Electrical engineering

1. Electrical engineering Transistors By Daniel roach DAVAUGHN jACKSON

2. Electrical Engineering Definition • Electrical engineering is a field of engineering that generally deals with the study and application of electricity, electronics and electromagnetism. The field first became an identifiable occupation in the late nineteenth century after commercialization of the electric telegraph and electrical power supply

3. History of Transistors • Prior to the development of transistors, vacuum tubes were the main active components in electronic equipment • The scientists that were responsible for the 1947 invention of the transistor were: John Bardeen, Walter Brattain, and William Shockley. • Their original patent name for the transistor was: “Semiconductor amplifier; Three-electrode circuit element utilizing semiconductive materials.” • They observed that when two gold point contacts were applied to a crystal of germanium, a signal was produced with the output power greater than the input.

4. How transistors works • http://www.youtube.com/watch?v=ZaBLiciesOU • Explains how a NPN or PNP bipolar transistor works.

5. Transistor as a Switch • In a grounded-emitter transistor circuit, as the base voltage rises, the base and collector current rise exponentially. The collector voltage drops because of the collector load resistance. If the collector voltage was zero, the collector current would be limited only by the load resistance and the supply voltage. The transistor is then said to be saturated - it will have a very small voltage from collector to emitter. The transistor provides current gain, allowing a relatively large current in the collector to be switched by a much smaller current into the base terminal. The ratio of these currents varies depending on the type of transistor, and even for a particular type, varies depending on the collector current. The resistor is chosen to provide enough base current to ensure the transistor will be saturated.

6. Transistor as an amplifier • The common emitter amplifier is designed so that a small change in voltage in (Vin) changes the small current through the base of the transistor; the transistor's current amplification combined with the properties of the circuit mean that small swings in Vin produce large changes in Vout. • Various configurations of single transistor amplifier are possible, with some providing current gain, some voltage gain, and some both.

7. Importance of Transistors • The transistor is the key active component in practically all modern electronics. Many consider it to be one of the greatest inventions of the 20th century • The transistor's low cost, flexibility, and reliability have made it a great device. • Lower possible operating voltages, making transistors suitable for small, battery-powered applications • Allowed for the development of small radios, computers, and various other everyday appliances.