I am learning about transistors, and can't seem to find the answer to a few questions which are stumping me. I will be referring to the TIP120/121/122 Darlington Transistor.
- As I understand transistors so far, I need to apply a current from my Arduino to the base of the transistor in order to allow current to flow between the collector and emitter. What I don't understand is how a microcontroller is used with the transistor in so many projects and tutorials. The arduino and other atmegas give ~50mA out of their pins, but according to the data sheet, the TIP needs 120mA at the base. On top of that, a resistor is used between the pin of the microcontroller and base of the transistor, which I would assume reduces the current going into the base even more. So what's going on here?
- I want to experiment with these transistors, but noticed that the TIP120 and 121 are more expensive than the TIP122. I am curious to know why this is, because as per the data sheet, it seems the TIP122 can handle higher voltages (which I suppose is a good thing), with all other things pretty much the same. So is there a scientific reason for this price discrepancy and is there any reason I should select the TIP120 over the 122 to use for my microcontroller projects?