Transistor as a switch

I am using a NTE 85 NPN transistor , attempting to switch a 12vdc supply for a pump circuit. I haven't actually hooked it up to my Arduino yet, just trying to get proof of operation first. I have a sketch created and it all works , just debugging the pump circuit first. As you can see from the print , i am applying 12vdc to collector , 5vdc from Arduino pin through a 10k resistor to base and the emitter would pump out 12vdc to pump tying grounds together for pump and Arduino.
For some reason when i try this and read from volt meter ,I get 12vdc from emitter regardless if bias is applied or not. On bread board I have built this circuit and then took from Arduino 5vdc to 10k resistor to base but when I remove the bias voltage it still gives me 12vdc. I can assume that it is a shorted NTE85 but doubt it, sorry I could have actually tested it but it was new in package.

Hook your NPN as seen in circuit A1.

Better still use C1 using a MOSFET.

Note: depending on the resistance of your motor, there power dissipation in the transistor may be too much for it to handle.

That will not work. Connect the emitter to GND, collector to pump minus and the other pump terminal to +12. 12 volt minus and GND connected together.


Thank you larryd and Railroader ,your information was helpful.

Nice to tead. Thanks.

Obviously you have your answer but your first attempt is called an emitter follower because the voltage on the emitter follows the voltage on the base minus about 0.6v.

Search for emitter follower for more information.

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