Field effect transistor free#
Majority carriers only contribute the current through the channel in the device, i.e., free electrons in n channel and holes in p channel and these are the reason why a transistor is called unipolar device.The current through the collector-emitter circuit of a BJT is controlled by the amount of current in the base-emitter circuit.Ideally, there will be no gate current in JFET.As in normal operating condition, the junction between input gate region and channel remains to reverse biased, the input impedance of the transistor is high.In other words, the electric field across the junction effects the operation of the transistor and that is why it is named as junction field effect transistor.
This is a voltage control device since the current through the channel gets controlled by gate voltage.A JFET can be used as a switch, as an amplifier etc. Depending on that typical property of the JFET we can use this JFET for many different electronic applications. Hence we can conclude that by controlling gate voltage we can control the drain current. If by changing the gate terminal voltage, the width of the depletion layer increases, it is extended into the channel and reduces the opening of the channel and therefore the current through the channel gets decreased. The opening of the channel depends on the width of the depletion layer. The width of the depletion layer of this PN junction can be varied by varying gate terminal voltage. The gate voltage is kept such in a JFET that the PN junction between the gate region and the channel is in reverse biased condition. In normal operating condition the drain terminal of n channel JFET is applied with positive potential and the drain terminal of a p channel JFET is applied with negative potential. The majority carriers enter into the channel through the terminal is referred as to source terminal and the terminal through which the majority carriers leave the channel is referred as to drain terminal. The current flowing through the channel due to drift of majority carriers. The space between two oppositely doped regions is referred to as channel of the device. If a voltage is applied between drain and source terminal, a current starts flowing through the device. NB:- Here in both types of junction field effect transistor both drain and source terminal can be interchangeable. The terminal attached to the side n-type region is the gate terminal. Here also the drain, and the source terminal are connected to two ends of the bar. The sides of the bar are highly doped with n-type impurities. Similarly, a p channel JFET is made of Si or GaAs bar doped with p-type impurities. A metallic terminal is connected to the gate region, and the terminal is called the gate terminal. The region which doped with p-type impurities is called gate region. Two sides of the bar are highly doped with p-type impurities. One of the terminals is called drain terminal, and the other is called the source terminal. One metallic terminal is attached to each of both ends of the bar. An n channel JFET is made of Si or GaAs bar.
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