Draw the V-I characteristics of Zener diode. With the help of V-I characteristics explain the working of Zener diode.
Q.) Draw the V-I characteristics of Zener diode. With the help of V-I characteristics explain the working of Zener diode.
Subject: electronic devices and circuitsThe V-I characteristics of a Zener diode can be drawn and understood in several steps. Below is a step-by-step approach to explain the working of a Zener diode using its V-I characteristics.
Step 1: Understanding the Zener Diode
A Zener diode is a special type of diode designed to reliably allow current to flow "backwards" when a certain set reverse voltage, known as the Zener voltage, is reached. Zener diodes are widely used for voltage regulation and protection circuits.
Step 2: Drawing the V-I Characteristics
The V-I characteristics of a Zener diode can be plotted on a graph where the x-axis represents the voltage across the diode (V) and the y-axis represents the current through the diode (I). The characteristics can be divided into two regions: the forward bias region and the reverse bias region.
Forward Bias Region
In the forward bias region, the Zener diode behaves like a normal diode. It has a forward voltage drop (usually around 0.7V for silicon diodes) after which the current starts to increase rapidly with a small increase in voltage.
Reverse Bias Region
The reverse bias region is where the Zener diode exhibits its unique behavior. When the reverse voltage is less than the Zener voltage (Vz), the current is very small and the diode is in the "off" state. As the reverse voltage reaches Vz, the current starts to increase significantly, but the voltage across the diode remains relatively constant, even with large changes in current. This is the Zener breakdown region and is the operating region for Zener diode voltage regulation applications.
Step 3: The V-I Characteristics Table
| Region | Voltage (V) | Current (I) | Behavior |
|---|---|---|---|
| Forward Bias | < 0.7V (approx for Si) | Low to moderate | Diode conducts after forward voltage drop |
| Reverse Bias (below Vz) | < Vz | Very low (leakage current) | Diode does not conduct |
| Zener Region (Vz) | ≈ Vz | Increases sharply | Diode conducts in reverse, voltage remains stable |
Step 4: Working of Zener Diode
When a Zener diode is reverse-biased and the voltage across it is less than the Zener voltage, it does not conduct significant current. However, once the voltage reaches the Zener voltage, the diode enters the breakdown region and starts conducting in the reverse direction. The Zener diode is designed such that it can operate in this breakdown region without damage, which is not the case for ordinary diodes.
The ability of the Zener diode to maintain a constant voltage across it in the breakdown region is used for voltage regulation. If the supply voltage or the load changes, the Zener diode adjusts the current through it to maintain a constant output voltage.
Step 5: Example
Consider a Zener diode with a Zener voltage of 5.6V. If this diode is connected in reverse bias across a power supply that varies from 6V to 9V, and in series with a current-limiting resistor, the voltage across the Zener diode will remain close to 5.6V, regardless of the fluctuations in the power supply voltage.
Conclusion
The V-I characteristics of a Zener diode show that it behaves like a typical diode in the forward bias region, while in the reverse bias region, it exhibits a controlled breakdown at the Zener voltage, allowing it to maintain a constant voltage over a wide range of currents. This makes the Zener diode an essential component for voltage regulation and protection in electronic circuits.