| 摘要 |
PURPOSE:To prevent the noise applied at the application and disconnection of power supply to the common transmission line, by providing the means delaying the leading of the power supply voltage and quickening the trailing of it to hold the driving circuit in nonoperation state. CONSTITUTION:When the power supply switch in ON and the voltage A of the terminal 21 of the power supply unit reaches a value, the phototransistor TR26 is conductive, TR32 is inconductive and TR36 is conductive, and the voltage B at the power supply terminal 29 appears at the power supply terminal 19 as the voltage C, and the delay time until this voltage C appears is selected longer than the time when the point t1 of power supply application until the time point t2 where the peripheral circuit is stable for the operation. This is because the operation of the driving circuit is stable from the time point t4 when the voltage C exceeds V2. Further, when the power supply to the driving circuit is disconnected, the trailing of the power supply voltage A to the peripheral circuit (time point t7) is delayed more than the trailing of the power supply voltage C (time point t6). Thus, the production of noise to the common transmission line at the application and disconnection of the power supply of the driving circuit can be prevented. |
