The major difference between BJT and FET is that in a field-effect transistor only majority charge carries flows, whereas in BJT both majority and minority charge carriers flow….
The main basic function of a BJT is to amplify current it will allow BJTs are used as amplifiers or switches to produce wide applicability in electronic equipment include mobile phones, industrial control, television, and radio transmitters.
A FET is a three terminal device, having the characteristics of high input impedance and less noise, the Gate to Source junction of the FET is always reverse biased. In amplifier application, the FET is always used in the region beyond the pinch-off. Obviously dual gate FETs have two gates and both need to be incorporated into the circuit symbol. Which of the following is not a valid type of a BJT? The mosfets are voltage controlled and have virtually no gate current, the gate acts as a low value capacitor a few picofarads to several nanofarads.
This can be of considerable advantage in switching and high current applications because the power bjts have a medium to low gain, which requires high base currents sometimes of the order of several amperes! To generate high currents. When a transistor is used to amplify a signal, the internal processes of the transistor will introduce some of this random interference.
Due to this reason, a bipolar junction transistor is used as a switch as well. The PNP junction also works with the same principle, but the base terminal is made with an N-type material and the majority of charge carriers in the PNP transistor are holes.
These regions are discussed below. It is comparatively insensitive toward VCE. In this region, it works as an amplifier. The transistor is ON in the saturation region, so the collector current changes extremely less through a change within the base current. In the PNP transistor, in between two p-type semiconductor layers, only the n-type semiconductor layer is sandwiched.
In an NPN transistor, in between two N-type semiconductor layers, only the p-type semiconductor layer is sandwiched. FET consists of three terminals namely source, drain, and gate terminals. The charge carriers of this transistor are holes or electrons, which flow from the source terminal to the drain terminal via an active channel.
This flow of charge carriers can be controlled by the voltage applied across the source and gate terminals. These two transistors have similar principles. The construction of p-channel JFET is shown below. In p-channel JFET , the majority of charge carriers flow from the source to drain.
Source and drain terminals are denoted by S and D. The gate terminal is connected in reverse bias mode to a voltage source so that a depletion layer can be formed across the regions of the gate and the channel where charges flow. Whenever the reverse voltage on the gate terminal is increased, the depletion layer increases.
So it can stop the flow of current from the source terminal to the drain terminal. So, by changing the voltage at the gate terminal, the flow of current from the source terminal to the drain terminal could be controlled. The transistor will be turned OFF in the cut-off region. So there is no conduction among the source as well as the drain when the voltage of gate-source is higher as compared with cut-off voltage. In the integrated circuit form FET is simpler to fabricate and it occupies less — space.
The high input impedance and low output impedance and low noise level make FET for superior of the bipolar transistor. Some of the circuit applications of FET are.
As a buffer amplifier: Because of high input impedance and low output impedance, a FET can act as an excellent buffer amplifier.
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