GaN Based High-Density Unregulated 48 V to x V LLC Converters with ??? 98% Efficiency for Future Data Centers

The two-stage 48 V voltage regulator module (VRM) with an unregulated first stage DC/DC converter providing intermediate bus voltage, followed by a multi-phase buck converter, has proven to be a scalable and efficient approach for 48 V rack architecture in data centers. In this work, eGaN(r) based first stage unregulated LLC converters with integrated magnetics are proposed. The converters are designed with fixed transformation ratios of (4:1) and (8:1). They provide a continuous power of 900 W, with maximum efficiencies of 98.4 % and 98.0 % in high-power-densities of 1600 W/in3 (98 KW/liter) and 1200 W/in3 (74 KW/liter), respectively. The bus voltage variation is evaluated to maximize the overall efficiency of the 48 V VRM.