In this script, we will discuss the most important topic of Operational Amplifier, we have already discussed this topic in another script

Now we will discuss

  • Noninverting Amplifier
  • Voltage Follower 
  •  Math Problem

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Noninverting Amplifier

A noninverting amplifier is an op amplifier circuit designed to provide a positive voltage gain. A noninverting amplifier connection is more widely used because it has better frequency stability. To determine the voltage gain of the circuit, we can use the circuit diagram, represent shown in Figure 1.1

Figure 1.1: Noninverting Amplifier

In this noninverting amplifier, the input voltage v1 is applied directly at the noninverting input terminal and resistor R1 is connected between the ground and the inverting terminal. We are interested in the output voltage and voltage gain. We know that an ideal op-amp “No current flows into the input terminal” of the amplifier and that “V1 always equals V2”. This was because the junction of the input and feedback signal ( V1 ) is at the same potential.

So, Applying the KCL at the inverting terminal gives

$${i1 }={i2} $$

$${0-v1\over R1 }={v1-vo\over Rf} $$

$${-v1\over R1 }={v1\over Rf} - {vo\over Rf}$$

$${vo\over Rf }={v1\over Rf} + {v1\over R1}$$

$${vo\over Rf }={v1({1\over Rf}+{1\over R1})}$$

$${vo}={v1({Rf\over Rf + R1})}$$

$${vo}={v1(1 + {Rf\over R1})}$$

$${Av}={vo\over v1} = { (1 + {Rf\over R1}) }$$

Here Av = is voltage gain, which does not have a negative sign. Thus the output has the same polarity as the input. So we can say a noninverting amplifier is an op-amp circuit designed to provide a positive voltage gain.


Voltage Follower 

We notice that the gain depends only on the external resistors. If feedback resistor Rf  0 (short circuit) or R1  (open circuit) or both, the gain becomes 1. Under these conditions (Rf  0 and R1  ), the circuit in Fig. 1.1 becomes that shown in Fig. 1.2.which is called a voltage follower (or unity gain amplifier) because the output follows the input. Thus, for a voltage follower

Figure 1.2: Voltage follower

V0 = v1

A circuit has a very high input impedance and is therefore useful as an intermediate-stage (or buffer) amplifier to isolate one circuit from another. The voltage follower minimizes interaction between the two stages and eliminates interstage loading.


Problem-1

Calculate the output voltage vo?


Solution:  Applying KCL at node a,

$$ {6-va \over 4} = {va-vo \over 10} $$

$$ { But va= vb =4, and so,}$$

$$ {6-4\over 4} = {4-vo \over 10} $$

$${5 = 4-vo} $$

$${vo =  -1v} $$