More on Fav Designs - switchmode power supplies

[Ken Stone]

>1)PC type supplies are designed for a heavy loading. If fact, most "flyback
topology" switchers suffer from the fact they need a minimum load to not
have the outputs over-voltage. In a PC, this can be as much as 500ma. As I
said before, a typical syth doesn't need much CURRENT: it needs low noise,
no ripple voltage. The terms "switcher" and "low noise" are seldom used in
the same way (yes, there are ways to get this, but a LM723 is easier).

Agreed. PC supplies are for driving noisy digital stuff. I do have a
switchmode in one part of my synth - the digital part, where I am driving
hoards of TTL on 5V. The rest I run on nice 723 or genuine Roland PSUs.

Some PC supplies will not even start with under minimum loading, especially
the older models. I have had these passed to me before for repair... "I
found it lying around. It doesn't go when I turned it on"... Of course, the
person was running it unloaded. Hanging an old harddrive or motherboard off
them gets them running.

In fact, I gutted one computer switch mode to build my Analog PSU into. A
nice convenient shielded case!

>921-9410  SOLA model SLT-12-20404-12 "open frame" style 5 at 2A, +-12 @400ma
>about $60

Now there's a fun supply. I used to work for Sola in Australia, and had a
few of these things on the bench. I don't recall ever having any problem
with them.

Ken
_______________________________________________________________________
Ken Stone   sasami at blaze.net.au  
Catgirl Paradise <http://www.anime.net/~kens/>
Australian Miniature Horses & Ponies <http://www.blaze.net.au/~sasami/>