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2021-11-22

First of all, let's talk about the definition of inductance quality factor Q:

The Q value is the main parameter to measure the inductance device. It refers to the ratio of the inductive reactance presented by the inductor to its equivalent loss resistance when it works under a certain frequency of AC voltage. The higher the Q value of the inductor, the smaller its loss and the higher the efficiency. The quality factor Q is an important parameter reflecting the quality of the coil. Improving the Q value of the coil can be said to be one of the key points to be paid attention to when winding the coil. So, how to improve the Q value of the wound coil, the following describes the specific method:

01. According to the working frequency, choose the wire of the coil

Inductance coils that work in low frequency bands are generally wound with insulated wires such as enameled wires. In circuits with a working frequency higher than tens of thousands of Hz but lower than 2MHz, the coil is wound with multiple insulated wires, which can effectively increase the surface area of the conductor, thereby overcoming the influence of the skin effect and making the Q ratio the same The cross-sectional area of a single wire wound coil is 30%-50% higher. In a circuit with a frequency higher than 2MHz, the inductance coil should be wound with a single thick wire, the diameter of the wire is generally 0.3mm-1.5mm. Inductance coils with indirect windings are used, usually made of silver-plated copper wire to increase the conductivity of the wire surface. At this time, it is not advisable to use multi-strand wire winding, because when the frequency of multi-strand insulated wire is very high, the coil insulation medium will cause additional loss, and its effect is not as good as a single wire.

02. Use high-quality coil bobbin to reduce dielectric loss

In the high frequency occasions, such as the short-wave band, the dielectric loss of the ordinary coil bobbin increases significantly. Therefore, high-frequency dielectric materials, such as high-frequency porcelain, polytetrafluoroethylene, polystyrene, etc., should be used as the skeleton. It is wound by the indirect winding method.

03. Choose a reasonable coil size

Selecting a reasonable coil size can reduce the loss of a single-layer coil with a certain outer diameter (φ20mm-30mm). When the ratio of the winding length L to the outer diameter D is L/D=0.7, the loss is the smallest; the multilayer coil with a certain outer diameter L/D＝0.2－0.5, when t/D＝0.25－0.1, the loss is the smallest. When the winding thickness t, the winding length L and the outer diameter D satisfy 3t+2L=D, the loss is also the smallest. The coil with shielding cover is best when its L/D = 0.8-1.2.

04. Select a reasonable diameter of the shielding cover

Using a shielding cover will increase the loss of the coil and reduce the Q value, so the size of the shielding cover should not be too small. However, if the size of the shield is too large, it will increase the volume, so a reasonable diameter size of the shield must be selected.

When the ratio of the shield diameter Ds to the coil diameter D satisfies the following value, that is, Ds/D=1.6 －2.5, the Q value decreases not more than 10%.

05. The use of magnetic cores can significantly reduce the number of coil turns

The use of a magnetic core in the coil reduces the number of turns of the coil, which not only reduces the resistance value of the coil, which is beneficial to the improvement of the Q value, but also reduces the volume of the coil.

06. Choose a larger coil diameter appropriately

It is beneficial to reduce the loss. When possible, the coil diameter is selected larger and the volume is increased, which is beneficial to reduce the loss of the coil. In general receivers, the diameter of a single-layer coil is 12mm-30mm, and a multi-layer coil is 6mm-13mm. However, considering the volume, it should not exceed the range of 20mm-25mm.

07. Reduce the distributed capacitance of the winding coil

Try to use the non-framework method to wind the coil, or the coil wound on the rib-type framework, can reduce the distributed capacitance by 15%-20%; the segmented winding method can reduce the distributed capacitance of the multilayer coil by 1/3～ l/2. For multilayer coils, the smaller the diameter D, the smaller the winding length L or the larger the winding thickness t, the smaller the distributed capacitance. It should be pointed out that the distributed capacitance of the coil after being diffused and sealed will increase by 20%-30%.

In short, when winding a coil, improving Q value and reducing loss are always the key considerations.

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