INTRODUCTION:
The crucial component of an electronic device is a controllable valve that lets a weak signal control a much larger flow much as a faucet controls the flow of water. At one time the controllable valve used in electronic circuits was the vacuum tube. The vacuum tube worked but it was bulky and used a lot of electrical power that ended up as heat which shortened the life of the tube itself. The transistor was a much more elegant solution to the needs of electronics. The transistor is small and uses much, much less power than the vacuum tube. Because it uses so little power there is little heat to dissipate and the transistor does not fail so quickly as does a vacuum tube.
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. 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 transitor was, in large part, Shockley’s creation. The crucial component of an electronic device is a controllable valve that lets a weak signal control a much larger flow much as a faucet controls the flow of water. At one time the controllable valve used in electronic circuits was the vacuum tube. The vacuum tube worked but it was bulky and used a lot of electrical power that ended up as heat which shortened the life of the tube itself.
The Term Paper on Automatic Railway Gate Control
Aim of this project is to control the unmanned rail gate automatically using embedded platform. Today often we see news papers very often about the railway accidents happening at un- attended railway gates. Present project is designed to avoid such accidents if implemented in spirit. This project is developed in order to help the INDIAN RAILWAYS in making its present working system a better one, ...
The transistor was a much more elegant solution to the needs of electronics. The transistor is small and uses much, much less power than the vacuum tube. Because it uses so little power there is little heat to dissipate and the transistor does not fail so quickly as does a vacuum tube. 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.
TRANSISTOR: A transistor is a semiconductor device used to amplify and switch electronic signals. It is made of a solid piece of semiconductor material, with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor’s terminals changes the current flowing through another pair of terminals. Because the controlled (output) power can be much more than the controlling (input) power, the transistor provides amplification of a signal. Today, some transistors are packaged individually, but many more are found embedded in integrated circuits.
TYPES OF TRANSISTOR: There are two types of standard transistors, NPN and PNP, with different circuit symbols. The letters refer to the layers of semiconductor material used to make the transistor. Most transistors used today are NPN because this is the easiest type to make from silicon. If you are new to electronics it is best to start by learning how to use NPN transistors. These terms refer to the internal operation of a transistor but they are not much help in understanding how a transistor is used, so just treat them as labels! A Darlington pair is two transistors connected together to give a very high current gain. In addition to standard (bipolar junction) transistors, there are field-effect transistors which are usually referred to as FETs. They have different circuit symbols and properties and they are not (yet) covered by this page.
The Dissertation on Related Literature to the Cash Flow Management
The role of cash flow information in discriminating between bankrupt and non-bankrupt companies remains a contentious issue. In a number of literature reviews on bankruptcy prediction (e. g. Zavgren, 1983; Jones, 1987; Neill et al. 1991; Watson, 1996) the common view is that cash flow information does not contain significant incremental information content over accrual information in ...
PNP transistor :
PNP Transistor Operation :
The PNP transistor works essentially the same as the NPN transistor. However, since the emitter, base, and collector in the PNP transistor are made of materials that are different from those used in the NPN transistor, different current carriers flow in the PNP unit. The majority current carriers in the PNP transistor are holes. This is in contrast to the NPN transistor where the majority current carriers are electrons. To support this different type of current (hole flow), the bias batteries are reversed for the PNP transistor. A typical bias setup for the PNP transistor is shown in figure 2-8.
Notice that the procedure used earlier to properly bias the NPN transistor also applies here to the PNP transistor. The first letter (P) in the PNP sequence indicates the polarity of the voltage required for the emitter (positive), and the second letter (N) indicates the polarity of the base voltage ( negative).
Since the base-collector junction is always reverse biased, then the opposite polarity voltage (negative) must be used for the collector. Thus, the base of the PNP transistor must be negative with respect to the emitter, and the collector must be more negative than the base. Remember, just as in the case of the NPN transistor, this difference in supply voltage is necessary to have current flow (hole flow in the case of the PNP transistor) from the emitter to the collector. Although hole flow is the predominant type of current flow in the PNP transistor, hole flow only takes place within the transistor itself, while electrons flow in the external circuit. However, it is the internal hole flow that leads to electron flow in the external wires connected to the transistor.
The Essay on Statement of Cash Flow
The importance of cash the cash flow statement help businesses and creditors understand how liquid a company is. Team A discussed some important factors about the statement of cash flow. The purpose of the statement of cash flow and how it is used in accounting is explained. The direct and indirect method of preparing a statement is used. Steps in preparation and classification are explained. The ...
Figure 2-8. – A properly biased PNP transistor.
USES OF TRANSISTOR:
Amplification:.Amplifiers use transistors to amplify sound. Microphones, guitars, keyboards and electronic drums use the transistors to send out electronic sound.
Switching:Switches turn on and off with the use of transistors. Switches can be found on amplifiers, airplanes, automobiles, houses, lamps and radios.
Computers:Many tiny transistors work within a computer to calculate and transmit binary codes to other transistors. The transistors work as a group called an integrated circuit.
Hearing Aids:Tiny transistors help people with hearing loss hear. The tiny transistors amplify sound at an adjustable level to the hearing aid owner.
Radios:Transistors helped bring personal radios to many people in the 1960s and helped improve communication.
Space Exploration:The improvements and new uses for transistors helped the cause of space exploration. With its use in computers, communications and switches, the transistor made it possible to launch humankind to the moon, and set into the planet’s orbit large telescopes to help with the study of the universe.
REFRENCES:1.www.sjsu.edu/faculty
2.www.wikianswers.com
3.answers.yahoo.com
4. ehow.com
