AC SYNCHRONIZING SIGNAL DETECTION CIRCUIT

PROBLEM TO BE SOLVED: To easily detect the synchronizing signal of an AC power supply, without having to separately provide a rectifying circuit by comparing first output for outputting a pulsation voltage obtained by changing an AC voltage to a DC voltage by a voltage doubler rectification circuit with second output for outputting a DC voltage, obtained by smoothing the AC voltage by the voltage double rectifying circuit. SOLUTION: A detection circuit 1 of an AC synchronizing signal utilizes a voltage doubler rectifying circuit 4, where an AC power supply 2 to an input side and a load 3 is connected to an output side, thus detecting an AC synchronization signal. In this case, first voltage-dividing resistors R1 and R2 divide a pulsation voltage that is changed to a DC voltage by rectifying diodes D1 and D2, and second voltage-dividing resistors R3 and R4 divide a DC voltage that is smoothed by voltage double rectification. Then, the divided pulsation voltage is compared with the DC voltage by a comparison part 6, thus connecting the output of the comparison part 6 to a signal formation circuit 7 for converting to a synchronizing signal that can be easily utilized by the load 3 or the like and corresponds to an arbitrary AC power supply phase angle.