1 Features

1• Control Boost PWM to 0.99 Power Factor

• Limit Line-Current Distortion to < 5

• World-Wide Operation Without Switches

• Feedforward Line Regulation

• Average Current-Mode Control

• Low Noise Sensitivity

• Low Startup Supply Current

• Fixed-Frequency PWM Drive

• Low-Offset Analog Multiplier and Divider

• 1-A Totem-Pole Gate Driver

• Precision Voltage Reference

2 Applications

• Offline AC-to-DC Converters

• Medical, Industrial, Telecom, and IT Power

Supplies

• Uninterruptible Power Supplies (UPS)

• Appliances and White Goods

3 Description

The UC1854 provides active-power factor correction

for power systems that otherwise would draw nonsinusoidal

current from sinusoidal power lines. This

device implements all the control functions necessary

to build a power supply capable of optimally using

available power-line current while minimizing linecurrent

distortion. To do this, the UC1854 contains a

voltage amplifier, an analog multiplier and divider, a

current amplifier, and a fixed-frequency PWM.

In addition, the UC1854 contains a power MOSFETcompatible

gate driver, 7.5-V reference, line

anticipator, load-enable comparator, low-supply

detector, and overcurrent comparator.

The UC1854 uses average current-mode control to

accomplish fixed-frequency current control with

stability and low distortion. Unlike peak current-mode,

average current control accurately maintains

sinusoidal line current without slope compensation

and with minimal response to noise transients.

The high reference voltage and high oscillator

amplitude of the UC1854 minimize noise sensitivity

while fast PWM elements permit chopping

frequencies above 200 kHz. The UC1854 is used in

single-phase and three-phase systems with line

voltages that vary from 75 V to 275 V and line

frequencies across the 50-Hz to 400-Hz range. To

reduce the burden on the circuitry that supplies power

to this device, the UC1854 features low starting

supply current.

These devices are available packaged in 16-pin

plastic and ceramic dual in-line packages, and a

variety of surface-mount packages.