Wireless Charging
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User Guide Rev 1.03
TSDMRX-19V20W-EVM Semtech
Wireless Charging Concepts
Wireless power transfer is, essentially, a transformer. Power is provi e to a primary coil which pro uces an
electromagnetic (EM) fiel . In this fiel , a secon ary coil is place . The EM fiel in uces a current into the
secon ary coil, provi ing power to whatever it is connecte to.
However, unlike a conventional power transformer that operates at line frequencies an requires an iron core for
efficiency, wireless power systems are esigne to operate in the 100 kHz range, an thus can perform efficiently
with an air core. As such, the primary an secon ary win ings, if closely space , can be in separate evices, the
primary being part of a transmitter an the secon ary within a receiver. This implementation can also be escribe
as a ra io broa cast process, an as such, these transformer coils can also be seen as antennas with equal vali ity,
an the two terms will be use interchangeably in this text.
Receiver
Transmitter
Control
Electromagnetic
Flux
Controller FETArray
Power
Supply
Supply
Regulation Rectifier
End
Equipment
Power
Wireless power systems iffer in another major aspect from conventional transformers, in that they are
intelligently manage . A transmitter will only provi e power when a receiver is present, an only pro uce the
amount of power requeste by the receiver. In a ition, the system is capable of recognizing when the
electromagnetic fiel has been interrupte by an uninten e element, a 'foreign object', an will shut own the
transfer to prevent any significant amount of power being absorbe by anything but a proper receiver. The
intelligent management of the wireless power transmission process is achieve though the programming of the
TS81000. When intro uce to a compliant transmitter, the TSDMRX-19V20W-EVM receiver informs the
transmitter of its power requirements, an transmission begins. The receiver then verifies the right amount of
power is being sent, an that none is being lost to foreign objects. The receiver continually provi es ongoing
requests for power to maintain the transaction. If these requests cease, the transaction terminates. Via this
protocol, even complex charging patterns can be supporte , as the transmitter can provi e varying amounts of
power at ifferent times, as requeste by the TSDMRX-19V20W-EVM. Shoul the TSDMRX-19V20W-EVM require
no further power, such as when a battery charge is complete , it can request no further power be sent, an the
transmitter will re uce its output accor ingly.
Wireless power systems have been broken into three basic power categories. “Wearable” evices, such as
hea sets, wrist-ban evices, me ical sensors, an so forth - all operate in the low power range, up to 5 watts.
Me ium power evices, in the 5- to 15-watt range, inclu e most han hel evices, such as cell phones, tablets,
an me ical electronics. High power wireless systems are inten e to support evices such as power tools, ra io
controlle (“RC”) evices such as rones, an other equipment requiring 15 to 100 watts of power.
