Bipolar Junction Transistor

The transistor is the most important active electronic device which is used in almost all electronic circuits either as an amplifier or as a switch. Transistors are of two types viz. NPN and PNP transistor. The basic difference between the two types of the transistor is that in NPN transistors, the three terminals are connected to the semiconductor material of n-type whereas, in a PNP transistor, the three terminals are connected to the semiconductor material of p-type. In this article, we will discuss the bipolar junction transistor (BJT). BJTs are two-terminal semiconductor devices that are used to amplify or switch electronic signals. They are made of semiconductor material of p-type and semiconductor material of n-type, which are connected by a metal base. We will look at the construction and operation of BJTs, and we will also explore some of their applications.

What Are Transistors?

A transistor is a device with properties of a semiconductor used to boost or change electronic signals & power. A semiconductor material is used with a minimum of three terminals for connecting to an external circuit. A charge or electricity current when applied to one of the pairs of the transistor’s terminals changes the current of the other terminals, due to the output power being higher than the input power, a transistor can boost the signal. The transistor is the fundamental building block of modern electronic devices and is ubiquitous in modern electronic systems.

What are the types of Transistors?

Transistors are of two types, NPN and PNP, which are made of different materials. NPN transistors are made of semiconductor materials like Silicon. PNP transistors are made of materials like Germanium. The main difference between the two types of transistors is the direction of the current flow. The flow of current through transistors of NPN type is through the output to input, transistors of PNP type, the flow of current through the input to the output.

What is a BJT Transistor?

Transistors that use both electrons and holes as charge carriers are known as Bipolar Junction Transistors (BJT). BJTs are made of three layers of semiconductor material, each capable of carrying a current. The upper layer is called the emitter, the middle layer is called the base, and the lower layer is called the collector. The function of each layer will be discussed in more detail later. When a BJT is used as an amplifier, the current flowing through the middle layer, the base, controls the current flowing through the other two layers, the emitter, and collector. The amount of current amplification is called the gain. The transistors you are using as amplifiers in your projects have a gain of about 100. That means that for every one-volt increase in the base voltage, the transistor will allow 100 times more current to flow through the collector than would otherwise be possible.

Bipolar Junction Transistors are of two types, namely: NPN (negative-positive transistor) and PNP (positive-negative-positive). Let’s read them in detail.

What is an NPN Transistor?

An NPN transistor is made up of two pieces of semiconductor material, placed side by side. The NPN transistor’s full name is Negative-Positive-Negative transistor. A base, emitter, and collector make up this three-terminal device. An NPN semiconductor device that is applied in both amplification and switching. It is comprised of two n-type regions separated by a thin layer of p-type material.

The emitter-base junction is the point where the emitter and base regions meet. The collector-base junction, on the other hand, is the meeting point of the collector and base areas. Due to the presence of two junctions in between three areas, it works as two PN junction diodes.

Each of the three regions has different levels of doping. There seems to be a lot of doping in the emitter region, and there is also a lot of doping in the base region. The doping level in the collector region is moderate, somewhere in between the emitter and the base region. The PNP transistor, on the other hand, has a N-region sandwiched between two P-Type regions.

What is a PNP Transistor?

A PNP transistor is a form of bipolar junction transistor (BJT) that uses two types of semiconductor materials for the construction of its two main terminals. The first terminal, called the base, is made from the semiconductor material of p-type. The second and third terminals are both made from the semiconductor material of n-type and are called the collector and the emitter. When used in an electronic circuit, PNP transistors can be used to amplify or switch electronic signals. PNP transistors can also be used to create negative feedback circuits, which are used to stabilise the voltage and current levels in a circuit. Like all transistors, PNP transistors are made up of three layers of semiconductor material.  The base layer is the middle layer and is made from the semiconductor material of p-type. 

The collector layer is the outermost layer and is made from the semiconductor material of n-type. The emitter layer is the innermost layer and is also made from the semiconductor material of n-type. PNP transistors are connected to a power supply so that the base-emitter voltage (VBE) is less than the collector-emitter voltage (VCE). This ensures that the transistor is turned on and can conduct current. When a PNP transistor is turned on, electrons flow from the emitter to the base, and then from the base to the collector. This creates a current flow from the output to the input.

Conclusion

Transistors are semiconductor devices used to amplify or switch electronic signals and electrical power. They are made of materials like germanium, silicon, and carbon,  and come in two main types: bipolar junction transistors (BJT) and field-effect transistors (FET). BJTs have three terminals—the base, the collector, and the emitter—and are made of two types of semiconductor materials, P-type and N-type. When the two materials are joined together, they create a P-N junction. There are two types of BJTs: PNP and NPN. Transistors are used in a variety of electronic devices, including radios, computers, and cell phones. They are also used in amplifiers, integrated circuits, and signal generators. The bipolar junction transistor is a very important device in electronics.