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Every hobbyist needs one of these; an ATX power supply made into an inexpensive ben top power supply. Capable of supplying a number of voltages, this simple project will be a center piece for any do-it-yourselfist needing a solution to their power needs in testing and fabricating other projects.
On a standard ATX power supply, the PS_ON pin can be identified by the green wire, number 16. When a computer is turned on, this pin is tied low and gives the PSU a signal to turn on its main voltages. Prior to activating the main voltages, pin 9 being +5VSB and purple, provides a constant +5VDC as a standby voltage and can be capable of delivering an amp or more while main voltage is off. It may be useful as an indicator of AC power or an always-on supply for small loads. Other voltages provided include +3.3, +5 main, +12, -12, and -5. Combining these will yield various other voltages that can be calculated by absolute potential.- ted
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Past experience has shown that many large switching power supplies have problems when used with little to no load, something a bench-top supply has to be able to handle. In the best case, they won’t operate. In the worst case, they operate with little regulation (typically an overvoltage).
One tip is that automobile headlights make pretty good “dummy” load resistors to provide both a clearly visible “power-on” signal and provide a constant load. Typically, it is only necessary to place these on the main power outputs.
This is a great project
Wad — I have addressed this by adding a 10ohm resistor to the 5V rail, as discussed in the write-up. This puts a 0.5A load on the rail and gives the PSU something to think about. Besides, when the power supply is on I am using it, so unless I leave it on for the pretty lights, there should be no problem.- ted
Ted, I really like this project! I advise extreme caution for anyone thinking of tinkering on the inside to consider this: switching power supplies can pack a lethal shock if handled inappropriately (just look at the size of those black caps!). Be careful.