"Micro Cooling Fan" alternating positive and negative power supply voltage, unlike the DC fan supply voltage is fixed, must rely on circuit control, make two sets of coils in turn work to produce different magnetic fields. "Micro Cooling Fan" because of the power frequency is fixed, so the rate of change in magnetic silicon steel produced is determined by the power frequency, the higher the frequency the faster switching magnetic field, in theory, the faster the speed will be like "Micro Cooling Fan" Poles more much faster the speed of the same principle. However, the frequency can not be too fast, too fast will cause difficulties fan activation principle