Difference between revisions of "CircuitJS/C3/Transistor-Characteristics/English"

Slide 2:

Learning Objective

Slide 4:

System Requirement

Slide 3:

Prerequisite

Slide 5:

What is a Transistor?

Slide 6:

Types of Transistors

There are two type of transistor

Slide 6:

In this tutorial we will discuss Bipolar Junction Transistor (BJT).

A BJT has three terminals: base, collector, and emitter.

There are two types of Bipolar Junction Transistors

Let us see how these 3 terminal semiconductors are formed.

A PNP transistor is formed using two diodes.

An N-type semiconductor is placed between two P-type semiconductors.

An NPN transistor is formed using two diodes.

A P-type semiconductor is placed between two N-type semiconductors.

The NPN and PNP transistors are denoted by this symbol.

The arrow represents the current flow in the transistor.

Current always flows from P to N.

Show the diagram

Let’s take the example of a water tap to understand the working of an NPN transistor.

Let’s assume, tap knob as base, water inlet as collector and outlet of the tap as emitter.

The knob of the tap controls the amount of water coming out of the outlet.

The base terminal voltage controls the intensity of light emitted by the LED.

When the knob is closed, no water flows through the outlet.

Likewise when voltage is not applied at the base terminal, LED will not glow and vice versa.

Using the same analogy, the working of the NPN transistor is explained below.

Let us see the working of NPN transistors in circuitjs interface.

Open the circuitjs interface.

Show the terminal

Open the circuitjs interface.

Click on File and select New Blank Circuit.

Click on Draw, go to Active Components and select Add Transistor (Bipolar, NPN).

Drag and draw the NPN transistor in the working area.

Click on Draw and select Add resistor.

Drag and draw the resistor in the working area.

Use the Edit option to change the resistor value to 100 Ohms.

Connect this resistor to the emitter terminal of the NPN transistor.

Click on Draw, go to Inputs and Sources and select Add Ground component.

Drag and draw the ground component in the working area.

Connect the ground component to the resistor as shown.

Click on Draw, go to Outputs and Labels, and select Add LED.

Drag and draw the LED in the working area.

Connect the LED to the collector terminal of the NPN transistor.

Click on Draw, go to Outputs and Labels, and select Add Ammeter.

Drag and draw the ammeter in the working area.

Use the Duplicate option to get ammeters.

Connect one ammeter to the base terminal of the NPN transistor.

Connect the other ammeter to the LED.

Use the Swap Terminals option to change the orientation of the ammeter.

Click on Draw, go to Inputs and Sources and select Add Variable Voltage component.

Drag and draw the variable voltage in the working area.

Use the Duplicate option to get two variable voltage supplies.

The default voltage range of the variable power supply is 0 to 5 volts.

Connect one variable power supply to the ammeter connected to the base terminal.

Then connect the other variable voltage supply to the Ammeter as shown.

Use the Edit option to change the voltage range of the variable power supply.

Change the voltage range to minimum 0 volts and maximum 20 volts and save the changes.

Let us see the V-I characteristics of the NPN transistor connected in this circuit.

Right click on the NPN transistor and select View in New Scope option.

A graph will appear at the bottom of your screen.

We can see a settings icon at the bottom left corner of the screen.

Click on the settings icon.

A pop-up window will open.

Here, first we have to select the X-Y plots option .

Then check the checkbox Show Vce vs Ic.

Click on the OK button to save the changes.

Increase the size of the graph window as shown.

There are two voltage sliders on the right side of your screen.

The first voltage slider is for the voltage supply V1.

The second voltage slider is for the voltage supply V2.

Let us first make both the voltage supply values to 0 volts using the respective sliders.

Click on the Reset button.

To show the V-I characteristics of the Transistor, we will keep the base current value constant.

Change the value of V1 to 1 volt using the slider.

Now, gradually increase the value of V2 using the other slider.

Notice the V-I characteristics of the graph.

The X-axis represents the voltage through the collector-emitter junction that is Vce.

And the Y-axis represents the current flowing through the collector that is Ic.

Let us perform the same exercise for different values of variable voltage V1.

First, reset the V2 power supply voltage to 0 volts using the slider.

Now, increase the V1 power supply to 2 volts using the slider.

Now, gradually increase the voltage supply V2 and observe the V-I characteristics.

You will see that after some point, the LED starts to glow.

In this case, you will see the current I is greater than the previous reading.

Note the current and voltage values of I and V shown in the box.

V-I Char_3Volt.png

Repeat the same process for variable voltage V1 of 3 volts.

Use a voltage slider to give precise value to the power supply.

The brightness of the LED depends on the power supply V1.

If the power supply V1 at the base terminal is zero, the LED will not glow in this circuit.

Note that the base voltage controls the current flowing through the transistor.

This is similar to the analogy of the water tap.

This shows that an NPN transistor can also be used as a switch.

Slide:

Importance of NPN over PNP

Let us see why NPN transistors are preferred over PNP transistors.

Slide:

Summary

Slide:

Assignment

Slide :

About Spoken Tutorial project

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This tutorial has been contributed by FOSSEE and Spoken Tutorial Project, IIT Bombay.

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