How can a jfet be used as a constant current source, Electrical Engineering

Assignment Help:

Q. How can a JFET be used as a constant current source? Explain from the drain characteristics.

As the VDS voltage is increased from 0 to a few volts, the current will increase as determined by ohm's law and the plot of ID versus VDS will appear as shown below.

2258_How can a JFET be used as a constant current source.png


The relative straightness of the graph reveals that for the region of low voltage level referred to as  VP. The depletion region will widen, causing a noticeable reduction in the channel width. The reduced path of conduction causes the resistance to increase and the curve in the graph to occur. The more horizontal the curve the more the resistance, suggesting that the resistance is approaching infinite ohms. If VDS is increased to a level where it appears that the two depletion regions will touch. A condition known as pinch off will result. The level of VDS that establishes this condition is referred to as pinch off voltage. The term pinch off is a misnomer which actually means that the value of ID has become 0 A. this is hardly the case as the ID still maintains a saturation level defined as IDSS. In reality a very narrow channel still exists, with a current of very high density. The fact that ID does not drop off to 0 at pinch-off and maintains a saturation level is verified by the fact : the absence of the drain current would remove the possibility of different potential levels through out the n channel material to establish the varying levels of reverse bias along the p-n junction. The result would be a loss of depletion region distribution that caused pinch off in the first place.

The fact about the constant current IDSS can be used to make a JFET a constant current source as its current value remain constant. The JFET is thus a very versatile device and can be used  as a current source with much stabler characteristics than a zener diode current regulator.


Related Discussions:- How can a jfet be used as a constant current source

Example of high resistivity material, Example of high resistivity material ...

Example of high resistivity material is (A) Nichrome              (B) Silver (C) Gold                      (D) Copper Ans: Nichrome is example of high resistivity

Define resistance in lumped-circuit, Q. Define Resistance in lumped-circuit...

Q. Define Resistance in lumped-circuit? An ideal resistor is a circuit element with the property that the current through it is linearly proportional to the potential differenc

What do you mean by conductors and insulators, Q. What do you mean by Condu...

Q. What do you mean by Conductors and Insulators? In order to put charge in motion so that it becomes an electric current, one must provide a path through which it can flow eas

Wye -delta conversion, how to write theory background on practical about t...

how to write theory background on practical about this topic.

Find the percent of probable error, Q. A voltmeter with a full scale of 100...

Q. A voltmeter with a full scale of 100 V has a probable error of 0.1% of full scale. When this meter is employed to measure 100 V, find the percent of probable error that can exis

Machine, function of a commutator in a DC motor

function of a commutator in a DC motor

Show basic construction of mosfet, Q. Show Basic Construction of MOSFET? ...

Q. Show Basic Construction of MOSFET? The basic construction of the n-channel depletion-type MOSFET is provided in Figure. A slab of p-type material is formed from a silicon

Auto transformer, winding turns of 415v step down transformer on 50%, 60% &...

winding turns of 415v step down transformer on 50%, 60% & 80% tapping

Find the directive gain, Q. Aconical horn has a side viewas shown in Figure...

Q. Aconical horn has a side viewas shown in Figure  The maximum value ofthe directive gain is given by GD ∼ = 5.13(D/λ) 2 , where D =√3.33λL1 and L1 = L/(1-d/D),in which d is the i

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd