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Potential difference across a diode

  1. Jan 20, 2013 #1
    Why is the potential difference across a conducting diode zero?
     
  2. jcsd
  3. Jan 21, 2013 #2

    dlgoff

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    If the potential difference across a diode in zero, it's not conducting.


    diod6.gif

    Looks like there's a nonzero voltage everywhere except when the current is zero. :wink:

    Unless of course it's shorted internally. But even then, you'll see a potential difference, albeit kinda small.
     
  4. Jan 21, 2013 #3
    but then in explaining the working of the signal circuits of the OR and AND gates , i found the book assuming that there can be no potential difference across a diode

    Pls refer to this youtube video from one of the best EEC professors in india(He says the same)

    I shall wait for your reply.

    Thank you.
     
    Last edited by a moderator: Sep 25, 2014
  5. Jan 21, 2013 #4

    NascentOxygen

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    The PD is small and approximately constant over a range of forward currents. In comparison with other voltages around the circuit, it is often convenient to think of it as 0 volts. (We may approximate 0.6V to 0 volts, especially when discussing applications where the difference does not matter. Alternatively, you can picture the discussion as involving idealized diodes.)

    It is usually convenient to think of a mechanical switch as having zero volts across it when it is in the ON position, though we all recognize that no practical switch can have 0.000000V across its contacts while conducting useful lighting current in the home.
     
  6. Jan 21, 2013 #5

    sophiecentaur

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    This is the world of Real Engineering, in which insignificant quantities can be validly regarded as zero. If the circuitry that follows a diode is not 'aware' that it isn't zero (when it is near zero) then it IS zero. In digital circuitry, we use 0 and 1 quite happily when neither of those voltage levels is actually 0 or 1.
     
    Last edited by a moderator: Sep 25, 2014
  7. Jan 21, 2013 #6

    dlgoff

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    I'm thinking that since this is a "Lecture Series on Electronics For Analog Signal Processing", the OP will need to understand the diode curve sooner or later. :biggrin:
     
  8. Jan 21, 2013 #7

    sophiecentaur

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    Oh yes, I agree but the link he gives in which the zero voltage drop statement is made is a lecture on diodes being used in logic circuits. He is taking what the teacher said, out of context.
     
  9. Jan 21, 2013 #8

    dlgoff

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    Yea. I wish he/she would have given a link to the lecture on his/her first post. Just trying to justify my response to it. :redface:
     
    Last edited: Jan 21, 2013
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