Lessons In Electric Circuits Volume III – Semiconductors Book

Chapter 3.1 Introduction

Lessons In Electric Circuits Volume III – Semiconductors Book
Pages 528
Views 6,133
Downloads : 9 times
PDF Size : 3.5 MiB

Summary of Contents

Lessons In Electric Circuits Volume III – Semiconductors Book

  • 98CHAPTER 3. DIODES AND RECTIFIERS 172,3.13 172,Other 172,diode 172,technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163 172,3.13.1 172,SiC 172,diodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163 172,3.13.2 172,Polymer 172,diode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163 172,3.14 172,SPICE 172,models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163 181,Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1723.1IntroductionA diodeis an electrical device allowing current to move through it in one direction with fargreater ease than in the other. The most common kind of diode in modern circuit design isthe semiconductordiode, although other diode technologies exist. Semiconductor diodes aresymbolized in schematic diagrams such as Figure 107,3.1. The term “diode” is customarily reservedfor small signal devices, I ≤ 1 A. The term rectifieris used for power devices, I > 1 A.Figure 3.1:Semiconductor diode schematic symbol: Arrows indicate the direction of electroncurrent flow.When placed in a simple battery-lamp circuit, the diode will either allow or prevent currentthrough the lamp, depending on the polarity of the applied voltage. (Figure 107,3.2)+-+-(a)(b)Figure 3.2:Diode operation: (a) Current flow is permitted; the diode is forward biased. (b)Current flow is prohibited; the diode is reversed biased.When the polarity of the battery is such that electrons are allowed to flow through thediode, the diode is said to be forward-biased. Conversely, when the battery is “backward” andthe diode blocks current, the diode is said to be reverse-biased. A diode may be thought of aslike a switch: “closed” when forward-biased and “open” when reverse-biased.Oddly enough, the direction of the diode symbol’s “arrowhead” points againstthe directionof electron flow. This is because the diode symbol was invented by engineers, who predomi-nantly use conventional flownotation in their schematics, showing current as a flow of chargefrom the positive (+) side of the voltage source to the negative (-). This convention holds truefor all semiconductor symbols possessing “arrowheads:” the arrow points in the permitted di-rection of conventional flow, and against the permitted direction of electron flow.