Potentiometer Smoking

[Muhasaresa]

Hello electronics people

I have a strange mystery that I need help with please. I was learning about transistors today and the Darlington pair. I made a test circuit of it using the diagram on the middle of this page http://www.technologystudent.com/elec1/transis2.htm

Everything went well with the fixed resistor. Then I replaced the fixed resistor at the base of the transistor with a 50k potentiometer. Unfortunately after a few seconds, it started to smoke and I paniced, switching off my new 9V battery.

I'm not sure why this happened. Nothing else got hot and the lamp functioned properly. My potentiometers worked fine before that...please can I have some help?

Thanks,
Muhasaresa

 

[GreenGiant]

was the resistor all the way on or was it down to a very low resistance?

I suspect that it was down to a very low resistance, when you use a pot in situations like that, you usually want to have another resistor in series with it (very small like 100 ohms give or take) so that when the pot reads as a short there is still something to limit the current through it

Im not sure what the power rating of the pot was, but Ill bet you exceeded it

 

[Muhasaresa]

Thanks! I'll try.

Muhasaresa

 

[shrtrnd]

.... and throw away that pot now.