What is a Transistor

When it comes to electronics, there are tons of terms you've likely heard. While you don't necessarily need to understand the underlying hardware to make a project function, understanding individual components and their purpose does provide many benefits. Learn all about transistors, from what is a transistor to what a transistor actually does, and common applications that use transistors!

What is a Transistor?

A transistor is a device that regulates voltage flow, or current. In simple terms, a transistor acts as a gatekeeper or switch for handling electronic signals. Three primary semiconductor components, able to carry an electric current, comprise a transistor. These materials are often silicon or germanium. 

The transistor was developed in 1947 by Bell Labs. Initially, it was an alternative to vacuum tubes for regulating electronic signals. 

What is a transistor in simple words: A gatekeeper for handling electronic signals. 

How is a Transistor Made?

A transistor is comprised of three distinct semiconductor layers. Each of these is able to conduct a current. The various semiconductor materials are afforded certain properties through the chemical process of doping which either adds additional electrons, an N-type with a negative charge, or makes holes in the material's structure thus generating a P-type with a positive charge. A transistor features an N-type, negative, semiconductor layer in between two P-Type, positive, layers as a PNP configuration, or an NPN set up with a P-type sandwiched between two N-type layers.    

How Does a Transistor Work?

Transistors serve two main functions: working as a switch or an amplifier. A transistor as a switch lets a small current turn on a larger one. Little current traveling through one part of a transistor is able to make a larger current flow through another section of a transistor. Since the switch is controlled by voltage rather than an actuator that requires a physical switch, voltage input flowing into a base exceeding a specific voltage then toggles on the transistor. 

On the other hand, a transistor may serve as an amplifier. The way a transistor amplifier function is such that a small electric current on one end, as an input, generates a much larger electric current as its output. 

Transistor as an Amplifier

Ok, great, so a transistor can function as a switch or an amplifier. But how does a transistor amplifier work? Since there are three layers, of differing charge, either PNP or NPN, a minor current or voltage change at the innermost semiconductor layer, the control electrode, creates a major change with traveling through the transistor as a whole. Everything's connected in a circuit. Within a transistor amp, you'll find three different terminals: emitter (E), base (B), and collector (C). The base activates the transistor, with a required minimum voltage to turn on the transistor. Then, the collector features the current flow, while the emitter drains from the collector and is usually hooked up to the ground pin. 

• Base: Pin that turns on/of the transistor by reaching a minimum voltage
• Collector: Current flows throughout this terminal
• Emitter: Current drains from the terminal

With using a transistor as an amplifier, you'll find a few situations. A common base finds no current gain, but a voltage gain. On the other hand, a common collector lacks a voltage gain but does have a current gain. Finally, a common-emitter has both current and voltage gains. 

Components of a transistor amp include resistors, capacitors, wires, a breadboard, power supply, oscilloscope, and transistor. When configured as an amplifier, a transistor utilizes three primary segments: a cut-off area, saturation region, and active space. Whilst the voltage between the base and the emitter remains less than a certain number, the transistor sits in a cut-off region. Then, with the voltage as the base-collector and base-emitter areas goes up, the transistor is in the saturation region. And the transistor is within the active region when the base voltage goes up but the bast to collector voltage is negative. 

• Cut-off region: Where the voltage rests between the base and the emitter below a certain voltage, the transistor remains within the cut-off region.
• Saturation region: While the voltage base to collector and base to emitter both increase, the transistor is in the saturation region. 
• Active region: If the base to collector voltage is negative but the base voltage increases the transistor is in the active region.

Transistor as a Switch

Alternatively, a transistor may work as a switch. Essentially, a small bit of electric current flowing through one part of a transistor can create a substantially larger current flow through another area. The lower current switches on the bigger current. When used as a switch, a small electric current flowing through a section of the transistor causes a substantially larger current flow in a different area. The small current switches on a bigger one. 

Types of Transistors

There are several different types of transistors. A bipolar junction transistor (BJT) features three terminals of semiconductor material. BJT devices are most often used for switches and amplifiers. Their name derives from a two-pole set up wherein electrons and holes use an emitter, collector, and base configuration to change a current between the collector and emitter. 

Two bipolar transistors hooked up where the amplified current from the first is even more amplified is a Darlington transistor. An insulated-gate bipolar transistor (IGBT) features three terminal power semiconductors. IGBT is used in switches and largely industrial applications like trains and cars. Finally, MOSFET transistors, or metal-oxide-semiconductor field-effect transistors are employed for integrated circuitry for conductivity control of a channel. MOSFETs are great for switches, power level limitation, and data storage. 

• Bipolar transistor: Three-terminal device comprised of semiconductor materials, best for amps and switches. Uses an emitter, collector, base configuration. 
• Darlington transistor: Two bipolar transistors where the current that's amplified in the first bipolar transistor is even more amplified by the second. 
• IGBT: Three-terminal semiconductor, most often used as a switch. 
• MOSFET: Deployed within integrated circuitry for controlling channel conductivity. 

How are Transistors Used - Common Transistor Applications

Transistors are easily some of the most versatile and widely-used devices on the planet. Therefore, transistors are employed in power regulators, both digital and analog switches, signal amplifiers, and more. A common transistor function is as an amplifier. Just turn to the classic diddly "Brown Eyed Girl" by Van Morrison. The line "Going down the old mine/With a transistor radio" gives the perfect example of a transistor put into action. And this is a use case for a transistor as an amplifier. Transistor radios are portable radio receivers outfitted with transistor circuits. Internal components include radio receivers, loudspeakers, and of course transistors implemented as amplifiers. A transistor radio works such that a radio frequency (RF) amplifier the signal received from a specific radio frequency band, or radio station. Other transistor amplifier applications include hearing aids. 

For an example of a transistor as a switch, think of RAM modules found in a computer. Sticks of RAM feature millions or billions of transistors that can be switched on or off as individual units. Memory chips are comprised of transistors and capacitors, where every transistor may be two different states, storing two distinct numbers: a zero or a one. It's this transistor that functions as a switch to tell the control circuitry within the RAM chip see the capacitor and change the state of the capacitor.  

Cell phones boast transistors as amplifiers. And power regulators require transistors as well. Microprocessors tout billions of transistors per chip. Everything from planes, trains, and automobiles to mobile devices, stoves, and radios use transistors. It's one of the most oft-used devices that you almost never see. 

What is a Transistor and How Does it Work? Final Thoughts

While you've probably heard about transistors in the past, you might not have known what one is, how it works, or common uses for transistors. As you can see, they're basically current or voltage flow regulators that can serve as switches and amplifiers. As such, transistors are incredibly popular for various purposes ranging from radios and hearing aids to RAM chips. Overall, they're incredibly functional electronics gateways made up of semiconductor chips. Chances are that, even if you've never seen one up close, you've probably used a device based on a transistor.