Motor driving device and electric power steering apparatus including motor driving device

A motor driving device comprising:

• an inverter portion including a plurality of switching elements that switches power supply to a winding group of a motor;
• a first relay portion connected between a power source and the inverter portion;
• a second relay portion connected between the first relay portion and the inverter portion;
• a motor relay portion connected between the inverter portion and the winding group of the motor;
• a plurality of inverter pre-driver circuits respectively driving the plurality of switching elements of the inverter portion;
• a first pre-driver circuit driving the first relay portion;
• a second pre-driver circuit driving the second relay portion and the motor relay portion;
• and
• a controller including a control section and a failure detecting section, the control section controlling driving of the inverter portion, the first relay portion, the second relay portion, and the motor relay portion through the plurality of inverter pre-driver circuits, the first pre-driver circuit, or the second pre-driver circuit, the failure detecting section detecting a failure of the first relay portion, the second relay portion, and the motor relay portion.