CERTIFICATE OF TRANSLATION ACCURACY
`
`I, Michael Fletcher, declare:
`
`1. I am a native speaker of English and am well versed in both the Japanese and English languages
`and have over 18 years of experience translating Japanese technical documents into English on a
`full-time basis.
`
`2. The following translation of the corresponding source text from Japanese into English is accurate
`and complete to the best of my knowledge.
`
`I declare under penalty of perjury under the laws of the United States of America that the foregoing is
`true and accurate.
`
`Statements made herein are to the best of my knowledge true and are based on information that I
`believe to be true and further these statements were made with the knowledge that willful false
`statements and the like so made are punishable by fine or imprisonment, or both, under Section 1001
`of Title 18 of the United States Code and that such willful false statements may jeopardize the validity
`of the patent application in the United States of America or any patent issuing thereon.
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`Executed this 10th day of February 2022, at Parowan, UT.
`
`Michael Fletcher
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`GOOGLE AND SAMSUNG EXHIBIT 1006, 0001
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`

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`(19) Japanese Patent
`Office (JP)
`
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`(12) Patent Publication Gazette
`(B2)
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`JP3692541B2 Sept. 7, 2005
`
` (11) Patent No.
` P3692541 (P3692541)
`
`(45) Date Issued: Sep 7, 2005
`ID Number
`(51) Int. Cl
`H 02 J 17/00
`
`H 02 J 7/00
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`JPO File Number
`H 02 J
`17/00
`H 02 J
`7/00
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` (24) Registration date: Jul. 1, 2005
`FI
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`Theme code (ref.)
`B
`301D
`Number of Claims: 14 Total pages: 20
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`(73) Patentee
`Sony Corporation
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`7-35, Kitashinagawa 6-chome, Shinagawa-ku,
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`
`Tokyo, Japan
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`(74) Agent, Attorney, or Firm:
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`
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`Patent Attorney TANABE, Keiki
`(72) Inventor:
`NAGAI, Tamizi
`
`c/o Sony Corporation 7-35, Kitashinagawa 6-chome,
`
`Shinagawa-ku, Tokyo, Japan
`(72) Inventor:
`TAKEI, Toshitaka
`
`c/o Sony Corporation 7-35, Kitashinagawa 6-chome,
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`Shinagawa-ku, Tokyo, Japan
`(72) Inventor:
`SUZUKI, Kuniharu
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`c/o Sony Corporation 7-35, Kitashinagawa 6-chome,
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`Shinagawa-ku, Tokyo, Japan
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`(21) Filed Appln. No.: H10-532727
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`(86) (22) Filed: Feb. 3, 1998
`(86) International application
`number: PCT/JP1998/000441
`(87) International publication
`number: W01998/034319
`(87) International Filing Date:
` Aug. 6, 1998
`Examination Request: Dec. 7, 2004
`(31) Priority Claim number:
` H09-20739
`(32) Priority Date: Feb. 3, 1997
`(33) Priority claiming country: JP
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`Continued on last page
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`(54) TITLE OF THE INVENTION
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`POWER TRANSFER DEVICE AND POWER TRANSFER METHOD
`
`(57) What is claimed is:
`[Claim 1]
`A power transmission device designed to transmit power between a primary coil and a secondary coil, comprising:
` signal generator means for generating and outputting an oscillation signal of a prescribed frequency;
` current supply means for supplying current to be conducted on the primary coil;
` drive means for driving and controlling conduction and interruption of the current supplied from the current supply means to the
`primary coil based on the frequency of the oscillation signal;
` the primary coil, which generates time-varying magnetic flux based on the frequency of the oscillation signal by conduction and
`interruption of the current based on the drive control; and
` the secondary coil, having a capacitance element connected in parallel, an induced electromotive force produced in accordance with
`the time varying magnetic flux interlinkage generated in the primary coil, and a higher resonant frequency than the frequency of the
`oscillation signal, and that together with the capacitance element, resonates the induced current generated based on the induced
`electromotive force; wherein
` power is transferred from the primary coil to the secondary coil based on the time varying magnetic flux interlinkage generated in the
`primary coil generating the induced electromotive force in the secondary coil.
`
`[Claim 2]
`The power transfer device according to claim 1, wherein
` the secondary coil rectifies and outputs the induced current generated by conduction and interruption of current in the primary coil.
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`GOOGLE AND SAMSUNG EXHIBIT 1006, 0002
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`

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`JP3692541B2 Sept. 7, 2005
`
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`[Claim 3]
`The power transfer device according to claim 1, wherein
` the primary coil and secondary coil are respectively wound around cores with a prescribed shape, and
` the core with the primary coil wound thereon and the core with the secondary coil wound thereon are arranged in a position with the
`centers thereof mutually offset.
`
`[Claim 4]
`The power transfer device according to claim 3, wherein
` the core with the primary coil wound thereon is formed with a larger cross-sectional area as compared to the core with the secondary
`coil wound thereon.
`
`[Claim 5]
`The power transfer device according to claim 1, comprising:
` detection means for detecting predetermined parameter fluctuations occurring in the primary coil;
` control means that outputs a first or second control signal based on the detection results;
` intermittent oscillation means that supplies the oscillation signal intermittently to the drive means at a prescribed timing for a
`prescribed amount of time if the first control signal is supplied and supplies the oscillation signal to the drive means continuously if
`the second control signal is supplied.
`
`[Claim 6]
`The power transfer device according to claim 1, comprising:
` a tertiary coil provided separately from the primary coil and secondary coil;
` detection means for detecting prescribed parameter fluctuations occurring in the tertiary coil;
` control means that outputs a first or second control signal based on the detection results;
` intermittent oscillation means that supplies the oscillation signal intermittently to the drive means at a prescribed timing for a
`prescribed amount of time if the first control signal is supplied and supplies the oscillation signal to the drive means continuously if
`the second control signal is supplied.
`
`[Claim 7]
`The power transfer device according to claim 6, wherein
` the tertiary coil is arranged in the vicinity of the secondary coil and in a position that interlinks with the magnetic flux generated in
`the primary coil.
`
`[Claim 8]
`The power transfer device according to claim 6 with the tertiary coil arranged in a position facing a prescribed metal member arranged
`in a prescribed position of an electronic device having the secondary coil, comprising:
` second signal generating means that generates and outputs a second oscillation signal at a prescribed frequency;
` second current supply means that supplies current conducted in the tertiary coil; and
` second drive means that drives and controls the current supplied from the second power supply means conducted in the tertiary coil
`based on the frequency of the second oscillation signal.
`
`[Claim 9]
`A method of power transmission designed to transmit power between a primary coil and a secondary coil in an non-contact manner,
`comprising:
` driving and controlling current conduction in the primary coil based on the oscillation signal with a prescribed frequency;
` producing time-varying magnetic flux in the primary coil through conduction and interruption of the current based on the drive
`control at the frequency of the oscillation signal; and
` resonating the current induced by the induced electromotive force of the secondary coil from interlinkage with magnetic flux
`generated in the primary coil for transferring power from the primary coil to the secondary coil and generated by the induced
`electromotive force at a frequency higher than the oscillation signal frequency.
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`(3)
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`JP3692541B2 Sept. 7, 2005
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`[Claim 10]
`The method of power transfer according to claim 9, wherein
` the induced current generated in the secondary coil at the timing when current conduction in the primary coil is interrupted is rectified
`and output.
`
`[Claim 11]
`The method of power transfer according to claim 9, wherein
` the primary coil and secondary coil consist of each being wound on a prescribed shaped core and the core centers thereof are arranged
`in mutually offset positions.
`
`[Claim 12]
`The method of power transfer according to claim 11, wherein
` the cross-sectional area of the core on which the primary coil is wound is larger than the cross-sectional area of the core on which the
`secondary coil is wound.
`
`[Claim 13]
`The method of power transfer according to claim 9, comprising:
` a detecting step of detecting prescribed parameter fluctuations that occur in the primary coil;
` a controlling step of outputting a first or second control signal depending on the detection results; and
` an intermittent oscillation switching step of driving and controlling intermittent conduction and interruption in the primary coil at
`prescribed timing if the first control signal is supplied and driving and controlling continuous conduction and interruption in the
`primary coil if the second control signal is supplied.
`
`[Claim 14]
`The method of power transfer according to claim 9, comprising:
` a detecting step of detecting prescribed parameter fluctuations that occur in a tertiary coil provided separately from the primary coil
`and the secondary coil;
` a controlling step of outputting a first or second control signal depending on the detection results; and
` an intermittent oscillation switching step of driving and controlling intermittent conduction and interruption in the primary coil at
`prescribed timing if the first control signal is supplied and driving and controlling continuous conduction and interruption in the
`primary coil if the second control signal is supplied.
`
`DETAILED DESCRIPTION OF THE INVENTION
`TECHNICAL FIELD
`The present invention relates to a power transfer device and a power transfer method, and is suitable for application to a power
`transfer device and a power transfer method used for a charging device that charges a secondary battery built into a small portable
`electronic device via a non-contact terminal, for example.
`
`BACKGROUND ART
`In recent years, the demand for small portable electronic devices such as headphone stereos, camera-integrated VTRs, and mobile
`communication terminal devices with reduced size has been increasing. These small portable electronic devices have a high-capacity
`rechargeable secondary battery built in as a power source, which is charged using a prescribed charging device.
`One such charging device is a contact type. A contact-type charging device has a spring-type electrical contact, for example, and the
`electrical contact on the small portable electronic device is brought into contact with this contact to electrically connect the two, and
`the charging current is supplied to the secondary battery in the small portable electronic device through the electrical path thus formed.
`
`However, in this type of charging device, the contact parts may become oxidized or contaminated over time. This manner of oxidation
`and contamination will cause poor contact between the two contact points, which will inhibit the supply of charging current to the
`secondary battery.
`A charging device that uses a non-contact type charging method is considered to avoid this manner of problems. One possible non-
`contact charging method is to supply charge current from the charging device to the secondary battery using electromagnetic
`induction.
`
`In other words, the primary coil is provided at the terminal on the charging device side, and the secondary coil is provided at the
`terminal on the small portable electronic device side, with the primary and secondary coils close together. When a current is applied to
`the primary coil under these conditions, the primary coil generates a magnetic flux. For example, if the current flowing in the primary
`coil is turned ON and OFF at regular intervals, the magnetic flux generated by the conduction of the current will vary with time. On
`the secondary coil side, the induced electromotive force is generated by electromagnetic induction due interlinkage of time-varying
`magnetic flux. The secondary coil uses the induced electromotive force as a power source to generate alternating current as AC
`current, with the direction of the current reversing according to the ON and OFF of the primary coil side conduction. The non-contact
`charging device performs charging by supplying the induction current generated in the secondary coil as the charging current to the
`secondary battery.
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`JP3692541B2 Sept. 7, 2005
`(4)
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`In this manner, the primary coil on the charging device side and the secondary coil on the small portable electronic device side are
`brought into close proximity during charging, and power is transmitted from the primary coil side to the secondary coil side using a
`magnetic connection through electromagnetic induction. A non-contact charging device can be implemented in this manner.
`
`In a charging device of this configuration, the primary and secondary coils are built into the charging device and electronic device,
`respectively, and power is transmitted from the primary coil to the secondary coil by electromagnetic induction enabling non-contact
`power transfer.
`
`However, in such a case, the coupling coefficient between the primary and secondary coils becomes worse with increased space
`between the primary and secondary coils (for the specific magnetic permeability of air), and the amount of magnetic flux generated in
`the primary coil interlinked to the secondary coil is reduced. For this reason, compared to a general transformer, a high degree of
`coupling is difficult to achieve between the primary coil and the secondary coil in such a power transmission device.
`
`This leads to the problem of low power transmission efficiency in power transmission devices as described above, due to power loss
`caused by low coupling.
`
`DISCLOSURE OF THE INVENTION
`The present invention came about in light of the points described above and proposes a power transfer device and power transfer
`method that improves the power transfer efficiency from the primary coil side to the secondary coil side.
`In order to resolve the problems described above, the present invention is a power transmission device designed to transmit power
`between a primary coil and a secondary coil and includes:
` signal generator means for generating and outputting an oscillation signal of a prescribed frequency;
` current supply means for supplying current to be conducted in the primary coil;
` drive means for driving and controlling conduction and interruption of the current supplied from the current supply means to the
`primary coil based on the frequency of the oscillation signal;
` the primary coil, which generates time-varying magnetic flux based on the frequency of the oscillation signal by conduction and
`interruption of the current based on the drive control; and
` the secondary coil, having a capacitance element connected in parallel, an induced electromotive force produced in accordance with
`the time varying magnetic flux interlinkage generated in the primary coil, and a higher resonant frequency than the frequency of the
`oscillation signal, and that together with the capacitance element, resonates the induced current generated based on the induced
`electromotive force; wherein
` induced electromotive force is transferred to the secondary coil through interlinkage of the time-varying magnetic flux generated in
`the primary coil.
`
`In this manner, the resonant frequency of the secondary coil side is set to a higher frequency than the frequency of the transmission
`signal of the primary coil side, which makes the apparent coupling coefficient between the primary and secondary coils higher by
`reducing capacitance and this enables increasing the power transfer efficiency from the primary coil to the secondary coil.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. 1 is a circuit diagram illustrating a configuration of a charging device and an electronic device according to embodiment 1 of the
`present invention.
`FIG. 2 is a circuit diagram illustrating the equivalent circuit of the electromagnetic induction part.
`FIG. 3 is a chart describing the relationship between the drive frequency of the primary coil and the resonant frequency of the
`secondary coil.
`FIG. 4 is a chart describing the drive voltage provided to the primary coil according to the drive frequency.
`FIG. 5 is a chart describing the induced voltage generated in the secondary coil.
`FIG. 6 is a circuit diagram illustrating a configuration of a charging device and an electronic device according to embodiment 2 of the
`present invention.
`FIG. 7 is a chart describing the induced voltage generated in the secondary coil.
`FIG. 8 is a schematic diagram illustrating a configuration of a charging device and an electronic device according to embodiment 3 of
`the present invention.
`FIG. 9 is a block diagram illustrating a configuration of a charging device and an electronic device according to embodiment 4 of the
`present invention.
`FIG. 10 is a chart illustrating control of induced voltage on the secondary coil side by varying the frequency of the primary coil side.
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`JP3692541B2 Sept. 7, 2005
`
`(5)
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`FIG. 11 is a chart describing maintaining of the induced voltage in the embodiments.
`FIG. 12 is a flowchart describing the procedure of frequency control through voltage detection.
`FIG. 13 is a block diagram illustrating a configuration of a charging device and an electronic device according to embodiment 5 of the
`present invention.
`FIG. 14 is a block diagram illustrating a configuration of a charging device according to embodiment 6 of the present invention.
`FIG. 15 is a block diagram illustrating a configuration of a charging device according to another embodiment.
`FIG. 16 is a block diagram illustrating a configuration of a charging device according to another embodiment.
`
`DESCRIPTION OF THE PREFERRED EMBODIMENTS
`Embodiments are described in detail using figures below.
`(1) Embodiment 1
`In FIG. 1, 1 illustrates the charging device as a whole, which is designed to charge the secondary battery in a prescribed electronic
`device by supplying power from a power supply 2 to the secondary battery built into the prescribed electronic device via an
`electromagnetic induction part 3. The electromagnetic induction part 3 consists of a primary coil L1 provided on the charging device 1
`side and a secondary coil L2 provided in the electronic device. The primary coil L1 and the secondary coil L2 are in a non-contact
`state. The primary coil L1 is arranged with a first terminal connected to the power supply 2, and the secondary coil L2 has both
`terminals connected to the secondary battery. The charging device 1 is set up with the primary coil L1 and secondary coil L2 each
`wound around a core of a prescribed shape, and the two cores are arranged so that they are facing each other during charging.
`
`In the charging device 1 a second terminal of the primary coil L1 is connected to a drive circuit 4, and the drive circuit 4 is connected
`to the drive frequency generator 5. The drive frequency generator 5 generates an outgoing signal with a prescribed frequency fOSC
`which is then supplied to the drive circuit 4. The outgoing signal thus provided to the drive circuit 4 is input to the base electrode of an
`emitter-grounded transistor Tr1 thereof. The transistor Tr1 conducts current between the emitter and collector electrodes thereof when
`the voltage level of the oscillation signal input to the base electrode is positive. This allows the current delivered by the power supply
`2 to flow into the primary coil L1.
`
`When the voltage level of the oscillation signal input to the base electrode of the transistor Tr1 becomes negative, the transistor Tr1
`cuts off conduction between the emitter and collector electrodes thereof. In this state, the current delivered from the power supply 2
`does not flow to the primary coil L1, and the LC circuit consisting of the primary coil L1 and the capacitor C1 of the drive circuit 4
`forms a resonance circuit generating a counter electromotive force in the primary coil L1. The voltage generated by this counter
`electromotive force is used as a power source to charge the capacitor C1, and when the capacitor C1 discharges to the primary coil, the
`current flows in the reverse direction in the primary coil L1. The current increases as the voltage of the capacitor C1 decreases, and
`reaches a maximum when the voltage of the capacitor C1 reaches zero. Thereafter, the capacitor C1 is charged by the voltage in the
`opposite direction. When the voltage exceeds the voltage of the power supply 2, the damper diode D1 in the drive circuit 4 conducts,
`causing the LC circuit to short-circuit. The LC circuit stops oscillating, and the current flowing in the primary coil L1 decreases
`linearly. When the current reaches zero, the transistor Tr1 turns ON, and the operation described above is repeated thereafter. In this
`manner, the current generated by the drive circuit 4 flowing in the primary coil L1 oscillates alternately in the forward and reverse
`directions. The voltage generated in primary coil L1 is a horizontal pulse shape that changes based on the drive frequency fOSC
`delivered from the drive frequency generator 5.
`
`The flow of current generates magnetic flux in the primary coil L1, and the flux changes with time according to the oscillation of the
`current described above. Induced electromotive force is generated in the secondary coil L2 based on the time-varying magnetic flux
`interlinked to the secondary coil L2. Based on the induced electromotive force thereof, this causes current that reverses with the time
`variation of the magnetic flux to flow in the secondary coil L2. This current oscillates (resonates) based on the secondary coil L2 and
`capacitor C2 connected in parallel to the secondary coil L2. Thus, the AC induced current generated in the secondary coil L2 is sent
`out through a diode D2. In electronic devices with a secondary coil L2, the induced current generated by the induced electromotive
`force as a power supply is rectified by the diode D2 and supplied to the secondary battery to perform charging. The charging device 1
`uses electromagnetic induction to transmit power supply 2 power from the primary coil L1 to the secondary coil L2 for charging.
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`JP3692541B2 Sept. 7, 2005
`(6)
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`FIG. 2 illustrates an equivalent circuit of the electromagnetic induction part 3, and LS2, illustrated in the diagram, is leakage
`inductance on the secondary coil L2 side.
`
`As illustrated in FIG. 3, in the charging device 1, when the frequency of the induced voltage, or resonant frequency, generated in the
`secondary coil L2 by the inverted induced electromotive force, is set to fOUT, the resonant frequency fOUT is set higher than the
`frequency at which the current flowing in the primary coil L1 is driven and controlled, or in other words, the drive frequency fOSC. The
`setting of the resonant frequency fOUT relative to the drive frequency fOSC is performed, for example, by adjusting the ratio of the
`number of turns of the secondary coil L2 to the number of turns of the primary coil, or by adjusting the capacitance of the resonance
`capacitor C2 connected in parallel to the secondary coil L2.
`
`As illustrated in FIG. 4, current flows in the primary coil L1 in the forward and reverse directions according to the ON and OFF states
`of the transistor Tr1 of the drive circuit 4, and the voltage generated in the primary coil L1 appears as a pulse waveform with the drive
`frequency fOSC. Here, e1 is the power component generated in the primary coil L1 when the transistor Tr1 is OFF, and e2 is the power
`component generated in the primary coil L1 when the transistor Tr1 is ON.
`
`As illustrated in FIG. 5, the time variation of the magnetic flux generated in the primary coil L1 generates an induced voltage at the
`resonant frequency fOUT. Here, e3 and e4 indicate the power components based on the voltage and current generated in the secondary
`coil L2. The power component e3 corresponds to the power component e1, and is generated in the secondary coil L2 when Tr1 is in
`the OFF state. Also, power component e4 corresponds to the power component e2, and is generated in the secondary coil L2 when Tr1
`is OFF [sic]. In an electronic device with a secondary coil L2, the induced current generated in the power component e3 is rectified
`and the power is extracted and supplied to the secondary battery. Since the winding direction of the primary coil L1 is opposite to that
`of the secondary coil L2, the drive frequency generated in the primary coil L1 and the resonant frequency generated in the secondary
`coil L2 are opposite in waveform.
`
`In the configuration described above, the transistor Tr1 of the drive circuit 4 is turned ON and OFF according to the frequency of the
`oscillation signal generated by the drive frequency generator 5. When the transistor is in the ON state, the current delivered from the
`power supply 2 flows into the primary coil L1. When the transistor Tr1 is in the OFF state, a counter electromotive force is generated
`in the primary coil L1 and the capacitor C1 is charged, and then the discharge from the capacitor C1 causes a current to flow in the
`primary coil L1 in the opposite direction to that when the transistor Tr1 is on. As the current direction reverses, the magnetic flux
`generated in the primary coil L1 varies with time.
`
`The electromotive force induced in the secondary coil L2 is generated by the magnetic flux interlinkage present in the primary coil L1,
`and the direction of the induced electromotive force changes in accordance with the time variation of the magnetic flux. Because of
`the reversal of the induced electromotive force, induced voltage is generated in the secondary coil L2 at the resonant frequency fOUT
`relative to the drive frequency fOSC of the primary coil L1.
`
`If the resonant frequency fOUT of the LC circuit on the secondary coil L2 side is set to be the same frequency as the drive frequency
`fOSC of the primary coil L1, the current conducted in the primary coil L1 is in phase with the voltage due to resonance. Therefore,
`when the voltage level is at a maximum, the current level is also at a maximum. If the secondary coil L2 side resonates at such a
`frequency, the power loss due to the internal impedance of the secondary coil L2 side LC circuit becomes large, and the power
`transmission efficiency cannot be improved.
`
`When the resonant frequency fOUT is set to be less than the drive frequency fOSC of the primary coil L1, the current value of the
`induced current generated on the secondary coil L2 side becomes small due to resonance at a frequency different than the drive
`frequency fOSC. However, since the time interval required for charging and discharging the resonance capacitor C2 connected in
`parallel to the secondary coil L2 becomes longer, equivalent capacitance C becomes larger and actual efficiency Q decreases, so a
`higher output voltage cannot be obtained.
`
`The induced current in the secondary coil L2 is an alternating current as described above, and by increasing the induced voltage and
`decreasing the induced current, the power loss due to internal impedance can be reduced and power can be extracted efficiently. As
`such, the induced voltage obtained on the secondary coil L2 side needs to be as high as possible.
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`JP3692541B2 Sept. 7, 2005
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`Therefore, as described above, for the charging device 1, the resonant frequency fOUT of the secondary coil L2 side is set to be higher
`than the drive frequency fOSC of the primary coil L1 side, so that the resonant current can be set low and the actual efficiency Q can be
`increased by reducing the equivalent capacitance C in the resonance circuit of the secondary coil L2 side. This allows the charging
`device 1 to improve the power transmission efficiency from the primary coil L1 to the secondary coil L2 by increasing the apparent
`coupling coefficient.
`
`On the electronic equipment side having the secondary coil L2, the part of the power component e3 from the induction current
`generated in the secondary coil L2 when the transistor Tr1 is OFF based on direction reversal of the current flowing in the primary
`coil L1 is rectified and extracted. In other words, the areas of the power components e3 and e4 (FIG. 5) are equal, and the current
`width T2 of the power component e4 is narrower than the current width T1 of the power component e3, and the voltage value of the
`power component e4 is larger than the voltage value of the power component e3. Therefore, when the power component e4 is rectified
`and extracted as power, a high output voltage can be obtained, but the current width T2 is narrower than the current width T1 of the
`power component e3, and the rectification conduction angle is also narrower, resulting in a more unstable output power supply than
`when the power component e3 is rectified.
`
`In the charging device 1, the induced current of the power component e3 is rectified on the electronic device side with the secondary
`coil L2 to extract power, which allows the rectification conduction angle to be made wider, and stable power supply power can be
`extracted.
`
`According to the above configuration, when power is transmitted from the primary coil L1 to the secondary coil L2 by
`electromagnetic induction between the primary coil L1 and the secondary coil L2, the resonant frequency fOUT generated on the
`secondary coil L2 side is set to a frequency higher than the drive frequency fOSC of primary coil L1. At the same time, the resonant
`voltage of the power component e3 when the transistor Tr1 is in the OFF state is rectified from the resonant voltage generated on the
`secondary coil L2 side to extract the power supply power. As a result, the power supply power can be obtained from the resonant
`voltage with a wide rectification conduction angle while the apparent coupling coefficient can be increased by increasing the actual
`efficiency Q. Thus, the power transmission efficiency can be improved and stable power supply power can be extracted.
`
`(2) Embodiment 2
`In FIG. 6, which illustrates the corresponding parts of FIG. 1 with the same signs, 10 illustrates a charging device, which has almost
`the same configuration as the charging device 1, including a power supply 2, an electromagnetic induction part 3, a drive circuit 4, and
`a drive frequency generator 5. The charging device 10 has a primary coil L1 wound around a core of a prescribed shape as the
`electromagnetic induction part 3 (FIG. 1). When charging, a core with a secondary coil L2 wound thereon is installed in the electronic
`device at a position opposite to the core with the primary coil L1 wound thereon.
`
`The charging device 10 turns the transistor Tr1 of the drive circuit 4 ON and OFF based the oscillation signal generated by the drive
`frequency generator 5 to drive and control the conduction to and cut-off of the primary coil L1 to cause current to flow alternately in
`the forward and reverse directions in the primary coil L1. In this manner, the current flowing in the forward and reverse directions
`generates a time-varying magnetic flux in the primary coil L1, and the magnetic flux interlinkage generates an induced electromotive
`force in the secondary coil L2, and resonant current flows through the LC resonance circuit with the secondary coil L2 and the
`capacitor C2 connected in parallel thereto. Similar to the charging device 1, the charging device 10 is designed so that the resonant
`frequency of the secondary coil L2 is higher than the drive frequency of the primary coil L1 (FIG. 3).
`
`In addition thereto, in the charging device 10, the secondary coil L2 is formed by connecting two coils wound in the same direction, as
`opposed to the charging device 1, where the secondary coil L2 is formed using a single coil. In other words, the charging device 10
`forms an electromagnetic induction part 3 by connecting coils L2A and L2B in series as the secondary coil L2. The resonance circuit