MODULE: ELECTRICAL LAB
MODULE CODE:
TITLE OF EXPERIMENT: ZENER VOLTAGE REGULATOR CIRCUITS
Introduction to Electronics and Devices 1
Experiment 1: Zener voltage regulator circuits
OBJECTIVES
1. To investigate the I-V characteristics of zener diode
2. To investigate zener voltage regulator circuits.
EQUIPMENT:
Digital Multimeter (DMM)
DC Power Supply (Variable)
1 - 1KΩ ½ W Resistor
1 – Resistance decade box
1 - 5.1V Zener Diode
THEORY
A zener diode is a heavily doped semiconductor device that is design to operated in a reversed
bias states. A zener diode in forward bias functions similarly to a regular diode. While reversed
bias when breakdown voltage is reached the diode will cause a current to flow in the opposite
direction. The zener diode can act as a regulator when connected in parallel with a load as it
acts a shunt when it reaches its knee voltage cause the voltage across the load to become
constant
Section A: Zener Diode Characteristics
Figure 1
1. Measure and record the actual value of R1.
2. Construct the circuit shown in figure 1 without the variable resistor. Set the DC supply to
the values in table 1 and measure and record both voltage across the diode, VZ and the
resistor, R1.
3. Calculate IZ using the formula IZ =VR/R1 (measured) to complete the table.
Table 1
VDC (V) 0 1 2 3 4 5 6 7
VZ (V) 0.555 1.126 2.08 3.06 3.84 4.295 4.52 4.66
VR (V) 0 0 0 0.023 0.222 0.796 1.56 2.49
IZ (mA) 0 0 0 0.023 0.222 0.796 1.56 2.49
8 9 10 11 12 13 14 15
4.75 4.81 4.86 4.90 4.93 4.96 4.98 5.003
3.37 4.28 5.225 6.23 7.18 8.18 9.15 10.08
3.37 4.28 5.225 6.23 7.18 8.18 9.15 10.08
4. The zener region is in the third quadrant of a complete diode characteristics curve.
Place a minus sign before both IZ and VZ . Using a suitable scale plot the curve of IZ versus
VZ Determine from the graph the zener voltage. How does the zener value determined from
the graph compare with the manufactured value?
Zener voltage=4.8
Section B: Zener Diode Regulator
1. Construct the circuit as shown in figure 1. With the power supply set at 10V set the
variable resistor to the load values, RL shown in table 2. Measure and record the
corresponding voltage across the variable resistor, VRL. (Note: Remove the variable resistor
from the circuit when measuring its value).
RL (KOhm) 0.1 0.2 0.5 2.0 5.0 7.0
VRL (V) 0.923 1.697 3.366 4.723 4.818 4.831
Table 2
Questions
1. Why was the output voltage, VL much less than the zener voltage in some of the
values?
The zener keeps the voltage low by shunting the current
2. Calculate the minimum load that would maintain the zener voltage?
10 − 𝐼𝑅 − 𝑉𝑧 = 0
𝐼𝑅 = 10 − 5. 1
𝐼𝑅 = 4. 9𝑉
𝐼 = 4. 9𝑉/1𝐾
𝐼 = 4. 9𝑚𝐴
𝐼𝑅𝐿 + 𝐼𝑧 = 4. 9𝑚𝐴
𝐼𝑅𝐿𝑚𝑎𝑥 = 4. 8𝑚𝐴
𝑀𝑖𝑛𝑖𝑚𝑢𝑚 𝐿𝑜𝑎𝑑 𝑅𝑒𝑠𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑤ℎ𝑖𝑐ℎ 𝑐𝑎𝑛 𝑏𝑒 𝑢𝑠𝑒𝑑 = 𝑉𝑅𝐿/𝐼𝑅𝐿𝑚𝑎𝑥
= 𝑉𝑧/𝐼𝑅𝐿𝑚𝑎𝑥 = 5. 1/0. 0048
= 1062. 5 𝑜ℎ𝑚
3. What would be the maximum output of the circuit in figure 1, if another diode, of exactly
the same characteristics, was placed in series in the same direction with the one already in
the circuit?
The output will remain the same
Show all calculations.
Discussion
In the first part of the experiment the circuit was connected without the variable resistor. The
voltage across the zener diode and the voltage across the 1Kohm resistor were both measured
as the supply voltage was increased from 0V to 15V in increments of 1V. Using the values for
the zener voltage Vz and the resistor Vr the current for the zener diode Iz could be calculated.
With the given values of Vz and Iz an I-V characteristic curve for the zener diode could be
plotted. From this curve the zener voltage was determined to be 4.8 which is less than the
factory value. The curve obtained aligns with the outcome of the first part of the experiment.
There is a small leakage current in the beginning but as the voltages
increases towards the value of the zener voltage the current begins to spike until both the
current and the voltage no longer increase beyond a certain value. No matter what how much
the supply voltage is increased the zener voltage does not increase beyond a certain point. At
this point the diode is operating in its normal operating region or zener region. In the second
part of the experiment the variable resistor was connected as shown in the diagram. This zener
voltage regulator circuit now consists of a current limiting resistor in series with a zener diode
now in parallel with a variable resistor. When the output voltage stabilized it remain the close if
not the same as the zener diode
Conclusion
The I-V characteristics of the zener diode were investigated
