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Transistors: The Key to Modern Electronics

20 May, 2019 | Quest Components

Transistors: The Key to Modern Electronics

Invented in 1947, point-contact transistors rapidly revolutionized electronics, replacing the bulky and fragile vacuum tubes that had themselves replaced relays in 1907. The invention of transistors paved the way for smaller, cheaper, more practical, and more affordable computers, calculators, radios, and other devices. Modern computers and smart devices contain hundreds of millions to billions of tiny transistors packed inside microchips. But what exactly is a transistor and what does it do?

Purpose of a Transistor

A transistor can do two basic jobs: act as an amplifier or act as a switch. As an amplifier, it takes a small input current and produces a much larger output current. An example is the set of transistors in a hearing aid. It takes in relatively quiet ambient sound and plays it back through a tiny loudspeaker at a much higher volume. 

As a switch, a small electric current that goes into one part of the transistor turns on the switch, producing a larger current flow through another part of the transistor. This is how computer chips work. Each of the hundreds of millions or billions of transistors inside the chip can be individually switched on or off. If you think of the off state as a zero and the on state as a one, you understand the basics of binary code—the language of computers.

Along with a form of logic known as Boolean algebra, in which all variables are either true or false (one or zero), binary code powers all computer and smart device functions. All the transistors inside a chip work in tandem, continuously switching between ones and zeros (on or off) to perform complex calculations nearly instantaneously.

What Are Transistors Made From?

Transistors are made from silicon, a semiconductor that is the major chemical element in sand. It can be “doped” (treated) with certain impurities to negatively charge it (n-type) or positively charge it (p-type). N-type silicon more readily loses electrons, while p-type silicon more readily gains them.

From Diodes to Transistors

Joining p-type silicon to p-type silicon and adding electrical contacts causes electrons to flow through the junction from the n-type side to the p-type side and then out through the circuit, but reversing the current stops the flow of electrons altogether. This type of junction is known as a diode, which only allows current to flow one way. It can be used to turn alternating current into direct current, or to give off light when electricity flows. You may be familiar with light-emitting diodes (LEDs) on electronic displays.

A junction transistor takes it a step further than a diode. Instead of simply joining one slice of p-type silicon to one slice of n-type silicon, now there are three layers: n-p-n. Each slice has electrical contacts. The contacts on the n-type pieces of silicon are the emitter and the collector, while the contact on the p-type is the base. Remember the base is positively charged (fewer electrons) and the emitter and collector are negatively charged (extra electrons). When positive voltage is applied, electrons move from the emitter to the base, and then from the base to the collector. So the transistor acts as both a switch (turning on when current is applied) and an amplifier (converting the small input current to a large output current).

A field-effect transistor (FET) also has layers of n-type and p-type silicon, but they are arranged differently and coated with metal oxides. In this case, the p-type silicon acts as a gate, preventing electrons from moving between the layers of n-type silicon. When an electric charge is applied to the gate, an electric field is created that provides a thin channel directly from one layer of n-type silicon to the other.


Transistors are normally powered by electric currents, but they can be hooked to logic gates that feed their outputs back into their inputs. This means that the transistor will remain in a stable state (on or off) even after the current is removed. It will not change its position until a new current causes it to flip the other way. This “flip-flop” arrangement is at the heart of modern computer memory chips.

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Here at Quest Components, we are committed to providing you with the information you need to help your business continue to run smoothly. An ISO 9001:2015 Certified Company headquartered in Industry, CA, Quest Components specializes in passive and active board level components. We also provide a variety of services to OEMs (original equipment manufacturers) and CEMs (contract electronics manufacturers) across the globe. Contact Quest Components today at 626-333-5858 for all your electronic component needs!

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