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ATX to Lab Bench Power Supply Conversion

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:

• +3.3V
• +5V
• +12V
• -12V
• +5V Standby (Always On)
• Power_On
• Power_Ok
• Ground

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.

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.

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Last modified: 2023-01-09 02:49:32 PM (EST)