Re: gEDA-user: ESR of 2.2u ceramic capacitor

[Dan McMahill <dan@xxxxxxxxxxxx>]

John Doty wrote:
> > What you are talking about here is "charge soak" which is often  
> > modelled as extra capacitance-plus-series-resistance in parallel  with 
> > the ideal capacitor you thought you were buying. I've seen  time 
> > constants varying from a few seconds to a number of minutes,  
> > depending on what I was doing. The charge is still in the  capacitor, 
> > but it's coming out slowly.
>
>
> It can take years. That's how "electrets" work. In the vacuum tube  era 
> (yes, I'm that old, barely) I remember reading about folks using   this 
> effect to make a rechargeable "bias cell" for grid bias!

Thats interesting.  You don't have any schematics by any chance?

Dielectric absorbtion and hysterysis in caps can cause unpleasant issues 
with various types of integrating A/D converters.  I seem to have a 
vague memory of someone (Nelson Wright maybe?) doing a thesis at MIT 
many years back which was a study of dielectric absorbtion and perhaps 
(can't recall now) some discussion of how to measure it and how it 
affects some circuits.

-Dan

(who has in fact designed with vacuum tubes)