SP4415DS/06

SP4415 Electroluminescent Lamp Driver

© Copyright 1996 Sipex Corporation

5

The H-bridge consists of two SCR structures that

act as high voltage switches. These two switches

control the polarity of how the lamp is charged. The

SCR switches are controlled by the f

which is the oscillator frequency divided by 128.

For a 32,768 Hz oscillator, f

When the energy from the coil is released, a high

voltage spike is created triggering the SCR switches.

The direction of current flow is determined by

which SCR is enabled. One full cycle of the

H-bridge will create 16 voltage steps from ground

to 80V (typical) on pins 6 and 7 which are 180

degrees out of phase with each other (see figure 3

on page 7). A differential view of the outputs is

shown in figure 4 on page 7.

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. This approach is large and

bulky, and cannot be implemented in most hand

held equipment. Sipex now offers low power single

chip driver circuits specifically designed to drive

small to medium sized electroluminescent panels.

All that is required is one external inductor.

Electroluminescent backlighting is ideal when used

with LCD displays, keypads, or other backlit

readouts. Its main use is to illuminate displays in

dim to dark conditions for momentary periods of

time. EL lamps typically consume less current than

LEDs or incandescent bulbs making them ideal for

battery powered products. Also, EL lamps are able

to evenly light an area without creating "hot spots"

in the display.

The amount of light emitted is a function of the

voltage applied to the lamp, the frequency at which

it is applied, the lamp material used and its size, and

lastly, the inductor used. There are many variables

which can be optimized for specific applications.