A New Single-Stage 48-V-Input VRM Topology Using an Isolated Stacked Half-Bridge Converter

Abstract

A buck-derived transformer-isolated converter topology has been proposed in this article for the single-stage 48-V voltage regulator module (VRM) application. The proposed converter uses a switched-capacitor voltage divider derived stacked half-bridge circuit in the primary side of the transformer. This simplifies the transformer structure and reduces device voltage ratings compared to the conventional half-bridge or a full-bridge circuit. Detailed circuit operation, analysis, and design of the proposed converter are presented. Further circuit modification is proposed to avoid unequal average inductor current sharing due to unequal resistances of the inductors in the secondary-side current doubler rectifier and consequent load-dependent dc shift in the transformer magnetizing current. An averaged small-signal ac equivalent circuit model of the converter is derived and validated against SIMPLIS simulation results. Finally, experimental results from a GaN device-based 45-A laboratory prototype demonstrates a maximum efficiency of 92.7%, which is higher than that of the state-of-the-art solution for the selected specifications, and exhibits faster dynamic response against load step variations.