EE 3101 ELECTRONICS I LABORATORY

EXPERIMENT 2 LAB MANUAL

POWER SUPPLY DESIGN CONSIDERATIONS

OBJECTIVES
In this experiment you will
• Learn how resonant circuits can be used to make band-pass and band-reject filters.
• Gain experience in measuring the frequency response of a simple network.
• Become familiar with the laboratory layout and equipment.

LAB NOTEBOOKS
The format of lab notebooks should be such that the information can be used to reproduce the
lab, including what values were used in a circuit, why the values were used, how the values were
determined, and any results and observations made. This lab manual will be used as a guide for
what calculations need to be made, what values need to be recorded, and various other questions.
The lab notebook does not need to repeat everything from the manual verbatim, but it does need
to include enough information for a 3rd party to be able to use the notebook to obtain the same
observations and answers. In the following numbered sections there are bolded words and/or
lines. These bolded words and/or lines are statements and/or questions that the lab TA will be
looking for an answer either in the lab preliminary, or lab notebook.

INTRODUCTION
The lecture part of this class covers the most-commonly-used rectifier configurations. Figure 1
shows the half-wave rectifier with a capacitive filter section. Figure 2 shows the classical full-
wave filter, and Figure 3 shows the full-wave bridge rectifier. The question logically arises as to
which configuration is the best choice for a given application.

Figure 1: The Half-Wave Rectifier with Capacitive Filtering.

Figure 3: The Full-Wave Bridge rectifier with Capacitive Filtering.

Each configuration has the following advantages and disadvantages:

HALF-WAVE RECTIFIER
Advantages Disadvantages

Less complex – requires only one diode Only half of the input sine wave is utilized
– input power factor is poor
A transformer is not required For a given C, ripple voltage and peak
current will be large
The Peak Inverse Voltage rating must be
 CLASSICAL FULL-WAVE RECTIFIER
Advantages Disadvantages

Both half cycles are utilized - input power Two diodes are needed
factor is improved

For a given C, ripple voltage and peak A center-tapped transformer is needed

> 2Vp

FULL-WAVE BRIDGE RECTIFIER

A Peak Inverse Voltage rating of only > Vp Four diodes are needed
is needed

For a given C, ripple voltage and peak There are now two diode drops during each
diode current will be less than in the case half cycle
of the half-wave rectifier

Generally, you will use a half-wave rectifier only when the load current is very small, and the
filter capacitance can be very small. The classical full-wave rectifier would be selected when
power conversion efficiency is the highest priority and the voltage drop across each diode is
significant with respect to the output voltage. The bridge rectifier has an advantage at high
voltages since the Peak Inverse Voltage (PIV) rating only has to be half the rating of the other
configurations, and diode drops are also relatively insignificant.

Another type of rectifier/filter is the voltage doubler, shown in Figure 4. The circuit in
Figure 4(a) is called the full-wave doubler. The circuit in Figure 4(b) is called the half-wave
doubler. The full-wave doubler can be used to produce an output voltage of roughly 2Vp, or + Vp
(if point X is grounded). The half-wave doubler is used when one lead of output and input must
share a common ground. These circuits are used extensively in high-voltage applications such as
cathode-ray tube (CRT) power supplies, TV sets, Geiger counters, stun guns, and so forth. One
can extend this principle to design voltage multiplier circuits. For example, a voltage tripler is
shown in Figure 5.
 (a) (b)

Figure 4: Two Forms of the Voltage Doubler.

Figure 5: A Voltage Tripler.

Normally, power supply design begins with the output specifications and working back
towards the input side. One of the last components specified is the transformer. However, if only
one or just a few power supplies are to be built, it may be more-economical to just buy an off-the-
shelf transformer that will work, but just not result in an optimum design. That is the approach
taken with this experiment for practical reasons.

PRELIMINARY
1. Find a data sheet for the general purpose rectifier model 1N4002. From the datasheet
find the following parameters to populate Table 1. Good places to find data sheets are;
www.digikey.com, www.mouser.com, www.newark.com, and www.onsemi.com.
 Table 1: 1N4002 Diode parameters.

Parameter Value

VRRM, Maximum Repetitive Peak Reverse

1. The circuit shown in Figure 6 demonstrates the full-wave rectifier design for this part of
the lab. The rectifier/filter circuit design will require approximately 16 VDC @ 130 mA
output capability, with a peak-to-peak voltage ripple less than 0.5 V. It is shown in the
textbook that for a full-wave rectifier the ripple voltage is [1]

𝑉𝑉𝑀𝑀
𝑉𝑉𝑟𝑟 =
2𝑓𝑓𝑓𝑓𝑓𝑓

where Vr, VM, f, R, and C, are the ripple voltage, peak voltage, frequency, load resistance,
and filter capacitance, respectively.

a. Calculate the required value for C1, as well as the required working voltage of the
capacitor.

b. Calculate the value of the load resistance, where it can be assumed that the load
resistance will satisfy the output voltage and current specifications given.

c. Note the resistance value and its power rating. When performing the lab, select a
capacitor from the lab stock that has at least the value calculated, and a load resistance
that is close to the value calculated. You will also need to consider that the power
rating is at least the value calculated.

2. It is also shown in the textbook that for a full-wave rectifier the peak and average diode
currents during a conduction interval are approximately

𝑉𝑉𝑀𝑀 2𝑉𝑉𝑀𝑀
𝑖𝑖𝐷𝐷,𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝 ≅ �1 + 𝜋𝜋� �
𝑅𝑅 𝑉𝑉𝑟𝑟

𝑉𝑉𝑀𝑀 𝜋𝜋 2𝑉𝑉𝑀𝑀
𝑖𝑖𝐷𝐷,𝑎𝑎𝑎𝑎𝑎𝑎 ≅ �1 + � �
𝑅𝑅 2 𝑉𝑉𝑟𝑟
 a. Calculate the peak diode current iD,peak and iD,avg over the conduction interval.

b. Calculate the PIV rating required for a diode to function safely in the rectifier
design.

Q1. Using the information in the data sheet, how much do you expect the diode drop
to be under full load? Explain your reasoning.

Q2. According to the data sheet, will a 1N4002 be sufficient in terms of current and
voltage? Think carefully about this and explain your reasoning. If you have doubts,
discuss your reasoning with your instructor.

3. If you know that there will be a voltage of VF, drop across one of the diodes between the
secondary output and the output voltage of the rectifier.

a. Calculate the peak voltage required of the secondary winding of the

b. Calculate the Root Mean Square (RMS) voltage of the secondary.

Figure 6: Schematic of the power supply to be designed.

PART A. POWER SUPPLY CIRCUIT USING A FULL WAVE RECTIFIER

When performing the lab, select a capacitor from the lab stock that has at least the value
calculated, and a load resistance that is close to the value calculated. You will also need to consider
that the power rating is at least the value calculated.

1. Obtain one of the transformers from the parts cabinet and use the DMM to measure the
output of one of the secondary terminals relative to the center tap connection. Note the
value.

Q3. Will the supplied transformer be suitable? Explain.

2. Construct the circuit of Figure 6. Have your lab partner(s) check over the circuit to make
sure the connections are right. Energize the circuit. Using the oscilloscope, observe the
output voltage. Sketch the output waveform, and measure both the peak-to-peak
ripple voltage and the dc average voltage.

Q4. How do the measured ripple and average values compare with your design values?
Explain any discrepancies.

3. Make sure you have written down all of the details of your circuit. You will be using a
similar circuit in next week’s experiment.

PART B. HALF-WAVE VOLTAGE DOUBLER

Consider the half-wave voltage doubler of Figure 7. Determine the voltage ratings
required for the capacitors and select suitable capacitors from the lab stock.

1. Construct the circuit without the load resistance 𝑅𝑅𝐿𝐿 and carefully check your connections.
Be careful since the voltages you are dealing with are potentially hazardous.

2. Connect the oscilloscope to the output and energize the circuit. Sketch the output
waveform, and measure both the peak-to-peak ripple voltage and the dc average
voltage.

3. Carefully remove the transformer cord from the wall socket and connect the load
resistance 𝑅𝑅𝐿𝐿 and energize the circuit again. Sketch the output waveform, and measure
both the peak-to-peak ripple voltage and the dc average voltage.
 Q5. What effect does the load have on the output voltage?

Q6. What would the advantage be if you could increase the frequency of the input AC?

Figure 7. A half-wave voltage doubler test circuit.

[1] Neamen, D. 2010. Microelectronics: Circuit Analysis and Design, Fourth Edition. New York,
NY. McGraw-Hill.