The Cyber-Spy.Com Usenet Archive Feeds Directly
From The Open And Publicly Available Newsgroup
This Group And Thousands Of Others Are Available
On Most IS NNTP News Servers On Port 119.
Cyber-Spy.Com Is NOT Responsible For Any Topic,
Opinions Or Content Posted To This Or Any Other
Newsgroup. This Web Archive Of The Newsgroup And
Posts Are For Informational Purposes Only.
From: firstname.lastname@example.org (john jardine)
Subject: Re: Wrestlemania Royale: Tantalum vs. Electrolytic Vs. Polys, etc.
Date: 28 Oct 2002 06:40:14 -0800
References: <email@example.com> <firstname.lastname@example.org> <3DBC659D.9802318D@imit.kth.se>
NNTP-Posting-Date: 28 Oct 2002 14:40:14 GMT
Uwe Zimmermann wrote in message news:<3DBC659D.9802318D@imit.kth.se>...
> john jardine wrote:
> > 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
> > properties.
> That's quite an optimistic view of an ideal capacitor. However all
> capacitors you buy, wherever you buy them, are far from ideal.
> A capacitor as you buy it is never fully represented by its
> capacitance and the deviation of capacitance over
> time/temperature/voltage alone. These little things are rather
> complicated circuit elements consisting of inductances and resistances
> in the leads and possibly in the metal foil, leakage resistance
> through the dielectric,....
> ____ ____ C
> Ls Rs | ____ |
> represents a simple model of a real capacitor. Whether or not the
> parasitics can be neglected depends mainly on the type and size of the
> capacitor and the frequency you intend to use. In the manufacturers
> datasheets you should normally find an impedance vs frequency plot,
> where you can see the frequency above which the parasitic inductance
> starts to dominate the behaviour. This can be several to several tens
> of kHz for electrolytics, some 100kHz to several MHz for plastic foil
> capacitors and up to several 100MHz for single layer ceramic
> (just to name a few)
In practice, I've found the electrolytics below 10u are surprisingly
good to >10MHz. A number of cases having less body inductive loss than
than the foil types. The biggest frequency limiting factor I've come
across is 'external' and resides in the nH's due to the component leg
lengths and PCB tracking distances.
Go Back To The Cyber-Spy.Com
Usenet Web Archive Index Of
The sci.electronics.design Newsgroup