May 1999

PRELIMINARY

ML4804

Power Factor Correction and PWM Controller Combo

1

GENERAL DESCRIPTION

The ML4804 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 enhancement of the industry-standard ML4824,

the ML4804 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. 1A gate-drive

outputs 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.

FEATURES

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Internally synchronized leading-edge modulated PFC

and trailing-edge modulated PWM in one IC

s

enhanced safety

s

s

Slew rate enhanced transconductance error amplifier

for ultra-fast PFC response

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Low power: 200µA startup current, 5.5mA operating

current

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Low total harmonic distortion, high PF

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Reduces ripple current in the storage capacitor

between the PFC and PWM sections

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Average current, continuous boost leading edge PFC

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PWM configurable for current-mode or voltage mode

operation

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Overvoltage and brown-out protection, UVLO, and soft

start

BLOCK DIAGRAM

15

VEAO

IEAO

VFB

IAC

VRMS

ISENSE

RAMP 1

OSCILLATOR

OVP

VCCOVP

TRI-FAULT

PFC ILIMIT

UVLO

VREF

PULSE WIDTH MODULATOR

POWER FACTOR CORRECTOR

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

VCC

-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

25µA

-

+

DC ILIMIT

+

–

16.4V

0.5V

+

–

+

-

-

+

17V