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A Ferrite Ring Core’s Purpose in Electronic Circuit Boards

Published Date
Author Cadence PCB Solutions

Key Takeaways

  • The operation of ferrite ring cores is governed by the law of conservation of energy.

  • The low impedance of the ferrite ring cores increases the efficiency as well as the electrical performance of the system or circuit where it is used. 

  • It is the ferrite ring cores that offset the antenna behavior of the cables and prevents the radiation of EMI noises. 

Ferrite ring core purpose

The ferrite ring core’s purpose in electronic circuits is to prevent interference from reaching or leaving the device

Electromagnetic interference (EMI) and radio frequency interference (RFI) are detrimental to the operation of electronic devices. Interferences influence the operation of the device and its neighboring devices. This is why preventing EMI is essential in electronic devices. A ferrite ring core’s purpose in electronic circuits is to prevent interference from reaching or leaving a device. 

Ferrite Ring Cores: Purpose and Characteristics

Ferrites are ceramic compounds that exhibit magnetic properties. The materials are commonly metal oxide ceramics consisting of oxides of iron, nickel-zinc, or magnesium-zinc. Ferrite ring cores are doughnut-shaped or cylindrical-shaped ferrite pieces.

The purpose of ferrite ring cores is to suppress noise present in the circuit without grounding. Ferrite ring cores suppress not only interference, but also noise, crosstalk, and other high-frequency disturbances from supply voltage lines, data signal lines, and ground planes. The ferrite ring cores are often used in circuit boards for controlling parasitic oscillation, RF coupling, and power supply decoupling. 

Shape

Ferrite ring cores are available in many shapes – including cylindrical, ribbon, or clamp-on cores. The table below gives the details of a few shapes.

Ferrite ring core shapes

Operation

The operation of ferrite ring cores is governed by the law of conservation of energy. According to the energy conservation law, energy can be neither created nor destroyed. While in operation, the ferrite ring cores obey the law of conservation of energy and dissipate unwanted signal energy in the form of heat. High-frequency noise and EMI are converted into thermal energy with the help of ferrite ring cores present in circuit boards.  

Cable Shielding

Cables are sources of high voltage spikes and noises if not properly shielded. Shielding is a necessity for protecting the hardware connected downstream of the cable. Ferrite ring cores are usually installed to ensure the cables are free of EMI, high voltage spikes, and other disturbances. It is the ferrite ring cores that offset the antenna behavior of the cables and prevent the radiation of EMI noises. The use of ferrite ring cores for cable shielding is an economical filtering method.

Advantages of Ferrite Ring Cores 

  • Provides high resistance and magnetic efficiency to external magnetic fields. 
  • Their uniform cross-sections, light weight, and small size reduce the area occupied on the circuit board. 
  • The toroidal shape of the ferrite ring cores makes the magnetic flux escape easily, thus reducing the chance of radiation.
  • Environmentally-friendly. 
  • The low impedance increases the efficiency as well as the electrical performance of the system or circuit where ferrite ring cores are used. 

Ferrite Ring Core Selection and the Influence of Impedance

The impedance of ferrite ring cores is frequency-dependent. The ferrite ring cores can be resistive, indicative, or capacitive, and the selection is dependent on the frequency of application. At self-resonating frequencies (SRF) or in closer range, the ferrite ring cores are resistive. Below the resonating frequency, the ferrite ring core impedance is significantly inductive. Above the self-resonating frequency, the capacitive reactance is prominent in ferrite ring cores.

To generate maximum thermal power loss, the ferrite ring core must be resistive. For such a function, ferrite ring core selection should be made so that it behaves as a resistor at the frequency of application. The ferrite ring cores are selected so that the frequency of operation is closer to its SRF. Such ferrite ring cores keep the low-frequency signals untouched while filtering the high-frequency noises. Usually, high-frequency ferrite ring cores are used in high-frequency electronic circuits, as they dissipate noise and EMI in the form of thermal energy. 

Ferrite Ring Core Datasheet Details

When choosing ferrite ring cores from the commercial-off-the-shelf products available, applications such as EMI suppression, cable shielding, and parasitic oscillation control need to be considered.

In ferrite ring cores, the EMI attenuation is generally specified in dB for data lines and power lines. The dimensional details as well as the electrical specifications including the inductance, tan 𝛿, etc. are provided with the plan and elevation of the ring core. The ferrite ring core’s purpose in the given application influences its selection of shape as well.

With Cadence’s PCB design and analysis software, you can design, simulate, and analyze your circuit with different filter options and find which one works best.

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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