Hello!
I'm getting started with the study of operational amplifier. Fist of all,
do you know any site which could explain clearly this matter? Could you
write some link?
In particular, I can't understand the reason why a saturation occurs when
the output signal is connected to the + terminal. The output is alway
connected to che other terminal, the - one.
Why? Can you help me?
Thank you anyway!

Rocky3


--
"Il sapere e la ragione parlano, l'ignoranza ed il torto urlano".

Arturo Graf / Indro Montanelli / Anonimo

Rocky3 wrote:
> Hello!
> I'm getting started with the study of operational amplifier. Fist of all,
> do you know any site which could explain clearly this matter? Could you
> write some link?

A really useful key word to add to Google searches is
"tutorial" (to teach).

http://www.williamson-labs.com/480_opam.htm
http://web.telia.com/~u85920178/begin/opamp00.htm
http://www.national.com/appinfo/amps/0,2175,967,00.html

> In particular, I can't understand the reason why a saturation occurs when
> the output signal is connected to the + terminal. The output is alway
> connected to che other terminal, the - one.

It has to do with the direction the output is sent when the
difference of the two input voltages is amplified. If the
voltage at the + input is more positive than that on the -
input, the output is driven in a positive direction, and
vice-versa.

When the output is connected to the - input, and there is a
difference between the voltage the output is producing and
that applied to the + input, the error (the difference
between the + and - input voltages) is amplified with a
polarity that drives the output voltage to reduce the error,
to send the output voltage toward the + input voltage. This
process stops when the two input voltages are almost
perfectly equal. This process makes the error (mismatch
between the two input voltages) smaller and is called
negative feedback.

If, instead the output is connected to the + input, any
difference between the voltage the output is producing and
the - input voltage, drives the output to change in the
direction that increases this difference, and that process
stops, only when the output saturates at one extreme or the
other. This process makes the error (mismatch between the
two input voltages) larger, and is called positive feedback.

One is not wrong and the other right, because both process
are useful in certain circumstances.

On Aug 11, 10:15 am, Rocky3 <pr...@prova.com> wrote:
> Hello!
> I'm getting started with the study of operational amplifier. Fist of all,
> do you know any site which could explain clearly this matter? Could you
> write some link?
> In particular, I can't understand the reason why a saturation occurs when
> the output signal is connected to the + terminal. The output is alway
> connected to che other terminal, the - one.
> Why? Can you help me?
> Thank you anyway!
>
> Rocky3
>
> --
> "Il sapere e la ragione parlano, l'ignoranza ed il torto urlano".
>
> Arturo Graf / Indro Montanelli / Anonimo

If I could add to Mr. Popelish's list, you also might want to take a
look at the Texas Instruments recent update of the Burr Brown
"Handbook of Operational Amplifier Applications" -- it's a classic,
and has been handled gently by Bruce Carter, apparently with the
approval and assistance of the original author, Thomas Brown:

http://focus.ti.com/lit/an/sboa092a/sboa092a.pdf

Jump right in -- the water's fine.

Good luck
Chris

Rocky3 wrote:

> In particular, I can't understand the reason why a saturation occurs when
> the output signal is connected to the + terminal.

It's called positive feedback.

Graham

Eeyore wrote:
>
> Rocky3 wrote:
>
>> In particular, I can't understand the reason why a saturation occurs when
>> the output signal is connected to the + terminal.
>
> It's called positive feedback.
>
> Graham
>

Feedback is a fundamental issue when studying amplifiers of any
description (positive AND negative feedback incidentally).

The OP should look not only at Opamps but perhaps also search for
tutorials on feedback.

Cheers

PeteS

Chris wrote:
> On Aug 11, 10:15 am, Rocky3 <pr...@prova.com> wrote:
>> Hello!
>> I'm getting started with the study of operational amplifier. Fist of all,
>> do you know any site which could explain clearly this matter? Could you
>> write some link?
>> In particular, I can't understand the reason why a saturation occurs when
>> the output signal is connected to the + terminal. The output is alway
>> connected to che other terminal, the - one.
>> Why? Can you help me?
>> Thank you anyway!
>>
>> Rocky3
>>
>> --
>> "Il sapere e la ragione parlano, l'ignoranza ed il torto urlano".
>>
>> Arturo Graf / Indro Montanelli / Anonimo
>
> If I could add to Mr. Popelish's list, you also might want to take a
> look at the Texas Instruments recent update of the Burr Brown
> "Handbook of Operational Amplifier Applications" -- it's a classic,
> and has been handled gently by Bruce Carter, apparently with the
> approval and assistance of the original author, Thomas Brown:
>
> http://focus.ti.com/lit/an/sboa092a/sboa092a.pdf
>
> Jump right in -- the water's fine.
>

Done.Thanks.