1 Features

• Transition Mode PFC Controller for Low Implementation Cost
• Industry Pin Compatibility With Improved Feature Set
• Improved Transient Response With Slew-Rate Comparator
• Zero Power Detect to Prevent Overvoltage Protection (OVP) During Light Load Conditions
• Accurate Internal VREF for Tight Output Regulation
• Two UVLO Options
• OVP, Open-Feedback Protection, and Enable Circuits
• ±750-mA Peak Gate Drive Current
• Low Start-Up and Operating Currents
• Lead (Pb)-Free Packages

2 Applications

• Single-Stage PFC Flyback Converters for Lighting and Motor Drives
• Switch-Mode Power Supplies for Desktops, Monitors, TVs, and Set Top Boxes (STBs)
• AC Adapter Front-End Power Supplies
• Electronic Ballasts

3 Description

The UCC38050 and UCC38051 are PFC controllers for low-to-medium power applications requiring compliance with IEC 1000-3-2 harmonic reduction standard. The controllers are designed for a boost preregulator operating in transition mode (also referred to as boundary-conduction mode or critical conduction-mode operation). They feature 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 turnon being governed by an inductor zero-current detector (ZCD pin), and the turnoff being governed by the current-sense comparator. Additionally, the controller provides features such as peak current limit, default timer, overvoltage protection (OVP) and enable.

1. For all available packages, see the orderable addendum at the end of the data sheet.

Simplified Application Diagram