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
A really useful key word to add to Google searches is "tutorial" (to teach).
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.
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:
Jump right in -- the water's fine.
Good luck Chris
It's called positive feedback.
Graham
Done.Thanks.
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
Have something to add? Share your thoughts — no account required.
Ask the community — no account required