Studies on Electromagnetic and Thermal Performance of GaN MOSFETs in an Isolated DC-DC converter

This paper presents the analysis, simulation and experimental studies of a GaN device-based full bridge isolated DC-DC converter switching at 500 kHz. For such high frequency converter boards involving small SMD packages, electromagnetic and thermal issues become much significant. These have been addressed in this work. The GaN half-bridge (HB) circuit modules have been developed as units for easier testing and maintenance in the lab. FEM based electromagnetic simulations have been performed for the GaN HB board to validate the reliability of performance at such high frequencies. From FEM-based electromagnetic studies, the board parasitics have been estimated. These results also serve as inputs to the thermal simulation package. The device-level thermal simulation is also performed using FEM. The thermal equivalent circuit diagrams are presented to calculate the temperature rise values analytically. Comparative studies on thermal aspect are presented for both hard switching (HS) and free-wheeling (FW)GaN devices and two GaN half-bridge cards. Experimental results have been recorded at 1.8 kW @500 kHz with 400 V DC Bus. It is found out that the simulation results are in good agreement with the experimental results.