Subject:
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RE: Electrolytic Capacitor Ratings [was Re: Choosing Parts?]
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Newsgroups:
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lugnet.robotics.handyboard
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Date:
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Thu, 22 Apr 1999 17:55:29 GMT
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Original-From:
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Raymond, Shelby <srr@cherry-semi.NOMORESPAMcom>
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Viewed:
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789 times
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Sorry to say, but the capacitance does change depending upon
the applied voltage. As you increase the plate voltage a force is
created pulling the plates together. This effectively INCREASES
the capacitance. The good news is that this enhancement is very
negligable.
In my personal experiance, Electrolytic caps suck. They are
usually at best +/- 20%. When I design a circuit, I use the
good old safety factor for the working voltage to be from 1.5 to 2
times the operating voltage. You never know if you will hook
up the circuit to a voltage sufficient to breakdown the lower
voltage caps.
> Shelby R. Raymond
>
> Capacitance is calculated using the area of the plates, the dielectric
> constant, and the distance between the plates.
> It does not have anything to do with the voltage.
> If a thicker dielectric is formed, it will reduce the capacitance. This
> is
> not because of the voltage it was made at, or the voltage it is going to
> be
> used at, it's simply because the dielectric is thicker, hence the distance
> between the plates is greater, and capacitance is inversely proportional
> to
> the distance between the plates.
>
> Admittedly, this is just theory from the textbook, but I doubt that the
> value of a capacitor is going to change if used in a circuit with a
> working
> voltage that is lower than what the capacitor is rated at.
>
> just my $0.02
>
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