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Select the option that is true regarding the following two statements labelled Assertion (A) and Reason (R).

Assertion (A): Avalanche breakdown is reversible while Zener breakdown is not reversible.

Reason (R): Avalanche breakdown can be reversible if we put a series resistor in a diode.


1. A is true but R is false
2. Both A and R are true but R is not a correct explanation of A
3.  A is false but R is true
4. Both A and R are true and R is the correct explanation of A

1 Answer

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Correct Answer - Option 3 :  A is false but R is true

Concept:-

Zener Breakdown:

  • In a heavily doped PN junction, under high reverse voltage (around 5 V), the electrons tunnel through the depletion region due to extremely small depletion region width.
  • Even though the electric field is very high the electrons can tunnel through due to very thin depletion regions.
  • This causes high reverse current to flow even in reverse bias. The junction is not destroyed can be used as a normal PN diode in forward bias.
  • Zener breakdowns are reversible.


Avalanche Breakdown:

  • In thinly doped PN junction diodes Zener effect is not possible, but under very high reverse voltage (< 8-10 V) the high electric fields (lower than Zener diode) cause the electrons to accelerate.
  • The accelerated electrons break free more electrons (called impact ionization) this newly free electron, in turn, creates more charge carriers causing a kind of avalanche effect.
  • This results in a huge reverse current, but the junction is destroyed to this effect.
  • These are not reversible but can be made reversible if we put a series resistor in the diode.


So we can say the Assertion is wrong but the reason is correct.

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