Electronics I - Laboratory 3 Rev B
Zener Diodes
I. Objectives
1. Develop the I/V Characteristics of A Zener Diode.
2. Build and evaluate a simple Zener diode voltage regulator.
II. Pre-Lab Requirements
1. Zener Diode
When a diode is subjected to reverse biasing it will not conduct except for a very small
“leakage” current (in the µA range); however, if the voltage applied to the diode in the
reverse bias direction is increase sufficiently, the diode will breakdown and “avalanche”
current will flow. In this avalanche region, current will flow easily and therefore large
currents will flow with little effect on voltage dropped across the diode. The voltage
where avalanche occurs is called the Zener voltage. The value of the Zener voltage is set
in the diode manufacturing process and Zener Diodes can be purchased with Zener
voltage values from 2V to 200 V.
A device that shows little change in voltage drop across it with significant changes in
current through it is often ideal for implementations requiring voltage regulation.
Figure 1. Zener Diode I/V Characteristics
A. Zener Diode Operation
When using a Zener diode in a circuit design, primarily voltage control or regulation
functions, the Zener diode must be operated in the Avalanche region. This requires
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use of a series resistor to ensure that the current through the diode exceeds the
Avalanche threshold but at the same time does not exceed the rated power of the
Zener diode (PR = IDZ * VDZ). The voltage regulator that you will construct in lab
will be configured as in Figure 2.
Figure 2. Zener Voltage Regulator
The methodology for operating the Zener diode in the avalanche region is to set RS at
a value where, with the load removed (so all the current I flows through the diode),
the current flowing through D1 times the voltage dropped across D1 (which is fairly
constant and near the Zener voltage) does not exceed the Zener’ rated voltage.
With addition of a load RL, some of the current I, will be diverted through RL in
accordance with Kirchhoff’s current law and the current division equation. Therefore,
with a load in the circuit, power consumed by D1 will decrease from the unloaded
condition which was selected to preclude exceeding the rated power of the Zener
diode. If however, the value of RL is decreased to a value where the current diverted
through it causes the Zener diode current to drop below the required value for
maintaining avalanche region operation, the Zener diode will cease to perform as a
regulator.
a. III. Laboratory Requirements
1. Required Parts and Equipment
A.
B.
C.
D.
E.
DC power supply
One bench DMM
2 - Fluke hand-held DMMs
1 - Proto-Board (PB-103)
1 – 1N4729 Zener diode
#
2
1
1
Value
1200
680
300
F. Wires and leads for circuit connections.
2. Required Information
A. Diode Pin Out Orientation
The black circumferential band on the diode denotes its negative pin.
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B. Diode Data Sheets
The following is a link to the specification sheet for the 1N4729A:
http://www.fairchildsemi.com/ds/1N/1N4729A.pdf
3. Laboratory Procedure
A. Measuring a Zener Diode I/V Characteristics
In Experiment 1, a 1N4729A Zener diode will be tested to produce voltage and
current data that will be used to plot the I/V characteristic curve of the diode. To
produce the data, a test circuit will be constructed using the PB-103 Proto-Board.
The test circuit will be powered by a DC power supply. Test equipment (TE)
consisting of DMMs will be used to measure the following parameters:
Circuit input voltage (Vin)

Voltage drop across the diode (Vd)

Current through the diode (Id).

Experiment 1 – Measuring the I/V Characteristics of a Zener Diode.
1. Construct the circuit shown in Figure 3. Utilize the Keithley DMM to measure the
current flowing through the diode (ID), a Fluke DMM to measure the voltage drop
across the diode (VD), and a Fluke DMM to measure the voltage input (V1) to the
circuit. Take data that shows the avalanche region, region of leakage current flow
(both forward and reverse biased) and the forward biased conduction region. Be
sure to monitor diode voltage and current so as not to exceed its rate power.
Figure 3. Zener Diode I/V Test Circuit
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B. Zener Voltage Regulator
In Experiment 2, a simple Zener voltage rectifier will be constructed using a
1N4729A diode. Two load resistors will be place at the output, one resistor with a
low resistance and another with a high resistance to verify the voltage regulation
capabilities of the circuit.
Experiment 2 – Zener Voltage Regulator
1. Construct the circuit shown in Figure 4. Select a value for RS to allow the
Zener diode to operate in the avalanche region and within its rated power
requirement. Evaluate the regulator’ performance with a 50 Ω resistor and
also with a 10K Ω resistor. Make the following measurements for each load:
 Input voltage
 Output voltage (VRL)
 Zener diode current
 Load current
Figure 6. Half-Wave Rectifier
4. Data Reduction and Lab Report
This Lab submittal will be an informal report. Your report should be in Word with
graphics pasted in.
The items listed below are the minimum that should be included in your report.
A. Experiment 1 Data: Measuring the I/V Characteristics of a Zener Diode
1. A schematic of your test circuit.
2. A table showing the measured values Vin, Vd, Id, and computed power being
dissipated by the diode (Wd).
3. An Excel scatter graph of your I/V data. Use smooth lines and size 3 markers.
Make sure all graph axes are labeled properly and the graph has a proper title.
4. Answers to the following questions:
a. Why are 4 parallel resistors used for the current limiting resistor?
b. At approximately what voltage does the diode begin to conduct any
appreciable current (≈1mA) when forward biased?
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c. What is the value of the reverse bias leakage current?
d. From the diode specification sheet what is the Zener current (IZ)?
e. From your measurements what is the Zener voltage?
B. Experiment 2 Data: Zener Voltage Regulator
1. A schematic of your circuit.
2. Computations used for determining RS
3. A table showing the measured values of RL, Vin, VRL, Id, and computed power
being dissipated by the diode (Wd).
4. From your data points, what is the change in output voltage as related to change
in load resistance?
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