Zener Diodes are a special kind of diodes used in various circuit applications. A Zener diode works like an ordinary diode for voltages below the Zener voltage (Vz). At voltages above the Zener voltage, the Zener diode will conduct in both forward and reverse directions. In forward conduction, the voltage across the diode is the same as an ordinary diode (about 0.7V), in reverse conduction, the voltage across the diode is the Zener voltage. The Zener voltage depends on the model of the Zener diode. For instance, a 3.6V Zener diode will have a voltage drop of 3.6V in reverse conduction. Zener diodes are always used in reverse bias. The Zener Voltage remains fairly constant despite variations in input voltage. This characteristic of the Zener Diode makes it a suitable choice for voltage regulation circuit applications. To avoid damage, always use a resistor in series with a Zener diode to limit the current through the Zener diode so as to limit power dissipation within the Zener diode.