JP2010226890A - Non-contact power transmission device - Google Patents

Abstract

Loss is reduced in a non-contact power transmission device including a power transmission unit and a detachable power reception unit.
When it is detected that a power receiving coil T2 of a secondary power receiving unit 2 is not electromagnetically coupled to a power transmitting unit 1 from a voltage change appearing in a power transmission coil T1, a self-excited oscillation circuit In the power receiving unit 2, when the control microcomputer 22 detects the full charge of the secondary battery BA and turns off the impedance element FET3 by using the intermittent drive circuit 122 that reduces the switching duty in 121, In addition, the terminals of the power receiving coil T2 are short-circuited by the switch element FET2. Therefore, when the load is light, the state in which the secondary side of the transformer is not electromagnetically coupled can be simulated, and the power transmission unit 1 can perform intermittent oscillation to further reduce the loss.
[Selection] Figure 1

Description

  The present invention is configured to include a power transmission unit and a power reception unit that is close to and away from the power transmission unit, that is, a detachable power reception unit, and transmits power from the power transmission unit to the power reception unit in a non-contact manner by electromagnetic induction. The present invention relates to a non-contact power transmission device that can charge a power receiving unit simply by placing it on the battery.

  In recent years, a power transmission unit is a primary side of a transformer, and includes a power transmission coil that transmits power, a resonance circuit including a resonance coil that resonates with the power transmission coil, a switching element that resonates the resonance circuit, and the switching A drive circuit for driving the element, and a power receiving unit is induced in the power receiving coil on the secondary side of the transformer, a resonance capacitor connected in parallel to the power receiving coil, and the power receiving coil. Rectifying / smoothing the current that is applied to the load and providing it to the load. By simply placing it on the power transmission unit as described above, power is transmitted from the power transmission unit to the power reception unit in a non-contact manner, and the power reception unit is charged. For example, Patent Documents 1 and 2 disclose a contactless power transmission device.

  In such a non-contact power transmission device, when the power reception unit is not placed on the power transmission unit, the inductance of the power transmission coil is smaller than that when the power reception unit is placed, and flows through the power transmission coil. As a result of the increase in current, there is a problem that standby power increases. However, Patent Document 1 is intended to stably oscillate a resonance circuit, and Patent Document 2 is also intended to reduce the size of the circuit, and any of the conventional techniques reduces standby power. Is not intended.

  Therefore, in Patent Document 3, immediately after the feeding unit starts feeding the power transmission coil, a change in the self-inductance of the power transmission coil is detected, and when the detected value of this change is equal to or less than a predetermined value, the power feeding is performed. Disclosed is a non-contact power transmission apparatus that reduces standby power by stopping power supply of the means and continuing power supply of the power supply means when the detected value is equal to or greater than a predetermined value. However, this prior art stops oscillation of the power transmission unit when there is no power reception unit, and there is a problem that power feeding is continued even when the secondary battery in the power reception unit is fully charged. This is because when there is a power receiving unit, the magnetic circuit does not change depending on whether charging is performed, i.e., whether power is being received, and the coil voltage and oscillation frequency are almost the same. This is because is hardly understood.

  Therefore, in Patent Document 4 by the present applicant, a switch element that softly shorts between the terminals is provided in the subsequent stage of the secondary side rectifier circuit, and the soft short circuit is caused when the charging voltage of the secondary battery is increased. Proposed is a non-contact charging device in which the voltage between the terminals of the secondary power receiving coil is limited, the voltage between the terminals of the primary detection coil is increased, and oscillation is stopped. .

Japanese Patent No. 3416863 Japanese Patent No. 3363341 JP 2008-236916 A JP-A-6-339232

  In the above-described prior art, since the primary side stops oscillating when fully charged, power saving is achieved and the problem of heat generation is reduced. However, the load is softened after the secondary side rectifier circuit. Since it is short-circuited, even if it is fully charged, a certain amount of current flows, and a voltage drop occurs due to a rectifier element such as a diode in the rectifier circuit. Energy is transmitted to the city, and there is still room for power saving.

  The objective of this invention is providing the non-contact electric power transmission apparatus which can further reduce a loss.

  A non-contact power transmission device of the present invention is configured to include a power transmission unit and a power reception unit that can approach and separate from the power transmission unit, and transmit power in a non-contact manner by electromagnetic induction from the power transmission unit to the power reception unit. In the contact power transmission device, the power transmission unit includes a power transmission coil serving as a primary side of a transformer capable of separating a primary side and a secondary side, and a resonance circuit connected in parallel to the power transmission coil. A resonant capacitor to be configured; a switching element that resonates the resonant circuit; a drive circuit that controls switching of the switching element; the power receiving unit is separated from the power transmitting unit; and a secondary side of the transformer is a primary side When not electromagnetically coupled, the drive circuit includes a load detection means for reducing the switching duty, and the power reception unit is a secondary side of the transformer. A power receiving coil; a resonance capacitor connected in parallel to the power receiving coil; a rectifying / smoothing circuit that rectifies and smoothes a current induced in the power receiving coil and applies the same to a load; and a state of the load A load state detecting means for detecting, and a current supplied from the rectifying / smoothing circuit to the load in response to a detection result of the load state detecting means provided between the power receiving coil and the rectifying / smoothing circuit Including a power transmission suppressing unit that simulates a state in which the secondary side of the transformer is not electromagnetically coupled when the load is a light load equal to or less than a predetermined value.

  According to the above configuration, the power transmission unit and the proximity and separation of the power transmission unit, that is, a power reception unit that is detachable, and configured to transmit power in a non-contact manner by electromagnetic induction from the power transmission unit to the power reception unit. For example, in a non-contact power transmission device in which a power receiving unit can be charged only by being placed on a power transmission unit, the power transmission coil of the power transmission unit is a primary side of a transformer, and the power receiving coil of the power reception unit is It becomes the secondary side of the transformer, and electric power is transmitted between them by the electromagnetic induction. For this reason, the power transmission unit resonates the resonance circuit by turning on / off a resonance capacitor connected in parallel to the power transmission coil to form a resonance circuit and a current flowing through the power transmission coil. A switching element, a drive circuit that controls switching of the switching element, and a voltage change that appears in the power transmission coil via the power reception coil when the power reception unit is separated from the power transmission unit. When detecting that the sides are not electromagnetically coupled, the drive circuit is provided with load detecting means for reducing the switching duty (secondary induced energy of the transformer), for example, stopping the switching. A resonance capacitor connected in parallel to the power receiving coil, and a power induced in the power receiving coil. Rectifying and smoothing a rectifying and smoothing circuit that gives to the load is provided with.

  Further, in the present invention, the power receiving unit is provided with load state detecting means for detecting the load state, and the detection result of the load state detecting means is provided between the power receiving coil and the rectifying / smoothing circuit. In response to the above, when the current supplied from the rectifying / smoothing circuit to the load is a light load equal to or less than a predetermined value, a state in which the secondary side of the transformer is not electromagnetically coupled is reproduced in a pseudo manner. Power transmission suppression means is provided.

  Therefore, using the power saving function that reduces the switching duty when the power receiving unit is away from the power transmitting unit, when the power receiving unit is a light load, for example, the load is a secondary battery, Switching duty can be reduced, power saving can be further promoted, and problems such as heat generation are eliminated. If the power transmission suppression means is provided between the rectifying / smoothing circuit and the load, a voltage drop occurs due to a rectifying diode, etc., and energy is propagated from the primary side to the secondary side of the transformer. However, the loss can be further reduced by providing it between the power receiving coil and the rectifying / smoothing circuit.

  Preferably, the load detection means is a feedback winding of the transformer.

  Preferably, the load is a secondary battery.

  In the non-contact power transmission device of the present invention, the power receiving coil has a center tap, and the output terminal of the rectifying / smoothing circuit is common to two diodes that respectively extract induced voltages from the taps at both ends. It consists of a smoothing capacitor connected to.

  According to said structure, loss is small and also large power can be obtained.

  Furthermore, in the non-contact power transmission device of the present invention, the power transmission unit includes a parallel circuit of a diode and a resistor between the resonance circuit and the switching element.

  According to the above configuration, the regenerative current when the switching element is OFF is regenerated to the starting circuit side through the body diode of the switching element, and the power is received in a state where the power receiving unit is close and in a state where the power receiving unit is separated. It is possible to prevent a difference in voltage generated in the transmission coil from being reduced.

  Therefore, it is possible to accurately determine whether or not the power reception unit is separated from the power transmission unit by the load detection unit and whether or not the power reception unit is a light load.

  Moreover, in the non-contact power transmission device of the present invention, the power transmission suppression means includes a switch element that short-circuits between taps of the power receiving coil, and the switch element is turned on when the light load is applied. Features.

  According to said structure, by short-circuiting between the taps of the said power receiving coil, the primary side of the said transformer operate | moves only with a leakage inductor, and a coil voltage and an oscillation frequency change. As a result, a state where the secondary side is not electromagnetically coupled, that is, a state where the power reception unit is separated from the power transmission unit can be reproduced in a pseudo manner.

  Furthermore, in the non-contact power transmission device of the present invention, the power transmission suppression means includes a switch element that disconnects the resonant capacitor from between taps of the power receiving coil, and the switch element is the light load. It is characterized by being turned off.

  According to the above configuration, by separating the resonant capacitor from between the taps of the power receiving coil, the secondary side of the transformer is not electromagnetically coupled, that is, the power receiving unit is separated from the power transmitting unit. The simulated state can be reproduced in a pseudo manner, and the loss can be greatly reduced.

  In the non-contact power transmission device of the present invention, the power transmission suppressing means includes a switch element that short-circuits a part of the power receiving coil, and the switch element is turned on when the light load is applied. And

  According to the above configuration, the secondary side of the transformer is not electromagnetically coupled by short-circuiting a part, such as between the tap at one end of the power receiving coil and the intermediate tap, that is, receiving power. The state in which the part is separated from the power transmission part can be reproduced in a pseudo manner. In addition, the power transmission unit side distinguishes between a state where there is no power reception unit and a state where power transmission is suppressed due to a light load even if the power reception unit is close by being partly short-circuited. Can do.

  As described above, the non-contact power transmission device of the present invention is configured to include a power transmission unit and a power reception unit that is close to and away from the power transmission unit, that is, a detachable power reception unit, and is non-contact by electromagnetic induction from the power transmission unit to the power reception unit. In a non-contact power transmission apparatus configured to transmit power, the power receiving coil of the power receiving unit on the secondary side of the transformer is not electromagnetically coupled to the power transmitting unit due to the voltage change appearing in the power transmitting coil. If the load detection means is provided in the drive circuit to reduce the switching duty, the power receiving unit is provided with load state detection means for detecting the load state, and the power receiving power is received. The secondary side of the transformer is not electromagnetically coupled between the power coil and the rectifying / smoothing circuit in response to the detection result of the load state detecting means and when the load is light. Providing a power transfer suppressing means for reproducing the state in a pseudo manner.

  Therefore, when the power receiving unit is lightly loaded, for example, when the load is a secondary battery, when the power receiving unit is away from the power transmitting unit, the power saving function is used to reduce the switching duty. However, the duty of switching can be reduced, power saving can be further promoted, and problems such as heat generation are eliminated. If the power transmission suppression means is provided between the rectifying / smoothing circuit and the load, a voltage drop occurs due to a rectifying diode, etc., and energy is propagated from the primary side to the secondary side of the transformer. However, the loss can be further reduced by providing it between the power receiving coil and the rectifying / smoothing circuit.

1 is an electric circuit diagram of a charging system to which a non-contact power transmission apparatus according to a first embodiment of the present invention is applied. It is sectional drawing which shows typically the mode of the coupling | bonding between the coils of the said charging system. It is a wave form diagram of the terminal voltage of the coil for electric power transmission. It is a wave form diagram of the terminal voltage of the coil for electric power transmission. It is a figure for demonstrating the arrangement position of the electric power transmission suppression means in the 1st Embodiment of this invention. It is a graph of a secondary side current waveform in the terminal voltage of the said coil for electric power transmission which shows the simulation result of this inventor. It is an electric circuit diagram of the charging system to which the non-contact electric power transmission apparatus which concerns on the 2nd Embodiment of this invention is applied. It is a wave form diagram for demonstrating the operation | movement of the 2nd Embodiment of this invention. It is an electric circuit diagram of the power receiving part in the charging system to which the non-contact electric power transmission apparatus which concerns on the 3rd Embodiment of this invention is applied. It is an electric circuit diagram of the charging system to which the non-contact electric power transmission apparatus which concerns on the 4th Embodiment of this invention is applied. It is a graph which shows the simulation result of the 4th embodiment of the present invention. It is an electric circuit diagram of one specific structural example of the charging system which concerns on the 4th Embodiment of this invention. It is an electric circuit diagram of the concrete other structural example of the charging system which concerns on the 4th Embodiment of this invention. It is an electric circuit diagram of the charging system to which the non-contact electric power transmission apparatus which concerns on the 4th Embodiment of this invention is applied.

(Embodiment 1)
FIG. 1 is an electric circuit diagram of a charging system to which a non-contact power transmission apparatus according to a first embodiment of the present invention is applied. The charging system includes a power transmission unit 1 and a power reception unit 2 that is close to and away from the power transmission unit, that is, a detachable power reception unit 2, and transmits electric power from the power transmission unit 1 to the power reception unit 2 in a contactless manner by electromagnetic induction. For example, it is a charging system in which the secondary battery BA in the power receiving unit 2 can be charged only by being placed on the power transmitting unit 1. As the power receiving unit 2, rechargeable electric devices such as an electric toothbrush, a mobile phone, a notebook computer, an electric razor, and an electric tool are employed.

  In this charging system, as shown in FIG. 2, the coils T1 and T2 wound around the magnetic cores 10 and 20 are opposed to each other with the insulating housings 100 and 200 interposed therebetween. The power transmission coil T1 of the power transmission unit 1 is a primary side of a non-contact transformer, and the power reception coil T2 of the power reception unit 2 is a secondary side of the transformer, and power is transmitted by electromagnetic induction between them. Is done.

  For this reason, the power transmission unit 1 is connected to the power transmission coil T1 in parallel with the resonant capacitor C4 constituting the resonance circuit 11, and the current flowing through the power transmission coil T1 is turned ON / OFF. A switching element FET1 that resonates the resonance circuit 11, a parallel circuit of a diode D2 and a resistor R5 interposed between the resonance circuit 11 and the switching element FET1, a drive circuit 12 that controls switching of the switching element FET1, When the power receiving unit 2 is separated from the power transmitting unit, it detects that the secondary side of the transformer is not electromagnetically coupled from the voltage change appearing in the power transmitting coil T1 via the power receiving coil T2, The drive circuit 12 reduces the switching duty (secondary induced energy of the transformer). A load detecting circuit 13 for stopping the quenching, the activation circuit 14, a power supply E, and the smoothing capacitor C1 is provided.

  On the other hand, the power receiving unit 2 is induced in the power receiving coil T2 and the resonance capacitor C6 that is connected in parallel to the power receiving coil T2 and is a matching capacitor provided to receive more power. The rectifying / smoothing circuit 21 that rectifies / smooths the obtained current and applies it to the secondary battery BA that is a load, the secondary battery BA that is charged by the output current from the rectifying / smoothing circuit 21, and the rectifying / smoothing An impedance element FET3 interposed between the circuit 21 and the secondary battery BA, and a control microcomputer 22 for controlling a charging current passing through the impedance element FET3 according to a terminal voltage of the secondary battery BA are provided. Yes. When the capacity of the resonance capacitor C6 is C and the inductance of the power receiving coil T2 is L, 1 / {2π√ (LC)} is equal to the resonance frequency of the resonance circuit 11 to extract the maximum power. Can do. The rectifying / smoothing circuit 21 includes a rectifier diode D3 and a capacitor C7 that smoothes the passing current.

  Returning to the power transmission unit 1 again, the power source E is composed of an AC-DC converter, for example, and converts, for example, a commercial voltage of 100 V into a DC voltage of 5 V. The voltage is smoothed by the smoothing capacitor C1 and becomes a power source of the charging system.

  The starting circuit 14 is formed by connecting a series circuit of a starting resistor R1 and a capacitor C2 in parallel to the power source E. When the power is turned on, the terminal voltage of the capacitor C2 rises, and the transformer constituting the load detection circuit 13 Is provided to the gate of the switching element FET1 through the feedback coil T3 and the resistor R3. Thus, when the gate capacitance of the switching element FET1 is charged and reaches a predetermined voltage, the switching element FET1 composed of an n-type FET is turned ON. As a result, a voltage is induced in the feedback coil T3 to maintain the gate of the switching element FET1 on the high side, and the ON state of the switching element FET1 is maintained.

  On the other hand, the drive circuit 12 includes a self-excited oscillation circuit 121 and an intermittent drive circuit 122. The self-excited oscillation circuit 121 includes a resistor R7 for converting the current flowing through the switching element FET1, a resistor R6 for extracting the terminal voltage, a capacitor C5 for smoothing the extracted voltage, and a charging voltage of the capacitor C5. And a transistor TR2 applied to the base. Therefore, when the switching element FET1 is turned on, a current flows from the capacitor C4 and the power transmission coil T1 to the resistor R7 via the diode D2 and the switching element FET1, and the accumulated amount of the current, that is, the charging voltage of the capacitor C5 is more than a predetermined value. When it becomes higher, the transistor TR2 is turned ON, the gate-source of the switching element FET1 is short-circuited, and the switching element FET1 is turned OFF.

  When the switching element FET1 is turned OFF, the current flowing in the power transmission coil T1 flows in the parallel resonance capacitor C4, and the power transmission coil T1 and the resonance capacitor C4 start to resonate. At this time, since the voltage of the power transmission coil T1 changes in the opposite direction, a voltage is induced in the feedback coil T3 to maintain the gate of the switching element FET1 on the low side, and the OFF state of the switching element FET1 is maintained. . Thereafter, when the switching element FET1 is turned off, the capacitor C5 discharges the charge via the resistors R6 and R7, and when the charging voltage falls below the threshold voltage of the transistor TR2, the transistor TR2 is turned off. Thus, after a while after the power transmission coil T1 and the capacitor C4 resonate, a positive voltage is generated again in the feedback coil T3 to turn on the switching element FET1, and the transistor TR2 is determined by the capacitor C5 and the resistors R6 and R7. The resonance circuit 11 is self-oscillated by turning on / off according to the constant.

  On the other hand, the intermittent drive circuit 122 includes a diode D1 that extracts a terminal voltage Vd of the power transmission coil T1, resistors R2 and R4 that divide the voltage, a capacitor C3 that is charged with the divided voltage, and a terminal voltage thereof. And a transistor TR1 provided to the base. When the power receiving unit 2 is not close and the terminal voltage Vd of the power transmission coil T1 becomes higher than a predetermined value, the gate and the source of the switching element FET1 are short-circuited, and the self-excited oscillation circuit 121 is self-excited. Stops oscillation. When the switching element FET1 is turned off, the capacitor C3 discharges the charge via the resistor R4. When the charging voltage is lower than the threshold voltage of the transistor TR1, the transistor TR1 is turned off. Thus, the transistor TR1 is turned on / off according to the time constant determined by the resistor R4 and the capacitor C3, and intermittently drives the self-excited oscillation circuit 121. This time constant is much larger than the time constants of the capacitor C5 and the resistors R6 and R7 for turning on / off the transistor TR2. The diode D1 prevents current backflow from the intermittent drive circuit 122 to the resonance circuit 11, thereby preventing the resonance operation of the resonance circuit 11 from becoming unstable.

  3 and 4 are waveform diagrams of the terminal voltage Vd of the power transmission coil T1. 3A and 4A show a state in which the power receiving unit 2 is close to each other, and FIGS. 3B and 4B show a state in which they are separated from each other. 3 (a) and 3 (b) show enlarged waveforms of FIGS. 4 (a) and 4 (b), respectively. That is, the waveforms in FIGS. 3A and 3B are waveforms obtained by enlarging the waveforms of two periods in FIGS. 4A and 4B. 4A and 4B show the base-emitter voltage Vc of the transistor TR2 on the lower side in accordance with the terminal voltage Vd shown on the upper side.

  As shown in FIGS. 3B and 4B, when the power receiving unit 2 is not provided, as described above, compared to the case where the power receiving unit 2 shown in FIGS. 3A and 4A is provided. The voltage amplitude of the power transmission coil T1 is large. This is because the self-inductance of the power transmission coil T1 is smaller when there is no power receiving unit 2 than when it is present. Therefore, when the power receiving unit 2 is not provided, the terminal voltage Vb of the power transmission coil T1 also increases, and the terminal voltage Vb can exceed the threshold voltage of the transistor TR1, and the transistor TR1 has the resistance R4 as described above. And ON / OFF is repeated according to the time constant determined by the capacitor C3. As a result, the self-excited oscillation circuit 121 can cause the resonant circuit 11 to self-oscillate as indicated by a period TM1 in FIG. 4B during the period when the intermittent drive circuit 122 turns on the switching element FET1. However, during the period in which the intermittent drive circuit 122 turns off the switching element FET1, the resonance circuit 11 cannot oscillate as shown in the period TM2 in FIG. 4B.

  On the other hand, when the power receiving unit 2 is provided, the terminal voltage Vb of the power transmission coil T1 is lower than when the power receiving unit 2 is not provided, so that the terminal voltage Vb exceeds the threshold voltage of the transistor TR1. The transistor TR1 cannot turn off the switching element FET1. As a result, the self-excited oscillation circuit 121 can cause the resonant circuit 11 to self-oscillate without being affected by the intermittent drive circuit 122, as shown in FIG.

  On the other hand, when resonance starts in the resonance circuit 11, as shown at time TA1 in FIGS. 3A and 3B, the terminal voltage Vd changes in an upwardly convex curve, and then at time TA2. As shown, it changes with a downwardly convex curve. Here, since the voltage that is 180 degrees out of phase with the terminal voltage Vd is induced in the feedback coil T3 as described above, the switching element FET1 is turned off as described above during the period from the time TA1 to the time TA2. maintain. Further, when resonance is started in the resonance circuit 11, that is, when the switching element FET1 is turned OFF, the capacitor C5 discharges electric charges via the resistors R6 and R7 as described above.

  In the period from time TA2 to time TA3, a positive voltage is generated in the feedback coil T3, whereby the switching element FET1 is turned on again. As described above, the self-excited oscillation circuit 121 resonates the resonance circuit 11 by repeatedly turning on / off the switching element FET 1 and transmits power to the power receiving unit 2.

  In addition, when there is no power receiving unit 2 shown in FIG. 3B, the amplitude of the terminal voltage Vd increases as compared with the case shown in FIG. 3A, so that the intermittent drive circuit 122 turns on the transistor TR1. Thus, the switching element FET1 is turned off, and intermittent oscillation can be performed. When the switching element FET1 is turned OFF, the resonance of the resonance circuit 11 is eventually stopped, and the self-excited oscillation circuit 121 cannot resonate the resonance circuit 11 as shown in a period TM2 in FIG. Thereafter, the capacitor C3 is discharged through the resistor R4, eventually turning off the transistor TR1, the switching element FET1 is turned on again, and the self-excited oscillation circuit 121 is shown in the period TM1 of FIG. The resonance circuit 11 is resonated again. Therefore, as described above, the period TM2 shown in FIG. 4B can be determined by the time constants of the capacitor C3 and the resistor R4, and the oscillation of the resonance circuit 11 can be stopped in the period TM2.

  With this configuration, the intermittent drive circuit 122 performs determination from the terminal voltage Vd of the power transmission coil T1 without providing a special configuration for determining whether or not the power receiving unit 2 is present. Since the self-excited oscillation circuit 121 is intermittently driven, standby power can be reduced and the problem of heat generation can be reduced when power is transmitted to the power receiving unit 2 in a non-contact manner.

  Further, in the parallel circuit of the diode D2 and the resistor R5 provided between the resonance circuit 11 and the switching element FET1, the regenerative current when the switching element FET1 is OFF is supplied to the capacitor C2 through the body diode D10 of the switching element FET1. By limiting the regenerative current, the peak value between the state where there is the power receiving unit 2 shown in FIG. 4A and the state where there is no power receiving unit 2 shown in FIG. This is to prevent the difference from being reduced, whereby the presence or absence of the power receiving unit 2 can be accurately determined.

  In the charging system configured as described above, it should be noted that in the present embodiment, the power receiving unit 2 includes a control microcomputer 22 that controls the load state, that is, the charge state of the secondary battery BA, in the load state. In response to the detection result, when an abnormal state such as full charge or overvoltage that is a light load occurs, the power receiving coil T2 that is the secondary side of the transformer is for power transmission that is the primary side That is, a switch element FET2 is provided that is a power transmission suppressing unit that is not electromagnetically coupled to the coil T1, that is, the state in which the power receiving unit 2 is not present. The switch element FET2 is provided between the power receiving coil T2 and the rectifying / smoothing circuit 21. When the secondary battery BA is fully charged and the impedance element FET3 is turned off, the control microcomputer 22 turns on the switch element FET2 to short-circuit between the terminals (both ends taps) of the power receiving coil T2. Therefore, on the power transmission unit 21 side, the feedback coil T3 is used as the load detection means, and the intermittent drive circuit 122 is used as the drive circuit.

  In addition, when the secondary side coil part is short-circuited with a general switching power supply circuit, the primary side leakage inductance is small and the primary side switching element is broken. However, in the case of non-contact power transmission, Since the leakage inductance is large, there is no problem at all. In addition, when the switching element on the secondary side is FET2, it is considered that the ON resistance voltage is generated and the FET2 generates heat. However, the power transmission unit 1 immediately reduces the duty (intermittent oscillation or switching element ON). Since the output is reduced by reducing the width, this is not a problem.

  With this configuration, when the power receiving unit 2 is away from the power transmitting unit 1, the power receiving unit 2 can detect the state of the magnetic circuit and reduce the switching duty by using the power saving function described above. Even when the load is light, that is, when the secondary battery BA is fully charged, the switching duty can be reduced, power saving can be further promoted, and problems such as heat generation can be eliminated. Further, as schematically shown in FIG. 5, when the FET 2 that is the power transmission suppressing means is provided between the rectifying / smoothing circuit 21 and the secondary battery BA that is the load (position of V1), A voltage drop occurs due to the diode D3 and the like, and energy is propagated from the primary side to the secondary side of the transformer. However, as described above, between the power receiving coil T2 and the rectifying / smoothing circuit 21 (V2 Loss) can be further reduced.

  FIG. 6 is a graph showing the simulation results of the present inventors. A solid line indicates a terminal voltage Vd appearing in the power transmission coil T1, and a broken line indicates a current I flowing in the power receiving coil T2. Therefore, in a state where the power receiving unit 2 shown in FIG. 6A is separated, no current flows through the power receiving unit 2. FIG. 6B shows a state in which the power reception unit 2 is in close contact with the power transmission unit 1 and the secondary battery BA is charged, and the self-inductance of the power transmission coil T1 increases, and the terminal voltage is increased. The voltage amplitude of Vd is small.

On the other hand, FIG. 6C and FIG. 6D both show a state in which the power receiving unit 2 is in close contact with the power transmitting unit 1 and the secondary battery BA is fully charged, and FIG. This is a case (coil short circuit) in which the FET 3 serving as the power transmission suppressing means is provided between the power receiving coil T2 and the rectifying / smoothing circuit 21 (position V2 in FIG. 5) as in the present embodiment described above. FIG. 6D shows the case of the comparative example (load short circuit) in which the FET 3 is provided between the rectifying / smoothing circuit 21 and the secondary battery BA (position V1 in FIG. 5). FIG. 6 (c) and FIG. 6 (d) are compared with FIG. 6 (a). In the present embodiment shown in FIG. 6 (c), the effective value and the average value of the terminal voltage Vd are different. 6 (a) is very close to the state where the power receiving unit 2 is separated. Therefore, comparing FIG. 6 (c) and FIG. 6 (d), the effective value of the current I on the secondary side is Is 105.8 mA in the embodiment, whereas it is 156.1 mA in the comparative example. Since the loss is I ² R, it is understood that the loss is half or less in the present embodiment.

  The reduction of the duty may be realized by either shortening the ON period of the switching element FET1, increasing the switching period, or a combination thereof. Thus, it is assumed that the proximity of the power receiving unit 2 is detected and the switching is completely stopped.

(Embodiment 2)
FIG. 7 is an electric circuit diagram of a charging system to which the non-contact power transmission apparatus according to the second embodiment of the present invention is applied. This charging system is similar to the above-described charging system shown in FIG. 1, and corresponding portions are denoted by the same reference numerals and description thereof is omitted. In this charging system, the configuration of the power receiving unit 2 is the same as that in FIG. It should be noted that the power transmission unit 1 described above performs self-excited oscillation, whereas in the power transmission unit 1a of the present embodiment, the drive circuit 12a includes a separately excited oscillation circuit 123 including a control microcomputer 123a and an intermittent drive circuit. 122a. The intermittent drive circuit 122a is the same as the intermittent drive circuit 122 described above, but is not provided with the transistor TR1. For this reason, the charging voltage of the capacitor C3 is input to the A / D conversion port of the control microcomputer 123a.

  The control microcomputer 123a operates using the output voltage of the smoothing capacitor C1 as the power supply VCC, and applies a PWM signal having a predetermined period to the gate of the switching element FET1 via the resistor R3a. Then, the control microcomputer 123a increases the duty of the PWM signal as shown in FIG. 8A during normal charging when the charging voltage of the capacitor C3 of the intermittent drive circuit 122a is less than a predetermined level, and the predetermined level. If it becomes above, it will determine with the state which does not have the power receiving part 2, or the secondary battery BA will be fully charged, and as shown in FIG.8 (b), the duty of the said PWM signal will be reduced.

  Therefore, as shown in FIG. 8B, even when the ON time is shortened, the self-impedance of the power transmission coil T1 is smaller in FIG. 8B, and the terminal voltage Vd is the same as that in FIG. Therefore, even with a small duty, stable operation is possible while continuously oscillating, and the secondary side input current can be reduced by reducing the duty. Even with this configuration, standby power can be reduced.

(Embodiment 3)
FIG. 9 is an electric circuit diagram of the power receiving unit 2a in the charging system to which the non-contact power transmission apparatus according to the third embodiment of the present invention is applied. This charging system is similar to the charging system shown in FIG. 1 and FIG. 7 described above, and corresponding portions are denoted by the same reference numerals, and description thereof is omitted. Any of the power transmission units 1 and 1a described above may be used in this charging system. It should be noted that in the power receiving unit 2a of the present embodiment, the rectification method is the center tap method.

  Therefore, the power receiving coil T2a has a center tap, and the rectifying / smoothing circuit 21a has a smoothing capacitor C7 whose output terminal is connected in common to the two diodes D3 and D3a that extract the induced voltage from the taps at both ends, respectively. Consists of Two switch elements FET2 and FET2a are used to short-circuit the power receiving coil T2a at the time of full charge, and short-circuit between the taps at each end and the center tap. With this configuration, loss is small and high power can be obtained.

(Embodiment 4)
FIG. 10 is an electric circuit diagram of a charging system to which the non-contact power transmission apparatus according to the fourth embodiment of the present invention is applied. This charging system is similar to the charging system shown in FIG. 1, FIG. 7 and FIG. 9 described above, and corresponding portions are denoted by the same reference numerals and description thereof is omitted. In this charging system, the power transmission unit 1 employs the self-excited configuration shown in FIG. 1. However, the power transmission unit 1 may have the other-excited configuration. A tap method may be used.

  It should be noted that in the present embodiment, in the power receiving unit 2b, as the power transmission suppressing means, a switching element that separates the resonant capacitor C6, which is a secondary side matching capacitor, from between the taps of the power receiving coil T2. SW1 is used. The control microcomputer 22 turns on the switch element SW1 during normal power transmission, and turns it off when it is desired to stop charging when charging is completed. The terminal voltage Vd in the power transmission coil T1 at that time is as shown in FIG.

  FIG. 11 is a graph showing the simulation results of the present inventors. Similarly to FIG. 6 described above, the solid line indicates the terminal voltage Vd appearing in the power transmission coil T1, and the broken line indicates the current I flowing in the power receiving coil T2. Compared with the short circuit between the terminals (tap) of the power receiving coil T2 shown in FIG. 6C, the amplitude of the terminal voltage Vd is reduced when the resonance capacitor C6 is disconnected as shown in FIG. 11A. The effective value of the current I on the secondary side can be significantly reduced to 37.1 mA. In this case, the loss can be further reduced to about 1/10, which is preferable.

  FIG. 11B shows a state where the resonance capacitor C6 is disconnected and the load side switch element FET3 is opened. Although the terminal voltage Vd increases, the secondary current I can be almost eliminated. Thus, for example, the standby power without the power receiving unit 2b is 0.285 W, but even when the power receiving unit 2 b is present, the standby power is suppressed to about 0.287 W when not charged. Can do. Even with this configuration, a state where the secondary side of the transformer is not electromagnetically coupled, that is, a state where the power receiving unit 2b is separated from the power transmitting units 1 and 1a can be simulated.

  Here, when the switch element SW1 is formed of an FET, the resonance capacitor C6 may not be completely disconnected due to a parasitic diode. Therefore, like the power receiving unit 2b1 shown in FIG. 12 and the power receiving unit 2b2 shown in FIG. 13, switch elements in series with the resonant capacitor C6 may be connected in series with opposite polarities. In the power receiving section 2b1 shown in FIG. 12, a switch element FET4 having the same polarity as the p-type switch element FET3 for controlling the charging of the secondary battery BA and an n-type switch element FET5 having the opposite polarity are connected in series. The elements FET3 and FET4 are both turned OFF by giving a high level via the gate resistors R11 and R12, and the switch element FET5 is turned OFF by giving a low level via the gate resistance R13. On the other hand, in the power receiving unit 2b2 shown in FIG. 13, a diode D11 is used instead of the switch element FET4. As a result, the amount of current passing through the parasitic diode can be further suppressed.

(Embodiment 5)
FIG. 14 is an electric circuit diagram of a charging system to which the non-contact power transmission apparatus according to the fourth embodiment of the present invention is applied. This charging system is similar to the charging system shown in FIG. 1, FIG. 7 and FIG. 9 described above, and corresponding portions are denoted by the same reference numerals and description thereof is omitted. In this charging system as well, the power transmission unit 1 employs the self-excited configuration shown in FIG. 1, but the other power-excited configuration shown in FIG. 7 may be used. A tap method may be used.

  It should be noted that in the present embodiment, in the power receiving unit 2c, the switch element FET2 as the power transmission suppressing means is partially short-circuited between the tap at one end and the intermediate tap of the power receiving coil T2b. Thus, a state in which the secondary side of the transformer is not electromagnetically coupled, that is, a state in which the power receiving unit 2c is separated from the power transmitting unit 1 is reproduced in a pseudo manner. Thus, even if a part of the power receiving coil T2b is short-circuited, the resonance frequency of the 1 / {2π√ (LC)} is greatly shifted, and the power cannot be taken out. In addition, due to a short circuit in a part, the power transmission unit 1 side has a state where there is no power reception unit 2c and a state where power transmission is suppressed due to a light load even if the power reception unit 2c is close. Can be distinguished.

  Here, in Japanese Patent Laid-Open No. 11-27870, a fuse is provided between the secondary side rectifier circuit and the secondary battery so that the secondary side circuit does not become an abnormally high voltage when the fuse is cut off. It is shown that the terminals of the power receiving coil are short-circuited. However, this prior art is intended to protect the secondary side circuit, and thus the primary side circuit stops oscillating and does not realize power saving.

1, 1a Power transmission unit 2, 2a, 2b, 2b1, 2b2, 2c Power reception unit 10, 20 Core 100, 200 Housing 11 Resonant circuit 12, 12a Drive circuit 121 Self-excited oscillation circuit 122, 122a Intermittent drive circuit 123 Other-excited oscillation circuit 123a Control microcomputer 13 Load detection circuit 14 Start-up circuit 21, 21a Rectification / smoothing circuit 22 Control microcomputer BA Secondary battery C1 Smoothing capacitor C2, C3, C5, C7 Capacitor C4, C6 Resonance capacitor D1, D2, D11 Diode D3, D3a Rectification Diode E Power supply FET1 Switching element FET2, FET2a, FET4 Switch element FET3 Impedance element R1 Starting resistance R2, R3, R3a, R4, R5, R6, R7 Resistance R11, R12, R13 Gate resistance SW1 Switch element T1 Power transmission coil 2, T2a power receiving coil T3 feedback coil TR1, TR2 transistors

Claims (8)

In a non-contact power transmission device configured to include a power transmission unit and a power reception unit that can be moved to and away from the power transmission unit, and to transmit power in a non-contact manner by electromagnetic induction from the power transmission unit to the power reception unit,
The power transmission unit
A power transmission coil serving as a primary side of a transformer capable of separating a primary side and a secondary side;
A resonant capacitor connected in parallel to the power transmission coil to form a resonant circuit;
A switching element for resonating the resonant circuit;
A drive circuit for controlling switching of the switching element;
Load detection means for reducing the switching duty in the drive circuit when the power reception unit is separated from the power transmission unit and the secondary side of the transformer is not electromagnetically coupled to the primary side. Configured,
The power receiving unit
A power receiving coil on the secondary side of the transformer;
A resonant capacitor connected in parallel to the power receiving coil;
A rectifying / smoothing circuit that rectifies and smoothes the current induced in the power receiving coil and applies it to a load;
Load state detecting means for detecting the state of the load;
A light load that is provided between the power receiving coil and the rectifying / smoothing circuit and has a current supplied from the rectifying / smoothing circuit to the load equal to or less than a predetermined value in response to the detection result of the load state detecting means. A non-contact power transmission device comprising: a power transmission suppression unit that simulates a state in which the secondary side of the transformer is not electromagnetically coupled.   The non-contact power transmission apparatus according to claim 1, wherein the load detection means is a feedback winding of the transformer.   The load is a secondary battery, and the power transmission suppression unit reproduces a state in which the secondary side of the transformer is not electromagnetically coupled when the secondary battery is fully charged. The contactless power transmission device according to claim 1 or 2, characterized in that   The power receiving coil has a center tap, and the rectifying / smoothing circuit is composed of a smoothing capacitor having an output terminal connected in common to two diodes that respectively extract induced voltages from taps at both ends. The contactless power transmission device according to any one of claims 1 to 3.   The non-contact power transmission apparatus according to claim 1, wherein the power transmission unit includes a parallel circuit of a diode and a resistor between the resonant circuit and the switching element.   The said power transmission suppression means is provided with the switch element which short-circuits between the taps of the said power receiving coil, This switch element is turned ON when it is the said light load. The non-contact power transmission device according to item.   The said power transmission suppression means is provided with the switch element which isolate | separates the said resonant capacitor from between the taps of the said power receiving coil, This switch element is turned off when it is the said light load. The non-contact power transmission device according to any one of the above.   The said power transmission suppression means is provided with the switch element which short-circuits a part of said coil for electric power receiving, and this switch element is turned ON when it is the said light load. The non-contact power transmission device described in 1.

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