Introduction to wireless battery charging systems

STWBC

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Introduction to wireless battery charging systems

Wireless battery charging systems replace the traditional power supply cable by means of

electromagnetic induction between a transmitting pad (TX) and a battery powered unit (RX),

such as a mobile phone or a battery pack.

The power transmitter unit is responsible for controlling the transmitting coil and generating

the correct amount of power requested by the receiver unit. The receiver unit continuously

feedbacks to the transmitter the correct power level requested by modulating the transmitter

carrier by means of a controlled resistive of capacitive insertion. Generating the correct

amount of power guarantees the highest level of end-to-end efficiency due to reduced

energy waste. Also, it helps maintaining a lower operational temperature.

The digital feedback is also used to detect foreign objects, i.e.: metal incorrectly exposed to

the coils. By stopping the application as soon as a foreign object is detected the risk of

damage is reduced.

Digital wireless battery transmitters can adapt the amount of energy transferred by the coil

by modulating the frequency, duty cycles or coil input voltage.

Figure 2. System view of a wireless charging system

Thanks to the internal STWBC 96 MHz clock, support for half-bridge and full bridge

topologies and protocol detection units, the STWBC can drive the power emitted by

a transmitting coil. The STWBC firmware sits on the top of the hardware to monitor and

control the correct wireless charging operations.