A variable-frequency one-cycle control for BCM flyback converter to achieve unit power factor

The single-stage flyback power factor correction (PFC) converter is well applied in medium and low power occasion such as adapters or LED drivers. Usually, the flyback PFC converter is preferred to operating in boundary conduction mode (BCM) for achieving high power factor (PF) and high efficiency at the same time. However, the conventional BCM control scheme such as input voltage tracking control or constant on-time control (COT) could not achieve unit PF for the flyback PFC converter. As input voltage increases, the PF and the total harmonic distortion (THD) of flyback converter deteriorate seriously. In this paper, a variable-frequency one-cycle control (VF-OCC) for BCM flyback single-stage PFC converter is presented to achieve unit power factor. Detailed theoretical analysis and design consideration for the VF-OCC are described. At last, two 54W/1.5A laboratory prototypes with two operation strategies have been built up. Experiment results show that the BCM flyback converter with VF-OCC can achieve high PF and low THD over universal input voltage range.