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Old 11th April 2009, 04:18 PM   #1
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Default ceramic capacitors ....

how good are ceramic capacitors ???
what is the range of application ???

we often hear that ceramics for input filters ,miller caps, feedback traces are better to be mkt or styroflex or silver mika ....( eventhough ceramics exist in comercial application )

then if its a low fi application like small psu with 7812 or 7805 is it ok to use there as decoupling or over the rectifier ????

thanks
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Old 11th April 2009, 04:27 PM   #2
AndrewT is offline AndrewT  Scotland
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Hi,
there are two downsides to ceramic that I'm aware of.
1.) capacitance varies with applied voltage.
2.) Non NPO/C0G vary capacitance and other parameters with temperature. NPO/C0G vary their other characteristics just like the hiK versions with temperature.

If you keep the voltage constant (eg. supply decoupling) most of the disadvantages of 1.) are avoided.
Some designers swear by ceramics for local or on pin decoupling. Even to the extent of recommending the high K specifically for this use.

I think everyone is agreed that ceramics are not good at passing Audio Signals.
Few, if any, other capacitor types can challenge the low inductance of ceramic. If low inductance dominates your requirement, then possibly ceramic might be your only solution.
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Old 11th April 2009, 04:49 PM   #3
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Default thanks andrew

the thing is that i got about 10.000 ceramics of any size and capacitance .... and it seems that i have to start using them somewhere cause i am runing out of time ....

i am not going to construct things in this life that will consume 10.000 ceramics .....
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Old 11th April 2009, 05:13 PM   #4
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Sakis,
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.... and it seems that i have to start using them somewhere cause i am runing out of time ....
Hopefully, not in audio....
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Old 11th April 2009, 05:40 PM   #5
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Default too old

Quote:
Originally posted by Lumba Ogir
Sakis,

Hopefully, not in audio....
to start dealing with other things like RF or microcontrollers ha ha
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Old 11th April 2009, 06:08 PM   #6
Mr Evil is offline Mr Evil  United Kingdom
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Ceramic capacitors can be useful. They are fine for supply bypassing, especially the SMT types which have very low inductance. You must consider what the actual capacitance will be at the voltage you use them at - look at the datasheet.

You might find it interesting to look at Cyril Bateman's article on capacitor distortion, which you can find on his website. It shows that C0G ceramic capacitors have very low distortion, while other types are very bad and thus should not be used in the audio path if you're at all concerned with sound quality.
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Old 11th April 2009, 06:18 PM   #7
fotios is offline fotios  Greece
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Hi Saki

It is true that some types (e.g. CD15 +/-1% series of Cornell Dubilier for 1,26 GBP/piece excluding VAT) of silvered mica caps offers great stabillity under any condition. This is usefull in timing circuits or other close tollerance applications like in filters included of course the Miller pole compensation etc.
Nothing more, nothing less. I have used them in my last amplifier project and i had a small improvement (it is very difficult to hear) in high frequencies. OTOH i had a great visual improvement on my project PCBs appearance
All above mentioned by Andrew, i think are very explanatory.

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Old 11th April 2009, 06:26 PM   #8
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Mr Evil,
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Ceramic capacitors can be useful.
Not if you care about the sound.
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Old 11th April 2009, 07:01 PM   #9
Mr Evil is offline Mr Evil  United Kingdom
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Quote:
Originally posted by Lumba Ogir
Mr Evil,

Not if you care about the sound.
Yes, even if you care about the sound. You just have to be aware of the properties of the capacitors you are using, e.g. don't use high-k types anywhere that linearity matters, but C0G types are fine for all sorts of purposes, e.g. they work fine as Miller compensation capacitors.
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Old 11th April 2009, 07:18 PM   #10
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Some multilayer C0G types are about as perfect as you can get, even with temperature. Low DF and low DA. They just don't come in high values nor are they very size efficient. Chances are you've got hi K parts good for bypassing, so maybe build a lot of digital circuits?
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