the n-channel JFET has a significant portion made of n-type semiconductors. The mutually-opposite two faces of this bulk material are from the source and the drain terminals. Further, it is also seen that there are two relatively-small p-regions embedded into this substrate which are internally joined together to form the gate terminal. Thus, here, the source and drain terminals are n-type while the gate is p-type. Due to this, two pn junctions will be formed within the device, whose analysis reveals the mode in which the JFET works.
Working of N-Channel JFET
In n-channel JFET, the majority of charge carriers will be the electrons as the channel formed in-between the source and the drain is of n-type. Further, the working of these devices depends upon the voltages applied at their terminals
Case I: Consider the case where no voltage is applied to the device i.e. VDS = 0 and VGS = 0. At this state, the device will be idle and no current flows through it i.e. IDS = 0.
Case II: Now consider that the drain terminal of the device is connected to the positive terminal of the battery while its negative is connected to the source i.e. VDS = +ve. However let the gate terminal remain at an unbiased state, which means VGS = 0. At this instant, the electrons within the n-substrate of the device start moving toward the drain being attracted by the positive force exerted by the battery. At the same time, the electron will also be repelled from the source as it is connected to the negative terminal of the voltage supply.
Construction of N-channel JFET
The construction of a junction field effect transistor (JFET) is shown in the above figure. The junction field effect transistor (JFET) in which the electrons as majority charge carriers due to this only current conduction takes place is known as N-channel JFET. The N-channel JFET consists N-type semiconductor that is a silicon bar with two P-type heavily doped regions distributed on opposite sides of its middle part. The two PN junctions are formed by P-type regions, and the space between the N-type regions is known as a channel. A single wire is taken out in the form of a terminal when both the P-type regions are connected internally is known as the gate (G). The electrical connection which is also known as ohmic contact is made to both ends of an N-type semiconductor and are taken in the form of two terminal called source (S) and drain (D).
Application
- Analog Switches
- Choppers
- Current Limiters