L9 : Semiconductor Diode & Biasing - Semiconductors, Physics, Class 12 Video Lecture - Class 12 | Best Video for Class 12

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ahead with part 9
so now it is time that we start studying
about practical applications of the
semiconductors so first we will talk
about semiconductor diode so what you
will see what is a semiconductor diode
how does it make use of a PN Junction
which we discussed just now so what is a
semiconductor diode it is a two terminal
device which allows unidirectional flow
of current so this is the key point when
we talk about a diode that is
unidirectional that means diode will
have two terminal maybe one is used for
input and the other one is for output it
will allow current to flow only in one
direction as you remember in the
introduction slide I was talking about
valves I told that valves well some
devices which allowed unidirectional
flow of current so this diode was again
a device which allowed unidirectional
flow of current so what is a diode I
mean when you look at its structure what
is it actually it is nothing but a PN
Junction with metallic contacts at ends
for application of external voltage so
diode is not not a new thing it is just
a PN Junction does that you add metallic
contacts on both sides of the PN
Junction so that you can apply some
external voltage to this PN Junction so
now under this topic of semiconductor
diode we will learn how the diode
behaves under application of different
voltages we will study all those things
so now you understand why and this time
in the PN Junction was so important now
how do you think how do we symbolically
represent a semiconductor diode it is
shown here see here if you look at it it
has a big arrow
what does this arrow represent it
represents the direction of conventional
current when I say conventional current
I mean the current in a direction
opposite to the direction of electron
flow right so this represents that it
allows current to flow only in this
direction so for a diode this is
positive this is negative because this
arrow is along this direction that means
it is telling that the conventional
current is along this direction so this
is positive and this is negative let us
now talk about biasing of a diode now
diode and m4 semiconductor diode we
normally use the term diode so what do I
mean by biasing of a diode as I
mentioned in the previous slide that
diode is nothing but a PN junction with
metallic contacts where we can apply
external voltage so application of
external voltage across a diode is known
as biasing of a diode if I am telling
that that this diode is biased
that means this diode has been supplied
with some external voltage so some
external voltage has been supplied
across the diode then the diode is said
to be biased now there are two kinds of
biasing of a diode one is called forward
biasing and the other one is reverse
biasing so what is a forward biasing
when the positive of the diode is
connected to the positive terminal of
the battery we say that the diode is
forward biased it is suppose if this is
the diode this is my PN Junction so this
is positive this is negative so the
positive of the diode is connected to
the positive terminal negative of the
diode is connected to the negative
terminal so this is forward biasing
similarly in case of reverse biasing
positive of the diode connected to the
negative of the battery so this is
positive which is connected to the
negative of battery again this is
negative which is
to the positive of battery if you use
the symbol for diode you can do it in
this way if this is my diode this is
positive this is negative so in forward
biasing it is connected like this in
reverse biasing it is connected like
this so this positive and this is
negative right so you understand what is
forward biasing and what is reverse
biasing thank you please visit exam few
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