Evaluation of GaN transistor losses at MHz frequencies in soft switching converters

Abstract

On paper, Gallium nitride (GaN) transistor promises exceptional performance when used in converters operating at high switching frequency; nonetheless, reduction in their performance when used in real circuits have been observed. Previous experiments show that tested GaN transistors can display excessive loss of up to three times their predicted values under certain test conditions. This paper evaluates power losses in GaN transistors when used in class Φ 2 resonant soft-switching inverter topologies at MHz frequencies. Thermometric loss calibration technique is used to calculate the power losses. To gain better insight, experiments are set up to subdivide these losses into two components, one associated with on-state transistors and one associated with off-state transistors. Two GaN devices from two different companies were selected for the study. Further, a control study with a silicon (Si) transistor is also done to confirm the validity of the test method, and to compare the performance of GaN transistors to an existing Si transistor. The following paper presents the loss separation method, and the resulting loss breakdown for the tested devices. The tested operating frequency ranges from 3.39 MHz to 27.12 MHz.