iam using a tip 31 power transistor to make a simple fan circuit where iam using on the base 5v adaptor with 800ma full range current
and connecting on the collector the 12v supply
and on the base iam adding a resistor of 10k and connecting to the ground and parrallel to it iam adding my motor
my probleeem is that the transistor output is only 2.45 volt and the fan doesnt want to work

 

Are you trying to make a switch?

Typical switch configuration places the device you want to turn ON between power supply and collector.

You have the device in parallel with emitter resistor. I am not sure why you did it that way.

 

Try this instead...

 

sry but i dont know how to connect as this connection one of my freinds told me about so can you pls tell me the right way to use transistor as switch (or isolator)

 

Try this instead...

ok i will try this and tell you

 

sry but i dont know how to connect as this connection one of my freinds told me about so can you pls tell me the right way to use transistor as switch (or isolator)

See above in post 3

 

Your original circuit is an emitter follower so the maximum output voltage is about 0.7V less than the voltage applied to the base.

 

If you connect the fan between collector and positive rail you will also need a reverse-biased diode in parallel with the fan, to suppress back-emf voltage spikes when the transistor switches off.

 

Try this instead...

Hola Gopher,

What program did you use for drawing?

 

Hola Gopher,

What program did you use for drawing?

"iCircuit" for the iPad. It is a simulation software with generic components and some customization for each. I paid something like 6 or 10 USD for it. I usually use free versions but this one is fairly nice. I used it for discussions and quick examples when I was helping with the tech clubs at my sons' high school.