Reduce Size and Increase Efficiency with GaN-based LLC Solution

This article was originally published in Bodo’s Power Systems November 2018 issue by Yajie Qiu, Senior Power Electronics Application Engineer. A small portion is available here and the rest can be read along with supporting graphics and charts in the PDF below.

GaN High Electron Mobility Transistors (GaN HEMT) have lower driving loss and shorter deadtime circuit benefits due to significantly reduced gate charge (Qg) and output capacitance (Coss) compared to Silicon MOSFETS. Therefore, GaN HEMTs show significant advantages over Silicon MOSFETs in high-frequency soft-switching resonant topologies such as an LLC resonant converter. With increased switching frequency (fsw), the transformer core size can be reduced. Furthermore, a 3-D PCB structure is employed to increase the power density. A 190-Watt, 400V-19V GaN Systems E-HEMT based LLC DC-DC resonant converter is carefully designed, and the transformer is optimized for high-end adapter applications operating above 600kHz. The converter shows a complete design with a power density over 63W/inch3, including the 400V bus capacitor, with a peak efficiency of 96%.

Introduction High power density is one key motivation for GaN HEMTs to be widely used in low power consumer applications such as laptop adapters, flat screen TVs, and all-in-one desktop computers. The LLC resonant converter topology is effective in improving efficiency, especially for high-input voltage applications where the switching loss is more dominant than the conduction loss. The series and parallel inductors are often integrated into the transformer using the leakage and the magnetizing inductance, thus reducing the component count. The purpose of this article is to demonstrate a high-power density and high-efficiency DC-DC LLC solution using GaN HEMTs…