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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
DESCRIPTION
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鈥檚 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.
BLOCK DIAGRAM
UDG-92055
6/98
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