comparative analyses for both the proposed converter and traditional buck converter in terms of total device power rating (TDPR) and normalized stored energy in inductors were performed. A 50-W prototype was built for 48 V-input and 4.0-6.0 V-output that corresponds to a voltage step-down ratio of 0.083-0.125. The converter operated with moderate duty cycles and the measured peak efficiencies were 90%-92%, verifying and demonstrating its performance.