Thursday, February 23, 2017

Basic Electronics On The Go - Inductance of an Inductor

From www.electronicshub.org/inductance-of-an-indcutor/

Like capacitors and resistors, an inductor is also a passive element. Simply, an Inductor is a twisted wire or coil of electroconducting material. Inductance is the property of an electric conductor or a circuit that opposes the change to a flow of current.

An electric conductor or a circuit element with the property of Inductance is called an Inductor. When there is a change of current in a coil or a twisted wire (inductor), it opposes this change by generating or inducing an electromotive force (EMF) in itself and nearby conducting materials.

Capacitance is the measure of the ability of a conductor to store electric charge i.e. electric field energy. In contrast, Inductance of an electrical conductor is the measure of its ability to store magnetic charge i.e. magnetic field energy.

An inductor stores the energy in the form of magnetic field. As magnetic field is associated with flow of current, inductance is associated with current carrying material. The inductance of a coil is proportional to the number of turns of the coil.


Di-electric materials like plastic, wood and glass have least inductance. But the Ferro magnetic substances (iron, Alnico, chromium ferroxide) will have high inductance.

The unit for inductance is Henry, micro Henry, milli Henry etc. It can also be measured in Weber/ ampere. The relation between Weber and Henry is, 1H = 1 Wb/A.
To understand the inductance of a coil, we should know about Lenz law, which explains us how the emf will induce in an inductor. Lenz’s law states an induced electromotive force that generates a current that induces a counter magnetic field opposing the magnetic field generating the current. 






Another definition of Inductance is “The electromagnetic force produced in a coil by applying the voltage of 1 volt, and is exactly equal to one Henry or 1 ampere/ second”.

In other words, for 1 volt of voltage VL and the rate of flow of current is 1 amp/ sec then the inductance of the coil is L, measuring 1 Henry. 
The induced voltage in the inductor (coil) is given as
V_L = -L di/dt (volts)
The negative sign indicates the opposing voltage in the coil per unit time (di /dt).
The inductance in a coil is of 2 types, they are
  • Self inductance
  • Mutual inductance


(to be updated)

Saturday, February 18, 2017

Basic Electronics On The Go - Inductive Reactance

From http://www.electronicshub.org/inductive-reactance/

When equal values of direct voltage and alternating voltage are applied to the same circuit which has inductor in series with the load, more current would flow in a DC circuit than in an AC circuit.
This is because, only induced voltage opposes the current flow in DC circuit when the current approaches to its maximum value and once it reaches to a steady state value, there will be no more inductive effect.

In the case of AC circuits, current is continuously changing, therefore inductive effect is present at all time. Consider the following DC and AC circuits to understand this concept.

DC Inductive Circuit



In the above figure, if the switch is operated from node A to node B and immediately from node B to node A, a change in current flows through the circuit.
This change in current induces an emf in the inductor proportional to the rate of change of current and this emf opposes the applied voltage (which is the cause for the production of current). This is called self induction.
Once the current reaches a steady state value, there will be no self induction in the inductor and hence no opposition to the current flow.


AC Inductive Circuit





We know that, when AC current is applied to the circuit, current continuously changes at a supply frequency rate and hence the back emf will change accordingly.
This back emf opposes the supply voltage and hence the flow of current is limited. Therefore, the actual opposition to the current flow created by an inductor in an AC circuit is referred as the inductive reactance.


Inductive reactance in an Inductor

In an inductive circuit by observing the self-inductance and its effect within the circuit, we can define the inductive reactance. The magnetic field induces the voltage in the inductor which is always opposite in polarity to the voltage that produces it, i.e., applied voltage.
This opposing voltage limits the current flowing through an inductor and it is called reactance (X). Since this reactance is caused due to inductance, it is called inductive reactance (XL). It is measured in Ohms.


The amount of inductive reactance offered by an inductor is proportional to the inductance and frequency of applied voltage. This reactance can be determined by the following formula.
XL = 2 π fL
Where XL= inductive reactance in ohms
π = 3.14
f = frequency in Hertz (Hz)
L = inductance in Henrys (H)
According to the ohm’s law, inductive reactance is directly proportional to the applied voltage and inversely proportional to the current. It can be expressed as
I = V/XL

From the above equation it is clear that increasing voltage or decreasing inductive reactance causes an increase in current. Likewise, current decreases with increase in inductive reactance and decrease in voltage.
Any practical inductor must be made with wound wire which consists of some resistance so it is not possible to obtain a purely inductive coil.
Therefore, there are two factors that oppose the current flow in an inductor, namely resistance associated with the coil (which is considered as separate resistor R in series with inductor) and inductive reactance offered by the  inductance property.

Thus the total current limiting property of an inductor in AC circuit is the combination of resistance and reactance which is called the  impedance, Z.


This impedance value is calculated by Ohm’s law and is given as
Z = V / I
Where Z = total opposition offered by inductor to the current flow, in ohms
V = applied voltage

I = current flowing through the circuit

Impedance Triangle

Another method of determining the impedance is the use of impedance triangle method when inductive reactance and resistance values are known. Below diagram shows an impedance triangle which consists of resistance and reactance vectors.




In the above figure, resistance vector is along with horizontal line (because resistance does not offer any phase shift) and inductive reactance vector is along with vertical line (because pure inductance offers 900 phase shift).
By connecting the ends of these two vectors, impedance, Z is obtained. Therefore, the total opposition to current or impedance can be calculated by
Z = √[(R)2+(XL)]
Where
Z = impedance in ohms
R = resistance in ohms
XL = inductive reactance in ohms
Also, from above diagram,
tan∅= XL/R
sin∅= XL/R
cos∅= R/Z


RL Circuits and Inductive Reactance

The figure below shows the relationship between applied voltage and current through an inductive circuit. In a pure inductive circuit, the current lags the source voltage by 900 . It can also be stated as source voltage leads the current by 900 in an inductive circuit.



When an inductor is connected in series with the resistor RL, series circuit is obtained as shown below. This can also be considered as inductance consisting of some resistance 



Thus, the current and voltage  not exactly maintains 900 phase shift, but less than that of purely inductive case as shown below.






The figure below shows the vector diagram of RL series circuit consisting of voltage drop vectors across resistor and inductor. AE represents the current reference line. AB represents the voltage drop across the resistance which is in phase with current line.
AD represents the inductive voltage drop which leads the current by 900. The resultant of these vectors gives the total voltage across the circuit.


By applying the Pythagoras’s theorem to above voltage triangle, we get
Vtotal= √(VL2+VR2)
tan∅= VL/VR
We know that VR=I×R and VL=I×XL
By these equations we can rewrite the Vtotal as
Vtotal= √((I×R)2+(I×XL)2 )
I = V/ √((R)2+(XL)2) = V/Z (Amps)


Thursday, February 16, 2017

Basic Electronics On The Go - Inductor Color Code

From http://www.electronicshub.org/indcutor-color-code/

An inductor establishes a magnetic field when current passes through it. Most of the inductors are in the range of milli Henry (mH) or micro Henry (µH). These are available with air, ferrite and iron cores. In today’s market there are several inductors available from various manufacturers and their size varies from larger to smaller units.


Inductor values can be determined mainly by two ways, namely text coding and color coding methods. Some inductors are larger in size, thus often their values are printed on their body (name plate details).

However, for smaller inductors, abbreviation or text is used because there may not be enough room , for printing the actual value on it. Also, some inductor values can be determined by reading color on the body of inductors by comparing them with color coding chart.



Inductor Value Identification using Text Marking


In this, the value of the inductor is printed on inductor body which consists of numerical digits and alphabets. For this marking, micro Henry is the fundamental unit of measurement (even if no units are given). The following are the steps of identifying the value of inductor by using text marking method.
  1. It consists of three or four letters (including alphabets and numerical digits).
  2. First two digits indicate the value.
  3. Third digit is the power to be applied for the first two , this means it is the multiplier and power of 10. For example, 101 is expressed as 10*101 micro Henry (µH).
  4. Suffix or fourth letter or alphabet represents the tolerance value of the inductor. Suppose if this letter is K, then tolerance value is ± 10%, for J it is ± 5%, for M it is ± 20% and so on. Follow the tolerance value table given below to know each letter value.


Example for Text Marking Method

Suppose if an inductor is labeled as 223K, find the exact value of inductor.

First two digits, i.e., 2 and 2 represent the first two digits of the inductor value. Third digit, 3 is the multiplier and hence it is 103 = 1000. Now, multiplying with first two digits we get 22000.
Now, it is to be noted that no units are given, hence this value is in micro Henry (µH). Thus the value becomes 22000 µH or 22mH.
Last letter K represents the tolerance and is equal to ± 10%.

Therefore, this is a 22000 µH or 22mH inductor with ± 10% tolerance.
Inductor Value Identification using Color Coding
The color coding system for inductors is very similar to that of resistors, especially in the case of molded inductors. This color coding is in accordance with the color code table. Starting from the band closest to the one end, this color code sequence is identified. 4-band and 5-band color coding methods are described below with examples.

4-Band Inductor Color Code



The above figure shows the 4-band inductor consisting four different color bands. Similar to the number coding, first and second color bands represents the first and second digits of the value, third color band is the multiplier and fourth band is the tolerance.


Therefore the value of inductor can be determined by reading the colors of inductor body and comparing them with color code chart. It is to be noted that the result of this color coded value is in the unit of micro Henry (µH).

The table below shown gives the color corresponding to the numerical values for a four band inductor.

5-Band Inductor Color Code (Military Standard Inductor Color Code)


Usually cylindrical molded inductors are marked with 5 coloured bands. In this, one end of the coil consists of a wide silver band which identifies the military radio-frequency inductors. The next three bands indicate the value of inductance in micro Henries while  the 4th band indicates the tolerance.

The table below shown gives the color corresponding to the numerical values for a five band inductor.





These inductors consist of tolerance values from 1% to 20%. For inductance values less than 10, the second or third band is gold which represents the decimal point. Then remaining bands indicates the two significant bits, and tolerance.

For inductance values equal or more than 10, first two bands represent the significant bits, third one is multiplier and fourth one is tolerance while considering MIL band.


Surface Mount Device (SMD) or Chip Inductor Codes

Some inductors consist of color dots on surface of the device instead of bands and these are very small in size. Generally these are coded according to the top colored dot on the surface. From this top dot we have to calculate the inductor value in the  clockwise direction. These dots will not indicate polarity. This type of inductors are in nano-henries.

Consider the following example:



Green and red color indicates the value of inductor in nano Henries and the orange color indicates the multiplier.
Thus the value of this inductor is 52  103=52,000 nH

If only single dot is represented, the specifications of the inductor must be referred from data sheet of that particular series to that of corresponding manufacture.



                                                                SMD Indcutor


RF Inductors Color Coding

These are also similar to chip inductors. These are smaller in size. Because of this size, the value of inductor is marked with a single or multiple color dots.
In a single color dot, colored dot is represented on one end or middle of the part as shown in below figure. This dot does not indicate the polarity but the value of inductance which is given on the data page of each type of inductor series.

In multi-dot colored representation, inductors are marked with three color dots. These dots do not indicate the polarity. The first and second colored dots on the chip indicate the inductance in nano Henries and the third dot indicates the multiplier as shown in below.






In the above figure, inductor is marked with three colors and hence the value of the inductor is given as
Yellow violet and orange = 47000 nF
Generally these RF variable inductors have the size and voltage specifications marked on the side of the inductors.


For Values Lower Than 10 nH
It is to be noted that, for inductors which are rated lower than 10nH, the third dot will not act like a multiplier. According to the series some of the inductor values are tabulated as below for inductors with coloured dots:



Sunday, February 12, 2017

Basic Electronics On The Go - Types of Inductors and Applications

From www.electronicshub.org/types-of-inductors-and-applications/

Inductor types based on core

There are different types of inductors. Depending on their material type they are basically categorized as follows

Air Core Inductor

Ceramic core inductors are referred as “Air core inductors”. Ceramic is the most commonly used material for inductor cores. Ceramic has very low thermal co-efficient of expansion, so even for a range of operating temperatures the stability of the inductor’s inductance is high. Since ceramic has no magnetic properties, there is no increase in the permeability value due to the core material.


Its main aim is to give a form for the coil. In some cases it will also provide the structure to hold the terminals in place. The main advantage of these inductors are very low core losses, high Quality factor. These are mainly used in high frequency applications where low inductance values are required.



Iron Core Inductor


In the areas where low space inductors are in need then these iron core inductors are the best option.These inductors have high power and high inductance value but are limited in high frequency capacity. These are applicable in audio equipments. When compared with other core inductors these have very limited applications.




inductor with iron core



Ferrite Core Inductor

Ferrite is also referred as ferromagnetic material. They exhibit magnetic properties. They consist of mixed metal oxide of iron and other elements to form crystalline structures . The general composition of ferrites is XFe2O4. Where X represents transition materials. Mostly easily magnetized material combinations are used such as manganese and zinc (MnZn), nickel and zinc (niZn).
Ferrites are mainly two types they are soft ferrites and hard ferrites. These are classified according to the magnetic coercivity. Coercivity is the magnetic field intensity needed to demagnetize the ferromagnetic material from complete saturation state to zero.



Soft Ferrite

These materials will have the ability to reverse their polarity of their magnetization without a significant amount of energy.

Hard Ferrite
These are also called as permanent magnets. These will keep the polarity of the magnetization even after removing the magnetic field.

Ferrite core inductor will help to improve the performance of the inductor by increasing the permeability of the coil which leads to increasing the value of the inductance. The level of the permeability of the ferrite core used within the inductors will depend on the ferrite material. This permeability level ranges from 20 to 15,000 according to the material of ferrite. Thus the inductance is very high with ferrite core when compared to the inductor with air core.


Iron Powder Inductor


These are formed from very fine particles with insulated particles of highly pure iron powder. This type of inductor contains nearly 100% iron only. It gives us a solid looking core when this iron power is compressed under very high pressure and mixed with a binder such as epoxy or phenolic. By this action iron powder forms like a magnetic solid structure which consists of distributed air gap.

Due to this air gap it is capable of storing high magnetic flux when compared to the ferrite core. This characteristic allows a higher DC current level to flow through the inductor before the inductor saturates. This  reduces the permeability of the core.

The initial permeability is mostly  below 100 only. Thus these inductors posses high 
temperature co-efficient stability. These are mainly applicable in switching power supplies.

Laminated Core Inductor

These core materials are formed by arranging many number of laminations on top of each other. These laminations may be made up of different materials and with different thicknesses. So this construction has more flexibility.These laminations are made up of steel with insulating material between them.
These are arranged parallel to the field to avoid eddy current losses between the laminations. These are used in low frequency detectors. They have high power levels so , they are mostly used at power filtering devices for excitation frequencies above several KHz.




Bobbin based inductor


These are wounded on cylindrical bobbin so these are named as bobbin based inductors. These are mainly used for mounting on printed circuit boards.
It consist of two types of leads they are axial lead and radial lead. Axial lead means lead exits from both sides of the core for horizontal mounting on PC board. Radial lead means lead exits from both sides of the core for vertical mounting on PC board. These are shown below



Toroidal Inductor


Wire wounded on core which has ring or donut shaped surface. These are generally made up of different materials like ferrite, powdered iron and tape wound etc. This inductor has high coupling results between winding and early saturation.
Its arrangement gives minimum loss in magnetic flux which helps to avoid coupling magnetic flux with other devices. It has high energy transferring efficiency and high inductance values at low frequency applications. These inductors are mainly used in medical devices, switching regulators, air conditioners, refrigerators, telecommunications and musical instruments etc.



Multi-layer Ceramic Inductors


The name itself indicates that it consist of multi layers. Simply by adding additional layers of coiled wire that is wound around the central core to the inductor gives multi-layer inductor. Generally for more number of turns in a wire , the inductance is also more.
In these multi-layer inductors not only the inductance of the inductor increases but also the capacitance between the wires also increases. The  advantage of these inductors is at lower operating frequencies, we can get higher inductance results.

These are being used at high frequencies to suppress noise, in signal processing modules like wireless LANs, Bluetooth etc. These are also used in mobile communication systems.



Film Inductor

This uses a film of conductor on a base material. Thus according to the requirement this film is shaped for conductor application. Film inductors in thin size are suitable for DC to DC converters that serve as power supplies in smart phones and mobile devices. The Rf thin film inductor is shown below:


Variable Inductor

It is formed by moving the magnetic core in and outside of the inductor windings. By this magnetic core we can adjust the inductance value. When we consider a ferrite core inductor , by moving its core inside and outside on which the coil is wounded , a variable ferrite core inductor can be formed.

These type of inductors are used in radio and high frequency applications where the tuning is required. These inductors are typically ranged from 10 μH to 100 μH and in present days these are ranged from 10nH to 100 mH.



Coupled Inductors


The two conductors connected by electromagnetic induction are generally referred as coupled inductors. We already seen that whenever the AC current is flowing in one inductor produces voltage in second inductor gives us mutual inductance phenomenon.

Coupled inductors will work on this phenomenon only. These can isolate two circuits electrically by transferring impedance through the circuit. A transformer is one  type of coupled inductor.


Molded inductors
These inductors or molded by plastic or ceramic insulators. These are typically available in bar and cylindrical shapes with wide option of windings.




Friday, February 3, 2017

Basic Electronics On The Go - Inductor Basics

From http://www.electronicshub.org/inductor-basics/

From https://en.wikipedia.org/wiki/Henry_(unit)


Introduction

Inductor consists of wire wound around a core of ferrite material that includes an air gap. Inductor stores the energy in the form of the magnetic field. Inductor has many electrical properties when subjected to a magnetic field. One of the important property of this inductor is whenever the current flows through the wire it creates the magnetic field around it. 

If we coil the wire , the magnetic field is stronger. When the electric current flows through the coil, the magnetic flux will increase exponentially and stabilize at particular point, then stores the electric energy in the form of magnetic energy. When electric supply stops then the magnetic energy will decrease exponentially and turns back into electrical energy. By this we can say that it will temporally store the energy. The faster the change in the magnetic field the induced emf or voltage will be greater. To know about current and magnetic flux relation let us learn about  Lenz’s Law.

Lenz’s Law

Before going to Lenz’s Law first we have to know about Faraday’s Law of induction. It states that the magnitude of emf induced in the coil is equal to the rate of change of flux that links with the coil.  For a tightly wound coil of wire, composed of N identical turns, each with the same ΦB, Faraday's law of induction states that

ԑ = -N (∂Φ_B / ∂t)

where N is the number of turns of wire and Φ_ B is the magnetic flux through a single loop.

Whereas the product of number of turns in the coil and flux related with the coil gives us the flux linkage.

Lenz’s Law states that an emf is generated by change in magnetic flux as stated in faraday’s law. The polarity of this induced emf is such that it produces a current such that magnetic field opposes the change which produces it. Lenz's law is shown by the negative sign in Faraday's law of induction:
ԑ = -N (∂Φ_B / ∂t)
Where ∂Φ_B = change in the magnetic flux
ԑ = induced emf
N = no. of turns


Working of inductor

When the electric current is flowing in the coil, the coil will build up the magnetic field around it. At the time of building the field , the coil inhabits the flow of current and once if the field is built up, current can flow normally through the wire. Due to this reason there will be exponential increase in the magnetic flow before reaching the steady state. When the electric current is turned off then the magnetic field around the coil will keep the current flow in the coil until the field collapses. This makes the electric current  decrease exponentially before it reaches its actual state.
When the wire is coiled as a series of continuous loops , it is called as solenoid. In this type , the magnetic field strength will increase or decrease with the increasing and decreasing currents respectively. It is similar to effect of bar magnet but with the variable field strength.

magnetic field of coil  and bar magnet

Inductor Symbols

The symbol of Air core




The symbol for Iron core



The symbol for Ferrite core



The symbol for Variable core







Inductance of Inductor

Inductance is the property of an Inductor .The current generated in the inductor due to magnetic field is proportional to the rate of change of magnetic field is called the inductance. The higher the inductance value, more the inductor will resists from the sudden changes in the current.
Inductance is given by  L = µN2A / l
Where
L – Inductance of the coil.
µ – Permeability of the core.
N-Number of tuns in the coil
A-Area of the coil.
l -Length of the inductor.


Self-inductance
A change in the current causes change in the voltage in that circuit due to the magnetic flux generated by the current flow. Simply inductance within the coil gives us self-inductance. Chokes are best example for self-inductance effect.
Mutual-inductance
A change in the current in one circuit causes the change in voltage of next circuit .The linkage of magnetic field between both circuits leads to mutual inductance. Transformers are best example for mutual inductance effect.



Inductors in series


When ‘n’ number of inductors are connected in series the total inductance value is the sum of all the individual inductances.
Ltotal = L1+L2+… +Ln

Inductors in parallel

When ‘n’ numbers of inductors are connected in parallel the total inductance value  is equated as follows
Ltotal = 1/ ((1/L1) + (1/L2) +..+ (1/Ln))
If we observe these two equations are very similar to the resistors connected in series and parallel.

Inductance Units

The SI unit of inductance is Henry. It is named after the American physicist Joseph Henry. This is denoted by ‘H’.
The inductance of an electric circuit is one henry when an electric current that is changing at one ampere per second results in an electromotive force of one volt across the inductor. This is equated as
H= (V.s)/A = Wb/A.
Where V = Volts, s = second, Wb = Weber, and A = Ampere.


Factors influencing inductance

1.Material of the core
One of the important factor that affects the inductance value is permeability. If the magnetic permeability of the core is more the inductance is more and if this permeability of the core is less, the inductance is also less. Because a core with higher permeability will generate greater amount of magnetic flux for any given amount of field force.



2.Number of turns of the inductor

If the number of turns of the inductor increases, inductance also increases. Because for any given amount of current , the amount of generated magnetic flux is always greater , if the inductor consists of more number of turns.
3.Length of the coil
If the coil length increases the inductance decreases. If the length is decreased, inductance is increased. 
                  4.Area of the coil
                    By taking the cross-sectional area of the coil, if the area                                increases the inductance increases and if the area decreases,                     value of the inductance will comparatively decreases. As the                       area increases more flux is induced and inductance is more.
The inductance value can also be affected by the external effects caused by the other wires and components which are near by the inductor, once it is assembled in the circuit. For accurate inductance value the approximated inductance value has to be calculated.

Let us consider a solenoid wound with a single layer of turns with some diameter of the wire and the turns are placed evenly, then the typical formula for approximating the inductance value is given as follows.
L = (d2n2)/(l + 0.45d)
Where
d = diameter of the coil in meters.
n = no. of turns in the coil.
L = inductance in henry.
l = length of the wire in meters.


Current, Voltage and power calculation


The work done by the source in order to remain the current flowing through the coil against the induce emf is power. It is given as
P = d/dt (½ (L x I2)).
The magnetic field density B (t) which is measured in tesla is equal to the magnetic field strength H (t), multiplied by the magnetic core permeability  ‘μ’ .

This is given as

B (t) = μ x H (t).

The magnetic flux which is measured in webers, is equal to the magnetic flux density B (t), multiplied by the cross-sectional area of the core ‘Ac’.
This is given as
Φ(t) = Ac x B (t).
The energy stored in an inductor is equal to the amount of work done to establish the current flow through the inductor and to generate magnetic flux.
This given as
E = ½ (L x I2)
Where
L = Inductance,
I = current flow through the inductor and
E = Energy stored.



Quality Factor

Since the inductors are formed by the electrically conductive metal wire , they will have a series resistance. This series resistance will generate heat by converting the electric current flowing through the coil. Due to this heat the sensitivity of the inductor decreases. Thus the quality factor is nothing but the ratio of the inductance to the resistance. This is given as
Q = ω L/R
Where
Q = quality factor
ω = angular frequency (Hz)
L = inductance (H)
R = resistance (Ω)


Back EMF generated in an inductor: The EMF produced in the inductor will depends on the source currents that is either the current is AC or DC.
The self-induced emf VL = – L di/dt is applicable only for the AC current because there will be rate of change of current that is di/dt is not equal to zero. If the flow of the inductor current is constant , that is at DC current the di/dt is zero. At this stage the inductor acts like a piece of wire.

Time constant of an inductor: Let us consider the circuit as shown below with an inductor and an open switch.


Since the switch is open there will be no flow of current in the circuit. Thus the rate of change of current di/dt is zero at this condition. We know that when di/dt is zero there is no self-induced emf in the circuit.

When we close the switch the current will flow through the circuit and slowly rise to its maximum value at the rate determined by the inductance of the inductor. 

This rate of current flowing through the inductor multiplied by the inductors inductance in Henry’s, results in some fixed value self-induced emf being produced across the coil as determined by Faraday’s equation above, VL = Ldi/dt.
This self-induced emf across the inductors coil, ( VL ) fights against the applied voltage until the current reaches its maximum value and a steady state condition is reached. The current which now flows through the coil is determined only by the DC or “pure” resistance of the coils windings as the reactance value of the coil has decreased to zero because the rate of change of current (di/dt) is zero in steady state. In other words, only the coils DC resistance now exists to oppose the flow of current.

Likewise, if switch, (S1) is opened, the current flowing through the coil will start to fall but the inductor will again fight against this change and try to keep the current flowing at its previous value by inducing a voltage in the other direction. The slope of the fall will be negative and related to the inductance of the coil as shown below.




Inductor Applications

  1. Inductor with inductances in the nano-henry range , will only filter out very high frequencies i.e., above 100 MHz so these are mainly used in radio frequency circuits like old boom box in 1980s.
  2. Inductors in micro-henry range will filter out the frequencies about 50 KHz to few MHz. These are typically used in D.C. power supplies to smooth out the voltage.
  3. Inductors in milli-henry range are very effective and these are used in audio crossover circuits to separate low and high frequency sounds.
  4. Inductor ideally acts like a low pass filter since the impedance of an inductor increases as the frequency of a signal increases.
  5. Since inductor will sense the magnetic fields from a distance these are used in inductive sensors. These inductive sensors are used in traffic signalling to detect the amount of traffic.
  6. By combining two inductors which have a shared magnetic field will acts like a transformer. These inductive based transformers are applicable only at lower frequencies.
  7. In fixed speed applications inductive motors are used.