High-Density High-Performance Server PSU with 3-Level Flying Capacitor PFC and 500 kHz LLC

Abstract:
In this paper, a 3.3k W power supply (PSU) for server applications implementing a 3-level flying capac-itor (3LFC) PFC is presented. The designed unit is capable of 3.3 kW maximum steady state output power at 230 V down to 180 V AC input, with 50 V output voltage, and features hold-up time as per server requirements. The proposed unit targets high power in very small form factor by means of wide-bandgap (WBG) power semiconductors: a multilevel PFC with 400 V SiC and a high-frequency LLC with GaN. The main design considerations for robust operation of 3LFC will be presented: charge of flying capacitor during start-up and driving of the 3LFC stacked devices. The presented PSU (REF_3K3W_3LFC_PSU) fits in 72 mm x 40 mm x 192 mm dimensions, with a total peak efficiency of 97.6% at 230 VAC input, resulting in a total power density of 96 W/in³.