Guide to ferrite beads, sleeves and cores
When designing electronic equipment, controlling the EMI (electromagnetic interference) is necessary to protect components, and often external equipment, from damage caused by high-frequency noise levels. In this guide, we’ll explain how to do that, covering:
What are ferrite beads?
Electromagnetic interference (EMI) happens when one electromagnetic field interferes with another, causing distortion of both fields.
Some common causes of EMI are switching-mode power supplies, arc welders, motor bushes, and electrical contacts. All of these can be problematic, not only in the equipment itself, but in other electronic equipment in the surrounding area.
The effect of stray EMI range from subtle to disastrous. For example, power sources produce low-frequency EMI where data cabinets and electric cable enclosures are concerned.
If cabling is not properly installed and protected, high voltage surges are possible, generating electrical noise. These surges can damage hardware, often corrupting data. This has the potential to disrupt business operation on many levels.
Ferrite beads, cores and sleeves counteract these risks. Ferrite beads are made up of a wound coil and two terminals. Ferrite material typically comprises ceramic compounds with iron oxides integrated with nickel, zinc and manganese compounds.
Ferrite beads are types of ferrite chokes. A ferrite bead is also commonly called a ferrite clamp. It’s a passive device that improves your PCB’s power quality, designed to suppress high-frequency signals on a power-supply line.
They’re typically placed around a power supply / ground line pair that’s incoming to a specific device. An example is the power cord for your laptop.
In essence, any DC current flowing through the ferrite bead will create a voltage drop in proportion to the DC resistance.
How do ferrite beads work?
Ferrite beads filter high-frequency noise energy over a broad frequency range. Ferrites are magnetic materials.
These beads consist of a conductor, which is inserted through a hollow cylinder of a highly permeable iron oxide ceramic material. This is why the electromagnetic properties influence current flow. The iron oxides’ permeability within the ceramic material supports the formation of a magnetic field when current flows through the conductor.
The beads work in line with Faraday’s Law: the magnetic core around a conductor induces a back EMF in the presence of a high-frequency signal. In turn, this attenuates the ferrite-frequency response.
The advantages of ferrite beads
Ferrite beads suppress high-frequency noise. They generate a clearer signal in the intended circuit. By equipping devices with ferrite beads, you’re eliminating, or minimising, interference. Think of it as a ferrite bead filter for EMIs.
The disadvantages of ferrite beads
As ferrite beads are resistive loads at high frequencies, they are capable of creating problems in your circuit. You’ll need to consider voltage and heat dissipation. Voltage drop wasn’t an issue when higher-voltage circuits were common. That’s no longer the case with low-power circuits that can operate with voltages of 2V.
Ferrite beads should be placed where they won’t create problems with voltage drop. They also absorb energy as heat, but this is only a problem when the ferrite bead dissipates high frequencies at high current. Always take into consideration the bead’s heat dissipation.
Are ferrite beads necessary?
They’re used for a range of applications – even as industrial generator parts. But depending on what you’re designing, they’re not always required. If the capacitors can do a good job of filtering out high frequencies, then give ferrite beads a pass.
What is the difference between an inductor and ferrite bead?
This isn’t a case of ferrite bead vs inductor. Ferrite beads are actually classified as inductors. Beads filter out unwanted high-frequency noise. This, in turn, dissipates in the form of heat. The bead acts as a low-pass filter, only allowing low frequencies to pass through the circuit.
What are ferrite sleeves?
First, they go by other names, such as clip-on ferrite, clip-on ferrite core, ferrite clip on, or even ferrite clips. These are typically hinged plastic casings that open up to permit the insertion of cable, then snaps together to secure the ferrite A5 core around the cable.
A clip-on ferrite works as any ferrite solution does, in that it suppresses and scatters high-frequency noise levels caused by electromagnetic devices. A ferrite sleeve is often used on power and control cabling on electronic and electrical devices to provide regulatory compliance, suppress EMIs and improve the devices’ performance. Note, sleeves don’t always have a casing – the term is universally interchanged with cores.
How do ferrite sleeves work?
They’re available in a range of cable diameters, and are usually installed after all cabling has been attached. Impedance values are based upon a single turn measurement. Their cases are often plastic, such as nylon, which has excellent insulation properties and makes the assembly of core halves – or split cores – easy.
The advantages of ferrite sleeves
They’re suitable for retrofit situations and testing, as they can be installed quickly and easily. The casing doesn’t require any special care. The nylon sleeve is robust and not easily damaged by EMI, nor does it require any special care.
Ferrite sleeves are typically used in computer monitors, data cables, medical devices and other electronic equipment and circuits. Smaller sleeves are also embedded in printed circuit boards and electrical circuits.
The disadvantages of ferrite sleeves
Their effectiveness depends on temperature and load current. You need to ensure it meets the exact specifications of your design. Take into account voltage drop and heat.
What are ferrite cores?
Ferrites on cable are common. The reason: ferrite cores prohibit cables from acting as antennas, thereby preventing radiated EMI noise. They’re typically made of metal-oxide ceramics that contain a mixture of iron oxide and oxides of magnesium-zinc or nickel-zinc. Once mixed, the material is pressed and extruded to form the core shapes needed.
Using properly installed and grounded shielded cables helps suppress EMIs. However, a ferrite core suppressor may also need to be installed on cabling as well. Ferrite cores come in different shapes. They attenuate any form of EMI emission and are often used either as a retrofit or for testing purposes when calculating ferrite core filter specifications and design requirements.
How do ferrite cores work?
The core is a metallic component, which has a magnetic field attracted to the magnetic field of its electrode. A ferrite core suppresses electromagnetic emissions by blocking low-frequency noise and absorbing high-frequency noise to avoid electromagnetic interference.
When current flows to an inductor, in this instance, a ferrite core, the core generates magnetic flux. The current energy is then converted into magnetic energy. When the current changes, the magnetic flux changes to, by converting back into current by electromagnetic induction.
In some applications, EMI suppression can be achieved with a ferrite core transformer design. The transformer itself is constructed by using a magnetic core in which coil (inductor) windings are made on a ferrite core component.
The advantages of ferrite cores
A benefit of ferrite cores is their high resistance to high current. They also provide low eddy current losses over a range of frequencies. Factor in their high permeability, and you have the ideal solution for use in high-frequency transformers and adjustable inductors.
The disadvantages of ferrite cores
Magnetic cores have side effects that you should consider. In AC devices, such as home appliances, they cause energy losses due to hysteresis – a lag between input and output – and eddy currents. This can also happen in applications such as transformers.
Before designing a transformer, check your requirement and exact application including input voltage, output voltage, current and frequency of operation.
Are ferrite cores necessary?
Ferrite cores have many applications and are most commonly found on cables. They are used to prevent a loss of electrical energy and their insulating properties can help reduce noise interference with the cable signals. Depending on the environment, ferrite cores may not be needed and other methods could be considered to prevent interference without a ferrite core.
How to install ferrite cores
Install a ferrite core between the grid and AC port of the inverter.
- Pass the AC cables through a ferrite core and circle them around the Ferrite Core for four turns.
- Insert the AC cables into the grid port at the bottom of the inverter.
- Insert the AC cables into the grid terminal and tighten them.
You can also use a ferrite sleeve, which contains a core. In this instance:
1. Open the sleeve
2. Lay the cable through the core
3. Loop the cable around so that it goes through the core again. Close the sleeve and pull the cable so that the loop tightens.
Examples of ferrites
Below are examples of different ferrite solutions to help you obtain EMI suppression.
These PCB multiline suppressor ferrite beads have a 236 Ω 25 MHz and 383 Ω 100 MHz ferrite bead impedance. They come with tinned copper jumper wires which complete the desired winding configuration on the PCB. The jumper wires are oxygen-free, high-conductivity copper with a 95/5 tin lead coating. Made of A5 material.
Note, a single circuit protection on a PCB uses a single, two-lead ferrite bead.
View our complete range of ferrite beads.
For outer cabling, a square plastic ferrite sleeve is often used. The core is contained in a hinged plastic casing that opens up to permit the insertion of the cable, then snaps together to secure the ferrite A5 core around the cable to suppress EMIs.
For installation on round power cables, you can also use a round nylon-casing ferrite sleeve. This example contains A5 material cores that attenuate any form of EMI emission. It has an impedance of 97 Ω at 25 MHz, and impedance of 207 Ω at 100 MHz.
These are thought of as transformer ferrite cores, which is why they’re sometimes called a ferrite toroidal core. Lightweight toroidal ferrite sleeves without casings, they’re ideal for transformers for their functional values and ability to conserve energy. Made of K5B material.
For looping cable through and around a ferrite core with no casing necessary, use a ferrite sleeve, round, no casing. See our complete range of ferrite sleeves.
For flat cables in electronic devices, use a flat cable ferrite core. Contains A5 material and is available in a range of lengths and widths.
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