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In my sophomore year of college at the University of Minnesota, I started into my main electronics classes, and needed a good power supply for working on the lab projects at home in my room. My roommate Adam told me about somebody online who had converted a spare ATX computer power supply into a lab bench power supply, so I decided to try and do the same thing. I scrapped the power supply from the PJRC MP3 Player, and started the conversion.
When I opened up the power supply, I found the following wires inside:
I connected the +5, +12, -12 voltage rails through individual 1 Amp fuses to the front binding posts. I connected the ground connection directly to the front binding post. I connected the switch between the Power_On signal and Ground. When the Power_On signal is connected to Ground, the power supply will turn on. I connected the +5V Standby through a resistor and LED to ground, which is useful as a "plugged in" indicator LED. The Power_Ok signal goes high (+5V) when the power supply has settled down after startup, and all voltages are in their proper ranges. It is connected to the other LED through a resistor. There is also a 10 Ohm, 10 Watt power resistor between +5V and Ground. It is used to provide a small load to keep the power supply in the On mode.
Note: While the diagrams show fuses on all voltage rails and no fuse on the ground line, when I actually built my power supply, I was young and foolish and only put a fuse on the ground wire. It's much safer and a better idea to put fuses on all signal lines and not the ground line. Thanks to many emails and messages on Instructables about this oversight.
I have included a handful of pictures here with descriptions, but all the pictures are available in my Lab Bench Power Supply group on Flickr
This project is also documented on the Instructables website.
|This is the original drawing I made to plan out the conversion.|
|This is the circuit diagram to show how to connect everything.|
|Here you can see my drawings on the side of the case. I had removed the insides so I could safely drill the holes. In this picture, the hole for the first binding post has been drilled, and I have marked out the locations of the fuse holder and power switch.|
|Finished drilling all four binding posts, as well as the pilot hole for the power switch. Yes, I am working in a garbage can, so the metal shavings don't get in the carpeting.|
|Test fitting all four binding posts, the fuse holder, and power switch.|
|I added two LED indicators to the front. Here you can see the back-side of the LED holders. They will be used to indicate "Standby (Plugged In)" and "Power On (Switch On)".|
|Here, I started to connect the binding posts to their proper wires. I have connected the +5V and GND in this picture. You can also see the LED's on the right side of the picture.|
|In this picture, you can see two green LED's in the holders. I eventually switched to red LED's because I have many more red ones than green ones. At this time I had already finished connecting all four binding posts.|
|Here, I have connected all the binding posts, the indicator LED's, and the power switch.|
|You can see the 10 Ohm, 10 Watt, power resistor connected to the back wall of the power supply. It connects 5V and GND, which provides a load to keep the power supply operating when I don't have anything connected to it.|
|I used regular breadboard wire to attach the power resistor to the back wall of the case.|
|The finished product, with the lid off.|
|Another view of the finished power supply.|
Copyright © 2004 - 2017, Matthew L. Beckler, CC BY-SA 3.0
Last modified: 2009-12-16 01:49:20 PM (EST)