[sdiy] "Zerolytics"

[Steve Lenham]

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 
were getting.

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 
well...

Cheers,

Steve L.
Benden Sound Technology