Zener Diode
A Zener diode generally behaves very similarly to a signal or rectifier diode, except that its breakdown voltage is lower.
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| Figure 26-7. 1N4740 Zener diode. |
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| zener diode symbol |
The Zener is intended to be reverse-biased; that is, conventional current is applied through it “in the wrong direction” compared with conventional diodes. As the current increases, the dynamic resistance of the Zener diode decreases. This relationship is shown in Figure 26-6, where the two colored curves represent the performance of different possible Zener diodes. (The curves are adapted from a manufacturer’s data sheet.) This behavior allows the Zener to be used in simple voltage-regulator circuits, as it can allow a reverse current to flow at a voltage limited by the diode’s breakdown voltage. Other applications for Zener diodes are described in “DC Voltage Regulation and Noise Suppression” (page 230). A typical Zener diode is shown in Figure 26-7.
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| Figure 26-7. Zener diode graph |
