Author Topic: Capcitors and Current  (Read 1654 times)

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Offline Falcon69Topic starter

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Capcitors and Current
« on: May 07, 2013, 06:24:27 am »
I searched for an hour tonight, and I just can't find information on this.  For a DC circuit, using a 1uF 0603 size ceramic capacitor rated at 16 volts, what is the maximum amount of current that can flow through it without damaging the capacitor? For a 0805 size? For a 1206 size?

It seems all manufacture data sheets only say maximum voltage.  Never mentions current.
 

Offline IanB

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Re: Capcitors and Current
« Reply #1 on: May 07, 2013, 07:02:28 am »
For electrolytic capacitors look on the data sheet for the maximum RMS ripple current. For small ceramic capacitors I don't think this is a big concern.

When considering DC, the average current through the capacitor is of course zero. For a small ceramic cap the peak instantaneous DC current (e.g. if you apply the rated voltage to a discharged capacitor) is not a limitation. The capacitor can handle it whatever it is.
 

Offline MacAttak

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Re: Capcitors and Current
« Reply #2 on: May 07, 2013, 06:25:50 pm »
For DC current, a capacitor is open-circuit. If you have any current at all going through it, then you've fried it and it has fused short.
 

Online ejeffrey

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Re: Capcitors and Current
« Reply #3 on: May 07, 2013, 07:33:39 pm »
If you can find an ESR spec, you can estimate the maximum ripple current by assuming a power rating similar to a resistor of the same package size.  So an ESR of 1 ohm in a 1/8 watt package can handle 350 milliamp RMS current.  Ceramic capacitors have very low ESR, so this is rarely an issue.

If you are talking about a supply filtering, it is important to remember that the DC current 'flowing past' the capacitor into the load has no effect at all.  You need to calculate the ripple current that actually flows through the capacitor.  That is, during each cycle, the capacitor will charge and discharge a little bit.  That charge/discharge cycle is the ripple current, and it is what is important for capacitor ratings.
 


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