Understanding P-N Junction Diodes and Zener Diodes
A normal p-n junction diode allows electric current only in forward biased condition, offering small resistance. When reverse biased, it blocks current. If the reverse biased voltage is highly increased, it can lead to zener or avalanche breakdown. Zener diodes are specifically designed for working in reverse bias, allowing current in the reverse direction. The zener breakdown voltage depends on the doping level applied. Zener diodes operate in breakdown region at low reverse voltages due to heavy doping. The symbol of a zener diode consists of two terminals: cathode and anode.
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A normal p-n junction diode allows electric current only forward biased voltage is applied to the p-n junction diode, it allows large amount of electric current. Hence, a forward biased p-n junction diode offer only a small resistance to the electric current. only in forward biased condition forward biased condition. When
When reverse biased voltage p-n junction diode, it blocks large amount of electric current. Hence, a reverse biased p-n junction diode offer large resistance to the electric current. reverse biased voltage is applied to the
If reverse biased voltage applied to the p-n junction diode is highly increased, a sudden rise in current occurs. At this point, a small increase in voltage will rapidly increases the electric current. This sudden rise in electric current causes a junction breakdown called zener which breakdown occurs is called zener voltage called zener zener or avalanche breakdown or avalanche breakdown. The voltage at zener voltage and the sudden increase in current is zener current. current.
A normal p-n junction diode does not operate in breakdown permanently damages the diode. A zener a special type of device designed to operate in the reverse like normal p-n junction diodes under forward biased condition (it allows large amount of electric current under forward biased voltage). Also, direction if the applied reverse voltage is greater than the zener voltage. connected specifically breakdown region region because the excess current zener diode Zener diodes diode is diodes acts reverse breakdown breakdown region region. Zener allows electric current in the reverse always direction. . Thus, it it is is always direction because to work Thus, in reverse connected in specifically designed in reverse designed to reverse direction work in because it it is is reverse direction
The is is depends the diode is heavily doped, zener breakdown occurs at low reverse voltages. On the other hand, if the diode is lightly doped, the zener breakdown occurs at high reverse voltages. Zener diode junction region electric current than the normal p-n junction diodes. Zener diodes are available with zener voltages in the range of 1.8V to 400V. The zener depends on zener breakdown on the amount of doping applied. If breakdown voltage voltage of of the the zener zener diode diode Zener diode is is heavily junction diode region. heavily doped diode. . Hence, Therefore, doped than Hence, it it has zener than the has very diodes the normal very thin allow normal p p- -n n thin depletion depletion more
The symbol of zener diode is shown in below figure. Zener diode consists of two terminals: cathode and anode. The symbol of zener diode is similar to the normal p-n junction diode, but with bend edges on the vertical bar
Power dissipation capacity is very high High accuracy Small size and Low cost
It is normally used as voltage reference Zener diodes are used in voltage stabilizers or shunt regulators. Zener diodes are used in switching operations Zener clamping circuits. diodes are used in clipping and
Diodes only allow a considerable current to flow when they are connected in forward bias. Therefore, they can be used to ensure that current in a circuit flows along a given direction. For For instance, instance, diodes diodes can can be be used used to to convert convert alternating alternating current current to to direct direct current current. .
However a large reverse voltage can cause reverse currents to flow. This is referred to as breakdown, and can take place either as Zener The differences between the two types of breakdown are outlined below. Zener breakdown breakdown or as avalanche avalanche breakdown breakdown.
The avalanche breakdown occurs in both normal diodes and zener diodes at at high high reverse reverse voltage voltage. .
When applied diode, the free electrons gains large accelerated velocities. moving collides knock off more electrons. These electrons are again accelerated and collide with other atoms. Because of this continuous collision with the atoms, a large number of free electrons are generated. As a result, electric current in the diode increases rapidly. When high to high reverse the reverse voltage p-n voltage junction is amount of to free high the energy and greater electrons speed atoms The at with will and
This sudden increase in electric current may permanently However, zener diodes may not be destroyed because operate Avalanche breakdown occurs in zener diodes with zener voltage (Vz) greater than 6V. destroys the normal diode. they in are carefully breakdown designed to avalanche region.
In terms of energy bands, the incoming charge carrier s kinetic energy must be larger than the energy gap between conduction and valence bands for impact place. Then, once the collision takes place and the electron-hole pair is formed, this electron and the hole are essentially in the conduction and valance bands respectively. impact ionization ionization to take
For most diodes, avalanche breakdown , avalanche breakdown is the dominant effect which is determined by: 1 1- - The material used to construct the junction. 2 2- - The level of doping.
In valence on the n n side In Zener valence band Zener breakdown band of the p p side side. breakdown, electrons tunnel side to the conduction tunnel from the conduction band band In classical physics, electrons should not have been able to cross over in this way. The electron charge region is narrower, and when the electric field is larger. Typically, Zener breakdown occurs where materials used to construct the p n junction are heavily doped. In these junctions, due to heavy doping, the space charge region is quite narrow even when the junction is under reverse bias. The probability higher when the space probability for for an an electron to to tunnel tunnel across is higher
When applied to the diode reaches close to zener voltage, the electric field in the depletion region is strong enough to pull electrons from their valence electrons energy field of depletion region will breaks bonding with the parent atom and become free electrons. These free electrons carry electric current from one place to another place. At zener breakdown region, a small increase in voltage will rapidly increases the electric current reverse biased voltage band. which from The gains strong valence sufficient electric the
Zener and involves electrons tunnelling from the valence band of the p side to the conduction band on the n side. Avalanche are accelerated by the electric field gain enough kinetic energy such that, when they collide with lattice atoms, they ionise the lattice atoms to produce electron-ion pairs. These pairs, in turn, cause further ionizations an avalanche effect Zener avalanche Zener breakdown breakdown occurs when the doping levels are high, Avalanche breakdown breakdown occurs when charge carriers which ionizations, leading to Zener breakdown avalanche breakdown breakdown occurs at low reverse voltage whereas breakdown occurs at high reverse voltage.
