What Is a Ferrite Core?

Key Takeaways

• A cylinder made of ferrite is the most commonly used ferrite core for cable noise or EMI suppression.

• As a ferrite core becomes lossier at the operating frequency, noise suppression improves. 

• Ferrite cores are effective at slowing down the rapid rising of electrostatic discharge current spikes or voltage surges in cables. 

Ferrite cores are low-cost, simple, and easily fitted filters for your power cords

If you are looking for a low-cost, simple, and easily fitted filter for your power cord, consider ferrite cores. By inserting a ferrite core into a wire, you can achieve noise filtering of power cord signals. With ferrite core-based noise filtering in cables, you won't need any other circuit component, which will eliminate the need for a circuit redesign. And, fortunately, ferrite cores do not involve mechanical redesign either. With a simple ferrite core, you can improve the quality of the signal flowing through a cable. Let’s learn more about what a ferrite core is as well as its applications and characteristics. 

What Is a Ferrite Core? An Overview of the Composition of Ferrite Cores

So, what is a ferrite core? Ferrites are ceramic compounds with permanent magnetic properties. Ferrite cores are made of metal oxide ceramics containing a mixture of iron oxide and oxides of magnesium-zinc or nickel-zinc. The mixture is pressed and extruded to form the required core shapes.

There is a variety of materials available to make ferrite cores. Given the array of ferrite materials, the shape is another important parameter to consider during the ferrite core design stage. The packaging style of ferrite cores also plays an important role in their application as electromagnetic interference (EMI) filters.

A cylinder made of ferrite is the most commonly used ferrite core for cable noise or EMI suppression. A cylindrical ferrite core can be easily slipped around a cable for power decoupling and filtering. With the material and shape selection, the characteristics of a ferrite core can be completely altered. The parameter that changes with the material and shape is ferrite impedance.

Ferrite Impedance

Ferrite impedance is an important characteristic to consider when designing ferrite cores. The ferrite impedance is influenced by factors such as material property, size of the core, the shape of the core, temperature, and operating frequency range.

The effectiveness of a ferrite core increases with frequency. At low frequencies, ferrite cores are predominantly inductive in nature, which makes them suitable for low-pass LC filter applications. As the frequency increases, the inductive reactance diminishes and the ferrite core becomes resistive. At high frequencies, ferrite cores behave like resistors and offer excellent characteristics for noise suppression. 

How Do Ferrite Cores Suppress Noise?

At high frequencies, the quality factor of ferrite cores is low and offers minimum issues associated with resonance. When a ferrite coil is inserted into a conducting wire, it forms a coil inductor of one turn. When current flows through the coil inductor, magnetic flux is produced in the ferrite core. The electrical energy is converted into magnetic flux in the core. Whenever the current flowing through the conducting wire changes, it changes the magnetic flux linked with the coil. According to Faraday's law of electromagnetic induction, any change in current causes magnetic energy conversion to electrical energy. The conversion to electrical energy is subjected to magnetic losses called hysteresis losses.

Some fraction of the noise in the current flowing through the conductor or cable gets eliminated as magnetic losses. This way, the ferrite core greatly helps suppress noise or EMI in the cable. If you analyze the impedance characteristics of ferrite cores used in noise or EMI suppression applications, you may find resistive components dominating at the operating frequency. As the ferrite core becomes lossier at the operating frequency, the noise suppression improves. 

Ferrite Cores as Low-Pass Filters

For a ferrite core to function as a low-pass LC filter, the connection pattern must be a followed-inserting wire through a ferrite coil. The impedance of the coil inductor formed increases with frequency. The coil inductor functions as a low-pass filter and blocks the high-frequency current. The attenuation characteristics of the ferrite core filter are good at high frequencies. 

Ferrite Cores as Surge Suppressors

Discussing the properties and applications of ferrite cores is a key part of answering the question of what a ferrite core is. Another property of the ferrite core is its ability to reduce the slew rate of electrostatic discharges or voltage surges in cables. The electrostatic discharge current pulses and voltage surges induced in cables are common and are detrimental to connected circuits or devices. If the surge crosses the current or voltage specification of a connected component, it is enough to burn off the component. Ferrite cores are employed to reduce the slew rate of current spikes or voltage surges by absorbing the transient energy rather than reflecting or diverting it to other components or subsystems. Ferrite cores are effective in slowing down the rapid rising of electrostatic discharge current spikes or voltage surges in cables.

The careful selection of ferrite material is critical when designing a ferrite core. Depending on the impedance characteristics at the operating frequency, the behavior of a ferrite core changes. With Cadence PCB design and analysis software, you can design, simulate, and analyze ferrite core functions in your circuit.

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