At 08:36 PM 4/7/2011, you wrote:
> > 2. Aluminum and ceramic capacitors are less touchy and can be=20
> used at closer
> > to the stated value but still should be derated (say, to 75%).
>
>Wet aluminium electrolytic capacitors should be run nearer to rather
>than further from their rated voltages. Running at low voltages wrt
>rated will lower lifetime.

You think, Rus? Why would this be true? There are zillions of low=20
value 50V caps
used in < 10V circuits and I have not noticed  problems, at least in
through-hole parts.

United Chemicon specifically states that there is
no appreciable effect on lifetime of applied voltage within the rated range=
..
See figure 7 here:
http://www.chemi-con.com/u7002/life_ms.php

Notwithstanding the Japanese data, I do believe that you're actually better
off to use a power supply capacitor that's rated for a higher voltage than
required simply because the can size will probably be one size or more larg=
er,
which means that there is more surface area to dissipate heat from
internal losses.

FWIW, I have noticed little to no problem with no-name parts used in non-
stressed applications (coupling caps, caps with little ripple current) etc.

Unusually small power supply filter caps from unknown makers are to be
treated with great suspicion.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the rewar=
d"
speff@interlog.com             Info for manufacturers: http://www.trexon.co=
m
Embedded software/hardware/analog  Info for designers:  http://www.speff.co=
m



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