Ferrite ring - what is it? How to make a ferrite ring with your own hands?

2024 Author: Howard Calhoun | [email protected]. Last modified: 2024-01-02 13:48

Each of us has seen small cylinders on power cords or on cables for matching electronic devices. They can be found on the most common computer systems, both in the office and at home, at the ends of the wires that connect the system unit to the keyboard, mouse, monitor, printer, scanner, etc. This element is called the "ferrite ring" (or ferrite filter). In this article, we will look at the purpose for which manufacturers of computer and high-frequency equipment equip their cable products with the mentioned elements.

Main purpose

The ferrite ring can reduce the effect of radio frequency and electromagnetic interference on the signal that is transmitted over the wire. Long signal and power cables of both computer and other power equipment have parasitic properties,that is, they act as antennas. They very effectively radiate various noises that are created inside the device to the external environment, thereby creating interference on radio stations when receiving a radio signal and on other electronic equipment. And vice versa, when receiving interference from the air from radio transmitting devices, a computer or other electronic device may malfunction. Here, to eliminate this phenomenon, they use a ferrite ring worn on a power or matching cable.

Physical properties

Ferrite is a ferrimagnet that does not conduct electricity, that is, in fact it is a magnetic insulator. Eddy currents are not created in this material, and therefore it remagnetizes very quickly - in time with the frequency of external electromagnetic fields. This material property is the basis for effective protection of electronic devices. The ferrite ring worn on the cable is capable of creating a large active impedance for common mode currents.

This material is formed from the chemical combination of iron oxides with oxides of other metals. It has unique magnetic characteristics and low electrical conductivity. Due to this, ferrites have practically no competitors among other magnetic materials in high-frequency technology. Ferrite rings 2000nm significantly increase the inductance of the cable (several hundred or thousand times), which ensures the suppression of high-frequency interference. This element is installed on the cord during its production or, cut into two semicircles, put on the wire immediately after its manufacture. ferriteThe filter is packed in a plastic case. If you cut it open, you can see a piece of metal inside.

Do I need a ferrite filter? Or is this another hoax?

Computers are very "noisy" (electromagnetically) devices. So, the motherboard inside the system unit is able to oscillate at a frequency of one kilohertz. The keyboard has a microchip, which also operates at a high frequency. All this leads to the so-called radio noise generation near the system. In most cases, they are eliminated by shielding the board from electromagnetic fields with a metal case. However, another source of noise is the copper wires that connect various devices. In fact, they act like long antennas that pick up signals from cables of other radio and television equipment, and affect the operation of "their" device. Ferrite filter eliminates electromagnetic noise and broadcast signals. These elements convert electromagnetic high-frequency vibrations into thermal energy. That is why they are installed at the ends of most cables.

How to choose the right ferrite filter

To install a ferrite ring on the cable with your own hands, you need to understand the types of these products. After all, it depends on the type of wire and its thickness which filter (from what material) you need to use. For example, a ring installed on a multicore cable (power cord, data cable, video or USB interface) creates a so-called common-mode transformer in this section, passinganti-phase signals carrying useful information, and also reflects common-mode interference. In this case, not absorbing ferrite should be used to avoid disruption of information transmission, but a higher frequency ferromaterial. But it is preferable to choose ferrite rings for the antenna cable from a material that will dissipate high-frequency interference, rather than reflect them back into the wire. As you can see, the wrong product can degrade the performance of your device.

Ferrite cores

Thick ferrite cylinders are the most efficient at dealing with interference. However, it should be borne in mind that filters that are too bulky are very inconvenient to use, and the results of their work in practice will hardly differ much from slightly smaller ones. Filters should always be the right size: ideally the inside diameter should match the wire and the width should match the width of the cable connector.

Don't forget that not only ferrite filters help to fight noise. For example, for better conductivity, it is recommended to use cables with a larger cross section. When choosing the length of the cord, you should not make a large margin of length between the connected devices. In addition, the poor quality of the connection between the wire and the connector can also serve as a source of interference.

Marking ferrite rings

The most common type of ferrite ring marking notation is as follows: K D×d×N, where:

- K is short for "ring";

- D - outer diameter of the product;

- d - inner diameter of the ferrite ring;

- H – filter height.

In addition to the overall dimensions of the product, the type of ferromagnetic material is encrypted in the marking. An example of an entry may look like this: M20VN-1 K 4x2, 5x1, 6. The second half corresponds to the overall dimensions of the ring, and the initial magnetic permeability is encrypted in the first (20 Μ_{i). In addition to these parameters, in the reference description, each manufacturer indicates the critical frequency, hysteresis loop parameters, resistivity and Curie temperature for a particular product.}

How else are ferrite rings used

Besides the well-known application as high-frequency shielding, ferromagnetic materials are used to make transformers. They are often seen in computer power supplies. It is well known that the ferrite ring transformer is very effective in balanced mixers. However, not everyone knows that there is a possibility of "stretching" balancing. This modification of the transformer is able to perform the balancing operation more accurately. In addition, transformers on ferrite rings are widely used to match the output and input resistances of the cascades of transistor devices. In this case, active and reactive resistances are transformed. Thanks to the latter, this device can be used to change the capacitance tuning ranges. Pull-down transformers work well below 10 MHz.

Conclusion

To those whoif you are interested in how to wind a ferrite ring yourself, it should be borne in mind that the series impedance introduced by a high-frequency ferrite core can easily be increased by making several turns of a conductor on it. As electrical engineering theory suggests, the impedance of such a system will increase with the square of the number of turns. But this is in theory, but in practice the picture is somewhat different due to the nonlinearity of ferromagnetic materials and losses in them.

A pair of turns on the core increases the impedance not four times as it should be, but slightly less. As a result, in order for several turns to fit in a cable filter, a ring of a obviously larger size should be chosen. If this is not acceptable, and the wire must remain the same length, it is better to use several filters.