Line Filter

[Göktuğ]

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A Line Filter is an electronic device that is placed between an electronic equipment and a line external to it, to attenuate conducted radio frequencies (RFI, a.k.a.: Electro-Magnetic Emissions, EMI) between the line and the equipment.

In particular, an AC Line Filter is used between the AC power line and the equipment.

Types of line filters

   * A Line Filter may be incorporated in a connector. For example:
         o An AC Line Filter may be incorporated in a modular IEC power inlet connector or Power Entry Module
         o A telephone line filter may be incorporated in a modular RJ11 connector
   * A line filter may be mounted on a PCB
   * An AC line filter may be a stand-alone device, chassis mounted inside the equipment
   * A facility AC Line Filter is mounted inside a room or cabinet, at the point where the AC power comes in

Characteristics of line filters

   * A line filter may be used to attenuate EMI in either direction. For example:
         o Emissions: It may be used to reduce the unintentional conducted emission from the equipment, to a level sufficiently low to pass regulatory limits (such as FCC part 15). For example, in switching power supplies.
         o Immunity: It may be used to reduce the level of EMI entering the equipment, to a level sufficiently low not to cause any undesired behavior. For example, in equipment used in Radio Transmitter facilities


   * The attenuation of Line filters is measured in 2 areas:
         o Common Mode - attenuation to signals that an appear identically on each of the wires going through the filter
         o Differential Mode - attenuation to signals that appear on just one of the lines
   * For each Mode, the attenuation is characterized over the frequency spectrum, and measured in dB

http://www.panasonic.com/industrial/components/inductive/ind_filters.htm
http://cor.com/Series/PCBoard/EDPEOP/
http://cor.com/Series/RFI.asp
http://www.schaffner.com/components/en/product/productL21.asp?level=3$2$1&language_id=12
http://www.schurterinc.com/wwwsc/con_pg06_1.asp