I present my doubts.
I know that a capacitor in AC circuits filter the DC component. It's behavior is like a resistor according to

.
On the LTSpice Simulator I tried to verify this behavior. This is the circuit:Cattura.PNG

With a sine voltage with amplitude

and DC component

in out as I expected I was only AC signal. Now my doubt focuses on how the C value influence the filter:

1 - Consider that DC component , if I change

I suppose that there aren't changes because

is unchange because

. But with simulator if I change

at

the DC componente is not completely filtered. Why?

2 - Consider the AC component equal to

if change

by making it very small I haven't change while I would expect a filter of the AC component because

increase. Why?

thanks for your patience and sorry for my english.

 

Hello,

That's not a filter, that's just a capacitor. You need a resistor load to see what happens really.
Add a resistor from output to ground, then see how that changes things.

The problem with just a single capacitor is that the DC component may take a very long time to disappear depending on various unseen factors like what the default parallel resistance is for the capacitor, if any, and how the calculations are done internally. It's best to swamp these effects by using a known value of resistance from output to ground, even if it is high like 1 Megohm. You also need to let enough time pass to see the full effect, so maybe 1 Megohm will be too high for some large cap values. You can try say 1k, 10k, 100k, like that.

 

Ok a single capacitor isn't a filter but why in simulator after the capacitor DC component disappear? And why if increase the C DC component not disappear but decreases only?

 

Because the knows that DC does not go through a capacitor. I am surprised that the simulation ran since (I believe) SPICE needs to see a DC path to ground from all nodes.

 

Spice will usually add a tiny leakage resistance, 1e12 or there abouts so that the equations can work out.

 

Great! I can stop adding it manually now!