SP4403DS/05

SP4403 Electroluminescent Lamp Driver

© Copyright 2000 Sipex Corporation

4

DESCRIPTION

The SP4403 contains a DC-AC inverter that

can produce an AC output of 180V

a

+2.2V to +4.5V input voltage. An internal block

diagram of the SP4403 can be found in Figure 1.

The SP4403 is built on Sipex's dielectrically

isolated BiCMOS process that provides the

isolation required to separate the high voltage

AC signal used to drive the EL lamp from the

low voltage logic and signal processing circuitry.

This ensures latch-up free operation in the

interface between the low voltage CMOS

circuitry and the high voltage bipolar circuitry.

The SP4403 is ideal for applications driving

EL lamps to backlight LCD displays, key

panels, and other backlit readouts used in

battery operated portable equipment.

A total of only six external components are

required for the standard operation of the

SP4403: an inductor, a fast recovery diode,

three capacitors and a resistor. A diagram of the

SP4403 in a typical application can be found

in Figure 2.

Electroluminescent Technology

An EL lamp is basically a strip of plastic that is

coated with a phosphorous material which emits

light (fluoresces) when a high voltage (>40V)

which was first applied across it, is removed or

reversed. Long periods of DC voltages applied

to the material tend to breakdown the material

and reduce its lifetime. With these considerations

in mind, the ideal signal to drive an EL lamp is

a high voltage sine wave. Traditional approaches

to achieving this type of waveform included

discrete circuits incorporating a transformer,

transistors, and several resistors and capacitors.

Figure 1. Internal Diagram of the SP4403

FF7

Q

Q

L1

470

µH

EL Lamp

SCR1

SCR2

45

2

COIL

EL2

EL1

OSC

450k

Ω

ELEN

SP4403

C1

0.1

µF

D1

1N4148

6

3

7

1

optional device

1800pF

C2

10nF

*

*

*