High-Power Density, 900-W LLC Converters for Servers Using GaN FETs: Toward Greater Efficiency and Power Density in 48 V to 6\/12 V Converters

A 1-MHz, 48-12-V LLC resonant converter was built using eGaN FETs. It can deliver 900 W with a power density of more than 1,500 Wfm 3 and has an experimental efficiency exceeding 98% and excellent thermal performance. The converter at full-load operation did not reach its thermal limit. The output power and power density can, therefore, be further pushed up. The keys to achieving this high-density and high-efficiency LLC converter were the low gate capacitance, low output charge, and low on-resistance of the eGaN FETs. The full-load efficiency and power density of this LLC converter compared to state-of-the-art commercial products and previously published research work implemented as a 48-12-V bus converter are plotted. This work stands out for demonstrating the highest power density and output power.