[sdiy] Capacitor types - which when?

[harrybissell]

Metrophage wrote: <snip & comment ;^)

> > Im just wondering as to the pros and cons or various types.  Ceramics
> > vs poly layer vs poly film etc.etc.
>
> Ceramics are typically used for bypass caps to reduce noise from the
> supply leads, or where accuracy is not very crucial.

good.

> Mica and Mylar are
> general purpose caps which are usually rated about 5% tolerance- more
> versatile than ceramic but not as cheep.

not quite. True for Mylar.   Mica caps are usually not found in real tight
tolerances...
but their stability puts them more in the league of polystyrene (very
good).

> Polystyrene caps are probably
> the most stable that you can find, typically made in small values.

True. They are no longer common in values larger than .01uF although they
used to
be common up to .1uF

>
> Polyester are nearly as tight as styrene, and made in more of a variety
> of values.

oops... Polyester IS Mylar...  they are not in the same class as
polystyrene. They are quite
poor in dielectric absorption and should be avoided for S/H and critical
VCO capacitors.

> Polycarbonate exhibit the least leakage, though appear to be
> seldom produced.

> Polycarbonate are quite good... but still not quite as good as
> polystyrene. They are improving

and will be the standard once polystyrene disappears !!!  They are produced
and are ideal for
higher temperature ranges. (Styrene dies at 85C)

I keep a real big selection of mylar caps for general use... I use
polystyrenes only for mission
critical applications (VCO, VCF timing... S/H for critical uses).

BTW small ceramic caps are available in NP0 or C0G dielectrics rival mica
caps in values
less than 500pF

H^) harry