[sdiy] "Zerolytics"

sleepy_dog at gmx.de sleepy_dog at gmx.de
Fri May 8 23:23:25 CEST 2020


Ben Stuyts wrote:
> Haha, you beat me to it with the EEVblog videos. :)

Why, here is another one! A newer one that I hadn't seen before, while
we're throwing links around ;)
A nice practical demo of the theory presented in the previous videos

Bypass Capacitors Visualised!
https://www.youtube.com/watch?v=1xicZF9glH0


>
> Ben
>
>> On 8 May 2020, at 18:45, sleepy_dog at gmx.de <mailto:sleepy_dog at gmx.de>
>> wrote:
>>
>>
>> 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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>>>
>>
>>
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