Quote Originally Posted by krazer View Post
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.
Yes the sense resistor is a low inductance thick film resistor. Test load was in this case just a 0.5 Ohm resistor. Wires were short arround 3cm or so. Peak current is 2A but the effect is also at 0.5A there.
I also think it is some parasitic effect. Maybe the only way to find out is to make a new layout. I think I will wire the circuit without board just with wires and see if the effect is still there. Just to exclude parasitic effects from the layout.