Transistor Current Question

[joe_1]

I got a very small circuit, and for some reason I am unable to get current out of it:

There is DC 5 volts going thru 1K resistor into the base of TIP31C (NPN transistor), the emitter is GND, and the collector is connected to 15V thru 10K resistor.
The output is between the collector and the 10K.
My purpose is to run DC motor from this 15V output.
Note that since I am getting the output from the collector, it is inverted. I took care of this by having an inverter at the base. So, if the input is 0V, it is inverted to 5V, and the output at the collector will be around zero. If the input is 5V, it is inverted to 0V at the base, so the output at the collector is 15V.
At the output (at the collector) I can actually measure 15V, but with almost no current. I cannot get more than few mA barely enough to provide a very dim light for small LED. I cannot run any motor with few mA.

Is there any reason why there is very little current coming out of it?
I tried two different power sources, and got the same results.

One thing I suspected was that the output of a transistor at the collector is hi-impedance, so I connected second stage with common collector (emitter follower), and I took the output between the emitter and the emitter resistor, but got same result.
I have no idea how to solve this issue.

Thanks for any input.

 

[Reloadron]

I am not quite understanding you? Remove the 10K resistor and insert motor. How much current does the motor draw?

<EDIT> Should be configured like the attached. </EDIT>

Ron

 

[joe_1]

Hi Ron,

I am trying to use the transistor as a switch, so I do need a resistor between the collector and the 15V.
I tried your circuit, and what I saw is that regardless of what the input at the base is, the motor always ran vigorously.

 

[ronv]

Should have worked. You should also add a diode - cathode to +15 anode to the collector. Might have zapped the transistor. If the motor draws more than 50 ma or so the 1k would need to be smaller.

 

[audioguru]

In your first circuit the 10k resistor powered the motor with a current of about 14.8V/10k= 1.48mA. If you tried a 1.8V red LED instead of the motor then its current was (15V - 1.8V)/10k= 1.32mA. The transistor simply shorted the motor or LED to turn it off.

The improved circuit uses the poweful transistor to apply 15V to the motor or to instantly burn out an LED.

 

[Reloadron]

Hi Ron,

I am trying to use the transistor as a switch, so I do need a resistor between the collector and the 15V.
I tried your circuit, and what I saw is that regardless of what the input at the base is, the motor always ran vigorously.

The circuit I posted uses the transistor as a switch. Also as Alec points out a diode should be added across the motor as a "flyback diode". If the motor runs continuously without any base current it indicates the transistor has an emitter collector short and is bad. Do you know what the motor current should be as in how large is this motor?

Ron