Need to provide regulated 5v for LL circuit on a car's 11-14v electrical system

Discussion in 'General Electronics Chat' started by elRey, Sep 14, 2009.

  1. elRey

    Thread Starter Active Member

    Feb 23, 2009
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    0
    I have a logic level circuit that I need to run of a car's electrical system that can vary from 11v to 14v. What's the simplest way to provide a regulated 5v source?

    Thanks,
    Rey
     
  2. Jony130

    AAC Fanatic!

    Feb 17, 2009
    3,957
    1,097
    Buy a LM7805 voltage regulator
     
  3. ke5nnt

    Active Member

    Mar 1, 2009
    384
    15
    Mouser is a good place to look for that part, only catch is shipping is flat rate by weight and you'll pay 24 cents for the part and then 8 bucks to have it delivered. If you can find one without outrageous shipping, that'd be better for you.

    CLICK HERE FOR LINK

    I should note that this regulator can support 1 amp current draw without the use of a heat sink, and peak current of 2.2 amps*.


    *These parameters, although guaranteed, are not 100% tested in production. (quoting the datasheet)
     
    Last edited: Sep 14, 2009
  4. bertus

    Administrator

    Apr 5, 2008
    15,645
    2,344
    Hello,

    What is the current needed by the logic circuit?
    What is your location?

    Greetings,
    Bertus
     
  5. elRey

    Thread Starter Active Member

    Feb 23, 2009
    65
    0
    I don't know the current draw. It's a pwm circuit with a 556 and a 339 that drive a LL MOSFET.

    I'm just north of Atlanta GA and I have a 7805 from Radioshack in hand. Do I hook it straight up or should a put caps between the pins? There's a Fry's local to me and a commerical/industrial electronics supply store a little further away (acksupply.com).
     
  6. bertus

    Administrator

    Apr 5, 2008
    15,645
    2,344
    Hello,

    There must be capacitors at the in and output of the 7805.
    This is to prevent the 7805 from oscillating.

    [​IMG]

    Greetings,
    Bertus
     
  7. Wendy

    Moderator

    Mar 24, 2008
    20,765
    2,535
    The caps are also at RS. Other than that, you're good to go with that part up to an amp, though you may need to heat sink it (if you go over 50ma). You'll know if this is the case, just don't burn yourself.
     
  8. elRey

    Thread Starter Active Member

    Feb 23, 2009
    65
    0
    The 7805 and caps worked. Thanks !
     
  9. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    Low dropout regulators are made for cars. They have reverse-polarity protection (sometimes a mechanic connects a new battery backwards) and high voltage input protection. I use the LM2931-5.0.
     
  10. Wendy

    Moderator

    Mar 24, 2008
    20,765
    2,535
    Why would you need low dropout for a 5V regulator connected to a 12V system? :confused: The polarity reversal feature I understand, though a diode also works.
     
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