![]() The drain current in the pinch-off region with V GS = 0 is referred to the drain-source saturation current, Idss). It is the normal operating region of the JFET when used as an amplifier. In this region the JFET operates as a constant current device since drain current (or output current) remains almost constant. It is also sometimes called the saturation region or amplifier region. ![]() The region of the characteristic in which drain current I D remains fairly constant is called the pinch-off region. From point A (knee point) to the point B (pinch-off point) the drain current I D increases with the increase In voltage V ds following a reverse square law. The pinch-off voltage Vp, not too sharply defined on the curve, where the drain current I D begins to level off and attains a constant value. all the free charges from the channel get removed), is called the pinch-off voltage V p. The value of voltage V DS at which the channel is pinched off (i.e. It approaches a constant saturation value. The drain current I D no longer increases with the increase in Vds. Eventually, a voltage Vds is reached at which the channel is pinched off. The reverse-biasing of the gate junction is not uniform throughout., The reverse bias is more at the drain end than that at the source end of the channel, so with the increase in Vds, the conducting portion of the channel begins to constrict more at the drain end. With the increase in drain current I D, the ohmic voltage drop between the source and channel region reverse-biases the gate junction. This region, (to the left of the knee point) of the curve is called the channel ohmic region, because in this region the FET behaves like an ordinary resistor. For small applied voltage V na, the N-type bar acts as a simple semiconductor resistor, and the drain current increases linearly with_the increase in Vds, up to the knee point. Initially when drain-source voltage V ns is zero, there is no attracting potential at the drain, so no current flows inspite of the fact that the channel is fully open. and the drain characteristic with shorted-gate is shown in another figure. The circuit diagram for determining the drain characteristic with shorted-gate for an N-channel JFET is given in figure. This characteristic is analogous to collector characteristic of a BJT: (a) Drain Characteristic With Shorted-Gate The curve drawn between drain current I p and drain-source voltage V DS with gate-to source voltage V GS as the parameter is called the drain or output characteristic. ![]() You may also like to read : Field Effect Transistors (FET) and JFET-Junction Field Effect Transistors 1. There are two types of static characteristics viz ![]() N-type JFET is more commonly used because they are more efficient due to the fact that electrons have high mobility. Similarly, the P-type material is doped with acceptor impurities so the current flowing through them is positive. The N-type material is made by doping Silicon with donor impurities so that the current flowing through it is negative. Instead of PN junctions, a JFET uses an N-type or P-type semiconductor material between the collector and emitter (Source & Drain). It is unipolar but has similar characteristics as of its Bipolar cousins. What is a Junction Field Effect Transistor?Ī JFET is a semiconductor with 3 terminals, available either in N-channel or P-channel types.
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