Originally Posted by
krazer
I still suspect that delays in your circuit may be contributing to the issue.
Looking at your mosfet (I can't quite read the part number, but I am guessing it is a IRLU9343) has a gate charge of about 5e-9 C Your opamp is supposed to be good for .1A, which can charge the capacitor in 5e-8s, or 50ns. The fet also has about 30ns of delay times on the turn on (10ns delay time, 20ns rise time), which all adds up to somewhere between .05-.1us of delay, which really isn't negligible in the circuit.
Although thinking about it more, the fact that the current takes a dive before it hits the set point is more worry some, and I have a hunch is being caused by stray inductance in the circuit somewhere. You did use a low inductance .1r resistor, right?
Also, what are you using for your dummy load? And what current are you running at for that matter.
