Bipolar Transistor

Fig:Bipolar transisitor

 Bipolar Transisitor:-
A bipolar transistor is a semiconductor device commonly used for amplification. The device can amplify analog or digital signals. It can also switch DC or function as an oscillator. Physically, a bipolar transistor amplifies current, but it can be connected in circuits designed to amplify voltage or power.

How Bipolar Transisitors work?

figure(2)

The way a transistor works can be described with reference to fig 2 which shows the basic doping of a junction transistor and Fig 4.2 the method of operation of the device.
The operation of the transistor is very dependent on the degree of doping of the various parts of the semiconductor crystal. The N type emitter is very heavily doped to provide many free electrons as majority charge carriers. The lightly doped P type base region is extremely thin, and the N type collector is very heavily doped to give it a low resistivity apart from a layer of less heavily doped material near to the base region. This change in the resistivity of the collector close to the base, ensures that a large potential is present within the collector material close to the base.

Importance of Bipolar Transisitor

1. The transistor is the key active component in practically all modern electronics.
2. Many consider it to be one of the greatest inventions of the 20th century. Its importance in today's society rests on its ability to be mass-produced using a highly automated process (semi-conductor device fabrication) that achieves astonishingly low per-transistor costs.
3. Although several companies each produce over a billion individually packaged (known as discrete ) transistors every year, the vast majority of transistors are now produced in integrated circuits (often shortened to IC, microchips or simply chips), along with diodes, resistors, capacitors and other electronic components, to produce complete electronic circuits
4. A logic gate consists of up to about twenty transistors whereas an advanced microprocessor, as of 2009, can use as many as 3 billion transistors (MOSFETs).
5. The transistor's low cost, flexibility, and reliability have made it a ubiquitous device. Transistorized mechatronic circuits have replaced electromechanical devices in controlling appliances and machinery.
6. It is often easier and cheaper to use a standard microcontroller and write a computer program to carry out a control function than to design an equivalent mechanical control function.

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