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BLOCK DIAGRAM

• 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

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

Summary of content (12 pages)

PAGE 1
UC1854 UC2854 UC3854 High Power Factor Preregulator FEATURES DESCRIPTION • 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 • The UC1854 provides active power factor correction for power systems that otherwise would draw non-sinusoidal current from sinusoidal power lines.
PAGE 2
UC1854 UC2854 UC3854 ABSOLUTE MAXIMUM RATINGS Supply Voltage VCC . . . . . . . . . . . . . . . . . . . . GT Drv Current, Continuous . . . . . . . . . . . . . GT Drv Current, 50% Duty Cycle. . . . . . . . . . Input Voltage, VSENSE, VRMS . . . . . . . . . . . . . Input Voltage, ISENSE, Mult Out . . . . . . . . . . . Input Voltage, PKLMT . . . . . . . . . . . . . . . . . . Input Current, RSET, IAC , PKLMT, ENA . . . . . Power Dissipation . . . . . . . . . . . . . . . . . . . . . Storage Temperature . . . . . .
PAGE 3
UC1854 UC2854 UC3854 Unless otherwise stated, VCC=18V, RSET=15k to ground, CT=1.5nF to ground, PKLMT=1V, ENA=7.5V, ELECTRICAL VRMS =1.5V, IAC=100µA, ISENSE=0V, CA Out=3.5V, VA Out=5V, VSENSE=7.5V, no load on SS, CA Out, CHARACTERISTICS VA Out, REF, GT Drv, –55oC
PAGE 4
UC1854 UC2854 UC3854 PIN DESCRIPTIONS (Pin Numbers Refer to DIL Packages) Gnd (Pin 1) (ground): All voltages are measured with respect to Gnd. VCC and REF should be bypassed directly to Gnd with an 0.1µF or larger ceramic capacitor. The timing capacitor discharge current also returns to this pin, so the lead from the oscillator timing capacitor to Gnd should also be as short and as direct as possible.
PAGE 5
UC1854 UC2854 UC3854 PIN DESCRIPTIONS (cont.) GT Drv (Pin 16) (gate drive): The output of the PWM is a totem pole MOSFET gate driver on GT Drv. This output is internally clamped to 15V so that the IC can be operated with VCC as high as 35V. Use a series gate resistor of at least 5 ohms to prevent interaction between the gate im- pedance and the GT Drv output driver that might cause the GT Drv output to overshoot excessively.
PAGE 6
UC1854 UC2854 UC3854 TYPICAL CHARACTERISTICS at TA = TJ = 25oC (cont.) Multiplier Output vs Multiplier Inputs with Mult Out=0V 600 250 VRMS=1.5V VRMS=3V VA Out=5V 500 200 VA Out=3.5V 400 150 300 VA Out=3V VA Out=2.5V Mult Out µA Mult Out µA 100 200 VA Out=2V VA Out=1.25V 50 100 VA Out=1.
PAGE 7
UC1854 UC2854 UC3854 APPLICATIONS INFORMATION (cont.) ISENSE/Mult Out (Line current): The voltage drop across the 0.25 ohm current-sense resistor is applied to pins 4 and 5 as shown. The current-sense amplifier also operates with high low-frequency gain, but unlike the voltage amplifier, it is set up to give the current-control loop a very wide bandwidth. This enables the line current to follow the line voltage as closely as possible.
PAGE 8
UC1854 UC2854 UC3854 FIGURE 1 - Typical Application This diagram depicts a complete 250 Watt Preregulator. At full load, this preregulator will exhibit a power factor of 0.99 at any power line voltage between 80 and 260 VRMS. This same circuit can be used at higher power levels with minor modifications to the power stage. See Design Note 39B and Application Note U-134 for further details.
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PACKAGE OPTION ADDENDUM www.ti.
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PACKAGE OPTION ADDENDUM www.ti.
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PACKAGE OPTION ADDENDUM www.ti.com 10-Jun-2014 Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties.
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