IEEE Power Electronics Magazine - March 2018 - 31

500

160
Rg 23 Ω
Rg 10 Ω
Rg 5 Ω
Rg 3 Ω

120
100

400
Voltage (V)

80
60
40
20
0

300
200
100
0

10
15
20
Load Current (A)

not perform as well in the megahertz range. In particular,
litz wire and MnZn ferrite soft magnetic materials can be
used to create extremely efficient components for frequencies of up to hundreds of kilohertz, but the losses in both
increase rapidly with frequency in the megahertz range.
Thus, continued progress in reducing the size, cost, and loss
of passives will be a greater challenge in future decades
than it has been in the past. Moreover, even in the kilohertz
range, magnetic components pose special challenges. Not
only do they contribute disproportionately to the cost, size,
and loss of most converters, they also typically require a
custom design, which is work that requires skills that are in
short supply.
Primarily, a custom design is more important for magnetics than for other power electronics components and
devices because magnetic components do not scale well to
small sizes. An array of 100 small-size inductors configured
in parallel or series will have larger volume and/or higher
loss than a single inductor matched to the requirement of
the circuit and the application [6]. This poor scaling inhibits
the mass production of standard parts.
The limitations of present magnetics technology with
respect to effectively using high switching frequencies and
scaling to smaller sizes motivated a consideration of other
possible passive component technologies [7]. Considering
their fundamental role in a power converter, to store energy
on the timescale of a switching cycle, the energy densities
of various energy storage mechanisms were considered,
particularly in resonant combinations, such as an inductance-capacitance or mass-spring oscillator. Mass-spring
oscillators can have a very high energy density and quality
factor but are primarily limited as passives in power converters by the energy conversion process between electrical
and mechanical domains. Electromagnetic transduction is
subject to many of the same limitations faced by inductors,
and piezoelectric passive components used in power electronics to date typically have low efficiency. However, the
analysis in [7] indicates that mechanical resonators using
piezoelectric transduction have the potential to offer high

Voltage (V)

FIG 3 The turn-off loss of a 60-mΩ/600-V-rated superjunction
device as a function of current and gate resistor switching
against a 6-A SiC Schottky barrier diode.

1.0

1.5
2.0
Time (ns)

2.5

3.0

500

400

300

200

100

Slew Rate (V/ns)

Switching Loss (µ J)

140

0
0

4
6
Time (ns)

(a)

(b)
FIG 4 (a) The measured turn-off transient of an e-mode GaN
HEMT exceeding 500-V/ns switching speed. (b) The corresponding power board layout using ceramic capacitors in close proximity and a highly dv/dt-immune driving scheme. (Photo courtesy of Gerald Deboy, Infineon Technologies.)

energy density and low losses. Substantial technological
development would be necessary to realize this potential.
One advantage of such components is that they scale well to
small sizes, and they could be configured as arrays of small
cells, an approach that is amendable to mass production
while also facilitating packaging approaches that minimize
switching-cell parasitic inductance.
However, the analysis in [7] indicates that electromagnetic resonators based on inductive and capacitive energy
storage could also achieve much better performance than
is achieved in typical power passives. In either improved
resonant components or in the passive components used

March 2018

z IEEE PowEr ElEctronIcs MagazInE

Table of Contents for the Digital Edition of IEEE Power Electronics Magazine - March 2018