ML4832

6

FUNCTIONAL DESCRIPTION

OVERVIEW

The ML4832 consists of an average current controlled

continuous boost power factor front end section with a

flexible ballast control section. Start-up and lamp-out retry

timing are controlled by the selection of external timing

components, allowing for control of a wide variety of

different lamp types. The ballast section controls the lamp

power using frequency modulation (FM) with additional

programmability provided to adjust the VCO frequency

range. This allows for the IC to be used with a variety of

different output networks.

POWER FACTOR SECTION

The ML4832 power factor section is an average current

sensing boost mode PFC control circuit which is

architecturally similar to that found in the ML4821. For

detailed information on this control architecture, please

refer to Application Note 16 and the ML4821 data sheet.

Figure 1. ML4832 Block Diagram

GAIN MODULATOR

The ML4832 gain modulator provides high immunity to

the disturbances caused by high power switching. The

rectified line input sine wave is converted to a current via

a series resistor. In this way, small amounts of ground noise

produce an insignificant effect on the reference to the

PWM comparator.

The output of the gain modulator appears on the positive

terminal of the IA amplifier to form the reference for the

current error amplifier. Please refer to Figure 1.

V

I

mA

MUL

SINE

VEA

V

=

×−07

34

.

.

16

(1)

VEA is the output of the error amplifier (Pin 1).

The output of the gain modulator is limited to 1.0V.

7

GND

IA OUT

IA +

EA OUT

EA –/OVP

10

16

17

11

2

4

3

1

18

OUT B

13

+

–

+

–

+

–

–

+

–

+

2.5V

2.5V

–1V

PREHEAT

TIMER

VARIABLE

FREQUENCY

OSC

UNDER-VOLTAGE

AND THERMAL

SHUTDOWN

–

+

S

R

Q

T

Q

Q

P GND

12

OUT A

14

PFC OUT

15

8

INTERRUPT

9

LFB OUT

6

LAMP FB

5

–

+

2.75V

7k

PWM (PFC)

OVP

7k

GAIN

MODULATORS