LED help

I have led lights in my RV and the one over the bed is bright while trying to watch tv, I purchased a wall switch with dimmer. When I hook it up it works but I get a buzzing sound from the led's unless its turned all the way up or just barely on. Here are some pics of what I have. Thanks for any help. Michael

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Leds dont buzz, it will be your power supply/dimmer

It's rare, but the ceramics can buzz. Usually the don't but not unheard of. There are two on that circuit board. As pointed out though, likely the dimmer since I assume you are running of 12V directly? You could be making your inverter/charger buzz depending on your setup.

SemiMan said:

... the ceramics can buzz...

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Don't I know it. Had to change them out for electrolytic on one of my designs. It wasn't loud, but audible, and the customer didn't like it.

Most commonly, unwanted buzzing sounds come from magnetic components - inductors and transformers. But we don't see any of those in your pictures.

The circuit on your LED board consists of a reverse-protection diode, (probably) a linear voltage regulator, and 4 strings of 3 LEDs with balancing resistors. The two caps are both on the output of the regulator. Though I can't quite make out the markings on the regulator (the largest component), it looks like a pretty reasonable design. Undoubtedly your dimmer is PWM, meaning it works by turning the LED board on and off rapidly. Leaving it on more than off makes it bright, leaving it off longer makes it dim. I'm guessing there is nothing between the dimmer and the LED board except wires?

If all that is correct and you're sure the noise is coming from the LED board, then the caps are a possible suspect. Or it could be the board itself moving from the electric fields or even thermal effects. It's pretty rare for any of these to make enough noise to be annoying (or even audible), so I'm only guessing. You might be able to learn something by poking the board while it's making the noise. If it's only a 12V or 24V system, it's quite safe to do with your fingers.

If it's the caps (small brownish parts) then you can probably only make a slight improvement by pressing on one or both of them. If it's something else, then poking at the board is likely to make a dramatic difference at some point. If you can't make any difference at all, then it's probably not actually coming from where it sounds like it's coming from. Pinning down the source of the noise will make a big difference in what solutions make sense to recommend.

I tried another led board I had and it works fine, the buzzing or high pitch is definitely coming from the led board itself. I guess I could swap them out for another board but the one I have is not as bright as that one. If I need to get some closer pics of the components I can. Thanks

I uploaded some component pics to the album if that helps. Thanks

What type of wall switch with dimmer are you using exactly? This one right? http://www.amazon.com/dp/B00A11UWY2/?tag=cpf0b6-20

There's a review on there describing a similar issue. They are saying the sound is coming from the dimmer itself. I wonder if it's a defect in that dimmer....

Hornnumb2 said:

I tried another led board I had and it works fine, the buzzing or high pitch is definitely coming from the led board itself. I guess I could swap them out for another board but the one I have is not as bright as that one. If I need to get some closer pics of the components I can. Thanks

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Hot melt glue over the caps usually works just fine to quiet them. You can use caulking, but many compounds will cause corrosion.

SemiMan said:

Hot melt glue over the caps usually works just fine to quiet them. You can use caulking, but many compounds will cause corrosion.

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+1 on hot glue. Works in 90% of the smd whine situations I've run into. RTV will work too but need to make sure it's electronics friendly/doesn't gas off and fog lenses/LED dome.

Well tried the hot glue on the 2 brown caps but still have the whine. These are the ones that I have that are quiet. http://www.ebay.com/itm/271616174796?_trksid=p2055119.m1438.l2649&ssPageName=STRK:MEBIDX:IT

What do I need to look for for brighter ones? Thanks

Your lower cost units have no on board supply, which is why no noise, confirming the other PCB with components is noisy because of the drive components. The 78M05 is a medium power linear regulator and should be noise free. I would say almost without question its the dimmer, try disconnecting the dimmer circuit to test this . If you need more light get the cheaper version but with more leds

Just to be clear, it's pretty likely the PWM of the dimmer is causing the noise, but the noise is actually coming from the capacitors. Like the dimmer is the amplifier and the capacitors are the speakers.

Great to know that hot glue can fix the whine. That goes in my toolbox. I have a major retail customer that uses hot glue to prevent vibration from breaking wires, so that's not unthinkable in at least some production applications.

More to the OP: The board that has the capacitors on it is probably more reliable than the others, because it has a regulator that's probably more able to handle any nastiness coming from your RV's electrical system. The regulator allows the designer to push the LEDs harder without having to worry about protecting them from the vagaries of the LEDs and the RV's electrical system. That's at least part of why that board is brighter.

Depending on how you use the lights in the RV, this difference may or may not be relevant.

Ok can somebody recommend a dimmer that would work better with the rv light that I have now? Thanks Michael

Do you hear the sound even when TV is switched off? PWM noise could be picked up by TV audio section and you may be feeling it is the LED. Something like alternator whine in our automobile audio. Especially, if TV, LED everything is powered by same source in RV.

It just on the bench right now, so that shouldn't be a problem.

Not sure if it will work in this situation or not, but you could try the trick of holding a screwdriver to your ear to pinpoint or narrow down the origin of the hum.
Pro tip: the big rounded end of the screwdriver goes to your ear, the pointy end onto the component being examined. Not the other way around. Oh, and make sure you don't short anything.

RoGuE_StreaK said:

Not sure if it will work in this situation or not, but you could try the trick of holding a screwdriver to your ear to pinpoint or narrow down the origin of the hum.
Pro tip: the big rounded end of the screwdriver goes to your ear, the pointy end onto the component being examined. Not the other way around. Oh, and make sure you don't short anything.

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Great tip. I even just make a quick paper tube for this so I don't worry about shorting things.

Wouldn't the screwdriver pick up magnetic field vibrations which may or may not be the source of the noise though?

Don't ask me, I just lurk here