MOSFET humming noise question

Discussion in 'The Projects Forum' started by russpatterson, Jul 13, 2012.

  1. russpatterson

    Thread Starter Member

    Feb 1, 2010
    351
    16
    [​IMG]
    I've built this circuit many times before, but this is the first time I've noticed an audible noise from the MOSFET that regulates the current from the solar panel. I'm using a bench power supply to simulate the panel. The noise is not coming from the power supply but from the circuit board.

    Is this a common occurrence? I'm curious as to how the noise is being generated. There's nothing moving inside the MOSFET, or anywhere else that I'm aware of.

    The panel (or power supply in this case) is being shorted to limit the current going to the battery.

    The MOSFET is being switched at 5Khz when the battery voltage reaches it's set point. PWM is turned off completely when the battery voltage is lower than set point.

    Everything seems to work fine but the noise is new. I also noticed an audible 'click' when powering up the board. Could it be the fuse and not the transistor? Just curious if anyone has any insight on this.

    Video demo at link below:
    http://www.youtube.com/watch?v=IpBGYAlnhtY
     
    Last edited: Jul 13, 2012
  2. wayneh

    Expert

    Sep 9, 2010
    12,094
    3,033
    How much current are we talking about? Maybe a magnetic field?

    A picture might help.
     
  3. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,750
    759
    U just found the supernatural door.
     
  4. russpatterson

    Thread Starter Member

    Feb 1, 2010
    351
    16
    @Wayneh,

    In the video I posted there is about 1.5 amps, charging a 12V SLA battery.

    http://www.youtube.com/watch?v=IpBGYAlnhtY

    Although I noticed the clicking noise when I had the bench supply limited at about 100mA.
     
  5. Sensacell

    Well-Known Member

    Jun 19, 2012
    1,128
    266
    There are two mechanisms that I know of that can cause this:

    1) Piezoelectric effects from some types of ceramic capacitors.
    They actually expand and contract when the voltage across them changes.
    This has driven me nuts when designing lighting dimmers, you get it all working and the client says "what's that noise?"

    2) Magnetostriction in an inductor or transformer core.
    Core materials do the shimmy-shimmy when the magnetic flux density changes.
    I believe this is why old CRT TV sets made that horrible high pitched whine.
    They used to make oscillators based on nickel rods that would resonate longitudinally inside a coil, always wanted to build one.
     
    Last edited: Jul 15, 2012
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