UC3854 High Power Factor Preregulator

The UC3854 provides active power factor correction for power systems that otherwise would draw non-sinusoidal 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 line-current distortion. To do this, the UC3854 contains a voltage amplifier, an analog multiplier/divider, a current amplifier, and a fixed-frequency PWM. In addition, the UC3854 contains a power MOSFET compatible gate driver, 7.5V reference, line anticipator, load-enable comparator, low-supply detector, and over-current comparator.

The UC3854 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 UC3854’s high reference voltage and high oscillator amplitude minimize noise sensitivity while fast PWM elements permit chopping frequencies above 200kHz. The UC3854 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 UC3854 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.

Features of UC3854

• Control Boost PWM to 0.99 Power Factor

• Limit Line Current Distortion To <5%

• World-Wide Operation Without Switches

• Feed-Forward Line Regulation

• Average Current-Mode Control

• Low Noise Sensitivity

• Low Start-Up Supply Current

• Fixed-Frequency PWM Drive

• Low-Offset Analog Multiplier/Divider

• 1A Totem-Pole Gate Driver

• Precision Voltage Reference