Constant on-time variable frequency control for critical conduction mode GaN-based totem-pole PFC converters

A constant on-time variable frequency control (COTVFC) with feed-forward for a critical conduction mode (CRM) totem-pole power factor correction (PFC) converter is proposed in this paper. This control method only requires a single voltage loop, where the output is taken as the on-time of the main switches of the converter. The off-time of the main switches in different switching cycles is calculated by the voltage-second balance principle, which ensures that the converter always operates in the CRM. Feed-forward is introduced to improve the dynamic response of the converter. The control model is established and the transfer function from the on-time to the output is derived. On this basis, the control parameters of the voltage loop are designed. Then a simulation model is built in PSIM for simulation verification. Finally, a two-phase interleaved parallel GaN-based totem-pole PFC converter prototype is made for experimental verification. Simulation and experimental results verify the feasibility and effectiveness of the control method proposed in this paper.