Apple revealed details of a highly sophisticated wireless charging system back in 2013 that utilizes near field magnetic resonance (NFMR) power supply. It's likely the long term approach that Apple will eventually introduce. Today a new patent application was published by the U.S. Patent & Trademark Office that reveals an Apple invention relating to impedance matching for inductive power transfer systems. With Samsung having wireless charging available for their smartphone line, it would definitely be nice to see such an option for Apple's iDevices in the not-too-distant future in one form or another.

Apple's Patent Background

Many portable electronic devices include one or more rechargeable batteries that require external power to recharge from time to time. Such devices may include cell phones, smart phones, tablet computers, laptop computers, wearable devices, navigation devices, sports devices, health devices, medical devices, accessory devices, peripheral input devices, and so on.

Some electronic devices may include an inductive charging system in lieu of a cable or tethered charging system. In these examples, a user may place the portable electronic device on an inductive charging surface ("dock") to replenish a rechargeable battery via electromagnetic induction. In these systems, an electromagnetic coil ("transmit coil") within the dock may inductively couple to an electromagnetic coil ("receive coil") within the portable electronic device. By alternating or switching the current through the transmit coil, current may be induced in the receive coil. The portable electronic device may be adapted to use the received current to replenish the charge of a rechargeable battery.

Many portable electronic devices may enter multiple power modes during an inductive power transfer. For example, a portable electronic device with a rechargeable battery may switch, after a period of time, from a trickle charging mode drawing low power to a constant current charging mode drawing relatively high power. Each of the several operational modes may present a different load condition as seen by the inductive power transmitter.

In many cases, changing load conditions decreases efficiency of power transfer between the transmitter and receiver. Accordingly, there may be a present need for a system and method for efficiently and rapidly delivering useful power to a portable electronic device across multiple power modes.

Apple's Invention: Impedance Matching for Inductive Power Transfer Systems

Apple's invention relates to methods, systems, and apparatuses for managing efficiency across an inductive charging interface. Such embodiments can include an inductive power transmitter and an inductive power receiver. An impedance controller may be coupled to the power receiving inductor and may be configured to increase or decrease an electrical impedance of the inductive power receiver in response to a change in a power requirement of a portable electronic device coupled to the inductive power receiver.

Many embodiments in Apple's patent filing may include a configuration in which the impedance controller is configured to maintain the effective impedance of the portable electronic device from the perspective of the inductive power transmitter at substantially the same value through all or substantially all load conditions of the portable electronic device.

Other embodiments may include a configuration in which the impedance controller may be a boost converter. In certain further embodiments, the impedance controller may be a buck converter. Still further embodiments include one of a buck or boost converter integrated within a bridge rectifier.

Apple notes that the inductive power receiver can be any suitable electronic device including a tablet computing device, phone, personal digital assistant, computer and a wearable communication device, a wearable health assistant (Apple Watch), a smart telephone, or a media player.

Apple points to a dock housing and a charging surface but never provides a patent figure to show a particular design. The focus of the patent is about the efficiency management for electromagnetic induction power transfer systems, and in particular to systems and methods for augmenting the impedance of an inductive power receiving accessory or inductive power receiving electronic device.

Apple's patent FIG. 2 noted below is a simplified signal flow diagram of one example of an inductive power receiver adapted to dynamically adjust receiver impedance; FIG. 3 is a simplified signal flow diagram of one example of an inductive power receiver adapted to dynamically decrease receiver impedance; FIG. 4 is a simplified signal flow diagram of one example of an inductive power receiver adapted to dynamically increase receiver impedance; and FIG. 8 is a simplified flow diagram illustrating example operations of a method of dynamically adjusting receiver impedance.

Patent Credits

Apple credits David Ritter, Jeffrey Terlizzi, Todd Moyer, Jeffrey Alves and Steven Herbst as the inventors of patent application 20150244341 which was filed in Q1 2015.. Considering that this is a patent application, the timing of such a product to market is unknown at this time.

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