A More Accurate Variable On-Time Control for CRM Flyback PFC Converters

In order to eliminate the effect of the negative primary current and delayed switching cycle, this paper proposes a more accurate variable on-time (VOT) control for critical mode (CRM) flyback PFC converters to obtain lower input current total harmonics distortion (THD). Systematic operation analysis is built considering actual resonance during soft-switching processes. A novel VOT expression is proposed based on the electric-charge perspective and numerical fitting method. Experimental results from a 21V/2.8A prototype are shown to verify the effectiveness of the proposed VOT control.