A Transistor is an electronic component used to amplify or convert electronic signals and electricity. The combination of the words “transistor” consists of two words: one (trans) means transfer, and the other (ister) means resistance.


Transistors are the active components of integrated circuits, consisting of billions of small devices attached to their shiny surfaces. Transistors are one of the most widely used components in modern electronics. The transistor consists of two PN diodes. It has three terminals: first emitter, second base, and third collector. The base is the middle part, which is made up of thin layers.

It consists of semiconductor material, usually with three pins to belong to the external circuit. A voltage or current applied to one pair of transistor leads controls the current from the other pair of leads. In other words, it is a switching device that controls and amplifies the electrical signal, such as voltage or current.

Working of Transistor

Different types of transistors are available today. The transistor connected at the rear of the two P-N junctions. One of them, twenty ammeter junction, is forward biased, while the other is base-collector junction reverse biased. It has been found that when current flows at the base ammeter junction, more current flows in the collector circuit, even if the base-collector junction is reverse biased.

For an explanation, an example of an NPN transistor is taken. The same argument can be used for a PNP device, except that the holes are the central carrier instead of the electrons.

When the current passes through the base-emitter junction, the electrons leave the emitter and flow into the base. However, doping is low in the region, and relatively few holes are available for recounting. As a result, most electrons can move directly to the base area and further to the collector region attracted to the positive potential.

Types of Transistors

Types of Transistors: The transistor has become an essential component of modern electronics, and we cannot imagine a world without transistors. A transistor is a semiconductor device based on three terminals to amplify or switch electronic signals and electricity.

There are different transistors available today, which are generally classified into two types: Bipolar Junction Transistors (BJT) and second Field-Effect Transistors (FET).

1: Bipolar Junction Transistor (BJT)

A Bipolar Junction Transistor (BJT) is also called a junction transistor. BJT has three terminals named Emitter (E), Base (B), and Collector (C). BJT transistors are classified as NPN and PNP transistors in terms of construction. An NPN transistor is one in which most current carriers are electrons. Generally, NPN transistors are preferred for convenience.

A small current flow entering the base region of the transistor causes a large current flow in the collector region from the emitter. Bipolar junction NPN and The term “bipolar” means that both electrons and holes are required to conduct current and conduction, and the term “junction” means that it includes a PN junction (actually two junctions).

The electron flowing from the emitter to the collector forms the basis of most of the current flowing through the transistor. There are more types of charge, holes, minority. PNP transistors are against it. In PNP transistors, the majority of the current carrier holes. BJT transistors are available in two types PNP and NPN.

PNP Transistor

This PNP transistor is a type of BJT. PNP transistors then use lower current and negative base voltage to drive higher emitter-to-battery current. In other words, PNP is more favorable for the transistor, for the base of the emitter, and the collector.

Basically, in the design of this transistor, the two diodes are swapped by setting the positive and negative positive types with the NPN type, with the arrow, which also inserted into the symbol of the transistor, this time. Indicates the emitter pinpointing to.

The base junction of the emitter connected to a forward bias that causes the emitter to push out holes in the base region. These holes form the ammeter current. When these electrons pass into an N-type semiconductor substance or base, they combine with the electrons.

The base of the transistor is thin and very light. Thus, only a few holes along with electrons and the rest of the savings have moved to the space charge layer of the collector.

NPN Transistor

NPN is another type of BJT. It consists of two kinds of semiconductor substances separated by a thin P-type semiconductor layer. An NPN transistor enters a weak signal at the base and generates a strong signal at the collector end.

NPN transistor consists of three layers: N-type semiconductors and the other is P-type semiconductor. It often said that two diodes are connected in reverse to form a transistor. Such transistors are mainly used in circuits because most of their charge carriers are electrons, which have higher mobility than holes.

Most of the charge is electrons in NPN transistors, while minority carriers have holes. Electrons are emitted from the terminal of the emitter to the terminal of the collector and form a current flowing inside the terminal of the base of the transistor. It’s used as an amplifier, switch, converter, and temperature sensor.

Field-Effect Transistors (FET)

A field-effect transistor (FET) is a three-terminal semiconductor device. The field-effect transistor consists of 3 terminals, a gate, a source, and a drain. Various bipolar transistors are devices powered by the voltage of a field-effect transistor.

The gate voltage source regulates the current flowing in the transistor channel. FETs have a very high input impedance, with very high impedance values ​​above several megohms. Because of this high resistance to entry, they flow very little in the current them.

These transistors designed to overcome the drawbacks of bipolar junction transistors. As the basic transistors have the junction of the emitter in the mode of forwarding bias, the device operates at low impedance levels.

These transistors are for troubleshooting bipolar junction transistors. Because the primary transistors have a forward-biased ammeter junction, the device operates at a low impedance level.

There are two main types of field-effect transistors first (JFET) and the second (MOSFET). JFET and MOSFET are very similar, but MOSFETs have more input impedance values ​​than JFETs. It also reduces the load on the circuit.

Junction-Field-Effect transistor (JFET)

Junction Field Effect Transistor(JFET) is a simple and basic types of FET transistor used, such as resistors, amplifiers, switches, etc. It is a voltage-controlled device and uses no biased current. Once the voltage is applied between the gate and the source terminals, it controls the current flowing between the source and the drain of the JFET transistor.

Junction field-effect transistors have two basic configurations, N-channel JFET and P-channel JFET. N channel JFET’s channel contaminated with donor impurities, which means that the current flowing through the channel is negative in the form of electrons.

The JFET voltage applied to the gate does not allow maximum current through the source and drain. Also, note that the amount of current allowed by the JFET is determined by the voltage signal rather than the current signal as in the case of bipolar transistors.

In fact, with the gate-source PN junction reverse binding, there should be near zero current through the gate connection. For this reason, we classify the JFET as the voltage control device and the bipolar transistor as the current control device.


MOSFET stands for M-Metal O- Oxide S- Silicon F- Field E- Effect T- Transistor. It is the most commonly used of all-transistor types. As the name suggests, the kit includes a metal gate lead. This transistor includes four pins as SourceSource, drain, gate, and body. MOSFET is also called IGFET or insulated-gate field-effect transistor.

It is either a core or an integrated circuit designed and manufactured as a single chip as the device is available in very small sizes. This is highly dependent on negative and positive charges. The big advantage of MOSFETs is that they do not require an input current to drive the load current compared to bipolar junction transistors (BJTs).

In a MOSFET in enhancement mode, a voltage applied to the gate terminal can increase conductance from a normally-off state. They are also highly scalable by increasing miniaturization and can be easily scaled down to smaller sizes.
It also has a faster switching speed and a much higher density (ideal for large-scale integration) than BJT.

The MOSFET must control the voltage and current between the SourceSource and drain pins. It is working like a switch, and the device’s functionality based on a MOS capacitor. When a drain-to-source voltage is applied between the drain and the SourceSource, a positive voltage is applied to the drain and a negative voltage to the Source.

The PN junction at the drain is reverse biased, and the PN junction at the SourceSource is forward biased. At this point, there will be no current between Drain and Source.

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