The circuit I tried is attached. Its the simple and ubiquitous op amp current source with a BJT.
Except for the op-amp I used a faster one TL072 powered @ 12V and BJT BD139.
The current sense resistor is 1ohm. When I give 1V at the input I was expecting around 1A at he output but I get around 0.5 to 0.6A.
I cannot find the max output current of the TL072, but I beleive the opamp cannot source the base current required for correct operation of the current source.
I tried also with a darlington transistor TIP122 in the same setup but the output oscillates.
I would have loved to use a mosfet and I did try with the STP55NF06 but again the output oscillates. For the mosfet I tried using additional components as given here
https://www.electronicsweekly.com/blogs/engineer-in-wonderland/current-sink-stability-2015-10/, an additional resistor(tried 1K and 10K) and capacitor (tried both 100pf and 1nF) but that wouldn't stop the oscillation.
The above circuits all had the drain / collector powered by 12V.
I have assembled the circuit on a breadboard.
My questions are
1. For the BJT version would I just need another transistor stage (like a 2N3904) in between the BD139 and opamp can safely source that amount of base current?
2. For the Mosfet version, how do stabilize the op amp and prevent it from oscillation?