Advantages of GaN in a high-voltage resonant LLC converter

LLC Resonant converters have been popular in recent years by providing highly-efficient, compact isolated power conversion for numerous applications. 48V to 12V and 400V to 12V step-down isolated converters are often required in server, telecom and automotive applications. While the switching losses in LLC converters are eliminated due to zero-voltage switching, the primary-side switch output capacitance limits switching frequency and thus places a lower-bound on the converter size. This switch-node capacitance can be significantly reduced by the use of high-voltage Gallium Nitride (GaN) power transistors. This paper demonstrates a 500W, 380V to 12V LLC converter using GaN transistors which achieves 97.85% efficiency with a 308 W/in³ power density.