Transistor

The Transistor is used as a amplifying element which is used to amplify the given signal. The amplifier is the semiconductor device and which contain 3 terminals for connection to external circuits. Materials most commonly used are silicon, gallium-arsenide, and germanium, into which impurities have been introduced by a process called “doping.” 

 The Transistor is the fundamental block of the electronic devices and most of the electronic systems. A transistor may be used as a switch and as an amplifier .The amount of current amplification is called the current gain, symbol h_FE. 

Types of transistor:

There are three main classifications of transistors each with its own symbols, characteristics, design parameters,

and applications. See below and the following pages for additional details and applications on each of these

transistor types. Several special-function transistor types also exist which do not fall into the categories below,

such as the unijunction (UJT) transistor that is used for SCR firing and time delay applications. These specialfunction

devices are described separately.

1. Bipolar transistors are considered current driven devices and have a relatively low input impedance. They

are available as NPN or PNP types. The designation describes the polarity of the semiconductor material

used to fabricate the transistor.

2. Field Effect Transistors, FET’s, are referred to as voltage driven devices which have a high input impedance.

Field Effect Transistors are further subdivided into two classifications: 1) Junction Field Effect Transistors,

or JFET’s, and 2) Metal Oxide Semiconductor Field Effect Transistors or MOSFET’s.

3. Insulated Gate Bipolar Transistors, known as IGBT’s, are the most recent transistor development. This hybrid device combines characteristics of both the Bipolar Transistor with the capacitive coupled, high impedance

input, of the MOS device

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