The SG6561/A PFC controller is an 8-pin boundary mode IC intended for controlling PFC pre-regulators. The SG6561/A is pin compatible with the L6561, and it has many new features. It 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 brownouts. An innovative multi-vector error amplifier is built in to provide rapid transient response and precise output voltage clamping. A built in circuit will disable the controller if the output feedback loop is opened. The start up current is lower than 20uA and the operating current has been shrunk to 4.5mA. The supply voltage can be up to 25 volts, maximizing application flexibility. The SG6561/A enables cycle-by-cycle current limiting protection for the external power MOSFET to be easily achieved.