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December 16, 2012 AT 6:35 am

EE Bookshelf: Temperature and Voltage Variation of Ceramic Capacitors, or Why Your 4.7µF Capacitor Becomes a 0.33µF Capacitor

A big thanks to @SiliconFarmer for the heads up on this interesting article on ceramic capacitors and voltage variation.  I switched to exclusively using ceramics a while back, except where there were specific circumstances that made a tantalum or electrolytic a more sensible choice.  They’re small, they’re affordable, and they have no polarity issue.  This great article from Maxim made me pull out some datasheets, though, and take another look at something I’ve just been adding and ignoring for ages: Temperature and Voltage Variation of Ceramic Capacitors, or Why Your 4.7µF Capacitor Becomes a 0.33µF Capacitor.

Update: The most common large ceramic caps I use are some 10µF 0805 16V X5R ceramics from AVX.  No mention whatsoever of capacitance loss over voltage in the 3 page datasheet, and you have to dig down to page 83 of the generic information for their entire family to find a single chart on this (shame on AVX) for such significant information and they only discuss AC, without going into any detail over package sizes and with DC voltage, etc. … though perhaps I just missed something?  Seems like a good experiment to pull some caps out and check the numbers myself!


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2 Comments

  1. Wow! If capacitance can vary so much over bias voltage, how linear are these things when you run AC with voltage swings that are a significant proportion of their voltage ratings? And what frequencies are most affected if we have to take internal swelling of the ‘plates’ into account?

  2. @KA10S, it depends on what frequency the AC is. At low frequencies you will actually see a rise in capacitance. The change is due to the dipoles in ceramic aligning with the electric field. At low frequencies, this alignment actually causes a slight rise in K.

    The temperature and voltage coefficients are one of the reasons KEMET offers a simulation tool. You can apply temperature and DC bias to ceramics to see how their capacitance will change. Our tool is based on actual measurements, not just calculations.

    http://www.kemet.com/kemet/web/homepage/kechome.nsf/weben/kemsoft

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