Transistor is a Semiconductor device with three terminals viz., Emitter (E), Base (B) and Collector (C) and thus has two junctions viz., Base-Emitter (BE) junction and Base-Collector (BC) junction used to amplify or switch electronic signals and electrical power. It was invented in 1947 by American physicists John Bardeen, Walter Brattain, and William Shockley at Bell Laboratory. It is one of the greatest inventions of the 20th century.
Types Of Transistor :
Acronyms :
- BJT - Bipolar Junction Transistor.
- FET - Field Effect Transistor.
- NPN - Negative, Positive, Negative.
- PNP - Positive, Negative, Positive.
- JFET - Junction gate Field Effect Transistor.
- MOSFET - Metal Oxide Semiconductor Field Effect Transistor.
Transistor acts as
- A Switch
- An Amplifier
Transistor as a switch :
Transistors are commonly used in digital circuits as electronic switches which can be either in an "on" or "off" state. A switch provides infinite resistance during its OFF condition and provides zero resistance during its ON condition. Hence a switch can be imagined as an ON-OFF controlled resistor, which provides either zero or infinite resistance to the circuit without any intermediate value.
A small “control current” can control big portion of a “main current” that is going to flow through it. Thereby, the transistor can amplify a signal.
FET : It is a voltage control device and it is a uni polar(depends either on electrons or holes).
J-FET :
MOSFET :
Transistor as an amplifier :
A small “control current” can control big portion of a “main current” that is going to flow through it. Thereby, the transistor can amplify a signal.
P-N-P Transistor :
In PNP Transistors, majority charge carriers are holes. It turns ON, when there is no current at the base of the transistor. The current flows from the emitter (E) to the collector (C).Thus, knowing this, a PNP transistor turns ON by a low signal.
N-P-N Transistor :
In NPN Transistors, electrons are the majority charge carriers. It turns on when the current flows through the base of the transistor. The current flows from the collector (C) to the emitter (E). It turns ON by a high signal (current).
Base : Very thin, lightly doped.
Emitter : Moderate size, heavily doped.
Collector : Large size, moderate doping.
FET : It is a voltage control device and it is a uni polar(depends either on electrons or holes).
Moore's Law :
Moore’s Law is an observation made by Gordon Moore stating that number of transistors per square inch on integrated circuits doubles approximately every two years.