ML4830CP 데이터 시트보기 (PDF) - Micro Linear Corporation

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ML4830CP

Electronic Ballast Controller

Micro Linear Corporation 

Mode

VCO

VCO-O

PWM

Pin 8

GND

OPEN

VREF

Definition

Frequency Modulation

Overlapping VCO F.M.

Pulse Width Modulation

Table 1. ML4830 Operating Modes

OSCILLATOR

In Table 1 above, the two VCO frequency ranges are

controlled by the output of the LFB amplifier (Pin 6). As

lamp current decreases, Pin 6 rises in voltage, causing the

C(T) charging current to decrease, thereby causing the

oscillator frequency to decrease. Since the ballast output

network attenuates high frequencies, the power to the

lamp will be increased.

In PWM Mode, ICHG is 0 so the oscillator’s frequency is

set per (1) below.

VREF

18

R(T)

ICHG

VREF

CONTROL

R(T)/C(T)

9

+

1.25/3.75 –

C(T)

5 mA

CLOCK

tDIS

VTH

C(T)

tCHG

VTL

Figure 2. Oscillator Block Diagram and Timing

ML4830

Also, in both VCO modes, the when LFB OUT is high,

ICHG = 0 and the minimum frequency occurs. The

charging current varies according to two control inputs to

the oscillator:

1. The output of the preheat timer

2. The voltage at Pin 6 (lamp current output)

In preheat condition, charging current is fixed at

ICHG(PREHEAT )

=

2.5

R(SET)

(1)

In running mode, charging current decreases as the VPIN7

rises from 0V to VOH of trhe LAMP FB amplifier. The

highest frequency will be attained when ICHG is highest,

which is attained when VPIN6 is at 0V:

ICHG(0)

=

5

R(SET)

(2)

The oscillator frequency is determined by the following

equations:

FOSC

=

1

tCHG +

tDIS

(3)

and

tCHG

=

RTCT



In

6.25

3.75

+ ICHG

+ ICHG

RT

RT





(4)

The oscillator’s minimum frequency is set when ICHG = 0

where:

FOSC

≅

1

0.51× RTCT

(5)

This assumes that tCHG >> tDIS.

Highest lamp power, and lowest output frequency are

attained when VPIN6 is at its maximum output voltage

(VOH).

In this condition, the minimum operating frequency of the

ballast is set per (5) above.

For the IC to be used effectively in dimming ballasts with

higher Q output networks a larger CT value and lower RT

value can be used, to yield a smaller frequency excursion

over the control range (VPIN6). The discharge current is set

to 5mA. Assuming that IDIS >> IRT:

tDIS(VCO) ≅ 490 × CT

(6)

7

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