Inductance is the strength of the current induced in a coil of wire when it is active in a magnetic field, and is measured in "Henrys" (H). It also refers to components made using this property.
Inductors (inductive coils) and transformers are electromagnetic induction components made of insulated wire (e.g., enameled wire, yarn-wrapped wire, etc.), and are one of the most commonly used components in electronic circuits, with related products such as ****-mode filters.
Inductors
diàn'gǎn [INDUCTOR], plural: INDUCTORS Both inductors (inductive coils) and transformers are electromagnetic sensing elements wound with insulated wires (e.g., enameled wires, yarn-coated wires, etc.), and are one of the commonly used components in electronic circuits. filters, etc.
Edit Self-inductance and mutual inductance
Self-inductance
When there is a current passing through a coil, a magnetic field is generated around the coil. When the current in the coil changes, the magnetic field around it also produces a corresponding change, this change in the magnetic field can make the coil itself produces an induced electromotive force (electromotive force is used to indicate the end voltage of the ideal power supply of the active component), which is the self-inductance.
Mutual inductance
Two inductive coils close to each other, an inductive coil of the magnetic field changes will affect the other inductive coil, this effect is mutual inductance. The size of the mutual inductance depends on the self-inductance of the inductor coils and the degree of coupling of the two inductor coils, the use of this principle made of components called mutual inductors.
Edit the role of inductors and circuit symbols
(a) the circuit symbols of inductors inductors are made of enameled wire, yarn-coated wire or plastic skinned wire, etc. in the insulating skeleton or core, the core of a group of coaxial turns in series, it is used in the circuit with the letter "L," said the left figure is the circuit symbols, the right figure is the physical picture.
(2) The role of the inductor The main role of the inductor is to isolate the AC signal, filtering, or with capacitors, resistors and other components of the harmonic inductor graphic symbols
Vibration circuit.
Types of Inductors
Categorized by structure
Inductors can be divided into wirewound inductors and non-wirewound inductors (multi-layer chip, printed inductors, etc.) according to their structure, and can also be divided into fixed inductors and adjustable inductors. According to the mounting method: there are chip inductors, plug-in inductors. At the same time on the inductor has an external shielding to become shielded inductors, coil bare Vertical, horizontal inductors
Exposed generally known as non-shielded inductors. Fixed inductors are also divided into hollow electronic watch inductors, magnetic chip inductors
Core inductors, iron core inductors, etc., according to its structural shape and pinning can also be divided into vertical inductors with the same direction of the pin, horizontal axial pin inductors, large and medium-sized inductors, small and delicate inductors and chip inductors and so on. Adjustable inductors are divided into magnetic core adjustable inductors, copper core adjustable inductors, sliding contact adjustable inductors, series mutual inductance adjustable inductors and multi-tap adjustable inductors.
Classification by operating frequency
Inductors can be divided into high frequency inductors, medium frequency inductors and low frequency inductors. Air core inductors, magnetic core inductors and copper core inductors are generally medium or high frequency inductors, while most of the iron core inductors are low frequency inductors.
Classification by application
Inductors can be divided into oscillating inductors, correction inductors, tube deflection inductors, current blocking inductors, filtering inductors, isolation Inductors
Inductors, being compensated for the inductors and so on. Oscillation inductor is divided into TV line oscillation coil, something pillow-shaped correction coil. The inductors are divided into line deflection coils and field deflection coils. Current-blocking inductor (also known as current-blocking coil) is divided into high-frequency current-blocking coil, low-frequency current-blocking coil, electronic ballast current-blocking coil, TV line frequency current-blocking coil and TV field frequency current-blocking coil and so on. Filter inductors are divided into power (industrial frequency) filter inductors and high-frequency filter inductors.
Edit the main parameters of the inductor
The main parameters of the inductor are inductance, allowable deviation, quality factor, distributed capacitance and rated current.
Inductance
Inductance, also known as the self-inductance coefficient, is a physical quantity that indicates the ability of an inductor to generate self-inductance.
The size of an inductor's inductance depends on the number of coils (turns), the winding method, the presence or absence of a magnetic core, and the material of the core, etc. Usually, the more coils there are, the more the inductance will be reduced. In general, the more turns a coil has and the more densely wound the coil is, the greater the inductance. A coil with a magnetic core has a larger inductance than a coil without a magnetic core; the larger the permeability of the magnetic core, the larger the inductance. The basic unit of inductance is the henry (Hen), which is expressed by the letter "H". Commonly used units are millihenry (mH) and microhenry (μH), the relationship between them is: 1H=1000mH 1mH=1000μH
Allowable deviation
Allowable deviation refers to the inductance of the inductors on the nominal inductance and the actual inductance of the permissible error value. Generally used in oscillation or filtering and other circuits inductors require high precision, the allowable deviation is ± 0.2% ~ ± 0.5%; while for coupling, high frequency current blocking and other coils of the accuracy requirements are not high; the allowable deviation is ± 10% ~ 15%.
Quality Factor
Quality factor, also known as Q value or superior value, is the main parameter to measure the quality of an inductor. It is the ratio of the inductance to its equivalent loss resistance when the inductor is operated at a certain frequency of AC voltage. The higher the Q value of an inductor, the lower its losses and the higher its efficiency. The quality factor of an inductor is related to the DC resistance of the coil wires, the dielectric loss of the coil skeleton, and the loss caused by the core and shield.
Distributed Capacitance
Distributed capacitance refers to the capacitance that exists between the turns of a coil and between the turns of a coil and the core. The smaller the distribution capacitance of an inductor, the better its stability.
Rated current
The rated current is the maximum value of current allowed to pass through the inductor when it has normal operation. If the operating current exceeds the rated current, the inductor will heat up and change the performance parameters, and even burn out due to overcurrent.
Related Readings on Inductors
***Modal Inductors and Iron-Based Nanocrystalline Alloys 1. Introduction With the increasing application of switching type power supplies in industrial and household appliances, mutual interference between electrical appliances is becoming an increasingly serious problem, and the electromagnetic environment is becoming more and more of a concern to people. There are many kinds of electromagnetic interference, of which ****mode interference below 30MHz is a very important class, they are mainly propagated by conduction, causing great harm to the safe and normal operation of the instrument, and must be controlled. Usually, a ***-mode filter is attached to the input to mitigate external ***-mode interference from entering the instrument through the power line, and to prevent the ***-mode interference generated by the instrument from entering the power grid. The core of the ***mode filter is a ***mode inductor with a soft magnetic core, the performance of which determines the level of the filter. 2, ***mode noise and ***mode inductor ***mode noise is mainly generated by various switching devices in the on and off, can be decomposed into different harmonic forms, has a relatively wide spectral range. For interference signals below 30MHz, it is generally propagated by conduction. The *** mode inductor consists of a soft magnetic core and two sets of coils wound in the same direction, as shown in Figure 1. For differential mode signals, since the two sets of coils produce magnetic fields in opposite directions, they cancel each other out and the iron core is not magnetized and has no suppression effect on the signal. For *** mode signals, the core is magnetized because the magnetic fields generated by the two sets of coils do not cancel each other out, but are superimposed on each other. Due to the high permeability of the core material, the core will produce a large inductance and the impedance of the coil causes the passage of the ****-mode signal to be suppressed. 3. Relationship between the performance of ****-mode inductors and material properties In order to make the ****-mode interference filtered out more effectively, ****-mode inductors should first of all have a sufficiently large inductance, and thus the core material has a high permeability is the most basic requirement for ****-mode inductors. On the other hand, the frequency characteristics of the core material is also a key factor in determining the performance of the device. Due to the *** mode interference has a wide frequency spectrum, and the core of the *** mode interference impedance only in a particular frequency band has the maximum value. Therefore, in order to filter out a certain band of ****-mode interference, the core frequency characteristics should be such that the impedance of the device in the band with the circuit behind the maximum mismatch, in order to ****-mode interference to produce a sufficiently large loss (known as insertion loss). For *** mode signals, *** mode inductance can be equated to the series connection of resistance and inductance, the total impedance of the device at this time is: where: for the real part of the core permeability caused by the inductive reactance associated with pure inductance. For the core permeability caused by the imaginary part of the loss-related impedance. l0 for the inductance of the hollow inductor. In an actual ***mode inductor, XL forms a reflection of ***mode interference, while XR is the portion that is absorbed and consumed due to core losses and so forth. Both of these parts form a suppression of ****-mode interference. Therefore, the total impedance of the ***-mode inductor core represents the device's ability to suppress ***-mode interference. Most suppliers of ****-mode inductor cores use impedance (or insertion loss when made into a device) versus frequency to represent the frequency characteristics of the product. The relationship between the permeability of a material and frequency is more complex. Generally, the real part of the permeability decreases with increasing frequency; the imaginary part of the permeability starts low, and has a peak at a certain frequency (called the cut-off frequency), and how it decreases with frequency. It should be noted that the device impedance change rule with frequency and permeability of the law is different, because the impedance in addition to determining the permeability, but also with the frequency. In general, *** mode inductor impedance and its frequency characteristics are determined by the core size, material properties, the number of turns and other factors. 4. Advantages of nanocrystalline alloys In order to get the best suppression effect on *** mode interference, *** mode inductor core must have high permeability, excellent frequency characteristics, etc. Previously, the majority of ferrite was used as the core. Ferrite is used as the core material of ****-mode inductor, which has the advantages of excellent frequency characteristics and low cost. However, ferrite also has some insurmountable weaknesses, such as poor temperature characteristics, low saturation magnetic inductance, etc., and is somewhat limited in its application. In recent years, the emergence of iron-based nanocrystalline alloys has added an excellent core material for ****-mode inductors. The manufacturing process of iron-based nanocrystalline alloys is as follows: firstly, amorphous alloy thin strip with thickness of about 20-30 microns is made by fast solidification technology, and then nanocrystals are formed after further processing by winding into iron core. Compared with ferrite, nanocrystalline alloys have some unique advantages: ? High saturation magnetic induction: the Bs of iron-based nanocrystalline alloys reaches 1.2T, which is more than twice that of ferrite. As a ****mode inductor core, an important principle is that the core can not be magnetized to saturation, otherwise the inductance decreases dramatically. In practice, there are a number of occasions where the interference intensity is large (e.g., high-power inverter motors), and if ordinary ferrite is used as a ***-mode inductor, there is a possibility of core saturation, which does not ensure noise suppression effect under large intensity interference. Due to the high saturation magnetic induction strength of nanocrystalline alloys, their anti-saturation characteristics are undoubtedly significantly better than ferrite, making nanocrystalline alloys very suitable for high-current strong interference resistance occasions. ? High initial permeability: The initial permeability of nanocrystalline alloys can reach 100,000, much higher than ferrite, so the ****mode inductors made of nanocrystalline alloys have large impedance and insertion loss in low magnetic fields, and have excellent suppression of weak interference. This is particularly suitable for weak interference ***mode filters that require very small leakage currents. In some specific cases (such as medical equipment), equipment through the ground capacitance (such as the human body) caused by the leakage current, easy to form **** mode interference, and the equipment itself is very strict requirements. At this time, the use of high permeability nanocrystalline alloys may be the best choice for the manufacture of ****-mode inductors. In addition, the high permeability of nanocrystalline alloys can reduce the number of turns of the coil, reduce the parasitic capacitance and other distribution parameters, and thus will be due to the distribution parameters caused by the insertion loss spectrum in the *** vibration peak frequency increase. At the same time, the high permeability of the nanocrystalline core allows the ****mode inductor to have a higher inductance and impedance value, or to reduce the size of the core with the same inductance. ? Excellent Temperature Stability: The Curie temperature of iron-based nanocrystalline alloys is up to 570oC or more. In the case of large temperature fluctuations, nanocrystalline alloys have a significantly lower rate of change in performance than ferrite, with excellent stability, and the change in performance is close to linear. Generally, the rate of change of the main magnetic properties of nanocrystalline alloys in the temperature interval of -50oC----130oC is within 10%. In contrast, ferrite's Curie temperature is generally below 250oC, and the rate of change of magnetic properties sometimes reaches more than 100% and is nonlinear and not easily compensated. This temperature stability of nanocrystalline alloys combined with their unique low-loss characteristics provides device designers with generous temperature conditions. ? Flexible frequency characteristics: through different manufacturing processes, nanocrystalline cores can obtain different frequency characteristics, with the appropriate number of turns of the coil can be obtained different impedance characteristics to meet the filtering requirements of different bands, and its impedance value is much higher than that of ferrite. It should be noted that any filter can not be expected to use a core material to achieve the entire frequency range of noise suppression, but should be based on the filter requirements of the filter band to select different core materials, size and number of turns, etc.. Compared with ferrite, nanocrystalline alloys can be more flexible by adjusting the process to obtain the desired frequency characteristics. Since their development in the late 1980s, iron-based nanocrystalline alloys have been widely used in switching power transformers, mutual inductors and other fields. Due to the high permeability, high saturation magnetic inductance, flexible and adjustable frequency characteristics of nanocrystalline alloys, and other advantages, in the field of anti-***mode interference filters and other areas are also becoming more and more important. Foreign countries have already existed can be supplied in large quantities of iron-based nanocrystalline alloy *** mode inductor core. With the gradual deepening of people's understanding of nanocrystalline alloys, it can be expected that their manufacturing ****-mode inductors in the domestic application prospects will be more and more broad. First, the first acquaintance *** mode inductor *** mode inductor (Common mode Choke), also known as *** mode choke, commonly used in computer switching power supply to filter *** mode of electromagnetic interference signal. In board design, **** mode inductors also play the role of EMI filtering, used to inhibit the high-speed signal lines generated by electromagnetic waves radiated to the outside. Various CMC Knowledge: EMI (Electro Magnetic Interference) The motherboard inside the computer is mixed with a variety of high-frequency circuits, digital circuits and analog circuits, which produce a large number of high-frequency electromagnetic waves interfere with each other, which is EMI. EMI will also be emitted through the motherboard wiring or external cable, resulting in electromagnetic radiation pollution, not only affecting other electronic equipment, but also the impact of EMI filtering. Pollution, not only affect the normal work of other electronic equipment, but also harmful to the human body. PC board chip in the work process is both an electromagnetic interference object, but also a source of electromagnetic interference. In general, we can divide these electromagnetic interference into two categories: serial mode interference (differential mode interference) and **** mode interference (grounding interference). To the motherboard on the two PCB alignments (connecting the motherboard components of the wire) as an example, the so-called series mode interference, refers to the interference between the two alignments; and *** mode interference is the two alignments and PCB ground potential difference between the interference caused by the ground. Serial mode interference current acting between the two signal lines, the direction of conduction and waveform and signal current; *** mode interference current acting between the signal line and ground, interference current in each of the two signal lines flow through one-half and the same direction, and to the ground as a common **** circuit. Serial and ****-mode interference If the ****-mode current generated by the board is not attenuated and filtered (especially the ****-mode current on high-speed interface alignments such as USB and IEEE 1394 interfaces), then the ****-mode interference current can easily pass through the interface data lines and generate electromagnetic radiation - ****-mode radiation in the cable due to the ****-mode current. The U.S. FCC, the International Radio Interference Special Committee's CISPR22 and China's GB9254 and other standards and specifications for information technology equipment communication ports ****-mode conducted interference and radiated emissions have relevant limitations on the requirements. In order to eliminate the signal line input interference signal and induction of various interference, we must reasonably arrange the filter circuit to filter *** mode and series mode interference, *** mode inductor is a component of the filter circuit. *** mode inductor is essentially a two-way filter: on the one hand, to filter out the signal line *** mode electromagnetic interference, on the other hand, to inhibit itself from sending out electromagnetic interference, to avoid affecting the normal operation of other electronic equipment in the same electromagnetic environment. *** mode inductor internal circuit diagram The above figure is our common *** mode inductor internal circuit diagram, in the actual circuit design, can also use multi-level *** mode circuit to better filter out electromagnetic interference. In addition, we can also see a chip-type ****mode inductor on the motherboard, whose structure and function are almost the same as the vertical ****mode inductor.
SMT CMC
Two, from the working principle of **** mode inductor Why **** mode inductor can prevent EMI?To figure this out, we need to analyze the structure of **** mode inductor from the beginning. ***mode inductor filter circuit The above figure contains ***mode inductor filter circuit, La and Lb is ***mode inductor coil. These two coils are wound on the same core with the same number of turns and phase (wound in reverse). In this way, when the normal current in the circuit flows through the ****-mode inductor, the current in the same phase winding of the inductor coil to produce a reversed magnetic field and cancel each other, at this time, the normal signal current is mainly affected by the coil resistance (and a small amount of leakage due to the damping caused by the inductance); when there is a ****-mode current flows through the coil, due to the isotropic ****-mode current, the coil will be generated inside the same direction of the magnetic field and increased inductance reactance, so that the The coil shows high impedance and produces a strong damping effect, which attenuates the ****-mode current and achieves the purpose of filtering.
In fact, by connecting one end of the filter circuit to the interference source and the other end to the interfered device, La and C1, Lb and C2 form two sets of low-pass filters, which can make the ****-mode EMI signal on the line be controlled at a very low level. The circuit can not only inhibit the incoming external EMI signals, but also attenuate the line itself when the work of the EMI signals generated, can effectively reduce the intensity of EMI interference.
Trivia: Leakage and Differential Mode Inductance For an ideal inductance model, when the coil is wound, all the magnetic flux is concentrated within the center of the coil. However, typically toroidal coils are not wound all the way around, or are not wound tightly, which can cause flux leakage. The ***mode inductor has two windings with a considerable gap between them, which causes flux leakage and creates a differential mode inductor. Therefore, ***mode inductors generally also have some ability to attenuate differential mode interference.
In filter design, we can also utilize leakage inductance. Such as in the ordinary filter, only a ****-mode inductor installed, the use of ****-mode inductor leakage inductance to generate the appropriate amount of differential mode inductance, to play the role of the inhibition of the differential mode current. Sometimes, it is also necessary to artificially increase the leakage inductance of the ****-mode choke to increase the amount of differential mode inductance to achieve a better filtering effect.
From looking at the overall design of the board to seeing the ****mode inductor on some motherboards, we can see the ****mode inductor, but on most motherboards, we will find that the component has been omitted, and some do not even have the location reserved. Such motherboards, qualified?
It is undeniable that the ****mode inductor on the motherboard's high-speed interface ****mode interference has a very good inhibition, can effectively avoid EMI through the cable to form electromagnetic radiation affecting the rest of the peripheral's normal work and our physical health. But also need to point out that the board's anti-EMI design is a fairly large and systematic project, the use of *** mode inductor design is only a small part of it. Boards with *** mode inductor design at the high-speed interface do not necessarily have an excellent overall anti-EMI design. Therefore, from the *** mode filter circuit we can only see one aspect of the board design, which is easy to be ignored by everyone, to make the mistake of not seeing the forest for the trees. Only after understanding the overall anti-EMI design of the board, we can evaluate the advantages and disadvantages of the board. So, what does a good board design generally do in terms of anti-EMI performance?
● Motherboard Layout (wiring) design For excellent motherboard wiring design, most of the clock alignments will be shielded or close to the ground to reduce EMI. multilayer PCB design, in the adjacent PCB alignment layer will be used to open the ring principle, the wire from one layer to another layer, in the design of the wire will be avoided to form a ring. If the alignment constitutes a closed loop, it plays the role of an antenna, which will enhance the intensity of EMI radiation.
The unequal length of the signal lines will also cause the impedance of the two lines to be unbalanced and form a ****-mode interference, therefore, in the board design, the signal lines will be processed in a serpentine manner to make their impedance as consistent as possible, to weaken the ****-mode interference. At the same time, serpentine wiring will also minimize the bending of the pendulum to reduce the area of the ring area, thereby reducing the intensity of radiation.
Snake routing for motherboards
In high-speed PCB design, the length of the alignment is generally not an integer multiple of 1/4 of the wavelength of the clock signal, otherwise it will resonate and generate severe EMI radiation. At the same time, the alignment should ensure that the return path is minimal and smooth. The design of decoupling capacitors, their settings should be close to the power supply pins, and capacitance of the power supply alignment and the area surrounded by the ground line should be as small as possible, so as to reduce the power supply ripple and noise, reduce EMI radiation. Of course, the above is only a small part of the principles of PCB anti-EMI design. Layout design of the motherboard is a very complex and profound study, and even many DIYers have this **** knowledge: Layout design is excellent or not, the overall performance of the motherboard has a very significant impact.
●The motherboard's wiring is cut off If you want to completely isolate the motherboard's circuits from each other, this is absolutely impossible, because we have no way to "wrap" the electromagnetic interference one by one, so we have to use other methods to reduce the degree of interference. Motherboard PCB in the metal wire is the main culprit in the transmission of interference current, it is like an antenna to transmit and emit electromagnetic interference signals, so in the right place "cut off" these "antenna" is a useful anti-EMI method. The "antenna" is broken, and then surrounded by a circle of insulator, it will greatly reduce the natural interference to the outside world. If the use of filter capacitors at the breakout point can also be further reduced electromagnetic radiation leakage. This design can significantly increase the stability of high-frequency operation and prevent the generation of EMI radiation, many major motherboard manufacturers have used this method in their designs. Calculation formula of inductance: Load the inductance according to the following formula: Coil formula Impedance (ohm) = 2 * 3.14159 * F (operating frequency) * Inductance (mH), set the need to use 360ohm impedance, so: Inductance (mH) = Impedance (ohm) ÷ (2*3.14159) ÷ F (operating frequency) = 360 ÷ (2*3.14159) ÷ 7.06 = 8.116mH Accordingly, we can calculate the number of coils: Number of Coils = [Inductance * { ( 18*Circle Diameter in inches) + ( 40 *Circle Length in inches)}] ÷ Circle Diameter in inches Number of Coils = [8.116 * {(18*2.047) + (40*3.74)}] ÷ 2.047 = 19 Coils Air Core Inductance Formula Air Core Inductance Calculation formula: L (mH) = (0.08) D.D.N.N)/(3D+9W+10H) D------ Coil Diameter N------ Coil Turns d----- Wire Diameter H---- Coil Height W---- Coil Width The unit is millimeter and mH respectively. Calculation formula for hollow coil inductance: l=(0.01*D*N*N)/(L/D+0.44) Coil inductance l unit: microhenry Coil diameter D unit: cm Coil turns N unit: turns Coil length L unit: cm Frequency inductance-capacitance calculation formula: l=25330.3/[(f0*f0)*c] Frequency of operation: f0 unit: MHZ The unit of this problem f0= 125KHZ = 0.125 resonance capacitance: c unit: PF This problem Jianyi c = 500... ...1000pf can be decided by yourself first. .1000pf can be decided by yourself, or by the Q value of the resonant inductance: l unit: microhenry coil inductance formula 1. for the ring CORE, there are the following formulas can be used: (IRON) L = N2.AL L = inductance (H) H-DC = 0.4πNI / l N = number of turns of the coil (circle) AL = coefficient of inductance H-DC = dc magnetizing force I = current (A) l = length of magnetic circuit (cm) = Length of magnetic circuit (cm) l and AL value, please refer to Micrometal comparison table. For example: T50-52 material, coil 5 ? turns, its L value for T50-52 (that is, OD for 0.5 inches), after checking the table, its AL value of about 33nH L = 33 ．(5.5)2 = 998.25nH ≈ 1 μH When the current flowed through the 10A, the change in the value of the L value can be from the l = 3.74 (check the table) H-DC = 0.4 πNI / l = 0.4 × 3.14 × 5.5 × 10 / 3.5 × 10 / 3.5 μH 5.5×10 / 3.74 = 18.47 (after checking the table) that is, we can understand the degree of decrease in the L value (μi%) 2. Introduce an empirical formula L = (k * μ0 * μs * N2 * S) / l where μ0 is the vacuum permeability = 4π * 10 (-7). (minus seven times 10) μs for the relative permeability of the core inside the coil, hollow coil when μs = 1 N2 for the square of the number of coils S cross-sectional area of the coil in square meters l length of the coil in meters k coefficient, depending on the radius of the coil (R) and the length of the coil (l) of the ratio. The unit of the calculated inductance is Henry (H).