How a Transistor Works

The Parts of a Transistor

A transistor is made of at least three external terminals on a piece of semiconducting material. The three terminals are labeled as the base (b), collector (c) and emitter (e). The most important part of a transistor is the semiconductor, which is generally made of materials, such as silicon. This semiconductor is the amplifier and rectifier for the system. During the construction of a transistor, certain impurities are placed in different parts of the semiconducting material. These impurities are either positively or negatively charged. The way they are placed in the semiconducting material determines the amplifying power of the transistor. The positive or negative impurities are generally placed in a way that creates junctions between the layers. In other words, no two positive impurities are placed next to each other. The arrangement of positive (p) impurities and negative (n) impurities can follow different arrangements to create junctions. Some sample arrangements are n-p-n and p-n-p. The junction between the negative and positive sections is called an n-p junction.

The Importance of the N-P Junction in a Transistor

The junctions between n and p sections of the semiconductor are the amplifiers for the transistor. The n-p junction is a rectifier, meaning that current can flow only in one direction. For an explanation of a transistor's function, the p-n-p type works well as an example. In a p-n-p transistor, there is a small layer of n material between two layers of p material. This means that the emitter terminal is connected to the p, the base is connected to the n and the collector is connected to the other p. It is very important that in all three terminal transistors, the base is connected to the opposite type of semiconducting material than the collector or emitter. The emitter, connected to the p, has a slightly negative voltage relative to the base terminal, which has a slightly positive voltage. The collector, connected to the other p, also has a positive voltage. Electricity flows from the emitter to the base due to their difference in voltage. The flow of current between the emitter and the base flows easily because there is very little resistance. The collector, which is connected to an output circuit, attracts the current flowing through the base because the collector is positive. The resistance between the base and collector is very high. This difference in the resistance between the base and emitter and the base and collector is the central reason a transistor is such a good amplifier of electricity. Because the resistance is low in the current flowing from the emitter to the base and the resistance is high in the current flowing from the base to the collector, a very small change in voltage from the emitter to the base will be magnified between the base and the collector. Hence, this transistor can adequately amplify electricity running through it. This process may seem complex, but it can easily be analogized to a water pump. If you think of the electricity as a flow of water, it is flowing from the emitter to the base to the collector. When it flows from the base to the collector, it is flowing through a smaller space, making its pressure build. This is a loose analogy, but it basically describes how a transistor transforms a small amount of electricity into a lot of electricity.

Uses of Transistors

Transistors can be used in many appliances, including radios, televisions and computer-guided missile systems. In these devices, transistors allow a small voltage to be put through the base and emit a much higher voltage out of the output wire. As a note, almost all modern electronics utilize an integrated circuit instead of a transistor. This is because the integrated circuit is much smaller and more efficient than a transistor.