ML4830CP MICRO-LINEAR [Micro Linear Corporation], ML4830CP Datasheet - Page 7

• Manufacturer Part Number: ML4830CP
• Description: Electronic Ballast Controller
• Manufacturer: MICRO-LINEAR [Micro Linear Corporation]

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, I
set per (1) below.
VCO
VCO-O
PWM
Mode
V
V
CLOCK
TH
C(T)
TL
Figure 2. Oscillator Block Diagram and Timing
C(T)
R(T)
Table 1. ML4830 Operating Modes
Pin 8
GND
OPEN
VREF
18
9
t
V
CHG
R(T)/C(T)
DIS
REF
5 mA
is 0 so the oscillator’s frequency is
Definition
Frequency Modulation
Overlapping VCO F.M.
Pulse Width Modulation
I
CHG
1.25/3.75
t
CHG
+
–
CONTROL
V
REF
Also, in both VCO modes, the when LFB OUT is high,
I
charging current varies according to two control inputs to
the oscillator:
In preheat condition, charging current is fixed at
In running mode, charging current decreases as the V
rises from 0V to V
highest frequency will be attained when I
which is attained when V
The oscillator frequency is determined by the following
equations:
and
The oscillator’s minimum frequency is set when I
where:
This assumes that t
Highest lamp power, and lowest output frequency are
attained when V
(V
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 C
value can be used, to yield a smaller frequency excursion
over the control range (V
to 5mA. Assuming that I
CHG
OH
1. The output of the preheat timer
2. The voltage at Pin 6 (lamp current output)
).
= 0 and the minimum frequency occurs. The
t
CHG
PIN6
I
OH
CHG PREHEAT
CHG
t
F
F
DIS VCO
R C In
OSC
OSC
is at its maximum output voltage
I
of trhe LAMP FB amplifier. The
CHG( )
T T
(
(
>> t
DIS
PIN6
PIN6
0
0 51
t
>> I
)
DIS
CHG
.
). The discharge current is set
6 25
3 75
is at 0V:
.
490
R SET
)
.
.
RT
(
1
1
R C
5
:
R SET
t
T T
DIS
(
2 5
T
)
I
I
C
CHG
CHG
.
value and lower R
T
)
CHG
R
R
T
T
ML4830
is highest,
CHG
PIN7
= 0
(1)
(2)
(3)
(4)
(5)
(6)
T
7