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Unwanted oscillations

C

CWatters

Jan 1, 1970
0
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?
 
C

CWatters

Jan 1, 1970
0
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
 
W

Watson A.Name - 'Watt Sun'

Jan 1, 1970
0
Some buzzers are nasty loads. You can try a 0.1 uF capacitor from collector
to ground. You can also try bypassing the base lead of the transistor to
ground with a capacitor. What kind of a buzzer are you using?

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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