Patent ID: 7705605

Claim:
A voltage detecting apparatus comprising: a direct-current power source insulated from earth; a capacitor; a voltage measuring unit for measuring a voltage between both terminals of the capacitor; a first switch connected between a positive electrode of the direct-current power source and one terminal of the capacitor; a second switch connected between a negative electrode of the direct-current power source and the other terminal of the capacitor; a third switch connected between the one terminal of the capacitor and the voltage measuring unit; a fourth switch connected between the other terminal of the capacitor and the earth; a fifth switch connected between the one terminal of the capacitor and the earth; and a switch controller for controlling the first, second, third, fourth and fifth switches selectively to be closed, wherein the voltage measuring unit includes a microcomputer having one terminal connected directly to the earth, and wherein, when a voltage between both terminals of the capacitor measured by the voltage measuring unit is greater than a predetermined value in a condition of controlling the third and fourth switches to be closed, the capacitor is discharged gradually and, when the voltage between both terminals of the capacitor is reduced to the predetermined value or less, the switch controller controls the fifth switch to be closed.