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.