Patent ID: 7661782

Claim:
A method for controlling the current through at least on heater element in a microfluid ejection device with a compensation circuit comprising: powering a plurality of heater elements with a power circuit; exciting the heater elements by providing current therethrough; coupling at least one logic switch to at least one heater element for selectively applying and controlling power from the power circuit to the at least one heater element; sensing the heater current through at least one heater element; inducing a signal from the heater current, the signal having a magnitude which corresponds to the difference between the magnitude of the current and a reference value; applying the signal to the switch to regulate the heater current and thereby change the magnitude of the difference between the current and reference value; modifying the signal to reflect the changing magnitude of the heater current; regulating the heater current to the reference value by applying the modified signal to the switch; and limiting the heater current through at least one resistor by applying a bias signal.