I'm trying to make a current regulator to power up some LEDs. For now I'm working only on PSpice models.
The circuit above works well if the sensing opamp is configured as voltage follower or even if the voltage of the shunt resistor is directly reported to the inverting input of the main opamp U2A w/out the U2B.
Now, if the U2B is used to amplifying the shunt voltage resistor, in order to make this lower of at least 10 times to absorb 10 times less power, the opamp should amplifying 10 times this voltage and report it on the inverting input of U2A.
Under PSpice, by varying the Vcc from 4.5 (the minimum to have opamps working under this input values) to 12V, with this U2B which apmplifies fo 10 times, the current is like this. Where noramlly should remains stable under 50mA. The average value that you can see depends also on the base resistor of the BJT.
What am I missing?