18.6 A 92.8%-Peak-Efficiency 60A 48V-to-1V 3-Level Half-Bridge DC-DC Converter with Balanced Voltage on a Flying Capacitor

Abstract

Demand for DC-DC voltage conversion from a 48V input has been on the rise due to proliferation of server and automotive applications with a 48V intermediate bus and 48V batteries, respectively. Compared to a 12V, the 48V architecture reduces the power loss thanks to the low distribution losses in the power delivery network. However, improving efficiency is a major challenge in the design of a 48V point-of-load (PoL) DC-DC converter due to the high step-down ratio and high output current. To improve conversion efficiency, several 48V PoL converters implemented with high-quality GaN transistors have been proposed [1], [3]. However, the non-isolated hybrid converter in [1] shows a moderate peak efficiency of 90.9% and requires a large number of switches and passive elements. The isolated converter in [2] shows high efficiency and maximum output current of 80A, requiring a high conversion-ratio planar transformer of 40:1, many switches, and a complicated controller, but offers a limited conversion range. In addition, the GaN transistor suffers from reliability issues [4]. Although an active-clamp forward converter in [5] is implemented with MOSFETs, the peak efficiency is limited to 89.5%. A half-bridge (HB) DC-DC converter with a current-doubler rectifier in [3] is a well-known architecture for high step-down ratio and high output current applications. However, the switching loss in the primary-side HB topology limits the overall efficiency. This paper presents a high-efficiency 3-level HB DC-DC converter with a current-doubler rectifier for power conversion from a 48-to-60V input to an output ranging from 0.5V to 1V.