Zener diode Characteristic (Practical)

As normal diode generally damage when they enter in break down region. On the other hand,Zener diode is designed to operate in the breakdown region without damage. By varying the doping level, it is possible produce Zener diodes with breakdown voltages in about 2V to 200V.Zener diode is a highly doped PN junction diode.
As we have discussed, the large current breakdown is brought about by two mechanisms, i.e. Zener and avalanche effect. When diode is heavily doped, the depletion region is very narrow. Whenever, the voltage across the diode is increased in reverse bias, the electric field in the depletion region become very intense. The Zener breakdown voltage is found to occur at electric field intensity of about 3×107V/m. At this field the electrons are pulled from the covalent bonds. A large number of electron-hole pairs are produced and current sharply increases in reverse direction. This is known as Zener effect. Avalanche effect occurs due to cumulative action. The external applied voltage accelerates the minority carriers in the depletion region. They gain sufficient energy to ionize atoms by collision. This creates electrons which are again accelerated to high enough velocities to ionize more atoms. Thus reverse current sharply increases.
Many diodes described as “Zener”diode rely on avalanche breakdown. Both types are used with the Zener effect predominating under 5.6V and avalanche breakdown above. If, the applied reverse voltage exceeds the breakdown voltage, Zener diode acts like a constant voltage source. For this reason, a Zener diode is like a constant voltage source termed as voltage reference diode.
The circuit symbol of a Zener diode is shown in figure You can find handwritten notes on my website in the form of assignments.
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Other stuff on this site is Lab manuals and question Papers.

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