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 V_{z}. 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 V_{NL} for R_{L }= ∞ 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 V_{0} begins to drop. The resistance values and the corresponding voltages are tabulated. The voltage for R_{L} = 200Ω is treated as the full load voltage V_{FL} and the percentage voltage regulation is calculated as,
V_{R}%(for R_{L} = 200Ω) = (V_{NL} – V_{FL})/V_{FL} x 100
A graph is plotted with R_{L} along Xaxis and V_{0} along Yaxis to show the load variation.
(b) To study the line variation
A resistance of 1000Ω is introduced in the resistance box. The regulated voltage V_{0} and the unregulated voltage input V_{i} are measured. Using the rheostat the unregulated voltage is decreased in steps, noting unregulated input voltage V_{i} and the regulated voltage V_{0 }each time. The readings are tabulated. A graph is plotted with V_{i} along Xaxis and V_{0 }along Yaxis to show the line variation.
Observation
(a) Load regulation
Unregulated voltage = Vi = …..V
Sl No: 
Load resistance R_{L}(Ω) 
Regulated voltage V_{0} (V) 
1 2 3 . . . . . 
∞ 10000 5000 . . 500 400 . 

Regulated voltage at no load (R_{L} = ∞) = V_{NL} = ….V
Voltage at full load (R_{L} = 200Ω) = V_{FL} = … V
Voltage regulation (for R_{L} =… Ω), VR = (V_{NL}  V_{FL})/V_{FL} = …
(b) Line regulation
Load resistance R_{L }= …Ω
Sl No: 
Unregulated Input Voltage V_{i }(V) 
Regulated Output voltage V_{0} (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 R_{L} = …Ω) = ….
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