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WizardStan

Mega GP Mania
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May 24, 2008
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See, here's the issue: whether EvilDragon does or does not use tantalum caps will not make a difference: the market exists for the product and the largest suppliers and consumers use unethical practices. Do or do not it will have absolutely no perceivable effect on the lives of those that are suffering because of it. To that end there is no reason not to, ethics be damned.
But EvilDragon obviously has a strong sense of personal morals about this, and I do not want to encourage him to do something he is opposed to unless there's a good reason. The remark that it could be heard up to 1m in a quiet room if you've got a heavy load on the USB does not sound like a good reason to me. I'm wearing headphones listening to music sitting 2m away from my PC and I can still hear the fan: a little ambient noise is not worth violating your principles.
 

gpsqueeek

Very Active Member
Joined
Nov 21, 2016
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My Pyra may be used as my alarm in the morning, i.e. stay (in airplane mode) next to my head while sleeping, therefore the noise might annoy me (or the person next to me for what it's worth).
As for the ethical thing, to all those saying it's no use to be ethical because it is only a couple of thousand products : have you heard of the colibri story ? A forest is on fire and all animals flee, except the colibri, taking a bit of water in its beak and spitting it out onto the flames. Another animal sees that and asks why the colibri does that, as it will never extinguish the fire because he is so small. And the answer of the colibri "I am doing my share ; if everybody does, then the fire will be extinguished ; if too many animals don't, all will burn".
Cheers to Evil Colibri \o/
 

hns

Well-Known Member
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544
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Oberhaching
Some background on the whining, audio and tantalum.

The real reason for the effect is that we have DC/DC converters from battery voltage to 5V for the USB ports.
Such USB host ports require to have 120µF decoupling capacitors to provide enough energy to USB clients.

We have designed for ceramic capacitors ("MLCC") and there was only one manufacturer who build 100µF ceramic capacitors small enough to fit.
So we did take one 100µF and a 22µF in parallel on the previous board revision. This time I can experiment with different mixtures like 2 x 68µF.

Why do these capacitory make noise? It is an piezoelectric effect: https://product.tdk.com/en/contact/faq/31_singing_capacitors_piezoelectric_effect.pdf
And it occurs only if there is an USB client that discharges the capacitors so that the DC/DC converter has to recharge. This gives some voltage ripple
which triggers the piezoelectric effect.

Does it have an effect on the audio system?
Not directly, because it is not an electric noise going into the headset or speaker wires. But unintended tiny buzzers on the mainboard... The noise level is below what you can detect with a typical microphone but loud enough to be annoying if you are alone in some room. Unfortunately the frequency range is so that the human ear has highest sensitivity. But you won't notice in a commuter train :) Or if you unplug all USB devices.

How can we avoid?
  • Use bigger sized ceramic capacitors which reduces the effect.
  • Have several small ones in parallel.
  • Or use non-ceramic (aka Tantalum) capacitors.
  • In theory a different (much higher) operating frequency of the DC/DC would help, but we can't modify it.
This is where tantalum comes in as an option. But they have different drawbacks: increased risk of burning or wearing out over time compared to MLCC. And they are usually bigger.

And the conflict material issue. Therefore I would like to avoid them completely and it would be a pity if we just have two of them amongst ca. 150 others because we give up to find a solution.

Hope this clarifies some concerns.
 
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Pyrate

Member
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Feb 9, 2017
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Hamburg, Germany
I would rather avoid the tantalum, too. Personally I do not have an issue with the noise whilst USB devices with large power draw are attached, as this is not going to be an often use case for me anyways...
 

elw3

ƐʍlƎ
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Aug 10, 2010
Messages
1,478
increased risk of burning or wearing out over time compared to MLCC. And they are usually bigger.
Now this little info changes a lot.

But heck, i am very sensitive to sirring noises. Ill take disadvantages any time as long as it makes no noise.
 

Askarus

Hardcore Member
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Sep 28, 2011
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I would rather avoid the tantalum, too. Personally I do not have an issue with the noise whilst USB devices with large power draw are attached, as this is not going to be an often use case for me anyways...

You did not hear the noise.
I thought the same until I heard it. It's not annoying but worse.
It makes things like Ethernet to USB not usable for a medium period of time. It is really loud and and annoying.
 

PowerGod

Hardcore Member
Joined
Jun 20, 2011
Messages
3,783
How can we avoid?
  • Use bigger sized ceramic capacitors which reduces the effect.
This is where tantalum comes in as an option. But they have different drawbacks: increased risk of burning or wearing out over time compared to MLCC. And they are usually bigger.

One option says "Use bigger ceramic", while the Tantalum option says them could be bigger :eek:
if everything is right here, seems to me that the obvious thing to do is using bigger ceramic capacitors
 

Letalis Sonus

Advanced Member
Joined
Mar 5, 2009
Messages
1,442
Now this little info changes a lot.
That does not apply to all tantalum caps, though. They actually have their origin in the military sector for their high durability, those older types using a fluid electrolyte do not suffer from these problems - they last forever without losing any capacity. It's too bad that the traditional axial format is not being manufactured anymore - I still have some of those, over 30 years old and still good to use. Those wet ones are fairly expensive, though.
 

NOP

Member
Joined
May 2, 2017
Messages
45
Even if it would be nice to have a mostly conflict free device, it is way more important to get rid of the noise.
If I understand correctly tantalum caps are the easiest fix one could apply.
And from what i have read the mtbf is also not really a problem.

As I am very sensible of this kind of noise (halve of my usb power supplies/chargers do this) and would be happy to see the pyra finished before the win2, I would also go with tantalum caps (maybe there are even some conflict free ones)

And even if on paper ceramic caps have longer mtbf, one should also think about the mechanical stress if the are producing audible sounds.
 

levi

Still fresh, damnit!
Joined
Oct 6, 2008
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13,516
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Somewhere off the coast of the EU
One option says "Use bigger ceramic", while the Tantalum option says them could be bigger :eek:
if everything is right here, seems to me that the obvious thing to do is using bigger ceramic capacitors
The way I read it is when talking about bigger ceramic caps, he was talking about their capacity in uF, but when referring to tantalum caps he was talking about their size in square millimeters. Now, significantly bigger ceramics are commonly found in bigger physically sized packages too, so either way it seems greater or lesser layout rework will be needed. Tantalum caps tend to be higher in electrical density, so would probably require simpler rework, but I'm slightly surprised you can't get tantalum caps in the same physical size as the cermaic one we were using, but perhaps the manufacturing process is more difficult to miniaturise to the same degree, as these SMT parts are often some kind of tiny.
 

DAP

Member
Joined
Aug 29, 2008
Messages
431
We have designed for ceramic capacitors ("MLCC") and there was only one manufacturer who build 100µF ceramic capacitors small enough to fit.
So we did take one 100µF and a 22µF in parallel on the previous board revision. This time I can experiment with different mixtures like 2 x 68µF.

Have you accounted for the drastic drop off of capacitance as a function of voltage high capacitance ceramic capacitors have? This can be as high as 90% near their rated voltage for some capacitors. The real problem here is that many manufacturers don't mention this drop off in their data sheets.
As an example, look at this part: http://ds.yuden.co.jp/TYCOMPAS/ut/d...me=JMK325ABJ337MM-P_SS&mode=specSheetDownload
Taiyo Yuden is pretty good about including the voltage vs capacitance curve in their data sheet (it is on the second page). This cap is pretty good, but it is still down by 60% at 5V. So when using ceramic capacitors at voltages greater than 1V, you may need to scale up the capacitance you use to ensure you have the required capacitance at the operating voltage.

Tantalum and electrolytic capacitors do not have this capacitance drop as a function of voltage, but they have their own problems.
 
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