Reducing the switching frequency variation range for CRM buck PFC converter by variable on-time control

Critical conduction mode(CRM) Buck power factor correction(PFC) with peak current-controlled of currentmode control, its traditional control is constant on-time control, the switching frequency varies with the input voltage and load variations, and a relatively large frequency range, lead to a large of switching loss. This paper proposes a variable on-time control strategy for a CRM Buck PFC converter. By injecting a certain amount of third harmonic in the peak current reference signal, obtaining the optimization of the switching frequency range, reduction of the switching loss and the ripple of output voltage. Analyzing the operating principle and performance of CRM Buck PFC converter with constant on-time and variable on-time control strategy respectively, further designing the control circuit. Simulation results show that the variable on-time control strategy can effectively reduce the switching frequency of the switch, improve the performance of CRM Buck PFC converter.