Chapter 2: Diode Applications

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Chapter 2: Diode Applications

The construction, characteristics, and models of semiconductor diodes were introduced in Chapter 1. The primary goal of this chapter is to develop a working knowledge of the diode in a variety of configurations using models appropriate for the area of application. By chapter's end, the fundamental behavior pattern of diodes in dc and ac networks should be clearly understood. The concepts learned in this chapter will have significant carryover in the chapters to follow. For instance, diodes are frequently employed in the description of the basic construction of transistors and in the analysis of transistor networks in the dc and ac domains.



This chapter demonstrates an interesting and very useful aspect of the study of a field such as electronic devices and systems:

Once the basic behavior of a device is understood, its function and response in an infinite variety of configurations can be examined.

In other words, now that we have a basic knowledge of the characteristics of a diode along with its response to applied voltages and currents, we can use this knowledge to examine a wide variety of networks. There is no need to reexamine the response of the device for each application.
In general:

The analysis of electronic circuits can follow one of two paths: using the actual characteristics or applying an approximate model for the device.

For the diode the initial discussion will include the actual characteristics to clearly demonstrate how the characteristics of a device and the network parameters interact. Once there is confidence in the results obtained, the approximate piecewise model will be employed to verify the results found using the complete characteristics. It is important that the role and the response of various elements of an electronic system be understood without continually having to resort to lengthy mathematical procedures.

This is usually accomplished through the approximation process, which can develop into an art itself. Although the results obtained using the actual characteristics may be slightly different from those obtained using a series of approximations, keep in mind that the characteristics obtained from a specification sheet may be slightly different from those of the device in actual use. In other words, for example, the characteristics of a 1N4001 semiconductor diode may vary from one element to the next in the same lot. The variation may be slight, but it will often be sufficient to justify the approximations employed in the analysis. Also consider the other elements of the network: Is the resistor labeled 100 exactly 100 ? Is the applied voltage exactly 10 V or perhaps 10.08 V? All these tolerances contribute to the general belief that a response determined through an appropriate set of approximations can often be "as accurate" as one that employs the full characteristics. In this book the emphasis is toward developing a working knowledge of a device through the use of appropriate approximations, thereby avoiding an unnecessary level of mathematical complexity. Sufficient detail will normally be provided, however, to permit a detailed mathematical analysis if desired.