FET TRANSISTOR LECTURE IN HINDI SERIES

Idealized transfer characteristics of an n-channel JFET. Construction of n-channel JFET.įigure 4 shows the typical transfer characteristics of a low-power n-channel JFET, and illustrates some important features of this type of device.įIGURE 4. All JFETs operate in the depletion mode, as already described.įIGURE 3. JFET DETAILSįigure 3 shows the basic form of construction of a practical n-channel JFET a p-channel JFET can be made by transposing the p and n materials. Basic structure of a simple n-channel JFET, showing how channel width is controlled via the gate bias. A p-channel version of the device can (in principle) be made by simply transposing the p and n materials.įIGURE 2. It is thus known as a ‘depletion-type’ n-channel JFET. Thus, the basic JFET of Figure 2 passes maximum current when its gate bias is zero, and its current is reduced or ‘depleted’ when the gate bias is increased. As the gate bias is increased, the ‘depletion’ region spreads deeper into the n-type channel, until eventually, at some ‘pinch-off’ voltage value, the depletion layer becomes so deep that conduction ceases. When negative gate bias is applied, a high resistance region is formed within the junction, and reduces the width of the n-type conduction channel and thus reduces the magnitude of the drain-to-source current. With zero gate bias applied, a current flow from drain to source via a conductive ‘channel’ in the n-type bar is formed. In normal use, the drain terminal is connected to a positive supply and the gate is biased at a value that is negative (or equal) to the source voltage, thus reverse-biasing the JFET’s internal p-n junction, and accounting for its very high input impedance. A p-type control electrode or gate surrounds (and is joined to the surface of) the middle section of the n-type bar, thus forming a p-n junction. It consists of a bar of n-type semiconductor material with a drain terminal at one end and a source terminal at the other. Comparison of transistor and JFET symbols, notations, and supply polarities.įigure 2 illustrates the basic construction and operating principles of a simple n-channel JFET. Figure 1 shows the symbols and supply polarities of both types of bipolar transistor, and compares them with both JFET versions.įIGURE 1. ‘N-channel’ and ‘p-channel’ versions of both types of FET are available, just as normal transistors are available in npn and pnp versions. The first of these is known as ‘junction-gate’ types of FETs this term generally being abbreviated to either JUGFET or (more usually) JFET.The second family is known as either ‘insulated-gate’ FETs or Metal Oxide Semiconductor FETs, and these terms are generally abbreviated to IGFET or MOSFET, respectively. Two distinct families of FETs are in general use. Its terminals are known as the source, gate, and drain, and correspond respectively to the emitter, base, and collector of a normal transistor. FET BASICSĪn FET is a three-terminal amplifying device.

FET TRANSISTOR LECTURE IN HINDI SERIES

Parts 2 to 4 of the series will show practical ways of using FETs.

Several different basic types of FETs are available, and this opening episode looks at their basic operating principles.

» Skip to the Extras FET (Field-Effect Transistor) Basicsįield-Effect Transistors (FETs) are unipolar devices, and have two big advantages over bipolar transistors: one is that they have a near-infinite input resistance and thus offer near-infinite current and power gain the other is that their switching action is not marred by charge-storage problems, and they thus outperform most bipolars in terms of digital switching speeds.

Fet transistor lecture in hindi