POWER SUPPLIES & BATTERIES
Safe and secure wireless power solutions
By Ralf Ködel and Ken Moore
The various benefits of wireless charging like convenience,
integration with multiple devices, mobility and flexibility
drive the market. Based on this the overall wireless
charging market is growing at a rapid pace. It is expected to
have a CAGR about 30 percent during the period 2019 - 2025,
reaching 27 billion USD in 2025. Infineon, partnering with Spark
Connected, offers complete solutions for wireless charging with
dedicated wireless power controller incl. software IP, MOSFETs,
drivers, security ICs and application optimized reference
designs.
Fig 1: Various wireless charging applications offer more
convenience to the users.
There are a number of challenges for designers of wireless
charging products, requiring a deep level of system knowledge
and expertise. In addition to issues associated with the charging
coils and their interaction with surrounding structures,
designers must address efficiency, mechanical packaging and
electromagnetic interference (EMI). However, with optimized
components and sufficient attention to alignment of charger and
device, size of coils and distance between coils, then a good
coupling factor can be achieved, and power can be transferred
with high efficiency. In addition, metallic foreign objects (such
as coins and keys) can be a safety hazard during charging and
must be reliably detected through a process called Foreign
Object Detection (FOD).
How wireless charging works
Wireless charging uses a changing magnetic field to transfer
energy between two objects via coils. The effectiveness of the
energy transfer between coils is referred to as “coupling”, and
depends on multiple parameters, including coil mechanical
design, spacing and alignment. When the coils are aligned and
in close proximity, wireless power transmission is nearly as efficient
as wired charging.
Wireless charging solutions have two key elements; the
transmitter and the receiver. The transmitter contains a MOSFET
based inverter to convert the DC power into an AC waveform
to drive the coil and create the alternating magnetic field.
In order to provide the flexibility and functionality required, the
inverter is controlled by a wireless power controller in real time
through the associated MOSFET driver components. The receiver
contains a rectifier to convert the incoming AC waveform
into DC power and a regulation stage to provide a conditioned
supply to the load. Most receivers also contain a wireless power
controller which is responsible for overall system management
and communication.
Two types of technology are commonly used to transfer
power wirelessly through alternating magnetic fields - inductive
and resonant. Reflecting the different benefits of these two
technologies, there are two standards bodies active in the wireless
charging market: the Wireless Power Consortium (WPC)
and the AirFuel Alliance. The main differences between the two
standards are shown in figure 2 at a glance.
Fig 2: Wireless charger transmitter topologies are based on
two dominating standards (WPC and Airfuel Alliance) with
tightly coupled (inductive) and loosely coupled (resonant)
architectures.
The Wireless Power Consortium (WPC) supports the Qi standard
for wireless charging, which is the leading standard in the
market. Qi uses inductive technology that supports efficient and
tightly coupled charging. In addition, the upcoming version of
the WPC Qi standard contains provisions that create a certified
authentication standard. Optiga Trust Qi is Infineon’s turnkey IoT
security solution, designed to meet the challenges of secured
wireless charging required by the Qi standard.
The single coil inductive approach is the most prevalent solution
on the market and consists of a single transmitter coil operating
between 80 - 205kHz. This approach requires centering
the device to be charged in relation to the transmitter coil and
is only able to charge a single receiver device at a time. With
good design and high-quality power conversion electronics the
efficiency of this type of charging can match wired charging. Extending
this approach to a charger with a multi-coil array brings
an additional benefit. The positioning of the device is much less
precise and smart systems can detect which coil is closest to
the device being charged and direct the power accordingly.
The AirFuel Alliance (AirFuel) has a broad technology platform
encompassing resonant and uncoupled technologies.
With resonant chargers, the 6.78MHz frequency of magnetic
resonance can achieve a much larger vertical range of 50mm
or more. Multiple devices can be charged using a single larger
transmitter coil, which also provides a larger active charging
area or “sweet spot”.
Ralf Ködel is Director Product Marketing Management
for Automotive & Industrial MicroControllers at Infineon
Technologies – www.infineon.com
Ken Moore is Chief Executive Officer at Spark Connected –
www.sparkconnected.com
www.eenewseurope.com eeNews Europe April 2020 News 29
/
/www.infineon.com
/www.sparkconnected.com
/www.eenewseurope.com
