Explain the V-I characteristics of Zener diode and explain its working as a voltage regulator.

V-I Characteristics of Zener Diode:

A Zener diode is a heavily doped semiconductor diode that exhibits a sharp increase in reverse current at a specific voltage, known as the Zener voltage (Vz). This unique property allows it to regulate voltage in electronic circuits. The V-I characteristics of a Zener diode can be divided into three regions:

1. Forward Bias Region:

   • When the Zener diode is forward biased (positive voltage applied to the anode and negative voltage to the cathode), it behaves like a regular diode.
   • Current flows easily in the forward direction, and the voltage across the diode is typically around 0.7V for silicon Zener diodes.

2. Reverse Bias Region (Breakdown Region):

   • As the reverse bias voltage increases, the Zener diode initially acts as an open circuit, blocking current flow.
   • However, at a certain voltage, called the Zener breakdown voltage (Vz), the diode undergoes a sudden breakdown, and the reverse current starts to flow.
   • The Zener breakdown is a controlled avalanche breakdown, where a large number of free charge carriers are generated, allowing significant current flow.
   • In this region, the voltage across the diode remains relatively constant at Vz, even as the reverse current increases.

3. Post-Breakdown Region:

   • As the reverse bias voltage is further increased beyond the Zener breakdown voltage, the reverse current continues to increase rapidly.
   • The Zener diode operates in this region when used as a voltage regulator.

Working of Zener Diode as a Voltage Regulator:

A Zener diode is commonly used as a voltage regulator to maintain a constant output voltage across a load. Here's how it works:

1. Zener Breakdown:

   • The Zener diode is connected in parallel with the load across the power supply.
   • When the input voltage from the power supply exceeds the Zener breakdown voltage (Vz), the Zener diode starts conducting in the reverse direction.

2. Voltage Regulation:

   • As the input voltage increases, the reverse current through the Zener diode also increases.
   • However, the voltage across the diode remains relatively constant at Vz due to the Zener breakdown.
   • This constant voltage is then supplied to the load, effectively regulating the output voltage.

3. Current Limiting:

   • The Zener diode also acts as a current-limiting device.
   • If the load current exceeds the Zener diode's maximum current rating, the diode will dissipate excessive power and may get damaged.
   • To prevent this, a series resistor is often connected in series with the Zener diode to limit the current flow.

In summary, the Zener diode's unique V-I characteristics allow it to regulate voltage effectively. By operating in the Zener breakdown region, it maintains a constant voltage across the load, despite variations in the input voltage or load current.