| 摘要 |
PURPOSE:To offer a high quality printing while maintaining a printing density at a constant level, by arranging the circuit which can change an applied voltage in accordance with an interval between pulse signals, in the thermal head-driving circuit which will feed pulse signals to a plurality of heat generating resistors for printing. CONSTITUTION:The common terminal (a) of the heat generating resistors 8 of a thermal head 3 is lead through a parallel connection composed of a resistor Ro and a voltage-dropping diode Di to an electric power source +V, and also put through a condensor Co to earth. The other terminals (bn) of the heat generating resistors 8 are lead to the collector of a drive transistor Tn. In case of type printing after a long break, a voltage to be charged to the terminal (a) is maintained at a level higher than that during a continuous type printing period, by an electric charge accumulated in the condenser Co. Consequently, it is possible to print types at a constant density from the beginning of the type printing operation. With the continuation of type printing, the applied voltage is gradually lowered by each of the generations of type printing pulses Cn, and stabilized at a voltage V1 suitable for the continuous type printing operation. |
