A GaN-based 97% efficient hybrid switched-capacitor converter with lossless regulation capability

DC-DC converters for large conversion ratio applications face challenges such as high device stress and large inductor size. Switched-capacitor (SC) converters are known to have reduced device stress and no inductors, but the associated large transient current and poor efficiency at regulated output have prevented their wide adoptions. In this work, a complete solution is proposed, including the control and design considerations for a magnetic hybrid type of SC converter, so that the capacitor charging loss is eliminated and high efficiency is maintained with voltage regulation. Compared to conventional buck converters, the proposed converter offers the advantages of higher efficiency and significantly reduced inductor size. A 170 V to 24 V, 70 W prototype with a wide input and output voltage operating range is implemented using GaN transistors. A low profile heat-sink is designed and built by 3D printing to sufficiently cool the converter. A peak efficiency of 97% and a power density of 276 W/in³ are achieved, which compare favorably to both conventional SC converters and buck converters.