June 1997

ML4826

*

PFC and Dual Output PWM Controller Combo

1

GENERAL DESCRIPTION

The ML4826 is a high power controller for power factor

corrected, switched mode power supplies. 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

specifications. The ML4826 includes circuits for the

implementation of a leading edge, average current “boost”

type power factor correction and a trailing edge, pulse

width modulator (PWM) with dual totem-pole outputs.

The device is available in two versions; the ML4826-1

Doubling the switching frequency of the PWM allows the

user to design with smaller output components while

maintaining the optimum operating frequency for the PFC.

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

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 transformer saturation.

FEATURES

s

Internally synchronized PFC and PWM in one IC

s

Low total harmonic distortion

s

Reduced ripple current in the storage capacitor

between the PFC and PWM sections

s

Average current, continuous boost, leading edge PFC

s

High efficiency trailing edge PWM with dual

totem-pole outputs

s

Average line voltage compensation with brown-out

control

s

PFC overvoltage comparator eliminates output

“runaway” due to load removal

s

Current-fed multiplier for improved noise immunity

s

Overvoltage protection, UVLO, and soft start

BLOCK DIAGRAM

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

VCC2

19

VEAO

IEAO

VFB

IAC

VRMS

ISENSE

RTCT

OSCILLATOR

OVP

PFC ILIMIT

UVLO

VREF

PULSE WIDTH MODULATOR

POWER FACTOR CORRECTOR

2.5V

+

-

-

+

20

2

4

3

7.5V

REFERENCE

18

VCC

17

VCCZ

VEA

7

-

+

IEA

1

+

-

+

-

PFC OUT

15

S

R

Q

Q

S

R

Q

Q

2.7V

-1V

RAMP 2

9

PWM 1

13

S

R

Q

Q

VDC

6

SS

5

DC ILIMIT

10

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

1.5V

50µA

-

+

13.5V

DC ILIMIT

RAMP 1

8

PWM 2

14

S

T

Q

Q

VCC2

PGND

16

PGND

12

AGND

11

8V