cap varieties

[Roy Tate]

Jeff <scopey at hooked.net> wrote:
>I've been wondering this for a while, and no one seems to know:  Is 
>there any difference between polyester and polycarbonate caps? 

>... Also, is it generally OK to substitute a mylar cap for a 
>ceramic one?  Again, what is the advantage of ceramic?

Page 20 of "The Art of Electronics" by Paul Horowitz and 
Winfield Hill has a wonderful chart comparing the different
capacitor types.  I've also seen similar information on either 
National Semi or on some "Electronic Design" site.

In these comments, "good leakage" means good leakage
characteristics.

Ceramics have poor accuracy, poor temperature stability,
moderate leakage.

Mylars (Polyester) have good accuracy, poor temperature stability,
good leakage.

Polycarbonates have excellent accuracy,  excellent temperature 
stability, good leakage.

Polypropylene have excellent accuracy, good temperature 
stability, excellent leakage.

Tantalum was rated Poor on all counts.

Electrolytics were rated "terrible, ghastly and awful."  :)

Keep in mind that using a capacitor in the signal chain means you
have to think about memory, stability, etc.  but things like ceramics
and electrolytics work just fine as power reserves for bypass or
power supply applications.

Regards,

Roy Tate
roytate at ionet.net
http://www.ionet.net/~roytate