Parasitic resistance compensation for thermal printers

摘要

A thermal printhead having a plurality of resistive heat elements receives electrical current from a power supply. The current is directed to selected ones of a plurality of heat elements in response to a sequence of data bits corresponding to the image to be recorded. The number of selected heat elements is determined by the current to the printhead or by counting the number of data bits and a signal representative of the number of selected heat elements is produced. The voltage coupled to the printhead is adjusted responsive to the sensed number of selected heat elements to maintain a prescribed voltage across the selected heat elements that is substantially constant independent of the number of selected heat elements.