Reverse wireless charging

A method and system for operating a power circuit capable of transmitting and receiving wireless power. The method includes determining that the power circuit is operating in receive mode, and, based thereon, having a first equivalent capacitance. The method further includes determining that the power circuit is operating in the transmit mode, and, based thereon, having a second equivalent capacitance. The first equivalent capacitance being different than the second equivalent capacitance.

TECHNICAL FIELD

The present disclosure relates generally to wireless charging, and, in particular embodiments, to a system and method for reverse wireless charging.

BACKGROUND

Wireless power systems provide a method for wireless energy transfer between at least two devices. The transmitting device generates an electromagnetic field, and the receiving device receives the energy using inductive coupling. The receiving device stores the energy in a battery or consumes the power in a load.

The efficiency of the energy transfer primarily depends on the coupling factor between the transmit and receive side coils, the angle of the coils, the condition of the load or the battery, and the operating temperatures of the transmitting and receiving devices.

Reverse wireless charging refers to a feature that makes it possible for the receiving device, in a first wireless power system, to act as a transmitting device, in a second wireless power system. As an example, a first mobile device that is capable of reverse wireless charging can, on the one hand, charge itself when placed on a charging pad, and, on the other hand, can charge a second mobile device when the second mobile device is placed on (or near) the first mobile device. Thus, the first mobile device has the benefit of being able to function as the charging pad for the second mobile device.

Generally, a device capable of reverse wireless charging uses the same coil to receive and transmit wireless energy. The inductive-capacitive (LC) tank circuit that includes the shared coil in the two operating modes determines the resonant frequency of the device. This rigidity in the structure of the LC tank circuit diminishes the coupling factor during the transmit operating mode because the design is generally optimized for the receive operating mode.

A robust and reliable system and method for improved coupling in both transmit and receive operating modes in a device capable of reverse wireless charging is therefore desired.

SUMMARY

A first aspect relates to a method of operating a power circuit; the method includes the power circuit having a first mode and a second mode, respectively, corresponding to receiving and transmitting power using inductive charging at a coil of the power circuit. The method further includes determining that the power circuit is operating in the first mode, and, based thereon, coupling the coil in series with a parallel coupling of a first capacitor of the power circuit and a second capacitor of the power circuit. Additionally, the method includes determining that the power circuit is operating in the second mode, and, based thereon, coupling the coil in series with the first capacitor and coupling the second capacitor to a reference potential.

In a first implementation form of the method according to the first aspect, a tank circuit of the power circuit in the second mode includes the coil in series with the first capacitor. An equivalent capacitance and inductance, respectively, of the tank circuit in the second mode is about 300 nanofarad and 8 microhenries.

In a second implementation form of the method, according to the first aspect as such or any preceding implementation of the first aspect, a resonant frequency of the power circuit is determined in accordance with an equivalent inductance and capacitance of the tank circuit.

In a third implementation form of the method, according to the first aspect as such or any preceding implementation of the first aspect, the second capacitor is coupled to a switch in series. Coupling the coil in series with the parallel coupling of the first capacitor and the second capacitor includes setting the switch in a closed position.

In a fourth implementation form of the method, according to the first aspect as such or any preceding implementation of the first aspect, the second capacitor is coupled to a switch in series. Coupling the coil in series with the first capacitor and coupling the second capacitor to a reference potential includes setting the switch in an open position.

In a fifth implementation form of the method, according to the first aspect as such or any preceding implementation of the first aspect, the second capacitor is coupled to a switch in series. The switch includes a first transistor arranged in series with a second transistor.

In a sixth implementation form of the method, according to the first aspect as such or any preceding implementation of the first aspect, the determining that the power circuit is operating in the first mode or the second mode is in accordance with a signal received from an external device.

A second aspect relates to a device including a coil, a tank circuit, a non-transitory memory storage, and a process. The coil is configured to operate in a first mode and a second mode, respectively, corresponding to receiving and transmitting power using inductive charging. The tank circuit includes the coil, a first capacitor, and a second capacitor in the first mode. The tank circuit includes the coil and the second capacitor in the second mode. The non-transitory memory storage includes instructions. The processor is in communication with the non-transitory memory storage and executes the instructions to (1) determine that the coil is operating in the first mode, and, based thereon, coupling the coil in series with a parallel coupling of the first capacitor and the second capacitor and (2) determine that the coil is operating in the second mode, and, based thereon, coupling the coil in series with the first capacitor and coupling the second capacitor to a reference potential.

In a first implementation form of the device according to the first aspect as such, the tank circuit in the second mode includes the coil in series with the first capacitor. An equivalent capacitance and inductance, respectively, of the tank circuit in the second mode is about 300 nanofarad and 8 microhenries.

In a second implementation form of the device, according to the second aspect as such or any preceding implementation of the second aspect, the second capacitor is coupled to a switch in series. Coupling the coil in series with the parallel coupling of the first capacitor and the second capacitor includes setting the switch in a closed position.

In a third implementation form of the device, according to the second aspect as such or any preceding implementation of the second aspect, the second capacitor is coupled to a switch in series. Coupling the coil in series with the first capacitor and coupling the second capacitor to a reference potential includes setting the switch in an open position.

In a fourth implementation form of the device, according to the second aspect as such or any preceding implementation of the second aspect, the second capacitor is coupled to a switch in series. The switch includes a first transistor arranged in series with a second transistor.

In a fifth implementation form of the device, according to the second aspect as such or any preceding implementation of the second aspect, the device is a semiconductor package.

In a sixth implementation form of the device, according to the second aspect as such or any preceding implementation of the second aspect, the device is a mobile device, a tablet, a cellular phone, a power bank, or a battery pack.

In a seventh implementation form of the device, according to the second aspect as such or any preceding implementation of the second aspect, determining that the coil is operating in the first mode or in the second mode is in accordance with a signal received from an external device.

A third aspect relates to a method that includes having an inductive-capacitive (LC) tank circuit configured to transmit and receive wireless power using a coil of the LC tank circuit, the LC tank circuit having an effective inductance and a first effective capacitance corresponding to transmitting wireless power, the LC tank circuit having the effective inductance and a second effective capacitance corresponding to receiving wireless power.

In a first implementation form of the method according to the third aspect, determining that the LC tank circuit is transmitting wireless power or receiving wireless power is in accordance with a signal received from an external device.

In a second implementation form of the method, according to the third aspect as such or any preceding implementation of the third aspect, the LC tank circuit includes a variable capacitor having a first capacitance value corresponding to the first effective capacitance and the variable capacitor has a second capacitance value corresponding to the second effective capacitance.

In a third implementation form of the method, according to the third aspect as such or any preceding implementation of the third aspect, the method further includes providing a control signal to the variable capacitor to vary a capacitance value of the variable capacitor between the first capacitance value and the second capacitance value in accordance with, respectively, transmitting wireless power or receiving wireless power.

In a fourth implementation form of the method, according to the third aspect as such or any preceding implementation of the third aspect, the LC tank circuit includes a coil used to transmit and receive wireless power. The effective inductance of the LC tank circuit corresponds to an inductance of the coil.

A fourth aspect relates to a method that includes having an inductive-capacitive (LC) tank circuit configured to operate in a transmit mode and a receive mode, respectively, for transmitting and receiving wireless energy. The method further includes arranging components of the LC tank circuit for transmitting wireless energy. The LC tank circuit has an effective inductance and a first effective capacitance. And, the method further includes arranging components of the LC tank circuit for receiving wireless energy. The LC tank circuit has the same effective inductance and a second effective capacitance different than the first effective capacitance.

Embodiments can be implemented in hardware, software, or in any combination thereof.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

This disclosure provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments are merely illustrative of specific configurations and do not limit the scope of the claimed embodiments. Features from different embodiments may be combined to form further embodiments unless noted otherwise. Variations or modifications described with respect to one of the embodiments may also be applicable to other embodiments. Further, it should be understood that various changes, substitutions, and alterations can be made herein without departing from the spirit and scope of this disclosure as defined by the appended claims.

While the inventive aspects are described primarily in the context of the Qi wireless interface standard for a device having a resonant frequency of around 100 kilohertz (kHz) and an operating frequency of approximately 125 kHz, it should also be appreciated that these inventive aspects may also be applicable to any other type of reverse wireless charging having different resonant and operating frequencies. Thus, the embodiments of this disclosure may be widely used to provide a shared inductive-capacitive (LC) tank circuit in a reverse wireless charging capable device, that can be optimally configured to provide a target resonant frequency in both transmit and receive modes. Further, embodiments of the present invention may operate without complying with the Qi standard.

Generally, a device capable of transmitting and receiving wireless energy has a shared LC tank circuit for operating in each of the transmit and receive operating modes. The LC tank circuit primarily includes a coil and a capacitance. The inductance of the coil in the device is dependent on—yet different from—the inductance of a typical transmit coil. The capacitance of the LC tank circuit is selected to provide a resonant frequency in combination with the inductance for optimal receive mode operation, as the typical use of the device is to charge a battery or to power up the device. Thus, the rigidity in the structure of the shared LC tank circuit, optimized for receive mode, provides weak coupling in transmit mode as the corresponding resonant frequency is shifted over the frequency spectrum from the desired frequency.

Thus, a need exists for an improved system and method to overcome these limitations in a reverse wireless charging capable device. Embodiments of this disclosure provide a system and method that provides a configurable LC tank circuit for each of the transmit and receive operating modes. In other words, the LC tank circuit has a first configuration optimized for receive mode, and a second configuration optimized for transmit mode.

Aspects of this disclosure provide an LC tank circuit that includes a switch used to disconnect or electrically couple a first capacitor from/to a second capacitor. Thus, the switch provides a first configuration corresponding to the receive mode operation, where the first capacitor is disconnected from the second capacitor, and a second configuration corresponding to the transmit mode operation, where the first capacitor is arranged in parallel with the second capacitor. In another embodiment, a variable capacitor is used that has a first value optimized for transmit mode and a second value optimized for receive mode. These and other details are discussed in greater detail below.

FIG.1illustrates a simplified schematic diagram of a wireless power system100. The wireless power system100includes a transmitting device110and a reverse chargeable device120. The transmitting device110wirelessly transfers power140to the reverse chargeable device120—the reverse chargeable device120is operating in receive mode inFIG.1. The power source112generates an alternating current (AC) at the transmit-coil116, which induces a magnetic field at the coil122. The induced magnetic field induces an AC voltage at the coil122through mutual coupling. The rectifier126converts the AC voltage to a DC voltage. The regulator130converts the DC voltage from the rectifier126to match a desired DC voltage for the load132.

The transmitting device110may be a base station, for example, a charging pad, which provides the inductive power to the reverse chargeable device120. The transmitting device110includes a power source112, a supply-side capacitor114, and a transmit-coil116.

The power source112is any device that generates an alternating current (AC) power supplied to the transmit-coil116. In embodiments, the transmitting device110may include a DC-to-AC inverter to provide the AC power.

The transmit-coil116may be a loop antenna or a magnetic antenna. The transmit-coil116may include a physical core (e.g., ferrite core) or an air core, and may be implemented as an antenna strip or using a Litz wire.

The supply-side capacitor114and the transmit-coil116combine to form a transmit LC tank circuit118. The power source112drives the transmit LC tank circuit118, which generates the electromagnetic field at the transmit-coil116.

The reverse chargeable device120may be, for example, a mobile device, a tablet, a cellular phone, a power bank, a battery pack, or other such devices. The reverse chargeable device120includes a coil122, capacitors124and128, a rectifier126, a regulator130, and a load132, which may (or may not) be arranged as shown inFIG.1. The reverse chargeable device120may include additional components not depicted inFIG.1, such as long-term storage (e.g., non-volatile memory, etc.), a non-transitory computer-readable medium, one or more antenna elements, drivers, demodulators, modulators, filter circuits, and impedance matching circuits.

The coil122is similar in feature and structure to the transmit-coil116and is arranged in series with the capacitor124, which in combination form the LC tank circuit123.

The rectifier126is a device that converts alternating current (AC) voltage to a direct current (DC) voltage. The rectifier126may be any type of rectifier, such as a low-impedance synchronous rectifier having full-wave or half-wave rectification, or an active rectifier. The rectifier126shown inFIG.1is a bridge rectifier; however, other types of rectifiers may also be contemplated.

The regulator130is a device that maintains a constant output voltage for the load132. The regulator130receives an input voltage from the rectifier126. The regulator130may be any type of voltage regulator, such as a linear regulator (e.g., low drop-out (LDO) linear regulator). In some embodiments, the rectifier126and regulator130may be part of a switched-mode power supply (SMPS) circuit.

The capacitor128is used to decrease any ripple at the input of the regulator130from the rectifier126. The capacitor128may be referred to as a smoothing or a reservoir capacitor.

The load132receives the transferred power. The load132may be a charge storage device, such as a battery. For instance, the load132may be a battery of a cellular phone.

FIG.2illustrates a simplified schematic diagram of a wireless power system200. The wireless power system200includes the reverse chargeable device120and a receiving device210. The reverse chargeable device120wirelessly transfers power240to the receiving device210—the reverse chargeable device120is operating in transmit mode inFIG.2. The power source212generates an alternating current (AC) at the coil122, which induces a magnetic field at the receive-coil222. The induced magnetic field induces an AC voltage at the receive-coil222through mutual coupling. The rectifier226converts the AC voltage to a DC voltage. The regulator230converts the DC voltage to match a desired DC voltage for the load232. The power source212provides the alternating current at the coil122using the energy stored in, for example, load132.

The receiving device210may be, for example, a mobile device, a tablet, a cellular phone, a power bank, a battery pack, or other such devices. In some embodiments, the receiving device210may be a second reversible charging device operating in receive mode.

The receiving device210includes the receive-coil222, capacitors224and228, the rectifier226, the regulator230, and the load232, which may (or may not) be arranged as shown inFIG.2. The receive-coil222, capacitors224and228, the rectifier226, the regulator230, and the load232are similar to their similarly named counterparts discussed in reference toFIG.1and the reverse chargeable device120. The receiving device210may include additional components not depicted inFIG.2, such as long-term storage (e.g., non-volatile memory, etc.), a non-transitory computer-readable medium, one or more antenna elements, drivers, demodulators, modulators, filter circuits, and impedance matching circuits.

The mutual inductance between the transmitting device110and the reverse chargeable device120inFIG.1depends mainly on the resonant frequency of the transmit LC tank circuit118and the LC tank circuit123and on the spacing and angle between the transmit-coil116and the coil122. Likewise, the mutual inductance between the reverse chargeable device120and the receiving device210inFIG.2depends primarily on the resonant frequency of the LC tank circuit123and the receive LC tank circuit223and on the spacing and angle between the coil122and the receive-coil222.

Generally, the performance characteristics of the transmit LC tank circuit118, the LC tank circuit123, and the receive LC tank circuit223is dependent on interconnects with other integrated circuit components in their respective devices. However, the LC tank circuits in the present disclosure are discussed in isolation and are generalized as the primary power transfer elements of, respectively, the transmitting device110, the reverse chargeable device120, and the receiving device210.

The inductance of the transmit-coil116, coil122, and receive-coil222generally depend on their windings and physical dimensions. The windings of the coils are typically tightly coupled, and typically the inner diameter of the receive-coil222is kept within about 75% to 100% of the inner diameter of the transmit-coil116to ensure proper system performance and for improved coupling. In other words, the inductance of the receive-coil222depends primarily on the inductance of the transmit-coil116.

Thus, in the reverse chargeable device120, the inductance and physical dimensions of the coil122are constrained by limitations imposed for operation in receive mode. By extension, the operating characteristics of the LC tank circuit123are constrained by these same limitations.

Interface standards regulate wireless power transfer and its related functions and provide a range of operating frequencies for proper power transfer from a transmitting device to a receiving device.

In an embodiment, the equivalent inductance and the equivalent capacitance of the transmit LC tank circuit118is selected based on a target resonant frequency for the transmitting device110. The inductance of the coil122, as noted previously, depends on the dimensions and value of the transmit-coil116. The value of the capacitor124is then selected to provide an enhanced mutual coupling between the LC tank circuit123and the LC tank circuit118. Typically, as the primary operational goal of a reverse chargeable device120is to charge or receive power from the transmitting device110, for optimal mutual coupling, the LC tank circuit123is designed for receive mode operations.

In an embodiment, to operate within the Qi standard, the capacitance and the inductance of the transmit LC tank circuit118are, respectively, about 400 nanofarads (nF) and about 6.3 microhenries (pH). The target resonant frequency of the transmitting device, thus, is about 100 kilohertz (kHz). In this embodiment, the inductance of the coil122is about 8 PH, and the capacitance of capacitor124is about 500 nF to ensure maximum efficiency in wireless power transfer.

Typically, the operating frequency of the transmitting device110is set above the resonant frequency of the transmit LC tank circuit118to allow adjustments and a level of control over the amount of energy being transferred. Thus, in an embodiment where the transmit LC tank circuit118is designed to resonate at a frequency of about 100 kHz, the operating frequency is greater than 110 kHz, for example.

In an embodiment, the resonant frequency of the transmit LC tank circuit118is about 100 kHz, and the operating frequency of the transmitting device110is about 125 kHz. In this exemplary embodiment, a decrease in the operating frequency from 125 kHz towards the resonant frequency of 100 kHz increases the power delivered to the reverse chargeable device120. In contrast, an increase in the operating frequency decreases the energy delivered to the reverse chargeable device120.

The LC tank circuit123ofFIG.2includes the coil122and capacitor124, previously described withFIG.1. The receive LC tank circuit223includes capacitor224and receive-coil222.

The resonant frequency (f) of a tank circuit can be approximated using the equation:

f=12⁢π×LC,
where L is the inductance and C is the capacitance of the tank circuit.

It should be appreciated that the value of the components and the resonant frequency may be determined by other means, such as empirical observations, for example, on a test bench.

In an embodiment where the inductance of the coil122is about 8 PH, and the capacitance of capacitor124is about 500 nF, the resonant frequency of the LC tank circuit123in transmit mode is approximately around 80 kHz, which is a shift of roughly 20% in the frequency spectrum from the desired resonant frequency of 100 kHz.

As the receive LC tank circuit223of the receiving device210would be designed for compatibility with the Qi standard of about 100 kHz, the shift in the resonant frequency reduces mutual coupling, resulting in reduced power transfer efficiency and increased charge time for the wireless power system200.

Embodiments of this disclosure provide a solution for improving mutual coupling in the reverse chargeable device120by providing a tank circuit that can be separately configured in each of the transmit and receive operating modes.

FIG.3Aillustrates a simplified block diagram of an embodiment reverse chargeable device300. The reverse chargeable device300may be used in place of the reverse chargeable device120in either wireless power system100or200. The reverse chargeable device300, advantageously includes an LC tank circuit310that can be selectively configured for operation in the transmit or receive modes.

The LC tank circuit310, in addition to the coil122, includes a switch306arranged in series with a capacitor302. The series switch306and capacitor302are arranged in parallel with the capacitor304. The switch306receives a control signal from the processor320to electrically couple or disconnect the capacitor302from the LC tank circuit310. The capacitor302is shown as a single capacitor, but in embodiments, the capacitor302may include one or more capacitors arranged in series or parallel with each other.

The processor320can be, for example, a microprocessor, a microcontroller, a digital signal processor, a field-programmable gate array (FPGA), or an application-specific integrated circuit (ASIC). The reverse chargeable device300is shown to have a single processor; however, in some embodiments, multiple processors may be included, and the various functions herein attributed to the processor320may be distributed across these multiple processors.

The memory330may be configured to store data, programs, firmware, operating systems, and other information and to make the data, programs, firmware, operating systems, and additional information accessible to the processor320. The memory330may include any type of non-transitory system memory such as static random access memory (SRAM), dynamic random access memory (DRAM), synchronous DRAM (SDRAM), read-only memory (ROM), or a combination thereof. In an embodiment, the memory330may include ROM for use at boot-up, and DRAM for program, firmware, and data storage for use while executing programs. The memory330may include, for example, one or more of a solid-state drive, hard disk drive, a magnetic disk drive, a removable memory drive, or an optical disk drive.

The processor320provides a control signal to close or open the switch306based on the operating mode of the reverse chargeable device120. When switch306is in the closed position, the equivalent capacitance of the LC tank circuit310is the sum of the capacitance values of capacitors302and304. Conversely, when the switch306is the open position, the equivalent capacitance of the LC tank circuit310is equal to the capacitance of the capacitor304.

The equivalent capacitance of the LC tank circuit310can be approximately determined using the equation:

C=14⁢π2×f2×L,
where C, f, and L are, respectively, the equivalent capacitance, the inductance, and the resonant frequency of the LC tank circuit310.

In an embodiment where the resonant frequency of the tank circuit is desired to be around 100 kHz in transmit mode and the inductance of the coil122is about 8 μH, the equivalent capacitance of the LC tank circuit310is approximately 300 nF. In such an embodiment, as the equivalent capacitance of the LC tank circuit310is desired to be around 500 nF to ensure maximum efficiency in the receive mode, the capacitance values of capacitors304and302are, respectively, approximately 300 nF (as calculated) and 200 nF (e.g., 500 nF-300 nF). In this embodiment, in receive mode, the switch306is in the closed position to provide an equivalent capacitance for the LC tank circuit310of approximately 500 nF. And, in transmit mode, the switch306is in the open position to provide an equivalent capacitance for the LC tank circuit310of approximately 300 nF.

Thus, the LC tank circuit310can provide better coupling with the transmitting device110and with the receiving device210by, respectively, electrically coupling and decoupling the capacitor302with the capacitor304within the LC tank circuit310. The selective disconnecting or electrically coupling provides a resonant frequency for the LC tank circuit310that is appropriate to the operating mode of the reverse chargeable device120.

It is noted that the switch306is shown to be arranged in series with the capacitor302; however, in some embodiments, the switch306may be arranged in series with the capacitor304. In such an embodiment, switch306is in the closed position for the receive mode operation, and the switch306is the open position for the transmit mode operation. And, the values of the capacitors304and302are selected appropriately for this modified operation.

The equivalent capacitance values presented herein are exemplary values, and appropriate numbers can be determined for any desired resonant frequency.

FIG.3Billustrates a simplified block diagram of another embodiment reverse chargeable device350. The reverse chargeable device350, similar to the reverse chargeable device300, may be used in place of the reverse chargeable device120in either wireless power system100or200. The reverse chargeable device350, advantageously includes an LC tank circuit360that can be configured for operation in the transmit or receive modes.

The LC tank circuit360includes the coil122and a variable capacitor362. The variable capacitor362can be adjusted using a signal from the processor320. In an embodiment, the variable capacitor is set to operate at a first capacitance value to provide a resonant frequency in transmit mode. In the embodiment, the variable capacitor is configured to operate at a second capacitive value in receive mode.

In an exemplary embodiment, the coil122has an inductance value of about 8 PH, and the variable capacitor362has a capacitance value of about 300 nF in transmit mode. In the exemplary embodiment, the variable capacitor362has a capacitance value of about 500 nF in receive mode.

FIG.4illustrates an exemplary schematic of the LC tank circuit310. The LC tank circuit includes the coil122, the capacitors302and304, and the switch306. The switch306includes resistors404and406, capacitor408, switch400, and transistors410and412.

The exemplary circuit illustrated inFIG.4, representing the switch306ofFIG.3A, is non-limiting, and other circuits that serve similar operational characteristics are contemplated.

The transistors410and412are arranged as back-to-back transistors, where the drain terminal of the transistor410is electrically coupled with the source terminal of the transistor412. The source terminal of the transistor412is electrically coupled to the capacitor302. The drain terminal of the transistor412is electrically coupled with the capacitor302. The gate of each transistor410and412are electrically coupled to the processor320.

The gate of each transistor410and412is electrically coupled to the source of the transistor410, which can be electrically coupled to a reference ground through the switch400—to reduce leakage at the reverse chargeable device in the transmit mode. In embodiments, the switch400is electrically coupled to a reference voltage, and not necessarily a reference ground, that has less voltage potential than the terminal of the switch electrically coupled to the resistor404. The processor320is electrically coupled to the gate of the transistor410, the transistor412, and the switch400. The processor320provides a signal VSIG1to activate or deactivate the transistors410and412and the switch400. The switch400is electrically coupled to the processor320and transitions between an open and closed mode depending on the signal VSIG2received from the processor320.

In an embodiment corresponding to the reverse chargeable device120being in transmit mode, the switch400is in an open position, and the transistor410and the transistor412are deactivated. In this embodiment, the equivalent capacitance of the LC tank circuit310is approximately equal in value to the capacitance of the capacitor304.

In an exemplary embodiment, the inductance value of the coil122is approximately 8 pH, and the capacitance value of the capacitor304is about 300 nF. In this exemplary embodiment, the capacitance value of the LC tank circuit310in transmit mode is, thus, 300 nF. The adjustment to the capacitance of the LC tank circuit310from the typical 500 nF to 300 nF, in an operating environment corresponding to an operating voltage of 10 V, an operating frequency of 125 kHz, and with a 10 ohm load, provides an approximately 60% increase in power transfer from about 8 watts (W) to about 12.7 W in transmit mode.

In an embodiment where the reverse chargeable device120is in receive mode, the switch400is in a closed position, and the transistor410and the transistor412are activated. In this embodiment, the equivalent capacitance of the LC tank circuit310is approximately equal in value to the sum of the capacitance of the capacitors302and304.

In an exemplary embodiment, the inductance value of the coil122is approximately 8 pH, and the capacitance value of the capacitors302and304, respectively, are about 300 nF and 200 nF. In this exemplary embodiment, the capacitance value of the LC tank circuit310in receive mode is, thus, 500 nF. As the capacitance of the LC tank circuit310remains within the preferred 500 nF range in receive mode, the power transfer remains relatively unchanged apart from a small and negligible amount of energy lost through leakage within the switch306.

FIG.5illustrates a flowchart of an embodiment method500for operating an LC tank circuit, as may be performed by the reverse chargeable device120. At step510, the processor320determines whether the reverse chargeable device120is operating in a first mode corresponding to receiving wireless energy from a transmitting device110or a second mode corresponding to transmitting wireless power to a receiving device210. In embodiments, the determining as to whether the device is operating in the first mode or the second mode is in response to a signal received from an external device, such as the transmitting device110or the receiving device210. In embodiments, the signal is an electromagnetic field generated by the external device. In other embodiments, the signal is a communication signal received from the external device, such as a near field communication.

At step520, the processor320arranges the LC tank circuit310to operate in receive mode. In an embodiment, the processor320activates the switch306to arrange the coil122in series with a parallel configuration of the capacitors302and304in the LC tank circuit310. In another embodiment, the processor320activates a variable capacitor362to provide a first capacitance value corresponding to proper operation in receive mode.

At step530, the processor320arranges the LC tank circuit310to operate in transmit mode. In an embodiment, the processor320deactivates the switch306to arrange the coil122in series with the capacitor302—and disconnects the capacitor304—in the LC tank circuit310. In another embodiment, the processor320activates the variable capacitor362to provide a second capacitance value corresponding to proper operation in transmit mode.

It is noted that the order of steps shown inFIG.5is not absolutely required, so in principle, the various steps may be performed out of the illustrated order. Also, specific steps may be skipped, different steps may be added or substituted, or selected steps or groups of steps may be performed in a separate application.

In the present description, when reference is made to terms qualifying absolute positions, such as terms “front,” “back,” “top,” “bottom,” “left,” “right,” etc., or relative positions, such as terms “above,” “under,” “upper,” “lower,” etc., or to terms qualifying directions, such as terms “horizontal,” “vertical,” etc., it is referred to the orientation of the drawings. Unless otherwise specified, the terms “approximately,” “substantially,” “about,” and “in the order of” are used herein to designate a tolerance of plus or minus 10%, preferably of plus or minus 5%, of the value in question.

Unless otherwise specified, when reference is made to two elements electrically connected together, this means that the elements are directly connected with no intermediate element other than conductors. When reference is made to two elements electrically coupled together, this means that the two elements may be directly coupled (connected) or coupled via one or a plurality of other elements.

The specification and drawings are, accordingly, to be regarded simply as an illustration of the disclosure as defined by the appended claims, and are contemplated to cover any and all modifications, variations, combinations, or equivalents that fall within the scope of the present disclosure.