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Why the n-jfet is operated with the negative voltage not the positive voltage?
In a JFET the only insulation between the gate and the channel is a reverse biased diode junction, if this junction becomes forward biased then the gate and channel are effectively shorted and the device no longer acts as a transistor (it will act as a forward biased diode instead). In the n-channel JFET, the gate is the P-side of this diode and the channel is the N-side of this diode. To keep this diode reverse biased (and the device operating as a transistor) therefor the gate MUST always be maintained at a voltage more negative than the most negative section of the channel.
How do you calculate the current gain of a transistor JFET?
FETs don't have current gain as no current flows through the gate. The gain of a FET is a voltage gain and is called mu.
What is the difference between jfet and mosfet?
1-BJT is bipolar while JFET is unipolar. 2-BJT has low input impedence while JFET has high input impedence. 3-JFET has low power discipation as compared to BJT. 4-JFET has low noise as compared to BJT. 5-BJT is current controlled while JFET is voltage controlled. 6-JFET is mostly used in digital circuits.
Difference between jfet and mosfet?
hi Main differences are, Bipolar Junction Transistor: switching speed is low;switching loss is more; conduction loss is less; frequency of switching is less we can use as amplifier;Current control; conduction due to electron & holes Junction field Effect Transistor: it an unipolar; switching speed is high;so loss is less voltage control; Metal oxide semiconductor fet: it nothiug bt fet, most of time v used for switching device in Smps do to power range A BJT is a bipolar transistor in the sense that there are two types of charge carriers in them. In npn trnsistor the primary carrier in the hole and in pnp the electron. In JFET there is only one type of carrier. In n-channel case the carrier is elctron and in p-channel hole. So JFET is unipolar in that sense. BJT is a current controlled device as the input current is amplified subjected to the mode of operation. For example in CE mode the input current is base current and output current is emmiter current which is (β+1) times amplified. The drop of this current across the load voltage is the output signal voltage. But a JFET is a voltage controlled device. The chalnnel conductance is determned by the voltage supplied at the gate terminal and depending on this the drain current flows. MOSFET is one kind of voltage controlled device like JFET where there is metal oxide in between the gate and the channel. Depending on the voltage supplied on the gate terminal a voltahe is 'induced' by electrostatic induction in the isolated channel. The channel therefore behaves as a capacitor where due to the voltage some charges are induced. These charges shrink or extend the effective chanel width. For example in Enhancement Mosfet the channel width effectively increases and in depletion mosfet it decreases. Depending on this the drain to source current increases or decreasesA BJT is a bipolar transistor in the sense that there are two types of charge carriers in them. In npn trnsistor the primary carrier in the hole and in pnp the electron. In JFET there is only one type of carrier. In n-channel case the carrier is elctron and in p-channel hole. So JFET is unipolar in that sense.
What are the differences betweeen e-mosfet and d-mosfet?
An e-mosfet is and "enhancement" mosfet. A d-mosfet is a "depletion" mosfet. These essentially show what mode the mosfet operates in when a voltage is applied to the gate. . An enhancement mode mosfet is normally non-conducting but conducts when the channel is enhanced by applying a voltage to the gate and pulling carriers into the channel. A depletion mode mosfet normally conducts but becomes more and more non-conducting as carriers are depleted or pulled out of the channel by applying a voltage. The polarity of the voltage depends on whether it is an N channel or P channel. P channel uses positively doped silicon while N channel uses negatively doped silicon. N channel fets are used wherever possible because N material conducts better than P material. There are basically two types of fet, the jfet and the mosfet. The jfet uses a single junction to control the channel hence draws some current. Bipolar transistors use two junctions. In the mosfet (Metal Oxide Semiconducting Field Effect Transistor) there is no such junction hence draw so little current for control purposes it can be regarded as zero. The gate is isolated from the channel by a very thin layer of metal oxide (usually chromium dioxide). An enhacement mode mosfet can be turned on by applying a voltage then removing the wire to the gate. The channel will then remain conducting for some time.
What is cut off voltage of jfet if its pinch off voltage is 5v?
5v
How jfet works?
A Jfet works by applying voltage to the drain of the jfet. A jfet will then conduct across from drain to source.
What are the applications of jfet?
• High Input Impedance Amplifier. • Low-Noise Amplifier. • Differential Amplifier. • Constant Current Source. • Analog Switch or Gate. • Voltage Controlled Resistor. • JFET as a Switch • JFET as a Chopper • JFET as a Current source • JFET as a Amplifier • JFET as a Buffer
The voltage of a given common source JFET amplifier is depend on what?
amplification factor
Does the channel width of the JFET remains constant at any point of time?
It depends on the topology of the circuit in which the JFET is operating.
Why Thermal runaway not a problem in jfet?
caz they have a positive temperature coefficient
2 What is Pinch-off voltage of JFET?
To find out the qualitative response to changes in Vgs and Vds, consider Vgs =0. In response to a small applied voltage Vds, a n-channel JFET acts as a simple semiconductor resistor and Id increases linearly with Vds. With increasing current, the ohmic voltage drop between the source and the channel region reverse biases the junction and the conducting portion of the channel begins to constrict. because of the ohmic drop along the length of the channel itself, the constriction is not uniform but is more pronounced at distances father from the source. Eventually, a Vds is reached at which the channel is "pinched off". At this voltage, Id begins to level off. and approach a constant value. It is not possible for the channel to close completely and reduce Id to zero. If that were the case, then the ohmic drop required to provide the back biasing would be lacking.Id is not equal to zero at Pinch off voltage.Thus, pinch off voltage can be defined as the gate reverse voltage that removes all the free charge from the channel.
What are current controllable devices?
BJT is a example for current controll device. And JFET is a voltage controlled device.
What is JFET and VVR?
JFET as a VVR-Voltage Variable ResistorFET is a device that is usually operated in the constant-current portion of its output characteristics. But if it is operated on the region prior to pinch-off (that iswhere VDS is small, say below 100 mV[ohmic region of JFET]), it will behave as a voltage-variable resistor (WE). It is due to the fact that in this region drain-to-source resistance RDS can be controlled by varying the bias voltage VGS. In such applications the FET is also referred to as a voltage-variable resistor or volatage dependent resistor. It finds applications in many areas where this property is useful.Figure shows the drain characteristic curves for a 2N 5951 in the ohmic region (i.e. for low VDS). From the characteristic curve it can be seen that RDS varies with VGS. For example, when VGS = 0, RDS = 133 ohm and when VGS = - 2 V, RDS = 250 ohm. Because of this a JFET operating in the ohmic region with small ac signals acts as a voltage-controlled resistance.Note that the drain curves shown in figure,extend on both sides of the origin. This means that a JFET can be employed as a voltage-variable resistorfor small ac signals, typically those less than 100 mV. When it is employed in this way, it does not require a dc drain voltage from the supply. All that is required is an ac input signal.
What type of transistor is a JFET?
JFET is a unijunction transistor.
What are the advantages and disadvantages of JFET over BJT?
An advantage of JFET is stable high current operation. A disadvantage of JFET is low capacitance. An advantage of BJT is constant voltage operation. A disadvantage of BJT is low thermal conductance.
What is bjt and jfet?
BJT is Bipolar junction transistor FET is Field effect Transistor It is a current controlled device It is voltage controlled device
