AN-6961

www.fairchildsemi.com AN-6961 Critical Conduction Mode PFC Controller Description This application note describes a power factor correction (PFC) circuit using the FAN6961. Both the features of this controller, as well as the operation of the power factor correction circuit, are presented in detail. Based on the proposed design guideline, a design example with detailed parameters demonstrates the performance of the controller. Introduction The FAN6961 PFC controller is an 8-pin Boundary Current Mode (BCM) IC intended for controlling PFC pre-regulators. The FAN6961 provides a controlled on-time to regulate the output DC voltage and achieve natural power factor correction. The maximum on-time of the switch is programmable to ensure safe operation during AC brownouts. An innovative multi-vector error amplifier is built in to provide rapid transient response and precise output voltage clamping. Once the output feedback loop is opened, the output driver (GD) is disabled to provide protection of the system. The start-up current is lower than 20µA and the operating current has been reduced to 5mA. The supply voltage can be operated up to 25V, maximizing application flexibility. The FAN6961 also enables cycle-by-cycle current limiting protection for the external power MOSFET. Figure 1. Power Factor Correction Circuit © 2009 Fairchild Semiconductor Corporation Rev. 1.0.2 4/8/09 www.fairchildsemi.com AN-6961 APPLICATION NOTE Basic Operation of the Boost Converter The typical...