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DC 12 volts to DC 9 volts??????

Discussion in 'Electronic Design' started by [email protected], Aug 13, 2005.

  1. Guest

    What would be the simplest was to knock a 12 volt lantern battery down
    to 9 volts?
     
  2. Guest

    Saw two cells off it.
     
  3. Pooh Bear

    Pooh Bear Guest

    The *simplest* way would be a linear voltage regulator like a 7809.

    http://www.onsemi.com/site/products/summary/0,4450,MC7809A,00.html

    It won't regulate the 9V output as the battery gets exhausted though. A
    switching regulator is more complicated but is better in this respect.

    Graham
     
  4. M. Smile

    M. Smile Guest

    Four 1N400x diodes in series with the battery, that is 4 x 0.7V = 2.8V drop.
     
  5. Guest

    thanks
     
  6. Tam/WB2TT

    Tam/WB2TT Guest

    Before you do this, make sure tthe 12V is really 12, and not something like
    14.5, which is what you would get in a car.12V power supplies sold for use
    with 2 way radios are set to 13.8. Even 8 new dry cells would be about
    12.8. I vote for an LDO series regulator.

    Tam
     
  7. M. Smile

    M. Smile Guest

    If it is a lantern battery as stated, the maximum voltage using 8 internal
    Alkaline cells would be 12.48V.
    A fresh Alkaline cell usually gives 1.56V so 8 x 1.56V would give 12.48V.
    This would give 9.68V after the diodes, still acceptable.
    But I agree that a voltage regulator, preferably a low dropout regulator
    could be better in some cases.

    M.S.
     
  8. Mac

    Mac Guest

    The original post was referring to a 12V lantern battery.

    Still, if the OP needs a regulated 9 V output, then the diode method might
    not be good enough, and some type of regulator might be required. 7809?

    But if the OP just needs 9V, more or less, then the diodes should work
    fine.

    --Mac
     
  9. Mac

    Mac Guest

    How much current do you need? How well regulated does the 9V have to be?

    Or, if you don't know, then what are you going to do with the 9V?

    --Mac
     
  10. Tam/WB2TT

    Tam/WB2TT Guest

    Yeah, I saw that the first time I read this, then forgot. Problem with a
    constant voltage drop is that if 12V gives you 9, then 10V gives you 7,
    whereas with the LDO anything over about 9.5V will still give you 9 out.
    Check out national.com.

    Tam
     
  11. Leonard

    Leonard Guest

    saw off the top 1/4th.
     
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