SP4426 Datasheet, PDF (5/11 Pages) Sipex Corporation – Electroluminescent Lamp Driver with High Output Drivers

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).
SP4426DS/01
SP4426 Electroluminescent Lamp Driver
5
© Copyright 1997 Sipex Corporation