Introduction to Inductive Basics

1.1 Definition of inductors：

The inductance is the ratio of the magnetic flux of the wire to the current that produces the alternating flux in and around the wire when the current passes through the wire.

1.2Inductive coils and Transformers

Inductive 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. The inductive coil is made from this by winding the wire(enameled wire, yarn or naked WIRE) in a circle(the wires are insulated from each other) on the insulating tube(insulator, iron core or magnetic core). In general, the inductor coil has only one winding.

When the DC current is passed through the inductor, only a fixed magnetic line appears around it, and it does not change with time; However, when the current is passed through the loop, the magnetic lines around it will appear to change over time. According to Faraday's law of electromagnetic induction, magnetic bioelectricity, the induced potential is generated at both ends of the changing magnetic wire coil. This induced potential is equivalent to a "new power source." When a closed loop is formed, this induced potential generates an induced current. From the law of Lenz, we know that the total amount of magnetic lines generated by the induced current is to try to prevent the change of the original magnetic lines. Since the original magnetic line change comes from the change of the external alternating power supply, it is seen from the objective effect that the inductor coil has the characteristic of preventing the current change in the AC circuit. The inductive coil has characteristics similar to inertia in mechanics, in electricity。

1.2Inductive coils and Transformers

Inductive 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. The inductive coil is made from this by winding the wire(enameled wire, yarn or naked WIRE) in a circle(the wires are insulated from each other) on the insulating tube(insulator, iron core or magnetic core). In general, the inductor coil has only one winding.

Transformers: When the current flowing through the inductor coil changes, not only the induction voltage is generated at both ends of the inductor coil, but also the induction voltage can be generated in the nearby coil. This phenomenon is called mutual inductance. Two coils that are not connected to each other but are close to each other and have electromagnetic induction between them are generally called Transformers.

1.3Inductor symbol and unit inductor symbol：L

Inductive unit：(H)、(mH)、(uH)，1H=103mH=106uH。

The nominal name of inductance: straight standard, color ring standard, non-standard inductance directionality: no direction

Method of Inductance Inspection: Measurement of inductance by electrical inductance measuring instrument; Using a multimeter to measure its pass-through, the ideal inductive resistance is small and nearly zero.

1.4：Classification of inductors

Classification by inductive form: fixed inductance, variable inductance.

Classified by magnet properties: empty core coil, ferrite coil, iron core coil, copper core coil.

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

Classified by winding structure: single-layer coil, multi-layer coil, hive coil. Classified by operating frequency: high frequency coil, low frequency coil.

Classified by structural characteristics: magnetic core coil, variable inductive coil, color code inductive coil, non-magnetic core coil and so on.

**二、**The role of inductors

Basic role: filter, oscillation, delay, trap wave and other image statement: "DC, resistance communication"

Detailed explanation: In an electronic circuit, the inductive coil acts on an AC finite flow. It can form a high-pass or low-pass filter, a phase-shifting circuit, and a resonant circuit with a resistor or capacitor. Transformers can carry out AC coupling, variational pressure, variational flow and impedance transformation.

By sensing XL = 2 L, the larger the inductor L, the higher the frequency F, and the greater the inductance. The voltage at both ends of the inductor is proportional to the inductor L, and is also proportional to the current change speed I / T. This relationship can also be expressed as follows:

The inductive coil is also an energy storage element. It stores electrical energy in the form of a magnet. The size of the stored electrical energy can be expressed as follows: WL = 1/2 Li2.

It can be seen that the larger the inductance of the coil, the larger the flow, the more electrical energy is stored.

The most common role of inductors in circuits is to form LC filter circuits together with capacitors. We already know that capacitors have the ability to "block DC, pass AC," and inductors have the function of "pass DC, resist AC." If direct current with many interference signals is passed through the LC filter circuit(as shown in the figure), then the AC interference signal will be consumed by the capacitor into heat energy; When the relatively pure DC current passes through the inductor, the AC interference signal is also turned into magnetic sensitivity and thermal energy, and the higher frequency is most likely to be impedance by the inductor, which can inhibit higher-frequency interference signals.

The inductance in the power part of the circuit board is generally surrounded by a very thick paint envelope of wire diameter on a circular core coated with various colors. And there are generally several tall filtered aluminum electrolytic capacitors nearby, which consist of the above LC filter circuit. In addition, the circuit board also uses a large number of "snake lines + patch capacitance" to form the LC circuit, because the snake line is folded back and forth on the circuit board, it can also be regarded as a small inductor.

2.1 Inductance L

The inductance L represents the inherent characteristics of the coil itself and has nothing to do with the current size. In addition to the special inductor coil(color code inductor), the inductance is generally not specifically marked on the coil, but is marked under a specific name.

2.2 Touchdown XL

The magnitude of the inductive coil's effect on the current hindrance is called the inductive XL, in ohms. Its relationship with inductance L and AC frequency f is XL = 2 L

The inductance in the power part of the circuit board is generally surrounded by a very thick paint envelope of wire diameter on a circular core coated with various colors. And there are generally several tall filtered aluminum electrolytic capacitors nearby, which consist of the above LC filter circuit. In addition, the circuit board also uses a large number of "snake lines + patch capacitance" to form the LC circuit, because the snake line is folded back and forth on the circuit board, it can also be regarded as a small inductor.

**三、**Main Characteristic Parameters of Inductors2.1 Inductance L

The inductance L represents the inherent characteristics of the coil itself and has nothing to do with the current size. In addition to the special inductor coil(color code inductor), the inductance is generally not specifically marked on the coil, but is marked under a specific name.

2.2 Touchdown XL

The magnitude of the inductive coil's effect on the current hindrance is called the inductive XL, in ohms. Its relationship with inductance L and AC frequency f is XL = 2 L

2.3 Quality factors Q

The quality factor Q is a physical quantity that represents the mass of the coil. Q is the ratio of the resistance XL to its equivalent resistance, ie: 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 loss of the dielectric of the skeleton, the loss caused by the shield cover or iron core, and the influence of the high-frequency skin effect. The Q value of the coil is usually tens to hundreds. The Q value of the coil can be increased by using a magnetic core coil and a plurality of thick coils.

**四、**Constant electrical sensing coil

4.1 A single-layer coil is a single-layer coil that is wound around the paper cylinder or gluon skeleton in a circle with an insulated wire. Such as a transistor radio wave antenna coil.

4.2 If the Honeycomb coil is wound, the plane of the coil is not parallel to the rotating surface, but intersects into a certain angle. This coil is called a honeycomb coil. And its rotation one week, the number of times the wire bends back and forth, often referred to as the number of turns. The advantages of Honeycomb winding are small size, small distributed capacitance, and large inductance. The hive coil is made by using a hive winding machine. The more folding points, the smaller the distributed capacitance.

4.3 The inductance of ferrite core coil and ferrite core coil is related to the presence or absence of core. The inclusion of ferrite cores in the empty core coil can increase the inductance and improve the quality factors of the coil。

4.4 Copper core coil copper core coil is used in the ultra-short wave range, using the position in the rotating copper core coil to change the inductance, this kind of adjustment is more convenient and durable.

4.5 The color code inductive coil is a high-frequency inductive coil. It is wrapped in some enamels and then packaged with epoxy resin or plastic. Its operating frequency is from 10KHz to 200MHz, and the inductance is generally between 0.1 uH and 3300uH. The color code inductor is an inductor with a fixed inductance, and its inductance marking method is marked with a color ring like a resistor. Its unit is uH。

**五、**Model, Specification and Naming of Inductors

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here are many inductive manufacturers at home and abroad, among which the famous brand manufacturers are SAMUNG, PHI, TDK, AVX, VISHAY, NEC, KEMET, ROHM, etc.. 。

5.1 Shackle inductance inductance：10NH~1MH,

Material: Accuracy of the ferrite winding ceramic laminate： J=5% K=10% M=20%

5.1 Shackle inductance inductance：10NH~1MH,

Material: Accuracy of the ferrite winding ceramic laminate： J=5% K=10% M=20%

5.2 Power inductance

Inductance：1NH~20MH

With a shield、 No shield.

尺寸：SMD43、SMD54、SMD73、SMD75、SMD104、SMD105；RH73/RH74/ RH104R/RH105R/RH124；CD43/54/73/75/104/105；

5.3 Fractured magnetic beads

type：CBG（Normal type）

CBH（High current.） impedance：30Ω~120Ω

CBY（Spikes） impedance：5Ω~2KΩ

specifications：0402/0603/0805/1206/1210/1806（Piece of magnetic beads）

specifications：SMB302520/SMB403025/SMB853025（A patch with a large current magnetic bead)

specifications：SMB302520/SMB403025/SMB853025（A patch with a large current magnetic bead)

5.4 Plug-in magnetic beads

5.5 Color ring inductance：0.1uH~22MH

size：0204、0307、0410、0510

Plug-in color ring inductor

5.6 Vertical inductance

Inductance：0.1uH~3MH

size：PK0455/PK0608/PK0810/PK0912

5.7Axial filter inductance

size：LGC0410/LGC0513/LGC0616/LGC1019

Inductance：0.1uH-10mH。

current-consumption：65mA~10A。

5.5 Color ring inductance：0.1uH~22MH

size：0204、0307、0410、0510

Plug-in color ring inductor

5.6 Vertical inductance

Inductance：0.1uH~3MH

size：PK0455/PK0608/PK0810/PK0912

5.7Axial filter inductance

size：LGC0410/LGC0513/LGC0616/LGC1019

Inductance：0.1uH-10mH。

current-consumption：65mA~10A。

5.8 Magnetic ring inductance

size：TC3026/TC3726/TC4426/TC5026

5.9 Vacuum core inductance

In order to obtain a larger inductance value, the hollow core inductor is often wound with more enamels. In order to reduce the effect of the circuit resistance of the inductor itself on the DC current, a thicker enamel wire is used. However, in some smaller products, the use of heavy and large air core inductors is not realistic, not only increasing costs, but also limiting the volume of the product. In order to increase the inductance value and maintain a lighter weight, we can insert a magnetic center and an iron center into the air core inductor to improve the inductance of the inductor, thereby increasing the inductance value. At present, in computers, most of them are magnetic center inductors.

Iron core series

Materials are: -2(red/transparent), -8(yellow/red), -18(green/red), -26(Yellow/White), -28(gray/green), -33(gray/yellow) , -38(grayblack), -40(green/yellow), -45(black), -52(greenue); Size: External diameter size from 30 to 400D(Note: External diameter from 7.8 mm to 102mm) 。

In order to obtain a larger inductance value, the hollow core inductor is often wound with more enamels. In order to reduce the effect of the circuit resistance of the inductor itself on the DC current, a thicker enamel wire is used. However, in some smaller products, the use of heavy and large air core inductors is not realistic, not only increasing costs, but also limiting the volume of the product. In order to increase the inductance value and maintain a lighter weight, we can insert a magnetic center and an iron center into the air core inductor to improve the inductance of the inductor, thereby increasing the inductance value. At present, in computers, most of them are magnetic center inductors.

**六、**Common magnetic core magnetic ringIron core series

Materials are: -2(red/transparent), -8(yellow/red), -18(green/red), -26(Yellow/White), -28(gray/green), -33(gray/yellow) , -38(grayblack), -40(green/yellow), -45(black), -52(greenue); Size: External diameter size from 30 to 400D(Note: External diameter from 7.8 mm to 102mm) 。

Iron Silicon Aluminum Series

The main U values are: 60, 75, 90, 125; Size: External diameter sizes from 3.5 mm to 77.8 mm.

In addition to the main ring, the specifications of the two products, another E shape, rod shape, etc., can also be customized according to the parameters provided by the customer. They are widely used in computer motherboards, computer power supplies, power supplies, mobile phone chargers, lighting variable-voltage dimmers, uninterruptible power supply(UPS), and various household appliances control boards.

VII. Points to Note in the Use of Inductors

7.1 Attention must be paid to the wet and dry conditions in which inductors are used, the temperature of the environment, the high or low frequency environment, and whether the inductance is sensitive or impedance characteristics.

7.2 The frequency characteristics of the inductor at low frequencies generally exhibit inductive characteristics, both of energy storage and of high frequency filtration.

However, at high frequencies, its impedance characteristics are obvious. There are energy consumption and fever, and the perceptual effect is reduced. The high-frequency characteristics of different inductors are different.

The following is an explanation of the inductance of ferrite materials:

The ferrite material is an iron-magnesium alloy or an iron-nickel alloy. This material has a high magnetic conductivity. It can be the minimum capacitance generated between the coil windings of the inductor at high frequency and high resistance. The ferrite materials are usually used at high frequencies because they are mainly inductive at low frequencies, making the loss on the line very small. At high frequencies, they are mainly reactance ratio and change with frequency. In practical applications, ferrite materials are used as high-frequency attenuators for RF circuits. In fact, the ferrite is better equivalent to the parallel resistance and inductance. The resistance is short-circuited by the inductor at low frequencies, and the inductance impedance becomes quite high at high frequencies, so that the current passes through the resistor. The ferrite is a consumption device, and high-frequency energy is converted into heat energy on top, which is determined by his resistance characteristics.

7.3 The maximum current to be subjected to the inductor design, and the corresponding heating conditions.

7.4 When using the magnetic ring, the corresponding L value is found against the magnetic ring part above, and the range of use of the material is corresponding. 7.5 Pay attention to wires(enamels, gauze or bare wires), commonly used enamels. To find the most suitable thread meridian.