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Unwanted oscillations

Discussion in 'Misc Electronics' started by CWatters, Jul 19, 2003.

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  1. CWatters

    CWatters Guest

    I've got a simple circuit that uses a BC337 NPN transistor to switch a DC
    buzzer on and off.. It's set up as a classic common emitter switch eg The
    Buzzer is in the collector circuit and the base is driven by a micro via a
    1K resistor. The problem is the pesky thing oscillates. I didn't do the PCB
    layout and I suspect that the cause is some inductance in the emiter trace?
    Any ideas for a cure?
     
  2. CWatters

    CWatters Guest

    Thanks for the reply. I'm using a small 12V Peizo buzzer.

    The data sheet is here...

    http://www.farnell.com/datasheets/28097.pdf

    .... but it's next to useless - no data on impedence etc.

    If I apply a Mk1 finger between base and collector the oscillations become
    audible - but I'm not sure that means a lot.

    Think I'll try decoupling the base first.

    Colin
     
  3. More to the point, do you have a diode across the buzzer coil, cathode
    to positive? If not, then the peak voltage may exceed the transistors
    max rating.

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