Power Supplies Given to Me

D. Schouten daniels at xs4all.nl
Fri Mar 24 19:11:37 CET 2000

I would add LC postfiltering. Something like :

SMPS output ->        ===    -> Cleaned up DC

Depending on how much HF ripple is present and
at which frequency, you should tweak around with
LC values. Try to find a ferrite toroid of about
1/2" OD or larger and wind 100 to 1000uH on it.
Choose a ceramic cap of about 1uF (parallel some if
neccesary) and you find quite some reduction of
HF noise. If you need more reduction add a second
LC low-pass filter after the first one, or use a
common mode inductor by putting two windings on the
core in anti phase, one for the minus line and one
for the plus line.

If it's pure clean DC you want out of a switcher, 
apart from taking the radiated emmision into account,
it isn't impossible. Nowadays there are quite some
SMPS designs out there used to supply very sensitive
circuits, without any problems.

Good luck!


----- Original Message ----- 
From: Scott Gravenhorst <chordman at flash.net>
To: <synth-diy at node12b53.a2000.nl>
Sent: Friday, March 24, 2000 07:28
Subject: Power Supplies Given to Me

> My manager was having outdated equipment tossed out and he
> told our team to take whatever we wanted and make it disappear.
> There were several power supplies for Epson printers, 24 volt
> DC at 1.5 ampere.  These are rather nice units with a power switch
> and power light.
> My question is:  Assuming these are switching supplies, is there
> some kind of circuit I can put on the output to eliminate switching
> noise?  I thought of a simple diode/capacitor thing, or small ohm 
> high wattage power resistor and a cap...  Comments?
> -- Scott Gravenhorst                    | Linux Rex, Linux Vobiscum
> -- FatMan: www.teklab.com/~chordman     | RedWebMail by RedStarWare
> -- NonFatMan: members.xoom.com/_XMCM/chordman/index.html
> -- The 21st century does NOT start in the year 2000!!!

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