交流輸入電子換向（EC）迷

　　電子換向（EC）的球迷是用來創建一個強制空氣流動設備幫助熱管理從而延長設備壽命。有AC和DC輸入風扇類型可用。本文將重點介紹AC輸入版本，突出它們的功能和優點。

　　A little motor background

　　Every electric motor is caused to turn by the interaction of two magnetic fields， one on the rotor and one on the stator， influencing each other. Different motor types create and control these fields differently.

　　Brushed DC motors

　　Brushed DC motors use a series of coils on the rotor to generate a magnetic field when a DC input is applied via mechanical carbon contacts （brushes） and a commutation ring. The field generated by the rotor interacts with permanent magnets embedded in the stator to cause the rotor to turn. However， as the rotor turns， the brushes mechanically wear and sparking occurs. Both of these actions will eventually degrade the brushes to a point where they will need to be replaced in order for the motor to operate normally again. Also， being DC driven， an external motor driver will be necessary to run this type of motor from AC mains. This adds complexity and cost to a design.

　　Single-phase induction motors

　　Single-phase induction motors， of which shaded-pole and permanent-split capacitor （PSC） types are commonly used for fans， use a series of stator coils controlled by an AC input to create a magnetic field. This stator field electromagnetically induces a rotor field which will interact with the stator field to turn the rotor.

　　Since induction motors are AC driven， they are designed to operate at peak efficiency at one point on their performance curve. The operating efficiency can decrease drastically when operating on either side of this operating point which makes them limited by synchronous speed requirements and susceptible to voltage fluctuations.