Common Base configuration of BJT (Voltage amplification)

In this type of configuration we have, the Base terminal of BJT is common with both input and output. Where input is provided to the Emitter and output is collected from the collector. The circuit of the configuration is shown in the figure below. This configuration is used for the voltage gain and current buffer. And we have an input impedance that is low and output impedance is high.

Application

Common base the configuration is not used for the low-frequency input signal and for low frequency operating circuit. Though it is used when there is low input impedance is connected or present. Such as preamplifier, in a where we have low signal and we have to strengthen it out. So there we use a common base configuration.
While mainly it is used for very high frequency and ultra-high frequency. It is because its input capacitance does not affect by the amplification process. Due to which high frequency does not degrade or change.

Circuit:

As you can see in the figure, that base is common with input and output, while Emitter is connected to the input, and the collector is connected to the output. There is a battery connected between base and emitter, to forward-biased base-emitter junction. To forward bias we need to connect the positive side of the battery to the P side of BJT and negative side of the battery to the N side of BJT (In PNP case emitter is P side and Base is N side). There is another battery connected between collector and base to reverse biased the collector-base junction. To do this we have connected the positive side with the base and negative side with the collector.

Working:

Current Gain

Let’s first see the current flow in this configuration. We all know that current flows from the positive terminal of the battery to the negative terminal of the battery. So, in this case, current I_E flows from V_BE towards the emitter, from there some of the current flows towards the base region which is I_B and remaining all the current goes towards the collector. So we can recall the equation,

I_E = I_B + I_C

I_E is the input current and I_C is the output current. So this equation shows that output current I_C can never be greater than input current I_E. So current gain could never be greater than 1. It will be “1” or “less than 1”.

Current Gain equation will be

$$ α= I_C/I_E , where\ "α"\ is \ current\ gain $$

Using this equation we can find out the current gain of a circuit.

Voltage gain

Now let’s see how it provides us the voltage gain (amplification).

As we have the current gain$$  α=I_C/I_E $$ 
And resistance gain              $$ = R_L/R_I_N , $$ So using Ohm’s law(V=IR), We get,
Voltage gain= Current gain x Resistance gain
Voltage gain = $$ I_C/I_E × R_L/R_I_N = {I_C R_L}/{I_E R_I_N} $$

So this equation shows that we can get the desired voltage gain by changing the amount of input and output resistance.

Input characteristics

Now let’s see what the input characteristics of the common base configuration are. Means when we change input voltages V_BE what effects does it has on input current I_E. And keeping the output voltage V_CB constant. We will plot a graph having V_BE on the x-axis as we are changing V_EB that’s why it is on the x-axis. While I_E will be on the y-axis. We will see that there is no current across input when V_EB is 0 to 0.6V. Because the starting voltage of the diode is 0.7V. So when V_EB cross 0.6 V. The I_E will start to grow up and will grow larger with small increase in voltage V_EB. So one case was with V_CB voltage was kept constant at 5V. Now observe another case with V_CB at 7V, and then with 10V. And at last plot a graph of all 3 cases as shown in the figure below.

Output characteristics

Now observe the output characteristics. We will change the output voltage V_CB and observe the change in output current I_C, with input current I_E will remain constant. So V_CB is on the x-axis because we will be changing it and I_C on the y-axis because it will be changed. We will observe that when we keep I_E constant at 0 and will change V_CB, it will have no effect on the I_C. I_C will remain zero at every value of V_CB (0V, 3V, 5V etc). While when we keep I_E constant at 1mA and change V_CB, then we will see I_C will come near to 1mA will remain constant for further increase in V_CB. Now keep I_E constant at 2mA, we will see that after changing V_CB, I_C will come near to I_E, means near to 2mA and will go constant for further increase in V_CB.Will draw plot for all the experiments. And we observe that I_C will never be greater than I_C. As equation 1 tells that.

Bipolar Junction Transistor(BJT) as a Amplifier

Amplification

As we have discussed the other uses of BJTs in previous posts, now there is another main use or advantage of Bipolar transistor is that it can amplify the input signal whether it is voltage or current. As some time we need to amplify the current and sometimes voltage. We provide an input signal to the BJT, and it produces the amplified signal at the output. The gain of the amplifier can be calculated by the ratio of output to the input value of current or voltage. The amplifier does not change the waveform or frequency. It just affects the current and voltage.

How to make BJT an Amplifier:

To make BJT work as amplifier we need to do some different types of configuration of it, in a circuit. There are three configurations, which we can do,

•        Common Base Configuration (only has voltage gain).
•       Common Emitter Configuration (has both voltage and current gain)
•       Common Collector Configuration (only has current gain)

Bi Polar Junction Transistor (BJT): Introduction, Construction and Working

Introduction:

BJT stands for Bipolar Junction transistor which means two polar junctions. The reason it is called Bipolar is that it uses both electrons and holes for carrying charge or to flow the current. While FET is known as a unipolar transistor.

Construction:

As we have discussed diode before, and how it is formed by the junction of two regions, P doped region, and n doped region. The BJT is formed by the combination of two back to back diodes. The Bipolar junction transistor or BJT has two junctions of the semiconductor. In one of the two types (PNP), a thin n-region is shared by two p-regions. And in another type (NPN), a thin p-region is shared by two n-regions, the figure below explains this.

          Fig (a)

                                                                                 Fig (b)

                                   

This complete structure of BJT has three terminals and has three layers. Each terminal for each layer. And the names of these layers are Emitter, Base, and collector shown in above figure. For NPN the arrow is going away from the Emitter terminal and for PNP the arrow is towards the emitter terminal. The reason is explained later.

 Functions of BJT:

BJT can be used for three purposes,

• Current controlling
• switching
• Amplification

Controlling Current:

BJTs are mostly used for controlling the amount of current flows from emitter to collector or collector to base. These are two cases for two different types of BJT (which are PNP and NPN). In PNP the current goes from Collector to emitter with the combination or addition of base current, see fig (a). While in NPN the current goes from Emitter to collector with separation or removal of base current see fig (b). In all this, the current which goes from emitter to collector or collector to emitter is the controlling current and the current which goes or comes from the base is controlled current. Now all this statement means that, the amount of current which have to go from emitter to collector in NPN transistor is decided by or controlled by the current flows towards the base as shown in the below picture.

           Fig(c)

                                                                                    Fig(d)

         

                                                                                          

Equations of current:

This thing also produce the equation of current,

I_E = I_B + I_C

Where I_E is the Emitter current, I_B is the base current and, I_C is collector current.

I_B = I_E - I_C

I_C = I_E - I_B

Diode or pn junction:Definition, explanation, construction

Definition:

"Diode is an electrical component which allow the current to flow in one direction."

Explanation:

Diode is use to flow the current only in one direction and to block the current, if it flows in other direction. This property of blocking current in one direction and allowing it in only one direction is due to its construction which is explain below. It does not change the current, it just block the current to flow in other direction in a circuit. It is also use to convert AC source into DC source.

By blocking the negative interval and allowing only positive interval and by using some filter, decreases the fluctuation.

Construction:-

The diode is made up by the junction of two semiconductor of same material, lets suppose Silicon (Germanium could also be used). One semiconductor is doped with p type material which is boron and other semiconductor with n type material which is phosphorus. This junction is known as P-N junction. 

                                 

In P there is holes which is majority charge and in N there is electrons which is majority charge.

When we make junction of these (p-type and n-type) then holes which are majority charges in P, moves towards the N, and combine with the electrons, and majority charges in 

N which are electrons moves towards the P junction and combine with the holes.

 During this process there form a junction which is known as PN junction. Which consists both holes and electrons. And no more transfer of electrons and holes occurs(because of this junction wall.).

Working:

In electric Circuit, we take symbol for diode is, 

There are bias (applying any source) condition for semiconductor diode. Forward bias and Reverse bias. Diode works only in forward bias. In reverse bias, it blocks the flow of current in circuit or in other words. It becomes open circuit. which is its main property to allow current in only in one direction.

how to forward bias the diode?

We could do it by connecting positive terminal of voltage source from the anode and negative terminal with the cathode. And for reverse bias its vice versa.

How it allows current to flow in forward bias?

It allows current to flow in forward bias, because we connect positive terminal of voltage source with anode and it attracts electron from the N type. So electrons start to flow towards the anode terminal. And there is junction wall between diode, so to overcome there needs voltage of 0.3 or 0.7 . so could say that it is diode starting voltage.

How it blocks current in reverse bias? 

It blocks current in reverse bias, because the positive terminal of voltage source is connected with the cathode so it attracts electron towards cathode terminal so because of it, negative electrons from P type and positive holes from N type goes into junction and increases it. so junction widens and blocks the transfer.

What is Charge, current, voltage? Definition explanation

Charge

Definition:

“Charge or Electrical charge is the property of, unit of a matter”

Explanation:

Charge does not physically exist; this is only a theoretical word. Yes, we use the word charge physically in many topics, just to describe the topic by taking a simple or basic thing (charge). Charge tells that how the matter will react with the other matter or in a magnetic field or in a electric field.

A matter is named as charge, only when there is a difference in number of electrons and number of protons in atom of that matter. If there are more electrons than proton in atom then it is negative charge and if there are more protons than electrons then it is positive charge. Hence this is two types of charge negative and positive charge.

Unit:-

The unit of charge is Coulomb and represented by q. 

Current

Definition:-

“Current is the rate of flow of electric charges.”

Explanation:-

Current is the flow of electric charges which is free electrons. Current flows in a circuit when there is pressure or some force applied to the charges in a circuit. Current flows from negative end to towards positive end. Rate of flow means, how much charges will flow in some fix time. There are two types of current. AC and DC.

AC means alternating current. The current which changes its direction of flow after half interval is known as alternating current.

DC means direct current. The current which flow in only one direction is known as DC current.

Each type of current has its own application.

Unit:-

Unit of current is A Ampere.

“When one coulomb charge will flow in one second through some point, then current will be one ampere.”

 Voltage

Definition:-

“Voltage is a force or pressure which causes the charges to flow through circuit.”

Explanation:

As we discuss in explanation section of current that , current flows through the circuit when some force or pressure applied to the charges in circuit. That force and pressure is Voltage. It is also known as potential difference. In some words, Voltage is the power of current. Means with how much power the current is flowing. The more the voltages the more the rate of flow of current in a circuit.

Unit:

Unit of voltage is V volt.

Electric Potential: definition, explanation, example.

Definition:

"Electric potential is the amount of word done in moving a point test charge from its original position(reference position) to some specific point or position, while moving the charge in direction opposite to direction of field in which charge is present."

Explanation:-

The definition above seem to be difficult to understand the electric potential but I will explain it briefly.
Consider their is a positive point charge A, which have its own electric field around it. And there is another positive test charge B which has no electric field.

 When we will move the test charge B towards the electric field of point charge A then test charge B will move away from the point charge A. This is natural that charge always move from high potential to low potential.

low potential is the area where the charge feels less force while high potential is the area where the force is high.

So to move charge, against its natural movements. we have to provide electric potential or force or to do work. To move test charge B towards the charge A we have to apply some potential which is electric potential, to move the charge from low potential to high potential. So charge B will gain potential energy while moving towards high potential from low potential.

Electric potential is the basic studies of charges behavior with each other. So if you feel there is some type of confusion feel free to comment. The post will be update!

Ampere's law: explanation, definition, formula

Definition:-

"Ampere's Law states that magnetic field around a conductor in which electric current is flowing, is directly proportional to the amount of electric current flowing through conductor."

Explanation:

Ampere's law provide us method or formula to calculate magnetic field, produced by electric current.
Just like electric field is directly proportional to the amount of charge, the magnetic field is directly proportional to the amount of electric current from which it is producing.

Formula:-

The most difficult in ampere's law is to derive its equation or make the formula for calculating the magnetic field around a long conducting wire.
So let's start this,
Consider we have long straight conducting wire, when electric current flows through it, the magnetic fields produces around the wire in concentric circle. As shown in below pic.

Every circle is for some specific part of wire and as we move forward in wire, the distance between these circles increases, that mean magnetic field is decreasing. Direction of magnetic field can be found by Fleming's right hand rule.(with direction of current giving)
Now to make the formula, consider there all the parts of wire( which have there magnetic field circuit) having length L and there magnetic field around these parts or elements is B for (every part).

So the equation will become,

And after removing proportionality,

where 𝝁 is the premiability of material or conductor.
B is the magnetic field and delta L is the sum of all length parts and I is the current flowing through the conductor,
sigma shows that the sum of all the length elements or parts with their magnetic field.
Where delta L could be replace by 2πr for particular(single part) length element.
So Then magnetic filed would become,

Gauss's Law: definition, explanation, formula

Definition:

"Gauss's Law states that, Electric flux around a closed surface is depends upon charged enclosed in that surface and permittivity of free space."

Explanation:

Gauss's law states tell us about electric flux through some closed surface or area,
Electric flux through some area depends upon the charge enclosed by that area and the permittivity of free space in that area.
consider there is a closed sphere and there is charge enclosed in it, the flux out of it or the electric field out of the whole area could be determined with the help of Gauss's law.

Consider we wan to find the electric flux through the green planer area, then it will be simple that electric field lines multiplied by area perpendicular to the lines.

But when there comes a closed surface then there is nothing best except Gauss's law to find electric flux through closed surface (enclosed charge.)

It is not necessary that the surface should be closed sphere it could be any type of closed surface. And we will use Gauss's law to determine the electric flux through it.

Formula:

Mathematically we can determine the electric flux through closed surface by formula,

Where Q is the amount of charge enclosed and Ɛ is the permittivity of free space and 𝛟 is electric flux through the surface.

Electric Charge density, definition, explanation

Definition:

"Electric charge density is the amount of charge on unit volume space or surface or area."

Explanation:

Electric charge density is the density of charge on unit area, the charge could be less or  more, and charge could be positive or negative.
as shown in figure 1 below, in which there is positive charge on surface but less and on figure 2, there is more positive charge.

So area in figure 2 have more electric charge density than figure 1.

The area or volume could be one dimensional, two dimensional and three dimensional. 

Formula:

The electric charge density can be written in the form,

Where p is the charge density and q is the amount of charge and v is the volume of space and unit area. we can replace the v by A, when there is unit area.

Electric flux density, definition, explanation

Definition:

"Electric flux density is the electric flux passing through some unit area, and its direction is perpendicular to that unit area."

Explanation:

"Electric flux density", when we break down this sentence into "electric flux" and "density".
Then it is easy to understand that, the density of electric flux across some area. Consider there is a unit area shown below.

Electric flux is passing through this, in direction perpendicular to the unit area. The amount of electric flux passing through this unit area, in direction perpendicular to the unit area is called Electric flux density.

Formula:

When we write mathematically the electric flux density it is equal to the product of electric field E and permittivity of material.

                                                                           D=Ɛ.E

Unit:

The unit of electric flux density is coulombs per meter squared. 

Coulomb's law, definition explanation

Definition:-

"The magnitude of electrostatic force of attraction and the magnitude of electrostatic force of repulsion between two point charges is directly proportional to the product of magnitude of both charges and inversely proportional to the square of distance between them(both charges)."

Formula:-

mathematically we can write this in the form,

where F is the force,

q1 is the charge 1 and q2 is the charge 2,

and r is the distance between them.

this proportionality can be removed by placing proportionality constant k. in the formula, 

where the value of this constant depends upon the medium between the two point charges.

When there will be air then its value will be 9.0 x 109 N • m2 / C2.

And this value of k will change, with the change in medium between the two charges.

Lenz's law, definition, explanation

Definition:-

"The electric current induced in a circuit or somewhere, always tries to decrease the source which produces it or flow in opposite direction to decrease its effect."  

Lenz's law expand the law of electromagnetism which only tell about induced electric current.

Explanation:-

As we came to know through Lenz's law that the current induced, always tries to do opposite, for the source which is producing it, 

Example:-

lets take an example of a permanent magnet and a coil. 

When we bring the magnet north pole near to the coil there will be change in magnetic field across coil as we move magnet, thus because of changing magnetic field there will induce electric current in it. As we bought the north pole of magnet to the coil, so current induced in coil will start to flow in such a direction that it will make north pole of it towards the permanent magnet north pole, as everybody knows that, like poles of magnet repel each other, hence there, these two north pole will also follow the same rule. And When we will try to bring back the magnet then the current induced in the coil will flow in such a direction, that it will make south pole towards the permanent magnet north pole, where unlike poles attract each other, hence they will attract each other. 

So by doing this current induced in the coil is trying to oppose the source(permanent magnet). By pushing it back when we bring near it(creating north pole towards north pole of magnet) and by pushing it closer when we bring back the magnet(by creating south pole towards the magnet.)

Faraday'laws of electromagnetic induction

Faraday's have proposed 2 main Laws,
Faraday's law of electromagnetic induction is also known as law of electromagnetism.

Faraday's first law:-

This law is the base of electric generators and motors.

Faraday's law stated that,
"When ever we place a conductor in a magnetic field which is varying with time then there will induced current in the conductor."
And if conductor is connected to a closed circuit then this current will flow through it.

Explanation:-

If a conductor is placed in a field of magnet, if both conductor and magnet are stationary then there will no induced emf in it. But when we will move magnet away from the conductor then magnetic field will change through conductor and then EMF(electromotive force) will induced in conductor. Even if we keep magnet stationary and move conductor then also emf will induced.

Faraday's Second law:-

We use this law often,

"The EMF induced in a coil is equal to the change of flux(by a magnet or something other) with the time. "

Where E is the induced EMF, and N is the number of turns of coil phi is the flux and t is the time.

Explanation:-

When a current is flowing through the coil then there is flux around the coil, when current will change then flux will also changes. And then EMF will induce in a coil.

The induced EMF could increase by:

1.By increasing the number of turns of coil.

2. By increasing rate of changing flux. by changing current rapidly.

3. By using good core on which coil is wound.

Self Induction, definition explanation formula unit

Self Inductance:-

"Self inductance is the property of coil to oppose change in current flowing through it"

Explanation:-

Consider there is a coil wire and current is flowing through it, whenever the current will change flowing through it, then there will induced emf which is known as self induced emf. And its direction will be opposite to the the current flowing through it. If current is increasing then self induced emf will try to decrease or flow in direction opposite to the current. But if current through the coil is decreasing then the induced emf will try to increase this current or will go in same direction as current is flowing.

In other simple words, Self induce emf will try to oppose in change in current.

This phenomena is known as Self induction.

Formula:-

The formula for self induction could be derive from the formula of induced emf formula.

Where L is the self induction, E is the induced emf and di/dt is the rate of changing current.

From this it is clear that self induction will increase when induced emf will increase and will decrease when rate of changing current will increase.

Unit:- 

Unit of self inductance is Henry(H).

"There will be 1 Henry of self inductance when induced voltage will be one and current will change 1 ampere in one second."

Capacitive and Inductive Reactance and their explanation

Capacitive Reactance:-

"Capacitive reactance is the resistance offer by capacitor to the current."

Explanation:-

Whenever there is current flows through the capacitor there is the opposition offer by it to the current, which causes delay in its charging. And its this reactance depends upon the frequency of AC current flowing through it. the more the frequency the less its reactance will be and less the frequency the more the reactance will be. The formula for the capacitive reactance is below.

Inductive Reactance:-

"Inductive reactance is the resistance offer by inductor to the current flowing through it."

Explanation:-

When AC current flows through the inductor it offer some resistance to the current. it depends upon the frequency of current. The more the frequency the more the reactance and less the frequency less the reactance. This behaviour is of inductor when AC current flows through it.

Inductor, Inductance, explanation, formula

Definition:-

"Inductor is an electronic device that is use to store energy in the form of magnetic field."

Explanation:-

Inductor store energy in magnetic field around it. Inductor is an coil of a conductor(wire). wire wounding on some rod or magnet. when a current passes through the conductor then there will be magnetic field around the wire. We wound the wire because by winding there would produce a strong magnetic field around this, we could increase the strength of  magnetic field around coil by taking efficient core like magnet and by increasing number of turns of coil and increasing cross sectional area of inductor. When current flows through the inductor there would produce magnetic field around it and in that magnetic field energy would be store (in the form electrons). It would be store until current is flowing through it. When current will stop it will release all the energy.

Inductor does not allow AC current to flow through it due its changing direction nature. While inductor resist to change in current so it becomes open in a circuit while AC current flows through the circuit. It allows DC current to flow through it. After charging completely it allows DC to flow through the circuit hence become short in circuit with zero resistance.

Inductance:-

Inductance is the property of a inductor which is that "whenever Flux is changed in it, it produces an EMF."

or in simple words

Inductance is the ability of an inductor to store energy in the form magnetic field.

Henry is the unit of Inductance.

Formula:

formula for inductance of inductor is,

Capacitor, definition, formula, explanation, Capacitance

Definition:-

"Capacitor is an electrical device which is used to store energy or charges between its plates."

Explanation:-

Capacitor is use to store charge so that we could use it later by discharging it. It stores electrical charge between its parallel plates which are known as conducting plates of capacitor. There is no connection between these conducting parallel plates. They are separated by air or some dielectric. We use dielectric in capacitor to increase its efficiency. By using dielectric we could store more charge between its plates.

Capacitor doesn't allow dc current to flow through it because DC current flows only in one direction. so, it after charging from dc current it allows to flow through it as there is nothing in the circuit.

While it allows AC current to flow through it because ac current changes its direction after half interval, so capacitor charges at first half and discharges at 2nd half.

Capacitance:-

Capacitance is the ability of a capacitor to store charge. Capacitance tells us that how much charge we can store between the plates of capacitor. Capacitance is the unit of capacitor in one way. While capacitance has unit Farad. Farad is define as,

"When there will be 1 volts across capacitor then it will charge one coulomb, its mean capacitor have one farad capacitance."

Formula:-

By seeing definition of farad we could write formula for the capacitance of capacitor,

Q = CV

C = Q/V

Power, its definition, explanation, formula, unit

Definition:-

"Power is define as rate of doing work or Work done per unit time."

Explanation:-

Power is the doing some work, taking less time. Power depends upon doing work and time taken to complete the work. A person have more power will do more work but take less time and person have less power will do less work but will take more time. So this is the concept of power. Work does not depend upon time while power depends upon. so this is the only difference between them.

Formula:-

The formula for power is work done per unit time.

Power = Work / time

as work is equal to 

work = F.d

so power would have,

Power = Force.displacement / time

P = F.d / t

Unit:-

Unit of power Watt  is define as " If one joule of work is done in one second then power will be one watt"

P = F.d / t

Watt= Newton. meter / seconds

Watt = joule / second.

Why like charges repel each other and unlike charges attract each other?

Why like charges repel each other?

"Like charges repel each other because, it depends upon where the two charges have their electric field forces directed."

As positive charge have electric field lines going away from it and when two positive charge particles come near to each other there electric field lines tries to bend each other and their lines of forces are opposite in direction with respect to each other so both particles tries to send away to each other and hence in this way they repels each other.

Below diagram explain all the things which is described above.

Why unlike charges attract each other?

Like charges attract each other because their electric field lines are in the same direction in respective to each other, as we know Negative charge have electric field lines towards it(or coming to each other), and positive charge have away from it or going away from it. so when both comes near to each other, while negative charge tries to attract positive charge and positive charge tries to move towards negative each other.

Below picture explain all the phenomena describe above.

Electric Fields lines and Forces

Electric Fields:-

"Electric Fields are the area or space or region around a body or particle which is charged, in which area it effects(attracts or repel) on other body or particle which is charged."

Explanation:-

Consider their is a charged particle A, it has Electric fields lines, because it is charged. When a unit positive charge(small charge) will come into its field lines then it will feel some force, which is the effect of Charged particle A. It will repel the unit charge (as positive and positive repel each other).

The unit positive charge will only feel this force when it will come into the region where there is Electric field lines of Particle A.

In above diagram unit charge 1 will feel force as it is in the field region of charged particle A, but 2 will not feel any force as it is out of field lines of charged particle A. 

Electric Forces:-

"The force which charged unit positive charge feel when it is in the electric field lines of charged particle (A)."

Explanation:-

As Charged particle have electric field region where it exerts some force on some other charged particle (when it comes in the electric field of that charge). There are two type of forces which is exert by the charged particle in its field region. Attractive force and Repulsive force. Positive charge exert repulsive force on other positive charged while it exert attractive force on negative charge. In general there is attractive forces in opposite charges and there is repulsive force in between like charges.  

In below pic A is positive charge and it is repelling other positive charge.

In below pic, A is positive charge which is attracting negative charge.