USB Powered LED Lights Emitting High Pitched Noise

Thread Starter

tnjohnst

Joined Apr 11, 2023
4
I'm am a woodworker with little electrical experience and am making LED lamps from low voltage (USB powered) color changing RGB light boards that come with remotes and switches. I have to unsolder and resolder them to put them in the lamps. I'm using a USB wall adapter to test them. They work perfectly, but some of them have a high pitched sound. I've read that it could be the dimmer, but changing it doesn't seem to help. Any ideas for why this is happening or how to remedy it? I know they are cheap components and my soldering skills probably aren't the best. I've considered casting them in resin to see if that stops the noise, but thought I would ask on a forum before attempting that experiment. Thanks so much!

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Audioguru again

Joined Oct 21, 2019
6,758
The extremely low price for a pair of the remote controlled lights tells you about its poor acceptance.
Maybe the dimmer in the circuit causes noisy sparking?
 

Thread Starter

tnjohnst

Joined Apr 11, 2023
4
Thank you all and sorry for the delayed reply. I did some testing and it seems that they do have some noise before mounting/soldering, but not as loud. The amount of noise is louder with some colors (ex. white light is louder than darker colors). Seems like it's most likely just dealing with cheap components. If anyone has suggestions on a better source, I'm all ears! Aliexpress was the only place I found that had everything in a package so I knew compatibility wouldn't be an issue.
 

Ya’akov

Joined Jan 27, 2019
9,234
The sound you are hearing is almost certainly one of two things:

1. The PWM (Pulse Width Modulation) circuitry used for dimming. The frequencies chosen for this application focus on eliminating visible flicker. It is generally also outside the hearing range but may not be, or may have artifacts that are audible. What frequency does it seem to be? Is is high enough that older people can’t hear it?

2. The frequency of a boost converter circuit which is a type of DC-DC converter that would be taking the USB’s ~5V in and making it a higher voltage if there are multiple LEDs in series which would raise the forward voltage. that is, the voltage at which the LEDs start to light up. The boost converter uses a high frequency AC to change a lower into a higher DC voltage at the cost of current (amps).

If this is the case, there is little practical that you can do about it. Better, much more expensive lights wouldn’t have this problem but even cheap ones don’t always do it. In fact they usually don’t in my experience.

I would try a few more examples of suitable lights that appear different to the ones you have tried. You will probably find something acceptable. If you do be sure to buy extras as replacements because there is no guarantee of getting them again.

I would also make sure that they are accessible for service. When you design the mounting be sure to think of the light as you would an old-fashioned light bulb, because just like the light bulb it will need to be replaced.
 

MrSoftware

Joined Oct 29, 2013
2,208
You can try conformal coating, or potting the circuits to muffle the noise, sometimes that's enough to stop or reduce the vibrations causing the noise. But be sure that doesn't cause a heat issue.
 

Thread Starter

tnjohnst

Joined Apr 11, 2023
4
The sound you are hearing is almost certainly one of two things:

1. The PWM (Pulse Width Modulation) circuitry used for dimming. The frequencies chosen for this application focus on eliminating visible flicker. It is generally also outside the hearing range but may not be, or may have artifacts that are audible. What frequency does it seem to be? Is is high enough that older people can’t hear it?

2. The frequency of a boost converter circuit which is a type of DC-DC converter that would be taking the USB’s ~5V in and making it a higher voltage if there are multiple LEDs in series which would raise the forward voltage. that is, the voltage at which the LEDs start to light up. The boost converter uses a high frequency AC to change a lower into a higher DC voltage at the cost of current (amps).

If this is the case, there is little practical that you can do about it. Better, much more expensive lights wouldn’t have this problem but even cheap ones don’t always do it. In fact they usually don’t in my experience.

I would try a few more examples of suitable lights that appear different to the ones you have tried. You will probably find something acceptable. If you do be sure to buy extras as replacements because there is no guarantee of getting them again.

I would also make sure that they are accessible for service. When you design the mounting be sure to think of the light as you would an old-fashioned light bulb, because just like the light bulb it will need to be replaced.

The frequency is definitely high enough where most people may not hear it. It look me a while to hear it, but now I can't unhear it. Some are louder than others and the "quiet" ones you really have to try to hear, so I don't see them as much of an issue. Sounds like I just need to look for another supplier and be aware of this when buying cheap lights. I appreciate the advise for making them accessible. I actually found a new mounting method yesterday that may eliminate the need for un-soldering/re-soldering and it'll make it easier to replace the light. This may also help with the noise, since the re-soldered ones seem to be louder. Thank you!
 

Thread Starter

tnjohnst

Joined Apr 11, 2023
4
You can try conformal coating, or potting the circuits to muffle the noise, sometimes that's enough to stop or reduce the vibrations causing the noise. But be sure that doesn't cause a heat issue.
I'm looking into conformal coating now. Seems like a great suggestion. Thank you.
 
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