# Important parameters of inductor coils: Q value

First, let's talk about the definition of the inductor quality factor Q.

The Q value is the main parameter for measuring inductor devices. It refers to the ratio of the inductive reactance to its equivalent loss resistance when the inductor works under an AC voltage of a certain frequency. The higher the Q value of the inductor, the smaller its loss and the higher its efficiency. The quality factor Q is an important parameter that reflects the quality of the coil. Improving the Q value of the coil can be said to be one of the key points to pay attention to when winding the coil.

So, how to improve the Q value of the winding coil? The following are specific methods:

1. According to the working frequency, select the wire of the coil

Inductor coils working in the low frequency band are generally wound with insulated wires such as enameled wire. In circuits with operating frequencies higher than tens of thousands of Hz and lower than 2MHz, multi-strand insulated wires are used to wind the coils. This can effectively increase the surface area of the conductor, thereby overcoming the influence of the skin effect and keeping the Q ratio the same The cross-sectional area of the coil wound by a single wire is 30%-50% higher.

In circuits with frequencies higher than 2MHz, the inductor coil should be wound with a single thick wire, and the diameter of the wire is generally 0.3mm-1.5mm. An inter-wound inductor coil is often used, which is often wound with silver-plated copper wire to increase the conductivity of the wire surface. At this time, it is not advisable to use multi-stranded wires for winding, because when the frequency of multi-stranded insulated wires is very high, the coil insulation medium will cause additional losses, and the effect is not as good as that of a single wire.

2. Choose high-quality coil skeleton to reduce dielectric loss

In situations with higher frequencies, such as short-wave bands, the dielectric loss of ordinary coil skeletons increases significantly. Therefore, high-frequency dielectric materials, such as high-frequency porcelain, polytetrafluoroethylene, polystyrene, etc., should be used as the skeleton. And it is wound using the interwinding method.

3. Choose a reasonable coil size

Choosing a reasonable coil size can reduce losses. A single-layer coil with a certain outer diameter (φ20mm-30mm) has the smallest loss when the ratio of winding length L to outer diameter D is L/D=0.7; a multi-layer coil with a certain outer diameter L/D=0.2-0.5, when using t/D=0.25-0.1, the loss is the smallest. When the winding thickness t, winding length L and outer diameter D satisfy 3t+2L=D, the loss is also minimal. For coils using shielded covers, L/D = 0.8-1.2 is optimal.

4. Select a reasonable diameter of the shielding cover

Using a shield will increase the loss of the coil and reduce the Q value, so the size of the shield should not be too small. However, if the size of the shielding cover is too large, it will increase the volume, so a reasonable diameter size of the shielding cover must be selected. When the ratio of the shield diameter Ds to the coil diameter D satisfies the following value, namely Ds/D=1.6-2.5, the Q value will be reduced by no more than 10%.

5. 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, is beneficial to improving the Q value, but also reduces the volume of the coil.

6. Choose a larger coil diameter.

If the coil diameter is appropriately selected, it is beneficial to reduce the loss. If possible, the coil diameter is selected to be larger and the volume is increased, which is beneficial to reducing the coil loss. For general receivers, the single-layer coil diameter is 12mm-30mm; the multi-layer coil diameter is 6mm-13mm. However, considering the volume, it should not exceed the range of 20mm-25mm.

7. Reduce the distributed capacitance of the wound coil

Try to use a frameless method to wind the coil, or wind the coil on a ribbed frame, which can reduce the distributed capacitance by 15%-20%; the segmented winding method can reduce the distributed capacitance of the multi-layer coil by 1/3~ l/2. For multi-layer 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 noted that the distributed capacitance of the coil after flooding and sealing will increase by 20%-30%.

In short, when winding coils, improving the Q value and reducing losses are always the focus of consideration.