Transistors

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Construction Mechanic Basic Volume 2

Electric Measurements

Transistors
A transistor (fig. 1-10) is an electrical device that is used in circuits to control the flow of current. It operates by either allowing current to flow or not allowing it to flow. Transistors operate electronically and have no moving parts to perform their function. This design allows for a longer operating life of the component. The major automotive applications of transistors are for electronic ignition systems and voltage regulators.

The PNP transistor (fig. 1-11) is the most common design in automotive applications. It is manufactured by sandwiching an N-type semiconductor element between two P-type semiconductor elements. A positive charge is applied to one of the P-type elements. This element is called the emitter. The other P-type element connects to the electrical component. This element is called the collector. The third element, which is in the middle, is made of N-type material and is called the base. The application of low current negative charge to the base will allow a heavy current to flow between the emitter and the collector. Whenever the current to the base is switched off, the current flow from the emitter to the collector is interrupted also.

The NPN transistor (fig. 1-11) is similar to the PNP transistor. The difference is that it is used in the negative side of the circuit. As the term NPN implies,

Figure 1-9.- Zener diode operation.

Figure 1-10.- Transistor configurations.

Figure 1-11.- Transistor operation. the makeup of this transistor is two elements of N-type material (collector and emitter) with an element of P-type material (base) sandwiched in between. The NPN transistor will allow a high current negative charge to flow from the collector to the emitter whenever a relatively low current positive charge is applied to the base.