Fig.1. Multiphase half-bridge current-doubler rectifier with magnetic integration and four-phase coupled inductors.
High-efficiency, high-power-density 48 V voltage regulator modules (VRMs) are crucial and also challenging for 48 V data center power architecture. In this paper, a single-stage 48 V converter with multiphase half-bridge current-doubler rectifiers, as shown in Fig. 1, is proposed for data center applications. Using the magnetizing inductors of the transformer as the output inductors, the power density can be greatly improved. During the integration of the transformer and the output inductors, negative coupling between the inductors can be created by the addition of an air gap in the center leg. Furthermore, the magnetic integration method can be extended to the multiphase current-doubler rectifier. Different magnetic structures are compared and optimized to reduce both loss and footprint. Current-sharing values among the paralleled secondary windings are analyzed and the winding arrangement is optimized to allow for smaller levels of transformer loss.
Finally, A 48V/1.8V prototype is designed, as shown in Fig. 2. It can achieve 93.1% peak efficiency and 1.04 kW/in
3 power density, including its gate-driver loss and size. The prototype can handle 120 A continuous current and 300 A peak current for 2 ms x 62 Hz, with 500 linear feet per minute (LFM) air cooling.
Fig. 2. Top and side views of the prototype next to a US quarter. The footprint is 42.2 mm × 18.6 mm and the height is 4.35 mm.
