# How do I learn OpAmp? Do I need to know the internal circuit? Are they works the same way?

I am learning OpAmp. I watched many good teachings on YouTube. Some teachings mentioned the OpAmp type/series he/she is explaining, such as uA741. But many other teachings without any explanation, like is in here and here. The fact, there are many type OpAmp mentioned, even in the CircuitLab which the software attached to this SE, there are many type of OpAmp included. Then my question:

• How do I learn OpAmp? Can I just think that they work the same way?
• Do I need to know the internal circuit and treat that every type is working specific based on their own design?
• Apart from the answers, you can find some application information in this answer: electronics.stackexchange.com/questions/189823/… Jan 14 '20 at 9:25
• Many thanks. The link help a lot. Jan 15 '20 at 2:21

There's an excellent free Ebook about opamps, it is called "Opamps for everyone" and you can download it here.

An Opamp is a device/circuit that tries to behave in a certain way, it amplifies the voltage difference between its inputs. Ideally an opamp would have an infinite gain and also work for every frequency and have no flaws at all. Obviously that's not possible so every opamp is a compromise.

The 741 was one of the first "usable" opamp ICs (a chip) and in its days (1970s to 1980s) it was very popular. We have moved on since then and have better technology to make better opamps. A limitation of the 741 is for example that it is useless at the low supply voltages we use today like 5 V. A 741 really needs a symmetric +/- 15 V supply.

I would not worry too much about what opamp is used as an example in teaching presentations. Usually the opamp is assumed to be "ideal" or at least good enough for the function that is explained.

The circuitry around the opamp, like a feedback network, stays the same whatever opamp you use. Focus on those circuits and how the opamp is used, not the model of the opamp as it doesn't matter much.

The internal circuit of an opamp is really only of interest to IC designers and experienced designers that can determine the limits of what the opamp can do depending on the circuit that is used. For example, I am an IC designer so I can look at the schematic of an opamp and see how close it can drive its output voltage to the supply rails from the architecture of the output stage (if that's an common emitter, common collector, common source etc...). However, in the specifications of the opamp there will also be information about this under "Output voltage range". So you don't need to know or look at the circuit, the information is also in a table. And that information is leading as it is guaranteed behavior. I could have missed something in the schematic or not understand it properly or the schematic could be incomplete (some manufacturers do that to protect their design).

• The circuitry around the opamp stays the same whatever opamp you use. This is the most important thing I need to know. This will help a lot. Jan 14 '20 at 7:53
• Focus on those circuits and how the opamp is used. Will you please explain this more? Can you give something like case example? Jan 14 '20 at 7:54
• The ebook I mention is full of those examples. Basically any circuit that uses an Opamp. Jan 14 '20 at 9:04
• OK, I downloaded the book but I have not real all. Many thanks for the explanation and the e-book. Jan 15 '20 at 2:17

Basically, all operational amplifiers have some common theoretical properties (e.g. open-loop gain is infinite, inputs show high impedance etc). Traditionally, these properties are shown on a 741. Having grasp of these properties makes you easier to understand all the op-amp applications (e.g. amplifiers, buffers, comparators, integrators, oscillators etc) since all of these applications are based on those properties. Studying on paper or in front of the PC is never enough. Building the circuit on a breadboard or at least simulating it is always needed. Don't hesitate to explode op-amp ICs :)

In most applications you won't need the internal structure. But you do need to know how to select an op-amp based on your needs (In other words, how to read the datasheet and analyze the parameters according to your needs). For example, you should know what dual-supply and single-supply are, and when to prefer one over another. Or, if you want to amplify very low voltages (e.g. less than 10mV) then you need a low-noise operational amplifier with very low input offset voltage. So, you need to know what input offset voltage is and how it affects the general performance. The examples can be populated.

• If you want to amplify very low voltages (e.g. less than 10mV) then you need a low-noise operational amplifier with very low input offset voltage. So, you need to know what input offset voltage is and how it affects the general performance. For beginner, where and how do I know such specific info? Is such info available in their datasheet? Jan 14 '20 at 7:57