Differentiating Op-Amp basic exercise

Femme_physics

Oh! I was not aware of this, technician. I will ask my teacher tomorrow morning as I have a class with him.

Thanks. I will let you know, I promise.

Duly noted

I like Serena

That's all right.



He must be really smart then!
Who is he?


Oh well, perhaps some day soon the fog will rise.

Femme_physics

Nice pic!

He is Klaas, The Klaasmaster of all Classes

I bet!

Femme_physics

As promised! Yes, you were right, my teacher confirmed it and also added it was not his exercise, and that there must be a mistake.

technician

Thank you so much for letting me know.
I hope you feel good about op-amps !!!!

Femme_physics

Almost! trying to figure out their basis of operation here.

And of course, you're the one who should be thanked!

technician

I have looked at your 'here'
It is a basic circuit.
I will put something together for you about op amps. There are lots of technical details and it is easy to get confused by them. Most of them are not important.
The basic principles are not hard to get to grips with.
I will keep in touch with you about op amps
Cheers

Femme_physics

Yes, most websites I've seen do include a lot of seemingly unnecessary confusing nitty-gritty info.
Well, I'm always here, ready to read watcha got
Cheers

cepheid

Hey Serenophile,

Maybe you can explain something. I thought that every op-amp was a differential amplifier in the sense that it amplifies the difference between the + input and the - input. Why, then, is there a specific configuration referred to as a differential amplifier above? Is it just because op-amps are never operated open-loop, and what you have above is the stable, closed-loop op-amp design that happens to produce a differential output?

cepheid

I should also probably contribute something useful to this thread rather than just hijacking it, right? Umm...okay. To the OP: here is a link to a site with some info on op-amps:

http://hyperphysics.phy-astr.gsu.edu...ampcon.html#c1

I like Serena

Hey Asterophile!

Yes it amplifies the difference by a million.
But for a difference we do not want amplification by a zillion, we want *just* the difference.
An additional complication with amplification by a zillion, or open-loop in general, is that the op-amp gets saturated and just gives off either max + or max -.

As an added bonus the differential amplifier configuration allows us to set an amplification that deviates from 1.

Nice link.

Femme_physics

While we use this thread to ask questions....how do you call this Op-Amp?

technician

It is an inverting amplifier because the input is connected to the -input

technician

Put some values in and follow it through.
Suppose the battery connected to the + input is 2V and the input resistor is 1kΩ.
The feedback resistor we will have as 2kΩ and the resistor on the output we will have as 500Ω
The volts at the + and - inputs must be equal (remember) so there is a voltage of 2V across this 1kΩ resistor. This means a current of 2/1000 A flows down the 1kΩresistor. This current must come from the output of the amplifier and flows through the 2kΩ resistor.
This means that the voltage across the 2kΩ resistor = 2x10^-3 x 2000 = 4V.
The voltage at the -input is 2V so the voltage at the output of the amplifier =2 + 4 = +6V
This means there is a current through the output resistor (you could call it the 'load' resistor)
of 6/500 = 0.012A.
What do you think of that???

Femme_physics

I'll take you on step by step hitting the second reply later.

How come it's an INVERTING amplifier if the only voltage source is connected to the MINUS leg? Doesn't it make it inverting?

I like Serena

Yes.
It's an inverting amplifier, because it looks most like this picture:


The fact that there is an additional resistor (and battery) after the circuit, and that a battery is used to change the ground potential, does not change the fact that it is an inverting amplifier.

technician

The -input is also known as the 'inverting' input so if the input is connected to the - input it is automatically an inverting amplifier. It is just a name, don't worry too much about the names.....can you follow the voltages and currents....that is the main thing.