dropping resistor value

Discussion in 'General Electronics Chat' started by Gompers, Feb 21, 2007.

  1. Gompers

    Thread Starter Member

    Feb 21, 2007
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    Newbie here Name's Ed. Trying to find the right dropping resistor value
    to convert a plug in DC power supply of 5.0 volts @1.0amps to 3.0 (DC)volts to power a miniature Am/Fm radio that eats up batteries.
    Thanx in advance Ed.
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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    It's hard to come up with a good value for a dropping resistor, as the value is only good for one load value. Just grab 4 diodes, like 1N914's, and tie then all in series. They will drop about 2.8 volts and make a better source for your radio.
     
  3. Ron H

    AAC Fanatic!

    Apr 14, 2005
    7,050
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    He only needs to drop 2 volts. Three diodes should do it.
     
  4. beenthere

    Retired Moderator

    Apr 20, 2004
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    Wow, how did I come up with 3 volts? Good catch.
     
  5. Gompers

    Thread Starter Member

    Feb 21, 2007
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    Thanx, Ron and Beenthere I have a whole boxful of diodes, but how do I identify a 1n914? ED
     
  6. wireaddict

    Senior Member

    Nov 1, 2006
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    The no. is usually printed on the side of the case but you'll need a magnifying glass unless your eyes are a lot better than mine.
     
  7. beenthere

    Retired Moderator

    Apr 20, 2004
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    Any silicon diode should do. The 1N914 is a signal diode, but a rectifier type, like a 1N4001 will also work.
     
  8. Gompers

    Thread Starter Member

    Feb 21, 2007
    18
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    Been and Ron thanx again used four silicon diodes and VOILA! works fine

    Next, I want to try to convert a similar plug-in to a lower voltage for use as battery eliminator for my Coolpix camera. Never thoughtof using diodes as resistors? Might make a decade box for quick voltage drop search??Cheers, Ed.
     
  9. beenthere

    Retired Moderator

    Apr 20, 2004
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    They are not really dropping resistors. They require a certain energy to be expended to push electrons across the P-N barrier. That's about .7 volts for silicon, and about .2 volts for germanium.

    They come in handy for wall wart voltage droppers.
     
  10. tek_fool

    New Member

    Feb 24, 2007
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    ..........
     
  11. tek_fool

    New Member

    Feb 24, 2007
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    ..........
     
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