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Rev. 1.0.2 • 4/8/09

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