I used 2n3055 and i will buy a third one later.The only thing i noticed is that the transistors became very hot in a 12v load with 2,5 amps current.....Is it normal?
The 2N3055 output transistors are powered from about 41V. If the output is 12V then the output transistors have 41V - 12V= 29V across them. Simple arithmetic calculates that they heat with 29V x 2.5A= 72.5W.
If the current is set to 3A and the output voltage is low or is shorted then the output transistors heat with 41V x 3A= 123W.
They need a pretty big heatsink to cool them enough. It is simple to calculate the thermal resistance needed for a heatsink and heatsink manufacturers specify the thermal resistance of their products.
Also if it is possible for you i would be glad to explain me how the current limiter works...
It has current regulation which is much more accurate than current limiting.
R7 senses the output current using Ohm's Law. Opamp U3 is used as a comparator with the current-setting pot on one input and the voltage developed by R7 on the other input. If the actual current is higher than the pot setting then the output of U3 goes low enough for D9 to reduce the output voltage until the actual current is the same as the pot setting.