Design of Inrush Current Limit Circuit for PFC Circuit using PTC Thermistor

In power conversion circuits featuring a large input capacitor or an input LC circuit, such as power factor correction (PFC) circuits, a high inrush current generally occurs during power start-up transients because of the sudden charging of the empty input capacitor or resonance within the LC circuit. The inrush current imposes severse electrical and thermal stress on circuit components, including power semiconductor switchers, passive elements and protection devices Thus, implementing an inrush current limiting circuit is crucial for the reliable operation of power conversion system. This paper presents the design of an inrush current limiting circuit using a positive temperature coefficient (PTC) thermistor with a bypass switch. the PTC thermistor offers self-protection under overcurrent conditions by rapidly increasing its resistance as temperature rises The design methodology focuses on determining the resistance and energy capacity of the PTC thermistor to optimize peak inrush current, capacitor pre-charging time, and thermal performance during the start-up transient of the PFC circuit. Simulation and experimental results are provided to validate the effectiveness of the proposed design.