Power reception device and non-contact power feeding system

A power reception device includes a power reception-side resonant circuit which includes a power reception-side coil and a metal plate in which an opening portion is provided in a position opposite the arrangement position of the power reception-side coil, and can receive, by a magnetic field resonance method, power from a power transmission device which includes a power transmission-side resonant circuit including a power transmission-side coil. A cancellation coil is arranged between the power reception-side coil and the opening portion, and a cancellation resonant circuit including a cancellation coil is provided separately in the power reception device. When an alternating magnetic field interlinks the cancellation coil, a current which cancels out variations in the resonant frequencies of the power reception-side resonant circuit and the power transmission-side resonant circuit caused by the presence of the metal plate flows through the cancellation coil.

CROSS REFERENCE TO RELATED APPLICATIONS

This is the U.S. national stage of application No. PCT/JP2016/080248, filed on Oct. 12, 2016. Priority under 35 U.S.C. § 119(a) and 35 U.S.C. § 365(b) is claimed from Japanese Application No. 2015-223256, filed on Nov. 13, 2015, the disclosure of which is also incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a power reception device and a non-contact power feeding system.

BACKGROUND ART

As one type of proximity wireless communication, there is wireless communication which is performed by NFC (Near field communication) that uses 13.56 MHz as a carrier frequency. On the other hand, a technology is also proposed which utilizes a coil used for NFC communication so as to perform non-contact power feeding by a magnetic field resonance method.

In the non-contact power feeding utilizing magnetic field resonance, a power transmission-side resonant circuit including a power transmission-side coil is arranged in a power transmission device, a power reception-side resonant circuit including a power reception-side coil is arranged in a power reception device and the resonant frequencies of the resonant circuits are set to a common reference frequency. An alternating current is then passed through the power transmission-side coil, and thus an alternating magnetic field at the reference frequency is generated in the power transmission-side coil. Then, the alternating magnetic field is transmitted to the power reception-side resonant circuit which resonates at the reference frequency, and thus an alternating current flows through the power reception-side coil. In other words, power is transmitted from the power transmission-side resonant circuit including the power transmission-side coil to the power reception-side resonant circuit including the power reception-side coil.

RELATED ART DOCUMENT

Patent Document

DISCLOSURE OF THE INVENTION

Problems to be Solved by the Invention

In a power reception device, a member which affects the properties and the operation of a power reception-side resonant circuit may be arranged. For example, a metal plate which is used for the enclosure of an electronic device and which is formed of aluminum or the like may be provided or a magnetic material sheet which is used for the unnecessary magnetic field shielding of an electronic circuit and which is formed of ferrite or the like may be provided, and these members can affect the properties and the operation of the power reception-side resonant circuit through magnetic coupling to a power reception-side coil. Furthermore, when a power transmission device is close to the power reception device, the members described above may also be magnetically coupled to a power transmission-side coil so as to affect the properties and the operation of a power transmission-side resonant circuit. These influences are not desirable for realizing the proper operations (including a power reception operation and a power transmission/reception operation) of the power reception device and a non-contact power feeding system.

When the operation of part of a circuit within the power reception device is not ideal, this may adversely affect the realization of a desired operation which is achieved in the non-contact power feeding system.

Hence, an object of the present invention is to provide a power reception device and a non-contact power feeding system which contribute to the realization of proper operations.

Means for Solving the Problem

A power reception device according to the present invention which can receive, from a power transmission device that includes a power transmission-side resonant circuit including a power transmission-side coil for transmitting power, the power by a magnetic field resonance method, includes: a power reception-side resonant circuit which includes a power reception-side coil for receiving the power; and an auxiliary resonant circuit which includes an auxiliary coil different from the power reception-side coil, where in a position in which a current flows through the auxiliary coil based on a magnetic field generated in the power transmission-side coil or the power reception-side coil, the auxiliary coil is arranged.

Specifically, for example, preferably, the power reception device further includes: a metal plate which is provided in such a position as to affect a resonant frequency of the power reception-side resonant circuit, where when an alternating magnetic field interlinks the auxiliary coil, a current which cancels out a variation in the resonant frequency of the power reception-side resonant circuit caused by the metal plate flows through the auxiliary resonant circuit.

For example, preferably, the metal plate is formed of aluminum or an aluminum alloy.

Specifically, for example, preferably, the power reception device further includes: a magnetic material portion which is provided in such a position as to affect a resonant frequency of the power reception-side resonant circuit, where when an alternating magnetic field interlinks the auxiliary coil, a current which cancels out a variation in the resonant frequency of the power reception-side resonant circuit caused by the magnetic material portion flows through the auxiliary resonant circuit.

For example, preferably, the magnetic material portion is formed of ferrite.

Specifically, for example, preferably, the auxiliary resonant circuit is a resonant circuit that is formed so as to include the auxiliary coil and an auxiliary capacitor whose capacitance can be changed.

Specifically, for example, preferably, the auxiliary resonant circuit further includes an auxiliary resistor, and the auxiliary resistor is connected in parallel to a parallel circuit of the auxiliary coil and the auxiliary capacitor or the auxiliary resistor is inserted in series with a series circuit of the auxiliary coil and the auxiliary capacitor.

A non-contact power feeding system according to the present invention includes: the power reception device; and the power transmission device which includes the power transmission-side resonant circuit including the power transmission-side coil for transmitting the power, where the non-contact power feeding system can transmit and receive the power by the magnetic field resonance method.

Specifically, for example, preferably, in the non-contact power feeding system, the power transmission device includes: a power transmission circuit which can supply an alternating current voltage to the power transmission-side resonant circuit; a detection circuit which detects an amplitude of a current flowing through the power transmission-side coil; and a power transmission-side control portion which performs power transmission control on the power by controlling the power transmission circuit based on an amplitude detection value of the detection circuit.

For example, preferably, in the non-contact power feeding system, the power reception device includes a change/short circuit which changes the resonant frequency of the power reception-side resonant circuit from a resonant frequency at a time of the power reception or short-circuits the power reception-side coil before the reception of the power from the power transmission device, the power transmission-side control portion includes: a first processing portion which controls the power transmission circuit such that in a state where in the power reception device, the resonant frequency of the power reception-side resonant circuit is changed or the power reception-side coil is short-circuited according to a signal by communication from the power transmission device, before the power transmission, a predetermined test magnetic field is generated in the power transmission-side coil; a second processing portion which determines, based on the amplitude detection value by the detection circuit when the test magnetic field is generated, whether or not the power transmission can be performed; and a third processing portion which realizes the power transmission by controlling the power transmission circuit such that after it is determined that the power transmission can be performed, a magnetic field for the power transmission larger than the test magnetic field is generated in the power transmission-side coil, and in the state, a current which cancels out an influence exerted by the power reception-side resonant circuit on the amplitude of the current flowing through the power transmission-side coil flows through the auxiliary resonant circuit.

For example, preferably, in the non-contact power feeding system, the power reception device further includes a power reception-side control portion which can stop a resonant operation of the auxiliary resonant circuit caused as a result of the alternating magnetic field interlinking the auxiliary coil, and the power reception-side control portion stops the resonant operation of the auxiliary resonant circuit when the power is transmitted and received.

For example, preferably, in the non-contact power feeding system, when the power transmission device and the power reception device are in a predetermined positional relationship for transmitting and receiving the power, the auxiliary coil is arranged between the power transmission-side coil and the power reception-side coil or is arranged in a position on a side opposite to an arrangement position of the power transmission-side coil when seen from the power reception-side coil.

Advantages of the Invention

According to the present invention, it is possible to provide a power reception device and a non-contact power feeding system which contribute to the realization of proper operations.

DESCRIPTION OF EMBODIMENTS

Examples of the embodiment of the present invention will be specifically described below with reference to drawings. In the drawings referenced, the same portions are identified with the same symbols, and the repeated description of the same portions will be omitted in principle. In the present specification, for simplification of description, signs or symbols which refer to information, signals, physical amounts, state amounts, members and the like are provided, and thus the names of the information, the signals, the physical amounts, the state amounts, the members and the like corresponding to the signs or symbols may be omitted or described in short. In an arbitrary flowchart which will be described later, a plurality of types of processing in an arbitrary plurality of steps can be arbitrarily changed in the order in which they are performed or can be performed at the same time unless otherwise a contradiction arises in the details of the processing.

First Embodiment

A first embodiment of the present invention will be described.FIG. 1AandFIG. 1Bare schematic external views of a power feeding device1and an electronic device2according to the first embodiment of the present invention. Specifically,FIG. 1Ais an external view of the power feeding device1and the electronic device2when they are in a separate state, andFIG. 1Bis an external view of the power feeding device1and the electronic device2when they are in a reference arrangement state. The significance of the separate state and the reference arrangement state will be described in detail later. The power feeding device1and the electronic device2form a non-contact power feeding system. The power feeding device1includes a power supply plug11which receives commercial alternating current power and a power feeding stage12which is formed of a resin material.

FIG. 2shows a schematic internal configuration diagram of the power feeding device1and the electronic device2. The power feeding device1includes: an AC/DC conversion portion13which generates a direct current voltage having a predetermined voltage value from a commercial alternating current voltage input through the power supply plug11and which outputs the direct current voltage; a power transmission-side IC100(hereinafter also referred to as an IC100) which is an integrated circuit that is driven by use of the output voltage of the AC/DC conversion portion13; and a power transmission-side resonant circuit TT (hereinafter also referred to as a resonant circuit TT) which is connected to the IC100. The AC/DC conversion portion13, the power transmission-side IC100and the resonant circuit TT can be arranged within the power feeding stage12. A circuit other than IC100which is driven by use of the output voltage of the AC/DC conversion portion13can be provided in the power feeding device1.

The electronic device2includes: a power reception-side IC200(hereinafter also referred to as an IC200) which is an integrated circuit; a power reception-side resonant circuit RR (hereinafter also referred to as a resonant circuit RR) which is connected to the IC200; a battery21which is a secondary battery; and a functional circuit22which is driven based on the output voltage of the battery21. The IC200can supply charging power to the battery21though the details thereof will be described later. The IC200may be driven by the output voltage of the battery21or may be driven based on a voltage from a voltage source other than the battery21. A direct current voltage which is obtained by rectifying a signal for NFC communication (which will be described in detail later) received from the power feeding device1may serve as a drive voltage for the IC200. In this case, even when the battery21does not have the remaining capacity, the IC200can be driven.

The electronic device2may be an arbitrary electronic device, and is, for example, a mobile phone (including a mobile phone classified as a smart phone), a portable information terminal, a tablet-type personal computer, a digital camera, an MP3 player, a pedometer or a Bluetooth (registered trademark) headset. The functional circuit22realizes an arbitrary function which needs to be realized by the electronic device2. Hence, for example, when the electronic device2is a smart phone, the functional circuit22includes a call processing portion for realizing a call with the device of a party on the other end, a communication processing portion for transmitting and receiving information to and from other devices through a network and the like. For example, when the electronic device2is a digital camera, the functional circuit22includes a drive circuit which drives an image sensing element, an image processing circuit which generates image data from the output signal of the image sensing element and the like. It may be considered that the functional circuit22is a circuit which is provided in a device outside the electronic device2.

As shown inFIG. 3, the resonant circuit TT includes a coil TLwhich is a power transmission-side coil and a capacitor TCwhich is a power transmission-side capacitor, and the resonant circuit RR includes a coil RLwhich is a power reception-side coil and a capacitor RCwhich is a power reception-side capacitor. In the following description, it is assumed that in order to give a concrete form to the description, unless otherwise described, the power transmission-side coil TLand the power transmission-side capacitor TCare connected in parallel to each other so as to form the resonant circuit TT as a parallel resonant circuit, and that the power reception-side coil RLand the power reception-side capacitor RCare connected in parallel to each other so as to form the resonant circuit RR as a parallel resonant circuit. However, the power transmission-side coil TLand the power transmission-side capacitor TCmay be connected in series with each other so as to form the resonant circuit TT as a series resonant circuit, and the power reception-side coil RLand the power reception-side capacitor RCmay be connected in series with each other so as to form the resonant circuit RR as a series resonant circuit.

As shown inFIG. 1B, when the electronic device2is placed within a predetermined region on the power feeding stage12, by a magnetic field resonance method (that is, by the utilization of magnetic field resonance), it is possible to perform communication, power transmission and power reception between the devices1and2. The magnetic field resonance is also referred to as magnetic field sympathetic oscillation or the like.

The communication between the devices1and2is wireless communication (hereinafter referred to as NFC communication) performed by NFC (Near field communication), and the frequency of a carrier for the communication is 13.56 MHz (megahertz). In the following description, 13.56 MHz is referred to as a reference frequency. Since the NFC communication between the devices1and2is performed by the magnetic field resonance method utilizing the resonant circuits TT and RR, the resonant frequencies of the resonant circuits TT and RR each are set to the reference frequency. In other words, the resonant frequency of the resonant circuit TT determined by the inductance value of the power transmission-side coil TLand the capacitance value of the power transmission-side capacitor TCand the resonant frequency of the resonant circuit RR determined by the inductance value of the power reception-side coil RLand the capacitance value of the power reception-side capacitor RCcoincide with the reference frequency. However, the resonant frequency of the resonant circuit RR can be temporarily changed from the reference frequency as will be described later.

The power transmission and the power reception between the devices1and2are the power transmission performed by the NFC from the power feeding device1to the electronic device2and the power reception performed by the NFC in the electronic device2. The power transmission and the power reception are collectively referred to as NFC power transfer or simply referred to as power transfer. Power is transmitted by the magnetic field resonance method from the coil TLto the coil RL, and thus the power transfer is realized in a non-contact manner.

In the power transfer utilizing the magnetic field resonance, an alternating current is passed through the power transmission-side coil TL, and thus an alternating magnetic field at the reference frequency is generated in the power transmission-side coil TL. Then, the alternating magnetic field is transmitted to the resonant circuit RR which resonates at the reference frequency (that is, which performs sympathetic oscillation) such that an alternating current flows through the power reception-side coil RL. In other words, power is transmitted from the resonant circuit TT including the power transmission-side coil TLto the resonant circuit RR including the power reception-side coil RL. In the following description, the magnetic field which is generated by the coil TLor the coil RLin the NFC communication or the power transfer is the alternating magnetic field which oscillates at the reference frequency unless otherwise described though the description thereof may be omitted.

A state where the electronic device2is placed within a predetermined power transmission region on the power feeding stage12(the power feeding device1and the electronic device2are in a predetermined positional relationship) such that it is possible to realize the NFC communication and the power transfer described above is referred to as the reference arrangement state (seeFIG. 1B). On the other hand, a state where the electronic device2is located sufficiently away from the power feeding stage12such that it is impossible to realize the NFC communication and the power transfer described above is referred to as the separate state (seeFIG. 1A). Although in the power feeding stage12shown inFIG. 1A, the front surface is flat, a recess or the like which corresponds to the shape of the electronic device2to be placed thereon may be formed in the power feeding stage12. The reference arrangement state may be interpreted so as to belong to a state where the electronic device2is present in the predetermined power transmission region (that is, the region for performing the power transmission and the power reception) in which it is possible to perform the transmission and reception of power between the power feeding device1and the electronic device2, and the separate state may be interpreted so as to belong to a state where the electronic device2is not present in the power transmission region.

FIG. 4shows a partial configuration diagram of the power feeding device1including an internal block diagram of the IC100. In the IC100, individual portions are provided which are represented by symbols110,120,130,140,150and160.FIG. 5shows a partial configuration diagram of the electronic device2including an internal block diagram of the IC200. In the IC200, individual portions are provided which are represented by symbols210,220,230,240and250. A capacitor23which outputs the drive voltage for the IC200may be connected to the IC200. The capacitor23can output the direct current voltage obtained by rectifying the signal for the NFC communication received from the power feeding device1.

The switching circuit110connects, under control of the control circuit160, either of the NFC communication circuit120and the NFC power transmission circuit130to the resonant circuit TT. The switching circuit110can be formed with a plurality of switches which are interposed between the resonant circuit TT and the circuits120and130. An arbitrary switch which is described in the present specification may be formed with a semiconductor switching element such as a field effect transistor.

The switching circuit210connects, under control of the control circuit250, the resonant circuit RR to either of the NFC communication circuit220and the NFC power reception circuit230. The switching circuit210can be formed with a plurality of switches which are interposed between the resonant circuit RR and the circuits220and230.

A state where the resonant circuit TT is connected through the switching circuit110to the NFC communication circuit120and where the resonant circuit RR is connected through the switching circuit210to the NFC communication circuit220is referred to as a communication connection state. In the communication connection state, the NFC communication can be performed. In the communication connection state, the NFC communication circuit120can supply an alternating current signal (an alternating current voltage) at the reference frequency to the resonant circuit TT. The NFC communication between the devices1and2is performed by a half-duplex method.

When in the communication connection state, the power feeding device1is a transmission side, an arbitrary information signal is superimposed on the alternating current signal supplied by the NFC communication circuit120to the resonant circuit TT, and thus the information signal is transmitted from the coil TLserving as a power feeding device-side antenna coil and is received by the coil RLserving as an electronic device-side antenna coil. The information signal received in the coil RLis extracted in the NFC communication circuit220. When in the communication connection state, the electronic device2is the transmission side, the NFC communication circuit220can transmit an arbitrary information signal (response signal) from the coil RLin the resonant circuit RR to the coil TLin the resonant circuit TT. As is known, this transmission is realized by a load modulation method in which based on an ISO standard (for example, ISO14443 standard), the impedance of the coil RL(the electronic device-side antenna coil) seen from the coil TL(the power feeding device-side antenna coil) is changed. The information signal transmitted from the electronic device2is extracted in the NFC communication circuit120.

A state where the resonant circuit TT is connected through the switching circuit110to the NFC power transmission circuit130and where the resonant circuit RR is connected through the switching circuit210to the NFC power reception circuit230is referred to as a power feeding connection state.

In the power feeding connection state, the NFC power transmission circuit130can perform a power transmission operation, and the NFC power reception circuit230can perform a power reception operation. The power transfer is realized by the power transmission operation and the power reception operation. In the power transmission operation, the power transmission circuit130supplies, to the resonant circuit TT, a power transmission alternating current signal (power transmission alternating current voltage) at the reference frequency so as to generate a power transmission magnetic field (power transmission alternating magnetic field) at the reference frequency in the power transmission-side coil TL, and thus power is transmitted by the magnetic field resonance method from the resonant circuit TT (the power transmission-side coil TL) to the resonant circuit RR. The power received in the power reception-side coil RLbased on the power transmission operation is fed to the power reception circuit230, and in the power reception operation, the power reception circuit230generates arbitrary direct current power from the received power and outputs it. With the output power of the power reception circuit230, it is possible to charge the battery21.

Although a magnetic field is also generated in the coil TLor RLwhen the NFC communication is performed in the communication connection state, a magnetic field intensity in the NFC communication falls within a predetermined range. The lower limit value and the upper limit value in the range are defined in the standard of the NFC so as to be 1.5 A/m and 7.5 A/m, respectively. By contract, in the power transfer (that is, the power transmission operation), the intensity of a magnetic field (the magnetic field intensity of the power transmission magnetic field) generated in the power transmission-side coil TLis more than the upper limit value described above so as to be, for example, about 45 to 60 A/m. In the non-contact power feeding system including the devices1and2, it is possible to alternately perform the NFC communication and the power transfer (NFC power transfer), and the state of a magnetic field intensity at that time is shown inFIG. 6.

The load detection circuit140detects the magnitude of a load for the power transmission-side coil TL, that is, the magnitude of a load for the power transmission-side coil TLwhen the alternating current signal is supplied from the power transmission circuit130to the power transmission-side coil TL.FIG. 7shows a relationship between the power transmission circuit130, the load detection circuit140and the resonant circuit TT in the power feeding connection state. InFIG. 7, the switching circuit110is omitted.

The power transmission circuit130includes: a signal generator131which generates a sinusoidal signal at the reference frequency; an amplifier (power amplifier)132which amplifies the sinusoidal signal generated in the signal generator131so as to output the amplified sinusoidal signal between lines134and135with reference to the potential of the line134; and a capacitor133. On the other hand, the load detection circuit140includes a sense resistor141, an envelope detector142, an amplifier143and an A/D converter144. Although the intensity of the sinusoidal signal generated by the signal generator131is fixed to a constant value, the amplification factor of the amplifier132is variably set by the control circuit160.

One end of the capacitor133is connected to the line135. In the power feeding connection state, the other end of the capacitor133is connected in common to one ends of the capacitor TCand the coil TL, and the other end of the coil TLis connected in common to the line134and the other end of the capacitor TCthrough the sense resistor141.

The power transmission operation is realized by supplying the alternating current signal (power transmission alternating current voltage) from the amplifier132through the capacitor133to the resonant circuit TT. In the power feeding connection state, the alternating current signal from the amplifier132is supplied to the resonant circuit TT, and thus an alternating current at the reference frequency flows through the power transmission-side coil TL, with the result that an alternating current voltage drop is produced in the sense resistor141. The solid line waveform ofFIG. 8is a voltage waveform of the voltage drop in the sense resistor141. When on the resonant circuit TT, under the conditions in which the intensity of the magnetic field generated in the power transmission-side TLis constant, the electronic device2is brought close to the power feeding stage12, a current based on the magnetic field generated in the power transmission-side coil TLflows through the power reception-side coil RLwhereas a counter electromotive force based on the current flowing through the power reception-side coil RLis generated in the power transmission-side coil TL, and the counter electromotive force acts so as to reduce the current flowing through the power transmission-side coil TL. Hence, as shown inFIG. 8, the amplitude of the voltage drop of the sense resistor141in the reference arrangement state is smaller than that in the separate state.

The envelope detector142detects the envelope of a signal of the voltage drop in the sense resistor141so as to output an analogue voltage signal proportional to the voltage v ofFIG. 8. The amplifier143amplifies the output signal of the envelope detector142and outputs it. The A/D converter144converts the output voltage signal of the amplifier143into a digital signal so as to output a digital voltage value VD. As is understood from the above description, the voltage value VDhas a value proportional to the amplitude of the current flowing through the sense resistor141(hence, the amplitude of the current flowing through the power transmission-side coil TL) (as the amplitude is increased, the voltage value VDis also increased). Hence, the load detection circuit140can be said to be a current amplitude detection circuit which detects the amplitude of the current flowing through the power transmission-side coil TL, and the amplitude detection value thereof can be considered to be the voltage value VD. The envelope detector142may be provided in a stage subsequent to the amplifier143. However, as shown inFIG. 7, when the envelope detector142is provided in a stage preceding the amplifier143, it is advantageously possible to adopt, as the amplifier143, an amplifier whose response performance for high-frequency waves is lower.

For the power transmission-side coil TLwhich generates a magnetic field, a coil such as the power reception-side coil RLwhich is magnetically coupled to the power transmission-side coil TLcan be considered to be a load, and depending on the magnitude of the load, the voltage value VDwhich is the detection value of the load detection circuit140is changed. Hence, it can also be considered that the load detection circuit140detects the magnitude of the load by the output of the voltage value VD. The magnitude of the load here can be said to be the magnitude of the load for the power transmission-side coil TLin the power transmission or can be said to be the magnitude of the load of the electronic device2in the power transmission which is seen from the power feeding device1. The sense resistor141may be provided within the IC100or may be provided outside the IC100.

The memory150(seeFIG. 4) is formed with a nonvolatile memory, and stores arbitrary information in a nonvolatile manner. The control circuit160comprehensively controls the operations of the individual portions within the IC100. The control performed by the control circuit160includes, for example, control on the switching operation of the switching circuit110, control on the details of the communication operation and the power transmission operation of the communication circuit120and the power transmission circuit130and control on whether or not the operations are performed, control on the operation of the load detection circuit140and control on the storage of the memory150and control on the reading thereof. The control circuit160incorporates a timer (unillustrated), and thereby can measure the length of a time between arbitrary timings.

The resonant state change circuit240(seeFIG. 5) in the electronic device2is a resonant frequency change circuit which can change the resonant frequency of the resonant circuit RR from the reference frequency to another predetermined frequency fMor a coil short circuit which can short-circuit the power reception-side coil RLin the resonant circuit RR.

A resonant frequency change circuit240A inFIG. 9is an example of the resonant frequency change circuit serving as the resonant state change circuit240. The resonant frequency change circuit240A is formed with a series circuit of a capacitor241and a switch242, one end of the series circuit is connected in common to one ends of the capacitor RCand the coil RLand the other end of the series circuit is connected in common to the other ends of the capacitor RCand the coil RL. The switch242is turned on or off under control of the control circuit250. When the switch242is turned off, the capacitor241is separated from the capacitor RCand the coil RL, and thus when a parasitic inductance and a parasitic capacitance are ignored, the resonant circuit RR is formed with only the coil RLand the capacitor RC, and the resonant frequency of the resonant circuit RR coincides with the reference frequency. In other words, when the switch242is turned off, a power reception-side capacitance for determining the resonant frequency of the resonant circuit RR is the capacitor RCitself. When the switch242is turned on, since the capacitor241is connected in parallel to the capacitor RC, the resonant circuit RR is formed with the coil RLand the combined capacitance of the capacitors RCand241, with the result that the resonant frequency of the resonant circuit RR is the frequency fMwhich is lower than the reference frequency. In other words, when the switch242is turned on, the power reception-side capacitance for determining the resonant frequency of the resonant circuit RR is the combined capacitance described above. Here, it is assumed that when the switch242is turned on, the frequency fMis separated from the reference frequency such that the resonant circuit RR does not function as the load for the power transmission-side coil TL(that is, such that magnetic field resonance is not sufficiently produced between the resonant circuits TT and RR). For example, the resonant frequency (that is, the frequency fM) of the resonant circuit RR when the switch242is turned on is set to several hundred kHz to 1 MHz.

As long as the resonant frequency of the resonant circuit RR can be changed to the frequency fM, the resonant frequency change circuit serving as the change circuit240is not limited to the resonant frequency change circuit240A, and the frequency fMmay be higher than the reference frequency. For example, the resonant frequency change circuit may be a circuit which switches connection and non-connection between the coil RLand the capacitor RCby turning on and off a switch that is inserted in series on a current loop for connecting the coil RLand the capacitor RC(when the state is switched to the non-connection, the resonant frequency (>>the reference frequency) of the resonant circuit RR is determined by the coil RLand the parasitic capacitance of the wiring). In other words, with consideration given to the fact that the power reception-side resonant circuit RR can be a series resonant circuit, the following can be said. The power reception-side resonant circuit RR includes the parallel circuit or the series circuit of the power reception-side coil (RL) and the power reception-side capacitance, and the power reception-side capacitance coincides with a predetermined reference capacitance, the resonant frequency fOof the power reception-side resonant circuit RR coincides with the reference frequency. The resonant frequency change circuit increases or decreases the power reception-side capacitance from the reference capacitance with necessary timing. In this way, in the power reception-side resonant circuit RR, the parallel circuit or the series circuit is formed with the power reception-side coil (RL) and the power reception-side capacitance which is higher or lower than the reference capacitance, with the result that the resonant frequency fOof the power reception-side resonant circuit RR is changed from the reference frequency.

A coil short circuit240B inFIG. 10is an example of the coil short circuit serving as the resonant state change circuit240. The coil short circuit240B is formed with a switch243that is connected (inserted) between a node to which the one end of the capacitor RCand one end of the coil RLin the resonant circuit RR are connected in common and a node to which the other end of the capacitor RCand the other end of the coil RLin the resonant circuit RR are connected in common. The switch243is turned on or off under control of the control circuit250. When the switch243is turned on, the coil RLin the resonant circuit RR is short-circuited (more specifically, both ends of the coil RLare short-circuited). In a state where the power reception-side coil RLis short-circuited, the power reception-side resonant circuit RR is not present (a state equivalent to the state where the power reception-side resonant circuit RR is not present is entered). Hence, while the power reception-side coil RLis being short-circuited, the load for the power transmission-side coil TLis sufficiently reduced (that is, a state as if the electronic device2were not present on the power feeding stage12is entered). As long as the power reception-side coil RLcan be short-circuited, the coil short circuit serving as the change circuit240is not limited to the coil short circuit240B.

In the following description, an operation of changing the resonant frequency fOof the power reception-side resonant circuit RR from the reference frequency to the predetermined frequency fMis referred to as a resonant frequency change operation, and an operation of short-circuiting the power reception-side coil RLwith the coil short circuit is referred to as a coil short circuit operation. For simplification of description, the resonant frequency change operation or the coil short circuit operation is also referred to as an fOchange/short circuit operation.

The control circuit250(seeFIG. 5) comprehensively controls the operations of the individual portions within the IC200. The control performed by the control circuit250includes, for example, control on the switching operation of the switching circuit210, control on the details of the communication operation and the power reception operation of the communication circuit220and the power reception circuit230and control on whether or not the operations are performed and control on the operation of the change circuit240. The control circuit250incorporates a timer (unillustrated), and thereby can measure the length of a time between arbitrary timings. For example, the timer in the control circuit250can measure a time during which the changing of the resonant frequency fOto the predetermined frequency fMor the short-circuiting of the power reception-side coil RLby the fOchange/short circuit operation is maintained (that is, the measurement of a time TMwhich will be described later; see step S207inFIG. 19).

Incidentally, the control circuit160of the power feeding device1determines whether or not a foreign object is present on the power feeding stage12, and can control the power transmission circuit130such that only when the foreign object is not present, the power transmission operation is performed. The foreign object in the present embodiment differs from the electronic device2and the constituent elements of the electronic device2(such as the power reception-side coil RL), and includes an object which can generate a current (current within the foreign object) based on the magnetic field generated in the power transmission-side coil TLwhen the object is brought close to the power feeding device1. In the present embodiment, the presence of the foreign object may be interpreted so as to mean that the foreign object is present in such a position that an unignorable current based on the magnetic field generated in the power transmission-side coil TLflows within the foreign object. The current flowing within the foreign object based on the magnetic field generated in the power transmission-side coil TLgenerates an electromotive force (or a counter electromotive force) in the coil (TLor RL) which is opposite the foreign object and is coupled thereto, with the result that the current can exert an unignorable influence on the properties of the circuit including the coil.

FIG. 11Ashows a schematic outline view of a foreign object3which is one type of foreign object, andFIG. 11Bshows a schematic internal configuration diagram of the foreign object3. The foreign object3includes a resonant circuit JJ which is formed with a parallel circuit of a coil JLand a capacitor JCand a foreign object internal circuit300which is connected to the resonant circuit JJ. The resonant frequency of the resonant circuit JJ is set to the reference frequency. Unlike the electronic device2, the foreign object3is a device which does not correspond to the power feeding device1. For example, the foreign object3is an object (such as a non-contact IC card) which includes a wireless IC tag having an antenna coil (the coil JL) of 13.56 MHz that does not respond to the NFC communication. For example, the foreign object3is also an electronic device which has an NFC communication function itself but in which the function is disabled. For example, a smart phone which has the NFC communication function but in which the function is turned off by a software setting can be the foreign object3. A smart phone in which the NFC communication function is enabled but which does not have a power reception function is also classified as the foreign object3.

If in a state where the foreign object3described above is arranged on the power feeding stage12, the power feeding device1performs the power transmission operation, the foreign object3may be destroyed by a strong magnetic field (for example, a magnetic field having a magnetic field intensity of 12 A/m or more) generated in the power transmission-side coil TL. For example, the strong magnetic field at the time of the power transmission operation may increase the terminal voltage of the coil JLin the foreign object3on the power feeding stage12to 100 to 200V, and unless a foreign object3which can withstand such a high voltage is formed, the foreign object3is destroyed.

[pFOD Processing (pFOD Processing Before Power Transfer)]

Foreign object detection processing for detecting whether or not the foreign object is present will be described with reference toFIG. 12.FIG. 12is a flowchart of the foreign object detection processing (hereinafter referred to as pFOD processing) which is performed by the power feeding device1before the power transfer.

When the pFOD processing is performed, the power transmission circuit130is connected to the resonant circuit TT. In the pFOD processing, the control circuit160first sets, in step S11, the magnetic field intensity H of the power transmission-side coil TLto a predetermined test intensity. The magnetic field intensity H is the intensity of a magnetic field generated in the power transmission-side coil TL, and more specifically, the magnetic field intensity H indicates the magnetic field intensity of an alternating magnetic field which is generated in the power transmission-side coil TLand which oscillates at the reference frequency. The setting of the magnetic field intensity H to the test intensity means the controlling of the power transmission circuit130such that a predetermined test alternating current signal (test alternating current voltage) is supplied to the resonant circuit TT, and indicates that a test magnetic field of the alternating magnetic field which has the test intensity and which oscillates at the reference frequency is generated in the power transmission-side coil TL. The test intensity which is the magnetic field intensity of the test magnetic field is significantly lower than the intensity of the magnetic field (that is, the magnetic field intensity of the power transmission magnetic field; for example, 45 to 60 A/m) generated in the power transmission-side coil TLin the power transfer (that is, the power transmission operation), and falls within a range from a lower limit value of “1.5 A/m” to an upper limit value of “7.5 A/m” in a communication magnetic field intensity. Hence, the foreign object3is prevented from being subjected to destruction or the like by the test magnetic field or is unlikely to be subjected thereto. The control circuit160controls the amplification factor of the amplifier132(seeFIG. 7) and thereby can variably set the magnetic field intensity H. The amplification factor of the amplifier132is preferably controlled such that when the test magnetic field is generated, the predetermined test alternating current voltage is supplied and applied to the resonant circuit TT and that when the power transmission magnetic field is generated, a predetermined power transmission alternating current voltage which has a larger amplitude than the test alternating current voltage is supplied and applied to the resonant circuit TT.

In step S12subsequent to step S11, the control circuit160uses the load detection circuit140so as to acquire, as a current amplitude detection value VpFOD, the voltage value VDwhen the test magnetic field is generated. The current amplitude detection value VpFODhas a value corresponding to the amplitude of the current flowing through the power transmission-side coil TLwhen the test magnetic field is generated in the power transmission-side coil TL. During a period in which the pFOD processing is performed, according to an instruction from the power feeding device1through the NFC communication, in the electronic device2, the fOchange/short circuit operation (the resonant frequency change operation or the coil short circuit operation) is performed. Hence, the resonant circuit RR (the power reception-side coil RL) does not substantially function as a load for the power transmission-side coil TL, and thus the current amplitude detection value VpFODis prevented from being reduced or is hardly reduced.

In step S13subsequent to step S12, the control circuit160determines whether or not the current amplitude detection value VpFODfalls within a predetermined pFOD normal range. Then, when the current amplitude detection value VpFODfalls within the pFOD normal range, the control circuit160determines that the foreign object3is not present on the power feeding stage12(step S14). This determination is referred to as a foreign object absence determination. On the other hand, when the current amplitude detection value VpFODfalls outside the pFOD normal range, the control circuit160determines that the foreign object3is present on the power feeding stage12(step S15). This determination is referred to as a foreign object presence determination. When the foreign object absence determination is made, the control circuit160determines that the power transmission operation can be performed by the power transmission circuit130so as to allow the performance of the power transmission operation (the power transmission using the resonant circuit TT) whereas when the foreign object presence determination is made, the control circuit160determines that the power transmission operation cannot be performed by the power transmission circuit130so as to prohibit the performance of the power transmission operation. When the control circuit160determines that the power transmission operation can be performed, in the power transmission operation, the control circuit160can control the power transmission circuit130such that a predetermined power transmission magnetic field is generated in the power transmission-side coil TL.

The pFOD normal range is a range which is equal to or more than a predetermined lower limit value VpREFLbut equal to or less than a predetermined upper limit value VpREFH(0<VpREFL<VpREFH). Hence, when a determination inequality “VpREFL≤VpFOD≤VpREFH” is satisfied, the foreign object absence determination is made whereas when the determination inequality is not satisfied, the foreign object presence determination is made.

In a case where the foreign object3is present on the power feeding stage12when the pFOD processing is performed, the resonant circuit JJ (the coil JL) of the foreign object3functions as a load for the power transmission-side coil TL, with the result that as compared with a case where the foreign object3is not present on the power feeding stage12, the current amplitude detection value VpFODis reduced.

As the foreign object, a foreign object3a(unillustrated) which is different from the foreign object3can also be considered. The foreign object3ais, for example, a metal object (an aluminum foil or an aluminum plate) which is formed so as to contain aluminum or a metal object which is formed so as to contain copper. In a case where the foreign object3ais present on the power feeding stage12when the pFOD processing is performed, as compared with a case where the foreign object3ais not present on the power feeding stage12, the current amplitude detection value VpFODis increased by electrical and magnetic action.

Before the power transfer is performed, the lower limit value VpREFLand the upper limit value VpREFHare previously set and stored in the memory150through experiments such that when the foreign object3is present on the power feeding stage12, the current amplitude detection value VpFODfalls below the lower limit value VpREFL, that when the foreign object3ais present on the power feeding stage12, the current amplitude detection value VpFODexceeds the upper limit value VpREFHand that when the foreign object (3or3a) is not present on the power feeding stage12, the current amplitude detection value VpFODfalls within the pFOD normal range.

When the power transmission magnetic field is generated in a state where the foreign object3ais present on the power feeding stage12, power may be absorbed by the foreign object3a, and thus the foreign object3amay generate heat. In the present embodiment, since it is assumed that the reference frequency serving as a carrier frequency in the power transfer is 13.56 MHz, it can be said that it is highly unlikely that the foreign object3agenerates heat. Hence, a configuration may be adopted in which without any consideration being given to the presence of the foreign object3a, only when the current amplitude detection value VpFODfalls below the lower limit value VpREFL, the foreign object presence determination is made, and in which when the current amplitude detection value VpFODis equal to or more than the lower limit value VpREFL, the foreign object absence determination is constantly made (in other words, the upper limit value VpREFHmay be abolished). However, in the invention according to the present embodiment, the reference frequency is not limited to 13.56 MHz, and when the reference frequency is set to, for example, several hundred kHz, it is highly likely that the foreign object3agenerates heat, with the result that it is preferable to adopt the above method in which not only the lower limit value VpREFLbut also the upper limit value VpREFHis determined to be within the pFOD normal range.

An additional description will be given of the method of determining the lower limit value VpREFL. The lower limit value VpREFLis determined in initial setting processing.FIG. 13is an operational flowchart of the initial setting processing. The initial setting processing is performed by the IC100under an initial setting environment below. In the initial setting environment, a load for the power transmission-side coil TLis not present at all or is small enough to be ignored, and an object (including a coil which is magnetically coupled to the power transmission-side coil TL) which can produce a current by the magnetic field generated in the power transmission-side coil TLis not present except the constituent components of the power feeding device1. The separate state ofFIG. 1Amay be considered to satisfy the initial setting environment. In order to ensure the acquisition of the initial setting environment, for example, the initial setting processing may be performed such as when the power feeding device1is manufactured or shipped. However, as long the initial setting environment can be acquired, the initial setting processing can be performed with arbitrary timing.

When the initial setting processing is performed, the power transmission circuit130is connected to the resonant circuit TT. Then, in step S21, the magnetic field intensity H of the power transmission-side coil TLis set to the predetermined test intensity, and in step S22subsequent thereto, in the set state, the voltage value VDacquired from the A/D converter144is obtained as a voltage value VDO. Thereafter, in step S23, the lower limit value VpREFLbased on the voltage value VDOis stored in the memory150. The lower limit value VpREFLis set lower than the voltage value VDOsuch that only under the presence of the foreign object3, the foreign object presence determination is made in the pFOD processing. For example, it is preferable to make a setting such that “VpREFL=VDO−ΔV” or “VpREFL=VDO×k”. Here, ΔV is a predetermined positive minute value (however, it is possible to make a setting such that ΔV=0). Here, k is a coefficient which has a positive predetermined value less than 1. The voltage value VDwhich can be obtained when under the initial setting environment, the magnetic field intensity H is set to the predetermined test intensity can be estimated in a design stage. Based on the value derived by this estimation, without the initial setting processing being performed, the lower limit value VpREFLmay be determined and stored in the memory150.

Consider first to fourth cases on the detection of the foreign object3with reference toFIG. 14AtoFIG. 14D. In the first case, only the electronic device2is present on the power feeding stage12. In the second case, the electronic device2and the foreign object3are present on the power feeding stage12. In the third case, only the foreign object3is present on the power feeding stage12. In the fourth case, neither the electronic device2nor the foreign object3is present on the power feeding stage12.

Since as described previously, during the period in which the pFOD processing is performed, in the electronic device2, the fOchange/short circuit operation is performed, in the first case, the load for the power transmission-side coil TLis sufficiently reduced (that is, the state as if the electronic device2were not present on the power feeding stage12is entered), and thus the current amplitude detection value VpFODis sufficiently increased, with the result that the foreign object absence determination is made. On the other hand, in the second case, although the resonant frequency of the resonant circuit RR is changed to the frequency fMor the power reception-side coil RLis short-circuited, since the foreign object3continues to be present as the load for the power transmission-side coil TL(since the resonant frequency of the resonant circuit JJ in the foreign object3remains the reference frequency), the current amplitude detection value VpFODis sufficiently decreased, with the result that the foreign object presence determination is made.

In the third and fourth cases, since the electronic device2which responds to the NFC communication is not present on the power feeding stage12, the power transmission operation is not necessary in the first place, and thus the pFOD processing itself is not performed. The power feeding device1can determine, by the NFC communication, whether or not the electronic device2which can handle the power transfer is present on the power feeding stage12. The state where the foreign object3is present on the power feeding stage12is not limited to a state where the foreign object3is in direct contact with the power feeding stage12. For example, as shown inFIG. 15, a state where the electronic device2is present so as to be in direct contact with the top of the power feeding stage12and where the foreign object3is present on the electronic device2also belongs to the state where the foreign object3is present on the power feeding stage12as long as the foreign object presence determination is made.

[Exchange of Signals Until Power Transfer:FIG. 16]

The exchange of signals between the devices1and2until the power transfer is performed will be described with reference toFIG. 16. In the following description, unless otherwise described, it is assumed that the electronic device2is present on the power feeding stage12in the reference arrangement state (FIG. 1B).

First, the power feeding device1serves as the transmission side and the electronic device2serves as the reception side, and the power feeding device1(the IC100) transmits, by the NFC communication, an inquiry signal510to a device on the power feeding stage2(hereinafter also referred to as a power feeding target device). The power feeding target device includes the electronic device2, and can include the foreign object3. The inquiry signal510includes, for example, a signal for inquiring the unique identification information of the power feeding target device, a signal for inquiring whether the power feeding target device is in a state where the power feeding target device can perform the NFC communication and a signal for inquiring whether the power feeding target device can receive power or the power feeding target device requires the transmission of power.

The electronic device2(the IC200) which receives the inquiry signal510transmits, by the NFC communication, to the power feeding device1, a response signal520for responding to the details of the inquiry in the inquiry signal510. The power feeding device1(the IC100) which receives the response signal520analyzes the response signal520, and when the power feeding target device can perform the NFC communication and can receive power or requires the transmission of power, the power feeding device1transmits a test requirement signal530to the power feeding target device by the NFC communication. The electronic device2(the IC200) serving as the power feeding target device which receives the test requirement signal530transmits a response signal540for the test requirement signal530to the power feeding device1by the NFC communication, and then immediately performs the fOchange/short circuit operation (the resonant frequency change operation or the coil short circuit operation). The test requirement signal530is, for example, a signal for requiring the performance of the fOchange/short circuit operation or providing an instruction to perform it, and the control circuit250of the electronic device2makes the resonant state change circuit240perform the fOchange/short circuit operation by being triggered by the reception of the test requirement signal530. Before the reception of the test requirement signal530, the fOchange/short circuit operation is not performed. As long as the test requirement signal530triggers the performance of the fOchange/short circuit operation, any signal may be used as the test requirement signal530, and the test requirement signal530may be included in the inquiry signal510.

The power feeding device1(the IC100) which receives the response signal540performs the pFOD processing described previously. During the period in which the pFOD processing is performed, the electronic device2(the IC200) continues to perform the fOchange/short circuit operation. Specifically, the electronic device2(the IC200) uses the internal timer so as to maintain the performance of the fOchange/short circuit operation only for a time corresponding to the length of a period in which the pFOD processing is performed, and then stops the fOchange/short circuit operation.

When in the pFOD processing, it is determined that the foreign object is not present on the power feeding stage12, the power feeding device1(the IC100) transmits an authentication signal550to the power feeding target device by the NFC communication. The authentication signal550includes, for example, a signal for notifying the power feeding target device of the information that the power transmission is performed from now. The electronic device2(the IC200) which receives the authentication signal550transmits a response signal560corresponding to the authentication signal550to the power feeding device1by the NFC communication. The response signal560includes, for example, a signal for providing a notification that the details indicated by the authentication signal550are recognized or a signal for allowing the details indicated by the authentication signal550. The power feeding device1(the IC100) which receives the response signal560connects the power transmission circuit130to the resonant circuit TT so as to perform the power transmission operation, with the result that power transfer570is realized.

Although in the first case ofFIG. 14A, the power transfer570is performed by the procedure described above, in the second case ofFIG. 14B, the processing proceeds up to the transmission and reception of the response signal540but in the pFOD processing, it is determined that the foreign object is present on the power feeding stage12, with the result that the power transfer570is not performed. One round of the power transfer570may be performed only for a predetermined time. A series of processing steps from the transmission of the inquiry signal510to the power transfer570may be repeatedly performed. In actuality, as shown inFIG. 17, the NFC communication, the pFOD processing and the power transfer (NFC power transfer) can be performed sequentially and repeatedly. In other words, in the non-contact power feeding system, the operation for performing the NFC communication, the operation for performing the pFOD processing and the operation for performing the power transfer (NFC power transfer) can be sequentially and repeatedly performed in a time division manner.

[Operational Flowchart of Power Feeding Device and Electronic Device]

The flow of the operation of the power feeding device1will then be described.FIG. 18is an operational flowchart of the power feeding device1. The operations of the communication circuit120and the power transmission circuit130are performed under control of the control circuit160.

When the power feeding device1is started up, in step S101, the control circuit160first connects the communication circuit120to the resonant circuit TT through the control of the switching circuit110. In step S102subsequent thereto, the control circuit160transmits the inquiry signal510to the power feeding target device by the NFC communication using the communication circuit120and the resonant circuit TT, and is thereafter, in step S103, on standby for the reception of the response signal520. When the response signal520is received in the communication circuit120, the control circuit160analyzes the response signal520, and when the power feeding target device can perform the NFC communication and can receive power or requires the transmission of power, the control circuit160determines that the power transmission target is present (Y in step S104), and the process proceeds to step S105, otherwise (N in step S104), the process returns to step S102.

In step S105, the control circuit160transmits the test requirement signal530to the power feeding target device by the NFC communication using the communication circuit120and the resonant circuit TT, and is thereafter, in step S106, on standby for the reception of the response signal540. When the response signal540is received in the communication circuit120, in step S107, the control circuit160connects the power transmission circuit130to the resonant circuit TT through the control of the switching circuit110, and then performs, in step S108subsequent thereto, the pFOD processing described previously.

After the pFOD processing, in step S109, the control circuit160connects the communication circuit120to the resonant circuit TT through the control of the switching circuit110, and the process proceeds to step S110. When in the pFOD processing of step S108, the foreign object presence determination is made, the process returns from step S110to step S102whereas when the foreign object absence determination is made, the process proceeds from step S110to step S111.

In step S111, the control circuit160transmits the authentication signal550to the power feeding target device by the NFC communication using the communication circuit120and the resonant circuit TT, and is thereafter, in step S112, on standby for the reception of the response signal560. When the response signal560is received in the communication circuit120, in step S113, the control circuit160connects the power transmission circuit130to the resonant circuit TT through the control of the switching circuit110, and then the process proceeds to step S114.

The control circuit160sets, in step S114, a power transmission allowance flag on, and starts the power transmission operation and mFOD processing, and thereafter the process proceeds to step S115. Although details will be described later, whether or not the foreign object is present in the power transfer is detected by the mFOD processing, and when the foreign object is detected, the power transmission allowance flag is turned off. The control circuit160measures the time which has elapsed since the start of the power transmission operation, and in step S115, compares the elapsed time with a predetermined time tA(for example, 10 minutes) and checks the state of the power transmission allowance flag. When the elapsed time reaches the predetermined time tAor when the power transmission allowance flag is set off by the mFOD processing, the process proceeds to step S116. In step S116, the control circuit160switches the power transmission allowance flag from on to off or keeps the power transmission allowance flag off, and stops the power transmission operation and the mFOD processing, and thereafter the process returns to step S101.

The flow of the operation of the electronic device2will then be described.FIG. 19is an operational flowchart of the electronic device2, and the processing starting from step S201is performed as the operation of the power feeding device1shown inFIG. 18is performed. The operations of the communication circuit220and the power reception circuit230are performed under control of the control circuit250.

When the electronic device2is started up, in step S201, the control circuit250first connects the communication circuit220to the resonant circuit RR through the control of the switching circuit210. When the electronic device2is started up, the fOchange/short circuit operation is not performed. In step S202subsequent thereto, the control circuit250uses the communication circuit220so as to be on standby for the reception of the inquiry signal510. When the inquiry signal510is received in the communication circuit220, in step S203, the control circuit250analyzes the inquiry signal510so as to generate the response signal520, and transmits the response signal520to the power feeding device1by the NFC communication using the communication circuit220. Here, when the control circuit250checks the state of the battery21, then the battery21is not fully charged and an abnormality is not recognized in the battery21, the control circuit250includes, in the response signal520, a signal which can receive power or requires the transmission of power. On the other hand, when the battery21is fully charged or an abnormality is recognized in the battery21, the control circuit250includes, in the response signal520, a signal indicating that it is impossible to receive power.

Then, when in step S204subsequent thereto, the test requirement signal530is received in the communication circuit220, the process proceeds to step S205. In step S205, the control circuit250transmits the response signal540to the power feeding device1by the NFC communication using the communication circuit220, and in step S206subsequent thereto, uses the resonant state change circuit240so as to perform the fOchange/short circuit operation. In other words, the resonant frequency fOis changed from the reference frequency to the frequency fMor the power reception-side coil RLis short-circuited. The control circuit250measures the time which has elapsed since the start of the performance of the fOchange/short circuit operation (step S207), and stops the fOchange/short circuit operation when the elapsed time reaches a predetermined time tM(step S208). In other words, the resonant frequency fOis returned to the reference frequency or the short-circuiting of the power reception-side coil RLis cancelled. Thereafter, the process proceeds to step S209. The time tMis previously set such that during the period in which the pFOD processing is performed in the power feeding device1(that is, during the period in which the test magnetic field is generated), the performance of the fOchange/short circuit operation is maintained, and that immediately after the period is completed, the fOchange/short circuit operation is stopped. In the test requirement signal530, the time tMmay be specified.

In step S209, the control circuit250uses the communication circuit220so as to be on standby for the reception of the authentication signal550. When the authentication signal550is received in the communication circuit220, in step S210, the control circuit250transmits the response signal560for the authentication signal550to the power feeding device1by the NFC communication using the communication circuit220. When the foreign object is present on the power feeding stage12, since the authentication signal550is not transmitted from the power feeding device1(see step S110inFIG. 18), the process is preferably returned to step S201in a case where the authentication signal550is not received for a certain period of time in step S209.

After the transmission of the response signal560, in step S211, the control circuit250connects the power reception circuit230to the resonant circuit RR through the control of the switching circuit210, and in step S212subsequent thereto, starts the power reception operation using the power reception circuit230. The control circuit250measures the time which has elapsed since the start of the power reception operation, and compares the elapsed time with a predetermined time is (step S213). Then, when the elapsed time reaches the time is (Y in step S213), in step S214, the control circuit250stops the power reception operation, and the process returns to step S201.

The time tBis previously determined or is specified in the authentication signal550such that the period during which the power reception operation is performed substantially coincides with the period during which the power transmission operation is performed in the power feeding device1. A configuration may be adopted in which after the start of the power reception operation, the control circuit250monitors a charging current for the battery21, and in which when the charging current value becomes equal to or less than a predetermined value, the control circuit250determines that the power transmission operation is completed so as to stop the power reception operation and transfer to step S201.

After the start of the power transmission operation, the foreign object may be placed on the power feeding stage12. The mFOD processing functions as the foreign object detection processing in the power transfer, and whether or not the foreign object is present in the power transfer is continuously monitored by the mFOD processing.

FIG. 20is an operational flowchart of the mFOD processing. During the period in which the power transmission operation is performed, the control circuit160repeatedly performs the mFOD processing inFIG. 20. In the mFOD processing, the control circuit160first acquires, in step S51, the latest voltage value VDas a current amplitude detection value VmFOD. The current amplitude detection value VmFODhas a value corresponding to the amplitude of the current flowing through the power transmission-side coil TLwhen the power transmission magnetic field is generated in the power transmission-side coil TL. In step S52subsequent thereto, the control circuit160determines whether or not the current amplitude detection value VmFODfalls within a predetermined mFOD normal range. When the current amplitude detection value VmFODfalls within the mFOD normal range, the foreign object absence determination is made (step S53), the process returns to step S51and the processing in steps S51and S52is repeated whereas when the current amplitude detection value VmFODfalls outside the mFOD normal range, in step S54, the foreign object presence determination is made such that the power transmission allowance flag is set off. The power transmission allowance flag is controlled by the control circuit160so as to be set on or off. When the power transmission allowance flag is on, the control circuit160allows the performance of the power transmission operation whereas when the power transmission allowance flag is off, the control circuit160prohibits the performance of the power transmission operation or stops the power transmission operation.

The mFOD normal range is a range which is equal to or more than a predetermined lower limit value VmREFLbut equal to or less than a predetermined upper limit value VmREFH(0<VmREFL<VmREFH). Hence, when a determination inequality “VmREFL≤VmFOD≤VmREFH” is satisfied, the foreign object absence determination is made whereas when the determination inequality is not satisfied, the foreign object presence determination is made.

Consider, with reference toFIG. 21A, for example, a case where when the power transmission operation is performed, the foreign object3which is formed as a non-contact IC card is inserted between the power feeding stage12of the power feeding device1and the electronic device2. In this case, the power reception-side coil RLof the electronic device2is magnetically coupled to the coil JLof the foreign object3, and thus the resonant frequency of the resonant circuit RR in the electronic device2is displaced from the reference frequency (13.56 MHz) together with the resonant frequency of the resonant circuit JJ in the foreign object3. Then, the power received in the power reception-side coil RLis lowered, and thus the load of the power transmission seen from the power transmission-side coil TLis reduced, with the result that the amplitude of the current flowing through the power transmission-side coil TLis increased (in this case, the upper limit value VmREFHis preferably determined such that “VmREFH<VmFOD”).

For example, with reference toFIG. 21B, when the power transmission operation is performed, if a foreign object3bserving as an iron plate or a ferrite sheet is inserted between the power feeding stage12of the power feeding device1and the electronic device2, a current flows within the foreign object3bthrough electrical and magnetic action, with the result that the amplitude of the current flowing through the power transmission-side coil TLis decreased (in this case, the lower limit value VmREFLis preferably determined such that “VmFOD<VmREFL”).

As described above, a change in the current amplitude detection value VmFODis produced by whether or not the foreign object including the foreign objects3and3bis present. Through experiments or the like with the assumption of the types of foreign objects and the states of arrangement thereof which can be considered, the lower limit value VmREFLand the upper limit value VmREFHwhich are previously appropriately determined are preferably stored in the memory150. To what degree the current amplitude detection value VmFODis changed by the presence of the foreign object in the power transfer may be estimated by theoretical calculation, and based on the result of the estimation, the lower limit value VmREFLand the upper limit value VmREFHmay be determined and stored in the memory150without need for the experiments. Here, for example, with reference to the center value of the mFOD normal range, an object which changes the current amplitude detection value VmFODby a predetermined rate of change or more may be defined as the foreign object.

The amplification factor of the amplifier143shown inFIG. 7is variable. The amplitude of the current flowing through the power transmission-side coil TLwhen the power transmission operation and the mFOD processing are performed is significantly larger than that when the pFOD processing is performed. Hence, when the mFOD processing is performed, the control circuit160sets the amplification factor of the amplifier143smaller than the amplification factor when the pFOD processing is performed, and thus the pFOD processing and the mFOD processing are set substantially the same as each other in the input signal range of the A/D converter144.

For example, between the envelope detector142and the A/D converter144(more specifically, between the envelope detector142and the amplifier143or between the amplifier143and the A/D converter144), a high-frequency reduction circuit (unillustrated) may be inserted. In this case, amplitude information which is obtained by performing high-frequency reduction processing (in other words, averaging processing or low-pass filtering) on a voltage drop signal for the sense resistor141can be obtained as the voltage value VDfrom the A/D converter144. In the high-frequency reduction processing here, the signal components of relatively low frequencies in the voltage drop signal for the sense resistor141are passed whereas the signal components of relatively high frequencies are reduced (attenuated). By the high-frequency reduction processing, the performance of control on the prohibition of the power transmission caused such as by noises or light vibrations in the electronic device2on the power feeding stage12is reduced.

For example, instead of the provision of the high-frequency reduction circuit between the envelope detector142and the A/D converter144, high-frequency reduction processing by computation may be performed on the voltage value VDof the output signal of the A/D converter144, and the voltage value VDafter the high-frequency reduction processing may be used as the current amplitude detection value VmFOD(the same may be true for the current amplitude detection value VpFODin the pFOD processing). The high-frequency reduction processing by computation is performed in the control circuit160, and in the high-frequency reduction processing by computation, the signal components of relatively low frequencies in the output signal of the A/D converter144are passed whereas the signal components of relatively high frequencies are reduced (attenuated).

The role of the mFOD processing is not limited to the determination as to whether or not the foreign object is present. In other words, the mFOD processing plays a role in turning off the power transmission allowance flag under any conditions that are unsuitable for the continuation of the power transmission operation, such as a condition in which the current amplitude detection value VmFODfalls outside the mFOD normal range. For example, when after the start of the power transmission operation, the electronic device2is removed from the top of the power feeding stage12, the load of the power transmission seen from the power transmission-side coil TLis reduced such that the current amplitude detection value VmFODexceeds the upper limit value VmREFHand thus the power transmission allowance flag is turned off (step S54inFIG. 20).

As described above, when the transmission of power is performed by the power transmission operation, the control circuit160monitors whether or not the current amplitude detection value VmFODfalls outside the mFOD normal range so as to control whether or not the continuation of the power transmission is allowed. In this way, under conditions, such as when the foreign object is placed on the power feeding stage12after the start of the power transmission operation, which are unsuitable for the continuation of the power transmission operation, the power transmission operation is stopped through the mFOD processing, and thus it is possible to prevent the destruction of the foreign object and the like caused by the continuation of the power transmission operation.

Second Embodiment

A second embodiment of the present invention will be described. The second embodiment and a third embodiment which will be described later are embodiments based on the first embodiment, and for items which are not particularly described in the second and third embodiments, the description of the first embodiment is also applied to the second and third embodiments unless otherwise a contradiction arises.

Before the technology of the second embodiment will be described with reference toFIG. 22, an X axis, a Y axis and a Z axis which are orthogonal to each other will first be defined. A plane parallel to the X axis and the Y axis, a plane parallel to the Y axis and the Z axis and a plane parallel to the Z axis and the X axis may be referred to as an XY plane, a YZ plane and a ZX plane, respectively. The X axis and the Y axis are parallel to the placement surface of the power feeding stage12, and thus the Z axis is orthogonal to the placement surface of the power feeding stage12. The placement surface of the power feeding stage12is a surface on which the electronic device2needs to be placed, and the electronic device2and the foreign object can be placed on the placement surface. In the description of the second embodiment and in the drawings referenced therein, unless otherwise described, it is assumed that the electronic device2is placed on the placement surface of the power feeding stage12in the reference arrangement state. In the reference arrangement state, the power feeding device1and the electronic device2are in a predetermined positional relationship for performing the transmission and reception of power.

Although details will be described later, in the electronic device2, a metal plate formed of aluminum or the like or a magnetic material plate (magnetic material sheet) formed of ferrite is often provided, and they may adversely affect the power transfer, the detection of the foreign object and the like. In an electronic device2according to the second embodiment, as shown inFIG. 23, a cancel circuit (auxiliary resonant circuit) GG for reducing such influences is provided.

InFIG. 24AandFIG. 24B, cancel circuits GG1and GG2which are the first and second examples of the cancel circuit GG are shown. The cancel circuit GG1is a parallel resonant circuit that is formed by connecting, in parallel, a coil GLwhich is a cancellation coil and a capacitor GCwhich is a cancellation capacitor, and the cancel circuit GG2is a series resonant circuit that is formed by connecting, in series, the coil GLand the capacitor GC. In each of the cancel circuits GG1and GG2, as a cancellation resistor, a resistor GRis also provided. In the cancel circuit GG1, the resistor GRis connected in parallel to the parallel circuit of the coil GLand the capacitor GC. In the cancel circuit GG2, the resistor GRis inserted and connected in series with the series circuit of the coil GLand the capacitor GC. The cancellation coil GLis an independent coil which is separated from the power reception-side coil RL.

The cancel circuit GG may be either the cancel circuit GG1or the cancel circuit GG2. However, in the following description, unless otherwise described, the cancel circuit GG is assumed to be the cancel circuit GG1serving as a parallel resonant circuit, and the resonant circuits TT and RR are assumed to be also parallel resonant circuits.

The cancellation capacitor GCis a capacitor which can change its capacitance, and is, for example, a trimmer capacitor which can change the capacitance by a manual adjustment or a varicap (variable capacitor) whose capacitance is varied depending on a voltage applied to itself. However, a capacitor whose capacitance cannot be changed can also be used as the cancellation capacitor GC. The resistor GRmay be a fixed resistor whose resistance is fixed. However, a variable resistor whose resistance value can be changed may be used as the resistor GR.

The cancel circuit GG is insulated from any circuit within the electronic device2including the power reception-side resonant circuit RR. However, when the cancellation capacitor GCis formed as a varicap, a circuit within the electronic device2which feeds a voltage signal to the varicap is connected to the cancellation capacitor GC. In any case, it can be said that the cancel circuit GG is insulated from at least the power reception-side resonant circuit RR in terms of alternating current (in terms of high frequency).

The resonant frequency of the cancel circuit GG is basically set higher or lower than the reference frequency (hence, the resonant frequencies of the resonant circuits TT and RR) by use of the cancellation capacitor GC, and the actions thereof will be described later.

FIG. 25AandFIG. 25Bare a first example of a schematic perspective view and a schematic cross-sectional view of the power transmission-side coil TL, the power reception-side coil RLand the cancellation coil GLin the power feeding device1and the electronic device2in the reference arrangement state. In a method of arranging the coil GLshown inFIG. 25AandFIG. 25B(hereinafter referred to as an intermediate arrangement method), in the reference arrangement state, the cancellation coil GLis arranged between the power transmission-side coil TLand the power reception-side coil RL(in other words, the coils RL, GLand TLare sequentially aligned along the direction of the Z axis).

FIG. 26AandFIG. 26Bare a second example of the schematic perspective view and the schematic cross-sectional view of the power transmission-side coil TL, the power reception-side coil RLand the cancellation coil GLin the power feeding device1and the electronic device2in the reference arrangement state. In a method of arranging the coil GLshown inFIG. 26AandFIG. 26B(hereinafter referred to as a back arrangement method), the cancellation coil GLis arranged on the back of the power reception-side coil RL. In other words, in a case where the back arrangement method is adopted, when seen from the power reception-side coil RLin the reference arrangement state, the cancellation coil GLis arranged in a position on the side opposite to the arrangement position of the power transmission-side coil TL(hence, the coils GL, RLand TLare sequentially aligned along the direction of the Z axis).

In any of the intermediate arrangement direction and the back arrangement method, the cancellation coil GLis arranged in such a position that when a magnetic field is generated in the power transmission-side coil TLor the power reception-side coil RL, the generated magnetic field interlinks the cancellation coil GLso as to pass a significant current through the cancellation coil GL.

FIG. 27AandFIG. 27Bare a schematic perspective view and a schematic cross-sectional view of the coils TLand JLin the power feeding device1and the foreign object3in a state where the foreign object3a typical example of which is a non-contact IC card is placed on the placement surface of the power feeding stage12.

InFIG. 25A,FIG. 26AandFIG. 27A, for simplification of illustration and prevention of complication, the windings of the coils TL, RL, GLand JLare represented by double circles (the same is true inFIG. 28Cand the like which will be described later). In the drawings including the illustration of the coils, line segments which are extended laterally from the double circles representing the coils indicate the drawn wires of the coils. The cross sections in the cross-sectional views ofFIG. 25B,FIG. 26BandFIG. 27Bare parallel to the YZ plane. Each of the coils TL, RL, GLand JLforms a loop antenna. In the reference arrangement state, the loop planes of the loop antennas serving as the coils TL, RLand GL(that is, the planes where the windings of the coils TL, RLand GLare arranged) are parallel to the XY plane, and hence, the center axes of the coils TL, RLand GLare parallel to the Z axis. The coil TLis formed by winding the winding wires (such as copper wires) around its center axis (the same is true for the coils RL, GLand JL). In a state where the foreign object3is placed on the placement surface of the power feeding stage12, the loop plane of the loop antenna serving as the coil JL(that is, the plane where the winding of the coil JLis arranged) is normally parallel to the XY plane as with the coil TL, and hence, the center axis of the coil JLis parallel to the Z axis.

In order for a coupling coefficient between the coils TLand RLto be increased, the coils TLand RLon the XY plane have the same shape as each other (however, they can have shapes different from each other). In the present specification, the shape of the coil indicates a conception which includes the size of the coil. It may be considered that on an arbitrary coil, the size of the coil refers to an area occupied by the outer circumference of the coil in a direction orthogonal to the center axis of the coil. When the coil forms a loop antenna, the area of a part surrounded by the winding of the coil in the loop plane of the loop antenna (that is, the plane where the winging of the coil is arranged) corresponds to the size of the coil.

On the other hand, although not particularly shown inFIG. 25AandFIG. 26A, on the XY plane, the shape of the coil GLmay be made to differ from the shapes of the coils TLand RLsuch that coupling between the coils TLand GLand coupling between the coils RLand GLare weaker than coupling between the coils TLand RL. The significance thereof will be obvious from a description which will be given later.

Although inFIG. 25AandFIG. 27Aand the like, the outer circumferential shapes of the coils TL, RL, GLand JL(that is, the outline shapes) are set to circles, the outer circumferential shapes of the coils TL, RL, GLand JL, are not limited to circles, and they may be oval or polygon (such as rectangular) or a straight line and a curve may be mixed in the outer circumferential shape of the coil.

In examples EX2_1A, EX2_1B, EX2_2A, EX2_2B, EX2_3A, EX2_3B and EX2_4 of the second embodiment, the actions and the like of the cancel circuit GG will be described below. Unless otherwise a contradiction arises, among a plurality of examples described below, an item which is described in an arbitrary example can be applied to another arbitrary example (in other words, two or more arbitrary examples among a plurality of examples can be combined).

The example EX2_1A will be described. In order to clearly describe the actions of the cancel circuit GG in the example EX2_1B which will be described later, in the example EX2_1A, for convenience, it is assumed that the cancel circuit GG is not provided in the electronic device2.

In the example EX2_1A, it is assumed that a metal portion (hereinafter referred to as a power reception-side metal portion MT2: unillustrated) is provided in the electronic device2. The power reception-side metal portion MT2may form the entire enclosure of the electronic device2or part thereof. Specifically, for example, the power reception-side metal portion MT2may be a box-shaped metal case serving as the enclosure of the electronic device2. For another example, the enclosure of the electronic device2may be formed of a resin material, and the power reception-side metal portion MT2may be fixed within the enclosure of the electronic device2. The power reception-side metal portion MT2is mainly provided, for example, so as to enhance the structural strength and the texture of the electronic device2.

The metal of the power reception-side metal portion MT2is assumed to be aluminum. The metal of the power reception-side metal portion MT2may be an alloy of aluminum and another metal, that is, an aluminum alloy (for example, a duralumin serving as an alloy of aluminum and copper). However, as long as the same influence as the case where the power reception-side metal portion MT2is formed of aluminum or an aluminum alloy is exerted on the coils RLand TL, the metal of the power reception-side metal portion MT2may be a metal other than aluminum and aluminum alloys.

Although the power reception-side metal portion MT2may have any shape, the power reception-side metal portion MT2is assumed to include a metal plate270which has an opening portion271as shown inFIG. 28A. In the reference arrangement state, the metal plate270is parallel to the XY plane. The opening portion271is a hole which is provided in the metal plate270so as to penetrate the metal plate270in the direction of the Z axis, and thus no metal is present in the opening portion271. On the XY plane, the opening portion271forms a closed region, and no contact is present between the opening portion271and the outer periphery of the metal plate270. Hence, in the XY plane, around the opening portion271, an electrical path (current loop) made of aluminum is formed. The opening portion271can be sealed with a material other than metal such as a resin material. The resin material is, for example, polycarbonate or polypropylene.

On the XY plane, the outline shape of the metal plate270is rectangular. However, on the XY plane, the outline shape of the metal plate270is not limited to this shape, and the outline shape may include a curve or a straight line and a curve may be mixed in the outline shape of the metal plate270. Although here, the shape of the opening portion271on the XY plane can be considered to be a circle (three-dimensionally considered to be a cylindrical shape), on the XY plane, the shape of the opening portion271is not limited to a circle, and the shape of the opening portion271may be oval or polygonal (such as rectangular) or a straight line and a curve may be mixed in the shape of the opening portion271.

The power reception-side metal portion MT2may include another metal portion in addition to the metal plate270. Specifically, for example, as shown inFIG. 29, when the power reception-side metal portion MT2is a box-shaped metal case CSMT2serving as the enclosure of the electronic device2, the metal plate270forms one surface (bottom surface) of the metal case CSMT2.

However, in the following description and the drawings (includingFIG. 28AtoFIG. 28C) referenced in the following description, for simplification of description and illustration, on the power reception-side metal portion MT2, attention is focused on only the metal plate270.FIG. 28Ais a perspective view of the metal plate270in the reference arrangement state, andFIG. 28Bis a transparent view of some components of the power feeding device1and the electronic device2in the reference arrangement state.FIG. 28Cis a plan view of the metal plate270and the power reception-side coil RLin the reference arrangement state when seen in the direction of the Z axis. The opening portion271is provided in an opposite position of the arrangement position of the power reception-side coil RL(position opposite the arrangement position of the power reception-side coil RL), and in the reference arrangement state, the opening portion271is located between the coils TLand RL, and the coils TLand RLare opposite each other through the opening portion271.

In the XY plane, the size of the opening portion271is larger than the sizes of the coils TLand RL, and when the coil RL, the opening portion271and the coil TLare seen along the direction of the Z axis, the outer circumferences of the coils RLand TLwhich are overlaid on each other are included within the opening portion271. When it is considered that the shape of the opening portion271and the outer circumferential shapes of the coils TLand RLare all circles, the centers of the circles are located on one straight line parallel to the Z axis, and as shown inFIG. 30, the radius r1of the circle serving as the shape of the opening portion271is larger than the radius r2of the circle serving as the outer circumferential shapes of the coils TLand RL. Hence, it is possible to satisfactorily realize the power transfer using the coils TLand RLthough a slight loss is caused. For example, when the radius r1is set 5 mm (millimeters) larger than the radius r2, a ratio of loss with respect to a case where the metal plate270is not present is about 10 to 20%.

The influence of the metal plate270formed of aluminum will be described.

With reference toFIG. 31A, in the reference arrangement state, the power transmission-side coil TLis magnetically coupled to the metal plate270which includes the opening portion271. When an alternating current I1flows through the power transmission-side coil TL, based on a magnetic field generated in the power transmission-side coil TLin this way, by electromagnetic induction, an alternating current I31in a direction opposite to the alternating current I1(that is, the alternating current I31whose phase is displaced 180 degrees) flows through an electrical path around the opening portion271within the metal plate270. When a coupling coefficient between the power transmission-side coil TLand the metal plate270is assumed to be K13, the alternating current I31is represented by “I31=K13×I1”.

On the other hand, with reference toFIG. 31B, within the electronic device2, the power reception-side coil RLis also magnetically coupled to the metal plate270which includes the opening portion271. When an alternating current I2flows through the power reception-side coil RL, based on a magnetic field generated in the power reception-side coil RLin this way, by electromagnetic induction, an alternating current I32in a direction opposite to the alternating current I2(that is, the alternating current I32whose phase is displaced 180 degrees) flows through the electrical path around the opening portion271within the metal plate270. When a coupling coefficient between the power reception-side coil RLand the metal plate270is assumed to be K23, the alternating current I32is represented by “I32=K23×I2”.

FIG. 31Cshows the currents I1, I2, I31and I32on a complex plane. The alternating current I2is a resonant current which flows through the power reception-side coil RLbased on the alternating current I1, and is represented by “I2=jQK12×I1”. Here, K12is a coupling coefficient between the coils TLand RLin the reference arrangement state, Q is Q in the power reception-side coil RLand j is an imaginary number. The current I2lags in phase with respect to the current I1by 90 degrees.

When the resonant frequency of the resonant circuit TT is considered, the presence of the metal plate270where the alternating current I31is generated acts so as to equivalently reduce the inductance of the power transmission-side coil TL(that is, so as to reduce the inductance component of the resonant circuit TT) and to consequently increase the resonant frequency of the resonant circuit TT.

When the resonant frequency of the resonant circuit RR is considered, the presence of the metal plate270where the alternating current I32is generated acts so as to equivalently reduce the inductance of the power reception-side coil RL(that is, so as to reduce the inductance component of the resonant circuit RR) and to consequently increase the resonant frequency of the resonant circuit RR.

Hence, when the power feeding device1and the electronic device2are designed regardless of the presence of the metal plate270, the resonant frequencies of the resonant circuits TT and RR are displaced from the reference frequency by the presence of the metal plate270so as to be increased. This displacement can exert influences such as a decrease in the efficiency of the power transfer utilizing magnetic field resonance.

When an alternating magnetic field is generated in the power transmission-side coil TL, a voltage based on a current which flows through the metal plate270by the magnetic field generated in the power transmission-side coil TLis generated in the power transmission-side coil TL, and the voltage acts so as to increase the amplitude of the current flowing through the power transmission-side coil TL. Consequently, even when the foreign object3is not present on the power feeding stage12, in the pFOD processing or the mFOD processing, the presence of the foreign object may be erroneously recognized. In other words, the metal plate270may be erroneously recognized as the foreign object (since the metal plate270is a constituent component of the electronic device2, it is naturally necessary to prevent the metal plate270from being erroneously recognized as the foreign object). Although it can be considered that in order for such an erroneous recognition to be avoided, the upper limit value in the pFOD normal range or the mFOD normal range is set higher, such a setting leads to the degradation of the detection performance of the foreign object to be actually detected. For example, when attention is focused on the detection of the foreign object3such as a non-contact IC card, in the pFOD processing, it is observed that the current amplitude of the power transmission-side coil TLis lowered by the presence of the foreign object3. However, when the current amplitude of the power transmission-side coil TLis increased by being affected by the metal plate270, such an increase functions as noise in the observation of the lowering of the current amplitude caused by the presence of the foreign object3, with the result that the detection of the foreign object3is not easily performed.

The example EX2_1B will be described. The example EX2_1B is an example in which the cancel circuit GG is provided in the electronic device2with reference to the example EX2_1A.

As described previously, here, the resonant circuits TT, RR and GG are assumed to be parallel resonant circuits. When the resonant circuits TT, RR and GG are series resonant circuits, the “lead” and the “lag” of a phase which will be described below are reversed.

When the resonant frequency of the resonant circuit TT is higher than the reference frequency due to the presence of the metal plate270, the reactance of the resonant circuit TT is inductive, and thus a current (which corresponds to i inFIG. 32) flowing through the entire resonant circuit TT lags in phase with respect to a voltage (which corresponds to e inFIG. 32) at the reference frequency applied to the resonant circuit TT. When the resonant frequency of the resonant circuit RR is higher than the reference frequency due to the presence of the metal plate270, the same phenomenon occurs in the resonant circuit RR. If it is possible to cancel out the phase lag of the currents in the resonant circuits TT and RR caused by the metal plate270, the resonant frequencies of the resonant circuits TT and RR which are increased by the metal plate270from the reference frequency coincide with or approach the reference frequency.

In order to realize this cancellation, it is preferable to exert, on the resonant circuits TT and RR, an influence opposite to the influence which is exerted by the metal plate270on the resonant circuits TT and RR, and it is preferable to provide, as a circuit for exerting the opposite influence, the cancel circuit GG which has a resonant frequency lower than the reference frequency (when the resonant circuits TT, RR and GG are series resonant circuits, the cancel circuit GG preferably has a resonant frequency higher than the reference frequency). The cancel circuit GG described above has the action of advancing the phases of the currents flowing through the entire resonant circuits TT and RR through the magnetic coupling of the cancellation coil GLto the power transmission-side coil TLand the power reception-side coil RL(seeFIG. 32).

The actions of the metal plate270and the cancel circuit GG in the example EX2_1B are listed inFIG. 33.

The magnetic field generated in the power transmission-side coil TLby the flow of the alternating current I1in the power transmission-side coil TLacts so as to pass the current I31(seeFIG. 31AandFIG. 31C) through the metal plate270, and the presence of the metal plate270where the current I31is generated acts so as to equivalently reduce the inductance of the power transmission-side coil TLand to consequently increase the resonant frequency of the resonant circuit TT.

On the other hand, the magnetic field generated in the power transmission-side coil TLby the flow of the alternating current I1in the power transmission-side coil TLacts so as to pass a current IG1through the cancellation coil GL, and the presence of the cancel circuit GG where the current IG1is generated acts so as to equivalently increase the inductance of the power transmission-side coil TLand to consequently reduce the resonant frequency of the resonant circuit TT.

In other words, the alternating magnetic field generated in the power transmission-side coil TLbased on the alternating current I1interlinks the cancellation coil GL, and thus the current IG1flowing through the cancellation coil GLhas a phase depending on the resonant frequency of the cancel circuit GG, with the result that the phase thereof acts so as to cancel out the displacement of the resonant frequency of the resonant circuit TT from the reference frequency caused by the metal plate270.

The magnetic field generated in the power reception-side coil RLby the flow of the alternating current I2in the power reception-side coil RLacts so as to pass the current I32(seeFIG. 31BandFIG. 31C) through the metal plate270, and the presence of the metal plate270where the current I32is generated acts so as to equivalently reduce the inductance of the power reception-side coil RLand to consequently increase the resonant frequency of the resonant circuit RR.

On the other hand, the magnetic field generated in the power reception-side coil RLby the flow of the alternating current I2in the power reception-side coil RLacts so as to pass a current IG2through the cancellation coil GL, and the presence of the cancel circuit GG where the current IG2is generated acts so as to equivalently increase the inductance of the power reception-side coil RLand to consequently reduce the resonant frequency of the resonant circuit RR.

In other words, the alternating magnetic field generated in the power reception-side coil RLbased on the alternating current I2interlinks the cancellation coil GL, and thus the current IG2flowing through the cancellation coil GLhas a phase depending on the resonant frequency of the cancel circuit GG, with the result that the phase thereof acts so as to cancel out the displacement of the resonant frequency of the resonant circuit RR from the reference frequency caused by the metal plate270.

When the alternating magnetic field is generated in the power transmission-side coil TL, the magnetic field generated in the power transmission-side coil TLcauses a voltage based on the current IG1flowing through the cancellation coil GLto be generated in the power transmission-side coil TL, and the generated voltage acts so as to reduce the amplitude of the current flowing through the power transmission-side coil TLas is understood from the fact that the influences exerted on the resonant circuit TT are opposite between the currents I31and IG1.

Since as described above, the cancel circuit GG provides the action opposite to the metal plate270to the resonant circuits TT and RR, it is possible to cancel out (reduce), with the cancel circuit GG, the influences on the resonant circuits TT and RR exerted by the presence of the metal plate270. Although the cancellation ideally means that a target to be cancelled out is completely cancelled out, the cancellation can be partial cancellation. Hence, the cancellation also means that the target to be cancelled out is reduced (the same is true in the other examples which will be described later).

As the capacitance value of the cancellation capacitor GCis varied, a relationship between the phases of the currents IG1and IG2and the phases of the currents I1, I2, I31and I32is varied, and thus the degree of the cancellation is varied by the variation of the relationship. Hence, the capacitance value of the cancellation capacitor GCis preferably adjusted such that the degree of the cancellation is optimized (maximized).

As the resistance value of the cancellation resistor GRis varied, the magnitudes of the currents IG1and IG2are varied through a variation in the Q value of the resonant circuit serving as the cancel circuit GG, and thus the degree of the cancellation is also varied by the variation of the magnitudes of the currents IG1and IG2. Hence, the resistance value of the cancellation resistor GRis preferably determined such that the degree of the cancellation is optimized, and when the cancellation resistor GRis formed as a variable resistor, the resistance value of the cancellation resistor GRis preferably adjusted such that the degree of the cancellation is optimized.

In the configuration of the example EX2_1B, the variation in the resonant frequency of the resonant circuit RR caused by the presence of the metal plate270is cancelled out by the cancel circuit GG, and the variation in the resonant frequency of the resonant circuit TT caused by the presence of the metal plate270in the reference arrangement state is cancelled out by the cancel circuit GG, with the result that the influences exerted by the displacement of the resonant frequencies are removed. Since the increase in the amplitude of the current flowing through the power transmission-side coil TLcaused by the presence of the metal plate270is cancelled out by the action of the cancel circuit GG, the influence based on the increase in the amplitude of the current is also removed. Hence, in the non-contact power feeding system of the example EX2_1B, only the cancel circuit GG is provided for the presence of the metal plate270, and thus it is possible to perform the same operation in the first embodiment.

Preferably, in actuality, as shown inFIG. 34, the intermediate arrangement method described previously (seeFIG. 25AandFIG. 25B) is adopted, and thus the cancellation coil GLis arranged between the power reception-side coil RLand the opening portion271.

In the example EX2_1B, the back arrangement method described previously (seeFIG. 26AandFIG. 26B) is adopted, and thus the cancellation coil GLcan also be arranged in the position on the side opposite to the arrangement positions of the opening portion271and the power transmission-side coil TLwhen seen from the power reception-side coil RL. However, in this case, the influence of the cancel circuit GG on the power transmission-side resonant circuit TT is significantly weak for the influence of the metal plate270on the power transmission-side resonant circuit TT, and thus the cancellation effect on the power transmission-side resonant circuit TT is weak. Hence, instead of the back arrangement method, the intermediate arrangement method as shown inFIG. 34is preferably adopted.

The example EX2_2A will be described. In order to clearly describe the actions of the cancel circuit GG in the example EX2_2B which will be described later, in the example EX2_2A, for convenience, it is assumed that the cancel circuit GG is not provided in the electronic device2.

In the example EX2_2A, a magnetic material portion MG2is assumed to be provided in the electronic device2. The magnetic material portion MG2is formed of an arbitrary magnetic material which indicates high permeability, and is formed of, for example, ferrite. The magnetic material portion MG2is provided in such a position as to affect the resonant frequency of the resonant circuit RR in the reference arrangement state (that is, when the power feeding device1and the electronic device2are in a predetermined positional relationship for the transmission and reception of power) or in such a position as to affect the resonant frequencies of both the resonant circuits TT and RR in the reference arrangement state.

It is first assumed that as shown inFIG. 35, between the power transmission-side coil TLand the power reception-side coil RL, a magnetic material plate281(which corresponds to the dotted region ofFIG. 35) is provided as the magnetic material portion MG2, and influences exerted by the presence of the magnetic material portion MG2will be described. The magnetic material plate281affects the resonant frequencies of both the resonant circuits TT and RR.

InFIG. 36AandFIG. 36B, a relationship of currents flowing through the power transmission-side coil TL, the power reception-side coil RLand the magnetic material portion MG2will be described.

In the reference arrangement state, the power transmission-side coil TLis magnetically coupled to the magnetic material portion MG2(the magnetic material plate281), and when the alternating current I1flows through the power transmission-side coil TL, this causes an alternating current I41in the same direction as the alternating current I1(that is, having the same phase as the alternating current I1) to flow through the magnetic material portion MG2based on a magnetic field generated in the power transmission-side coil TLas shown inFIG. 36A.

The current I41is a current in a direction opposite to the current I31(seeFIG. 31A) which flows through the metal plate270and which is assumed in the examples EX2_1 A and EX2_1B. Hence, the magnetic material portion MG2provides, to the power transmission-side resonant circuit TT, the action opposite to the metal plate270. Specifically, the presence of the magnetic material portion MG2where the current I41is generated acts, in an opposite manner to the metal plate270having the opening portion271, so as to equivalently increase the inductance of the power transmission-side coil TL(that is, so as to increase the inductance component of the resonant circuit TT), to consequently reduce the resonant frequency of the resonant circuit TT and to also reduce the amplitude of the current flowing through the power transmission-side coil TL.

Within the electronic device2, the power reception-side coil RLis magnetically coupled to the magnetic material portion MG2(the magnetic material plate281), and when the alternating current I1flows through the power reception-side coil RL, this causes an alternating current I42in the same direction as the alternating current I2(that is, having the same phase as the alternating current I2) to flow through the magnetic material portion MG2based on a magnetic field generated in the power reception-side coil RLas shown inFIG. 36B.

The current I42is a current in a direction opposite to the current I32(seeFIG. 31B) which flows through the metal plate270and which is assumed in the examples EX2_1 A and EX2_1B. Hence, the magnetic material portion MG2provides, to the power reception-side resonant circuit RR, the action opposite to the metal plate270. Specifically, the presence of the magnetic material portion MG2where the current I42is generated acts, in the opposite manner to the metal plate270having the opening portion271, so as to equivalently increase the inductance of the power reception-side coil RL(that is, so as to increase the inductance component of the resonant circuit RR), to consequently reduce the resonant frequency of the resonant circuit RR and to also reduce the amplitude of the current flowing through the power reception-side coil RL.

Hence, when the power feeding device1and the electronic device2are designed regardless of the presence of the magnetic material portion MG2, the resonant frequencies of the resonant circuits TT and RR are displaced from the reference frequency by the presence of the magnetic material portion MG2so as to be reduced. This displacement can exert influences such as a decrease in the efficiency of the power transfer utilizing magnetic field resonance.

The decrease in the amplitude of the current flowing through the power transmission-side coil TLcaused by the presence of the magnetic material portion MG2leads to the deterioration of the accuracy of detection of the foreign object which relies on the amplitude of the current flowing through the power transmission-side coil TL.

The example EX2_2B will be described. The example EX2_2B is an example in which the cancel circuit GG is provided in the electronic device2with reference to the example EX2_2A.

As described previously, here, the resonant circuits TT, RR and GG are assumed to be parallel resonant circuits. When the resonant circuits TT, RR and GG are series resonant circuits, the “lead” and the “lag” of a phase which will be described below are reversed.

When the resonant frequency of the resonant circuit TT is lower than the reference frequency due to the presence of the magnetic material portion MG2, the reactance of the resonant circuit TT is capacitive, and thus a current (which corresponds to i inFIG. 37) flowing through the entire resonant circuit TT leads in phase with respect to a voltage (which corresponds to e inFIG. 37) at the reference frequency applied to the resonant circuit TT. When the resonant frequency of the resonant circuit RR is lower than the reference frequency due to the presence of the magnetic material portion MG2, the same phenomenon occurs in the resonant circuit RR. If it is possible to cancel out the phase lead of the currents in the resonant circuits TT and RR caused by the magnetic material portion MG2, the resonant frequencies of the resonant circuits TT and RR which are reduced by the magnetic material portion MG2from the reference frequency coincide with or approach the reference frequency.

In order to realize this cancellation, it is preferable to exert, on the resonant circuits TT and RR, an influence opposite to the influence which is exerted by the magnetic material portion MG2on the resonant circuits TT and RR, and it is preferable to provide, as a circuit for exerting the opposite influence, the cancel circuit GG which has a resonant frequency higher than the reference frequency (when the resonant circuits TT, RR and GG are series resonant circuits, the cancel circuit GG preferably has a resonant frequency lower than the reference frequency). The cancel circuit GG described above has the action of delaying the phases of the currents flowing through the entire resonant circuits TT and RR through the magnetic coupling of the cancellation coil GLto the power transmission-side coil TLand the power reception-side coil RL(seeFIG. 37).

The actions of the magnetic material portion MG2and the cancel circuit GG in the example EX2_2B are listed inFIG. 38.

The magnetic field generated in the power transmission-side coil TLby the flow of the alternating current I1in the power transmission-side coil TLacts so as to pass the current I41(seeFIG. 36A) through the magnetic material portion MG2, and the presence of the magnetic material portion MG2where the current I41is generated acts so as to equivalently increase the inductance of the power transmission-side coil TLand to consequently reduce the resonant frequency of the resonant circuit TT.

On the other hand, the magnetic field generated in the power transmission-side coil TLby the flow of the alternating current I1in the power transmission-side coil TLacts so as to pass a current IG1′ through the cancellation coil GL, and the presence of the cancel circuit GG where the current IG1′ is generated acts so as to equivalently reduce the inductance of the power transmission-side coil TLand to consequently increase the resonant frequency of the resonant circuit TT.

In other words, the alternating magnetic field generated in the power transmission-side coil TLbased on the alternating current I1interlinks the cancellation coil GL, and thus the current IG1′ flowing through the cancellation coil GLhas a phase depending on the resonant frequency of the cancel circuit GG, with the result that the phase thereof acts so as to cancel out the displacement of the resonant frequency of the resonant circuit TT from the reference frequency caused by the magnetic material portion MG2.

The magnetic field generated in the power reception-side coil RLby the flow of the alternating current I2in the power reception-side coil RLacts so as to pass the current I42(seeFIG. 36B) through the magnetic material portion MG2, and the presence of the magnetic material portion MG2where the current I42is generated acts so as to equivalently increase the inductance of the power reception-side coil RLand to consequently reduce the resonant frequency of the resonant circuit RR.

On the other hand, the magnetic field generated in the power reception-side coil RLby the flow of the alternating current I2in the power reception-side coil RLacts so as to pass a current IG2′ through the cancellation coil GL, and the presence of the cancel circuit GG where the current IG2′ is generated acts so as to equivalently reduce the inductance of the power reception-side coil RLand to consequently increase the resonant frequency of the resonant circuit RR.

In other words, the alternating magnetic field generated in the power reception-side coil RLbased on the alternating current I2interlinks the cancellation coil GL, and thus the current IG2′ flowing through the cancellation coil GLhas a phase depending on the resonant frequency of the cancel circuit GG, with the result that the phase thereof acts so as to cancel out the displacement of the resonant frequency of the resonant circuit RR from the reference frequency caused by the magnetic material portion MG2.

When the alternating magnetic field is generated in the power transmission-side coil TL, the magnetic field generated in the power transmission-side coil TLcauses a voltage based on the current IG1′ flowing through the cancellation coil GLto be generated in the power transmission-side coil TL, and the generated voltage acts so as to increase the amplitude of the current flowing through the power transmission-side coil TLas is understood from the fact that the influences exerted on the resonant circuit TT are opposite between the currents I41and IG1′.

Since as described above, the cancel circuit GG provides the action opposite to the magnetic material portion MG2to the resonant circuits TT and RR, it is possible to cancel out (reduce), with the cancel circuit GG, the influences on the resonant circuits TT and RR exerted by the presence of the magnetic material portion MG2.

As the capacitance value of the cancellation capacitor GCis varied, a relationship between the phases of the currents IG1′ and IG2′ and the phases of the currents I1, I2, I41and I42is varied, and thus the degree of the cancellation is varied by the variation of the relationship. Hence, the capacitance value of the cancellation capacitor GCis preferably adjusted such that the degree of the cancellation is optimized (maximized).

As the resistance value of the cancellation resistor GRis varied, the magnitudes of the currents IG1′ and IG2′ are varied through a variation in the Q value of the resonant circuit serving as the cancel circuit GG, and thus the degree of the cancellation is also varied by the variation of the magnitudes of the currents IG1′ and IG2′. Hence, the resistance value of the cancellation resistor GRis preferably determined such that the degree of the cancellation is optimized, and when the cancellation resistor GRis formed as a variable resistor, the resistance value of the cancellation resistor GRis preferably adjusted such that the degree of the cancellation is optimized.

In the configuration of the example EX2_2B, the variation in the resonant frequency of the resonant circuit RR caused by the presence of the magnetic material portion MG2is cancelled out by the cancel circuit GG, and the variation in the resonant frequency of the resonant circuit TT caused by the presence of the magnetic material portion MG2in the reference arrangement state is cancelled out by the cancel circuit GG, with the result that the influences exerted by the displacement of the resonant frequencies are removed. Since a decrease in the amplitude of the current flowing through the power transmission-side coil TLcaused by the presence of the magnetic material portion MG2is cancelled out by the action of the cancel circuit GG, the influence based on the decrease in the amplitude of the current is also removed. Hence, in the non-contact power feeding system of the example EX2_2B, only the cancel circuit GG is provided for the presence of the magnetic material portion MG2, and thus it is possible to perform the same operation in the first embodiment.

Preferably, when as with the magnetic material plate281shown inFIG. 35, the magnetic material portion MG2is present between the power transmission-side coil TLand the power reception-side coil RL, the intermediate arrangement method described previously (seeFIG. 25AandFIG. 25) is adopted, and thus the cancellation coil GLis arranged between the power reception-side coil RLand the magnetic material portion MG2(the magnetic material plate281) or the magnetic material portion MG2(the magnetic material plate281) is arranged between the power reception-side coil RLand the cancellation coil GL.

However, when a magnetic material plate282serving as the magnetic material portion MG2is present in a position as shown inFIG. 39, either the intermediate arrangement method (seeFIG. 25AandFIG. 25B) or the back arrangement method (seeFIG. 26AandFIG. 26) may be adopted.

FIG. 40shows a positional relationship between the coils TL, RLand GLand the magnetic material plate282in the reference arrangement state when the magnetic material plate282is provided as the magnetic material portion MG2and the back arrangement method is adopted. In the reference arrangement state, the magnetic material plate282is provided in a position on the side opposite to the arrangement position of the power transmission-side coil TLwhen seen from the power reception-side coil RL, and the cancellation coil GLis arranged between the power reception-side coil RLand the magnetic material plate282. In other words, in the reference arrangement state, the magnetic material plate282, the cancellation coil GL, the power reception-side coil RLand the power transmission-side coil TLare aligned in this order along the direction of the Z axis.

When the arrangement relationship as shown inFIG. 40is adopted, a distance between the power transmission-side coil TLand the magnetic material plate282is relatively long. Hence, in the reference arrangement state, the magnetic material portion MG2serving as the magnetic material plate282may affect only the resonant frequency of the resonant circuit RR in the resonant circuits TT and RR or may fail to have the action of reducing the amplitude of the current flowing through the power transmission-side coil TL. In other words, a variation in the resonant frequency of the power transmission-side resonant circuit TT and a decrease in the amplitude of the current flowing through the power transmission-side coil TLcaused by the presence of the magnetic material portion MG2may be small enough to be ignored. In this case, it can also be said that the cancel circuit GG is mainly provided in order to cancel out the influence exerted by the magnetic material portion MG2on the power reception-side resonant circuit RR.

FIG. 41shows an example of the utilization of the magnetic material plate282. As shown inFIG. 41, in the electronic device2, a substrate SUB is provided on which an electronic circuit EL including an integrated circuit such as a power reception-side IC200is mounted. In the configuration example ofFIG. 41, the magnetic material plate282is inserted between the electronic circuit EL and the power reception-side coil RL, and the electronic circuit EL, the magnetic material plate282, the cancellation coil GL, the power reception-side coil RLand the power transmission-side coil TLare aligned in this order along the direction of the Z axis. Here, preferably, for example, the electronic circuit EL is mounted on the component surface of the substrate SUB, and the magnetic material plate (magnetic material sheet)282is adhered to the surface on the side opposite to the component surface of the substrate SUB. In this way, the magnetic field which is not necessary for the operation of the electronic circuit EL and which is generated in the coil RLor TLis absorbed in the magnetic material plate282, and thus an erroneous operation and the like of the electronic circuit EL are reduced. As described above, in order to interrupt a magnetic field to the electronic circuit EL, the magnetic material plate282is often provided within the electronic device2. The cancel circuit GG helps the magnetic material plate282cancel out undesirable influences which can be exerted on the power transfer, the detection of the foreign object and the like.

With consideration given to the fact that the magnetic material portion MG2and the metal plate270exert, on the resonant circuits TT and RR, the influences opposite to each other, it is also useful to adopt a method of fitting the magnetic material portion MG2(the magnetic material plate281inFIG. 35) into the opening portion271of the metal plate270. In this way, it is possible to cancel out the influences of the magnetic material portion MG2and the metal plate270without use of the cancel circuit GG. However, the degree of an effect exerted by this method depends on the shapes and the arrangement positions of the magnetic material portion MG2and the metal plate270, and it is often not easy to change the shapes and the like thereof due to the constraint of the structure even if the effect is not optimal. By contrast, in the cancel circuit GG, it is easy to make an adjustment such as by utilization of a trimmer capacitor.

The example EX2_3A will be described. In order to clearly describe the actions of the cancel circuit GG in the example EX2_3B which will be described later, in the example EX2_3A, for convenience, it is assumed that the cancel circuit GG is not provided in the electronic device2.

The fOchange/short circuit operation (the resonant frequency change operation or the coil short circuit operation) utilizing the resonant state change circuit240is performed, and thus, ideally, the resonant circuit RR does not function as a load for the power transmission-side coil TLat all, and the same conditions as when the resonant circuit RR is not present are achieved. However, the resonant frequency of the resonant circuit RR after being changed by the resonant frequency change operation is not sufficiently different from the reference frequency or the changing of the resonant frequency of the resonant circuit RR or the short-circuiting of the power reception-side coil RLis performed through a circuit having nonlinearity, with the result that in actuality, even while the fOchange/short circuit operation is being performed, based on the magnetic field generated in the power transmission-side coil TL, a certain amount of current (hereinafter referred to as a power reception-side unnecessary current) may flow through the power reception-side coil RL. Hence, a voltage based on the power reception-side unnecessary current flowing through the power reception-side coil RLis generated in the power transmission-side coil TL, and thus the voltage produces a variation in the amplitude of the current flowing through the power transmission-side coil TL. This variation leads to the deterioration of the accuracy of detection of the foreign object in the pFOD processing which relies on the amplitude of the current flowing through the power transmission-side coil TL.

FIG. 42shows an example of the resonant state change circuit240which is formed so as to be able to realize the coil short circuit operation. InFIG. 42, the resonant circuit RR is assumed to be a parallel resonant circuit, and the resonant state change circuit240includes a transistor SS and a resistor Rss. The transistor SS is formed as an N-channel MOSFET. A rectifier circuit DD is a full-wave rectifier circuit which is formed with diodes (rectifier elements) D1to D4. In the electronic device2, a circuit which is formed with the rectifier circuit DD, the transistor SS and the resistor Rss can be provided between the resonant circuit RR and the communication circuit220or between the resonant circuit RR and the power reception circuit230. The switching circuit210(seeFIG. 5) which needs to be interposed between the resonant circuit RR and the rectifier circuit DD is omitted inFIG. 42.

In the circuit ofFIG. 42, one end of the power reception-side coil RLand one end of the power reception-side capacitor RCare connected in common to a line LN1whereas the other end of the power reception-side coil RLand the other end of the power reception-side capacitor RCare connected in common to a line LN2. The line LN1is connected in common to the anode of the diode D1and the cathode of the diode D3, and the line LN2is connected in common to the anode of the diode D2and the cathode of the diode D4. The cathodes of the diodes D1and D2are connected in common to a line LN3, and the anodes of the diodes D3and D4are connected in common to a line LN4. In the transistor SS, the drain is connected to the line LN3, the source is connected to the line LN4and the gate is connected to the line LN4through the resistor Rss.

The control circuit250of the electronic device2controls the gate voltage of the transistor SS so as to turn on or off the transistor SS. When the transistor SS is off, an alternating current flows through the power reception-side coil RLbased on a magnetic field generated in the power transmission-side coil TL, and power based on the alternating current is propagated through the rectification of the rectifier circuit DD between the lines LN3and LN4. By the power propagated between the lines LN3and LN4, the power reception operation and the like can be performed.

On the other hand, when the transistor SS is on, the power reception-side coil RLis short-circuited through the rectifier circuit DD (more specifically, through a combination of the diodes D1and D4or a combination of the diodes D2and D3), and thus no voltage is generated between the lines LN3and LN4(for simplification of description, the voltage between the drain and the source of the transistor SS is assumed to be zero). Although as described above, the transistor SS ofFIG. 42corresponds to the switch243ofFIG. 10, in the circuit ofFIG. 42, between the resonant circuit RR and the transistor SS, the circuit (DD) which is formed with the semiconductor elements (D1to D4) having nonlinearity is interposed.

Hence, in a region where the voltage between the lines LN1and LN2is low, the diodes D1to D4are in a non-conducting state, and thus even when the transistor SS is on, the power reception-side coil RLis prevented from being short-circuited, with the result that the power reception-side unnecessary current flows through the power reception-side coil RL.

The example EX2_3B will be described. The example EX2_3B is an example in which the cancel circuit GG is provided in the electronic device2with reference to the example EX2_3A.

The cancel circuit GG in the example EX2_3B is a circuit which corresponds to that the fOchange/short circuit operation is not ideal. On the other hand, the fOchange/short circuit operation is performed in the pFOD processing, and is not performed in the power transfer and the like. Hence, in the example EX2_3B, as shown inFIG. 43, the control circuit250feeds, to the cancel circuit GG, an on-control signal or an off-control signal according to whether or not the fOchange/short circuit operation is performed.

When the on-control signal is fed to the cancel circuit GG, in the cancel circuit GG, a parallel resonant circuit or a series resonant circuit is formed by the parallel connection or the series connection of the coil GL, the capacitor GCand the resistor GR, and thus when the alternating magnetic field interlinks the coil GL, a resonant operation is performed in the cancel circuit GG (a current flows through the coil GL).

When the off-control signal is fed to the cancel circuit GG, in the cancel circuit GG, the connection between the coil GL, the capacitor GCand the resistor GRis interrupted or the coil GLis short-circuited such that the parallel resonant circuit or the series resonant circuit is prevented from being formed, with the result that even when the alternating magnetic field interlinks the coil GL, the resonant operation is not performed in the cancel circuit GG (no current flows through the coil GL).

Preferably, for example, in the cancel circuit GG, a switch is inserted in series on wiring connecting the coil GLand the capacitor GC, and when the on-control signal is received, the switch is turned on whereas when the off-control signal is received, the switch is turned off, with the result that the connection between the coil GL, the capacitor GCand the resistor GRis interrupted. Preferably, for another example, in the cancel circuit GG, a switch is connected in parallel to the coil GL, and when the on-control signal is received, the switch is turned off whereas the off-control signal is received, the switch is turned on, with the result that the coil GLis short-circuited.

The control circuit250outputs the on-control signal to the cancel circuit GG only during a period in which the resonant state change circuit240is made to perform the fOchange/short circuit operation, and during a period other than the period described above (including a period in which the NFC communication and the NFC power transfer are performed), the control circuit250outputs the off-control signal to the cancel circuit GG, with the result that the resonant operation of the cancel circuit GG is stopped.

In the example EX2_3B, conditions in which the on-control signal is fed to the cancel circuit GG will be considered below.

FIG. 44is referenced. A symbol “iA” represents a power reception-side unnecessary current which flows through the power reception-side coil RLbased on the magnetic field generated in the power transmission-side coil TLwhile the fOchange/short circuit operation is being performed. A symbol “is” represents a current which flows through the cancellation coil GLbased on the magnetic field generated in the power transmission-side coil TLwhile the fOchange/short circuit operation is being performed. InFIG. 44, the currents iAand is are shown as current vectors on a complex plane. When the currents iAand is are opposite in direction to each other (that is, the currents iAand is differ in phase from each other by 180 degrees), the currents iAand is provide, to the resonant circuit TT, actions opposite to each other, and thus the influence of the power reception-side unnecessary current iAon the amplitude of the current flowing through the power transmission-side coil TLis cancelled out (reduced). Furthermore, when the magnitudes of the currents iAand is are equal to each other, the influence of the power reception-side unnecessary current iAon the amplitude of the current flowing through the power transmission-side coil TLis completely cancelled out by the current is.

Hence, the cancel circuit GG is formed such that the currents iAand is are opposite in direction to each other (that is, that the current is has a phase which differs from the power reception-side unnecessary current iAby 180 degrees), and is preferably formed such that the currents iAand is are opposite in direction to each other and are equal in magnitude to each other. The resonant frequency of the cancel circuit GG described above is naturally displaced from the reference frequency.

As the capacitance value of the cancellation capacitor GCis varied, a relationship between the phases of the currents iAand iBis varied, and thus the degree of the cancellation is varied by the variation of the phase relationship. Hence, the capacitance value of the cancellation capacitor GCis preferably adjusted such that the degree of the cancellation is optimized (maximized).

As the resistance value of the cancellation resistor GRis varied, the magnitude of the current IBis varied through a variation in the Q value of the resonant circuit serving as the cancel circuit GG, and thus the degree of the cancellation is also varied by the variation of the magnitude of the current IB. Hence, the resistance value of the cancellation resistor GRis preferably determined such that the degree of the cancellation is optimized, and when the cancellation resistor GRis formed as a variable resistor, the resistance value of the cancellation resistor GRis preferably adjusted such that the degree of the cancellation is optimized.

In the configuration of the example EX2_3B, the influence which is exerted by the power reception-side unnecessary current on the amplitude of the current flowing through the power transmission-side coil TLcan be removed, and thus it is possible to keep high the accuracy of detection of the foreign object in the pFOD processing.

The example EX2_4 will be described.FIG. 45shows an arrangement positional relationship between the power reception-side coil RLand the cancellation coil GLon the XY plane. InFIG. 45, the outer peripheral shapes of the coils RLand GLare assumed to be rectangular, and for simplification of illustration and prevention of complication, the windings of the coils RLand GLare represented by double rectangles. Line segments which are extended laterally from the double rectangles indicate the drawn wires of the coils.

The cancellation coil GLis provided, for example, in order to cancel out the influence of the metal plate270, and thus it is hardly necessary to increase the degree of magnetic coupling to the power reception-side coil RL. When the coupling to the metal plate270is considered, no matter how the cancellation coil GLis rotated around the Z axis, the degree of the coupling is not changed at all or is little changed (the same is true for the magnetic material plate281or282).

Hence, preferably, as shown inFIG. 45, on the XY plane, for example, when the outer peripheral shapes of the coils RLand GLare rectangular, the long axes of the outer peripheral shapes of the coils RLand GLare directed in directions different from each other (for example, are directed so as to be orthogonal to each other) in order to reduce the coupling between the coils RLand GL. When the outer peripheral shape of the power reception-side coil RLis set to be rectangular, the outer peripheral shape of the power transmission-side coil TLis also set to be the same rectangular, and in the reference arrangement state, the long axes of the outer peripheral shapes of the coils RLand GLare directed in the same directions as each other in order to enhance the coupling between the coils TLand RL.

For a similar purpose, on the XY plane, the shape of the coil GLmay be made to differ from the shapes of the coils TLand RL.

Third Embodiment

A third embodiment of the present invention will be described. In the third embodiment, a method of adjusting and determining the capacitance value of the cancellation capacitor GCwill be described. The method described in the third embodiment can be applied to the non-contact power feeding system of the second embodiment.

Although attention is not given in the first and second embodiments, the control circuit160in the power feeding device1sets, to its operation mode, any one of a plurality of modes including a normal mode and a test mode, and performs operations in the operation mode which is set, and likewise, the control circuit250in the electronic device2sets, to its operation mode, any one of a plurality of modes including the normal mode and the test mode, and performs operations in the operation mode which is set. The modes in the control circuit160and the modes in the control circuit250may coincide with or differ from each other. Although the modes in the control circuits160and250can include modes other than the normal mode and the test mode, in the following description, attention is focused on only the normal mode and the test mode.

All the operations of the power feeding device1and the electronic device2described in the first and second embodiments are operations which are performed when the operation modes of the control circuits160and250are set to the normal mode (however, the initial setting processing is omitted).

At the time of the startup of the power feeding device1or with arbitrary timing after the startup of the power feeding device1, the control circuit160of the power feeding device1sets its operation mode to the test mode only when receiving an input of a predetermined test mode setting instruction, otherwise the control circuit160sets its operation mode to the normal mode. Likewise, at the time of the startup of the electronic device2or with arbitrary timing after the startup of the electronic device2, the control circuit250of the electronic device2sets its operation mode to the test mode only when receiving an input of the predetermined test mode setting instruction, otherwise the control circuit250sets its operation mode to the normal mode.

With reference toFIG. 46, the power feeding device1includes an input reception portion170for receiving the inputs of various instructions including the test mode setting instruction, and the electronic device2includes an input reception portion270for receiving the inputs of various instructions including the test mode setting instruction.

For example, the input reception portion170may be formed with push button switches, a touch panel or the like for receiving an input of the test mode setting instruction from an operator. For another example, the input reception portion170may be formed with a communication port which can receive a signal transmitted from an external device. In this case, the reception of a predetermined test mode transfer requirement signal in the communication port of the input reception portion170from the external device corresponds to the input of the test mode setting instruction to the power feeding device1and the input reception portion170, and by the reception of the test mode transfer requirement signal, the operation mode of the control circuit160is set to the test mode. The external device is a device which is different from the power feeding device1and the electronic device2, and may be, for example, a computer device4(seeFIG. 47) which will be described later.

Likewise, for example, the input reception portion270may be formed with push button switches, a touch panel or the like for receiving an input of the test mode setting instruction from the operator. For another example, the input reception portion270may be formed with a communication port which can receive a signal transmitted from the external device. In this case, the reception of the predetermined test mode transfer requirement signal in the communication port of the input reception portion270from the external device corresponds to the input of the test mode setting instruction to the electronic device2and the input reception portion270, and by the reception of the test mode transfer requirement signal, the operation mode of the control circuit250is set to the test mode.

In the control circuit160of the power feeding device1, the operation mode is set to the test mode, thereafter the power supply of the power feeding device1is turned off, the power feeding device1is restarted and thus the operation mode is changed to the normal mode. The control circuit160may have a configuration in which after the control circuit160sets its operation mode to the test mode, when a predetermined condition holds true (for example, when the input reception portion170receives an input of a normal mode transfer instruction different from the test mode setting instruction), the control circuit160can transfer its operation mode to the normal mode.

In the control circuit250of the electronic device2, the operation mode is set to the test mode, thereafter the power supply of the electronic device2is turned off, the electronic device2is restarted and thus the operation mode is changed to the normal mode. The control circuit250may have a configuration in which after the control circuit250sets its operation mode to the test mode, when a predetermined condition holds true (for example, when the input reception portion270receives an input of the normal mode transfer instruction different from the test mode setting instruction), the control circuit250can transfer its operation mode to the normal mode.

FIG. 47shows the appearance of the computer device4which is an example of the external device together with the appearance of the power feeding device1.FIG. 48is a schematic internal block diagram of the computer device4. The computer device4includes individual portions which are represented by symbols41to44.

The computation processing portion41is formed with a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory) and the like, performs various types of computation processing and comprehensively controls the individual portions within the computer device4. The display portion42is formed with a liquid crystal display panel or the like, and displays arbitrary information as images under the control of the computation processing portion41. The recording portion43is formed with a magnetic disk, a semiconductor memory and the like, and records arbitrary information.

The communication processing portion44performs wireless or wired communication with a device different from the computer device4. Here, it is assumed that between the power feeding device1and the computer device4, wired communication in conformity with a predetermined wired communication standard (for example, the standard of a USB (Universal Serial Bus)) can be performed, and that a communication port provided in the power feeding device1and a communication port provided in the computer device4are connected with a predetermined communication cable so as to be able to perform bidirectional communication on arbitrary information between the power feeding device1and the computer device4. However, when the function of performing wireless communication with the computer device4is provided in the power feeding device1, the communication between the power feeding device1and the computer device4may be wireless communication.

In one form of the test mode, the control circuit160can generate the test magnetic field in the power transmission-side coil TLthrough the control of the switching circuit110and the power transmission circuit130, and the control circuit250uses the resonant state change circuit240so as to be able to perform fOchange/short circuit operation.

Here, a first test form and a second test form inFIG. 49AandFIG. 49Bare assumed.

In the first test form, the control circuit160is set to the test mode, the test magnetic field is generated in the power transmission-side coil TLand the initial setting environment described previously is adjusted (that is, the electronic device2and the foreign object are not placed on the power feeding stage12).

In the second test form, the control circuit160is set to the test mode and the test magnetic field is generated in the power transmission-side coil TLwhereas the control circuit250is set to the test mode, the fOchange/short circuit operation is performed and the electronic device2is placed on the power feeding stage12in the reference arrangement state.

FIG. 50is a flowchart of processing for adjusting the capacitance value of the cancellation capacitor GCby utilization of the test mode. It is assumed that when the processing is performed, the power feeding device1and the computer device4are connected so as to be able to communicate with each other.

First, in step S11, the test mode setting instruction is provided to the power feeding device1and the electronic device2, and thus the operation modes of the control circuits160and250are set to the test mode. When the cancellation capacitor GCis formed as a trimmer capacitor, a state where an adjuster can manually adjust the capacitance value of the cancellation capacitor GCis adjusted.

In step S12subsequent thereto, the first test form is adjusted, and the control circuit160acquires the voltage value VDin the first test form. The voltage value VDacquired in the first test form is referred to as a detection value and is represented by VTEST1. Furthermore, in step S13, the second test form is adjusted, and the control circuit160acquires the voltage value VDin the second test form. The voltage value VDacquired in the second test form is referred to as a detection value and is represented by VTEST2. The detection values VTEST1and VTEST2may be fed to the computer device4.

In the control circuit160of the power feeding device1or the computation processing portion41of the computer device4, a test processing portion (unillustrated) is provided. In step S14subsequent to step S13, the test processing portion compares an absolute value |VTEST1−VTEST2| with a predetermined positive threshold value ΔTH. When “|VTEST1−VTEST2|≤ΔTH” holds true, it is determined that the capacitance value of the cancellation capacitor GCis appropriate, and thus the adjustment of the capacitance value is completed whereas when “|VTEST1−VTEST2|≤ΔTH” does not hold true, the process proceeds to step S15. Preferably, when “|VTEST1−VTEST2|≤ΔTH” holds true, the test processing portion displays, on the display portion42, information indicating that the adjustment may be completed.

In step S15, the test processing portion determines whether or not “(VTEST2−VTEST1)>0” holds true, and when “(VTEST2−VTEST1)>0” holds true, in step S16, the test processing portion outputs a resonant frequency reduction instruction, and then the process returns to step S13whereas when “(VTEST2−VTEST1)>0” does not hold true, in step S17, the test processing portion outputs a resonant frequency increase instruction, and then the process returns to step S13.

When the cancellation capacitor GCis formed as a trimmer capacitor, and the capacitance value of the cancellation capacitor GCis manually adjusted, the resonant frequency reduction instruction and the resonant frequency increase instruction are instructions which are provided to the adjuster. In this case, the resonant frequency reduction instruction prompts the adjuster to manually operate the trimmer capacitor such that the resonant frequency of the cancel circuit GG is reduced, and for example, an image indicating the instruction is displayed on the display portion42. By contrast, the resonant frequency increase instruction prompts the adjuster to manually operate the trimmer capacitor such that the resonant frequency of the cancel circuit GG is increased, and for example, an image indicating the instruction is displayed on the display portion42.

When the cancellation capacitor GCis formed as a varicap, and the capacitance value of the cancellation capacitor GCis adjusted without depending on a manual operation, the resonant frequency reduction instruction and the resonant frequency increase instruction are provided to the electronic device2by the NFC communication. However, in this case, each time the processing in steps S13to S15is performed, the power feeding device1and the electronic device2are brought into a state where they can perform the NFC communication, and a signal indicating the resonant frequency reduction instruction or the resonant frequency increase instruction is transmitted by the NFC communication from the power feeding device1to the electronic device2. The control circuit250has the function of varying a voltage applied to the varicap, and when the control circuit250receives the signal indicating the resonant frequency reduction instruction, the control circuit250varies, only by a predetermined amount, the voltage applied to the varicap such that the resonant frequency of the cancel circuit GG is reduced whereas when the control circuit250receives the signal indicating the resonant frequency increase instruction, the control circuit250varies, only by a predetermined amount, the voltage applied to the varicap such that the resonant frequency of the cancel circuit GG is increased.

When the resonant frequency of the cancel circuit GG is reduced according to the resonant frequency reduction instruction, VTEST2is expected to be reduced. When the resonant frequency of the cancel circuit GG is increased according to the resonant frequency increase instruction, VTEST2is expected to be increased.

For example, when the metal plate270is provided in the electronic device2, though the amplitude of the current flowing through the power transmission-side coil TLis increased by the action of the metal plate270(consequently, “(VTEST2−VTEST1)>0” easily holds true), if the cancel circuit GG is made to have a resonant frequency lower than the reference frequency, the amplitude of the current flowing through the power transmission-side coil TLis reduced by the action of the cancel circuit GG, with the result that the actions of the metal plate270and the cancel circuit GG on the amplitude of the current cancel out each other. Hence, when “(VTEST2−VTEST1)>0”, the resonant frequency reduction instruction is output. When the magnetic material portion MG2is provided in the electronic device2, the opposite situation occurs. Moreover, |VTEST2−VTEST1| is brought close to zero, and thus an influence exerted by a non-ideal fOchange/short circuit operation is also absorbed.

Since a state where the adjustment of the capacitance value of the cancellation capacitor GCin the processing ofFIG. 50is performed is equivalent to a state where in the pFOD processing, the electronic device2is not present on the power feeding stage12, it is possible to accurately determine whether or not the foreign object is present. That the detection value VTEST1acquired when the electronic device2is not placed on the power feeding stage12is equal to the detection value VTEST2acquired when the electronic device2is placed on the power feeding stage12while the fOchange/short circuit operation is being performed means that the action of varying the resonant frequency from the reference frequency by the metal plate270or the like is appropriately cancelled out in the cancel circuit GG.

Consideration on the Present Invention

The present invention embodied in the embodiments described above will be considered.

A power reception device W1according to one aspect of the present invention which can receive, from a power transmission device that includes a power transmission-side resonant circuit (TT) including a power transmission-side coil (TL) for transmitting power, the power by a magnetic field resonance method, includes: a power reception-side resonant circuit (RR) which includes a power reception-side coil (RL) for receiving the power; and an auxiliary resonant circuit (GG) which includes an auxiliary coil (GL) different from the power reception-side coil, where in a position in which a current flows through the auxiliary coil based on a magnetic field generated in the power transmission-side coil or the power reception-side coil, the auxiliary coil is arranged.

For example, although in the power reception device, a member (such as a metal plate) which affects the properties and the operation of the power reception-side resonant circuit may be arranged, the auxiliary resonant circuit described above is provided, and thus it is possible to cancel out the influences, with the result that it is possible to perform a proper power reception operation and the like.

Here, a description will be given of a relationship between the power reception-side coil and the auxiliary coil with attention focused on the power reception-side coil RLused as an example of the power reception-side coil and the cancellation coil GLused as an example of the auxiliary coil in the embodiments. As long as in the embodiments described above, the power reception-side coil RLand the cancellation coil GLare provided separately, the former can form the power reception-side resonant circuit RR and the latter can form the cancel circuit GG, a specific method of configuring the coils RLand GLis arbitrary.

For example, when the circuits RR and GG are shown in a circuit diagram, the circuits RR and GG may have a relationship as shown inFIG. 51. In the circuit ofFIG. 51, the circuits RR and GG each are formed as parallel resonant circuits, and a line (wiring) to which one ends of the coil GL, the capacitor GCand the resistor GRare connected in common and a line (wiring) to which one ends of the coil RLand the capacitor RCare connected in common are a common line LL1whereas a line LL2to which the other ends of the coil GL, the capacitor GCand the resistor GRare connected in common and a line LL3to which the other ends of the coil RLand the capacitor RCare connected in common are separate lines, with the result that a current loop (closed circuit) through the lines LL1to LL3is not formed. The cancellation coil GLand the power reception-side coil RLin the circuit configuration ofFIG. 51are naturally coils different from each other, and they can be said to be coils which are provided separately and which are separated from each other.

Although as shown inFIG. 52, most of the winding forming the cancellation coil GLand the most of the winding forming the power reception-side coil RLare separate windings, part of the former winding and part of the latter winding can be formed in common (the part formed in common can be a wiring part which cannot be referred to as part of the winding). Even in the winding configuration described above, it can be said that the cancellation coil GLand the power reception-side coil RLare coils different from each other. InFIG. 52, the cancellation resistor GRis omitted.

For another example, as shown inFIG. 53, a configuration can be adopted in which the power reception-side coil RLis provided as a first pattern coil on a first surface of a substrate (printed substrate) installed in the electronic device2whereas the cancellation coil GLis provided as a second pattern coil different from the first pattern coil on a second surface on the side opposite to the first surface of the substrate.

A non-contact power feeding system W2according to one aspect of the present invention includes: the power reception device W1; and the power transmission device which includes the power transmission-side resonant circuit including the power transmission-side coil for transmitting the power, where the non-contact power feeding system can transmit and receive the power by the magnetic field resonance method.

Specifically, for example, preferably, in the non-contact power feeding system W2, the power transmission device includes: a power transmission circuit which can supply an alternating current voltage to the power transmission-side resonant circuit; a detection circuit which detects the amplitude of a current flowing through the power transmission-side coil; and a control circuit which performs power transmission control on the power by controlling the power transmission circuit based on the amplitude detection value of the detection circuit.

For example, preferably, the power reception device includes a change/short circuit which changes the resonant frequency of the power reception-side resonant circuit from a resonant frequency at the time of the power reception or short-circuits the power reception-side coil before the reception of the power from the power transmission device, the power transmission-side control portion includes: a first processing portion which controls the power transmission circuit such that in a state where in the power reception device, the resonant frequency of the power reception-side resonant circuit is changed or the power reception-side coil is short-circuited according to a signal by communication from the power transmission device, before the power transmission, a predetermined test magnetic field is generated in the power transmission-side coil; a second processing portion which determines, based on the amplitude detection value by the detection circuit when the test magnetic field is generated, whether or not the power transmission can be performed; and a third processing portion which realizes the power transmission by controlling the power transmission circuit such that after it is determined that the power transmission can be performed, a magnetic field for the power transmission larger than the test magnetic field is generated in the power transmission-side coil, and in the state, a current which cancels out an influence exerted by the power reception-side resonant circuit on the amplitude of the current flowing through the power transmission-side coil flows through the auxiliary resonant circuit.

Even when the change/short circuit is operated due to, for example, the nonlinearity of a circuit for changing the resonant frequency of the power reception-side resonant circuit or short-circuiting the power reception-side coil, based on the magnetic field generated in the power transmission-side coil, a certain amount of current may flow through the power reception-side resonant circuit, and the current may generate a magnetic field so as to produce a variation in the amplitude of the current flowing through the power transmission-side coil. This variation is not desirable for the determination as to whether or not the power transmission can be performed which is performed based on the amplitude of the current flowing through the power transmission-side coil. In the configuration described above, such a variation is cancelled out by the function of the auxiliary resonant circuit, and thus the determination as to whether or not the power transmission can be performed is made proper.

The power feeding device1itself in the embodiments described above may function as the power transmission device according to the present invention or part of the power feeding device1in the embodiments described above may function as the power transmission device according to the present invention. Likewise, the electronic device2itself in the embodiments described above may function as the power reception device according to the present invention or part of the electronic device2in the embodiments described above may function as the power reception device according to the present invention.

VARIATIONS AND THE LIKE

The embodiments of the present invention can be variously changed as necessary within the technical idea indicated in the scope of claims. The embodiments described above are simply examples of the embodiment of the present invention, and the significance of the terms in the present invention and the configuration requirements is not limited to the description of the above embodiments. The specific values indicated in the above description are simply illustrative, and can naturally be changed to various values. As explanatory notes which can be applied to the embodiments described above, explanatory notes 1 to 3 will be described below. The details described in the explanatory notes can be arbitrarily combined unless otherwise a contradiction arises.

Although in the embodiments described above, the frequencies and the resonant frequencies of various types of signals are set to 13.56 MHz serving as the reference frequency, 13.56 MHz is a target value for the setting, and in the actual device, the frequencies include errors.

Although the present invention embodied in conformance with the standard of the NFC is described in the embodiments, and thus in the description, the reference frequency is 13.56 MHz, the reference frequency may be any frequency other than 13.56 MHz. In relation to what has been described above, the communication and the power transfer between the power feeding device and the electronic device to which the present invention is applied may be communication and power transfer in conformance with a standard other than the NFC.

Even in a case where the reference frequency of the non-contact power feeding system according to the present invention is set to a frequency other than 13.56 MHz (for example, 6.78 MHz), and where the resonant frequency of the resonant circuit JJ in the foreign object3formed as a non-contact IC card is 13.56 MHz, when the foreign object3is placed on the power feeding stage12, a corresponding change in the voltage value VDis produced in the pFOD processing or the mFOD processing. Hence, even in such a case, it is possible to detect the foreign object3by the method described above.

A target device which is the power reception device or the power transmission device according to the present invention can be formed by hardware such as an integrated circuit or a combination of hardware and software. An arbitrary specific function which is the entire function realized in the target device or part thereof may be described as a program, and this program may be stored in a flash memory that can be mounted on the target device. Then, the program may be executed on a program executing device (for example, a microcomputer which can be installed in the target device) so as to realize the specific function. The program can be stored and fixed in an arbitrary recording medium. The recording medium in which the program is stored and fixed may be installed in or connected to a device (such as a server device) which is different from the target device.

LIST OF REFERENCE SYMBOLS