Patent ID: 7271579

Claim:
An alternating current signal level detection circuit comprising: a first comparator ( 52 , 82 ) which receives a rectified voltage obtained by rectifying an alternating current signal generated by an alternating current power source, compares an instantaneous value of the rectified voltage with a first reference voltage (V 2 ), and represents by a first comparison result periods in which the instantaneous value exceeds the first reference voltage; a second comparator ( 40 , 70 , 90 ) which compares the instantaneous value of the rectified voltage with a second reference voltage (V 1 ) which is higher than the first reference voltage, and represents by a second comparison result periods in which the instantaneous value exceeds the second reference voltage; a storage unit ( 53 a , 54 , 83 a , 84 ) which stores information representing whether or not the rectified voltage exceeds the second reference voltage in each period in which the instantaneous value exceeds the first reference voltage (V 2 ), based on the first comparison result and the second comparison result; and a determination signal output unit ( 53 b , 55 , 83 b , 85 , 86 ) which represents by a high-low determination signal whether a level of the alternating current signal generated by said alternating current power source is high or low in each cycle of the rectified voltage, based on the information stored in said storage unit.