Zener diode:
A Zener diode sometimes called breakdown diode or stabilitrone,is designed to operate in the reverse breakdown, or Zener, region, beyond the peak inverse voltage rating of normal diodes. This reverse breakdown voltage is called the Zener or, reference voltage, which can range between –2,4 V and –200 V (Fig. 1.12). The Zener effect causes a “soft” breakdown whereas the avalanche effect causes asharper turnover. Both effects are used in the Zener diode. The manufacturer predetermines the Zener and avalanche voltages.
A significant parameter of the Zener diode is the temperature coefficient that is the breakdown voltage deviation during the temperature rise or fall. The temperature coefficient of the Zener diode changes from negative to positive near –6 V. Because of this, by selecting the current value the designer may minimize the instability of the device. In all types of devices, the output levels are affected by variations in the load. Lower percentage values, approaching 0%, indicate better regulation. The Zener diode is the backbone of voltage regulators, circuits that hold the load voltage constant despite the large changes in line voltage and load resistance. When used as a voltage regulator, the Zener diode is reverse biased so that it will operate in the breakdown region with highly stable Zener voltage. In this region, changes in current through the diode have no effect on the voltage across it. The Zener diode establishes a constant voltage across the load within a range of output voltages and currents. Out of this range, the voltage drop remains constant and the current flow through the diode will vary to compensate the changes in load resistance.A power Zener diode is called an avalanche diode.It can withstand kilovolts voltages and currents of some thousands of amperes.
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