Wireless power transmitter and wireless power receiver

An automatic tuning assist circuit is coupled with a transmission antenna. The transmission antenna injects a first correction current into, or otherwise draws the first correction current from, the transmission antenna. In the first state, the first auxiliary coil is coupled with the transmission antenna. In this state, the first correction current IA, which corresponds to a current that flows through the first auxiliary coil, is injected into or drawn from the transmission antenna. In the second state, the first auxiliary coil is decoupled from the transmission antenna. In this state, the current that flows through the first auxiliary coil flows through a current path which is independent of the transmission antenna. The state is switched between the first state and the second state with the same frequency as that of the driving voltage.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wireless power supply technique.

2. Description of the Related Art

In recent years, wireless (contactless) power transmission has been receiving attention as a power supply technique for electronic devices such as cellular phone terminals, laptop computers, etc., or for electric vehicles. Wireless power transmission can be classified into three principal methods using an electromagnetic induction, an electromagnetic wave reception, and an electric field/magnetic field resonance.

The electromagnetic induction method is employed to supply electric power at a short range (several cm or less), which enables electric power of several hundred watts to be transmitted in a band that is equal to or lower than several hundred kHz. The power use efficiency thereof is on the order of 60% to 98%.

In a case in which electric power is to be supplied over a relatively long range of several meters or more, the electromagnetic wave reception method is employed. The electromagnetic wave reception method allows electric power of several watts or less to be transmitted in a band between medium waves and microwaves. However, the power use efficiency thereof is small. The electric field/magnetic field resonance method has been receiving attention as a method for supplying electric power with relatively high efficiency at a middle range on the order of several meters. Related techniques are disclosed in Non-patent document (A. Karalis, J. D. Joannopoulos, M. Soljacic, “Efficient wireless non-radiative mid-range energy transfer” ANNALS of PHYSICS Vol. 323, Jan. 2008, pp. 34-48), for example.

FIG. 1is a diagram showing a wireless power transmission system according to a comparison technique. The wireless power transmission system1rincludes a wireless power supply transmitter2rand a wireless power receiver4r. The wireless power supply transmitter2rincludes a transmission coil LTX, a resonance capacitor CTX, and an AC power supply10r. The wireless power receiver4rincludes a reception coil LRX, a resonance capacitor CRX, and a load70.

The resonance frequency is an important factor in magnetic field (electric field) resonance power transmission. The resonance frequency of the transmitter side LC resonance circuit is represented by fTX=1/(2π√(LTX·CTX)). The resonance frequency of the receiver side LC resonance circuit is represented by fRX=1/(2π√(LRX−CRX)). Thus, in order to provide high-efficiency electric power transmission, there is a need to appropriately adjust the transmitter-side and receiver-side resonance frequencies and the frequency of the AC power supply10r. However, in actuality, such resonance frequencies fluctuate depending on various kinds of factors. It is difficult for the power receiver side to tune the fluctuating resonance frequency based on the magnetic field (or electric field) itself as it has been transmitted from the power supply transmitter. This is because, in some cases, the resonance frequency detected by the power receiver side further changes depending on the resonance frequency and the phase conditions of the power receiver side.

SUMMARY OF THE INVENTION

The present invention has been made in order to solve such a problem. Accordingly, it is an exemplary purpose of an embodiment of the present invention to provide a wireless power supply transmitter, a wireless power receiver, and a wireless power supply system, which are capable of automatically tuning the resonance frequency.

An embodiment of the present invention relates to a wireless power supply transmitter configured to transmit an electric power signal comprising any one from among an electric field, a magnetic field, and an electromagnetic field to a wireless power receiver. The wireless power supply transmitter comprises: a transmission antenna comprising a transmission coil; a power supply configured to apply an AC driving voltage between both ends of the transmission antenna; and an automatic tuning assist circuit coupled with the transmission antenna, and configured to inject a first correction current into, or otherwise to draw a first correction current from, the transmission antenna. The automatic tuning assist circuit comprises a first auxiliary coil. The automatic tuning assist circuit is configured to alternately switch between (1) a state in which the first auxiliary coil is coupled with the transmission antenna, and the first correction current that corresponds to a current that flows through the first auxiliary coil is injected into or otherwise drawn from the transmission antenna, and (2) a state in which the first auxiliary coil is decoupled from the transmission antenna, and the current that flows through the first auxiliary coil flows through a current path which is independent of the transmission antenna.

Also, the state may be switched between the first state and the second state with the same frequency as that of the driving voltage, or otherwise with a frequency obtained by multiplying or otherwise by dividing the frequency of the driving voltage by an odd number.

In a case in which the resonance frequency of the transmission antenna matches the frequency of the driving voltage, the current that flows through the first auxiliary coil becomes zero. In this state, the first correction current also becomes zero.

In a case in which the resonance frequency of the transmission antenna does not match the frequency of the driving voltage, the impedance of the resonance circuit including the transmission antenna functions as a capacitor or otherwise as an inductor. Thus, a current flows through the transmission antenna with a phase delayed or otherwise advanced with respect to the driving voltage. In this case, by switching the state between the first state and the second state, a current is generated so as to flow through the first auxiliary coil. The magnitude (and direction) of the current is (are) adjusted so as to provide phase matching between the current that flows through the transmission antenna and the driving voltage. By means of the first correction current generated as a result of this operation, such an arrangement corrects the difference between the current that is to flow through the transmission antenna in the resonant state and the current that flows through the transmission antenna in a case in which such an automatic tuning assist circuit is not used. Thus, such an arrangement provides a quasi-resonant state.

Such an embodiment provides automatic tuning of the transmission antenna with respect to the driving voltage without adjusting the capacitance of the resonance capacitor or the like.

Another embodiment of the present invention also relates to a wireless power supply transmitter. The wireless power supply transmitter comprises: a transmission antenna comprising a transmission coil; a power supply configured to apply an AC driving voltage between both ends of the transmission antenna; and an automatic tuning assist circuit coupled with the transmission antenna, and configured to inject a correction current into, or otherwise draw the correction current from, the transmission antenna. The automatic tuning assist circuit comprises: a first terminal and a second terminal coupled with the transmission antenna; an H-bridge circuit arranged between the first terminal and the second terminal; and a third auxiliary coil arranged between output terminals of the H-bridge circuit.

The H-bridge circuit may be switched on and off with the same frequency as that of the driving voltage, or with a frequency obtained by multiplying or otherwise dividing the frequency of the driving voltage by an odd number.

With such an embodiment, during a half period from a predetermined phase of the driving voltage, of the four switches of the H-bridge circuit, a first pair of oppositely positioned switches are turned on. Furthermore, during the following half period, a second pair of switches are turned on. In the half period in which the first pair of switches are turned on, the current that flows through the third auxiliary coil is supplied to the transmission antenna in a first direction. On the other hand, in the half period in which the second pair of switches are turned on, the current that flows through the third auxiliary coil is supplied to the transmission antenna in a second direction.

In a case in which the resonance frequency of the transmission antenna matches the frequency of the driving voltage, the current that flows through the third auxiliary coil becomes zero.

In a case in which the resonance frequency of the transmission antenna does not match the frequency of the driving voltage, the impedance of the resonance circuit including the transmission antenna functions as a capacitor or otherwise as an inductor. Thus, a current flows through the transmission antenna with a phase delayed or otherwise advanced with respect to the driving voltage. In this case, by switching the H-bridge circuit, a current is generated so as to flow through the third auxiliary coil. The magnitude (and direction) of the current is (are) adjusted so as to provide phase matching between the current that flows through the transmission antenna and the driving current. By means of the third correction current generated as a result of this operation, such an arrangement corrects the difference between the current that is to flow through the transmission antenna in the resonant state and the current that flows through the transmission antenna in a case in which such an automatic tuning assist circuit is not used. Thus, such an arrangement provides a quasi-resonant state.

Such an embodiment provides automatic tuning of the transmission antenna with respect to the driving voltage without adjusting the capacitance of the resonance capacitor or the like.

Yet another embodiment of the present invention relates to a wireless power receiver configured to receive an electric power signal comprising any one from among an electric field, a magnetic field, and an electromagnetic field, transmitted from a wireless power supply transmitter. The wireless power receiver comprises: a reception antenna comprising a reception coil; and an automatic tuning assist circuit coupled with the reception antenna, and configured to inject a first correction current into, or otherwise draw a first correction current from, the reception antenna. The automatic tuning assist circuit comprises a first auxiliary coil. The automatic tuning assist circuit is configured to alternately switch between (1) a state in which the first auxiliary coil is coupled with the reception antenna, and the first correction current that corresponds to a current that flows through the first auxiliary coil is injected into or otherwise drawn from the reception antenna and (2) a state in which the first auxiliary coil is decoupled from the reception antenna, and the current that flows through the first auxiliary coil flows through a current path which is independent of the reception antenna.

Also, the state may be switched between the first state and the second state with the same frequency as that of the electric power signal, or otherwise with a frequency obtained by multiplying or otherwise dividing the frequency of the electric power signal by an odd number.

In a case in which the resonance frequency of the reception antenna matches the frequency of the electric power signal, the current that flows through the first auxiliary coil becomes zero. In this state, the first correction current also becomes zero.

In a case in which the resonance frequency of the reception antenna does not match the frequency of the electric power signal, the impedance of the resonance circuit including the reception antenna functions as a capacitor or otherwise as an inductor. Thus, a current flows through the reception antenna with a phase delayed or otherwise advanced with respect to the electric power signal. In this case, by switching the state between the first state and the second state, a current is generated so as to flow through the first auxiliary coil. The magnitude (and direction) of the current is (are) adjusted so as to provide phase matching between the current that flows through the reception antenna and the electric power signal. By means of the first correction current generated as a result of this operation, such an arrangement corrects the difference between the current that is to flow through the reception antenna in the resonant state and the current that flows through the reception antenna in a case in which such an automatic tuning assist circuit is not used. Thus, such an arrangement provides a quasi-resonant state.

Such an embodiment provides automatic tuning of the reception antenna with respect to the electric power signal without adjusting the capacitance of the resonance capacitor or the like.

Yet another embodiment of the present invention also relates to a wireless power receiver. The wireless power receiver comprises: a reception antenna comprising a reception coil; and an automatic tuning assist circuit coupled with the reception antenna, and configured to inject a correction current into, or otherwise draw the correction current from, the reception antenna. The automatic tuning assist circuit comprises: a first terminal and a second terminal coupled with the reception antenna; an H-bridge circuit arranged between the first terminal and the second terminal; and a third auxiliary coil arranged between output terminals of the H-bridge circuit.

The H-bridge circuit may be switched on and off with the same frequency as that of the electric power signal, or with a frequency obtained by multiplying or otherwise dividing the frequency of the electric power signal by an odd number.

With such an embodiment, during a half period from a predetermined phase of the electric power signal, of the four switches of the H-bridge circuit, a first pair of oppositely positioned switches are turned on. Furthermore, during the following half period, a second pair of switches are turned on. In the half period in which the first pair of switches are turned on, the current that flows through the third auxiliary coil is supplied to the reception antenna in a first direction. On the other hand, in the half period in which the second pair of switches are turned on, the current that flows through the third auxiliary coil is supplied to the reception antenna in a second direction.

In a case in which the resonance frequency of the reception antenna matches the frequency of the electric power signal, the current that flows through the third auxiliary coil becomes zero.

In a case in which the resonance frequency of the reception antenna does not match the frequency of the electric power signal, the impedance of the resonance circuit including the reception antenna functions as a capacitor or otherwise as an inductor. Thus, a current flows through the reception antenna with a phase delayed or otherwise advanced with respect to the electric power signal. In this case, by switching the H-bridge circuit, a current is generated so as to flow through the third auxiliary coil. The magnitude (and direction) of the current is (are) adjusted so as to provide phase matching between the current that flows through the reception antenna and the electric power signal. By means of the third correction current generated as a result of this operation, such an arrangement corrects the difference between the current that is to flow through the reception antenna in the resonant state and the current that flows through the reception antenna in a case in which such an automatic tuning assist circuit is not used. Thus, such an arrangement provides a quasi-resonant state.

Such an embodiment provides automatic tuning of the reception antenna with respect to the electric power signal without adjusting the capacitance of the resonance capacitor or the like.

Yet another embodiment of the present invention relates to a wireless power supply system. The wireless power supply system may comprise: the aforementioned wireless power supply transmitter configured to transmit an electric power signal comprising any one from among an electric field, a magnetic field, and an electromagnetic field; and the aforementioned wireless power receiver configured to receive the electric power signal.

DETAILED DESCRIPTION OF THE INVENTION

In the present specification, the state represented by the phrase “the member A is connected/coupled to/with the member B” includes a state in which the member A is indirectly connected/coupled to the member B via another member that does not substantially affect the electric connection therebetween, or that does not damage the functions or effects of the connection therebetween, in addition to a state in which the member A is physically and directly connected/coupled to the member B.

Similarly, the state represented by the phrase “the member C is provided between the member A and the member B” includes a state in which the member A is indirectly connected to the member C, or the member B is indirectly connected to the member C via another member that does not substantially affect the electric connection therebetween, or that does not damage the functions or effects of the connection therebetween, in addition to a state in which the member A is directly connected to the member C, or the member B is directly connected to the member C.

FIG. 2is a circuit diagram showing a configuration of a wireless power supply transmitter2according to a first embodiment. The wireless power supply transmitter2transmits an electric power signal S1to a wireless power receiver (not shown). As such an electric power signal S1, the wireless power supply transmitter2uses the near-field components (electric field, magnetic field, or electromagnetic field) of electromagnetic waves that have not yet become radio waves.

The wireless power supply transmitter2includes a power supply10, a transmission antenna20, an automatic tuning assist circuit (ATAC)30, and a control unit40.

The transmission antenna20includes a transmission coil LTXarranged between its first terminal21and its second terminal22. A resonance capacitor CTXis arranged in series with the transmission coil LTX. The resonance capacitor CTXand the transmission coil LTXmay also be mutually exchanged.

The power supply10applies an AC driving voltage VDRVhaving a predetermined transmission frequency fTXbetween both ends of the transmission antenna20. The driving voltage VDRVmay have a desired AC waveform, examples of which include a rectangular waveform, a trapezoidal waveform, a sine waveform, and the like. With the present embodiment, the driving voltage VDRVis configured as a rectangular wave signal which swings between a first voltage level (power supply voltage VDD) and a second voltage level (ground voltage VGND=0 V).

The power supply10includes a DC power supply12, a first high-side switch SWH1, and a first low-side switch SWL1. The DC power supply12generates a DC power supply voltage VDD. The first high-side switch SWH1and the first low-side switch SWL1are sequentially arranged in series between the output terminal of the DC power supply12and a fixed voltage terminal (ground terminal). The control unit40switches on and off the first high-side switch SWH1and the first low-side switch SWL1in a complementary manner, with a transmission frequency fTX. The power supply10may be configured as an H-bridge circuit.

The automatic tuning assist circuit30is directly or indirectly coupled with the transmission antenna20. The automatic tuning assist circuit30injects the first correction current IAinto the relay antenna20(in the form of a source current). Otherwise, the automatic tuning assist circuit30draws the first correction current IAfrom the relay antenna20(in the form of a sink current). The automatic tuning assist circuit30inFIG. 2is directly coupled with the transmission antenna20. Description will be made in the present embodiment with the first correction current IAthat flows in the direction from the transmission antenna20to the automatic tuning assist circuit30(in the form of a sink current) as the first correction current IAhaving a positive value.

The automatic tuning assist circuit30includes a first auxiliary coil LA1. The automatic tuning assist circuit30alternately repeats the first state φ1and a second state φ2with the same frequency fTXas that of the driving voltage VDRV.

In the first state φ1, the first auxiliary coil LA1is coupled with the transmission antenna20. In this state, a first correction current IAthat corresponds to the current that flows through the first auxiliary coil LA1is injected into or otherwise drawn from the transmission antenna20.

In the second state φ2, the first auxiliary coil LA1is decoupled from the transmission antenna20. In this state, the current ILA1that flows through the first auxiliary coil LA1flows through a current path which is independent of the transmission antenna20.

Specifically, the automatic tuning assist circuit30includes a first terminal31, a second terminal32, a first switch SW1, a second switch SW2, and a control unit40, in addition to the first auxiliary coil LA1. The first terminal31and the second terminal32are coupled with the transmission antenna20. The first switch SW1and the first auxiliary coil LA1are arranged in series between the first terminal31and the second terminal32. The second switch SW2is arranged in parallel with the first auxiliary coil LA1.

The control unit40switches on and off the first switch SW1and the second switch SW2in a complementary manner, with the same frequency fTXas that of the driving voltage VDRV, and with a predetermined phase difference θTXwith respect to the driving voltage VDRV. Specifically, in the first state φ1, the control unit40turns on the first switch SW1and turns off the second switch SW2. In the second state φ2, the control unit40turns off the first switch SW1and turns on the second switch SW2. The phase difference θTXmay preferably be set to a value in the vicinity of +0 degrees or otherwise 180 degrees. That is to say, a part of the control unit40functions as a component of the automatic tuning assist circuit30.

In the first state φ1, the first switch SW1is turned on, and thus, the first auxiliary coil LA1is coupled with the transmission antenna20. In the second state φ2, the second switch SW2is turned on. In this state, the current ILA1that flows through the first auxiliary coil LA1flows through a loop path including the second switch SW2.

The first switch SW1and the second switch SW2may each be configured employing a MOSFET (Metal Oxide Semiconductor Field Effect Transistor), IGBT (Insulated Gate Bipolar Transistor), bipolar transistor, or the like.FIGS. 3A through 3Fare diagrams each showing an example configuration of a switch employing a MOSFET.

FIG. 3Ashows a configuration of the switch employing an N-channel MOSFET.FIG. 3Bshows a configuration of the switch employing a P-channel MOSFET. In a case in which the back gate of the MOSFET is connected to its source, the body diode that forms between the back gate and the drain is in the connection state regardless of the gate voltage. Thus, such a switch configured as a single MOSFET is not capable of blocking a current that flows in one particular direction. In the present specification, such a switch will be referred to as a “uni-directional switch”.

The switches shown inFIGS. 3C through 3Feach comprise two N-channel MOSFETs or otherwise two P-channel MOSFETs connected such that their body diodes are connected in reverse directions (back-to-back connection). With the switches shown inFIGS. 3C through 3F, in the off state, no current flows in either direction. In the present specification, such a switch will be referred to as a “bi-directional switch”.

With the present embodiment, the switches SW1and SW2may each be configured as a uni-directional switch or otherwise a bi-directional switch. It should be noted that, in a case in which the switches SW1and SW2are each configured as a uni-directional switch, the switches SW1and SW2each require a rectifier diode arranged in series. Detailed description of such a modification will be made later.

The above is the configuration of the wireless power supply transmitter2. Next, description will be made regarding the operation thereof.

Let us consider an arrangement in which the switches SW1and SW2are each configured as a bi-directional switch which is capable of blocking a current in both directions in the off state.

FIG. 4shows waveform diagrams each showing the operation of the wireless power supply transmitter2shown inFIG. 2. The vertical axis and the horizontal axis shown in the waveform diagrams and the time charts in the present specification are expanded or reduced as appropriate for ease of understanding. Also, each waveform shown in the drawings is simplified for ease of understanding.

FIG. 4shows, in the following order beginning from the top, the driving voltage VDRV, the resonance voltage VTXbetween the transmission coil LTXside end and the resonance capacitor CTXside end, the resonance current ITXthat flows through the transmission antenna20, the voltage at the first switch SW1, the voltage at the second switch SW2, the first auxiliary current IA, and the current ILA1that flows through the first auxiliary coil LA1. In the waveform diagram for each switch, the high level represents the on state, and the low level represents the off state. It should be noted thatFIG. 4shows the waveforms of the resonance current ITXand the resonance voltage VTXobtained after a sufficient time has elapsed after the automatic tuning assist circuit30starts to operate.

As shown inFIG. 4, the driving voltage VDRVhaving a rectangular waveform is applied to the transmission antenna20. The control unit40switches on and off the first switch SW1and the second switch SW2in a complementary manner, with the same frequency as that of the driving voltage VDRV, and with the same phase θTX(=0 degrees) as that of the driving voltage VDRV.

By repeatedly switching the state between the first state φ1and the second state φ2, such an arrangement allows the magnitude and the direction of the current ILA1that flows through the first auxiliary coil LA1to be made to converge to the resonance point such that the phase difference between the driving voltage VDRVand the resonance current ITXbecomes zero, i.e., such that the resonant state is obtained.

In the second state φ2, the current ITATflows through a loop including the second switch SW2. In this state, the level of the current ITATis maintained at a constant value. In the first state φ1, the current ITATis supplied to the transmission antenna20as the first correction current IA. That is to say, the automatic tuning assist circuit30can be regarded as a correction current source configured to supply the first correction current IAto the transmission antenna20.FIG. 5is an equivalent circuit diagram of the wireless power supply transmitter2shown inFIG. 2.

FIG. 6Ais a waveform diagram showing a state in which the automatic tuning assist circuit30does not operate, andFIG. 6Bis a waveform diagram showing a state in which the automatic tuning assist circuit30operates.

First, description will be made with reference toFIG. 6Aregarding the state in which the automatic tuning assist circuit30does not operate, i.e., a state in which the first switch SW1is fixed to the off state, and the second switch SW2is fixed to the on state. That is to say, a state in which the correction current IAis zero is shown.

The impedance Z of the transmission antenna20is represented by the following Expression (1). The resonance frequency fCof the transmission antenna20is represented by the following Expression (2). The following Expressions (1) and (2) represent the impedance and the resonance frequency assuming that the resistance component is negligible. However, it is needless to say that, in actual circuits, the resistance component connected in series contributes to the circuit impedance.
Z=jωLTX+1/(jωCTX)  (1)
fC=1/2π√(LTX·CTX)  (2)

In a case in which the frequency fTXof the driving voltage VDRVis higher than the resonance frequency fC(fTX>fC), the transmission antenna20functions as an inductor. In this case, the resonance current ITXthat flows through the transmission antenna20has a phase which is delayed with respect to the phase of the driving voltage VDRV. Conversely, in a case in which the frequency fTXof the driving voltage VDRVis lower than the resonance frequency fC(fTX<fC), the transmission antenna20functions as a capacitor. In this case, the resonance current ITXhas a phase which is advanced with respect to the driving voltage VDRV.

FIG. 6Ashows a state in which fC>fTX. In this state, the resonance current ITXhas a phase which is advanced by the phase difference φ with respect to the driving voltage VDRV. It should be noted that the phase difference φ is not 90 degrees. This is because the resonance circuit includes a non-negligible resistance component (not shown) connected in series. In the non-resonant state, the impedance Z exhibits a high value, leading to a reduced amplitude of the resonance current ITX. In this state, such an arrangement is not capable of transmitting a large amount of electric power.

Next, description will be made with reference toFIG. 6Bregarding a case in which the automatic tuning assist circuit30operates.

In a case in which the automatic tuning assist circuit30operates, the correction current IAis supplied to the transmission antenna20with a phase difference with respect to the driving voltage VDRV. As a result, phase matching is obtained between the resonance current ITXand the driving voltage VDRV, thereby providing a quasi-resonant state. In this state, the resonance current ITXhas a greater amplitude than that in the non-resonant state.

FIG. 7is a phasor diagram (vector diagram) for describing the quasi-resonant state provided by the automatic tuning assist circuit30.

The correction current IA(fTX) represents the fundamental wave component (having the frequency fTX) of the correction current IAshown inFIG. 4. The correction current IA(fTX) has a phase difference θ with respect to the driving voltage VDRV.

Based on the “principle of superposition”, the resonance current ITXis configured as the sum of the current component IDRVinduced by the driving voltage VDRVand the correction current IA(fTX). By optimizing the amplitude of the correction current IA, such an arrangement is capable of providing phase matching between the driving voltage VDRV(having a phase of 0 degrees) and a resultant current obtained by combining the two current components IDRVand IA(fTX), i.e., the resonance current ITX. That is to say, it can be clearly understood that such an arrangement provides a quasi-resonant state.

The above is the principle and the operation of the wireless power supply transmitter2.

As described above, without adjusting the resonance frequency fCof the transmission antenna20, the wireless power supply transmitter2is capable of automatically tuning the circuit state so as to provide the quasi-resonant state. In the wireless power transmission, the resonance frequency changes over time according to the position relation between the wireless power supply transmitter2and the wireless power receiver4. The wireless power supply transmitter2is capable of following the change in the resonance frequency with high speed, thereby providing high-efficiency electric power transmission.

Furthermore, in a case in which a large amount of electric power is transmitted by means of wireless power transmission, a very high voltage develops between both ends of the resonance capacitor CTX, which limits the use of a variable capacitor. With the wireless power supply transmitter2, there is no need to adjust the capacitance of the resonance capacitor CTX. Thus, such an arrangement does not require such a variable capacitor or the like, which is another advantage.

Description has been made above regarding a case in which the first switch SW1is switched on and off with a phase difference θTX=0 degrees with respect to the phase of the switching of the first high-side switch SWH1(driving voltage VDRV). However, the phase difference θTXbetween the first switch SW1and the first high-side switch SWH1is not restricted to 0 degrees. Also, an arrangement may be made in which the phase difference θTXbetween the first switch SW1and the first high-side switch SWH1is set to 180 degrees. In this case, the direction in which the current IAflows is automatically adjusted such that it is reversed.

That is to say, in a case in which fC<fTX, by setting the phase difference θTXto 0 degrees or otherwise 180 degrees, such an arrangement provides a quasi-resonant state.

Also, the phase difference θTXmay be moved away from 0 degrees or 180 degrees. In this case, in the vector diagram shown inFIG. 7, the phase difference θTXbetween the current components IDRVand IAdoes not match 90 degrees. However, even in such a case, the correction current IAis automatically adjusted such that the resultant resonance current ITXobtained by combining the current components IDRVand IAhas a phase of 0 degrees. It should be noted that, as the phase difference θTXbecomes closer to 0 degrees or otherwise 180 degrees, the required value of the amplitude of the correction current IAbecomes smaller. This is an advantage in employing an arrangement in which the phase difference θTXis set to a value in the vicinity of 0 degrees or otherwise 180 degrees.

The wireless power supply transmitter2is capable of automatically providing a quasi-resonant state not only in a case in which fC<fTX, but also in a case in which fC>fTX. In this case, the phase difference θTXis preferably set to 180 degrees.

FIG. 8is a phasor diagram for describing a quasi-resonant state provided by the automatic tuning assist circuit30in a case in which fC>fTX. Description will be made below assuming that the driving voltage VDRVhas a phase of 0 degrees, and the correction current IAhas a phase θ. In a case in which fC>fTX, the current has a phase which is advanced with respect to that of the voltage. Such an arrangement also provides a quasi-resonant state even in such a case.

It should be noted that, in a case in which fC>fTX, the phase difference θTXmay be set to a value in the vicinity of 0 degrees. In this case, the direction in which the correction current IAflows is automatically reversed so as to provide a quasi-resonant state.

Next, description will be made regarding modifications of the wireless power supply transmitter2. Each modification may be combined with any one of the other modifications, which is encompassed within the scope of the present invention.

FIG. 9is a circuit diagram showing a configuration of an automatic tuning assist circuit30aaccording to a first modification. The automatic tuning assist circuit30aincludes a second auxiliary coil LA2in addition to the configuration of the automatic tuning assist circuit30shown inFIG. 2.

In the first state φ1, the second auxiliary coil LA2is decoupled from the transmission antenna20. In this state, the current ILA2that flows through the second auxiliary coil LA2flows through a current path that is independent of the transmission antenna20. In the second state φ2, the second auxiliary coil LA2is coupled with the transmission antenna20. In this state, the second correction current IA2that corresponds to the current ILA2that flows through the second auxiliary coil LA2is injected into or otherwise drawn from the transmission antenna20.

A third switch SW3and the second auxiliary coil LA2are arranged in series between the first terminal31and the second terminal32. A fourth switch SW4is arranged in parallel with the second auxiliary coil LA2. In the first state φ1, a control unit40aturns on the fourth switch SW4. In the second state φ2, the control unit40aturns on the third switch SW3.

FIG. 10is a waveform diagram showing the operation of the automatic tuning assist circuit30ashown inFIG. 9. It should be noted thatFIG. 10shows the waveforms of the resonance current ITXand the resonance voltage VTXobtained after a sufficient time has elapsed after the automatic tuning assist circuit30astarts to operate.

The automatic tuning assist circuit30ashown inFIG. 9can be regarded as an arrangement comprising two automatic tuning assist circuits30shown inFIG. 2, which are configured to operate with reverse phases. With such an arrangement, the correction current IA1supplied by the first auxiliary coil LA1and the correction current IA2supplied by the second auxiliary coil LA2have opposite polarities. The correction current IAsupplied to the transmission antenna20is configured as the sum of the two correction currents IA1and IA2.

With the automatic tuning assist circuit30ashown inFIG. 9, such an arrangement also provides a quasi-resonant state.

With a second modification, the first switch SW1and the second switch SW2are each configured using a uni-directional switch.FIGS. 11A and 11Bare circuit diagrams each showing a configuration of an automatic tuning assist circuit according to the second modification.

InFIGS. 11A and 11B, the first switch SW1includes a uni-directional switch SW1aand a rectifier diode D1barranged in series with the uni-directional switch SW1a. The rectifier diode D1bis arranged in a direction that is the reverse of the forward direction of a parasitic diode (body diode) D1aconfigured as an inversely conducting element formed in the uni-directional switch SW1a. The switch SW1aand the rectifier diode D1bmay be mutually exchanged.

The second switch SW2has the same configuration as that of the switch SW1. That is to say, the second switch SW2includes a uni-directional switch SW2aand a rectifier diode D2barranged in series with the uni-directional switch SW2a. The rectifier diode D2bis arranged in a direction that is the reverse of the forward direction of a parasitic diode (body diode) D2aconfigured as an inversely conducting element formed in the uni-directional switch SW2a. The switch SW2aand the rectifier diode D2bmay be mutually exchanged.

By arranging the rectifier diodes D1band D2bin directions that are the reverse of the forward directions of the parasitic diodes D1aand D2a, such an arrangement is capable of preventing the first switch SW1and the second switch SW2from turning on at an unintended timing.

It should be noted that, in a case in which the first switch SW1and the second switch SW2are each configured as a bi-directional switch, the automatic tuning assist circuit30allows the correction voltage IAto have both a positive value and a negative value. In contrast, the automatic tuning assist circuit30shown inFIG. 11Ais capable of generating the correction current IAhaving a positive value. However, the automatic tuning assist circuit30cannot generate the correction current IAhaving a negative value. Conversely, the automatic tuning assist circuit30shown inFIG. 11Bis capable of generating the correction current IAhaving a negative value. However, the automatic tuning assist circuit30cannot generate the correction current IAhaving a positive value. That is to say, with the automatic tuning assist circuits30shown inFIGS. 11A and 11B, the switching phases of the first switch SW1and the second switch SW2are restricted.

Also, the automatic tuning assist circuit30ashown inFIG. 9may be configured using a uni-directional switch.FIG. 12is a circuit diagram showing a configuration of an automatic tuning assist circuit according to a third modification. In the automatic tuning assist circuit30ashown inFIG. 12, the first switch SW1and the second switch SW2are each configured in the same way as shown inFIG. 11A. The third switch SW3and the fourth switch SW4are each configured in the same way as shown inFIG. 11B. With the automatic tuning assist circuit30ashown inFIG. 12, such an arrangement also provides the same advantages as those provided by the automatic tuning assist circuit30ashown inFIG. 9.

FIG. 13is a circuit diagram showing a configuration of a wireless power supply transmitter2bincluding an automatic tuning assist circuit30baccording to a second embodiment. The automatic tuning assist circuit30bis coupled with the transmission antenna20. The automatic tuning assist circuit30binjects the correction current IAinto the transmission antenna20, or otherwise draws the correction current IAfrom the transmission antenna20.

The automatic tuning assist circuit30bincludes: a first terminal31and a second terminal32coupled with the transmission antenna20; an H-bridge circuit36; a third auxiliary coil LA3, and a control unit40b. The H-bridge circuit36is arranged between the first terminal31and the second terminal32. The H-bridge circuit36is switched on and off with the same frequency as that of the driving voltage VDRV. The third auxiliary coil LA3is arranged between the output terminals P1and P2of the H-bridge circuit36. The control unit40bswitches on and off the H-bridge circuit36with a predetermined phase difference θTXwith respect to the driving voltage VDRV.

FIG. 14is a waveform diagram showing the operation of the wireless power supply transmitter2shown inFIG. 13. The H-bridge circuit36inFIG. 14performs switching with the same phase (θTX=0 degrees) as that of the driving voltage VDRV.

During the half period from a predetermined phase of the driving voltage VDRV, of the four switches SW11through SW14of the H-bridge circuit36, a first pair of oppositely positioned switches SW11and SW14are turned on. Furthermore, during the following half period, a second pair of switches SW12and SW13are turned on. In the half period in which the first pair of switches SW11and SW14are turned on, the current ILA3that flows through the third auxiliary coil LA3is supplied to the transmission antenna20in a first direction In the half period in which the second pair of switches SW12and SW13are turned on, the current ILA3that flows through the third auxiliary coil LA3is supplied to the transmission antenna20in a second direction.

The switches SW11through SW14may each be configured using a uni-directional switch or otherwise a bi-directional switch. Here, description will be made regarding the configuration and the operation of an arrangement employing bi-directional switches. It should be noted that, in a case of employing such uni-directional switches, there is a need to arrange a rectifier diode in series with each of the switches SW11through SW14. Description will be made later regarding such a modification.

The operation and mechanism of the automatic tuning assist circuit30bshown inFIG. 13are the same as those of the automatic tuning assist circuit shown inFIG. 2orFIG. 9. The automatic tuning assist circuit30bgenerates a correction current IAhaving the same waveform as that of the correction current IAshown inFIG. 10. The wireless power supply transmitter2bshown inFIG. 13also provides the same advantages as those provided by the wireless power supply transmitter described above.

Furthermore, with the automatic tuning assist circuit30bshown inFIG. 13, such an arrangement requires only a single coil to provide the same advantages as those provided by the automatic tuning assist circuit30ashown inFIG. 9.

Next, description will be made regarding a modification of the automatic tuning assist circuit30baccording to the second embodiment.

FIG. 15is a circuit diagram showing a modification of the automatic tuning assist circuit30bshown inFIG. 13. In this modification, the switches SW11through SW14are each configured using a uni-directional switch.

The switches SW11through SW14each have the same configuration as that described with reference toFIGS. 11A, 11B, orFIG. 12. The switches SW11and SW12each have the same configuration as that of the switches SW1and SW2shown inFIG. 11A. The switches SW13and SW14each have the same configuration as that of the switches SW1and SW2shown inFIG. 11B.

Such a modification shown inFIG. 15provides the same advantages as those provided by the automatic tuning assist circuit30bshown inFIG. 13.

Various modifications may be made with respect to the configuration of the coupling between the automatic tuning assist circuit30,30a, or30b(which will simply be referred to as the “automatic tuning assist circuit30” hereafter) and the transmission antenna20.FIGS. 16A through 16Gare circuit diagrams each showing the configuration of a coupling between the automatic tuning assist circuit30and the transmission antenna20.

The automatic tuning assist circuits30inFIGS. 16A through 16Dare directly coupled with the transmission antenna20. The automatic tuning assist circuits30inFIGS. 16E and 16Fare magnetically coupled with the transmission antenna20.

FIG. 16Ashows the same configuration as shown inFIG. 2 or 9. The automatic tuning assist circuit30inFIG. 16Bis coupled with the resonance capacitor CTX. Specifically, the first terminal31of the automatic tuning assist circuit30is connected to one end of the resonance capacitor CTX. Furthermore, the second terminal32of the automatic tuning assist circuit30is connected to the other end of the resonance capacitor CTX.

A tap33is provided to the transmission coil LTXinFIG. 16C. The first terminal31of the automatic tuning assist circuit30is connected to the tap33. Furthermore, the second terminal32is connected to the other end of the transmission coil LTX.

The transmission antenna20shown inFIG. 16Dincludes two resonance capacitors CTXand CTX2arranged in series with the transmission coil LTX. The first terminal31of the automatic tuning assist circuit30is connected to one end of one of the resonance capacitors, i.e., the resonance capacitor CTX2. Furthermore, the second terminal32is connected to the other end of the resonance capacitor CTX2.

The wireless power supply transmitter shown inFIG. 16Efurther includes a first coil L1magnetically coupled with the transmission coil LTX. The first terminal31of the automatic tuning assist circuit30is connected to one end of the first coil L1. Furthermore, the second terminal32of the automatic tuning assist circuit30is connected to the other end of the first coil L1.

The wireless power supply transmitter shown inFIG. 16Ffurther includes a transformer T1. The primary winding W1of the transformer T1is arranged in series with the transmission antenna LTX. The first terminal31of the automatic tuning assist circuit30is connected to one end of the secondary winding W2of the transformer T1. Furthermore, the second terminal32of the automatic tuning assist circuit30is connected to the other end of the secondary winding W2.

In the wireless power supply transmitter2shown inFIG. 16G, the power supply10and the transmission antenna20are coupled with each other via a transformer T2. From another viewpoint, the power supply10and the transformer T2provide a power supply10aconfigured to apply the driving voltage VDRVbetween both ends of the transmission antenna20. It should be noted that, inFIG. 16G, the automatic tuning assist circuit is not shown. The automatic tuning assist circuit may be coupled with the transmission antenna20using any one of the coupling configurations shown inFIGS. 16A through 16F.

With such modifications shown inFIG. 16Athrough16G, or with other circuits similar to such modifications, such an arrangement also provides a quasi-resonant state.

In addition, with the configurations shown inFIGS. 16C through 16F, such an arrangement allows the voltage between the terminals31and32of the automatic tuning assist circuit30to be reduced, as compared with the configurations shown inFIGS. 16A and 16B. Thus, such an arrangement allows a low breakdown voltage element to be employed as a switch which is a component of the automatic tuning assist circuit30. This facilitates the circuit design, or this provides a reduced cost.

Description has been made in the first and second embodiments regarding the wireless power supply transmitter including the automatic tuning assist circuit configured to operate with a switching frequency which is equal to the frequency of the driving voltage VDRV. However, the automatic turning assist circuit may be configured to operate with a switching frequency that differs from the frequency of the driving voltage VDRV, which also provides a quasi-resonant state. For example, the automatic tuning assist circuit30may be configured to operate with a switching frequency obtained by multiplying or otherwise dividing the frequency of the driving voltage VDRVby an odd number. The relation between the switching frequency and the frequency of the driving voltage may preferably be determined giving consideration to the overall efficiency of the system, etc.

The aforementioned automatic tuning assist circuit may be employed in a wireless power receiver. Description will be made regarding such a wireless power receiver.

FIG. 17is a circuit diagram showing a configuration of a wireless power receiver4according to the first embodiment. The wireless power receiver4receives the electric power signal S1transmitted from the aforementioned wireless power supply transmitter or otherwise a wireless power supply transmitter having an entirely different configuration. The electric power signal S1is configured using the near-field components (electric field, magnetic field, or electromagnetic field) of electromagnetic waves that have not yet become radio waves.

The wireless power receiver4includes a reception antenna50, an automatic tuning assist circuit60, and a load70to be supplied with electric power. The load70may include an unshown rectifier circuit, detector circuit, or the like, as a built-in component.

The reception antenna50includes a reception coil LRXand a resonance capacitor CRXarranged in series between a first terminal51and a second terminal52.

The automatic tuning assist circuit60is coupled with the reception antenna50. The automatic tuning assist circuit60injects the first correction current IAinto, or otherwise draws the first correction current IAfrom, the reception antenna50.

The automatic tuning assist circuit60includes a first terminal61, a second terminal62, a first auxiliary coil LA1, a fifth switch SW5, a sixth switch SW6, and a control unit64. The automatic tuning assist circuit60has the same configuration as that of the automatic tuning assist circuit30described above.

The automatic tuning assist circuit60repeatedly switches between a first state φ1and a second state φ2with the same frequency as that of the electric power signal S1. In the first state φ1, the fifth switch SW5is turned on, which couples the first auxiliary coil LA1with the reception antenna50. In this state, the first correction current IAthat corresponds to the current ILA1that flows through the first auxiliary coil LA1is injected into, or otherwise drawn from, the reception antenna50.

In the second state φ2, the sixth switch SW6is turned on. Furthermore, the first auxiliary coil LA1is decoupled from the reception antenna50. In this state, the current ILA1that flows through the first auxiliary coil LA1flows through a current path (SW6) which is independent of the reception antenna50.

The control unit64may switch between the first state φ1and the second state φ2with the same frequency as that of the driving voltage applied to the transmission antenna included in a wireless power supply transmitter (not shown), and with a predetermined phase difference with respect to the driving voltage.

The fifth switch SW5and the sixth switch SW6are each configured as a uni-directional switch or otherwise a bi-directional switch. In a case in which these switches are each configured as a uni-directional switch, the control unit64switches each switch such that no current flows through the inversely conducting element formed in each switch.

The load70is coupled with the reception antenna50. The configuration of the coupling between the load70and the reception antenna50is not restricted in particular.

The above is the configuration of the wireless power receiver4. Next, description will be made regarding the operation thereof.FIG. 18is an equivalent circuit diagram of the wireless power receiver4shown inFIG. 17. As with the automatic tuning assist circuit30of the wireless power supply transmitter2, the automatic tuning assist circuit60can be regarded as a correction current source configured to supply the correction current IAto the reception antenna50.

FIG. 19is a waveform diagram showing the operation of the wireless power receiver4shown inFIG. 17.

FIG. 19shows, in the following order beginning from the top, the resonance voltage VRXbetween a circuit formed of the reception coil LRXand the resonance capacitor CRX, the resonance current IRXthat flows through the reception antenna50, the voltage at the fifth switch SW5, the voltage at the sixth voltage SW6, the correction current IA, and the current ILA1that flows through the first auxiliary coil LA1. In the waveform diagrams showing the resonance current IRXand the resonance voltage VRX, the solid line represents the waveform of a steady state (quasi-resonant state) after a sufficient period of time elapses after the automatic tuning assist circuit60starts to operate, and the broken line represents the waveform of a non-resonant state when the automatic tuning assist circuit60does not operate.

In order to provide a quasi-resonant state, there is a need to switch on and off the fifth switch SW5and the sixth switch SW6with a suitable frequency fTXand with a suitable phase θRX. In order to meet this requirement, the wireless power supply transmitter2may be configured to transmit the data which represents the frequency fTXand the phase θRXto the wireless power receiver4. Also, the wireless power receiver4may be configured to sweep the phase θRXso as to detect the optimum phase θRX.

The above is the operation of the wireless power receiver4.

As described above, with the wireless power receiver4shown inFIG. 17, such an arrangement automatically provides a resonant state without a need to adjust the capacitance of the resonance capacitor CRX.

Next, description will be made regarding modifications of the wireless power receiver4.

FIG. 20is a circuit diagram showing a configuration of an automatic tuning assist circuit60aaccording to a first modification. The automatic tuning assist circuit60ahas the same configuration as that of the automatic tuning assist circuit30ashown inFIG. 9. The automatic tuning assist circuit60aincludes a seventh switch SW7, an eighth switch SW8, and a second auxiliary coil LA2, in addition to the configuration of the automatic tuning assist circuit60shown inFIG. 17. Such a modification provides a quasi-resonant state in the same way as with the wireless power receiver4shown inFIG. 17.

In the same way as the wireless power transmitting apparatus2, the switches of the wireless power receiver4may each be configured using a uni-directional switch. In a wireless power receiver4aaccording to a second modification, the automatic tuning assist circuit60is configured using uni-directional switches. Specifically, the switches of the automatic tuning assist circuit60have the same configuration as that of the automatic tuning assist circuit30shown inFIGS. 11A and 11B.

The wireless power receiver4may be effectively configured by making a combination of the first modification and the second modification. The automatic tuning assist circuit60according to a third modification has the same configuration as that of the automatic tuning assist circuit30shown inFIG. 12.

FIG. 21is a circuit diagram showing a configuration of a wireless power receiver4baccording to a second embodiment. The wireless power receiver4bincludes an automatic tuning assist circuit60b. The automatic tuning assist circuit60bincludes an H-bridge circuit66and a second control unit64bin the same way as with the automatic tuning assist circuit30bshown inFIG. 13. The second control unit64bswitches between a first state in which a first pair of switches SW11and SW14of the H-bridge circuit66are turned on and a second state in which a second pair of switches SW12and SW13are turned on, with the same frequency as that of the electric power signal S1.

The automatic tuning assist circuit60bshown inFIG. 21requires only a single auxiliary coil to provide the same functions as those provided by the first or third modification of the first embodiment.

In the wireless power receiver4according to the second embodiment, uni-directional switches may also be employed. In this modification, the automatic tuning assist circuit60bmay preferably be configured in the same manner as the automatic tuning assist circuit30bshown inFIG. 15.

FIGS. 22A through 22Fare circuit diagrams each showing a configuration of coupling between the automatic tuning assist circuit60and the reception antenna50.FIGS. 22A through 22Fcorrespond toFIGS. 16A through 16F, respectively. InFIGS. 22A through 22D, the automatic tuning assist circuit60is directly coupled with the reception antenna50. InFIGS. 22E and 22F, the automatic tuning assist circuit60is magnetically coupled with the reception antenna50.

FIG. 22Ashows the same configuration as shown inFIG. 17. The automatic tuning assist circuit60inFIG. 22Bis coupled with the resonance capacitor CRX. A tap63is provided to the reception coil LRXinFIG. 22C. The first terminal61of the automatic tuning assist circuit60is connected to the tap63. Furthermore, the second terminal62is connected to one end of the reception coil LRX.

The reception antenna50inFIG. 22Dincludes two resonance capacitors CRX1and CRX2arranged in series with the reception coil LRX. The first terminal61of the automatic tuning assist circuit60is connected to one end of the resonance capacitor CRX2, which is one of the aforementioned resonance capacitors. Furthermore, the second terminal62is connected to the other end of the resonance capacitor CRX2.

The wireless power receiver inFIG. 22Efurther includes a second coil L2magnetically coupled with the reception coil LRX. The first terminal61of the automatic tuning assist circuit60is connected to one end of the second coil L2. Furthermore, the second terminal62is connected to the other end of the second coil L2.

The wireless power receiver inFIG. 22Ffurther includes a transformer T2. The primary winding W1of the transformer T2is arranged in series with the reception antenna LRX. The first terminal61of the automatic tuning assist circuit60is connected to one end of the secondary winding W2of the transformer T2. Furthermore, the second terminal62is connected to the other end of the secondary winding W2.

With such modifications shown inFIGS. 22A through 22For with other circuits similar to these modifications, such an arrangement also provides a quasi-resonant state.

In addition, with the configuration shown inFIGS. 22Cthrough22F, such an arrangement allows the voltage between the terminals61and62of the automatic tuning assist circuit60to be reduced, as compared with the configurations shown inFIGS. 22A and 22B. Thus, such an arrangement allows a low breakdown voltage element to be employed as a switch which is a component of the automatic tuning assist circuit60. This facilitates the circuit design, or this provides a reduced cost.

Description has been made in the first and second embodiments regarding the wireless power receiver including the automatic tuning assist circuit configured to operate with a switching frequency which is equal to the frequency of the electric power signal. However, the automatic turning assist circuit may be configured to operate with a switching frequency that differs from the frequency of the electric power signal, which also provides a quasi-resonant state. For example, the automatic tuning assist circuit60may be configured to operate with a switching frequency obtained by multiplying or otherwise dividing the frequency of the electric power signal S2by an odd number, which also provides a quasi-resonant state. The relation between the switching frequency and the frequency of the driving voltage may preferably be determined giving consideration to the overall efficiency of the system, etc.

By combining the wireless power transmission apparatus and the wireless power receiver described above, such an arrangement provides a wireless power transmission system.

By respectively providing the automatic tuning assist circuits30and60to the wireless power supply transmitter2and the wireless power receiver4, such an arrangement allows the maximum electric power to be transmitted to the load70. It is needless to say that any one of the aforementioned wireless power supply transmitteres2including the modifications thereof may be combined with any one of the aforementioned wireless power receiveres4including the modifications thereof.

It should be noted that both the wireless power supply transmitter2and the wireless power receiver4do not necessarily require such an automatic tuning assist circuit. Also, an arrangement may be made in which such an automatic tuning assist circuit30is provided to only the wireless power supply transmitter2, and the wireless power receiver4adjusts the resonance capacitor CRXin the same way as with conventional techniques.

Conversely, an arrangement may be made in which such an automatic tuning assist circuit60is provided to only the wireless power receiver4, and the wireless power supply transmitter2adjusts the resonance capacitor CTXin the same way as with conventional techniques.

Also, an arrangement may be made in which such an automatic tuning assist circuit30is provided to only the receiver4has no adjustment mechanism. Alternatively, an arrangement may be made in which such an automatic tuning assist circuit60is provided to only the wireless power receiver4, and the wireless power supply transmitter2has no adjustment mechanism.

With such arrangements, tuning is performed by means of a single automatic tuning assist circuit so as to provide impedance matching between the power supply10and the load70, thereby providing high-efficiency electric power transmission.

Description has been made regarding the present invention with reference to the embodiments. The above-described embodiments have been described for exemplary purposes only, and are by no means intended to be interpreted restrictively. Rather, it can be readily conceived by those skilled in this art that various modifications may be made by making various combinations of the aforementioned components or processes, which are also encompassed in the technical scope of the present invention. Description will be made below regarding such modifications.

With the wireless power supply transmitter2including the automatic tuning assist circuit30, in some cases, such an arrangement is capable of providing a quasi-resonant state even without including the resonance capacitor CTX. In this case, such a resonance capacitor CTXmay be omitted. In the same way, an arrangement may be made in which the wireless power receiver4including the automatic tuning assist circuit60does not include the resonance capacitor CRX.

The wireless power supply transmitter2encrypts the electric power signal S1by changing at least one of the frequency fTXand the phase of the driving voltage VDRVaccording to a predetermined rule (encryption code). In a case in which the wireless power receiver4knows the encryption code, the wireless power receiver4controls the switching frequency and phase of the automatic tuning assist circuit60based on the encryption code. As a result, even if the electric power signal S1is encrypted, such a wireless power receiver4is capable of decrypting the electric power signal S1and receiving the power supply. In a case in which a wireless power receiver does not know the encryption code, the wireless power receiver cannot appropriately control the switching operation of the automatic tuning assist circuit60. Thus, such a wireless power receiver cannot receive electric power. With wireless power transmission, there is a problem of potential power theft by malicious users. However, by employing such an automatic tuning assist circuit, such a problem can be solved.

Also, in a case in which a single wireless power supply transmitter2supplies electric power to multiple wireless power receiveres4, by employing such an automatic tuning assist circuit, such an arrangement is capable of controlling the amount of electric power to be supplied to each terminal.

The usage of the automatic tuning assist circuit30is not restricted to such wireless power transmission. Rather, the present invention is applicable to various kinds of applications which require tuning.