Op-Amp (Operational Amplifier) Practice Problems

Josh stated in the op-amp intro tutorial that operational amplifiers (op-amps) are really quite easy because of the two golden rules of op-amps but didn't give any examples of how to use those rules. In this tutorial, Josh goes through three practical operational amplifier practice problems to show how to utilize those rules to simplify circuit analysis with op-amps.

Parts of the video:
0:00 Introduction
0:30 Review of the 2 Golden Rules
0:55 First Practice Problem
4:45 Second Practice Problem
7:33 Third Practice Problem
10:27 Summary
11:54 The toast will never pop up

CircuitBread is joining the fight to help people more easily learn about and use electronics. With an ever-growing array of equations, tools, and tutorials, we're striving for the best ways to make electronics and electrical engineering topics more accessible to everyone. Come learn electronics with us!

Connect with CircuitBread:

[memirandawong]

Mistakes make this learning experience even more real!

[kaleevans]

Best description on op amps I've found yet... And I've looked around a lot. Subscribed! Thank you sir🙏🏾

[sirhuman]

amazing explanation and bringing us in your mind to let us learn how to think while solving problems. thank you!

[zjmullan]

great video man, reminded me of how the ideal op-amp calculations work after almost a year of not doing them

[manekineko]

very clear explanation. Thank you for taking the time out of your life to do this.

[chuckbenedict]

I was confused about the sign of example 1 until I realized equation 2 should be (0-V0 ) = (50 microamps)(25K ohms), yielding V0=-1.25V. The voltage drop across the 25K resistor is 0-V0, which is the tricky part. In example 2, its strange to think about negative resistance (IMHO), so I'd suggest R = -V0/i1. It's the same math, just seems to better reflect what is happening in the circuit. In example 3, I believe the equation to compute V0 should be 2-V0 = (1mA)(5K) = -7V.

[memirandawong]

Truth be known, I'm obsessed with this device (and the transistor, LOL). I was a circuit board designer (mechanical layout of circuits) for years and was always impressed by the many uses I've see with op-amps. This video instills great confidence! Thank you for the time you put into making these videos!

[INONAuto]

i am writing on the 9th nov, you saved me from lot of anxiety

[menkveld]

I never understood anything about those things. Seeing those 2 rules being applied made it all click. Thanks!

[sunrayseducation]

Sir, thank you for this explaination and including the mistakes that I do.

[monfry]

All understandable in a easy way ! Thanks good buddy !

[andrewpervez]

Excellent and straight forward. Thank you.

[remcooosten]

Nice video, thanks.
In the last example, I think you have 1mA flowing through 2kΩ + 5kΩ, which gives us 1mA * 7kΩ = 7V

[wediadi]

Another method of calculating Vout using the gain of the opamp. Gain=Vout/Vin, since same current I1 is flowing through both resistors, Vout=Gain*Vin=2.5*0.5=1.25V. The sign of Vout should be negative because the input on the inverting port of the opamp is higher than that on the non-inverting. So Vout=-1.25V

[Zzzzzzzzz]

Seeing you get a bit lost in the solution made me feel slightly better about myself, lol. But it was well explained, and I've subscribed to your channel.

[gkdresden]

These were more the theoretical problems with op amps. The practice problems are much different, like:

- the input current is not really zero, especially not in the case of bjt op amps
- in certain cases you need to take care of the input offset voltage, especially in the case if you use op amps as comparators.
- when you operate with pulse voltages at the inputs you have to make sure, that the operating voltage stays stable, even if you need to operate with a certain capacitive load at the output. So you have to use stabilization capacitors between the Vcc and GND pin of your op amp or two of them if you operate with a symmetrical operating voltage. Otherwise your circuit will fall into oscillations
- the nonlinearities of the op amp input circuit can demodulate rf. So if you want to build up an audio amplifier it is sometimes necessary to use a low pass filter at the signal input to suppress rf interferences to avoid that you have some closely located radio station music in the background of your audio amplifier output.
- if you need higher voltage amplifications (for microphone or phono signals), you need to make sure, that the gain bandwidth product doesn't compromize your amplifier at the higher frequencies. Also the input referred voltage offset and noise voltage become important in such application cases.

etc.

[armisol]

how do u calculate in the third practice problem the 2 volts. cause i dont understand that part

[michaeldrake]

This doesn’t have nearly enough views! I would literally lose sleep over how op-amps worked and circuit analysis in general. Thanks to this I’ll sleep peacefully now.


I really feel that the theory for electronic circuits is made overly complicated by those that are teaching this but the way you’ve explained this was straight to the point!

Perhaps that’s something to do with limited application of their skills outside of an academic course.

I think it’s brilliant you leave your mistakes in because, even though it’s simple algebraic operation still so easy to make a mistake. Seeing the reasoning is good

[wediadi]

My question is why do'nt we consider the 25K resitor when we are calculating I1? Isn't the same current I1 flowing through both resistors?

[WalyB]

Putting the formula their gives your brain more power to calculate other stuff. Basically like working memory on a pc. Weirdly enough we are wired quite similarly