SP4425 Datasheet, PDF (6/14 Pages) Sipex Corporation – Electroluminescent Lamp Driver Low Voltage Applications

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. Both voltage and
frequency are directly related to light output. In
other words as the voltage or the frequency of the
EL output is increased the light output will also
increase. The voltage has a much larger impact on
light output than the frequency does. For example,
an output signal of 168V_PP with a frequency of
500Hz can yield 15Cd/m², in the same application
a different EL driver could produce 170V with a
PP
frequency of 450Hz and can also yield 15Cd/m².
Variations in peak to peak voltage and variations
in lamp frequency are to be expected, light output
will also vary from device to device however
typical light output variations are usually not
visually noticeable.
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 7 and 8).
SP4425DS/20
SP4425 Electroluminescent Lamp Driver
6
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