| 摘要 |
PURPOSE:To keep supply electric energy substantially constant and to make printing density constant, by controlling two high and low voltage power sources corresponding to the number of simultaneously driven heat generating elements. CONSTITUTION:At the time of operation, when image signals are transmitted to a shift register from an input terminal 13, the number of ''1'' signals in said image signals are counted by a counter 21 and blackening ratio is operated by a ratio operator 23 to supply the same to a function generator 23. A control pulse P2 corresponding to the blackening ratio is issued from the function generator 23 in response to the rising of the control pulse P1 and, at the beginning of the control pulses P1, P2, switching elements 18, 19 are brought to a continuity state and the driving of fhe switching element 19 due to a high voltage power source V(H) is performed. When the control pulse P2 is extincted, because the switching element 19 is blocked but the switching element 18 is still held under the continuity state, a heating current is supplied to the heat generating element selected corresponding to the image signal from a low voltage source V(L) through a diode. By this method, electric energy supplied to the heat generating element is kept almost constant even if the blackening ratio is changed. |
