1

April 1998

ML4812

*

Power Factor Controller

GENERAL 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, over-

voltage protection, ramp compensation, as well as a high

current output. In addition, start-up is simplified by an

under-voltage 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%.

FEATURES

s

Precision buffered 5V reference (±0.5%)

s

Current-input gain modulator reduces external

components and improves noise immunity

s

Programmable ramp compensation circuit

s

1A peak current totem-pole output drive

s

Overvoltage comparator helps prevent output

voltage “runaway”

s

Wide common mode range in current sense

comparators for better noise immunity

s

Large oscillator amplitude for better noise immunity

5V

OVP

ISENSE

GM OUT

EA OUT

ISINE

RAMP COMP

CT

RT

ERROR

AMP

IEA

OSC

1k

Ω

UNDER

VOLTAGE

LOCKOUT

SHDN

OUT

PWR GND

VREF

VCC

GND

CLOCK

VCC

EA–

32V

5

1

2

10

12

11

14

13

15

9

3

4

6

7

16

8

+

–

5V

+

–

5V

+

–

–

5V

S

R

Q

Q

GAIN MODULATOR

* Some Packages Are End Of Life