THERMAL PRINTER DRIVE SYSTEM

PURPOSE:To ensure that no irregularities occur in print density even if a load varies by adjusting the width of a current pulse in accordance with the number of selected segment resistors. CONSTITUTION:A printing head 1 consists of segment resistors 11 to 17 connected in parallel and receives an electric current from a power supply 3. Transistor switches 41 to 47 are connected to the segment resistors 11 to 17, and an electric current is supplied to the bases of the switches from a microcomputer 5 to set the segment resistors to be selected. A motor 2 moves the printing head and is driven by the switching operation of a transistor 48. The transistors 41 to 48 constitute a driver. A combined load resistance is obtained by the number of segment resistors to be selected from among the resistors 11 to 17, and an optimal pulse width is set by the obtained combined load resistor. After that, the switching time of the transistors 41 to 47 is controlled so as to obtain any appropriate pulse width for the number of the selected segment resistors.