ELECTRIC POWER STEERING SYSTEM

摘要

A power supply (40) has a power supply circuit constituted of a main power supply circuit (50) having a high voltage battery (51) and a step-down circuit (55) for lowering the voltage of the high voltage battery (51), and a sub-power supply circuit (60) having a low voltage battery (61) and a step-up circuit (70) for raising the voltage of the low voltage battery (61). The main power supply circuit (50) and the sub-power supply circuit (60) are connected in parallel, and the output voltage of the sub-power supply circuit (60) is set lower than the output voltage of the main power supply circuit (50). When the output voltage of the main power supply circuit (50) drops below target voltage of the sub-power supply circuit (60), the voltage is raised by the step-up circuit (70) before being supplied to a motor drive circuit (32). Power supply to an electric power steering system can be backed up at low cost.