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What is Operational Amplifiers, Uses, Operations, Feedbacks

What is Operational Amplifiers (Op-amp)

Operational amplifiers (op-amp) are very useful integrated circuit amplifiers that can be used to realize an incredible number of electronic circuit designs.

Uses of the Operational Amplifiers (Op-amp)

The various electronic circuits we can use the op-amp to design include but not limited to the following:

  1. Amplifiers circuits
  2. Voltage regulators circuits
  3. Current to voltage converters
  4. Voltage-to-current converters
  5. Oscillators or oscillator circuits
  6. Mathematical circuits (Adders, subtractors, multipliers, differentiators, integrators, etc.)
  7. Waveform generators
  8. Active filters
  9. Active rectifiers
  10. Peak detectors
  11. Sample and hold circuits

The list goes on. Operational amplifiers are one of the electronic components that is very useful to the electronic circuit designer, with an op-amp, you can achieve a lot of designs.

Operational Amplifier Circuit and Pin Configuration

Below is the image of a typical operational amplifier circuit and pin configuration symbols.

Operational Amplifier symbol
Figure 1. Operational Amplifier Symbol
Operational Amplifier Pin Configuration
Figure 2. Operational Amplifier Pin Configuration

A typical operational amplifier integrated circuit is the 741 operational amplifier IC, the pin configuration of the IC is as shown in Figure 2 above.

The IC has 8 pins. Out of these 8 pins, one pin is not used at all, while 2 pins are rarely used. The pins commonly used are:

  • Pin 7: positive voltage supply
  • Pin 4: negative voltage supply
  • Pin 6: output pin
  • Pin 2: inverting input
  • Pin 3: non-inverting input

Figure 1 above is the circuit symbol of the Operational Amplifier. When drawing a an Operational Amplifier circuit, use the symbol in Figure 1.

Operation of the Operational Amplifier

Operation of the operational amplifier is very simple, as an integrated circuit, you must connect power to the op-amp before it does its work in the circuit. See image below.

Op -amp with supply voltages
Figure 3. Op -Amp With Supply Voltages

Once you have connected power to the operational amplifier as shown above, the Operational amplifier will be ready to go into operation. If you then connect input voltages to the inverting and non-inverting terminals, the terminal with higher input voltage will cause the output of the op-amp to saturate towards that terminal with higher input voltage.

Therefore, if the voltage connected to the inverting input is higher than the voltage connected to the non-inverting input, the output will produce a negative voltage, and if the voltage connected to the non inverting input is higher than the voltage connected to the inverting input, the output will produce positive voltage.

Same thing will happen if you supply voltage to one terminal and ground the other terminal. In this case, the output produces a voltage that saturates towards the terminal that is not connected to ground.

Op-Amp With with Input Voltages
Figure 4. Op-Amp With with Input Voltages

With the circuit in Figure 4 above, if we make the voltage in pin 3 greater than the voltage in pin 2, the output at pin 6 will produce positive voltage, see image below.

Op-Amp Producing Positive Output Voltage
Figure 5. Op-Amp Producing Positive Output Voltage

While if we make the voltage at pin 2 greater than the voltage at pin 3, the output at pin 6 will produce a negative voltage, see image below.

Op-Amp Producing Negative Voltage
Figure 6. Op-Amp Producing Negative Voltage

If the work of the operational amplifier is to produce outputs that switch between positive and negative voltages depending on the nature of the input voltage, then it does not look very impressive; Nevertheless, the strength of the op-amp lies on what we call feedback.

What is Feedback in Operational Amplifiers?

Feedback simply means sending some portions of the output voltage of the operational amplifier back to the input. It is with the help of this feedback that we are able to realize different kinds of electronic circuits that we talked about with the operational amplifier.

Types of Operational Amplifier Feedbacks

There are two main types of feedbacks in operational amplifier

  1. Negative feedback
  2. Positive feedback

What is Negative Feedback in Operational Amplifier?

Negative feedback Involves sending back part of the output of the operational amplifier to the inverting input terminal. This can be done through a resistor or capacitor or any other electronic component of choice. Show below is simple negative feedback circuit.

Operational Amplifier Negative Feedback Circuit
Figure 7. Operational Amplifier Negative Feedback Circuit
  • Vin = Input Voltage
  • Iin = Input Current
  • Rin = Input Resistance
  • If = Feedback Current
  • Rf = Feedback Resistor
  • Vout = Output Voltage

Sometimes, for some design reasons, it can be done without a resistor, when an op-amp is connected in a design to have a negative feedback without some other components, the circuit realized is called a unity gain amplifier or buffer. The image below is an operational amplifier connected in negative feedback as a unity gain amplifier or buffer. We shall discus more about negative feedback as we proceed.

Unity Gain Amplifier - Buffer Amplifier
Figure 7. Unity Gain Amplifier – Buffer Amplifier

NB: The power supply pins are hidden in the diagram above.

What is Positive Feedback in Operational Amplifier?

Positive feedback on the other hand involves sending portions of the output voltage back to the non-inverting input of the operational amplifier. The positive feedback is not used very often in designs, but it has great application in the design of oscillators. We shall also discuss the positive feedback in details as we proceed in the tutorial.

Operational Amplifier Positive Feedback Circuit
Figure 8. Operational Amplifier Positive Feedback Circuit
  • Vin = Input Voltage
  • Iin = Input Current
  • Rin = Input Resistance
  • If = Feedback Current
  • Rf = Feedback Resistor
  • Vout = Output Voltage

NB: If you connect the input voltage to the inverting terminal, then the output will be invert, and if you connect the input voltage to the non-inverting input terminal, the output will not be invert. These and more we shall see later on.

In the next tutorial. We will learn how an Operational amplifier works. if you have any questions, let me know in the comment section.

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