IEEE Power Electronics Magazine - September 2021 - 66

Expert View
b y Phil Davies
Achieving Higher Power Density
With Good-Old Si MOSFETs
I
n 1984 I had the honor of travelling
around Europe with the
great Rudy Severns on a new
technology teaching tour for Siliconix.
I was a young applications engineer
and the new technology then
was the silicon power MOSFET.
Engineers were using bipolar transistors
in their switching power supplies,
and Rudy in his " Advanced
Power MOSFET Seminar " pointed
out the many advantages of the silicon
(Si) MOSFET, which offered
higher switching frequencies and
lower power losses. Rudy discussed
how to use and apply them correctly
and how to overcome various dV/dt
fai lure modes when switching
inductive loads.
That was over 37 years ago. Fast
forward to 2021: we are in a similar
place with multiple startups and
large power semiconductor companies
introducing new wide bandgap
(WBG) gallium nitride (GaN) and silicon
carbide (SiC) compound semiconductor
switches to chase off the
Si MOSFET, citing higher switching
frequencies, lower losses and higher
breakdown voltages with lower
R(DS)ON. The opportunity for the new
WBG MOSFETs has been created by
the significant power increases in
automobiles due to electrification
and in data centers with the ramp in
GPU-based artificial intelligence (AI)
Digital Object Identifier 10.1109/MPEL.2021.3099467
Date of current version: 13 September 2021
applications. In these markets, power
system footprint, efficiency and
weight have tremendous impact on
end-system performance and value,
which has escalated the importance
of power system design. Even
as some power design engineers
begin to adopt WBG MOSFETs,
advanced topologies and power
architectures can st i l l achieve
higher efficiencies and power density
with silicon components.
Next Generation Power
Challenges
Power system design engineers are
continually challenged to design a
power delivery network (PDN) that
takes up very little space, has the lowest
weight, the highest efficiency and
optimized thermal management.
Achieving the best possible specifications
in these areas defines a leadership
product that can deliver a major
competitive advantage.
Take for example battery range
(distance) and fast-charging specifications
for electric vehicles, or an AI
supercomputer's speed and rack
power density. These are highly competitive
performance specifications
and must be achieved while delivering
50 kW to 150 kW of power. As a
result, traditional power converters,
regulators and their silicon components
are having a very difficult
time delivering the critical performance
specifications for PDN size
and weight.
66 IEEE POWER ELECTRONICS MAGAZINE z September 2021
The Power System Designer's
Dilemma
Every system designer will ask basic
questions at the beginning of any new
project: Do I need to change my
design from the last successful project?
Can I use the same design, components
and suppliers I am familiar
with and have built trust with over the
years? Can I just modify the design a
little or does the new specification call
for radical change? Are there enough
advances in performance with what I
know how to do, or do I need to develop
a new architecture, topology or
control system? How much risk can I
take and will my team accept the risk
in exchange for the reward in higher
performance and maybe an important
competitive edge?
This is no different for the power
module designers at Vicor who ask
these same questions in order to stay
on the forefront of power module performance
in terms of density, efficiency
and flexibility.
Minimizing Tradeoffs and
Workarounds using High Voltages
One way around the power delivery
challenge is to use higher voltages.
Since the power term and power losses
are based upon voltage levels and
the square of the current (P = IV and
P = I2R). By using higher voltages,
PDN current levels and distribution
losses in cables and connectors can
be significantly reduced. This benefit
has resulted in a move from 12 V to
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