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The higher the Q value, the lower the loss when winding the coil

August 12 , 2021

Lets first talk about the definition of inductor quality factor Q


Coil


The Q value is the basic main parameter to consider the inductance. It refers to the ratio of the inductance exhibited by the inductance to its equivalent circuit loss resistance when the inductance 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 the main parameter that reflects the quality of the coil. Improving the Q value of the coil can be said to be one of the important points that need to be paid attention to when winding the coil.


So, how to improve the Q value of the wound coil, the specific method is described in detail below:


1. According to the power, a transmission line with a coil is used


Inductor coils that work in low frequency bands generally use insulated transmission line coil inductors such as enameled wires. In circuits with a power higher than tens of thousands of Hz but less than 2MHz, use multi-strand insulated transmission lines to wind the coil, so that the surface area of the electrical conductor can be increased reasonably, and the influence of the concentrating effect can be adjusted, making the Q value more than other The coils wound by a single transmission line with the same cross-sectional area are 30%-50% higher. In a circuit with a frequency higher than 2MHz, the inductance coil should be a single thick transmission line inductance coil, and the diameter of the transmission line is generally 0.3mm-1.5mm. Choose inductive coils wound in between, common gold-plated copper core wire inductance coils to improve the conductivity of the surface of the transmission line. At this time, it is not suitable to use a multi-core transmission line inductance coil, because the multi-core insulated cable will cause additional loss when the frequency is high, and the actual effect is not as good as a single transmission line.


2. Use high-quality coil frame to reduce dielectric loss


In places with higher frequencies, such as medium and short wave stock bands, due to the general coil frame, the dielectric loss is significantly increased. Therefore, high-frequency material materials such as high-frequency porcelain, polytetrafluoroethylene, polyethylene, etc. should be used. It is the frame, and the inductance coil is wound by the indirect winding method.


3. Select effective coil specifications


Selecting effective coil specifications can reduce the loss of single-layer coils with a certain diameter (φ20mm-30mm). When the ratio of the winding length L to the diameter D is L/D=0.7, the loss is the least; the multi-layer coils with a certain diameter L/D =0.2-0.5, when t/D=0.25-0.1, the loss is the least. When the winding thickness t, the winding length L and the diameter D reach 3t+2L=D, the loss is the least. It is best to choose the anti-interference magnetic ring coil, and its L/D=0.8-1.2.


4. Choose a reasonable and effective shield diameter


With a shielding cover, the Q value is reduced, which will increase the loss of the coil, so the Q value reduction specification cannot be too small. The shielding cover should not be too large to enlarge the volume. Therefore, a reasonable diameter size of the shielding cover should be selected.


When the ratio of the shield diameter Ds to the coil diameter D reaches the following standard value, that is, Ds/D=1.6-2.5, the Q value will not exceed 10%.


5. The selection of magnetic core can significantly reduce the number of turns of the coil


The use of magnetic cores in the coil reduces the number of turns of the coil, not only reduces the resistance of the coil, but also increases the Q value, and the volume of the coil also shrinks.


6. Choose a moderately large coil diameter


Choose a moderately large coil diameter, which will help reduce loss. Under the most likely standard, choose a larger coil diameter and enlarge the volume, which will help reduce the loss of the coil. For general receivers, the diameter of single-sided coil is 12mm-30mm; the diameter of multi-layer coil is 6mm-13mm, but considering the volume, it is not suitable to exceed the range of 20mm-25mm.


7. Reduce the distributed capacitance of the winding coil


If possible, choose non-skeleton method to wind the coil, or the coil wound on the rib-type skeleton, which can reduce the distributed capacitance by 15%-20%; the segmented winding method can reduce the distributed capacitance of the multilayer coil by 1/3l/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. What should be emphasized is that the distributed capacitance of the coil after being flooded and sealed will increase by 20%-30%.


All in all, when winding the coil, improving the Q value and reducing the loss are the key considerations from beginning to end.


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