AC POWER-SUPPLY VOLTAGE DETECTING METHOD AND THREE PHASE AC POWER-SUPPLY DETECTING CIRCUIT

摘要

PROBLEM TO BE SOLVED: To detect an AC power supply voltage by a simple process without employing an expensive circuit by a method wherein the AC power-supply voltage is detected from a period and a set voltage of the AC power-supply voltage, and an ON time of a photoisolator. ;SOLUTION: An AC power supply voltage input is compared with a set voltage by a comparator 4. When the AC power supply voltage is lower than a set voltage, a signal at H level is output from the comparator 4 and a photoisolator 5 becomes in an OFF state. When a T phase of the AC power supply voltage input is lower than a R phase and it is higher than the set voltage, a signal at L lever is output from the comparator 4 and the photoisolator 5 becomes in an ON state. A power supply voltage can be detected from a power supply period, a set voltage and an ON time by measuring this ON time.;COPYRIGHT: (C)1998,JPO