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Adjustable Lab Power Supply

06/02/2010

Ever since I got into electrical engineering I wanted a lab power supply, unfortunately I don’t have 2oo bones to toss around.  A few months ago I stumbled across this site on how to make a lab power supply on the cheap. Since the ATX power supply only offers particular voltages, I wanted to take the project a step further. I wanted to be able to adjust the voltage being supplied. I had previously worked with the adjustable voltage regulators from Radio Shack, but was not impressed with the current output level. So I decided to beef up the voltage regulator with something more power demanding like this guy.

Run down on parts used:

ATX Power Supply (Hopefully you have one laying around)
Three Way Binding Posts
(As many as you think you need, view COLOR)
Switch

LED

Heat Shrink
(Highly recommended)
100-ohm Resistor
(1-Watt is probably overkill but there is potential for heavy current flow)
LM350K Voltage Regulator (DATA SHEET)
Potentiometer
Knob (To clean up appearance)
Multimeter (Get a cheap on from eBay)

As far as tools went – A soldering iron, a drill gun, and a screwdriver is a must. A Dremel came in handy when I had to trim the potentiometer, and a lighter was used to fit the heat shrink.  Also I would recommend you take a multimeter and measure the output voltages for yourself and instead of relying on the wikiHow article. Lastly the input voltage for the adjustable voltage regulator is a +12V line from the power supply. The power supply can only adjust from approximately 1.4 V – 11.5 V.

The final product is not want I had envisioned. I planned on having the multimeter LCD screen display the voltage inside the ATX case. Not on the outside as depicted. However, after taking apart a cheap multimeter, the inner circuitry was way more complex than I had anticipated and I ended up throwing it in the trash. I also had intended on all of it being no bigger than the orignal ATX case. As you notice the encasing is almost 2 times bigger than the original housing. This was due to my poor planning and layout.

I wish I had documented this project to share with you all. I began recording and taking of video of the process and the the batteries on my camera died, frankly I am glad they did. The video was of me messing up a lot. That is when I realized that I should film the process of building one, after I have done so successfully.

Aesthetically the project did not turn out as intended, but functionality wise it works perfectly. The three bottom posts are all ground (disregard the color, I ran out of black). The top far-left and far-right posts are the adjustable voltages (This allows a multimeter to be plugged in).  The mid-left-top is +12V and to its right is -12V (This would be great if I ever wanted to use the application for an op-amp circuit).

My intent in the future is release a better/improved version which is well documented and filmed. I wanted a cheap and dirty lab power supply, I didn’t want it to look cheap and dirty. Have fun.

-Garza

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