Bipolar Junction Transistors (BJTs) and Field Effect Transistors (FETs)

 

Bipolar Junction Transistors (BJT) and Field Effect Transistor (FET) are known as active semiconductors. They are using based on their characteristics they are operating frequency, current, voltage and power ratings. Commonly these both types of transistors have three terminals.

What is BJT?

BJT is made with majority and minority charge carriers. BJT devices are available in two types such as PNP and NPN. It can use as conductor or insulator based on the applied input signal due to its properties. BJT have three terminals, heavily dropped emitter, lightly dropped base and moderately dropped collector. BJT have Active, cut-off and saturation regions and also it have three configuration types, these are Common Emitter, Common Base and common Collector. Depending on requirement and the application BJT can be configuring any of these configurations. This transistor can use in Digital electronic circuits as switch or it can use as amplifier in analog electronics. It is use as amplifier at active region and it is use as switch at cut-off and saturation regions. When talk about characteristic of BJT It has high efficiency, instant operation and it is robust and cheap transistor. BJT is applied on as a detector or demodulator, in wave shaping and clipping circuits, time delay circuits and used as an oscillator.

 

What is FET?

This Transistor is also three terminal unipolar semiconductors device which uses the electric field to control the flow off current. Three terminals of FET is known as Gate, Drain, Source. In FET Current flow from Drain to Source terminal. This current can be control by applying voltage between the gate and source terminals. So this applied voltage generates the electric field. There is a two type of FETs. Those are JFET and MOSFET. FET also having three operation models. Those are Common source configuration, Common gate configuration and Common drain configuration. FET has four types of regions, (Ohmic Region, Cut-off or inch-off Region, Saturation Region and Breakdown Region.) When we talk about characteristic of FETs it has High efficiency, and specially it has very high impedance, les noise and its gate to source junction is always reversed biased. FETs are widely used as input amplifiers in oscilloscopes, electronic voltmeters and other measuring and testing equipment. And also field effect transistors are used in chopper and Current Limiter circuits.