What is CV rating and its significance in capacitor specifications?

[TheAnalogKid83]

Can anyone tell me what this means in a capacitor spec, other than that I know its associated with leakage current? Is CV for capacitance*voltage, or coulombs*voltage? If its cap*voltage, I will get units in coulombs (coulombs/volt * volt), so what do they imply then to get your leakage current? Maybe the datasheet I'm looking at is just a poor example, since it just says CV <= 0.01

 

[Pumblechook]

Dunno exactly..found this...

Capacitance x Voltage across the capacitor. The time is specified to reveal how much charge remains after the given time.

Applies to electrolytics mainly I think.

ESR is another parameter.

 

[uart]

CV mean capacitance times voltage.

What is your issue with leakage current?

 

[berkeman]

CV mean capacitance times voltage.

The CV rating is a reflection of the volumetric efficiency of a capacitor and its chemistry. In general, the higher the capacitance, the larger the volume of the capacitor. And given some capacitance value, the higher the voltage rating, the larger the volume of the capacitor.

So when a capacitor has a "high CV rating", that means that it is volumetrically efficient, and offers a small physical size compared to other capacitor types.


EDIT -- here's a typical link: http://www.eeproductcenter.com/showArticle.jhtml?articleID=164903830

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[uart]

Yes I'm very well aware of the relationship of CV to physical size of a capacitor. I was trying to get the original poster to state exactly what his actual question is regarding CV rating.

 

[berkeman]

Yes I'm very well aware of the relationship of CV to physical size of a capacitor. I was trying to get the original poster to state exactly what his actual question is regarding CV rating.

Sorry for any confusion, uart. I was replying to the OP's question, but plagiarizing your statement for clarification.

 

[Enthalpy]

Except that CV is poorly related to the volume. CV² is much more closely related - except at very low voltages, when electrodes are much thicker than the insulator, which is rather uncommon now even with electrolytic capacitors.

I think one shouldn't attempt to understand more subtle things than "big" when reading "CV rating".

 

[Proton Soup]

i'm having a bit of difficulty here. is CV capacitance*voltage, which would equal the charge, or something else? when I'm looking at Vishay capacitors, they're spec'ing capacitance-voltage as two numbers, which makes a lot more sense. I'm thinking that CV by itself means very little, and "high CV" is only meaningful at a specific voltage or capacitance.

 

[berkeman]

I'm thinking that CV by itself means very little, and "high CV" is only meaningful at a specific voltage or capacitance.

The way we use it here at work, is to look at "high CV" capacitors when we are trying to find the smallest SMT caps we can for tight layouts. They tend to cost a little more, since you are paying for the "feature" of smaller-than-standard size for a particular capacitance and voltage rating. You should be able to use Digikey, for example, to see that a cap in a high CV series costs a little bit more than one in a standard series, and you should see the size breakpoints at different places for high CV caps versus standard ones.

The high CV rated caps only come into play for very dense/tight SMT PC assemblies, AFAIK.

 

[Proton Soup]

yeah, but I'm thinking that when you call something a "high CV series", that's a marketing term.

 

[berkeman]

yeah, but I'm thinking that when you call something a "high CV series", that's a marketing term.

Most definitely. It has some technical uses, but it's marketing dividing up their product offerings, and justifying a little higher price. Much like low-ESR caps, or long-life ALEL caps. There are technical reasons that you choose to use those higher-cost families sometimes.