Ferrite filter. Ferrite filter: what are the cylinders on the ends of computer cables for? Snap-on ferrite cable filters - operating principle

Monitors, printers, video cameras and other computer equipment, a ferrite cylinder in a plastic shell.

What is it for?

A ferrite cylinder is a shield that protects against electromagnetic interference and interference: it prevents distortion of the signal transmitted via the external electromagnetic field, and also prevents radiation electromagnetic field(interference) from the cable to the external environment.

What is the principle of protection based on?

Internal and external computer equipment can act as miniature antennas as they convert so-called voltage and current noise into electromagnetic radiation. Unshielded ones emit noise due to common-mode noise flowing through their copper conductors, that is, high-frequency current flowing in the same direction through all conductors. This current creates a magnetic field of a certain magnitude and direction.

Ferrite is a ferromagnet that does not conduct electric current (that is, ferrite is actually a magnetic insulator). Eddy currents are not created in ferrites, and therefore they very quickly remagnetize - in time with the frequency of the external electromagnetic field (the effectiveness of their protective properties is based on this).

Ferrite rings without a shell can also be found inside the block.

How to Increase the Noise Reduction Effectiveness of Ferrite

1. Increase the length of the part covered by the ferrite core.

2. Increase the cross-section of the ferrite core.

3. The inner diameter of the ferrite should be as close as possible (ideally equal) to the outer diameter.

4. If allowed design features cable-ferrite pairs, you can make several turns (usually one or two) around the ferrite core.

To summarize the above, we can say that the best ferrite core is the longest and thickest that can be placed on a particular one. In this case, the inner diameter of the ferrite should, if possible, coincide with the outer diameter.

How to use ferrite

Sometimes on sale you can find detachable ferrites in a plastic shell (heat-shrink tube) with two latches. How to use them?

The open ferrite cylinder is placed on the cable, which must be protected from electromagnetic interference and interference, approximately 3 cm from the tip. A loop is made around the cylinder shell. After this, the shell snaps into place. For reliability, you can equip the other end with a ferrite cylinder.

Goodbye interference, hello undistorted signal!..

Ferrite chip filters are designed to suppress electromagnetic interference in various components of electronic equipment that use high density components, high operating frequencies, where a high level of noise immunity and reduction of EMI levels are required. Taiwanese company using the most modern technologies, produces a wide range of multilayer ferrite chip filters with an excellent price-quality ratio.

A ferrite filter is a passive electrical component used to suppress high frequency noise in electrical circuits. Ferrite filter beads are designed in the form of a ferrite hollow cylinder, ring or torus, inside which a current conductor passes. To increase the inductance of the ferrite filter, a multi-turn toroidal winding can be used. Ferrite filters are used both on signal wires to reduce external interference, and on power wires to reduce their own RF interference.

Multilayer Ferrite Chip Filters

For surface mounting, the design of ferrite filters is realized through the use of multilayer film structure technology. To increase the efficiency of filters in small volumes, high density inductance is required. For this purpose, an integral winding made on a multilayer film structure is used.

On each layer of a thin substrate, a film structure of a half-turn winding is formed. One turn of the winding is performed on two layers. By sintering tens or hundreds of layers, sections of conductors are connected, resulting in the formation of a three-dimensional coil with a ferrite rod inside. The layers can be located both in the horizontal plane (standard design) and in the vertical plane (filters for the microwave range above 1 GHz). Figure 1 shows the layer topologies in the ferrite chip filter structure.

The structure uses manganese-zinc and nickel-zinc ferrite films. The use of different ferrite materials, sizes, and layer topologies provides chip filters with different parameters.

Figure 2 shows the structure of a chip filter with a horizontal topology of integral winding layers.

Using an additional coil structure instead of a conventional monolithic ferrite rod allows for higher impedance in a smaller package. In fact, a certain part of ferrite chip filters are designed exactly like a ferrite rod with two electrodes.

Ferrite chip filters for filtering electromagnetic interference are manufactured using multilayer technology using nickel-zinc ferromagnetic materials. Figure 3 shows the structure and formation process of multilayer ferrite chip filters. The coil structure is formed in several layers of ferrite material.

The technology for producing multilayer ferrite EMI filters is exactly the same as for the production of multilayer chip inductors. Only in them different types of materials are used to form ferrite layers. For ferrite chip filters, a material with high absorption is used, and for chip inductors, on the contrary, with less absorption at high frequencies.

Ferrite chip filters are very similar in appearance to ceramic capacitors. Figure 4 shows appearance Chilisin ferrite chip filter.

Main parameters of Chilisin ferrite chip filters

The main parameters by which chip filters are selected are: operating frequency range, impedance at a test frequency of 100 MHz (in Ohms), DC resistance (in Ohms), maximum permissible current, permissible impedance deviation from the nominal, form factor ( housing dimensions), as well as operating temperature range.

The nominal impedance is usually given at a frequency of 100 MHz. For the microwave range, typical impedance values ​​are given at a frequency of 1000 MHz.

The permissible deviation from the nominal value is given in relative units. Dimensions, impedance rating, and impedance spread are included in the component name. To select the required filter, it is important to know other parameters that are not given in the name. They are given in the technical documentation for the component. This:

• DC inductance resistance (in Ohms);
• maximum operating current at which the ferrite material of the inductance does not saturate (in mA);
• type of impedance frequency response.

Table 1 shows possible sizes for Chilisin ferrite chip filters.

Table 1. Standard sizes of Chilisin ferrite chip filters

Code	Size (LxWxH), mm	EIA code
060303	0.6×0.3×0.3	0201
100505	1.0×0.5×0.5	0402
160808	1.6×0.8×0.8	0603
201209	2.0×1.2×0.9	0805
201212	2.0×1.2×1.25	0805
321611	3.2×1.6×1.1	1206
321616	3.2×1.6×1.6	1206
322513	3.2×2.5×1.3	1210
451616	4.5×1.6×1.6	1806
453215	4.5×3.2×1.5	1812

Rated current

This is the maximum DC current that can flow through the filter chip. For ferrites, it is defined as a current at which the heating of the component does not exceed 20°C. With higher currents flowing through the component, the ferrite becomes saturated and, as a result, the impedance decreases by up to 25%.

DC resistance

The DC resistance value of a chip filter depends on the length of the chip, the number of layers in the ferrite, thickness and configuration. Resistance is measured at room temperature. Chip filters have a DC resistance ranging from several mOhms to several Ohms, depending on the type.

Impedance Frequency Characteristics of Ferrite Chip Filters

The equivalent circuit of a ferrite chip filter is an inductance and resistance connected in series.

The amount of resistance strongly depends on the frequency of the passing signal. Ferrite EMI filters are inductors with high magnetization reversal losses. This feature is the main difference between chip filters and chip inductors.

Chip filters are made from special ferrites with high magnetization reversal losses. This energy is released in the form of heat. Heat is generated through active resistance, not through inductance! The impedance of a chip filter is determined by two components: active and reactive. Formula for determining impedance:

where R is the active component and X is the reactive component. Both components are frequency dependent. The documentation for the chip inductance for each series provides the frequency characteristics of the impedance and its components. Figure 5 shows a typical impedance frequency response of a ferrite chip filter. X is the reactive part of the impedance, R is the active part, Z is the total impedance.

As can be seen from the figure, after 30 MHz the active resistance prevails over the reactive one. Below the resonant frequency, the component's impedance is essentially determined by the inductive component. In the range of 50...100 MHz the situation changes. The active component of losses dominates with increasing frequency, and the inductive component tends to zero. The impedance of chip filters increases with frequency, which is also typical for chip inductors. The main characteristic of inductive impedance (Z) is reactance (X). On the other hand, since the filter is based on ferrite material, which has high losses at high frequencies, the main characteristic in the high frequency range is the resistive component (R). Compared with conventional inductance, ferrite chip filter has better EMI energy absorption ability, providing high-frequency noise suppression effect.

Designation system for Chilisin multilayer ferrite chip filters

Figure 6 shows the designation system for Chilisin ferrite chip filters. This designation system is applicable for the following series of Chilisin chip ferrite EMI filters: SB, GB, PB, UPB, NB, HF, VPB.

• the name of the series is determined by the technology, as well as design and application features;
• body dimensions: A, B, C, mm;
• type of packaging: T (type reel) – in a reel, B (bulk) – in bulk;
• the nominal impedance value is given at a test frequency of 100 MHz, for example, 10...1000 Ohm;
• code for the spread of permissible impedance values ​​from the nominal one. The permissible deviation from the nominal value for different groups is given in relative units;
• deviation codes: Y = ±25%; M = ±20%; T = ±30%.

It should be noted that for ferrite EMI filters, it is not so much the high accuracy of the impedance rating that is important, but the accuracy of the inductance value for ferrite chip inductors.

Table 2 shows the main parameters for various series of ferrite multilayer chip filters produced by Chilisin.

Table 2. Basic parameters of Chilisin ferrite chip filters

Name	Size code, mm/inch	Impedance, Ohm	Limit operating current, mA
For LF signal circuits up to 1 GHz
NEW!	0603/0201	60…470	200…300
	1005/0402	6…2500	100…500
	1608/0603	7…2700	200…500
	2012/0805	7…2700	100…600
	3216/1206	11…1500	200…600
	3216/1206	25…70	500
	3225/1210	26…2000	200…500
	4516/1806	33…170	500…600
	4532/1812	30…125	500
NEW!	0603/0201	10…600	100…500
	1005/0402	6…330	100…500
	2012/0805	5…56	500…600
	3216/1206	8…60	500…600
	3216/1206	25…60	500
	3225/1210	32…120	500
	4516/1806	33…100	500…600
	4532/1812	70…150	500
	1608/0603	6…2700	200…500
	2012/0805	60…2700	200…500
	3216/1206	70…2700	300…500
	3216/1206	70	500
	1608/0603	10…1500	150…1000
	2012/0805	60…2000	400…800
	3216/1206	70…2000	400…800
	2012/0805	7…40	800…1000
	3216/1206	19…60	800…1000
For power rails up to 1 GHz
NEW!	0603/0201	10…240	350…1000
	1005/0402	7…120	1200…2000
	1608/0603	6…1500	500…4000
	2012/0805	5…1500	1000…6000
	3216/1206	7…1500	800…6000
	3225/1210	19…120	2500…4000
	4516/1806	19…1300	2000…6000
	4532/1812	19…1300	1500…6000
	1005/0402	10	2000
	1608/0603	10…1000	800…4000
	2012/0805	7…1000	1500…6000
	3216/1206	11…1500	800…6000
	3225/1210	60…90	3000…4000
	4516/1806	50…150	2000…6000
	4532/1812	30…130	3000…6000
NEW!	1005/0402	33…600	900…3000
NEW!	1608/0603	26…330	1500…3300
	1608/0603	10…180	2000…5000
	2012/0805	11…330	3000…6000
	2012/0805	50…120	5000…6000
	3216/1206	11…220	4500…6000
	4516/1806	60…110	4000…7000
	4532/1812	40…150	6000…9000
For filtering RF signal chains up to 1 GHz bandwidth
	1005/0402	3…240	250…500
	1608/0603	4…500	200…700
	2012/0805	80…300	400…500
	0603/0201	10…120	100…300
	1005/0402	6…600	200…500
	1608/0603	5…2500	100…700
	2012/0805	5…2700	200…800
	3216/1206	15…1500	300…600
For filtering microwave signal chains with a bandwidth above 1 GHz
	1005/0402	200…1000	250…450
	1005/0402	600…1800	200…300
For filtering microwave circuits with a bandwidth above 1 GHz and high current
NEW!	1005/0402	120…220	700…1500
For filtering high current circuits with bandwidth up to 1 GHz
	1608/0603	10…600	2000…6000

Typical Frequency Impedance Characteristics of Ferrite Chip Filters

To select a suitable chip filter, it is important to know and take into account the frequency response of the impedance. Below, for reference, are typical impedance frequency characteristics for several popular series of chip filters used for filtering in signal and power circuits.

GB Series

Figure 7 shows typical frequency characteristics of the GB series.

As the frequency increases, the filter impedance increases. The filter is used in relatively low-frequency circuits with operating frequencies up to 1 GHz.

HF Series

The design of the new high-frequency series of HF ferrite chip filters with an operating frequency band above 1 GHz uses not a longitudinal arrangement of layers (horizontal), but a transverse (vertical) one. Figure 8 shows the impedance frequency response of the HF100505T series chip filter.

PBY Series Chip Filter

Figure 9 shows the frequency response of the impedance of the PBY series ferrite chip filter, designed for use in high-current circuits with operating currents up to 6 A.

Selection and application of Chilisin chip filters

To select the optimal type of ferrite chip filter, the spectrum of interference, the required level of suppression and the range of operating currents are first determined. Based on the application conditions, the impedance and permissible DC resistance of the chip filter are selected. Based on the obtained parameters, a series and type of chip filter with the required effective noise suppression band is selected. The current value and resistance are especially important when installing chip filters in power circuits. First of all, you need to choose types that ensure the filter operates without saturation. The DC resistance value will ensure the minimum voltage drop.

Table 3. Characteristic impedance values ​​for various circuits

Typical applications for ferrite chip filters are:

• filtering “ringing” in data lines;
• supply voltage decoupling;
• land decoupling.

The filtering effect increases with:

• using shunt capacitors connected to ground. The choice of capacitor value depends on the interference spectrum and attenuation frequency;
• low output impedance of the source.

Chip filters are usually installed as close as possible to the interference source device in order to reduce the effective length of the antenna wire with high-frequency noise.

Installing EMI filters at interface cable connection points

The greatest suppression of interference in interface cables can be achieved by using ferrite chip filters at the cable connection points. When designing a board, it is very important to ensure a minimum impedance at high frequencies between the ground pin (GND) of the EMI filter on printed circuit board and a metal body.

Filtering on clock signal buses

High frequency clock signals are sources of RF interference. The clock and noise frequencies may be close to each other. Therefore, it is necessary to use filters with a high attenuation coefficient and slope of the frequency response - ferrite chip filters for high-speed signal transmission lines.

Installing EMI filters on signal buses

Parallel data buses contain multiple signal lines that switch simultaneously. Changing the signals on the address and data buses causes a significant increase in pulse current flowing in the ground (GND) and power circuits. Therefore, it is necessary to limit the current flowing through the signal lines.

Installation of chip filters at LVDS cable connection points

The cable connection between the laptop motherboard and the LCD display increases the level of noise emitted by the computer due to harmonics of LVDS signals and interference from integrated circuits located along the signal transmission line. Since the frequency of transmitted LVDS signals reaches hundreds of megahertz, it is recommended to use NB series chip filters to prevent signal waveform distortion and suppress common-mode interference. When transmitting differential LVDS signals, the magnetic fluxes created by the flowing current cancel out, resulting in reduced interference. However, the presence of reflected signals can lead to unequal currents flowing through pairs of conductors. In this case, common mode chokes act as transformers to balance currents, which ultimately reduces the level of electromagnetic interference.

Noise Suppression in LCD Interface

The graphics controller is connected to the LCD drivers by multiple signal lines that switch simultaneously. These switchings cause a large pulse current to flow through the power and ground circuits. Therefore, the current should be limited to signal lines. Ferrite chip filters of the NB series are well suited for these purposes. On clock signal lines, especially those operating at high speeds and at high levels of interference, filters of the HF or HP series are used, which have a high attenuation coefficient and steepness of frequency response slopes. Interference caused by transient currents also occurs in power circuits. Therefore, to suppress interference in power circuits, ferrite chip filters, as well as shunt capacitors, are installed. Table 4 shows examples of typical applications of ferrite chip filters in electronic equipment.

Table 4. Typical applications of Chilisin ferrite chip filters of various series

Name	Category applications	Typical applications	Basic parameters
			Current, mA	Impedance, kOhm
Filtering interference in signal circuits with a bandwidth up to 1 GHz
S.B.	General Application	Smartphones, consumer electronics, digital cameras	50…500	0.005…2.7
G.B.	General Application	Smartphones, mobile equipment	100…500	0.007…2
Filtering interference in signal circuits with a bandwidth of about 1 GHz
N.B.	Digital RF signals	Video decoders, DSP circuits, Bluetouth, smartphones, digital cameras, satellite receivers, tuners	50…500	0.005…2.7
Filtering interference in signal circuits with a bandwidth greater than 1 GHz
HF; HP	Microwave signals above 1 GHz	Microwave receivers and transceivers	50…2000	0.12…1.8
Filtering noise in power circuits with currents up to 6 A
P.B.	General Purpose Power Circuits	DC/DC converters, video decoders, USB/IEEE1394 circuits, LAN interfaces, video cards, digital cameras	800…6000	0.005…1.5
UPB	High current circuits	DC/DC converters	4000…6000	0.005…0.33

Compatibility and interchangeability

The multilayer ferrite chip filter technology used by Chilisin is fully consistent with the multilayer ferrite chip filter technology used by leading manufacturers such as TDK, Murata, T-Yuden, Vishay, Sumida, Kemet. Chilisin ferrite chip filters are completely identical in their parameters to chip filters from other manufacturers, and can be recommended as an alternative replacement. The series of ferrite chip filters presented in Table 5 are complete or close analogues of the corresponding Chilisin components.

Table 5. Correspondence of analogues of Chilisin ferrite chip filters from various manufacturers

Size code mm/inch	Company
	Chilisin	Murata	TDK	Taiyo Yuden
Series SB
0603/0201			MMZ0603SхххC
1005/0402			MMZ1005SхххC
1608/0603			MMZ1608SхххC
2012/0805	/		MMZ2012SхххC
0603/0201			MMZ0603YxxxC
1005/0402			MMZ1005YxxxC	/
1608/0603			MMZ1608YxxxC	/
2012/0805			MMZ2012YxxxC	–
GB Series
1608/0603			MMZ1608SхххC	–
2012/0805	/		MMZ2012SхххC
Series NB
1005/0402
1608/0603
2012/0805				–
1005/0402
1608/0603		–
0603/0201		BLM03AX(PG)	MPZ0603SхххC
1005/0402

A huge variety of means have appeared in our everyday life. computer technology, which operates at high frequency currents. After all, the higher the frequency, the higher the speed of information processing.

However, high-frequency currents impose a number of technical limitations on connecting cables for transmitting such signals. This is primarily due to side effects electromagnetic radiation and tips (PEMIN).

The simplest way to combat PEMIN is to increase the inductance.

Inductance is an indicator of the relationship between the amount of current passing through a circuit and the magnetic flux it creates. If we're talking about about straight wires, then by inductance we mean a quantity characterizing the energy of the magnetic field (here the current is considered a constant value).

The inductance can be increased by using a special ferrite ring. You can see what ferrite filters look like on cables in the photo below.

Ferrite rings- These are electrical circuit components that are used as passive elements to filter high-frequency interference by increasing the inductance of the conductor and absorbing interference above a given threshold.

Such properties of a ferrite filter are given by the material from which it is made – ferrite.

Ferrite is the general name for compounds based on iron oxide and oxides of other metals. Ferrites combine the properties of ferromagnets and semiconductors (sometimes dielectrics) and therefore are used as coil cores, permanent magnets, act as absorbers of high-frequency electromagnetic waves, etc.

Snap-on ferrite cable filters - operating principle

The performance of a ferrite filter directly depends on the characteristics of the material from which it is made. Due to special additions of oxides of various metals, the properties of ferrite change.

There are fundamentally several ways to use ferrite rings:

1. On single-core (single-phase) wires, it can, on the contrary, absorb radiation in a certain range, converting interference into thermal energy. In this way, negative frequencies can be absorbed (cut off) by the ferrite ring.
2. On single-core wires, where it works as a kind of amplifier, as it returns part of the high-frequency magnetic field back into the cable, which leads to amplification of the signal in a given range.
3. On multi-core wires, the ferrite acts as a common-mode transformer that passes unbalanced signals in the cable (current pulses, for example, in data cables or power circuits DC) and suppresses symmetrical signals (which can potentially be caused in such cables only by electromagnetic interference).

Where to use and how to choose a ferrite filter

If we talk about the practice of application, then on power cables, ferrite rings are used to reduce interference that the cables themselves can create, and on signal (transmitting data) ferrites dampen possible external interference and interference.

Ferrite cable filters can be built-in (the cable is sold already with a ferrite ring) or separate (most often these are models that snap around the wire), which do not require any modifications to the cable itself.

The wire can be inserted into the center of the ferrite filter (a single-turn coil is obtained), or it can form several turns around the ring (toroidal winding). The latter method significantly increases the efficiency of the filter.

To select a ferrite ring to meet the specified requirements, you need to know the characteristics of the material from which it is made and the dimensions of the product.

As an example, the table below shows the main characteristics of ferrite filters offered on the market.

Marking	RF-35M	RF-50M	RF-70M	RF-90M	RF-110S	RF-110A	RF-130S	RF-130A
Impedance, Ohm (for a frequency of 50 MHz)	165	125	95	145	180	180	190	190
Graph of impedance versus frequency, in Figure No.	4	5	6	7	3	8	3	3
Diameter holes, mm	3.5	5	7	9	11	11	13	13
Size, mm	25x12	25x13	30x16	35x20	35x20	33x23	39x30	39x30
Weight, g	6	6.5	12	22	44	40	50	50

Frequency versus impedance graph

Impedance is the total internal resistance of an electrical circuit element to alternating (harmonic) current (signal). It is measured, like regular resistance, in ohms.

Another important parameter of ferrite filters is their magnetic permeability.

Magnetic permeability is a coefficient that characterizes the relationship between magnetic induction and magnetic field strength in a substance.

Based on the above, in order to indicate the main properties of ferrite filters, manufacturers resort to the following markings:

3000HH D * d * h, where:

1. 3000 is an indicator of the initial magnetic permeability of ferrite,
2. HH is a grade of ferrite (most often these are HH - general purpose ferrites, or HM - for weak magnetic fields),
3. D – largest (external) diameter,
4. d – smaller (internal) diameter,
5. h is the height of the toroid.

Here are typical examples of the use of ferrites:

• Grade 100NN can be used for cables with frequencies up to 30 MHz,
• 400NN - with frequencies not higher than 3.5 MHz,
• 600NN - with frequencies up to 1.5 MHz
• 1000NN - up to 400 kHz.

That is, for example, the antenna ferrite filter should be of the HH brand.

But it is best to choose a ferrite filter for a USB cable with the HM brand (for cables with a weak magnetic field).

The ratio of brands and frequencies is as follows:

• 1000NM - used with cables operating with a frequency of no more than 1 MHz,
• 1500NM - no more than 600 kHz,
• 2000NM and 3000NM - no more than 450 kHz.

In most cases, it is enough to select the correct ferrite filter and snap it onto the cable closer to the connection point to the device.

Scheme of winding turns around a ferrite ring

However, in some cases, to increase the impedance, you can make the cable several turns around the ferrite ring and then the impedance will increase as a multiple of the square of the number of turns. That is, from two turns it is 4 times, and from 3 turns it is already 9 times.

In practice, of course, the actual increase is slightly less than the theoretical one.

In order for the ferrite ring to snap into place after winding, it is necessary to determine in advance the number of turns of the wire and calculate the internal diameter of the filter so that it closes without crushing the cable.

You have probably noticed more than once that on the wires from a laptop, monitor and other electronic equipment there are strange bulges in the form of a cylinder. This is done for a reason or for beauty. The fact is that the plastic cylinder is a special ferrite filter. People often call it a filter for suppressing high-frequency interference, or more simply, a “noise” filter. Why and what is it needed for?

The fact is that any device connected to electrical network, is a source of electromagnetic waves, which, in turn, are high-frequency interference that affects the operation of other devices located nearby. Long external power and interface cables act as a kind of antennas, which quite strongly emit interference into the external environment that is created by the equipment during operation. This may greatly affect the performance of wireless WiFi networks, radio equipment and precision instruments. To prevent this from happening, the cable must be shielded. But then its price will rise significantly! A ferrite ring and filters made of this material came to the rescue.

How does a ferrite filter work?

Ferrite is a special material consisting of a compound of iron oxide and a number of other metals that does not conduct current and effectively absorbs electromagnetic waves. The ferrite ring is an excellent magnetic insulator and thus filters out high-frequency interference and electromagnetic noise. It absorbs the electromagnetic waves coming out of electronic equipment before they are amplified in the cable, as in an antenna.

A ferrite filter is a cylinder-shaped core made of this material, which is put on the cable either immediately in production or later. When installing it yourself, it must be located as close as possible to the source of interference. Only this will prevent the transmission of interference through other elements of the device’s design, where it is much more difficult to filter it out.

On regular computer systems, which you can find at home or in the office, at the ends of the wires connecting system unit with mouse, keyboard, monitor, etc. there are small cylinders. They can also often be seen on cables leading from a laptop or printer to the power supply. This element is called a ferrite filter (or ferrite ring, ferrite cylinder). Its purpose is to reduce the effect of electromagnetic and radio frequency interference on the signal transmitted through the cable.

A ferrite filter is simply a solid piece of ferrite: a chemical compound of iron oxide with the oxides of other metals, which has unique magnetic properties and low electrical conductivity, due to which ferrites have no competitors among other magnetic materials in high-frequency technology. The use of a ferrite ring significantly (several hundred or even a thousand times) increases the inductance of the wire, which ensures suppression of high-frequency interference. The ferrite ring is installed on the cable during its production or, cut into two parts, can be put on the cable after production. The ferrite is packaged in a plastic case - if you cut it open, you will see a piece of metal inside.

Computers are very noisy devices. Motherboard in a computer case oscillates at a frequency of about one kilohertz. The keyboard has a separate processor, which also oscillates at high frequencies. All this leads to the generation of radio noise around the system. In most cases, these noises can be eliminated by using a metal housing that acts as a shield for electromagnetic fields.

Another source of noise is the wires connecting devices. They act as good, long antennas that pick up signals from other cables, radio and television transmitters, and also affect the operation of radio and TV devices. Ferrite eliminates broadcast signals. Ferrite cylinders transform high-frequency electromagnetic vibrations in the warmth. That's why they are installed at the ends of most wires.

Depending on the type of cable and its thickness, rings made of various types ferrite. For example, a filter installed on a multi-core cable (such as a data cord, power cable, or interface: USB, video, etc.) creates an in-phase transformer in this area, which, passing antiphase signals (carrying useful information), reflects ( does not pass) common mode interference. In this case, absorbing ferrite should not be used to avoid disruption of data transmission, and the use of higher frequency ferromaterials is desirable. If the cable is single-core, it is preferable to look for a filter made of material that will scatter high-frequency signals rather than reflect them back into the cable.

Thicker ferrite cylinders help combat interference more effectively. But we must pay attention to the fact that filters that are too large are not convenient to use and the result of their work will no longer differ in practice from slightly smaller filters. Therefore, filters of optimal sizes should be used: the width of the hole in the ring should ideally match the thickness of the wire, and the width of the ring itself should be approximately equal to the width of the connectors of this cable.

Do not forget that not only ferrite rings help combat noise. For better conductivity, use thicker cables! Choose the length of the wire based on the distance between the connected devices; do not buy a longer cable. ABOUT maximum length various cables, in which they transmit information without loss, we said