An inductor is the ratio of the magnetic flux of a wire to the current that produces in and around the wire when an alternating current passes through the wire, and the magnetic flux of the wire is the ratio of the current that produces this flux.

When a DC current passes through the inductor, only fixed magnetic field lines appear around it, which do not change with time; However, when an AC current passes through the coil, it will be surrounded by magnetic field lines that change over time. According to Faradhi's law of electromagnetic induction- the analysis of magnetoelectric electricity, the changing magnetic field lines will produce an inductive potential at both ends of the coil, which is equivalent to a "new power supply".

When a closed loop is formed, this induced potential generates an induced current. The total amount of magnetic field lines generated by the induced current is known by The Law of The Rings is intended to prevent the original changes in the magnetic field lines. Since the original magnetic field line change is derived from the change of the applied alternating power supply, from the objective effect, the inductive coil has the characteristic of preventing the current change in the AC circuit.

Inductor coil has similar characteristics to inertia in mechanics, electrically named "self-induction", usually in the opening of the gate switch or on the brake switch at the moment, a spark will occur, which is the phenomenon of self-inductance caused by a high inductive potential.

➤ In short, when the inductor coil is connected to the AC power supply, the magnetic field lines inside the coil will change with the alternating current, resulting in electromagnetic induction in the coil. This electromotive force, which is generated by changes in the current of the coil itself, is called "self-induced electromotive force". It can be seen that the inductance is only a parameter related to the number of coils, the size and shape and the medium, which is a measure of the inertia of the inductor coil and has nothing to do with the applied current.

3.1 Inductance (L)

The inductance L represents the inherent characteristics of the coil itself, independent of the current size. In addition to the special inductance coil (color code inductor), the inductance value is generally not specifically marked on the coil, but marked with a specific name.

3.2 Inductive reactance (XL)

The size of the inductor coil's obstruction effect on the AC current is called the Inductive reactance-XL, and the unit is Ohm. Its relationship with the inductance L and the AC frequency f is XL=2πfL

3.3 Quality Factor (Q)

The quality factor Q is a physical quantity that represents the mass of the coil, and Q is the ratio of the inductive impedance XL to its equivalent resistance, i.e., Q = X L / R.
The higher the Q value of the coil, the smaller the loss of the loop. The Q value of the coil is related to factors such as the DC resistance of the wire, the dielectric loss of the skeleton, the loss caused by the shield or core, the effect of the high-frequency skin effect, and so on. The Q value of the coil is usually tens to hundreds. Using a core coil, multiple strands of coil can increase the Q value of the coil.

3.4 DC Resistance (DCR)

The inductor coil measures the resistance at non-alternating current, in the inductor design, the smaller the DC resistance, the better, and its measurement unit is Ohm, usually marked by its maximum value.

3.5 Distributed Capacitance

The capacitance present between the turns and turns of the coil, between the coil and the shielding cover, and between the coil and the bottom plate is called the distributed capacitor. The presence of distributed capacitance reduces the Q value of the coil and makes the stability worse, so the smaller the distributed capacitance of the coil, the better. The use of segmented winding reduces the distributed capacitance.

3.6 Impedance value

The impedance value of the inductor refers to the sum (complex number) of all its impedances under the current, including the AC and DC parts, the impedance value of the DC part is only the DC resistance (real part) of the winding, and the impedance value of the AC part includes the reactance (imaginary part) of the inductor. In this sense, inductors can also be thought of as "AC resistors".

3.7 Rated current

Allowing the continuous DC current intensity of an inductor, the intensity of this DC current is based on the maximum temperature rise of the inductor at the maximum rated ambient temperature, the rated current is related to the ability of an inductor to reduce the loss of the winding by a low DC resistance, and is also related to the ability of the inductor to disperse the energy loss of the winding, therefore, the rated current may be increased by reducing the DC resistance or increasing the inductor size to increase the current waveform of the low frequency. The RMS current value can be used in place of the DC rated current, which is not related to the magnetism of the inductor.

According to the inductance form classification :  fixed inductor, variable inductor.

Classified according to the nature of the conductive magnet : air core coil, ferrite coil, iron core coil, copper core coil.

According to the nature of work : antenna coil, oscillation coil, choke coil, notch coil, deflection coil.

Classification by winding architecture : single-layer coil, multi-layer coil, hive coil.

According to the operating frequency classification : high frequency coil, low frequency coil.

Classified according to architecture characteristics : core coil, variable inductance coil, color code inductance coil, non-core wire

 

➤ Classification by inductive process :