Adjust the pot to vary the current draw.
The circuit draws a constant current from the power. The current draw can be varied between 22.7mA and 2.25A. Constant current is drawn from the source by ensuring that there is a constant voltage drop across the 100mohm shunt. When there is a constant voltage drop across the shunt, there is a constant current flowing through it.
Make sure to put the power MOSFET on a big heatsink. In this configuration, the tranny is dissipating 22.275W of power. (It's the voltage drop across the tranny time the current through it).
The 2.5V comes from a voltage reference (like the tl431).
