Introduction: Modified ATX Power Supply

Power supply units are always the essential part of any project, powering all your circuits during testing and analyzing. But these are kind of expensive in the market, the kind that goes beyond my budget. I was kind of fed up of always having to set up a transformer-rectifier-filter circuit each time I needed a DC source. Fortunately I got my hands on one of those ATX supplies used in desktop computers. So this was a simple and straightforward project that didn't require any fancy electronics skills to create. So in the end I had my own bench power supply

Step 1: Analyzing It

So these are designed to power the various components of the CPU so it provides standard output voltages of

3.3V (orange wires )

5V (Red wires)

12V ( Yellow)

Common/ground (Black)

Standby +5v (Purple)

-12V (Blue)

3.3V sense (brown)

Power on (Green)

and few other that we may not need.

The power supply is rated for 450W and can dish-out about 35A max on the 5V line( not sure where and when I will need such high current). So the only downside using this is that it only provides the above standard voltage values and does not have a current control or current limiter found in normal power supplies. Well the board can be modified to make the output voltage variable and add an current control feature but its a bit difficult and I didn't want to poke around with it too much and destroy the only one board I had. Besides, I had a Boost converter module I had bought out of curiosity a while back so attaching that thing to the 5V line I could actually get a variable supply upto 40V which will be more than enough.

Step 2: The Enclosure

The best and the most common way to do the enclosure is use its own one. Drill the necessary holes for connecting the output lines and you're done. But no, I wanted to make it a bit more professional so I went out and bought a metal casing which was a bit bigger than the original one and was cheap (less than $2). This one did not have a front panel so I had to make one. I used something I believed was plywood sheet leftover from some interior fabrication work. Then again I lacked the necessary tools required for mechanized drilling and cutting so I had to use a chisel, hacksaw blade and a hammer to get the work done.

So after some brutal handicraft I was able to make the necessary holes.I decided to go with one port each for 3.3V, 5V, 12V and GND and a separate port for variable output of the boost converter. I made separate ports instead of just the variable boost output in order to connect heavier loads since the boost converter could only handle 2A max at output.

Then I fixed the binding posts, switch and the pot for the converter also put one of those DC volt, amp meter

Step 3: Connections

Doing the connections was easy enough, connect wires according to the color code to the appropriate binding posts and maybe use 2 or 3 wires per rail for facilitating higher currents. The green and black go to the switch as shorting the green and ground turns the supply on. Also connect the sense wire of the voltmeter to a slide switch and connect leads form each of the ports to the slide switch so we can switch the sense wire to any of the output ports. The ammeter connection goes in series at the common ground and secure all the exposed wires and connections using heat shrinking tubes.

Then I fixed the input plug socket at the back as well as the cooling fan.

That was pretty much it, then I screwed the cover tight and turned it on, did testing with some loads and worked just fine.