Large LED strips on PWM cause reboot at high power

Other Hardware Motors, Mechanics, Power and CNC
1

Hi Folks,

I’ve built some crown molding lights with 12v LED strip lights down a 25’ section of crown molding. The Arduino PWM’s a mosfet which switches the ground just like in examples here and on the adafruit site. For shorter stings up to about 10 or 15’ I’ve had no trouble, I use the exact same board for undercabinet lights without a problem. But I can’t get the big long strip of them to light up more than about an analog write level of around 100 out of the possible 255 before the board starts rebooting or hanging.

The power supply is a 15amp 12v supply and powers both the arduino and the strips and is about 4x the amps that I calculated the strips would use, but it’s what I had.

The problems only happen when the load is high so I’m suspecting power supply noise under load? Or some combination of noise and the PWM frequency is giving the arduino fits. There is, of course, an on board decoupling cap but it’s small. I can place a large cap just across the 12v input to the regulator, or the 5v output from the regulator to smooth out the power. I dont think the power supply can be sinking under load far enough to drop out the 5v regulator since the LED’s are nicely bright still. So it’s got to be noise or other interference?

Any thoughts on where to go next for debugging greatly appreciated. Thank you!

2

Hi PlanetaryGear, and welcome.

Supply the Arduino with another external supply and be sure to connect the GNDs.
If this solves your problem, expect to eat this:

I dont think the power supply can be sinking under load far enough to drop out the 5v regulator...

.

If you have done this, you can decide on what to do next.
So this (the test with the external supply) is just to get a step ahead in the right direction.

3

heh, it’s always the things we assume can’t be related to the problem isn’t is :slight_smile: thank you, I will throw away that assumption and test with the arduino powered by batteries with the ground linked in so that the LED’s can be powered by the power supply.

4

Large numbers of LEDs need large amounts of decoupling, since the rate of change
of current is extreme (due to the fast logic speeds involved). Its common to
compromise on the speed of the switching transistor/MOSFET to help reduce the
problem, and to provide lots of electrolytic decoupling.

You also need to adopt good layout, avoiding loops in the wiring (twisted pair
where possible to reduce flux-linkage), and ground planes are good too. Try to
minimize any area in the loop between decoupling caps, LEDs and switching device,
since this is the rapidly changing current circuit.