The depletion layer which act as an insulator it reduces the effective cross section of the n-channel and therefore restricts the flow of electrons. The causes a depletion layer which becomes greater at the bias increases i.e the depletion layer is greater nearer to the drain. Also the p-n junction is reverse biased and this bias is greater nearer the drain than nearer the source. It follows that electrons nearer the drain also experience a higher voltage with respect to the gate, hence the voltage across the p-n junction is greater at the right hand end than at the left. The drain source current is still flowing and therefore the n-channel voltage becomes greater as electron flow from the source towards the drain. To bring the gate into action first connect it to the source. Being semiconductor material the voltage / current relationship is almost linear and the n-channel more or less behaves as a resistor. The application of the drain source voltage causes conventional current to flow from the drain to the source the current consists of electrons which are the majority carriers in the n-channel moving from the source to the drain. Since we are considering an n-channel JUGFET consider dc supply connected with the drain positive with respect to the source. The principal of the action of a JUGFET can be first explained by considering the operation of the source and drain while the gate left disconnected. The two end contacts are termed the source S and the drain D, while that to the tube or shroud is the gate G. Non rectifying contacts are connected to each end of the n-type piece and to the p-type tube. This consists of a piece of n-type silicon effectively within a tube of p-type silicon, the interface between the two materials being the same intimate junction as in the bipolar transistor junctions. The most common variety of JUGFET is the n-channel type. Like the bipolar junction transistor all FETs are three electrode devices the electrodes are the source, the gate and the drain which can be taken as corresponding to the emitter, base and collector respectively. The IGFET has two distinct modes of operation, one known as the depletion mode and the other as thee enhancement mode, again and again each mode subdivides into p-channel and n-channel. The JUGFET can be in two forms, p-channel and n-channel, depending on the type of semiconductor forming the basis of the transistor. Unlike the bipolar junction transistors which are all basically similar in spite of a variety of constructional forms the FET is more a collective term for a family of transistor devise of which there are two principal groups: So these are few differences between FETs and BJTs. FETs provides thermal stability and generates less noise and high frequency. The power consumption of the FETs are less than BJTs and that’s why they are preferred in many high power applications as well as in the computing applications particularly where the required power consumption should be minimum. For example they are used as amplifier or oscillator in many application and apart from that also used as analogue switch in many application but the biggest difference between the field effect transistor and the BJT is that the input impedance of the field effect transistor is very high and due to that they are used as a buffer amplifier in many applications. FETs does not contain minority carrier therefore they are suitable for switching application because there is no charge store problem. Now in terms of application FETs are used in almost all the applications where the BJTs are used. Field effect transistor is voltage control device.įET is unipolar device which consists of either free electron or holes. And that is why it is known as field effect transistor. So basically in this field effect transistor by controlling the electric field we can control the flow of the current. So the applied voltage generates the electric field within the device and by controlling this electric field or in a way by controlling the voltage we can control the flow of the current through the device. And this can be controlled by applying the voltage between the gate and the source terminal. So in FET the current used to flow between the drain and the source terminal also it is more temperature stable than BJTs and are smaller than BJTs therefore suitable for use in integrated circuits. The drain, gate and source are the three terminals of the FET. In fact today most of the integrated circuits including the computers are designed using the FETs. And it is very useful in many applications. The field effect transistor is three terminals and unipolar because it depends upon on either holes or electrons which use the electric field to control the flow of current through device. IGFET (Insulated gate field effect transistor):.
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