JP2010022076A - Contactless power transmitter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a contactless power transmitter which can avoid degradation in power transmission efficiency due to variation in parts or displacement of a coil so as to enhance transmitting efficiency. <P>SOLUTION: The contactless power transmitter includes an oscillation circuit (13) and transmits power by driving primary winding with alternating current based on the output of the oscillation circuit and converting alternating current induced in secondary winding opposed to the primary winding into direct current. The oscillation circuit is comprised of a variable-frequency oscillation circuit whose oscillating frequency is variable. Input power supplied from a power supply to the primary winding is detected and an oscillating frequency at which the input power is maximized is found. Then the oscillation circuit is driven at the oscillating frequency. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a technology for improving the efficiency of a non-contact (non-contact) power transmission device, for example, a technology effective when used for a charging device for charging a secondary battery built in a portable electronic device.

  In recent years, portable electronic devices such as a handset of a parent / child phone and a PDA (Personal Digital Assistance) have a built-in rechargeable secondary battery as a power source and are charged using a predetermined charging device. Yes. Conventionally, there are a contact type (contact type) and a non-contact type (non-contact type) as charging methods in an electronic device incorporating a secondary battery.

  The contact-type charging device has a spring-type electrical contact, contacts the electrical contact on the electronic device side to electrically connect both, and supplies a charging current to the built-in secondary battery. Supply. Such a contact-type charging device has a problem that contact failure occurs at a contact portion due to secular change or the like, and supply of a charging current to the secondary battery is hindered.

On the other hand, the non-contact type charging device is provided with a primary coil on the charging device side, a secondary coil on the electronic device side, and an electromagnetic current flowing through the primary coil with the secondary coil facing the primary coil. The battery is charged by rectifying the alternating current induced in the secondary coil by induction. Since the non-contact type charging device does not have a contact, there is an advantage that there is no problem of reduction in power transmission efficiency due to secular change. In addition, as invention regarding a power transmission apparatus, there exist some which are disclosed by patent document 1 or patent document 2, for example.
Japanese Patent No. 3692541 JP 2006-314151 A

  In non-contact type charging devices, the resonance frequency is shifted due to variations in parts (particularly the inductance value of the coil), or the center of the primary coil and the center of the secondary coil are shifted when an electronic device is placed on the charging device. Then, there exists a subject that electric power transmission efficiency falls. However, in the inventions disclosed in Patent Document 1 and Patent Document 2 described above, the primary side coil is driven by an oscillation signal having a predetermined frequency, so that the power transmission efficiency decreases due to component variations and coil displacement. Is difficult to avoid.

  The present invention has been made paying attention to the problems as described above, and the object of the present invention is to avoid a reduction in power transmission efficiency due to component variations and coil position shift, and to improve transmission efficiency. The object is to provide a non-contact power transmission device.

  In order to achieve the above-described object, the present invention is provided with an oscillation circuit and driven by an AC drive of a primary side winding based on an output of the oscillation circuit and induced in a secondary side winding opposed to the primary side winding. In the non-contact power transmission apparatus for converting the alternating current into the direct current and transmitting the power, the oscillation circuit is configured by a variable frequency oscillation circuit having a variable oscillation frequency, and the input power supplied from the power source to the primary winding is received. In this configuration, the oscillation frequency that detects and maximizes the input power is searched and the oscillation circuit is operated at the oscillation frequency.

  More specifically, an oscillation circuit having a variable oscillation frequency, and a drive circuit that AC drives the primary winding based on the output of the oscillation circuit, the secondary side facing the primary winding A contactless power transmission device for transmitting electric power by converting alternating current induced in a winding to direct current, a detection circuit for detecting input power supplied to the primary winding, and a detection circuit that detects the input power A storage circuit that stores the input power value, a comparison circuit that compares the input power value stored in the storage circuit with the input power value detected by the detection circuit, and the output based on the output of the comparison circuit An oscillation frequency control circuit that searches for an oscillation frequency that maximizes input power and operates the oscillation circuit at the oscillation frequency is provided.

  According to the above means, the resonance frequency of the primary side deviates from the design value because the parts have variations or the primary side winding and the secondary side winding face each other in a misaligned state. Even so, since the oscillation circuit is controlled to oscillate at the frequency at which the maximum input power is obtained, the power transmission efficiency can be improved.

  Preferably, the detection circuit includes a voltage detection circuit that detects an input voltage, a current detection circuit that detects a current flowing out of the drive circuit, a product of an output of the voltage detection circuit and an output of the current detection circuit. And a multiplication circuit for calculating. As a result, each time the operating condition changes, the input power is accurately detected and the oscillation circuit can oscillate at a frequency that provides the maximum input power.

  The detection circuit may be only a current detection circuit that detects a current flowing out of the drive circuit. In a system where the input DC voltage is stable, the detected current is proportional to the input power. Therefore, by changing the frequency of the oscillation circuit according to the detected current value, the maximum input power can be achieved with a simple circuit. It becomes possible to control to.

  More preferably, the current detection circuit includes a resistance element connected between the drive circuit and a ground point, and a filter circuit that averages a voltage that is current-voltage converted by the resistance element. In addition, the storage circuit includes a sampling capacitor and a switch element provided between the output terminal of the detection circuit and the sampling capacitor. Thereby, a current detection circuit and a memory circuit can be realized with a circuit having a relatively simple configuration and without changing the process.

  Preferably, the control circuit includes switching means capable of switching between a constant voltage for causing the oscillation circuit to oscillate at a predetermined initial frequency and an oscillation control voltage output from the control circuit and supplying the oscillation circuit to the oscillation circuit. First, the switching means supplies the constant voltage to the oscillation circuit to oscillate at an initial frequency, and then stores the input power value detected by the detection circuit as a reference power value in the storage circuit. A first operation for increasing or decreasing the oscillation frequency of the oscillation circuit by a predetermined amount in accordance with a power value and an input power value detected by the detection circuit, and then an input power value detected by the detection circuit again. Is stored as a reference power value in the storage circuit, and the oscillation frequency of the oscillation circuit is determined according to the reference power value and the input power value detected by the detection circuit thereafter. The second operation for increasing or decreasing the number by an amount smaller than the predetermined amount can be controlled. By repeating the first operation and the second operation, the oscillation frequency of the oscillation circuit corresponds to the maximum input power. Configure to be close to the frequency. Thereby, the oscillation circuit can be oscillated at a frequency corresponding to the maximum input power in a relatively accurate and short time.

  According to the present invention, there is an effect that it is possible to realize a non-contact power transmission device that can avoid a reduction in power transmission efficiency due to component variations and coil position shift and can improve transmission efficiency.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the drawings. In the following, an example in which the present invention is applied to a charging device will be described as an example of an effective contactless power transmission device, but the contactless power transmission device to which the present invention can be applied is limited to this. is not.

  FIG. 1 is a block diagram showing a circuit configuration of an embodiment of a non-contact power transmission apparatus according to the present invention.

  The non-contact power transmission device 10 of this embodiment passes a current through a DC power supply device (AC-DC converter) 11 such as an AC adapter that rectifies an AC voltage (AC) and converts it into a DC voltage, and a primary coil L1. A drive circuit 12 including a switching transistor, an oscillation circuit 13 that generates an oscillation signal supplied to the drive circuit 12, and a control circuit 14 that controls the oscillation frequency of the oscillation circuit 13 are provided. The oscillation circuit 13 includes a variable capacitance element (for example, a varactor diode) and the like, and a voltage controlled oscillation circuit whose oscillation frequency is variable according to the control voltage Vc supplied from the control circuit 14 is used.

  FIG. 2 shows a specific circuit example of the drive circuit 12. Of these, FIG. 2A shows a full-bridge type coil drive circuit composed of four MOSFETs (field effect transistors) Q1 to Q4 connected in series two by two, and FIG. 2B shows two pieces. 1 shows a half-bridge type coil drive circuit in which MOSFETs Q1 and Q2 are connected in series.

  2A, Q1 and Q2 are simultaneously turned on and Q3 and Q4 are turned on and off at the same time, and Q1, Q2 and Q3 and Q4 are turned on and off in a complementary manner. Thus, the coil L1 is controlled so that the forward and reverse currents flow alternately. In the half-bridge drive circuit of FIG. 2B, Q1 and Q2 are complementarily turned on and off, so that currents in forward and reverse directions are alternately supplied to the coil L1. 2A and 2B is an example, and the present invention is not limited to the one using the drive circuit having such a configuration.

  Further, the control circuit 14 in the embodiment of FIG. 1 includes a voltage detection circuit 41 that detects a voltage level of the input voltage Vin, a current detection circuit 42 that detects a current I1 flowing out from the drive circuit 12, and an output of the voltage detection circuit 41. And a multiplication circuit 44 for calculating (multiplying) the input power value by taking the product of the current and the output of the current detection circuit 42.

  Further, the control circuit 14 is held in the sample hold circuit 45 as a power value storage circuit that captures and holds the output of the multiplication circuit 44 at a predetermined timing, and the output voltage of the multiplication circuit 44 and the sample hold circuit 45. The comparator 46 for comparing the voltage, the oscillation frequency control circuit 47 for generating the control voltage Vc of the oscillation circuit 13 based on the output of the comparator 46, the control voltage Vc output from the oscillation frequency control circuit 47 or the oscillation circuit A changeover switch 48 is provided that selects any one of the constant voltages Va that gives an initial frequency and supplies the selected voltage to the oscillation circuit 13.

  The voltage detection circuit 41 can be configured by an error amplifier that receives an input voltage Vin and a predetermined reference voltage and outputs a voltage corresponding to a potential difference. The current detection circuit 42 is connected between the drive circuit 12 and the ground point, and has a resistor Rs provided so that a current I1 flowing from the drive circuit 12 to the ground point flows, and a current-voltage by the resistor Rs. And a filter FLT that outputs an average voltage of the converted and changed voltage.

  Further, the multiplication circuit 44 is configured as a multiplication circuit using an operational amplifier circuit or the like. The sample hold circuit 45 includes a capacitor Cs connected between the inverting input terminal of the comparator 45 and the ground point, and a switch element SW1 connected between the capacitor Cs and the output terminal of the multiplier circuit 44. It is comprised by. Although not particularly limited, the control circuit 14 or the control circuit 14 and the oscillation circuit 13 are formed as a semiconductor integrated circuit (hereinafter referred to as a control IC) on one semiconductor chip such as single crystal silicon. The On the other hand, a discrete power transistor is used as the switching transistor constituting the drive circuit 12. This switching transistor may also be configured as one semiconductor integrated circuit together with the control circuit 14 and the oscillation circuit 13.

  The electronic device 20 that is supplied with power from the non-contact power transmission device 10 rectifies the secondary side coil L2 facing the primary side coil L1 and the alternating current induced in the secondary side coil L2 to direct current. A rectifier circuit 21 for conversion and a smoothing capacitor C2 are provided, and the secondary side of the primary side coil L1 is rectified by rectifying and smoothing the alternating current induced in the secondary side coil L2 by AC driving the primary side coil. Electric power is transmitted to the side coil L2. The primary side coil L1 and the secondary side coil L2 are preferably formed in a planar shape or disposed so that the cores of the coils face the same direction when facing each other.

  The non-contact power transmission apparatus 10 of this embodiment detects the primary power (input power) by taking the product of the input voltage Vin and the current I1 flowing through the primary coil L1, and maximizes this input power. Further, the oscillation frequency of the oscillation circuit 13 is changed, and the transistor of the drive circuit 12 having the configuration as shown in FIGS. 2A and 2B is turned on and off by the oscillation output. . Each circuit in the control circuit 14 operates sequentially when the internal clock signal and control signal are changed in a predetermined order, thereby realizing control that maximizes the input power.

  Here, the fluctuation control of the oscillation frequency is performed within the operable range of the transistor (for example, 100 kHz or less). Further, the control range of the oscillation frequency may be determined according to the variation of the inductance value of the coil and the assumed fluctuation range of the resonance frequency when the primary side coil L1 and the secondary side coil L2 are opposed to each other. Although not particularly limited, in this embodiment, the coils are not varied, and the primary side coil L1 and the secondary side coil L2 are opposed to each other in an ideal state in which their cores coincide with each other, thereby maximizing power transmission. The resonance frequency fr when the efficiency is obtained is designed to be 50 kHz, and the variable frequency range of the oscillation circuit is set to 10 kHz to 100 kHz. Note that the resonance frequency viewed from the primary side is the resonance frequency of the circuit including the coil L1, the secondary coil L2, the rectifier circuit 21, and the smoothing capacitor C.

  In the ideal state, the input power of the non-contact power transmission device of FIG. 1 is maximized when the oscillation frequency fosc of the oscillation circuit 13 matches the design target resonance frequency fr as shown in FIG. is there. However, in an actual manufactured product, as shown by a broken line B in FIG. 3B, due to variations in the inductance value of the coil and displacement between the primary side coil L1 and the secondary side coil L2, the power transmission characteristics of the circuit. Deviates from the ideal characteristic (solid line A). In such a case, the non-contact power transmission apparatus according to the present embodiment has characteristics of the oscillation frequency fosc of the oscillation circuit 13 while searching for the actual power transmission characteristic B within the variable frequency range as shown in FIG. Control is performed so as to match the frequency f0 that is the maximum input power of B.

  Hereinafter, the oscillation frequency control operation in the non-contact power transmission apparatus of this embodiment will be described in detail with reference to the flowchart of FIG.

  When the power is turned on and the apparatus is started, first, the changeover switch 48 is set to the constant voltage Va side (step S1). Then, the oscillation circuit 13 starts oscillation at the initial frequency fa corresponding to the constant voltage Va. This initial frequency fa is set to be the frequency fr of the maximum power point in design, for example. Then, at the timing when the oscillation is stabilized, the switch SW1 of the sample hold circuit 45 is turned on, and the output (input power value) of the multiplier circuit 44 at that time is taken into the sampling capacitor Cs as the reference power value (step S2).

  Next, the control voltage Vc supplied from the oscillation frequency control circuit 47 to the oscillation circuit 13 is changed by a predetermined amount, and the changeover switch 48 is switched to increase the oscillation frequency of the oscillation circuit 13 (step S3). Then, the comparator 46 compares the reference power value taken into the sample and hold circuit 45 with the output value of the multiplication circuit 44 at that time to determine whether or not the current power value is larger than the reference power value. (Step S4).

  Here, when it is determined that the current power value is smaller than the reference power value, the process proceeds to step S5, and the output (input power value) of the multiplication circuit 44 is again taken into the sample hold circuit 45 as the reference power value. Thereafter, the oscillation frequency of the oscillation circuit 13 is lowered (step S6). The amount of change in the oscillation frequency at this time is set to a value (for example, half of the previous time) smaller than the amount of change in the oscillation frequency raised in step S3.

  Subsequently, it is determined again whether or not the current power value is larger than the reference power value (step S7). If it is determined that the current power value is smaller than the reference power value, the process returns to step S1, the output of the multiplier circuit 44 is taken into the sample hold circuit 45 as the reference power value, and steps S3 to S7 are repeated.

  On the other hand, if it is determined in step S7 that the current power value is larger than the reference power value, the process proceeds to step S8, where the current oscillation frequency is higher than the lower limit value fmin of the preset variable frequency range. Judge whether or not. Specifically, the determination is made by comparing the control voltage Vc supplied to the oscillation circuit 13 with the voltage corresponding to the lower limit value fmin. If it is determined in step S8 that the current oscillation frequency is higher than the lower limit value fmin, the process returns to step S5 and the output (input power value) of the multiplier circuit 44 is again taken into the sample hold circuit 45 as a reference power value.

  If it is determined in step S8 that the current oscillation frequency is lower than the lower limit value fmin, the process proceeds to step S9 and the output (input power value) of the multiplier circuit 44 is taken into the sample and hold circuit 45 as a reference power value. The oscillation frequency of the oscillation circuit 13 is increased (step S10). The amount of change in the oscillation frequency at this time is set to a smaller value (for example, half) than the amount of change in the previous oscillation frequency. Then, the process proceeds to step S11 to determine whether or not the current power value is larger than the reference power value. When it is determined that the current power value is larger than the reference power value, the process returns to step S1, and when it is determined that the current power value is smaller than the reference power value, the process returns to step S5 and the above operation is repeated.

  Further, when it is determined in step S4 that the current power value is larger than the reference power value, the process proceeds to step S12 to determine whether or not the current oscillation frequency is lower than the upper limit value fmax of the variable frequency range. . Specifically, the determination is made by comparing the control voltage Vc supplied to the oscillation circuit 13 with the voltage corresponding to the upper limit value fmax.

  If it is determined in step S12 that the current oscillation frequency is lower than the upper limit value fmax, the process returns to step S2 and the output (input power value) of the multiplication circuit 44 is taken into the sample and hold circuit 45 as a reference power value. On the other hand, if it is determined in step S12 that the current oscillation frequency is higher than the upper limit value fmax, the process proceeds to step S13, and the output (input power value) of the multiplier circuit 44 is taken into the sample and hold circuit 45 as a reference power value. The oscillation frequency of the oscillation circuit 13 is lowered (step S14). The amount of change in the oscillation frequency at this time is set to a smaller value (for example, half) than the amount of change in the previous oscillation frequency.

  Then, the process proceeds to step S15 to determine whether or not the current power value is larger than the reference power value. When it is determined that the current power value is smaller than the reference power value, the process returns to step S2, and when it is determined that the current power value is larger than the reference power value, the process proceeds to step S5.

  Next, as a specific example of the adjustment operation of the oscillation frequency by the control operation according to the above procedure, the actual power transmission characteristic is shifted to the higher frequency as shown by the solid line B in FIG. A description will be given of the operation in the case where it has occurred.

  In this case, first, the oscillation operation of the oscillation circuit 13 is started at the initial frequency fa ((1) in FIG. 3C). Next, the oscillation frequency of the oscillation circuit 13 is increased by Δf1 ((2) in FIG. 3C). Then, it is determined that the current power value is smaller than the reference power value, and the oscillation frequency of the oscillation circuit 13 is increased by Δf2 (Δf2 <Δf1) ((3) in FIG. 3C). Subsequently, it is determined that the current power value is smaller than the reference power value, and the oscillation frequency of the oscillation circuit 13 is increased by Δf3 (Δf3 <Δf2) ((4) in FIG. 3C). Here, it is determined that the current power value is larger than the reference power value, and the oscillation frequency of the oscillation circuit 13 is lowered by Δf4 (Δf4 <Δf3) ((5) in FIG. 3C). By repeating such an operation, the oscillation frequency of the oscillation circuit 13 is gradually brought closer to the frequency f0 corresponding to the maximum input power of the actual power transmission characteristics.

  Although not shown in FIG. 4, when the oscillation frequency is changed and the frequency f0 is approached, the oscillation circuit 13 is finally fixed to the frequency and operated. Specifically, for example, it can be terminated when the change amount Δf of the oscillation frequency becomes a predetermined amount or less, or when the change of the oscillation frequency is performed a predetermined number of times. Further, the procedure for detecting the point having the maximum input power differs depending on how to select the frequency Δf and the initial frequency fa to be changed at a time, and is not limited to the procedure shown in FIG.

  In FIG. 5, the 1st modification of the non-contact electric power transmission apparatus of the said embodiment is shown. In this modification, the voltage detection circuit 41 and the multiplication circuit 44 in FIG. 1 are omitted, and the oscillation frequency change control is performed based on the output of the current detection circuit 42. Since the input power of the primary coil is represented by the product of the input voltage Vin and the current I1 flowing out of the drive circuit 12, if the input voltage Vin is constant, the power can be known by detecting the current I1 from the drive circuit 12. It is possible to control the oscillation frequency. Therefore, the modification of FIG. 5 is effective when applied to a system in which the voltage of the DC power supply 11 is stable.

  In FIG. 6, the 2nd modification of the non-contact electric power transmission apparatus of the said embodiment is shown. In this modification, the voltage detection circuit 41 and the current detection circuit 42 in FIG. 1 are omitted, and an auxiliary coil L3 disposed so as to overlap with the primary side coil L1 and a current or current from an alternating current induced in the auxiliary coil L3. A detection circuit 49 for detecting electric power is provided, and oscillation frequency change control is performed based on the output of the detection circuit 49.

  Although the invention made by the inventor has been specifically described based on examples, the present invention is not limited to the above-described embodiment, and various modifications can be made. For example, in the above-described embodiment, MOSFETs are used as the switching transistors Q1 to Q4 that allow current to flow through the primary coil L1, but it is also possible to use bipolar transistors. In the above-described embodiment, the AC adapter is used as the DC power supply 11. However, a DC-DC converter may be used.

  Further, when the primary side power supply of the contactless power transmission device is turned on in the absence of electronic equipment as a load, almost no current flows out from the drive circuit 11, and therefore, for example, the output voltage of the current detection circuit 42 and a predetermined voltage A comparator for comparing with the reference voltage may be provided so that the oscillation circuit 3 oscillates at a frequency corresponding to the lower limit value fmin of the variable frequency range, for example, when the detected current is a predetermined value or less.

  In the above description, the case where the invention made mainly by the present inventor is applied to a non-contact power transmission device used in a charging device for a secondary battery built in a portable electronic device, which is a field of use behind it, is described. However, the present invention is not limited to this, and the present invention can also be used for an apparatus that transmits power with two coils facing each other, such as an IC card power transmission apparatus.

It is a block diagram which shows the circuit structure of one Embodiment of the non-contact electric power transmission apparatus which concerns on this invention. (A), (B) is a circuit diagram which shows the specific example of the drive circuit which drives a coil, respectively. It is a characteristic view which shows the relationship between the resonant frequency and transmission power in a non-contact electric power transmission apparatus. It is a flowchart which shows an example of the procedure of correction | amendment of the resonant frequency in the non-contact electric power transmission apparatus of embodiment. It is a block diagram which shows the 1st modification of the non-contact electric power transmission apparatus of embodiment. It is a block diagram which shows the 2nd modification of the non-contact electric power transmission apparatus of embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Contactless power transmission device 11 DC power supply 12 Drive circuit 13 Oscillation circuit 14 Control circuit 41 Voltage detection circuit 42 Current detection circuit 44 Multiplication circuit 45 Sample hold circuit 46 Comparator 47 Oscillation frequency control circuit 48 Changeover switch L1 Primary side coil L2 Secondary Side coil FLT filter Cs Sampling capacity

Claims (7)

Equipped with an oscillation circuit that drives the primary winding based on the output of the oscillation circuit, converts the alternating current induced in the secondary winding facing the primary winding to direct current, and transmits power A non-contact power transmission device,
The oscillation circuit is composed of a variable frequency oscillation circuit having a variable oscillation frequency. The oscillation circuit detects the input power supplied from the power source to the primary winding and searches for the oscillation frequency that maximizes the input power, and oscillates at the oscillation frequency. A contactless power transmission apparatus configured to operate a circuit. An oscillation circuit having a variable oscillation frequency, and a drive circuit that AC drives the primary side winding based on the output of the oscillation circuit, and is induced in the secondary side winding opposed to the primary side winding. A non-contact power transmission device for transmitting power by converting alternating current to direct current,
A detection circuit for detecting input power supplied to the primary winding;
A storage circuit for storing an input power value detected by the detection circuit;
A comparison circuit that compares the input power value stored in the storage circuit with the input power value detected by the detection circuit;
An oscillation frequency control circuit that searches for an oscillation frequency that maximizes the input power based on the output of the comparison circuit and operates the oscillation circuit at the oscillation frequency. .   The detection circuit includes a voltage detection circuit that detects an input voltage, a current detection circuit that detects a current flowing out of the drive circuit, a multiplication circuit that calculates a product of an output of the voltage detection circuit and an output of the current detection circuit, The non-contact power transmission device according to claim 2, wherein the non-contact power transmission device is configured as follows.   The non-contact power transmission device according to claim 2, wherein the detection circuit is a current detection circuit that detects a current flowing out of the drive circuit.   The current detection circuit includes a resistance element connected between the drive circuit and a ground point, and a filter circuit that averages a voltage that is current-voltage converted by the resistance element. The contactless power transmission device according to 3 or 4.   6. The memory device according to claim 2, wherein the storage circuit includes a sampling capacitor, a switch element provided between the output terminal of the detection circuit and the sampling capacitor. Contact power transmission device. A switching means capable of switching between a constant voltage for oscillating the oscillation circuit at a predetermined initial frequency and an oscillation control voltage output from the control circuit and supplying the oscillation circuit to the oscillation circuit;
The control circuit includes:
First, the switching means supplies the constant voltage to the oscillation circuit to oscillate at an initial frequency,
The input power value detected by the detection circuit is stored as a reference power value in the storage circuit, and the oscillation frequency of the oscillation circuit is set according to the reference power value and the input power value detected by the detection circuit thereafter. A first action to increase or decrease by a predetermined amount;
Then, again, the input power value detected by the detection circuit is stored as a reference power value in the storage circuit, and the oscillation circuit of the oscillation circuit is changed according to the reference power value and the input power value detected by the detection circuit thereafter. A second operation that increases or decreases the oscillation frequency by an amount less than the predetermined amount, and is controllable,
7. The non-contact power transmission apparatus according to claim 2, wherein the first operation and the second operation are repeated to bring the oscillation frequency of the oscillation circuit close to a frequency corresponding to the maximum input power.

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