| 摘要 |
PURPOSE:To prevent the occurrence of uneven density of printed pictures due to the dropping of voltage in common line by a method in which potential on farthermost side from the DC power source of common line is detected and the voltage of DC power source is fedback to negative controllably. CONSTITUTION:DC current is supplied through a transistor gate 15 to a common line 3 formed on the base plate 1 of a thermal head. In case where the print data of line-1 input to a shift register 5 are all black, the potential in the farthermost point B power source on the common line is lowered. The base voltage of NPN transistor 16 is lowered, and the current of collector is raised. As a result, the impedance of the a transistor gate 15 is lowered, and potential at the point A of the common line is raised. The potential at the point B of the common line is also raised and current flowing in the heating resistor 2 near the point B is increased. The heat quantity of the heating resistor 2 near the point B is increased, enabling printed pictures of high density to be formed. When even smaller amount of black print information is present in printing data, the reverse is the case. Printed pictures of adequate density can thus be obtained. |
