WORKING OF TRANSISTORS

How Transistors Work – A Simple Explanation :

Transistors are composed of three parts a base, a collector, and an emitter. The base is the gate controller device for the larger electrical supply. The collector is the larger electrical supply, and the emitter is the outlet for that supply. By sending varying levels of current from the base, the amount of current flowing through the gate from the collector may be regulated. In this way, a very small amount of current may be used to control a large amount of current, as in an amplifier.

 The same process is used to create the binary code for the digital processors but in this case a voltage threshold of five volts is needed to open the collector gate. In this way, the transistor is being used as a switch with a binary function: five volts  ON, less than five volts OFF. 

quantum mechanical transistor  :

The quantum mechanical transistor is the equivalent of turning on a light bulb without closing a switch: Electrons "tunnel" from path to path through a barrier that, according to classical physics, is impenetrable.
The process takes place with extreme rapidity.
The term "tunneling" may bring to mind moles or the highway department, but physicists use it to describe an effect in which particles, like electrons, appear in places where by rights they should not be able to go. In effect, they have tunneled under an energy barrier the same way cars use a tunnel to appear at a new location without having to drive over an impossibly high summit. The atomic-scale effect is explained only by quantum mechanical principles.

The device, dubbed DELTT (Double Electron Layer Tunneling Transistor), offers promise of significant improvements in the speed of computers and in the accuracy of sensors. 

The very fast device may run at a trillion operations a second, as have other, more primitive tunneling devices. This is roughly ten times the speed of the fastest transistor circuits currently in use. Actual speed has not yet been measured

 **The extremely fast device also runs at extremely low power tens of millivolts and microamps  as compared with the few volts and milliamps needed by transistors currently in use.

How it works :

The technique relies in part upon the dual wave-particle nature of matter. In the device, two gallium arsenide layers, each only 150 angstroms thick, are separated by a 125 angstrom aluminum-gallium- arsenide barrier , the equivalent of the yards of two houses separated by a sturdy fence. Ordinarily, gallium arsenide electrons in one yard do not have the energy to climb the fence to reach the other yard. But the tiny thickness of the barrier causes the electrons to behave like waves, which can poke into the barrier.

When an electron is adjusted to have the same energy and momentum states in both regions -- something that can be done by applying a voltage to these regions -- it can pass from one region to the other without any scattering, as occurs in normal electron motion due to crystal imperfections. In effect, they tunnel under the barrier fence.

Types of transistor  :

There are two main types of transistors-junction transistors and field effect transistors.

 Each works in a different way. But the usefulness of any transistor comes from its ability to control a strong current with a weak voltage. For example, transistors in a public address system amplify (strengthen) the weak voltage produced when a person speaks into a microphone. The electricity coming from the transistors is strong enough to operate a loudspeaker, which produces sounds much louder than the person's voice. 

Bipolar junction transistor  ( BJT ) : 

A junction transistor consists of a thin piece of one type of semiconductor material between two thicker layers of the opposite type. For example, if the middle layer is p-type, the outside layers must be n-type. Such a transistor is an NPN transistor. One of the outside layers is called the emitter, and the other is known as the collector. The middle layer is the base. The places where the emitter joins the base and the base joins the collector are called junctions. 

The layers of an NPN transistor must have the proper voltage connected across them. The voltage of the base must be more positive than that of the emitter. The voltage of the collector, in turn, must be more positive than that of the base. The voltages are supplied by a battery or some other source of direct current. The emitter supplies electrons. The base pulls these electrons from the emitter because it has a more positive voltage than does the emitter. This movement of electrons creates a flow of electricity through the transistor. 

The current passes from the emitter to the collector through the base. Changes in the voltage connected to the base modify the flow of the current by changing the number of electrons in the base. In this way, small changes in the base voltage can cause large changes in the current flowing out of the collector.

there is 4 common types of biasing of transistor,

1. BASE BIAS
2. COMMON EMITTER BIAS
3. COLLECTOR FEEDBACK BIAS
4. VOLTAGE DEVIDER BIAS

FIELD EFFECT TRANSISTORS :

                                                                                                         

A field effect transistor has only two layers of semiconductor material, one on top of the other. Electricity flows through one of the layers, called the channel.

 A voltage connected to the other layer, called the gate, interferes with the current flowing in the channel. Thus, the voltage connected to the gate controls the strength of the current in the channel. There are two basic varieties of field effect transistors-the junction field effect transistor(JFET) 

and the metal oxide semiconductor field effect transistor (MOSFET).

 ***Most of the transistors contained in today's integrated circuits are MOSFETS's.

Applications of Transistors :

A . The transistor as an amplifier 

1. A transistor can be used to amplify current. This is because a small change in base current causes a large change in collector current.

2. Example is a microphone. 

3. Sound waves that are fed into the microphone cause the diaphragm in the microphone to vibrate. 

4. The electrical output of the microphone changes according to the sound waves. 

5. As a result, the base current is varying because of the small alternating voltage produced by the microphone. 

6. A small change in the base current causes a large change in the collector current. 

7. The varying collector current flows into the loudspeaker. There, it is changed into the sound waves corresponding to the original sound waves. 

8. The frequencies of both waves are equivalent but the amplitude of the sound wave from the loudspeaker is higher than the sound waves fed into the microphone. 

Component: Function

Microphone: To change sound signal to electrical signal 

Capacitor: To block a steady current from flowing into the transistor and microphone. 

Potential divider: To apply a proportion of the total voltage across the emitter-base junction so that 

the junction is forward-biased. 

Transistor: To amplify the input wave form. 

Loudspeaker: To change the electrical signal to sound wave. 

B. The transistor as switch 

1. In a transistor, no current can flow in the collector circuit unless a current flows in the base circuit. This property allows a transistor to be used as switch.

2. The transistor can be turned on or off by changing the base. 

3. There are a few types of switching circuits operated by transistors. 

C. Light-Operated Switch

1. The circuit is designed to light the bulb in a bright environment and to turn it off in the dark.

2. One of the components in the potential divider is a light-dependent resistor (LDR). When it is placed in DARKNESS, its resistance is large. The transistor is switched OFF. 

3. When LDR is lighted by bright light, its resistance falls to small value resulting in more supply voltage and raising the base current. The transistor is switched on, collector current flows and bulb lights up. 

D. Heat-operated switch

1. One important component in the circuit of a heat-operated switch is the thermistor.

2. Thermistor is type of resistor that responds to the surrounding temperature. Its resistance increases when the temperature is low and vice versa. 

3. When heat is applied to the thermistor, its resistance drops and a greater share of supply voltage is dropped across R. The base current increases followed by a greater increase in the collector current. The bulb will glow and the siren will sound. 

4. This particular circuit is suitable as a fire alarm system. 

E. Integrated Circuits 

1. An integrated circuit (IC) consists of transistors, resistors, diodes and capacitors combined together in one wafer-thin chip of silicon.

2. This is one wafer-thin chip is called a microchip. 

3. The microchip is only a few millimeters square with a thickness of 0.5 mm.

HOW ZENER DIODE WORKS

Zener Diode Working Function

Zener diodes are normal P-N junction diodes operating in a reverse biased condition. Working of the Zener diode is similar to a P-N junction diode in forward biased condition, but the uniqueness lies in the fact that it can also conduct when it is connected in reverse bias above its threshold / breakdown voltage.

 These are among the besic types of diodes used frequently, apart from the normal diodes.

Principle behind Zener diode Working :

As stated above the basic principle behind the working of a zener diode lies in the cause of breakdown for a diode in reverse biased condition. Normally there are two types of breakdown- Zener and Avalanche.

   

Zener Breakdown :

This type of breakdown occurs for a reverse bias voltage between 2 to 8V.  Even at this low voltage, the electric field intensity is strong enough to exert a force on the valence electrons of the atom such that they are separated from the nuclei. This results in formation of mobile electron hole pairs, increasing the flow of current across the device.  Approximate value of this field is about 2*10^7 V/m.

This type of break down occurs normally for highly doped diode with low breakdown voltage and larger electric field. As temperature increases, the valence electrons gain more energy to disrupt from the covalent bond and less amount of external voltage is required. Thus zener breakdown voltage decreases with temperature.

Avalanche breakdown

This type of breakdown occurs at the reverse bias voltage above 8V and higher.  It occurs for lightly doped diode with large breakdown voltage.  As minority charge carriers (electrons)flow across the device, they tend to collide with the electrons in the covalent bond and ,cause the covalent bond to disrupt.As voltage increases, the kinetic energy (velocity) of the electrons also increases and the covalent bonds are more easily disrupted, causing an increase in electron hole pairs. The avalanche breakdown voltage increases with temperature.So there is a relation between tempareture.

Zener diode applications :

Voltage regulator :

The load voltage equals breakdown voltage V-Z of the diode. The series resistor limits the current through the diode and drops the excess voltage when the diode is conducting.

Zener diode in overvoltage protection :

If the input voltage increases to a value higher than the Zener breakdown voltage, current flows through the diode and create a voltage drop across the resistor; 

this triggers the SCR and creates a short circuit to the ground. The short circuit opens up the fuse and disconnects the load from the supply.

Zener Diode Clipping Circuits :

Zener diodes are used to modify or shape AC waveform clipping circuits.

The clipping circuit limits or clips off parts of one or both of the half cycles of an AC waveform to shape the waveform or provide protection.

Zener Diode Reference
	Here is a handy zener diode list if you work with these critters.  This list is far from complete, but these are some common numbers we encounter.

                                                    

HOW A DIODE WORKS

Introduction to Diodes :

The Diode can be considered as the simplest and most fundamental element in electronics, which is composed of a p-n Junction. It is a two terminal device,

 shows its schematic symbol, where the "+" terminal is called Anode and is connected to the p-Region and the "-" terminal is called Cathode and is connected to the n-Region.

Symbol of Diode :

The symbol of a diode is shown below. The arrowhead points in the direction of conventional current flow.

We can create a simple P-N junction diode by doping donor impurity in one portion and accept impurity in other portion of silicon or germanium crystal block. These doping make a P-N junction at the middle part of the block beside which one portion becomes p-type (doped with trivalent or accept impurity), and another portion becomes n-type (doped with prevalent or donor impurity). We can also form a P-N junction by joining a p-type (doped with a trivalent impurity) and n-type ( doped with a prevalent impurity) together with a special fabrication technique. Hence, it is a device with two elements, the p-type forms anode, and the n-type forms the cathode.

Working Principle of Diode

Forward Biased Diode

In a P-N junction diode when the forward voltage is applied i.e. positive terminal of a source is connected to the p-type side, and the negative terminal of the source is connected to the n-type side, the diode is said to be in forward biased condition. We know that there is a barrier potential across the junction. This barrier potential is directed in the opposite of the forward applied voltage. So a diode can only allow current to flow in the forward direction when forward applied voltage is more than barrier potential of the junction. This voltage is called forward biased voltage. For silicon diode, it is 0.7 volts. For germanium diode, it is 0.3 volts. When forward applied voltage is more than this forward biased voltage, there will be forward current in the diode, and the diode will become short circuited.

Hence, there will be no more voltage drop across the diode beyond this forward biased voltage, and forward current is only limited by the external resistance connected in series with the diode. Thus, if forward applied voltage increases from zero, the diode will start conducting only after this voltage reaches just above the barrier potential or forward biased voltage of the junction. The time, taken by this input voltage to reach that value or in other words, the time, taken by this input voltage to overcome the forward biased voltage is called recovery time.

Reverse Biased Diode

Now if the diode is reverse biased i.e. positive terminal of the source is connected to the n-type end, and the negative terminal of the source is connected to the p-type end of the diode, there will be no current through the diode except reverse saturation current. This is because at the reverse biased condition the depilation layer of the junction becomes wider with increasing reverse biased voltage. Although there is a tiny current flowing from n-type end to p-type end in the diode due to minority carriers. This tiny current is called reverse saturation current. Minority carriers are mainly thermally generated free electrons and holes in p -type and n- type respectively. Now if reverse applied voltage across the diode is continually increased, then after certain applied voltage the depletion layer will destroy which will cause a huge reverse current to flow through the diode.

 If this current is not externally limited and it reaches beyond the safe value, the diode may be permanently destroyed. This is because, as the magnitude of the reverse voltage increases, the kinetic energy of the minority charge carriers also increase. These fast moving electrons collide with the other atoms in the device to knock-off some more free electrons from them. The free electrons so released further release much more free electrons from the atoms by breaking the covalent bonds. This process is termed as carrier multiplication and leads to a considerable increase in the flow of current through the p-n junction.


Quantum tunneling relation with diode : 

is the passing of electrons through an insulating barrier which is thin compared to the de-Broglie .electron wavelength. If the “electron wave” is large compared to the barrier, there is a possibility that the wave appears on both sides of the barrier.

In classical physics, an electron must have sufficient energy to surmount a barrier. Otherwise, it recoils from the barrier. (Figure) Quantum mechanics allows for a probability of the electron being on the other side of the barrier. If treated as a wave, the electron may look quite large compared to the thickness of the barrier. Even when treated as a wave, there is only a small probability that it will be found on the other side of a thick barrier. See green portion of curve, (Figure). Thinning the barrier increases the probability that the electron is found on the other side of the barrier.

Tunnel diode: 

The unqualified term tunnel diode refers to the esaki tunnel diode, an early quantum device. A reverse biased diode forms a depletion region, an insulating region, between the conductive anode and cathode. 

This depletion region is only thin as compared to the electron wavelength when heavily doped– 1000 times the doping of a rectifier diode. With proper biasing, quantum tunneling is possible. 

Types of Diode

The types of diode are as follow :

1. Zener diode

1. P-N junction diode

1. Tunnel diode

1. varactor diode

1. Schottky diode

1. Photo diode

1. PIN diode

1. LASER diode

1. Avalanche diode

1. Light emitting diode

RELATION BETWEEN PHYSICS AND THE ELECTRONICS

Physics is the study of matter and energy at fundamental level.relativity describes the nature of spacetime.quantum mechanics is a mathamatical formulation that explains fundamental particles.so physics is related to chemistry,biology,electronics and all other scientific fields.electrodynamics is the study of electromagnetic force(one of the four fundamental forces of nature).electronics is all about using pure physics to build something useful like transistor,diode,amplifier,logic gates etc.

it is the mathematical and experimental study of these components.it includes both equations and graphs between various parameters.electronics is completely based on kirchoff laws,faradays law or to be more precise Maxwell's equations.other areas like fermi dirac statistics,plank equation, Maxwell boltzmann statistics explain semiconductors and lasers.band gap of semiconductors can be explained by solving schrodinger equations.the crystal structure study is required by methods like x ray diffraction for development of compents.

                                                           

electronics is an abstraction.electronic engineers often make things simple.like they may assume a bulb in a circuit to be simple resistor.they don't need to study what materials are used in bulb,how the filament ignites,what is the wavelength of light emitted,electronic configuration of atoms and so on. An electronic engineer bachelor doesn't need to know deeply quantum mechanics but should have basic knowledge.a master should know quantum mechanics because modern electronic circuits are small and compact in the order of quantum realm.nano electronics is the application of quantum mechanical properties to make fast,small and energy efficient components.electrical inventors like Tesla 
who discovered transformers,tesla coil,ac currents,antenna used the concepts of Maxwell electromagnetics.Shockley couldn't have developed semiconductors if quantum mechanics had not been developed. Modern physics research requires many electronic components.telescopes like Hubble,Chandra,gravitational waves detector(LIGO),LHC all are very complex devices that use various electronic components,sensors,transducers directly or indirectly(ie computers). After all no science is completely independent of other.everything is related.

How do protons and electrons relate to electricity?

Protons and Neutrons . Protons don't really relate to electricity. Electron do because electricity is the flow of electrons through a wire.. Answer . Protons don't really relate to electricity except in some nuclear physics applications. 

  

                                           

But protons are not generally thought of as associated with "normal" electricity.

Electrons do because electricity, by definition, is the flow of electrons through a wire.. Answer .

 In its most fundamental form, electricity is the movement of charged particles.

in this image you can see how a electron is moved..for this how current is flowing.


What is the difference between Electronic and Electronics  :

electronic is something that describes an equipment or gadget while electronics is the science that deals with the movement of electrons in a vacuum, plasma, semiconductor or gaseous media

What is the relation between electricity and electronics:

Answer . According up to my knowledge the electricity is the branch of physics which deals with the study of flow of current mostly throw pure conductor, while electronics is also the branch of physics but that deals with the mostly the study of flow of electrons throw semiconductor devices.. In other words i want to explain the electricity is the basic thing which causes the electronic appliances to work on and electronics helps in controlling and maintainence of electrical supplies.. Electronics is a physical study of electrons emission. Electricity is the result of current flow.

What is the difference between Electronic and Electronics:

electronic is something that describes an equipment or gadget while electronics is the science that deals with the movement of electrons in a vacuum, plasma, semiconductor or gaseous media.


What is the relation between electrons and gravity :


Electrons have a mass, so gravity affects them just as it would as anything else. In the search for a unified theory of physics, a better link may be established, but at the moment, that's all we know.

What is the physics in electronics  :

Firstly electricity is the flow of electrons. An electric current moves in the opposite direction to that of the electrons themselves (unless i think you live in Canada... at any rate one country changed it) and as such is thought of as the 'positive' flow of electrons. So although electrons move from the negative to the positive terminal of a circuit, the current flows from the positive to the negative. basic formula for looking at circuits: V=I*R V= voltage (in volts, the amount of energy that each coulomb has (Joules/coulomb)) I= current (in Amperes, basically speed of electricity(Coulombs/second)) R= resistance (in ohms, the amount of J*s/C^2, or total energy divided by coulombs squared). Electrons are orbiting charge particles around the nucleus and the number differs as shown in the periodic table. However if a potential is applied they leave said orbit and flow to the next nucleus leaving a hole behind. therefore as the electrons flow from positive to a more negative potential these HOLES flow in the opposite direction as a consequence. In the USA it is acceptable as electron flow. But the principle and result is the same if you understand it.

How does physics and mathematics connect to electronics :


Physics is a branch of science studies the nature and properties of matter. Electrons are constituent parts of matter and so their study is a part of physics.

The behaviour of electrons is governed by mathematical rules and that is why mathematics is critical for electronics.