ELECTROLUMINESCENT_PANEL_DRIVER

Published:2009/7/13 20:27:00 Author:May | From:SeekIC

Driving electroluminescent (EL) panels, such as those used for backlighting LCD screens in portable devices,is a challenge because they are capacitive loads and require high-voltage ac drive signals. Typically, EL panels exhibit about 3 nF/in2 capacitance. The LT1305 circuit shown can drive an EL panel with up to 100 nF total capacitance. The LT1305 micro power dc-to-dc converter contains an internal power switch capable of up to 2 A switch current. The high-power switch drives the primary of fly back transformer T1. A minimum input voltage of 1.8 V ensures operation with two-cell supplies. The input voltage is boosted to a voltage that ranges from 166 to 248 Vdc, as set by R1. The ac drive waveform is created by an external square-wave control signal turning on and off the NPN transistor, bringing point A to ground and inverting the voltage across the panel and then returning to a high positive voltage. By adjusting R1, the panel ac drive voltage can be set from 83 to 115 Vrms to alter the display brightness. The color or hue of the display can also be slightly varied by changing the frequency of the square-wave drive signal. This control signal can be from a system microprocessor output pin.



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