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

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    Diode Reverse Zero
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Discussion Overview

The discussion centers around the behavior of diodes when reverse-biased, specifically why the current or voltage is perceived to be zero in this state. Participants explore the underlying principles and analogies related to diode operation, including the concept of reverse leakage current.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant expresses confusion about why current or voltage is zero when a diode is reverse-biased and seeks clarification.
  • Another participant asserts that current does not go to zero in reverse bias but instead flows as a small reverse leakage current, referencing the diode equation and its characteristic plot.
  • A participant provides an analogy comparing a diode to a cliff, suggesting that while electrons can easily flow in one direction, they face a significant barrier when attempting to flow in the reverse direction.
  • Discussion includes a specific example of a common diode rectifier (35Z5) used in transformerless AM radios, explaining the flow of electrons based on the relative voltage of the cathode and plate.
  • A later reply humorously corrects the previous post, clarifying that the term "common diode rectifier" refers to vacuum tubes rather than semiconductor diodes, indicating potential confusion among participants.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the behavior of diodes in reverse bias, with some asserting the presence of reverse leakage current while others seem to maintain the notion of zero current or voltage. The discussion remains unresolved regarding the specifics of diode behavior in reverse bias.

Contextual Notes

Some assumptions about diode operation and definitions of terms like "reverse leakage current" may not be fully articulated, leading to potential misunderstandings. The discussion also reflects varying levels of familiarity with diode characteristics and terminology.

mmmboh
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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.
 
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mmmboh said:
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.

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.
 
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 :)
 
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.
 
Bob S said:
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.

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

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