Even if a device is designed with noise in mind and layout, grounding, or filtering on the board, it may still generate high levels of noise or be susceptible to noise when other devices are connected to the interface cable. In particular, since cables have a high specific surface area due to their long length, they can emit or receive electromagnetic waves. In this regard, to suppress interference, it is advisable to use special devices, for example, a ferrite filter with a snap on the cable (see Figure 1).

The appearance of the filter with a latch on the cable is shown in Figure 1.
Ferrite Cable Snap Filter consists of a ferrite core, which consists of two halves housed in a plastic flexible housing characterized by a long service life. This design allows you to attach it to the cable in one movement without cutting it. Since such a filter can be installed after the device is assembled, its use becomes especially relevant in cases where interference problems occur immediately before transportation. Figure 1 b shows a filter that is mounted on a cable inside the device.

The snap-on cable filter consists of a ferrite core, which consists of two halves housed in a plastic flexible housing characterized by a long service life. A large number of product types are available for order, produced in accordance with cable diameters.

Common mode filter type

Adjusting the winding size

As a complement to network adapters power supply (AC), a variety of peripheral devices, such as digital cameras or mobile phones, are connected using various interface cables to terminals in the form of laptop PCs. Cable snap filters are installed on these interface cables and their effect on interference suppression is assessed.

Connecting the AC power cable

Noise emission spectrum from mobile phone Before and after connecting the ZCAT1518-0730 self-clamping filter to the power cable is shown in Figure 2. In this test, the cable had a double wrap around the filter. The measurement results are presented in Figure 3. Before installation, noise was recorded in the frequency range from 250 to 600 MHz, barely meeting the VCCI Class B standard. After installing a ferrite filter with a snap on the cable, the noise was reduced by approximately 5...10 dB.

Mobile phone connection

As shown in Figure 4, the portable terminal was connected to the phone using an exclusive type of cable, ZCAT1518-0730 filter was installed on the power cable. The measurement results are shown in Figure 5. Before installing the filter, noise was recorded in a wide frequency range from 100 to 600 MHz. As in previous testing, after double winding the exclusive cable around the filter, the noise level was reduced to 5..10 dB. In addition, it was discovered that interference at 600 MHz and above, which did not change after installing the filter, was caused by sources other than the cable.

Cable snap ferrite filters improve ESD resistance

By installing a snap-on filter on the cable, not only does the noise level decrease, but it also reduces the likelihood of errors caused by external noise sources such as power surges or static electricity. An ESD (electrostatic discharge) test based on the international standard IEC61000-4 for immunity testing was conducted to investigate the frequency or change in the number of errors before and after installing the filter.

Electrostatic discharge is a phenomenon that occurs when electric charge, accumulated on the surface of the body due to reasons such as friction with clothing, is discharged upon contact with the body of an electronic device. Noise immunity is resistance to noise from external sources.

Measuring method

As shown in Figure 6, under working conditions, the connection between the portable terminal and the printer was carried out. The portable terminal (PC) was discharged static electricity. The conditions under which errors occurred were recorded. The electrical shock was applied 10 times at one second intervals to the cable connector (where it connects to the cable) on the handheld terminal side. The discharge was applied using the contact discharge method in accordance with the international standard IEC61000-4-2. The pulse waveform for testing described in the IEC61000-4-2 standard is shown in Figure 7. The test voltages (discharge levels) were: 2 kV, 4 kV and 6 kV.

Test results

The test results are presented in Table 1. When the filter was not yet installed, errors such as stopping some printer operations were observed at a test voltage of 4 kV. At 6 kV the printer stopped working completely. When using the ZCAT2035-0930A (single winding) filter, there were no problems resulting from operations at 4 kV test voltage, but few operational errors were noted at 6 kV. When using a filter with a double winding, no errors were detected. The ESD waveforms before and after installing the filter are shown in Figure 8. A double winding was used. Electrostatic discharge was significantly reduced thanks to the filter. Signals were observed at a position near the filter on the cable between the filter and the printer.

ESD Noise Reduction on a Parallel Two-Wire Data Line

The ESD noise suppression effect of a snap-on cable ferrite filter was evaluated experimentally when installed on a parallel two-wire line. The comparison was carried out using the example of the filter discussed above.

Measurement setup

The measurement setup is shown in Figure 9. Two parallel wires of 1 m length were placed at a height of 0.1 m from the ground plane. A voltage of 6 kV, generated by an electrostatic generator, was applied to the input of the line using an electrostatic discharge generator. Contact has occurred between the electrostatic discharge and the line. The static electricity pulse shape generated by the electrostatic generator corresponded to a high-speed peak voltage with a rise time of 0.7 to 1 ns. Filters ZCAT2035-0930A (ZCAT) and board-mounted common mode choke ZJYS51R5-2P (ZJYS) were installed in the middle of the parallel wires. Next, a change in the shape of the electrostatic discharge signal at the output was observed. As shown in Figure 10, two types of boards were used on which ZJYS components were installed. The first board was 1 mm thick and there was no copper foil layer on the back side. The thickness of the second board was 0.3 mm, the entire surface reverse side was a grounding plate.

High-level impulse noise suppression effect

Wide range of manufactured components

In conclusion, the selection chart for TDK's ZCAT series filter line is shown in Table 2. TDK provides various series of components covering a wide range of applications, from general purpose cables to flat cables.

Application	Type	Cable diameter, (mm)	Order code	Image
Cables	Self-clamping mechanism	3...5	ZCAT1325-0530A (-BK)
		4...7	ZCAT1730-0730A (-BK)
		6...9	ZCAT2035-0930A (-BK)
		8...10	ZCAT2235-1030A (-BK)
		10...13	ZCAT2436-1330A (-BK)
	The cable is attached to the body with a nylon strap	7 max.	ZCAT1518-0730 (-BK)
		9 max.	ZCAT2017-0930 (-BK)
		9 max.	ZCAT2032-0930 (-BK)
		11 max.	ZCAT2132-1130 (-BK)
		13 max.	ZCAT3035-1330 (-BK)
Flat cables	20 core flat cables	12 max.	ZCAT3618-2630D (-BK)
	26-core flat cables	13 max.	ZCAT4625-3430D (-BK)
	40 core flat cables	17 max.	ZCAT6819-5230D (-BK)

Monitors, printers, video cameras and more computer equipment, 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 cable from exposure to an external electromagnetic field, and also prevents the radiation of the electromagnetic field (interference) from the cable into 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, in fact, ferrite is a magnetic insulator). Eddy currents are not created in ferrites, and therefore they are very quickly remagnetized - 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 the design features of the cable-ferrite pair allow, 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!..

Internal and external computer cables can act as miniature antennas as they convert voltage and current noise into electromagnetic radiation.

Ferrite rings for flat and round cables provide effective suppression of noise currents before they are emitted as electromagnetic interference.

Unshielded cables emit noise due to common-mode noise flowing through their copper conductors, that is, high-frequency current flowing in the same direction along all cable conductors. These currents create a magnetic field of a certain magnitude and direction.

Cable ferrites attenuate noise currents by “trapping” the magnetic field and dissipating some of its energy as heat, i.e., a ferrite element placed on the cable conductors creates a high active impedance for common-mode currents. Ferrites can be used on internal power cables with DC or alternating current, and on conductors through which analog and digital signals are transmitted.

Electronic equipment manufacturers use ferrites to suppress electromagnetic radiation from external power and signal cables of computer system units, monitors, keyboards, printers and other peripheral devices.

Long external power and signal cables act as antennas, effectively radiating interference generated inside the device housing to the outside environment. The use of ferrite products reduces the shielding requirements for external cables and, in many cases, makes it possible to reduce their cost.

Cable ferrites for EMI suppression should be selected based on the specific application; the cable ferrite should produce the maximum series impedance for the noise signal frequencies.

Once the core material and approximate dimensions have been selected, the series impedance it produces and the noise reduction performance can be optimized by:

1. Increasing the length of the part of the conductor covered by ferrite; 2. Increasing the cross-section of the ferrite core (especially for power circuits);

3. Selecting a core with an internal diameter closest to the external diameter of the conductor or cable;

faqhard.ru

Ferrite filter - what is it for?

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.

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 are talking about straight wires, then by inductance we mean a quantity that characterizes 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 are components electrical circuit, which 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 practical application, then on power cables ferrite rings are used to reduce interference that can be created by the cables themselves, and on signal (data transmitting) 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.

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.

And here is a ferrite filter for USB cable It is best to choose the HM grade (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.

How to wind ferrite rings

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.

However, in some cases, to increase the impedance, you can make several turns of the cable 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.

filteru.ru

Why do you need a ferrite filter or ring on 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 can have a big impact on performance. wireless networks WiFi, 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.

set-os.ru

What are ferrite filters used for?

Many of you, of course, have seen small cylinders at the ends of the wires. These are ferrite filters. Do you know what role they play? Let's try to figure this issue out together.

Why install ferrite filters?

Very often on forums I come across the statement that ferrite rings only serve to prevent the cable from emitting interference! Is this statement true? This is partly true. But this is only true for power wires. Then, why do they install ferrite filters on HDMI? After all, the wire does not emit interference!!!

It's simple! Ferrite, due to its unique properties, is able to capture a magnetic field and dissipate it in the form of heat, in other words, it is able to attenuate noise interference in the cable. And this plays a big role for quality digital signal.

Then why on many HDMI cables no ferrite rings? Because ferrite rings are not the only way to protect a wire from interference. Wire shielding is no less effective.

Will the signal quality improve if you install ferrite rings on the wire? The answer is it will increase!!! But this does not mean at all that you will notice it.

Have you ever noticed a small cylinder on your laptop's power cable? If not, take a closer look at charging any laptop computer. There is a small plastic barrel on the cord near the connector that is inserted into the laptop.

No, of course I knew that there was not some kind of complex device there and not just a piece of plastic, but I still couldn’t get around to finding out everything exactly and in more detail.

Today turned out to be such a day. Are you sure you know? Check yourself just in case...

It turns out that this inconspicuous cylinder performs a very important function! It plays the role of a high-frequency filter and neutralizes interference that may come from the power cable. This device is called a ferrite ring, or ferrite filter.

Surprisingly, there are no microchips or other components inside this barrel. electronic devices. If you open it up and look at the insides, you won’t see anything interesting there. The cord simply passes through a small hollow cylinder of hard material. In some cases, the cord loops around it.

This cylinder is made of ferrite - a chemical compound of iron oxide with oxides of other metals, which is essentially a magnetic insulator. Eddy currents do not arise in this substance, so the ferrites very quickly remagnetize in time with the frequency of the electromagnetic field.

It's no secret that anyone unshielded cable power supply is a source of electromagnetic interference, which can distort information signals inside the computer. And the ferrite ring plays the role of a filter and prevents the spread of this interference.

Previously, shielding of the entire cable with copper braiding was used for this purpose, but ferrite rings are much cheaper, which is why they are widely used in modern electrical engineering.

By the way, ferrite rings not only prevent the formation of unwanted electromagnetic fields, but also protect the signal inside the cable from external interference. Therefore, such cylinders, in addition to power cables, can also be found on connection cords for monitors, cameras or cameras.

How to Increase the Noise Reduction Effectiveness of Cable Ferrite
1. Increase the length of the cable part covered by the ferrite core.
2. Increase the cross-section of the ferrite core.
3. The inner diameter of the cable ferrite should be as close as possible (ideally equal) to the outer diameter of the cable.
4. If the design features of the cable-ferrite pair allow, you can make several turns (usually one or two) of the cable around the ferrite core. To summarize the above, the best ferrite core is the longest and thickest that can be placed on a particular cable. In this case, the internal diameter of the cable ferrite should, if possible, coincide with the external diameter of the cable.

Yes, exactly, sometimes I came across the following barrels separately attached to the equipment:

How to use cable ferrite?

Sometimes on sale you can find detachable cable 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 cable tip. A loop is made around the cylinder shell. After this, the shell snaps into place. For reliability, you can equip the other end of the cable with a ferrite cylinder.

Then why don't all cables have ferrite rings? Because ferrite rings are not the only way to protect a wire from interference. Wire shielding is no less effective. Or the cable is simply cheap and of poor quality.

sources