Transistors are an incredible revolution to the world; if this didn’t exist, you wouldn’t see the revolution of new technology in the world. Men have discovered electricity, which can harm small devices like computers, cameras, and many such tools which use a small amount of power. Also, we are familiar with AC, which can damage an appliance when given directly; in such cases, a small instrument called Transistor came to the field of electronics.

To make the devices applicable to use such a large amount of current or voltage, we have to use DC currents and voltages, so in this case, Transistors play a vital role that can control the CURRENT and VOLTAGE according to our need.

Hence, the question arises here how it controls the electricity; it’s discussed step by step.

Who invented the transistor?

The scientists responsible for the invention in 1947 that led to the creation of transistors were John Bardeen, Walter Brattain, John Bardeen, and William Shockley. Bardeen was a scientist with a Ph.D. in math and physics at Princeton University, was an expert in the properties of electron conductivity of semiconductors. Brattain, Ph.D., was an expert on the structure of the crystal structures of the solid at the surface and solid-state Physics. Shockley, Ph.D., was the director of research in transistors at Bell Labs.

Their original patent title of the transistor is “Semiconductor amplifier; Three-electrode circuit component made up of semiconductive material.’ In the year 1956, the team received the Noble Prize in Physics for the invention of the transistor. The year 1977 was when John Bardeen was awarded the Presidential Medal of Freedom.

What is meant by Transistor?

The Transistor is defining as “The semiconductor device, made of silicon and Germanium.”
                                  OR
“Transistor is a semiconductor device used to amplify or switch the electronic signals and electrical power.”
Transistors are still utilized in electronic devices in the present. where did the word “transistor” come from? The word is derived directly from the words “transfer” and “resistor” since an electrical current inside the transistor is transmitted across resistors, which are which is a component with two terminals in electronics.

Types of transistors?

There are two main types.

  1. BJT
  2. FET

BJT Transistor:

NPN and PNP transistors are Bipolar junction transistors (BJT); BJT’s control current, which means they only amplify flow. A current at the base terminal of BJT’s allows a large (current) at the emitter and collector terminal. NPN and PNP transistors have the same function of {AND Capability}.

Transistors
NPN and PNP

 

Remember that NPN points the arrow to the outer. PNP leads the shaft to the inner.


If you want to remember this, here is a trick for you;

For NPN;
N=Never
P=Points

N=In

For PNP;
P= Points
N=In
P=Permanantly

 

How does NPN Transistor work?

Its working is explained according to the figure below.

Transistors
NPN Transistor

 

When we connect the supply to the LED and current passes through, it won’t glow because the flow is not passing through the emitter terminal. The current got blocked at the collector, as shown in the figure above.
To make the LED glow, we have to close the switch to make the circuit complete. BJT’s transistor only works when a sufficient amount of current is supplied to the base terminal, as shown below.
Transistors
NPN Transistor

 

In PNP, When we provide a positive voltage to the collector terminal, and then current flows from the collector terminal to the emitter terminal when there is a sufficient amount of base current.
An NPN can be ON when a sufficient amount of current to the base terminal is provided; therefore, it connects the positive terminal to the supply.

 

How does PNP transistor work?

 The working of PNP is described in the figure below.
Initially, the switch is open; hence when the voltage is applied to the emitter side of the PNP current, it will not pass through the collector terminal of PNP, so the LED won’t be able to glow.
PNP Transistor working

 

When the switch is close, the current passes from a positive terminal to the negative terminal of the supply, and hence the current creates this path. Accordingly, the current is passed through the collector terminal of PNP, so the LED glows.
When the positive voltage is applied to the emitter terminal, current flows from emitter to the collector and when a sufficient amount of negative current is applied to the base terminal.
The only difference between PNP and NPN is that;
  1. In NPN, the Load is connected with the Collector terminal.
  2. In PNP, the Load is connected with the Emitter terminal.
  3. In NPN  positive terminal of supply is connected with the base terminal.
  4. In PNP negative terminal of supply is connected with the base terminal.
Difference between NPN and PNP

 

FET:

The FET (field effect transistor) is the three-terminal device that uses an electric field to control the flow of current through the machine. Today most of the integrated, including the computer, use FETs.

FET Working

The three-terminal of FET ;

  1. Gate
  2. Drain
  3. source

In FET current flows from drain through the source, and in this way, the current is controlled by applying a voltage between gate and source. This voltage generates an electric field within the device, so by controlling this voltage, the flow of current is monitored.
 In simple words, by controlling the electric field, the flow of current is monitored. That’s why it is known as a Field-Effect Transistor or FET. So it is said the Field-Effect Transistor is a voltage control device.



Difference between FET and BJT Transistors ;

  1. BJT’s are current controlling devices.
  2. FET’s are voltage controlling devices.
  3. BJT’s are Bi-polar device.
  4. FET’s are Uni-polar device.
  5. BJT’s Input impedance is very high.
  6. FET’s have high input impedance.
  7. BJT’s are larger then FET’s
  8. FET’s are smaller then BJT’s that’s why it can be found in integrated circuits.
  9. FET’s uses low power consumption then BJT’s.

 

Application Of Field-Effect Transistor:

FET’s are used almost everywhere, where BJT’s are used. Some of the claims are as under.

  1. FET’s are used in amplifiers.
  2. They can also be used in the analogue switch.
  3. FET is used in integrated circuits.
  4. It is used as a buffer amplifier.
  5. It can be used as an oscillator.

for more info, you can check in Wikipedia

 

Transistors as a switch:

How to use it as a switch?
The switch means a device used to On or Off the lights or any loads in houses manually. Similarly, if we want to On the fan, we use the switch to On or Off it.
But in electronic PCV or other devices, the switch is made automatically.

At first, let’s know about transistor work,

What is the work of the transistor?

Transistor has two uses.

• The first uses of the Transistor is, it works as switching. On and Off work is work taken from it. The Transistor is used as a switch.

• The second use of a transistor is that it also works as an amplifier for any signals in a circuit.

How can transistors can be used for switching purposes in a circuit?

First of all, choose a transistor. Like in the given diagram, the value of the Transistor is S8550. If you are using any transistor, use it according to its value. In the diagram, the transistor has three pins, and the other diagram shows the symbol, known as the NPN Transistor.

Transistor as a switch

Below are the steps of how to select the transistor.

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Differentiate Between Transistors Types:

If the arrow is downward, it’s known as the NPN.
If the same arrow is upward, it would be known as the PNP.
PINS: If we talk about transistor pins, every Transistor has different pins. It has Ammeter, Collector, and base.

 

How to differentiate between these Pins?

For differentiation of pins, a multimeter is used. Through that device, the switch could be divided into Ammeter, Collector, and Base.
If the device, a multimeter is not available. You can find it through google, just put the value of the Transistor in the search bar. It will show you which one is an ammeter, collector, and base.

 

Switching using Transistor: 

Consider a lamp and a battery in the circuit where the Transistor is also attached.
For making the Transistor for automatic switching, the ammeter and collector terminals are sorted by applying a low voltage to the base. Once they get sorted, the lamp will be turned On.

Transistor as a switch
As shown in the figure, the negatives terminal is directly connected to the lamp.  When the positive terminal is attached to the transistor, and the base of a transistor is given a low voltage supply or signal supply. It will make the ammeter and the collector get sorted, or in simple words, the current will move directly from ammeter to collector and then to the lamp.
Once the supply current is Off, the terminal will shut down.
For example, the water motors.
When the level of water in the tank is low, the water motor gets started automatically, and when the tank is full, the water motor stops because of the sensor in it when water touches the sensor. The circuit gets completed and gives supply to the base of the Transistor, the ammeter and collector are sorted, and then the Load is On or Off.

Uses of Transistors:

Is this topic, you will come to know where it is used?

The transistor is basically used in every electronic device such as radio, tv, computer, calculator, telephone. In all these devices, the motherboard is mended in them.

Why are Transistors operated?

The Transistor is wielded because, in electronics, it provides us with two types of work.
1= It is used for switching purposes. For example, a bulb, a switch is used for it’s On and Off annually.

In the same way in every electronic for the flow of current Transistor is present.

2= Transistor is similarly used for Amplification as it converts weak signals to strong signals, for example, Mic, water tank, fire alarm, power supply.

USES:

• In water tanks, the Transistor is fixed when the water tank gets full. The jingles in alarm is recognized by the sensor.

•In fire alarm, the Transistor is fixed when the fire took place the light or smoke of the fire is detected, and the signal is activated.

• In the power supply circuit, more than one transistor is used.

• To make a device with more transistors, then it’s circuit is quite complicated and expensive, so a small IC is used. In one IC, approximately 2000 or 3000 electronics transistors, can be placed.

In some IC, you can place up to one lac transistor. Its benefit is it’s cheap and easy. You only have to check it’ the s datasheet for all the information.

As you know that computer language is binary code, transistors play a vital role in conversion from binary to common words.


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