Re: Star Wars Power Supply

On Mon, 16 Aug 1999, John Robertson wrote:

> These days it is usually a good idea to replace critical supply voltage
> with switching power supplies. Computer power supplies are so cheap and
> reliable, plus they have nice failure modes (they shut down, not short
> out!). I would have a relay connected to the +12 and use it to disconnect
> the monitor if the supply goes down.

        Here it comes....someone just hit one of my pet peeves....must
resist.....must resist.......can't resist....

        Of course I disagree. Switching supplies, while cheap and
compact, are noisy (meaning the voltage they produce) and just as
unreliable. I am looking at literally stacks of old PC cases that our CAD
department is throwing out due to bad power supplies. Somewhere along the
line someone got the notion that switchers were more reliable than linear
power supplies, and that's just not true. It's, of course, true that any
new power supply is more reliable than an older power supply (just like a
new car is more reliable than an old car....unless the new car is an
American car, and the old car is a Mercedes :P ) ...and I think that's
where that notion came from.

        Linear supplies produce quiter voltages, which, leads to, among
other things, nicer sounding audio when you run amps off of them. No amp
has an infinite PSRR, so when you hit it with the horrendous supply
voltages that switchers produce (I'm no expert on switching supplies, but
I think they switch at around 20 kHz, which gives you nice noise right at
the "annoying edge" of the audio band) you'll get some distortion.

        Not to mention that I'd rather not hack up my Star Wars just to
put a switcher on the +5V line (I'd have to keep the stock power supply in
there anyway for the monitor voltages.)

Joe
Received on Tue Aug 17 10:52:18 1999