Patent ID: 7583069

Claim:
A booster in an electric power steering system having a manual steering input member mechanically connected to apply a manual steering input to at least one road wheel and a motor as a driving source connected for applying assisting force to the power steering system to assist the manual steering input, comprising: a booster circuit outputting an output voltage to the motor of the electric power steering system, the output voltage being obtained by boosting a power supply voltage; and a control section controlling the output voltage of the booster circuit through a feedback control based on a deviation of the output voltage from a target voltage, wherein the control section includes a feedback gain determination section that determines a feedback gain of the feedback control based on the deviation, and wherein the feedback gain determination section determines the feedback gain such that the feedback gain has a value of a low responsivity in an initial state of the booster circuit based on a start signal or a restart signal, the responsivity increasing from the low responsivity as the deviation of the output voltage from the target voltage decreases.