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Push-Pull Amplifier

Push-Pull Amplifier

The Push-Pull Amplifier commonly used in power amplifier. It is employed in the output stages of the circuits. It is used to get high output power at high efficiency. The audio power amplifiers used in transistor receivers, tape recorders etc. Distortion is greatly reduced by using push-pull operation employing two transistor in a single stage. There systems are usually operated by batteries.

READ – What is Transistor?

Circuit Arrangement

Two transistor Q1 and Q2 placed back employed. The emitter terminals of the two transistor Q1 and Q2 connected together. Both transistors are operated in class B operation. The input signal is applied to the input of two transistors through centre tapped step up transformer. The input transformer is called Driver transformer. Driver transformer supplies equal and opposite voltages to the base circuits of two transistors.

push-pull amplifier

The output transformer has the centre tapped primary winding. The load speaker is connected across the secondary of the output transformer.

Working or Operation

The primary of driver transformer connected to AC supply. The input signal appears across the secondary AB of the driver transformer. During first half of the input signal A becomes positive and end B negative. Here we have used two NPN transistors. This will make the base emitter junction of Q1 forward biased and that of Q2 forward biased. Now the current will conduct through Q1 while Q2 remains in non conducting state.

working of push-pull amplifier

The current conduction through transistor Q1 shown by solid arrow. The amplified signal appears in the upper half of the output transformer.

During Negative half cycle of the supply the terminal A becomes negative and B becomes positive. This will make the case emitter junction of Q1 reverse biased and that of Q2 forward biased. The transistor Q2 and transistor Q1 remains in non-conducting state.

operation of push-pull amplifier

The amplified signal appears in the lower half of the output transformer.

The centre-tapped primary of the output transformer combines two collector currents to form a sine wave output in the transformer.

Advantageous

  1. Less distortion for a given power output due absence of even harmonics.
  2. Elimination of dc component at output.

Disadvantageous

  1. Requirement of two transistors.
  2. Need of bulky and expensive transformer.

 

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Transistor

Transistor

Transistor is a three terminals (namely emitter, collector, base) three layer and two junction semiconductor device. It is used to amplify or process an electrical signal. A transistor consists of two two pn junctions formed either P type or N type semiconductor between a pair of opposite types. There are two types transistor.

  • PNP Type Transistor
  • NPN Type Transistor

PNP Type Transistor

In this type, the N type is sandwiched between two P-type layers. A PNP transistor composed of two p-type semiconductors separated by thin section of n-type semiconductor. PNP transistor shown in figure

pnp transistor

NPN Type Transistor

In this type, the P-type is sandwiched between two N-type layers. A NPN transistor composed of two n-type semiconductors separated by thin section of p-type semiconductor.

NPN transistor

Symbol of Transistor

symbol of transistor

Transistor Terminals

There are three terminals in transistor, called emitter, collector and base. We have discussed above the transistor has three different layers or sections. The all layers or sections are different in size and having different doping level. According to this, different terminals are explained below:-

Emitter

The emitter is heavily doped and moderate in size. Emitter supplies a large number of majority carries. The emitter is always forward biased w.r.t to base. So that it can supply a large number of majority carries to its junction with the base.

Collector

The other outer layer of the transistor that collects the majority carries supplied by the emitter is called collector. The collector-base junction is always reverse biased.

It is moderately doped and larger in size, so that it can collect most of the majority carries supplied by the emitter.

Base

The middle of the transistor of the transistor. The base is lightly doped and small in size so that it can pass most of majority carries supplied by the emitter to the collector. The base forms two circuits.

Connections of Transistors

connections of transistor

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Zener Diode

Zener Diode

Zener diode is a special purpose diode that permits current not only in the forward direction like an ordinary diode, but also in the reverse direction. This diode will conduct in reverse biased only and only if the voltage is larger than the breakdown voltage.

This breakdown voltage is known as “Zener Knee Voltage” or Zener Voltage VZ.

The device was named after Clarence Zener.

it is sometimes called the breakdown diode.

The ordinary diode are optimized to operate in forward biased condition and never operated in breakdown region because this may damage them.

The silicon or germanium material is used manufacture the  diode.

Silicon is preferred over germanium for the construction of this diode because of higher operating temperature and current capability. The Knee point is also sharper in case of silicon diode.

By varying the doping level of silicon diode, the ordinary diode makes a Zener diode or breakdown diode.

The difference between ordinary diode and Zener diode is different level of doping in both diode.

Symbol of Zener Diode

In symbol  bar is tuned into Z-shape.

Construction

It is like an ordinary diode except. It is properly doped so as to have a sharp breakdown voltage. Zener diode one junction, two layers and two terminal device.

Characteristics of zener diode

From Above Characteristics Following Points is Worth Noted

  • It is like an ordinary diode but it is optimized to operate in the breakdown region at breakdown voltage.
  • It is always reverse biased.
  • The Zener voltage is almost constant over the operating region, so we can say that it has sharp breakdown voltage.
  • The forward biased characteristics of Zener diode are similar to ordinary diode.
  • During operation it will not burn as long as the external circuit limits the current following through it below the burn out value.

Equivalent Circuit of an Ideal and Actual Zener Diode

In Ideal Case

In ideal case the diode ideally acts like a battery.

In Actually Case

In this case, the diode visualized as if a resistance RZ is connected in series with a battery.

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Varactor Diode

Varactor Diode

Varactor diode is a semiconductor variable capacitor, basically it is a reverse-biased junction diode whose mode of operation based on the transition capacitance.

Varactor diode is also called varicap, voltcap, epicap, voltage dependent, variable capacitor.

This diode consists of two junction P and N junction. P junction carry positive charge and N junction carry negative charge. It is reverse biased.

varactor diode

P junction is connected to negative terminal of the battery and N junction is connected to positive terminal of the battery as shown in above figure. The depletion region forms a barrier which separates the positive and negative charges on each side of the junction. These charges can be compared to the charges on opposite plates of a capacitor, with the depletion layer acts like a dielectric medium.

Due to reverse bias, the depletion layer increase regularly as the reverse bias voltage increase. The holes from P junction moves towards the negative terminal and electrons from the N junction moves towards the positive terminal of the battery. This increase the depletion layer or region.

As the width of depletion layer or region increases with incre4ase in reverse voltage, the junction capacitance is decreased.

A varactor diode is a special purpose PN junction diode with a suitable impurity concentration profile and optimized to operate in reverse biased conditions.

The transition capacitance of a varactor is given by the relation.

E = the permittivity of depletion region of the diode.

A = area of the junction.

W = the width of depletion layer or region.

Characteristics of Varactor Diode

Characteristics of Varactor Diode

The above characteristics show that, the value of transition capacitance is inversely proportional to the reverse voltage. At minimum value of reverse voltage the transition capacitance is maximum and vice versa.

Applications

It is used in high frequency applications. Such as television receivers, FM receivers, automobile radios, adjustable band-pass filters and communication equipment’s.

 

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Semiconductor Diodes | PN junction Diode | Light emitting diode | Varactor Diode | Types of Diode

INTRODUCTION

Semiconductor diodes is considered very important component for construction of electronic circuits. we know that domestic supply is in AC nature, So convert AC into DC Semiconductor Diodes are used and for various function in electronic circuits  special purpose  are used, such as Varactor diode, Light emitting diode, Photo diode, tunnel diode etc. In this article we will discuss about semiconductor diode. A semiconductor diode made by using P-type and N-type semiconductor materials. Therefore, it is also known as PN junction diode.




SEMICONDUCTOR DIODE

The semiconductor diodes is a two terminal device, Positive terminal is taken from P-type material of diode and Negative terminal is taken out from N-type material of diode.

The positive terminal of semiconductor diodes is known as the “Anode”. The negative terminal of semiconductor diodes is known as the “Cathode”.

Semiconductor diodes also known as a crystal diode because it is developed out of crystal like germanium or silicon. A semiconductor diodes operated only when it is forward biased i.e. P-side of diode connected to the positive terminal of the battery and N-side of diode connected to the negative terminal of the supply. When N-side of diode is connected to the positive terminal P-side is connected to the positive terminal , then diode does not conduct. Hence, it is reversed biased.

Symbol of diode

VI CHARACTERISTICS OF SEMI-CONDUCTOR DIODE

The V-I characteristics of a semiconductor diodes is the curve drawn between the voltage and current of the circuit. To draw the curve, we have a circuit which consists of a resistance, a semi-conductor diode, voltmeter, ammeter and a battery. A resistor R is connected in series with semiconductor diode which controls the forward current from increasing the permitted value. The characteristics are explained under four regions.

fig-2-copy

Zero external voltage region.

Forward biasing region.

Reverse biasing region.

Breakdown region.

ZERO EXTERNAL VOLTAGE

When external voltage is not applied to the circuit i.e. the switch K is open (fig-2) then no current flow through the circuit.

FORWARD BIASING REGION

In forward biasing region, P-side of diode is connected to the positive terminal of the battery and N-side of diode is connected to negative terminal of the battery. When switch K of the circuit (fig-2) is closed, then the PN junction is forward biased. At forward bias, the current increased slightly till the barrier potential is wiped off.

fig-2-copy

V-I characteristics in the forward region reveals that the current is negligibly small for voltage smaller than 0.5v. This value is known as “cutin voltage”. The current slowly rised because applied voltage is used to overcome the potential barrier (0.7v for si) of PN junction. When the potential barrier is eliminated and supply voltage is increased further. Then circuit current rises very sharply. This curve is linear.




The forward voltage 0.7v for silicon diode at which current through semi-conductor diode start rising is known as “knee voltage”. If forward current increased more than the rated value, then diode can be damaged.

vi characteristics of semiconductor diode

REVERSE BIASING REGION

In reverse biasing region, P-side of diode is connected to negative terminal and N-side of diode is connected to the positive terminal of the battery. Then PN junction act as reverse biased (fig 4). Under such condition, potential barrier increased at the junction and no current flow through the circuit because junction resistance becomes very high. In actual, very small current flow through the circuit (in order of μA) due to minority carriers. 

reverse bias circuit

The reverse current increase slowly with increase is reverse bias voltage. For silicon diodes, the maximum value of reverse current is 1 μA.

BREAKDOWN REGION

The breakdown region occurs with when reverse voltage increased continuously and exceeded the threshold voltage level that is enough to the particular diode, called as Breakdown Region.

At this stage, kinetic energy of electrons increased that they knock out electrons from semiconductor bonds, so breakdown region occurs at this stage. This may destroy the junction.

TYPES OF DIODES

As we know semiconductor diodes are mainly used for rectification but there are different types of diode which are used in non-rectifier applications. There diodes are given below.

Zener diode

Light emitting diode (LED)

Schottky diode

Varactor diode

Tunnel diode

ZENER DIODE

Zener diode is a special purpose diode which is used to operate in the breakdown region. But normal diode can not worked in breakdown region because this can be damaged them.

Zener diode have highly doped PN junction and it permits current to flow in the reverse direction. When its Zener voltage reached. It s symbol is shown in the fig 5 below. Its symbol is similar to ordinary diode except that its bar turned in Z-shape.

fig-5

VI-CHARACTERISTICS OF ZENER DIODE

The V-I characteristics of the Zener diode are similar to the ordinary diode. Except that it has sharp breakdown voltage which is known as Zener voltage (vZ). This voltage us almost constant over the operating region.

Zener diode can also operated in the forward region like an ordinary diode and used for rectification purpose.

During the operation, it will not damaged as long as external circuit controls the current flowing through it below the maximum rating current of Zener i.e. IZM. The characteristics of Zener diode as shown in figure.

symbol of zener diode

ADVANTAGES

It controls the reverse current flowing through it.

It has small size.

It is compatible with many electronic circuits. However, Zener diodes are preffered method to regulate voltage.




DISADVANTAGES

It cannot be used for rectification because of high cost.

It has poor regulation ration than the transistor.

APPLICATION OF ZENER DIODE

Some important application is given below.

Voltage regulation

Voltage regulation is also known as Zener diode shunt regulator or voltage stabilizer. It has ability to maintain a constant output voltage even when the input voltage or load current has variation. Fig shows the circuit arrangement of voltage regulation.

fig-7

As shown in the fig , the series resistance RS is used to limit the reverse current flow thorough the diode. The Zener diode reversely connected across the load resistance RL across which constant voltage is required. To get the constant voltage, we used series resistance RS which absorb the variation of output voltage.

When the value of vin is less than the Zener voltage VZ , then no current flow through the diode and same voltage appear across RL. When Vin voltage is more than VZ, then Zener diode conducted and large current flow through diode. Thus, the input voltage excess of VZ is absorbed by RS and constant voltage VOUT is maintained across RL.

ADVANTAGES OF ZENER VOLTAGE REGULATOR

They are smaller in size and lighter in weight.

They are also simple and cheaper.

They have longer life.

DISADVANTAGES

Their efficiency is low.

Output voltage varies slightly due to impedance.

METER PROTECTION

Zener diodes are also used in multimeter to protect the movement of meter against damaged from accidental overloads. In the circuit, Zener diodes are connected in parallel across the meter. Most of current will pass through the Zener diode. Thus protect the meter movement from damage, which have two Zener diodes connected can provide overload protection regardless of the applied polarity.

meter protection zener diode

ZENER DIODE AS A PEAK CLIPPER

Zener diode is also used as a peak clipper which clipping off the input wave. It is used to convert the sine wave into square wave. Peak clipper circuit shown below in fig.

peak input

Zener diode act like a short circuit when forward biased and open circuit when reversed biased till it go into breakdown region at VZ. For positive half cycle of input Zener diode D1 is forward biased and act as short circuit while diode DZ is reversed biased and act as circuit upto Zener voltage VZ. Therefore diode D2 comes into breakdown because of reversed biased and take the output voltage come out at VZ till the input voltage comes below VZ. St this time both the diodes act as short circuit.

When input voltage less than the Zener diode voltage VZ then diode D2 come out of breakdown and act as open circuit. During negative half cycle, the diodes D1 and D2 are forward biased. Then the result of output voltage waveform clipped off an both peak of input.

SWITCHING OPERATION

Zener diode is useful for switching operation, which can produce to change from low current to high current.

LIGHT EMITTING DIODE (LED)

LED operated on the phenomenon of electro luminance which emits the light from a semi-conductor under the effect of electrical field. When a diode is forward biased, the recombination of charge carrier take place as electrons cross from N-region to P-region and recombine with holes. Free electrons are in conduction band and holes in valance band of the energy band. There free electrons give up energy in form of heat and light in fig 11.

symbol; of LED

The light emitting diodes made from different materials. There are made by gallium arsenide phosphide (GaAsp) and gallium phosphide (GaP). With these semi conductor material, the electron give up their energy by emitting photons. ELD emits no light when it is reverse biased.

LED have voltage level from 1.5v to 2.5 v and currents about 10 to 50 mA. Generally, 2V of voltage drop is used while designing any circuit and the brighters of LED depends upon the current of circuit.

APPLICATION OF LED

LED’s are used in digital watches, calculator, multimeter, telephone switch boards and panel indicators. In there systems, we visible light (such as red, green, blue). On the other hand, infrared LED’s used in burglar alarm system and other areas which require invisible radiation.

PHOTO DIODE

A photo diode is a semi conductor device and is a kind of light detector. This is used to convert the light into voltage or current.

When photo diode is reverse biased, a small current flow throught the diode due to minority carriers. These carrier exist because of thermal energy which knock the valance electrons to produce the free electrons and holes.

When light energy falls on the PN junction, it gives energy to valance electrons and light striked on junction control the reverse current in a diode. The magnitude of the reverse current depends upon the intensity of light falling on the diode. Stronger the light larger the reverse current. Symbol and circuit shown in fig 12.

symbol of photo diode

APPLICATION OF PHOTO DIODE

It is used in optical communication devices.

Medical devices

Position sensors

Scanners

VARACTOR DIODE

Varactor diode is also known as varicap diode, variable capacitance diode, variable reactance diode or tuning diode. The symbol of Varactor diode is shown in fig .

fig-13

As shown in fig diode symbol consist of capacitor symbol at cathode side of diode which represents the capacitor characteristics, hence the named variable capacitance diode.

When the junction is reversed biased, the depletion region form a barrier which separates the positive and negative charger of the junction.

When reverse voltage applied, the width of depletion region incr3ease with increase in voltage and junction capacitance decreases as shown in fig.

characteristics of varactor diode

APLICATIONS

As a variable reactor, it’s used in microwave circuits.

It used in television receivers and communication equipments.

It is used as voltage controlled.

TUNNEL DIODES

Tunnel diode is also called as Esaki diode which exhibits negative resistance i.e. when the voltage increased, the current decreased through it. It is highly doped semi conductor device. 

Tunnel diodes are such types of diodes which have breakdown at OV(zero volt). When we increase the doping level of junction, with this heavier doping the forward curve of diodes is also distorted.

When diode is forward biases, then current reached to the maximum value of the peak (IP) at the peak voltage (VP). After with increased the valley voltage (VV).

Current decrease with increase in voltage between the peak and valley point. This is known as negative resistance region.

APPLICATIONS

Tunnel diodes are used in high frequency oscillatory circuit.

Also used as an amplifier.




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Intrinsic and Extrinsic Semiconductor Materials

INTRINSIC AND EXTRINSIC SEMICONDUCTORS

INTRINSIC SEMICONDUCTORS

The semiconductor available in an extremely pure form is known as intrinsic semiconductor. We know that a semiconductor at absolute zero temperature behave as an insulator because at absolute zero temperature valance band is completely filled and conduction band is completely empty. When some thermal energy is given to in covalent bond is broken and electrons cross over the conduction band and a vacancy leave behind is equal to the number electrons enters in the conduction band. The electrons reaching at the conduction band are free to move at random and similarly holes created also move at a random in semiconductor.




WHAT IS HOLES?

A vacancy left behind in the valence band due to entering of electrons in the conduction band. Holes in created in the place of electrons in in valence band when electron leave the valence band and enters in the conduction band. The charge on hole is positive charge. Holes are created when some external energy such as heat is given the semiconductors.

WHAT IS RECOMBINATION OF ELECTRON HOLE?

When some heat energy supplied to the semiconductor. The electrons in the valence band move away and enter in the conduction band. There is a vacancy left in the valence band. This vacancy is called holes. Electrons and holes are move randomly with in the crystal lattice, there is a possibility of an electrons meeting a hole when a free electron approaches the hole it gets attracted and falls into a hole. This merging of a free electrons and a hole is called recombination.




EXTRINSIC SEMICONDUCTOR

Intrinsic semiconductor is not usefu8l for making devices or components because it has little current conduction capability at ordinary room temperature. To improve the current conduction capability of the semiconductor small amount added in the pure or intrinsic semiconductor. The obtained semiconductor is called extrinsic or impure semiconductor. The above explanation tells why impurity is added in the intrinsic semiconductor?

DOPING: – The process of adding impurity in a pure semiconductor is called Doping. One impurity atom is added to 108 atoms of a semiconductor. The purpose of adding impurity in the semiconductor crystal is to increase the number of free electrons or holes to make it conductive. There are two types of impurity which is added to a pure semiconductor crystal. One is called pentavalent impurity and trivalent impurity. When pentavalent impurity is added to a pure semiconductor a large number of free electrons will exist in it. When a trivalent impurity is added to a pure semiconductor, a large number of holes will be generated. Accordingly the impurity added to a semiconductor, the extrinsic semiconductor my be classified as:-

N – TYPE EXTRINSIC SEMICONDUCTOR

N – Type semiconductor is obtained by added pentavalent impurity to pure semiconductors. Arsenic, antimony, bismuth or phosphorus are the examples of Pentavalent impurity. Penta means five. It means the atom has five electrons are present in the valance shell of the atom. When pentavalent impurity is added in semiconductor, four electrons is pentavalent atom share with four electrons of semiconductor. One spare valence shell electron is produce for each impurity atom added. Each spare electron so produced enters the conduction band of a pure semiconductor as free electrons. This free electron improves the conductivity of the material. We have seen there is large number of free electrons available in semiconductor. The charge on electron is negative. That is why this is called N-type extrinsic semiconductor because N is stands for negative. Pentavalent impurity is also called donar impurity.

n type semiconductor materials

 

P-TYPE EXTRINSIC SEMICONDUCTORS

P type semiconductor is obtained by adding trivalent impurity to pure semiconductors. Boron, Gallium, Indium or Aluminium are the examples of trivalent impurity. Tri mean three. It means the atom has three electrons are present in the valence shell of the atom. When a trivalent impurity is added to a semiconductor atoms. These impurity atoms from covalent bonds with four surrounding intrinsic semiconductors atoms but one bond is left incomplete and it incomplete bond creates a hole in simple words. One electron is less to make a bond. This missing electron is called holes. Small amount of trivalent impurity provides millions of holes in the semiconductors. Holes have a positive charge that is why it is called P-type extrinsic semiconductor P is stands for positive charge. This type of impurity is called acceptor impurity.

intrinsic semiconductor



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Rectifiers

Rectifiers

We know that electrical energy is generated at power plants in the form of ac due to many reasons such as ac system is economical but for the operation electronic devices or circuits, dc supply is required cells and batteries cannot meet the demands. So there is conversion of ac into dc is necessary. In Article we will study about, Half Wave Rectifiers and Full wave rectifiers.

What is Rectifier?

Rectifier is a electronic device which converts alternating current (ac) into direct current (dc).




According to their operation rectifiers divided into two types

  • Half wave rectifier
  • Full wave rectifier

Full wave rectifier further divided into two types

  • Centre-tap full wave rectifier
  • Full wave bridge rectifier

Half wave rectifiers

In half wave rectifier only one half of the supply of the alternating current is conducts. At output we have only one half cycle the other half of the supply is skipped.

Construction of Half wave rectifier

In half wave rectifier a semiconductor diode is connected in series with load RL. A transformer is used. Basically step down transformer is used. Secondary side diode and load is connected and Primary side of transformer is connected to the ac source.

<img = "half wave rectifier">

Operation or working

When primary side of the transformer connected to ac source of induced in secondary side.

  • During positive half cycle of the supply end B become negative. At this time diode D become forward biased and starts conduct and current start flowing through the load RL.



  • Path of current during positive half cycle is A – Load – B.
  • During negative half cycle of the supply end A of the transformer become negative and end B of the transformer become positive. At this time, the diode D become reverse biased and it does not conduct current and diode remains always in non-conducting state.

Output wave form

wave1

Centre-tap full wave rectifier

In full wave rectifier both half cycle of the alternating supply conducts.

Construction

In such type of rectifier two diodes are used. These diodes are D1 and D2 a centre tapped transformer is used. The secondary of the transformer is centre tapped. The load RL is connected in such a way that it carry the current in one direction.

full wave centre-tapped rectifier

Operation or working

The ac supply is connected to the transformer. During positive half of the supply end A of the secondary winding become positive and end B become negative. At this time D1 become forward biased and diode D2 become reverse biased. The diode D1 conduct while diode D2 does not. The current through D1 and load RL. During negative half of the supply end A of the secondary winding become negative and end B of the secondary winding become positive. At this time, diode D1 become reverse biased and diode D2 become forward biased. Now diode D2 conducts while diode D1 does not. The start flowing through diode D2 and load RL. The direction of flow of current is same, so the output is unidirectional. In this rectifier when one diode is conducts the other diode remains off condition means does not conduct.

Output wave form

wave form of full wave centre apped rectifier

Full wave bridge rectifier

In this rectifier four diodes are used. This type of circuit also conduct both half cycle of the alternating current.

Construction of full wave bridge rectifier

In such type of circuits the four diode (D1 D2 D3 and D4) connected in such a way the two diodes are conduct during positive half cycle of the supply and other two diodes are conduct negative half cycle of the supply. In this rectifier ordinary two winding transformer is used.

circuit of full wave bridge rectifier

Operation or working 

Ac supply is connected to the primary side of the transformer. By mutual induction e.m.f is induced in secondary winding of the transformer.

  • During positive half cycle of the ac supply end terminal A of the secondary winding become positive and  B become negative. At this time, diode D1 and D3 conduct while diode D2 and D4 does not. The current will flow through D1, load and D2. The current flows in one direction in same direction as the positive half cycle of the supply.
  • During negative half cycle of the ac supply terminal B of the secondary winding become positive and  A become negative. At this time, diode D2 and D4 conduct while diode D1 and D3 does not. The current will flow through D2, load and D4. The current flows in one direction in same direction as the positive half cycle of the supply.

Output wave form

wave form of full wave bridge rectifier




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Electronics Component | Active Component | Passive Component

To perform a particular function, electronic circuits are designed by connecting suitable components. Theses components are active components and passive components. All the electronic circuits are contains these components. Both components are important to design a electronic circuits.

ACTIVE COMPONENTS

Active components are those components which are capable of amplifying or processing an electrical signal. There are two types of active components which are called tube devices and semiconductor devices. Vacuum diode, vacuum triode, vacuum pentode, thyratron etc are the example of tube devices. Where as PN junction diode, Zener diode, photo diode bipolar junction transistor (BJT), field effect transistor or FET, Unijunction transistor or UJT, silicon controlled rectifier SCR or thyristor, metal oxide semiconductor field effect transistor MOSFET, TRIAC, DIAC etc are belongs to semiconductor devices family. In above components tube devices are not used in present days because these components are bulky in size and high in cost.

PN JUNCTION DIODE

A PN junction diode is known as semiconductor diode. It has two terminals. Semiconductor diodes are used as a rectifier. It is also known as crystal diode.

BIPOLAR JUNCTION TRANSISTOR




Transistor is a three terminal three layer (PNP or NPN) semiconductor device. Transistor used as an amplifier because it can process the electrical signal. Bipolar junction transistor is so called because current conduction in transistor due to both charge carriers (electrons and holes). BJT is a current controlled devices.

FIELD EFFECT TRANSISTOR (FET)

Field effect transistor is a three terminal semiconductor device like bipolar junction transistor. The operation of FET depends upon the flow of majority carriers (either by electrons or by holes). A FET is a voltage controlled devices in which output current is controlled by the input voltage.

SILICON CONTROLLED RECTIFIER (SCR)

Silicon controlled rectifier is a three terminal (namely Anode, Cathode and Gate) four layer, three junction semiconductor device which is used for rectification, inversion purpose etc. SCR is used where large power has to be handled.

PASSIVE COMPONENTS

Passive components are those components which are not capable of amplifying or processing an electrical signal. The example of passive components is Resistors, inductors and capacitors we can not design electronic circuits without the use of passive components. In electronic circuit these components are as important as active.

RESISTORS

Resistors are the components which are used to limit the electric current in a circuit. It is also used to divide the voltage in the electronic circuits. The ability to restrict the electric current in a circuit is called resistance. The unit of resistance is Ohm.

TYPES OF RESISTORS

According to the operating conditions, the resistors may be divided into two types:-

Fixed resistors and variable resistors.

Fixed resistors may be classified as carbon composition resistors and wire wound resistors.

CARBON COMPOSITION RESISTORS

Carbon resistors are used in electronic circuits with lower power rating. It is made of mixture of carbon and clay. The value of resistors depends upon the properties of carbon and clay. The resistor element is enclosed in a plastic case, for insulation (to avoid leakage of current) and for providing necessary mechanical strength to the resistor element. This type of resistors mostly used in electronic circuits. The value of carbon resistor ranging from few Ohm to mega Ohm. The power rating of carbon resistor is generally ¼ W, 1/2W, 1W and 2W. The cost of this type of resistor is very low.

WIRE WOUND RESISTORS

The material used for wire is constantan ( 60% copper 40% nickel) and manganin. The materials should have high resistivity and low temperature coefficient of resistance. The wire wound resistors is coated with an insulating material such as baked enamel.




RESISTOR COLOR CODING

The size of carbon composition resistors is very small. So it is very difficult to print the value of resistance on their body. To overcome this difficulty color bands are printed on the body of the resistors. The method to representing the value of resistance is called color coding. There are four bands are printed on the resistors. The color band always read left to right from the end that has the band nearer to it. The first two band represent the digit. Third band represent the multiplier (the value which is multiplied by the significant digits). The fourth band shows the tolerance of the resistor. If there is no color in fourth band, then it shows in fourth band, then it shows that the resistor has ±20% tolerance.

IMG-20160818-WA0017

resistor

INDUCTORS

Inductor is a device or component which opposes the any change of current in the circuit is called an inductor. The property of a coil by virtue which it oppose change the magnitude and direction of current flowing through the circuit is called inductance. Inductor offers high impedance to ac but low impedance to dc. The function of inductor in electronic circuit is to block ac component but to pass dc component. There are two types of inductors fixed inductors and variable inductors. Filter chokes, iron core chokes and Radio-frequency inductors are the example of inductors.

CAPACITORS

Capacitor is a passive component. Capacitor consist of two plates and electrodes which are separated by an insulating material. The insulating material is basically a dielectric material. The function of a capacitor is to store electric charge. The ability of store electric charge in a capacitor is called its capacitance. Capacitance is the ratio of charge per unit voltage or potential difference. The unit of capacitance is farad (F). A capacitor is component which offers low impedance to ac but very high impedance to dc another may we can say that capacitor block the dc signal but pass the ac signal. Capacitor is main components which are used in electronic circuits. It is used in coupled circuit, by passing and filter circuits. The capacitors may be fixed and variable.

TYPES OF CAPACITORS

The most commonly used dielectrics are air, mica, paper etc. A capacitor is generally named after the dielectric used for example air capacitor mica capacitor, etc. The capacitor may be fixed value capacitor and variable capacitor. The different types of capacitor used in electronic circuits are paper capacitors, Mica capacitors, ceramic capacitor, electrolytic capacitors, Air capacitors etc.

PAPER CAPACITOR

Paper capacitor is most commonly used capacitor in electronic circuits. Paper capacitor consist of two electrode (Aluminum or tin) separated by paper impregnated with dielectric such as wax or oil. Paper capacitors are in available in wide range of capacitance values and voltage ratings.

MICA CAPACITORS

These capacitors are made of sheet of metals which are separated by dielectric medium such as mica sheets. These types of capacitors are mostly used in rf tuned circuits.

CERAMIC CAPACITORS

In these capacitors two electrodes or plates are separated by a ceramic materials titanium oxide or other silicates are used to obtain very high value of dielectric constant of ceramic material. Ceramic capacitors are available in different shapes such as disc type ceramic capacitors tubular ceramic capacitors etc.

ELECTROLYTIC CAPACITORS

In these capacitors electrolytic medium is used as a dielectric medium. The electrolyte may be borax, phosphate etc. These capacitors are used in filter circuits to reduce the ripples from the rectified output in rectifier circuit. These capacitors must be connected in the circuit as per polarity marked on the capacitor.




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