| 摘要 |
According to the voltage VU that occurs at one end of at least one of multiple coils of a fan motor, a back electromotive force detection circuit generates a detection signal BEMFU asserted in a cyclic manner when a fan motor is stably rotating. A lock protection circuit detects a lock state of the fan motor rotor. A period detection unit measures the detection signal BEMFU period. A synchronization pulse generating circuit generates a synchronization pulse having a period that is 1/N (N represents an integer of 2 or more) of that of the detection signal BEMFU measured in a previous cycle. A lock judgment unit counts the synchronization pulse in increments of cycles of the detection signal BEMFU. When the count value exceeds a predetermined threshold value M (M represents an integer of 2 or more) which is greater than N, the lock mode judgment signal is asserted. |
