| 摘要 |
PURPOSE:To keep accurately a center duty ratio at 50% by detecting the deviation of a pulse duration modulation ratio from duty ratio 50% by a difference of time average value of output signals and 1/2 of peak level. CONSTITUTION:When time the average value of duty ratio of a pulse width modulation output D exceeds 50%, the center level supplied to a + terminal of a comparator circuit 13 becomes greater than 1/2 of peak level supplied to a - terminal, and the comparator circuit 13 outputs an error signal in positive polarity. This error signal heightness the DC level of saw tooth wave from a saw tooth wage geneator, and the duty ratio of output D is corrected in the direction of decrease. Conversely, when time average value of duty ratio of output D becomes less than 50%, the comparator 13 outputs an error signal in negative polarity. Duty ratio of the output D is corrected in the direction of increase by this error signal. Thus, a center duty ratio can be maintained exactly at 50%. |
