op amp Basic Frequency Control Circuit

Posted on Feb 5, 2014

R4 prevent the output voltage drifting towards one of the supply rails to the op amp I understand that R4 has to have a high resistance but I do not know why That looks like a Circuit Lab schematic! It would be great if you could post a link to the schematic so that answerers could edit, highlight, and reconfigure it if necessary. Kevin Vermeer May 14 `12 at 18:13 I love Circuit Lab,

op amp Basic Frequency Control Circuit
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but for some reason I cannot save anything I have drawn on it. Otherwise I would, any suggestions on how to save and I would gladly post a link user1083734 May 15 `12 at 8:30 I`ve since found out that the save functions aren`t supported by the Chrome I`m using, I will post a link once I have redrawn using Firfox user1083734 May 15 `12 at 8:59 With R4 removed, there is no DC feedback path from the op-amp output to the input. So if the b node drifts away from ground, there`s nothing the op-amp can do to drive it back towards ground (which it will try to do to keep the two inputs equal). If b drifts high, the output will tend to rail negative, and if b drifts low the output will tend to rail positive, according to the open-loop gain of the op-amp. With R4 in place, you have a DC feedback path. If b drifts high, the op-amp output can go a little bit low and pull it back to ground. If b drifts low, the op-amp output can go a little bit high and pull it back to ground.

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