Buck Converter and WS2812 LEDs

Question

So to start off I am powering 70 LEDs through a 24V 6A power supply. The WS2812 LEDs require 5V operating voltage and about 50mA at their brightest setting (white light). I'm having this really strange power issue and I'm hoping to get some help.

Baseline

With 10 LEDs powered straight through my Raspberry Pi I am essentially just shifting colors like a sun cycle. Black, red, gold, white sustained light for about an hour and then all in reverse. I'm able to do this flawlessly and with a good transition (no flickering). The past month, I've moved the set up from 10 to 70 LEDs through a LM2596 buck converter (From 24V to 5V) and then into the power supply as stated above. Again, they've been working awesome. The specs state this voltage conversion is completely within operating values. Here is where the issue is.

The Problem

These buck converters are rated at 2A which I recognize is above the threshold of 70 LEDs so what I did was lower the number of LEDs and wire another buck converter to the same terminal but in parallel to share the current draw (still 5V). This worked for a few weeks but now I'm getting flickering. Usually you would think that this flicker happens throughout the whole LED cycle but this ONLY happens during color transitions. So if I'm holding a constant color (the day cycle of the transition) then there is no flickering. What is really weird is that this buck converter, like stated above, worked completely fine for a long period of time. I'm absolutely below my current budget so I'm not pushing these past 4A

What I've Tried

• I've changed out buck converters and this has just caused me to burn through more
• Lowered LED Count to 5 but flickering is still occurring through the buck converter
• Played with refresh rate of code but it doesn't help
• Changed brightness levels but it will still flicker no matter what
• Measured Voltage across the 24V power supply terminal and it's providing an adequate and stable output voltage
• Change Wall outlets
• Recheck wiring

I'm very familiar with these LEDs so I can say with certainty that it isn't my code or anything software related. It's very strange and I'd like some thoughts on why this is happening on JUST the flickering sequence.

Next Steps

I'll be looking at more robust buck converters along with more research on why this is happening on such a strange part of the light cycle.

Answer 1

Sorry, you cannot wire two standard buck converters in parallel. They are not designed to share current. Try separating the LEDs into sets where the number of LEDs in each set does not exceed 2A. The GND and control signals can be wired together but not the power.

Why? Each buck converter is trying to achieve an output voltage of 5.000V. Due to component tolerances, the actual voltage produced by each buck converter will vary perhaps by tens of millivolts or more. If the two voltages are not exactly the same (and they won't be) they will fight each other.

If you absolutely, positively need to parallel the buck converters, you can try droop sharing. Droop sharing requires careful calibration of the module output voltage and you have to waste some power with series resistance and the current sharing may not be great, but it might be an option for you.

Checkout page 5 of this document.

But... it's better and simpler to separate the LEDs into sets that can be independently powered.