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How come when you reverse a diode the current/voltage? is zero?

  1. Mar 4, 2009 #1
    Hi I have been looking through my book, and even online for the answer because I don't understand why this happens, but I can't find the proper answer anywhere...can someone help me? Thanks.
     
  2. jcsd
  3. Mar 4, 2009 #2

    berkeman

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    Staff: Mentor

    Actually, it doesn't go to zero in reverse bias, it goes to a small reverse leakage current Is.

    Here's a reasonable intro:

    http://en.wikipedia.org/wiki/Diode

    You need to look at the "diode equation" and its plot at that page to see the overall diode I(v) characteristic.
     
  4. Mar 4, 2009 #3
    Imagine a diode as being like a cliff for the electrons. It's much easier to jump off the cliff, but much more difficult to climb back up. It's not a perfect analogy, but if you think of it in terms of potential barriers that is quite close to what is happening. If you're looking for more than an analogy then the Wikipedia page is probably a good start :)
     
  5. Mar 5, 2009 #4
    For a common diode rectifier such as the 35Z5 used in transformerless AM radios, electrons flow to the plate (pin 5) from the cathode (pin 8) when the cathode is negative relative to the plate, and stop flowing when the cathode is positive relative to the plate. The cathode is indirectly heated by the filament and is very hot, and is a good source of electrons. The plate is not.
     
  6. Mar 5, 2009 #5

    berkeman

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    Staff: Mentor

    LOL. "common diode rectifier" for vacuum tubes, not semiconductor diodes. Just in case anybody was getting confused by this post.
     
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