BJT

BBIPOLARIPOLAR J JUNCTIONALUNCTIONAL TTRANSISTORRANSISTOR

Syllabus Introduction Basic concept Types of transistors structure & symbols Transistor operation Conventional current flow Relation between different Currents in transistor Transistor amplifying action Transistor configurations- CB, CE & CC Circuit diagram to find the characteristics ,Input/output

characteristics Transistor parameters- input resistance, output resistance,

,, relation between them. Comparison between three configurations Transistor specifications Vcesat, Icmax, Vceo, Iceo, Vce, ,,Vcebreakdown, Power dissipation

(to be explained during practical using data sheets) Testing of Transistor multimeter(To be shown during practical)

Introduction The transistor is a three terminal, solid state electronic device. In a

three terminal device we can control electric current or voltage between two of the terminals by applying an electric current or voltage to the third terminal. This three terminal character of the transistor is what allows us to make an amplifier for electrical signals, like the one in our radio. With the three-terminal transistor we can also make an electric switch, which can be controlled by another electrical switch. By cascading these switches (switches that control switches that control switches, etc.) we can build up very complicated logic circuits.

The transistor was successfully demonstrated on December 23, 1947 at Bell Laboratories in Murray Hill, New Jersey. Bell Labs is the research arm of American Telephone and Telegraph (AT&T). The three individuals credited with the invention of the transistor were William Shockley, John Bardeen and Walter Brattain. William Shockley played a quite different role in the invention than the other two. Shockley had been working on the theory of such a device for more than ten years. While he could work out the theory successfully but after eight years of trying he could not build a working model. Fig 4.1 shows the first designed transistor.

44

Bardeen and Brattain were called in to handle the engineering and development, which they did in the relatively short time of two years, to the consternation of Shockley. Shockley, as their supervisor, shared in the glory. What Bardeen and Brattain had created was the "point-contact" transistor. Shockley subsequently designed a new type of transistor called the "bipolar" transistor which was superior to the point- contact type and replaced it. Thus the transistor was, in large part, Shockley's creation.

Fig.4.1.First transistor made by Shockley, Bardeen and Brattain

William Shockley was raised in Palo Alto, the son of a mining engineer and his Stanford-educated wife. He did his undergraduate work at the California Institute of Technology (Cal Tech) in Pasadena and went on for his Ph.D. in physics at M.I.T. When he completed his doctorate, specializing in quantum physics, he went to work for Bell Labs.

Shockley had started working in 1936 on the solid state physics theory that was the basis for the transistor. There was a precedence for this type of device. The early radios had signal detectors which consisted of a fine wire, called a cat's whisker, impinging upon a galena (lead sulfide) crystal. The radio user had to move the cat's whisker around upon the germanium crystal to find a suitable point of contact where a radio signal could be picked up. These early radios worked but only imperfectly. Nevertheless the principle upon which the crystal detector worked was the basis for the "point-contact" transistor.

Bardeen and Brattain used germanium instead of galena in that first transistor. They also used the equivalent of cat's whiskers, but two rather than one. Shockley's design, the bipolar transistor, eliminated the delicate, troublesome point contacts. Later transistors were made from silicon, a much more common element and one that was protected from corrosion by a thin layer of silicon dioxide.

Texas Instruments of Dallas, Texas first started commercial production of junction transistors for portable radios in 1954. The Sony Company of Japan soon acquired the right to produce transistors and came to dominate the market. In the 1960's Sony began to manufacture television sets using

transistors rather than vacuum tubes. Soon afterwards vacuum tube technology became obsolete.

In 1956 Shockley returned to Palo Alto to founded his own company. He brought talented engineers and scientists to his company but he was a very difficult person to work with him.

For one thing, he insisted upon posting of the salaries of all the employees. This produced unnecessary friction among the employees. Ultimately the top staff joined together in leaving the company. They wanted to continue to work together in another company and Steven Fairchild of Fairchild Camera was induced to create Fairchild Semiconductor for the group.

Bardeen and Brattain continued in research (and Bardeen later won another Nobel). Shockley quit to start a semiconductor company in Palo Alto. It folded, but its staff went on to invent the integrated circuit (the "chip") and to found Intel Corporation

The bipolar junction transistor was the first solid-state amplifier element and started the solid-state electronics revolution. Bardeen, Brattain and Shockley at the Bell Laboratories invented it in 1948 as part of a post-war effort to replace vacuum tubes with solid-state devices. Solid-state rectifiers were already in use at the time and were preferred over vacuum diodes because of their smaller size, lower weight and higher reliability. A solid-state replacement for a vacuum triode was expected to yield similar advantages. The work at Bell Laboratories was highly successful and culminated in Bardeen, Brattain and Shockley receiving the Nobel Prize in 1956.

Transistor When a third doped element is added to a crystal diode in such a way

that two PN junctions are formed the resulting device is known as transistor. Details of the transistor are shown in fig 4.2 , 4.3

Basically it consists of three layers and two PN junctions. These three layers are:- 1) Emitter 2) Base 3) Collector

Hence according to third element added, two PN junctions are formed sandwiching P or N type semiconductor between a pair of opposite semiconductor. Depending upon three layer transistor are of two types

1) NPN - transistor2) PNP – transistor

Significance of name TransistorAs studied in chapter 1 semiconductor diode, The forward biased

junction has a low resistance path whereas a reverse biased junction has a resistance path. Since main purpose of transistor is to amplify weak signal, this weak signal is applied in Forward biased junction having low resistance

path and transferred to reverse bias junction having high resistance. Since this signal is transferred from low resistance to high resistance path it is called “transistor” ie “Trans” means the signal transfer property of the device , whereas “istor” means solid element in the same general family of the resistor

Trans + istor = Transistor

Fig.4.2 Constructional details , two-diode equivalent , symbol of transistor

Fig.4.3 Cross Sectional View , Transistor , Fabricated

Transistor

Constructional Details of the transistorFig.4.3 shows the constructional details of the transistor. Fig shows that

transistor has three separate region . The middle region is called as Base. Out of the two outer region one is called as Collector and other is called as Emitter. Although two outer region are made up of same material their function cannot be interchanged. This is because two region have different physical size and electrical properties. Feature of all the three layers is as follows

Fig.4.5. Symbol of Transistor

The terminals of transistor are 1) Emitter 1.It is the outermost layer of the transistor.

2.It is heavily doped because its main function is to supply(emit) majority charge carriers to the base.

3.Resistance of emitter is low, width is moderate and 4.Emitter is always forward biased with base.

2) Base 1.It forms the middle section of the transistor. 2.It is very thin 3.It is lightly doped compared to emitter and collector because

its function is to control the charge carriers from emitter to collector

4.Resistance of the base layer is high and

3) Collector 1.It is other outer layer of the transistor. 2.Its main function is to collect majority charge carriers. 3.Its region is made larger than emitter and base because it has

to dissipate more power. 4.Also resistance of collector is moderate. Its Collector to Base

junction is generally made reverse biased.

Fig.4.5 shows the symbol of NPN and PNP transistor, in this horizontal Line is called as Base and the two angular lines represent Emitter and Collector. An arrow is placed on one of the angular lines represent the Emitter. The arrow head on the emitter lead indicates the direction of the conventional current in a transistor.

From the Figure it is clear that the conventional current flow from positive to negative terminal,

In case of PNP transistor the conventional current flow emitter to base the arrow head is shown in inward direction ie from P to N.

In case of NPN transistor the conventional current flow base to emitter the arrow head is shown in outward direction ie from P to N.

Hence the direction of arrowheads at the emitter in NPN and PNP transistor are in opposite direction.

Transistor without Supply Unbiased BiasingA transistor, with three terminals (i.e., Emitter, Base and Collector) left

open, is called an unbiased transistor or an open-circuited transistor. Under these conditions, the diffusion of free electrons across the junction

(a)(b)

Fig.4.4 Unbiased Transistor

junction produces two depletion layers as shown in Fig.4.4(a). The barrier potential, for each of these layers at 25°C, is approximately 0.7 V for silicon transistor and 0.3 V for germanium transistor. Since the three regions have different doping levels, therefore the depletion layers do not have the same width.

In a more heavily doped region has the greater concentration of ions near the junction. It has been observed that an emitter-base depletion layer penetrates slightly into the emitter, as it is a heavily doped region, whereas it penetrates deeply into the base as its a lightly doped region. Similarly, the collector-base depletion layer penetrates more into the base region and less into the collector region. Both these depletion layers are as shown in Fig.4.4(b).

It may be noted that emitter-base depletion layer width is smaller than that of collector base depletion layer. An unbiased transistor is never used in actual practice. Its terminals are always connected suitably, to the dc voltage sources (or a battery) for proper transistor action.

Transistor With Supply Biased TransistorThe application of a suitable dc voltages, across the transistor

terminals, is called biasing. Each junction of a transistor may be forward biased or reverse-biased independently. There are following three different ways of biasing a transistor, which are also known as modes of transistor operation.

Fig.4.5.Active Region Fig.4.6.Saturation Region

1. Active : In this mode, the emitter-base junction of a transistor is forward biased and the collector base junction is reverse biased as shown in Fig.4.5 In a forward active biasing the negative terminal of a battery is connected to N-side and positive terminal to P-side. In reverse biasing the negative terminal of a battery is connected to P-side and positive terminal to N-side.

N P N

VEE VCCC

CE

N P N

VEE VCCC

CE

N P N

VEE VCCC

CE

Fig.4.7.Reverse Bias2. Saturation : In this mode, both the emitter-base and

collector-base junctions of a transistors are forward-biased as shown in Fig.4.6. In this mode, the transistor has a very large value of current. The transistor is operated in this mode, when it is used as a closed switch.

3. Cut-off : In this mode, both the emitter-base and collector-base junctions of a transistor are reverse biased as shown in Fig.4.7. In this mode, the transistor has practically zero current. The transistor is operated in this mode, when it is used as an open switch.

Region Emitter-Base Junction

Collector-Base Junction

Application

Active Forward Reverse AmplifierSaturation Forward Forward Closed Switch

Cut-off Reverse Reverse Open SwitchInverse mode Reverse Forward Not used

Fig.4.8. Table showing Different Operating Modes

Transistor OperationFig.4.9 Shows the biased transistor setup of learning its operation. From the figure following things are understood

1. The battery VEE acts to for ward bias the emitter junction, 2. The battery Vcc acts to reverse-bias the collector junction. 3. Switches S1 and S2 have been provided in the emitter

and collector circuits. When the two switches are open, the two junctions are unbiased. We thus have depletion or space-charge regions at the two junctions.

Fig.4.9.Operation of Transistor

Operation of Transistor can be studies by considering following cases of switch S1 and S2.

Case 1 : Switch S1 closed , Switch S2 open

If we close the switch S1, and keep the switch S2 open, the emitter junction will be forward biased as shown in Fig. 4.10.

Fig.4.10.Transistor Operation with S1 closed and S2 openThe barrier at the emitter junction is reduced. Since, emitter and base

regions are just like those in a PN diode, Hence large current due to forward biasing. This current consists of majority carriers diffusing across the junction. Electrons diffuse from the emitter to the base, and holes from the base to the emitter. The total current flowing across the junction is the sum of the electron diffusion current and the hole diffusion current.

In a transistor, the base is region is doped very lightly compared to the emitter region. Because of this, there are very few holes in the base region. As a result, over 95-99% , of the total current is carried by the electrons (diffusing from the emitter to the base). The emitter current IE and the base current IB in Fig. 4.10 are quite large. The two currents must be equal (IE = IB. The collector current IC is zero(IC = 0).

Case 2 : Switch S1 open , Switch S2 closedIf we open the switch S1, and keep the switch S2 closed, the collector

junction will be reversed biased as shown in Fig. 4.11.

Fig.4.11. Transistor Operation with S1 Open and S2 ClosedVery Small current flows across this reverse-biased junction. The

reverse leakage current is due to the movement of minority carriers. These carriers are accelerated by the potential barrier. As in case of PN-junction diode this leakage current is very much temperature dependent.

S2 OpenS1 Closed

IB

IE

IB

IC

S1 Open

S2 Closed

The current flow into the collector lead and out of the base lead. There is no emitter current IE 0). The small collector current is called the collector leakage current. It is denoted by symbol, ICBO. The subscript CBO in this symbol signifies that it is a current between Collector and Base, when the third terminal the emitter) is Open. What Happen when both Switch are closed ?

As per Fig. 4.9 And from the above discussion, it should be expected that both IE and IB to be large and Ic to be very small. However, the result of closing both switches turn out to be very shocking. The emitter current IE is large, as it was expect But IB turns out to be a very small current, and Ic turns out to be a large current. Which was entirely unexpected. It is because of this unexpected result that the transistor is such a great invention. Hence the actual action of transistor is discussed in next topic case 3

Case 3 : When S1 closed and S2 closedFig.4.12 Show the transistor is operated in active region. The emitter-

base junction is forward biased by VEE and the collector-base junction is reverse-biased by Vcc. The directions of various currents that flow in the transistor are also indicated in Fig.4.12. As is the usual convention, the direction of current flow has been taken opposite to the direction of electron movement. To understand the action of the transistor, we have numbered some of the electrons and holes. This will simplify the description

Fig.4.12.Transistor Action in Active regionThe emitter junction is forward-biased (may be, by a few tenths of a

volt). The barrier potential is reduced. The space-charge region at the junction also becomes narrow. As such, majority charge carriers diffuse across the junction. The resulting current consists of electrons moving from the emitter to the base, and holes passing from the base to the emitter.

But only the electron current is useful in the action of the transistor. Therefore, the electron current is made much larger than the hole current. This is done by doping the base region more lightly than the emitter region. In Fig. 4.12, we have shown electrons 1, 2, 3 and 4 cross from the emitter to the base, and hole 7 from the base to the emitter. The total sum of these charge-carrier movements constitutes the emitter current IE. Only a portion of this current is due to the movement of electrons 1, 2, 3 and 4. These are the electrons injected by the emitter into the base.

IBIc

IE

VEE Vcc

Once the electrons are injected by the emitter into the base, they become minority carriers (in the base region). These electrons do not have separate identities from those which are thermal(Leakage/Minority) generated in the base region itself.

The transistor action is that the base is made very narrow (about 25 µm) and is very lightly doped. Because of this, most of the minority carrierselectrons) traveling from the emitter end of the base region to its collector do not recombine with holes in this journey. Only a few electrons like 3) may recombine with holes (like 6). The ratio of the number of electrons arriving at collector to the number of emitted electrons is known the base transportation factor. It is designated by symbol . Typically = 0.995.

As per Fig.4.12, Movement of hole 8 from the collector region and electron 5 from the base region constitutes leakage current, ICBO. Movement of electron 3 and hole 7 constitute a part of emitter current IE. These two currents are not equal. Actually, the number of electrons (like 3) and holes (like 7) crossing the emitter-base junction is much more than the number of electrons (like 5) and holes (like 8) crossing the collector-base junction. The difference of these two currents in the base region makes the base current IB.

The collector current is less than the emitter current. There are two reasons for this.

a. A part of the emitter current consists of holes that do not contribute to the collector current.

b. Not all the electrons injected into the base are successful in reaching the collector.

Hence in transistor IE = IC + IB IE IC Since IB << small

and total collector current is IC = ICMajority + ICMinority

NPN Transistor OperationFig.4.12 Show the transistor is operated in active region. The emitter-base

junction is biased by VEE and the collector-base junction is biased by Vcc.

Fig.4.12 Operation of NPN Transistor

N P N

VEE Vcc

IE ICIB

EB Junction

CB Junction

1. In this base emitter junction is forward biased by VEE and collector base junction is reversed biased by VCC.

2. Due to forward bias barrier voltage of Base Emitter junction is reduced and due to reverse bias collector base junction is increased.

3. The forward bias causes the electron in N-type emitter to

flow in to base This gives rise to emitter current IE .

4. These electron flow through P-type base and they tend to combine with hole. As the base is lightly doped and very thin therefore only few electron (approximately. 2-5%) combine with holes which gives rise to current IB.

5. The remaining 95-98% of electron cross over into the collector region and constitute collector current IC . Hence almost all emitter current flow in emitter. Hence

IE =IC + IB If IB is neglectedIE IB

6. The collector current is comprised of two components:1. Due to majority carrier2. Due to minority carrier Therefore IC = IC majority + IC minority IC =IC +ICO

7. IC0 = It is collector to base current with Emitter open (ICBO

≈ ICO )

8. IC0 is temperature dependent and it increases with every 100C rise in temperature.

Operation of PNP TransistorAs shown in the fig.4.13. emitter junction is forward biased and whereas

collector junction is reversed biased due to this potential barrier voltage reduces on emitter side

Fig.4.13.Operation of PNP Transistor1. The holes to repel emitter move toward base and constitute emitter

current IE.

P N P

VEE Vcc

IE ICIB

EB Junction

CB Junction

2. As the base is lightly doped and very thin only few (2-5%) of holes combine with electron and generate base current IB.

3. The remaining holes from base are attracted towards collector by negative terminal of battery VCB.

4. Hence 95-98% of majority carrier (holes) move into collector region and give rise to collector current IC.

5. In this way entire emitter current flow in the collector circuit The current conduction within transistor is due to holes but in external connecting wires the current is still due to electrons

IE = IC + IB If IB <<small neglect IB

IE IC

6. The collector current is comprised of two components1. Due to majority carrier2. Due to minority carrier

Therefore IC = ICmajority + ICminority

IC =IC +ICO

7. IC0 = It is collector to base current with Emitter open (ICBO ≈ ICO )

Current and Terminal Voltage in Transistor

Fig.4.14 Different Voltages in NPN and PNP transistor

VCB = Voltage between Collector and Base make Collector Base junction reverse bias

VBE = Voltage between Base and Emitter make base emitter junction forward bias , its value is 0.7V for Si and 0.3V for Ge

VCE = Voltage between Collector and Emitter

Different Current in Transistor

VCE

VBE

VCB

+

-

+

-

+

-

VCE

VBE

VCB

+

-

+

-+

-

Fig.4.15.Direction of currents in NPN and PNP Transistor

Fig.4.16.Direction of current in the NPN and PNP transistor

The directions of conventional currents in an n-p-n transistor are as shown in Fig.4.15 and fig.4.16. Figures show the conventional currents using the schematic symbols of n-p-n and p-n-p transistors, respectively. It is seen that the arrow at the emitter of the transistor’s symbol points in the direction of conventional current.

PNP transistorThe current flowing into the emitter terminal is referred to as the

emitter current and identified as IE. The currents flowing out of the collector and base terminals are referred to as collector current and base current respectively. The collector current is identified as IC and base current a IB.

Reverse Collector Saturation Current ICBO

When emitter is open circuited, IE = 0, and the base and collector act as a reverse biased diode. Due to this, the collector current IC equals the reverse saturation current. It is denoted as ICO. The is nothing but the ICO

(Reverse saturation current) of transistor. It is also defined as the current when emitter current is zero. As ICBO is defined for transistor, it constitutes the leakage current flowing around the junction. Emitter current From the Fig.4.15 and 4.16 it is clear that

IE = IC + IB

But IB is so small because base is lightly doped and its very thin , Hence IE IC

Why Transistor is called as BJT ?Ans. Bipolar The conduction in a bipolar junction transistor takes place due to both i.e. electrons and holes. Junctional It has two junction ie collector an emitter junction Transistor Since it transferred from low resistance to high resistance path

B(Bipolar) J(Junctional) T(Transistor)

Configuration of TransistorAs there are 3 terminals in transistor i.e. Emitter, base and collector,

Depending upon the terminal made common to input and output there are three different types of configurations.

1)Common Base: Base is common between input and output.

2)Common Emitter : Emitter is common between input and output.

3)Common Collector: Collector is common between input and output.

For each connection there are specific advantages and disadvantages. But the common thing for all these configurations is

1) Emitter base junction is forward biased 2) Collector base is reversed biased.

Common Base ConfigurationAs shown in fig.4.17. the base made common between input and

output i.e. input is applied between Emitter and base junction and output is taken from collector and base.

In this configuration emitter current IE is the input current and collector current IC is output current. IB is the base current whose direction and flow is as shown in the figure.

Fig4.17 shows both NPN and PNP transistor in Common Base Configuration.

Fig.4.17. Common Base Configuration (NPN and PNP)

Current amplification factor ( The ratio of change in collector current(IC) to the change in emitter current (IE )at constant collector to base voltage (VCB)is known as current amplification factor i.e = change in collector current

change in emitter current at constant collector base voltage

It is clear from expression IE > IC by the factor of IB as shown above, Hence collector current is less than unity. Practical value of is from 0.9 to 0.99

Output Current - Collector current IC

As seen from transistor action , we now know that collector current is constituted due to two components

1. The current produced by normal transistor action. This current is due majority charge carrier injected by emitter, hence it is called as injected current. Its value is IE and it is due to majority charge carrier.

2. The another component is due to minority charge or thermally generated charge carrier which flows is collector junction due to reverse bias . Its value is ICBO. It is as shown in fig 4.18

Fig.4.18 Leakage CurrentICBO = Collector to base current with emitter openICBO is usually very small but it is temperature dependent. It doubles itself per 100C rise in temperature. The value for ICBO is usually nano Amperes(A) for silicon and micro Amperes (µA) for germanium transistor at room temperature.

Detail Study of Common Base ConfigurationIn order to understand the complete and thorough behavior of

transistor it is necessary to study the relation ship between the various component of Voltage and current in transistor. These relation ships are plotted graphically which are commonly known as characteristic of transistor. For any configuration there are two types of characteristics those are

1. Input characteristics is curve plotted between input current and input voltage keeping output voltage constant.

2. Output characteristics is a curve plotted between output current and output voltage keeping input current constant.

Detail study of Common Base configurationInput characteristic

= IC IE at constant VCB

Hence total collector current is given by IC = IE + ICBO

Here ICBO

Collector Base OpenEmitter

Fig.4.19 shows the setup to plot input and output characteristic if CB configuration. Input characteristics is a graph plotted between emitter current IE(mA) and emitter to base voltage VBE(V) at constant collector base voltage VCB (V).Fig.4.20 shows the Plotted input characteristics.

Fig.4.19 Setup for plotting characteristics of CB Configuration

Analysis of input characteristics

1. Input characteristics looks like PN junction characteristics in forward biased because base emitter junction is nothing but forward biased PN junction.

2. After the cut-in voltage (0.7 fo Si and 0.3 for Ge) Emitter current IE increases rapidly with a small increase in VBE i.e its input resistance is very low

3. The Emitter current IE is

independent of collector base voltage VCB

Fig.4.20. Input characteristic of Common base Configuration

4. Input resistance :- It is defined as ration of emitter base voltage (VBE ) to the resulting change in emitter current (IE ) at constant collector base voltage (VCB )i.e

Rin = change in emitter to base voltage change in emitter current at constant VCB

The input resistance is quite small and is of the order of a few ohms. Its value is between 20 - 100 and typical value is 50.It value is low because input junction is forward biased and a small change in VBE produce large change in IE.

Output CharacteristicOutput characteristics is a graph plotted between collector current

IC(mA) to the collector base voltage VCB(V) keeping constant emitter current IE.Fig.4.21 show output characteristic graph.

Analysis of output characteristics Fig.4.21. Output characteristics of Common Base Configuration. It is clear from the graph that characteristics is divided into three regions , those are saturation , Active and Cut-off.

1. The saturation region is towards extreme left where VCB = 0V.Here current increases exponentially as VCB is increased towards 0v.As shown in fig.4.21 ,collector current IC change large with small change in VCB only at low voltages (less than 1V) .This region is called as Saturation region, were both the junctions are forward biased. Transistor is not operated in this region.

Rin = V BE

IE VCB = constant

Fig4.21 Output Characteristics of Common Base configuration2. Next region is active region, the collector current(IC) is almost constant,

and it is equal to emitter current (IE).When VCB is increased above 1-2v the collector becomes almost constant i.e. independent of VCB but dependent on IE.A very large change in VCB produce small change in IC, this means that output resistance is very high. In this region emitter-base (EB) junction is forward biased and collector-base(CB) junction is reversed biased. For every transistor maximum value of reverse bias is defined.

3. The region below were IE is marked as 0mA , cutoff region. Here Both junction of transistor are reversed biased.

4. Output characteristic can be used determine two factorsi. Output Resistance (Ro)ii. Current Amplification factor ()

5. Output resistance: It is ratio of change in collector base voltage (VCB)to the resulting change in collector current IC ( IC)at constant emitter current IE.

Ro= Change in collector base voltage

Change in collector current at constant Emitter current

The output resistance is very high and of the order of several hundreds of kilo-ohms. This is is because a very large change is Vcb produce a small change in IC

RO = V CB IC at constant IE

Summary of Common Base Configuration In common Base, base terminal is made common between Emitter and

Collector. Input is applied between emitter and base circuit, which is forward

biased. Input voltage applied is VBE and Input current is IE. Output is taken across collector and Base circuit which is reverse

Biased. Output Voltage is VCB and output current is IC. Total collector Current is IC = IB + ICBO

Current amplification factor is less than unity , typical value is upto 0.99

Input resistance is very Low ranging from 20 - 100 , typical value is 50

Output resistance is very high upto several hundreds of K ,typical value is 1M

Leakage current ICBO is very low , typically 4µA for germanium 0.02µA for silicon and it is temperature dependent.

Common Emitter ConfigurationAs shown in fig.4.22. the emitter made common between input and

output i.e. input is applied between Base and Emitter junction and output is taken from collector and emitter.

In this configuration base current IB is the input current and collector current IC is output current. IE is the emitter current whose direction and flow is as shown in the figure.

Fig4.22 shows both NPN and PNP transistor in Common Base Configuration.

Fig.4.22 Common Emitter Configuration (NPN and PNP)Base current amplification factor () Base current amplification factor () is the ratio of change in collector current (ICto the change in base current (IB)at constant collector to emitter voltage is called as base current amplification factor ( ).

= change in collector current change in Base current at constant collector emitter voltage

It is clear from expression IC > IB ,Therefore the value of is greater. It

value ranges from 20 to 500.This configuration is widely used where amplifier and for good frequency response.

Relation between and = common base current amplification factor = common collector current amplification factor.

= I C (1)IE

= IC (2)IB

For any transistor configurationIE = Ic + IB

IB = IE – IC (3)

Substitute equation (3) in equation (2) = I C . (4)

(IE – IC)

Multiply and divide equation (4) by IE

= IC . x IE

(IE – IC) IE

= IC / I E

1- (IC / IE )

Example : Let for a common base configuration current amplification factor = 0.98 find common base current amplification factorSolution : Given = 0.98

Find = 1-

Hence current amplification by common emitter configuration is more than common base configuration.

= IC IB VCE = constant

= 1-

Collector Current As discussed in CB configuration that total collector is comprising two

components , same fact is true here. Here total collector current is due to two factors

1.Due to majority charge carrier ie IB2.Due to minority charge carrier ie ICEO as shown if fig 4.28

Therefore IC = IB + ICEO

In common base configuration total collector current isIC = IE + ICBO

But IE = IC + IBIC = (IC + IB) + ICBO IC = IC + IB + ICBO

IC - IC = IB + ICBO

IC(1- ) = IB + ICBO

IC = IB + ICBO

1- 1- Comparing the equation with CE equation we get

CEO = ICBO

(1- (1-

IC = IB + ICEO

Above equation indicates that leakage current in CE is much more than CB configuration.

Example : For a common base configuration leakage current is 10A then find leakage current in common Emitter configuration. Let beSolution :

Given ACEO = ICBO = 10 * 10 -9

(1- 1 – 0.98

CEO = 500A

Hence it indicates that common emitter configuration has leakage current more than common base configuration.

Detail study of Common Emitter configurationInput characteristic

Fig.4.23 shows the setup to plot input and output characteristic if CE configuration. Input characteristics is a graph plotted between base current IB(mA) and base to Emitter voltage VBE(V) at constant collector emitter voltage VCE (V).Fig.4.24 shows the Plotted input characteristics.

IC = IB + ICBO

(1-

Fig.4.23. Setup for plotting characteristics of CE Configuration

Analysis of input characteristics 1) Input characteristic looks like

forward biased PN junction because input junction is forward biased and base emitter junction is like diode.

2) Upto a voltage called as cut-in voltage which is 0.7V for Si and 0.3 V for germanium. Characteristics shows very small change is current with voltage.

3) After cut-in voltage, current IB

shows large change with change in voltage VBE.

Fig.4.24. Input characteristic of Common emitter Configuration

4) This indicates that input resistance is low because small change in VBE

produces large change in IB. But input resistance of CE is slightly more than that of CB configuration because the base current does not change rapidly as that ion case of CB configuration.

5) The base current is independent of collector emitter voltage VCE. But the curve is shifted downward , this occurs because of the fact that as VCE is increased the depletion layer width is the base region is increased. This reduces the effective base width and hence base current is reduced.

Input resistance Input resistance is defined as ratio of change in base to emitter voltage

(VBE) to the change in base current (IB) at constant collector to emitter voltage(VCE)

Rin = change in base emitter voltage change in base current

at constant collector emitter voltage.

Input resistance is of the order of few hundred which is slightly greater

than input resistance of CB configuration. Its value ranges from 600 to 4K

Output CharacteristicOutput characteristics is a graph plotted between collector current

IC(mA) to the emitter voltage VCE(V) keeping constant base current IB .Fig.4.25. show output characteristic graph. This characteristics is also called as collector characteristics.

Analysis of output characteristics Fig.4.25 Show the output characteristic of transistor a in CE

configuration.

Fig.4.25.Output characteristics of Common Base Configuration

1. The output characteristics consist of three regions like Saturation region, active region and cut-off region.

2. At voltage below knee Voltage, where VCE(upto 1V) is reduced to such a small value that collector –base junction get forward biased and base emitter junction is already forward biased. Below knee voltage Ic follows VCE i.e. till that voltage collector junction is forward biased transistor operates in saturation region.

3. In these the curve is almost horizontal. In active region collector base junction is reversed biased. As VCE is increased there reverse bias get increased, due to this depletion region spread more in the base than the collector, reducing the recombination in the base. The change in collector current is more sharper as compared to CB configuration.

4. After knee voltage Ic is almost independent of VCE & IC is dependent of IB. Now transistor is operated in active region. After knee voltage IC

Rin = V BE

IB VCE = constant

almost constant. but a large change in VCE produce very small Ic. hence Output resistance is very high.

5. When the input base current is made equal to zero (IB = 0) , the collector current(IC), due majority carrier is zero and is due minority carrier ie ICEO. The region below IB = 0 is called as cut-off region. In this region both junction are reversed biased.

Output resistance Output resistance is the ratio of change in collector emitter voltage VCE

to the change in collector current IC at constant base current IB

Output resistance = change in collector to emitter voltagechange in collector current

at constant base current

From characteristics it is clear that it has some slope indicating that output resistance of CE is little less than Output resistance of CB configuration.

The output resistance of CE configuration is of the order of few KGenerally it is 10 K-50 K .Typically it is of 20 K

Summary of Common Emitter Configuration In common Emitter, emitter terminal is made common between Base

and Collector. Input is applied between base and emitter circuit, which is forward

biased. Input voltage applied is VBE and Input current is IB. Output is taken across collector and emitter circuit which is reverse

Biased. Output Voltage is VCE and output current is IC. Total collector Current is IC = IB + ICEO Current amplification factor is very high , its value is ranges from 20

- 500 Input resistance is very Low ranging. Its value ranges from 600 to

4K. But its value is greater than that of Common base configuration. Output resistance is very high up to several of K , Generally it is 10

K-50 K .Typically it is of 20 K Leakage current ICEO is low , it is temperature dependent, but its value

is greater than that in case of CB configuration.

Common Collector Configuration

Rout = VCE

IC at constant IB

As shown in fig.4.26 the collector is made common between input and output i.e. input is applied between Base and collector junction and output is taken from emitter and collector.

In this configuration base current IB is the input current and emitter current IE is output current. IC is the collector current whose direction and flow is as shown in the figure.

Fig.4.26 Shows the NPN and PNP transistor connection in CC configuration

Fig.4.26.Common collector Configuration (NPN and PNP)

In this circuit battery VBB makes emitter junction forward biased & Vcc reverse biases collector junction

Fig.4.27 Common Collector configuration

Current amplification factor ( ) Current amplification factor( ) is ratio of change in emitter current IE

to the change in emitter current IE to change in base current IB at constant collector to emitter voltage VCE.

= change in emitter current change in base current

at constant collector to emitter voltage

Current gain is high as that of common emitter but voltage gain is less

than unity.

Relation between and

= IE IB VCE =

constant

= common collector current amplification factor = common base current amplification factor.

= I C (1)IE

= IE (2)IB

For any transistor configurationIE = Ic + IB

IB = IE – IC (3)

Substitute equation (3) in equation (2) = I E . (4)

(IE – IC)

Multiply and divide equation (4) by IE

= IE . x IE

(IE – IC) IE

= IE / I E

1- (IC / IE )

Example : Let for a common base configuration current amplification factor = 0.98 find current amplification factor for common collector configurationSolution : Given = 0.98

Find = 1-

Hence current amplification by common collector configuration is more than that of common base configuration and common emitter configuration . The value for highest as compared to and

Emitter current As discussed in CB and CE configuration that total collector is

comprising two components , same fact is true here. Here total emitter current is due to two factors

1.Due to majority charge carrier ie IB2.Due to minority charge carrier ie ICEO as shown if fig 4.28

Therefore IE = IB + ICEO (1)In common base configuration total collector current is

IC = IE + ICBO (2)But IE = IC + IB (3)Susbstuting (2) in (3) IE = IE + ICBO + IB

= 1-

IE - IE = ICBO + IBIE(1 - ) = ICBO + IB

Fig.4.28 Leakage current in CC configuration

Above equation indicates that leakage current in CC is much more than CB configuration and almost equal to that CE configuration.

IE = IB + ICBO 1 -

(1 - )

IE = IB + ICEO

which indicates that leakage current is very high as compared to CB.

Example : For a common base configuration leakage current is 10A then find leakage current in common Collector configuration. Let beSolution :

Given A

CEO = ICBO = 20 * 10 -9 (1- 1 – 0.98

CEO = 1000A = 1mA

Hence it indicates that common Collector configuration has leakage current more than common base configuration.

Q.Why Common emitter Configuration is the Best configurationAns. Out of the three configurationsCommon emitter is most widely used CE configuration is used in 90 to 95% of all transistor application. The main reason for these are

1) High current gainThe current gain of CB is less than 1 hence low value of will not make it good amplifier. But current gain of CE is more than 1 typically 20-500 make CE as good amplifier.

2) High voltage and power gain Due to high current gain. CE circuit has high voltage and power gain because in CB circuit current gain is less than 1 and in CC circuit voltage gain is less than 1.

3) Moderate output to input resistance ratio In common emitter circuit the ratio of output impedance to input

impedance is moderate. These make this circuit arrangement an ideal for coupling between various stages.

Because of above three reasons CE configuration is widely used.

Comparison of CB , CE , and CC Configuration

ICEO = ICBO

(1 - )

Characteristics Common Base Common Emitter

Common Collector

Input resistance Low resistance about 100

Medium about 750

Very High about 750 k

Output resistance

Very High about 450 k

High about 450 k

Low about 50

Input Current Emitter Current IE

Base Current IB Base Current IB

Output Current Collector Current IC

Collector Current IC

Emitter Current IE

Input Voltage applied

Emitter and Base VEB

Base and Emitter VBE

Base and Collector VCB

Output Voltage applied

Collector and Base VCB

Collector and Emitter VCE

Emitter and Collector VEC

Voltage gain High about 150 High about 500 Less than 1Current gain Less than 1 High HighPhase shift from Input to Output

0o 180o 0o

Leakage current

Low ICBO High ICEO= 1 ICBO

1 -

High ICEO = 1 ICBO

1- Application Used for high

frequency application

Used for audio frequency application

Used as impedance matching circuit.

Common Terminal

Base between input and Output

Emitter between input and Output

Collector between input and Output

Diagrams

Fig .4.29 . Table of Comparison of Different Configuration

Application of TransistorApplication of Transistor are as Follows

1) It is used an amplifier.2) It is used as an oscillator.3) It is used as an wave shaping circuit.4) It is used as an multi vibrator circuit.5) It is used as electronic switch.

6) It is used as an impedance matching circuit.7) It is used in Radio transmitter and receiver.8) It is used in output amplifier.

Specification of Transistor areDifferent specification from data sheet are

1) Collector base voltage (VCB ) It is the maximum voltage that can be applied across base and collector of a transistor.

2) Collector to emitter voltage ( VCE )It is the maximum voltage which can be applied across collector and emitter of transistor.

3) Collector saturation voltage ( VCE sat) It is the collector emitter voltage of fully conducting transistor, it is denoted by VCE sat.

4) Collector current ( IC ) It is the maximum value of collector current that a transistor handle

safely.

5) Collector cutoff current (ICEO ) It is the reverse current or reverse saturation current flowing between collector and emitter of transistor with base open.

6) Forward current gain It is the maximum ration of output current to input current of CE configuration which decides maximum forward current.

7) Maximum collector dissipation (Pd max) It is the maximum value of power dissipated in collector of transistor at 250c.

8) Collector-to-Base Breakdown Voltage (BVCB0) It is the maximum value if allowable reverse voltage that can be applied across the collector and base of a transistor with emitter open. It is specified at 25°C.

9) Collector-to-Emitter Breakdown Voltage(BVCE) It is the maximum value of allowable reverse voltage that can be applied across the collector emitter of a transistor with base open. It is specified at 25°C.

10) Emitter-to-Base Breakdown Voltage (BVEBO) It is the maximum value of allowable voltage that can be applied across the emitter to base of transistor with collector open. It is specified at 25°C.

11) Collector-Cutoff Current (ICBO)

It is the reverse saturation current flowing between collector and base of a transistor with emitter open.

12) Transition Frequency (FT) It is the transition frequency at which the common emitter forward current gain is unity and denoted by FT. Its significance is that the product of gain and bandwidth equals the transition frequency. Hence, if both gain and bandwidth are to be large, FT has to large, particularly at high frequencies where bandwidth is large.

Transistor RatingA transistor like any other electronic device, has limitations on its

operation. These limitations are stated in terms of maximum ratings. If these ratings are exceeded, it may cause either permanent damage to transistors or temporarily change their operating characteristics. The maximum ratings are normally specified on the manufacturer’s data sheet. Following are some of the important maximum ratings of a transistor

1. Maximum collector current.2. Maximum collector dissipation at 25° C.3. Maximum allowable collector-to-base voltage.4. Maximum allowable collector-to-emitter voltage.

1. Maximum Collector CurrentIt is defined as the absolute maximum value of the current which a collector can handle safely and is designated by IC(MAX). This limitation is due to the localized hot spots which can occur within the transistor due to high current densities at unavoidable current path restrictions or high resistance points within the transistor. A common source of difficulty is the junction area and the wire bonds that connect the transistor terminals to the external leads.

2. Maximum Collector DissipationIt is defined as the ability of transistor to dissipate heat in the collector junction. Thus it is a rating used to indicate the limits on the power handling capability of a transistor. In normal operation of a transistor, two junctions carry approximately the some current (IE IC). But the collector-base junction has a much higher voltage across it than emitter-base junction. As a result of this, the power dissipation in a collector-base junction is of more importance. Mathematically, the maximum collector (or power) dissipation is given by

PD(max) = VCE X IC(max) = VCE(max) X Ic

The value of maximum power dissipation, PD(max) is usually specified at an ambient temperature of 25°C For higher temperature, the value of P (max) will be less.

3. Maximum Output VoltageIn most of the applications, the collector-base junction is subjected to the highest voltages. Since there is a possibility of voltage breakdown at high voltages, therefore, it is necessary to specify the maximum allowable

collector-base voltage or collector-emitter voltage or both. The voltage breakdown, which can occur in a transistor is of two types, namely avalanche breakdown and punch-through.

4. Maximum Output VoltageThe absolute maximum value of collector-to-base VCB(max) or collector-to- emitter voltage VCE(max) which a transistor can handle safely is called maximum output voltage.

NPN transistors

Code StructureCasestyle

IC

max.VCE

max.hFE

min.Ptot

max.

Category(typical use)

Possiblesubstitutes

BC107 NPN TO18 100mA 45V 110 300mWAudio, low power

BC182 BC547

BC108 NPN TO18 100mA 20V 110 300mW

General purpose, low power

BC108C BC183 BC548

BC108C NPN TO18 100mA 20V 420 600mW

General purpose, low power

BC109 NPN TO18 200mA 20V 200 300mW

Audio (low noise), low power

BC184 BC549

BC182 NPN TO92C 100mA 50V 100 350mW

General purpose, low power

BC107 BC182L

BC182L NPN TO92A 100mA 50V 100 350mW

General purpose, low power

BC107 BC182

BC547B NPN TO92C 100mA 45V 200 500mWAudio, low power

BC107B

BC548B NPN TO92C 100mA 30V 220 500mW

General purpose, low power

BC108B

BC549B NPN TO92C 100mA 30V 240 625mW Audio (low

BC109

noise), low power

2N3053 NPN TO39 700mA 40V 50 500mW

General purpose, low power

BFY51

BFY51 NPN TO39 1A 30V 40 800mW

General purpose, medium power

BC639

BC639 NPN TO92A 1A 80V 40 800mW

General purpose, medium power

BFY51

TIP29A NPN TO220 1A 60V 40 30W

General purpose, high power

TIP31A NPN TO220 3A 60V 10 40W

General purpose, high power

TIP31C TIP41A

TIP31C NPN TO220 3A 100V 10 40W

General purpose, high power

TIP31A TIP41A

TIP41A NPN TO220 6A 60V 15 65W

General purpose, high power

2N3055 NPN TO3 15A 60V 20 117W

General purpose, high power

Please note: the data in this table was compiled from several sources which are not entirely consistent! Most of the discrepancies are minor, but please consult information from your supplier if you require precise data.

PNP transistors

Code StructureCasestyle

IC

max.VCE

max.hFE

min.Ptot

max.

Category(typical use)

Possiblesubstitutes

BC177 PNP TO18 100mA 45V 125 300mWAudio, low power

BC477

BC178 PNP TO18 200mA 25V 120 600mW

General purpose, low power

BC478

BC179 PNP TO18 200mA 20V 180 600mW

Audio (low noise), low power

BC477 PNP TO18 150mA 80V 125 360mWAudio, low power

BC177

BC478 PNP TO18 150mA 40V 125 360mW

General purpose, low power

BC178

TIP32A PNP TO220 3A 60V 25 40W

General purpose, high power

TIP32C

TIP32C PNP TO220 3A 100V 10 40W

General purpose, high power

TIP32A

Please note: the data in this table was compiled from several sources which are not entirely consistent! Most of the discrepancies are minor, but please consult information from your supplier if you require precise data.

Testing of Transistor

Meter check of a transistor Decided whether transistor is OKBipolar transistors are constructed of a three-layer semiconductor "sandwich," either PNP or NPN. As such, they register as two diodes connected back-to-back when tested with a multimeter's "resistance" or "diode check" functions: Fig.4.30 and Fig.4.31 shows testing of Transistor.

Fig.4.30.Testing of PNP Transistor

Here I'm assuming the use of a multimeter with only a single continuity range (resistance) function to check the PN junctions. Some multimeters are equipped with two separate continuity check functions :

1. Resistance and 2. "Diode check,"

each with its own purpose. If your meter has a designated "diode check" function, use that rather than the "resistance" range, and the meter will display the actual forward voltage of the PN junction and not just whether or not it conducts current.

Fig.4.31.Testing of PNP TransistorMeter readings will be exactly opposite, of course, for an NPN transistor, with both PN junctions facing the other way.

If a multimeter with a "diode check" function is used in this test, it will be found that the emitter-base junction possesses a slightly greater forward voltage drop than the collector-base junction. This forward voltage difference is due to the disparity in doping concentration between the emitter and collector regions of the transistor: the emitter is a much more heavily doped piece of semiconductor material than the collector, causing its junction with the base to produce a higher forward voltage drop.

Knowing this, it becomes possible to determine which wire is which on an unmarked transistor. This is important because transistor packaging, unfortunately, is not standardized. All bipolar transistors have three wires, of course, but the positions of the three wires on the actual physical package are not arranged in any universal, standardized order.

Suppose a technician finds a bipolar transistor and proceeds to measure continuity with a multimeter set in the "diode check" mode. Measuring between pairs of wires and recording the values displayed by the meter, the technician obtains the following data. Fig.4.32, fig.4.33 shows how lead of unknown transistor can be found using multimeter.

Fig.4.32. Finding the lead of Transistor

1. Meter touching wire 1 (+) and 2 (-): "OL" 2. Meter touching wire 1 (-) and 2 (+): "OL" 3. Meter touching wire 1 (+) and 3 (-): 0.655 volts 4. Meter touching wire 1 (-) and 3 (+): "OL" 5. Meter touching wire 2 (+) and 3 (-): 0.621 volts 6. Meter touching wire 2 (-) and 3 (+): "OL"

The only combinations of test points giving conducting meter readings are wires 1 and 3 (red test lead on 1 and black test lead on 3), and wires 2 and 3 (red test lead on 2 and black test lead on 3). These two readings must indicate forward biasing of the emitter-to-base junction (0.655 volts) and the collector-to-base junction (0.621 volts).

Now we look for the one wire common to both sets of conductive readings. It must be the base connection of the transistor, because the base is the only layer of the three-layer device common to both sets of PN junctions (emitter-base and collector-base).

In this example, that wire is number 3, being common to both the 1-3 and the 2-3 test point combinations. In both those sets of meter readings, the black (-) meter test lead was touching wire 3, which tells us that the base of this transistor is made of N-type semiconductor material (black = negative). Thus, the transistor is an PNP type with base on wire 3, emitter on wire 1 and collector on wire 2:

Fig.4.33. Finding the lead of the transistor

Please note that the base wire in this example is not the middle lead of the transistor, as one might expect from the three-layer "sandwich" model of a bipolar transistor. This is quite often the case, and tends to confuse new students of electronics. The only way to be sure which lead is which is by a meter check, or by referencing the manufacturer's "data sheet" documentation on that particular part number of transistor.

Knowing that a bipolar transistor behaves as two back-to-back diodes when tested with a conductivity meter is helpful for identifying an unknown transistor purely by meter readings. It is also helpful for a quick functional check of the transistor.

If the technician were to measure continuity in any more than two or any less than two of the six test lead combinations, he or she would immediately know that the transistor was defective (or else that it wasn't a bipolar transistor but rather something else -- a distinct possibility if no part numbers can be referenced for sure identification

Summary1. Tested with a multimeter in the "resistance" or "diode

check" modes, a transistor behaves like two back-to-back PN (diode) junctions.

2. The emitter-base PN junction has a slightly greater forward voltage drop than the collector-base PN junction, due to more concentrated doping of the emitter semiconductor layer.

3. The reverse-biased base-collector junction normally blocks any current from going through the transistor between emitter and collector. However, that junction begins to conduct if current is drawn through the base wire. Base current can be thought of as "opening a gate" for a certain, limited amount of current through the collector.

Transistor codesThere are three main series of transistor codes 1. Codes beginning with B (or A), for example BC108,

BC478 The first letter B is for silicon, A is for germanium (rarely used now). The second letter indicates the type; for example C means low power audio frequency; D means high power audio frequency; F means low power high frequency. The rest of the code identifies the particular transistor. There is no obvious logic to the numbering system. Sometimes a letter is added to the end (eg BC108C) to identify a special version of the main type, for example a higher current gain or a different case style. If a project specifies a higher gain version (BC108C) it must be used, but if the general code is given (BC108) any transistor with that code is suitable.

2. Codes beginning with TIP, for example TIP31A

TIP refers to the manufacturer: Texas Instruments Power transistor. The letter at the end identifies versions with different voltage ratings.

3. Codes beginning with 2N, for example 2N3053 The initial '2N' identifies the part as a transistor and the rest of the code identifies the particular transistor. There is no obvious logic to the numbering system.

Question Bank for 4 marks1. Explain constructional details of transistor and draw its

symbol?2. Why is this device called as transistor?3. Why is it called as a “Bipolar” Transistor ?4. Explain the operation of transistor ?5. Explain operation of NPN transistor ?6. Explain the operation of PNP transistor ?7. Explain different operating modes of transistor ?8. Explain different configurations in which transistor can be

used?9. Explain operation of transistor as an amplifier?10. Explain common base configurations with proper

diagram?11. What do you mean by characteristics of transistor?12. Explain input characteristics configuration of common

base configuration13. Explain the output characteristics of common base

configuration with neat wave form.14. Explain with Circuit diagram common emitter

configuration of transistor? Derive relation between and 16. Explain input characteristic with neat diagram.17. Explain Output characteristic of CE configuration18. Explain with neat label diagram the common collector

configuration.19. Give relation between and ?20. Give expression for emitter current in common collector

configuration?21. List the characteristics of CB,CC,CE Amplifier ? 22. Compare CB,CC,CE configuration ?23. Which of three (CB,CC,CE) configuration is widely used.24. List application of transistor?25. List specification of transistor?26. Describe the terms Active , Cutoff , Saturation related to

transistor operation

Question for 2 marks1. State the meaning of emitter , base , and collector ?2. State function of emitter , base , and collector ?3. Describe why doping of emitter , base , and collector is different ?

4. Describe why doping of emitter is high?5. Describe why doping of base is low ?6. Describe why doping of collector is moderate ?7. Describe why width of emitter , base , and collector is different ?8. Describe why width of emitter is moderate?9. Describe why width of base is thin ?10. Describe why width of collector is high ?

11. State the resistance of all three layer ?12. Draw symbol for NPN and PNP transistor ?13. Why transistor is called as BJT ?14. What B stand for in BJT ?15. What J stand for in BJT ?16. What T stand for in BJT ?17. Define of common base configuration ?18. Define of common emitter configuration ?19. Define of common collector configuration ?20. Define the term Input and Output resistance of Transistor ?21. State three configuration of Transistor ?22. List four mode of operation of transistor ?23. State the biasing condition of junction in Active mode ?24. State the biasing condition of junction in cutoff mode ?25. State the biasing condition of junction in saturation mode ?26. State the biasing condition of junction in inverse mode ?27. Why saturation mode of operation is called as Closed switch ?28. Why cutoff mode of operation is called as open switch ?29. What is resistance of BE junction of NPN transistor when it is forward

biased ?30. What is resistance of CB junction of NPN transistor when it is reverse

biased ?31. What is resistance of BE junction of PNP transistor when it is forward

biased ?32. What is resistance of CB junction of PNP transistor when it is reverse

biased ?33. Find of transistor if is 0.9 34. Find of transistor if is 0.9 35. Find of transistor if is 25036. Find of transistor if is 20037. Find Leakage current ICEO if is 0.9 and ICBO = 100A38. Find the total collector current of CB configuration if is 0.9 , IE =

10mAand leakage current ICBO = 100A

39. Find the total collector current of CE configuration if is 0.92 , IB = 10µAand leakage current ICBO = 150A

40. Find the total collector current of CE configuration if is 0.96 , IB = 10µA

and leakage current ICBO = 250A

Mr Manoj S. Kavedia9423088039Institute of Technology UlhasnagarSr.Lecturer

The End