In this first transistor lecture, well spend time applying our familiar semiconductor. It consists of an input impedance, r p, an output impedance r 0, and a voltage controlled current source described by the transconductance, g m. Most electrons cross the base junction and are swept into collector why. Boring analysis that removes the transistor from the circuit leaving an open circuit. Power bipolar junction transistor bjt background the bipolar junction transistor was invented in 1947 by shockley, brattain, and bardeen. Bipolar junction transistor npn bjt shown 3 terminals. The principle of operation of the two transistor types. The bipolar junction transistor was invented in 1947 by shockley, brattain, and bardeen. A selection of typical bipolar junction transistors bjts is shown in fig 3.
A bipolar junction transistor or bjt is a fundamental electronic component because of its expansive and essential applications across numerous electronic devices such as radio transmitters 1, televisions, desktop computers, and portable computing devices such as smartphones and tablet computers, among others. The word transistor is derived from the words transfer and resistor it describes the operation of a bjt i. And the saturation current is a very small number, typically about 1 times 10 to the minus 15 amps. Introduction to bipolar junction transistors bjt youtube. In this picture, i c is independent of v bc and v ce as long as v be v t i c i s e 0 0 0 ce d bc be ce d ce v v v v v v v. Introduction to bipolar junction transistor bjt duration. When both junctions are forward biased, th e transistor is in the saturation region of its operation. Let us start our discussion of the bipolar junction transistors or the bjt in short. Bipolar junction transistor bjt function is usually considered in terms of currents.
Function of bipolar junction transistor bjts are of two types namely npn and pnp based on doping types of the three main terminals. Bjts use two junctions between two semiconductor types, ntype and ptype. The operation of npn and pnp transistors are same if the roles played by the electrons and holes are interchanged. Introduction to bipolar junction transistors bjt bipolar. A bipolar junction transistor or bjt is a three terminal electronic device that amplifies the flow of current. Bipolar transistors general purpose bipolar transistors available in the variety of packages having the nature such as smallsignal, thin and highpower to cover the market extensively. The bipolar junction transistor bjt was named because its operation involves conduction by two carriers. The very first bipolar junction transistors were fabricated from a bar of germanium with two closely spaced alloyed contacts. The three layers are called the emitter, base and collector.
Bipolar junction transistors tlt8016 basic analog circuits 20052007 12 4. The point contact junction has very low value of the capacitance. Bipolar junction transistor is 3 terminal semiconductor device which can be used as a switch or as an amplifier in the electronic circuits. Lecture series on electronics for analog signal processing i by prof. One way to look at a bjt transistor is two backtoback diodes, has very different characteristics. Bjt bipolar junction transistor this name is a representation for a device having transfer resistors. May 11, 2018 today, i am going to discuss the details on the introduction to bjt bipolar junction transistor. Chapter 4 bipolar junction transistor bjt noise measurements object the objective of this experiment is to measure the meansquare equivalent input noise, v2 ni, and base spreading resistance, rx, of some npn bipolar junction transistors bjts. If we put a small current into one of the terminals, called the base, then the switch is oncurrent may flow. Technical feats previously requiring relatively large, mechanically fragile, powerhungry vacuum tubes were suddenly achievable with tiny, mechanically rugged, powerthrifty specks of crystalline silicon. Bjt bipolar junction transistor construction, types and. Bipolar junction transistor 8 typical operation of junction transistor amplifier typically the collector current, ic, is 100 to times greater than the base current ib, depending on the type of transistor used if we take the base current ib as an input and the collector current ic as an output, then we can say that. Oct 08, 2014 in this lecture, well introduce one of the fundamental analog devices.
An npn transistor consists of two semiconductor junctions that have a thin pdoped anode region and pnp transistor also consists of two semiconductor junctions that have a thin n doped cathode region. One pn junction of a transistor is reversebiased, whereas the other is forwardbiased. The first bipolar transistor was invented at bell labs by william shockley, walter brattain, and john bardeen so late in 1947 that it was not published until 1948. I will have a composite structure in which two transistors will be merged together which gives li2. Bipolar power devices are the traditional power devices because of their capability to provide high currents and high blocking voltages. Radhakrishna rao, department of electrical engineering,iit madras. Equivalent to an off state when transistor is used as a switch. Bipolar junction transistors base emitter collector base emitter collector pnp transistor npn transistor p n p n p n bipolar.
We will begin looking at transistors with the bipolar junction transistor. These can have the configuration of npn or pnp and the various layers can either be. Note that in both cases the minority carrier injection is predominately into the lightly doped side. Bipolar junction transistors learn about electronics. Because of this, such junctions are very useful for operation at the frequencies as high as 10 ghz. Introduction to bjt bipolar junction transistor the. Germanium was used since it could easily be purified such that the minority carrier diffusion length was comparable to the distance between the two alloyed contacts. Contacts are made to all three regions, the two outer regions called the emitter and collector and the middle region called the base. In addition we eliminate the basecollector junction current by setting v bc 0. As we have seen a semiconductor offer less resistance to flow current in one direction and high resistance is another direction and we can call transistor as the device mode of the semiconductor.
In bipolar junction transistor, electric current is conducted by both free electrons and holes. P517617 lec 5, p7 transistors transistors are the heart of modern electronics replaced vacuum tubes voltage and current amplifier circuits high frequency switching computers impedance matching low power small size, can pack thousands of transistors in mm2 in this class we will only consider bipolar transistors. Bipolar junction transistors the transistor is a threelayer semiconductor device consisting of either two n and one p type layers of material or two p and one n type layers of material. Bipolar junction transistor physics and radioelectronics. A bipolar junction transistor bipolar transistor or bjt is a type of transistor that uses both electrons and holes as charge carriers. Bipolar transistors are current regulating devices that control the amount of current flowing through them in proportion to the amount of biasing voltage applied to their base terminal acting like a currentcontrolled switch. Bipolar junction transistor bjt few most important applications of transistor are.
The invention of the bipolar transistor in 1948 ushered in a revolution in electronics. As emitter is heavily doped, a large number of electrons diffuse. The bipolar transistor can be switching from its onstate to the blocking state by reversing the bias applied to the base region. The base current i b controls the collector current i c regions of bjt operation. In a conventional transistor, the operation depends upon the flow of majority and minority carriers. More about bjt fabrication and realization of pnp transistor. Bipolar junction transistors tlt8016 basic analog circuits 20052007 9 example 4.
In this lecture, well introduce one of the fundamental analog devices. Here we will describe the system characteristics of the bjt. Chapter 4 bipolar junction transistor bjt noise measurements. Alan doolittle lecture 20 bipolar junction transistors bjt. Emitter p n collector base pnp transistor emitter n p base npn transistor. Collector npn transistor pnp transistor p n p n p n. Introduction to bipolar junction transistor bjt youtube. Each junction can be forward or reverse biased independently. The bipolar junction transistor can be considered essentially as two pn junctions placed backtoback, with the base ptype region being common to both diodes. In summary, during this lesson i introduced the bipolar junction transistor, a three terminal device that consists of two pn injunctions. Presentation on bipolar junction transistor slideshare uses cookies to improve functionality and performance, and to provide you with relevant advertising.
General purpose bipolar transistors product search. How to use bjt bipolar junction transistor beginners. Bipolar junction transistors emitter p n collector base pnp transistor emitter n p base npn transistor bipolar. Theory equivalent input noise it can be shown that v2 ni. It is a semiconductor device and it comes in two general types. As the name suggests, it is composed of two junctions called emitterbase junction and collectorbase junction. The bjt has two pn junctions, the base emitter junction and the base collector junction. As we have seen a semiconductor offers less resistance to flow of current in one direction and high resistance in another direction, we call the device made of semiconductors as a transistor.
However, if a junction is made by joining ptype semiconductor to ntype semiconductor a useful device is produced known as. Bjts are of two kinds pnp transistor and npn transistor. Thus a junction transistor is formed by sandwiching a thin layer of ptype semiconductor between two layers of ntype semiconductor and vice versa. Transistor action baseemitter junction is forward biased and collectorbase junction is reverse biased electrons emitted into base much more than holes since the doping of emitter is much higher magic. Mosfet metal oxide semiconductor field effect transistor the fet has several advantages over conventional transistor. Introduction to bipolar junction transistors bjt topics covered.
It is a currentdriven device mosfet is voltage driven, the output current is equal to the input current times a factor which is called gain. The bipolar junction transistor is a semiconductor device which can be used for switching or amplification in the diode tutorials we saw that simple diodes are made up from two pieces of semiconductor material to form a simple pn junction and we also learnt about their properties and characteristics. The multifold advantages of replacing vacuum tubes with a solidstate device rapidly promulgated its use in applications. Buh515 high voltage 1500v high power 50w npn fast switching transistor in an isowatt218 package, originally designed for use in analogue tv timebases but also used in switched mode power supplies. The operation of the transistor is very dependent on the degree of doping of the various parts of the. Bipolar junction transistors transistor operation the biasing of the two types of transistor has been illustrated in the figures. The forward active mode is obtained by forwardbiasing the baseemitter junction. The availability of singlecrystal silicon technology with higher purity levels together. Bipolar junction transistors types of bipolar junction transistors. Bipolar junction transistors solidstate device theory.
For the bjt to operate as an amplifier, the base emitter junction. Igbt insulated gate bipolar transistor working in power electronics by engineering funda duration. Draw the directions of all currents for these two transistors one npn and one pnp, clearly identifying which of. Bipolar junction transistors bjt general configuration and definitions the transistor is the main building block element of electronics. Combining this relationship with that for the commonemitter current gain.
These transistors are also known as bipolar junction transistor bjt and are our subject of study in this section. As we will go through the topic, we will know about the transistor, mainly bipolar junction transistor or bjt. The base current i b controls the collector current i. Unipolar transistors, such as fieldeffect transistors, only use one kind of charge carrier. There are two junctions in bipolar junction transistor. One can also make pnp bipolar junction transistors summary of i c as a function of v ce for a given i b. Bipolar junction transistor 1 introduction to bipolar junction transistors transistors are three port devices used in most integrated circuits, such as amplifiers transistors are active components recall that resistors, capacitors and inductors are passive there are two types of transistor. How a bjt bipolar junction transistor works its all in the doping the way a transistor works can be described with reference to fig.
The hybrid pi model of a bjt is a small signal model, named after the plike equivalent circuit for a bipolar junction transistor. A bipolar junction transistor bjt consists of three differently doped re gions. The bipolar junction transistor bjt is constructed of three regions. The minoritycarrier distribution in the quasineutral regions of the bipolar transistor, as shown. Analog circuits video course course outline this course is an introduction to amplifiers using transistors. The early voltage va has a typical value of 150 volts. Bjts are of two types namely npn and pnp based on doping types of the three main terminals.
If you continue browsing the site, you agree to the use of cookies on this website. The bipolarbased power devices include highpower bipolar transistors, darlington transistors consisting of two transistors with a common collector, thyristors also called silicon controlled rectifiers srcs and triacs, a complementary thyristor. A bipolar junction transistor consists of two backtoback pn junctions, who share a thin common region with width, w b. Bipolar junction transistors bjt transistor basics a bipolar junction transistor is a three layer npn or pnp semiconductor device.
Bipolar junction transistors bjt and its applications. The reverse bias not only stops the injection of minority carriers from the emitterbase junction but also removes some of the charge stored in the base region. Note also that it is the doping level of the more lightly doped junction that determines the magnitude of the current, and as the doping level on the lightly doped side decreases, the. Analysis that replaces the transistor with a pair of batteries representing the two junction turn on voltages cvd model. Bipolar junction transistor working, definition, application.