EE375 Electronics 1: lab 1

CTU: EE 375 – Electronics 1: Lab 1: Regulated DC Power Supply 1

Colorado Technical University
EE 375 – Electronics 1
Lab 1: Regulated DC Power Supply
February 2010
L. Schwappach and C. Fresh

ABSTRACT: This lab report was completed as a course requirement to obtain full course credit in EE375, Electronics 1 at
Colorado Technical University. This lab report investigates the design and implementation of a DC Power Supply. Hand calculations
are developed using the properties of Diodes and then verified using P-Spice schematic calculations to determine the viability of design
prior to a physical build of the design. P-Spice simulation results and hand calculations are then verified by physically modeling the
design on a bread board and taking measurements for observation. The results are then verified by the course instructor. The results
of this Lab illustrate the performance of a DC power supply built using discrete diodes as a bridge rectifier, a filter capacitor, and
finally a 10V Zener diode used as an output shunt voltage regulator.

If you have any questions or concerns in regards to this laboratory assignment, this laboratory report, the process used in
designing the indicated circuitry, or the final conclusions and recommendations derived, please send an email to
LSchwappach@yahoo.com or Cfresh24@comcast.net. All computer drawn figures and pictures used in this report are of original and
authentic content. The authors authorize the use of any and all content included in this report for academic use.

zone acts as an insulator, preventing any significant electric
current flow. However, if the polarity of the external voltage
I. INTRODUCTION opposes the built-in potential, recombination can once again
proceed, resulting in substantial electric current through the p-
DC power supplies are necessary to run many
of today’s appliances. Diodes are important n junction.
For silicon diodes, the built-in potential is
basic components of these power supplies, both for
rectification in the original AC power supply and in regulation approximately 0.6 to 0.7 V. Thus, if an external current is
of the output voltage. This lab assignment uses a simple AC passed through the diode, about 0.6 to 0.7 V will be developed
transformer; a bridge rectifier, a filter capacitor, and finally a across the diode and the diode is said to be “turned on” as it
Zener diode to build a regulated DC power supply. has a forward bias. In this lab the forward bias diode potential
is approximately 0.7V.
II. OBJECTIVES The I-V characteristic of an ideal diode is:
The objective of this lab is to study the design and
performance of this simple DC power supply at each stage. Where I is the diode current, Is is the reverse bias saturation
First the design is built with discrete diodes and integrated current, VD is the voltage across the diode, VT is the thermal
bridge rectifier. Next, a RC filter (with a ripple less than 10% voltage (Approximately 25.85 mV at 300K), and n is the
of Vm) is added to the design and output ripple measurements emission coefficient, also known as the ideality factor.
are taken. Finally, a Zener Diode and resister are added and Zener Diodes are diodes that can be made to conduct
the output shunt voltage performance is measured. backwards. This effect, called breakdown, occurs at a
precisely defined voltage, allowing the diode to be used as a
precision voltage reference or output shunt voltage regulator
III. DIODE THEORY as which is demonstrated by this lab.
Some of the equations needed to perform circuit
A diode is a two-terminal electronic component that calculations used when including Zener diodes are:
conducts electric current in only one direction. This
unidirectional behavior is called rectification, and is used to
convert alternating current to direct current, and remove
modulation from radio signals in radio receivers. Special
types of Diodes are used to regulate voltage (Zener diodes),
electronically tune radio and TV receivers (varactor diodes),
generate radio frequency oscillations (tunnel diodes), and
produce light (light emitting diodes).
Today most diodes are made of silicon, but other
semiconductors such as germanium are sometimes used.
If an external voltage is placed across the diode with
the same polarity as the built-in potential, the diodes depletion


V. HAND CALCULATIONS
A diode bridge is an arrangement of four diodes in a The following hand calculations below build a DC
bridge configuration (see PSpice diagram for an illustration) power supply into three phases. In phase 1 the circuit is
that provides the same polarity of output for either polarity of constructed using the transformer, a bridge rectifier and a load
input. The most common application of a diode bridge is used resister. In the second phase the Circuit is expanded to
for conversion of an alternating current input into direct include a filter capacitor which drastically lowers the “ripple”
current a direct current output. This configuration is known as of the bridge rectifier. In the final phase a Zener diode is
a bridge rectifier. added to the design demonstrating the voltage shunting ability
For many applications, especially with single phase of the Zener in limiting the output voltage so long as the Zener
AC where the full-wave bridge serves to convert an AC input diodes power rating is not exceeded. The hand calculations
into a DC output, the addition of a capacitor (this labs filter below illustrate each stage.
capacitor) may be desired because the bridge alone supplies an
output of fixed polarity but continuously varying or
"pulsating" magnitude, an attribute commonly referred to as
"ripple". This filter capacitor lessons the variation, or
smooth’s the rectified AC output from the bridge.
The equation needed to calculate the ripple voltage
after including the capacitor in the lab design is:

A rectifier is an electrical device that converts
alternating current to direct current, a process known as
rectification. A full-wave rectifier converts the whole of the
input waveform to one of constant polarity (positive or
negative) at its output. Full-wave rectification is achieved
using four diodes in a configuration known as a bridge and
converts both polarities of the input waveform to a single
polarity direct current. Figure 1: Hand Calculations for Part 1 (Design using
transformer and bridge rectifier). See attachments section
for full size image.
IV. DESIGN APPROACHES/TRADE-OFFS
This lab was built upon three design approaches.
First the lab approached the design using only the transformer
and four diodes as a bridge rectifier and a single resister to
provide a load. Although the trade-offs in this design allowed
for rectification of the AC signal to a DC signal, there was no
signal smoothing nor could the output be shunted to a specific
constant voltage. This made the design impractical for use as
a steady DC power supply.
The second lab design included the previous design
with a capacitor to filter out the pulsating ripple of after the
bridge rectifier. The trade-offs in this design allowed for a
smoother output with the additional cost of a capacitor as the
only drawback.
The third lab design included the previous designs
with an added resistor and Zener diode which acted as an
output shunt voltage regulator, limiting the direct current
voltage to a constant linear voltage. The advantage to this
design is a constant direct current output which is essential to
today’s electronics with only the cost of an extra diode and
small resistor.


VI. CIRCUIT SCHEMATICS
The circuit schematics below were built in PSpice
and allowed our team to analyze the circuit digitally before
performing the physical build.

Figure 4: PSpice Schematic of Design 1 (Part 1). See
attachments section for full size image.

Figure 2: Hand Calculations for Part 2 (Design using Part
1 Design with addition of filter capacitor). See
attachments section for full size image.

Figure 5: PSpice Schematic of Design 2 (Part 2), RL=1k.
See attachments section for full size image.

Figure 6: PSpice Schematic of Design 2 (Part 2) RL=10k.

Figure 3: Hand Calculations for Part 3 (Design using Part
2 Design with addition of Zener Diode). See attachments
section for full size image.

Figure 7: PSpice Schematic of Design 2 (Part 2) RL=100.


capacitance.
 A oscilloscope for viewing the input and output
waveforms of the circuit.
 A power supply/transformer capable of converting
a 110(rms)V @ 60Hz to 12.6(rms)V.
 A 423.75Ω(220+220) resistor for Ri, and 200Ω
(200.2), and 1kΩ (1.05k), 10kΩ (9.98k),
150kΩ(149.5k) resistors for testing RL.
 A 83.33µF (100)
 Bread board with wires.
Figure 8: PSpice Schematic of Design 3 (Part 3) RL=1k.  NOTE: Resistors can normally provide around +/-
See attachments section for full size image. 5%-25% difference between actual and designed
values while Capacitors generally provide around
20%-50% difference between actual and designed
values. You can add resisters in series as (R1+R2)
to closer approximate required resistance values
and you can add Capacitors in parallel as (C1+C2)
to closely approximate required capacitance.

VIII. PSPICE SIMULATION RESULTS

Figure 9: PSpice Schematic of Design 3 (Part 3) RL=10k.

Figure 12: PSpice Simulation Results of Design 1 (Part 1)
Figure 10: PSpice Schematic of Design 3 (Part 3) RL=1k and 10k. See attachments section for full size
RL=150k. See attachments section for full size image. image.

Figure 11: PSpice Schematic of Design 3 (Part 3) RL=200.

VII. COMPONENT LIST
The following is a list of components that were used in
building the final DC power supply. (The actual values our Figure 13: PSpice Simulation Results of
group used in the build are in parenthesis). Design 2 (Part 2) RL=1k. See attachments
 A digital multimeter for measuring circuit section for full size image.
voltages, resistor resistances, and capacitor


Figure 14: PSpice Simulation Results of Figure 17: PSpice Simulation Results of
Design 2 (Part 2) RL=10k. See attachments Design 3 (Part 3) RL=10k. See attachments
section for full size image. section for full size image.

Figure 15: PSpice Simulation Results of
Design 2 (Part 2) RL=100. See attachments Figure 18: PSpice Simulation Results of
section for full size image. Design 3 (Part 3) RL=150k. See attachments

Figure 16: PSpice Simulation Results of
Design 3 (Part 3) RL=1k. See attachments
section for full size image. Figure 19: PSpice Simulation Results of
Design 3 (Part 3) RL=200. See attachments


IX. EXPERIMENTAL DATA produced a greater “ripple” than was allowed by the initial
design constraints. However we also observed that the higher
The following table illustrates the measurements the value of RL the less “ripple” observed.
taken at each stage of the lab. Stage 3:
After adding the Zener diode the ripple in our filter
rectifier remained constant regardless of whether we used a
STAGE 1: Bridge (10k, or 1k resistor). This is most likely due to the voltage
Rectifier limiting characteristics of the Zener diode. The V ripple was
RL (Actual) VL (Actual) exactly the same “ripple” we achieved from the previous
design.
10k (9.98k) 0V to 16.419V After adding the Zener diode, RL produced a
1k (1.05k) 0V to 16.419V constant voltage of approximately 10V. This was true for the
1k, 10k, and 150k resistors. However the 200 ohm resistor
100 (99.2) 0V to 16.419V pushed the Zener diode outside of its Power limitation of .5W
Table 1: Stage 1: circuit measurements (Rectifier without producing unstable results at 4.97V. Again all measurements
Filter Capacitor) observed were within 10% of Hand and PSpice calculated
results.
STAGE 2: Includes XI. CONCLUSIONS
Filter Capaciter
This lab was effective in demonstrating the AC to DC
RL (Actual) VL (Actual) rectification capabilities produced by using a bridge rectifier
10k (9.98k) .2V and the power of diodes in restricting current in one direction.
Through adding the filter capacitor in phase 2 our team
1k (1.05k) 2.2V observed the how the “ripple” could be smoothed and reduced
Table 2: Stage 2: circuit measurements (Rectifier with to exact specifications. Finally in phase 3 after designing the
Filter Capacitor) Zener Diode we observed the voltage shunting capabilities of
such a diode and observed the importance of choosing a value
STAGE 2: Includes of Ri that would allow for lower load impedances in your
Filter Capaciter design. This lab was incredibly effective in providing a visual
look at diodes and their usefulness in power supplies and
RL (Actual) VL (Actual) circuit design.
10k (9.98k) 9.99V
XII. ATTACHMENTS
1k (1.05k) 9.983V
All figures above follow.
150k (149.5) 10.004V
200 (200.2) 4.97
REFERENCES
Table 3: Stage 3: circuit measurements (with Stage 2 and
[1] D. A. Neamen, “Microelectronics: circuit analysis and design - 3rd ed.”
added Zener diode.) McGraw-Hill, New York, NY, 2007. pp. 1-107.

X. ANALYSIS
Stage 1:
In design 1 the bridge rectifier efficiently produced
an expected DC voltage, however the was a tremendous
“ripple” that would not have been good for using the Power
supply as a stable power supply.
Stage 2:
After adding the filter capacitor the output ripple
closely approximated hand and PSpice calculations within
10%.
The output ripple was also smoothed and greatly
reduced by the capacitor producing a more stable DC output.
Our physical calculations, hand and PSpice calculations again
were within 10% proving the validity of our design.
Since our filter capacitor was designed using a worst
case scenario of a 1k resister at RL, changing RL below 1k

EE375 Electronics 1: lab 1

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