The motor is controlled via a 2N2222A NPN transistor. The hobby motor is 3vdc and pulls about
50mA. I've placed a diode in series to drop the voltage a bit. All in all (correct me if I'm wrong),
the transistor and diode in series drops the voltage down close to the 3vdc requirement of the
motor. (5-.7-.7)= 3.6vdc. I've got a snub diode to remove any negative swings from the
This motor energizes when a positive value is placed on the base of the transistor and turns off
when the base is ground as designed. But it always fails. I have replaced all circuit components
with no results. The transistor is not shorted. The transistor can switch up to 800mA.
Here is the failure:
The voltage on the collector of the transistor goes up from 5vdc to 6-7 vdc. It does not matter if
the base of the transistor is high or low. At times there is a square wave
on the collector that slows the motor down. Funny thing is that I can ground the motor on
the collector and it will work for a while, then the transistor will not turn ON.
Am I missing something here - It seems like a very simple circuit? Do I have the wrong transistor?
Thanks for your time - any suggestions would be helpful.