Advice on silencing power supply noise

Discussion in 'General Electronics Chat' started by joshzstuff, Jan 9, 2012.

  1. joshzstuff

    Thread Starter Member

    Sep 22, 2010
    Below is the patient.

    The high frequency noise is coming from the area I circled. It is not extremely loud, but I can hear it in a quiet room.

    I know that some PC computer supplies will 'whine' when taxed by heavy graphics processes, however my noise problem is the reverse, it 'whines' UNTIL it is placed under load.

    Power specs:
    The Power supply is a 5volt charger powering my Picaxe controller and a small total load of ~300-400ma Or another circuit could take it close to a full Amp in total current (well within the supplies limits)

    The noise seems to me to be emanating from the blue 1nF 1KV ceramic cap.
    At least that is what I think it is. The markings are:


    Possible solutions:

    I'm interested in any high or low tech solutions you may know of.

    -I read that when the inductor or chokes whine you can coat them with nail polish or other substances. I'm not sure if that would help here.

    I have 2 Power Supplies, so I can experiment on one of them, but since they both have the same noise from the same general spot, I'm inclined to dismiss manufacture fault. (I.E. re- soldering components)

  2. PaulEE


    Dec 23, 2011
    Sometimes the sound is literally the result of the components vibrating at the resonant frequency (or rather switching frequency) of the supply itself. Perhaps a blob of hot glue will keep them quiet?
  3. hgmjr


    Jan 28, 2005
    One frequent source of audible noise in power supplies is from the transformer. The windings can sometimes be loose enough to vibrate. Also the laminations that were used to build up the transformer can mechanically vibrate to a harmonic of the frequency of oscillation.

  4. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    Put some hot glue on it, and on the transformer if the windings are exposed.

    Do them one at a time and see which one fixes it. I'd suspect the transformer/inductor.
  5. JMac3108

    Active Member

    Aug 16, 2010
    If you can't resolve the problem with all the great suggestions here, and you only use this PS for the PICaxe and small load you mentioned ... then get a power resistor and solder it to the output of the PS to provide a minimum load. You'll have to experiment to find the minimum load that stops the noise. I admit this is really LOW TECH, but sometimes you have to just be happy with solving the problem regardles of the method used :D
  6. joshzstuff

    Thread Starter Member

    Sep 22, 2010
    Ok, so are you perhaps indicating that it is mostly the physical characteristics of the offending component?
    (rather than it's electrical significance in the circuit)
    i.e. the location on the board, proximity to the coil, and mounting characteristics?

    I will try the hot glue, if that doesn't work are there any drawbacks to moving to a firmer epoxy?

    When I searched for a solution I expected to find the problem in the windings, however I made a make-shift mechanics stethoscope from a straw and it really seams like culprit is the ceramic cap.

    Hot glue is an easy fix. I'll try that on my spare PS and get back here with my results.
    Thanks for your input.
    I hope it works!
  7. joshzstuff

    Thread Starter Member

    Sep 22, 2010
    Thanks JMac3108,

    I thought of the power resistor idea too. I'm going to try deadening measures first since there are at least 2 drawbacks given my design:

    1) efficiency/heat - When my circuit draws full power it gets hotter than I'd like. Of course, I have been hesitant to put more ventilation holes in the case because of the noise, so once this problem is solved I could then vent the case.

    2) it will negate my program memory capacitor. -
    It's not a critical function of my circuit, but I have a super-cap holding a real time clock position.
    True - I could design around this, but then it wouldn't be simple anymore.

    Although, if it comes down to it though I'd rather have it quiet.
  8. bountyhunter

    Well-Known Member

    Sep 7, 2009
    It usually is a transformer or inductor whose core or winding is vibrating.
  9. sheldons

    Active Member

    Oct 26, 2011
    first off i would change all electrolytics,especially the smaller of the two on the primary side of your power supply....
  10. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    The noise is most likely the transformer coil, they are hard to fix you need to remove the coil and epoxy it in a vacuum chamber to get epoxy between the windings.

    And even if successful the transformer may run hotter which is not a good thing as those nasty little SMPS supplies run close to destruction anyway. ;)
  11. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    Changing electrolytic won't help.

    But replacing the pF and nF's might.

    then again...put it in the one and bake it, this might help if you don't have the stuff used in the transformers and such

    and OP thinks a capacitor is singing.....
  12. sheldons

    Active Member

    Oct 26, 2011
    if you press the chopper tx with a screwdriver(the handle)if it is producing the noise it should change in pitch or stop ....have had failures of electrolytics goin hi esr cause power supply noise.its either change the tx if it is that or try the advice already given
  13. t06afre

    AAC Fanatic!

    May 11, 2009
    Almost everyone has some old 5 volt cell phone charges lying around just taking up space. They have max load around 500mA. I would suggest that approach. Instead of fixing the current one