N-Channel MOSFET - Current driver

Other Hardware General Electronics
12

The current fluctuations may be due to power supply.
I would measure (and show here)

  1. Drain-source voltage
  2. Voltage over the load
  3. The supply voltage (GND close to the shunt, probe at the load + end).

Is 150 mA significant if the current is 3 A?

You need a proper freewheel diode!