I am trying to build a huge array of WS2812b's and the wiring is all done. Now, I am in the process of installing it into it's final destination. However, I have read that these WS2812b LEDs are very fragile parts and are destroyed by such voltage transients. So, I have not yet hooked up the LEDs nor the control board to the power supply and have measured the supply without a load and there are huge >20V spikes (see screenshots). The output is supposed to be 5V and is getting stable after less than one second. Is there any way to prevent these spikes from destroying my precious LEDs and the controller? Would an inductor maybe help to prevent these spikes?

This is the supply in question: https://www.ebay.de/itm/Schaltnetzteil-LED-Strip-Netzteil-5-12-24V-AC-to-DC-Power-Supply-Netzadapter-TOP/252712276489?ssPageName=STRK%3AMEBIDX%3AIT&var=551690817312&_trksid=p2057872.m2749.l2649

These screenshots are with DC-coupling and no load:

Screenshot 1

Screenshot 2

Here are some screenshots with a 50 Ohm resistive load and DC-coupling:

Screenshot 3

Screenshot 4

50 Ohm and AC-coupling (times 10 probe):

Screenshot AC coupling

Thanks, Benedikt

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    \$\begingroup\$ Measurements in the presence of massive EMI from a crappy switching power supply can be difficult to get right. I really doubt there are 20V spikes across the 5V output. \$\endgroup\$ – Spehro Pefhany Jan 8 '18 at 1:33
  • \$\begingroup\$ @SpehroPefhany Do you have a suggestion for me how to measure this best? I really can't have any accidents plugging it in for the first time. I am generally not used to mains powered and high power electronics. Usually I am only working with battery powered systems. \$\endgroup\$ – Benedikt M. Jan 8 '18 at 1:35
  • \$\begingroup\$ It is best to measure Supply noise with an AC coupled 50 ohm load. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Jan 8 '18 at 1:40
  • \$\begingroup\$ The reason for the above is to suppress all the false readings from probe inductive pickup and suppress high impedance noise that wont' affect results. It's usually caused by excessive long probe ground leads, which may be poorly placed but very inductive and using x1 probes instead of x10 with short ground leads. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Jan 8 '18 at 1:53
  • \$\begingroup\$ Alright, thank you @TonyStewart.EEsince'75. I have added the new screenshots. They are made with AC coupling enabled and on the PSU loaded down with a 50 Ohm 1W resistor. EDIT: Uploaded the wrong screenshots. \$\endgroup\$ – Benedikt M. Jan 8 '18 at 2:05

You can try to add a 5V varistor. But if the spikes last longer than 100 milliseconds, then you have a problem with your supply.

  • \$\begingroup\$ I have ordered some and they are going to arrive sometime next week. Then I will test and see how well they work. Thanks for the input! \$\endgroup\$ – Benedikt M. Jan 13 '18 at 17:24
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    \$\begingroup\$ PLease post the result of your test here. I'm also interrested. :) \$\endgroup\$ – Fredled Jan 13 '18 at 22:43
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    \$\begingroup\$ Varistors wear out if they are consistently activated, it will fail eventually. Other protection methods might work, but usually you are better off finding the noise source. \$\endgroup\$ – Zekhariah Jan 27 '19 at 6:55

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