GaN Based DC-DC Converter for 48 V Automotive Applications

Enhancement-mode GaN transistors (eGaN (R)) are a key enabling technology for high-performance bidirectional power conversion, a component of the emerging 48 V / 12 V bus architecture in mild-hybrid electric vehicles. With GaN, a conventional half-bridge topology can be scaled to multiple phases and achieve high power density at efficiencies exceeding 97%. Design considerations include switching frequency, inductor selection, control, sensing, and thermal design. This paper will discuss a five-phase fully regulated bi-directional 48 V to 12 V DC-DC converter built using GaN FETs. A hardware prototype was constructed and experimentally verified to achieve a peak efficiency greater than 97%, and a full power efficiency greater than 96% at 3 kW. A high-performance scaleable thermal design was implemented that maintained a FET temperature rise of less than 10 degrees C above the heatsink. Plans for a new prototype will also be discussed, with higher density power modules and interchangeable inductor boards for further optimization.