The performance index of the inductor is mainly the amount of inductance. In addition, the wire wound around the inductor coil generally has a certain resistance. Usually, this resistor is small and can be ignored. But when the current flowing in some circuits is very large, this small resistance of the coil can not be ignored, because a large current will consume power on this coil, causing the coil to heat up or even burn out, so sometimes it is necessary to consider The electrical power that the coil can withstand.
The inductance L represents the inherent characteristics of the coil itself, regardless of the current magnitude. Except for the special inductor (color code inductor), the inductance is generally not marked on the coil, but is marked with a specific name. The inductance is also called the self-inductance coefficient, which is a physical quantity indicating that the inductor generates self-inductance. The amount of inductance of the inductor depends mainly on the number of turns of the coil (number of turns), the winding method, the presence or absence of the core and the core material. Generally, the more coil turns, the denser the wound coil, and the greater the inductance. A coil with a core has a larger inductance than a coil without a core; a coil with a larger magnetic permeability has a larger inductance.
The basic unit of inductance is Henry (referred to as Henry), which is represented by the letter "H". Commonly used units are millihenry (mH) and microhenry (μH).
The magnitude of the inductance coil's resistance to alternating current is called XL, and the unit is ohm, the symbol is Ω. Its relationship with inductance L and AC frequency f is XL=2π quality factor
The quality factor Q is a physical quantity indicating the quality of the coil, and Q is the ratio of the inductive reactance XL to its equivalent resistance, that is, Q = XL / R. It refers to the ratio of the inductive reactance exhibited by the inductor to its equivalent loss resistance when operating at an AC voltage of a certain frequency. The higher the Q value of the inductor, the smaller the loss and the higher the efficiency. The Q value of the coil is related to the DC resistance of the wire, the dielectric loss of the skeleton, the loss caused by the shield or the iron core, and the influence of the high frequency skin effect. The Q value of the coil is usually from several tens to several hundreds. The quality factor of the inductor is related to the DC resistance of the coil wire, the dielectric loss of the coil bobbin, and the loss caused by the core and the shield.
Any inductor coil, between the 匝 and 匝, between the layers, between the coil and the reference ground, between the coil and the magnetic shield, there is a certain capacitance, these capacitors are called the distributed capacitance of the inductor. If these distributed capacitances are combined, they become an equivalent capacitor C in parallel with the inductor. The presence of the distributed capacitance reduces the Q value of the coil and the stability is deteriorated, so that the distributed capacitance of the coil is as small as possible.
The rated current is the maximum current allowed to pass through when the inductor is in normal operation. If the operating current exceeds the rated current, the inductor will change its performance parameters due to heat generation, and even burn out due to overcurrent.