What is Zener diode ?It is a type of diode which is operate in reverse biased condition.Zener diode is highly doped specially design diode .
Working principle of Zener diode
When PN junction diode is reverse biased by connected the battery positive terminal to N type side and negative terminal to P-type side of diode. When this reverse biased voltage increased continually the depletion layer become more wide .At the same time there will be constant reverse saturation current which is due to minority carriers.
After a certain limit of reverse saturation voltage ,the minority carrier will get sufficient kinetic energy due to strong electric field .The free electron due to sufficient kinetic energy collide with ions of the depletion layer and knock out more free electron.
Due to the same electric field the newly created free electron also created more electron by collision cumulatively. Due to this commutative process hug free electron get created and the entire diode will become conductive .This type of depletion layer breakdown is called avalanche Breakdown
But is type of breakdown is not sharp .There is another type of breakdown which to sharper then the avalanche breakdown which is called Zener breakdown .If we highly doped the PN junction then concentration of atom in the crystal become high .
Due to this higher concentration of impurity atom ,the concentration of ion in the depletion region become also higher .Therefore the width of the depletion region become thinner than that in the normally doped diode.
Voltage gradient or electric field strength across the depletion region is high due to this thinner depletion region. If we increase the voltage across the diode continuously then after a certain voltage ,electron from the covalent bond within the depletion region come out due to which the depletion region become conductive .This type of breakdown is called Zener Breakdown. The voltage at which Zener breakdown occur is called Zener voltage .
If the voltage across the it is more then Zener breakdown voltage then it will provide conductive path to the current hence there is no further chance of avalanche breakdown.The Zener breakdown is much sharper then the avalanche breakdown.
The Zener voltage is adjusted during to manufacture of Zener diode with proper doping process.The voltage across the Zener diode remain fixed irrespective of the source voltage if we connected Zener diode across the voltage sources which is above the Zener voltage.The current through the Zener diode depend upon the load .Due to the fixed voltage characteristic we used Zener diode mainly for controlling voltage in different circuits
Symbol of Zener Diode
Zener diode Symbol are given below with there circuit.
Zener Diode Characteristic
If we connected the Zener diode in forward biased then it act as normal diode but when we connected it in reverse biased by provding voltage greater then Zener voltage then a sharp breakdown occur which is called Zener Breakdown. In the V-I Characteristic Vz is Zener voltage also called Knee voltage. After this voltage level the current increase very rapidly.
- It is is used as a voltage references and also shunt regulator to regulate voltage across the small circuit.
- It is used as a surge protector to limit the transient voltage spikes .
- It is used in noise which is causes due to avalanche breakdown.
- It is used as voltage shifter in a circuit.
- It is used as a waveform clipper in clipping circuit.
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