Transistor

Fig : Assorted discrete transistors. Packages in order from top to bottom: TO-3, TO-126, TO-92, SOT-23

A transistor is a semiconductor device used to amplify and switch electronic signals and power. It is composed of a 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, a transistor can amplify a signal. Today, some transistors are packaged individually, but many more are found embedded in integrated circuits.

The transistor is the fundamental building block of modern electronic devices, and is ubiquitous in modern electronic systems. Following its release in the early 1950s the transistor revolutionized the field of electronics, and paved the way for smaller and cheaper radios, calculators, and computers, among other things.

Advantages :

The key advantages that have allowed transistors to replace their vacuum tube predecessors in most applications are

1. Small size and minimal weight, allowing the development of miniaturized electronic devices.
2. Highly automated manufacturing processes, resulting in low per-unit cost.
3. Lower possible operating voltages, making transistors suitable for small, battery-powered applications.
4. No warm-up period for cathode heaters required after power application.
5. Lower power dissipation and generally greater energy efficiency.
6. Higher reliability and greater physical ruggedness.
7. Extremely long life. Some transistorized devices have been in service for more than 50 years.
8. Complementary devices available, facilitating the design of complementary-symmetry circuits, something not possible with vacuum tubes.
9. Insensitivity to mechanical shock and vibration, thus avoiding the problem of microphonics in audio applications.