PROBLEM TO BE SOLVED: To provide a brushless DC motor driver capable of reliably starting even when a blower fan is idling at a slow speed due to an outside wind or immediately after a driver has stopped operation.SOLUTION: The brushless DC motor driver includes: induction voltage detection means 14 that detects an induction voltage generated on a phase of winding; rotor estimation means 17 that estimates the position of a rotor 4; and threshold value setting means 22 that outputs a predetermined threshold value. The induction voltage detection means 14 compares the induction voltage generated on one phase of the winding and threshold value output from the threshold value setting means 22 to output a signal. The rotor estimation means 17 estimates the position of the rotating rotor 4 based on timing at 1/2 period when the induction voltage gets larger than a threshold value and when the induction voltage gets smaller than the threshold value.
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