ML4813CP 데이터 시트보기 (PDF) - Micro Linear Corporation

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ML4813CP

Flyback Power Factor Controller

Micro Linear Corporation 

April 1997

ML4813*

Flyback Power Factor Controller

GENERAL DESCRIPTION

The ML4813 is a PWM controller designed for use in a

discontinuous "flyback" or "buck-boost" type power factor

correction (PFC) system for low power, low cost

applications.

The circuit includes a precision reference, oscillator, error

amplifier, over-voltage comparator, over-current

comparator, and an extra op-amp as well as a high

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

under-voltage lockout circuit.

In a typical application, the ML4813 functions as a

voltage mode regulator. By maintaining a constant duty

cycle, the current follows the input voltage, making the

impedance of the entire circuit appear purely resistive.

With the flyback circuit, power factors of 0.99 are easily

achievable with a small output inductor and a minimum

of external components.

FEATURES

s Precision buffered 5V reference

s Extra op-amp for output voltage instrumentation

amplifier

s Overcurrent comparator for switch protection

s Soft start and under-voltage lockout for easy low surge

off-line starting

s 1A peak current Totem-pole output drive

s Overvoltage comparator eliminates output "runaway"

due to load removal

s Large oscillator amplitude for better noise immunity

* This Part Is End Of Life As Of August 1, 2000

BLOCK DIAGRAM

VFB

4

ERROR

AMPLIFIER

-

5V +

SOFT START

2

ILIMIT

1

1V

CURRENT LIMIT

COMPARATOR

+

-

OVP

5

5.6V

OVP

COMPARATOR

+

-

COMP

3

CT

16

RT

9

SYNC

10

-

+

PWM

COMPARATOR

OSCILLATOR

7V

60µA

UNDERVOLTAGE

LOCKOUT

SQ

RQ

OA OUT

6

OA+

8

7

OA-

VREF

14

VCC

13

32V

OUT

12

PWR GND

11

GND

15

1

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