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BLOCK DIAGRAM

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Control Boost PWM to 0.99 Power Factor

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Limit Line Current Distortion To <5%

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World-Wide Operation Without Switches

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Feed-Forward Line Regulation

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Average Current-Mode Control

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Low Noise Sensitivity

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Low Start-Up Supply Current

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Fixed-Frequency PWM Drive

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Low-Offset Analog Multiplier/Divider

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1A Totem-Pole Gate Driver

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Precision Voltage Reference

The UC1854 provides active power factor correction for power sys-

tems that otherwise would draw non-sinusoidal current from sinusoi-

dal 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 line-current distortion. To do this,

the UC1854 contains a voltage amplifier, an analog multiplier/divider,

a current amplifier, and a fixed-frequency PWM. In addition, the

UC1854 contains a power MOSFET compatible gate driver, 7.5V ref-

erence, line anticipator, load-enable comparator, low-supply detector,

and over-current 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 UC1854’s high reference voltage and high oscillator amplitude

minimize noise sensitivity while fast PWM elements permit chopping

frequencies above 200kHz. The UC1854 can be used in single and

three phase systems with line voltages that vary from 75 to 275 volts

and line frequencies across the 50Hz to 400Hz 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.

UC1854

UC2854

UC3854

High Power Factor Preregulator

FEATURES

DESCRIPTION

UDG-92055