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what cause SMPS to make audible noise??

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nimeshasilva

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Hi all,
I have a little problem
what cause some SMPS to make audible noise??
is it normal or any issue involved?? coz most of the SMPSs don't make any audible noises as far as I know.

Thank you
 

decreasing the input voltage needs to increase in switching speed of the choper So that the audioble noise comeout
 

Thanx for quick reply,

I'm providing the correct input voltage. (110V in my most recent case, and also I have experienced the noise with a 230V computer power supply unit)
 

It depends on design. In some power IC, when operating frequency is detected to enter audio range, some actions are taken to run out of that frequency range.
 

I am not an expert... as you referred a computer... i think there is a problem in the exhaust Fan..... or it can be due to large rate of voltage fluctuations in your mains voltage(i,e; 110v / 230v)... the second case can occur if you are not using an UPS (uninterrupted power supply)....
 

I have experienced the noise with a 230V computer power supply unit
Click to expand...

You are taking about Computer power supply fan noise??
 

The noise is simply changes in currents in inductors causing magnetic fluctuations which results in a slight mechanical movement in and around them. They are acting like tiny loudspeakers.
Some SMPS have switching frequencies higher than the audible range so you don't hear them, others have more rigid components so they move less. Changes in current or voltage will change the switching frequency or waveform, that's why the sound changes. It's quite normal, if annoying at times!

Brian.
 

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yes i agree with ,betwixt . That post may helpful right ?
 

is the noise dependent on voltage/ load ?

even a lab smps can make a buzzing kind of noise.
 

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in general SMPS creates sound due to its exhaust cooling fan.....
Click to expand...
Personally, I expect, that the original poster will be able to distinguish between fan noise and a buzzing sound emitted from the SMPS transformer core and is referring to the latter...

If we talk about transformer noise, we can further distinguish continuous high frequency tones and erratic chirping or croaking sounds, that are mostly load dependant. Tones indicate an audible switching frequency, inconstant sounds are typical caused by an instable or bad designed voltage control circuit.
 
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    thannara123

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right FvM.....
Audible or whinning noise from an SMPS shall be from the pulse transformer due to poorly designed feedback loop which cause oscillations.......or physically oscillate the core splitting......

i feel this definitely depends on the load......because the magnetic flux in transformer varies largely with the load which can produce audible noise.......
 
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There exists other rare source of noise :

In SMPS witch works at switching frequency bellow ~4KHz ( not so usual ) it is possible to use laminated cores.
Due to bad glue varnishing process, the most external lamines could oscilate at switching frequency according Lorentz force effect.

In order to confirm the phenom, you could touch the transformer with the finger ( taking proper safe care ) and observe if soud is reduced.

+++
 

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andre_teprom said:
There exists other rare source of noise :

In SMPS witch works at switching frequency bellow ~4KHz ( not so usual ) it is possible to use laminated cores.
+++
Click to expand...


sir Smps working frequency ,
is it ~4khz means ?
 

hi tannara,

Sorry...did not undertand. Could you elaborate few more the question ?

+++
 

I understand, that tannara wonders, if you actually mean a switching frequency of 4 kHz? I would hardly expect switching frequencies below 16 or 20 kHz with recent SMPS, most have 25 to 30 kHz or even more. That means, that you won't hear the switching frequency, if the device is opearting continuously.
 
thanx all for replying especially betwixt, FvM and ninju
And its definitely not the fan noise,

and thanx andre_teprom for the tip, I'll check it out.

and it seems this noise will make no harm to output voltage, is it??
and yes, the noise changes with the load. and it has no cooling fan.

Actually my problem is this, the subject PSU is providing the power to a offset printing machine main board (with Z-80 CPU with 5 D8255 PPIs) made in 1989. its a Japanese one that's why 110V. the problem was after some time of powering up, the system starts to behave quite unexpected way. most of the times it switches on all the outputs, including the ones which should not turn on simultaneously.

I have check most of the components for a fault but nothing found. so I suspected the noisy PSU coz power glitches can result in such a behavior..

After I remove the metal cover, I saw that its not a single PSU but 2 PSUs assembled on a single board.. and IR3M01 is the controller and have 2 of them to provide 5V and 24V.

I checked the output voltage with my Multimeter, the voltages are OK, but the sudden spikes cannot be detected by the MM no, so that's why I suspect..

Any ideas??
 

something might be wrong with the capacitors. check all electrolytic capacitors. They are the only component which can fail over such a long period of time.

They'll be bulging. i had a similiar problem with an old pentium 2 motherboard.
 

1) Audible noise means, inbetween 20 to 20KHZ frequency ocilated in tr, winding through mosfet or transi ter. (To avoid this change the fr, range)
2) One or more parts are viabrate as per frequency, like a speaker cone, Most chance is transformer core due to pour lamination.(Bound good lamination or change tr.)
3) Use EMI filter at input AC side.

Thanks
 

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