A Two-Stage Rail Grade DC/DC Converter Based on GaN Device

A two-stage GaN-based dc/dc converter is proposed for the railway applications. This isolated converter needs to deal with a wide input voltage (from 64V to 160V) and provide a regulated output voltage (24V). In this paper, a two-phase interleaved buck converter serves as the frond-end stage. This regulation stage can convert the wide input to a constant 48-V dc bus, and then an unregulated LLC converter is used for 48V/24V conversion. For both stages, the suitable GaN devices are evaluated and compared through experiments. Then the voltage regulation mechanism is discussed for the first stage, which works under critical mode (CRM) with inversely coupled inductors. The equivalent inductances are used to discuss the zero voltage switching (ZVS) capability, based on which the ZVS extension are developed. Finally, a digitally controlled prototype system using quarter-brick footprint is implemented with a low-cost microcontroller (TMS32028027). In the experiment, the measured peak efficiency and power density can reach 95.1% and 130W/in ³ respectively.