Re: gEDA-user: bypass caps

[Steve Meier <smeier@xxxxxxxxxxxxxxxxxxx>]

A more expansive question is about  the selection of inductors and
capacitors for power supplies. The issue as I under stand it is that we
put inductors comming out of power supplies to insure a "constant"
current and capacitors are there for a "constant" voltage. In reality
these devices help but arn't perfect so that there isn't a constant
current or voltage but there is an approximation that has an amount of
ripple which is dependent upon the selection "intentional or not" of the
amount of inductance and capacitance. The amount of ripple can be
critical. hmmm ask any drunk they might tell you the more the ripple the
happier we can be.

For your furnace controller i suspect we are talking low frequencies so
either .1 or 1 uF will probably do just as well. For high frequency
systems the ripple might become critical. Look at recomndations for
Altera or xilinx devices... uhmmmm from a practicle purpose toss in a
few extra land points for capacitors or be preparied to stack them.
Power supplies sometimes do require tweeking.

Steve Meier

DJ Delorie wrote:
>0.1 uF or 1 uF ?  Same footprint (0603), the 1uFs are a few cents more
>each (er, ~ 40% more cost for 10x the capacitance).
>
>Don't know if the 0.1uFs have some benefits inductance-wise or
>ESR-wise, in general.
>
>
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