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Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
I'm just starting to learn PIC programming, and I bought a couple of 2x20 lcd displays (eBay) They are Hitachi LM032LN with Electroluminescent backlighting. The data sheet says 100Vrms, 16mArms at 400Hz which is 1.6 Watts! surely that can't be right?
Anyway, I've Googled for a while and can't find a circuit for an EL power supply/invertor, Can anyone tell me the type of invertor normally used (preferably with some hints/tips or a URL) Thanks
Registered Member #27
Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058
I have a sheet of backlighting material that is about 50 cm^2, the inverter uses 22 mA running from 3V. The datasheet for the sheet suggests 100V at 0,14mA/cm^2.
That is a power discrepancy by a factor of 10. Maybe the the 0.14mA/100V is some sort of maximum before it bursts into flames.
The output of the inverter is a distorted positive squarewave with a peak of 45V and a RMS of 18V at 565 Hz.
I don't know if this sheet is typical since it is the only one I can measure at the moment. It is not very bright so the numbers seems quite resonable.
Registered Member #239
Joined: Thu Feb 23 2006, 03:15AM
Location: canada
Posts: 23
That seems too high. I have a 2x24 panel and found a datasheet that quoted about 2.5mA rms at 100V and 400Hz.
I used the circuit below to test, and 2-5mA seemed right. After a certain point the brightness seemed to level off, so I didn't try any higher.
I replaced the 4 transistors with 3904/3906, and changed the RC to get 400Hz. Only problem is you need the right transformer..
But from what bjorn said, its probably better to make something like a boost regulator, and switch on and off the output to the EL panel. For some reason I thought it required a symmetric wave so I didn't try this approach.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
EL panels are basically capacitors with a slightly lossy dielectric that happens to convert the dielectric losses to light. So their power factor is probably very poor. If it was 0.1, that would explain the factor of 10 discrepancy mentioned by Bjørn.
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Electroluminescent drive for 2x20 lcd panel
