Magnetics Analysis and Optimization Techniques for a 2 MHz GaN-based Active-Clamped Isolated SEPIC Converter

This paper presents the magnetics optimization of the 2 MHz, 12 V, 600 mA, GaN-based Active-Clamped Isolated SEPIC Converter (ACISC) discussed in [1], which supports full Zero- Voltage Switching (ZVS) operation throughout the 9 V-18 V automotive range and provides isolation and power interface between the 12V battery and the low-power subnet. Since the converter leverages the high switching frequency enabled by GaN devices, it is crucial to create ad-hoc PCBs for the involved magnetics, realized here as a planar structure, to reduce both the significant winding losses and the inter-winding capacitance which is a critical parasitic capacitance of the converter in the common mode noise perspective. Both the theoretical model specifically developed for full ZVS resonant Discontinuous Con-duction Mode (DCM) operation, as well as the design and step- by -step optimization of the magnetics, are discussed. The analysis, which is verified through simulations and experimental measurements taken on a 7.2 W GaN-based prototype, reveals a peak efficiency of 89.2 % for the optimized ACISC operating in nominal conditions, approximately 2 % higher than the one illustrated in [1].