ml4836 Microsemi Corporation, ml4836 Datasheet - Page 6

• Manufacturer Part Number: ml4836
• Description: Compact Fluorescent Electronic Dimming Ballast Controller
• Manufacturer: Microsemi Corporation

ML4836
FUNCTIONAL DESCRIPTION
6
The ML4836 implements a triple frequency operation
scheme: programmable three-frequency sequence for pre-
heat, ignition, and dimming, that extends lamp life,
simplifies lamp network design, and starts lamps at any
dimming level without flashing. This addresses the need
for a high-Q network for starting sequence and low-Q
network for operation, minimizing parasitic losses and
improving overall power efficiency. The values for the
pre-heat, start, operation, and restart can be programmed
or selected (Figure 2).
TRANSCONDUCTANCE AMPLIFIERS
The Lamp voltage feedback amplifier is implemented as
an operational transconductance amplifier. It is designed
START AND OPERATION,
SET TIME VALUES
FOR PREHEAT,
AND RESTART
IQ –
gmV
Figure 2. Three Frequency Design Model
2
(Continued)
IN
Figure 3. Output Configuration
IQ +
gmV
2
IN
ML4836
IN
IN
CURRENT
CURRENT
MIRROR
MIRROR
to have low small signal forward transconductance such
that a large value of load resistor (R1) and a low value
ceramic capacitor (<1µF) can be used for AC coupling
(C1) in the frequency compensation network. The
compensation network shown in Figure 5 will introduce a
zero and a pole at:
Figure 3 shows the output configuration for the operational
transconductance amplifiers.
A DC path to ground or V
transconductance amplifiers will introduce an offset error.
OUT
OUT
HIGH Q
f
START
Z
=
f 2
2
p
R C
PREHEAT
1
1 1
f 1
LOW Q
io = gmV
OPERATION
f 3
IN
f
P
=
CC
2
p
at the output of the
R C
1
1 2
(2)