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ML4812
Power Factor Controller
Features
Precision buffered 5V reference ( 0.5%) Current-input gain modulator reduces external components and improves noise immunity Programmable ramp compensation circuit 1A peak current totem-pole output drive Overvoltage comparator helps prevent output voltage "runaway" Wide common mode range in current sense comparators for better noise immunity Large oscillator amplitude for better noise immunity

Description
The ML4812 is designed to optimally facilitate a peak current control boost type power factor correction system. Special care has been taken in the design of the ML4812 to increase system noise immunity. The circuit includes a precision reference, gain modulator, error amplifier, overvoltage protection, ramp compensation, as well as a high current output. In addition, start-up is simplified by an undervoltage lockout circuit with 6V hysteresis. In a typical application, the ML4812 functions as a current mode regulator. The current which is necessary to terminate the cycle is a product of the sinusoidal line voltage times the output of the error amplifier which is regulating the output DC voltage. Ramp compensation is programmable with an external resistor, to provide stable operation when the duty cycle exceeds 50%.

Block Diagram (Pin Configuration Shown is for DIP Version)
OVP
5

SHDN S

5V
1

Q

10

ISENSE 5V GM OUT EA OUT

VCC OUT
12

R

Q PWR GND

2 3

11

EA
4

ERROR AMP

UNDER VOLTAGE LOCKOUT IEA

VREF
14

VCC
13

5V

32V

6

ISINE

GAIN MODULATOR

GND
15

RAMP COMP
7 16

5V

CT CLOCK
9

8

RT

1k OSC

REV. 1.0.4 5/31/01

ML4812 Datasheet Fairchild Download PDF

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ML4812 DATASHEET