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50V ceramic cap on 5V rail?

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grizedale

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If i put a 50V ceramic 100n cap on a 5V rail, will it still act properly as a capacitor.?...or will it not "form" correctly, and not have the desired capacitve effect............i know this is the case with electrolytics.
 

Externet

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A 50 V rated capacitor tells you the maximum rail voltage it can work on. Will be very happy on a 5V rail and last forever..
 

alexan_e

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If i put a 50V ceramic 100n cap on a 5V rail, will it still act properly as a capacitor.?...or will it not "form" correctly, and not have the desired capacitve effect............i know this is the case with electrolytics.

So you mean that a 50v electrolytic will not work properly at 5v?
I haven't heard about this, do you have any links that explain this?

Alex
 

barry

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This 'forming' business, I think this was more true 50 years ago when electrolytes weren't as good. Regardless, as long as the cap hasn't sat idle for several years, it should be ok. Even if it HAS sat around, I think it will 'reform' once put back into service. This only applies to electrolytics. Further, why would you use a larger, more expensive part if you didn't need it?
 

FvM

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You have been originally asking about ceramic caps, so there's one thing we should add. A 100 nF/50 V/ X7R dielectricum capacitor will typically show a reduced capacity of 85 nF at rated voltage, which is a good reason no to fully utilize the rating. You'll observe even higher voltage dependency with high Er materials like X5R.

Secondly, low capacitance Al-electroylyte caps, e.g. 1 µF will be mostly stocked with 50 V rating at least. You'll possibly face difficulties to get them with lower voltage ratings.
 

barry

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Secondly, low capacitance Al-electroylyte caps, e.g. 1 µF will be mostly stocked with 50 V rating at least. You'll possibly face difficulties to get them with lower voltage ratings.

I would just use a ceramic for that low a capacitance. Ceramics have gotten so good that they replace tantalums in a lot of applications.
 

grizedale

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hi , thanks,

Barry:
I would use a larger cap than needed because its cheaper to use, say seven 100n,50V ceramics...as opposed to six 100n,50v ceramics and one 10v,100n ceramic.

Alexan_e:
The reference about el caps at low voltage is in the babani book "ic 555 projects" page 11.
this was first published in 1978., but reprinted 2006.
 

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