Regulated current source for thermal printhead

Details Regulated current source for thermal printhead Regulated current source for thermal printhead

1982-12-22

1984-02-28

Reynolds, B. A.

Electric heating

Heating devices

Combined with diverse-type art device

400120, 346 76PH, 307 18, 307 24, 323313, B41J 320

Patent

active

044343566

ABSTRACT:
A current-drive circuit (FIG. 1) is provided to drive each of forty electrodes 41. Voltage at the electrodes 41 is monitored on line 49 as a control-input to a voltage-regulator circuit (FIG. 2), to produce the drive voltage Vdr. Vdr minus a current-level reference Vlev is applied as the input of a differential amplifier (transistors 3, 15, 51 and 53), thereby applying Vdr-Vlev on line 27. A constant current through the electrode 41 is produced across register 25. As the lowest voltage at all driven electrodes shifts, the regulator circuit (FIG. 2) shifts Vdr the same amount, employing differentially connected transistors 72 and 74, and Zener 120 to set the level of Vdr. Since most of the active elements operated within narrow limits, the circuit can be extensively miniaturized.

REFERENCES:
patent: 3457493 (1969-07-01), Shoemaker
patent: 4092649 (1978-05-01), Miller
patent: 4345845 (1982-08-01), Bohnhoff et al.
patent: 4350449 (1982-09-01), Countryman et al.
patent: 4404567 (1983-09-01), Katsuragi
IBM Technical Disclosure Bulletin entitled "Constant Current (Current Source) Resistive Ribbon Print Head Array Drive Scheme," by G. P. Countryman et al., vol. 22, No. 2, Jul. 1979, at pp. 790-791.

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