# Voltage-controlled current source design problem

I am trying to design a voltage-controlled current source circuit. After some research, I decided to use an op-amp.

In the circuit shown below, when V1 is 0.3 V, then Vr is 0.3 V and the current is 0.3 A. These values are OK but when I use V1 is 2 V, Vr is 0.5 V.

What is wrong in this circuit? I also noticed that if I use a 12 V supply for the op-amp then there is no problem.

First:

Second:

But, you have a 5 volt power rail and the op-amp cannot drive 6.8 volts. You need a higher voltage power supply or a MOSFET with a significantly lower $$\V_{GS(THRESHOLD)}\$$.