A line filter is the kind of
electronic filter
Electronic filters are a type of signal processing filter in the form of electrical circuits. This article covers those filters consisting of lumped electronic components, as opposed to distributed-element filters. That is, using components ...
that is placed between electronic equipment and a line external to it, to
attenuate
In physics, attenuation (in some contexts, extinction) is the gradual loss of flux intensity through a medium. For instance, dark glasses attenuate sunlight, lead attenuates X-rays, and water and air attenuate both light and sound at vari ...
conducted radio frequencies --
RFI, also known as
electromagnetic interference
Electromagnetic interference (EMI), also called radio-frequency interference (RFI) when in the radio frequency spectrum, is a disturbance generated by an external source that affects an electrical circuit by electromagnetic induction, electrost ...
(EMI) -- between the line and the equipment.
In particular, an AC line filter is used between the AC power line and the equipment (SMPS or an electronic circuit).
Types of line filters
* A line filter may be incorporated in a connector. For example:
** An AC line filter may be incorporated in a modular
IEC 60320
IEC 60320 Appliance couplers for household and similar general purposes is a set of standards from the International Electrotechnical Commission (IEC) specifying non-locking connectors for connecting power supply cords to electrical appliances ...
power inlet connector or
power entry module
** 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:
** 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
The Federal Communications Commission (FCC) is an independent agency of the United States federal government that regulates communications by radio, television, wire, satellite, and cable across the United States. The FCC maintains jurisdictio ...
part 15). For example, in switching power supplies.
** 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 two areas:
**
Common mode - attenuation to signals that appear identically on each of the wires going through the filter
**
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
See also
*
AC-line filter capacitor
References
{{DEFAULTSORT:Line Filter
Mains power connectors
Wireless tuning and filtering
Tone, EQ and filter