ML4836
FUNCTIONAL DESCRIPTION (Continued)
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).
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:
1
1
fZ
fP
(2)
2 R1C1
2 R1C2
Figure 3 shows the output configuration for the operational
transconductance amplifiers.
TRANSCONDUCTANCE AMPLIFIERS
The Lamp voltage feedback amplifier is implemented as
an operational transconductance amplifier. It is designed
A DC path to ground or V at the output of the
CC
transconductance amplifiers will introduce an offset error.
PREHEAT
f
1
SET TIME VALUES
HIGH Q
FOR PREHEAT,
START AND OPERATION,
AND RESTART
ML4836
LOW Q
f
f
3
2
START
OPERATION
Figure 2. Three Frequency Design Model
CURRENT
MIRROR
IN
OUT
gmV
2
IN
IQ +
io = gmV
IN
gmV
2
IN
IQ –
IN
OUT
CURRENT
MIRROR
Figure 3. Output Configuration
6
MICRO-LINEAR [ MICRO LINEAR CORPORATION ]
