May 1997

ML4819

*

Power Factor and PWM Controller “Combo”

1

GENERAL DESCRIPTION

The ML4819 is a complete boost mode Power factor

Controller (PFC) which also contains a PWM controller.

The PFC circuit is similar to the ML4812 while the PWM

controller can be used for current or voltage mode control

for a second stage converter. Since the PWM and PFC

circuits share the same oscillator, synchronization of the

two stages is inherent. The outputs of the controller IC

provide high current (>1A peak) and high slew rate to

quickly charge and discharge MOSFET gates. Special care

has been taken in the design of the ML4819 to increase

system noise immunity.

The PFC section is of the peak current sensing boost type,

using a current sense transformer or current sensing

MOSFETs to non-dissipatively sense switch current. This

gives the system overall efficiency over average current

sensing control method.

The PWM section includes cycle by cycle current limiting,

* Some Packages Are Obsolete

precise duty cycle limiting for single ended converters,

and slope compensation.

BLOCK DIAGRAM

+

–

INV A

OVP

EA OUT A

–

–

RAMP COMP

ERROR

AMP

+

5V

OSC

SLOPE

COMPENSATION

UNDER

VOLTAGE

LOCKOUT

S

R

Q

S

R

Q

DUTY CYCLE

PWM B

OUT B

PGND B

PGND A

GND

OUT A

GM OUT

5V

5V

0.7V

1V

10

20

12

7

11

9

8

14

18

17

16

15

13

1

3

2

5

4

6

19

GAIN MODULATOR

PWM

CONTROLLER

POWER FACTOR

CONTROLLER

+

–

FEATURES

s

Two 1A peak current totem-pole output drivers

s

Precision buffered 5V reference (±1%)

s

Large oscillator amplitude for better noise immunity

s

Precision duty cycle limit for PWM section

s

Current input gain modulator improves noise immunity

s

Programmable Ramp Compensation circuit

s

Over-Voltage comparator helps prevent output

“runaway”

s

Wide common mode range in current sense

compensators for better noise immunity

s

Under-Voltage Lockout circuit with 6V hysteresis

Please

See Ml48

24 for New

Designs