Factor Q is an important parameter of coil quality. The value of Q indicates that the larger the loss of inductance coil is, the smaller the loss of inductance coil is; on the contrary, the larger the loss of inductance coil is.
Quality factor Q is defined as the ratio of inductance to coil DC resistance when the coil works at a certain frequency of AC voltage. It can be expressed by formula as follows:
In the formula: W - - working angle frequency L - - coil inductance R - - total loss resistance of coil
According to the use of different occasions, the quality factor Q requirements are also different. For the inductance coil in the tuning loop, the Q value is higher, because the higher Q value, the lower the loss of the loop and the higher the efficiency of the loop; for the goose-coil, the Q value can be lower; for the low-frequency or high-frequency choke, it can not be required.
In fact, the improvement of Q value is often limited by some factors, such as DC resistance of conductor, dielectric loss of coil skeleton, loss caused by core and shielding, skin effect in high frequency operation, etc. Therefore, the Q value of the coil can not be very high. Usually, the Q value is dozens to one hundred, and the maximum is only four or five hundred.
Main characteristic parameters of inductance
1. Inductance L and Accuracy
The inductance L represents the inherent characteristics of the coil itself and is independent of the current. In addition to the special inductance coil (color code inductance), inductance is generally not specifically labeled on the coil, but labeled with a specific name. The inductance of the coil is mainly determined by the diameter of the coil, the number of turns and the iron core. The inductance coils are used for different purposes, and the inductance required is also different. For example, in high frequency circuits, the inductance of coils is generally 0.1uH-100H.
The accuracy of inductance, that is, the error between actual inductance and required inductance, depends on its use. The requirement for oscillating coil is high, 0.2-0.5%. The requirements for coupling coils and high frequency choke coils are low, allowing 10-15%. For some occasions requiring high accuracy of inductance, it can only be tested by instrument after winding, by adjusting the distance between turns near the edge or the position of the magnetic core in the coil.
2. Reactance XL
The size of the inductance coil's impediment to AC current is called the inductance resistance XL, in ohms. The relationship between inductance L and AC frequency f is XL=2 PI fL.
3. Quality factor Q
Coil Quality Factor
Quality factor Q is used to indicate the size of coil loss. High frequency coils are usually 50-300. The Q value of the tuning loop coil is required to be higher, and the resonant circuit composed of high Q value coil and capacitor has better resonant characteristics, while the resonant circuit composed of low Q value coil and capacitor has no obvious resonant characteristics. For the coupling coil, the requirements can be lower, but for the high frequency choke coil and the low frequency choke coil, there is no requirement. The magnitude of Q affects the selectivity, efficiency, filtering characteristics and frequency stability of the circuit. Generally, it is hoped that the Q value of the coil is large, but it is not easy to improve the Q value of the coil. Therefore, appropriate requirements for the Q value of the coil should be put forward according to the actual use situation.
Coil quality factor is:
Q= Omega L/R formula:
_ - working angle frequency;
L - inductance of coil;
R - The total loss resistance of the coil. It consists of DC resistance, high frequency resistance (caused by skin effect and proximity effect) and dielectric loss. "
In order to improve the quality factor Q of the coil, silver-plated copper wire can be used to reduce the high frequency resistance; multiple insulating wires can be used instead of single wire with the same president plane to reduce skin effect; and high frequency porcelain with low dielectric loss can be used as the framework to reduce dielectric loss. Although the core loss is increased by using magnetic cores, the number of coil turns can be greatly reduced, thus reducing the DC resistance of the conductor, which is beneficial to improving the Q value of the coil.
Quality factor Q is a physical quantity representing the quality of coil. Q is the ratio of inductance XL to its equivalent resistance, that is Q = XL / 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 the DC resistance of the conductor, the dielectric loss of the skeleton, the loss caused by the shield cover or iron core, and the influence of high frequency skin effect. The Q value of the coil is usually tens to hundreds. The Q value of coils can be increased by using magnetic core coils and multiple thick coils.
4. Distributed capacitance
The capacitance between turn and turn of coil, between coil and shielding cover, between coil and bottom plate is called distributed capacitance. The existence of distributed capacitance makes the Q value of the coil decrease and the stability worse, so the smaller the distributed capacitance of the coil, the better. The distributed capacitance can be reduced by using the sectional winding method.
5. Inherent capacitance
Distributed capacitance exists between turns of coil winding and between layers of multi-layer winding. These distributed capacitors can be equivalent to a capacitor C parallel to the coil.
6. Permissible error
The difference between the actual value of inductance and the nominal value is divided by the percentage of the nominal value.
7. Nominal current
The allowable current of the coil is usually expressed by letters A, B, C, D and E. The nominal current values are 50mA, 150mA, 300mA, 700mA and 1600mA.
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