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Investigatory Project on Zener Diode as Voltage Regulator

Investigatory Project on Zener Diode as Voltage Regulator


Aim: To construct a voltage regulator using zener diode and to study its

(a) load variation and

(b) line variation

 

Materials and apparatus


(i) 6.2 V, 400 mW zener diode

(ii) Unregulated power supply of about 16 V

(iii) Resistors

(iv) 10 kΩ resistance box

(v) rheostat

(vi) Multimeter

(vii) Circuit board etc.


Principle


The zener diode is designed to operate in the reverse break down region and has a predetermined reverse break down voltage Vz. When connected in reverse bias in series with a current limiting resistor, the voltage across the zener diode remains constant as long as a certain minimum current flows through it. The zener diode thus acts as a simple voltage regulator.

 

Procedure


The circuit is wired up as shown in the figure. The unregulated voltage is connected through a potential divider arrangement using the rheostat. The resistance box is connected as load across the zener diode and the regulated voltage across it is measured using the multimeter.

Components: Zener diode: 6.2 V, 400 mW

Resistor R : 270 Ω, 1 W

 

(a) To study the load variation


The unregulated power supply is switched on and the potential divider is adjusted for maximum unregulated voltage. The no load voltage VNL for RL = ∞ is measured. The resistance in the box is decreased in steps, noting the voltage V, across it each time. The observations are continued till the voltage V0 begins to drop. The resistance values and the corresponding voltages are tabulated. The voltage for RL = 200Ω is treated as the full load voltage VFL and the percentage voltage regulation is calculated as,


VR%(for RL = 200Ω) = (VNL – VFL)/VFL x 100


A graph is plotted with RL along X-axis and V0 along Y-axis to show the load variation.

 

(b) To study the line variation


A resistance of 1000Ω is introduced in the resistance box. The regulated voltage V0 and the unregulated voltage input Vi are measured. Using the rheostat the unregulated voltage is decreased in steps, noting unregulated input voltage Vi and the regulated voltage V0 each time. The readings are tabulated. A graph is plotted with Vi along X-axis and V0 along Y-axis to show the line variation.

 

Observation


(a) Load regulation

Unregulated voltage = Vi = …..V

Sl No:

Load resistance RL(Ω)

Regulated voltage V0 (V)

1

2

3

.

.

.

.

.

10000

5000

.

.

500

400

.

 

Regulated voltage at no load (RL = ∞) = VNL = ….V

Voltage at full load (RL = 200Ω) = VFL = … V

Voltage regulation (for RL =… Ω), VR = (VNL - VFL)/VFL = …

 

(b) Line regulation


Load resistance RL = …Ω

Sl No:

Unregulated Input Voltage Vi (V)

Regulated Output voltage V0 (V)

1

2

3

.

.

.

 

 

Result


(i) A voltage regulator using zener diode is constructed and its load and line variations studied.

(ii) Percentage voltage regulation (for RL = …Ω) = ….

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