The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Oct. 18, 1994
Filed:
Jan. 21, 1993
Jaime H Bohorquez, Escondido, CA (US);
Hewlett-Packard Company, Palo Alto, CA (US);
Abstract
A circuit for controlling the power applied to the heater resistor of a thermal inkjet printer printhead wherein the heater resistor is connected to a first source of current. The inventive circuit includes a first transistor having a first terminal connected to the heater resistor, a second terminal connected to a return path for the heater resistor and a simple circuit for maintaining a constant voltage at a third terminal of the transistor. In a particular embodiment, the circuit for maintaining a constant voltage at the third terminal of the transistor includes a diode connected between the second and third terminals and a resistor connected between a second source of current and the third terminal of the transistor. In the illustrative embodiment, the transistor is a bipolar NPN transistor and the anode of the diode is connected to the base terminal thereof. In the best mode, the diode is fabricated by connecting the base and collector terminals of a second transistor fabricated on a substrate with the first transistor. The invention provides a simple, low cost, reliable system for controlling the power applied to the heater resistor of a thermal inkjet printhead which consumes little power.