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  • 19v to 12v question

    I hope I don't get in trouble for double posting, but thought those in this forum might better understand electronics.

    It appears I have a constant 18.76v (~19v) going into the original broken lcd screen of my dell inspiron. All I need is a circuit that will convert ~19v to constant 12v, since I'm assuming my 8" lcd touchscreen uses similar or less power. I've looked at something like this:

    [media]http://www.elecfree.com/electronic/wp-content/uploads/2007/11/circuit_regulator_for_78xx.jpg[/media]

    It appears I wouldn't need the rectifier since I'm already in DC. I'd probably need a small heatsink on the 7812 (12v) regulator, and just a few capacitors to get this to work?

    Any thoughts? This seems to be simplier/easier than using a double pronged DC adapter for the screen and laptop separately. I get way to much buzzing using a friend's inverter.

    thanks,

  • #2
    That will work. Because it is a linear regulator, it is going to generate some heat so you definitely need a heat sink on it. Make sure the screen doesn't exceed the current draw of the regulator.
    Originally posted by ghettocruzer
    I was gung ho on building a PC [until] just recently. However, between my new phone having internet and GPS and all...and this kit...Im starting to have trouble justfiying it haha.
    Want to:
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    • #3
      thanks for the quick reply. I just did a boot up and down and its pretty stable at 18.86.

      I also messed around with the other wires in the lcd harness and found one of about 2v. When I put those two together the voltage difference is about 17v, which would produce a little less heat. (similar to the 7v mod on computer fans). I'm just not sure if this is good to do though.

      Upon further reading, it appears the 7812 only needs those capacitors if the power supply is an "appreciable distance from the power filter" (Cin) and "to improve transient response (C out). Do you think those are really needed in this case?

      thanks for the help! I appreciate it.

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      • #4
        You should still use a cap on the output of the 7812 regulator to stabilize the output.
        Kids, don't play with too many knives! -Crack Stuntman

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        • #5
          Originally posted by orangezero View Post
          I also messed around with the other wires in the lcd harness and found one of about 2v. When I put those two together the voltage difference is about 17v, which would produce a little less heat. (similar to the 7v mod on computer fans). I'm just not sure if this is good to do though.
          DO NOT DO THIS. If you have a ground connection elsewhere for your screen (eg, through the VGA or LVDS or whatever else video connection you have), then you have just shorted 2v to ground. And the ground is often used as a signal reference. If it is at 2v then all your signals appear 2v lower.

          It works for fans because those are the only two connections to the fan.

          Personally I wouldn't even be tapping the 19v line for regulating down to 12v unless you know for sure how much current it can provide. EVen if the power of the screens is comparable, the fact that you are throwing a bunch of power away as heat means that you'll need more amps at 12v.
          Old Systems retired due to new car
          New system at design/prototype stage on BeagleBoard.

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          • #6
            Well, I broke down and spent $10 on an adapter at radioshack instead. Probably saved me a lot of grief.

            I do appreciate the help!!!

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            • #7
              Sometimes it pays to buy the solution rather than roll your own! :-)
              Originally posted by ghettocruzer
              I was gung ho on building a PC [until] just recently. However, between my new phone having internet and GPS and all...and this kit...Im starting to have trouble justfiying it haha.
              Want to:
              -Find out about the new iBug iPad install?
              -Find out about carPC's in just 5 minutes? View the Car PC 101 video

              Comment

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