Power supply makes a hissing noise when LEDs are off or really dim

I have a Switch Power Supply of 5V and 10A (limited to 7A in WLED) and when I turn off the LEDs or when they are in the minimum brightness, the power supply makes an awful hissing noise.

How can I eliminate the noise (or something close)?

Taken from an electrical technical forum. This should answer your question.

As an electronics engineer who works on many types of rather expensive
switch mode power supply (but not PC ones) I believe I can answer your
It could be dried out caps gone low in capacitance or high
in ESR causing an instability, but it can also be a function of the supply
being too efficient for it’s own good. When a switched mode supply is asked
to deliver very low output power (i.e. standby) then it has to reduce the
switching waveform width to a very narrow pulse so as to achieve a low
average power output. The pulse width modulator (PWM) IC will only work
reliably down to a certain width pulse which may still be too wide to
achieve the low power required. The result is that the feedback that is
there to maintain a constant output voltage controls the PWM IC by
‘chopping’ the switching pulses, so you may get a string of pulses followed
by a period of no pulses, then another string of pulses, another gap etc
etc. This isn’t too precise, so the number of pulses and gap times varies a
bit; the overall choppiness usually occurs at audio frequencies and can
sound very much like a hissing noise being radiated by the output inductors
or transformers.

A resistor across the standby 5v to waste a bit of power would cure this if
it’s the cause, possibly something like 47 - 100 ohms 1 watt but I’m
guessing. A lot of switch mode supplies have a minimum load rating so doing
this is normal practice with a lot of designs anyway. If it doesn’t fix it
then I would say change the supply as it’s probably a cap failing.

1 Like

Thank you!
When I have some free time I will try that.

Hey guys,
I have a similar problem so I decided to continue your topic.
Mine is more specific. I always have a coil whine while the leds are changing brightness and color which is fine. Here comes the issue :
After updating to version 11 (both releases) Mirai after turning my leds off an awful whining sound can be heard. After reverting the nodemcu to v10 everything is fine when turned off. I’ve fiddled with the source code and compiled a version of the 11 where I removed the “turn off LED” of the nodemcu portion because I thought it can be the source of the wine, but No…
Is there someone else that has a similar problem after updating to v11 ?

My setup is :
Rpi3 running osmc /w hyperion.ng
nodemcu with wled flashed
ws2812 led strip 3m 30leds/m total of 60
5v 10A power supply

Before you suggest changing the adapter or what not see above that with v10 is ok v11 is noisy so it’s more of a combination of software/hardware issue.

HI, Although switch mode power supply noise is fairly common, there is nothing relating to software in any revision of Wled that can influence the noise or whine of a PSU.
There can only be two possibilities -

  1. The loading on the PSU created by the amount of pixels and their colour. White being the most power hungry.

  2. The PSU is starting to fail with intermittent sounds heard at random times. The sounds may just have not been present when you were running a different version of Wled.

Cheaper designs of PSU can have inferior components such as capacitors mentioned in the above post. This can contribute to the noise often heard.
If you are practically minded there are some great mods for old disused pc power supplies. These work brilliantly for this type of project and often provide 30 amps plus of current available at 5v.

Hi, that’s the same problem that I have . If it is an effect with low current consumption (eg.: a few LEDs blinking, the entire strip being with a low brightness or the strip being turned off) I can hear the coil whine sound and if the LEDs are changing brightness or color, like in your case, i can hear the coil whine tone changing.

Has mentioned by Modelman the problem could be some capacitors failing or cheap components (probably my culprit, since I bought a cheap PSU form China). I tried loading the PSU with some type of load and the coil whine basically disappeared. It’s not the most elegant solution, but If it works don’t touch it and I don’t want to waste time disassembling the PSU, desolder the old caps, put new ones and after all the work the problem keep appearing.

About the coil whine only showing in V11 and not V10 for you maybe is because the v11 was optimised for a lower power consumption(?)

Sorry in advance for my not so great English.

Best regards,

The power consumption of an ESP32 irrespective of software will vary between 30ma (idle) to 240ma (max load / transmit) . Even at the maximum current this would have little impact on power supply performance. An ESP8266 under normal use consumes around 70ma

Some supplies have a minimum-output current spec.

Agreed, and why they hiss and whine without a dummy load.
Even the pc supplies I’ve modded prefer a resistive dummy load on the 5v output. Not because they are noisy but it helps pull up the 12v rail to full voltage.

Still does not make sense why it starts to make the noise after the update. I guess it’s because of the optimizations that Dias mentioned.
I’ve installed a new 1m led strip with another nodeMCU with a 5v/3A and it does not have the problem. I guess I’ll stick with v10 for the other one :slight_smile:
Thanks for the tips.