IEEE Power Electronics Magazine - June 2015 - 64

White Hot

by Robert V. White

The State of Design

n a LinkedIn group that I follow, a
young engineer recently asked for
help with a new design, a boost
converter with a 12-V input and an output of 48 V at 700 W. For that, he had
found an application note from one IC
company, but it was for a 250-W converter. Because it was not the right
output power, the young engineer was
stuck. He asked the members of this
group if they knew of any app notes
for a 700-W converter.
I was taken aback by the request.
To me, scaling up the 250-W app note
design to 700 W is what we do as power
electronic engineers. That this young
engineer was lost without someone
giving him an app note that exactly met
his requirements left me dismayed and
disconcerted. It also caused me to reflect on my own design experience and
the state of design today.
My first design outside the university laboratory was in 1979, between
my junior and senior years. I worked
as a summer engineer at General Electric's Power System Business Unit in
Philadelphia. I was working at a facility dominated by copper, silicon steel
laminations, and 50/60 Hz. Since I had
already taken the power electronics
class, I was asked to design a dc-dc
converter to convert a 48-Vdc input to
isolated ±15-Vdc outputs. I don't recall
the power level, but it was perhaps
30 W (1 A at each output). I was given

Digital Object Identifier 10.1109/MPEL.2015.2420854
Date of publication: 24 June 2015

IEEE POWER ELECTRONICS MAGAZINE

surrounded by a team of very experithis task as a way of keeping me busy
enced power supply engineers, and I
and not bothering the regular staff.
had a great supervisor.
With a sample kit of Ferroxcube cores
The SG3527A was a basic PWM conand bobbins, I set to work.
troller. It had an oscillator, ramp generWhat I came up with was a conator, reference voltage, error amplifier,
verter that today we could call a pricomparator, latch,
mary-side-regulated
and output drivers. It
peak-current-mode
could be used for any
constant-off-time flyIf we fast-forward to
kind of power supply
back. It did not have
today, what I see, in
or dc-dc converter.
a PWM regulator IC. I
contrast, are power
It was a flexible chip
built this design using
supply control chips
that worked well.
only a single LM339
If we fast-forward
quad comparator and
that are very
t
o
t od ay, wh a t I
few discrete composophisticated but are
see, in contrast, are
nents. It used a power
point solutions to
power supply control
MOSFET for the main
specific problems.
chips that are very
switch-an extravasophisticated but
gant luxury in 1979.
are point solutions to
The converter actuspecific problems. For example, I really worked pretty well. I don't think the
cently helped a client with some probother engineers really expected anylems with a low-power offline battery
thing from the "summer engineer," and
charger. The power supply was a flythey were surprised that I succeeded.
back that used a valley mode switchLooking back, it was an interesting
ing control IC. The chip had several
achievement, and I wish I had the scheoperating modes designed to optimize
matic for my scrapbook.
efficiency over various operating conThe following summer, after graduditions and modes.
ating with my B.S.E.E. degree, I went
The first thing I did was to try to
to work in a power supply group at
recreate the client's design. I wanted to
the Digital Equipment Corporation. I
check the choice of component values
was assigned the task of designing the
and the transformer design in particupower supply for Digital's first desktop
lar. I ran into difficulty when trying to
computer. While I did not have an app
apply my knowledge of flyback design.
note, I was given the documentation for
The rules I knew just did not seem to
several other power supplies and told
apply. As I studied the data sheet and
to use what I could. I was also told that
I would use the SG3527A PWM as the
control IC. Instead of app notes, I was
(continued on p. 62)

 June 2015

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