"Tiny Cooling Fan" inductors governor, which uses a series in different core inductor inductance of the motor circuit, including the external inductor and use different tap primary coil motor, the principle is the same. Another kind, mainly used in "Tiny Cooling Fan" on, and the lamp dimmer, like using a triac. Different use SCR conduction angle, half cycle of the alternating current on-time can be adjusted to achieve the purpose of changing the motor operating voltage can be stepless. "Tiny Cooling Fan" high efficiency, small size; it will produce a large number of harmonic power, interfere with radio and so on.