• According to this latest study, the 2020 growth of Ferrite Core Inductor will have significant change from previous year. By the most conservative estimates of global Ferrite Core Inductor market size (most likely outcome) will be a year-over-year revenue growth rate of XX% in 2020, from US$ 716.3 million in 2019.
• Ferrite E cores and pot cores offer the advantages of decreased cost and low core losses at high frequencies. For switching regulators, power materials are recommended because of their temperature and DC bias characteristics. By adding air gaps to these ferrite shapes, the cores can be used efficiently while avoiding saturation.
• Coilcraft has teamed with Nuhertz Technologies to offer this customized version of their powerful FilterSolutions® software. You can create elliptic low pass filters using actual Coilcraft inductance values, not just ideal components. Then request free inductor.
• Choosing a Powder Core Material While Molypermalloy and Ferrite cores are fea- tured in this brochure, Magnetics Kool Mu and High Flux powder cores are also excellent for inductor applications.

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In electronics, a ferrite core is a type of magnetic core made of ferrite on which the windings of electric transformers and other wound components such as inductors are formed. It is used for its properties of high magnetic permeability coupled with low electrical conductivity (which helps prevent eddy currents). Because of their comparatively low losses at high frequencies, they are extensively used in the cores of RF transformers and inductors in applications such as switched-mode power supplies, and ferrite loopstick antennas for AM radio receivers.

Ferrites[edit]

Ferrites are ceramic compounds of the transition metals with oxygen, which are ferrimagnetic but nonconductive. Ferrites that are used in transformer or electromagneticcores contain iron oxides combined with nickel, zinc, and/or manganese compounds. They have a low coercivity and are called 'soft ferrites' to distinguish them from 'hard ferrites', which have a high coercivity and are used to make ferrite magnets. The low coercivity means the material's magnetization can easily reverse direction while dissipating very little energy (hysteresis losses), at the same time the material's high resistivity prevents eddy currents in the core, another source of energy loss. The most common soft ferrites are:

• Manganese-zinc ferrite (MnZn, with the formula Mn_aZn_(1−a)Fe₂O₄). MnZn have higher permeability and saturation levels than NiZn.
• Nickel-zinc ferrite (NiZn, with the formula Ni_aZn_(1−a)Fe₂O₄). NiZn ferrites exhibit higher resistivity than MnZn, and are therefore more suitable for frequencies above 1 MHz.

For applications below 5 MHz, MnZn ferrites are used; above that, NiZn is the usual choice. The exception is with common mode inductors, where the threshold of choice is at 70 MHz.^[1]

As any given blend has a trade off of maximum usable frequency, versus a higher mu value, within each of these sub-groups manufacturers produce a wide range materials for different applications blended to give either a high initial (low frequency) inductance, or lower inductance and higher maximum frequency, or for interference suppression ferrites, a very wide frequency range, but often with a very high loss factor (low Q).

It is important to select the right material for the application, as the correct ferrite for a 100 kHz switching supply (high inductance, low loss, low frequency) is quite different from that for an RF transformer or ferrite rod antenna, (high frequency, low loss, but lower inductance), and different again from a suppression ferrite (high loss, broadband)

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Applications[edit]

There are two broad applications for ferrite cores which differ in size and frequency of operation: signal transformers, which are of small size and higher frequencies, and power transformers, which are of large size and lower frequencies. Cores can also be classified by shape, such as toroidal cores, shell cores or cylindrical cores.

The ferrite cores used for power transformers work in the low frequency range (1 to 200 kHz usually) and are fairly large in size, can be toroidal, shell, or shaped like the letters ‘C’, ‘D’, or ‘E’. They are useful in all kinds of electronic switching devices – especially power supplies from 1 Watt to 1000 Watts maximum, since more powerful applications are usually out of range of ferritic single core and require grain oriented lamination cores.

Ferrite Core Inductor Design

The ferrite cores used for signals have a range of applications from 1 kHz to many MHz, perhaps as much as 300 MHz, and have found their main application in electronics, such as in AM radios and RFID tags.

Ferrite rod aerial[edit]

Ferrite rod aerials (or antennas) are a type of small magnetic loop (SML) antenna^[2][3] very common in AM radiobroadcast bandtransistor radios, although they began to be used in vacuum tube ('valve') radios in the 1950s. They are also useful in very low frequency (VLF) receivers,^[4] and can sometimes give good results over most of the shortwave frequencies (assuming a suitable ferrite is used). They consist of a coil of wire wound around a ferrite rod core (usually several inches longer than the coil, but sometimes over 3 feet long^[5]). This core effectively ‘concentrates’ the magnetic field of the radio waves^[6] to give a stronger signal than could be obtained by an air core loop antenna of comparable size, although still not as strong as the signal that could be obtained with a good outdoor wire aerial.

Other names include loopstick antenna, ferrod, and ferrite-rod antenna. 'Ferroceptor'^[7] is an older alternative name for a ferrite rod aerial, particularly used by Philips where the ferrite core would be called a 'Ferroxcube' rod (a brand name acquired by Yageo from Philips in the year 2000). The short terms ferrite rod or ‘loop-stick’ sometimes refers to the coil-plus-ferrite combination that takes the place of both an external antenna and the radio’s first tuned circuit, or just the ferrite core itself (the cylindrical rod or flat ferrite slab).

See also[edit]

References[edit]

1. ^'Learn More Ferrites - Magnetics®'.
2. ^'page5'.
3. ^'Very Weak Signal Reception with Small Magnetic Loop Antenna'.
4. ^'The Creative Science Centre - by Dr Jonathan P. Hare'.
5. ^05-25-2012, DB8MW. 'A Joy Stick Antenna Experiment by DB8MW'.CS1 maint: numeric names: authors list (link)
6. ^'Ferrite Rod Antenna :: Radio-Electronics.Com'.
7. ^Service manual from Philips Radioplayer: Model BZ456A

Ferrite beads are generally used for high frequency EMI noise suppression

Sometimes, I wish I could see electromagnetic waves. It would make detecting EMI much easier. Instead of having to mess around with complicated setups and signal analyzers, I could just look and see what all the fuss is about. While we may not be able to see EMI, we can sometimes hear it when it comes through audio circuits. One possible fix for that kind of interference is a ferrite bead.

Unfortunately, ferrite beads (also called a ferrite choke, ferrite clamp, ferrite collar, EMI filter bead, or even a ferrite ring filter) can be a bit of a mystery. The ferrite core function resembles that of an inductor, but the ferrite frequency response deviates from this functionality at high frequencies. Additionally, different types of beads, such as wirewound ferrite beads and chip ferrite beads, provide different responses to noise reduction. For example, wirewound ferrite beads operate over a wide range of frequencies but offer less resistance in direct current setups. In order to use them properly, you’ll need to understand their electromagnetic characteristics and how they change during use. After you’ve got a handle on the theory behind ferrite bead uses, you can deliberately select one for your circuit board. If you don’t, you could end up causing more problems than you fix.

This image shows why a ferrite bead is sometimes called a ferrite ring or ferrite choke

What is a Ferrite Bead and How Do Ferrite Beads Work?

Ferrite beads are passive electronic components that can suppress high frequency signals on a power supply line. They are normally placed around a power/ground line pair that is incoming to a particular device, such as the power cord for your laptop. These beads work according to Faraday’s Law: the magnetic core around a conductor induces a back EMF in the presence of a high frequency signal, essentially attenuating the ferrite frequency response. Standard ferrite beads can be acquired from specialized manufacturers such as Coilcraft, though certain projects may require customized beads.

Ferrites are magnetic materials, and placing this material in a ferrite clamp around the power supply/ground line allows provides a source of inductive impedance for signals passing through the line. That might tempt you to think of them as a standard inductor, but they’re more complex than that. In reality, a ferrite bead is a nonlinear component; the impedance it provides changes was the load current and voltage drop across the ferrite change. The simplified circuit model of a ferrite bead will help you understand its frequency characteristics. However, keep in mind that these attributes can change as a function of current and temperature.

Ferrite Core Inductor Software Systems

Load current can change the impedance of your ferrite.

What are Ferrite Beads Used For?

Because ferrite bead impedance is inductive, ferrite bead inductors are used to attenuate high-frequency signals in electronic components. When a ferrite bead choke is placed on the power line connecting to an electronic device, it removes any spurious high frequency noise present on a power connection or that is output from a DC power supply. This ferrite clamp use is one of many approach to noise suppression, such as that from a switched-mode power supply. This application of ferrite beads as a ferrite filter provides suppression and elimination of conducted EMI.

Among the various uses of ferrite beads as filters, an EMI filter bead/power supply filter bead is usually rated for a certain DC current threshold. Currents greater than the specified value can damage the component. The troublesome thing is that this limit is drastically affected by heat. As temperature increases, the rated current quickly decreases. Rated current also affects the ferrite's impedance. As DC current increases, a ferrite bead will 'saturate' and lose inductance. At relatively high currents, saturation can reduce the ferrite bead impedance by up to 90%.

Ferrite Bead vs. Inductor

Although a ferrite bead can be modeled as an inductor, ferrite bead inductors do not behave as a typical inductor. If you’re wondering how to measure the behavior of a ferrite bead vs. inductor behavior, you would send an analog signal through the bead and sweep the frequency across several orders of magnitude. If you create a Bode plot for the frequency-swept measurements for a ferrite bead, you’ll find that the ferrite bead provides steeper roll-off at higher frequencies compared to an inductor with similar low frequency behavior.

A simple yet accurate model of a ferrite bead connected to an AC power source.

A ferrite bead can be modeled as capacitors and inductors, and also a resistor in parallel with this RLC network wired with a series resistor. The series resistor quantifies the device’s resistance to DC currents. The inductor in this model represents a ferrite beads primary function of attenuating high-frequency signals, i.e., providing inductive impedance through Faraday’s Law. The parallel resistor in this model accounts for losses in eddy currents that are induced within the ferrite bead at high frequencies. Finally, the capacitor in this model accounts for the component’s natural parasitic capacitance.

When looking at a ferrite bead impedance curve, the primarily resistive impedance is extremely high in only a thin band. The inductance of the bead dominates within this thin band. At higher frequencies, the ferrite bead impedance begins to appear capacitive over and the impedance rapidly decreases. Eventually, as frequency continues increasing, the capacitive impedance will drop to a very small value, and the ferrite bead impedance appears purely resistive.

The ferrite core in a ferrite bead provides a similar function as the ferrite core in a transformer.

Ferrite Bead Selection Guide

Now that you’ve got the ferrite theory under your belt, it’s time to choose one for your device. This is not very difficult, and if you want to know how to select a ferrite bead for a design, you just have to pay attention to a bead’s specifications. You may be wondering, are ferrite beads necessary for my design? Like many engineering decisions, the answer is not so simple. If you know that your board will experience conducted EMI within a specific frequency range, and you need to attenuate these frequencies, then a ferrite bead may be the right choice for your design.

Based on the inductive behavior of ferrite beads, it is natural to conclude that ferrite beads “attenuate high frequencies” without much further consideration. However, ferrite beads do not act like a wideband low-pass filter as they can only help attenuate a specific range of frequencies. You must choose a ferrite bead selection and choke where your undesired frequencies are in its resistive band. If you go a little too low or a little too high the bead will not have the desired effect.

Before selecting a specific ferrite bead for your design, you should see if the manufacturer can provide you with impedance vs. load current curves for the ferrite bead. By far, this is the best tool you can use if you are unsure of how to select a ferrite bead. If your load currents are very high, you’ll need to select a ferrite bead that can withstand them without saturating and losing their impedance within the desired frequency range.

Cautions

Ferrite beads and ferrite chokes are essentially resistive loads at high frequencies, which means they can cause a few problems in your circuit. When placing a bead you’ll need to think about voltage drop and heat dissipation.

Ferrite Core Toroid

In the days of higher voltage circuits, voltage drop wasn’t a big deal. Now we have lots of low power circuits that can use voltages down around 2 V. At those levels, you can’t afford to lose much. Ferrite beads cause a DC voltage drop in your circuit. It may not seem like much, but if your integrated circuits (ICs) have a short high-current draw state, the loss could become significant. Place your ferrite beads where they won’t cause voltage drop issues.

Since ferrite materials are resistive at high frequencies, they primarily dissipate the absorbed energy as heat. This heat isn’t necessarily a problem for your PCB when a ferrite choke is used on a power supply line, but it can become one when it is used to dissipate high frequencies at high current. If your system is especially noisy and the bead will be absorbing lots of high frequencies, this heat could become more of an issue. Make sure to take the bead’s heat dissipation into account.

Ferrite Core Inductor Software Scanner

Ferrite bead impedance will change with temperature.

Ferrite beads can be quite useful, but only if you understand exactly how they work. Remember that they attenuate signals in a fairly small band, and their effectiveness depends on temperature and load current. In order to best use a ferrite bead, you should make sure it meets your exact specifications. Then, when placing the bead, be sure to take voltage drop and heat into account.

We often discuss the importance and function of ferrite beads. If you'd like more info on ferrite beads, check out Everything You Need To Know About Ferrite Beads by industry expert Kella Knack.

Dealing with things like ferrite beads can be difficult, but designing your printed circuit board doesn’t have to be. Altium Designer® is state of the art PCB design software with tools that can help you build the optimal board. It even has add-ons like the power delivery network, which can help you deal with problems like voltage drop and heat dissipation.

Have more questions about ferrite beads? Call an expert at Altium.