Method and apparatus for checking insulation of ungrounded power source

摘要

An apparatus includes an insulated first switching element and a capacitor which are connected in series between one of positive and negative main circuit wirings connected to an ungrounded power source and a ground potential section (vehicle body); a second switching element with one terminal thereof connected to a junction point of the first switching element and the capacitor; switching element control device for selectively closing the first switching element for a predetermined time so as to charge the capacitor and for closing the second switching element so as to discharge the capacitor while the first switching element is opened; device for detecting the electric charge accumulated in the capacitor; and device for determining the insulation between the other of main circuit wirings and the ground potential section in accordance with the detected amount of charge.