All You Need to Know About Transistors

The continuous flow of electric current through a wire should be regulated for power distribution. Generally, transistors are key components that are used as amplifiers in regulating electric current from higher to lower levels, as well as for frequency stages, modulators, detectors, the functioning of circuits, and to switch the current from one machine to another. Electrical devices have more than one transistor in their assembly, including low, medium, and high power transistors that are used in different frequencies and voltages. Moreover, their versatility makes them a significant invention in the electrical field. This blog will discuss the different types, applications, and construction of transistors.

Transistors are electrical devices that are established through the layering of p- and n-type semiconductors into an assembly that regulates current or voltage flow. The semiconductor materials are generally constructed from a material such as germanium or silicon for the means of providing the perfect amount of conductivity needed for operations. Depending on the application at hand, there are a few different types of transistors that one may take advantage of.

Types of Transistors

As discussed above, various transistors have different features that allow them to be used in both amplification and switching applications. However, transistors have one unique subtype known as a phototransistor, that of which usually responds to the amount of light it receives to produce electric flow. Transistors are classified into BJTs and FETs, but each category has its subtypes which we will now cover.

Bipolar Junction Transistors (BJTs) - BJTs are constructed with three regions: the base, collector, and emitter, all of which help the device efficiently control current. The low amount of current that enters the base of the transistor will become a large amount of current as it flows from the emitter to the collector region. There are two types of bipolar junction transistors: PNP and NPN.

The PNP transistor is a type of BJT transistor that includes two p-type and one n-type semiconductor. A thin n-type semiconductor is placed between the two p-type materials with holes as the majority charge carriers and electrons as minority charge carriers. The arrow shape of PNP transistors indicates that the current flow is directed from the emitter region to the collector region. The PNP transistor will be turned on when the base terminal has a lower current than the emitter.

Meanwhile, the NPN transistor is a type of BJT transistor that includes two n-type and one p-type semiconductor where a thin p-type semiconductor is placed in between the two n-type semiconductors. NPN transistors have electrons as their majority charge carriers and holes as their minority charge carriers. When electrons are flowing from the emitter to the collector, they will create a current flow through the base region of the transistor. A low power flow in the base region can create a large amount of current flow from the emitter to the collector region. NPN transistors are commonly used due to the higher mobility of electrons when compared to the holes.

Field-Effect Transistors (FETs) - Unlike bipolar transistors, FETs can control the voltage from their three regions: a gate, source, and drain. The applied voltage at the gate will regulate the current flow from the source and the drain of the transistor. In addition, FETs work on high input impedance that creates less current flow through the transistors. Hence, field-effect transistors collect less current from the circuit without disturbing the original circuit power with which they are connected. FETs are classified into two main types, JFETs and MOSFETs, and both are quite similar. Despite this, MOSFETs have higher input impedance values, meaning that less loading occurs in a circuit.

JFETs are junction-field-effect transistors used as the initial type of FETs for resistors, amplifiers, switches, etc. JFETs control the current flow at the source before controlling it at the drain after the voltage is applied to the gate and source region. The other type of FET is the metal-oxide-semiconductor field-effect transistor which includes a metal gate region with four other terminals, such as a source, drain, gate, and substrate. MOSFETs are commonly used in numerous applications and have many benefits over other transistors as they provide both high i/p and low o/p impedance. Moreover, MOSFETS are often used in lower power circuits during the design of chips. For their classification, MOSFETS may either be a p- or n-channel type.

Small Signal Transistors - Small signal transistors work as switches and amplify the low-level signals available in hFE ranges between 10 to 500, with the highest current rating ranging from 80 to 600 mA. PNP and NPN types are two forms of small-signal transistors that operate at the highest frequency between 1 and 300 MHz. These are used for amplification to bolster gain as amplifiers or switches.

High-Frequency Transistors - As the name implies, high-frequency transistors work at high frequencies with high-frequency signals and can switch on/off with ample speed. The maximum range of frequency rating for such components is approximately 2000 MHz, with the highest range of collector current being between 10mA to 600 mA. Generally, these devices can be obtained in NPN and PNP forms. Moreover, these transistors are for small signals used with HF, UHF, VHF, MATV, and CATV amplifiers and oscillator applications.

Power Transistors - Power transistors work as a heat sink that dissolves surplus power, and their collector terminal is associated with the metallic base terminal. The highest attainable value of collector current is between 1A - 100A, and such components are available in PNP and NPN forms. For power transistors, the range of power ratings is from 10 W to 300 W, and the frequency range is 1 MHz to 100 MHz.

Darlington Transistors - Darlington transistors combine two bipolar transistors so that there is a much higher ability to achieve current gain. These transistors are designed in a way that the first transistor amplifies the current before it is further amplified by the second transistor. The benefit of this transistor is that they demand less space than other options as all elements share the same collector. In the Darlington transistor, every transistor hFE value is multiplied mutually, helping components such as audio amplifiers measure even a minimal amount of current flowing through water. The sensitivity of this type of transistor is so high that it can even pick up current from skin.


Transistors seem simple, yet they play a vital role in the electrical field. As such, quality and reliability is necessary when sourcing such devices. With AOG Unlimited, you can find top-quality transistors and other electrical parts. AOG Unlimited is an ASAP Semiconductor-owned and operated website with an inventory of over two billion parts from more than five thousand reputed manufacturers. Our inventory includes different parts and components for aviation, vehicles, IT, and hardware, with various bearings, fasteners, and transistors readily in-stock today. We guarantee quality assurance on every part and guarantee a rapid delivery time. We are always ready to fulfill the needs of our customers, 24/7x365, so get in touch with a representative today! 


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