ucc28051,pdf datasheet (TRANSI

The UCC38050 and UCC38051 are PFC controllers for low-to-medium power applications requiring compliance with IEC 1000-3-2 harmonic reduction standard. It is designed for controlling a boost preregulator operating in transition mode (also referred to as boundary conduction mode or critical conduction mode operation). It features a transconductance voltage amplifier for feedback error processing, a simple multiplier for generating a current command proportional to the input voltage, a current-sense (PWM) comparator, PWM logic and a totem-pole driver for driving an external FET.

In the transition mode operation, the PWM circuit is self-oscillating with the turn-on being governed by an inductor zero-current detector (ZCD pin) and the turn-off being governed by the current-sense comparator.