| 摘要 |
PURPOSE:To improve measurement accuracy and reliability by imposing PMW on the voltage value of a shunt resistance on a detection side and the digital value of an isolated measurement side, and integrating them through a photoisolator. CONSTITUTION:The voltage across the shunt resistance 1 corresponding to the level of a bus current I is applied to an operational amplifier 2 through resistances 101 and 102. The output voltage of the amplifier 2 is supplied to one input terminal of a comparator 3 and said bus current which is fed back and integrated is applied to the other input terminal of the comparator 3, so that the difference between both inputs is outputted to a 1st photoisolator 4. A DC voltage 5 is passed through a resistance 105 corresponding to the period of the voltage applied to the primary side of this isolator 4 to control an up/ down counter 6. Namely, the digital output of the counter 6 is converted by a pulse width modulating circuit 7 into a voltage value having a shaped pulse width corresponding to the digital value and inputted to the primary side of a 2nd photoisolator 8 with a DC voltage 10, and passed through an LPF 9 from its secondary side, and the voltage is converted into an analog voltage, which is fed back to the comparator 3.
|
