Regulated voltage and approximate constant power for thermal printhead

摘要

Electrodes 1a through 1n are driven by operational amplifier 4 under control of a reference current source 25. The voltage at each electrode 1a through 1n is monitored by diodes 19a through 19n so that point 21 is set at that of the lowest electrode voltage. A current source provides equal currents through diode 23 and the conducting one of diodes 19a through 19n. The potential of control input 5 is therefore that of the lowest potential of all of electrodes 19a through 19n. Feedback through resistor 27 produces a differential amplifier system in which V2 is set by source 25. The output of amplifier 4 and the magnitude of resistors 15a through 15n are selected so that the nominal voltage on line 13 is reduced by one-half across the resistor 15a through 15n. This approximates constant power to ribbon 2. The voltage regulation and constant power each act to limit power dissipation at the ribbon surface. This reduces debris at the printhead.