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The Zener diode structure is optimised to ensure the required performance - this entails some differences to the structure of an ordinary diode. There are two effects that can be used in Zener diodes. One is called Zener breakdown, and the other, impact or avalanche ionisation. The Zener effect predominates below 5.
The two reverse breakdown effects in the diode have very similar characteristics, but they are not the same. In most cases it is possible to ignore the difference between the two effects and use a diode in the same manner. The reverse conduction effects, in common with many other aspects of semiconductor technology are subject to temperature variations.
It is found that the impact ionisation and Zener effects have temperature coefficient in opposite directions. The Zener effect which predominates below 5. However the avalanche effect which is the major effect above 5. As a result Zener diodes or voltage reference diodes with reverse voltages of around 5. The actual reverse voltage is repeatable for a given diode and is dependent upon the internal geometry and characteristics of the diode. Zener voltage reference diodes are able to run in reverse breakdown condition within their specifications very reliably.
If a conventional PN junction diode is run into reverse breakdown it is most likely to be irreparably damaged. When a reverse voltage is applied to a conventional PN junction diode and the voltage is increased it will eventually breakdown and it will be subject to high current due to avalanche breakdown. IF this current is not limited by the surrounding circuitry, the diode is very likely to be destroyed because of overheating.
A Zener diode exhibits almost the same properties, except the device is specially designed to have a reduced breakdown voltage. Also the Zener diode or voltage reference diode topology is designed in a way that the diode exhibits a controlled breakdown and allows the current to keep the voltage across the Zener diode close to the breakdown voltage.
Zener diodes are widely used for a host of different applications where a stable voltage is needed. Although there are two effects that exhibit the stable reverse breakdown voltage, the diodes are universally referred to as Zener diodes. Building the gymnastic body po polsku pdf file. Zener diode theory and operation There are two effects that can be used in Zener diodes.
The two effects are totally different, although they produce almost identical effects. It is the quantum mechanical effect tunnelling effect, but when applied to the voltage reference diode, it retains the Zener name after the man who discovered it. Top of the world bridgit mendler audio book. Under most conditions electrons are contained within atoms in the crystal lattice.
In this state they are in what is called the valence band. If a large electric field is placed across the semiconductor this may be sufficient to pull the electrons out the atom into what is called the conduction band. When they are free from the atom they are able to conduct electricity, and this gives rise to the name of the conduction band. For them to pass from the valence band into the conduction band there must be a certain force to pull them free.
It is found that once a certain level of electric field is present a large number of electrons are pulled free creating allowing current to suddenly start to flow once a certain reverse voltage is reached.
Electrons are strongly attracted and move towards the positive potential. In view of the high electric field their velocity increases, and often these high energy electrons will collide with the semiconductor lattice.
When this occurs a hole-electron pair is created. This newly created electron moves towards the positive voltage and is accelerated under the high electric field, and it may collide with the lattice.
The hole, being positively charged moves in the opposite direction to the electron. If the field is sufficiently strong sufficient numbers of collisions occur so that an effect known as avalanche breakdown occurs.
This happens only when a specific field is exceeded, i. Diode operation The reverse conduction effects, in common with many other aspects of semiconductor technology are subject to temperature variations. Difference between stand and Zener diode operation Zener voltage reference diodes are able to run in reverse breakdown condition within their specifications very reliably. Supplier Directory For everything from distribution to test equipment, components and more, our directory covers it.
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