steve at bendentech.co.uk
Fri May 8 11:08:01 CEST 2020
On 08/05/2020 05:15, ColinMuirDorward wrote:
> I'm wondering, is anyone using ceramic 10uf at the power inlet of their
> synth modules?
> Is there a good reason why it never occurred to me to try this out before?
> I enjoy that the electrolytics look like proud little sentinels, but if
> an smd robot can deploy an equally effective 0805 ceramic, all the better.
I've been doing this in my day job recently and it's fine, as long as
you are aware of the one big drawback of this kind of cap. As others
have already said, the capacitance of these cheap
high-value-per-unit-volume ceramic parts is voltage-dependent to a
degree that you will find hard to believe when you first read it.
e.g. a standard part for one of my clients is a 10uF/16V 0805 ceramic
made by Murata. Great, very useful. But if you put 12V of DC bias on it
- like by using it as a decoupling cap on a +/-12V supply - then the
capacitance reduces to 1.1uF, about one-tenth of what you thought you
Sometimes that doesn't matter and sometimes it does. For places where it
does, I have had to start using a 10uF/50V part in a 1206 package. With
a 12V bias on that, you get just under 9uF.
You can buy much better high-value SM ceramic caps with stable
capacitance values but they have to use less "ambitious" dielectrics and
as a result are much larger. They also tend to be expensive.
The moral of this story is that you rarely get something for nothing and
if it seems too good to be true (10uF in 0805?) it usually is.
The other moral? Always read the datasheet!
BTW, if you like the look of electrolytics then they do come in SM as
Benden Sound Technology
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