RC circuit

Hello.
This question is taken from the course 'Microwaves and transmission lines'.

It was said there that Vc(t=∞) = 2Vin, and that is since at t=∞ the capacitor behaves as a cut-off, and therefore the reflection coefficient at the load (load=capacitor) equals 1, which means that V(LOAD) = (V+) + (V-) = 2Vin.

It doesnt get along with what we learned in earlier courses which was that Vc(t=∞) = Vin.

Could you please explain that?

Thank you.

It seems that in this circuit its impassible to achieve Vout=2Vin.
But in this circuit you can almost achieve Vout=2Vin.
Capacitor, Reverse bias diode and resistor circuit - All About Circuits Forum

alphacat said:

Hello.
This question is taken from the course 'Microwaves and transmission lines'.

It was said there that Vc(t=∞) = 2Vin, and that is since at t=∞ the capacitor behaves as a cut-off, and therefore the reflection coefficient at the load (load=capacitor) equals 1, which means that V(LOAD) = (V+) + (V-) = 2Vin.

It doesnt get along with what we learned in earlier courses which was that Vc(t=∞) = Vin.

Could you please explain that?

Thank you.

Click to expand...

Beware. If you say that t = infinite, then you won't work with wave relflections (transient). t = infinite means that you entered in the permanent steaty state (long after the transient time).

Hi,

t=infinite can really mean two different things depending on what kind of signals you are working with.
For DC transient circuits t infinite means a time way into the future where all the signals have stopped changing.
For AC transient circuits t infinite can mean a steady state AC signal, such as 1v peak for example. That's still
considered steady state but it's a sine wave. That could mean reflections depending on the physical size of the
system relative to the wavelength.

The only thing that confuses me about this question is that the source is drawn as a step function. That could
possibly generate reflections but i would think they would die out after some time t less than infinite, so we would
be back to a steady DC output at t infinite. Perhaps something is drawn incorrectly or the question is not
stated exactly correct. Just some guesses.

Thank you very much guys.

I was indeed confused by the terms t=∞ and having a unit-step source.

I'll have to check it out since its indeed misleading.

Thanks for helping me.