- Zener Diode Definition: A Zener diode is defined as a diode that operates in reverse bias to regulate voltage.
- Reverse Biased Operation: Zener diodes work in reverse bias due to their narrow depletion region, which prevents damage.
- Breakdown Voltage: Zener diodes have a specific breakdown voltage where they maintain a constant voltage drop despite increased current.
- Voltage Regulation with Zener Diodes: Zener diodes are used as voltage regulators by maintaining a steady voltage across a load, even if input voltage fluctuates.
- Circuit Diagram Explanation: In a circuit, a Zener diode is connected in reverse bias parallel to the load, ensuring the voltage across the load does not exceed the breakdown voltage.
A Zener diode is defined as a specially designed diodes that works mainly in reverse bias conditions. These diodes are more heavily doped than ordinary ones, giving them a narrow depletion region. Unlike regular diodes that get damaged when the voltage exceeds the reverse breakdown voltage, Zener diodes function in this region. The depletion region in a Zener diode returns to normal when the reverse voltage is removed. This makes Zener diodes useful as voltage regulators.
Before understanding how a Zener diode acts as a voltage regulator, let’s first learn how it works.
When a reverse voltage is applied to a Zener diode, only a small current flows. However, if the voltage exceeds the Zener breakdown voltage, a significant current flows with minimal voltage drop. As the reverse voltage increases, the voltage across the diode stays constant at the breakdown voltage, but the current continues to rise. The breakdown voltage can range from 1.2V to 200V, depending on the application.
We can choose a Zener diode with a specific breakdown voltage to use it as a voltage regulator in our circuit. For instance, if we want the voltage across a load to stay below 12 volts, we can use a Zener diode with a 12-volt breakdown voltage. Even if the input voltage goes above 12 volts, the voltage across the load will not exceed this value.
Let us try to understand that with a circuit diagram
Here the Zener diode is connected across the load RL. We want the voltage across the load to be regulated and not cross the value of Vz. Depending on our requirement, we choose the suitable Zener diode with a Zener breakdown voltage near to the voltage we require across the load. We connect the Zener diode in reverse bias condition. When the voltage across the diode exceeds the Zener breakdown voltage, a significant amount of current starts flowing through the diode. As the load is in parallel to the diode, the voltage drop across the load is also equal to the Zener breakdown voltage. The Zener diode provides a path for the current to flow and hence the load gets protected from excessive currents. Thus the Zener diode serves two purposes here: Zener diode as a voltage regulator as well as it protects the load from excessive current.
