| 摘要 |
PURPOSE:To maintain a constantly fixed density irrespective of data to be printed, by a system wherein series circuits of a diode and a resistor are connected to output terminals for heating resistors, other ends of the series circuits are connected in common, and energy to be applied to the heating resistors is determined by the charging level of a capacitor having an end connected to the common connection. CONSTITUTION:The other ends of the plurality of series circuits 4 are connected in common to the capacitor 7.By appropriately selecting the values of resistors 91, 93, a Zener diode 92, the capacitor 7, the resistors 6 or the like, it is possible to set the time constants for charging and discharging to be approximate to those of cooling and heating, respectively. With the charging level Vc as a reference, the charging time for a pulse width converting capacitor 10 is converted into a pulse width tw through a voltage-comparing circuit 14, whereby the pulse width tw is set to be smaller for a lower value of Vc, namely, for a higher thermal head temperature and to be larger for a higher value of Vc, resulting in that the applied energy is so controlled that the printed density is constantly suitable for the temperature of the thermal head 1. |
