Green Digit Electronics

ATX power supply (aka Lab Supply V2)

Creative Commons-Licentie

Introduction

After builing a LM317 variable power supply a few years ago it was time to upgrade.
The easiest and probably safest way to upgrade is to start from scratch, and to stay away from the 230VAC.
Thats why a prebuild SMPS is a great way to start from.
I chose to use a fairly new ATX surplus PSU i had around but any 12V (and up) SMPS will do.
The handy part about a ATX supply is that it already has dedicated 3V3 and 5V lines. If you work with opamps you'll certainly love the -12V rail that is available too. Older supply's do have a -5V rail available as well.
Do note that an ATX supply does have the abbility to drive much higher currents then a 'normal' benchtop PSU, be carefull and keep track of the current. You could blow shit up with 500W.


The Schematic

Connectors

ATX power supply's use a 20 or 24 pole molex connector. As a big Würth Elektronik fan i chose the Würth compatible connector.
For the 20 or 24 pole connector i chose the WR-MPC4 family connector, these exist in both the straight and angled version.
To add some more current capability i added 2 extra 12V power connectors. Most ATX supply's have these.

Connectors

Controller

The heart of the SMPS will be a PIC microcontroller, The PIC18F46K40 (or the pin compatible PIC18F46K42, when a 12bit DAC is prefered).
To reduse possible noise on the μC i added a ferrite (L1 and L2) and the standard caps for each power pin of the controller.

Controller

Power Switch

Switch

Switching

Switch

Power Sensing

Switch

Shutdown

Switch Switch

Filter

Switch

Varia

Full schematic available