For various electronic equipment, it is recommended to use mains filters. For example, for audio or television equipment, instrumentation, computer monitors and other similar devices that are sensitive to network noise. In good quality equipment, such filters are usually pre-provided and already installed by the manufacturer (for example, in computer power supplies).
If there is no such filter in the device, then its simplest version is not difficult to make on your own.
The purpose of such a filter is to eliminate or significantly reduce the level of high-frequency interference that may be present in the 230 volt AC electrical circuit. The principle of operation is based on mutual compensation of high-frequency oscillations in two mains supply wires ("zero" and "phase"). This article will provide practical examples of the simplest options for such filters.
The first figure shows a variant of the filter, which is connected between the input of the mains wire, fuses and the terminals of the primary winding of the "power" transformer of the electronic device. Such a filter can be wound, for example, on a ferrite ring (magnetic core) with dimensions of about K28x16x9 made of M2000NM ferrite.
The wire for winding can be of the brands MGShV, PEL, PEV, PELSHO, with a section of 0.2... 1.0 mm.kv. In principle, any wire of sufficient cross-section in insulation is suitable for this. The dimensions of the magnetic circuit and the cross-section of the wire for winding depend on the power consumed by the device from the network.
It is better to wind both windings simultaneously in two wires (see the figure below), folded together, until the “ring” is completely filled (usually from 8 to 20 turns). When connecting such a choke, it is important to observe the beginning and end of the winding (on the diagram, the beginning of the winding is marked with a dot).
The second option is even simpler and does not even involve disassembling the electronic device itself. In this case, a magnetic core (ferrite ring) of a larger standard size will be required, and the power cord itself will serve as a "winding" (see the figures below). The power cord should be cut as close to the housing of the electronic device as possible, wound about 8 turns around a ring with it, and then reconnected.
In both cases, ferrite rings can be of other standard sizes, close to those given here, and have a magnetic permeability up to 3000NM.