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Power supply hum

Discussion in 'General Electronics Chat' started by andrew24, Jul 18, 2012.

  1. andrew24

    Thread Starter Active Member

    Aug 20, 2008
    76
    0
    Hello,

    I have a problem with a power supply 50Hz hum. When i power my telephone with a switching adapter (it doesn't have protective earth, it's a cheap china product) i hear a 50Hz hum/noise.

    But when i power it with a lab power supply or power supply adapter which has a transformer and a diode bridge in it and etc (it's not switching type adapter), then the 50Hz hum disappears.

    Also, when i touch my telephone PCB's ground with my finger or oscilloscope probe, the 50Hz hum disappears too.

    What is happening here? is it something related with ground loops?
    How could i reduce it? (when using the cheap switching power adapter)
     
  2. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Use earth connection dummy!
     
  3. andrew24

    Thread Starter Active Member

    Aug 20, 2008
    76
    0
    But the lab power supply doesn't have earth connection too. Why using it everything is ok?
     
  4. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    what makes u think tht?
     
  5. andrew24

    Thread Starter Active Member

    Aug 20, 2008
    76
    0
    Because i don't hear any when using non switching type power supply.
    And my device isn't intended to be earthed.

     
  6. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    OK...at frequency do u think switching type operates?
     
  7. DigitalReaper

    Member

    Aug 7, 2010
    70
    2
    The switching supply could be unregulated, it's not unheard of in cheap chinese stuff.
     
  8. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    tht was not what I asked.

    but u can try replacing the capacitors
     
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