4.2.3 The Zener Diode

Chapter 4.2.3 The Zener Diode

Physics Lecture Notes – Phys 395 Electronics Book
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Physics Lecture Notes – Phys 395 Electronics Book

  • CHAPTER 4. DIODE CIRCUITS68b)conductionregionnon−conductionregionIVIfa)Figure 4.4: a) Schematic symbol for a diode and b) current versus voltage for an ideal diode.approximations are referred to as the linear element model of a diode.idealdiodesIr-+IfVPNRrRfRrRfVPNFigure 4.5: Equivalent circuit model of a junction diode.4.2.3The Zener DiodeThere are several other types of diodes beside the junction diode. As the reverse voltageincreases the diode can avalanche-breakdown (zener breakdown). This causes an increasein current in the reverse direction. Zener breakdown occurs when the electric field near thejunction becomes large enough to excite valence electrons directly into the conduction band.Avalanche breakdown is when the minority carriers are accelerated in the electric field nearthe junction to sufficient energies that they can excite valence electrons through collisions.Figure 4.6 shows the current-voltage characteristic of a zener diode, its schematic symboland equivalent circuit model in the reverse-bias direction. The best zener diodes have abreakdown voltage (VZ)of6-7 V.4.2.4Light-Emitting DiodesLight-emitting diodes (LED) emit light in proportion to the forward current through thediode. LEDs are low voltage devices that have a longer life than incandescent lamps. They