Op-Amp: Operational Amplifier Basics and Applications

This page covers the basics of the Operational Amplifier (op-amp), its use as an inverting amplifier, non-inverting amplifier, summing amplifier, voltage comparator, and more. “Op-amp” stands for Operational Amplifier. Originally, op-amps were built using discrete components and were used in analog computers for functions like addition and division.

Nowadays, operational amplifiers are available in IC (Integrated Circuit) form and are used in a wide range of applications. A common use is as a high-gain DC and AC voltage amplifier. A typical op-amp device consists of about 20 transistors and a few resistors and capacitors.

Op-amp devices have the following basic properties:

Op-Amp Properties

• A very high voltage gain: approximately $10^5$
• A very high input impedance: typically about $10^6$ to $10^{12}$ Ohms
• A very low output impedance: About 100 Ohms

The following table shows the ideal and practical values of different op-amp properties.

Op-Amp Specifications

Operational Amplifier Working

As shown in the figure, the op-amp has two inputs and one output. The non-inverting input is marked with ”+” and the inverting input with ”-” on the amplifier symbol.

The figure depicts a TL081C or 741 op-amp in IC form with pin details. The $+/-V_s$ voltage range is from $+/-5V$ to $+/-15V$. Basically, an op-amp is a differential amplifier that amplifies the difference between the voltages $V_1$ and $V_2$ applied at its inputs.

There are three conditions, and the appropriate output is produced based on these:

• If $V_2 > V_1$, then $V_o$ is positive.
• If $V_2 < V_1$, then $V_0$ is negative.
• If $V_2 = V_1$, then $V_o$ should be zero.

In general, the output is given by:

$V_o = A_o \times (V_2 - V_1)$

Where, $A_o$ is the open loop voltage gain.

As mentioned, there are many uses for op-amps, including:

• Inverting amplifier
• Summing amplifier
• Non-inverting amplifier
• Voltage comparator
• Power supply applications
• Integrated circuits for special applications, such as audio pre-amplifiers, audio power amplifiers, and high-frequency amplifiers.