Physics Help Forum Op Amp circuit and RC circuit transient analysis.
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 Sep 4th 2017, 06:48 AM #1 Junior Member   Join Date: Sep 2017 Posts: 1 Op Amp circuit and RC circuit transient analysis. I have unable to figure out this 2 problem. Please help me understand them. For the first one #1, (Op Amp), I know that all ideal opAmp has V+ = V- but the problem states that Vout = A ( V+ - V-). If there were equal, Vout will be 0 then. For the second one #2 ( I am really have a hard with how to redraw the circuit and derive the differential equation. I have been out of school for some time so I am a bit rusty. Please help Attached Thumbnails
 Sep 6th 2017, 02:02 PM #2 Senior Member   Join Date: Nov 2013 Location: New Zealand Posts: 548 The first looks like a controlled gain circuit (So A shouldn't figure in final analysis). I think you should be able to solve that with Kirchoff's laws. https://en.wikipedia.org/wiki/Kirchh...s_circuit_laws. The voltage $\displaystyle V^{+} = V_{in}$ as there is no voltage drop across RS as no current is flowing through the inputs of the op amp. R1 and R2 comprise a voltage divider which you can work out the voltage drop between them from ohms law. That should give you V- and from there you should be able to calculate $\displaystyle V_{out}$ and the gain $\displaystyle \frac{V_{out}}{V_{in}}$. The second just looks like a capacitor resistance network. From google the current formula for a capacitor is $\displaystyle I = C \frac{dV}{dt}$. I would assume the two $\displaystyle V_{dd}$ points are connected, as they are at the same potential, even though they are not drawn that way. You should be able to solve this using Kirchoff's current laws. __________________ Burn those raisin muffins. Burn 'em all I say. Last edited by kiwiheretic; Sep 7th 2017 at 12:14 AM.

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