Introduction to Inductors

Previously, inductors have created content of the right, but this content has been created in more detail for series continuity. The inductor is a passive electrical component consisting of a wire coil designed to benefit from the relationship between magnetism and electricity as a result of an electric current passing through the coil.

In our training on electromagnetism, we found that when an electric current passes through a wire conductor, a magnetic flux forms around that conductor. This effect produces a relationship between the direction of the magnetic flow circulating around the conductor and the direction of the current passing through the same conductor. This results in a relationship between the current and magnetic flux direction, called "Fleming's Right Hand Rule".


However, there is another important feature related to a winding coil; that is inducing a secondary voltage to the same coil, as it resists or resists any changes in the current of electricity flowing by the movement of the magnetic battery.


In its most basic form, an inductor is nothing more than a wire coil wrapped around a central core. For most coils, the current flowing from the coil ( i ) produces a magnetic flux (NΦ) proportional to this electric current flow around it. An inductor, also called a coil, is another passive type electrical component consisting of a wire coil designed to take advantage of this relationship by inducing a magnetic field in itself or in its core as a result of the current passing through the wire coil.

Inductors are formed by wire tightly wrapped around a solid central core, which can be a flat cylindrical rod or a continuous loop or ring to intensify their magnetic flux.

The schematic symbol of an inductor is roughly a wire coil, so a wire coil can also be called an inductor. Inductors are usually divided into categories, such as hollow core (free air), solid iron core or soft ferrite core, and different types of cores are distinguished by adding continuous or dotted parallel lines next to them, depending on the type of inner core they are wrapped around.

Types of coils

The current passing through an inductor produces a magnetic flux proportional to it. However, unlike a capacitor that opposes voltage change along its plates, an inductor opposes the rate of change of the current flowing through it due to the accumulation of self-induced energy within its magnetic field.

In other words, inductors resist or oppose current changes, but can easily pass a constant DC current. The current is indicated by the i and magnetic flux NΦ. After Joseph Henry, henry units (H) are called Inducents, which are given the L symbol.

Since Henry is a relatively large inducing unit in its own right, Henry's subunits for smaller inductors are used to indicate its value. Eg:

PrefixSymbolMultiplierTenth Force
Inducktans Prefixes

1mH = 1 milli-Henry = equals one thousandth (1/1000) of a Henry.
100μH = 100 micro Henry = equals one in 100 million (1/1,000,000) of a Henry.

Inductors or coils are very common in electrical circuits, and there are many factors that determine the inductiveness of a coil, such as the shape of the coil, the number of windings of the ins isolated wire, the number of wire layers, the gap between the windings; The permeability of the core material, the size of the core or the section area, etc.

An inductor coil has a central core area (A) with a fixed number of wire wraps (l) per unit length. Therefore, if an N-turn coil is connected with some magnetic flux, then the flux connection of the coil is NΦ, and any current flowing from the coil will produce a magnetic flux induced in the opposite direction of the coil ( i ). Then, according to the Faraday Act,any change in this magnetic flux connection produces a self-induced voltage in a single coil.


N is the number of
rotations A is the cross-section area in m2
the amount of flux in Φ Weber
μ is the permeability of the core material
l, the length of the coil in meters
is di/dt, the current change rate in amps/sec

A magnetic field that changes over time induces a voltage that is proportional to the rate of change of the current that produces it, and this is a positive value indicating an increase in emk and a negative value indicating a decrease in emk. This equation for self-induced voltage, current and inductace can be found by replacingμN 2A /l with L, which indicates the proportion constant called inductive of the coil.

The relationship between the flux in the inductor and the current passing through the inductor is given as follows: NΦ = Li. Since an inductor consists of a coil consisting of conductive wire, this reduces the equation above to give the self-induced emk, sometimes called the back emk induced in the coil:

Suck it back.
Where: L is self-induced and the current change rate is di/dt.

Therefore, from this equation we can say "self-induced emk = induced X current change rate", and the induced induced part of a circuit will be an emf of one volt in the circuit when the current is induced in a Henry circuit.

An important point to consider about the equation above. It only associates the emk produced throughout the inductor with changes in the current, since if the flow of the inductor current is constant and does not change as in a fixed DC current, then the induced emk voltage will be zero because the instantaneous current change rate is zero, di/dt = 0.

With a constant DC current flowing through the inductor and therefore zero induced voltage, the inductor acts as a short circuit equal to a piece of wire, or at least a very low-value resistance. In other words, the contrast to the flow of the current presented by an inductor is very different between ac and DC circuits.

Inductor Time Constant

Now we know that in an inductor the current cannot change instantly, because for this to happen, the current must change in a finite amount in zero time, which causes the current change rate to be infinite, di/dt = ∞, it is not possible to make the induced emk infinite and accept it endlessly. However, if the current flowing from an inductor changes very quickly, such as fast switching, high voltages can be induced along the inductor coil.


Think of it as a pure inductor circuit on the left. When the switch (S1) is on, no current passes through the inductor coil. Since no current passes through the inductor, the rate of change (di/dt) of the current in the coil will be zero. If the rate of change of the current is zero, there is no self-induced back-emk (VL = 0) in the inductor coil.

If we turn off the switch (t = 0), a current will flow from the circuit and slowly rise to its maximum value at a rate determined by the inductance of the inductor. This current speed flowing from the inductor is multiplied by the inducing of the inductors in Henry, the Faraday equation above results in the production of some fixed value self-induced impetus along the coil, as determined by VL = -Ldi/dt.

Self-induced along the inductor coil, this absorbent (VL) fights against the voltage applied until the current reaches its maximum value and the constant state is reached. Now the current flowing from the coil is determined only by the DC or "pure" resistance of the coil windings, since the reassurance value of the coil drops to zero, since the rate of change of the current (di/dt) is zero. stable status. In other words, in a real coil, only the coils have DC resistance to resist the flow of the current from within itself.

In the same way that if the switch (S1) is turned on, the current passing through the coil will start to fall, but the inductor will again fight against this change and try to keep the current at its former value by inducing another voltage in the other direction. The slope of the fall will be negative and will be related to the inducta of the coil, as shown below.

Current and Voltage in inductor


How much induced voltage is generated by the inductor depends on the current change rate. In our tutorial on electromagnetic induction, Lenz Law told us: "An induced aspect of emfin is always opposed to the change that causes it." In other words, an induced emk will always be in the opposite direction to the movement or change that initiated the induced emk in the first place.

Thus, with a decreasing current, voltage polarity will act as a source and voltage polarity will act as a load with an increased current. Therefore, for the same rate of current change along the coil, it will be the same to increase or decrease the size of the induced emk.

Inductor Question Example


A constant direct current of four amps passes through a 0.5H solenoid coil. What happens to the average back-emcrement voltage induced in the coil if the switch on the left circuit is turned on at 10mS and the current passing through the coil decreases to zero amps?


Power in the Inductor

We know that an inductor in a circuit is against the flow of the current, ( i ) because the flow of this current induces an emf that opposes it. Then work must be done by the external battery supply to ensure that the current flows against this induced emk. The instantaneous power used to force the current is given from above against this self-induced emk (VL):


The power in a circuit is given as P = V*I, so:


An ideal inductor has no resistance, it only has inductives, so it Ω R = 0, and therefore power is not expended inside the coil, so we can say that an ideal inductor is zero power loss.

Energy Stored in inductor

When power flows into an inductor, the energy is stored in its magnetic field. When the current passing through the inductor increases and the di/dt is greater than zero, the instantaneous power in the circuit must also be greater than zero (P > 0), which means that energy is stored in the inductor.

Similarly, if the current passing through the inductor decreases and the di/dt is less than zero, then the instantaneous power must also be less than zero, ( P < 0 ) yani negatif, bu da indüktörün enerjiyi devreye geri döndürdüğü anlamına gelir. Then, by integrating the above power equation, the total magnetic energy stored in the inductor, which is always positive, is given as follows:

Energy stored by the inductor

W is in joule, L is in Henry, and i is in Amperage

The energy is actually stored in the magnetic field surrounding the inductor by the current flowing through it. In an ideal inductor without resistance or capacitance, the current is not released until the current decreases and the magnetic field collapses, as the energy flowing into the inductor increases and is stored there without loss within its magnetic field.

Then, in an alternate current, an inductor in the AC circuit continuously stores and transmits energy in each cycle. If the current passing through the inductor is constant as in a DC circuit, there is no change in the stored energy to P = Li(di/dt) = 0.

Therefore, inductors can be defined as passive components because they can both store and energize the circuit, but they cannot generate energy. An ideal inductor is classified as less loss, that is, it can store energy indefinitely as there is no loss of energy.

However, real inductors will always have resistance associated with the windings of the coil, and when the current flows through a resistance, energy in the form of heat is lost due to the Ohm Act ( P = I2 R ), regardless of whether the current is an alternative. constant.

Then the primary use for inductors is in filtration circuits, resonance circuits and current limitation. An inductor can be used in circuits to block or reshape alternate current or a series of sinusoidal frequencies, and in this role an inductor can be used to "adjust" a simple radio receiver or various types of oscillators. It can also protect sensitive equipment from destructive voltage spikes and high currents.

In the next lesson about inductors, we will see that the effective resistance of a coil is called Inductace, and as we now know, this inductee, characteristic of an electrical conductor that "opposes a change in current", can be internal. induced, self-induced or externally induced, called mutual induced.