EXP-5

EXP. NO. 5. ZENER DIODE CHARACTERISTICS AND ZENER AS VOLTAGE REGULATOR

AIM . To find the Zener Break down voltage regulation condition.

APPARATUS:

S.No Name of the Apparatus Range Quantity 1 Zener Diode (IN 4735A) 1 2 Resistors 1KΩ, 10KΩ 1 3 Regulated Power Supply (0-30)V DC 1 4 Bread Board 1 5 Digital Ammeter (0-200)mA 1 6 Digital Voltmeter (0-20)V DC 1 7 Connecting Wires As Required

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 ever may be the current through it, i.e., it has very low dynamic resistance. It is used in voltage regulators.

PROCEDURE:

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 (lz), 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.

CIRCUIT DIAGRAM:

OBSERVATIONS:

REGULATION CHARACTERISTICS:

It is able to maintain a nearly constant voltage across itself once it enters the reverse breakdown region. This stable voltage, called the Zener voltage (Vz), is maintained even when the input voltage or load current fluctuates significantly, allowing it to be used as a voltage regulator.

V-I & REGULATION CHARACTERISTICS:

A Zener diode's V-I characteristics have two main regions: it acts like a normal diode in forward bias (conducts after a cut-in voltage) and in reverse bias, it blocks current until the Zener voltage (Vz) is reached. At (Vz), a reverse breakdown occurs, and the voltage across the diode becomes nearly constant even as the current increases sharply. This reverse breakdown region is the basis for its voltage regulation capability, as it maintains a stable output voltage across a wide range of current changes.

PRECAUTIONS:

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

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

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

RESULT: The Characteristics of Zener Break Diode Voltage Regulation from the Characteristics are Observed.