Zener Diode Video Lecture | Physics Class 12 - NEET

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before going ahead with part 14 Zener
diode what is the Zener diode it is a
special-purpose semiconductor diode
which is named after the scientist Zener
who also who found it took this diode
operates under the reverse bias in the
breakdown region so that means as I
mentioned the VI characteristics of the
semiconductor diode what did we see we
saw these kind of occurs so what you see
in the reverse bias region that means in
this region in the breakdown region that
means beyond the breakdown voltage so
this Zener diode operates and let that
region so what is the purpose of Zener
diode it is used as a voltage regulator
so what we will see here we will see
here how does this Zener diode act as a
voltage regulator voltage regulator what
do you mean by this it means that
sometimes in at your home also you would
have seen that there is some voltage
fluctuation the voltage increases
suddenly again drops down suddenly
so those fluctuations can cause or can
damage the elements of the circuit so
Zener diode helps to regulate those
voltage variations so how that we will
see now so symbol to represent the Zener
diode is very similar to the normal
semiconductor diode just that here
instead of the straight line we have a
red kind of a symbol so in for
semiconductor we have it like this and
for a single diode we have it like this
so that is the only difference so
whenever you have this symbol you should
know that it is a Zener diode which is
operating in the reverse bias breakdown
region so let us look at some of the
basic characteristics or basic behavior
of Zener diode as you know tiled has
cave
doping on both P and n sides of the
junction so what what do why do you
think that both the P side as well as
the N side is heavily doped heavily
doped means it has more amount of
impurities that so the P side has more
amount of trivalent impurity and the N
side has more amount of interval and
impurity so what will happen if we have
heavy doping heavy doping means more
amount of impurity that means more
amount of carriers because every
impurity will contribute a free electron
or a free whole right so every impurity
will contribute a carrier so greater the
amount of impurity move as the carrier
therefore mode of the current now if the
current is more then the depletion
region will be think as the extra
carrier given by the donor or the
acceptor right so what how is this heavy
doping related with a Zener diode or
what does this heavy doping single bias
heavy doping would mean more carriers of
current more carriers would mean more
current this will again mean a thin
depletion region thanks everything is
interrelated how does the Zener diode
behave under forward bias if we look at
its characteristic all of you if we look
at the graph of the voltage with current
so we see that when we apply a forward
bias that is when the forward external
voltage increases with in case of
forward bias the current also increases
initially doesn't increase much but then
it starts increasing with the increase
in voltage now when we talk about a
reverse bias how does it behave and that
reverse bias in reverse bias also as the
reverse bias voltage increases initially
the increase is not there but suddenly
at a specific voltage which is known as
the break
down voltage here we call this as Zener
voltage VZ this LED denotes the zenith
so when the voltage is equal to this
Zener voltage the change in current is
extremely large so that reverse so we
see that in case of a Zener diode at
beyond the breakdown voltage the amount
of current is extremely large and the
Zener voltage remains constant so the
Zener voltage does not change beyond
that doesn't matter how much ever the
current increase but the Zener voltage
remains constant so based on these
properties of Zener diode it finds its
application as a voltage regulator so
let us look at the VI characteristics of
a Zener diode if we see in the forward
bias it increases with increasing
voltage but when we look at the reverse
bias we see that at the Zener voltage
that is at the breakdown voltage the
current is increasing current is
extremely high and the Zener voltage
remains constant so from this we can say
that the reverse current increases
doesn't matter whether there in what if
how much ever the reverse current
increases the Zener voltage still
remains constant that means VZ remains
constant irrespective of the change in
current right so this property of Zener
diode makes it suitable as a voltage
regulator so now the question is why
does the Zener diode behave differently
at this playground foliage now what
happens if you think of that
semiconductor PN Junction what happens
at as the reverse bias increases what
happens the electric field strength also
increases now again think of your PN
Junction this is P this is n and this is
log Junction
now what happens as the reverse bias
increases that means and this voltage V
keeps increasing in reverse bias what
will happen that thickness of this
depletion region will keep increasing
now as the thickness of the depletion
region increases the electric field due
to this depletion region also increases
so we can say that as reverse bias
increases the electric field strength
will also increases now at V is equal to
V Z so at V is equal to V Z electric
field becomes so strong that it holds
all the electrons from P side and
accelerate it to the N side because when
as as the electric field increases what
happens the minority carriers of P
gradually drift towards n similarly the
minority carriers of n gradually drift
toward speed that is what that happens
right but when the voltage becomes equal
to this Zener voltage the electric field
becomes so strong that all electrons
from P and pull towards N and similarly
all electrons all electrons from P are
accelerated towards N and similarly all
holes from N and pool and accelerated
towards P so at one go all the electrons
or all the minority carriers are good
therefore the current increases heavily
and this is this results in a high
reverse correct this electron emission
is known as field emission or field
ionization because electric field causes
emission of electrons so this results in
high reverse current
right so this is this is the basic
behavior of a single diode now let us
see how does a Zener diode act as a
voltage regulator if you see we have a
circuit where we have an unregulated
voltage VI which is my input voltage the
input voltage is applied across this end
it is connected to a resistance R s and
then connected to the Zener diode and
then the output is measured across the
load resistance RL so now it is seen
that the output is a regulated voltage
we have denominated the output as BZ so
what happens in this case in this case
Adina's Zener diode obviously it will
operate in the reverse bias region so
now what happens in this case VI is
unregulated voltage that means VI can
increase or decrease any time it is not
regulated so the increase and decrease
will be sudden and it will be very
distinct right so as your input voltage
increases or decreases what happens
current through this resistance RS also
increases or decreases so current
through R s also increases or decreases
like but even though the current
increases extremely or it decreases
extremely the Zener voltage remains
constant like so now if the Zener
voltage remains constant then what will
happen the voltage which is measured as
the output voltage will be a regulated
voltage because the voltage will be
measured here this is my output voltage
so if this Zener voltage if the voltage
across the Zener diode remains constant
that means what is happening whatever
unregulated is there that the sudden
increase or decrease in the voltage
Zener diode is keeping it to do only
this resistor so it is not allowing it
to reflect on across the Zener diode now
since this change in voltage
is not reflected across the Zener diode
therefore the output which we get is
also a regulated voltage right so this
is housing a diode acts as a voltage
regulator thank you please visit exam
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