Power supply?

[gstopp at fibermux.com]

     On 11/19/96 e6erik at etek.chalmers.se wrote:
     
     >
     > Power supply for a modular:
     > (taken from computers I think)
     >
     > 5V/100A 5V/15A 12V/5A -12V/5A Qulidyne switched
     >
     > 5V/2A 12V/1.5A -12V/0.3A
     >
     > 5V 20V 12V -12V
     > linear
     >
     > Could something like this work at all?
     >
     > Could I make use of a +/- 12V for any applications?
     >
     
     Most analog circuits will work fine on +12/-12 rather than +15/-15. 
     Some loss of range may result, but that totally depends on the 
     specific circuit. I built a Minimoog ladder filter once (+10/-10) and 
     it worked fine on either 12 or 15 volt systems.
     
     Switching power supplies (like you find in PC's) can be used to power 
     analog audio equipment, no problem. They may need some filtering on 
     their DC outputs to reduce noise. Also they will radiate 
     electromagnetic waves at high frequencies, so they might need to be 
     located further from the audio circuits than a linear supply needs to 
     be. It also may be a good idea to enclose them in a grounded metal box 
     to help minimize emissions.
     
     Switchers can be tempermental - some will shut off if a certain 
     minimum load is not present, some will shut off if the load is changed 
     rapidly, and all will shut off if their output is shorted. Almost all 
     of them have all voltage regulation functions tracking the +5 output 
     *only*, which means if you load down the +5 to close to it's current 
     limit, it will be working hard and the +12 and -12 outputs will be 
     around 14 volts each! Pretty sucky regulation. Also if something goes 
     wrong inside, they will appear to be dead to the world, and (in my 
     opinion) it's cheaper to throw them away than to try to fix them. Most 
     cheap switchers have a lot of design tricks in them just to get them 
     to work in the first place, so it's difficult to just look at the 
     components and then figure out how the thing works and what 
     replacement components can be used. Besides much of their guts consist 
     of special custom transformers and such.
     
     The 5V/100A 5V/15A 12V/5A -12V/5A must be huge. I would think that 
     this power supply would be way overkill for a typical DIY project. It 
     is really intended to power many logic circuit boards, probably a 
     whole cabinet the size of a minicomputer. Also one hundred amps is 
     quite a dangerous amount of current to have around - if you don't take 
     many, many precautions you can cause a fire! Even though the supply 
     will certainly have a shutdown feature on this output, it is designed 
     to drive extremely low impedance loads so it can easily turn a wire 
     harness into a flaming molten mass. Also clouds of sparks a couple 
     feet in diameter could be made. Hey sounds like fun, huh.
     
     One thing that needs to be kept in mind when using standard 
     off-the-shelf switchers for audio, is that analog circuits usually 
     only need +12/-12 or +15/-15 volts, and there is no need for the +5 at 
     all. Well the +5 voltage is really the main reason for the switching 
     supply's existence in the first place - the +12/-12 outputs are just 
     secondary outputs to power the RS-232 ports which don't need much in 
     the way of amps. Also the -12 output is usually the wimpiest of the 
     bunch, because it's hardly ever used for anything (most designers have 
     a subconcious bias towards using positive voltages all the time). Many 
     analog circuits (such as synthesizers) center everything around ground 
     so that the plus and minus supplies are best made symmetrical.
     
     However much merit must be given to the idea that since switching 
     power supplies (especially PC power supplies!) are cheap and widely 
     available, they may be useful for synthesizer projects. Now that this 
     topic has come up I think it may be a good idea to examine a typical 
     PC supply to see how it will work for analog audio. I think I'll go 
     mess with one the next chance I get.
     
     - Gene
     gstopp at fibermux.com


______________________________ Reply Separator _________________________________
Subject: Power supply?
Author:  Erik Forsling <e6erikf at etek.chalmers.se> at ccrelayout
Date:    11/19/96 1:33 AM


Power supply for a modular:
(taken from computers I think)
     
5V/100A 5V/15A 12V/5A -12V/5A Qulidyne 
switched
     
5V/2A 12V/1.5A -12V/0.3A
     
5V 20V 12V -12V
linear
     
Could something like this work at all?
     
Could I make use of a +/- 12V for any applications?
     
--- 
=-=-=-=-=-=-=-=-=-=-=-=-=-=
Erik Forsling 
     
<e6erikf at etek.chalmers.se>