In a dc circuit, zener diode can be used as a voltage regulator or to provide voltage reference. On the other hand, avalanche breakdown occurs in the device due to the collision of electrons moving at high speed. For lightly doped diodes, zener break down voltage becomes high and breakdown is thus predominantly by avalanche multiplication. Different types of breakdown diodes and their applications. The main difference between zener breakdown and avalanche breakdown is their mechanism of occurrence. Why zener breakdown is less than avalanche breakdown. Both refer to breakdown of a diode under reverse bias. This is observed in zener diodes having v z 5 to 8 volts this is observed in zener diodes having v z greater than 8 volts 2. If a p and n region are heavily doped then the breakdown voltage can be reduced. Avalanche breakdown occurs in lightlydoped pnjunctions where the depletion region. The collisions happening in avalanche breakdown dissippiate thermal energy and may cause damage of normal diodes. Zener breakdown and avalanche breakdown the avalanche breakdown and zener breakdown are two different mechanisms by which a pn junction breaks.
The zener and avalanche breakdown both occur in diode under reverse bias. The valence electrons are pulled into conduction due to very intense electric field appearing across the narrow depletion region. Avalanche zener breakdown cont zener occurs in highly doped junctions quantum tunneling effect. Difference between pn junction diode and zener diode. Thus after reaching zener breakdown voltage zener remains undamaged, can be used again. It occurs in a reverse biased pn diode when the electric field enables tunneling of electrons from the valence to the conduction band of a semiconductor, leading to numerous free minority carriers which suddenly increase the.
But when this reverse breakdown voltage is exceeded, the diode experiences an avalanche breakdown. Difference between zener and avalanche wikidifferences. The basic function of the diode is, it allows the current flow in only one direction and blocks in the reverse. When the voltage across the terminals is reversed and the potential reaches the zener voltage or knee, the junction will break down and current will flow in the reverse direction a desired characteristic.
The electrons so released further release much more electrons from the atoms by breaking the covalent bonds. When the diode is reverse biased, the kinetic energy of the electrons increases and they move at a high velocity. For normally doped pn diode, depletion region is thick. Zener breakdown occurs when the high electric field is created across the junction. Can zener breakdown be converted to avalanche breakdown. In zener breakdown the electrostatic attraction between the negative electrons and a large positive voltage is so great, that it pulls electrons out of their covalent bonds and away from their parent atoms. Most of the diodes are made up of semiconductor materials like silicon and germanium etc. What is the difference between a zener diode and an. Zener breakdown occurs for smaller reverse bias voltages, as it relies on the mechanism of electron quantum tunneling, which occurs when the high electric field across the depletion region causes the generation of electronhole pairs due to the br. Introduction the zener diode is a silicon pn junction devices that differs from rectifier diodes because it is designed for operation in the reverse breakdown region. Zener breakdown refers to the phenomenon whereby electrons pass through, characteristics a typical zener diode voltagecurrent characteristic is shown in figure 1. The zener diode working principles and its various. Typically zener breakdown causes the diode junction to break down below 5v and will not damage the device unless there is no provision made to release the heat generated.
A zener diode is a type of diode that allows current to flow in the conventional manner from its anode to its cathode i. Zener breakdown avalanche breakdown in the zener effect or zener breakdown, the electric field enables tunneling of electrons from the valence to the conduction band of a semiconductor in a reverse biased pn diode. At this point, a small increase in voltage will rapidly increases the electric current. If the electric field e in the transition region is large, an electron entering from the p side may be accelerated to high enough kinetic energy to cause an ionizing collision with the lattice.
Avalanche breakdown is a phenomenon that can occur in both insulating and semiconducting materials. The main use of zener diode lies in the fact that the voltage across a zener diode remains constant for a larger change in current. Breakdown mechanisms in bjts the breakdown mechanisms of bjts are similar to that of pn junctions. Difference between zener breakdown and avalanche breakdown. The other differences between them are explained below in the comparison chart. Zener breakdown and zener characteristic electrical4u. The zener diodes breakdown characteristics are determined by the doping process zeners are commercially available with voltage breakdowns of 1. Zener breakdown has a negative temperature coefficient of voltage, while avalanche breakdown has a positive temperature coefficient. Therefore zener breakdown voltage is less than avalanche breakdown. A conventional reverse biased diode, when subjected to its breakdown voltage allows a significant amount of current.
If reverse biased voltage applied to the pn junction diode is highly increased, a sudden rise in current occurs. The device was named after clarence zener, who discovered this electrical property. Moreover, the zener breakdown voltage has a negative temperature coefficient meaning which the zener breakdown voltage reduces with the increase in the junction temperature. This process is termed as carrier multiplication and leads to a considerable increase in the flow of current through the pn junction. This crystal structure returns to the normal state when when excess reverse bias is removed, provided that overheating has not permanently damaged the crystal. With the help of this post we have tried to explain the concept of zener breakdown. Avalanche breakdown is a form of electric current conduction that allows very large. An avalanche breakdown is going to keep electricity running until the entire system burns up. Major difference between zener and avalanche breakdown. Difference between zener and avalanche breakdown with. Since the basecollector junction is reversed biased, it is this junction where breakdown typically occurs. The basic property of the diode is to conduct the electrical current in only in one direction and block the current which is in the opposite direction. In electronics, the zener effect is a type of electrical breakdown, discovered by clarence melvin zener.
Avalanche breakdown needs collision of minority carriers and covalent bonds to provide electrons and holes. Zener breakdown and avalanche breakdown basic electronics. This behavior is due to the avalanche breakdown or to the zener breakdown phenomena. The avalanche breakdown occurs because of the ionisation of electrons and hole pairs whereas the zener diode occurs because of heavy doping. The voltage curve is defined by the changing of the diode and line capacitance over the. Now it needs some ti me to charge the diode and line capacitance with the low source current up to the avalanche breakdown voltage level before another electron can trigger an. In electronics, the zener effect employed most notably in the appropriately named zener diode is a type of electrical breakdown, discovered by clarence melvin zener. One is called zener breakdown and the other is called avalanche. Zener breakdown occurs in a zener diode at low reverse voltages. Explain zener breakdown mechanism in zener diode with vi.
It occurs in a reverse biased pn diode when the electric. For the love of physics walter lewin may 16, 2011 duration. In the zener breakdown mechanism, the electric field becomes as high as 10 7 vm in the depletion layer with only a small applied. In silicon diodes the zener breakdown appears before 5 to 6 v and the avalanche breakdown afterwards. It is a form of electric current multiplication that can allow very large currents within materials which are otherwise good insulators. When the reverse bias breakdown voltage is exceeded, a conventional diode is subject to high current due to avalanche breakdown. Those two phenomena are 1 zener breakdown and 2 avalanche breakdown. A zener diode is heavily doped to reduced the breakdown voltage. Some operate on the principle of zener breakdown, while others operate on the principle of avalanche breakdown. Avalanche zener breakdown cont reverse bias very little current flow open circuit as reverse voltage a point is reached where current dramatically, therefore dynamic resistance. October 2015 learn how and when to remove this template message. At this breakdown voltage, the crystal structure breaks down. Differnece between zener breakdown and avalanche breakdown. Zener effect and avalanche effect electrical engineering.
Zener diode and avalanche diode are terms often used interchangeably. A or lower the abrupt bre akdown drops the applied voltage below the avalanche breakdown level, so that the avalanche stops again. One is zener breakdown and another one is avalanche breakdown. There are two processes which causes junction breakdown. The associated phenomenon is called avalanche breakdown shown in red color in the figure and the corresponding voltage is avalanche breakdown. Avalanche breakdown in simple words is a large mass of prisoners exponentially coming together and revolting by running and breaking the gates of prison. The zener effect is a type of electrical breakdown in a reverse biased pn diode in which the electric field enables tunneling of electrons from the valence to the conduction band of a semiconductor, leading to a large number of free minority carriers, which suddenly increase the reverse current, the avalanche breakdown is due to minority carriers accelerated enough to create. Voltage breakdown mechanisms figure 3 depicts the extension of reverse biasing to the point where voltage breakdown occurs. This sudden rise in electric current causes a junction breakdown called zener or avalanche breakdown.
In such a diode for reverse bias in excess of 6v, the breakdown is through process of avalanche multiplication or secondary emission. Not all zener diodes break down in the exact same manner. Difference between pn junction diode and zener diode definition of pn junction diode and zener diode diode is an electronic component that allows the flow of electricity in one direction without resistance or with very little resistance while in the opposite direction has. Both sides of pn junction are heavily doped in zener breakdown. Avalanche breakdown occurs when the applied voltage is so large that electrons that are pulle. For lightly doped junctions, electron tunnelling is negligible. The breakdown diode is an electrical component which will have the two electrodes. Whereas zener doesnt have much thermal dissippiation. A single such interaction results in carrier multiplication. Hbd854 zener theory and design considerations handbook. This manual was prepared to acquaint the engineer, the equipment designer and. The importance of this detail is that zener diodes around 5.
Zener diodeas voltage regulator linkedin slideshare. A conventional solidstate diode will not allow significant current if it is reversebiased below its reverse breakdown voltage. These two phenomena are quite like a natural occurrence. When the doping is heavy, even the reverse voltage is low, the electric field at barrier will be so strong thus the electrons in the covalent bonds can break away from the bonds. Zener breakdown occurs because of the high electric field whereas, the avalanche breakdown occurs because of the collision of free electrons with atoms. Electrons are transferred from the valence to the conduction band. The avalanche breakdown voltage increases with temperature.
Which type of breakdown occurs first out of zener and. The width of depletion layer depends upon the doping level. Electrical break down of any material say metal, conductor, semiconductor or even insulator can occur due to two different phenomena. The zener breakdown takes place in a very thin junction, i. The crucial difference between the zener and avalanche breakdown is the operating mechanism. Consider the heavily doped pn junction shown to the left and then apply a reverse bias to the junction. Avalanche and zener processes the first of two breakdown mechanisms is zener breakdown the zener effect is the breakdown mechanism if the reverse bias required to force breakdown occurs at low voltages. The avalanche process occurs when carriers in the transition region are accelerated by the electric field to energies. A zener breakdown is going to be a controlled breakdown. Although all pn junctions exhibit a voltage breakdown, it is important to know that there are two distinct voltage breakdown mechanisms. Just like for a pn junction the breakdown mechanism can be due to either avalanche multiplication as well as tunneling. This phenomenon is called zener breakdown or avalanche breakdown. Avalanche breakdown and zener breakdown electronics physics and spirituality.
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