FREQUENCY DETECTOR FOR AC POWER SUPPLY

摘要

PROBLEM TO BE SOLVED: To set an apparatus so as to be usable even when a noise or the like is superposed on an AC power supply in such a way that a frequency cannot be judged. SOLUTION: In the frequency detector in accordance with this invention, a conversion circuit which generates a fundamental clock from a commercial AC power supply is provided, and a frequency detection means which detects the cycle of a pulse signal to be output from the conversion circuit, which detects the frequency of the AC power supply and which sets the reference clock of a load circuit according to a frequency detected at the time when the power supply is turned on is provided. The frequency detection means is constituted in such a way that a pulse signal to be output from an oscillation circuit used to oscillate a fundamental clock for microcomputer operation is input as the fundamental clock at the time when the frequency cannot be judged within a preset prescribed time after the power supply is turned on.