doyle@sjs.sj.ate.slb.com (Matt Doyle, 408-437-5284) (11/09/88)
Extracted-News: sjs sci.electronics:716 In article <1176@microsoft.UUCP> gordonl@microsoft.UUCP (Gordon Letwin) writes: >I have an LCD which is backlit by an electroluminescent panel. These >things take a few milliamps of AC in the 60 to 80 V range, 60 hz to >400 hz, typically. > >This is part of a battery backed up system. I can brute force design >a 12V DC to 70 VAC convertor, but it's crude and complex: an oscillator >driving a voltage doubler chain followed by 2 complementary pairs to >couple the panel's leads to the + and - DC, alternately, producing >AC square wave. > >A small transformer would be better, and would guarantee true AC, but >I'm having troubles locating an appropriate one. Yes and NO, A small transformer will enable you to build a simpler more reliable circuit but it will give you less light output. An EL device is nothing more than a light emitting capacitor. The two factors determining the intensity of the light output are dV/dT and F. A square wave gives you the maximum dV/dT. I did some consulting work at a company manufacturing EL displays, and one of my tasks was to build a hand-held demo box. Being battery operated I had to play some games to extend the battery life beyond 5 min. I drove the panel with a small pot-core x-former, pulsing it to about 200v then letting it ring down to about 80v [if you think it out and get your phasing right you create a very nice tank circuit between the seconary of the x-former and the EL panel]. As for the transformer I couldn't find one off the shelf any where so I had to make my own. I found that the best one was a pot-core made out of 3C8 with somthing like 10 turns ct of 28ag in the center followed by 200-250 turns of 32ag on the outside. As for driving the primary I used one of those nifty all-in-one PWM chips ( IP3526 ?) it allows you to set the pulse width, frequency, and has extra op amps so you can monitor the core for saturation. > >I've heard that there are small power supplies designed to drive these >devices - DC to AC convertors of appropriate voltage and current. Does >anyone have any pointers on these devices and where they might be obtained? > > thanks > > gordon letwin > microsoft ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Experiments should be reproducible - They should fail in the same way. DISCLAIMER: These are MY opinions and not necessarily those of my employer. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~