Hi ShayaanQ#1) We know that we use Op-amp with closed loop not with open loop. But why we use negative feedback why don't positive feedback?
Yes it is correct .Q#2) Here is diagram of the simple Op-amp with feedback. We know due to high input impedance of the Op-amp the current flows through the feedback resistor as shown in the figure below. Right?
Exactly wrong ! don't forget that current will go through the RF and don't forget that inverting input can be considered as an imaginary ground ! thus the out put voltage have 180 degree phase shift !But when output is received(i.e. Vo) across RL then some part is fed back to the input in order to control the gain. Right? But the current flows in the reverse direction as shown in the figure below.
Why do you think that we have two current ? don't forget principles of imaginary ground !I am just confused how one feedback provides two way current, like this,
G=-RF/RiG = -Rj/Rf.
Exactly wrong ! don't forget that current will go through the RF and don't forget that inverting input can be considered as an imaginary ground ! thus the out put voltage have 180 degree phase shift !
Hello sir..
That is what I am trying to say you so far. In your own diagram, look, you have draw current from blue line through Rf and with red line through Rf. This is I am asking for, how only one feedback path provides blue line and red line current at a time?
Blue and red arrows should point the same way. It is the same current. When input voltage is positive, then output voltage is negative. So current flows only one way - from input to output.I am just confused how one feedback provides two way current, like this,
View attachment 78248 Blue is current from output to input and Red is the current from input to output due to high input impedance
Hi dear LvW and dear godfreyl
I think you misunderstood my meaning , my mean is when input is positive , out put is negative and the current through RF is that blue shape . and when input is negative the out put is positive and the current is negative . Red and blue are instead of different inputs . aren't you gentlemans agree with me ?
Best Regards
Goldsmith
Hi dear LvWYes - agreed, but this was not clear from the drawing. Why do you use two different voltages with inverse polarity in one single drawing?
This is really confusing - and, more than that, we gain absolutely nothing from using the negative input voltage.
All currents reverse in direction. So what?
i should drew them in two pictures . hence sorry because of created confusion .
Hi dear LvWat too much (redundant) information can cause confusion.
We use cookies and similar technologies for the following purposes:
Do you accept cookies and these technologies?
We use cookies and similar technologies for the following purposes:
Do you accept cookies and these technologies?