PSN-L Email List Message

Subject: Re: Re[2]: noisy power supply
From: CapAAVSO@.......
Date: Thu, 6 Jul 2000 10:56:10 EDT

In a message dated 7/6/00 12:01:48 AM Eastern Daylight Time, 
angel@............ writes:

<< I have some -+ 12 volt supplies I have made for other projects.
 Where should I make the connections??  Do you suggest cutting
 and splicing the main power connector that goes to the ATX mother
 board??  This my first ATX computer and it seems that the power is
 switch on and off a bit differently than on an AT computer.  The power
 off is just a software thing.
 Best regards,
  Angel                            mailto:angel@............ >>

Hi Angel,
    The power supplies I described in my email of 07/05/00 made from radio 
shack parts are described again below:

    << Dual plus and minus power supplies (non-switching) are easily made 
from parts all of which are usually in stock at your local Radio Shack. Buy 
two 12.6 Volt transformers, two full-wave bridge rectifiers, two 1000 mfd 
electrolytic capacitors, two 12-volt positive voltage regulators and two 0.1 
mfd capacitors. Build two separate 12-volt power supplies and hook them 
together in series to make a +12V, -12V dual power supply. Where they connect 
together goes to ground. Radio Shack sells a little book about power supplies 
which you should also buy if you are not sure how to hook the above stuff 
together. With the help of the little book anybody can build their own dual 
power supply for far less than an off-the-shelf dual supply would cost.>>

    These are two separate power supplies not connected to each other in any 
way, although they can be side by side on the same circuit board. Their 
outputs are floating, that is, isolated and not connected together as would 
be the case if you used one center tapped transformer and a negative voltage 
regulator. Connect the floating minus output of one power supply to the 
floating plus output of the other power supply. The point where the two 
connect together should then be connected to ground or neutral in whatever 
device they provide power for. The other two outputs provide the plus 12V and 
minus 12V to power the device. A dual + and - 5V supply can be made from two 
6.3 Volt transformers and two plus 5 Volt regulators. The reason for using 
two transformers and two positive voltage regulators is Radio Shack does not 
carry negative voltage regulators. The above is a way to make one trip to 
Radio Shack and come home with everything you need to make a good homemade 
regulated dual power supply for far less money than you could buy a ready 
made one.
    I have never gotten into the guts of my computer so I think I should let 
someone else explain the details of just how to go about connecting the above 
dual power supply into your computer.

Best regards,

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Larry Cochrane <cochrane@..............>