AW: multiple power supplies in a modular

The Dark force of dance batzman at gist.net.au
Fri Feb 6 02:04:15 CET 1998


Y-ellow Y'all.

At 12:49 PM 2/5/98 +0100, Haible Juergen wrote:

>I never made serious experiments on this, but reportedly it's not that
>important
>to filter out everything down to a couple of hertz if you are using
>*opamp*
>circuits.
>Opamps tend to have excellent power supply rejection at low frequencies,
>but poor rejection as frequency increases. So maybe even combinations
>of 22 Ohm / 10uF (or something similar) make sense.

Yup. Likewise. I've always used a rule of thumb. If you've got enough room
on the board, whack in a big cap. If not, a small one will do. :) Actually
I've found that even 1u works on your avarage op-amp. I've noted some
circuits using a simialr appraoch using 0.1u and even a few puffs. I figure
they were filtering for a specific problem in those cases. 100 ohms is fine
for most op-amps where swing isn't so importent. Which is why I usually
stock a couple of thousand 100 ohm metal films at a time. But! where I have
had problems is when the supply is lower. Most of the time we use supplies
of +/-12 to +/-15 volts but often I've had to use odd supplies like +/-5 to
+/-7.5 volts when in combination with CMOS and other gadgetry. 100 ohms can
become a little problematic at these voltages. You may notice an increas in
distortion or lack of useable gain etc. You have to make a trade off. Of
course what would be extrememly useful at these voltages is a couple of
low-drop-out regulators. But since I can't just rund down the street and get
such things I have to take matters into my own hands.

But I think the operative here is. Any filtering is better than none.

Be absolutely Icebox.
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