Inductance

Except for fixed inductors and some choke coils, which are common components (as long as they have the same specifications, they can be used on various electronic devices), the rest are dedicated components such as televisions and radios. Special components are generally one model corresponding to one model (except for substitutes). The component model should be used as the main basis when purchasing and using. The specific parameters do not need to be considered. If you need to know, you can check the corresponding product manual or related information, here It is impossible to give examples one by one. Let's talk about the main parameters and identification of fixed inductors and choke coils.

Ⅰ. The main technical parameters of the inductor:

1. Inductance L:The inductance L is also called the self-inductance coefficient, which is a physical quantity that represents the self-inductance of the inductance element. When the magnetic flux passing through a coil (that is, the number of lines of magnetic force passing through a certain area) changes, an electric potential is generated in the coil, which is an electromagnetic induction phenomenon. The generated electric potential is called the induced electric potential, and the magnitude of the electric potential is proportional to the speed of magnetic flux change and the number of turns of the coil. When a changing current flows through the coil, the magnetic flux generated by the coil also changes. The magnetic flux passes through the coil, and an induced electric potential is generated at both ends of the coil. This is the phenomenon of self-induction. The direction of the self-induced potential always prevents the current from changing, just like the coil has inertia. The magnitude of this electromagnetic inertia is represented by the inductance L. The size of L is related to the number of turns, size and magnetic material of the coil. Using silicon steel sheet or ferrite as the core of the coil, a larger inductance can be obtained with a smaller number of turns. The basic unit of L is H (Hen), and the more commonly used units are mH (millihenry) and IxH (microhenry). The conversion relationship between the three is as follows: 1H=103mH=106 μH. 

2. Induction XL:Inductance XL is generally not found in the inductance component parameter table, but it is closely related to the inductance, the classification quality factor Q of the inductance component and other parameters, and it is often used in the analysis circuit, so here is a special introduction. As mentioned above, since the self-induced potential of the inductance coil always prevents the current in the coil from changing, the coil has a resistance to alternating current, and the resistance is represented by the inductive reactance XL. XL is proportional to the coil inductance L and the alternating current frequency f. The calculation formula is: XL (Ω)=2лf(Hz)L(H). It is not difficult to see that XL is small when the coil passes low-frequency current. XL is zero when passing direct current, and only the DC resistance of the coil acts as resistance. Because the resistance is generally small, it is almost a short circuit. XL is large when high-frequency current is passed, and if L is also large, it is almost an open circuit. This characteristic of the coil is just the opposite of the capacitance, so the use of inductance elements and capacitors can form various high-frequency, intermediate-frequency and low-frequency filters, as well as tuning loops, frequency selection loops, choke circuits, and so on.

3. Quality factor Q:This is a parameter that indicates the quality of the inductor, and is also called the Q value or figure of merit. When the coil works under a certain frequency of AC voltage, the ratio of its inductance XL to the equivalent loss resistance is the Q value, and the expression is as follows: Q=2лL/R. It can be seen that the larger the inductance of the coil and the smaller the loss resistance, the higher its Q value. It is worth noting that when the frequency f is low, the loss resistance can be regarded as basically based on the DC resistance of the coil; when f is high, due to the dielectric loss of the coil bobbin and the impregnation, the loss of the iron core and the shielding cover, and the high wire The frequency skin effect loss and other effects are more obvious, and R should include the equivalent loss resistance including various losses, not just the DC resistance.

The value of Q is mostly in the tens to hundreds. The higher the Q value, the smaller the loss of the circuit and the higher the efficiency. However, after the Q value is increased to a certain level, it will be restricted by various factors, and many circuits do not have high requirements on the Q value of the coil, so the specific Q value should be determined Depends on circuit requirements.

4. DC Resistance:That is, the DC resistance of the inductor coil itself can be directly measured with a multimeter or an ohmmeter.

5. Rated current:It usually refers to the value of the DC current allowed to pass through the inductor for a long time. When selecting inductive components, if the current flowing through the circuit is greater than the rated current value, it is necessary to switch to other types of inductors whose rated current meets the requirements.

Ⅱ. Identification of inductors:

The identification of inductive components is very easy. Fixed inductors generally have the inductance and model number directly marked on the surface, which can be known at a glance. Some inductors are only marked with model or inductance, and some inductance components are marked with only model and trademark. If you need to know other parameters, you can only consult the product manual or related materials.