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National Bird Day is celebrated every year on 5 January . This day is observed to spread awareness about birds, their importance in nature, and the need to protect them. Birds are beautiful living beings and play a very important role in keeping our environment healthy. Origin of National Bird Day National Bird Day was first celebrated in the year 2002 . It was started by bird lovers and environmental groups to protect birds from dangers like deforestation, pollution, and illegal hunting. The main aim of this day is to teach people, especially students, why birds are important and how we can help save them. Why Is National Bird Day Celebrated Every Year? National Bird Day is celebrated every year because many bird species are disappearing due to human activities. Cutting trees, using plastic, pollution, and climate change are harming birds and their homes. This day reminds us that: Birds need protection Nature should be respected Everyone has a responsibil...
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Breakdown and resistance of diode | Electronics | Semiconductor diode

Breakdown and resistance of diode

Breakdown of a diode 

  • On applying reverse bias to the diode, two types of breakdown occurs, which are responsible to the sudden increase of current in the reverse bias condition.

Avalanche breakdown

  • In this mechanism, the minority charge carriers gain enough kinetic energy from the applied reverse voltage to collide with the valence electrons of the atom and liberate them.
  • In this process the covalent bond breaks and create a large number of electron-hole pairs.
  • The new charge carriers so produced generate the additional electron-hole pairs.
  • In this way the number of free electrons and holes increases continuously.
  • This phenomenon is known as avalanche multiplication and it produces a sharp increase in the reverse current.
  • The magnitude of avalanche breakdown voltage can be increased by increasing the temperature.

Zener breakdown

  • If the junctions are heavily doped and have a very narrow depletion region, then the breakdown occurs is known as Zener breakdown.
  • Since in this case there exist a high electric field (E = V/d), across the junction.
  • This electric field is so strong to break the covalent bond and generate the electron-hole pairs.
  • On further increasing the Zener voltage, the large number of carriers generate, which increase the reverse current suddenly.
  • This breakdown is a field emission phenomena.
  • On increasing the temperature the Zener breakdown voltage can be decreased.

Resistance of a diode 

 

Static or dc resistance 

  • When only dc current flows through the diode, then the resistance offered by it is static or dc resistance.
  • It is the ratio of the dc voltage across the diode to the dc current flowing through it.
  • Rdc = V / I
  • In forward bias the static resistance of diode is RF and in reverse bias RR.
  • RR >> RF
  • For Ge, RR : RF = 4000 : 1.

Dynamic or ac resistance

  • When only ac current or a small ac current along with dc current flows through the diode, then the resistance offered by it is dynamic or ac resistance.
  • It is reciprocal of the slope of the current-voltage characteristic of the diode.
  • Rac = ΔV / ΔI
  • When the diode is sufficiently forward biased, then at any temperature T

  • Here k = Boltzmann constant, and e = charge of electron.
  • For Ge, η = 1, and at T = 300 K
  • Rac = 26 / I
To know more about breakdown and resistance of diode please click on https://youtu.be/T39lWWPfLFo
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  1. Smith KaylorOctober 30, 2022 at 12:54 AM

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