Design & Construction of Switched Mode Power Supplies Sachin Mehta Reno Nevada

1. Design & Construction of Switched Mode Power Supplies
Written By: Sachin Mehta
University of Nevada, Reno

2. Abstract: This laboratory experiment—conducted over a several week period provided us with
an insight into key elements of electrical engineering and power regulation. Using specific
circuits we were able to vary the outputs, such as the voltage, that can be used in a variety of
different types of problems. For example, when a piece of electronics needs a certain voltage
input, but a higher voltage is the only one available—a buck converter can assist in giving the
CD player, or whatever it might be the proper power. This experiment allowed us to maintain
a knowledge of circuits and an understanding of power regulation.
Procedure/Results:
Part 1: Completed
Part 2: In order to complete this laboratory experiment, we needed to be able to apply circuit
theory relating to power conversion and regulation. Among the various types of converters,
the first portion of this lab was to design a dc-dc step down converter with certain
specifications that are listed in Table 1 below. This portion of the laboratory experiment used
electrical engineering and circuit theory in order to determine the correct voltage, current, and
power ratings for the various components that we needed to implement.
Table 1: DC-DC Step Down Specifications
input voltage (V) 10
output voltage (V) 5
output current (mA) 250
output voltage ripple (mV) 50
Part 3: The following calculations involve various parameters from above that give rise to
certain specifications that we were then able to input and use in the construction of the DC-DC
step down converter. In addition: the saturation voltage, the forward voltage, and frequency
were taken from the MC34063 and 1N5819 datasheets. They are 1.0 V, 0.6 V, and 100 kHz
respectively.
𝑡 𝑜𝑛
𝑡 𝑜𝑓𝑓
=
𝑉𝑜𝑢𝑡 + 𝑉𝐹
𝑉𝑖𝑛(𝑚𝑖𝑛) − 𝑉𝑠𝑎𝑡 − 𝑉𝑜𝑢𝑡
=
5 + 0.6
10 − 1 − 5
= 1.4 𝑉
𝑡 𝑜𝑛 + 𝑡 𝑜𝑓𝑓 =
1
𝑓
=
1
100 𝑘𝐻𝑧
= 10 µ𝑠
𝑡 𝑜𝑓𝑓 =
𝑡 𝑜𝑛 + 𝑡 𝑜𝑓𝑓
𝑡 𝑜𝑛
𝑡 𝑜𝑓𝑓
⁄ + 1
=
10 µ𝑠
1.4 + 1
= 4.17 × 10−6
𝑠
𝑡 𝑜𝑛 = 10 µ𝑠 − 4.17 × 10−6
= 5.833 µ𝑠

3. 𝐶 𝑇 = (4 × 10−5) 𝑡 𝑜𝑛 = (4 × 10−5)(5.833 × 10−6) = 233.33 𝑝𝐹
𝐼 𝑝𝑘( 𝑠𝑤𝑡𝑐ℎ) = 2 × 𝐼𝑜𝑢𝑡 = (2)(250𝑚𝐴) = 500 𝑚𝐴
𝑅 𝑆𝐶 =
0.3
𝐼𝑝𝑘( 𝑠𝑤𝑡𝑐ℎ)
=
0.3
500 𝑚𝐴
= 0.6 Ω
𝐿 𝑚𝑖𝑛 =
𝑉𝑖𝑛 − 𝑉𝑠𝑎𝑡 − 𝑉𝑜𝑢𝑡
𝐼𝑝𝑒𝑎𝑘
× 𝑡 𝑜𝑛 =
10 − 1 − 5
500 𝑚𝐴
× 5.833 µ𝑠 = 46.7 µ𝐻
𝐶 𝑂 =
𝐼𝑝𝑒𝑎𝑘 (𝑡 𝑜𝑛 + 𝐼𝑜𝑓𝑓)
8 𝑉𝑟𝑖𝑝𝑝𝑙𝑒(𝑝𝑝)
=
500 𝑚𝐴 × 10 µ𝑠
8 × 50 𝑚𝑉
= 12.5 µ𝐹
𝑉𝑜𝑢𝑡 = 1.25 (1 +
𝑅2
𝑅1
) = 5 𝑉
The component ratings for the DC-DC step down converter are now depicted in Table 2 below.
Table 2: Component Ratings
Component Type Vmax Imax Iavg Pmax
Transistor 10 500 250 5
Inductor 10 500 250 5
Resistor 10 500 250 5
Capacitor 10 N/A N/A 5
Diode 10 500 250 5
Part 4: Using Mouser.com, it was possible to determine real parts that could be used for the
inductor, diode, and capacitor.
The inductor that would be used in the design: Cooper Bussmann, Part #: 04-SDH2812-470-R
Diode that would be used in the design: Vishay Semiconductors, Part #: 78-V1OWM100 M3/I
Capacitor used in design: Kemet, Part #: 80-C1812X102JDG
Part 5: This portion of the laboratory experiment asked for circuit design and implementation
using the program known as MultiSim. This software has uses among the engineering
community in order to simulate various circuits, allowing for study before buying all the real
physical hardware, capacitors, voltage sources, etc. For this section of the experiment, the
circuit designed with MultiSim can be seen below in Fig. 2.

4. Figure 2: DC-DC Step Down Converter MultiSim Circuit Schematic
When running simulations of the circuit, outputs were obtained that looked very reasonable in
regards to what results we were supposed to have obtained.
Figure 3 shows the inductor voltage output from the DC-DC step down converter that was
developed in MultiSim.
Figure 3: MultiSim Output of Inductor Voltage
On the other hand, Fig. 4 clearly shows the spikes in the plot of current in response to time of
the inductor in the DC-DC step down converter simulation. The voltage rises and decreases in a
similar way to a spike shape form.

5. Figure 4: Transient Analysis of Inductor Current in DC-DC Step Down Converted from MultiSim
Figure 5, 6, 7, and 8 depict the transient analyses of the output voltage, output current,
transistor voltage, and diode voltage respectively.
Figure 5: Output Voltage of DC-DC Step Down Converter

6. Figure 6: Output Current of DC-DC Step Down Converter from MultiSim
Figure 7: Transistor Voltage from DC-DC Step Down Converter

7. Figure 8: MultiSim Output of DC-DC Step Down Converter’s Diode Voltage
Part 6: After simulation of the step down converter was completed using MultiSim, the next
part of the laboratory experiment called for obtaining a resistive load for the circuit and
implementing the circuit on a breadboard. Waveforms were then obtained for both the
discontinuous and continuous modes of the DC-DC step down converter. The continuous
mode voltage and current outputs of the different components can be seen below in Fig. 9 to
Fig. 14.

8. Part 7:
Figure 9: Inductor Voltage in Continuous Mode
Figure 10: Inductor Current in Continuous Mode

9. Figure 11: Continuous Mode Output Current
Figure 12: Continuous Mode Diode Voltage

10. Figure 13: Transistor Voltage in Continuous Mode
Figure 14: Continuous Mode Output Voltage
In order to complete this part of the laboratory experiment, discontinuous mode outputs of the
DC-DC Step Down Converter were acquired. They can be seen below in the next figures.

11. Figure 15: Discontinuous Mode Inductor Current
Figure 16: Discontinuous Mode Output Voltage

12. Figure 17: Output Current of the Discontinuous Mode
Figure 18: Inductor Voltage from Discontinuous Mode of DC-DC Step Down Converter

13. Figure 19: Transistor Voltage of Discontinuous Mode
Figure 20: DC-DC Step Down Converter Discontinuous Mode Diode Voltage
Part 8: In order to measure the waveforms of the inductor current, as well as the output
current many methods could be implemented. One process would be to place a 1 Ω resistor in
series with the inductor or by using a 1 Ω load to determine current. Then, dividing the newly
obtained voltage of the load or inductor component by that resistance (the 1 Ω resistance)
gives the output desired. This would result in the current (in amperes) through either the
inductor, or the load in question.

14. Part 9: Determining the efficiency, η, for the DC-DC step down converter was accomplished by
comparing the output and input current and voltage. It is known that the ideal relationship
between power, voltage, and current is defined as Eq. (1) shows below.
𝑃 = 𝑉 × 𝐼 (1)
Table 3: Measurements of DC-DC Step Down Converter Output & Input Current & Voltage
Input Voltage
(V)
Input Current
(A)
Power
(W)
Output Current
(A)
Output
Voltage(V)
Power Out
(W)
Efficiency
(%)
10 0.154 1.54 0.236 5.12 1.21 78.5
10 0.143 1.43 0.231 5.18 1.2 83.7
10 0.13 1.3 0.215 5.16 1.11 85.3
10 0.115 1.15 0.191 5.15 0.98 85.5
10 0.102 1.02 0.164 5.17 0.86 84.6
10 0.86 0.86 0.143 5.17 0.74 86
10 0.72 0.72 0.117 5.22 0.61 84.8
10 0.54 0.54 0.94 5.19 0.49 90.3
10 0.4 0.4 0.75 5.18 0.39 97.1
Plotting the data from above resulted in an efficiency graph of the DC-DC Step Down Converter.
Fig. 21 shows the Output Current vs. Efficiency.
Figure 21: Output Current vs. Efficiency
It is important to note that the plot above clearly demonstrates that as the output current
increases, efficiency of the converter decreases at a somewhat steady rate and ceases at nearly
80%. Note, that this also means that as the load resistance increases the efficiency, η,
decreases—which can have major consequences in operation. Efficiency of any circuit is
desired to be as a high percentage as possible, but cannot always be achieved.
Part 10: The data discovered from Table 3 is reminiscent of the plots from earlier in the report
(Fig. 3 to Fig. 8), which implies correct measurements were obtained and the DC-DC step down

15. converter was developed concisely and properly for the laboratory experiment. The fact is that
the figures and data from prior in the report reflect a somewhat more ideal environment with
the MultiSim software. On the other hand, the efficiency curve shown in Fig. 21 was obtained
from data taken from a physical circuit, implemented on a breadboard. Therefore, this data
had sources of error stemming from equipment calibration (or lack thereof), component
tolerances, and human error. This laboratory experiment being part of student curriculum
meant that the equipment and components that we were given to use were not of the best and
most ideal nature and accuracy. If this was research material, or along those lines, better
diodes, capacitors, etc. would have been implemented—resulting in a more specific and precise
plot of efficiency. In addition, the MultiSim simulation outputs used a MOSFET and diode that
were overall different parts than what was used in the bread-boarded circuit. This is a major
reason as to why simulation results did not completely reflect the measured results. In
addition, switching overvoltages were present in the DC-DC step down converter that was
developed and built. In order to ‘bypass’ this error it would have been better to use such
capacitors in a parallel setup with the other components. This would have resulted in a
somewhat filter effect that would polish and reduce ripples on the voltage.
Part 11: This portion of the laboratory experiment, onward, focused on the design and analysis
of another type of converter: DC-DC Step Up Converter. Different specifications were
implemented for this converter design than were used in the previous step-down configuration.
These specifications are as follows:
However, similarly to before, the saturation voltage, forward voltage, and frequency were
taken from the MC34063 and 1N5819 datasheets. They are 0.45 V, 0.6 V, and 100 kHz
respectively. The following section details the mathematical calculations that were made to
obtain some of the circuit parameters.
𝑡 𝑜𝑛
𝑡 𝑜𝑓𝑓
=
𝑉𝑜𝑢𝑡 + 𝑉𝐹 − 𝑉𝑖𝑛
𝑉𝑖𝑛(𝑚𝑖𝑛) − 𝑉𝑠𝑎𝑡 − 𝑉𝑜𝑢𝑡
=
10 + 0.6 − 5
5 − 0.45
= 1.23 𝑉
𝑡 𝑜𝑛 + 𝑡 𝑜𝑓𝑓 =
1
𝑓
=
1
100 𝑘𝐻𝑧
= 10 µ𝑠
𝑡 𝑜𝑓𝑓 =
𝑡 𝑜𝑛 + 𝑡 𝑜𝑓𝑓
𝑡 𝑜𝑛
𝑡 𝑜𝑓𝑓
⁄ + 1
=
10 µ𝑠
1.23 + 1
= 4.48 × 10−6
𝑠

16. 𝑡 𝑜𝑛 = 10 µ𝑠 − 4.83 × 10−6
= 5.52 µ𝑠
𝐶 𝑇 = (4 × 10−5) 𝑡 𝑜𝑛 = (4 × 10−5)(5.52 × 10−6) = 220.70 𝑝𝐹
𝐼 𝑝𝑘( 𝑠𝑤𝑡𝑐ℎ) = 2 × 𝐼𝑜𝑢𝑡 (
𝑡 𝑜𝑛
𝑡 𝑜𝑓𝑓
+ 1) = (2)(250𝑚𝐴)(1.23 + 1) = 0.446 𝐴
𝑅 𝑆𝐶 =
0.3
𝐼𝑝𝑘( 𝑠𝑤𝑡𝑐ℎ)
=
0.3
446 𝑚𝐴
= 0.672 Ω
𝐿 𝑚𝑖𝑛 =
𝑉𝑖𝑛 − 𝑉𝑠𝑎𝑡 − 𝑉𝑜𝑢𝑡
𝐼𝑝𝑒𝑎𝑘
× 𝑡 𝑜𝑛 =
10 − 1
446 𝑚𝐴
× 5.517 µ𝑠 = 56.3 µ𝐻
𝐶 𝑂 = (9)
𝐼 𝑝𝑒𝑎𝑘 (𝑡 𝑜𝑛 + 𝐼𝑜𝑓𝑓)
8 𝑉𝑟𝑖𝑝𝑝𝑙𝑒(𝑝𝑝)
= (
0.1 𝑚𝐴 × 5.517 µ𝑠
50 𝑚𝑉
)(9) = 99.3 µ𝐹
𝑉𝑜𝑢𝑡 = 1.25 (1 +
𝑅2
𝑅1
) = 10 𝑉
Part 12: This portion of the laboratory experiment required determining the voltage, current,
and power ratings for all of the necessary components for the step-up converter. Table 4
below depicts these ratings.
Table 2: Component Ratings for Step-Up Converter
Component Type Vmax Imax Iavg Pmax
Transistor 10 100 50 1
Inductor 10 100 50 1
Resistor 10 100 50 1
Capacitor 10 N/A N/A 1
Diode 10 100 50 1
Part 13: Simulation of this converter with MultiSim can be seen below where the circuit
schematic depicts the configuration of the DC-DC step up converter. The circuit shows a
MOSFET (metal oxide semiconductor field-effect transistor) and a Schottky diode among other
types of circuit components. The schematic diagram of the DC-DC step up converter is depicted
in Fig. 22.

17. Figure 22: DC-DC Step Up Converter MultiSim Circuit Schematic
For this circuit converter, simulations were configured using MultiSim as prior in the report and
are shown in the next several figures. For example, Fig. 23 can be viewed as the waveform
voltage across the inductor.
Figure 23: Inductor Voltage

18. Figure 24: Current through Inductor
Figure 25: Output Voltage

19. Figure 26: Output Current
Figure 27: Transistor Voltage

20. Figure 28: Diode Voltage
Part 14: A resistive load was designed for the step-up converter and it was then implemented
on the breadboard as a physical circuit. Actual components were used such as various passive
circuit components and equipment such as the function generator. This allowed the design to
be able to tested, studied, and analyzed—and was done next in the laboratory experiment
procedure.
Part 15: The DC-DC Step Up Converter was implemented and analyzed—with the resulting
waveforms shown amongst the next diagrams and figures. The following set of waveforms are
outputs of the continuous conduction mode of the inductor.

21. Figure 29: Inductor Voltage in Continuous Mode
Figure 30: Continuous Mode of Inductor Current

22. Figure 31: Continuous Mode Output Voltage
Figure 31: Output Current from the Continuous Mode

23. Figure 32: Continuous Mode Diode Voltage
Figure 33: Continuous Mode Transistor Voltage
Part 16: In order to measure a parameter of output current and inductor current, various
processes could have been implemented in the experiment. This would happen in the most
ideal way if a simple resistor was placed in series with the inductor from the circuit in Fig. 22.

24. Then performing division of the inductor would result in the parameter of ‘inductor current’ in
ampere units. In order to analyze the DC-DC Step Up Converter in a different way of thinking,
another means of reflection was performed and the efficiency of this step-up converter was
determined. The output voltage was measured in response to the input voltages, in addition to
the current using the relationship from Eq. (1). This showed that the voltage is related
seamlessly to both current through and the power. By providing an input voltage and varying
the current—measurements and data were obtained that are depicted below in Table 3.
Table 3: Efficiency Data from DC-DC Step Up Converter
Figure 34: Efficiency Plot of DC-DC Step Up Converter
Part 17: The measurements from the efficiency curve that is shown above shows that the data
are reflections of the simulation results shown prior in the report. Differences between these

25. data and the plots that were obtained from the MultiSim simulation result from the fact that
occur the simulated outputs are from MultiSim, which uses exact input voltages and
component parameters, at the very least. Essentially, these simulations arise from a more
‘ideal’ environment—not a complete ideal—but closer than the efficiency curve data. The plot
that is shown in Fig. 34 has data points that stem from environmental factors affecting the
experiment and therefore the results that were obtained. A method to improve this could be
to implement a higher quality type of equipment pieces—and more precise components like
the diodes, transistors, and capacitors. Improving the condition of switching overvoltages
would be to simply add capacitors in a parallel scheme with the components from the DC-DC
Step Up Converter that were already inputted in place in the circuit.
Summary: This laboratory experiment used and implemented various aspects of engineering
processes and provided an in depth insight into a major part of many electrical systems. The
switching regulator essentially boils down to the conversion of what is available into the
needed or desired portion. In terms of this laboratory experiment, given a voltage—the
requirement is to decrease that voltage, or increase it. Which one is chosen all depends on the
type of work that is being performed, what equipment is available, and the methodology. The
DC-DC Step Up Converter, or Boost Converter, uses the ideology that is the output voltage is
increased, the available output current must decrease. These converters use MOSFETs or some
sort of power switching process that stems from speed and cost considerations for choice. The
components that are used and implemented in the DC-DC Step Down Convert, or Buck
Converter, are all those that are used in the Boost and are just rearranged in design. Both
simulations and actual circuits were analyzed over the two week period of this laboratory
experiment which showed that there is differences and sources of error among the DC-DC
converters that were implemented on breadboards. A major source of error that can be seen
in the efficiency curve data stems from the fact that the components that were being used had
tolerances and were not precise in their parameters. What is meant by this is that the 100 Ω
resistor that was used in the Boost Converter circuit was, in fact, 99.2 Ω. This was determined
using one of the pieces of equipment in the laboratory room. However, these equipment
pieces are not being used for highly sensitive research so their calibration was most likely not
completed. Lastly, human error is always a suspicious portion that could take hold of an
experiment and affect data negatively. Although the circuit design was performed with a close
eye, there is always a possibility that error was made by me or my partner. This laboratory
experiment conducted studies of both the Buck and Boost Converter types and provided a
quick, but thorough view into their operations and mechanisms of action. With these
considerations, I am now more confident in a very important portion of electronics
engineering—making me a better versed engineer.