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DIODES

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In this chapter, the characteristics of diodes are presented. Diode circuit analysis techniques will be discussed. Problems involving diode circuits are solved using MATLAB. | Attia John Okyere. Diodes. Electronics and Circuit Analysis using MATLAB. Ed. John Okyere Attia Boca Raton CRC Press LLC 1999 1999 by CRC PRESS LLC CHAPTER NINE DIODES In this chapter the characteristics of diodes are presented. Diode circuit analysis techniques will be discussed. Problems involving diode circuits are solved using MATLAB. 9.1 DIODE CHARACTERISTICS Diode is a two-terminal device. The electronic symbol of a diode is shown in Figure 9.1 a . Ideally the diode conducts current in one direction. The current versus voltage characteristics of an ideal diode are shown in Figure 9.1 b . anode cathode -----o a V b Figure 9.1 Ideal Diode a Electronic Symbol b I-V Characteristics The I-V characteristic of a semiconductor junction diode is shown in Figure 9.2. The characteristic is divided into three regions forward-biased reversed-biased and the breakdown. 1999 CRC Press LLC In the forward-biased and reversed-biased regions the current i and the voltage V of a semiconductor diode are related by the diode equation i IS e v nVT - 1 9.1 where IS is reverse saturation current or leakage current n is an empirical constant between 1 and 2 VT is thermal voltage given by kT VT ----- 9.2 q and k is Boltzmann s constant 1.38x10 23 J oK q is the electronic charge 1.6x10 19 Coulombs T is the absolute temperature in oK At room temperature 25 oC the thermal voltage is about 25.7 mV. 1999 CRC Press .