What do you mean by zener breakdown and avalanche breakdown?

Answer Posted / rigzin namgyal nit kkr

"'Zener diode' and 'avalanche diode' are terms often used
interchangeably, with the former much more common. Both
refer to breakdown of a diode under reverse bias.
Specifically, when a diode is reverse biased, very little
current flows, and the diode is to a first order
approximation an open circuit. As the reverse voltage is
increased, though, a point is reached where there is a
dramatic increase in current. Equivalently, there is a
dramatic reduction in the dynamic resistance (slope of the
V-I curve) that can be as low as 1- 2 W in this region.ÝThis
voltage is called the reverse breakdown voltage and it is
fairly independent of the reverse current flowing.ÝThis
property makes it ideal as a voltage reference.Ý

"Avalanche breakdown is caused by impact ionization of
electron-hole pairs.ÝWhile very little current flows under
reverse bias conditions, some current does flow.ÝThe
electric field in the depletion region of a diode can be
very high. Electron/holes that enter the depletion region
undergo a tremendous acceleration.Ý As these accelerated
carriers collide with the atoms they can knock electrons
from their bonds, creating additional electron/hole pairs
and thus additional current.ÝAs these secondary carriers are
swept into the depletion region, they too are accelerated
and the process repeats itself.ÝThis is akin to an avalanche
where a small disturbance causes a whole mountainside of
snow to come crashing down.Ý The efficiency of the avalanche
effect is characterized by a so-called multiplication factor
M that depends on the reverse voltage (Equation 1).


Equation 1: Multiplication Factor

"Here n is in the range 2 - 6, V is the applied (reverse)
voltage, and Vbr is the breakdown voltage.ÝThis is an
empirical relationship, as are many of the relationships
used to describe both Zener and avalanche breakdown.Ý

"Avalanche breakdown occurs in lightly-doped pn-junctions
where the depletion region is comparatively long.ÝThe doping
density controls the breakdown voltage.ÝThe temperature
coefficient of the avalanche mechanism is positive.ÝThat is,
as the temperature increases, so does the reverse breakdown
voltage.ÝThe magnitude of the temperature coefficient also
increases with increasing breakdown voltage. For example,
the temperature coefficient of a 8.2 V diode is in the range
3 - 6 mV/K while the temperature coefficient of an 18 V
diode is in the range ofÝ 12 - 18 mV/K.

"Zener breakdown occurs in heavily doped pn-junctions.ÝThe
heavy doping makes the depletion layer extremely thin. So
thin, in fact,Ýcarriers canít accelerate enough to cause
impact ionization.ÝWith the depletion layer so thin,
however, quantum mechanical tunnelingÝ through the layer
occurs causing current to flow.ÝThe temperature coefficient
of the Zener mechanism is negativeóthe breakdown voltage for
a particular diode decreases with increasing
temperature.ÝHowever, the temperature coefficient is
essentially independent of the rated breakdown voltage, and
on the order ofÝ -3 mV/K.

"In a 'Zener' diode either or both breakdown mechanisms may
be present. At low doping levels and higher voltages the
avalanche mechanism dominates while at heavy doping levels
and lower voltages the Zener mechanism dominates.ÝAt a
certain doping level and around 6 V for Si, both mechanism
are present with temperature coefficients that just cancel.
It is possible to make Zener diodes with quite small
temperature coefficients.Ý

"Neither Zener nor avalanche breakdown are inherently
destructive in that the crystal lattice is damaged.ÝHowever,
the heat generated by the large current flowing can cause
damage, so either the current must be limited and/or
adequate heat sinking must be supplied."

Is This Answer Correct ?    7 Yes 6 No



Post New Answer       View All Answers


Please Help Members By Posting Answers For Below Questions

What are the advantages of current commutated chopper?

681


Which questions ask for ccna certified candidates

1112


Pull the best out of people Put other people above yourself Challenge ideas from another viewpoint Passionate about people Dedication to serving others Pushing people past their limits Never give up Generous of sharing Make other people feel important Thinking outside the box Alternative thinking Complete honesty Wealth of information Easily accessible Work long hours Finding the right answers Working with all ages Dealing with tough situations Making the rounds with other people Compassionate for what people need Diverse in decision Step outside self

1829


how many type of network protocol

1825


What is working principle of profibus?

826






State different methods of voltage control inverters. Describe about pwm control in inverter?

712


How to convert a binary number into bcd number directly and vice-versa, without converting it into any other number system?

653


What are level triggered flip flop?

680


What is the turn-off time for converter grade scrs and inverter grade scrs?

733


Loop check when we do ???before solo run test or dis two activities not related .plz explain me

1418


What is the conductivity of perfect dielectric?

793


What is transponder? Give the difference between transducer and transponder?

691


In order to find out stack fault of a three input nand gate how many necessary input vectors are needed ?

4597


Explain what is a differential amplifier?

682


Define what do you understand by reverse saturation current of a diode?

705