Filter capacitors, common mode inductors, and magnetic beads are all typical components in  EMC  design circuits, and they're the three main tools for reducing electromagnetic interference.

I suppose there are still many engineers who are unsure about the roles of these three in the circuit. The notion of removing the three principal  EMC weapons from the design is examined in-depth in this article.

Ⅰ. Filter capacitor

Although the capacitor's resonance is undesirable in terms of filtering high-frequency noise, it is not necessarily damaging.

After determining the frequency of the noise to be filtered, the capacitor's capacity can be adjusted so that the resonance point is exactly on the disturbance frequency.

The frequency of electromagnetic noise that must be filtered in real-world engineering is often hundreds of MHz or even more than 1 GHz. Through-core capacitors must be utilized to efficiently filter out such high-frequency electromagnetic noise.

Ordinary capacitors  are unable to efficiently filter out high-frequency noise for two reasons:

(1)One reason is that the capacitor lead inductance causes capacitor resonance, which causes the high-frequency signal to be coupled, which reduces the filtering effect;

(2) another reason is that the parasitic capacitance between the wires causes the high-frequency signal to be coupled, which weakens the bypass effect of the high-frequency signal.

The feedthrough capacitor can successfully filter out high-frequency noise since it does not have any lead inductance, which causes a problem with the capacitor resonance frequency being too low.

In addition, the through-core capacitor can be mounted directly on the metal panel, which is useful for high-frequency isolation. When employing feedthrough capacitors.  however, the issue to be aware of is installation.

The feedthrough capacitor's major flaw is that it is terrified of high temperatures and temperature impacts, which makes welding the through-core capacitor to the metal panel extremely difficult.

During the welding process, several capacitors are damaged. When a significant number of through-core capacitors must be mounted on the panel, it is difficult to repair if one is damaged, because removing the damaged capacitor will damage other capacitors adjacent.

Ⅱ. Common mode inductance

Because common-mode interference causes the majority of EMC difficulties, common-mode inductors are one of our most widely utilized and powerful components.

A common mode inductor is a ferrite-cored common mode interference suppression device. It is made up of two identical coils with the same number of turns twisted symmetrically on the same ferrite toroidal core to generate a four-terminal coil. The device should have a suppressive effect on the common-mode signal's huge inductance, while the differential mode signal's modest leakage inductance should have almost no effect.

When the common-mode current flows, the magnetic flux in the magnetic ring superimposes on each other, resulting in a large inductance that suppresses the common-mode current. The magnetic flux in the magnetic ring is increased when the two coils flow via the differential mode current. The differential mode current can flow without attenuation since the passes cancel one other out and there is essentially no inductance.

As a result, the common-mode inductance in the balanced line efficiently suppresses the common-mode interference signal while having no effect on the differential mode signal that the line ordinarily transmits.

During production, common-mode inductors  should meet the following requirements:

(1)The wires wound on the coil core should be insulated from each other to ensure that no breakdown short circuit occurs between the turns of the coil due to instantaneous overvoltage; 

(2) The magnetic core in the coil should not be saturated when the coil flows through the instantaneous large current;

(3)The magnetic core in the coil should be insulated from the coil to prevent breakdown between the two due to transient overvoltage;

(4) The coil should be insulated from the magnetic core in the coil to prevent breakdown between the two This can lower the coil's parasitic capacitance and improve its ability to provide transient overvoltage.

Under normal situations, pay special attention to selecting the frequency band that will be filtered simultaneously. The more common-mode impedance there is, the better. As a result, when choosing a common-mode inductor, we must consider the device data, particularly the impedance frequency curve.

In addition, when choosing, consider the impact of differential mode impedance on the signal, focusing on differential mode impedance and paying specific attention to high-speed ports.

Ⅲ. Magnetic beads

Magnetic beads are frequently used in the EMC design process of product digital circuits. Iron-magnesium alloys or iron-nickel alloys are used to make ferrite. Magnetic permeability is high in this substance. It could be between the inductor's coil windings. When there is a high frequency and a high resistance, the capacitance generated is the minimum.

Ferrite materials are commonly employed in high-frequency applications because their inductance properties are mostly at low frequencies, resulting in minimal line loss. They primarily display the reactance characteristic ratio and how it changes with frequency at high frequencies. Ferrite materials are employed as high-frequency attenuators in radio frequency circuits in practical applications.

In fact, ferrite is a better analogy for a parallel resistance and inductance connection. At low frequencies, the inductance short-circuits the resistance, while at high frequencies, the inductance's impedance becomes fairly high, allowing all current to flow through the resistance.

Ferrite is a consuming device that converts high-frequency energy into heat energy, as defined by its resistance properties. Ferrite beads have greater high-frequency filtering qualities than regular inductors, 

Ferrite is resistive at high frequencies, equating to an inductor with a very low-quality factor, allowing it to maintain a high impedance across a wide frequency range, enhancing high-frequency filtering efficiency.

The inductive reactance of the inductance makes up the impedance in the low-frequency range. R is very tiny at low frequencies, and the magnetic core permeability is high, hence the inductance is considerable. L takes the lead, and electromagnetic interference is reflected and suppressed; at the same time, the magnetic field is reflected and suppressed. The device is a low-loss, high-Q inductor with a minimal core loss. Resonance is easily caused by this inductance. As a result, when ferrite beads are utilized, interference may increase in the low-frequency band.

Resistance components make up the impedance in the high-frequency band. The permeability of the magnetic core reduces as the frequency rises, resulting in a decrease in the inductor's inductance and a decrease in the inductive reactance component.

However, the loss of the magnetic core increases at this period, as does the resistance component, resulting in an increase in total impedance. The electromagnetic interference is absorbed and turned into heat to be dissipated when the high-frequency signal passes through the ferrite.

Printed circuit boards, power lines, and data cables all use ferrite suppression components. Adding ferrite suppression components to the printed board's power cord, for example, can filter out high-frequency interference.

On signal lines and power lines, ferrite magnetic rings or magnetic beads are employed to prevent high-frequency interference and spike interference. It can also absorb interference from electrostatic discharge pulses. The choice between chip magnetic beads and chip inductors is mostly dependent on the application.

In the resonant circuit, chip inductors are required. Chip magnetic beads are the finest solution when it comes to eliminating unwanted  EMI  noise.

Ⅳ. Applications of chip beads and chip inductors 

Chip inductors: Information technology equipment, radar detectors, automobile electronics, cellular phones, pagers, audio equipment, personal digital assistants (PDAs), wireless remote control systems, and low-voltage power supply modules are all examples of RF and wireless communications.

Chip beads: Internal I/O input/output connectors (such as serial port, parallel port, keyboard, mouse, long-distance telecommunications, local area network), radiofrequency circuit, and vulnerable In computers, printers, video recorders (VCRs), TV systems, and mobile phones, the power supply circuit filters out high-frequency conduction interference and lowers  EMI noise between interfering logic components.

Because the magnetic bead's unit is nominal according to the impedance it creates at a given frequency, and the unit of impedance is also ohm, the magnetic bead's unit is the ohm.

The magnetic beads' DATASHEET usually includes frequency and impedance characteristic curves that are based on 100MHz. At a frequency of 100MHz, the impedance of the magnetic beads, for example, is 1000 ohms.

The bigger the magnetic bead impedance, usually above 600 ohms, the better for the frequency band we want to filter.

Furthermore, when selecting magnetic beads, you must consider the flux of the magnetic beads. In most cases, you'll need to derate by 80%. When used in a power circuit, keep in mind the effect of  DC  impedance on voltage drop.