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12vdc to 1.5vdc for car

Discussion in 'Electronic Basics' started by Bach Mai, Dec 28, 2003.

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  1. Bach Mai

    Bach Mai Guest

    I am trying to set up a circuit for a clok in my car that will take
    the 12v from the battery and output 1.5v to a clock, I need the
    circuit to fit inside a gauge pod that is 3 inchs in diameter and
    about 2 deep, thanks for any help
     
  2. Norm

    Norm Guest

    So you need 12VDC to 1.5VDC C.
    Why don't you use a 1.5v Battery?
     
  3. You need to measure the current the clock draws from a 1.5 volt source
    (like a dry cell). The regulator may be as simple as a dropping
    resistor and a red LED as a voltage clamp and perhaps, a capacitor,
    across the clock terminals.
     
  4. Michael

    Michael Guest

    The first thing that comes to mind would be a variable voltage regulator.
    My favorite would have to be the LM317 (datasheet:
    http://www.national.com/ds/LM/LM117.pdf) Check out the circuit called
    "Adjustable Regulator with Improved Ripple Rejection" on page 14 of that
    datasheet. That should be exactly what you need. I dunno what kind of
    current your clock needs - but it's probably pretty low - so you won't need
    too substantial of a LM317 - since it *probably* won't be dissipating too
    much current. I should think one in a TO-220 package should work just fine
    :)


    Now I was just thinking - so you'll have to tune that circuit to 1.5V. No
    sweat when you have a nice constant 12V to work with. But I've heard that
    voltage in a car's electrical system can spike to as much as 100V DC -
    which would throw that circuit off quite a bit. Maybe someone else would
    have some input as to how to smooth that out?

    Good luck, and have fun!

    Michael
     
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