# How to make an opamp out of transistors?

Nov 27, 2023
28
So, an op-amp will convert a sine wave into a square wave.

But if u don't have an op-amp, you can build an op-amp out of transistors instead.

Would someone like to draw this little circuit out for me?
It would be fun for me to see someone to show me their version of it.

Here is radiofun, this guy on you tube, built a schmitt trigger from 2 transistors->

So what is the op- amp version?

#### Harald Kapp

##### Moderator
Moderator
Nov 17, 2011
13,632
So, an op-amp will convert a sine wave into a square wave.
No.
Simplified: An opamp, short for operational amplifier, is a differential amplifier with a very high gain. This universal amplifier is set up for specific operation by adding a suitable feedback network. Depending on the kind of feedback network the operational amplifier can be used for various purposes such as,but not exclusively, e.g.:
• linear amplifier
• filter
• non-linear amplifier (e.g. guitar distortion)
• analog math element (adder, subtractor, integrator, differentiator)
• lots more
You'll find lots of examples and tutorials easily with a quick web search.

So, an op-amp will convert a sine wave into a square wave.
One can use an opamp as a comparator, but this is not recommended. An opamp is not dsigned to go into saturation, which is, however, what happens when used as a comparator. Most opamps will be rather slow to come out of saturation. There are even examples of opamps which flip the output when saturated.
A comparator circuit on the contrary is designed to switch very fast. It will not show the lag or even flipping of the output. The design of opamps and comparators may seem similar, but it is loosely related at best.

this guy on you tube, built a schmitt trigger from 2 transistors-
A Schmitt-trigger is not a comparator. My impression is you're mixing up terms and concepts. A Schmitt-trigger circuit is one that reacts on the input signal with two different thresholds, typically:
- a high level threshold to turn on
- a low level threshold to turn off
This is used to make the input less sensitive to a noisy input signal. You will also find heaps on detailed info with a quick web search.

Would someone like to draw this little circuit out for me?
I doubt you'll find someone here to do this chore for you. Why don't yu give it a try yourself and show us your result? You can even use a simulator like e.g. falstad or LTSpice to check your analysis without building the real thing.

So what is the op- amp version?
Why use an opamp when 2 transistors are enough?
But if you insists: There are also tons of tutorials on this on the internet.

Obviously you know how to use a search engine, otherwise you wouldn't have found us.
You're welcome to ask specific questions when you fail to understand what's already availabel, but we're not going to do the search for you.

#### kellys_eye

Jun 25, 2010
6,469
Would someone like to draw this little circuit out for me?
Seriously?

It's drawn there on the page right beside the working example!

Nov 27, 2023
28
Why use an opamp when 2 transistors are enough?
But if you insists: There are also tons of tutorials on this on the internet.
oh so you've already done it before. Yes, dont need opamps if you have a transistor and a few resistors.
And a schmitt trigger, if u have the transistor, already makes both the more high level constructs.

#### kellys_eye

Jun 25, 2010
6,469
oh so you've already done it before. Yes, dont need opamps if you have a transistor and a few resistors.
And a schmitt trigger, if u have the transistor, already makes both the more high level constructs.
"What choo talkin' bout Willis"?

Nov 27, 2023
28
transistors can be put together to make schmitt triggers, and opamps.

Just like how Harold said.

#### Delta Prime

Jul 29, 2020
1,792
transistors can be put together to make schmitt triggers, and opamps.

Just like how Harold said

I know you're talking about operational amplifiers but for a matter of perspective! 16 years ago I was 12 years old,I'm 28 years old now. In 2007 Intel® Core™2 Quad processor for desktop PCs, as well as two additional quad￾core server processors claims more than
580 million transistors on a chip. And those are dinosaurs!

Nov 27, 2023
28
580 million transistors on a chip. And those are dinosaurs!

How many transistors it has doesn't mean how good it is.

#### Delta Prime

Jul 29, 2020
1,792
How many transistors it has doesn't mean how good it is.
This is true. thank you for the correction.

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