What Are Ferrite Cores and Why Are They Used on Cables
Whether you are plugging in a laptop to a wall outlet for charging or are inserting a USB cable into a computer, you may have noticed the commonality of a large, nondescript cylinder that is located close to the connecting end of the cable. While you may not have thought much about the cylinder common to cables, it serves a very important role in connections and transfers. Known as ferrite cores, beads, or chokes, these cylinders are relied on for EMI management across a number of devices. While ferrite cores may play a diverse set of roles based on the application, this blog will be concerned with the operations of ferrite cores when they are specifically found on electronic cables.As an element used for EMI protection, a ferrite core serves as a lowpass filter to guard a device. In a standard circuit, capacitors will operate as open when frequencies are low, while high frequencies will have them function as shorts. With consideration to Kirchoff’s voltage law, the total voltage of the loop will be equal to the sum of the drop across each component. It is important to know that both capacitors and inductors have a value known as capacitive reactance which is a counterpart to real number resistance. By adding resistance and reactance together as vectors, one will find the impedance value.
Utilizing impedance values, it is easier to understand an RC circuit as a voltage divider where reactance terms will raise under lower frequencies and drop under higher ones. As such, the reactance term of impedance will cause the capacitor to operate as an open when dominating below a certain cutoff frequency, while the capacitor will act as a short when impedance dominates above the cutoff frequency. With an understanding of such principles, one can see how circuit functionality changes based on a cutoff frequency. When conditions are at the cutoff frequency specifically, the power of the output signal will be halved, and an attenuation factor of 22 will be attained as resistance and reactance are equalized. With the dynamic response of the low pass circuit, the attenuation of signals will be permitted when values are equal to or greater than the cutoff frequency.
Through such properties, the ferrite bead serves as an non-idealized inductor acting as a short under low frequencies and an open at high frequencies. While low frequency conditions are present, current will move through the circuit unabated. However, one the cutoff frequency is met or surpassed, the ferrite bead will act as a short. Inductors store magnetic energy, and ferrite beads function to dissipate energy as heat. This ensures that cables do not transmit or receive RF signals to deter EMI issues. As such, they are quite useful for a grand number of applications, ensuring that power and data transfer is conducted with low issues or EMI. If you are in the market for various cable components and industrial parts, we have you covered here on NSN Orbit.
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