The gate is made up of P-type semiconductor material (holes are in majority).There are two reversed biased P-N junctions. In P-channel JFET the source terminal “S” is connected to the +Ve end of the drain voltage supply (for obtaining holes which flows through the channel). In N-channel JFET the source terminal “S” is connected to the -Ve end of the drain voltage supply (for obtaining electrons which flows through the channel).
The Source terminal is always connected to that end of the Drain voltage supply which provides the necessary charge Carriers that are majority charge carriers. So the gate current I G is practically zero I G = 0. Operation of JFET:įor the proper operation of JFET the gate is always reversed Biased. it is similar to the base of bi-polar junction T/r. It can change the conductivity of the channel. Gate: The two P-regions are internally connected and a single terminal is brought out which is called gate terminal, it is a control terminal, it produces electric field. This terminal is similar to collector of bi-polar junction T/r. Source resembles with emitter in bi-polar junction T/r.ĭrain: It is the terminal through which majority carriers leave the bar. Source: It is the terminal through which majority carriers enter into the bar towards drain, so it provides majority charge carriers (electrons for N-channel and holes for P-channel). It is a three terminal device namely source, drain, and gate. The arrow head is always at gate terminal “G” and for N-type channel arrow is into the gate and for P-type channel the arrow head is out of gate as shown in figure below. Now the structure and symbolic representation of N-channel JEFT is given as. The lower end of the bar having lead is called source terminal and is denoted by “S” upper end of bar having lead is called drain terminal and is denoted by “D”. direct electrical connections are made at the two ends of the bar. The gate bar is denoted by “G” this bar behaves like a resistance. The two P-regions are internally connected and a single lead is brought out, which is called gate terminal as shown in the figure given below. Channel is the conducting path b/w source and drain. The area b/w these gates is called channel. These junctions form two PN-junctions (diode) called gates. Two P-type junctions are diffused on opposite sides of the middle part of the bar shown in figure below. For fabricating N-channel JEFT, first of all, a bar of N-type semi-conductor (silicon) is taken as shown below.
Hence we can say that JFETs are of two types.īut we will prefer N-channel (for its higher speed of current). It is generally fabricated with either N-channel or P-channel. Junction field-effect T/r JFET: JFET Construction:
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