Actions of Transistors

According to research, our brain has 100 billion cells that help us to remember and think about something. Similarly, we know that a computer has many miniature cells known as transistors. Transistors are semiconductor devices prepared with silicon and are the chemical compound seen in the sand. 

Transistors have a huge impact on the revolution of the electronic industries. Transistor was founded in 1947 by John Bardeen, William Shockley, and Walter Houser Brattain. Those who don’t know, a transistor is a semiconductor having three terminals. It has the capability of amplification as well as rectification of signals.

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This article will enlighten students to learn about the chapter for Transistor CBSE Board in detail. Proper concepts are given here about the Transistor Class 12 topic.

Transistor Notes

We use the transistors in the electric circuits to either switch or amplify the signals. Also, it is used to provide power to the circuit. A transistor is made up of two PN diodes linked consecutively. There are three terminals available in a transistor called collector, base, and emitter.

The working principle of a transistor is that it allows manipulating the passage of current via one path by alternating the intensity of the smallest amount of current, passing via a second channel.

Transistor Action

As mentioned earlier, that a transistor possesses three terminals, viz: emitter, base, and collector. Now, there are two types of transistors called n-p-n transistor and p-n-p transistor.

Here are some facts that explain the transistor action:

1. As we know, emitter, base, and collector are the three regions of a transistor. The collector is broader than the base as well as emitter, whereas the base is much thinner than the emitter to make a confined design of a transistor 

2. When the emitter of the transistor is massively doped, it can give a jab of a huge quantity of charge into the base.

3. The design of the base is very thin and lightly doped. The base helps to recombine about 5% of charge, which comes from the emitter. The base helps to pass the injected charge carriers from the emitter to the collector.

4. In the transistor, the collector is lightly doped. 

5. There are two PN junctions in the transistor, which means it is similar to two diodes. The emitter-base is the junction between the base and emitter. It is also known as the emitter diode in simple terms. The collector diode or the collector-base diode is in the junction between the collector and base.

6. The behavior of the collector diode is constantly reverse biased, and the emitter diode is constantly forward biased.

7. The collector diode resistance is a little stronger than that of the resistance of the emitter diode. That is why in the case of the collector diode, a reverse bias is much higher, and the emitter diode is applied with a small forward biasing.

NPN Transistor Definition 

The NPN Circuit Diagram is given below:

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This is the figure of a forward-biased NPN transistor with the emitter-base junction, and in the collector-base junction, it is reverse biased. This current comes as the emitter current IE. 

Due to the forward biased condition, the electrons present in the n-type emitter travel towards the base. Electrons combine with the holes when they travel via the p-type base.

Only 5% of electrons combine with holes to create base current IB. Only a few electrons combine with holes due to the doping of the base—the rest amount of electrons, i.e. 95% combines with the collector region to form the current IC.

PNP Transistor Diagram 

Here is the PNP Transistor Working and diagram:

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In this figure, in the p-type emitter, the holes flow towards the base as it is forward biased. It helps to create the emitter current IE.

Only 5% of holes merge with electrons as the base is lightly doped and very thin. The rest 95% of the holes merge with the collector to make-up the collector current IC.

Transistor Formulas

These given diagrams show the symbols of NPN and PNP transistors:

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For the NPN transistor, the emitter current is the total of base and collector current.

IE = IC + IB

For the PNP transistor, the collector current is the difference between emitter current and base current.

IC = IE - IB

Classification of Transistor

The figure given below shows its different categories:

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The transistors are categorized by its applications and we have many types of transistors nowadays.

1. Bipolar Junction Transistor (BJT)

We call it Bipolar Junction Transistor as BJT in short. It contains two p-n junctions to regulate the current in the device. The device is manufactured to serve in two different ways, like NPN and PNP.

2. Field-effect Transistor (FET)

We name Field-Effect Transistor as FET in short. It is a voltage-controlled device. It is also a unipolar device, which signifies that either p-type or n-type material is used to build the FET. The function of this device is to regulate the current.