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Thread: Why do high-powered LED flashlights make a high-pitched noise?

  1. #1

    Why do high-powered LED flashlights make a high-pitched noise?


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    I just got a klarus xt11. Awesome light. But it's a little annoying how in its highest mode it makes a high pitched noise. Everyone I have talked to who owns one says it does this. Just curious why. Lower end lights I have don't do this. Thanks!

  2. #2
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    That's not coming from the torch, it's the billion space mosquitos living under the surface of the moon who you've woken up with your ultrabright flashlight.

    Or, it's a special device installed by the manufacturers (on the suggestion of parents) to ensure that people 18 and younger won't want to use this flashlight and will make do with a less noisy (and cheaper) version

  3. #3
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    Some brainiacs say that it is the its the inductor in the regulation circuitry. Link. A few of my lights do that too. Some of the more spendy lights are regulated (so as to maintain a flat output as voltage drops), which is why you are more likely to hear it in a spendy light than a less expensive one. The cheap ones are not regulated.

  4. #4
    Quote Originally Posted by powernoodle View Post
    Some brainiacs say that it is the its the inductor in the regulation circuitry. Link. A few of my lights do that too. Some of the more spendy lights are regulated (so as to maintain a flat output as voltage drops), which is why you are more likely to hear it in a spendy light than a less expensive one. The cheap ones are not regulated.
    I guess that makes sense
    I just find it odd that they wouldn't find a way to make sure they were quiet...to me at least, it's annoying and seems like a quality control issue.
    Thanks for the response!
    This light is so amazing other than that..so it drives me crazy haha

  5. #5
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    It's called microphonics. There are two common causes in flashlights.

    But first, you have to understand a bit about how the flashlight works. The modern emitter, the LED itself, is usually an array of multiple LEDs. This makes it brighter, but it's also how to get white light. While each LED requires a voltage of somewhere between about 1.5 and 2.5Volts. When you have multiple LEDs to drive, you can either drive each one individually with its required voltage, or you can strige them in series and drive the chain with the total voltage. The later is easier. But, it requires a voltage perhaps in the 10V range. Batteries typically product 1.5V. You can stack up several for higher voltage, but to get to 10 or 12V, you'd need seven or eight batteries and people don't want a flashlight that big and heavy.

    So, there's a power converter circuit in these high-brightness LED flashlights that changes the voltage.

    We know that changing a voltage is possible; we see it around us. We see transmission lines on tall towers with "Danger -- High Voltage" signs. And we know that somehow the power in those high-voltage lines ends up in our homes at a voltage that -- while still demanding our care and respect -- is much less dangerous. Somehow that voltage gets changed. The answer, as I suspect that most of us know, is transformers. No, not cartoon robots, but those cylinders we see hanging off of utility poles and those sort of stark-looking big boxes we see through the fences of substations.

    But there is a critical difference: batteries produce and LEDs use DC power. Power utilities distribute AC power (in the downtown areas of some cities including Portland, Oregon, they do distribute some DC power used mostly for elevators). Transformers work for AC power, but not DC. So, we can't just connect a transformer between the battery and the LED array.

    There are several ways to increase a DC voltage, but they all boil down to some variation of converting it AC. One technique is to convert to AC, use a transformer to increase the voltage, and then convert the higher-voltage AC back to DC. This technique is not the most efficient possible, but it is the easiest to understand.

    Anyway, regardless of the exact circuit topology you use, you are going to have a form of AC (at least discontinuous DC) going on.

    Sometimes, when you walk near a power distribution transformer, you can hear a low "hum." This is literally the core of the transformer "rattling around" as the AC current changes direction 60 times each second. The sound is actually unintended and a defect, but sometimes making it go away would cost more than its worth.

    That "buzz" is at 60Hz (60 oscillations per second) in the US. In some countries, it's at 50Hz, just a bit lower pitch. The physical size and weight of a transformer depends largely on the frequency of the current it must transform. Flashlight designers don't want to use 60Hz because the resulting circuitry would be physically quite large. Instead, they will use 10,000, or 100,000Hz or some such thing, a high frequency.

    But the same things happen at higher frequencies. The cores of transformers and inductors physically rattle. Also, the plates of capacitors rattle. This is actually quite common. The ceramic capacitors used at these higher frequencies have very thin plates and they physically rattle and give off a buzzing sound.

    Rattling cores in transformers and inductors is annoying. In theory, it's not good for the component, but it's not so bad as to concern the designer in most cases; something else will still fail first. But, those capacitor plates are a problem; those ultra-thin and very brittle ceramic plates can literally crush themselves.

    This all makes sense when the switching frequency in the circuit is an audio frequency such as 10,000Hz (human hearing is generally 20-20,000Hz) but to get smaller components, the converter circuits often run much higher, in the 100,000 or even 1,000,000Hz. So, how does that end up being audible? The answer is that if you are tapping your foot to keep time with some music you are enjoying, you can tap with every beat, every other best, every third, every fourth, etc. and still be keeping time with the music.

    If the plates in the capacitor or the core of a transformer or inductor can't physically move 1,000,000 times per second, they may move with every 1000th beat and end up buzzing at 1000Hz which is audible.

    In general, microphonics in small power converters can be eliminated with minor and inexpensive tweaks to the circuits and/or component selection.

    Anyway, the bottom line for me as an electrical engineer is that microphonics in circuits are unacceptable. Leaving them unremediated is sloppy design an can be a precursor of premature failure.
    Last edited by Gollnick; 09-25-2012 at 11:40 AM.
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  6. #6
    Wow, Gollnick...thanks for such an in-depth response! That all made a lot of sense.
    When I was a kid I worked with my dad as an electrician so I'm familiar with electricity in general, just not on the scale of an LED.
    So what you're saying is that manufacturer's don't deem microphonics enough of a problem to make it something they correct when making the lights?
    It's unfortunate...

  7. #7
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    Several years ago, I was involved with the design of a product that included a power converter circuit that ended up with some small microphonic buzz. When the product was in its enclosure, the buzz was completely muffled; it could not be heard. But, we elected to fix the problem because the product would have a five-year warranty. The fix added about two cents to the product cost.

    If I was spending a lot of my money on a fancy flashlight, I would insist on no microphonics.
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  8. #8
    Quote Originally Posted by Gollnick View Post
    Several years ago, I was involved with the design of a product that included a power converter circuit that ended up with some small microphonic buzz. When the product was in its enclosure, the buzz was completely muffled; it could not be heard. But, we elected to fix the problem because the product would have a five-year warranty. The fix added about two cents to the product cost.

    If I was spending a lot of my money on a fancy flashlight, I would insist on no microphonics.
    Aside from the annoyance factor, based on all of that logic, wouldn't you have to be using the flashlight for ridiculously long periods of prolonged use over a long period of time for it to have any real physical effects on the light itself?

  9. #9
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    I can't tell you want affect it will have on reliability. Why take that chance... especially on something as expensive as some of these fancy flashlights are?

    I would rather have the engineer spend a few extra cents remediating the microphonics than making the thing flash "eat at Joe's" in Morse Code.

    A good-quality product simply shouldn't have microphonics.
    Balisongs -- because it don't mean a thing if it ain't got that swing!
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  10. #10
    Quote Originally Posted by Gollnick View Post
    I can't tell you want affect it will have on reliability. Why take that chance... especially on something as expensive as some of these fancy flashlights are?

    I would rather have the engineer spend a few extra cents remediating the microphonics than making the thing flash "eat at Joe's" in Morse Code.

    A good-quality product simply shouldn't have microphonics.
    But a lot of the higher quality lights do...that's why I was wondering.
    They wouldn't be highly regarded lights if the microphonics had any kind of serious affect...especially since all the lights have at least 2 year warranties.

  11. #11
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    Inasmuchas I was not involved in the design or development of any of those products, I don't know what their thinking is. It's up to you. This electrical engineer and product developer doesn't want any buzzing flashlights


    I may be wrong. Maybe one of the engineers who does design these products can step up and say, "Chuck, what you're missing is ..." and convince me otherwise. But, knowing what I know now, I see it as a design defect.
    Last edited by Gollnick; 09-25-2012 at 04:40 PM.
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