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From: email@example.com (john jardine)
Subject: Re: Wrestlemania Royale: Tantalum vs. Electrolytic Vs. Polys, etc.
Date: 26 Oct 2002 07:02:44 -0700
NNTP-Posting-Date: 26 Oct 2002 14:02:44 GMT
firstname.lastname@example.org (The little lost angel) wrote in message news:<email@example.com>...
> So is there some kind of resource that lists some sort of guidelines
> in layman terms?
> I've been trying to figure out what capacitor to use. The shops have a
> range of them and no description which for which.
> I found some that would describe in length details about the various
> parameters/properties of various capacitors... and don't really make
> sense out of it.
> Say for a low voltage 10~20v, low current 0.2A, what would be the best
> type of capacitor with smallest physical size?
Basically, there are no clear rules for selecting caps, as at the end
of the day they all do the same thing. A 10n capacitor of whatever
type or maker will electrically always work as a 10n cap should work.
Some types are good at holding their manufactured value over time.
Some hold their value well against temp' changes. Some change in a
fixed manner with temp'. Some types work well at high voltages. Some
have exceedingly low losses. Some have 'self healing' aspects. Many of
these products can (in varying degree) have a range of these
You dont have to know the details by heart. When the occasional real
need arises to pick a cap with a particular feature then start
rummaging through the catalogues looking for a cap that fits your
bill. It's a pain but that's 'design'.
E.g During a circuit design, you might want a cap' with a mix of
desirable features. Say you have just done a quite sharp, 2kHz active
band pass filter using an op-amp and you need a couple of 10n caps for
it. In this case the circuit would be wanting caps with a good
tolerance (say 1%) or the filter frequency would change. It would also
need caps that are not polarized as the signals are swinging around
0V. It would also need caps that are stable over time. You'd also be
thinking about the cost of them as well.
Search the catalogues for a cap with these qualities and you'll
probably turn up a polypropylene film 1% type (Yes, I've just had a
rummage!). Though many other types could fit in as well.
For 99.9% of all day to day uses, just look at the Electrolytics if
you need polarised, rough and ready, high cap' values. Look at the
ceramics for decoupling type jobs. Look at the Polyesters for passing
low voltage ac signals.
(If you need hi value, non polarised, for ac use, then redesign the
Fortunately, you'll find all these cap' types are the cheapest.
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