Patent ID: 7863845

Claim:
An electric power steering apparatus, comprising: an electric motor supplied with power from a power supply apparatus; and motor control means for controlling operation of the electric motor according to a steering state of a steering wheel to apply a steering force to steerable wheels, wherein the power supply apparatus comprises at least two power supply circuits, including a primary power supply circuit which includes a high-voltage battery to supply electrical power of a first voltage and a step-down circuit to step down the voltage of the high-voltage battery and which supplies the electrical power of the high-voltage battery having a stepped down voltage, and a secondary power supply circuit which includes a low-voltage battery to supply electrical power of a second voltage lower than the first voltage and a step-up circuit to step up the voltage of the low-voltage battery and which supplies the electrical power of the low-voltage battery having a stepped up voltage, and the primary power supply circuit and the secondary power supply circuit are connected in parallel, and the stepped up voltage output from the secondary power supply circuit is set to be lower than the stepped down voltage output from the primary power supply circuit.