The Zener Diode

Chapter 9.13 The Zener Diode

Fundamental Electrical and Electronic Principles Third Edition Book
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Fundamental Electrical and Electronic Principles Third Edition Book

  • 276Fundamental Electrical and Electronic Principles In Fig. 9.17 , VZ represents the zener breakdown voltage, and if it were an ideal device, this p.d. across it would remain constant, regardless of the value of current, IZ, fl owing through it. In practice the graph will have a fairly steep slope as shown. The inverse of the slope of the graph is defi ned as the diode slope resistance, rZ, as follows rVIZDZohm(9.1)with very little chance of collisions taking place. This type of breakdown is known as zener breakdown and such diodes are called zener diodes. 9.13 The Zener Diode The main feature of the zener diode is its ability to operate in the reverse breakdown mode without sustaining permanent damage. In addition, during manufacture, the precise breakdown voltage (zener voltage) for a given diode can be predetermined. For this reason they are also known as voltage reference diodes. The major application for these devices is to limit or stabilise a voltage between two points in a circuit. Diodes are available with zener voltages from 2.6 V to about 200 V. The circuit symbol for a zener diode is shown in Fig. 9.16 . or Fig. 9.16 The forward characteristic for a zener diode will be the same as for any other p-n junction diode, and also, since the device is always used in its reverse bias mode, only its reverse characteristic need be considered. Such a characteristic is shown in Fig. 9.17 . VD (V)IZ (min)IZ (mA)VZOidealactual Fig. 9.17