A fluid ejection device having an internal power supply path and a power regulator providing an offset voltage from the internal power supply path voltage. A self-calibration circuit in the inkjet printhead determines a regulation band of the power regulator defined by a lower set point offset voltage and an upper set point offset voltage. The inkjet printhead includes a group of nozzles, a corresponding group of firing resistors, and a corresponding group of switches controllable to couple a selected firing resistor of the group of firing resistors between the internal power supply path and the offset voltage to thereby permit electrical current to pass through the selected firing resistor to cause a corresponding selected nozzle to fire.