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Thread: Power directly from pc to LCD

  1. #1
    Newbie
    Join Date
    Aug 2000
    Location
    London
    Posts
    4

    Question Power directly from pc to LCD

    I want to wire up my LCD to take power from one of the 5V wires inside my PC. I read that the current is about 30 amps but the lcd says it takes about 2 tops. I want to reduce this down LOADS. I seem to remember something about running stuff in parallel to reduce the current in my physics lessons but can someone help me here. Has anyone done this before or is the general thing to use batteries?

  2. #2
    Newbie
    Join Date
    Aug 2000
    Location
    Olympia, WA USA
    Posts
    18

    Lightbulb

    Okay, people correct me if I'm wrong on this one... If I remember from reading on ohm's law, etc. that a device will only draw as much current as it needs. It this case, if the LCD presents a load to the PSU that demands 2 amp, that's all it will get. Voltage doesn't follow the same rules, however. A device will take as many volts as you throw at it, which is why it is so important to have a PSU powerful enough to handle it. If the voltage drops, amperage increases, possibly overloading circuit traces on the PCB and causing it to burn out.
    Think of it this way... the battery in your car is capable of spikes of 500 amps or more. Think of what you would destroy if a circuit would pull all the current it could get. Since current draw is a function of resistance, the more resistant a load is, the less current it draws. The starter in your car has such low resistance, it will demand that full 500 amps. The bottom line: you don't need to do anything special as long as the voltage requirements are met. Does this make sense?
    Keep thinking! =)

  3. #3
    Constant Bitrate
    Join Date
    Jun 2000
    Location
    landing, NJ, USA
    Posts
    134

    Post

    what ever typhoon say is 100% correct. you win the prize of $1000000 if i have it.
    anyway, i just wanna add one more thing into this.
    bpc1, you can add an series resister to the power line (5v) that go to your lcd. this resister will bring down the current also add a capacitor like 22uf in parallel to the resistor so it will trim down noise in your line
    <pre>
    ---->pwr(5v)-----(resistor)-----------(lcd)
    |
    |
    (capacitor)
    |
    |
    (GND)
    </pre>

  4. #4
    Constant Bitrate
    Join Date
    Jul 2000
    Location
    Israel
    Posts
    134

    Post

    Do you want to power LCD itself or it backlite?If it only LCD, it's ok, but you can't do it for backlite,cause it will try to take about 1/4 or 1/2 A ,depends on LCD type.
    Enjoint life!

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