12 or 6 VDC to 5 VDC using diodes

Discussion in 'General Electronics Chat' started by sajib, Nov 3, 2008.

  1. sajib

    Thread Starter New Member

    Nov 3, 2008
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    is it possible to get 12 or 6 VDC to 5 VDC using diodes?
     
  2. sajib

    Thread Starter New Member

    Nov 3, 2008
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    help any 1
     
  3. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    Yes, using a few diodes in series it is possible. But it provides no regulation, and is dependant on the load current.
     
  4. Wendy

    Moderator

    Mar 24, 2008
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    We'll need a bit more information. As kubeek said, by themselves they won't regulate, just drop around .6V each, more or less.

    There are classes of diodes that will regulate, but not quite the way I think you're thinking of. They are Zener diodes, and can be found in the AAC eBook here. Matter of fact, reviewing the chapter, a lot of it will answer your questions.
     
  5. SgtWookie

    Expert

    Jul 17, 2007
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    The voltage drop across an individual diode is reasonably stable, if the load is reasonably stable.

    However, if the load is dynamic (like a microcontroller or a motor) then the voltage drop across the diode will vary considerably.
     
  6. sajib

    Thread Starter New Member

    Nov 3, 2008
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    my device requires 5 VDC about 750 mamp and i have a ac to dc converter which can produce 6 or 12 volt dc current is about 1000 mamp if i use a diode in series to get the voltage, then what type of diode is required ? ie. rating of the diode?
     
  7. Wendy

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    If you were to use qty 1 1N4001 in series you would get 5.4V, with qty 2 you would get 3.8V. Read the chapter I pointed out to you, it shows a different way.
     
  8. SgtWookie

    Expert

    Jul 17, 2007
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    Ahh, I think you're a bit off, Bill.
    I graphed the response of a 1N4002 over a range of currents several months back.
    I only went from 10uA to 100mA, but a simple extrapolation of the results I received tells me that with 750mA current, our OP would likely see more like a 0.9v drop across a 1N4001 through 1N4007 diode. The datasheet specifies a 1.1V drop with a 1A current, which also agrees with the extrapolation; particularly when you consider that when you're approaching the high end of the diode's rating, the Vf increases more rapidly.

    So with a supply that was 6V even, with a 750mA load, one 1N4002 diode would have a Vf of around 0.9V for 5.1V out, and two 1N4002 diodes in series would give 4.2V out.

    If the load varies, the Vf of the diode will vary.
     
  9. AG3Y

    New Member

    Nov 4, 2008
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    Wouldn't you just be as well off to use a 3 terminal voltage regulator such as a 7805 ?

    Feed it 12 volts, get out 5 :

    http://www.national.com/mpf/LM/LM78M05.html

    Almost the same parts count, although there would be a little more expense involved. Are you going to be doing this in a production run, or just making up an individual device ?

    Good luck, Jim
     
  10. SgtWookie

    Expert

    Jul 17, 2007
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    That's true if you're trying to go from 12v to 5v. Can't go from 6v to 5v with a 7805 though; as dropout is 2v.
     
  11. AG3Y

    New Member

    Nov 4, 2008
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    I think that was addressed. OP original question:
    "Is it possible to get 12 or 6 VDC to 5 VDC using diodes?"
     
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