400V/50V LLC Converter with Integrated Magnetics and Enhanced Hold-Up Capability

The datacenter rack is typically powered by an AC line, fed to AC-DC power supply units (PSUs) that convert it to a regulated 50V DC for compute trays. These PSUs include a power factor correction stage, an isolated LLC converter for step-down and regulation, and bulk capacitors for ripple filtering and hold-up energy. As power demands rise while space remains largely fixed, PSU power density must increase. This paper proposes a 98.7%-efficient, 1300 W/in³, 3 kW LLC power module, vertically mounted to minimize footprint and fully utilize 1U rack height. Multiple modules can be paralleled to scale power. Higher power also increases bulk capacitance needs to sustain output during AC loss, but this can be reduced by extending the LLC gain range. Therefore, a selective SR phase-shift control method is proposed to expand gain beyond conventional frequency modulation. This enables regulated 50V output over a 200–400V input range, reducing required bulk capacitance by 36%.