IEEE Power Electronics Magazine - March 2020 - 89

White Hot

(continued from page 92)

the LED module lit up, although how
well the dimming worked and how well
they met the specifications in general
varied quite a bit.
After the end of my second time
teaching the project lab, I decided to
rethink the entire approach. It is a
challenge to create a design concept,
do the electrical design, layout a
printed circuit board (PCB), wind the
transformer, assemble the converter,
debug it, take data for a test report,
and do an in-person demonstration
for an instructor in one semester.
So I thought long and hard about
how best to achieve the educational
objectives. To get the students to
working hardware would be much
easier if they were given a step-by-step
guide. This is when I realized, "You
don't learn to cook from a cookbook."
I have cooked for myself most of
my adult life. I made good use of cookbooks and was able to prepare good
meals. But it was not until I took cooking classes from a professional chef
and started studying cooking instruction that showed the science of cooking, such as Alton Brown's TV show
Good Eats and Cook's Illustrated magazine, that I really learned cooking
versus just following a recipe. Knowing not just how to combine a given
list of ingredients, but why, greatly
improved my cooking. My wife and I
only very occasionally eat at a restaurant as I can make tasty, healthier, and
less expensive meals at home.
So the task for me was to figure out
how to teach the students more than
just how to follow step-by-step directions that they would find in a power
supply design cookbook. I wanted to
teach more of the original thinking,
why this particular circuit is used and
not just how. Yet, the reality is that
the class in only a semester long. The
question was how to find the balance
between giving them a recipe from a
cookbook and inspiring them to make
their own original creation.
I describe the approach I came up
with as "dumping the Legos on the
table." The first six weeks of the

semester were devoted to showing
the students the various circuit building blocks they would need to create
their LED driver. I told them in lecture about each block, what it did,
and how to design it to achieve a
desired performance. I did not tell
them much about where in their LED
driver each block might be used. I
even threw in some extra blocks that
they would not need, just to test their
design thinking.
Another change for this semester
came from a suggestion by Prof. Bob
Erickson. When Roger and I discussed with him the problem of students not understanding how to plan
out the steps they needed to complete their design, he suggested we
make the students turn in something
every week. Whether this was graded in detail or was a simple "check
off" did not matter. The goal was to
keep the students moving forward
on their design.
Roger and I discussed this and
appreciated the value of the students
doing something every week. If we
simply told them to give us an update
each week, letting them make their
own way through the design process,
it was highly likely they would flounder about and lose precious time. If
we gave them specific weekly deliver-

ables, like their transformer design,
for example, we would be venturing
into giving them a recipe and taking
away from the learning experience.
Because the students really have no
idea about how to structure their
work when doing an original design,
we decided that the advantages of
having weekly deliverables, and
hopefully learning a bit about the
design process, outweighed the "giving them a recipe" factor.
For this past fall, we started the
semester with six weeks of intense
lecture and weekly assignments.
Most of the lectures were classroom.
For a couple of lectures on topics that
we considered review, such as opamps and op-amp circuits, we only
provided the slides.
The first assignment was an intensive review of op-amp and TL431 circuits, focusing on circuits they would
need in their design. The second
assignment was a basic design of a
flyback and single transistor forward
converter. From there, the assignments became more focused on their
design. In successive weeks, the students had to develop a design concept for their LED driver (topology,
operating mode, choice of control IC),
a first pass schematic and parts list, a
transformer/flyback inductor design,

FIG 1 A student's LED driver board. (Source: Robert V. White.)

March 2020

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