- #1

Abdullah Almosalami

- 49

- 15

Alright. So I'm getting two different solutions depending on how I look at this problem, and I know one is correct but I don't know why the other would be incorrect. So, given this general circuit of a constant current source driving an RC circuit in parallel:

Now, what they tell me in class is that this is a DC source, so after transients have gone, the capacitor will be an open circuit, so v should just be i*R. And indeed in simulation, this is what I get. However, if I do try to apply KCL and solve for V, without knowing that say after transients the capacitor will be essentially an open circuit, I get my two different solutions:

- If I keep the circuit as it is and attempt to solve for v, I get the following:

You can see at the very bottom there, I get v(t) = iRC + (vc0 - iRC)exp((-1/RC)t). This converges to iRC! Not iR as I'm expecting. I'm not sure if I did a mathematical error in there somewhere, but as of right now, I can't tell.

- If I source transform the the current source in parallel with the resistor to a voltage source in series with a resistor, then I get:

This version will indeed converge to iR. And I know this must be correct, so what happened?

Now, what they tell me in class is that this is a DC source, so after transients have gone, the capacitor will be an open circuit, so v should just be i*R. And indeed in simulation, this is what I get. However, if I do try to apply KCL and solve for V, without knowing that say after transients the capacitor will be essentially an open circuit, I get my two different solutions:

- If I keep the circuit as it is and attempt to solve for v, I get the following:

You can see at the very bottom there, I get v(t) = iRC + (vc0 - iRC)exp((-1/RC)t). This converges to iRC! Not iR as I'm expecting. I'm not sure if I did a mathematical error in there somewhere, but as of right now, I can't tell.

- If I source transform the the current source in parallel with the resistor to a voltage source in series with a resistor, then I get:

This version will indeed converge to iR. And I know this must be correct, so what happened?