Zener Diode

Posted by Unknown On Sunday, February 20, 2011 4 comments



A Zener diode is a type of diode that permits current not only in the forward direction like
a normal diode, but also in the reverse direction if the voltage is larger than the breakdown
voltage known as "Zener kneevoltage" or "Zener voltage". The device was named after
Clarence Zener, who discovered this electrical property.
A conventional solid-state diode will not allow significant current if it is reverse-biased 
below its reverse breakdown voltage. When the reverse bias breakdown voltage is exceeded
, a conventional diode is subject to high current due to avalanche breakdown. Unless this
current is limited by circuitry, the diode will be permanently damaged due to overheating.
In case of large forward bias (current in the direction of the arrow), the diode exhibits a
voltage drop due to its junction built-in voltage and internal resistance. The amount of the
voltage drop depends on the semiconductor material and the doping concentrations.
A Zener diode exhibits almost the same properties, except the device is specially 
designed so as to have a greatly reduced breakdown voltage, the so-called Zener voltage.
By contrast with the conventionaldevice, a reverse-biased Zener diode will exhibit a 
controlled breakdown and allow the current to keep the voltage across the Zener diode
 close to the Zener voltage. For example, a diode with a Zener breakdown voltage of 3.2 V
 will exhibit a voltage drop of very nearly 3.2 V across a wide range of reversecurrents. 
The Zener diode is therefore ideal for applications such as the generation of a reference 
voltageor as a voltage stabilizer for low-current applications.
The Zener diode is mainly made of heavely dooped with impurities.
Another mechanism that produces a similar effect is the avalanche effect as in the 
avalanche diode. Thetwo types of diode are in fact constructed the same way and 
both effects are present in diodes of this type. In silicon diodes up to about 5.6 volts
, the Zener effect is the predominant effect and shows a marked negative temperature
coefficient. Above 5.6 volts, the avalanche effect becomes predominant andexhibits
a positive temperature coefficient[1]. In a 5.6 V diode, the two effects occur together 
and their temperature coefficients neatly cancel each other out, thus the 5.6 V diode
is the component of choicein temperature-critical applications. Modern manufacturing
techniques have produced devices with voltageslower than 5.6 V with negligible 
temperature coefficients, but as higher voltage devices are encountered,the temperature
coefficient rises dramatically. A 75 V diode 
has 10 times the coefficient of a 12 V diode.
The V-I characteristics of Zener Diode will be like:


All such diodes, regardless of breakdown voltage, are usually marketed under the umbrella term of 
"Zener diode".

4 comments:

Anonymous said...

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Anonymous said...

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Ro6o$ap!3n said...

thanx..!

Anonymous said...

It's very good yarr

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