12v - 5v Converter

Discussion in 'General Electronics Chat' started by liquid_0xygen, Jun 5, 2009.

  1. liquid_0xygen

    Thread Starter New Member

    Jun 5, 2009
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    Hi, I need some help. In a car, running ~14v while running, I need to knock this down to 5v for a few sending units for some gauges I'm adding. The sending units use the chassis ground, they only have 2 wires, input and output. I was wondering what I can do to get a good RELIABLE 5v to these?
     
  2. Wendy

    Moderator

    Mar 24, 2008
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    How much current? This subject comes up quite often.

    The most likely way is LM7805 linear regulators. They are cheap and easy to get. They have to have a 0.1µF cap on the input and ouput, but other than that they are good to go.
     
  3. radiohead

    Active Member

    May 28, 2009
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    Don't forget to heat sink the 7805 to dissipate the heat that will be generated.
     
  4. liquid_0xygen

    Thread Starter New Member

    Jun 5, 2009
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    0
    well they never really give any specifications for how much current they take...

    After doing a little research, I found at 160degrees it has .12v and .54kohms, and @-40degrees it has 4.91v and 115.23kohms... so the most it will ever see is about... ~0.002 and I need to so.. 0.004 amps roughly if my calcualtions are correct

    So the LM7805, to wire that in all I would have to do is add a 12v power and ground, then the other will be my 5v source? Sorry, brand new to this, never had to limit voltage before...
     
    Last edited: Jun 5, 2009
  5. Wendy

    Moderator

    Mar 24, 2008
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    The 780X series of regulators is an old established line. It has three leads, input, output and ground. It is an integrated circuit, so the apparant simplicity will fool ya. The currents you require it will not need a heatsink. It might get warm to the touch though.

    Datasheet
     
    Last edited: Jun 5, 2009
  6. radiohead

    Active Member

    May 28, 2009
    474
    31
    The ones I use from Fairchild can handle up to 1 ampere and can handle up to 36 VDC in to produce 5VDC out. If you put more than 12VDC, I would still recommend a heat sink, although the tab is a heat sink, it depends on how warm it gets.
     
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