 
Hey friends, welcome to the YouTube
channel ALL ABOUT ELECTRONICS. So in this
video we are going to talk about the
non-inverting op-amp configuration and
we will see how to use this op-amp as a
voltage follower. Now in the last video,
we had seen the inverting op-amp
configuration and in that configuration
we had seen that using the negative
feedback we can control the gain of this
op-amp. And in that configuration we have
applied the input to this inverting
terminal of the op-amp and we have
grounded the non-inverting terminal. Now
let us see what happens when we apply
this input to this non-inverting
terminal.
So let's say we have applied
the input to this non inverting terminal
and we have grounded this inverting
terminal. So, this kind of configuration
is known as a non-inverting op-amp
configuration because here the output
and input are in a phase. so now for this
configuration let us find the relation
between this output and the input
voltage. so now before we find the
relationship between the output and
input voltage let me redraw the same
circuit so that you can have a better
idea about the circuit. So here I have
redrawn the same circuit in a different
way. So here we have applied the input to
this non-inverting input terminal and we
have a feedback resistance Rf between
the output and the inverting input
terminal. And if you see here the one end
of this resistance R1 is connected to
the resistance Rf and another end of
this resistor R1 is connected to the
ground . So if you see here the fraction
of output voltage is going as a feedback
to this inverting input terminal.So let
us say here at this point the voltage is
Vx and this Vx voltage is going as a
feedback to this inverting input
terminal. Now using the voltage divider
rule we can say that this voltage Vx
that is equal to R1 divide by R1 plus Rf
into Vout .So this voltage will be going
as a feedback to this inverting input
terminal. so at this point also the
voltage will be equal to Vx.  Now in the
last video we had seen that whenever we
are using this op-amp in a negative
feedback configuration then there will
be a virtual shot between the both the
input terminals of this op-amp. It means
that whatever
voltage that appears at one end of this
input terminal, the same voltage will
appear at the another end of the input
terminal. It means that V Plus that is
equal to V minus and that is because of
this virtual shot between this
non-inverting and the inverting input
terminal.So here in this configuration
we are applying the input voltage to
this non-inverting terminal that means V
Plus that is equal to Vin so because of
this virtual shot at this inverting
input terminal also the voltage should
be equal to Vin, that means V minus
should be equal to Vin. And we know that
V minus that is equal to Vx. So we can
write this input voltage Vin that is
equal to R1 divide by R1 plus Rf into Vout.
Or we can say that V out divide by Vin
that is equal to R1 plus Rf divide by R1.
That is equal to 1 plus RF divide by R1. So
this will be the closed loop gain of
this non-inverting op-amp configuration.
So in non-inverting op-amp configuration
the relation between the output and
input is equal to 1 plus RF divide by R1.
So in this non-inverting of op-amp
configuration also just by controlling
the value of this RF and R1, we can
control the gain of this op-amp.
But in this non-inverting op-amp
configuration, the output and input will
have a same phase. so let's say if I
apply 1 volt of DC signal at this
non-inverting input terminal and if I
take value of R 1 as 1 kilo ohm, then my
gain of this op-amp will be equal to 1
plus 2 divided by 1, that is equal to 3.
So at the output I will get 3 volt of DC
signal. Or instead of DC voltage let's
say if I apply a 1 volt of sinusoidal
signal and if I have a value of RF as 2
kilo ohm and R1 as 1 kilo ohm then at the
output I will get a 3 volt of amplified
AC signal which is having a same phase
with respect to input signal. So in this
non-inverting op-amp 
configuration just by controlling the value
of this feedback resistance RF and R1, we
can control the gain of this op-amp and in
this configuration the output and input
are in a phase. so this is all about the
non-inverting op-amp configuration. so
now here the question is what is the
advantage of this non-inverting op-amp
configuration over this inverting op-amp
configuration because if you see both
the configurations in both the
configurations we can control the gain
using this feedback resistance RF and R1.
so let us find out some of the
advantages of non-inverting open
configuration over this inverting op-amp
configuration. Now one of the obvious
advantage of this non inverting open
configuration is that the output and
input both are in a  phase. while in case of
this inverting op-amp configuration,
there is a 180 degree phase shift
between the output and the input voltage.
Apart from this, if you see this
non-inverting op-amp configuration then
in this configuration the input
impedance of the circuit is very high
and if we consider the ideal op-amp
then in that case the input impedance of
the circuit is infinite. While in case of
this inverting op-amp configuration, the
input impedance depends upon the value
of R1. So if we consider the ideal op-amp,
then in that case the input impedance of
this inverting op-amp will be equal to
R1. So now let us derive the expression
for this input impedance in case of this
inverting as well as the non-inverting
op-amp configuration. So now if you see
the inverting op-amp configuration then
in this configuration the input
impedance is the impedance that is seen
through this voltage source Vin or in
another words we can say that the input
impedance of this configuration is equal
to the input voltage divided by the
current that is going into the circuit.
So let us say the current Iin is going
into this circuit . So now here the ratio
of input voltage divided by this input
current will gives us the input
impedance of this configuration. now we
know that in this inverting op-amp
configuration, this node will act as a
virtual ground because here this
non-inverting terminal is already
grounded. so we can say that this Iin
that is equal to Vin divide by R1. Or we
can say that R1 that is equal to Vin
divided by  Iin. Now we know that Vin
divided by Iin is equal to input
impedance. So we can say that the input
impedance of this inverting op-amp
configuration is equal to R1. so the
input impedance of this configuration
depends upon the value of R1. so let's
say if value of rR is very low then in
that case the input impedance of the
circuit will be low. so similarly let us
find the input impedance of this
non-inverting open configuration. So in
this non-inverting op-amp configuration
also the input impedance is the
impedance that is seen through this
voltage source Vin. So let us once again
assume that current that is being
supplied by this voltage source is Iin.
And the ratio of this V in divided by I in
will gives us the input impedance of
this non-inverting op-amp configuration.
So now if we consider this open as ideal
op amp then there will not be any
current that is going into this
inverting and the non-inverting
terminals. Or we can say that this input
current Iin that is equal to
approximately zero and hence we can say
that the input impedance is equal to
infinite. so now in any circuit whenever
we have a very high input impedance then
that will ensure that the source that is
connected to that circuit will not be
get loaded. so let us understand this
point. so let us say we have one voltage
source Vs and it is having source
resistance RS. And it is connected to one
circuit, and this circuit has an input
impedance Zin. so now whenever the value
of this input impedance is comparable to
the value of this Rs then in that case,
the voltage that appears across the two
terminal of the circuit will be equal to
Z in divide by Zin plus RS into V s. And as Zin
is equal to RS then the value of voltage
V will be equal to Vs by 2. so only half
of the voltage will appear across this
circuit. so in any circuit the value of
input impedance should be very high, so
that whatever voltage that is being
applied to that circuit will entirely
appear across that circuit. so in this
case of non-inverting op-amp configuration,
as the input impedance is approximately
equal to infinite or in practical case it
is very high so whatever voltage that is
applied to that circuit will entirely
appear across that circuit. so that is
the advantage of this non-inverting open
configuration. Now in this non-inverting
op-amp configuration, let us say we have
Rf  that is equal to 0 and R1 that is
equal to infinity. Then the circuit will
look like this. so this circuit is known
as the open as a voltage follower
circuit or open as a buffer. so here we
have shorted this output terminal with
this inverting open terminal. so at this
point voltage will be equal to Vout and
because of the feedback V minus that is
equal to V plus or we can say that
because of the feedback we have a
virtual shot between this inverting and
the non-inverting op-amp terminals. so we
can say that V minus will be equal to Vin, or we can say that Vin will be equal
to Vout.  so it means that whatever
voltage that is applied to this
non-inverting op-amp terminal, the same
voltage will appear at the output of
this op-amp.
So we can say that the output voltage
follows the input voltage and that is
why this circuit is known as the voltage
follower circuit. So the characteristic
of this circuit is that the input
impedance of the circuit is very high or
ideally it is infinite and the output
voltage will be equal to input voltage.
so because of these two characteristics
this circuit is also known as the buffer
circuit because it will pass whatever
input that is coming to it as it is and
it will provide the very high input
impedance. So using this buffer circuit,
we can isolate the two different
circuits and at the same time we can
ensure that whatever voltage that is
appearing at the output of the one
circuit will appear at the input of the
another circuit, and that is particularly
useful when we have a low input
impedance in one circuit. So I hope in
this video you understood the
non-inverting op-amp configuration and the
advantages of this non-inverting op-amp
configuration over the inverting op-amp
configuration and how to design the
voltage follower or the buffer
circuit using this op-amp. so if you have
any question or solution do let me know
in the comment section below. if you like
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