Patent ID: 8294399

Claim:
A motor controller, comprising: a position sensor detecting a rotational position of a motor; an upper arm switching element comprising a gate to be driven and configured to connect and disconnect a corresponding terminal of the motor and a positive electrode of a DC power supply; a lower arm switching element comprising a gate to be driven and configured to connect and disconnect the corresponding terminal of the motor and a negative electrode of the DC power supply; a processor selectively outputting an on-signal to either one of the upper arm switching element and the lower arm switching element based upon a detected position by the position sensor, an upper arm gate driver inputting a driving voltage to the gate of the upper arm switching element by shifting a level of the on-signal from the processor to the upper arm switching element; a lower arm gate driver inputting a driving voltage to the gate of the lower arm switching element by shifting a level of the on-signal from the processor to the lower arm switching element; and a bootstrap capacitor configured to be charged while the upper arm switching element is turned off and to behave as a voltage supply for the upper arm gate driver while the upper arm switching element is turned on, wherein the processor comprises: a setting process portion setting a duty ratio based upon a target speed of rotation of the motor; a PWM process portion modulating width of the on-signal based upon the set duty ratio; and a timer process portion timing an interval of update of the detected position by the position sensor, wherein the setting process portion is configured to reduce the set duty ratio when the set duty ratio is equal to or larger than a predetermined value and the timed interval by the timer process portion exceeds a first predetermined time.