Firing circuit nozzle printer for thermal inkjet.

A circuit (100) for shooting a nozzle printing thermal inkjet comprising: a resistor (104) for heating ink (114) to cause ink to be ejected from the nozzle, having the heating resistor one first end and a second end, said second end connected to a ground (110); and a circuit (116) ignition voltage; and a switch (102) to control activation of the heating resistor having the switch a first end connected to a source (106) voltage and a second end connected to the first end of the heating resistor, wherein the switch (102) operates in a constant current mode, such that an at least substantially constant current flows through the resistor (104) heating after activation, wherein the switch comprises a transistor having a drain ( D) at the first end (122), a source (S) at the second end (130), and a gate (G) connected to the circuit (116) ignition voltage, a threshold voltage of the transistor being defined between the door (G) and source (S), wherein a voltage (0-VppLogic) in the circuit (116) voltage to turn on the switch (102) in order to activate the resistance (104) heating is greater to a tee nsion the source (106) by a voltage difference at least equal to the threshold voltage of the transistor, so that operation of the switch (102) remains in the constant current mode.