A High-Power-Density High-Efficiency Three-Level Buck Converter for Cellphone Battery Charging Applications

This paper introduces a high-power-density low-profile high-efficiency three-level buck converter for cellphone battery charging applications. This converter is designed to deliver up to 40 W across a 4:1 input voltage range, as enabled by the latest USB standard. A comprehensive methodology based on augmented state-space modeling is used to accurately predict the converter's waveforms and optimize its design. The converter's inductor is realized using a custom-shaped low-profile ferrite core., with its winding and core losses minimized using 3D finite-element analysis. To maximize efficiency, the converter is designed to achieve zero-voltage switching (ZVS) at light-to-medium loads. A prototype three-level buck converter with a PCB area of 358 mm², component height of 1 mm, an input voltage range of 5 V-20 V, an output voltage range of 3 V-4.2 V, and a maximum output current of 10 A is built and tested. The prototype converter achieves a peak efficiency of 98.5% at 2:1 conversion ratio, maintains high efficiency across its entire operating range, and achieves a power density of 704 W/in³.