| 摘要 |
PROBLEM TO BE SOLVED: To prevent erroneous operation due to noise while prolonging the backup time by an arrangement wherein a microcomputer decides whether an AC commercial power supply is interrupted or not by counting pulse voltages. SOLUTION: An AC power supply 1 supplies power to the power supply terminal 6 of a microcomputer 5 through a transformer 2, a diode 3 and a capacitor 4. A phototransistor 20b on the output side of a photocoupler 20 has collector connected with a pull-up resistor 23 which is connected with the power supply terminal 6 of the microcomputer 5 and the collector voltage is introduced to the power interruption detection terminal 7 of the microcomputer 5. Consequently, the photocoupler 20 produces a pulse output voltage synchronized with the AC commercial power supply voltage. Since pulses synchronized with the AC commercial power supply are employed as an input for detecting power interruption and the microcomputer 5 decides whether power supply is interrupted or not by counting the number of continuous pulses, erroneous operation due to noise is suppressed while improving the accuracy of time required for deciding occurrence of power interruption. |
