Design of high power density DC Bus Converter based on LLC resonant converter with synchronous rectifier

The LLC resonant converter can easily achieve soft-switching and magnetic components integration that makes it an excellent candidate for DC bus converter. In low voltage high output current applications, the design of synchronous rectifier (SR) and transformer is the key issue. A SR driving scheme with less circuit complexity is adopted for switching frequency at the resonant frequency in this paper. Using magnetic motive force (MMF) diagrams both in space and time, the loss model of the center-tapped planar transformer is proposed that provides insight into the mechanism of the skin and proximity losses and that also yields quantitative results. The finite-element analysis (FEA) is applied to demonstrate the loss model. A prototype of 1/4 brick, 48 V to 12 V, 500 W output bus converter is built to verify the result. 96.6% efficiency at full load and 300 W/in³ power density are achieved.