Transistor

Transistor
Classification of Transistor

Transistor



Semiconductor devices that have-three or more elements are called Transistors. The term transistor was derived from the words transfer and resistor. This term was adopted because it best describes the operation of the transistor - the transfer of an input signal current from a low-resistance circuit to a high-resistance circuit. Basically, the transistor is a solid-state device that amplifies by controlling the flow of current carriers through its semiconductor materials.

The transistor is a three terminal device which are as follow:

Emitter: The one side section which supplies charge carriers(electron or holes) is known as the emitter. The emitter is always kept in forward-bias with respect to base because it may provide a large number of majority carriers.

Collector: The other side section of the transistor which collects the charges, is known as the collector. Collector is always kept in reverse bias. It removes charges from its junction with the base.

Base: The middle section of the transistor which makes two p-n junction between the emitter and collector,is known as the base. The base-emitter junctions is kept at forward bias to provide low resistance for the emitter circuit. The base-collector junction is kept at reverse bias to provide high resistance in the collector circuit.

















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Classification of Transistor























Bipolar Transistors

A bipolar (junction) transistor (BJT) is a three-terminal electronic device constructed of doped semiconductor material and may be used in amplifying or switching applications. Bipolar transistors are so named because their operation involves both electrons and holes. Charge flow in a BJT is due to bidirectional diffusion of charge carriers across a junction between two regions of different charge concentrations. This mode of operation is contrasted with unipolar transistors, such as field-effect transistors, in which only one carrier type is involved in charge flow due to drift. By design, most of the BJT collector current is due to the flow of charges injected from a high-concentration emitter into the base where they are minority carriers that diffuse toward the collector, and so BJTs are classified as minority-carrier devices.

Bipolar Transistors have  two types--

1) N-P-N Transistors

2) P-N-P Transistors  


Field-Effect Transistors

The Field Effect Transistor is a unipolar device that has very similar properties to those of the Bipolar Transistor ie, high efficiency, instant operation, robust and cheap, and they can be used in most circuit applications that use the equivalent Bipolar Junction Transistors, (BJT). They can be made much smaller than an equivalent BJT transistor and along with their low power consumption and dissipation make them ideal for use in integrated circuits such as the CMOS range of chips.






















All FETs have a gate, drain, and source terminal that correspond roughly to the base, collector, and emitter of BJTs.




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