Toroidal coil inductor is also one of the commonly used components in household appliances, instrumentation and other electronic products, and is an electronic component that uses the principle of electromagnetic induction to work. Its electrical characteristics are the opposite of those of capacitors, "low frequencies and high frequencies". High-frequency signals will encounter great resistance when passing through the inductance coil, which is difficult to pass; However, the resistance to the passage of the low-frequency signal is relatively small, that is, the low-frequency signal can pass through it more easily. The resistance of the inductor coil to DC is almost zero.
Inductance coil: When there is an electric current in the wire, a magnetic field is established around it. Usually，we wind the wire into a coil to enhance the magnetic field inside the coil. In this way, an inductance coil is made by wrapping wires (enamelled, yarn or bare wires) around an insulating tube (insulator, iron core or magnetic core) one by one (the wires are insulated from each other). In general, an inductance coil has only one winding.
The structure of the coil
The coil is usually composed of a skeleton, a winding, a magnetic core and a shielding cover, etc., according to the different occasions of use, some coils do not have a shielding cover, some do not have a magnetic core, and some do not even have a fixed frame, only windings.
1. Skeleton
The commonly used materials for skeletons are ceramic, plastic, bakelite and electrical cardboard. The material of the skeleton has a certain impact on the quality and stability of the coil, which is generally selected according to the working conditions.
2. Winding
Most of the windings are made of insulated wires wound on the coil skeleton, and insulated wires are commonly used in various specifications of enameled wires and magnet wires. Generally speaking, the greater the amount of inductance required for the winding, the greater the number of coils. The diameter of the wire should be determined according to the current value through the winding and the Q value of the coil. When the current is large, the Q value is high, so the diameter of the coil wire should be thicker. In the case that the inductance is less than a few micro-yomes, the winding is often wound with bare silver-plated copper coins to reduce the surface resistance of the wire and improve the performance of the coil.
3. Shielding cover
In order to reduce the influence of the external electromagnetic field on the coil and the donation of the electromagnetic field generated by the coil to the external circuit, the coil is often enclosed in the structure by a metal cover and reliably grounded to meet the requirements of isolation from the external circuit.
4. Core
When the coil is loaded with a core, the amount of inductance of the coil can be increased, or the number of coils with a core can be reduced compared to a coil without a core with the same amount of inductance, so that the volume and distributed capacitance of the coil can be reduced, and the Q value of the coil can be increased. Sometimes in order to adjust the amount of inductance of the coil, it is possible to adjust the position of the core in the coil. The cores are usually made of manganese-zinc ferrite or nickel-zinc ferrite magnetic materials, and can be made into various shapes according to the different requirements of use.
The principle of an inductance coil
Inductance is the ratio of the magnetic flux of the wire to the current used to produce the alternating magnetic flux generated in and around the wire when an alternating current passes through the wire.
When a DC current is passed through an inductor, there are only fixed magnetic field lines around it, which do not change with time, but when an alternating current is passed through the coil, there are time-varying magnetic field lines around it. According to Faraday's law of electromagnetic induction, magnetic electricity, the changing magnetic field lines generate an induced electric potential at both ends of the coil, which is equivalent to a "new power source". When a closed loop is formed, this induced potential generates an induced current. From Lenz's law, we know that the total amount of magnetic field lines generated by the induced current should try to prevent the change of the original magnetic field lines. Since the original change of magnetic field lines comes from the change of the external alternating power supply, from the objective effect, the inductance coil has the characteristic of preventing the current change in the AC circuit. The inductance coil has similar characteristics to the inertia in mechanics, and is named "self-induction" in electricity, usually at the moment when the knife switch is opened or turned on, a spark will occur, which is caused by the high induced potential generated by the self-induction phenomenon.
In short, when the inductance coil is connected to the AC power supply, the magnetic field lines inside the coil will change all the time with the alternation of current, resulting in continuous electromagnetic induction in the coil. This electromotive force, which is generated by the change in the current of the coil itself, is called "self-induced electromotive force".
It can be seen that the inductance is only a parameter related to the number of coils, size, shape and medium of the coil, and it is a measure of the inertia of the toroidal coil inductor and has nothing to do with the impressed current.
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Q: What is the function of the inductance coil?
A: Inductance coils play many important roles in electronic circuits. On the one hand, it can adjust the frequency of the circuit, control the voltage, isolate the signal, etc., and on the other hand, it can also be used for the filtering and data transmission of electronic equipment.
Q: What are the types of inductance coils?
A: Inductance coils are usually divided into two categories: iron core inductance coils and air core inductance coils. An iron core inductor coil usually has a magnetic core in the center, while an air core inductor coil has no magnetic core.
Q: What are the selection factors for inductance coils?
A: The choice of toroidal coil inductor mainly depends on the voltage, current, frequency, capacity and other factors in the circuit. When selecting inductor coils, it is also necessary to select them according to factors such as actual application requirements and environmental requirements of electronic equipment.
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