| 摘要 |
PURPOSE:To enhance printing quality by uniforming the heat distribution on a thermal head by providing a constant current control circuit for keeping the current proportional to a control level constant at every printing control unit and driving the resistor of the thermal head by the output current of the constant current control circuit. CONSTITUTION:An operational amplifier 7 constitutes an adder circuit along with input resistors 8-10 and a feedback resistor 11. The out current IO of a constant current is controlled on the basis of the output VOP of the operational amplifier 7 and the base potential of a transistor 19 is controlled by a resistor 17 and the collector current flowing to the transistor 19, that is, the supply current of a resistor 20 is made variable. A transistor 1 and a resistance ladder circuit consisting of resistors RHn2, RLn3, RRn4, RR(n+1)5 are arranged according to thermal head arrangement. The resistance ladder circuit has such a characteristic that potential is gradually lowered from the center of a continuous current supply element to the end part thereof and considerably lowered with respect to an isolated current supply element and, therefore, an extremely good characteristic is developed when the distribution state of temp. is corrected. |
