Frequency whistling noise and RF shielding of power supplies - Page 1
Forum section: electronics / general

author: jancelot
author_rank: Regular Contributor
timestamp: December 07, 2016, 12:49:06 pm
content: I'm a little bit worried about the comment of this guy in Amazon, about an Anker car charger. He says that hears an extremely annoying high frequency whistling with this charger:-Anker Quick Charge 3.0 39W Dual USB Car Charger, PowerDrive Speed 2 for Galaxy S7 / S6 / Edge / Plus, Note 5 / 4 and PowerIQ for iPhone 7 / 6s / Plus, iPad Pro / Air 2 / mini, LG, Nexus, HTC and MoreMy concern is, why those highly reputed companies don't perform the proper tests and shield properly their devices, avoiding the generation of the problem in the first place?Don't know if it's related, but newer iPhone 7 and iPhone 7 Plus emit hissing sound when under load:-Why are some iPhone 7s making hissing noises?-iPhone 7 and 7 Plus handsets are making a mysterious hissing soundAs a plus, how can this be measured properly?

author: jancelot
author_rank: Regular Contributor
timestamp: December 07, 2016, 01:04:42 pm
content: This is another complain of an Anker car charger emitting an harmonic frequency of 125 kHz and causing interference with the Volkswagen Golf 7 wireless ignition key:(Anker Quick Charge 3.0 24W USB Car Charger, PowerDrive+ 1 for Galaxy S7 / S6 / Edge / Plus, Note 5 / 4 and PowerIQ for iPhone 7 / 6s / Plus, iPad Pro / Air 2 / mini, LG, Nexus, HTC and More)Tadellose Ladefunktion. Aber Kessy-Problem.More complains with high frequency noise:https://www.amazon.de/gp/customer-reviews/R1HDX8ASV91CRH/ref=cm_cr_getr_d_rvw_ttl?ie=UTF8&ASIN=B010D75XZQ

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 07, 2016, 02:28:40 pm
content: Audible whistle is a loop compensation problem. RF "whistle" is an EMC problem.Likely, the whistle is helping them, though not enough. A high audio frequency modulation of the control loop will contribute some spread spectrum action. Though, I'm sure, nowhere near what's needed to fix the poor thing.Audible whistle is sign that it won't deliver accurate and stable DC for your device, anyway.Automotive attachments are probably one of those markets where companies aren't under much pressure to check emissions. Simple: don't buy cheap, uncertified crap!Tim

author: jancelot
author_rank: Regular Contributor
timestamp: December 07, 2016, 02:34:07 pm
content: Quote from: T3sl4co1l on December 07, 2016, 02:28:40 pmYes, but now tell me which devices are "certified" and what that does mean based on the context.

author: jonovid
author_rank: Super Contributor
timestamp: December 07, 2016, 02:43:08 pm
content: odd sound is this it a bad Ceramic Capacitor?EEVblog #855 - Ceramic Capacitor Piezoelectric Effect

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 07, 2016, 02:52:43 pm
content: ^ Probably not the capacitors, actually, but inductors exhibit an identical effect, and are often seen "singing" in converters that run the inductor at low frequency, or have compensation problems.In that case, the effect is magnetostriction: an expanding or squashing effect, in the direction of the applied magnetic field, and proportional to the field intensity squared (since it's a square-law effect, the field polarity doesn't matter, anyway). It's usually on the order of ppm's, but that's still enough to be audible when the frequency is high enough.Capacitors may exhibit electrostriction or piezoelectricity as well. The latter is typical of type 2 ceramic dielectrics. The former is typical of the rest. (Polyester capacitors, used in across-the-line applications, can emit a buzzing noise, for this reason.)You can tell the difference between piezoelectricity and electrostriction because piezo will emit the same frequency as the driven frequency (it's linear, not square-law), while -striction emits twice the frequency.If the converter is so poorly compensated that it's signing due to control loop instability, the capacitors probably are emitting sound as well. (Since, it's a capacitor, you need a change in voltage to hear anything. Just as you need a change in current, in the inductor, to hear anything.)I should rephrase my earlier reply -- pulse-skipping type converters "sing" by design, and being audible is a design problem, not an electrical problem. Singing or hissing under load is definitely a compensation problem.Tim

author: jancelot
author_rank: Regular Contributor
timestamp: December 08, 2016, 03:16:34 pm
content: Quote from: T3sl4co1l on December 07, 2016, 02:28:40 pmBy the way, what do you mean by EMC?Quote from: T3sl4co1l on December 07, 2016, 02:52:43 pmSo basically, you are saying that the sound you hear from capacitors under load, is the ripple of the voltage, the higher the load the higher the sound in some way, and while no load there should be no sound (expect that from the parasitic drains which should be negligible).I guess the only way to experience it is to buy the car charger by myself and see what sound it emits.In any case, I find it quite dangerous that some hardware emit noise near the hearing thresholds, because it can cause you deafness since they are overloading your ears along that frequency that some people could barely hear while others could. I think human beings perceive volume differently depending on frequencies, so you can hear it as very low but still be high in absolute terms thus may damage your ears.In another order of things, it could upset too some animals which have higher hearing range than humans.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 08, 2016, 07:20:26 pm
content: Quote from: jancelot on December 08, 2016, 03:16:34 pmElectromagnetic Compatibility -- most important part here being the emitted radio waves. "RF whistle" as in, you might not hear it by ear, but over the car radio -- or other cars' radios or worse!QuoteYes, but also that the ripple voltage is usually small, so you don't usually hear it from that source. The inductor is most common, because it has large ripple.But both are possible.QuoteThese things I don't think will be very loud, just irritating in a quiet environment. Televisions at 15.7kHz used to be an annoyance, sometimes quite loud when failing. Big things can be irritatingly loud, like power distribution substations (100/120Hz or 300/360Hz mains harmonics). Military substations, running at 400Hz, can be particularly bad, since the harmonics (800Hz+) are right in the middle of the audible peak, and the emitted sound is that much more intense (same change in strain, higher frequency --> more emitted energy).Tim