Earth leakage detecting device, and vehicular power supply system

A leakage detecting device comprising:

• a coupling capacitor, the coupling capacitor including one end connected to a current path of a power storage unit connected to a load, the power storage unit being in a state of being insulated from a ground;
• a first voltage output unit that generates a cyclic voltage in a leakage determination state, the first voltage output unit applying the cyclic voltage to another end of the coupling capacitor via a first resistance;
• a second voltage output unit;
• a second resistance and a third resistance that are connected in series between a node and the second voltage output unit, the node being between the coupling capacitor and the first resistance;
• a voltage measurement unit that measures a voltage at a voltage dividing point between the second resistance and the third resistance;
• a leakage determining unit that in the leakage determination state of the cyclic voltage being outputted from the first voltage output unit, determines whether or not a current leakage occurs between the current path of the power storage unit and the ground, based on a voltage measured by the voltage measurement unit;
• and
• a diagnosing unit that in a diagnostic period of two types of fixed voltages being applied to the voltage dividing point in order, determines whether the leakage detecting device is in a normal state, based on a voltage measured by the voltage measurement unit, the diagnostic period distinct from the leakage determination state,
• wherein the first voltage output unit is configured to output one or more reference voltages during the diagnostic period, and
• the second voltage output unit is configured to output one or more reference voltages during the diagnostic period,
• wherein the voltage measurement unit is connected to the voltage dividing point without the second resistance nor the third resistance interposed between the voltage dividing point and the voltage measurement unit.