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Old 1st September 2006, 01:10 AM   #1
johndiy is offline johndiy  Greece
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Default whats ripple current of c

hi

what is ripple current of a capacitor
the one quoted in the ratings of a capacitor

john
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Old 1st September 2006, 10:01 AM   #2
sreten is offline sreten  United Kingdom
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Hi,

A power supply may draw constant current but the capacitors
will charge only at the peaks of the incoming AC, so the charging
current is much higher but shorter time, this is the ripple current.

/sreten.
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Old 1st September 2006, 10:47 AM   #3
AndrewT is offline AndrewT  Scotland
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Hi,
the ripple current is responsible for most of the heating in a smoothing capacitor.

The ripple rating varies with ambient temperature. Keep your capacitors COOL. Locate then away from hot heatsinks/sources and provide ventilation.

You can use PSUD11 to investigate the ripple current in your proposed application, but do try to use as little of the permitted rating as possible.
Multiple parallel caps offer a solution to high ripple currents but have other downsides and a few upsides.
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Old 1st September 2006, 11:00 AM   #4
AKN is offline AKN  Sweden
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Specified ripple current capability on a capacitor is specified in Arms, peak currents can be higher.
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Old 1st September 2006, 11:38 AM   #5
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Default Useful tool for power supply design

this will give you an idea of what ripple-current rating your caps will need

http://www.duncanamps.com/psud2/index.html
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Old 1st September 2006, 03:56 PM   #6
mikeks is offline mikeks  United Kingdom
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Alternatively, see Vishay
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Old 1st September 2006, 11:42 PM   #7
cpemma is offline cpemma  United Kingdom
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Quote:
Originally posted by AndrewT
You can use PSUD11 to investigate the ripple current in your proposed application...
That confused me and Google. PSUD-Latin 2 as per bremen nacht's link?
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Old 2nd September 2006, 12:26 AM   #8
johndiy is offline johndiy  Greece
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Hi and thanks
i still dont understand it, i know it relates to ripple but why
is it useful, how do you apply it to power supply design

high ripple currents c's are they better than low ones?

thanks

john
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Old 2nd September 2006, 09:05 AM   #9
AndrewT is offline AndrewT  Scotland
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Hi,
high ripple capacity rating is better than low ripple capacity rating.

Using less than the ripple capacity rating is better than using all the ripple capacity rating.

Overstepping the ripple capacity rating is dangerous (if continued for more than a brief moment).
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Old 2nd September 2006, 12:37 PM   #10
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All caps have a finite resistance. Typically it is called ESR - equivalent series resistance. The power loss is I^2 * R and the power heats up the cap. The temperature rise is a function of the thermal resistance (from the cap hot spot to the surrounding air) and the life of the cap is strongly related to it's hot spot temperature. So, in general, lower ESR make for longer life.
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