Electronics Components: The Most Important Transistor Specifications
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Electronics Components: Why Transistors Were Invented

Think of a transistor as an electronic lever. A lever is a device that lets you lift a large load by exerting a small amount of effort. In essence, a lever amplifies your effort. That's what a transistor does: It lets you use a small current to control a much larger current.

The basic idea behind a transistor is that it lets you control the flow of current through one channel by varying the intensity of a much smaller current that's flowing through a second channel.

As you can see, transistors come in a variety of different sizes and shapes. One thing all of these transistors have in common is that they each have three leads.

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Devices that performed the function of transistors had been around for 30–40 years prior to the invention of the transistor. They were called vacuum tubes. A vacuum tube consisted of a vacuum chamber made from glass or metal, a heating element that heated the space inside the chamber, and electrodes that protruded into the chamber.

One specific type of vacuum tube was called a triode; it had three electrodes. In a triode, a large current flowing through two of the electrodes (called the anode and the cathode) could be regulated by placing a wire grid (called the control grid) between the cathode and the anode. Applying a small current to this grid slowed down the flow of electrons between the cathode and the anode.

It didn't take long to figure out that you could use a fluctuating signal such as a radio or audio wave on the control grid. When you did that, the current on the anode followed the fluctuations of the control grid current, but with much larger variations. Thus, the triode was an electronic lever: Small variations in current at the control grid were amplified to create large variations in current at the anode.

The vacuum tube triode was patented in 1907 and was the key invention that enabled the development of radio, television, and computers. But vacuum tubes had many serious limitations: They were expensive to manufacture, big (the small ones were about the size of your thumb), required a lot of power to operate, generated a lot of heat, and lasted only a few years before they burned themselves out.

The transistor changed all that. A transistor performs the same function as a vacuum tube triode, but using semiconductor junctions instead of heated electrodes in a vacuum chamber.

Although the transistor didn't do anything that the vacuum tube triode didn't already do, it did it in a radically different way that had huge advantages over the vacuum tube. The earliest transistors were small, required very little power to operate, generated much less heat, and lasted much longer than vacuum tubes.

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