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The role of the inductor

Inductor coil - basic knowledge
The inductor works by 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 the electromagnetic field itself is in the range of the electromagnetic field. The wire is inductive. The effect on the wire that produces the electromagnetic field itself is called "self-inductance"; the effect on other wires in the electromagnetic field is called "mutual inductance."
The electrical characteristics of the inductor are opposite to those of the capacitor, "resisting high frequency, passing low frequency". That is to say, when the high-frequency signal passes through the inductor, it will encounter a large resistance and it is difficult to pass; while the resistance of the low-frequency signal will be relatively small, that is, the low-frequency signal can pass through it easily. The resistance of DC is almost zero.
Resistance, capacitance and inductance, they will have a certain resistance to the flow of electrical signals in the circuit. This resistance is called the "impedance". The inductance of the inductor is the impedance of the current signal. The inductance of the coil is sometimes used. We refer to it simply as "inductance" or "coil", which is indicated by the letter "L". When winding an inductor, the number of turns of the coil is generally referred to as the "turn" of the coil.
 
Inductor Coil-II. Main performance indicators
 
The performance index of the inductor coil is mainly the magnitude of the inductance. In addition, the wire wound around the inductor coil generally has a certain resistance. Usually, this resistor is small and can be ignored. But when it flows through some circuits. This small resistance of the coil can not be neglected when the current is large, 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 considered.
III. Category
There are several types of inductive coils commonly used in circuits: if they are divided according to the material of the coil core used in the inductor, there are core inductors, copper inductors, ferrite inductors, and hollow inductors. Etc.; if divided according to the winding method of the inductor coil, there are single-layer coils, multi-layer coils, close-wound coils, inter-wind coils, tire-wound coils, honeycomb coils, chaotic coils, etc. And if according to the use of the inductor in the circuit, there are oscillating coils, choke coils (flow blocking coils), filter coils and so on.
 
Inductor Coil - III. Category
 
There are several types of inductive coils commonly used in circuits: if they are divided according to the material of the coil core used in the inductor, there are core inductors, copper inductors, ferrite inductors, and hollow inductors. Etc.; if divided according to the winding method of the inductor coil, there are single-layer coils, multi-layer coils, close-wound coils, inter-wind coils, tire-wound coils, honeycomb coils, chaotic coils, etc. And if according to the use of the inductor in the circuit, there are oscillating coils, choke coils (flow blocking coils), filter coils and so on.
 
Inductor coil - inductor coil
 
The inductor coil is wound around the insulating tube by a loop of the wire, and the wires are insulated from each other, and the insulating tube may be hollow or may include a core or a magnetic powder core, which is referred to as an inductor. Expressed by L, the unit is Henry (H), milli-henry (mH), micro-Henry (uH), 1H = 10^3mH = 10^6uH.
First, the classification of inductance
Classified by inductance: fixed inductance, variable inductance.
Classified according to the nature of the magnetizer: air core coil, ferrite coil, iron core coil, copper core coil.
Classified according to the nature of the work: antenna coil, oscillating coil, choke coil, trap coil, deflection yoke.
Classified by winding structure: single layer coil, multilayer coil, honeycomb coil.
Second, the main characteristic parameters of the inductor
1, inductance L
The inductance L represents the inherent characteristics of the coil itself, regardless of the current magnitude. Except for the special inductor (color code inductor), the inductance is generally not marked on the coil, but is marked with a specific name.
2, the anti-XL
The size of the inductive coil that blocks the AC current is called XL, and the unit is ohm. Its relationship with inductance L and AC frequency f is XL=2πfL
3. Quality factor Q
The quality factor Q is a physical quantity indicating the quality of the coil, and Q is the ratio of the inductive reactance XL to its equivalent resistance, that is, 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 skeleton, 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 from several tens to several hundreds.
4, distributed capacitance
The capacitance between the turns and turns of the coil, between the coil and the shield, and between the coil and the master is called a distributed capacitance. The presence of the distributed capacitance reduces the Q value of the coil and the stability is deteriorated, so that the distributed capacitance of the coil is as small as possible.
Third, the common coil
1, single layer coil
The single-layer coil is wound around the paper tube or bakelite skeleton in a circle with insulated wires. Such as a transistor radio wave antenna coil.
2, honeycomb coil
If the coil is wound, its plane is not parallel to the plane of rotation, but intersects at a certain angle. This coil is called a honeycomb coil. And the number of times the wire is bent back and forth, often referred to as the number of vertices. The advantage of the honeycomb type winding method is that the volume is small, the distributed capacitance is small, and the inductance is large. The honeycomb coils are wound by the honeycomb winding machine. The more the folding 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 a ferrite core into the air core coil increases the inductance and improves the quality of the coil.
4, copper core coil
Copper core coils are used in the ultrashort wave range. The position of the copper core in the coil is used to change the inductance. This adjustment is convenient and durable.
5, color code inductor
A color code inductor is an inductor with a fixed inductance. The method of marking the inductance is marked with a color ring like a resistor.
6, choke (choke)
The coil that restricts the passage of alternating current is called a choke, and is divided into a high frequency choke coil and a low frequency choke coil.
7, deflection coil
The deflection yoke is the load of the output stage of the television scanning circuit. The deflection yoke requires: high deflection sensitivity, uniform magnetic field, high Q value, small size and low price.
 
Inductor coil - the role of the inductor
 
1. Inductive coil choke action: The self-induced electromotive force in the coil of the inductor is always resistant to the current in the coil. The inductance coil has an obstructive effect on the alternating current, and the magnitude of the resistance is called xl, and the unit is ohm. The relationship between the inductance l and the alternating current frequency f is xl=2πfl, and the inductor can be mainly divided into a high frequency choke coil and a low frequency choke coil.
2. Tuning and frequency selection: The inductor coil and the capacitor are connected in parallel to 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 inductive reactance and capacitive reactance of the loop are also equal, so that the electromagnetic energy oscillates back and forth between the inductor and the capacitor, and the resonance phenomenon of the lc loop. When the resonance, the inductive reactance and capacitive reactance of the circuit are reversed, the inductive reactance of the total current of the loop is the smallest, and the current is the largest (refers to the AC signal of f="f0"). The lc resonant circuit has the function of selecting the frequency and can An AC signal of a frequency f is selected.
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