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Optimal Design of Planar Magnetic Components for a Two-Stage GaN-Based DC/DC Converter

Fig. 1. Prototype system
  A rail-grade converter in the transportation industry provides isolated dc power for such electronics as LED displays, audio amplifiers, safety monitors, lighting, and communications systems.
  This paper develops a 200 W wide-input-range (64–160-to- 24-V), rail-grade dc-dc converter based on gallium nitride devices. A two-stage configuration is proposed. The first regulated stage is a two-phase interleaved buck converter (>400 kHz), and the second unregulated stage is an LLC (2 MHz) dc transformer. In order to achieve high frequency and high efficiency, critical-mode operation is applied for the buck converter, and the negatively coupled inductors are used to reduce frequency and conduction losses. Then, a systematic methodology is proposed to optimize the planar-coupled inductors. The unregulated LLC converter can always work at its most efficient point, and an analytical model is used to optimize the planar transformer. Finally, the proposed dc–dc converter, built in a quarter-brick form factor, is demonstrated with a peak efficiency of 95.8% and a power density of 195 W/in3.
Efficiency curve
Fig. 2. Efficiency and power density comparison for a closed-loop system