Zener diode characteristics and Zener as voltage regulator

Zener diode characteristics and Zener as voltage regulator

Aim

1. To observe and draw the V‒I characteristics and Regulation characteristics of a Zener diode.

2. To find the Zener break down voltage in reverse biased condition.

Apparatus

Circuit diagram

(i) V‒I Characteristics

(ii) Regulation characteristics

Theory

A zener diode is heavily doped p‒n junction diode, specially made to operate in the break down region. A p‒n junction diode normally does not conduct when reverse biased. But if the reverse bias is increased, at a particular voltage it starts conducting heavily. This voltage is called break down voltage. High current through the diode can permanently damage the device.

To avoid high current, we connect a resistor in series with zener diode. Once the diode starts conducting it maintains almost constant voltage across the terminals what every may be the current through it, i.e., it has very low dynamic resistance. It is used in voltage regulators.

Procedure

(i) V‒I Characteristics

1. Connections are made as per the circuit diagram.

2. The Regulated power supply voltage is increased in steps.

3. The zener current (I_Z), and the zener voltage (V_Z) are observed and then noted in the tabular form.

4. A graph is plotted between zener current (I_Z) on y‒axis and zener voltage (V_Z) on x-axis.

(ii) Regulation characteristics

1. Connections are made as per the circuit diagram.

2. The Regulated power supply voltage is increased in steps.

3. The voltage across the diode (Vz) remains almost constant although the current through the diode increases. This voltage serves as reference voltage.

4. The zener current (Iz), and the zener voltage (Vz) are observed and then noted in the tabular form.

5. A graph is plotted between zener current (Iz) on y‒axis and zener voltage (Vz) on x‒axis.

Observations

(i) V‒I Characteristics

(ii) Regulation characteristics

V‒I and Regulation Characteristics

Precautions

1. While doing the experiment do not exceed the ratings of the zener diode. This may lead to damage the diode.

2. Connecting voltmeter and Ammeter in correct polarities as shown in the circuit diagram.

3. D not switch ON the power supply unless you have checked the circuit connections as per the circuit diagram.