"DC Fan" HALL IC and the strength of the magnetic field changes polarity judgment, output control signals to control operation of the fan motor. When the 9141 closest S-pole permanent magnet rotor, in a strong magnetic field, the Hall voltage generated assembly hall, through a series of signal processing, the final 9141 PIN3 output low, PIN3 conduction (9141 PIN2 high potential output), through the red coil L1 of the stator current I1 4-pole, respectively, to produce the opposite pole: P1 → S; P2 → N; P3 → S; P4 → N; and a rotor (magnetic stripe) 4-pole, the occurrence of magnetic force, pushing against the rotor clockwise rotation.