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GaN-based, High-density, Unregulated LLC Converters for Two-stage 48V Voltage Regulator Module

Two-stage 48V VRM Solution
Fig.1. Two-stage 48V VRM Solution
With the rapid increase of power consumption at data centers, efficient power management solutions and architectures are gaining more attention. 48V voltage regulator modules (VRMs) have been used in telecom applications for years. A recent study indicates 48V VRMs, instead of 12V VRMs, are deemed as well a more efficient and cost effective archi-tecture for data center applications.

Two-stage 48V VRM architecture can help achieve the required efficiency and power density for the target appliaction with a quicker integration to the existing data centers. As shown in Fig.1, the first stage is an unregulated DC/DC (DCX) converter stepping down the input voltage to an intermediate bus voltage and is followed by the mature technology of a multi-phase buck converter. The soft switching capabilities of the first stage combined with the simplicity and scalability of the second stage promote this solution as a suitable candidate for future data centers to achieve the required efficiency and power density. One key element to achieve these goals is the first stage unregulated converter design.
In this work, a LLC converter with matrix transformer structure is proposed for the first stage converter. Two DCX converters are designed with different transformation ratios to evaluate the overall efficiency of the two stages with different intermediate bus voltages. With GaN devices and integrated magnetic structure, the two converter prototypes shown in Fig. 2 are designed, and they achieve very high efficiency (> 98 %) and power density (> 1200 W/in3). The effeciency of the two stages is then evaluated with the conclusion that 6V for the intermediate bus will help achieve higher efficiency for the two-stage architecture.

Prototype Figure
Fig.2. High efficiency and density GaN based 48/xV prototypes
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