| 摘要 |
<p>PURPOSE:To enhance detection accuracy and a frequency characteristic, by providing the voltage converting part with an operational amplifier connected to the output terminal of a current transformer on the input side thereof. CONSTITUTION:The output terminal of a current transformer 13 is directly connected to the non-inversion input terminal (+) and inversion output terminal (-) of an operational amplifier 14 and the input terminal (+) is connected to a ground line GND. An absolute value amplifying circuit 16 is equipped with a plurality of resistors R, operational amplifiers 17, 18 and diodes 19, 20 and takes the absolute value of the voltage value at the output terminal of the amplifier 14 to output the same to the output terminal of the amplifier 18 and outputs DC voltage across both terminals of the smoothing capacitor 22 connected through a resistor 21. By this constitution, the secondary current of the current transformer 13 flows through the loop consisting of the feedback resistor 15 and output terminal of the amplifier 14 and the ground line GND but, since the input terminals of each operational amplifier is regarded as in an imaginary short state in general, the load impedance of the current transformer 13 becomes almost zero. Therefore, detection accuracy and a frequency characteristic can be enhanced.</p> |
