Zener diode is basically like an ordinary PN junction diode but normally works in the reverse biased state. However, the ordinary PN junction diode connected in reverse biased state is practically not used as a Zener diode. A Zener diode is a specially designed multi-doped PN junction diode.
Working Principle of Zener Diode
When a PN junction diode is reversed, the depletion layer expands. If this inverted voltage across the diode increases continuously, the depletion layer expands further. At the same time, there will be a constant reverse saturation current due to the minority carriers.
Minority carriers from the crossing after a certain reverse voltage, acquire sufficient kinetic energy due to the strong electric field. Free electrons with sufficient kinetic energy collide with the fixed ions of the depletion layer and scatter more free electrons. These newly created free electrons obtain sufficient kinetic energy due to the same electric field and cumulatively generate more free electrons through collision. Due to this alternating phenomenon, very soon huge free electrons are formed in the depletion layer and the entire diode becomes conductive. This type of breakdown of the depletion layer is known as avalanche breakdown, but this breakdown is not very sharp. There is another type of depression in the depletion layer that is sharper than avalanche spill, and it is called Zener dump. When a PN junction diode is highly doped, the concentration of impurity atoms will be high in the crystal. This higher concentration of impurity atoms results in a higher concentration of ions in the depletion layer, so for the same applied reverse-biased voltage the width of the depletion layer is normally thinner than the value for a doped diode.
Due to this thinning thinning layer, the gradient of electric field strength across the voltage strain layer is quite high. If the reverse voltage continues to increase, after an applied voltage, the electrons from the covalent bonds in the depletion region go out and make the depletion region conductive. This breakdown is called the Zener distribution. The voltage at which this distortion occurs is called the Zener voltage. If the reverse voltage applied across the diode is more than the Zener voltage, it provides a conductive path to the current through the diode, so there is no possibility of further avalanche breakage. Theoretically, Zener breakdown occurs at low voltage level, then folded for avalanche breakdown in a diode, specifically Zener breakdown. Zener destruction is much sharper than avalanche destruction. The Zener voltage of the diode is adjusted during manufacture with the necessary and appropriate doping aid.Zener diode is connected to a voltage source and source voltage is greater than Zener voltage, voltage across Zener diode remains constant regardless of source voltage. Although in this case the current flowing through the diode can be any value depending on the load associated with the diode. Therefore, we mainly use a Zener diode to control voltage in different circuits.
Zener Diode Circuit
We noted that the Zener Diode is nothing more than a single diode connected to a reverse bias. A diode connected to the reverse bias position in a circuit is shown below,
A circuit symbol Zener diode is also shown below.
Features of Zener Diode
Now, when discussing diode circuits, we should review the graphical representation of the device’s operation. zener diode . Normally referred to as VI characteristics of a Zener diode.
The diagram above shows the VI characteristics of a zener diode When the Diode is connected to the forward bias, this diode acts as a normal diode, but a sharp breakdown occurs when the reverse bias voltage is greater than the zener voltage. At the VI specifications above, V z is the Zener voltage. It is also the knee voltage because the current increases very rapidly at this point.