
_🚧 Work in Progress 🚧_

I needed a benchtop power supply for my electronics projects and opted to
utilize an ATX power supply. They're cheap, standardized, and notably output
3.3V, 5V & 12V DC with more than sufficient current draw (10A+). The only
downside is that they don't have a variable voltage output, but that could be
resolved with a buck-boost converter.

Despite the potential for numerous customizations, there persists a direct
correlation between project features and cost. To begin with, I chose a
simplistic design.

## Required Parts

- [x] ATX Power Supply (It's already a power supply)
- [x] Binding Posts (USB, Banana, etc.)
- [x] Fuses (1.5x Max Current)
- [x] Switch (Optional for Power On)
- [x] LED (Optional for Power On & Standby)
- [x] Load Resistor (Optional)[^1]

## Tools

_Minimum_

- [x] Multimeter
- [x] Soldering Iron
- [x] Wire Strippers
- [x] Screwdriver

_Optional_

- [x] Drill
- [x] Drill Bits
- [x] Hot Glue Gun

## Step by Step guide

| ![ATX Power Supply](/posts/atx-psu-stats.webp) | ![Required Parts](/posts/atx-psu-top.webp) |
| :--------------------------------------------: | :----------------------------------------: |

Firstly, it's important to understand the wire colors for ATX power supplies.
These are standardized and correspond with different functions:

<table>
  <tr>
    <th>Color</th>
    <th>Description</th>
  </tr>
  <tr>
    <td style="background-color: #E8590C">Orange</td>
    <td>+3.3 VDC</td>
  </tr>
  <tr>
    <td style="background-color: #E03131;">Red</td>
    <td>+5 VDC</td>
  </tr>
  <tr>
    <td style="background-color: #FFD43B; color: #000000">Yellow</td>
    <td>+12 VDC</td>
  </tr>
  <tr>
    <td style="background-color: #1971C2;">Blue</td>
    <td>-12 VDC</td>
  </tr>
  <tr>
    <td style="background-color: #6741D9;">Purple</td>
    <td>+5 VDC standby supply (STD)</td>
  </tr>
  <tr>
    <td style="background-color: #2F9E44; color: #000000">Green</td>
    <td>Power on signal (PSO)</td>
  </tr>
  <tr>
    <td style="background-color: #343A40;">Gray</td>
    <td>Power good signal (PG)</td>
  </tr>
  <tr>
    <td style="background-color: #000000; color: #F1F1F1">Black</td>
    <td>Ground</td>
  </tr>
</table>

Here's what the wires look like on my power supply:

| ![wires in 30a header](/posts/atx-psu-wires.webp) | ![example of spade terminals used](/posts/wires-finished.webp) | ![ATX Power Supply 3v w/multimeter](/posts/jerry-rig.webp) |
| :-----------------------------------------------: | :------------------------------------------------------------: | :--------------------------------------------------------: |

Next, the power on wire (PSO), indicated by the green color, must be connected
to the ground to turn the power supply on. The ground wires are the black ones.
For this operation, you can choose to use a switch, or you can simply connect
the two wires.

Moving forward, the +3.3 VDC (Orange), +5 VDC(Red), and +12 VDC (Yellow) wires
will be connected to different binding posts. Note, that each binding post
should have an attached fuse for safety. This ensures that any excess current
flow will be stemmed, avoiding any chance of damage or fire.[^2]

To provide a visual indication of the power supply state, we're going to use two
LEDs. These can be connected to the Power Good signal (Gray) and Standby Supply
(Purple) wires respectively, indicating when the power supply is active or in
standby mode.

| ![ATX Power Supply 12v w/multimeter](/posts/3v.webp) | ![ATX Power Supply 5v w/multimeter](/posts/5v.webp) | ![Close up of single finished wire](/posts/12v.webp) |
| :--------------------------------------------------: | :-------------------------------------------------: | :--------------------------------------------------: |

## Further Reading

- [ATX Power Supply Pinout and Connectors](https://www.smpspowersupply.com/connectors-pinouts.html)

[^1]:
    This load resistor is optional and is only necessary if your PSU needs a
    load to produce the correct output voltages. However, most modern PSUs do
    not require this.

[^2]:
    The fuses should be rated at 1.5 times the maximum current draw of the
    circuit. For example, if you're using a 5 A circuit, you should use a 7.5 A
    fuse.

## Safety Notice

Working with mains power can be dangerous. Take all necessary precautions to
prevent electrical shocks, including unplugging the power supply before
starting, wearing appropriate safety gear, and working in a dry, non-conductive
surface.


A guide to repurposing an old ATX power supply into a functional benchtop power supply.

DIY Benchtop ATX Power Supply