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Zener Diode

Basic Operation

Basic Theory:

A semiconductor unit blocks current within the reverse direction, however, can suffer from premature breakdown or harm if the reverse voltage applied across becomes too high. The Zener diode is sort of an all-purpose signal diode. once biased within the forward direction it behaves a bit like a traditional signal diode, however, once a reverse voltage is applied to that, the voltage remains constant for a large vary of currents. Zener diodes have an extremely doped contact. traditional diodes will break down with a reverse voltage however the voltage and sharpness of the knee don’t seem to be further outlined as for a Zener diode. Also, traditional diodes don’t seem to be designed to work within the breakdown region, however, Zener diodes will faithfully operate during this region.

It is primarily a special property of the diode instead of any special kind of instrumentation. The person named Clearance Zener made-up this property of the diode that’s why it’s named once him as a remembrance. The special property of the diode is that there’ll be a breakdown within the circuit if the voltage applied across a reversely biased circuit. once a diode is heavily doped, it’s depletion region are going to be slender. once a high reverse voltage is applied across the junction, there’ll be an awfully sturdy field at the junction. and also the electron-hole try generation takes place. therefore serious current flows. this is often called Zener break down.

I-V Characteristics curve :

The higher than diagram shows the V-I characteristics of the Zener diode behaviour. once the diode is connected in forwarding bias diode acts sort of a traditional diode. once the reverse bias voltage is bigger than a planned voltage then the Zener breakdown voltage happens. 

The reverse characteristic is obtained by taking reverse voltage on – ve coordinate axis and reverse current on –ve coordinate axis. because the reverse voltage reaches an explicit worth, the reverse current will increase to an outsized worth, however, the voltage across the diode remains a continuing. the every day forward voltage at temperature with a current of around one mA is around zero.6 volts. within the reverse bias condition, the Zener diode is an associate electric circuit and solely any low escape current is flowing as shown on the exaggerated plot. because the breakdown voltage is approached the present can begin to avalanche. The initial transition from escape to breakdown is soft then again the present apace will increase as shown on the plot. The voltage across the Zener diode within the breakdown region is extremely nearly constant with solely any low increase in voltage with increasing current. At some high current level, the ability dissipation of the diode becomes excessive and therefore the half is destroyed.


There are 2 effects which will be utilized in Zener diodes. One is termed Zener breakdown, and therefore the different, impact or avalanche ionization. The Zener impact predominates below five.5 volts whereas impact ionization is that the major impact higher than this voltage. the 2 effects are laid low with temperature variations. this implies that the Zener diode voltage might vary because of the temperature changes. it’s found that the impact ionization and Zener effects have temperature constant in opposite directions. As a result, Zener diodes with reverse voltages of around five.5 volts wherever the 2 effects occur virtually equally have the foremost stable overall temperature constant as they have an inclination to balance one another out for the optimum performance.

Zener Breakdown Effect :

Zener breakdown result is that the one from that the diode gains its fashionable name. it’s the quantum mechanical result tunnelling result, however once applied to the voltage reference diode, it retains the Zener name once the person WHO discovered it. though the physics behind the result is kind of sophisticated, it is thought-about that this result happens once the electrical field inside the semiconductor Bravais lattice is sufficiently high to drag leptons out of the lattice to form a hole and electron. The lepton then moves beneath the influence of the sector to supply an electrical current.

Impact ionization:

Impact ionization is extremely completely different to Zener breakdown and it happens once a high field of force is a gift in a very semiconductor.  Electrons are powerfully attracted and move towards the positive potential. an insight of the high field of force their rate will increase, and infrequently these high energy electrons can run into the semiconductor lattice. once this happens associate degree lepton could also be free, departure a hole. This recently freed lepton then moves towards the positive voltage and is accelerated beneath the high field of force, and it to might run into the lattice.

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