JP2015223009A - Non-contact charging method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To promptly detect that a metallic foreign substance 5 is set on a charging platform 1.SOLUTION: A non-contact charging method includes: setting battery built-in equipment 2 on the charging platform 1; electromagnetically coupling a power reception coil 4 of the battery built-in equipment 2 to a power transmission coil 3 of the charging platform 1; and transferring power from the power transmission coil 3 to the power reception coil 4 by means of electromagnetic induction action, so as to charge the battery of the battery built-in equipment 2 by power induced on the power reception coil 4. Further, the non-contact charging method includes detecting a variation (ΔH) in the inductance of a detection coil K, using an increase of inductance of the detection coil K caused by magnetic shield etc. when the battery built-in equipment is set, and a decrease of the inductance when a metallic foreign substance is set, so as to judge whether or not the metallic foreign substance 5 is set in the vicinity of the battery built-in equipment 2.

Description

  In the present invention, a power transmission coil and a power reception coil are arranged close to each other so as to be electromagnetically coupled, and power is transferred from the power transmission coil to the power reception coil by electromagnetic induction, and the battery is charged with the power induced in the power reception coil. The present invention relates to a contactless charging method, and more particularly to a contactless charging method for detecting that a metal foreign object is set on a charging stand.

  A contactless charging method has been developed in which a battery built-in device with a built-in power receiving coil is set on a charging stand with a built-in power transmitting coil and power is transferred from the power transmitting coil to the power receiving coil to charge the battery of the battery built-in device. . (See Patent Document 1)

  In this contactless charging method, the battery built-in device is set on the charging stand so that the power transmission coil of the charging stand and the power receiving coil of the battery built-in device are electromagnetically coupled, and power is transferred from the power transmitting coil to the power receiving coil. The built-in battery of the battery built-in device is charged with the electric power induced in the receiving coil. In this charging method, it is not necessary to connect the battery built-in device to the charging stand via the connector, and the built-in battery can be conveniently charged by a non-contact method.

  In this charging method, when a metallic foreign object such as a clip is placed, a dielectric current flows through the metallic object and heat is generated by Joule heat. In addition, since an induction current flows through the metal foreign object and consumes power wastefully, there is a disadvantage that the battery cannot be charged efficiently from the charging stand. In order to eliminate this drawback, the charging base of Patent Document 1 has a large number of temperature sensors arranged vertically and horizontally on the upper surface. The temperature sensor is placed on the charging stand and detects that the metal foreign object generates heat. In this charging stand, when AC power is supplied to the power transmission coil with a metal foreign object placed on top of the charging stand, a dielectric current flows through the metal object to generate heat. It is detected by the temperature sensor.

JP 2008-17562 A

  Since the above charging stand detects the rise of the temperature of the metal foreign object with the temperature sensor and detects that the metal foreign object has been set, there is a detection that cannot quickly detect that the metal foreign object has been set. Further, since it is not specified where the metal foreign object is set, it is necessary to arrange a large number of temperature sensors on the top surface of the mounting table. For this reason, the number of temperature sensors increases and component cost becomes high. Further, since it is not specified which temperature sensor detects heat generation depending on the position where the metal foreign object is placed, it is necessary to determine that the metal foreign object has been placed from the detection temperatures of all the temperature sensors provided in large numbers. Therefore, the detection circuit for detecting that a metal foreign object is placed from the detection temperatures of a large number of temperature sensors becomes complicated, and there is a drawback that the metal foreign object cannot be detected with a simple circuit.

The present invention was developed for the purpose of eliminating the above-described adverse effects, and an important object of the present invention is to provide a contactless charging method capable of quickly detecting that a metal foreign object has been set on a charging stand. There is.
Another important object of the present invention is to provide a contactless charging method capable of reliably detecting a metal foreign object with a simple circuit configuration.

Means for Solving the Problems and Effects of the Invention

  In the contactless charging method of the present invention, the battery built-in device 2 is set on the charging stand 1, the power receiving coil 4 of the battery built-in device 2 is electromagnetically coupled to the power transmitting coil 3 of the charging stand 1, and the power receiving coil 4 receives power from the power transmitting coil 3. Then, the electric power is conveyed by electromagnetic induction, and the battery of the battery built-in device 2 is charged by the electric power induced by the power receiving coil 4. Furthermore, the contactless charging method of the present invention detects the amount of change (ΔH) in the inductance of the detection coil K provided on the charging stand 1, and detects the amount of change in inductance (ΔH) on the charging stand 1 in the vicinity of the battery built-in device. It is determined that the metal foreign object 5 has been set.

  The contactless charging method of the present invention detects a metallic foreign object from the amount of change (ΔH) in the inductance of the detection coil. However, the present invention does not directly detect the inductance, but the parameter specified by the inductance, for example, the inductance and the like. It also includes a method of detecting a metallic foreign object by detecting a resonance frequency specified by the capacitance of the capacitor and an impedance specified by the inductance and the frequency and detecting the inductance via the frequency and the impedance. For example, a capacitor is connected to the detection coil, and an oscillation circuit that identifies the oscillation frequency based on the inductance of the detection coil and the capacitance of the capacitor is provided. By detecting the oscillation frequency of this oscillation circuit, metal foreign objects are detected from the oscillation frequency. can do. This method can detect the metal foreign object by indirectly detecting the inductance of the detection coil via the oscillation frequency. Moreover, since the impedance with respect to alternating current also changes when the inductance of the detection coil increases, it is possible to detect the metal foreign object by detecting the inductance of the detection coil via the impedance. Although the method for detecting metallic foreign matter from the oscillation frequency and impedance does not directly detect the inductance of the detection coil, it detects the metallic foreign matter by detecting the inductance through the frequency and impedance specified by the inductance. In this case, a metal foreign object is detected from the change in inductance. Therefore, in this specification, “detecting the amount of change (ΔH) in the inductance of the detection coil” is not only a method for directly detecting the inductance of the detection coil, but also the amount of change in the parameter specified by the inductance (ΔH ) Is also used to include the method of detecting.

  The contactless charging method described above can quickly determine that a metal foreign object has been set in the vicinity of the battery built-in device on the charging stand. This is because the contactless charging method described above detects the amount of change (ΔH) in the inductance of the detection coil K and determines from the amount of change in inductance (ΔH) that a metal foreign object has been set.

  In general, the inductance of a coil increases as a high-permeability object such as a magnetic shield approaches as compared with a normal state, and conversely, when a metal approaches, the magnetic flux cancels out due to eddy current and decreases. The inductance of the detection coil K provided on the charging stand also increases due to the influence of the magnetic shield when a battery built-in device having a magnetic shield on the back of the coil approaches. However, if there is a metal foreign object in the vicinity, the inductance is offset by the metal foreign object, and the expected amount of inductance change (ΔH) is reduced. Therefore, the metal foreign object can be detected from the amount of change in inductance (ΔH). If the change amount (ΔH) of the inductance of the detection coil is large in the state where the battery built-in device is set, it is determined that the battery built-in device is arranged close to the detection coil K, and if the change amount (ΔH) is small, the battery built-in device At the same time, it can be determined that the metallic foreign object has been approached and set. The increase in the inductance of the detection coil is not delayed as in the temperature detected by the temperature sensor, and changes immediately when a metal foreign object is set. Therefore, the metal foreign object can be detected quickly from the amount of change in inductance (ΔH). .

  Furthermore, the contactless charging method described above detects metallic foreign matter from the amount of change in inductance of the detection coil (ΔH), so it is reliably stable with a simple circuit configuration compared to the method of detecting temperature rise with a temperature sensor. Thus, the feature that metal foreign matter can be detected is also realized.

In the contactless charging method of the present invention, the charging stand 1 stores a threshold value for determining that the metal foreign object 5 is set from the inductance change amount (ΔH), and stores the threshold value to be stored and the inductance change amount (ΔH). In comparison, in a state where the amount of change in inductance (ΔH) is smaller than the threshold value, it can be determined that a metal foreign object has been set near the battery built-in device.
The non-contact charging method described above is easier because the amount of change in inductance (ΔH) is compared with a threshold value, and if the amount of change (ΔH) is smaller than the threshold value, it is determined that a metal foreign object has been set at the same time as the battery built-in device. The metal foreign object 5 can be detected with a simple circuit configuration.

The contactless charging method of the present invention detects the amount of change in inductance (ΔH), and if the detected amount of change in inductance (ΔH) is greater than the threshold, the battery built-in device 2 is set and no metal foreign matter is set. Thus, it is possible to start power conveyance to the battery built-in device 2.
The above contactless charging method compares the amount of change in inductance (ΔH) with a threshold and determines that the battery built-in device is set when the amount of change (ΔH) is greater than the threshold. It can be detected that the battery built-in device 2 has been set, and power transfer can be started.

  In the contactless charging method of the present invention, in the state where the battery built-in device 2 is set from the battery built-in device 2 set on the charging stand 1 to the charging stand 1, an inductance change value that increases the inductance of the detection coil K is used as a threshold value. The charging stand 1 compares the inductance change amount (ΔH) of the detection coil K with the threshold value transmitted from the battery built-in device 2, and the metal foreign object 5 is in the vicinity of the battery built-in device 2. It can be determined that it has been set.

  In the above non-contact charging method, since the inductance change value in which the inductance of the detection coil K increases is transmitted as a threshold value in a state where the battery built-in device is set on the charging stand, the charging stand uses the inductance change amount (ΔH) as the threshold value. As compared with the above, it can be more accurately determined that the metal foreign object is set near the battery built-in device. In particular, it is possible to accurately determine a state in which a metal foreign object is set near the battery built-in device while setting various types of battery built-in devices. In the state where the battery built-in device is set on the charging stand, the inductance of the detection coil K increases. In this state, the rate of increase in inductance is the material of the magnetic shield material behind the power receiving coil built in the battery built-in device, Varies with size, shape, etc. In the above contactless charging method, since the battery built-in device is set on the charging stand and the inductance change value at which the inductance of the detection coil increases is transmitted in advance to the charging stand as a threshold value, the change amount (ΔH) of the detection coil inductance is calculated. By comparing with the threshold value, it can be accurately determined that a metal foreign object has been set in the vicinity of the battery built-in device.

  Also, for devices with built-in batteries that do not transmit the threshold value of inductance change value, first use the minimum value that can be thought of as a common sense as the threshold value. The ID can be stored in the power transmitter body.

In the contactless charging method of the present invention, when the charging stand 1 detects the amount of change in inductance (ΔH) and the detected amount of change in inductance (ΔH) is larger than the threshold value transmitted from the battery built-in device 2, It can be determined that the internal device 2 is set, and power transfer to the battery internal device 2 can be started.
In the above contactless charging method, the amount of change in inductance (ΔH) is compared with the threshold value transmitted from the battery built-in device to determine that the battery built-in device is set. This can be accurately detected and power transfer can be started.

In the contactless charging method of the present invention, a capacitor is connected to the detection coil K of the charging stand 1 and an oscillation circuit for specifying an oscillation frequency based on the inductance of the detection coil K and the capacitance of the capacitor is provided. By detecting the frequency, the amount of change in inductance (ΔH) can be calculated from the oscillation frequency and the capacitance of the capacitor.
The above contactless charging method can accurately detect the amount of change in inductance (ΔH) with a simple circuit configuration.
In the contactless charging method of the present invention, when detecting the oscillation frequency of the oscillation circuit, a detection circuit is connected at the time of detection, and the detection circuit is disconnected at the time of non-detection.
The above contactless charging method of the present invention can reduce the influence of the capacitor of the detection circuit by disconnecting the detection circuit at the time of power transmission that is not detected and at the time of charging.
Furthermore, in the contactless charging method of the present invention, in detecting the oscillation frequency of the oscillation circuit, a capacitor is connected to the detection coil of the charging stand, and an FET as a switching element is connected between one end of the detection coil and the capacitor. By connecting one end of the detection coil and one end of the FET and connecting the gate of the FET to one end of the detection coil, a circuit for detection is connected at the time of detection, and the detection circuit is disconnected at the time of non-detection.
The above contactless charging method of the present invention can reduce the influence of the capacitor of the detection circuit by disconnecting the detection circuit at the time of power transmission that is not detected and at the time of charging.
The contactless charging method of the present invention detects a positional deviation between the power transmitting coil and the power receiving coil based on the amount of change in inductance when the power receiving coil is short-circuited.
In the contactless charging method of the present invention described above, the amount of change in inductance when the power receiving coil is short-circuited changes according to the degree of the position shift, so that the position shift can be detected.
The contactless charging method of the present invention detects the degree of positional deviation between the power transmission coil and the power receiving coil based on the amount of change in inductance when the power receiving coil is short-circuited. The threshold value to be determined is changed.
The contactless charging method of the present invention described above can be changed to an appropriate threshold value because the amount of change (ΔH) in the inductance of the detection coil provided on the charging stand changes according to the degree of displacement.

  The contactless charging method of the present invention can detect the metal foreign object 5 by moving the detection coil K. This contactless charging method can reliably detect a metal foreign object set at any position on the charging stand.

  The contactless charging method of the present invention can detect an inductance change amount (ΔH) by using a power transmission coil in combination with a detection coil. This contactless charging method does not require a dedicated coil to detect the amount of change in inductance (ΔH), and can simplify the circuit configuration.

In the contactless charging method of the present invention, a metal detection coil is provided as a dedicated detection coil K for detecting a power transmission coil 3 and a metal foreign object 5 on the charging stand 1, and the metal foreign object 5 is detected by the metal detection coil. Can do.
The contactless charging method described above is provided with a dedicated detection coil K for detecting the amount of change in inductance (ΔH), so that the metal detecting coil has an optimum shape for detecting metal foreign matter from the amount of change in inductance (ΔH). And can be designed in inductance and shape.
In this method, a metal detection coil that can be designed to have an optimal shape and inductance for detecting a metal foreign object is provided as a detection coil. Therefore, the resolution of the metal foreign object detection is increased, and even a very small metal foreign object can be changed in inductance. It can be detected from (ΔH). In addition, this method can reliably detect even small metallic foreign objects without transmitting the inductance change value from the battery built-in device as a threshold value. In addition to the power transmission coil, a metal detector coil with a small diameter and a large inductance is placed at the center of the power transmission coil or at the four corners, and the battery built-in device is set. By moving while moving in a spiral, regardless of the magnetic shield of the battery built-in device, detecting the metal foreign object using the fact that the inductance of the metal detection coil suddenly decreases when approaching the metal foreign object Because it can. For this reason, this method does not require transmission of the inductance change value from the battery built-in device to the charging stand as a threshold value, and can detect even a small metal reliably.

  In the contactless charging method of the present invention, the power transmission coil 3 of the charging base 1 is moved, a change curve in which the current consumption of the power transmission coil 3 changes is detected, and the metal foreign object 5 is set due to the asymmetry of the change curve. Can also be detected.

  The above method has a feature that metal foreign matter can be detected without transmitting threshold data from the battery built-in device to the charging stand. Moreover, since it can detect that the metal foreign material 5 is set to the vicinity of a receiving coil, it can detect that only a battery built-in apparatus is set, and can start electric power conveyance safely. When current consumption is detected while moving the power transmission coil in a state where the battery built-in device is set on the charging stand, the current consumption of the power transmission coil increases as the power transmission coil approaches the power reception coil and decreases as the power supply coil moves away. Therefore, the center of the coil can be easily specified from the maximum point of current consumption. If the current consumption of the power transmission coil is also measured during this movement, the change curve of the current consumption becomes symmetric with respect to the coil center. In this state, when a metal foreign object is set in the vicinity of the battery built-in device, the current consumption changes due to the metal foreign object, so the change curve of the current consumption is not symmetric with respect to the coil center and is asymmetric. There is a possibility that a metal foreign object may be placed in the center of the power receiving coil. In this state, the charging stand can prevent the start of power transfer by a detection method that does not detect the battery built-in device. As a detection method, a detection pulse is output from the coil provided on the charging stand to the battery built-in device, the receiving coil is excited by this detection pulse, the excited receiving coil outputs an echo signal, and this echo signal is output by the coil. There is a detection method that has already been used to detect that a battery built-in device has been set. According to this detection method, if there is a metal foreign object at the center of the power receiving coil, it is not detected that the battery built-in device is set, and power transfer is not started. The reason why the echo signal is not detected when there is a metal foreign object at the center of the power receiving coil is that the detection pulse is absorbed by the metal foreign object and the power transmission coil is not excited, which does not output the echo signal. Therefore, it can be determined that a metal foreign object has been set in the vicinity of the battery built-in device by detecting that the current consumption change curve is asymmetric. In particular, this method can accurately determine that a metal foreign object has been set in the vicinity of the battery built-in device, that is, in the vicinity of the power receiving coil. Can start. This is because when the metal foreign object 5 is set in the vicinity of the battery built-in device and power is transferred, the metal foreign object 5 generates heat due to the Joule heat of the induced current.

Furthermore, in the contactless charging method of the present invention, the battery built-in device 2 is set on the charging stand 1, and the power receiving coil 4 of the battery built-in device 2 is electromagnetically coupled to the power transmitting coil 3 of the charging stand 1 to receive power from the power transmitting coil 3. A non-contact charging method in which power is conveyed to the coil 4 by electromagnetic induction and the battery of the battery built-in device 2 is charged by the power induced by the power receiving coil 4, and the inductance of the detection coil K provided on the charging stand 1 is used. An oscillation circuit 23 for specifying the oscillation frequency is provided, a change amount (ΔH) of the inductance of the detection coil K is detected from a change amount (Δf) of the oscillation frequency of the oscillation circuit 23, and a change in the oscillation voltage of the oscillation circuit 23 is further detected. The amount (ΔV) is detected, and it is determined that the battery built-in device 2 and the metal foreign object 5 are set on the charging stand 1 from both the amount of change (Δf) of the oscillation frequency and the amount of change (ΔV) of the oscillation voltage. it can.
The non-contact charging method described above has a feature that can quickly and reliably determine that the battery built-in device and the metal foreign object are set on the charging stand. The contactless charging method described above is provided with an oscillation circuit that specifies the oscillation frequency by the inductance of the detection coil, and the amount of change in the oscillation frequency (Δf) of the oscillation circuit and the amount of change in the oscillation voltage of the oscillation circuit (ΔV) This is because it is determined that both the battery built-in device and the metal foreign object are set. According to this method, it can be determined that the battery built-in device has been set from the amount of change in the oscillation frequency (Δf) of the oscillation circuit, and a metal foreign object has been set incorrectly from the amount of change in the oscillation voltage (ΔV) of the oscillation circuit. Can be determined. Therefore, it is possible to reliably determine that the battery built-in device and the metal foreign object are set from both the change amount (Δf) of the oscillation frequency and the change amount (ΔV) of the oscillation voltage.

Furthermore, the contactless charging method of the present invention stores a threshold value for determining the metal foreign object 5 from the change amount (ΔV) of the oscillation voltage, compares the stored threshold value with the change amount (ΔV) of the oscillation voltage, It can be determined that the battery built-in device 2 and the metal foreign object 5 are set on the charging stand 1 in a state where the change amount (ΔV) of the oscillation voltage is larger than the threshold value.
According to the above contactless charging method, the amount of change (ΔV) in the oscillation voltage is compared with a threshold value, so that it is possible to accurately detect that a metal foreign object has been set. In particular, this method has a feature that it can reliably detect even a metallic foreign material of a magnetic material. This is because the oscillation voltage of the oscillation circuit is lowered regardless of whether the metal foreign object is a magnetic material or a nonmagnetic metal.

Furthermore, the contactless charging method of the present invention is such that the amount of change in the oscillation frequency (Δf) is smaller than the threshold value or the amount of change in the oscillation voltage (ΔV) is larger than the threshold value, and the charging stand 1 has a battery built-in device. 2 and the metal foreign object 5 can be determined to be set.
According to the above contactless charging method, the amount of change in the oscillation frequency (Δf) is compared with the threshold value, and the amount of change in the oscillation voltage (ΔV) is compared with the threshold value. Can be determined accurately.

It is a block diagram of the charging stand and battery built-in apparatus used for the non-contact charge method concerning the Example of this invention. It is a graph which shows the characteristic in which the detection signal of a power transmission coil changes in the state in which the metal foreign material was set to the vicinity of the battery built-in apparatus. It is a block diagram which shows the battery built-in apparatus and charging stand which are used for the non-contact charge method concerning the other Example of this invention. It is a circuit diagram which shows the oscillation circuit used for the non-contact charge method concerning one Example of this invention. It is a circuit diagram which shows the other oscillation circuit used for the non-contact charge method concerning one Example of this invention. It is a figure which shows the variation | change_quantity of the frequency by the change of the inductance of the power transmission coil according to the degree of position shift concerning one Example of this invention. It is a figure which shows the circuit in the battery built-in apparatus which short-circuits the receiving coil concerning one Example of this invention. It is a block circuit diagram of the charging stand used for the non-contact charge method concerning the other Example of this invention.

  Embodiments of the present invention will be described below with reference to the drawings. However, the embodiment shown below exemplifies a contactless charging method for embodying the technical idea of the present invention, and the present invention does not specify the contactless charging method as the following method or circuit configuration.

  FIG. 1 shows a state in which a battery built-in device 2 is placed on a charging stand 1 and the battery 6 of the battery built-in device 2 is charged by the contactless charging method of the present invention.

  The charging stand 1 is provided with an upper surface plate 7 on which the battery built-in device 2 is placed on the upper surface of the case, and the power transmission coil 3 is disposed inside the upper surface plate 7. The power transmission coil 3 is connected to an AC power supply 8 and controls the AC power supply 8 using a control circuit 9. The control circuit 9 detects the detection signal transmitted from the transmission circuit 10 of the battery built-in device 2 by the receiving circuit 11, and controls the power supplied to the power transmission coil 3 with the detection signal to be detected. To carry power.

  Further, the charging stand 1 detects a change amount (ΔH) of the inductance of the detection coil K, and from the change amount (ΔH) of the detected inductance, a metal foreign object 5 is placed on the charging stand 1 in the vicinity of the battery built-in device 2. A foreign object detection circuit 12 for determining whether or not the battery has been set is provided. The charging stand 1 of FIG. 1 determines that the metal foreign object 5 has been set on the top plate 7 in the vicinity of the battery built-in device 2 by using the power transmission coil 3 together with the detection coil K. However, in the contactless charging method of the present invention, as shown in FIG. 3, without using the power transmission coil 3 as the detection coil K, a metal detection coil 14 dedicated to foreign matter detection is provided, and the proximity of the battery built-in device. It is also possible to detect that a metallic foreign object has been set.

  The charging stand 1 electromagnetically couples the power transmission coil 3 to the power reception coil 4 and carries power from the power transmission coil 3 to the power reception coil 4. The charging stand 1 for charging the battery 6 by setting the battery built-in device 2 at a free position on the top plate 7 incorporates a mechanism (not shown) for moving the power transmission coil 3 so as to approach the power reception coil 4. ing. In the charging stand 1, the power transmission coil 3 is disposed below the upper surface plate 7 of the case and moved along the upper surface plate 7 to approach the power receiving coil 4. However, the charging base does not necessarily have a built-in mechanism for moving the power transmission coil so that the power transmission coil approaches the power reception coil. The battery built-in device is arranged at a fixed position of the charging base, and the power transmission coil is used as the power reception coil. An approaching structure can also be used.

  The power transmission coil 3 is a flat coil wound in a spiral shape on a surface parallel to the upper surface plate 7, and radiates an alternating magnetic flux above the upper surface plate 7. The power transmission coil 3 radiates an alternating magnetic flux orthogonal to the upper surface plate 7 above the upper surface plate 7. The power transmission coil 3 is supplied with AC power from the AC power source 8 and radiates AC magnetic flux above the top plate 7. The power transmission coil 3 is substantially equal to the outer diameter of the power reception coil 4 and efficiently conveys power to the power reception coil 4.

  The AC power supply 8 supplies, for example, high frequency power of 20 kHz to 1 MHz to the power transmission coil 3. The charging stand 1 that moves the power transmission coil 3 so as to approach the power receiving coil 4 connects an AC power supply 8 to the power transmission coil 3 via a flexible lead wire. The AC power supply 8 includes an oscillation circuit and a power amplifier that amplifies the AC output from the oscillation circuit.

  The charging stand 1 is a state in which the power transmission coil 3 is brought close to the power reception coil 4, and in a state where the metal foreign object 5 is not set, the AC power supply 8 supplies AC power to the power transmission coil 3 to convey the power. In the state where the metal foreign object 5 is set in the vicinity of, power is not conveyed. The AC power of the power transmission coil 3 is conveyed to the power receiving coil 4 and charges the battery 6. When the battery 6 is fully charged, the charging stand 1 stops the power supply to the power transmission coil 3 by a full charge signal transmitted from the battery built-in device 2 and stops the charging of the battery 6.

  The foreign object detection circuit 12 detects the change amount (ΔH) of the inductance of the power transmission coil 3 used together with the detection coil K, and compares the detected change amount (ΔH) of the inductance with a threshold value to determine whether the metal foreign object 5 is set. Determine if. The inductance of the power transmission coil 3, which is the detection coil K, is an object having a high magnetic permeability such as a magnetic shield compared to a state where nothing is set on the top plate 7, that is, a state where neither the battery built-in device 2 nor the metal foreign object 5 is set. It increases when approaching. On the other hand, the inductance decreases when a metal foreign object is in the vicinity. Therefore, when the metal foreign object is set near the battery built-in device, the increase in inductance is offset by the metal foreign object and does not increase to the expected value. Further, as shown in FIG. 3, the charging stand provided with a dedicated metal detection coil 14 as a detection coil separately from the power transmission coil 3 is affected by the magnetic shield of the battery built-in device with the metal detection coil 14. The metal foreign object can be detected by utilizing the fact that the inductance is rapidly reduced when the metal detecting coil approaches the metal foreign object.

The inductance of the detection coil K realized by the power transmission coil 3 is such that a capacitor is connected to the detection coil K, which is the power transmission coil 3, and an oscillation circuit that specifies the oscillation frequency by the inductance of the detection coil K and the capacitance of the capacitor is formed. It can be calculated from the oscillation frequency of the oscillation circuit and the capacitance of the capacitor.
The oscillation frequency (f) of the oscillation circuit is specified by the following formula from the inductance (L) of the detection coil K constituted by the power transmission coil 3 and the capacitance (C) of the capacitor.

  The oscillation frequency is detected by a frequency counter. When the oscillation frequency (f) is detected, the inductance (L) of the detection coil K is calculated from the oscillation frequency (f) and the capacitance (C) of the capacitor using the following formula.

  When the inductance is calculated, the calculated inductance is compared with a threshold value, and it can be detected that a metal foreign object is set near the battery built-in device. However, it is also possible to detect that a metal foreign object has been set in the vicinity of the battery built-in device from the frequency specified by the inductance without calculating the inductance and comparing it with the threshold value. This is because when the inductance changes, the oscillation frequency also changes, so that the method of detecting the metallic foreign object by comparing the frequency with the threshold substantially detects the metallic foreign object by comparing the inductance with the threshold. The method of determining a metal foreign object from the value of the frequency counter without calculating the inductance can more easily determine the metal foreign object. Further, it is possible to detect a metallic foreign object from the impedance specified by the inductance.

  The inductance of the power transmission coil 3 used together with the detection coil K when the battery built-in device 2 is set on the top plate 7 is increased because the magnetic shield built in the battery built-in device 2 is the power transmission coil 3 of the detection coil K. It is because it approaches. The battery built-in device 2 is provided with a magnetic shield 13 to shield the battery and the circuit board from the AC magnetic field of the power transmission coil 3. For the magnetic shield 13, a sheet having high magnetic permeability such as ferrite is used. In the battery built-in device 2 without the magnetic shield 13, the dielectric current flows through the outer can of the battery due to the AC magnetic field of the power transmission coil 3, and generates heat due to Joule heat due to the eddy current. give. As shown in FIG. 1, the battery built-in device 2 that prevents this harmful effect is provided with one side of the power receiving coil 4 facing the power transmitting coil 3 and a magnetic shield 13 on the opposite side. Since the magnetic shield 13 is made of ferrite having a high magnetic permeability, it approaches the power transmission coil 3 of the detection coil K and increases the inductance of the power transmission coil 3.

  When the metal foreign object 5 is set on the upper surface plate 7 of the charging stand 1, the metal foreign object 5 approaches the power transmission coil 3 of the detection coil K, and the inductance of the power transmission coil 3 that is the detection coil K is reduced. The rate at which the metal foreign object 5 decreases the inductance of the detection coil K varies depending on the area, but in any case, the amount to be increased by the magnetic shield of the battery built-in device is offset. Therefore, the foreign object detection circuit 12 can determine that the metal foreign object 5 has been set in the vicinity of the battery built-in device 2 based on the magnitude of the change in inductance (ΔH), and if the change amount (ΔH) is large, the battery built-in device. If only the inductance is set and the inductance decreases or decreases, it can be determined that a metal foreign object has been set in the vicinity of the battery built-in device. The foreign object detection circuit 12 compares the amount of change in inductance (ΔH) with a threshold value, and determines that only the battery built-in device 2 is set when the amount of change (ΔH) is greater than the threshold value. It is determined that the metal foreign object 5 is set in the vicinity of the device 2. The threshold value is stored in advance in the foreign object detection circuit 12 or transmitted from the battery built-in device 2.

  The amount of change (ΔH) that increases the inductance of the power transmission coil 3 that is the detection coil K when the battery built-in device 2 is set on the upper plate 7 of the charging stand 1 varies depending on each battery built-in device 2. This is because the material, size, shape, distance from the power transmission coil 3 to the magnetic shield, and the like of the magnetic shield 13 of the power receiving coil 4 built in the battery built-in device 2 are different. The battery built-in device 2 is set on the upper surface plate 7 of the charging stand 1, the amount of change (ΔH) in the inductance of the power transmission coil 3 that is the detection coil K is detected, and the detected amount of change in inductance (ΔH) is detected for each battery. By storing the data in the memory of the internal device 2, the foreign object detection circuit 12 can determine the battery internal device 2 and the metal foreign object 5 more accurately. In a state where the battery built-in device 2 is set on the charging stand 1, a threshold value of the amount of change in inductance (ΔH) is transmitted from the battery built-in device 2 to the charging stand 1, and the foreign object detection circuit 12 of the charging stand 1 This is because the battery built-in device 2 and the metal foreign object 5 can be determined by comparing the change amount (ΔH) of the battery with this threshold value. However, when the battery built-in device 2 is set on the charging stand 1, the amount of change (ΔH) in the inductance of the power transmission coil 3 that is the detection coil K is increased. A threshold for determining that the battery is set is stored in the charging stand 1, and the battery built-in device 2 and the metal foreign object 5 can be determined from the threshold.

  The foreign object detection circuit 12 controls the AC power supply 8 via the control circuit. When the foreign object detection circuit 12 determines that the battery built-in device 2 is set, the control circuit controls the AC power supply 8 to supply AC power from the AC power supply 8 to the power transmission coil 3 to start power conveyance. If it determines with the metal foreign material 5 having been set, electric power conveyance will not be started as the state which does not supply electric power to the power transmission coil 3 from the alternating current power supply 8. FIG. Further, when the metal foreign object 5 is detected in the state where power is being conveyed, the power conveyance is stopped.

  The foreign object detection circuit 12 uses, as a reference inductance, the inductance of the power transmission coil 3 that is the detection coil K when neither the battery built-in device 2 nor the metal foreign object 5 is set on the upper plate 7 of the charging stand 1. On the other hand, from the amount of change (ΔH) in which the inductance increases, it is determined that the battery built-in device 2 is set. That is, if the inductance does not increase beyond a certain value, it is determined that the metallic foreign object has been set together, and charging is not started. The foreign object detection circuit 12 detects the amount of change (ΔH) in the inductance of the detection coil K at a predetermined cycle (for example, 1 second cycle) in a state where the battery built-in device 2 is not set, and a metal near the battery built-in device 2 It is determined whether or not the foreign object 5 has been set. When it is determined that only the battery built-in device 2 is set, power transfer is started. When it is determined that the metal foreign object 5 is set near the battery built-in device 2, power transfer is not started.

  The charging stand 1 can move the power transmission coil 3 so as to approach the power receiving coil 4 of the battery built-in device 2 to determine the battery built-in device 2 and the metal foreign object 5 set on the upper surface plate 7. When the battery built-in device 2 is set, the amount of change (ΔH) in the inductance of the power transmission coil 3 that is the detection coil K becomes larger than the threshold when the power transmission coil 3 approaches the power receiving coil 4 of the battery built-in device 2. It is. Further, as shown in FIG. 3, the charging stand 1 moves the metal detection coil 14, which is a dedicated detection coil disposed at the four corners or the center of the power transmission coil 3, to the entire surface of the upper surface plate 7. It can be detected that the metal foreign object 5 is placed. Since the inductance of the metal detection coil 14 decreases when the power transmission coil 3 approaches the metal foreign object 5, if there is a metal foreign object, the amount of change (ΔH) to be reduced becomes larger than usual. Metal foreign matter can be detected from the amount (ΔH).

  The charging stand 1 in which the power transmission coil 3 does not move is used with the battery built-in device 2 set at a predetermined position. When the battery built-in device 2 is set at a fixed position on the charging stand 1, the power transmission coil 3 approaches the power reception coil 4. The charging stand 1 detects the inductance of the power transmission coil 3 that is the detection coil K, and determines that the battery built-in device 2 is set. When the battery built-in device 2 is set, the inductance of the power transmission coil 3 used together with the detection coil K of the charging stand 1 increases from the reference inductance in a state where the battery built-in device is not set, and the change amount (ΔH) This is because exceeds the threshold. The charging stand 1 detects that the inductance change amount (ΔH) of the power transmission coil 3 used in combination with the detection coil K exceeds the threshold, determines that only the battery built-in device 2 is set, and Transport can be started. Further, in this charger, when the inductance of the power transmission coil 3 used in combination with the detection coil K increases and the amount of change (ΔH) is smaller than the threshold value, the metal foreign object 5 decreases the amount of increase in inductance (ΔH). As a result, it is determined that not only the battery built-in device 2 but also the metal foreign object 5 is set at the same time.

  The charging stand 1 that moves the power transmission coil 3 can detect the state in which the current consumption changes by moving the power transmission coil 3 with the foreign object detection circuit 12, and can determine the battery built-in device 2 and the metal foreign object 5 from the change curve of the current consumption. . The foreign object detection circuit 12 detects the current of the power transmission coil 3 in a state in which AC power is supplied from the AC power source 8 to the power transmission coil 3, and changes the current consumption around the maximum point of the current consumption, that is, the center of the power reception coil. Detect curves. In the state where only the battery built-in device 2 is set on the charging stand 1 and the metal foreign object 5 is not set, when the power transmission coil 3 is moved in a straight line and the current consumption change curve is detected, the change curve is a solid line in FIG. As shown by, the same curve and symmetry in the approaching state and the leaving state. This is because the current of the power transmission coil 3 increases as the power transmission coil 3 approaches the power reception coil 4, and the current decreases as it moves away. However, when the metal foreign object 5 is set in the vicinity of the power receiving coil 4 of the battery built-in device 2, the metal foreign object 5 changes the current of the power transmission coil 3 to change the current consumption as shown by the chain line in FIG. The curve is asymmetric with respect to the center of the receiving coil. This is because the metal foreign object 5 becomes a load on the power transmission coil 3 and increases the current of the power transmission coil 3. Therefore, it is possible to determine that the metal foreign object 5 is set in the vicinity of the battery built-in device 2 by moving the power transmission coil 3 linearly. This method can reliably determine the metal foreign object 5 set on the charging stand 1 in the vicinity of the battery built-in device 2. According to this method, the metal foreign object 5 set in the vicinity of the battery built-in device 2 can be reliably detected by moving the power transmission coil 3 along the upper surface plate 7 of the charging stand 1. The charging stand 1 determines that the battery built-in device 2 is set and starts power transfer, determines that the metal foreign object 5 is set near the battery built-in device 2 and starts power transfer. do not do.

  The above method can determine that both sides of the battery built-in device 2 and the metal foreign object 5 have been set. Therefore, even if the metal foreign object 5 is set while power is being transferred to the battery built-in device 2, the metal foreign object 5 Can be determined. The charging stand 1 that moves the power transmission coil 3 to the position of the power reception coil 4 and starts power conveyance is in a position where the power transmission coil 3 approaches the power reception coil 4 in the state of power conveyance. After separating the power transmission coil 3 at this position from the power reception coil 4, it moves linearly so as to approach the power reception coil 4 and away from it, detect the current consumption, and the metal foreign object 5 is detected from the change curve of the current consumption. Determine if set. When the metal foreign object 5 is not set and only the battery built-in device 2 is set, the change curve is symmetric as shown by the solid line in FIG. 2, and when the metal foreign object 5 is set, the chain line in FIG. As shown, the change curve shows asymmetry. Therefore, if the change curve shows asymmetry, it is determined that the metal foreign object 5 is set in the vicinity of the battery built-in device 2, and the power transfer is stopped. While the power is being transferred, the above operation can be repeated at a predetermined cycle to detect that the metal foreign object 5 has been set in the vicinity of the battery built-in device 2 and stop the power transfer.

  The charging stand 1 in FIG. 3 detects the metal foreign object 5 by providing the metal detection coil 14 as the dedicated detection coil K without using the power transmission coil 3 as the detection coil K. In this charging stand 1, in the same manner as the power transmission coil 3, the metal detection coil 14 detects the amount of change in inductance (ΔH), and a metal foreign object is set on the charging stand 1 in the vicinity of the battery built-in device. Determine.

  Further, the charging stand 1 in FIG. 3 detects the amount of change in inductance (ΔH) by placing a metal detection coil 14 in the vicinity of the power transmission coil 3 in a state in which the power transmission coil 3 is brought close to the power reception coil 4. Thus, the metal foreign object 5 set in the vicinity of the power receiving coil 4 can be detected. In a state where the metal foreign object 5 is set in the vicinity of the battery built-in device 2, that is, in the vicinity of the power receiving coil 4, and in a state where the metal foreign object 5 is not set, the amount of change (ΔH) in inductance detected by the metal detection coil 14 is In contrast, when there is no metal foreign object, the inductance detected by the metal detection coil does not change, but when there is a metal foreign object, the inductance value detected by the metal detection coil decreases in the vicinity of the metal foreign object so that it can be easily detected. It is. The metal detection coil is smaller than the power transmission coil so that even a small metal foreign object can be detected, and has a larger inductance than the power transmission coil so that a change in inductance can be easily detected. The metal detection coil is disposed in the vicinity of the power receiving coil and can detect a metal foreign object set in the vicinity of the power receiving coil. This is because when the metal detection coil approaches a metal foreign object, the inductance decreases rapidly. This metal detection coil, for example, moves while rotating spirally from the periphery of the power receiving coil to the center, and detects metal foreign objects near the battery built-in device regardless of the magnetic shield of the battery built-in device. it can. This is because when the metal detection coil approaches the metal foreign object, the inductance decreases rapidly, and therefore the metal foreign object can be detected from the change amount (ΔH) detected by the inductance. Since this method detects a metal foreign object set in the vicinity of the battery built-in device from the amount of change (ΔH) in which the inductance of the metal detection coil decreases, the amount of change (ΔH) to be reduced becomes larger than the set value. It can be determined that a metal foreign object has been set, and small metal can be reliably detected.

  The charging stand 1 detects a change amount (ΔH) in which the inductance is decreased by moving the metal detecting coil 14 in the vicinity of the power receiving coil 4 in a state where the power transmitting coil 3 is brought close to the power receiving coil 4, and a change to be detected. It is determined from the amount (ΔH) whether or not the metal foreign object 5 is set in the vicinity of the battery built-in device 2. When it is detected that the metal foreign object 5 is set in the vicinity of the battery built-in device 2, the power transfer is not started. The charging stand 1 sets the battery built-in device 2 at a fixed position of the charging stand 1 and brings the power transmission coil 3 close to the power receiving coil 4 or detects the position of the power receiving coil 4 by a known method. Then, the power transmission coil 3 is moved to the vicinity of the power reception coil 4, and the metal detection coil 14 detects the amount of change in inductance (ΔH) to detect the metal foreign matter.

  Further, the charging base 1 starts the power transfer and moves the metal detecting coil 14 in the vicinity of the power receiving coil 4 in the middle of the power transfer from the power transmitting coil 3 to the power receiving coil 4 to change the inductance. The amount (ΔH) is detected, and it can be detected from the change amount (ΔH) to be detected that the metal foreign object 5 is set in the vicinity of the battery built-in device 2 during the charging. When the charging stand 1 detects the metal foreign object 5 during the power transfer, it can stop the power transfer and can safely transfer the power to the battery built-in device 2.

  The battery built-in device 2 includes a power receiving coil 4 that is electromagnetically coupled to the power transmitting coil 3 of the charging stand 1, and charges the battery 6 with the power induced in the power receiving coil 4. The battery built-in device 2 is a portable device including a battery 6 that can be charged, and includes a battery such as a pack battery, a mobile phone, a portable acoustic device, and a charger that incorporates a battery for charging the portable device. It is a portable device.

  1 includes a battery 6, a power receiving coil 4, and a charge control circuit 15 that converts the alternating current induced in the power receiving coil 4 into a direct current to charge the battery and detects full charge of the battery. The battery built-in device 2 is set on the charging stand 1, and a transmission circuit 10 that stores a change amount (ΔH) that increases the inductance of the power transmission coil 3 as a threshold value and transmits the threshold value to the charging stand 1 is provided. . The battery built-in device 2 can also be detachably built in with a battery to be charged as a battery pack.

  The battery 6 is a lithium ion battery or a lithium polymer battery. However, the battery can be any rechargeable battery such as a nickel metal hydride battery or a nickel cadmium battery. The battery built-in device 2 contains one or more batteries 6. The plurality of batteries are connected in series or in parallel, or connected in series and in parallel.

  The charge control circuit 15 charges a lithium ion battery, a lithium polymer battery, or the like at a constant voltage / constant current, and charges a nickel metal hydride battery or a nickel cadmium battery at a constant current. Further, the charge control circuit 15 detects the full charge of the battery 6 and transmits a full charge signal to the charging stand 1 via the transmission circuit 10. The charging stand 1 detects the full charge signal transmitted from the transmission circuit 10 with the reception circuit 11. When detecting the full charge signal, the control circuit 9 controls the AC power supply 8 to stop the power supply to the power transmission coil 3.

  The transmission circuit 10 transmits various values such as an inductance change amount (ΔH) threshold, a battery charging current, a charging voltage, an efficiency threshold signal, a battery full charge signal, and an ID signal from the battery built-in device 2 to the charging stand 1. Transmit the signal. The transmission circuit 10 transmits various transmission signals to the power transmission coil 3 by changing the load impedance of the power reception coil 4. Although not shown, the transmission circuit 10 has a modulation circuit connected to the power receiving coil. The modulation circuit connects a load such as a capacitor or a resistor and a switching element in series, controls on / off of the switching element, and transmits various transmission signals to the charging stand 1.

  The receiving circuit 11 of the charging stand 1 detects a transmission signal transmitted from the transmission circuit 10 by detecting an impedance change, a voltage change, a current change and the like of the power transmission coil 3. When the load impedance of the power receiving coil 4 changes, the impedance, voltage, or current of the power transmitting coil 3 that is electromagnetically coupled to the power receiving coil 4 changes. Therefore, the receiving circuit 11 detects these changes and A transmission signal can be detected.

  However, the transmission circuit may be a circuit that modulates and transmits a carrier wave, that is, a transmitter. The reception circuit for the transmission signal transmitted from the transmission circuit is a receiver that receives a carrier wave and detects the transmission signal. The transmission circuit and the reception circuit can have all circuit configurations capable of transmitting a transmission signal from the battery built-in device to the charging stand.

The circuit disclosed in FIG. 4 can be used as the oscillation circuit having the oscillation frequency (f) specified by Equation 1 above. In the figure, a self-excited oscillation circuit (used in the figure) is applied by applying a DC power supply circuit VCC in place of the AC power supply 8 during power transmission to a tank capacitor C1 connected in series with a power transmission coil (detection coil) L1. Although it is a crap type, it can be a Colpitts type or a Hartley type).
And the circuit which connects a capacitor | condenser to the power transmission coil L1 is provided. A power supply voltage is applied to the collector of the NPN transistor Q1 through the switch S1 from the power supply circuit VCC that outputs the DC power supply voltage in series with the capacitors C2, C3, C4, and the base of the transistor Q1 and the capacitor A power supply voltage is applied to a contact point between C2 and C3 via a resistor R1. A resistor R2 (for example, 1 KΩ) is connected in series to the emitter of the transistor Q1, and this end is grounded. One end of the capacitor C4 is grounded, and the other end is connected in parallel to the resistor R2. Further, the output of the oscillation circuit is output from OSC OUT to the emitter of the transistor Q1 via the capacitor C5. Then, when the switch S1 is turned on by the circuit of FIG. 4, the transistor Q1 is turned on. Based on the output from the OSC OUT, a circuit (not shown) is separately provided, and the non-illustrated circuit and arithmetic circuit, as in the above formula, Since the output circuit becomes high impedance during power transmission, the capacitance of the capacitor C1 is ignored and oscillates at the frequency of the following formula, so that the frequency is specified and calculated.
Here, (C2 // C3 // C4) indicates the series capacitance of the capacitors C2, C3, and C4. A clap oscillation circuit is formed by the capacitors C2, C3, and C4.

In the circuit of FIG. 4, even if the switch S1 is turned off and no power supply voltage is applied, the capacitors C2, C3, and C4 remain connected to the power transmission coil L1, so that power transmission is started by the power transmission coil L1. Sometimes, the transmission current also flows through the capacitors C2, C3, C4, and the transmission efficiency is deteriorated. It is desirable to disconnect before charging and transmission.
However, an alternating current of several tens of volts is applied to both ends of the coil and cannot be separated by an inexpensive electronic switch. Even if the transistors are connected and disconnected, the ON resistance during conduction is high, and the Q of the detection circuit is lowered, so that the circuit does not operate. There is a problem that the capacitor connected to the ground cannot be separated due to the effect of the body diode even if it is attempted to separate the capacitor connected to the FET.

On the other hand, such a problem can be solved in the circuit shown in FIG.
Capacitors C2, C3, and C4 are connected in series to the power transmission coil L1, an N-type FET Q3 is connected to the power transmission coil L1 side of the capacitor C2, the source thereof is connected to the power transmission coil L1, and N capacitor is connected to the ground side of the capacitor C4. The type FET Q5 is connected with its source at the ground side. A power supply voltage is applied from the power supply circuit VCC to the collector of the NPN transistor Q1 via the switch S1, and a power supply voltage is applied to the contact between the base of the transistor Q1 and the capacitors C2 and C3 via the resistor R1. Is done. A resistor R2 is connected in series to the emitter of the transistor Q1, this end is grounded, and the other end is connected to a connection point between the capacitor C3 and the capacitor C4. In addition, the power supply voltage from the switch S1 is connected to the gate of the N-type FET Q5, and the power supply voltage from the switch S1 is connected to the emitter of the PNP-type transistor Q4, whose collector is the base of the FET Q3, And it connects to the power transmission coil L1 via resistance R3. Further, the output of the oscillation circuit is output from OSC OUT to the emitter of the transistor Q1 via the capacitor C5.
Here, since the other end of the power transmission coil L1 is grounded when the power transmission circuit is not working, the DC voltage at one end of the power transmission coil L1 is also equal to the ground voltage. When the switch S1 is turned on by the circuit of FIG. 5, the FET Q5 is turned on, the transistor Q4 is activated, and the FET Q3 is also turned on. Based on the output from OSC OUT, the output circuit becomes high impedance during non-power transmission due to a separately provided circuit (not shown) and an arithmetic circuit, so that the capacity of the capacitor C1 is ignored and oscillates at the same frequency as the above Equation 3 Therefore, the frequency is specified and calculated.
Then, in the circuit of FIG. 5, when the switch S1 is turned off, no power supply voltage is applied, and the power transmission circuit is activated, the FET Q5 is turned off, the transistor Q4 is deactivated, and the gate of the FET Q3 is caused by the resistor R3. It always becomes equal to the voltage at the terminal of the power transmission coil L1, and the FET Q3 is turned off even when the power transmission coil L1 becomes a negative voltage (for example, minus several tens of volts). That is, the transistor Q4 becomes inactive, thereby preventing the FET Q3 from being turned on when the power transmission coil L1 becomes a negative voltage.

  When the clap oscillation circuit as shown in FIG. 5 is used for measuring the coil inductance L and the oscillation frequency, the other end of the power transmission coil L1 is connected to the ground. At this time, one end of the power transmission coil L1 that is not on the ground side is also at a grant level in terms of DC. A switching element is connected between one end of the power transmission coil L1 of the oscillation circuit and the capacitor. Specifically, as shown in FIG. 5, one end of the power transmission coil L1 and the source of the FET Q5 are connected, the drain of the FET Q5 is connected to the capacitor C2, and the gate of the FET Q5 is connected to one end of the power transmission coil L1. When the switch S1 is turned off and the power supply voltage is not applied, the gate of the FET Q5 is connected to one end of the power transmission coil L1, so that the voltages are equal, the switching element FET Q5 is turned off, and the oscillation circuit is coiled. Can be separated from.

In the above-described embodiment, the amount of change (ΔH) in the inductance of the detection coil provided on the charging stand is detected, and a metal foreign object is set near the battery built-in device on the charging stand from the amount of change in inductance (ΔH). In the contactless charging method for determining this, if the alignment of the power transmission coil and the power reception coil is not accurate, erroneous detection, erroneous determination, malfunction, and the like may occur. This is because the amount of change in inductance (ΔH) increases when the coils are slightly misaligned than when both coils are accurately aligned.
And when a user arrange | positions a battery built-in apparatus on a charging stand and sets it as the structure where a power transmission coil approaches a power receiving coil, the positional relationship of a power transmission coil and a power receiving coil may be in the state which shifted | deviated.
FIG. 6 shows the change in inductance of the power transmission coil in accordance with the degree of positional deviation expressed as a self-excited oscillation frequency (change).
The power transmission coil used is a flat circular coil having an outer diameter of 40 mm and an inner space diameter of 10 mm. The power receiving coil used is a planar circular coil having an outer diameter of 30 mm and an inner space diameter of 10 mm, and a magnetic shield is provided on the opposite surface of the surface facing the power transmission coil.
In the figure, the horizontal axis shows the deviation (unit: mm) between the center points of both coils, and the vertical axis shows a frequency of about 250 KHz when the inductance of the power transmission coil is oscillated by the self-excited oscillation circuit when counted for 200 milliseconds. This is shown as a count change amount (ΔF).
Here, since the relationship between the frequency f and the inductance L is the relationship of the above-described formulas 1 and 2, etc., the amount of change (ΔF) corresponds to the amount of change (ΔH), and the amount of change (ΔF) is When it becomes negative, the amount of change (ΔH) increases, and when the amount of change (ΔF) becomes positive, the amount of change (ΔH) decreases. That is, the frequency variation (ΔF) has the same meaning as the inductance variation (ΔH), and the variation (ΔF) can be interpreted as the variation (ΔH).
Curve A shows the amount of change in frequency (ΔFH) due to the change in inductance of the power transmission coil. When there is no displacement (horizontal axis 0 mm), the variation is about 1200 counts, and the degree of displacement increases. The amount of change increases. This is because even if the power receiving coil is open, if the entire surface of the power transmission coil is covered, even a small eddy current of each coil cannot be ignored, and the inductance of the power transmission coil is reduced. This is because the increase in inductance by the shield of the receiving coil is more dominant than the decrease in inductance. Furthermore, when the degree of positional deviation increases (deviation of about 18 mm or more), the overlap between both coils decreases, and the influence of the magnetic shield decreases, so that the change amount (ΔFH) decreases. In the curve A, the amount of change (ΔF) is on the negative side. This means that the self-excited oscillation frequency is lowered, that is, the inductance of the power transmission coil is increased.
Curve B shows the amount of change (ΔF) of the power transmission coil when the power reception coil is short-circuited, as will be described in detail later. As shown in the drawing, the smaller the degree of positional deviation between the two coils, the larger the change amount (ΔF) is on the plus side. Further, when the degree of positional deviation between both coils increases, the amount of change (ΔF) becomes negative. In curve B, the amount of change (ΔF) is on the plus side. This means that the self-excited oscillation frequency increases, that is, the inductance of the power transmission coil decreases.
As described above, as shown by the curve A, when the periphery of both coils overlaps, that is, when the positional deviation is about 10 to 20 mm on the horizontal axis, the amount of change (ΔF) is large and the change in value is small. It is difficult to determine and detect the degree of positional deviation and positional deviation from the amount (ΔF). On the other hand, in the change amount (ΔF) of the power transmission coil when the power reception coil indicated by the curve B is short-circuited, when the periphery of both coils overlap, that is, from the positional deviation of about 10 to 20 mm on the horizontal axis, Until the value becomes small, it changes roughly and continuously. From this inductance change amount (ΔH), it is possible to determine and detect the degree of positional deviation and positional deviation. In particular, when the degree of positional deviation is small, that is, when the positional deviation is smaller than about 8 mm on the horizontal axis, it is a positive change and the amount of change is large, so that the degree of positional deviation and positional deviation can be determined and detected accurately. can do.

Next, as described above, a circuit and a method for short-circuiting the power receiving coil to detect the amount of change (ΔH) in the inductance of the power transmitting coil and to determine and detect the degree of positional deviation and positional deviation will be described below. explain. The battery built-in device is placed on the charging stand, and the power transmission coil is brought close to the power receiving coil. FIG. 7 shows a circuit in the battery built-in device 2. A bridge circuit B that rectifies the alternating current from the power receiving coil 4, a CPU including a microcomputer that operates using the output from the power supply as a power source, and a load LOAD that consumes the output (a rechargeable secondary battery, an electronic device such as a mobile phone) It may be a device). The output from the bridge circuit B to the load LOAD is turned on / off by a P-type FET Q3 controlled by the CPU. Until the power receiving coil is short-circuited and the inductance is measured, the P-type FET Q3 is still off and only the CPU is operated without being connected to the load. In addition, a capacitor C1 that stores electric power is connected in parallel to the output of the bridge circuit B. In order to short-circuit this at both ends of the receiving coil 4, N-type FETs Q1 and Q2 are connected to each source, and each drain is connected to both ends of the receiving coil 4, and each gate of the FETs Q1 and Q2 is connected to one. Then, it is controlled by the CPU.
From the circuit described above, power is induced in the power receiving coil 4 by power transmission and transmission from the power transmission coil 3, rectified by the bridge circuit B, the capacitor C1 is charged and stored, and power is supplied to the CPU. In the present embodiment, the P-type FET Q3 is a switch that supplies power to the load LOAD although it remains off. When power transmission and transmission from the power transmission coil 3 starts, the power receiving device (battery built-in device) notifies the power transmission side of the shield and coil parameters (the values of the curves A and B shown in FIG. 6). Upon receiving this notification, the power transmitter (charging stand) stops power transmission for a certain period of time and enters the inductance measurement mode. During this period, the power receiving device operates the CPU only with the electric power stored in C1, drives the gates of the FETs Q1 and Q2 to short the power receiving coil, and thus finishes the measurement in as short a time as possible. At this time, on the power transmission side, as described above, the oscillation frequency is specified and calculated using the circuits of FIGS. 4 and 5 described above, and the inductance of the power transmission coil 3 when the power receiving coil 4 is short-circuited. Is calculated, and as described above, the amount of change in inductance from the state where the battery built-in device is not arranged is calculated. Similarly, the oscillation frequency is specified and calculated in a state where the power receiving coil 4 is not short-circuited, and the inductance of the power transmitting coil 3 is calculated when the power receiving coil 4 is short-circuited. The amount of change in inductance from the state is calculated.
As described above, it is possible to detect the positional deviation between the power transmission coil and the power reception coil based on the amount of change in inductance when the power reception coil is short-circuited.
The degree of positional deviation between the power transmitting coil and the power receiving coil is detected from the amount of change in inductance when the power receiving coil is short-circuited, and the threshold value for determining the metal foreign object is changed according to the degree of positional deviation.

The charging stand foreign object detection circuit 12 can additionally have the following functions.
As described above, the parameters of the shield and coil (values of curve A and curve B shown in FIG. 6) transmitted from the battery built-in device are received, stored, used, or stored in advance in the foreign object detection circuit 12 as shown in FIG. The values of curve A and curve B shown are stored and used. The amount of change in the inductance when the power receiving coil is short-circuited is applied to the amount of change in curve B to determine whether or not there is a displacement (for example, if there is a displacement of about 5 mm or more) and the degree of displacement. It can be displayed on a display (not shown) of the charging stand.
Further, the threshold value for determining the metallic foreign object is applied to the amount of change in curve B based on the amount of change in inductance when the power receiving coil is short-circuited, and according to the degree of positional deviation (horizontal axis deviation, unit mm). change. That is, the threshold value is changed without making the threshold value for determining that the metal foreign object 5 is set in the change amount (ΔH) of the inductance of the power transmission coil in a state where the power receiving coil is not short-circuited. For example, as shown by a curve A in FIG. 6, if a predetermined percentage value (for example, a value of 50%) of a change amount at each degree of positional deviation (horizontal axis deviation, unit mm) is used as a threshold, An appropriate metal foreign object can be determined according to the degree of deviation (horizontal axis deviation, unit mm).
That is, it can be determined that the metal foreign object 5 has been set in the vicinity of the battery built-in device 2 based on the magnitude of the change in inductance (ΔH). If the change (ΔH) is large, only the battery built-in device is set. When becomes small or decreases, it can be determined that a metal foreign object is set near the battery built-in device. The foreign object detection circuit 12 compares the amount of change in inductance (ΔH) with a threshold value, and determines that only the battery built-in device 2 is set when the amount of change (ΔH) is greater than the threshold value. It is determined that the metal foreign object 5 is set in the vicinity of the device 2.

  When the battery built-in device 2 is set on the charging stand 1 and a magnetic material such as the magnetic shield 13 built in the battery built-in device 2 approaches the detection coil K of the charging stand 1, the inductance of the detection coil K increases. This is because the magnetic material increases the magnetic flux density of the detection coil K. For this reason, the inductance of the detection coil K increases when the battery built-in device 2 is set on the charging stand 1. That is, the inductance of the detection coil K increases in the state where the battery built-in device 2 is set as compared with the state where the battery built-in device 2 is not set in the charging stand 1. Therefore, it is determined that the inductance of the detection coil K is increased, and it is determined that the battery built-in device 2 is set on the charging stand 1. In this state, the power is transferred from the power transmission coil 3 to the power receiving coil 4 and the battery built-in device 2 The built-in battery 6 can be charged.

  However, the user may accidentally place the metal foreign object 5 together with the battery built-in device 2. When power is conveyed in this state, an eddy current flows through the metal foreign object 5. The eddy current causes the metal foreign object 5 to generate heat by Joule heat. In order to prevent this harmful effect, it is necessary to stop the power transfer when the metal foreign object 5 is set together with the battery built-in device 2. In order to realize this, it is necessary to detect that the metal foreign object 5 is set together with the battery built-in device 2.

  When the metal foreign object 5 is set on the charging stand 1, the inductance of the detection coil K is reduced by the metal foreign object 5. This is because the eddy current flowing through the metal foreign object 5 reduces the inductance of the detection coil K. Using this characteristic, it can be determined that the metal foreign object 5 is set on the charging stand 1. If the metal foreign object 5 is a nonmagnetic metal such as copper or aluminum, the inductance of the detection coil K is reduced by the eddy current. However, if the metal foreign object 5 is a magnetic metal such as iron or stainless steel, the inductance of the detection coil K is reduced by eddy current, but the magnetic metal metal foreign object 5 increases the magnetic flux density and increases the inductance of the detection coil K. To do. That is, when the metal foreign material 5 is a magnetic metal, the inductance decreases due to eddy current and increases as the magnetic flux density increases. That is, even if the inductance is reduced due to the eddy current, the decrease in the inductance is offset by the increase in the magnetic flux density. For this reason, if the metal foreign object 5 is a non-magnetic metal such as copper or aluminum, it can be accurately detected that the metal foreign object 5 is set together with the battery built-in device 2 due to a decrease in inductance due to eddy current. If the metal foreign object 5 is a magnetic material such as iron or stainless steel, the decrease in inductance due to the eddy current is offset by the increase in magnetic flux density, and it is accurately set that the metal foreign object 5 is set simultaneously with the battery built-in device 2. It becomes difficult to detect.

  The foreign object detection circuit 22 of FIG. 8 detects the change amount (ΔV) of the oscillation voltage of the oscillation circuit 23 due to the eddy current of the metal foreign object 5 in addition to the change amount of inductance (ΔH), and detects the metal foreign object of the magnetic material. Also detect accurately. The foreign object detection circuit 22 includes an oscillation circuit 23 that changes the oscillation frequency by the inductance of the detection coil K, and detects the change amount (ΔH) of the inductance as the change amount (Δf) of the oscillation frequency. In order to realize this, an oscillation circuit 23 for specifying an oscillation frequency by the inductance of the detection coil K is provided. The foreign matter detection circuit 22 detects the change amount (ΔH) of the inductance of the detection coil K from the change amount (Δf) of the oscillation frequency of the oscillation circuit 23, and further determines the change amount (ΔV) of the oscillation voltage of the oscillation circuit 23. It is detected and it is determined that the battery built-in device 2 and the metal foreign object 5 are set on the charging stand 1 from both the change amount (Δf) of the oscillation frequency and the change amount (ΔV) of the oscillation voltage.

  When the metal foreign object 2 is set on the charging stand 1, the oscillation voltage of the oscillation circuit 23 decreases due to the eddy current flowing through the metal foreign object 5. Since the eddy current flows regardless of whether the metal foreign material 5 is a nonmagnetic material or a magnetic material, when the metal foreign material 5 is set, the oscillation voltage of the oscillation circuit 23 decreases. Therefore, a decrease in the oscillation voltage due to the eddy current of the metal foreign object 5 can be detected, and it can be detected that the metal foreign object 5 is set regardless of whether the metal foreign object of the magnetic material or the metal foreign object of the nonmagnetic material is set.

  The oscillation circuit 23 in FIG. 8 specifies the oscillation frequency by the inductance of the detection coil K. The oscillation frequency (f) is a frequency represented by the following equation depending on the inductance (L) of the detection coil K and the series capacitance (C) of the capacitors C1, C2, and C3 connected in series to the detection coil K.

  Since the series capacitance (C) of the capacitors C1, C2, and C3 is constant, the oscillation frequency (f) changes as shown by the following expression with respect to the inductance (L) of the detection coil K.

  Therefore, the oscillation frequency (f) of the oscillation circuit 23 decreases as the inductance (L) increases, and increases as the inductance (L) decreases. The inductance (L) can be specified from the oscillation frequency (f), and the inductance The oscillation frequency (f) is specified from (L).

  The transistor Q1 of the oscillation circuit 23 has a base connected to the detection coil K via a capacitor C1 and a switch S2. The switch S2 is switched on in a state where the inductance of the detection coil K is detected, that is, in a state where the oscillation circuit 23 is in an oscillation state, and is switched off in a state where the inductance is not detected. In the oscillation circuit 23, a power transmission coil can be used in combination with the detection coil K. However, the detection coil can be a dedicated coil for detecting a battery built-in device and a metal foreign object.

  The transistor Q1 of the oscillation circuit 23 has a base connected to the ground via a capacitor C2 and a capacitor C3 connected in series. The transistor Q1 has an emitter connected to a connection point between the capacitor C2 and the capacitor C3. Further, the transistor Q1 has a collector connected to the base via a resistor R1.

  Further, the transistor Q1 constituting the oscillation circuit 23 has an emitter connected to the base of the transistor Q2 on the output side via a coupling capacitor C4. The AC signal of the transistor Q1 is input from the emitter of the transistor Q1 to the base of the transistor Q2. The transistor Q2 amplifies and outputs the AC signal input from the transistor Q1 of the oscillation circuit 23. Further, the output side transistor Q2 connects the collector to the base of the output transistor Q3, and outputs an AC signal to the output transistor Q3. The output transistor Q3 outputs an AC signal to the Δf detector 24.

  The Δf detector 24 has a built-in counter 25, counts the input alternating current, detects the oscillation frequency, and detects the variation (Δf) of the oscillation frequency from the detected frequency. Since the oscillation frequency of the oscillation circuit 23 is specified by the inductance of the detection coil K, the foreign object detection circuit 22 of FIG. 8 detects the change amount (ΔH) of the inductance as the change amount (Δf) of the oscillation frequency. The Δf detection unit 24 outputs the change amount (Δf) of the oscillation frequency to the determination unit 26. The determination unit 26 compares the amount of change (Δf) in the oscillation frequency with a threshold value and detects that the battery built-in device 2 is set. That is, if the change amount (Δf) of the oscillation frequency is larger than the threshold value, it is determined that the battery built-in device 2 is set. Moreover, when the variation | change_quantity ((DELTA) f) of an oscillation frequency is smaller than a threshold value, it will determine with the metal foreign material 5 having been set with the battery built-in apparatus 2. FIG. This is because, when the metallic foreign object 5 is set, the amount of change in inductance (ΔH) is reduced by the eddy current flowing therethrough.

  Further, the foreign matter detection circuit 22 of FIG. 8 rectifies the output via the coupling capacitor C5 to the collector of the transistor Q2 connected to the output side of the oscillation circuit 23 in order to detect the oscillation voltage of the oscillation circuit 23. Thus, a diode D1 for converting to direct current is connected. The coupling capacitor C5 cuts the DC component from the collector of the transistor Q2 and supplies the AC component to the diode D1. The diode D1 rectifies the AC component of the transistor Q2 supplied from the coupling capacitor C5, and outputs a DC voltage corresponding to the amplitude of the AC component. The DC voltage output from the diode D1 is output to the ΔV detection unit 27. The ΔV detector 27 detects the oscillation voltage at a direct current level from the direct current voltage input from the diode D1. The change amount (ΔV) of the oscillation voltage detected by the ΔV detection unit 27 is output to the determination unit 26. The determination unit 26 detects the change amount (ΔV) of the oscillation voltage from the signal input from the ΔV detection unit 27 and detects that the metal foreign object 5 is set.

  The ΔV detector 27 uses the output voltage when both the battery built-in device 2 and the metal foreign object 5 are not set as the reference voltage, and detects the change amount (ΔV) of the oscillation voltage as the change amount from the reference voltage. Since the oscillation voltage decreases when the metal foreign object 5 is set, the determination unit 26 compares the amount of change (ΔV) in the oscillation voltage with a threshold value, and determines that the metal foreign object 5 has been set when the threshold value is greater than the threshold value. Since the oscillation voltage of the oscillation circuit 23 decreases regardless of whether the metal foreign object 5 is a magnetic material or a non-magnetic metal, the foreign object for detecting the metal foreign object 5 by comparing the amount of change (ΔV) in the oscillation voltage with a threshold value. The detection circuit 22 can reliably detect the metallic foreign material 5 of the magnetic material.

  In the foreign matter detection circuit 22 described above, the determination unit 26 is based on both the amount of change in oscillation frequency (Δf) detected by the Δf detection unit 24 and the amount of change in oscillation voltage (ΔV) detected by the ΔV detection unit 27. Thus, it is detected that either one or both of the portable device 2 and the metal foreign object 5 are set. However, the determination unit 26 always needs to detect both the change amount (Δf) of the oscillation frequency and the change amount (ΔV) of the oscillation voltage to detect that the portable device 2 and / or the metal foreign object 5 is set. However, the set state of the portable device 2 and / or the metal foreign object 5 is determined based on the change amount (Δf) of the oscillation frequency detected by the Δf detection unit 24, and the determination is difficult only by the change amount (Δf) of the oscillation frequency. Only in this case, the set state of the portable device 2 and / or the metal foreign object 5 can be determined based on the change amount (ΔV) of the oscillation voltage detected by the ΔV detection unit 27.

  Since the contactless charging method of the present invention detects that a metal foreign object has been set on the charging stand for charging the internal battery of the battery built-in device, it prevents the adverse effects such as heat generation of the metal foreign material, and makes the battery built-in device safe. It is most suitable for the electric power board to be charged.

DESCRIPTION OF SYMBOLS 1 ... Charging stand 2 ... Battery built-in apparatus 3 ... Power transmission coil 4 ... Power reception coil 5 ... Metal foreign material 6 ... Battery 7 ... Top plate 8 ... AC power supply 9 ... Control circuit 10 ... Transmission circuit 11 ... Reception circuit 12 ... Foreign material detection circuit 13 DESCRIPTION OF SYMBOLS ... Magnetic shield 14 ... Metal detection coil 15 ... Charge control circuit 22 ... Foreign substance detection circuit 23 ... Oscillation circuit 24 ... Δf detection part 25 ... Counter 26 ... Determination part 27 ... ΔV detection part K ... Detection coil

Claims (17)

Electric power that is induced in the receiving coil by setting the battery built-in device on the charging stand, electromagnetically coupling the power receiving coil of the battery built-in device to the power transmitting coil of the charging stand, and carrying power by electromagnetic induction from the power transmitting coil to the power receiving coil A non-contact charging method for charging the battery of the battery built-in device,
A non-contact type that detects the amount of change (ΔH) in the inductance of the detection coil provided on the charging stand and determines that a metal foreign object is set on the charging stand in the vicinity of the battery built-in device from the amount of change in inductance (ΔH) Charging method.   The charging stand stores a threshold value for determining a metallic foreign object from an inductance change amount (ΔH), compares the stored threshold value with an inductance change amount (ΔH), and the inductance change amount (ΔH) is greater than the threshold value. The contactless charging method according to claim 1, wherein it is determined that a metallic foreign object is set simultaneously with the battery built-in device in a small state.   The charging stand detects an inductance change amount (ΔH), and if the detected inductance change amount (ΔH) is larger than a threshold value, it is determined that the battery built-in device is set, and power is transferred to the battery built-in device. The contactless charging method according to claim 2, which starts. In the state where the battery built-in device is set from the battery built-in device set on the charging stand to the charging stand, the inductance change value that increases the inductance of the detection coil is transmitted to the charging stand as a threshold,
The charge base compares the amount of change (ΔH) in the inductance of the detection coil with a threshold value transmitted from the battery built-in device, and determines that a metal foreign object is set near the battery built-in device. A contactless charging method as described.   The charging stand detects an inductance change amount (ΔH), and if the detected inductance change amount (ΔH) is larger than a threshold transmitted from the battery built-in device, it is determined that the battery built-in device is set, The contactless charging method according to claim 4, wherein power transfer to the battery built-in device is started.   A capacitor is connected to the detection coil of the charging stand, and an oscillation circuit for specifying the oscillation frequency by the inductance of the detection coil and the capacitance of the capacitor is provided. The oscillation frequency of the oscillation circuit is detected, and the oscillation frequency and the capacitor The contactless charging method according to claim 1, wherein an inductance change amount (ΔH) is calculated from the capacitance.   The contactless charging method according to claim 1, wherein the charging stand detects a metal foreign object by moving a detection coil.   The contactless charging method according to claim 1, wherein an inductance change amount (ΔH) is detected by using the power transmission coil together with the detection coil.   The contactless charging according to any one of claims 1 to 8, wherein a metal detection coil is provided as a dedicated detection coil for detecting a power transmission coil and a metal foreign object on the charging stand, and the metal detection coil is used to detect the metal foreign object. Method. Electric power that is induced in the receiving coil by setting the battery built-in device on the charging stand, electromagnetically coupling the power receiving coil of the battery built-in device to the power transmitting coil of the charging stand, and carrying power by electromagnetic induction from the power transmitting coil to the power receiving coil A non-contact charging method for charging the battery of the battery built-in device,
A contactless charging method of detecting a change curve in which the current consumption of the power transmission coil changes by moving the power transmission coil of the charging stand, and detecting that a metal foreign object is set from the asymmetry of the change curve.   7. The contactless charging method according to claim 6, wherein in detecting the oscillation frequency of the oscillation circuit, a detection circuit is connected at the time of detection, and the detection circuit is disconnected at the time of non-detection.   In the detection of the oscillation frequency of the oscillation circuit, a capacitor is connected to the detection coil of the charging stand, an FET as a switching element is connected between one end of the detection coil and the capacitor, one end of the detection coil and one end of the FET The contactless charging method according to claim 11, further comprising: connecting a gate of the FET to one end of the detection coil to connect a detection circuit when detecting, and disconnecting the detection circuit when not detecting.   The contactless charging method according to claim 1, wherein a positional deviation between the power transmission coil and the power reception coil is detected based on an amount of change in inductance when the power reception coil is short-circuited.   The degree of positional deviation between the power transmission coil and the power receiving coil is detected based on the amount of change in inductance when the power receiving coil is short-circuited, and the threshold value for determining the metal foreign object is changed according to the degree of positional deviation. The contactless charging method described in 1. Electric power that is induced in the receiving coil by setting the battery built-in device on the charging stand, electromagnetically coupling the power receiving coil of the battery built-in device to the power transmitting coil of the charging stand, and carrying power by electromagnetic induction from the power transmitting coil to the power receiving coil A non-contact charging method for charging the battery of the battery built-in device,
An oscillation circuit for specifying an oscillation frequency by an inductance of a detection coil provided on the charging base is provided, and an amount of change in inductance of the detection coil (ΔH) is detected from an amount of change in oscillation frequency of the oscillation circuit (Δf). Furthermore, the amount of change (ΔV) in the oscillation voltage of the oscillation circuit is detected,
A contactless charging method for determining that a battery built-in device and a metal foreign object are set on a charging base from both an oscillation frequency change amount (Δf) and an oscillation voltage change amount (ΔV). The threshold value for determining the metallic foreign object from the change amount (ΔV) of the oscillation voltage is stored, and the stored threshold value is compared with the change amount (ΔV) of the oscillation voltage.
The contactless charging method according to claim 15, wherein it is determined that the battery built-in device and the metal foreign object are set on the charging stand in a state where the change amount (ΔV) of the oscillation voltage is larger than the threshold value.   16. The method according to claim 15, wherein it is determined that the battery built-in device and the metal foreign object are set on the charging stand in a state where the change amount (Δf) of the oscillation frequency is smaller than the threshold value or the change amount (ΔV) of the oscillation voltage is larger than the threshold value. A contactless charging method as described.