JP2013219854A - Wireless power transmission device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wireless power transmission device capable of significantly reducing standby power without degrading convenience.SOLUTION: The wireless power transmission device transmits electric power from a transmitter 10 to a receiver 20 in a non-contact manner. The transmitter 10 includes: detection means 13 that detects at least either one of the presence/absence or position of the receiver 20 in a power transmission available range; a control circuit 14 that controls the detection means 13; and a vibration sensor 15 that detects vibration, and starts the control circuit 14 when the vibration sensor 15 detects the vibration.

Description

  The present invention relates to a wireless power transmission apparatus.

  In recent years, electromagnetic induction type wireless power transmission devices for portable devices have become widespread. Electric power is transmitted to a power receiving coil built in a power receiver such as an electronic device by an AC magnetic field generated from a power transmitting coil built in the power transmitter. The power transmitted to the power receiving coil is supplied to a load such as a secondary battery via a rectifier circuit. Since the secondary battery in the power receiver can be charged simply by placing the power receiver on the surface of the power transmitter, there is no need to connect or disconnect the power connector, and there are advantages such as excellent convenience, waterproofing, and dustproofing.

  In such a wireless power transmission device, if an AC magnetic field is always generated from the power transmission coil, a large amount of power is consumed even when the power receiver is not placed on the surface of the power transmitter. For this reason, a standby mode in which the presence or absence of a power receiver is always checked while power is intermittently sent to the power transmission coil is generally provided to reduce standby power.

JP 2008-178195 A

  However, in a wireless power transmission device used for general purposes such as charging a portable device, the standby time in the standby mode is longer than the charging operation time. Therefore, no matter how high the power transmission efficiency and the charging efficiency, when the standby power increases, the overall power efficiency decreases. For example, a standby power of about 0.6 W is consumed in a 5 W class wireless power transmission device. Thus, the power consumption in the standby mode is a factor, and the standby power increases in the wireless power transmission device as compared with the conventional cord type charging device.

  Of course, standby power can be eliminated by providing a power switch in the wireless power transmission device and manually turning on the power only during charging. However, the convenience that is the main merit of the wireless power transmission device is impaired. Therefore, it is difficult to achieve both convenience of the wireless power transmission device and reduction of power consumption.

  The present invention has been made in consideration of such a problem, and an object thereof is to provide a wireless power transmission apparatus capable of significantly reducing standby power without impairing convenience.

  In order to achieve such an object, the present invention is a wireless power transmission device that performs power transmission from a power transmitter to a power receiver in a contactless manner, and the power transmitter is within the range in which power transmission is possible. A detection means for detecting at least one of presence or absence or position, a control circuit for controlling the detection means, and a vibration sensor for detecting vibration, and the control circuit is activated when the vibration sensor detects vibration It is characterized by doing.

  The wireless power transmission device of the present invention can significantly reduce standby power while ensuring convenience.

Block diagram of the wireless power transmission device of the present invention Structure and mounting example of piezoelectric vibration sensor in wireless power transmission device of the present invention Flowchart of wireless power transmission device of the present invention The block diagram of the modification of the wireless power transmission apparatus of this invention

  Hereinafter, embodiments of the present invention will be described.

  FIG. 1 is a block diagram of a wireless power transmission device of the present invention. The power transmitter 10 includes a power transmission coil 11, a drive circuit 12, a detection unit 13, a control circuit 14, a piezoelectric vibration sensor 15, and an amplifier circuit 16. The power receiver 20 includes a power receiving coil 21.

  First, the configuration of the power transmitter 10 will be described. AC power is supplied from the drive circuit 12 to the power transmission coil 11. The detection means 13 detects at least one of the presence / absence of the power receiver 20 and the position of the power receiver 20 with respect to the power transmitter 10 in a range where power can be transmitted from the power transmitter 10. The operations of the drive circuit 12 and the detection means 13 are controlled by the control circuit 14. As an example, the control circuit 14 is configured by a microcomputer or the like. A load resistor R3 is connected to both ends of the piezoelectric vibration sensor 15. The output signal of the piezoelectric vibration sensor 15 is amplified by the amplifier circuit 16 and supplied to the control circuit 14.

  Next, the configuration of the amplifier circuit 16 will be described. The amplifier circuit 16 includes a resistor R1, a resistor R2, a capacitor C1, and an operational amplifier OP1. The output signal of the piezoelectric vibration sensor 15 is supplied to the non-inverting input terminal of the operational amplifier OP1. The inverting input terminal of the operational amplifier OP1 is grounded via the resistor R1 and the capacitor C1. A feedback resistor R2 is connected between the inverting input terminal and the output terminal of the operational amplifier OP1. A signal output from the operational amplifier OP1 is supplied to the control circuit 14.

  Next, the configuration of the power receiver 20 will be described. The power receiving coil 21 receives power from the power transmitting coil 11 by electromagnetic induction. Although not shown, the voltage applied to the power receiving coil 21 is rectified by a rectifier circuit and supplied to a load such as a secondary battery.

  Here, the structure and mounting example of the piezoelectric vibration sensor 15 in the wireless power transmission device of the present invention are shown in FIG. FIG. 2 shows the internal structure of the power transmitter 10. The piezoelectric vibration sensor 15 includes a short rail-shaped metal plate 31 and a piezoelectric material 32. The piezoelectric vibration sensor 15 is a unimorph type in which a piezoelectric ceramic is pasted as a piezoelectric material 32 on one surface of a short rail-shaped metal plate 31. One end of the piezoelectric vibration sensor 15 is fixed to the printed board 34 by a fixing member 33 and has a cantilever structure. The plane of the piezoelectric vibration sensor 15 and the plane of the printed circuit board 34 are arranged in parallel directions. The plane of the printed circuit board 34 is disposed so as to be substantially parallel to the surface of the power transmitter 10 on which the power receiver 20 is disposed. In addition, the surface of the power transmitter 10 is formed in a planar shape so that the power receiver 20 can be placed thereon.

  When the power receiver 20 is placed on the surface of the power transmitter 10, vibration is generated mainly in a direction perpendicular to the surface of the power transmitter 10. When slight vibration occurs in a direction perpendicular to the surface of the power transmitter 10, flexural vibration occurs in the thickness direction of the piezoelectric material 32. Therefore, an AC voltage signal having a natural vibration frequency of the cantilever is output from the piezoelectric vibration sensor 15 due to the piezoelectric effect. When the power receiver 20 is placed, the direction in which vibration is mainly generated, that is, the direction perpendicular to the surface of the power transmitter 10 and the vertical direction of the metal plate 31 are substantially matched. Vibration can be detected efficiently. Further, by using a cantilever structure, high sensitivity can be obtained in low frequency vibration.

  The piezoelectric vibration sensor 15 may be a bimorph type in which a piezoelectric ceramic is pasted as a piezoelectric material 32 on both surfaces of a short rail-shaped metal plate 31. Further, instead of the cantilever structure, other structures may be used as long as vibration can be detected.

  Thus, the piezoelectric vibration sensor 15 detects vibration applied to the power transmitter 10. In order to detect minute vibrations, a weak voltage signal generated from the piezoelectric vibration sensor 15 is amplified by the operational amplifier OP1. R3 which is the load resistance of the piezoelectric vibration sensor 15 is appropriately about 1 MΩ so as not to decrease the output signal of the piezoelectric vibration sensor 15.

  In addition, when the piezoelectric vibration sensor 15 has a large capacitance, a DC bias is generated at the input terminal of the operational amplifier OP1. For this reason, it is necessary to suppress the amplification of the DC component by the operational amplifier OP1.

  Here, the resistance value of the resistor R1 is r1, the resistance value of the resistor R2 is r2, and the impedance of the capacitor C1 is Xc1. Then, the amplification factor A of the operational amplifier OP1 is A = r2 / (r1 + Xc1) +1. Therefore, if the capacitor C1 having a sufficient capacitance value is used, Xc1 becomes ∞ with respect to the DC component, and therefore the amplification factor A = 1. On the other hand, for an AC signal, r1 + Xc1≈r1, so that amplification factor A≈r2 / r1 + 1. That is, the DC component is not amplified, and only the AC signal detected by the piezoelectric vibration sensor 15 can be amplified. The capacitor C1 connected in series with the resistor R1 can suppress the amplification of the DC component supplied to the operational amplifier OP1 and improve the detection sensitivity of the piezoelectric vibration sensor 15.

  In this way, the vibration generated when the power receiver 20 is placed on the surface of the power transmitter 10 is detected by the piezoelectric vibration sensor 15. The obtained detection signal is supplied to the control circuit 14 via the amplifier circuit 16. The control circuit 14 controls the operation of the detection means 13 and the drive circuit 12 according to the vibration detection signal of the piezoelectric vibration sensor 15.

  Here, a flowchart of the wireless power transmission apparatus of the present invention is shown in FIG. The operation flow of the power transmitter 10 will be described with reference to the flowchart shown in FIG. Hereinafter, a microcomputer incorporating the control circuit 14 is used.

First, when power is supplied, the microcomputer of the power transmitter 10 enters a sleep state. In the sleep state, since the system clock is stopped, most functions are stopped and the power consumption is extremely reduced. At this time, the operations of the detection means 13 and the drive circuit 12 are also stopped. (Step S1).
Next, it is determined whether or not the piezoelectric vibration sensor 15 detects vibration. If the piezoelectric vibration sensor 15 does not detect vibration, the process returns to the first step S1 described above, and the microcomputer continues the sleep state (step S2).
When the piezoelectric vibration sensor 15 detects vibration, the microcomputer is activated from the sleep state by using the interruption function of the microcomputer (step S3).
And it transfers to the power receiver detection mode which detects the presence or absence and position of the power receiver 20 in the range in which electric power transmission from the power transmitter 10 is possible. Hereinafter, operations of the detection unit 13 and the drive circuit 12 will be described. First, the microcomputer controls the drive circuit 12 to intermittently send power to the power transmission coil 11. And the detection means 13 detects the change of the electric current which flows into the power transmission coil 11 by the approach of the power receiver 20, the high frequency electromagnetic echo signal reflected from the power reception coil 21 by the detection coil, etc. Based on these detection results, the presence / absence and position of the power receiver 20 are specified. Here, the piezoelectric vibration sensor 15 detects not only vibration when the power receiver 20 is placed but also environmental vibration such as when the location of the power transmitter 10 is moved. Therefore, even if the piezoelectric vibration sensor 15 detects vibration, the power receiver 20 is not necessarily near the power transmitter 10. Therefore, a time limit is provided in a period for confirming the presence or absence and position of the power receiver 20. If the power receiver 20 is not detected within the time limit, the output of the piezoelectric vibration sensor 15 is considered to be due to environmental vibration, the process returns to the first step S1 described above, and the microcomputer enters the sleep state again (step S4). ).
When the presence / absence of the power receiver 20 and its position are reliably detected, the power transmission coil 11 and the power reception coil 21 are aligned (step S5).
When the alignment of the power transmission coil 11 and the power reception coil 21 is completed, the process proceeds to the next ID authentication or charging mode (step S6).
After the charging operation is completed, the process returns to the first step S1 described above, and the microcomputer again enters the sleep state (step S7).

  As described above, the piezoelectric vibration sensor 15 has an auxiliary role for the detection of the power receiver 20. When vibration is detected by the piezoelectric vibration sensor 15, it is determined that the power receiver 20 may exist on the surface of the power transmitter 10, and the microcomputer is activated. Then, power transmission is started intermittently from the power transmitter 10, and the presence or absence of the power receiver 20 and the position thereof are reliably confirmed.

  In the standby mode of the conventional wireless power transmission device, intermittent power transmission from the power transmitter must be continued at all times. Therefore, in order to suppress standby power, it is necessary to shorten the on-period ratio of intermittent power transmission as much as possible. It was. In contrast, in the present embodiment, the intermittent power transmission from the power transmitter 10 is performed only within a predetermined time after vibration detection. Therefore, power consumption can be suppressed even if the ratio of the on period of intermittent power transmission is increased, and options for a method of detecting the power receiver 20 can be increased, thereby increasing design flexibility.

  For example, according to the industry standard of wireless power transmission, when the power receiver 20 receives power from the power transmitter 10 continuously for about 100 ms, the rectified voltage or power data of the power receiver 20 (generally, (Referred to as signal strength) must be communicated to the transmitter 10. Based on this, it is possible to determine whether the power receiving coil 21 is in the vicinity of the power transmitting coil 11 or whether the alignment is appropriate.

  Specifically, when vibration is detected by the piezoelectric vibration sensor 15, the microcomputer starts from the sleep state. Then, while transmitting intermittent power of 100 ms on / 200 ms off from the power transmitter 10, it is confirmed whether the power receiving coil 21 is close to the power transmitting coil 11. Once the power transmitter 10 receives the signal strength from the power receiver 20, it can be seen that the power receiving coil 21 is close to the power transmitting coil 11. Furthermore, when the signal strength is greater than or equal to a certain threshold value, it is determined that the alignment of the power transmission coil 11 and the power reception coil 21 has been completed. If the signal strength cannot be received within a predetermined time after vibration detection, it is determined that there is no power receiver 20 in the vicinity of the power transmitter 10, the intermittent power transmission is stopped, and the microcomputer returns to a sleep state waiting for vibration.

  By providing the piezoelectric vibration sensor 15 in the power transmitter 10 of the wireless power transmission device, vibration generated when the power receiver 20 such as a portable device is placed on the power transmitter 10 can be detected. Thereby, since the presence or absence of the power receiver 20 can always be checked without intermittently transmitting power from the power transmitter 10 in the standby state, standby power can be greatly reduced.

  In the present embodiment, the piezoelectric vibration sensor 15 is used to detect vibration applied to the power transmitter 10, but any vibration sensor may be used as long as vibration can be detected. Other vibration sensors such as conductive rubber, silicon piezoresistive type, eddy current type, capacitance type, and optical type may be used.

  Next, a block diagram of a modification of the wireless power transmission device of the present invention is shown in FIG. In addition, the same code | symbol is attached | subjected to the site | part which has the same function as embodiment mentioned above, and description is abbreviate | omitted.

  In the above-described embodiment, the piezoelectric vibration sensor 15 is used as the vibration sensor. However, the power transmitter 10 ′ according to the present modification uses the piezoelectric buzzer 17 instead of the piezoelectric vibration sensor 15. The operation of the piezoelectric buzzer 17 is controlled by the control circuit 14. A buffer circuit 18 is provided between the control circuit 14 and the piezoelectric buzzer 17. The control signal supplied from the control circuit 14 is supplied to the non-inverting input terminal of the operational amplifier OP2 in the buffer circuit 18. The inverting input terminal of the operational amplifier OP2 is connected to the output terminal. The signal output from the operational amplifier OP2 is supplied to the piezoelectric buzzer 17.

  In the wireless power transmission device, various state information such as detection of the power receiver 20, displacement, end of alignment, charging, completion of charging, and occurrence of an error is generally displayed with light such as an LED. Thereby, a charging condition etc. are clearly shown to a user. However, it is more intuitive and convenient to use the piezoelectric buzzer 17 in addition to the LED to inform the user of the state information as described above by light and voice.

  The basic structure of the piezoelectric buzzer 17 is basically a unimorph structure in which a circular metal plate and a piezoelectric ceramic plate are bonded together. When a pulse signal is applied to the piezoelectric buzzer 17, bending vibration is excited in the circular unimorph and sound is generated. Conversely, when vibration is applied to the piezoelectric buzzer 17, a voltage signal is generated due to the piezoelectric effect, so that the piezoelectric buzzer 17 can function as a vibration sensor in principle.

  When sound is generated from the piezoelectric buzzer 17, a PWM drive signal is supplied from the control circuit 14 to the piezoelectric buzzer 17 via the buffer circuit 18. Then, the piezoelectric buzzer 17 operates as a sounding body. On the other hand, when the piezoelectric buzzer 17 receives vibration, an electric charge (voltage signal) is generated and supplied to the control circuit 14 via the amplifier circuit 16. Thus, the piezoelectric buzzer 17 can also operate as a vibration sensor. Similarly to the embodiment described above, the power consumption can be reduced by activating the control circuit 14 (microcomputer) when the piezoelectric buzzer 17 detects vibration.

  When the piezoelectric buzzer 17 is used for vibration detection and voice notification, when the piezoelectric buzzer 17 and the PWM drive circuit in the control circuit 14 are directly connected, the weak charge generated in the piezoelectric buzzer 17 due to vibration is absorbed by the PWM drive circuit. Sometimes. As described above, by driving the piezoelectric buzzer 17 via the buffer circuit 18, it is possible to prevent charge absorption and to prevent a decrease in sensitivity when the piezoelectric buzzer 17 operates as a vibration sensor. The sensitivity when the piezoelectric buzzer 17 operates as a vibration sensor varies greatly depending on the type of buffer amplifier. In order to prevent a decrease in sensitivity, it is desirable to reduce the output capacity of the operational amplifier OP2 used in the buffer circuit 18.

  As described above, by using the vibration sensor for detection of the power receiver 20, extremely low standby power can be realized. In addition, it is possible to use a power receiver detection unit that temporarily consumes a large amount of power while suppressing standby power, thereby improving the design flexibility of the power transmitter. In addition, when the power transmitter is provided with a piezoelectric buzzer for voice notification, the piezoelectric buzzer can be used as a vibration sensor, and the above-described function can be realized at low cost.

  Note that power may be supplied in a non-contact manner using a technique such as magnetic field resonance or electric field coupling instead of supplying power from the power transmitter to the power receiver by electromagnetic induction. Further, the method for detecting the presence or absence and the position of the power receiver is merely an example, and other methods may be used. The present invention can be modified as appropriate without departing from the technical idea.

DESCRIPTION OF SYMBOLS 10 Power transmitter 11 Power transmission coil 12 Drive circuit 13 Detection means 14 Control circuit 15 Piezoelectric vibration sensor 16 Amplifier circuit 17 Piezoelectric buzzer 18 Buffer circuit 20 Power receiver 21 Power reception coil 31 Metal plate 32 Piezoelectric material 33 Fixing member 34 Printed circuit board

Claims (5)

A wireless power transmission device that performs non-contact power transmission from a power transmitter to a power receiver,
The power transmitter includes a detection unit that detects at least one of the presence and position of the power receiver in a range in which power transmission is possible, a control circuit that controls the detection unit, and a vibration sensor that detects vibration.
A wireless power transmission device that activates the control circuit when the vibration sensor detects vibration.   2. The wireless power transmission device according to claim 1, wherein the operation of the control circuit is stopped when at least one of the presence and the position of the power receiver cannot be detected within a predetermined time after the control circuit is activated.   An amplification circuit for amplifying the output of the vibration sensor is further provided, the amplification circuit amplifies only an AC signal supplied from the vibration sensor, and activates the control circuit based on the output signal of the amplification circuit. The wireless power transmission device according to 1 or 2. The vibration sensor is a piezoelectric buzzer,
The wireless power transmission device according to any one of claims 1 to 3, wherein the piezoelectric buzzer notifies state information of the power receiver. The wireless power transmission device according to claim 4, wherein a buffer circuit is provided between the piezoelectric buzzer and the control circuit.

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