Can a capacitor decouple into floating ground?

crutschow

Joined Mar 14, 2008
23,494
re post #19
And what does that buy you?
Where is there a path for any current through C8?

You still don't seem to understand that all current flow requires a complete return path.
When you can show that, then you will have a compete circuit.
The next circuit modification you post, show the complete current path.
 
Last edited:

MrAl

Joined Jun 17, 2014
6,608
Hello again,

The short answer is, no, it does not work to try to filter a signal using a floating ground as reference. That's because the main circuit and secondary circuit are considered isolated from each other. In a circuit with a cap connected to an isolated floating ground the two terminals of the cap will stay at about the same voltage, so if you have ripple on one terminal you have that same ripple on the other terminal so the cap does absolutely no good to help the filtering. So no it does not work.

The best you could do probably is connect capacitors in series to create higher voltage capacitors, but you do have to ensure that they share the voltage equally. If you have worked with high voltage then you might be aware of the trick of using transistors with their collectors and emitters in series and how you have to ensure that they all share the voltage equally, and doing the caps would be a similer situation when they are in series.

Now if you already had a second DC source that you could connect the other end of the cap to, then you you would be filtering. So for example if your primary source was at 200v and your secondary source was at 100v then you might be able to connect a cap from the 200 to the 100 volt source and see filtering action occur. That's if the 100v source can handle the extra ripple current and the two sources start up properly when the power is first turned on. That cap could then have a voltage rating less than 200v.
 
Top