This post was last posted by qwqwqw2088 on 2019-2-25 09:59 Edit 1. Definition of Inductor 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 the wire.
When a direct current passes through an inductor, only fixed magnetic lines of force appear 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 will 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 supply, from an objective point of view, the inductor 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 named "self-induction" in electricity. Usually, sparks will occur at the moment of pulling open or connecting the knife switch. This is caused by the self-induction phenomenon generating a very high induced potential. In short, when the inductor is connected to an AC power source, the magnetic lines of force inside the coil will change constantly 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. 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 coil is made by winding the wire (enameled wire, yarn-wrapped wire or bare wire) one circle after another (the wires are insulated from each other) on an insulating tube (insulator, iron core or magnetic core). Generally, the inductor coil has only one winding. Transformer: When a changing current flows through an inductor coil, it not only generates an induced voltage at both ends of itself, 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. 3. Symbol and unit of inductance Inductor symbol: L. Inductance units: Henry (H), millihenry (mH), microhenry (uH). Conversion relationship: 1H=1000mH=10*10*10*10*10*10uH. 1mH=1000uH. 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; Classified by winding structure: single-layer coil, multi-layer coil, honeycomb coil; Classified by working frequency: high-frequency coil, low-frequency coil; Classified by structural characteristics: magnetic core coil, variable inductance coil, color-coded inductance coil, coreless coil, etc. 5. Main characteristic parameters of inductance 1. Inductance L Inductance L represents the inherent characteristics of the coil itself and has nothing to do with the current. Except for special inductance coils (color-coded inductance), inductance is generally not specifically marked on the coil, but marked with a specific name. 2. Inductive reactance XL The magnitude of the inductance coil's resistance to alternating current is called inductive reactance XL, and the unit is ohm. Its relationship with inductance L and AC frequency f is XL=2πfL. 3. Quality factor Qr] The quality factor Q is a physical quantity that indicates the quality of the coil. Q is the ratio of the 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 iron core, and the influence of the high-frequency skin effect. The Q value of the coil is usually tens to hundreds. The use of magnetic core coils and multi-strand thick coils can increase the Q value of the coil. 4. Distributed capacitance The capacitance between the turns of the coil, between the coil and the shielding cover, and between the coil and the base is called distributed capacitance. The existence of distributed capacitance reduces the Q value of the coil and deteriorates its stability. Therefore, the smaller the distributed capacitance of the coil, the better. The distributed capacitance can be reduced by adopting segmented winding. 5. Allowable error The percentage obtained by dividing the difference between the actual value of inductance and the nominal value by the nominal value. 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. The nominal current values are 50mA, 150mA, 300mA, 700mA, and 1600mA.
6. Commonly used inductance coils 1. Single-layer coil 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. 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 when it rotates one circle 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 there are, the smaller the distributed capacitance. 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. 4. Copper core coil Copper core coil is widely used in the ultra-short wave range. The position of the copper core in the coil is rotated to change the inductance. This adjustment is convenient and durable. 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 the inductance is generally between 0.1uH and 3300uH. Color-coded inductors are inductors with fixed inductance. Their inductance is marked with color rings in the same way as resistors. The unit is uH. 6. Chokes The coil that limits the passage of alternating current is called a choke, which is divided into high-frequency chokes and low-frequency chokes. 7. Deflection Coil 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. 7. The role of inductance in the circuit Basic role: filtering, oscillation, delay, notch, etc.; Figurative statement: "pass DC and block 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-shifting circuits and resonant circuits with resistors or capacitors. The transformer can perform AC coupling, voltage transformation, current conversion and impedance transformation. 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 rate △i/△t. The inductor 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=1/2Li2. It can be seen that the larger the inductance of the coil, the greater the flow, and the more electrical energy is stored. 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. 8. Models, specifications and naming of inductors There are many inductor manufacturers at home and abroad, among which the famous brand manufacturers include SAMUNG, PHI, TDK, AVX, VISHAY, NEC, KEMET, ROHM and so on. 1. Chip inductor Inductance: 10NH～1MH; Material: Ferrite winding type ceramic laminate; Accuracy: J=±5% K=±10% M=±20%; Size: 04020603080510081206121018121008=2.5mm*2.0mm1210=3.2mm*2.5mm. 2. Power inductor Inductance: 1NH～20MH; Shielded or unshielded; Size: SMD43, SMD54, SMD73, SMD75, SMD104, SMD105; RH73/RH74/RH104R/RH105R/RH124; CD43/54/73/75/104/105. 3. Chip ferrite beads Types: CBG (ordinary type) impedance: 5Ω～3KΩ; CBH (high current) impedance: 30Ω～120Ω; CBY (spike type) impedance: 5Ω～2KΩ; Specifications: 0402/0603/0805/1206/1210/1806 (chip beads); Specifications: SMB302520/SMB403025/SMB853025 (chip high current beads). 4. Plug-in beads Specifications: RH3.5. 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%; 6. Plug-in color ring inductor; Reading: the same as the color ring resistor. 7. Vertical inductor Inductance: 0.1uH～3MH; Specifications: PK0455/PK0608/PK0810/PK0912. 8. Axial filter inductor Specifications: LGC0410/LGC0513/LGC0616/LGC1019; Inductance: 0.1uH-10mH; Rated current: 65mA~10A; High Q value, generally low price, and high self-resonant frequency. 9. Magnetic ring inductor Specifications: TC3026/TC3726/TC4426/TC5026; Size (unit: mm): 3.25~15.88. 10. Air core inductor In order to obtain a larger inductance value, air core inductors are often wound with more enameled wires. 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 inductors in computers are magnetic core inductors. Nine. 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, 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 resisted by the inductor, which can suppress the higher frequency interference signal. The inductor of the power supply part of the circuit board is generally composed of a very thick enameled wire wrapped around a round magnetic core coated with various colors. And there are usually several tall filter aluminum electrolytic capacitors nearby, which 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 snaking wires bend back and forth on the circuit board and can also be regarded as a small inductor. 10. 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 supply filtering circuits, while 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. 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 (DDRSDRAM, RAMBUS, etc.) all need to add magnetic beads to the power input part, while 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 ferrite bead (or more precisely, the characteristic curve of the ferrite bead) depends on the frequency of the interference wave that the ferrite bead needs to absorb. Magnetic beads block high frequencies, with low resistance to DC and high resistance to high frequencies. For example, 1000R@100Mhz means that it has a resistance of 1000 ohms to a signal with a frequency of 100M. Because the unit of the ferrite bead is nominally based on the impedance it produces at a certain frequency, the unit of impedance is also ohms. The datasheet of the ferrite 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 ferrite bead is 600 ohms at 100MHz. LC filter circuit. In addition, the circuit board also uses a large number of "snaking wire + chip tantalum capacitors" to form an LC circuit, because the snaking wire bends back and forth on the circuit board and can also be regarded as a small inductor. 10. 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 supply filtering circuits, while 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. 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 (DDRSDRAM, RAMBUS, etc.) all need to add magnetic beads to the power input part, while 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 ferrite bead (or more precisely, the characteristic curve of the ferrite bead) depends on the frequency of the interference wave that the ferrite bead needs to absorb. Magnetic beads block high frequencies, with low resistance to DC and high resistance to high frequencies. For example, 1000R@100Mhz means that it has a resistance of 1000 ohms to a signal with a frequency of 100M. Because the unit of the ferrite bead is nominally based on the impedance it produces at a certain frequency, the unit of impedance is also ohms. The datasheet of the ferrite 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 ferrite bead is 600 ohms at 100MHz. LC filter circuit. In addition, the circuit board also uses a large number of "snaking wire + chip tantalum capacitors" to form an LC circuit, because the snaking wire bends back and forth on the circuit board and can also be regarded as a small inductor. 10. 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 supply filtering circuits, while 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. 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 (DDRSDRAM, RAMBUS, etc.) all need to add magnetic beads to the power input part, while 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 ferrite bead (or more precisely, the characteristic curve of the ferrite bead) depends on the frequency of the interference wave that the ferrite bead needs to absorb. Magnetic beads block high frequencies, with low resistance to DC and high resistance to high frequencies. For example, 1000R@100Mhz means that it has a resistance of 1000 ohms to a signal with a frequency of 100M. Because the unit of the ferrite bead is nominally based on the impedance it produces at a certain frequency, the unit of impedance is also ohms. The datasheet of the ferrite 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 ferrite bead is 600 ohms at 100MHz.
11. Calculation formulas for some inductors 1. Toroidal inductor For toroidal CORE, the following formulas can be used: (IRON) L=N2*ALL=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 the values of l and AL, please refer to the Micrometa comparison table. For example: with T50-52 material and 5 and a half turns of winding, its L value is T50-52 (indicating OD is 0.5 inches). After looking up the table, its AL value is about 33nH; L=33*(5.5)2=998.25nH≈1μH; when a current of 10A passes through, its L value changes from l=3.74 (look up the table); H-DC=0.4πNI/l=0.4×3.14×5.5×10/3.74=18.47 (after looking up the table); you can understand the degree of L value decrease (μi%). Inductance calculation Introduce an empirical formula: L=(k*μ0*μs*N2*S)/l; wherein, μ0 is the magnetic permeability of vacuum = 4π*10(-7). (10 to the negative seventh power); μs is the relative magnetic permeability of the magnetic core inside the coil, and 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 is the coefficient, which depends on the ratio of the radius (R) to the length (l) of the coil; The calculated inductance is in Henry; The above are all theoretical values, and the actual amount of electricity shall be subject to actual measurement. 12. Inductance measurement There are two types of instruments for measuring inductance: RLC measurement (can measure resistance, inductance, and capacitance) and inductance meter; Inductance measurement: no-load measurement (theoretical value) and measurement in actual circuit (actual value); Since there are too many actual circuits where inductance is used, it is difficult to give an example. So we will explain the measurement under no-load condition. Inductance measurement steps: (RLC measurement) 1. Familiarize yourself with the instrument's operating rules (instructions for use) and precautions; 2. Turn on the power and prepare for 15 to 30 minutes; 3. Select the L position and select the inductance measurement; 4. Clamp the two clips together and reset them to zero; 5. Clamp the two ends of the inductor with two clips respectively, read the value and record the inductance; 6. Repeat steps 4 and 5 and record the measured values. There should be 5 to 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 the inductor; if the difference is too big (0.3uH), repeat steps 2 to 6 until the theoretical value of the inductor is obtained; Different instruments can measure different inductor parameters. Therefore, be familiar with your measuring instrument before making any measurement. What your instrument can do. Then follow the operating instructions it gives you. Thirteen. Matters needing attention during the use of inductors 1. Occasions for the use of inductors Pay attention to moisture and dryness, high and low ambient temperatures, high or low frequency environments, whether the inductor should show inductive or impedance characteristics, etc. 2. Frequency characteristics of inductors At low frequencies, inductors generally show inductive characteristics, which only store energy and filter high frequencies. But at high frequencies, its impedance characteristics are very obvious. There are phenomena such as energy consumption and heat generation, and reduced inductive effect. The high-frequency characteristics of different inductors are different. The following is an explanation of the inductance of ferrite materials: Ferrite materials are iron-magnesium alloys or iron-nickel alloys. This material has a very high magnetic permeability. It can be the smallest capacitance generated between the coil windings of the inductor under high frequency and high resistance conditions. Ferrite materials are usually used in high-frequency conditions because they mainly show inductive characteristics at low frequencies, making the loss on the line very small. In high-frequency conditions, they mainly show reactance characteristics and change with frequency. In practical applications, ferrite materials are used as high-frequency attenuators in radio frequency circuits. In fact, ferrite is better equivalent to the parallel connection of resistance and inductance. At low frequency, the resistance is short-circuited by the inductance, and at high frequency, the impedance of the inductance becomes quite high, so that all the current passes through the resistance. Ferrite is a consumption device, and high-frequency energy is converted into heat energy on it, which is determined by its resistance characteristics. The maximum current that the inductor is designed to withstand, and the corresponding heating conditions. When using a magnetic ring, refer to the magnetic ring part above to find the corresponding L value and the range of use of the corresponding material. Pay attention to the wire (enameled wire, yarn-wrapped or bare wire), commonly used enameled wire. Find the most suitable wire diameter.
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