Patent ID: 8084973

Claim:
A motor driving circuit, which generates pulse driving signals so as to control the ON/OFF state of a switching circuit connected to a coil of a motor to be driven, thereby controlling the conduction period of said motor, comprising: a driving signal generating circuit which generates the driving signals such that they are pulse modulated according to a torque target value for said motor, and which outputs the driving signals thus generated to said switching circuit; a current detection circuit which detects a current flowing through said coil of said motor; and a current limiting circuit which controls the logical values of the driving signals generated by said driving signal generating circuit such that a current detected by said current detection circuit does not exceed a predetermined current upper limit, wherein said current limiting circuit increases the current upper limit according to the time elapsed in the starting operation of said motor, wherein said current limiting circuit includes a detection resistor, one terminal of which is set to a fixed electric potential, the detection resistor being provided on a path for the current that flows through the coil of said motor and said switching circuit; and outputs a voltage drop across said detection resistor as a detection voltage that corresponds to the current flowing through the coil of said motor; wherein said current limiting circuit compares the detection voltage with an upper limit voltage which is set according to the current upper limit, controls the logical values of the driving signals such that the detection voltage does not exceed the upper limit voltage, and increases the upper limit voltage in the starting operation of said motor; wherein said current limiting circuit includes a comparator which compares the detection voltage with the upper limit voltage, and wherein, in a case that the detection voltage exceeds the upper limit voltage, each of the logical values of the driving signals generated by said driving signal generating circuit is set to a fixed value so as to instruct said switching circuit to stop the supply of current to said motor, following which the fixed logical values thus set are released at a predetermined timing.