| 摘要 |
PURPOSE:To eliminate the offset voltage of a triangle wave generating circuit and of a comparator, by inputting alternately two positive/negative inputs equal in absolute value being the 1st input of a pulse width modulating circuit to the comparator, inverting the output and obtaining a value averaged in time. CONSTITUTION:A switch SW3 switching an AC signal Ev proportional to a voltage of an electric system to be used for measuring the power and its inverting signal -Ev, an EOR logical gate L2 inverting an output Vg of a comparator CP3, and a toggle type flip-flop FF3 inverted by a pulse SDELTA generated once per one period of a triangle wave and outputting a pulse frequency-dividing the SDELTA into a half, are provided additionally between a triangle wave generating circuit 10 and a pulse generating circuit 20. An output ST of the FF3 is a signal switching the switch SW3 and the gate L2 at a prescribed period. The effect of the offset voltage is offset by observing one period of the switching signal ST, i.e., two periods' share of the triangle wave. |
