Extreme noob electronic question

[Paul Maddox]

As tony says, it's good practice to do both.
One of the main reasons is that every component includes an element of
resistance, all be it small.
so whilst in theory a 220uF should cover every from quite low frequency to
very high, in practice it won't. So you'll often see a 100nF and a
something between 50uF and 220uF to make sure the 5V line is as stable as
possible.

You could use almost any value you wanted, but 100nF is a bog standard
value available anywhere in almost any pin format and it's widely
considered the defacto standard for decoupling (the practice of shorting HF
to ground and stabalising a power rail).
it's good engineering to do what you can to keep things stable, and 100uF
(or 220uF) caps are only a few pennys and can save a lot of hassle with
debugging a circuit which has a 5V rail that's jumping around like a mad
thing :)

What you building?

Paul

On 18 January 2013 15:47, Tony Hardie-Bick <tony at entity.net> wrote:

> On 18/01/13 15:17, Marc Nostromo [M-.-n] wrote:
>
>> While I'm digging the subject, why is there a 100n and a 220u
>> condenser next to each other in  Olivier's 'Mutable' regulators.
>>
>
> this is down to the imperfections of real world capacitors. generally,
> the bigger they are, the more inductance they have, which prevents them
> from smoothing especially fast transients (like the transistor switching
> Paul mentioned), so a common solution is to put a high value and a low
> value right next to each other. In a microprocessor circuit, you might
> know that all the switching is the instantaneous stuff, like zero to 5V
> in 25nS etc, which only a small capacitor can deal with, and in fact,
> the microcontroller usually has some fairly tight specifications for
> placing such a capacitor nearby, and, if you're really pushing it,
> specifically what make and model of capacitor you can use (most extreme
> examples being switched mode inverters).
>
> fun fun fun....
>
> actually, electrolytic capacitors are an awesome example of applied
> nanotech,
> although nobody ever calls it that. manufacture involves creating an
> insulator
> a few atoms thick, by passing a current through the structure. As the
> insulator
> grows, it leaves gaps which attract more of the current, so these get
> filled in
> while the existing insulator fails to grow any thicker. amazing, but i
> digress...
>
> Tony (HB)
>
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