Inductance calculation formula of circuit inductance and how to play a role?

In the use of household electrical appliances, the use of inductors should be more extensive, look at the inductors today!

Definition of inductor

Definition of inductance:

Inductance is the ratio of the magnetic flux of a wire to the current that produces the alternating flux in and around the wire when an alternating current passes through the wire.


When dc current is passed through the inductor, only fixed magnetic field lines around it do not change with time.But when alternating current is passed through the coil, it is surrounded by magnetic field lines that change with time.According to Faraday’s law of electromagnetic induction – the generation of electricity by magnetism – changing magnetic field lines generate an induced potential at both ends of the coil, which ACTS as a “new source”.

When a closed loop is formed, the induced potential generates an induced current.Lenz’s law knows that the total number of magnetic field lines produced by induced current is intended to prevent the original field lines from changing.Since the change of magnetic field line is caused by the change of external alternating power supply, the inductance coil has the characteristic of preventing the change of current in ac circuit.Inductance coil has similar characteristics to inertia in mechanics, which is called “self-induction” in electricity, and usually sparks occur at the moment the knife switch is opened or closed, which is caused by the high induction potential of self-induction phenomenon.

In short, when the inductance coil is connected to the ac power supply, the magnetic field line inside the coil will change constantly with the alternating current, causing the coil to generate electromagnetic induction constantly.The electromotive force generated by the change of the current in the coil itself is called self-induced electromotive force.

It can be seen that inductance is only a parameter related to coil winding number, size and shape and medium. It is a measure of inductance coil inertia and has nothing to do with applied current.

Inductance coil and transformer

Inductance coil: when a current is present in a wire, a magnetic field is established around it.We usually wind the wire into a coil to strengthen the magnetic field inside the coil.An inductance coil is made by wrapping a wire (enameled wire, yarn covered wire, or bare wire) around an insulator (insulator, iron core, or magnetic core), coil by coil (wire insulation from wire to wire).In general, the inductor has only one winding.

Transformer: inductance coil through the change in the current, not only in itself at both ends of the induction voltage, but also can cause the induction voltage in the nearby coil, 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 commonly called transformers.

Symbol and unit of inductance

Inductance symbol: L;

Inductance units: heng (H), hai-heng (mH), wei-heng (uH), 1H=10*10*10mH=10*10*10*10* 10uH.

Inductance classification:

Classified by inductance form: fixed inductance, variable inductance;

According to the properties of magnetic conductivity: hollow coil, ferrite coil, iron coil, copper coil;

According to the nature of work: antenna coil, oscillation coil, choke coil, trap coil, deflection coil;

According to the structure of winding: single-layer coil, multi-layer coil, honeycomb coil;

Classified by working frequency: high-frequency coil, low-frequency coil;

According to the structure characteristics of the classification: magnetic core coil, variable inductance coil, color code inductance coil, core-free coil.

Main characteristic parameters of inductance

Inductance L: represents the inherent characteristics of the coil, independent of the current.In addition to the special inductance coil (color code inductance), the inductance value is usually not specially labeled on the coil, but labeled with a specific name.

Inductance XL: the inductance coil’s resistance to ac current is called inductance XL in ohms.Its relation to inductance L and ac frequency f is XL=2 PI fL.

Quality factor Q: quality factor Q is a physical quantity representing the coil mass, and Q is the ratio of inductive reactance XL to its equivalent resistance, i.e., Q=XL/R.The higher the Q value of the coil, the less the loss of the loop.The Q value of the coil is related to the direct current resistance of the wire, the dielectric loss of the frame, the loss caused by the shield or the iron core, and the effect of high-frequency skin effect.The Q value of the coil is usually tens to hundreds.Using magnetic core coil, multiple thick coil can increase the Q value of coil.

Distributed capacitance: the capacitance existing between turns of the coil, between the coil and the shield, between the coil and the substrate is called the distributed capacitance.The existence of distributed capacitance reduces the Q value of the coil and leads to poor stability, so the smaller the distributed capacitance of the coil, the better.The distributed capacitance can be reduced by piecewise winding.

Permissible error: the difference between the actual value of the inductance and the nominal value divided by the percentage of the nominal value.

Nominal current: refers to the amount of current allowed through the coil, usually expressed by letters A, B, C, D and E respectively, with nominal current value of 50mA, 150mA, 300mA, 700mA and 1600mA.

Common inductance coil

Single coil

A single-layer coil is a coil of insulated wire wound around a paper tube or baklava frame.Such as transistor radio medium wave antenna coil.

Honeycomb coil

If the plane of the coil is not parallel to the plane of rotation but intersects at an Angle, the coil is called a honeycomb coil.The number of times the wire bends back and forth as it rotates around is often called the number of points.The advantages of honeycomb winding method are small volume, small distributed capacitance and large inductance.Honeycomb coil is wound by honeycomb winding machine. The more folding points, the smaller distribution capacitance.

Ferrite core and iron powder core coil

The inductance of a coil is related to the presence or absence of a core.By inserting ferrite core into hollow coil, inductance and quality of coil can be increased.

Copper coil

Copper coil is widely used in the ultra-short wave range. It is convenient and durable to change the inductance by rotating the position of copper core in the coil.

Color coded inductor coil

It is a kind of high frequency inductance coil. It is made of epoxy resin or plastic after wrapping some enameled wires around the magnetic core.Its operating frequency is 10KHz to 200MHz, and the inductance is generally between 0.1uH and 3300uH.Color code inductors are inductors with fixed inductance, which are marked by color rings as well as resistors.The units are uH.

Choke coil

The coil that restricts the flow of alternating current is called a choke coil, divided into a high-frequency choke coil and a low-frequency choke coil.

Deflection coil

The deflection coil is the load of the output level of the TV scanning circuit. The deflection coil requires high deflection sensitivity, uniform magnetic field, high Q value, small volume and low price.

The role of inductance in circuit

Basic functions: filtering, oscillation, delay, notch, etc.

Image statement: “through dc, resistance to the exchange”;

Detailed explanation: in the electronic circuit, the inductance coil ACTS on the ac finite current, and it and the resistor or capacitor can form high-pass or low-pass filter, phase-shifting circuit and resonance circuit, etc.Transformer can be ac coupling, transformer, transformer and impedance transformation.

As inductive reactance XL=2 PI fL, the greater the inductance L, the higher the frequency f, the greater the inductive reactance.The size of the voltage at both ends of the inductor and inductance L is proportional to, but also with the current change speed delta I/delta t is proportional.

Inductance coil is also an energy storage element, which stores electric energy in the form of magnetic field. The stored electric energy can be expressed in the following formula: WL=1/2 li2.Thus, the greater the inductance and flow of the coil, the more electrical energy is stored.

Symbol of inductance

Nominal value of inductance: straight standard type, color ring standard type, non-standard type;

Inductance directivity: no direction;

Method of checking inductance: measure inductance with inductance measuring instrument;Measured with a multimeter, the ideal inductance resistance is small, close to zero.

The application of inductance in circuit

The most common function of inductance in circuit is to form LC filter circuit together with capacitor.We have known that capacitors have the ability to “stop dc, stop ac”, while inductors have the ability to “stop dc, stop ac”.If the dc current with many interfering signals is passed through the LC filter circuit, then the ac interfering signal will be consumed by the capacitor into heat energy.When the pure dc current flows through the inductance, the ac interference signal is also changed into magnetic sensation and heat energy. The higher frequency is the most vulnerable to the inductance impedance, which can suppress the interference signal of higher frequency.

LC filter circuit

The inductance in the power supply part of the circuit board is generally surrounded by a round core with various colors and a very thick enameled wire.In addition, there are several tall aluminum electrolytic capacitors nearby, which are composed of the above mentioned LC filtering circuit.In addition, the circuit board also USES a large number of “snake line + chip tantalum capacitor” to form LC circuit, because the snake line on the circuit board fold back and forward, can also be seen as a small inductor.

The connection and difference between inductance and magnetic bead

What relation and distinction do inductance and magnetic bead have

1. Inductors are energy storage elements, while magnetic beads are energy conversion (consumption) devices;

2. Inductance is mostly used in power filter circuit, magnetic beads are mostly used in signal circuit and EMC countermeasures;

3. Magnetic beads are mainly used to suppress electromagnetic radiation interference, while inductors are mainly used to suppress conductive interference.Both can be used to deal with EMC and EMI problems.The two EMI pathways, namely, radiation and conduction, are inhibited in different ways.The former with magnetic beads, the latter with inductance;

4. Magnetic beads are used to absorb uhf signals. For example, some RF circuits, PLL, oscillation circuits and uhf memory circuits (DDRSDRAM, RAMBUS, etc.) need to add magnetic beads to the power input part.

5. Inductance is generally used for circuit matching and signal quality control.General connection and power connection.Magnetic beads are used where analog and digital fields are combined.Magnetic beads are also used for signal lines.

The size of the magnetic bead (or rather the characteristic curve of the bead) depends on the frequency of the interfering wave that needs to be absorbed by the bead.Magnetic beads are resistance to high frequency, low resistance to dc, high resistance to high frequency.For example, 1000R@100Mhz means that there is a resistance of 1000 ohms to a signal of 100M frequency.Because the magnetic bead is labeled in terms of the impedance it produces at a certain frequency, the unit of impedance is also the ohm.Datasheet datasheet datasheet datasheet datasheet datasheet datasheet datasheet datasheet datasheet datasheet datasheet datasheet datasheet datasheet datasheet datasheetNormally 100MHz is the standard, such as 2012B601, which refers to the Impedance of 600 ohm of magnetic bead at 100MHz.

Calculation formula of partial inductance

Loop inductance

For ring CORE, the following formula can be used :( IRON)

L=N2*ALL= inductance (H)AL= inductance;

H-DC=0.4 PI NI/lN== winding turns (turns);

H-DC= DC magnetizing force I= passing current (A)l= magnetic circuit length (cm);

L and AL values can be compared with Micrometa table.For example, the L value of t50-52 is t50-52 (indicating OD is 0.5 inch), and the AL value is about 33nH according to the table.

L = 33 * (5.5) 2 nH material 1 mu = 998.25 H;

When the current of 10A is passed, the change of L value can be expressed as L =3.74(see table).

H-dc =0.4 PI NI/l=0.4×3.14×5.5×10/3.74=18.47 (after table lookup);

You know how far down the L value is (mui %).

Inductance calculation

Introduce an empirical formula:

L = (k * * * mu mu 0 s N2 * s)/L.

Among them,

Mu0 is vacuum permeability =4 PI *10(-7).(10 to the minus 7);

Mus refers to the relative permeability of the magnetic core inside the coil, and when the coil is hollow, mus =1.

N2 is the square of the number of lines;

Section area of S coil in square meters;

L length of coil in meters;

K coefficient depends on the ratio of the radius (R) of the coil to the length (l);

The unit of inductance calculated is Henry;

All the above are theoretical values, and the actual electric quantity is subject to the actual measurement.

Eight, inductors in the use of the process to pay attention to matters

Where inductors are used

Attention should be paid to humidity and dryness, ambient temperature, high frequency or low frequency, whether the inductance is sensitive or impedance.

Frequency characteristics of inductors

At low frequency, inductance generally presents inductance characteristics, which only store energy and filter high frequency.

At high frequencies, however, its impedance characteristics are apparent.There is energy consumption and heating, perceptual effect reduction and other phenomena.Different inductors have different high-frequency characteristics.

The inductance of ferrite material is explained below:

Ferrite material is ferromagnesium alloy or ferronickel alloy, this material has a high permeability, it can be inductance between the winding at high frequency and high resistance to produce the smallest capacitance.Ferrite materials are usually used at high frequencies, because at low frequencies they are mainly inductance properties, resulting in low line losses.At high frequencies, they are reactance ratio and change with frequency.In practice, ferrite materials are used as high frequency attenuators in rf circuits.In fact, ferrite is better equivalent to the parallel resistance and inductance, the resistance is short-circuited by inductance at low frequency, inductance impedance becomes quite high at high frequency, so that all the current passes through the resistance.Ferrooxide is a device-consuming device on which high-frequency energy is converted to heat energy, as determined by its resistive properties.


Post time: Aug-17-2019
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