How to build an Inverting Operational Amplifier

Welcome to another exciting Tutorial from Aaenics. Still on the linear electronics series and if you’ve been following for a couple of weeks now you’ll know we’ve being playing around the operational amplifier, the LM358 dual op-amp to be specific.
Today in this wonderful tutorial, we will learn briefly what an inverting op-amp is, and how to actually build one for your self .

What is an Inverting Operational Amplifier?

An inverting Operational Amplifier circuit like any other op-amp circuit can or will take a small signal you input, amplify it and then give you a larger output. The special thing here is that, the output signal of the inverting amp will be out of phase with the input signal. Maybe you will be asking what it means for one signal to be out of phase with the other, what this means in simple English is that, one signal at a particular time will be completely opposite in direction to the other signal.

So for example, if my input is 0.3V DC, and my inverting amplifier has a gain of x(-10), my output will be -3V, which you can see that though it has been amplified ten times, it is opposite in polarity to the original 0.3V. So the work of the inverting amp here is to amplify and give me the opposite polarity of my input. As simple as that. Also if the input signal was to be -0.3v, the amp would have given out 3V.

 Okay so from here we are going to build an inverting amp circuit that will give us a practical understanding of inverting amp circuits.

This is a schematic diagram of what is to be built.

This is also a virtual breadboard view of the circuit.

The first part of the circuit is simply a dual power supply which we learnt how to build in the previous tutorial, you will need it to power your op-amp. Here is what you need to build it.

  • Power Supply, preferably a 9v battery.

  • 2 Resstors of the same value.

 

  • Two capcitors of the same value.

  • A few jumper wires.

The Above components will be used to build the dual polarity power supply for the op-amp ic.

The rest below is needed to build the inverting amp it self.

  • 1 potentiometer

  • The op-amp Ic to be used. The LM358 dual op-amp is used in our case.

  • Select 2 LEDs of different colors
  • Two 220ohm resistore for Rf and Rin

  • Okay so we are going to build an inverting operational amplifier circuit. Inverting amps are used in a whole lot of applications or specific projects but in this tutorial we are aiming at building a general response inverting amp circuit that will toggle two different LEDs  depending on the kind of output signal we get.
  • From the schematics, you can see LED1(green) and LED2(red) are connected in parallel but opposite to the other. One end of the Parallel structure is connected to the output(PIN 1) of the LM358 IC. and the other end of the two LEDs is connected to ground(0 volts) through a series resistor.
  • The non inverting Input(that is pin 3) of the IC is also connected to ground(0 volts). Note that the ground(0 volts) is in the middle  of the voltage divider of the power supply.
  • Since no feed back resistor is used in this circuit, the gain of the amplifier is infinity.
  • A potentiometer takes input from the +vcc and –vcc of the supply and its middle pin is connected to the input of the op-amp. It is this potentiometer that will control or vary the input signal.
  • After establishing all connections you will realize that, when the potentiometer is tuned to one end (let say the positive), the op-amp’s output will be negative, hence turning on the reverse biased LED while the forward biased one remains constant. The opposite will happen when the potentiometer is turned to the other end(the negative end.) When it is turned to the negative end, the op-amp’s output will be positive and hence the forward biased resistor will come on while the other is turned of.

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