The electrical circuits of all electronic devices depend on transistors as switches and amplifiers. When transistors are used for amplification purposes, they may be used as modulators, oscillators, frequency stages, and detectors. If they are digital circuits, then transistors are utilized as switches. Whenever a function must be performed within an electrical circuit, a transistor is needed.
There are many different types of transistors. The semiconductor materials used to make transistors are what differentiate them from one another. These materials influence the positive and negative charges of the three terminals and how they’re arranged. You can have high power transistors, medium power transistors, and low power transistors to accommodate different levels of frequency and voltage from a device.
A transistor will have either an NPN connection or a PNP connection (Negative-Positive-Negative or Positive-Negative-Positive). When you have an NPN connection, the emitter terminal receives a flow of electrons and emits a flow of electric current. When you have a PNP connection, the flow of the electric current goes into the emitter rather than go out of it.
Let’s take a look at the most common types of transistors.
1) Bipolar Junction Transistor
Bipolar junction transistors have three layers (or terminals). These layers are the base, collector, and emitter. The purpose of a bipolar junction transistor is to control the flow of current. For example, small electric current flows into the base terminal of the bipolar junction transistor and causes the emitter terminal to release a bigger flow of electric current. The transistor may either have an NPN connection, which mostly carries electrons, or a PNP connection, which mostly carries holes.
2) Field Effect Transistor
Field-effect transistors also have three terminals, but they’re called a gate, source, and drain. They are different than bipolar junction transistors because field-effect transistors are devices that control voltage rather than current. They also have extremely high input impedance, which means their level of resistance can have many megaohms. But with such high input impedance, there is less current flow. This means a field-effect transistor won’t draw much current from the power source of the electrical circuit.
3) Heterojunction Bipolar Transistor
Heterojunction bipolar transistors are commonly utilized in digital microwave applications as well as analog microwave applications. The advantage of using heterojunction bipolar transistors is they offer faster switching speeds in comparison to the slower silicon bipolar transistors. Heterojunction bipolar transistors also offer simpler broadband impedance, better base resistance, better injection efficiency of the emitter, and greater breakdown voltages. You’ll find these transistors in more expensive electronic applications and hardware. They serve as powerful amplifiers in laser drivers, and smartphones, for example.
4) Darlington Transistor
Darlington transistors are quite unique because they’re comprised of two transistors in one, which gives them a much greater chance of gaining current. These transistors may be part of an integrated electrical circuit. Sound amplifiers may use Darlington transistors because of their sensitivity. In fact, you can even feel the current in your body because of the sensitivity. If you want to make a touch-sensitive button, then a Darlington transistor is perfect to utilize.
5) Multiple-Emitter Transistor
Multiple-emitter transistors are basically special types of bipolar transistors with emitters that receive input signals from integrated circuit transistor-transistor logic NAND logic gates. When logical high voltage drives each emitter, the flow of collector current comes to a halt. If you want to reduce power and switching times in your electronic applications, then a multiple-emitter transistor is the best to use.
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There are literally thousands of different transistors available because of the variety of semiconductor materials available. The five transistors listed above are the most commonly found in our everyday electronic devices.