TEXAS INSTRUMENTS UC1852, UC2852, UC3852 Technical data

DESCRIPTION

The UC1852 provides a low-cost so lution to active power-f actor corr ection (PF C)
for systems that would otherwise draw high peak current pulses from AC power
lines. This circuit implements zero-current switched boost conversion, producing
sinusoidal input currents with a minimum of external components, while keeping
peak current substantially below that of fully-discontinuous convert ers.

The UC1852 provides controlled switch on-time to regulate the output bulk DC
voltage, an off-time defined by the boost inductor, and a zero-current sensing
circuit to reactivate the switch cycle. Even though switching frequency var ies with
both load and instantaneous line voltage, it can be maintained within a reasonable
range to minimize noise generation.

While allowing higher peak switch currents than continuous PFCs such as the
UC1854, this device offers less extern al circuitry and smaller inductors, yet better
performance and easier line-noise filtering than discontinuous current PFCs with
no sacrifice in complexity or c ost. The ability to obtain a power fact or in excess of

0.99 makes the UC1852 an optimum choice for low-cost applications in the 50 to
500 watt power range. Protect ion features of these devices include under-v oltage
lockout, output clamping, peak-current limiting, and maximum-frequency
clamping.

The UC1852 family is available in 8-pin plastic and ceramic dual in-line packages,
and in the 8-pin small outline IC package (SOIC). The UC1852 is specified for
operation from -55°C to +125°C, the UC2852 is specified for operation from -40°C
to +85°C, and the UC3852 is specified for operation from 0°C to +70° C.

UC1852
UC2852
UC3852

查询UC1852供应商

High Power-Factor Preregulato r

FEATURES

Low-Cost Power Factor

•

Correction

• Power Factor Greater Than 0.99

• Few External Parts Required

• Controlled On-Time Boost PWM

• Zero-Current Switching

• Limited Peak Current

• Min and Max Frequency Limits

• Starting Current Less Than 1mA

• High-Current FET Drive Output

• Under-Voltage Lockout

TYPICAL APPLICATION

10/94

UDG-92001

SOIC–8 (TOP VIEW)

D Package

Unless otherwise stated, VCC=2 4V, ISET=50k Ω to GND, RAMP=1nF to GND, ISNS=
–0.1V, VFB conne cted to COM P, no load on OU T, –5 5 °C<Ta<+125°C for the UC1852,
–40°C<Ta<+85°C f or the UC2852, and 0 °C<Ta<+70°C for the UC3852, and Ta=Tj.

ABSOLUTE MAXIMUM RATINGS

Supply Voltage (Lo w-im peda nce Sou rce )..........................30.0V

Supply Current (High-impedance Source)......................30.0mA

OUT Current, Peak.................. .... .... .... .... .... ... .... .... .... .... ....±1.0A

OUT Energy, Capacitive Load................ .... .... .... .... ..... .... ...5.0 µJ

Input Voltage, ISNS............................................................±5.0V

Input Voltage, VFB.............................................–0.3V to +10.0V

COMP Current...............................................................±10.0mA

ISET Current............ .... ... .... .... . .... ... .... .... . .... ... .... .... . .... ..–10.0mA

Power Dissipation at T a≤25°C (Note 3) ..............................1.0W

Storage Temperature .......................................–65°C to +150°C

Lead Temperat ur e (Soldering, 10 Sec onds )...................+300°C

CONNECTION DIAG RAM

Note 1: All voltages with respe ct to GND (Pin 1).
Note 2: All current s are posit iv e into the specif ied term inal.
Note 3: Refers to DIL-8 Packa ge. Consu lt Packaging Sec tion of
Unitrode Inte gra ted C ircuit s datab ook f or thermal lim ita tion s and
consideratio ns of package.

ELECTRICAL CHARACTERIST ICS

PARAMETER TEST CONDITIONS MIN. TYP. MAX. UNITS

Timer Sectio n

ISET Voltage 4.5 5.0 5.5 V
RAMP Charge Current RAMP=2.5V 88 98 108
RAMP Discharge Current ISNS= –1.0V, RAMP= 1 .0V 12 28 50 mA
RAMP Saturation Volt age
RAMP Threshold - Maximum Fre quen cy VFB=10V, COMP open 0.92 1.02 1.12 V
RAMP Threshold - PWM Comp ara tor 3.9 4.3 4.8 V

Current Sense Co mparator

ISNS Restart Threshold –18 –10 –4 mV
ISNS Fault Thres hold –550 –45 0 –350 mV
ISNS Input Current –100 –30 100

Error Amplifier Se cti o n

VFB Input Voltage 4.6 5.0 5.3 V
VFB Input Bias Current –5.00 –0.03 5.00
COMP Sink Current COMP=7.5V 10 mA
COMP Source Current COMP=2.5V –300 –175 –100
COMP Clamp Voltage VFB=0.0V, COMP open 9.2 10.0 10.6 V

OUT Output

OUT Saturation Voltag e High VCC=13V, I
OUT Saturation Voltag e Lo w I
OUT Saturation Voltag e Low @ 10m A I
OUT Clamp Voltage I
OUT Voltage during UVLO I

Overall Secti on

Inactive Supply Current VCC=10V 0.2 0.4 1.0 mA
Active Supply Current 3.0 6.0 10.0 mA
VCC Clamp Voltage ICC=25mA 30 33 36 V
VCC Turn-On Threshold 14.5 16.3 17.5 V
VCC Turn-Off Threshold 10.5 11.5 13.0 V
VCC Threshold Hysteresis 3 5 7 V

ISNS= –1.0V, I

OUT=200mA, ISNS= –1.0V 0.5 1.6 2.2 V
OUT=10mA, ISNS= –1.0V 0.05 0.40 V
OUT= –200mA, RAMP=2V 10.0 12.0 14.5 V
OUT=100mA, VCC=0V 0.5 1.0 2.2 V

RAMP=100µA

OUT= –200mA, RAMP=2V 0.5 1.7 2.5 V

2

UC1852
UC2852
UC3852

DIL–8 (TOP VIEW)

J or N Package

UDG-92002

µA

0.006 0.200 V

µA

µA

µA

DETAILED BLOCK DIAGRAM

UC1852
UC2852
UC3852

UDG-92003

PIN DESCRIPTIONS

COMP: COMP is the output of the error amplifier and the

input of the PWM comparator. To limit PWM on-time, this
pin is clamped to approximately 10V. To implement soft
start, the COM P pin can be pulled low and ramped up with
a PNP transistor, a capacitor, and a resistor.

GND: Ground for all functions is through this pin.
ISET: The dominant function is of this pin is to program

RAMP charging current. RAMP charging current is
approximately 5V divided by the external resistor placed
from ISET to ground. Resistors in the range of 10kΩ to

50kΩ are recommended, producing currents in the range
of 100µA to 50 0 µA.

A second function of ISET is as reference output. T he ISET
pin is normally regulated to 5V ±10%. It is critical that this
pin only see the loading of the RA MP programming res istor,
but a high input-impedanc e comparator or amplifier may be
connected to this p in or to a tap on t he RAMP programming
resistor if required.

The third function of the ISET pin is as a FAULT output . In
the event of an over-current fault, the ISET pin is forced to
approximately 9V by the f ault comparator. This can be used
to trip an external protection circuit which can disable the
load or start a fault restart cycle.

ISNS: This input to the zero and over curr ent com parator s
is specially built to allow operation over a ±5V dynamic
range. In noisy systems or systems with very high Q
inductors, it is desirable to filter the s ignal entering the ISNS
input to prevent premature restart or fault cycles. For best

accuracy, ISNS should be connected to a current sense
resistor through no more than 200 ohms.

OUT: The output of a high-current power driver capable of
driving the gate of a power MOSFET with peak currents
exceeding ±500mA. To prevent damage to the power
MOSFET, the OUT pin is internally driven by a 12V supply.
However, lead inductance between the OUT pin and the
load can cause overshoot and ringing. External current
boost transistors will increase this ov ershoot and ringing. If
there is any significant distance between the IC and the
MOSFET, external clamp diodes and/or series damping
resistors may be required. OUT is actively held low when
the VCC is below the UVLO threshold.

RAMP: A controlled on-time PWM requires a timer whose
time can be modulated by an external voltage. The timer
current is programmed by a resistor from ISET to GND. A
capacitor from RAMP to GND sets the on time in
conjunction with the voltage on COMP. Recommended
values for the timer capacitors are between 100pF and 1nF.

VCC: VCC is the logic and contr ol power connection for this
device. VCC current is the sum of active device supply
current and the average OUT current. Knowing the
maximum operating frequency and the MOSFET gate
charge (Qg), average OUT current can be estimated by:

I

OUT

= Q

× F

g

To prevent noise problems, bypass VCC to GND with both
a ceramic and an electrolytic capacitor.

VFB: VFB is the error amplifier inverting input. This input
serves as both the voltage sense input to the error amplifier

3

UDG-92006

UDG-92008

TYPICAL CHARACTERISTI CS

UC1852
UC2852
UC3852

Gain

(dB)

Phase

(deg)

Error Amplifier Gain and Phase

100

80

Phase

60

40

Gain

20

0

-20
10 100 1000 10000

Frequency, kHz

UDG-92005

Maximum

Frequency,

kHz

Max Frequency vs. Rset and Ct

1000

100

100pF
500pF

1nF
3nF

10

1 10 100

Rset, k

Ω

Maximum

On-Time

µ

s

Max On-Time vs. Rset and Ct

1000

100

10nF

3nF

10

1nF

300pF

100pF

1

1 10 100

Rset, k

Ω

UDG-92007

ns

OUT Rise and Fall Time

200

Fall Time

150

100

Rise Time

50

0

0510

Load Capacitance, nF

4

APPLICATIO N INFO RMATIO N: A 100 Watt Power Factor Preregulator

UC1852
UC2852
UC3852

UDG-92004

This circuit demonstrates a complete power factor preregulator based on the UC3852. This preregulator will supply
up to 100 watts at 400VDC and exhibit power factor greater than 0.995 with less than 10% total harmonic distortion.
Operating input range is 90V to 160V RMS at 50Hz to 60Hz.

This design is intentionally simple, yet fully funct ional. The UC3852 can also be used in designs featuring soft start,
over-voltage protection, wide power-line voltage operation, and fault latching. For more information on applying
the UC3852, refer to Unitrode Application Note U–132.

PARTS LIST

C1 0.47µF/250VAC X2 Class Polyester
C2 1nF/ 16V Cer amic
C3 68µF/35V Aluminum Electrolytic
C4 180pF/16V Ceramic
C5 0.1µF/16V Polyester or Ceramic
C6 82µF/450V Aluminu m Electrolyt ic
D1 2A/500V Bridge Rect ifier (Collmer

KBPC106 or Powertex MB11A02V60)
D2 100mA/5 0V Sw itchin g Diode (1N4148 )
D3 2A/50 0V 250n s Recovery -Tim e Rect if ie r

(Motorola MR856 )
IC1 UC3852N Power Factor Controller IC

Q1 IRF830 4.5A/500V 1. 5 Ω Power FET
L1 680µH (Renco RL3792 with

10 Turn 24 AWG Secondary)
R1 150kΩ,
R2 0.2Ω,
R3 10Ω,
R4 13.3kΩ,
R5 1MΩ,
R6 20kΩ,
R7 200kΩ,
R8 200kΩ,

1

⁄4W

1

⁄2W Carbon Composition

1

⁄4W

1

⁄4W

1

⁄4W

1

⁄4W

1

⁄2W

1

⁄2W

UNITRODE INTEGRATED CIRCUITS
7 CONTINENTAL BLVD. • MERRIMACK, NH 03054
TEL. [phone] • FAX [phone]

5

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