# Led drive high pitch wine



## shiftline (Feb 18, 2015)

I just received a led reef light from China. 

The light is consists of 40x 3w bridgelux bxce/bxcd leds on 4 different color channels 

The issue is Ch 1/2 have a high pitch whine when dimmed down (still there at 100% but not as loud). Ch3/4 don't have those issue. 

Did I just get 2 dud drivers ? I haven't taken it apart yet to investigate. But is this a common issue? Is there any quick fixes ?



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## Norm (Feb 18, 2015)

:welcome:
This has been fairly well covered in the past - Norm


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## shiftline (Feb 18, 2015)

Norm said:


> :welcome:
> This has been fairly well covered in the past - Norm



I read a big article on its the switching of the current in the driver at a high frequency. It just seems odd the out of 4 identical drivers some do it and some don't. I guess I'll keep searching the forums for answers 

Ps thanks for the link!

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## Norm (Feb 18, 2015)

Probably due to a lack of QC so it can be hit or miss. 

Norm


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## shiftline (Feb 18, 2015)

Thanks norm. 
Is it generally the capacitors? Would replacing the driver capacitors likely remedy it?


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## Norm (Feb 18, 2015)

I think the usual culprit is the inductor in a boost circuit. 

Norm


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## more_vampires (Feb 18, 2015)

It could be the inductor.... or maybe it could be the *dark side*!


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## DIWdiver (Feb 18, 2015)

It can be the caps if they are ceramic. I had a design where we had to change from ceramic to electrolytic caps for this reason.


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## shiftline (Feb 19, 2015)

I'll strip it down tomorrow and see what's in there 


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## shiftline (Feb 19, 2015)

The board inside is extremely simple and I belvie the nosie is comming from a current regulator/driver Part# AMC7140DLA
Datasheet > https://www.dropbox.com/s/hziv3k07grlsl9j/AMC7140DLA.pdf?dl=0

Is there anything i can do about it? I can try to order some more of that part# and replace them... they all seem to make noise.. 2 are just a little loud.
is there anything else to try or is that my only option?


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## DIWdiver (Feb 19, 2015)

The AMC7140 is a linear device, and definitely should not be doing anything that could result in audible noise. In fact, I don't see anything in either of your pictures that looks like there should be switching or AC involved, which would be necessary to create audible noise.

Maybe the problem is off-camera? What powers this light bar? Maybe the switching is in there, and the noise is being generated on the light bar in response to the AC input.


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## shiftline (Feb 20, 2015)

The Noise is defiantly coming from that board at the end of the light. All led boards are the same so it may be related to the power supply or controller?
Its louder the lower the channel is dimmed. at 100% its not bad but 1-40% is very noticeable and gets quieter as the light gets more power (and the regulars don't work as hard?)

39V 2.5A power supply goes into the light





Power supply is bottom the left 2 wires. The controller is the right batch






LED Controller





Controller - 2 boards





Bottom of top board






Bottom board





This high pitch noise is driving me nuts so i defiantly appreciate your help on troubleshooting this!


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## DIWdiver (Feb 20, 2015)

I think it's pretty likely that the controller is using PWM to dim the lights (which is turning the voltage on and off very rapidly). Something on the board at the end of the light is bending, warping, or otherwise moving in response to the changing voltage, acting like a speaker converting electrical signals into sound.

I'd guess the culprit is one capacitor associated with each IC. Most likely, both sides of that capacitor would connect to input wires. If you could find the one, and replace it with an electrolytic cap, your problem might go away.


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## shiftline (Feb 20, 2015)

Thanks for the input. So you suspect source is a capacitor (or 4) inside the controller box?

I'll do some poking or see if another led controller will work for the signal to test. 

Or maybe build a simple arduino pwm to test it 



The output wires connect to these 4 pad on the board
TOp





Bottom of board in the same square


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## DIWdiver (Feb 20, 2015)

The source of the sound would be where you hear it, in the LED bar, right near where the wires come in if I understand you correctly. That's where the offending caps would be.

Think of it like a music player. You have a music signal, which goes through a power amplifier, across some wires to a speaker. You hear the sound at the speaker, even though the music starts back before the power amp.

This system is very similar. You have a microprocessor on the control board creating a PWM signal (like the music), you have a transistor or two (power amp), wires (to the LED bar) and capacitors (speakers).

In the music system, if you replace the speaker with a resistor/capacitor/inductor network with the same impedance as the speaker, everything in the system is exactly the same, except no sound comes out. This is what you want to do in your system. You don't want to mess up the PWM, because that's how you get dimming.

If you find the caps that make noise and replace them with ones that don't, problem solved!

That is, assuming it's caps making the noise, which at this point is only an educated guess.


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## shiftline (Feb 20, 2015)

That concept "resonates" with me a lot more than it happening in the controller (although it's likely helping cause it..). 

if the AMC7140 indeed can not produce noise then it has to be one of the SMD capacitors or Resistors right beside the AMC7140. Is there any way to test/ know what vales of the unmarked capacitors.


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## FRITZHID (Feb 21, 2015)

You could also just try reflowing the suspects, a lose solder joint could allow vibration causing noise. Easier, cheaper & faster then replacing components. You never know, you might get lucky.


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## shiftline (Feb 21, 2015)

Worth a try! I'm getting desperate to fix this. The sound is driving my nuts!




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## Lynx_Arc (Feb 21, 2015)

Get a piece of hose or long drinking straw and stick it in your ear and stop up the other ear and use that to pinpoint the noise.


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## shiftline (Feb 21, 2015)

Good call. I'll try that tonight and try to pin point it 


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## shiftline (Feb 21, 2015)

So I have narrowed it down to a couple of the capacitors. Tube method works great! I can try resoldering them.. Or re "floating". 

Is there any way to tell what value it is? Would putting it a standard capicator bugger anything up or work?


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## shiftline (Feb 21, 2015)

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## FRITZHID (Feb 21, 2015)

Only way to get those values is either obtain the schematic OR pull the cap and check it with a dmm that can check caps....and even then, if it's bad you'll get a wrong reading.


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## FRITZHID (Feb 21, 2015)

Those are RoHs soldered, hopefully reflowing will fix it. Use a little flux if you can


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## shiftline (Feb 21, 2015)

I'll try resoldering first. Do I need to do it with an air/heat gun or is the tip of a soldering iron good enough?

They all seem to do it( 2 per channel) so I suspect they are just a shotty batch. I wouldn't mind using better ones if I knew what they were.

Would putting in bigger ones do any damage? Won't it only hold the voltage that you give it.. So wouldn't a large one be okay? 


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## FRITZHID (Feb 21, 2015)

A soldering iron is actually the preferred method for this type of reflowing. Use a toothpick or something to hold the cap in place or it may stick to your iron tip.
Using "bigger"? As in voltage rating..... That shouldn't be too much of an issue but you don't want to change the value of it (mfd, ufd, pfd). Better quality units could help but need to know the stock values.


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## shiftline (Feb 21, 2015)

I emailed the company a pic so hopefully they ship out a replacement board or atleast tell me what the values are. 

For now I'll try the solder/toothpick/flux method 

Thanks again for your help!


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## FRITZHID (Feb 21, 2015)

No prob! Hope you get it sorted out and are whine free soon!


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## shiftline (Feb 21, 2015)

I tried flux and re flowing the solder for 2 of the caps on ch1 and no change. How ever if I use an eraser and apply pressure around the caps it quiets it down quite a bit. This worked for other Chanel's on the board. Almost like the ceramic smt caps vibrate and transfer the vibration to the board to amplify the sound 



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## Lynx_Arc (Feb 21, 2015)

It's possible the caps are acting like passive radiators (speakers) and something is sending vibrations through the board itself like maybe a transformer. One more thing you can do is try a hard wooden rod and press it on the board and on you head with your ears stopped and on several areas and hard components to see if some are buzzing louder or not


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## uk_caver (Feb 21, 2015)

It's only a thought, but might a blob of silicone or epoxy help regarding damping?

Ideally, silicone would be the acid-free electonic-compatible variety, though that could be a pain if only a small amount is needed. The tube I have was eye-wateringly expensive compared to regular silicone, but I use it for lots of things, so per use it's fairly cheap.

And is noise purely a ceramic/electrolytic divide, or are some kinds of ceramic caps predictably more prone to this than others?


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## shiftline (Feb 21, 2015)

I also read people using hot glue over the caps sometimes help. If I press across the row with a strip of wood it dampens it. Hot glue or silicone may do the trick... How hard would it be to remove in the off chance they wanted me to send the board back and warranty it? (It's Chinese New Year so not much for replies over the next week)

Something to bond it all together or apply pressure to make it one and stop the vibration likely would fix it. Such a strange problem to have!


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## FRITZHID (Feb 21, 2015)

Better to try crazy glue. Unlike epoxy or silicone, it will flow under the cap more and then harden..... As well as easier removal then epoxy if it doesn't work.


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## DIWdiver (Feb 21, 2015)

shiftline said:


> Almost like the ceramic smt caps vibrate and transfer the vibration to the board to amplify the sound.



That's exactly what's happening. Ceramic capacitors have a piezoelectric effect, where voltage changes cause mechanical changes, and vice-versa. Every watch or other small electronic device that emits a single-tone beep uses this effect to generate the sound. Also the backup warnings on most commercial vehicles (yes, those really loud beepers) use this effect.

The problem is that the PWM controller causes large voltage changes at the input to the light bar (the small board where the offending caps are). The caps are too low in value to smooth this out, which is by design. If they were large enough to smooth out the voltage changes, they would overload the controller.

This is not an issue caused by low quality or defective caps, or by bad solder joints, but by the intrinsic nature of ceramic caps. You can try various methods to muffle the sound, but to eliminate it you have to either eliminate the piezoelectric effect by removing the PWM or switching to electrolytic caps, or mechanically de-couple the caps from the sounding surface (the PCB). If you unsoldered the caps from the board and raised them up even 1/4" or so on wires it might make a huge difference.


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## shiftline (Feb 21, 2015)

DIWdiver said:


> That's exactly what's happening. Ceramic capacitors have a piezoelectric effect, where voltage changes cause mechanical changes, and vice-versa. Every watch or other small electronic device that emits a single-tone beep uses this effect to generate the sound. Also the backup warnings on most commercial vehicles (yes, those really loud beepers) use this effect.
> 
> The problem is that the PWM controller causes large voltage changes at the input to the light bar (the small board where the offending caps are). The caps are too low in value to smooth this out, which is by design. If they were large enough to smooth out the voltage changes, they would overload the controller.
> 
> This is not an issue caused by low quality or defective caps, or by bad solder joints, but by the intrinsic nature of ceramic caps. You can try various methods to muffle the sound, but to eliminate it you have to either eliminate the piezoelectric effect by removing the PWM or switching to electrolytic caps, or mechanically de-couple the caps from the sounding surface (the PCB). If you unsoldered the caps from the board and raised them up even 1/4" or so on wires it might make a huge difference.



Thanks for the detailed explanation. If I can figure out the vales electrolytic caps may be the way to go.. Otherwise I'm some what curious to try raising the caps off the board... May be another backup plan 


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## SemiMan (Feb 22, 2015)

Don't use crazy glue. Its hard and will increase sound transfer. You want something dense but pliable .. Silicone etc. 

Through hole ceramic in the air are usually better. Same value electrolytics may be short lived due to high ripple current.

If you can trace and draw the schematic ..then could guess at values.


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## Brightholzer (Feb 22, 2015)

DIWdiver said:


> That's exactly what's happening. Ceramic capacitors have a piezoelectric effect, where voltage changes cause mechanical changes, and vice-versa. Every watch or other small electronic device that emits a single-tone beep uses this effect to generate the sound. Also the backup warnings on most commercial vehicles (yes, those really loud beepers) use this effect.
> 
> The problem is that the PWM controller causes large voltage changes at the input to the light bar (the small board where the offending caps are). The caps are too low in value to smooth this out, which is by design. If they were large enough to smooth out the voltage changes, they would overload the controller.
> 
> This is not an issue caused by low quality or defective caps, or by bad solder joints, but by the intrinsic nature of ceramic caps. You can try various methods to muffle the sound, but to eliminate it you have to either eliminate the piezoelectric effect by removing the PWM or switching to electrolytic caps, or mechanically de-couple the caps from the sounding surface (the PCB). If you unsoldered the caps from the board and raised them up even 1/4" or so on wires it might make a huge difference.



Not only that but a ringing for parallel high-Q/low ESR ceramics exchanging energy. Input ceramic capacitance can "ring" causing the input or (far more likely) output series inductor in a PWM or switch mode controller to be the ultimate source of the tones. The output inductor is the storage device (buck), the input is line-conducted filtering (probably not present, China). This situation can make a switch-mode controller look like it has stability issues when observing the input and output ripple voltages.

You have good sense on this. Reflow or rework on the solder connections, (especially given the photos), is likely not the issue. Where I differ in opinion is that the most common cause is not the PCB substrate being made the audible radiator. These undetectable tones are really high and none of the PCBs are small enough in area. I would stethoscope all the wound inductors first. Reading this thread, it is still not certain what board in what position is the culprit.


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## SemiMan (Feb 22, 2015)

No inductors ... And the op has already sound traced to caps.


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## Brightholzer (Feb 22, 2015)

SemiMan said:


> No inductors ... And the op has already sound traced to caps.



I didn't catch that in the thread just that the first stage may have been linear. The group of photos have some L's. I doubt the linear regulators are ringing input ceramic capacitance without any cause down stream.


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## DIWdiver (Feb 22, 2015)

SemiMan said:


> Through hole ceramic in the air are usually better. Same value electrolytics may be short lived due to high ripple current.



Good catch. I forgot about that.


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## uk_caver (Feb 23, 2015)

I did have some issues with inductor-free circuits (using AMC7135s) making noise, which I eventually sorted by dropping the PWM frequency from a KHz or two to some hundreds of Hz.
I had wondered what the source was, but thanks to the very useful information in this thread it seems likely that it was ceramic caps.

As a side issue, are there thought to be any long-term component degradation issues related to piezoelectic effects?


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## Steve K (Feb 23, 2015)

I haven't run into any piezo issues with ceramic caps yet, but that may say more about the stuff I'm working on than anything else.

A search for piezo effects on ceramic caps does produce some good info. Murata has this info on their website:

"Ferroelectric barium titanate ceramics are generally used as a dielectric material in high dielectric type ceramic capacitors that represent the X5R/B,X7R/R characteristic of the temperature characteristics, and a phenomenon called the piezoelectric effect exists as a distinctive physical property.

The vibration variation of the "acoustic noise" phenomenon of monolithic ceramic capacitors is only about 1pm-1nm, which is an extremely low level between 1/10 to several tenths of piezoelectric applied products. Therefore, we have determined that there is no reliability problem, including the effect on the monolithic ceramic capacitor itself and the adjacent parts.

Representative products that actively use ferroelectric ceramics include piezoelectric vibrating gyroscopes, piezoelectric buzzers, piezoelectric speakers, ceramic resonators, and others."


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## DIWdiver (Feb 23, 2015)

Thanks. I did some searching and didn't find anything informative about reliability.


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## shiftline (Mar 2, 2015)

Silicone or hot glue? What do you think would be best to coat the offending capacitors in?


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## Lynx_Arc (Mar 4, 2015)

shiftline said:


> Silicone or hot glue? What do you think would be best to coat the offending capacitors in?
> 
> 
> Sent from my iPhone using Candlepowerforums


If you think you ever would need to replace the caps I would say hot glue because you can melt it off while some silicone sealants have acetic acid in them for curing which can harm circuit boards, you would have to make sure and get the right silicone sealant without acid in it.


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## uk_caver (Mar 4, 2015)

As a side note, I've often used regular clear epoxy to coat things for protection from damp, and the times when I have wanted to remove it later, I've found that heating with a soldering iron (normally using an old/damaged bit) usually softens it enough to be picked/peeled away with a fine jeweller's screwdriver.
It can be a bit time-consuming, but it does work.


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## shiftline (Mar 15, 2015)

So hot glue helped. It's quieter and doesn't annoy me from across the room.. You only really hear it from about 3' away. I'm not sure if there is anything else to try or add in to the mix to dampen it further..?


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## night.hoodie (Mar 15, 2015)

shiftline said:


> I'm not sure if there is anything else to try or add in to the mix to dampen it further..?



If not for foam ear plugs, I would not even be half-sane. Subtracting 30db makes everything better. Of the major drug chains, CVS has the best ones. Get the big pack.


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## Lynx_Arc (Mar 15, 2015)

shiftline said:


> So hot glue helped. It's quieter and doesn't annoy me from across the room.. You only really hear it from about 3' away. I'm not sure if there is anything else to try or add in to the mix to dampen it further..?
> 
> 
> Sent from my iPhone using Candlepowerforums


depends on the setup if it doesn't interfere with things you could add some sound insulation in the area of the circuitry but leave air space for the electronics to "breathe" so it won't overheat.


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## shiftline (Mar 16, 2015)

The leds do but does the little driver board need to breath?


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## FRITZHID (Mar 16, 2015)

Yes. The driver has the same electronic limitations as the LEDs. They are both semiconductors.


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## Lynx_Arc (Mar 17, 2015)

shiftline said:


> The leds do but does the little driver board need to breath?


Electronics in general that output power to devices (LEDs) tend to not do it 100% efficiently and "lose" power in doing so which is usually transferred to the surroundings as heat that needs to be dissipated otherwise the heat builds up and destroys the electronics.


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## Anders Hoveland (Mar 18, 2015)

Lynx_Arc said:


> Electronics in general that output power to devices (LEDs) tend to not do it 100% efficiently and "lose" power as heat that needs to be dissipated otherwise the heat builds up and destroys the electronics.


The electronics can handle more heat than the actual LED emitters can when on. That is why some LED bulb designs, such as Xledia, separate the heat sink (which is used to dissipate the heat being given off by the emitters) from the heat coming from the electronic power supply. It does not make sense to have a big aluminum heat sink dissipating heat that does not need to be dissipated.


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## DIWdiver (Mar 18, 2015)

Anders Hoveland said:


> The electronics can handle more heat than the actual LED emitters can when on. That is why some LED bulb designs, such as Xledia, separate the heat sink (which is used to dissipate the heat being given off by the emitters) from the heat coming from the electronic power supply. It does not make sense to have a big aluminum heat sink dissipating heat that does not need to be dissipated.



Actually that couldn't be further from the truth. Unless the driver efficiency is awful, the LEDs will be generating far more heat than the rest of the electronics put together, and they can handle it.

I think what you meant to say is that the electronics can handle more _temperature_ than the LEDs can.

However, that's also not really true. While many high-power LEDs are now characterized at 85C, they have max junction temperatures up to 150C. While some power FETs have max junction temps of 175C, many FETs and other power semiconductors are rated at 125C or less. I don't recall ever seeing an electrolytic capacitor with a rating higher than 105C, although I know they do exist up to at least 150C. I'm guessing they must sacrifice something for that rating, like size, cost, ESR, or some combination thereof, which is why I've never worked with them. And to reach expected lifetimes of 50,000 hours, most need to be operated 30-50 degrees below rated temp. The electronics industry has known for decades that as it is for LEDs, operating any electronic component, even resistors, at or near their max temp for extended periods will seriously compromise their expected reliable lifetime.

One reason I can think of that you might want to separate most or all of the electronics is they can then be kept cooler than the LEDs, thus dramatically improving the overall system reliability.

Oh, and ALL of the heat needs to be dissipated. Otherwise the temperature will continue to climb. No system can reach thermal equilibrium until the total heat being dissipated is equal to the total heat being generated and/or absorbed.


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