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Thread: I need a power supply for my LCD backlight..

  1. #1
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    Post I need a power supply for my LCD backlight..

    NOW!!!!
    I need the schmatics for a simple inverter that will power the backlight in my 40X4 LCD, and I need it within a week, and the parts have to be readily available..
    What voltage do they need, I asked this a while back, and couldn't seem to get an answer..
    HELP!!!!!

  2. #2
    Retired Admin Aaron Cake's Avatar
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    I believe they need around 150V or so....One thought I just had would be an old camera flash board. Remove the capacitor and you have a source of about 150V where the old capacitor was connected. These things usually run on 1.5V, but I have run them on 3V to roughly double the output current. A small linear regulator will work to provide the correct input voltage.

    Of course, I have never actually done this, so I don't know if it will work. But I don't see any reason why it wouldn't. Plus, these camera boards are available at any photo place that deals with disposable cameras pretty cheaply...ie. free.
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  3. #3
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    Originally posted by Aaron Cake:
    <STRONG>I believe they need around 150V or so....One thought I just had would be an old camera flash board. Remove the capacitor and you have a source of about 150V where the old capacitor was connected. These things usually run on 1.5V, but I have run them on 3V to roughly double the output current. A small linear regulator will work to provide the correct input voltage.

    Of course, I have never actually done this, so I don't know if it will work. But I don't see any reason why it wouldn't. Plus, these camera boards are available at any photo place that deals with disposable cameras pretty cheaply...ie. free.</STRONG>
    He He, your smart, but I am smarter, I aleady tried that, and with 1.5volts input, the screen isn't very bright at all, and with 3volts input, the screen can't light at all, I don't think the small transformer can supply enough current..

    but thanx anyway, that would probably be a good idea, and work well for smaller LCD screens.. D

  4. #4
    Retired Admin Aaron Cake's Avatar
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    Hmmm...Try removing the single rectifier diode they use and out a voltage doubler circuit in place of it. Then tap off of the output of that doubler.

    Another option would be to connect two of the little transformers in parallel. Double the output current. Or rig up two boards with two different voltage doubled output, and parallel them.

    If you have access to any dead notebook computers, just grap the LCD backlight inverter circuit from them. I'm looking at one right now, and it should easily produce enough current to fire up a small backlight. You may need a ballast resistor.
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  5. #5
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    Originally posted by Aaron Cake:
    <STRONG>Hmmm...Try removing the single rectifier diode they use and out a voltage doubler circuit in place of it. Then tap off of the output of that doubler.

    Another option would be to connect two of the little transformers in parallel. Double the output current. Or rig up two boards with two different voltage doubled output, and parallel them.

    If you have access to any dead notebook computers, just grap the LCD backlight inverter circuit from them. I'm looking at one right now, and it should easily produce enough current to fire up a small backlight. You may need a ballast resistor.</STRONG>

    I had an inverted board from a laptop, but that was before I had an LCD screen, and I blew the transformer in it trying to measure the voltage..

  6. #6
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    um, if you are running a 40x4 character lcd, then you need only 5 volts, if you have use more, or less, you may have fried it... since 40x4 lcds use LEDs to light them, unless they are EL, then you must get the polarity correct, if it is EL, you may need an inverter, but i doubt it, as many EL lcds run on aaa batterys, it would have to be a hell of an inverter

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