DEVICE AND METHOD FOR DETECTING CYCLE AND PHASE OF CYCLICALLY CHANGING VOLTAGE

摘要

The purpose of the present invention is to accurately detect fluctuating cycles and phases of a cyclically changing voltage, such as AC voltage, half wave/full wave rectified voltage, or rectangular waves. A positive/negative voltage threshold crossing detector (13), using a cycle detection counter, initiates a count-up each time that an input voltage from a cyclically changing voltage (11) crosses a positive voltage threshold or a negative voltage threshold; using a below-positive voltage threshold duration counter, measures the duration for which the cyclically changing voltage is below the positive voltage threshold; and using an above-negative voltage threshold duration counter, measures the duration for which the cyclically changing voltage is above the negative voltage threshold. A cycle/phase detection processor (14), using the count value held in the cycle detection counter at count-up to a point just prior to the timing of crossing of the positive voltage threshold or the negative voltage threshold, which count value has been detected after the count value of the below-positive voltage threshold duration counter or the above-negative voltage threshold duration counter has exceeded a value equivalent to a prescribed time threshold that has been determined on the basis of the maximum value among a predetermined number of past count values, detects the cycles and phases of the cyclically changing voltage.