Complete works of inductance details

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 stop the current from flowing when the circuit is connected; If the inductor is in a state of current flow, it will try to keep the 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: Convert electric energy into magnetic energy and store it Essence: Electronic component Function: Prevent the change and development of current, structure, inductance classification, self-inductance, transformer, common types, small inductance, adjustable inductance, choke inductance, characteristics, inductance measurement, circuit diagram, good or bad judgment, precautions, functions and uses, and patches. Rated current, calculation formula, inductance unit, connection and difference between inductance and magnetic beads, and the most original inductance in the development process is 183 1 year iron core coil used by M Faraday in Britain. 1832, J. Henry of the United States published a paper on self-induction. People call the unit of inductance Henry for short. /kloc-in the middle of the 0/9th century, inductors were actually used in telegraph, telephone and other equipment. 1887 German H.R. Hertz, 1890 American N. Tesla used very famous inductors in the experiment, called Hertz coil and Tesla coil respectively. Structural inductance is generally composed of skeleton, winding, forbidden cover, packaging material, magnetic core or iron core. 1, skeleton skeleton generally refers to the bracket for winding coils. Some large fixed inductors or adjustable inductors (such as oscillating coils and chokes). ) The enameled wire (or yarn wrapped wire) is wound around the skeleton, and then the magnetic core, copper core and iron core are put into the inner cavity of the skeleton to improve its 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 on the iron core. Air-core inductance (also known as bare coil or air-core coil, which is mostly used in high-frequency circuits) does not need magnetic core, skeleton and cover, but is wound on the mold before demoulding, with a certain distance between coils. 2. Winding refers to a group of coils with specific functions, which is the basic component of inductor. Winding can be divided into single layer and multilayer. There are two forms of single-layer winding: dense winding (wires are wound one by one) and indirect winding (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. Magnetic cores and bars Magnetic cores and bars are generally made of materials such as nickel-zinc ferrite (NX series) or manganese-zinc ferrite (MX series), and have various shapes such as I-shaped, cylindrical, hat-shaped, e-shaped, and can-shaped. 4. Iron core materials mainly include silicon steel sheet and permalloy. Its shape is mostly "E". 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 shielding cover (such as the oscillating coil of a transistor radio) is added. Inductor with forbidden shield will increase the loss of coil and reduce Q value. 6. Some inductances of packaging materials (such as color code inductance and color ring inductance). ) and seal the coil and core with packaging material. The packaging material is plastic or epoxy resin. The inductance of a copper coil is the ratio of the alternating magnetic flux generated around the conductor to the magnetic flux of the conductor and the current that generates this magnetic flux when alternating current passes through the conductor. When DC current passes through the inductor, only a fixed magnetic field line appears around it, which does not change with time; When alternating current passes through a copper coil, a time-varying magnetic field will be generated around it. According to Faraday's law of electromagnetic induction-magnetic induction, an 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, the total amount of magnetic field lines generated by induced current should be prevented from changing as much as possible. The change of magnetic field lines comes from the change of external AC power supply, so from the objective effect, the inductance coil has the characteristic of preventing the current change in AC circuit. Induction coil has similar inertia characteristics in mechanics and is named "self-inductance" in electricity. Sparks usually occur at the moment when the knife switch is turned on or off, which is caused by the high induced potential. In short, when the inductance coil is connected to AC power supply, the magnetic field lines inside the coil will change with AC power at any time, resulting in electromagnetic induction of the coil. This electromotive force generated by the current change of the coil itself is called "self-induced electromotive force". It can be seen that inductance is only a parameter related to the number of turns, size, shape and medium of the coil. It measures the inertia of the inductor coil, regardless of the applied current. Substitution principle: 1, the inductance coil must be replaced by the original value (the number of turns is equal and the size is the same). 2. The patch inductors only need to be the same size, and they can also be replaced by 0 Ω resistors or wires. Inductance classification self-inductor: When the 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 changes accordingly. 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 active components), which is self-induction. An electronic component with a certain number of turns and a certain self-inductance or mutual inductance, which is formed by winding wires, is usually called an inductance coil. In order to increase inductance, improve quality factor and reduce volume, iron cores or iron cores made of ferromagnetic materials are often added. The basic parameters of inductor include inductance, quality factor, inherent capacitance, stability, passing current and working frequency. The inductance composed of a single coil is called self-inductor, and its self-inductance is also called self-inductance coefficient. When two inductors of a transformer are close to each other, the magnetic field change of one inductor will affect the other inductor, which is mutual inductance. The magnitude of mutual inductance depends on the self-inductance of the inductance coil and the coupling degree of 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, such as copper wires, wound around the magnetic core, or the magnetic core can be removed or replaced with ferromagnetic materials. The core material with higher magnetic permeability than air can confine the magnetic field more tightly around the inductive element, thus increasing the inductance. There are many kinds of inductors, most of which are wound on ferrite spools with enameled wires, while some protective inductors completely put the coils in ferrite. The magnetic cores of some inductive elements are adjustable. So that that size of the inductance can be chan. Small inductors can be directly etched on PCB by laying spiral tracks. 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, based on actual constraints, the circuit called "rotator" is the most widely used. It uses a capacitor and an active element to show the same characteristics as an inductive element. Inductive elements used for high frequency isolation are usually made of metal wires passing through magnetic columns or beads. Small inductance and small fixed inductance are usually made of enameled wire directly wound on the magnetic core, which is mainly used in circuits such as filtering, oscillation, trap and delay. It has two packaging forms: sealed and unsealed, both of which have vertical and horizontal external structures. 1, vertical sealed fixed inductor The vertical sealed fixed inductor adopts the same direction pin, and the domestic inductance range is 0. 1~2200μH (directly marked on the shell), the rated working current is 0.05~ 1.6A, and the error range is 5% ~ 10%. The range of imported inductance is. Imported TDK series color-coded inductors are marked with color dots on the surface of the inductors. 2. Horizontal seal fixed inductor The horizontal seal fixed inductor adopts axial pin, with LG 1. LGA and LGX series made in China. The inductance range of LG 1 series inductors is 0. 1~22000μH (directly marked on the shell). LGA series inductors are subminiature structures, which are similar in appearance to 1/2W color ring resistors. The inductance range is 0.22~ 100μH (marked on the shell by color ring), and the rated current is. LGX series color code inductors are also of small package structure, with the inductance range of 0. 1 ~ 10000μh and rated current of 50mA, 150mA, 300mA,1.6a. The commonly used adjustable inductors are transistor radio oscillation coil, TV line oscillation coil and line. 1. Oscillating coil of transistor radio: This oscillating coil, together with the variable capacitor in transistor radio, forms a local oscillator circuit for generating a local oscillator signal 465kHz higher than the radio signal received by the input tuning circuit. Its exterior is a metal shield, and its interior is composed of nylon lining frame, I-shaped iron core, magnetic cap, needle seat and so on. I-shaped iron 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 the intermediate frequency trap coil of TV is similar to that of the oscillating coil, except that the magnetic cap can adjust the magnetic core. 2. Line oscillating coil for TV: Line oscillating coil was used in early black-and-white TV. It forms a self-excited oscillation circuit (three-point oscillator or intermittent oscillator, multivibrator) with peripheral resistance-capacitance elements and linear oscillation transistors, and is used to generate a rectangular pulse voltage signal with the frequency of 15625HZ. There is a square hole in the center of the magnetic core of the coil, and the line synchronization adjustment knob is directly inserted into the square hole. By turning the line synchronization adjustment 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 beside 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 choke choke refers to the inductance coil used to block the AC current path in the circuit, which is divided into high-frequency choke and low-frequency choke. 1, high-frequency choke: high-frequency choke, also known as high-frequency choke, is used to prevent high-frequency AC current from passing through. High-frequency chokes work in high-frequency circuits, and usually use 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 multilayer flat winding method. 2. Low-frequency choke: Low-frequency choke, also known as low-frequency choke, is used in current circuit, audio circuit or field output circuit to prevent low-frequency AC current from passing through. The low-frequency choke used in general audio circuit is called audio choke, the low-frequency choke used in field output circuit is called field choke, and the low-frequency choke used in current filter circuit is called filter choke. Low-frequency chokes generally use "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, appropriate gap characteristics should be left in the iron core during installation. The characteristics of inductance are just the opposite of capacitance, which has the characteristics of preventing alternating current 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 characteristic of inductance is to block AC through DC. The higher the frequency, the greater the coil impedance. Inductance usually forms LC filter, LC oscillator, etc. together with capacitance in the circuit. In addition, people also use the characteristics of inductance to make chokes, transformers, relays and so on. DC: Indicates that the inductance is close to DC. If the resistance of the inductor coil is not considered, the direct current can pass through the inductor "unimpeded". For direct current, the resistance of the coil itself has little influence on direct current, so it is often ignored in circuit analysis. Alternating current resistance: when alternating current passes through the inductance coil, the inductance has a blocking effect on alternating current, and it is the inductance of the inductance coil that blocks alternating current. Inductance measurement There are two kinds of instruments for inductance measurement: RLC measurement (which can measure resistance, inductance and capacitance) 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 list them one by one. It can only explain the measurement under no-load condition. Measurement steps of inductance (RLC measurement): 1. Be familiar with the operating procedures (instructions for use) and precautions of the instrument. 2. Turn on the power and prepare for 15-30 minutes. 3. Select L gear and measure the inductance. 4. Clamp 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 (0.2uH), take the average value and remember the theoretical value of inductance; If the difference is too large (0.3uH), repeat steps 2- 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, know what the instrument can do, and then follow the operating instructions it gives you. Marking method of circuit diagram 1 and direct marking method: the main parameters such as inductance, allowable error and maximum working current of the inductor coil are directly marked on the shell of the inductor coil with numbers and words. Inductance 2, color coding method: color coding method: that is, the color ring represents 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 at the buzzer diode, put the stylus on the two pins, and see the reading of the multimeter. 2. Good or bad judgment: At this time, the reading of patch inductance should be zero. If the multimeter reading is too large or infinite, the inductance is damaged. For inductance coils with more turns and smaller wire diameter, the readings will reach tens to hundreds. Usually, the DC resistance of a coil is only a few ohms. Damage is manifested as burn or obvious damage to the magnetic ring of the inductor. If the inductance coil is not seriously damaged and cannot be determined, the inductance can be measured by inductance meter or judged by replacement method. Precautions 1. Inductive components, whose cores and windings are prone to inductance changes due to temperature rise effect, should pay attention to its body temperature must be within the scope of use specifications. Second, the winding of the inductor is easy to form an electromagnetic field after the current passes. When placing components, it is necessary to keep adjacent inductors away from each other or the winding groups at right angles to each other to reduce mutual inductance. 3. Gap capacitance will also occur between the windings of the inductor, especially between multiple turns of thin wires, which will cause high-frequency signal bypass and reduce the actual filtering effect of the inductor. Fourthly, when measuring inductance and Q value with an instrument, in order to obtain correct data, the test lead should be as close as possible to the component body ... Functional inductance mainly plays the roles of filtering, oscillation, delay and notch in the circuit, as well as shielding signals, filtering noise, stabilizing current and suppressing electromagnetic interference. The most common function of inductance in circuit is to form LC filter circuit with capacitance. Capacitors have the characteristics of "DC resistance and AC resistance", while inductors have the functions of "DC resistance and AC resistance". If DC with more interference signals passes through LC filter circuit, AC interference signals will be converted into heat energy by inductance and consumed; When 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 interference signal with higher frequency. Inductor has the characteristics of preventing alternating current from passing and allowing direct current to pass smoothly. The higher the frequency, the greater the coil impedance. Therefore, the main function of inductance is to isolate and filter AC signals or form a resonant circuit with capacitors and resistors. Patch inductor is an electromagnetic induction element wound with insulated wire. Belonging to common inductive elements. The function of patch inductor is to transfer DC resistance to alternating current. This is a simple statement, that is, isolate and filter the AC signal or form a resonant circuit with capacitors and resistors. Function of tuning frequency-selective inductor: inductance coil and capacitor can be connected in parallel to form LC tuning circuit. Any current of the patch inductance in the circuit will produce a magnetic field, and the magnetic flux of the magnetic field will act on the circuit. When the current flowing through the patch inductor changes, the DC potential generated in the patch inductor will prevent the current from changing. When the current passing through the inductor coil increases, the self-induced electromotive force generated by the inductor coil is opposite to the current direction, which prevents the current from increasing, and at the same time, part of the electric energy is converted into magnetic field energy and stored in the inductor; When the current flowing through the inductance coil decreases, the self-induced electromotive force is in the same direction as the current, which prevents the current from decreasing and releases the stored energy to compensate for the current decrease. Therefore, after inductive filtering, not only the pulsation of load current and voltage is reduced, but also the waveform becomes smooth and the conduction angle of rectifier diode increases. The function of inductor is 1: The color ring inductor has the function of blocking current: the copper core in the color ring inductor always resists the current change in the coil. The color ring inductance can block the AC current used in the circuit. The magnitude of blocking effect is called inductance XL, and the unit is ohm. Its relationship with inductance L and AC frequency F is XL=2πfL, and the color ring inductance can be mainly divided into high frequency choke and low frequency choke. The second function of inductance: the color ring inductance has the function of tuning and frequency selection: the parallel connection of color ring inductance and electrolytic capacitor can form an LC tuning circuit. When the color loop inductance resonates, the inductive reactance and capacitive reactance of the circuit are equivalent and opposite, that is, the natural oscillation frequency f0 of the circuit is equal to the frequency f of the non-alternating signal, so are the inductive reactance and capacitive reactance of the circuit, but the use of the color loop inductance is generally not very high, and the color loop inductance used in the circuit is generally stable.

The third function of inductance: The biggest function of color ring inductance is to shield signals, filter noise, stabilize current and suppress electromagnetic interference. The basic function of color ring inductor is charging and discharging, but many circuit phenomena extended from this basic charging and discharging function make color ring inductor have many uses. Now the color ring inductor has been used by customers, but the role played by small inductors can not be underestimated. Main parameters The main parameters of inductance include inductance, allowable deviation, quality factor, distributed capacitance and rated current. Inductance inductance, also called self-inductance coefficient, is a physical quantity indicating the self-inductance ability of an inductor. The inductance of the inductor mainly depends on the number of turns of the coil, the winding mode, whether there is an iron core and the material of the iron core. Generally speaking, the more turns of the coil, the denser the wound coil and the greater the inductance. The inductance of the coil with magnetic core is greater than that of the coil without magnetic core; The greater the permeability of the magnetic core, the greater the inductance. The basic unit of inductance is Henry (abbreviated as Hen), which is represented by the letter "H". Commonly used units are milli-Hen (mH) and micro-Hen (μH), and the relationship between them is:1h =1000 MH1MH =1000 μ h The allowable deviation refers to the allowable error value between the nominal inductance and the actual inductance. Inductors commonly used in oscillating or filtering circuits require high accuracy, and the allowable deviation is 0.2% ~ 0.5%. However, the accuracy of coils used for coupling and high frequency chokes is not high; The allowable deviation is 10% ~ 15%. Quality factor, also known as Q value or quality factor, is the main parameter to measure the quality of inductance. It refers to the ratio of inductance to its equivalent loss resistance when the inductance works under a certain frequency AC voltage. The higher the Q value of the inductor, the smaller the loss and the higher the efficiency. The quality factor of inductance is related to the DC resistance of the coil wire, the dielectric loss of the coil skeleton and the loss caused by the iron core and the forbidden cover. Distributed capacitance refers to the capacitance between coil turns, between coil and core, between coil and ground, and between coil and metal. The smaller the distributed capacitance of the inductor, the better its stability. Distributed capacitance can make the equivalent energy dissipation resistance larger and the quality factor larger. In order to reduce the distributed capacitance, we usually use winding or multi-strand enameled wire, and sometimes we also use honeycomb winding method. Rated current Rated current refers to the maximum current that the inductor can withstand under the allowable working environment. If the working current exceeds the rated current, the performance parameters of the inductor will change due to heating, and even burn out due to overcurrent. Calculation formula Inductance calculation is as follows: Coil formula: impedance (ohm) =2 * 3. 14 159 * F (working frequency) * inductance (h), and 360 ohm impedance is required for setting. Therefore: inductance (H)= impedance (ohm) ÷(2*3. 14 159)÷ F (working frequency) = 360 ÷ (2 * 3.14/kloc-0. Circle diameter (inch)) +(40 * circle length (inch)}] Circle diameter (inch) turns = [8.116 * {(18 * 2.047)+(40 * 3.74)}] (. Calculation formula of air-core coil inductance: l = (0.f0=1* d * n * n)/(l/d+0.44) coil inductance: l, unit: micro-constant coil diameter: d, unit: cm coil turns: n, unit: turn coil length: l, unit: cm frequency inductance and capacitance calculation formula. Kloc-0/25KHZ=0.65... 125. Or the resonant inductance is determined by the q value: L unit: inductance calculation formula of micro-constant coil 1. For a circular magnetic core, the following formula can be used: (iron cm) l = N2. Al l = inductance value (H) H-DC=0.4πNI/l N= coil turns (turns) AL= inductance H-DC= DC magnetization i. For example, if T50-52 is used and the coil is five and a half turns, its L value is T50-52 (indicating an outer diameter of 0.5 inches). The al value is about 33 NH l = 33 (5.5) 2 = 998.25 NH ≒1μ h, and the value can be changed from l=3.74 (look-up table) h-DC = 0.4 π ni/l = 0.4× 3.14. (negative seventh power of 10) μs is the relative permeability of the inner core of the coil, μs= 1 N2 is the cross-sectional area of the square s coil of the coil in the air-core coil, and the unit is the coil length, the unit is square meter L, and the unit is the m k coefficient, which depends on the ratio of the radius (r) to the length (l) of the coil. The unit for calculating inductance is Henry (h). Inductance unit inductance symbol: l Inductance units: Heng (h), Milli Heng (mH) and Micro Heng (μH), and the conversion relationship is:1h =103mh =106μ h =109nh. Conversion: the value X 10 to the nth power, such as 103, is the cubic of 10X 10, and nh is 10uh. In addition, there are general inductance and precision inductance: the error value is 20%, expressed by m; The error value is 10%, denoted by K. Precision inductance: the error value is 5%, denoted by J; The error value is 1%, expressed by f, for example, 100M, which means 10μH, with an error of 20%. The connection and difference between inductance and magnetic beads 1, inductance is an energy storage element, and 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 EMC countermeasures; 3. Magnetic beads are mainly used to suppress electromagnetic radiation interference, and inductors are used to suppress conducted interference, both of which can be used to deal with EMC and EMI problems; EMI has two ways: radiation and conduction, and different ways adopt different suppression methods, the former uses magnetic beads and the latter uses inductance; 4. Magnetic beads are used to absorb UHF signals, such as some RF circuits, phase locked loops, oscillation circuits and circuits containing UHF memories (DDRSDRAM, RAMBUS, etc.). Inductor is a kind of energy storage element, which is used in LC oscillation circuit, medium and low frequency filter circuit, etc. , its application frequency range rarely exceeds 50MHZ；; 5. Inductors are generally used for circuit matching and signal quality control, and are generally connected to the power supply. Use magnetic beads where analog and digital are combined. Magnetic beads are also used for signal lines. The size of magnetic beads (accurately, it should be the characteristic curve of magnetic beads) depends on the frequency of interference waves that magnetic beads need to absorb. Magnetic beads have high frequency resistance, low DC resistance and high frequency resistance. Because the unit of magnetic bead is nominal according to the impedance it produces at a certain frequency, the unit of impedance is also ohm. Frequency and impedance characteristic curves are usually attached to the data sheet of magnetic beads. The general standard is 100MHz, such as 20 12B60 1, that is to say, the impedance of magnetic beads at 100MHz is 600 ohms.