Electronic Circuits and Diagram-Electronics Projects and Design

Power MOSFETs are usually constructed in V-configuration, as shown in figure. That is why, the device is sometimes called the V-MOSFET or V-FET. V-shaped cut penetrates from the device surface almost to the N+ substrate through N+, P and N~ layers, as seen from figure. The N+ layers are heavily doped, low resistive material, while the N~ layer is a lightly doped, high-resistance region. The silicon dioxide dielectric layer covers both the horizontal surface and V-cut surface. The insulated gate is metal film deposited on the Si02 in the V-cut. Source terminals make contact to the upper N+ and P-layers…

Cross-view of a dual-gate N-channel depletion type MOSFET is shown in figure. It acts as if two FETs are connected in series, as is obvious from figure. The middle block acts as drain for unit no 1 and source for unit no 2. Thus the current flow through the MOSFET is controlled by the voltage of both the gates. Drain current ID can be cut­off by making either gate sufficiently negative.

Although DE-MOSFET is useful in special applications, it does not enjoy widespread use. However, it played an important role in history because it was part of the evolution towards the E-mode MOSFET, a device that has revolutionized the electronic industry. E-MOSFET has become enormously important, in digital electronics and. In the absence of E-MOSFET’s the personal computers (PCs) that are now so widespread would not exist. Construction of an EMOSFET: Figure shows the construction of an N-channel E-MOSFET. The main difference between the construction of DE-MOSFET and that of E-MOSFET, as we see from the figures given below the E-MOSFET…

We know that when the gate is biased negative with respect to the source in an N-channel JFET, the depletion region widths are increased. Theincrease in the depletion regions reduces the channel thickness, which increases its resistance. The net result is that drain current ID is reduced. If the polarity of VGG were reversed so as to apply a positive bias to the gate with respect to source, the P-N junctions between the gate and the channel would then be forward biased. Since a forward bias reduces the width of a depletion region, the thickness of channel would increase with…

Introduction to MOSFET-Metal Oxide Semiconductor Field Effect Transistor, Metal-oxide-semiconductor field-effect transistor (MOSFET) is an important semiconductor device and is widely employed in many circuit applications. Since it is constructed with the gate terminal insulated from the channel, it is sometimes called insulated gate FET (IGFET). Like, a JFET, a MOSFET is also a three terminal (source, gate and drain) device and drain current in it is also controlled by gate bias. The operation of MOSFET is similar to that of JFET. It can be employed in any of the circuits covered for the JFET and, therefore, all the equations apply…

Unlike BJTs, thermal runaway does not occur with FETs, as already discussed in our blog. However, the wide differences in maximum and minimum transfer characteristics make ID levels unpredictable with simple fixed-gate bias voltage. To obtain reasonable limits on quiescent drain currents ID and drain-source voltage VDS, source resistor and potential divider bias techniques must be used. With few exceptions, MOSFET bias circuits are similar to those used for JFETs. Various FET biasing circuits are discussed below: Fixed Bias. DC bias of a FET device needs setting of gate-source voltage VGS to give desired drain current ID . For a…

From the circuit named “looking into the drain” of the FET it is seen (for small signal operation) an equivalent circuit consisting of two generators in series, one of – u times the gate signal voltage Vin and the second (u + 1) times the source-signal voltage Vs and the resistance rd + ((a + 1) RG. Note that the source-signal voltage Vs and the resistance in the source lead are both multiplied by the same factor, (u + 1).

CHARACTERISTICS OF JFETS There are two types of static characteristics viz (1) Output or drain characteristic and (2) Transfer characteristic. 1. Output or Drain Characteristic. The curve drawn between drain current Ip and drain-source voltage VDS with gate-to source voltage VGS as the parameter is called the drain or output characteristic. This characteristic is analogous to collector characteristic of a BJT: (a) Drain Characteristic With Shorted-Gate. The circuit diagram for determining the drain characteristic with shorted-gate for an N-channel JFET is given in figure. and the drain characteristic with shorted-gate is shown in another figure. Initially when drain-source voltage Vns is zero,…

As already mentioned, JFETs are of two types viz N-channel JFETs and P-channel JFETs.Generally N-channel JFETs are preferred. N-channel and P-channel JFETs are shown in figures.   Basic Construction. Its structure is quite simple. In an N-channel JFET an N-type silicon bar, referred to as the channel, has two smaller pieces of P-type silicon material diffused on the opposite sides of its middle part, forming P-N junctions, as illustrated in fig. The two P-N junctions forming diodes or gates are connected internally and a common terminal, called the gate terminal, is brought out. Ohmic contacts (direct electrical connections) are made at…

INTRODUCTION to FET-Field Effect Transistor So far we have discussed the circuit applications of ordinary transistors, in which both holes and electrons take part. This is the reason that these are sometimes called the bipolar transistors. Such transistors have two main drawbacks namely low input impedance because of forward biased emitter junction and considerable noise level. Both of these drawbacks have been overcome, to a great extent in the field effect transistor (FET), which is an electric field (or voltage) controlled device. FET’s because of possessing all the advantages that tubes and ordinary transistors (BJTs) have, are replacing both the…