PB failing when power to LEDs is increased (dimmable power supply)

I’m having some sort of power issue I can’t figure out. My PB works fine until I turn up the brightness or run a pattern with larger power requirements.

I have a strip of 300 ws2815 (12V) LEDs. The strip can use up to 90W, but I haven’t tried pushing it past 30W. They’re powered by a 60W 12V dimmable LED driver (no dimmer switch). The PB power is wired in parallel with a 5V (3A max) buck/step-down converter. All grounds are connected. I’ve confirmed the voltage going into the LEDs is 11.5-12.0V and into the PB is 5.0-5.2V. The animations run fine with the 12V current < 1.0A, but if I set it to anything beefier the PB fails after updating the LEDs. The orange LED on the PB stays dimly lit, but it appears to otherwise be off. Resetting the system (by cycling the power) basically starts up the PB again, but it immediately fails after the LEDs turn on.

I thought the dimmable driver might be causing issues even though I’m not using a dimmer switch, but I don’t have another PSU to test it with right now. Otherwise I’m out of ideas.

Thanks for the help.

Try with a stronger power supply

Hi Steve -

I don’t have a strong inkling (everything sounds right from what you posted) but here’s a few things I might run down:

  1. How are you measuring current coming out of the 12V driver?
  2. Make a static pattern so you can precisely control how much current is being demanded.
  3. Does the 12V dip as you approach the level where the Pixelblaze will cut out? Using 1A of the 5A (60W) max, it shouldn’t. Does the 5V output of the buck dip when you approach the 1A problematic draw off the 12V driver?
  4. Is the dimming input floating? Is the dimming output method supposed to be regulating current or PWM? PWM input to the buck could have unintended consequences.
  5. Do you have a scope? I’d look for noise coming out of the 12V PS and the buck. If you do see a lot of high frequency noise, you can google for the right capacitor to put across the supply output to serve as a low pass filter.
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Dimming drivers often work by Pulse Width Modulation or PWM. The supply is 100% on for some time, and 0% on for some time. The ratio between these 2 states varies based on the “brightness” input.

Even if it was at 99% brightness, its supplying nothing for 1% of the time. During that time LEDs and Pixelblaze are still drawing current - probably surviving on the small charges in capacitors used to level out voltage fluctuations inside the buck converter and PB itself.

A multimeter will probably not have the sampling speed to make these dips apparent. You’d need an oscilloscope to see them.

I would not recommend a dimmable power supply with digital LEDs or other electronics like a buck converter.

Buck converters work by switching power to an inductor often using PWM or Pulse Distance Modulation (PDM). Its quite possible that at higher current draws the OFF state of the dimming driver happens at the same time as the buck converter is in an ON state trying to draw current to charge the inductor and power Pixelblaze.


This was it. Got a new non-dimmable power supply and it worked. Thanks for the education!