Parasitic Capacitance of Switching Devices and Its Application to Improve the Design Accuracy for VHF DC–DC Converters

As dc–dc converters operate at the very high-frequency (VHF, 30–300 MHz) range, the nonlinear parasitic capacitance of switching devices increasingly impacts their performance, especially since the ON-state resistance of the switch is highly related to the parasitic capacitance. Conventional design methods typically approximate the nonlinear parasitic capacitance with a fixed value, which significantly limits design accuracy and may compromise soft-switching performance as nonlinearity increases. Hence, this article proposes an optimal design method that first employs a discrete iterative numerical solution to perform steady-state analysis for the inverter and rectifier stages, considering nonlinear parasitic capacitance. Then, the gradient descent algorithm is used to decouple their design. Compared with existing design methods, the proposed one can effectively capture the nonlinear behavior in the design process, resulting in higher accuracy under highly nonlinear parasitic capacitances. This is beneficial for selecting switching devices with small ON-state resistancerdsonto improve efficiency and reduce external discrete capacitance to enhance power density. Finally, both simulation and experimental results verify the proposed method by designing a 30-MHz, 20-W Class E VHF converter, achieving 91.6% efficiency of prototype with a smallrdsonGaN switch and 91.7% parasitic capacitance utilization of the switch.