Opamp

[beenuseren]

Hi all,

 

I am very confused about Opamp.

 

This is what I know about an opamp.

 

An Opamp has 5 pins. Two of them are the inputs and another two of them are connected to the power supply, and the remaining pin is the output.

 

1) When the voltage at the positive input is higher when compared with the input at the negative input then the output goes positive and vice versa. Is it true?

 

2) How is that the feedback from the input to the output is responsible for the amplified output?

 

Please explain me this,

 

thanks,

[Qfwfq]

Are you asking help for homework?

 

The best place is "Science Projects and Homework". :hyper: We can move the thread into there.

[beenuseren]

No, no. These are my doubts. But if the right place for this thread is "Science Projects and Homework", then we can move it there. By the way how to move the thread?

 

thanks,

[Qfwfq]

Mods can move it, if necessary. I just asked because there had been a necessity due to some people cluttering up the place with thread after thread, each for some (often trivial) difficulty with a homework exercise. Normally there isn't much of a problem with questions asked to learn. Topic-wise, it could also be Technology (Computers and). :beer:

 

The op amp, or differential amp, has an output essentially equal to the difference between the two input pins, times a (very large) factor called A or differential gain. This is idealized as infinite (and the common mode gain should be practically zero), without negative feedback the output would always be either full positive or full negative, unless the two inputs are clamped equal. Also, the input terminals take negligible current.

 

Most practical applications use a negative feedback, to create a stable equilibrium in which the two inputs are at (almost) equal voltage level, if the output changed slightly, this would change the input so as to go against the change, if you know what I mean. In this way, given an input at the + terminal, the output must be such that gives the same on the - terminal.

 

Try working things out from this, and consider that, very often, the + terminal is connected to mass (zero volt reference) and so the - terminal will be a virtual mass because it too will be at zero volt by stable equilibrium, but the sum of currents will be zero (Kirchoff).

 

HTH

[VS Prasad]

SERIES FEEDBACK: The standard series-feedback opamp

gain stage is shown at its simplest. This stage gives a

gain of four times (+12dB) and something similar is

widely used for fader post-amplifiers in mixing

consoles, and after the volume control in hifi preamps.

Note that I have assumed that DC-blocking will be

required for audio use; hence the input and output

capacitors. These are shown as electrolytics as a large

value is usually required, especially on the output.

 

SHUNT FEEDBACK. The shunt-feedback configuration has

the following characteristics: Low to medium input

impedance. Minimum gain is zero. Noisier than the

series configuration, as the noise gain (qv) is always

one more than the signal gain. The noise gain

is 4 times.

Opamp Design

OPAMP operational amplifiers Information - Integration Circuit Amplifier

 

(1) When the voltage at the positive input is higher

when compared with the input at the negative input it

takes the potential difference between the two.

"Opamp Test and Design Board"

 

(2) You have to design a circuit according

Control Engineering theory.

Analog Devices : Virtual Design Center : Interactive Design Tools : Operational Amplifiers: OpAmp Stability Effects when Driving Capacitive Loads

Opamp Circuits