an Inductor is an element that can convert electric energy into magnetic energy and store it. The structure of inductor is similar to that of transformer, but there is only one winding. Inductor has a certain inductance, which only hinders the change of current. If the inductor is in a state where no current passes, it will try to block the current from flowing through it when the circuit is turned on; If the inductor is in the state of current flowing, it will try to keep the holding current constant when the circuit is disconnected. Inductors are also called chokes, reactors and dynamic reactors. Chinese name: Inductor mbth: inductor alias: choke, reactor, dynamic reactor function: converting electric energy into magnetic energy and storing it essence: electronic component function: preventing the change and development of current, structure, inductance classification, self-inductor, transformer, common types, small inductor, adjustable inductor, choke inductor, Characteristics, inductance measurement, circuit diagram, good or bad judgment, matters needing attention, function and use, patch inductance, main parameters, inductance, allowable deviation, rated current, calculation formula, inductance unit, the connection and difference between inductance and magnetic beads, the most primitive inductor in the development process is the iron core coil used by M Faraday in England in 1831 to discover electromagnetic induction. In 1832, J. Henry of the United States published a paper on self-induction. People call the unit of inductance Henry for short. In the mid-19th century, inductors were actually used in telegraph, telephone and other devices. In 1887, H.R. Hertz in Germany, and in 189, N. Tesla in the United States used very famous inductors, which were called Hertz coil and Tesla coil respectively. Structural inductors are generally composed of skeleton, winding, forbidden cover, packaging material, magnetic core or iron core. 1. Skeleton generally refers to the bracket for winding coils. Some large fixed inductors or adjustable inductors (such as oscillating coils, choke coils, etc.) mostly wrap enameled wires (or yarn-wrapped wires) around the skeleton, and then put the magnetic core, copper core and iron core into the inner cavity of the skeleton to improve their inductance. Skeletons are usually made of plastic, bakelite and ceramics, and can be made into different shapes according to actual needs. Small inductors (such as color-coded inductors) generally do not use the skeleton, but directly wind the enameled wire around the core. Air-core inductors (also known as bare coils or air-core coils, which are mostly used in high-frequency circuits) don't need magnetic cores, skeletons and forbidden covers, but they are wound around the mold before taking off the mold, and the coils are separated by a certain distance. 2. Winding refers to a set of coils with specified functions, which is the basic component of an inductor. Winding can be divided into single layer and multi-layer. Single-layer winding has two forms: dense winding (when the wires are wound one by one) and indirect winding (when the wires are wound at a certain distance); There are many kinds of multilayer windings, such as layered flat winding, random winding and honeycomb winding. 3. Cores and magnetic bars Cores and magnetic bars are generally made of materials such as nickel-zinc ferrite (NX series) or manganese-zinc ferrite (MX series), which have various shapes such as I-shaped, cylindrical, hat-shaped, E-shaped, and can-shaped. 4. Iron core materials mainly include silicon steel sheet, permalloy, etc., and their shapes are mostly "E" type. 5. Forbidden Cover In order to prevent the magnetic field generated by some inductors from affecting the normal work of other circuits and components, a metal screen cover (such as transistor radio's oscillating coil) was added. The inductor with forbidden shield will increase the loss of the coil and reduce the Q value. 6, packaging materials Some inductors (such as color code inductors, color ring inductors, etc.) are wound, and the coil and core are sealed with packaging materials. The packaging material is plastic or epoxy resin. The inductance of copper coil is the ratio of alternating magnetic flux generated around the inside of the conductor when alternating current passes through the conductor, and the magnetic flux of the conductor to the current that produces this magnetic flux. When DC current passes through the inductor, only a fixed magnetic field line appears around it, which does not change with time; The copper coil will present a time-varying magnetic field around it when alternating current passes through it. According to Faraday's law of electromagnetic induction-magnetic induction, the induced potential will be generated at both ends of the changing magnetic field lines, which is equivalent to a "new power supply". When a closed loop is formed, this induced potential will generate an induced current. According to Lenz's law, it is known that the total amount of magnetic field lines generated by induced current should try to prevent the change of magnetic field lines. The change of magnetic field lines comes from the change of external alternating power supply, so from the objective effect, the inductance coil has the characteristic of preventing the current change in AC circuit. Inductive coil has similar characteristics to inertia in mechanics, and it is named "self-induction" in electricity. Usually, sparks will occur at the moment when the knife switch is opened or turned on, which is caused by the high induced potential. In short, when the inductance coil is connected to the AC power supply, the magnetic field lines inside the coil will change with the alternating current at all times, resulting in electromagnetic induction of the coil. This electromotive force generated by the change of the current of 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 inductance coil and has nothing to do with the applied current. Substitution principle: 1. Inductor coil must be substituted with original value (equal number of turns and same size). 2. The patch inductors only need to be the same size, and they can also be replaced by Ω resistors or wires. Inductance-classified self-inductor: When a current passes through the coil, a magnetic field will be generated around the coil. When the current in the coil changes, the magnetic field around it also changes correspondingly. This changing magnetic field can make the coil itself produce induced electromotive force (electromotive force is used to represent the terminal voltage of the ideal power supply of the active element), which is self-induction. An electronic component with a certain number of turns and a certain amount of self-inductance or mutual inductance, which is formed by winding wires, is often called an inductance coil. In order to increase inductance, improve quality factor and reduce volume, iron cores or cores made of ferromagnetic materials are often added. The basic parameters of an inductor include inductance, quality factor, inherent capacitance, stability, passing current and operating frequency. An inductor composed of a single coil is called a self-inductor, and its self-inductance is also called the self-inductance coefficient. When two inductance coils of a transformer are close to each other, the change of magnetic field of one inductance coil will affect the other inductance coil, which is mutual inductance. The magnitude of mutual inductance depends on the degree of coupling between the self-inductance of the inductance coil and the two inductance coils, and the components made by using this principle are called transformers. Common types of inductors can be made of conductive materials wound around magnetic cores, such as copper wires, or the magnetic cores can be removed or replaced with ferromagnetic materials. The core material with higher permeability than air can confine the magnetic field more tightly around the inductance element, thus increasing the inductance. There are many kinds of inductors, most of which are made of enamel coated wire around ferrite spool, while some protective inductors completely place the coil in ferrite. The cores of some inductive elements can be adjusted. So that that size of the inductance can be chan. Small inductance can be etched directly on PCB, using a method of laying spiral track. Small-value inductors can also be manufactured in integrated circuits by the same process as transistors. In these applications, aluminum interconnects are often used as conductive materials. No matter what method is used, the circuit called "rotator" is the most widely used based on practical constraints. It uses a capacitor and active components to show the same characteristics as inductive components. Inductive elements for high frequency isolation are often made of a metal wire passing through a magnetic column or bead. Small inductor Small fixed inductor is usually made by winding enameled wire directly on the magnetic core, which is mainly used in circuits such as filtering, oscillation, trap, delay, etc. It has two packaging forms: sealed and unsealed, and both forms have vertical and horizontal external structures. 1. Vertical sealed fixed inductor The vertical sealed fixed inductor adopts the same direction pin. The domestic inductance range is .1~22μH (directly marked on the shell), the rated working current is .5~1.6A, and the error range is 5% ~ 1%. The imported inductance and current range is larger, but the error is smaller. TDK series color-coded inductors are imported, and the inductance is marked on the surface of the inductor with color dots. 2. Horizontal sealed fixed inductor The horizontal sealed fixed inductor adopts axial pin, and there are LG1.LGA and LGX series made in China. The inductance range of LG1 series inductors is .1 ~ 22, μ h (directly marked on the shell). LGA series inductors are of ultra-miniature structure, similar in appearance to 1/2W color ring resistors, with inductance range of .22~1μH (marked on the shell with color ring) and rated current of .9~.4A. LGX series color-coded inductors are also small package structures, with inductance ranging from .1 to 1, μ h and rated current of 5mA, 15mA, 3mA and 1.6A. Adjustable inductors commonly used adjustable inductors include transistor radio oscillating coil, TV line oscillating coil, line linear coil, intermediate frequency trap coil, audio frequency compensation coil, wave blocking coil, etc. 1. Oscillating coil for transistor radio: This oscillating coil, together with a variable capacitor, forms a local oscillation circuit in the transistor radio, which is used to generate a local oscillation signal that is 465kHz higher than the radio signal received by the input tuning circuit. Its exterior is a metal forbidden cover, and its interior is composed of nylon lining frame, I-shaped core, magnetic cap and pin seat, etc. The I-shaped core is wound with high-strength enameled wire. The magnetic cap is installed on the nylon frame in the forbidden cover and can rotate up and down. The inductance of the coil can be changed by changing its distance from the coil. The internal structure of intermediate frequency trap coil of TV set is similar to that of oscillating coil, except that the magnetic cap can adjust the core. 2. Line oscillating coil for TV set: The line oscillating coil was used in early black-and-white TV sets, and it formed a self-excited oscillation circuit (three-point oscillator or intermittent oscillator, multivibrator) with peripheral resistance-capacitance elements and line oscillating transistors to generate a rectangular pulse voltage signal with a frequency of 15625HZ. The center of the magnetic core of the coil has a square hole, and the line synchronization adjusting knob is directly inserted into the square hole. By turning the line synchronization adjusting knob, the relative distance between the magnetic core and the coil can be changed, thus changing the inductance of the coil, keeping the line oscillation frequency at 15625HZ and generating synchronous oscillation with the line synchronization pulse sent by the automatic frequency control circuit (AFC). 3. Line linear coil: Line linear coil is a kind of nonlinear magnetic saturation inductance coil (its inductance decreases with the increase of current), which is generally connected in series in the loop of line deflection coil, and its magnetic saturation characteristics are used to compensate the linear distortion of the image. The linear coil is made of enameled wire wound on an I-shaped ferrite high-frequency core or ferrite bar, and an adjustable permanent magnet is installed next to the coil. By changing the relative position between the permanent magnet and the coil, the inductance of the coil is changed, so as to achieve the purpose of linear compensation. Choke inductor Choke inductor refers to the inductance coil used to block the AC current path in the circuit, which is divided into high-frequency choke coil and low-frequency choke coil. 1. High-frequency choke coil: High-frequency choke coil is also called high-frequency choke coil, which is used to prevent high-frequency AC current from passing through. The high-frequency choke coil works in the high-frequency circuit, and usually adopts hollow or ferrite high-frequency cores. The skeleton is made of ceramic material or plastic, and the coil is wound in sections by honeycomb or multi-layer flat winding. 2. Low-frequency choke coil: Low-frequency choke coil, also known as low-frequency choke coil, is used in current circuit, audio circuit or field output circuit to prevent low-frequency AC current from passing through. Generally, the low-frequency choke coil used in audio circuit is called audio choke coil, the low-frequency choke coil used in field output circuit is called field choke coil, and the low-frequency choke coil used in current filter circuit is called filter choke coil. The low-frequency choke coil generally adopts "E"-shaped silicon steel sheet core (commonly known as silicon steel sheet core), permalloy core or iron oxide core. In order to prevent magnetic saturation caused by large DC current, proper gap characteristics should be left in the core during installation. The characteristics of inductor are just the opposite to those of capacitor, which has the characteristics of preventing AC from passing and allowing DC to pass smoothly. When the DC signal passes through the coil, the resistance is the resistance of the wire itself, and the voltage drop is very small; When AC signal passes through the coil, self-induced electromotive force will be generated at both ends of the coil, and the direction of self-induced electromotive force is opposite to the direction of applied voltage, which hinders the passage of AC. Therefore, the characteristics of inductor are to pass DC and block AC, and the higher the frequency, the greater the coil impedance. Inductors often work with capacitors in circuits to form LC filters, LC oscillators, etc. In addition, people also use the characteristics of inductance to manufacture choke coils, transformers, relays and so on. Direct current: It means that the inductor is closed to direct current. If the resistance of the inductor coil is not taken into account, the direct current can pass through the inductor "unimpeded". For direct current, the resistance of the coil itself has little obstacle to direct current, so it is often ignored in circuit analysis. Alternating current resistance: When alternating current passes through the inductor coil, the inductor has a blocking effect on alternating current, and it is the inductance of the inductor coil that blocks alternating current. Inductance measurement There are two kinds of instruments for inductance measurement: RLC measurement (resistance, inductance and capacitance can be measured) and inductance measuring instrument. Measurement of inductance: no-load measurement (theoretical value) and measurement in actual circuit (actual value). Because there are too many practical circuits used in inductors, it is difficult to enumerate them. Only the measurement under no-load condition can be explained. Measurement steps of inductance (RLC measurement): 1. Be familiar with the operating rules (instructions for use) and precautions of the instrument. 2. Turn on the power supply and prepare for 15-3 minutes. 3. Select L gear and measure inductance. 4. Clip the two clips together and reset them to zero. 5. Clamp the two clamps at both ends of the inductor respectively, read the value and record the inductance. 6. Repeat steps 4 and 5 and record the measured values. There must be 5-8 data. 7. Compare several measured values: if the difference is not big (.2uH), take the average value and remember the theoretical value of inductance; If the difference is too large (.3uH), repeat step 2-step 6 until the theoretical value of inductance is obtained. The inductance parameters that can be measured by different instruments are different. Therefore, before making any measurement, be familiar with the measuring instrument used, understand what the instrument can do, and then follow the operating instructions it gives you. Marking method of circuit diagram 1. Direct marking method: The main parameters such as inductance, allowable error and maximum working current of the inductance coil are directly marked with numbers and words on the shell of the inductance coil. Inductor 2, color code method: color code method: that is, the color ring is used to represent the inductance, the unit is mH, the first two digits represent the significant number, the third digit represents the magnification, and the fourth digit represents the error. Good or bad judgment 1. Inductance measurement: set the multimeter to the buzzer diode, put the stylus on the two pins, and see the reading of the multimeter. 2. Good or bad judgment: The reading of the patch inductance should be zero at this time. If the multimeter reading is too large or infinite, it means that the inductance is damaged. For inductance coils with more turns and smaller wire diameter, the reading will reach tens to hundreds. Usually, the DC resistance of the coil is only a few ohms. The damage is characterized by burning or obvious damage to the inductor magnetic ring.