SP4426 datasheet(5/11 Pages) SIPEX

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SP4426DS/01

SP4426 Electroluminescent Lamp Driver

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 a voltage step

from ground to 80V (typ) on pins 5 and 6 which

are 180 degrees out of phase with each other (see

figure 3 page 8). A differential view of the outputs

is shown in figure 4 on page 8. If Line Noise is of

concern it is advisable to add a decoupling cap

at Vdd.

Electroluminescent Technology

What is electroluminescence?

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 if all that is required is

one external inductor fast recovery diode and two

capacitors.

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 than LEDs

or 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. Sipex supplies characterization charts

to aid the designer in selecting the optimum circuit

configuration (see page 6 and 7).

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