ML4836

6

Figure 2. Three Frequency Design Model

Figure 3. Output Configuration

START

HIGH Q

LOW Q

OPERATION

PREHEAT

f3

f2

f1

ML4836

SET TIME VALUES

FOR PREHEAT,

START AND OPERATION,

AND RESTART

CURRENT

MIRROR

IN

OUT

CURRENT

MIRROR

IN

OUT

IQ +

2

IQ –

2

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

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:

f

RC

f

RC

ZP

==

1

2

1

2

11

1 2

pp

(2)

Figure 3 shows the output configuration for the operational

transconductance amplifiers.

transconductance amplifiers will introduce an offset error.