Electronic – arduino – ATX PSU turns itself off when uploading sketch to Arduino

arduinoatxgroundpower supplystepper-driver

I'm trying to power a stepper motor with the 5V rail of an ATX PSU and control it using arduino. To keep the PSU running, I have shorted the PS_ON pin to ground. Also, I have connected PSU ground to arduino ground. The arduino is powered over USB.

The problem I'm having is that the PSU turns off automatically when I upload a new sketch to arduino. I can reproduce the problem with these steps:

  1. Turn on power (PSU is running fine)
  2. Set one motor pin (e.g. digital pin 9) to HIGH
  3. Upload a new sketch to arduino (doesn't matter which one, e.g. the Blink example)

-> PSU turns itself off.

Why does this this happen and what can I do to prevent it? The PSU seems to perform well otherwise.

schematic

simulate this circuit – Schematic created using CircuitLab

Edit: I just found these alternative steps to reproduce:

  1. Power on
  2. Set one motor pin to HIGH
  3. Disconnect 5V rail of PSU from motor driver

-> PSU turns off

Further tests:

  1. Disconnect motor from driver
  2. Power on
  3. Set one motor pin to HIGH
  4. Upload new sketch

-> PSU stays on!

  1. Connect motor to driver
  2. Power on
  3. Set one motor pin to HIGH
  4. Disconnect motor from driver

-> PSU turns off

It seems to me that the PSU doesn't like losing load on 5V after it has seen load once.

Best Answer

As multiple comments have said, most ATX supplies require a minimum load on the 5V line for proper regulation, many tutorials use ~10 Ohm resistor or smaller on the 5V rail.

This is due to the type of SMPS topology, typically an LLC resonant converter, that requires a minimum load for tuning of the resonant circuit within a given frequency range.

Solution: Try putting a constant load on the 5V line, and your issue may go away.

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