Getting Rid of Audible acoustic noise in Wall Wart Switching PSU's

[Whoops]

Hello,
I've been tired lately with the amount of acoustic noise coming from the Wall Wart Switching PSU's in my house.
The noise normally is an High Pitch frequency around 10Khz,
I have it coming from my iphone charger, ipad charger, Router Wall Wart, a misc wall warts for equipment.
The only thing in common is they're all switching power supplies.

A lot of people don't notice it, but as we deal with audio we are much more susceptible with those high pitch noises.

Is there any way to modify Switch mode power supplies Wall Warts to reduce or even get rid of the 10Khz acoustic noise?

Thank you

 

[JohnRoberts]

May be a design tradeoff to save cost... I encountered one odd switching PS that was noisy as a buzz saw... (it had two regulated output voltages, that required a transformer,  and the odd ball transformer was not quiet. )

I redesigned the PS to be a single output (with a pass regulator for the other voltage) using a standard off the shelf inductor that was dead silent.

If the PS is making noise it's because something is vibrating, magnetics can have epoxy put in between the windings to make them quieter.

Perhaps try a few different PS vendors to find a quiet one...I don't think ALL switchers have to be noisy.  (while I could hear the switchers inside the CFL lightbulbs in my bathroom before I changed them to LED).

JR 

 

[Whoops]

Definitely a cost saving issue.

All the Routers I have, 3 in total, have +-10khz noise.

I tried today 5 different iPhone chargers I have , 4 of them make that horrible noise also, some more than the others.
Some make less noise when loaded, but still the noise is always there.

I will open some of them to try to damp the sound, I will try epoxy like you suggested.

If you have any more tips or trick let me know and I will try it also

 

[JohnRoberts]

The epoxy is inside the magnetics, not sure adding it externally will help.. may impact thermal dissipation, but try it. What's the worst that could happen?

JR

 

[Whoops]

Opened 2 UBS wall wart chargers today.

A smaller one with 2x USB sockets and a bigger one with 6x USB sockets.

In the smaller one touching the small transformer frame was enough to stop the high pitch noise, I applied Epoxy to the transformer and the noise is gone.

The bigger PSU, touching the transformer didnt stop the noise, I tried in all the angles, I still applied epoxy on the transformer, Sides, top, bottom. In the process I must have broken some connection on the board that when I turned it on again , the Fuse on the pcb exploded, also the cheap chinese power chord burned on the solder joint, and tripped the circuit breaker at the workshop.
This one got a straight trash bin treatment

 

[JohnRoberts]

Opened 2 UBS wall wart chargers today.

A smaller one with 2x USB sockets and a bigger one with 6x USB sockets.

In the smaller one touching the small transformer frame was enough to stop the high pitch noise, I applied Epoxy to the transformer and the noise is gone.

The bigger PSU, touching the transformer didnt stop the noise, I tried in all the angles, I still applied epoxy on the transformer, Sides, top, bottom. In the process I must have broken some connection on the board that when I turned it on again , the Fuse on the pcb exploded, also the cheap chinese power chord burned on the solder joint, and tripped the circuit breaker at the workshop.
This one got a straight trash bin treatment

Sounds like you fixed it for both...  ;D

JR

 

[Whoops]

LOLOLOL

Now I will take care of the wall warts of my Routers.

John on the cheap chinese switching PSU wall warts is it possible to replave the small noisy transformers for something better and less noise?

Is it easy to know what could be the specs for a replacement (like replacing the power transformer in a Linear PSU) or the variety is to broad to know what could work in each case?

thanks

 

[JohnRoberts]

LOLOLOL

Now I will take care of the wall warts of my Routers.

John on the cheap chinese switching PSU wall warts is it possible to replave the small noisy transformers for something better and less noise?

Is it easy to know what could be the specs for a replacement (like replacing the power transformer in a Linear PSU) or the variety is to broad to know what could work in each case?

thanks

I expect those PS are made by small companies, as cheaply as possible.. It would be an interesting learning experience to try to reverse engineer one to source better western parts, while any similar parts we can find are probably made in China too.

Speaking of cheap switchers, and I shared this story before... when setting up my surround system I bought a cheap decoder... It wouldn't boot up properly as I discovered by unplugging and replugging the external power cord, after the external supply had stabilized. I bought a similar (cheap) external PS from DIGIKEY for a few dollars and now it boots up.

I suspect these companies that use the small switchers do not make or design their own, but just buy what is cheapest they can find locally that week.

For modest power you could design your own, or perhaps buy a premium PS (maybe). Sounds like a large effort for a small problem, especially if some epoxy helps... another alternative is a sound box, but at some point they may over heat without ventilation.

JR

 

[Whoops]

For modest power you could design your own, or perhaps buy a premium PS (maybe).

JR

Yes JR,
I would like to design my own, at least one specific unit.

The PSU that burned was a 6 USB outputs/sockets that I bought in Hong Kong.

To have 6 USB plugs is great for me when doing FOH, I can reach the venue and have a place to charge my iPhone, iPad and iPod.
iPhone I use for flashlight, music for the PA/Spotify, and RTA analizer
iPAD that I used for remote control of consoles, and RTA analizer
iPOD Classic that I use for PA testing and music

The PSU that I bought in Hong Kong made terrible 10Khz high pitch noise, and also sometimes it would interfere with the local power making interference in audio also.

I would like to build the same thing now but on my own with quality parts, could be a simple linear PSU, thats easy enough.
The problem is that iPhone, iPad and iPod don't charge from a normal PSU or just from 5V sent to the right USB pins, there needs to be some kind of electrical circuit inside the PSU that tell the units they can charge or give the "OK" to charge.

So that circuit is what I'm missing and don't know how to do or if it's possible to DIY

 

[Whoops]

Ok,
I researched a bit.

It's simple enough:

 

[Whoops]

Well, this website sums up what I needed on Apple USB chargers:

http://www.plutanium.cz/babca/cs/1718-apple-ipad-charging-modes-analysis

 

[Monte McGuire]

An issue with the most modern 'green' switching controllers is that they will do 'pulse skipping' when running at low power, in order to reduce switching losses and therefore improve efficiency.

What this means is that a switching regulator that would normally work at an ultrasonic switching frequency can effectively shift down to lower frequencies as it 'skips' a whole bunch of switching pulses, in order to save energy.

If a power supply is more properly sized to the load, then it will not run at a tiny fraction of its capacity, and will not enter 'pulse skipping mode' where it could generate audible acoustic output. The bad solution is to load the supply to prevent it from going into pulse skipping mode, but, this wastes a lot of power.

A better plan is to arrange for the device to not require significant transient vs. steady state power, and size the supply so that the maximum can be supplied when needed, but when run at a low power condition, it will not enter into 'pulse skipping mode', since the minimum won't be something miserable like 5% of the required maximum power.

It's possible that the devices you bought were fitted with completely oversized, very modern 'green' power supplies, and they were thus destined to run in conservation (pulse skipping) mode, generating annoying acoustic output. A more modestly rated supply can still be just as efficient, but will not enter pulse skipping mode, and will thus be acoustically a _lot_ nicer.

Having said all of that, to solve this problem, you need to honestly define the device's power consumption, and find a supply that will not have to run at 5-10% of rated capacity when power the device at idle. Measuring the circuit's actual power consumption is very useful, but requires some test gear and some knowledge. Then, you need to find a supply that can handle that, but which si also not extremely over-capacity, to avoid pulse skipping mode.

At the end of the day, an empirical study of wall warts for your application will be best, but hopefully this perspective can guide you away from oversized switchers that can get noisy to satisfy their "green" rating when run at 5-10% or so of their rated power.

 

[Whoops]

Hi, thank you so much for your reply and explanations.

It makes perfect sense what you explained although in this situation none of the wall wart  PSUs seem oversized, maybe some of the cheap mobile phone chargers are undersized but never oversized.
I measured the power consumption on the devices.

The Acoustic audible noise in not at idle, its when loaded.

 

[JohnRoberts]

If you don't care about efficiency you can make a linear 5V supply that will absolutely not make 10kHz noise.

Switchers do not have to be noisy, the last one I messed with was dead silent using a standard off the shelf inductor (IIRC it switched up around 100kHz).

JR

 

[Whoops]

If you don't care about efficiency you can make a linear 5V supply that will absolutely not make 10kHz noise.

Thats what Im thinking in doing at least for the Phone and tablet charger. I need something bigger to charge multiple devices.

I have to replace the orignal wall warts that came with  the Router and Modem also.

I had a friend last week telling me she was allergic to wifi, that wifi signals made her nervous and anxious and that she could hear the wifi signals. And disconnected when not in use.
I went to her house just to discover the "WiFi signal noise" was just the noise comming from the wall wart of her wireless router.
I replaced the he wall wart with an old one I had at home, she is not complaining about Wifi Allergy any longer.

 

[JohnRoberts]

Sounds like there may be a market niche for a PS that doesn't suck so bad....

JR