Unwanted oscillations

[CWatters]

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?

 

[CWatters]

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




"Charles Schuler" <charlesschuler@comcast.net> wrote in message
news:BkednUXqQIUrSYSiXTWJiA@comcast.com...

"CWatters" <colin.watters@pandora.be> wrote in message
news:GSiSa.21483$F92.2194@afrodite.telenet-ops.be...
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?

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?

 

[Watson A.Name - 'Watt Sun]

In article <BkednUXqQIUrSYSiXTWJiA@comcast.com>,
charlesschuler@comcast.net mentioned...

"CWatters" <colin.watters@pandora.be> wrote in message
news:GSiSa.21483$F92.2194@afrodite.telenet-ops.be...
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?

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.

--
@@F@r@o@m@@O@r@a@n@g@e@@C@o@u@n@t@y@,@@C@a@l@,@@w@h@e@r@e@@
###Got a Question about ELECTRONICS? Check HERE First:###
http://users.pandora.be/educypedia/electronics/databank.htm
My email address is whitelisted. *All* email sent to it
goes directly to the trash unless you add NOSPAM in the
Subject: line with other stuff. alondra101 <at> hotmail.com
Don't be ripped off by the big book dealers. Go to the URL
that will give you a choice and save you money(up to half).
http://www.everybookstore.com You'll be glad you did!
Just when you thought you had all this figured out, the gov't
changed it: http://physics.nist.gov/cuu/Units/binary.html
@@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@u@e@n@t@@