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• # The role of inductance coil

Inductance coil-basic knowledge

Inductance works by using the principle of electromagnetic induction. When a current flows through a wire, a certain electromagnetic field is generated around the wire, and the wire of this electromagnetic field itself will affect the electromagnetic field in the range of the electromagnetic field. The wire has an induction effect. The effect on the wire itself that generates the electromagnetic field is called "self-inductance"; the effect on other wires in the electromagnetic field is called "mutual inductance".

The electrical characteristics of inductance coils are opposite to those of capacitors, "blocking high frequencies and passing low frequencies". That is to say, high-frequency signals will encounter a lot of resistance when passing through the inductor coil, and it is difficult to pass; while the resistance presented by low-frequency signals passing through it is relatively small, that is, low-frequency signals can pass through it more easily. The resistance of direct current is almost zero.

Resistance, capacitance and inductance, they all present a certain resistance to the flow of electrical signals in the circuit. This resistance is called "impedance". The impedance presented by the inductor to the current signal uses the self-inductance of the coil. Sometimes the inductor We call it "inductance" or "coil" for short, which is represented by the letter "L". When winding an inductance coil, the number of turns of the coil we generally call it the "number of turns" of the coil.

Inductance coil-Ⅱ. Main performance index

The performance index of the inductor coil is mainly the size of the inductance. In addition, the wire that winds the inductor coil generally has a certain resistance. Usually this resistance is very small and can be ignored. But when it flows in some circuits When the current is large, the small resistance of the coil cannot be ignored, because a large coil will consume power on this coil, causing the coil to heat up or even burn out, so sometimes the electric power that the coil can withstand is also considered.

Ⅲ. Category

There are roughly the following categories of inductors commonly used in circuits: if they are divided according to the material of the coil core used in the inductor, there are iron core inductors, copper core inductors, ferrite core inductors, and air core inductors. And so on; if it is divided according to the winding method of the inductance coil, there are single-layer coils, multi-layer coils, close-wound coils, indirect-wound coils, out-of-the-box coils, honeycomb coils, random-wound coils, etc. ; And if divided according to the purpose of the inductance coil in the circuit, there are oscillating coils, choke coils (choke coils), filter coils and so on.

Inductance coil-Ⅲ. Category

There are roughly the following categories of inductors commonly used in circuits: if they are divided according to the material of the coil core used in the inductor, there are iron core inductors, copper core inductors, ferrite core inductors, and air core inductors. And so on; if it is divided according to the winding method of the inductance coil, there are single-layer coils, multi-layer coils, close-wound coils, indirect-wound coils, out-of-the-box coils, honeycomb coils, random-wound coils, etc. ; And if divided according to the purpose of the inductance coil in the circuit, there are oscillating coils, choke coils (choke coils), filter coils and so on.

Inductance coil-Inductance coil

The inductance coil is made of wires wound around an insulating tube one by one. The wires are insulated from each other. The insulating tube can be hollow, or it can contain an iron core or a magnetic powder core, referred to as inductance. Expressed by L, the units are Henry (H), millihenry (mH), microhenry (uH), 1H=10^3mH=10^6uH.

1. Classification of inductance

Classified according to the form of inductance: fixed inductance, variable inductance.

According to the nature of the magnetic conductor: air core coil, ferrite coil, iron core coil, copper core coil.

Classified by work nature: antenna coil, oscillating coil, choke coil, trap coil, deflection coil.

Classified by winding structure: single-layer coil, multi-layer coil, honeycomb coil.

Two, the main characteristic parameters of the inductance coil

1. Inductance L

The inductance L represents the inherent characteristics of the coil itself and has nothing to do with the magnitude of the current. Except for special inductance coils (color code inductance), the inductance is generally not specifically marked on the coil, but marked with a specific name.

2. Inductive resistance XL

The hindering effect of the inductance coil on the alternating current is called the inductive reactance XL, and the unit is ohm. Its relationship with inductance L and alternating current frequency f is XL=2πfL

3. Quality factor Q

The quality factor Q is a physical quantity that represents the quality of the coil, and Q is the ratio of the inductive reactance XL to its equivalent resistance, namely: Q=XL/R. The higher the Q value of the coil, the smaller the loss of the loop. The Q value of the coil is related to the DC resistance of the wire, the dielectric loss of the frame, the loss caused by the shield or the iron core, and the influence of the high-frequency skin effect. The Q value of the coil is usually tens to hundreds.

4. Distributed capacitance

The capacitance between the turns of the coil, between the coil and the shield, and between the coil and the base plate is called distributed capacitance. The existence of distributed capacitance reduces the Q value of the coil and the stability becomes worse. Therefore, the smaller the distributed capacitance of the coil, the better.

3. Commonly used coils

1. Single layer coil

Single-layer coils are wound around a paper tube or bakelite frame with insulated wires. Such as the medium wave antenna coil of a transistor radio.

2. Honeycomb coil

If the plane of the coil being wound is not parallel to the rotating surface, but intersects at a certain angle, this kind of coil is called a honeycomb coil. The number of times the wire is bent back and forth after one rotation is often called the number of bending points. The advantages of the honeycomb winding method are small size, small distributed capacitance, and large inductance. The honeycomb coils are all wound by the honeycomb winding machine, the more the turning points, the smaller the distributed capacitance

3. Ferrite core and iron powder core coil

The inductance of the coil is related to the presence or absence of a magnetic core. Inserting the ferrite core in the air-cored coil can increase the inductance and improve the quality factor of the coil.

4. Copper core coil

Copper core coils are widely used in the ultrashort wave range. The position of the copper core in the coil is used to change the inductance. This adjustment is more convenient and durable.

5. Color code inductor

The color code inductor is an inductor with a fixed inductance, and its inductance marking method is the same as a resistance with a color ring.

6. Choke coil (choke coil)

The coil that restricts the passage of alternating current is called a choke coil, which is divided into a high-frequency choke coil and a low-frequency choke coil.

7. Deflection coil

The deflection coil is the load of the output stage of the TV's scanning circuit. The deflection coil requires: high deflection sensitivity, uniform magnetic field, high Q value, small size, and low price.

Inductance coil-the role of inductance coil

1. Inductance coil blocking effect: the self-induced electromotive force in the inductance coil is always reacting to the current change in the coil. The inductance coil has an obstructive effect on the alternating current, and the size of the obstructive effect is called the inductive reactance xl, and the unit is ohm. Its relationship with inductance l and alternating current frequency f is xl=2πfl, and inductors can be divided into high-frequency choke coils and low-frequency choke coils.

2. Tuning and frequency selection: inductance coil and capacitor in parallel can form an lc tuning circuit. That is, the natural oscillation frequency f0 of the circuit is equal to the frequency f of the non-AC signal, and the inductance and capacitive reactance of the loop are also equal, so the electromagnetic energy oscillates back and forth between the inductance and the capacitance, which is the resonance phenomenon of the lc loop. At resonance, the inductive reactance and capacitive reactance of the circuit are reversed. The inductive reactance of the total loop current is the smallest and the current is the largest (referring to the AC signal with f="f0"). The lc resonant circuit has the function of selecting the frequency and can An AC signal of frequency f is selected.

# The role of inductance coil

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