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Does a capacitor charges smooth, or in stairs?
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Nominal Animal:

--- Quote from: RoGeorge on June 06, 2020, 03:49:04 pm ---What he's talking there is about the capacitor's plates themselves.
--- End quote ---
For a long skinny capacitor (a contrived example, he says himself).  For a short wide capacitor, or indeed a capacitor formed from circular discs, you get funky wave interactions, and no clear steps.  That is because there is no single reflected wave.  Similarly if the electrical connection is not a single point at one end, but multiple points with different path lengths.

If you consider something like current ceramic capacitors that are stacks of plates separated by dielectric ceramic, connected at one end, they really don't match that long skinny capacitor model.

Something like a big bulk capacitance at the end of a long pair of wires, though; that should be measurable.


--- Quote from: RoGeorge on June 06, 2020, 03:49:04 pm ---The capacitors do charge and discharge in stair steps
--- End quote ---
As I said, I believe that only applies to certain circuits, and/or certain shapes of capacitors.  I don't like the claim.


--- Quote from: RoGeorge on June 06, 2020, 03:49:04 pm ---Also, doesn't matter much for the day to day electronics.
--- End quote ---
Power transmission line engineers might disagree.  I seem to vaguely recall seeing something about this in that context, but can't be sure.
T3sl4co1l:
Neither: the voltage is a continuous function of time and, for the pure capacitance of a component, obeys I = C dV/dt.

Current is unspecified, so an exponential charge or discharge is certainly not assured.  Nor is the stepwise motion of an ideal transmission line driven by an ideal step.

It's an interesting exercise to perform this measurement yourself: how slow can the step be, how lossy can the transmission line be, before the apparently stepwise motion ceases and ordinary exponential charge/discharge (assuming a resistive source) is apparent?

Therein lies the deeper truth: we use ideal models for near-ideal situations, and when one situation ceases to be near that ideal, we typically switch to another; a mixed model is therefore necessary to explain the overall behavior.

FWIW, most of my capacitors are fully end connected rolls of metallized film, so exhibit no appreciable transmission line behavior.  If they did, it would be with Zo << 1 ohm probably, and T < 100ps.  The leads (T ~ 100ps, Zo ~ 100 ohms) clearly dominate, and it looks like a lumped equivalent -- hence the three-element series equivalent traditionally used for capacitors. :-+

I think TL behavior is sensible (if insignificant in intended applications) in some film-oil caps, where the connection is usually made with a pair of ribbons to the middle of the roll.  Zo is still quite low because the roll is wide, but the electrical length is modest, so that assuming you can get a reasonable step through those ribbons (which again have a high Zo), you can probably observe a small ripple as it rings down.

Tim
Labrat101:
I Have seen his videos and Only once did he use a scope CT100 . the picture was on purpose out of focus.
 Sorry the Theory maybe correct, but in Practice No.
I used to work for a large electronic manufacture and this was not ever mention nor did we ever have staircase from any capacitor.
 That was visible on a scope .. At micro level or down to chemical structure of curtain materials maybe visible. but not on a CT100.
 Over the plates there will never be a 100% perfect transmission of electron movement. But these small factors are so small that 99.9% will never come into play .
Each Step would be few electrons But a scope uses pixels which are 1000s of times larger so the whole staircase would fit in 1 pixel .
  Need a good eye sight as well.
Low grade capacitors will have errors . that's why they are cheap.
RoGeorge:


 ;D
Labrat101:
The Earth is also Flat  :-DD  my spirit level shows it to be true  ..  :-DD

Show a video of an actual working model with a schematics so we can all enjoy .


 

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