A Zener diode is a component that takes an unregulated DC voltage source to produce a regulated output. A series resistor “Rs” is typically required to produce a voltage drop and the absence of this resistor would result in damage to the diode.
In this circuit diagram, the unregulated input voltage is Vs, and the regulated output voltage is “Vz” produced across the diode. The series resistor “Rs” provides a voltage drop and its value calculated from the formula shown. Due to the simplicity of the circuit, it is a cost-effective way to produce a reference voltage.
These diodes operate in reverse conduction due to the Zener effect, described by the breakdown region in the diode characteristics curve.
It is able to regulate the voltage across it by passing a limited amount of current through it in reverse conduction. It is a very simple and interesting phenomenon worth reading about.
The reverse voltage “Vz”, and the reverse current “Iz” are the main parameters to consider when choosing a suitable diode for regulation purposes. These parameters are also called “Zener current”, and “Zener voltage” in literature.
Resistor Calculator Formula
To calculate the value of the series resistor, you only need Vz and Iz, found from the table below, and the input voltage Vs, which you would know.
Therefore, as you can see, this article makes it far easier to calculate the resistance value using commonly available parameters.
Choosing Vz, and Iz
The reverse conduction voltage -- engineered to occur at desired values -- enables this type of diode to regulate at specific voltages.
The chart below shows a typical range of reverse conduction voltages Vz and their associated reverse currents Iz expected from a common garden-variety BZXC family of diodes.
|Vz (V)||Iz (mA)|