Design of Digital-controlled Two-stage AC/DC Converter Based on GaN HEMT

In this paper, a two-stage AC/DC converter based on GaN devices is investigated and designed. The bridgeless totem pole power factor correction (PFC) converter and PFM control mode based half-bridge LLC resonant converter are applied to the first stage AC/DC conversion part and the second stage DC/DC conversion part, respectively. The absence of reverse recovery in GaN devices enables bridgeless totem pole PFC converter to operate in continuous conduction mode. Meanwhile, a mixed-mode soft-start control strategy is proposed for the LLC resonant converter to solve the issue of large start-up inrush current. In addition, the burst control strategy is employed to improve the gain adjustment range of the LLC circuit. Finally, a 200W digital controlled experimental prototype is designed to verify the feasibility of the control system design.