EE375 Electronics 1: lab 1

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

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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

[email protected] or [email protected]. 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.

I. INTRODUCTION

power supplies are necessary to run many

of today’s appliances. Diodes are important

basic components of these power supplies, both for

rectification in the original AC power supply and in regulation

of the output voltage. This lab assignment uses a simple AC

transformer; a bridge rectifier, a filter capacitor, and finally a

Zener diode to build a regulated DC power supply.

II. OBJECTIVES

The objective of this lab is to study the design and

performance of this simple DC power supply at each stage.

First the design is built with discrete diodes and integrated

bridge rectifier. Next, a RC filter (with a ripple less than 10%

of Vm) is added to the design and output ripple measurements

are taken. Finally, a Zener Diode and resister are added and

the output shunt voltage performance is measured.

III. DIODE THEORY

A diode is a two-terminal electronic component that

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

zone acts as an insulator, preventing any significant electric

current flow. However, if the polarity of the external voltage

opposes the built-in potential, recombination can once again

proceed, resulting in substantial electric current through the p-

n junction.

For silicon diodes, the built-in potential is

approximately 0.6 to 0.7 V. Thus, if an external current is

passed through the diode, about 0.6 to 0.7 V will be developed

across the diode and the diode is said to be “turned on” as it

has a forward bias. In this lab the forward bias diode potential

is approximately 0.7V.

The I-V characteristic of an ideal diode is:

Where I is the diode current, Is is the reverse bias saturation

current, VD is the voltage across the diode, VT is the thermal

voltage (Approximately 25.85 mV at 300K), and n is the

emission coefficient, also known as the ideality factor.

Zener Diodes are diodes that can be made to conduct

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

as which is demonstrated by this lab.

Some of the equations needed to perform circuit

calculations used when including Zener diodes are:

DC

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A diode bridge is an arrangement of four diodes in a

bridge configuration (see PSpice diagram for an illustration)

that provides the same polarity of output for either polarity of

input. The most common application of a diode bridge is used

for conversion of an alternating current input into direct

current a direct current output. This configuration is known as

a bridge rectifier.

For many applications, especially with single phase

AC where the full-wave bridge serves to convert an AC input

into a DC output, the addition of a capacitor (this labs filter

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.

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.

V. HAND CALCULATIONS

The following hand calculations below build a DC

power supply into three phases. In phase 1 the circuit is

constructed using the transformer, a bridge rectifier and a load

resister. In the second phase the Circuit is expanded to

include a filter capacitor which drastically lowers the “ripple”

of the bridge rectifier. In the final phase a Zener diode is

added to the design demonstrating the voltage shunting ability

of the Zener in limiting the output voltage so long as the Zener

diodes power rating is not exceeded. The hand calculations

below illustrate each stage.

Figure 1: Hand Calculations for Part 1 (Design using

transformer and bridge rectifier). See attachments section

for full size image.


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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 3: Hand Calculations for Part 3 (Design using Part

2 Design with addition of Zener Diode). See attachments

section for full size image.

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



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Figure 10: PSpice Schematic of Design 3 (Part 3)

RL=150k. See attachments section for full size 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

group used in the build are in parenthesis).

A digital multimeter for measuring circuit

voltages, resistor resistances, and capacitor

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.

NOTE: Resistors can normally provide around +/-

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 12: PSpice Simulation Results of Design 1 (Part 1)

RL=1k and 10k. See attachments section for full size

image.

Figure 13: PSpice Simulation Results of

Design 2 (Part 2) RL=1k. See attachments



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Design 2 (Part 2) RL=100. See attachments












Design 3 (Part 3) RL=200. See attachments



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IX. EXPERIMENTAL DATA

The following table illustrates the measurements

taken at each stage of the lab.

STAGE 1: Bridge

Rectifier

RL (Actual) VL (Actual)

10k (9.98k) 0V to 16.419V

1k (1.05k) 0V to 16.419V

100 (99.2) 0V to 16.419V

Table 1: Stage 1: circuit measurements (Rectifier without

Filter Capacitor)

STAGE 2: Includes

Filter Capaciter


10k (9.98k) .2V

1k (1.05k) 2.2V

Table 2: Stage 2: circuit measurements (Rectifier with

Filter Capacitor)

STAGE 2: Includes

Filter Capaciter


10k (9.98k) 9.99V

1k (1.05k) 9.983V

150k (149.5) 10.004V

200 (200.2) 4.97

Table 3: Stage 3: circuit measurements (with Stage 2 and

added Zener diode.)

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

produced a greater “ripple” than was allowed by the initial

design constraints. However we also observed that the higher

the value of RL the less “ripple” observed.

Stage 3:

After adding the Zener diode the ripple in our filter

rectifier remained constant regardless of whether we used a

(10k, or 1k resistor). This is most likely due to the voltage

limiting characteristics of the Zener diode. The V ripple was

exactly the same “ripple” we achieved from the previous

design.

After adding the Zener diode, RL produced a

constant voltage of approximately 10V. This was true for the

1k, 10k, and 150k resistors. However the 200 ohm resistor

pushed the Zener diode outside of its Power limitation of .5W

producing unstable results at 4.97V. Again all measurements

observed were within 10% of Hand and PSpice calculated

results.

XI. CONCLUSIONS

This lab was effective in demonstrating the AC to DC

rectification capabilities produced by using a bridge rectifier

and the power of diodes in restricting current in one direction.

Through adding the filter capacitor in phase 2 our team

observed the how the “ripple” could be smoothed and reduced

to exact specifications. Finally in phase 3 after designing the

Zener Diode we observed the voltage shunting capabilities of

such a diode and observed the importance of choosing a value

of Ri that would allow for lower load impedances in your

design. This lab was incredibly effective in providing a visual

look at diodes and their usefulness in power supplies and

circuit design.

XII. ATTACHMENTS

All figures above follow.

REFERENCES

[1] D. A. Neamen, “Microelectronics: circuit analysis and design - 3rd ed.” McGraw-Hill, New York, NY, 2007. pp. 1-107.

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EE375 Electronics 1: lab 1