Voltage Follower, Voltage Follower in Voltage Divider Circuits, Advantages of Voltage Follower, Applications of Voltage Follower

1. Presented by
Dr. R. RAJA, M.E., Ph.D.,
Assistant Professor, Department of EEE,
Muthayammal Engineering College, (Autonomous)
Namakkal (Dt), Rasipuram – 637408
MUTHAYAMMAL ENGINEERING COLLEGE
(An Autonomous Institution)
(Approved by AICTE, New Delhi, Accredited by NAAC, NBA & Affiliated to Anna University),
Rasipuram - 637 408, Namakkal Dist., Tamil Nadu.
Voltage Follower

2. Voltage Follower
 Voltage follower is an Op-amp circuit whose output voltage straight away
follows the input voltage. That is output voltage is equivalent to the input
voltage. Op-amp circuit does not provide any amplification. Thus, voltage gain
is equal to 1. They are similar to discrete emitter follower. The other names of
voltage follower are Isolation Amplifier, Buffer Amplifier, and Unity-Gain
Amplifier. The voltage follower provides no attenuation or no amplification but
only buffering. This circuit has an advantageous characteristic of very high
input impedance.
 This high input impedance of voltage follower is the reason of it being used in
several circuits. The voltage follower gives an efficient isolation of output from
the input signal. The circuit of voltage follower is shown below.
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3. Contd..
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4. Contd..
 For understanding this concept and the use of voltage follower, we can go
through the following examples.
 First, we can consider a circuit of low impedance load and a power source is
feeding it shown below. Here, a large amount of current is drawn by the load
due to the low resistance load as explained by Ohm’s law. Thus, the circuit
takes a large amount of power from the power source, resulting in high
disturbances in the source.
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5. Contd..
Next, we can consider that we are giving the same power to the voltage follower.
Because of its very high input impedance, a minimal amount of current is taken by
this circuit. The output of the circuit will be same as that of the input due to the lack
of feedback resistors.
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6. Contd..
Voltage Follower in Voltage Divider Circuits
 In every circuit, voltage is shared or distributed to the impedance or resistance
of the connected components. When Op-amp is connected, the major part of
voltage will drop across it due to high impedance. So, if we use voltage
follower in voltage divider circuits, it will let adequate voltage to be supplied
across the load.
 Let us go through a voltage divider circuit with voltage follower as shown in
the figure below.
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7. Contd..
Here, the voltage divider is in the middle of two 10 KΩ resistors and the Op-amp.
This Op-amp will offer input resistance of some hundreds of megaohm. Now, we can
assume it to be 100 MΩ. So the equivalent parallel resistance will be 10 KΩ || 100
KΩ.
So, we get 10KΩ || 10KΩ. We know that the voltage divider which comprises of two
similar resistances will offer exactly the half of the voltage in the power source. We
can prove it using voltage divider formula as follows:
Thus, this 5V will drop across the 10KΩ resistance in the top and 5V drop across the
resistance 10KΩ in the bottom and the load resistance 100Ω (since 10 KΩ||100 Ω,
same voltage will drop in resistors which are in parallel).
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8. Contd..
 From this, we have seen how the Op-amp works as a buffer for getting the
desired voltage to the connected load. In the same circuit with the absence of
voltage follower, it will not work due to the lack of supply of sufficient voltage
across the load.
 Mainly, voltage follower is implemented in circuits for two reasons. One is
isolating purpose, and the other is for buffering the output voltage from an
electrical or electronic circuit to get the desired voltage to the connected load.
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9. Contd..
Advantages of Voltage Follower
 Provides power gain and current gain.
 Low output impedance to the circuit which uses the output of the voltage follower.
 The Op-amp takes zero current from the input.
 Loading effects can be avoided.
Applications of Voltage Follower
 Buffers for logic circuits.
 In Sample and hold circuits.
 In Active filters.
 In Bridge circuits via transducer.
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10. Thank You
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