Motor control circuit with current limiter and bypass switch

Claim 1

A spindle motor driving apparatus for a disc device, said apparatus comprising: a spindle motor for driving a magnetic disc, a driving circuit electrically connected to a power supply and to said motor, a rotary angle position sensor outputting a signal in response to the rotation of said motor, a target turning speed generator setting a target turning speed of said motor and generating an output signal representative thereof, a turning speed comparator comparing the output signal of said sensor with the output signal of said target turning speed generator and generating a control signal to said driving circuit to operate said motor at a predetermined turning speed, a current limiting resistor between the power supply and said driving circuit of said motor to limit current supplied to said driving circuit, a shorting switch provided at said limiting resistor and operable to bypass said limiting resistor, a switching instruction unit setting a condition for closing said shorting switch at a predetermined time after said motor is started and generating an output signal responsive thereto, and a deciding unit comparing the output signal of said sensor with the output signal of said switching instruction unit and operated to close said shorting switch when the closing condition is satisfied.