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!

 

Do they make noise before you mount them?

Perhaps they are vibrating, and the lamp is amplifying the sound.

 

Do they all make the noise, or only some of them? Do they only make the noise after you unsolder/re-solder them?

 

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?

 

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.

 

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.

 

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.

 

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!

 

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.

 

I have the same problem. I have a LED ring light that I have to use for video conferences and as soon as I dim the intensity level, it emits a very high pitched sound. So I have a choice between annoyingly bright light and unbearable sound. Ofc I have to go with the light... another case of epic fail crap electronics that haven't been properly tested. Have you found a solution to fix your device by any chance? I might just buy another one, but I'm afraid that if I don't get to test it first, I might end up with another one that's problematic...

 

PWM works by switching ON and OFF rapidly. The percentage of time ON versus the percentage OFF is what does the apparent dimming. It works out to be an average. 50% of 5 volts is 2.5 volts. But electronically speaking, it's on at 5V half the time and off at 0V half the time. When the light is anything other than full on or full off it can be noisy. I THINK a capacitor across the output might aid in quieting down the noise. It'll smooth out the chopping between full on and full off and give a smoother average voltage.

 

I have a LED ring light that I have to use for video conferences and as soon as I dim the intensity level,

Is the dimmer part of the light?

 

Try a different (better, higher current) wall adapter, and/or replace the USB cable with thicker wire. A coating of silicone sealant (RTV, silastic) on the back of the circuit board might dampen vibrations; see if putting your fingers on it (in an insulated glove if necessary) affects the sound.