February 1999

PRELIMINARY

ML4803

8-Pin PFC and PWM Controller Combo

1

BLOCK DIAGRAM

GENERAL DESCRIPTION

The ML4803 is a space-saving controller for power factor

corrected, switched mode power supplies that offers very

low start-up and operating currents.

Power Factor Correction (PFC) offers the use of smaller,

lower cost bulk capacitors, reduces power line loading

and stress on the switching FETs, and results in a power

supply fully compliant to IEC1000-3-2 specifications. The

ML4803 includes circuits for the implementation of a

leading edge, average current “boost” type PFC and a

trailing edge, PWM.

The ML4803-1’s PFC and PWM operate at the same

frequency, 67kHz. The PFC frequency of the ML4803-2 is

automatically set at half that of the 134kHz PWM. This

higher frequency allows the user to design with smaller

PWM components while maintaining the optimum

operating frequency for the PFC. An overvoltage

comparator shuts down the PFC section in the event of a

sudden decrease in load. The PFC section also includes

peak current limiting for enhanced system reliability.

FEATURES

s

Internally synchronized PFC and PWM in one 8-pin IC

s

Patented one-pin voltage error amplifier with advanced

input current shaping technique

s

Peak or average current, continuous boost, leading

edge PFC (Input Current Shaping Technology)

s

High efficiency trailing-edge current mode PWM

s

Low supply currents; start-up: 150µA typ., operating:

2mA typ.

s

Synchronized leading and trailing edge modulation

s

Reduces ripple current in the storage capacitor

between the PFC and PWM sections

s

Overvoltage, UVLO, and brownout protection

s

ISENSE

3

VEAO

4

VDC

5

ILIMIT

6

GND

2

PWM OUT

8

PFC OUT

1

–

+

–

+

COMP

COMP

35µA

16.2V

17.5V

VCC

+

–

COMP

+

–

–1V

SOFT START

PFC/PWM UVLO

DUTY CYCLE

LIMIT

OSCILLATOR

PFC – 67kHz

PWM – 134kHz

VREF

VREF

1.2V

26k

40k

M1

R1

C1

30pF

M2

M7

M3

M4

M6

PWM

CONTROL

LOGIC

–

+

1.5V

DC ILIMIT

PFC ILIMIT

PWM COMPARATOR

VCC OVP

PFC OFF

ONE PIN ERROR AMPLIFIER

LEADING

EDGE PFC

TRAILING

EDGE PWM

+

–

COMP

7V

+

–

COMP

–1

–4

REF

VCC

7

PFC

CONTROL

LOGIC