Constant current mode firing circuit for thermal inkjet-printing nozzle

Patent metadata

Field	Value
Publication number	US-9815276-B2
Application number	US-201615011200-A
Country	US
Kind code	B2
Filing date	Jan 29, 2016
Priority date	May 20, 2005
Publication date	Nov 14, 2017
Grant date	Nov 14, 2017

Abstract

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.

First claim

We claim:

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 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.

2. The inkjet-printing device of claim 1 , further comprising a ground,
wherein the heater resistor has a first end and a second end, the second end connected to the ground.

3. The inkjet-printing device of claim 2 , wherein the switch has a first end connected to the fi voltage source and a second end connected to the first end of the heater resistor.

4. The inkjet-printing device of claim 2 , wherein the ground to which the second end of the heater resistor is connected is a local ground, such that a voltage at the second end of the heater resistor is unregulated.

5. The inkjet-printing device of claim 2 , wherein the ground to which the second end of the heater resistor is connected is an absolute ground, such that a voltage at the second end of the heater resistor is regulated to zero volts.

6. The inkjet-printing device of claim 2 , wherein the parasitic resistance is a first parasitic resistance, a second parasitic resistance at the ground minimized as compared to the first parasitic resistance.

7. The inkjet-printing device of claim 1 , wherein a voltage at a first end of the heater resistor tracks a voltage at the gate, and a current through the heater resistor remains constant, regardless of any fluctuation to a voltage provided by the first voltage source at the drain.

8. The inkjet-printing device of claim 1 , wherein operation of the switch in the constant current mode causes the heater resistor to have a voltage at the first end thereof regulated.

9. The inkjet-printing device of claim 1 , wherein the switch operates in a source follower mode so that operation of the switch remains in the constant current mode.

10. The inkjet-printing device of claim 1 , further comprising the turn-on voltage circuit to translate a firing logic signal to a greater voltage needed to turn on the switch to activate the heater resistor.

11. The inkjet-printing device of claim 1 , wherein the switch comprises a transistor.

12. The inkjet-printing device of claim 10 , wherein the transistor is a laterally diffused metal-oxide semiconductor (LDMOS) transistor.

13. 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,
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,
wherein a gate of the switch 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.

14. The inkjet-printing device of claim 13 , wherein a parasitic resistance of the firing circuits is concentrated at the first voltage source,
and wherein for each firing circuit that is activated a difference between a voltage at the 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.

15. The inkjet-printing device of claim 13 , 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.

Assignees

• Hewlett Packard Development Co Lp

Inventors

• Liao Hang
• Clark Richard R
• Kawamoto Galen H
• Schloeman Dennis J
• Yeh Bao

Classifications

• B41J2/04555

  detecting current · CPC title

• B41J2/0458

  controlling heads based on heating elements forming bubbles · CPC title

• B41J2/0457

  Power supply level being detected or varied · CPC title

• B41J2/04541 Primary

  Specific driving circuit · CPC title

• B41J2/0455

  Details of switching sections of circuit, e.g. transistors · CPC title