Capacitors (was Re: elctric mistress ic help)

[jorgen.bergfors at idg.se]

>Poly and electrolitic are different, Poly caps can be connected either 
>way, electrolytics can't... also poly caps tend to be smaller values, 
>down to pF rather than uF.

Poly what? There are Polyester, polystyrene, polypropylene and polycarbonate 
caps. All of them are better than electrolytics but some are better than others.

Polypropylene have low tolerance (10%), low temperature coefficient and aren't 
very expensive in the range 100p to 10n. Above that they get big and expensive. 
The largest value at my supplier is 33n.

Polycarbonate is available up to around 1uF and are very stable. 10% tolerance. 
A bit expenisve and bulky for larger values.

Polystyrene is good but bulky and hard to find.

Polyester is cheap, small and available up to at least 10uF. They have high 
tolerance, large temperature coefficient and are leaky and unreliable compared 
to the others. But still a lot better than electrolytics.

Use polypropylene or polycarbonate for timing caps and in the signal path. 
Polyester are good enough for power supply bypass and other less critical 
applications.

Both polypropylene and polycarbonate are available as metallized and non 
metallized. I don't know what difference it makes. Any ideas?

/Jorgen