"Micro Cooling Fan" and DC fan distinction. The former AC power supply, power supply voltage alternating positive and negative, unlike the DC fan power supply voltage is fixed, we must rely on the circuit control, so that 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 produced is determined by the power frequency, the higher the frequency, the faster switching magnetic field, in theory, the faster speed will be like "Micro Cooling Fan" Poles more much more fast speed the same principle. However, the frequency can not be too fast, too fast will cause activation problems.