| 摘要 |
PURPOSE:To provide a power-supply turning-on circuit which outputs a stable signal even when a power-supply voltage whose power-supply has been cut off instantaneously is restored. CONSTITUTION:A power-supply turning-on circuit is provided with a differentiating circuit which is constituted of a capacitor and of a resistor and with a power-supply switch, and the power-supply turning-on circuit turns on a power- supply circuit by an output signal which has differentiated a signal at the turning-on operation of the power-supply switch by means of the differentiating circuit. Consequently, a voltage detection circuit 7 which detects a power-supply voltage is installed on the input side of the differentiating circuit 3, the voltage detection circuit 7 sets an input impedance to a high impedance when a detected voltage is higher than a set detection level, and it sets the input impedance to a low impedance when the detected voltage is lower than the set detection level. When a power supply is cut off instantaneously, the electric charge of a capacitor 3-1 for the differentiating circuit 3 is discharged quickly. |
