Electronic Basics #21: OpAmp (Operational Amplifier)

if you ever used Isis in your projects then you might have noticed that most of them contain a triangle-shaped component in their simplified schematic those triangles are called operational amplifiers also known as op amps and since they are very common and useful for analog and digital electronics I have used them before in a couple of different projects so in this video I will show you what op amps are capable of doing and how to handle them properly let's get started first off you can get opened by sees in a dual inline package with evil 14 pins that usually features four bamps and sides or eight pins that features two or only one op-amp insides as an example I will use the popular LM three 5/8 jewel of amp whose ground pin I connected to zero volts and V plus pin to twelve volts which is fine because it does not exceed the single supply range of the IC next I apply the voltage of plus 1 volts to the plus inputs aka the non-inverting input of the op amp as well as a 10 kilo ohm pulldown resistor to set the reference voltage to ground then I created a voltage divider consisting of a five-point 1 kilo ohm and a 1 kilo ohm resistor in this constellation between the output pin and the negative inputs aka the inverting input as a result I received the voltage of six point one volts at the outputs which equals an amplification factor of six point one but why well the first golden rule of op amps gives us the answer the output of an op amp will always attempt everything to keep the voltage difference between the inputs at zero volts that means there needs to be the same voltage drop across R 1 as the input voltage be in if we now add the voltage divider formula to this and the fact that the gain is the output voltage divided by the input voltage we finally get the classical formula for the gain of a non-inverting op-amp such a circuits can be used to amplify the signal from a sensor like for example a PT 100 temperature sensor or the AC signal from an electret microphone this one creates maximum voltage peaks of around 100 Mille volts ac a which I can now easily amplify with a gain of 48 by changing the 5 point 1 kilo ohm resistor to 47 kilo ohm but when we observe the outputs we notice another problem only the positive AC voltage got amplified because the output voltage swing is limited to the supply voltage that means we would need positive and negative 12 volts to successfully amplify the comp AC signal which I can demonstrate with my lab bench power supply but since that is normally not an option we could also add a DC offset to the past inputs this way the complete amplification does work to some extent but because we are amplifying a DC voltage as well this time we hit the 10.8 board output limits of the op-amp pretty quickly y 10.8 volts instead of the 12 volts of the supply voltage well there is no perfect op-amp the ideal one would also have an infinite high input impedance and thus no input current could flow which is not true it would have an output impedance of zero which means we could draw as much current as we want which is not true and the list goes on and on but on the other hand that does exist red rail op amps that can achieve an output voltage which equals their supply voltage and as long as you don't want to create precision circuits such non-ideal parameters do not matter that much but let's get back to the microphone amplifier a more suitable circuit for this task would be an inverting op-amp in this constellation the pass input is connected to ground which means the minus inputs must have a voltage potential of zero volts as well and since the second golden rule of op amps says that the input draws no currents the current through r1 must be the same as through r2 this results in the classical formula for the inverting op-amp circuits and by connecting the pass inputs to a DC offset voltage instead of ground we can amplify the microphone AC signal completely year without amplifying any DC voltage the output signal can then be connected to a speaker but just like I said before because of the small maximum output currents the sound is almost unhittable the last important rule when working with op amps is that when no feedback is attached between the outputs and inputs the output will either jump up to the maximum output voltage when the plus inputs has a higher voltage than the minus inputs on reverse the outputs will jump down to the minimum output voltage when the minus inputs has a higher voltage and the person puts the reason is the high open-loop gain of the op-amp and such a configuration is called a comparator and there also exists separate comparator C's that achieve a faster response time than the average op-amp and with those three golden rules Minds you can understand and build constant current sources and loads voltage followers integrators differentiators inverting non-inverting difference and summing amplifiers Schmitt triggers and the list goes on and on as you can see it is a versatile components and there's much more to say about it and what I just presented but that is a subject for another video until then don't forget to Like share and subscribe consider supporting me your through patreon to keep such videos coming stay creative and I will see you next time

Channel: GreatScott!

Views: 966,463

Keywords: opamp, op-amp, opamps, op-amps, op amp, operational amplifier, tutorial, how to, explain, basic, basics, rule, golden rule, inverting, non inverting, comparator, electronic, electronics, greatscott!, greatscott, mic amp, electret mic, microphone, AC

Id: kqCV-HGJc6A

Length: 6min 0sec (360 seconds)

Published: Sun May 22 2016