Op Amps

I just need a general explanation about op amps. I have attempted to read a few articles online about this but I don't seem to understand it. It would extremely help if I could have a simplified explanation.

Op amps have 2 inputs, + & -.
The op amp tries to drive the output so that the input & output match - feedback from the output to one of the input pins provides a path for that.
It there is no feedback, the opamp acts as a comparator - the output will go to the positive power rail if the + input is a higher voltage than the - input; the output will go to the negative power rail if the - input is a higher voltage than the + input. See the LM358 comparator for the autovoltage select and the LED driver from D13 for examples of that.

Everything is feedback driven. If the feedback is just resistors, you can have an amplifier with some gain. The signal may be inverted or not inverted from the input. Summing amplifiers use additional resistor to add signals together - maybe two AC signals, maybe one AC and some DC offset.
Sometimes small caps are used with the resistors take out high-frequency oscillation that can occur, 'stabilizing' the circuit.
If the feedback involves other components (capacitors usually), it may be designed as a filter, letting low frequencies thru (low pass filter), high frequencies (high pass filter) (think bass & treble tone knobs), neither high nor low, but something in between (band pass filter) - think audio multi-band equalizer), or high and low but Not something in between (notch filter, like for blocking 60Hz hum from power lines).
Other uses are just as buffers, no gain provided but stronger current drive can be made available.

Sometimes diodes are added to introduce distortion - guitar fuzz box!

Did you have a specific question?

Note this feedback is negitave feedback. This means it is reducing the gain to a controlable level. Without this the gain is in the order of a million or so. You can only have a voltage output up to the power supply rails, and normally not even that much. So without feedback the smallest interfering signal sends the output crashing to its maximum.

There are some circuits that actually use positive feedback, in these the output is always at the rail voltage, either positive or negitave rail. This is used to get hysteresis into an analogue comparator.

I don’t know if this is one of the articles you attempted to read but I’ve found this website pretty excellent for basic explanations of a whole bunch of topics.

It seems like Op Amps aren’t very intuitive to a lot of people. I’m an electrical engineer and, even after a whole semester of “introduction” to them at university, a lot of my classmates struggled.

If you’re only interested in how to use them for simple circuits, you will most likely be using them in the most basic inverting or non-inverting amplifier configuration. Both arrangements only use two resistors so just memorising the connection arrangement and transfer function equations for those two will get you through 99% of your tasks.

Hi
It’s worth your time and energy to understand Operational Amplifiers. They are actually the most predictable and controllable amplifiers.

George Philbrick was one of the main people who figured this out in the 50’s. Some of us were There…

In the 60’s some of us were able to do things that were previously very difficult like sending “Transmitter Readings” from Broadcast transmitters to automatic recording devices. We looked like Gurus, but actually OpAmps made it easy. We bought OpAmps from Philbrick in plastic modules and Made Stuff that worked.

There are many sources of information but nothing is more important than hooking stuff up and making it work YOURSELF, and figuring out WHY when it doesn’t work…

Even before my time (which is REALLY Ancient History) there were Opamps. Made with Vacuum Tubes! . Don’t believe it? Look at THIS! . Maybe only those of us who have a little drawer labelled “Octal Sockets” can believe this :slight_smile:

Walt Jung did a great job of showing how to APPLY opamps to all kinds of designs; See:
Opamp Applications HERE

MIT has a nice Applications chapter online HERE…

There seems, to me, to be a Thing about ANALOG. Maybe some of these guys were just internally Analog. Along with Walt Jung, I learned so much from Bob Widlar, Bob Pease, and Arne Hansen (Who proved to me at IBM that I needed LESS bypass capacitors rather than more. BODE Whatever.

Just DO IT, you’ll be glad you did.

Hi,

The simplest explanation of an op amp is a VCVS which stands for “voltage controlled voltage source”. That has two inputs + and - and two outputs + and - but the - output is connected to ground to emulate an op amp.

The VCVS is a basic dependent voltage circuit element, so if you have covered those then you are there already. If not, study the VCVS first and the op amp will be easy then.

The VCVS emulates the ‘ideal’ op amp as the real life op amp has more limitations, but after you know how the VCVS works you’ll be in a better position to understand how those limitations affect the real life op amp.

There’s also the VCCS (voltage controlled current source) and the CCCS (current controlled current source) models that also can be used to emulate the op amp, but the simplest one is the VCVS talked about above.

The op amps real or emulated are almost always used with some negative feedback, and in some cases positive feedback and in other cases no feedback when they are used themselves to emulate a comparator. The most common use however is with negative feedback.

The simplest example of an op amp circuit is a ‘voltage follower’ which is a buffer amplifier with a gain of 1. The construction is easy, just connect the output to the inverting input and use the non inverting input as the input to the amplifier.
These are often used to buffer a signal.

Also in circuit theory the gain of the op amp is often assumed to be infinite just to make the rest of the circuit easier to understand. The practical real life op amp always has limits on that too though.

So to recap, study the VCVS and you’ll start to understand the op amp really quick.

To design with an opamp you simply add an equation saying that the inverting and non-inverting
inputs have the same voltage - so long as the feedback is negative and stable, this holds. This turns
out to be very powerful, you can emulate inductors using an opamp circuit with resistors and capacitors,
google "gyrator" and "negative impedance converter"

Since no one else has mentioned it, Op Amps for Everyone is a very good book about Op Amps. Very complete.

3rd Edition:
http://www.siongboon.com/projects/2008-04-27_analog_electronics/op%20amps%20for%20everyone%20third%20edition%202009%20(Texas%20Instrument).pdf

Purchase 4th Edition:

Op Amps for Everyone is a very good book about Op Amps

Chapter 1 is the best overall history of Amplifier Evolution I've seen. Worth reading!!

W->K->A is that evolution??

Wow, that takes me back to sophomore year in college. I forget what the class was called, but there was a lot of op amp theory in it. I still have my copy of Op Amp Theory and Circuits textbook (something like that) with its light blue cover that I look stuff up in occasionally.

ezlikespie:
I just need a general explanation about op amps. I have attempted to read a few articles online about this but I don't seem to understand it. It would extremely help if I could have a simplified explanation.

EEVblog #600 - OpAmps Tutorial - What is an Operational Amplifier?

Even if I do not agree with approach (I prefer inside view and math background, as this is very simple IC), this is the best explanation I have ever seen. There is some math misses, but all in all very clear. Only lack info how to handle unused op-amps inside multiple op-amps ICs which is as well important info and in many circuits they do it wrong.

This is as well interesting for inside view and test, getting familiar with basic functionality:

The XL741 Discrete Operational Amplifier
http://www.evilmadscientist.com/2014/the-xl741/

arduino_314:
Only lack info how to handle unused op-amps inside multiple op-amps ICs which is as well important info and in many circuits they do it wrong.

Could you explain that a little more?

ElCaron:
Could you explain that a little more?

https://e2e.ti.com/blogs_/archives/b/thesignal/archive/2012/11/27/the-unused-op-amp-what-to-do

Thanks