INTERNET OF THINGS HANDBOOK
Basics of wireless power transmission design CONTRIBUTED BY IDT CORP.
Most consumer devices that transfer power over wireless links follow the Qi standard. The construction of these power transfer systems is simpler thanks to the availability of new reference designs.
Typical wireless charging scenario
Examine the wireless charging setup used in the passenger compartment of most vehicles and you are likely to find a system that follows the Qi standard. Promoted by the Wireless Power Consortium, Qi applies to power transfer over distances of up to 40 mm (1.6 in). Charging takes place via magnetic induction between a charging pad and a compatible wireless receiver. Qi divides charging into low and medium-power categories. Low-power covers up to 5-W chargers as are typical of smartphones, Bluetooth earpieces, and so forth. Charging takes place via a signal in the 110 to 205 kHz range. Medium-power chargers deliver up to 120 W via signals ranging between 80 and 800 kHz. A limited data transmission takes place between the charger and the mobile device being charged. Transmitted data provides information about the state of charge and similar parameters so the charger can shut down when the battery is charged. The charger first begins charging when it detects a change in capacitance or resonance in its transmitter coil. When the charger detects an object, it sends an 8-bit data string on the charging carrier. The mobile device then must respond with information about the signal strength it detects. The charger in turn sends multiple pings back indicating the optimum positioning for the mobile device. Charging commences when the mobile device has been validated and positioned correctly. During the charge process, the mobile device sends data packets (at about 2 kbps) that adjust the power level and finally end charging. Qi chargers also can sense the presence of foreign objects in the charging field. When this happens, the charger cuts out.
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DESIGN WORLD — EE NETWORK
IDT — Internet of Things HB 04-19_v2.indd 10
4 • 2019
Typical wireless simplified schematic
The Wireless Power Consortium spells out a number of mechanical and electrical parameters for Qi wireless charging, including the make-up and configuration of the charging coils.
eeworldonline.com | designworldonline.com
4/15/19 10:26 AM
