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PICList Thread
'[EE]: Bypass Capacitors'
2003\06\14@161737 by Dave Dilatush

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Al Margolis wrote...

>Searching Digikey, I can only find 0.1uf X5R capacitors in surface mount
>packages, so that's off my list.

I use Digi-Key part # 399-1863-1-ND for my hobby stuff (0.1uF,
50V, X7R).

>Searching for 0.1uf, Z5U or X7R, non-SMT capacitors, the lowest voltage
>rating offered is 50v.  Is there any disadvantage going to that high a


>Is it necessary to be this specific, or would it be safe to say something
>like "any 0.1uf ceramic capacitor with a voltage rating greater than 10v" ?

That's about all that matters, for bypassing purposes.

>How much flexibility from that 0.1uf rating is reasonable?

I've seen people use anywhere from 0.01uF to 0.22uF.

>How critical are these capacitors for these types of applications?

The exact value doesn't matter much; but it's important to use
them.  Not doing so invites trouble.

>I have been building a number of these circuits lately and have had good
>success without bypass capacitors.  Have I just been lucky?

Yep.  You'll understand just how lucky, the first time you build
a circuit and it DOESN'T work properly due to lack of adequate
supply bypassing.  The kind of problems this causes (when it
causes them) can be an absolute nightmare to troubleshoot.

>How do I explain that?  I hate to say "you have to do this" to kids when
>I know they can say "see, it works without it".  They don't pay any
>attention to the next "must".

If they're old enough, explain to them that it's kind of like
"safe sex" except (a) bypass capacitors don't cost as much as
condoms, and (b) they don't take as much fun out of whatever it
is you're doing.  If they're not old enough for that, try a
bicycle helmet analogy.  Bottom line is, it's better to be safe
than sorry.

Dave D.

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