The q value of the electric toothbrush coil is the main parameter for measuring the quality of the inductive device. Its working method refers to the ratio of the inductance to the equivalent loss resistance when the inductance works under a certain frequency voltage. The higher the Q value of the electric toothbrush coil inductance, the loss The smaller, the higher the efficiency.
Electric toothbrush coils that work in low frequency bands are generally wound with insulated wires such as enameled wires. In circuits with operating frequencies higher than tens of thousands of hertz and below 2 MHz, the coil is wound with multiple insulated wires, which can effectively increase the surface area of the conductor , so as to overcome the influence of the skin effect and make the Q value 30%-50% higher than the coil wound by a single wire with the same cross-sectional area.
In circuits with a frequency higher than 2MHz, the electric toothbrush coil should be wound with a single thick wire, the diameter of the wire is generally 0.3 mm-1.5 mm, and the inductance coil is indirectly wound, generally using silver-plated copper wire to increase the surface of the wire. At this time, it is not suitable to use multi-strand wire winding, because when the frequency of multi-strand insulated wire is high, the insulating medium of the coil will cause additional loss, and the effect is not as good as a single wire.
The quality factor of the electric toothbrush coil is:
Q=L\/R, where:
- working angular frequency;
L - coil inductance;
R - the total loss resistance of the coil The total loss resistance of the coil consists of DC resistance, high frequency resistance (caused by skin effect and proximity effect) dielectric loss, etc. 39;
In order to improve the quality factor Q of the electric toothbrush coil, silver-plated copper wire can be used to reduce high-frequency resistance. Multi-strand insulated wires are used to replace single wires of the same length to reduce skin effect; high-frequency porcelain with low dielectric loss is used as the skeleton, Reduce the dielectric loss. Although the use of the magnetic core increases the loss of the magnetic core, it can greatly reduce the number of turns of the coil, thereby reducing the DC resistance of the wire and improving the Q value of the coil.
Choosing a reasonable electric toothbrush coil size can reduce the loss of a single-layer coil with a certain outer diameter (20mm-30mm). When the ratio of the winding length L to the outer diameter D is L\/D=0.7, the loss is the smallest. , L\/D=0.2-0.5, when T\/D=0.25-0.1, the loss is the smallest.
The use of the magnetic core in the electric toothbrush coil reduces the number of turns of the coil, which not only reduces the resistance value of the coil, but also improves the Q value and reduces the volume of the coil.
The electric toothbrush coil has the smallest loss when the winding thickness t, the winding length l, and the outer diameter d meet the conditions of 3t 2l=d. The coil with a shield is preferably L\/D=0.8-1.2.