LLC Converters with GaN: Commutation Loop Capacitance

Wide-Bandgap (WBG) devices based on Silicon-Carbide (SiC) or Gallium-Nitride (GaN) are pushing the boundaries of switching frequencies, power densities, and efficiencies of modern power converters. To utilize the full potential of these devices, the parasitic elements formed by the printed circuit board (PCB) layout requires special attention. This work analyzes the parasitic capacitance of common commutation loop PCB designs and the consequent impact on the efficiency of a soft-switched application with WBG devices. In particular this work describes the critical parasitic capacitance of vertical and lateral loop designs based on their geometry and analyzes the consequent impact on an LLC application with high voltage GaN devices. The analysis shows that parasitic capacitance influences the conversion efficiency significantly, especially in low-loading conditions. Further, the analysis surfaces that vertical designs suffer from significantly higher parasitic capacitance than lateral designs. The analysis is verified through circuit simulation, Finite Element Analysis (FEA) and experiments which demonstrate good alignment with the theoretical analysis.