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Op-Amp, Operational Amplifier

This page on op-amp cover Operational Amplifier basics, its use as inverting, non inverting, summing amplifier, voltage comparator and more.

op-amp stands for Operational Amplifier. Earlier op-amps were made using discrete components. They were used in analog computers for various functions such as addition, division and so on. Now-a-days operational amplifiers are available in IC form. They are used for many applications. The popular among them is; as high gain DC and AC voltage amplifier.

Typical Op-amp device consists of 20 transistors and few of resistors as well as capacitors. Op-amp devices will have following basic properties.

Op-Amp properties

•  A very high voltage gain: about 105
•  A very high input impedance: typically about 106 to 1012
•  A very low output impedance: About 100 Ohm


op-amp,operational amplifier

Following table mentions values of different properties of OP-AMP.

Specifications Ideal Value Practical Value
Voltage Gain 106
Input resistance 106Ω or 1MΩ
Output resistance zero 10Ω to 100Ω
Bandwidth 106Hz or 1 MHz
CMRR 106 or 120 dB
Slew Rate 80 V/µsec

Operational Amplifier Working

As shown in the figure, there are two inputs and one output of op-amp. Non inverting is marked as + and inverting is marked as - as shown on the amplifier symbol. Figure depicts TL081C or 741 op-amp in IC form with pin details. +/-Vs has range from +/-5V to +/-15V.

Basically an op-amp is a differential amplifier which amplifies difference between voltages V1 and V2 provided at its inputs. There are three conditions and based on these appropriate output is produced as mentioned below.

•  If V2>V1, then Vo is positive
•  If V2<V1, then V0 is negative
•  If V2=V1, Vo should be zero

In general, output is given by,
Vo=Ao X (V2-V1),
Where, Ao is the open loop voltage gain.

As mentione there are many uses of op-amp as mentioned below.
•   Operational amplifier can be used as inverting amplifier.
•   Op-amp can be used as summing amplifier.
•   Op-amp can be used as non inverting amplifier.
•   It can be used as a voltage comparator.
•   It can be used in a power supply.
•   It can be used in a integrated circuit for special applications, such as audio pre-amplifier, audio power amplifier and high frequency amplifier etc.

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