July 2000

PRELIMINARY

Electronic Dimming Ballast Controller

GENERAL DESCRIPTION

The ML4832 is a complete solution for a dimmable/non-

dimmable, high power factor, high efficiency electronic

ballast. The BiCMOS ML4832 contains controllers for

“boost” type power factor correction as well as for a

dimming ballast.

The power factor circuit uses the average current sensing

method with a gain modulator and overvoltage protection.

This system produces a power factor of better than 0.99

with low input current THD at > 95% efficiency. Special

care has been taken in the design of the ML4832 to

increase system noise immunity by using a high amplitude

oscillator, and a current-fed multiplier. An overvoltage

protection comparator inhibits the PFC section in the

event of a lamp out or lamp failure condition.

The ballast section provides for programmable starting

scenarios with programmable preheat and lamp out-of-

socket interrupt times. The IC controls lamp output through

frequency modulation using lamp current feedback.

FEATURES

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Complete power factor correction and dimming

ballast control in one IC

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Low distortion, high efficiency continuous boost,

average current sensing PFC section

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Programmable start scenario for rapid or instant

start lamps

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Lamp current feedback for dimming control

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Variable frequency dimming and starting

s

Programmable restart for lamp out condition to

reduce ballast heating

s

Over-temperature shutdown replaces external

heat sensor for safety

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PFC overvoltage comparator eliminates output

“runaway” due to load removal

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Large oscillator amplitude and gain modulator

improves noise immunity

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Low start-up current <0.5mA

1

BLOCK DIAGRAM

7

VARIABLE FREQUENCY

OSCILLATOR

8

10

PRE-HEAT

AND INTERRUPT

TIMERS

CONTROL

&

GATING LOGIC

2

IA OUT

4

IA+

POWER

FACTOR

CONTROLLER

UNDER-VOLTAGE

AND THERMAL

SHUTDOWN

OUTPUT

DRIVERS

3

1

EA OUT

18

EA–/OVP

17

PFC OUT

15

GND

11

16

PGND

12

OUT B

13

OUT A

14

LFB OUT

6

LAMP FB

5

INTERRUPT

9

(* Indicates part is End Of Life as of July 1, 2000)