Motor controller and electric tool having the same

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.