Hello, So this thread is about using transistor as a current source. I understood the concept and all. But the main point of this thread is to finally seal my knowledge of transistor in saturation mode. We did an lab exercise about current sources, by biasing transistor with voltage divider. Here is the scheme. [PLAIN]http://pokit.org/get/7573eb06b9996b33837a1cc9841f1d8a.jpg [Broken] This Ropt, you can look at that as variable resistor that goes up to 1k. I did a simulation at National Instruments, after doing a Real life exercise, and everything is ok. Current is constant always at this Ropt, until transistor hits saturation. This is where it gets interesting. First question(check up) is: When I am moving potentiometer, current has to be the same at collector, so the base current "automatically" changes itself to a need value in order to have the constant collector current? But when voltage across the Ropt is high enough, transistor goes into saturation(voltage across the transistor is below ~0,2 V. Question: What happens with potentials in this circuit? Each point: Vbb, voltage across R2 etc? I also noticed that base current is very large, in saturation mode. As expected. Where does this current go? To emitter? Is a consequence of saturation, to have a forward biased diode B-E and it has large current? P.S. U=V at this picture, in my country the convention for voltage is U.