IEEE Power Electronics Magazine - June 2020 - 102

The anode of the C122F was connected to the +12-V output. When the
SCR fired, it would short circuit
("crowbar") the +12-V output. There
was also a Schottky diode connected
from the +5-V output to the +12-V output such that, as the +12-V output
voltage decreased below the +5-V output, the Schottky became forward
biased, and the +5-V output was also
pulled down. Along the way, the high
output current would trigger the
overcurrent protection, stopping the
power switching until the input
power was cycled.
There was no overtemperature
protection in the power supply or in
the system. I was once asked what
would happen if the fan failed. I said
that the power supply would overheat,
either one of the main power transistors or output diodes would fail, and
the input circuit breaker would be
tripped. This was acceptable because
the fan was in the power supply. If the
fan failed, the entire power supply
would have to be replaced anyway
Later, during system testing, there
was a fan failure. The power supply
did not overheat, but the system did.
The temperature in the system was
so high that a floppy disk melted and
dripped into the floppy drive. The
system folks were irate. It was the
only time I have been yelled at because
my power supply did not fail.
The overall design had an efficiency of roughly 75%, which was pretty
typical for a switching power supply at

the time. What was not typical was
the cost. As I recall, the assembled
cost was approximately US$120, or
US$0.6/W. This was a very low cost for
a power supply at the time. More typical costs were in the US$2-5/W range.
DEC started manufacturing the
H7862C power supply in the plant in
Albuquerque, New Mexico. My technician, Jim, and I got to spend several
weeks in Albuquerque helping the
new product introduction and production test teams get production
running smoothly. Jim and I took
advantage of our time there by taking
the tram to the top of Sandia Peak,
hiking in Bandelier National Monument, touring through Los Alamos
and the Jemez Canyon areas, and getting a fine introduction to the worldfamous New Mexico chiles. Watching
the H7862C come off the end of the
production line, get packed, and be
sent to the shipping dock gave me a
great feeling of "I designed that."
Later, DEC transferred production
to Phoenix, where we were able to
take day trips to the Grand Canyon
and the Sedona area. Production was
later transferred to Hong Kong.
Instead of sending Jim and me to
Hong Kong, DEC sent the Hong Kong
engineers to Maynard. This was a
great experience for me in learning
how to work internationally.
I do not think I could have asked for
a better first job, first supervisor, or
first project. I established relationships and friendships that last to this

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day. My supervisor, Dave Bertetti, gave
me the project and let me run with it,
backing my decisions and providing
coaching when needed. I also learned
a lot being part of the design team for
the whole system: mechanical, thermal, human factors, product safety,
electromagnetic interference, and system engineering, in general. I credit
this experience for laying a very solid
foundation for the rest of my career. I
was very, very fortunate to have landed when and where I did, and I will be
forever grateful for that experience.

About the Author
Robert V. White (bob.white@ieee
.org) has more than 30 years of industry experience as a power electronics
engineer. He has worked in product
design, systems and applications engineering, and technology development.
He has been an active volunteer with
the IEEE Power Electronics Society,
serving several years on the Administrative Committee, two terms as technical vice president, and as a Chapter
chair. He earned a B.S.E.E. degree
from the Massachusetts Institute of
Technology and an M.S.E.E. degree
from Worcester Polytechnic Institute.
He is currently pursuing a Ph.D.
degree in power electronics at the
University of Colorado, Boulder. Presently, he is the chief engineer of
Embedded Power Labs, a power electronics consulting company. He is a
Fellow of the IEEE.

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IEEE Power Electronics Magazine - June 2020

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