Detailed introduction to inductors and inductor materials

1.1 Definition of inductance:
Inductance is the ratio of the magnetic flux of the wire to the current that produces the alternating magnetic flux inside and around the wire when an alternating current passes through it. When a

direct current passes through the inductor, only fixed magnetic lines of force are present around it, which do not change with time; however, when an alternating current passes through the coil, magnetic lines of force that change with time will appear around it. According to Faraday's law of electromagnetic induction - magnetoelectricity, the changing magnetic lines of force will generate an induced potential at both ends of the coil, and this induced potential is equivalent to a "new power source". When a closed loop is formed, this induced potential will generate an induced current. Lenz's law shows that the total amount of magnetic lines of force generated by the induced current should try to prevent the change of the original magnetic lines of force. Since the change of the original magnetic lines of force comes from the change of the external alternating power source, from an objective point of view, the inductor coil has the characteristic of preventing the change of current in the AC circuit. The inductor has a characteristic similar to inertia in mechanics, which is called "self-induction" in electricity. Usually, sparks will occur at the moment of opening or closing the knife switch. This is caused by the high induced potential generated by the self-induction phenomenon.

In short, when the inductor is connected to an AC power supply, the magnetic lines of force inside the coil will change all the time with the alternating current, causing the coil to continuously generate electromagnetic induction. This electromotive force generated by the change of the current in 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 turns, size, shape and medium of the coil. It is a measure of the inertia of the inductor and has nothing to do with the external current.
1.2 Inductor and transformer
Inductor: When there is 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 inductor is made by winding the wire (enameled wire, yarn-wrapped wire or bare wire) one circle by one circle (the wires are insulated from each other) on an insulating tube (insulator, iron core or magnetic core). Generally, an inductor has only one winding.
Transformer: When a variable current flows through an inductor, it not only generates an induced voltage at both ends of the inductor, but also generates an induced voltage in nearby coils. 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.
1.3 Symbol and unit of inductance
Inductance symbol: L
Inductance unit: Henry (H), millihenry (mH), microhenry (uH), 1H=103mH=106uH.
1.4 Classification of inductors:
Classification by inductance form: fixed inductance, variable inductance.
Classification by magnetic conductor properties: air core coil, ferrite coil, iron core coil, copper core coil.
Classification by working properties: antenna coil, oscillation coil, choke coil, trap coil, deflection coil. Classification by
winding structure: single-layer coil, multi-layer coil, honeycomb coil.
Classification by working frequency: high-frequency coil, low-frequency coil.
Classification by structural characteristics: magnetic core coil, variable inductance coil, color code inductance coil, coreless coil, etc.
2. Main characteristic parameters of inductance
2.1 Inductance L
Inductance L represents the inherent characteristics of the coil itself and has nothing to do with the current size. Except for special inductance coils (color code inductance), the inductance is generally not specifically marked on the coil, but marked with a specific name.
2.2
Inductive reactance XL The magnitude of the inductance coil's resistance to AC current is called inductive reactance XL, and the unit is ohm. Its relationship with inductance L and AC frequency f is XL=2πfL
2.3 Quality factor Q
The quality factor Q is a physical quantity that represents the quality of the coil. Q is the ratio of 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 factors such as the DC resistance of the wire, the dielectric loss of the skeleton, the loss caused by the shielding cover or the core, and the influence of the high-frequency skin effect. The Q value of the coil is usually tens to hundreds. Using a magnetic core coil and a thick multi-strand coil can improve the Q value of the coil.
2.4

Distributed capacitance The capacitance between the turns of the coil, between the coil and the shield, and between the coil and the bottom plate is called distributed capacitance. The existence of distributed capacitance reduces the Q value of the coil and deteriorates the stability, so the smaller the distributed capacitance of the coil, the better. The distributed capacitance can be reduced by using the segmented winding method.
2.5 Allowable error: The percentage obtained by dividing the difference between the actual value and the nominal value of the inductance by the nominal value.
2.6 Nominal current: refers to the current allowed to pass through the coil, usually represented by the letters A, B, C, D, and E respectively, and the nominal current values ​​are 50mA, 150mA, 300mA
, 700mA, and 1600mA.
3. Commonly used inductance coils
3.1 Single-layer coils
Single-layer coils are made of insulated wires wound one by one on a paper tube or bakelite frame. Such as the medium wave antenna coil of a transistor radio.
3.2 Honeycomb coil

If the plane of the wound coil is not parallel to the rotating plane, but intersects at a certain angle, this coil is called a honeycomb coil. The number of times the wire bends back and forth during one rotation is often called the number of inflection points. The advantages of honeycomb winding are small size, small distributed capacitance, and large inductance. Honeycomb coils are all wound using honeycomb winding machines. The more inflection points, the smaller the distributed capacitance.
3.3 Ferrite core and iron powder core
coils The inductance of the coil is related to whether there is a magnetic core. Inserting a ferrite core into an air-core coil can increase the inductance and improve the quality factor of the coil.
3.4 Copper core coil
Copper core coils are widely used in the ultra-short wave range. The inductance is changed by rotating the position of the copper core in the coil. This adjustment is more convenient and durable.
3.5 Color code inductor coil

It is a high-frequency inductor coil, which is made by winding some enameled wire on the magnetic core and then encapsulating it with epoxy resin or plastic. Its operating frequency is 10KHz to 200MHz, and its inductance is generally between 0.1uH and 3300uH. Color-coded inductors are inductors with fixed inductance, and their inductance is marked with color rings in the same way as resistors. Its unit is uH.
3.6 Chokes
A coil that limits the passage of alternating current is called a choke, which is divided into high-frequency chokes and low-frequency chokes.
3.7 Deflection coils
The deflection coil is the load of the output stage of the TV scanning circuit. The deflection coil requires: high deflection sensitivity, uniform magnetic field, high Q value, small size, and low price.
4. The role of inductance in the circuit
Basic role: filtering, oscillation, delay, notch, etc.
Image statement: "Passing DC and blocking AC"

Detailed explanation: In electronic circuits, the inductor has a limited current effect on AC. It can form high-pass or low-pass filters, phase shift circuits and resonant circuits with resistors or capacitors; transformers can perform AC coupling, voltage conversion, current conversion and impedance conversion, etc.
From the inductive reactance XL=2πfL, we know that the larger the inductance L is, the higher the frequency f is, and the larger the inductive reactance is. The voltage across the inductor is proportional to the inductance L and the current change speed △i/△t
. This relationship can also be expressed by the following formula:
The inductor coil is also an energy storage element. It stores electrical energy in the form of magnetism. The amount of stored electrical energy can be expressed by the following formula: WL=1/2 Li2.
It can be seen that the greater the inductance of the coil, the greater the flow, and the more electrical energy is stored.
Inductor symbol
Nominal inductance: direct mark type, color ring mark type, no mark type
Directionality of inductance: no direction
Methods for checking the quality of inductance: use an inductance meter to measure its inductance; use a multimeter to measure its on and off. The ideal inductor resistance is very small, almost zero.
5. Model, specification and naming of inductors.
There are many inductor manufacturers at home and abroad, among which famous brands include SAMUNG, PHI, TDK, ****X, VISHAY, NEC, KEMET, ROHM, etc.
5.1 Chip inductor
Inductance: 10NH~1MHMaterial
: Ferrite winding type ceramic laminate
Accuracy: J=±5% K=±10%M=±20%
Size: 0402 0603 08051008 1206 1210 1812 1008=2.5mm*2.0mm
1210=3.2mm*2.5mmIndividual
diagram: Chip winding inductor Chip laminate
inductor5.2 Power inductor
Inductance: 1NH~20MH
with shielding, without shielding

Size: SMD43, SMD54, SMD73, SMD75, SMD104, SMD105; RH73/RH74/RH104R/RH105R/RH124; CD43/54/73/75/104/105;
Individual schematic diagram: SMD power inductor Shielded power inductor
5.3 Chip ferrite beads
Type: CBG (ordinary type) Impedance: 5Ω~3KΩ
CBH (high current) Impedance: 30Ω~120Ω
CBY (peak type) Impedance: 5Ω~2KΩ
Individual schematic diagram: SMD ferrite beads SMD high current magnetic beads Specifications

: 0402/0603/0805/1206/1210/1806 (SMD magnetic beads)
Specifications: SMB302520/SMB403025/SMB853025 (SMD high current magnetic beads)
5.4 Plug-in magnetic beads
Specifications: RH3.5


Specifications ABC Impedance value (Ω)
10mHz 100mHz
RH3.5X4.7X0.8 3.5±0.15 4.7±0.3 62±2 20 45
RH3.5X6X0.8 3.5±0.15 6±0.3 62±2 25 65
RH3.5X9X0.08 3.5±0.15 9±0.3 62±2 40 105
5.5 Color ring inductor
Inductance: 0.1uH~22MH
Size: 0204, 0307, ​​0410,
0512 Bean-shaped inductor: 0.1uH~22MH
Size: 0405, 0606, 0607, 0909, 0910 Accuracy
: J=±5% K=±10%M=±20%
Accuracy: J=±5% K=±10%M=±20%
Plug-in color ring inductor Reading method: Same as the color ring resistor mark
5.6 Vertical inductor
Inductance: 0.1uH~3MH
Specifications: PK0455/PK0608/PK0810/PK0912

5.7 Axial filter inductor
Specifications: LGC0410/LGC0513/LGC0616/LGC1019
Inductance: 0.1uH-10mH.
Rated current: 65mA~10A.
High Q value, generally low price, high self-resonant frequency.

5.8 Magnetic ring inductor Specifications
: TC3026/TC3726/TC4426/TC5026
Size (unit: mm): 3.25~15.88
5.9 Air core inductor

In order to obtain a larger inductance value, air core inductors are often wound with more enameled wires, and in order to reduce the influence of the line resistance of the inductor itself on the DC current, thicker enameled wires should be used. However, in some products with smaller volumes, it is not realistic to use very heavy and large air core inductors, which not only increases the cost, but also limits the volume of the product. In order to increase the inductance value while maintaining a lighter weight, we can insert a magnetic core or an iron core into the air core inductor to increase the self-inductance of the inductor and thereby increase the inductance value. At present, most of the computers are magnetic core inductors.
VI. Application of inductors in circuits

The most common function of inductors in circuits is to form LC filter circuits together with capacitors. We already know that capacitors have the ability to "block DC and pass AC", while inductors have the function of "passing DC and blocking AC". If DC current accompanied by many interference signals passes through the LC filter circuit (as shown in the figure), then the AC interference signal will be converted into heat energy by the capacitor and consumed; when the relatively pure DC current passes through the inductor, the AC interference signal in it is also converted into magnetic induction and heat energy, and the higher frequency is most easily impedance by the inductor, which can suppress the higher frequency interference signal.
LC filter circuit

The inductor in the power supply part of the circuit board is generally composed of very thick enameled wire wrapped around a round magnetic core coated with various colors. And there are generally several tall filter aluminum electrolytic capacitors nearby, and the two together form the above-mentioned LC filter circuit. In addition, the circuit board also uses a large number of "snaking wires + chip tantalum capacitors" to form LC circuits, because the serpentine wires bend back and forth on the circuit board, which can also be regarded as a small inductor.

VII. Common magnetic cores and rings
Iron powder core series

Material: -2 (red/transparent), -8 (yellow/red), -18 (green/red), -26 (yellow/white), -28 (gray/green), -33 (gray/yellow), -38 (gray/black), -40 (green/yellow), -45 (black), -52 (green/blue); Size: outer diameter from 30 to 400D (Note: outer diameter from 7.8mm to 102mm).
Sendust series
Main u values: 60, 75, 90, 125; Size: outer diameter from 3.5mm to 77.8mm.


In addition to the main ring shape, the specifications of the two products also include E-shaped, rod-shaped, etc., and can be customized according to the various parameters provided by customers. They are widely used in computer motherboards, computer power supplies, power supplies, mobile phone chargers, lighting transformer dimmers, uninterruptible power supplies (UPS), various household appliance control panels, etc.
8. The connection and difference between inductors and magnetic beads
What is the connection and difference between inductors and magnetic beads
1. Inductors are energy storage components, while magnetic beads are energy conversion (consumption) devices
2. Inductors are mostly used in power filter circuits, and magnetic beads are mostly used in signal circuits and for EMC countermeasures
3. Magnetic beads are mainly used to suppress electromagnetic radiation interference, while inductors are used in this regard to focus on suppressing conducted interference. Both can be used to deal with EMC and EMI problems.
There are two ways of EMI, namely: radiation and conduction, and different ways use different suppression methods. The former uses magnetic beads, and the latter uses inductors.
4. Magnetic beads are used to absorb ultra-high frequency signals. Some RF circuits, PLL, oscillation circuits, and ultra-high frequency memory circuits (DDR
SDRAM, RAMBUS, etc.) all require magnetic beads to be added to the power input part. Inductors are energy storage components used in LC oscillation circuits, medium and low frequency filter circuits, etc., and their application frequency range rarely exceeds 50MHZ.
5. Inductors are generally used for circuit matching and signal quality control. General ground connection and power supply connection.
Magnetic beads are used where analog ground and digital ground are combined. Magnetic beads are also used for signal lines.
The size of the magnetic beads (or more precisely, the characteristic curve of the magnetic beads)
depends on the frequency of the interference wave that the magnetic beads need to absorb. Magnetic beads are high-frequency blocking, with low DC resistance and high high-frequency resistance. For example, 1000R@100Mhz means that there is a resistance of 1000 ohms for a 100M frequency signal. Because the unit of the magnetic bead is nominal according to the impedance it generates at a certain frequency, the unit of impedance is also ohms. The datasheet of the magnetic bead usually has a characteristic curve of frequency and impedance. Generally, 100MHz is used as the standard, for example, 2012B601 means that the impedance of the magnetic bead is 600 ohms at 100MHz.
IX. Calculation formulas for some inductances
9.1 Ring inductance
For ring CORE, the following formulas can be used: (IRON)
L=N2*AL L=Inductance (H) AL= Inductance coefficient
H-DC=0.4πNI /lN==Number of winding turns (turns)
H-DC=DC magnetizing force I=Current passing through (A) l=Magnetic path length (cm) For
l and AL values, refer to the Micrometa comparison table. For example:
With T50-52 material, winding 5 and a half turns, its L value is T50-52 (indicates OD is 0.5 inches), and its AL value is about 33nH after checking the table.
L=33*(5.5)2=998.25nH≈1μH.
When 10A current passes through, its L value change can be obtained from l=3.74 (check the table)
H-DC=0.4πNI / l =0.4×3.14×5.5×10 / 3.74 = 18.47 (after checking the table)
to understand the degree of L value drop (μi%)
9.2 Inductance calculation
Introduce an empirical formula
L=(k*μ0*μs*N2*S)/l,
where
μ0 is the vacuum permeability = 4π*10(-7). (10 to the negative seventh power)
μs is the relative magnetic permeability of the magnetic core inside the coil, μs=1 for an air-core coil
N2 is the square of the number of turns
of the coil S is the cross-sectional area of ​​the coil, in square meters
l is the length of the coil, in meters
k coefficient, which depends on the ratio of the radius (R) to the length (l) of the coil.
The unit of the calculated inductance is Henry. K value table
2 K corresponding to R/l K corresponding to 3R/l K corresponding to 3R/l K corresponding to 4R/l
0.1 0.96 0.6 0.79 2 0.52 10 0.2
0.2 0.92 0.8 0.74 3 0.43 20 0.12
0.3 0.88 1 0.69 4 0.37