The Engineering Projects

Junction Field Effect Transistor (JFET) Simulation in Proteus ISIS

Hello Learners, hope you are doing well. I am here with a new tutorial. We'll discuss about Junction Field Effect transistors. In this tutorial, we will learn the basic Introduction to JFET nad will also have a look at its practical Implementation and simulation in Proteus. Basically, Junction Field Effect is a type of transistor, similar to Bipolar Junction Transistors but they have different characteristics due to some reasons as discussed below:

Introduction to JFET

We Define the JFET as:

"Junction Field Effect transistors or simply JFET is the semiconductor ,Voltage Control, three terminal device that is present in both configurations either N channel or P channel."

JFET  are named so because the the operation of JFET relies on the Field of the input gate voltage thus they are voltage operated devices. The Input of JFET is called Gate whereas, the output is said to be Drain.

Explanation about JFET

Junction Field Effect Transistors are important Devices in the world of electronics. They look similar to the transistors but are different in their Production.

Terminals of JFET:

JFET's have two Ohmic connections at either side of the channels. These channels are called Source and Drain. the Connection of Drain and source is said to be Gate. This is the point where PN Junction is formed. Source and Drain Collectively makes resistive path through which the current Id passes due to the Voltage Vds. The channel is semiconductor due to which current is passed equally well at both sides. But, because of the resistivity of the channel, the voltage becomes less Positive when we move from Drain to Source. Subsequently, the PN junction contains the high reverse bias at Drain as compared to the Source. Thus, the a Depletion Region is formed due to biasing whose width increase with the increase in the Biasing and vise Versa.

Configuration of JFET:

We know that Transistors are made by two type of materials i.e, N type and P type. The Terminals are connected by a current path between Drain and Source. these two terminals work as Collector and Emitter, respectively. Hence we observe two Configurations of JFETs:

1. N-Type.
2. P-Type.

Within the P-Type Configuration, we observe the doping of acceptors. hence holes are abundant in this region. by the same token, N- type configuration contain the doping of the electrons hence we get the faster conduction in N-Type region. We'll use N type JFET for the experiment.

Types of JFET:

Base upon their Production, we classify the JFET in two types:

1. Standard JFET
2. Insulated Gate JFET

The 2nd type i.e, IGJFET is most Commonly called Metal Oxide Junction Field Effect Transistor or simply MOSFET.

Conduction of JFET:

JFET are unipolar Devices and their efficiency mainly depends upon the Conduction of holes and electrons in P-Channel and N-channel, respectively.

 Implementation of JFET in Proteus ISIS

The Junction field effect transistors has very specific characteristics that can easily observed on the graph at a glance. Hence, let's start the simulation for best understanding.

Material Required:

1. Junction Field Effect Transistor (2N3819)
2. DC Power Supply
3. Ground Terminal
4. Current Probe
5. DC Transfer Curve Analysis

Procedure for the characteristics of JFET:

• Fire up your Proteus Software.
• Pick Up the JFET from the Pick Library through the "P" button.
• Set the JFET on the working area.
• Foster the "DC" from the power Generation mood of the Proteus.
• Fix 1 DC power supply at the Gate Terminal and the other on the Drain Terminal.
• Pick the Ground terminal from "Terminal mode" and fix it with the Source.
• At this stage, the circuit should look like the picture given below:

• Place the Current probe taken from the side of the Proteus at the Drain.

One point must be clear here, the direction of the probe should be towards the drain showing that the current passes from the Current source towards the Drain terminal of JFET.

• Name the Gate source as "Vgs".
• Name the Drain power supply as "Vds".
• Mark the Current Probe as "Ids".
• Choose "Transfer" from the Graph mode at the left most bar of the Proteus.
• Click on the Working area and make a window of the "DC Transfer Curve Analysis".
• To get the output, we will drag the Id at the graph area.

• At the instance, we have to set the Graph according to our need. Truss, Double click the graph to edit the Properties.
•  Set the Values according to diagram:

Now, when we simulate the graph by left click>simulate the graph, we find a simulation log.

• Simulate the graph through the Play button.
• Maximize the screen through left click at Graph>maximize and Observe the output.

Observations of JFET Characteristics:

• Vgs applied to the Gate Controls the Current flowing between Drain and the Source.
• No current flow through the Gate hence the Source current that is flowing out of the device is equal to the Drain current moving into the device.

Mathematically,

Is=Id

• We observe the four types of regions here:

1. OHMIC Region: JFET acts like a voltage resistor when voltage VGS =0 because the depletion region at this point is very less.
2. Pinch-off region: Resistance is maximum when Vgs is sufficient to cause the JFET to act as an open Circuit. This region is also called Cut-off region.
3. Saturation Region: In this Region, the JFET becomes the Good Conductor and be controlled by Vgs. The Vds has very less effect.
4. Breakdown Region: We observed that the in this region, the Vds becomes maximum and is controlled.

Advantages of JFET:

• They are replaced by the BJT because they are similar to BJT in characteristics like efficiency , robust, instant operation but are smaller than the equivalent Bipolar Junction Transistors. Thus they are better.
• Due to the size, they have less power consumption and low power dissipation, therefore are ideal to use in ICs and the CMOS range of circuit.
• They have extremely high input Impedance tat can be more than thousands.

Consequently, We learnt about extremely important features of the Junction Field Effect Transistor, Perform the experiments for the characteristics and observed the Advantages of JFETs.

JFET Applications | Constant Current Source | Chopper

Hi Pupils, Welcome to another Experiment of Proteus at The Engineering Projects. Previously, we saw what are the Junction Field Effect Transistors. Today we'll learn about some of the applications of Junction Field Effect Transistors.

Just before the Experiment, it is useful to revise that: Transistors are three terminal, unipolar Devices. The terminals of Junction Field Effect Transistor are named as :

• Drain
• Source
• Gate

The Gate Terminal is common to both Source and Drain. Prior to start, let's clear some Concepts about Junction Field Effect Transistor.

Resistor

Resistor is an electrical device. we define the resistors as:

"A Resister is a two terminal Passive electrical device that shows the electrical resistance and is useful in almost every Circuit.

Resistors can be used to reduce or control the flow of current , terminate transition lines and such other functions.

Pinch off voltage

The basic Definition of Pinch off voltage is:

"The voltage applied between the Drain and the source at which the current maximum current flows through the circuit provided the Gate voltage is zero is called the Pinch off voltage."

when the value of voltages is less than the pinch off region, the voltage enters to another region called ohmic region of JFET and the transistor acts as a resistor in this region.

Controlling Voltage

The Controlling Voltage of Junction field effect transistor is defined as: "The controlling Voltage is the voltage of transistors from gate to source.  To set its value, the Voltage from gate to source is made negative and it is referred as Vgs." FET's are widely used in the worlds of electronics because of their size and the performance. We'll apply JFET's in the making of two of circuits:

1. Constant Current Source.
2. Chopper.

During the Implementation of the Circuits, we'll use N-type JFET because of the better flow of electron of this kind of JFET. In N-type JFET the majority charge carriers are electrons. I am going to explain it one after the other.

Constant Current Source

A Field Effect Transistor can be use as a constant current Source. That spell out that if JFET's are designed so, they can provide a constant current across the load resistor, no matter how much current is provided at its input. The ability is due to the near horizontal line in the drain characteristics of the JFET. Recall that resistor is a two terminal Device that reduces the current flow, divide voltage or adjust signal lines. But, carefully Controlled JFET can be used to overcome the resistance through the resistor that come in between the JFET and the Voltage source. In the circuit, when the Vgs is greater than the pinch off voltage. mathematically,

V-IR>|V|

Implementation in Proteus ISIS

To make the circuit for Constant current Source, we need the Components as:

Component Required:

1. Junction Field Effect Transistor
2. Resistor
3. Ground Terminal
4. Direct Current Power Supply
5. Connecting Wires

Procedure

• Fire up your Proteus Software.
• Choose the JFET and Resistor from the Pick library through the "P" button.
• Take the Ground Terminal from Terminals library from the left most tab.
• Take DC power source from the "Generator mode".
• To measure the Current we'll add a DC ammeter from the "Virtual Instrument Mode".

This is the step where the Circuit should be arranged so, to get the required output.

• Connect the Source with the Drain thorough a wire.
• Join the Ground Terminal with the wire that connects Source and Gate.
• Connect the Components on the Working area according to the diagram:

• Double Click the Battery and give it a value of 9 volts.
• Double click the voltmeter and change the display Range to milliamps.
• By the same token, Double tap the resistor and give it the value of 1k ohm.

NOTE: you can also use a variable resistor.

•  Record the values of the ammeter.
• At first observations, Change the value of resistor to 1kohm.
• Pop the play button.

The ammeter shows the value of the 0.40 miliamps.

• Take seven reading by changing the value of resistor and make a table.

  Resistance	Current
  1k ohm	0.40 *10-3
  2k ohm	0.40 *10-3
  3k ohm	0.40 *10-3
  4k ohm	0.40 *10-3
  5k ohm	0.40 *10-3
  6k ohm	0.40 *10-3
  7k ohm	0.40 *10-3

   

The same experiment can be done by varying the value of battery and recording the values.

Chopper

A Chopper is the application of Transistor that show us the output as the square wave. We define the Chopper as: "Chopper is an electronic circuit used to take the amplified Direct current by using some type of transistor or other device." One can use any kind of transistor  e.g Bipolar Junction Transistor tor make the Chopper circuit. But, Junction Field Effect Transistors are better for this purpose due to the field control of the JFETs. In Choppers, the FET act as a variable resistance.   Lets rush towards Proteus to apply the circuit.

Implementation of Choppers in Proteus ISIS

• Fire up your Proteus ISIS.

Material Required

1. Junction Field Effect Transistor
2. Resistor
3. Alternating current source
4. Ground
5. Oscilloscope

• Pick the Vsine , Resistor and JFET from the Pick library by the mean of "P" button.
• Take the Oscilloscope form "Virtual Instrument Mode" and fix it just above the Circuit.
• Connect Channel A just after the AC source and channel B with the Source.
• Put the Ground terminal below the circuit by choosing it from "Terminal".
• Change the value of resistance connected to AC as 100ohm.
• Change the value of resistance connected to Source as 200ohm.
• Give the frequency to 1000Hz and Amplitude of 12V to Vsine.
• Join the circuit according to the image given below:

Seems like our circuit is complete now.

• Press the Play button to simulate the graph.
• Set the Value of Channel A to 1V.
• Set the channel B to 20V.

The Output of the circuit is:   This Conversion is important in some Circuits. The output of the Chopper is in the form of square waves. Thus, today we learnt about the JFET along with the applications of JFET as Constant current and Chopper in detail and saw their Implementation in the Proteus.