What are the common inductors | GETWELL

Like resistors and capacitors, inductors are one of the most commonly used passive devices in circuit design. Inductor is an energy storage element, which can convert electric energy and magnetic energy into each other, and mainly plays a role in filtering, oscillating, stabilizing current and restraining electromagnetic interference in the circuit. When inductors are used in this circuit, you have to know these parameters of inductors!

When you look at some circuit schematics, you will find that inductance symbols are used in the circuit. After looking at the parameters on the symbol, I became even more confused. When did the unit of inductor become OHM? In fact, this is not an inductor, but a magnetic bead. Next, we will add some knowledge about the difference and connection between inductors and magnetic beads.

First explain the function of magnetic beads in the circuit, the greatest role of series magnetic beads in the signal transmission line is to suppress the interference signal, from the principle point of view, the magnetic beads can be equivalent to an inductor, note that this is a simple inductor. The real inductor coil has distributed capacitance, that is, the inductor we use is equivalent to an inductor connected in parallel with a distributed capacitor.

Overview of Inductance

Theoretically, to suppress the conducted interference signal, it is required that the larger the amount of inductance, the better, but for the inductor coil, the greater the inductance, the greater the distributed capacitance of the inductor coil, and the effects of the two will cancel each other out.

At the beginning, the impedance of the inductor coil increases with the increase of frequency, but when its impedance increases to the maximum, the impedance decreases rapidly with the increase of frequency, which is due to the effect of parallel distributed capacitance. When the impedance increases to the maximum, it is the place where the distributed capacitance of the inductor coil resonates with the equivalent inductor in parallel. The larger the inductance of the inductor coil is, the lower the resonant frequency is. If we want to further improve the suppression frequency, then the final choice of the inductor coil will have to be its minimum limit, the magnetic bead, that is, the through-heart inductor, is an inductor coil with less than 1 turn. However, the distributed capacitance of the through-core inductor is several times to dozens of times smaller than that of the single-loop inductor coil, so the working frequency of the through-heart inductor is higher than that of the single-loop inductor coil. The inductance of magnetic beads is generally relatively small, about between a few microbeads and dozens of microbeads. Another use of magnetic beads is to do electromagnetic shielding, its electromagnetic shielding effect is better than the shielding effect of shielding wire, which most people do not pay much attention to. The method of use is to let a pair of wires pass through the middle of the magnetic beads, so when there is an electric current flowing out of the double wires, most of the magnetic field will be concentrated in the magnetic beads, and the magnetic field will no longer radiate outward. Because the magnetic field produces eddy current in the magnetic bead, the direction of the eddy current producing the power line is just opposite to that of the power line on the surface of the conductor, which can counteract each other. Therefore, the magnetic bead also has a shielding effect on the electric field, that is, the magnetic bead has a strong shielding effect on the electromagnetic field in the conductor.

The advantage of using magnetic beads for electromagnetic shielding is that the magnetic beads do not need to be grounded, and the trouble of grounding required by the shielding wire can be avoided. Using magnetic beads as electromagnetic shielding, for double wires, it is equivalent to connecting a common-mode suppression inductor in the line, which has a strong suppression effect on common-mode interference signals.

It can be seen that the inductor coil is mainly used for EMI suppression of low-frequency interference signals, while magnetic beads are mainly used for EMI suppression of high-frequency interference signals. Therefore, for EMI suppression of a wide-band interference signal, several inductors of different properties must be used at the same time to be effective. In addition, to suppress the common mode conducted interference signal by EMI, we should also pay attention to suppressing the connection position between the inductor and the Y capacitor. The Y capacitor and suppression inductor should be as close as possible to the input of the power supply, that is, the position of the power outlet, and the high frequency inductor should be as close as possible to the Y capacitor, while the Y capacitor should be as close as possible to the ground wire connected to the earth (the ground wire of the three-core power cord), which is effective for EMI suppression.

The above is the introduction of common inductors, if you want to know more about inductors, please feel free to contact us.