CONSTANT CURRENT MODE FIRING CIRCUIT FOR THERMAL INKJET-PRINTING NOZZLE

摘要

A firing circuit for a thermal inkjet-printing nozzle includes a heater resistor and a switch. The heater resistor heats ink to cause the ink to be ejected from the nozzle. The heater resistor has a first end and a second end, the second end connected to a ground. The switch controls activation of the heater resistor. The switch has a first end connected to a voltage source and a second end connected to the first end of the heater resistor. The switch operates in a constant current mode, such that an at least substantially constant current flows through the heater resistor upon activation.

主权项

1. An inkjet-printing device comprising:
a plurality of inkjet-printing nozzles; a plurality of firing circuits corresponding to the nozzles; and a first voltage source at which a parasitic resistance of the firing circuits is concentrated, wherein each firing circuit comprising:
a heater resistor to heat ink to cause the ink to be ejected from the nozzle; and,a switch to control activation of the heater resistor,wherein the switch operates in a constant current mode, such that an at least substantially constant current flows through the heater resistor upon activation; and a controller to selectively activate the firing circuits to cause the nozzles to eject ink, such that for each firing circuit that is activated a difference between a voltage at a gate of the switch and a voltage at a drain of the switch is less than or equal to a voltage between the gate and a source of the switch, regardless of the parasitic resistance decreasing the voltage at the drain, the parasitic resistance based on and increasing in correspondence with a number of the firing circuits that are currently firing, wherein the gate is connected to a turn-on voltage circuit including a second voltage source different than the first voltage source to provide a turn-on voltage greater than a threshold voltage defined between the gate and the source, and wherein the voltage at the gate when the heater resistor is activated is greater than a voltage at the first voltage source by at most a threshold voltage of the switch, so that operation of the switch remains in the constant current mode.