CHAPTER 4 - SOLID-STATE DEVICES AND CIRCUITS

Since the invention of the transistor, solid-state devices have been developed and improved at an unbelievable rate. Great strides have been made in the manufacturing techniques, and there is no foreseeable limit to the future of these devices. Solid-state devices made from semiconductor materials offer compactness, efficiency, ruggedness, and versatility. Consequently, these devices have invaded virtually every field of science and industry.

As the applications of solid-state devices mount, the need for knowledge about these devices become increasingly important. You, as a Construction Electrician first class, will have to understand solid-state devices if you are to become proficient in the repair and maintenance of electronic equipment. In this chapter, we will define the common semiconductor components and describe some of their applications in field equipment. We will also discuss the use of electronic test equipment required to perform troubleshooting in the field.

This chapter will not, repeat, will not provide solid-state theory of semiconductor devices. The introduction to solid-state devices and power supplies is explained in the Navy Electricity and Electronics Training Series (NEETS), Module 7, NAVEDTRA 172-07-00-82. It is highly recommended that you complete Module 7 before starting this chapter.

SEMICONDUCTOR DEVICES AND SYMBOLS

There are many different types of semiconductors. The specific devices commonly used are rectifier diodes, zener diodes, silicon controlled rectifiers (SCRs), transistors, unijunction transistors (UJTs), and integrated circuits (ICs).

To clarify the purpose of each of these devices in the circuit, we will describe each of these devices and its function.

RECTIFIER DIODE

The rectifier is a device that will allow current to flow through it in only one direction. Its purpose is to convert alternating current (ac) to direct current (dc), and it is used extensively in battery chargers, fire alarm systems, and voltage regulators. The schematic symbol and physical package are shown in figure 4-1. The current flows from the bottom (cathode) of the rectifier to the top (anode). This is known as a forward polarity rectifier. Other rectifiers are manufactured with

Figure 4-1.\Rectifier diode.

Figure 4-2.\Rectifier diode polarity.

reverse polarity (fig. 4-2), and the flow of current is then in the opposite direction (top [cathode] to bottom [anode]). This type of reverse polarity rectifier is easily identified by the letter R stamped on the case or by the arrow pointed in the opposite direction on the case. Whenever it is necessary to change a rectifier, it is important to observe these polarity marks to ensure that the rectifier used as a replacement has exactly the same polarity with the arrow pointed in the same direction.