IEEE Power Electronics Magazine - September 2021 - 34

resistive parameters in the operating frequency range of
700 kHz and 1 MHz. Calculating the inductance with the
initial permeability value will only result in an inductance
value at the initial condition (10 kHz, no current). It is a solid
base, but insufficient for optimizing the inductor frequency
and load behavior.
Based on the available material choice and operating
conditions a core material was chosen for the design of the
inductor with the parameters given in Table 1.
Having chosen the core and using the mechanical and
converter constraints, a core geometry and winding structure
was designed using an iterative process. Building from
experiences, a few geometries and core combinations are
selected. Then the best one is optimized with the help of
Table 1. Chosen core material parameters.
Parameter,
Symbol, Unit Test Conditions Temperature
Initial permeability
µi
Saturation
magnetic flux
density Bs (mT)
Coercive force
Hc (A/m)
Optimum frequency
(kHz)
Hysteresis material
constant hB
(/mT)
Power loss Pv
(mW/cm3)
10 kHz,
1.5 ~ 3.0 mT
1 MHz, 50 mT
25 °C
60 °C
100 °C
Curie temperature
Tc (°C)
Density d
(g/cm3)
10 kHz,
B < 0.25 mT
25 °C
4.8
150
150
160
290
25 °C
10 kHz,
B < 0.25 mT
50 Hz,
H = 1194 A/m
100 °C
25 °C
100 °C
430
45
38
500 - 5000
< 0.4 x 10-6
2.5
2
1.5
1
0.5
05 10 15 20 25 30
Average Inductor Current (A)
FIG 6 Measured inductance of the inductor as function of
average inductor current.
25 °C
25 °C
Value
900 ± 20%
500
finite element analysis. This process yielded an inductor
that measures 18 mm × 25 mm and has an inductance of
2.2 µH with DCR of 1.96 mΩ, as shown in Figure 5. The inductor
was constructed and the inductance, as function of average
inductor current, was measured as shown in Figure 6.
EMI Consideration for the Inductor Design
The fast-switching transients of eGaN FETs impact the
operation of inductors where high frequency currents and
voltages are present on the windings that can couple into
the core, other parts of the circuit, or radiate from various
parts of the circuit including the inductor. This requires that
EMI must be an integral part of the inductor design [16].
Recent techniques to address EMI design in inductors
assigns each terminal a specific function based on its physical
position within the inductor structure [17]. For example,
the start terminal of the inductor winding is positioned
close to the surface of the PCB where high frequency voltages
and currents encounter lower impedance paths that
can be used to couple back to the " electrically quiet " node
of the circuit. The end terminal of the inductor is then connected
to an " electrically quiet " node, such as the dc output
in a buck converter, and can thus reduce EMI emanating
from the inductor by shielding it. This technique is shown in
Figure 7 and can reduce EMI by as much as 10 dB.
Shielding Area
" Noisy Terminal "
" Quiet Terminal "
FIG 5 Basic image of the design inductor.
34 IEEE POWER ELECTRONICS MAGAZINE z September 2021
FIG 7 Inductor terminal assignment based on connection to
electrically " quiet or noisy " nodes in the circuit [18].
Inductance (µH)
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