THERMAL HEAD DRIVER

PURPOSE:To prevent the deterioration of an image quality by a method wherein a temperature detection means for detecting a head temperature is provided in a thermal head, and an electric conduction amount to the thermal head is controlled in accordance with an input signal from the temperature detection means and the number of lines of printing dots from the start of printing. CONSTITUTION:The number of ON dots in one line is counted by a printing ratio counter 4, and the printing line number and a printing ratio are found. In accordance with gradation data of dots and a reference temperature table selected at the start of printing, a heat accumulation correction ROM 3 outputs a conduction amount for every printing line. A printing ratio correction ROM 5 outputs a printing ratio correction factor in accordance with a printing ratio per printing line. With the output of the conduction amount per dot and the printing ratio correction factor, a multiplier 7 operates the conduction amount per dot and the printing ratio correction factor. In accordance with a correction conduction amount outputted from the multiplier 7, a conduction time is set by a timer 8. In accordance with image data transmitted to a thermal head drive circuit 9, an electric conduction to a thermal head 10 is controlled.