Variable ATX Power supply

Specifications

small board 5cm x 5cm ie: 2in x 2in
on/off switch
standard ATX connector 20 pins. (a 24 pins connector can be used)
standard voltages (fused) on banana plugs / pin-header
- +12V 750mA (hold) 1.5A (trip)
- +5V 1A (hold) 2A (trip)
- +3.3V 1A (hold) 2A (trip)
variable voltage (fused) on banana plug and pin-header
- 1.25V to 11V 750mA (hold) 1.5A (trip)
USB-A female 5V (unfused)
auto-reset fuses
- switch on/off to reset the fuse
footprint for power resistor if needed
footprints for switching from external signal (arduino, RaspberryPi ...)
- 3.3V or 5V

Usage

External control

If needed the PSU can be switched on/off from a digital output of a micr-controler. Needed components footprints are on the board, but components are not populated.

You will need :

an optocoupler
- one LTV35x, PC357 or equivalent
a resistor (0603 size)
- 105 ohms for 3.3V logic
- 190 ohms for 5V logic
a 3 pins pin-header (optional)

Note: The +5VSB pin of ATX is available on the same connector. You can get 5V from it, even when the ATX PSU is switched off. So you can power your µ through that.

Populate

First, solder the optocoupler on bottom side of the board. Following picture show you a red rectangle left of the ATX connector (U2 component). Pin 1 is identified by the arraow (or the dot on the board).

Now, on top of the board, solder the choosen resistor. This time, it's on right of the ATX connector. Also, see the red rectangle on the picture below. Direction of the component does not matter.

See above to choose the resistor value.