[sdiy] "Zerolytics"

sleepy_dog at gmx.de sleepy_dog at gmx.de
Fri May 8 18:45:14 CEST 2020


Steve Lenham wrote:
> 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.


Here's a video explanation about that, for those who'd like more explanation
https://www.youtube.com/watch?v=2MQyQUkwmMk

And while we're at it: Bypass Capacitor Tutorial
https://www.youtube.com/watch?v=BcJ6UdDx1vg



>
> 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
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