Abstract:

An improved soft switching constant on-time (COT) control method is proposed to address the issues of high conduction loss caused by turn-on voltage of the Boost-PFC circuit in critical conduction mode (CRM) and poor EMI caused by high du/dt during conduction.The circuit switching transistors adaptively realize ZVS at low input voltage instantaneous value and valley conduction at high input voltage instantaneous value.The switching voltage and switching loss of the switching transistor are reduced.The du/dt of switching transistor is reduced and EMI performance of circuit is improved.The Boost-PFC circuit of CRM,the principle and working process of the proposed control method are analyzed.The influence of the proposed control method on EMI characteristics of the circuit is explored.The key parameters are designed.Finally,the simulation and experiment results show the input and output characteristics,efficiency curves and EMI curves of the prototype,which can verify the effectiveness of the proposed control method.

Key words: Boost-PFC circuit, improved COT control, switching loss, EMI, adaptively