www.fairchildsemi.com

REV. 1.0.6 11/7/03

Features

• Internally synchronized PFC and PWM in one IC

• Low total harmonic distortion

• Reduces ripple current in the storage capacitor between

the PFC and PWM sections

• Average current, continuous boost leading edge PFC

• Fast transconductance error amp for voltage loop

• High efficiency trailing edge PWM can be configured for

current mode or voltage mode operation

• Average line voltage compensation with brownout

control

• PFC overvoltage comparator eliminates output

“runaway” due to load removal

• Current fed gain modulator for improved noise immunity

• Overvoltage protection, UVLO, and soft start

General Description

The ML4824 is a controller for power factor corrected,

switched mode power supplies. Power Factor Correction

(PFC) allows the use of smaller, lower cost bulk capacitors,

reduces power line loading and stress on the switching FETs,

and results in a power supply that fully complies with

IEC1000-2-3 specification. The ML4824 includes circuits

for the implementation of a leading edge, average current,

“boost” type power factor correction and a trailing edge,

pulse width modulator (PWM).

switching frequency of the PWM allows the user to design

with smaller output components while maintaining the best

operating frequency for the PFC. An over-voltage compara-

tor shuts down the PFC section in the event of a sudden

decrease in load. The PFC section also includes peak current

limiting and input voltage brown-out protection. The PWM

section can be operated in current or voltage mode at up to

250kHz and includes a duty cycle limit to prevent trans-

former saturation.

Block Diagram

15

VEAO

IEAO

VFB

IAC

VRMS

ISENSE

RAMP 1

OSCILLATOR

OVP

PFC ILIMIT

UVLO

VREF

PULSE WIDTH MODULATOR

POWER FACTOR CORRECTOR

2.5V

+

–

–

+

16

2

4

3

7.5V

REFERENCE

14

VCC

13

VCCZ

VEA

7

+

–

IEA

1

+

–

+

–

PFC OUT

12

S

R

Q

Q

S

R

Q

Q

2.7V

–1V

RAMP 2

8

PWM OUT

11

S

R

Q

Q

VDC

6

SS

5

DC ILIMIT

9

VCC

DUTY CYCLE

LIMIT

–

+

1V

–

+

2.5V

VFB

–

+

8V

8V

VIN OK

GAIN

MODULATOR

VCCZ

x 2

(-2 VERSION ONLY)

3.5k

Ω

3.5k

Ω

1.25V

50

µA

–

+

13.5V

DC ILIMIT

ML4824

Power Factor Correction and PWM Controller

Combo