Noise suppression mains filter. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Protection of equipment from emergency operation of the network

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The proposed surge protector is assembled from available parts and does not need to be adjusted. To take up his independent production of the author was prompted by a sharp deterioration in the quality of the image on the TV screen when the computer was turned on. Interference somehow began to appear in other TVs located tens of meters from this computer. Rearrangement and replacement of antennas had little effect on the situation. Moreover, as soon as the computer was turned off, the interference disappeared.

Of course, other experiments were also carried out. In particular, they tried to use network "filters" purchased in retail trade. This word is not in vain taken in quotation marks. their disassembly showed that, despite the loud name, in most of them there are no interference-suppressing elements inside. Only one found a 2,2 mH inductor without any capacitors.

Naturally, such devices do not change the interference environment and can serve as nothing more than extension cords.

In the end, the filter, designed and manufactured independently according to the scheme shown in the figure, helped. For greater efficiency, it consists of two links connected in series.

The first (capacitors C1, C4, C5, C6, two-winding choke L2) is responsible for suppressing interference with a frequency above 200 kHz. The second link (two-winding choke L1 with the rest of the capacitors) suppresses interference, the spectrum of which extends below the specified frequency - up to a few kilohertz.

Thanks to the magnetic coupling between the windings of the chokes, common-mode interference is suppressed - those that are induced simultaneously on both network wires or are emitted by them. Therefore, the windings of each inductor must be the same and symmetrically wound on the magnetic circuits. It is important to ensure the correct phasing of the windings. their beginnings are indicated by dots in the diagram.

Inductor L1 is wound with doubled wire. PELSHO with a diameter of 0,63 mm (87 turns) on a Sh12x14 ferrite magnetic core with a self-made frame made of electric cardboard. The brand of ferrite, unfortunately, is unknown.

The inductance of each winding measured by the LP235 is about 20 mH. For the L2 choke, the B22 armored magnetic core made of 2000NM1 ferrite was used. Its windings contain 25 turns and are wound with the same wire and in the same way as the windings of the inductor L1. the inductance of each winding of the inductor L2 is 120 μH. It was decided not to use ring ferrite magnetic circuits for chokes due to the increased laboriousness of winding wires on them.

Capacitors of the first link of the filter are mica.

Since there are no small-sized capacitors of this type required for the filter capacitance for the desired voltage, it was necessary to connect in pairs in parallel KSO-5 capacitors of a smaller capacity.

A similar solution, but with pairwise serial connection of capacitors C2, C3 and C6, C7 (foreign-made film), was also adopted in the second section of the filter to provide the required operating voltage. Resistors R1-R4 connected in parallel with the capacitors equalize the values ​​of the voltage applied to them. They also provide a quick discharge of all capacitors after the filter is disconnected from the mains. Capacitor C9 - K78-2.

The filter board is placed in a grounded metal box.

Author: Zyzyuk A.

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