交流输入电子换向（EC）迷

　　交流输入电子换向（EC）迷

　　电子换向（EC）的球迷是用来创建一个强制空气流动设备帮助热管理从而延长设备寿命。有AC和DC输入风扇类型可用。本文将重点介绍AC输入版本，突出它们的功能和优点。

　　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.