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SP4426 Datasheet(PDF) 5 Page - Sipex Corporation |
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SP4426 Datasheet(HTML) 5 Page - Sipex Corporation |
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5 / 11 page 
SP4426DS/01 SP4426 Electroluminescent Lamp Driver © Copyright 1997 Sipex Corporation 5 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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