Path: utzoo!mnetor!uunet!seismo!sundc!pitstop!sun!decwrl!hplabs!hp-pcd!hplsla!tomb
From: tomb@hplsla.HP.COM (              Tom Bruhns)
Newsgroups: sci.electronics
Subject: Re: Capacitors (and more capacitors)...
Message-ID: <5170012@hplsla.HP.COM>
Date: 9 Feb 88 17:43:11 GMT
References: <23947@linus.UUCP>
Organization: HP Lake Stevens, WA
Lines: 31

RE:  Capacitor dielectrics.  To do justice to a reply to your questions
would take tooooo much net bandwidth -- but there is a fairly easy way
to get the info.  Look in any of a number of electronics text or
reference books.  One of my favorites is ITT/Howard Sams' Reference
Data for Radio Engineers; its latest incarnation is just called
Reference Data for Engineers.  Chapter 5, pages 5-16 through 5-28
cover pretty much all the basics you asked about.  Each dielectric
(and its associated manufacturing technique) yeilds different
characteristics in a number of areas, including, but not limited to:
leakage, linearity w/applied voltage (read this as: possible
distortion in an audio circuit), effective series resistance,
self-healing, operating life, storage life, dielectric storage, cost,
size, operating/storage temperature range, changes in each of these
(but especially in capacitance) with temperature, . . .  Each type
of capacitor has a practical range of values over which it is
competitive with other types.  Given several possible choices for a
particular value capacitance/voltage rating, arrange your priorities
and make a choice!  For example, if I want very low dissipation factor
in a 1000pF cap, and don't care about operation at high temp, I might
well choose polystyrene dielectric.  If I want very small size, I might
choose multilayer ceramic. . .

The electrolyte in electrolytic caps is a conductor which allows
effective very close "plate" spacing with attendant high capacitance
per unit volume.  The electrolyte forms/maintains an oxide coating
on a metalic electrode; that coating is actually the dielectric.
Again, see a ref. book.

BTW, _Reference Data for Engineers: Radio, Electronics, Computer,
and Communications_, seventh edition, Howard W. Sams & Co.,
Indianapolis, IN 46268, ISBN 0-672-21563-2