Patent ID: 8134335

Claim:
A car power source apparatus provided with a leakage detection circuit comprising: a battery having a plurality of battery units connected in series; a first series circuit made up of first leakage detection resistors and a first leakage detection switch to connect a first connection node of the series connected battery units to ground; a second series circuit made up of second leakage detection resistors and a second leakage detection switch to connect a second connection node of the battery units to ground; voltage detection circuits to detect voltage of the first leakage detection resistors and the second leakage detection resistors; and a failure detection circuit to control the first leakage detection switch and the second leakage detection switch ON and OFF and determine failure of the leakage detection circuit from voltages detected by the voltage detection circuits; wherein the failure detection circuit turns the first leakage detection switch and the second leakage detection switch OFF in a first step, a first voltage for the first leakage detection resistors and a second voltage for the second leakage detection resistors are detected, and a first voltage ratio for the first step is determined from (the first voltage)/(the second voltage); in a second step, the first leakage detection switch and the second leakage detection switch are turned ON, a first voltage for the first leakage detection resistors and a second voltage for the second leakage detection resistors are detected, and a second voltage ratio for the second step is determined from (the first voltage)/(the second voltage); in a third step, the first leakage detection switch is turned ON and the second leakage detection switch is turned OFF, a first voltage for the first leakage detection resistors and a second voltage for the second leakage detection resistors are detected, and a third voltage ratio for the third step is determined from (the first voltage)/(the second voltage); in a fourth step, the first leakage detection switch is turned OFF and the second leakage detection switch is turned ON, a first voltage for the first leakage detection resistors and a second voltage for the second leakage detection resistors are detected, and a fourth voltage ratio for the fourth step is determined from (the first voltage)/(the second voltage); and leakage detection circuit failure is determined from the first voltage ratio, the second voltage ratio, the third voltage ratio, and the fourth voltage ratio.