GaN-Based 400V/48V DC-DC Converter with 97% Efficiency and PCB Magnetics for Automotive Applications

Electric vehicles are attracting great attention with their 48V electrification system. In this paper, the design of a two-stage 400V/48V automotive DC-DC converter based on PCB magnetics is presented. A two-phase buck converter with a coupled inductor is used as the first stage to perform voltage regulation and guarantee good load transient performance. The second stage is an LLC resonant converter with a matrix transformer which provides isolation and behaves as a step-down DC transformer (DCX). The switching frequency is pushed to 500kHz to help reduce converter size and weight. By pushing the operation to high frequencies, the windings of the transformer of the LLC converter and those of the coupled inductor of the buck converter are integrated and built into the PCB. This not only improves the power density, but also minimizes the use of labor-intensive components/processes to enable truly automated manufacture. The thermal management for such converters is especially challenging due to the harsh environments it is situated in. This is accomplished using a custom-engraved aluminum baseplate to provide low thermal resistivity and increase converter reliability. The converter can achieve an efficiency of 97% and a power density of 5 kW/L.