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  • zener diode

    pradeep madhav

    pradeep madhav

    @pradeep-madhav-kuzmRN
    Updated: Feb 16, 2010
    Views: 1.3K
    hi
    we know that a zener diode operated in a reverse biased condition , eventhough when the reverse voltage applied across the zener diode increases more than its breakdown voltage the voltage drop across the zener diode remains constant ,why does this happen ? what actually happens inside the zener diode during that situation
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  • reachrkata

    Member • Feb 18, 2010

    The principle is called zener breakdown.
    Due to the way the diode is doped, when a reverse voltage is applied, the depletion region widens and creates an electric field

    [​IMG]

    As the reverse bias increases, the electric field reaches a point when it is high enough to energize the electrons into breaking out of their covalent bonds and becoming free electrons. And these free electrons cause the high current.

    The point to note here is after this breakdown point, higher reverse bias just creates more free electrons, but the depletion layer potential does not change any more. It is this potential that gets fixed as the zener voltage.

    -Karthik
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  • pradeep madhav

    Member • Feb 18, 2010

    thanks 4 reply
    but the question was y is that voltage across the depletion region constant (for voltage greater than breakdown) , is that because (i think )
    when more electrons are created the resistance of the diode adjusts itself by lowering its value so there will be a compensation and hence constant voltage ,let me know is this right
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  • reachrkata

    Member • Feb 20, 2010

    In a way yes !!!

    -Karthik
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