FREQUENCY ABNORMALITY DETECTING CIRCUIT

摘要

A frequency abnormality detecting circuit for detecting the frequency abnormality of an AC power source, comprises a waveform shaping circuit for shaping an output waveform (detection waveform) of the AC power source, which is an object to be detected; a frequency demultiplier for demultiplying an output of the waveform shaping circuit at least by one period of the detection waveform; a counter for counting an output pulse of a reference oscillator by the leading edge of an output pulse of the demultiplier; a memory circuit such as a read only memory (ROM) for storing bit data using output data of the counter as an address; an OR gate for performing an OR operation of an output of the memory circuit, a switch device for inputting the output of the memory circuit into the OR gate; and a flip-flop for operating in synchronism with the output pulse of the frequency demultiplier using an output of the OR gate as data input.