Question

Define the limitations in the operation conditions of a p-n junction.

Answer 1

Ans)

Every pn junction has limiting values of maximum forward current, peak inverse voltage and maximum power rating. The pn junction will give satisfactory performance if it is operated within these limiting values. However, if these values are exceeded, the pn junction may be destroyed due to excessive heat.

(i) Maximum forward current: It is the highest instantaneous forward current that a pn junction can conduct without damage to the junction. Manufacturer‘s data sheet usually specifies this rating. If the forward current in a pn junction is more than this rating, the junction will be destroyed due to overheating.

(ii) Peak inverse voltage (PIV): It is the maximum reverse voltage that can be applied to the pn junction without damage to the junction. If the reverse voltage across the junction exceeds its PIV, the junction may be destroyed due to excessive heat. The peak inverse voltage is of particular importance in rectifier service. A pn junction i.e. a crystal diode is used as a rectifier to change alternating current into direct current. In such applications, care should be taken that reverse voltage across the diode during negative half-cycle of a.c. does not exceed the PIV of diode.

(iii) Maximum power rating: It is the maximum power that can be dissipated at the junction without damaging it. The power dissipated at the junction is equal to the product of junction current and the voltage across the junction. This is a very important consideration and is invariably specified by the manufacturer in the data sheet.

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