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suited to general-purpose wireless charging
stations, such as those found in public places
where a wide variety of devices could be
charged. Class D is suitable for a wide range of
power levels. In contrast to the Class D topol-
ogy, Class E is optimized for a particular design
point and, at this point, will show greater effi-
ciency. However, the Class E efficiency falls
off more rapidly away from this point. Thus
this topology is best suited to high power
and for 1:1 charging of a specific device that
is either charged close to target power or not
charged at all. The BOM costs associated with
Class E are very similar but tend to be slightly
lower than those of Class D. The Infineon
product range includes an extensive suite of
solutions for wireless charging transmitters
and chargers that give designers the ability to
use components and subsystems with known
compatibility. Central to the transmitter
design is a microcontroller for system control
and intelligence. The Infineon XMC range
includes the XMC1400 and XMC4400 that
are suited for wireless charging via Class D
and E topologies. The MOSFETs are directly
driven by EiceDRIVER gate drivers that trans-
late the microcontroller signals. Class D uses
the new 2EDL71 and Class E uses the estab-
lished 1EDN. The company is well known for
their extensive MOSFET range. Designers are
presented with significant choice of package
size as well as RDS(ON) and Qg and voltage
classes from 30V to 250V. As such, designers
are able to design wireless chargers with the
same base technology at multiple power lev-
els. Class D or E power inverters (as well as
synchronous rectification topologies) are best
served by OptiMOS technology and Cool-
MOS devices are very suitable for ACDC
adapters. Infineon also offers a range of fly-
back controllers for the power adapters that
work well alongside the CoolSET integrated
IC and power stage.
Apart from the technical challenges, design-
ers are being required to bring new designs
to fruition in ever-shortening timescales. To
support this, a test board for a Class D trans-
mitter was developed that allows designers to
get a head start in designing wireless charging
solutions. Designers that want to evaluate the
performance of Infineon MOSFETs in a Class
D configuration power amplifier will find the
board a very valuable resource. The board
comprises two half-bridges formed from two
80V 2x2 Infineon MOSFETs (IRL80HS120)
as well as related drivers making prototyp-
ing a simple task. Users can evaluate either
single-ended configurations (only one half-
bridge is active) or differential configurations
(both half-bridges are active), making the
switch between the two easy. Users can rely
on the embedded 6.78 MHz oscillator or use
an external pin and BNC connector to inject
other frequencies from a waveform generator.
Everything needed for zero voltage switching
(ZVS) power solutions are included with the
board. There is even an on-board linear reg-
ulator to supply the board logic with a stable
supply voltage. If a wireless charging capable
receiver device is available then a complete
wireless charging design can be created using
the second BNC connector to connect and
evaluate external transmitting coils for wire-
less power transfer.
Many consumers consider that the ability to
wirelessly charge mobile devices is long over-
due. The recent consolidation and advance-
ments of the relevant standards has played a
large part in moving towards a truly wireless
society. Leading semiconductor companies,
such as Infineon, have brought their broad
strengths in power and magnetic design to
bear on finding solutions. Drawing on their
extensive experience of microcontrollers,
MOSFETs and drivers they now offer a fully
integrated solution with components that
have demonstrated compatibility. Beyond this,
Infineon is also releasing valuable design tools
such as their Class D test board that allows
designers to rapidly prototype and evaluate
wireless charging systems.
Figure 1. Comparison of efficiency vs displacement for inductive and resonant approaches
Figure 2. Typical wireless charging systems consist of three main elements.
Figure 3. Simplified block diagram of the Class D test board
