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Spoiled diode

  1. Nov 9, 2012 #1
    When a diode is reverse biased by a very large voltage, then it will be spoiled permanently due to overheating.
    Then what is happening inside the diode?
    Why will it spoil? Is that because the silicon atom inside the spoiled diode is changed? Can a spoiled diode be fixed?
    Thank you.
  2. jcsd
  3. Nov 10, 2012 #2


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    Staff: Mentor

    It will be permanently damaged unless you include a large series resistance to limit the current. Otherwise, reverse breakdown can cause a small region to dissipate excessive heat, causing the diode to be ruined. In that case, the only fix is to throw it away and solder in a new one.
  4. Nov 10, 2012 #3
    What do you mean by 'to dissipate excessive heat'? So when the diode is spoiled what makes it cant be reused eg. any atoms or bond will permanently changed ?
  5. Nov 10, 2012 #4
    Yes that is pretty well what he means, except that the atoms themselves are not changed - heat alone cannot do that - but the crystal structure that makes a junction is disrupted.

    Note also that he said a small area ie the important small area at the junction - not the whole crystal.
  6. Nov 10, 2012 #5
    When the diode "avalanches," which simply means that it starts pulling current due to excess voltage, it may or may not break depending on whether the current is sufficiently limited by the surrounding circuitry and whether the diode is "avalanche rated."
    Vendors will generally note in their data sheet whether a device is avalanche rated. Avalanche rated devices will act like zener diodes and will only die if too much heat accumulates at some point on the die. Then, localized melting will typically poison the junction and the diode will usually be shorted. That is, unless sufficient current is available. Then, the device and package will typically burst apart as the current burns it open.
    Some devices, like Schottky rectifiers die due to punch through. This is somewhat like an ESD failure in appearance. It occurs due to a sudden breakdown of the devices ability to hold off voltage in one place. When this happens, you can see a physical pit in the metallization at the point of failure. To offset the occurrence of this problem, manufacturers will build in a zener device in the structure. This is typically about the outer edge and serves to avalanche at a lower voltage, thus protecting from punch through.

    If your really interested in rectifiers, their idiosyncrasies, and the inside on manufacturers, I can give you more than you'd probably care to hear :), so feel free to message.
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