www.fairchildsemi.com

REV. 1.0.5 9/25/01

Features

• Internally synchronized leading-edge PFC and trailing-

edge PWM in one IC

• TriFault Detect™ for UL1950 compliance and enhanced

safety

• Slew rate enhanced transconductance error amplifier for

ultra-fast PFC response

• Low power: 200µA startup current, 5.5mA operating

current

• Low total harmonic distortion, high PF

• Reduced ripple current in storage capacitor between PFC

and PWM sections

• Average current, continuous boost leading edge PFC

• PWM configurable for current-mode or voltage mode

operation

• Current fed gain modulator for improved noise immunity

• Overvoltage and brown-out protection, UVLO, and soft

start

General Description

The ML4800 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

IEC1000-3-2 specification. Intended as a BiCMOS version

of the industry-standard ML4824, the ML4800 includes

circuits for the implementation of leading edge, average

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

edge, pulse width modulator (PWM). It also includes a

TriFault Detect™ function to help ensure that no unsafe

conditions will result from single component failure in the

PFC. Gate-drivers with 1A capabilities minimize the need

for external driver circuits. Low power requirements improve

efficiency and reduce component costs.

An over-voltage comparator 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 brownout

protection. The PWM section can be operated in current or

voltage mode, at up to 250kHz, and includes an accurate

50% duty cycle limit to prevent transformer saturation.

Block Diagram

15

VEAO

IEAO

VFB

IAC

VRMS

ISENSE

RAMP 1

OSCILLATOR

OVP

PFC ILIMIT

UVLO

VREF

PULSE WIDTH MODULATOR

POWER FACTOR CORRECTOR

TRI-FAULT

2.5V

+

-

-

+

16

2

4

3

7.5V

REFERENCE

14

VCC

13

VCC

VEA

7

-

+

IEA

1

+

-

+

-

+

-

PFC OUT

12

S

R

Q

Q

S

R

Q

Q

2.75V

0.5V

-1V

RAMP 2

8

PWM OUT

11

S

R

Q

Q

VDC

6

SS

5

DC ILIMIT

9

VCC

DUTY CYCLE

LIMIT

-

+

1.0V

-

+

2.45V

VFB

-

+

VREF

VIN OK

GAIN

MODULATOR

VCC

1.6k

Ω

1.6k

Ω

1.25V

25

µA

-

+

DC ILIMIT

17V

ML4800

Power Factor Correction and PWM Controller

Combo