Patent ID: 8729839

Claim:
A driving apparatus for a sensorless fan motor including a plurality of coils, the driving apparatus comprising: a back electromotive force detection circuit configured to compare, in a state in which the sensorless fan motor is rotating, a back electromotive force voltage that occurs at one terminal of each of the plurality of coils with an intermediate-point voltage that occurs at a common connection node at which the plurality of coils are connected together, and to generate a rotation detection signal which indicates a comparison result; a rotor position detection circuit configured to detect, in a state in which the sensorless fan motor is stopped, the position of a rotor of the sensorless fan motor, and to generate a rotor position detection signal which indicates the position of the rotor; a forced synchronization signal generating unit configured to generate a forced synchronization signal having a predetermined frequency; a driving signal synthesizing circuit configured to generate a driving control signal for driving the sensorless fan motor; and a driving circuit configured to drive the sensorless fan motor according to the driving control signal, wherein the driving signal synthesizing circuit is configured to generate the driving control signal according to the rotor position detection signal upon reception of an instruction to start up the sensorless fan motor, and thus, (1) when the back electromotive force voltage occurs, the sensorless driving operation is started, in which the driving control signal is generated based upon the rotation detection signal, and (2) when the back electromotive force voltage does not occur, the driving control signal is generated based upon the forced synchronization signal, and following which, when the back electromotive force occurs, a sensorless driving operation is performed in which the driving control signal is generated based upon the rotation detection signal.