KR101785637B1 - Wireless power receiving apparatus controlling output voltage by changing resonant frequency - Google Patents

Wireless power receiving apparatus controlling output voltage by changing resonant frequency Download PDF

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Publication number
KR101785637B1
KR101785637B1 KR1020160007255A KR20160007255A KR101785637B1 KR 101785637 B1 KR101785637 B1 KR 101785637B1 KR 1020160007255 A KR1020160007255 A KR 1020160007255A KR 20160007255 A KR20160007255 A KR 20160007255A KR 101785637 B1 KR101785637 B1 KR 101785637B1
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KR
South Korea
Prior art keywords
load
circuit
capacitor
switch
power receiving
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KR1020160007255A
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Korean (ko)
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KR20170087352A (en
Inventor
박시홍
임창종
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단국대학교 산학협력단
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J50/00—Circuit arrangements or systems for wireless supply or distribution of electric power
    • H02J50/10—Circuit arrangements or systems for wireless supply or distribution of electric power using inductive coupling
    • H02J50/12—Circuit arrangements or systems for wireless supply or distribution of electric power using inductive coupling of the resonant type
    • H02J7/025—
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/02—Conversion of ac power input into dc power output without possibility of reversal
    • H02M7/04—Conversion of ac power input into dc power output without possibility of reversal by static converters
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H7/00—Multiple-port networks comprising only passive electrical elements as network components
    • H03H7/01—Frequency selective two-port networks
    • H03H7/0115—Frequency selective two-port networks comprising only inductors and capacitors
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H7/00—Multiple-port networks comprising only passive electrical elements as network components
    • H03H7/38—Impedance-matching networks
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03K—PULSE TECHNIQUE
    • H03K17/00—Electronic switching or gating, i.e. not by contact-making and –breaking
    • H03K17/51—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used
    • H03K17/56—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used by the use, as active elements, of semiconductor devices
    • H03K17/687—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used by the use, as active elements, of semiconductor devices the devices being field-effect transistors

Abstract

A power receiving apparatus according to an embodiment of the present invention includes a resonance circuit that receives electric power from a power transmitting apparatus by using a resonance phenomenon to generate an alternating current, And when the magnitude of the impedance of the load is out of a predetermined range, the resonance frequency of the resonance circuit is changed And a frequency control circuit for controlling the frequency.

Description

TECHNICAL FIELD [0001] The present invention relates to a wireless power receiving apparatus for controlling an output voltage through resonance frequency conversion. [0002]

The present invention relates to a wireless power receiving apparatus for controlling an output voltage by changing a resonant frequency of a resonant circuit that receives power from a power transmitting apparatus through resonance.

Recently, there has been an increasing interest in the technology of transmitting power wirelessly. In fact, many practical applications are being developed that can wirelessly charge various types of mobile devices, such as smartphones, tablet PCs, and MP3 players, to reflect this trend. One of these recent wireless power transmission technologies is one that utilizes the resonance characteristics of RF components.

A wireless power transmission system using resonance characteristics includes a power transmitting device for supplying power and a power receiving device for receiving power. Such a power transmitting apparatus and a power receiving apparatus include an LC circuit composed of an inductor and a capacitor, and such an LC circuit has a resonance frequency inherent to circuit characteristics. When the resonance frequency is equal between the power transmitting apparatus and the power receiving apparatus, the current of the power transmitting apparatus induces the current of the power receiving apparatus by the resonance phenomenon, and power transmission and reception are performed.

One of the important factors in implementing such a wireless power transmission system is to supply a voltage within a certain range to the load. When the power receiving apparatus receives power from the power transmitting apparatus and supplies the power to the load, if an overvoltage is applied to the load, the load or elements constituting the power receiving apparatus may be damaged. In order to prevent such a phenomenon, a power receiving apparatus generally includes a circuit for controlling a voltage applied to a load.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram illustrating a conventional wireless power transmission system. FIG. 1, the wireless power transmission system 1 may include a power receiving apparatus 2 and a power transmitting apparatus 3, and the power receiving apparatus 2 may include a resonant circuit 4, a rectifying circuit 5 ), An overvoltage protection circuit (6), and an output voltage regulation circuit (7). The resonance circuit 4 receiving the electric power through the resonance from the power transmission device 3 generates an alternating current and the generated alternating current is inputted to the rectifying circuit 5 and rectified, .

There may occur a situation in which the impedance between the output terminals of the rectifying circuit 5 increases abruptly such that the load 8 is suddenly removed and the output terminals of the rectifying circuit 5 are opened have. At this time, the current supplied through the resonance circuit 4 is continuously accumulated in the rectification capacitor C1, so that the voltage of the output terminal of the rectifying circuit 5 greatly increases.

In order to prevent such abrupt increase of the voltage, the prior art wireless power transmission system 1 is equipped with an overvoltage protection circuit 6. The overvoltage protection circuit 6 may include a control block 9 for measuring a voltage applied to the load and generating a control signal when the voltage exceeds a predetermined value.

1, the resonance circuit 4 includes an inductor L1, a first capacitor C1, a second capacitor C2, a third capacitor C3, a fourth capacitor C4, a first switch S1 And a second switch S2. The control block 9 measures the voltage applied to the load and switches the first switch S1 and the second switch S2 from the OFF state to the ON state when the voltage exceeds the preset value do. Then, the current generated in the resonance circuit 4 flows through the inductor L1, the first capacitor C1, the third capacitor C3, the first switch S1, and the second switch S2, the fourth capacitor C4, the second capacitor C2, and the inductor L1 in this order. Therefore, the current is not transferred to the load 8, so that the excessive voltage rise on the side of the load 8 can be prevented.

However, this method only prevents the generated current from being transmitted to the load 8, and does not interrupt the generation of the current itself. Therefore, the current continues to exist in the resonance circuit 4, and energy loss due to the flow of current occurs in the resonance circuit. In addition, the devices in the current path may be stressed by the current, which may adversely affect the lifetime of the device.

Since the output voltage of the power receiving apparatus 2 according to the prior art can vary greatly depending on the variation of the load 8, the output voltage adjusting circuit 12, as an additional component for adjusting the voltage applied to the load 8, (7). The output voltage adjusting circuit 7 prevents the voltage rise due to some current that may leak to the rectifying circuit 5 side in addition to the current flowing through the closed circuit by the frequency control circuit 6, As shown in FIG. This output voltage regulation circuit 7 can be generally implemented through a DC-DC converter (DC-DC converter). The presence of such an output voltage adjusting circuit 7 may adversely affect the efficiency of the power receiving apparatus 2. [ In addition, the disadvantage that the size of the circuit becomes large due to the relatively large-sized device such as the DC-DC converter, which is disadvantageous for downsizing and integration of the power receiving apparatus 2 also becomes a problem.

Korean Unexamined Patent Publication No. 10-2014-0144874 (published April 5, 2014)

SUMMARY OF THE INVENTION It is an object of the present invention to provide a wireless power transmission apparatus capable of more effectively protecting a circuit and increasing energy efficiency by blocking current generation of a power transmission apparatus in a situation where an overvoltage is applied to a load. Another object of the present invention is to provide a wireless power transmission apparatus that can be downsized and integrated by controlling an output voltage according to a variation of a load without a separate output voltage adjustment circuit such as a DC-DC converter.

It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. will be.

A power receiving apparatus according to an embodiment of the present invention includes a resonance circuit that receives electric power from a power transmitting apparatus by using a resonance phenomenon to generate an alternating current, And when the magnitude of the impedance of the load is out of a predetermined range, the resonance frequency of the resonance circuit is changed And a frequency control circuit for controlling the frequency.

In addition, the frequency control circuit can calculate the magnitude of the impedance of the load using the voltage applied to the load.

The frequency control circuit may include a control block and a measurement resistor connected in parallel to the load, wherein the measurement resistor has a first resistor and a second resistor connected in series and having a size greater than or equal to a predetermined value, Wherein the control block calculates a voltage across the load by measuring a potential of a node between the first resistor and the second resistor, and the control block calculates a resonance frequency of the resonance circuit based on the voltage across the load, The frequency can be changed.

In addition, the rectifying circuit may include a rectifying capacitor connected in parallel to the load.

In addition, the frequency control circuit can change the resonant frequency of the resonant circuit by changing the equivalent capacitance value of the resonant circuit.

In addition, both ends of the inductor may be electrically connected to one end of the inductor having a lower potential than the other end when the current flows through the load by the rectifying circuit at both ends of the load, through the switch, When the voltage applied to the load reaches the upper limit of the preset range, the switch is turned on. When the voltage applied to the load reaches the lower limit of the preset range, the switch is turned off You can switch.

The switch may be a field effect transistor, and the frequency control circuit applies a control signal to a gate of the field effect transistor to turn ON / OFF the field effect transistor Can be controlled.

In addition, the rectifier circuit may include a bridge rectifier circuit having a plurality of diodes.

All or some of the diodes of the bridge rectifier circuit may be implemented through a pair of field effect transistors connected in a cross-coupled fashion.

In addition, all or part of the diodes of the bridge rectifier circuit may be implemented through a field effect transistor having a gate and a source shorted to each other and having an intrinsic diode.

The resonant circuit may include a first inductor, a first capacitor, a second capacitor, a third capacitor, and a fourth capacitor, wherein the first capacitor and the second capacitor are connected in series to each other, The third capacitor and the fourth capacitor may be connected in series to each other and may be connected to the other end of the first inductor, and a node between the first capacitor and the second capacitor and a node between the third capacitor and the fourth capacitor, The node between the four capacitors can be connected to one end of the node having a lower potential than the other end through a switch when a current flows through the load by the rectifying circuit at both ends of the load, When the voltage reaches the upper limit of the predetermined range, switches the switch to the ON state, After reaching the lower limit of the predetermined range may switch the switch to an off (OFF) state.

The switch may be a field effect transistor, and the frequency control circuit applies a control signal to a gate of the field effect transistor to turn ON / OFF the field effect transistor Can be controlled.

According to an embodiment of the present invention, when the size of the load connected to the wireless power receiving apparatus is out of a predetermined range, the generation of the resonant current can be blocked by changing the resonant frequency of the resonant circuit included in the wireless power receiving apparatus. This prevents loss of energy due to the resonance current to achieve high energy efficiency and also prevents the lifetime of the device from being reduced. By controlling the voltage output to the load through changing the resonance frequency, The wireless power receiving apparatus can be realized more simply. Further, according to an embodiment of the present invention, the size of elements constituting a wireless power receiving apparatus is wider and the width of element selection is wider as compared with the prior art, so that the apparatus can be miniaturized and integrated, do.

1 is a circuit diagram of a conventional wireless power transmission system.
2 is a diagram illustrating a configuration of a wireless power transmission system according to an embodiment of the present invention.
3 is a circuit diagram of a wireless power transmission system according to an embodiment of the present invention.
4A and 4B are diagrams for comparing the current in the resonant circuit according to the prior art and the current in the resonant circuit according to the embodiment of the present invention.
5 is a circuit diagram of a wireless power transmission system to which a field effect transistor is applied as a switch of a resonant circuit, according to an embodiment of the present invention.
6 is a circuit diagram of a wireless power transmission system including a bridge rectifier circuit according to an embodiment of the present invention in which a bridge rectifier circuit is applied with a cross-occlusion scheme.
7 is a circuit diagram of a wireless power transmission system using a field effect transistor including a bridge rectifier circuit and a built-in diode in a bridge rectifier circuit, in accordance with an embodiment of the present invention.
8 is a circuit diagram of a wireless power transmission system capable of selectively converting a resonant frequency according to an embodiment of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention and the manner of achieving them will become apparent with reference to the embodiments described in detail below with reference to the accompanying drawings. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. To fully disclose the scope of the invention to those skilled in the art, and the invention is only defined by the scope of the claims.

In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear. The following terms are defined in consideration of the functions in the embodiments of the present invention, which may vary depending on the intention of the user, the intention or the custom of the operator. Therefore, the definition should be based on the contents throughout this specification.

2 is a diagram illustrating a configuration of a wireless power transmission system according to an embodiment of the present invention. The wireless power transmission system 10 of FIG. 2 may include a power receiving device 100 and a power transmitting device 101. The power receiving apparatus 100 includes a resonant circuit 110, a rectifying circuit 120, and a voltage adjusting circuit 130 for transmitting the power transmitted from the power transmitting apparatus 101 to the load 140 . However, since the wireless power transmission system 10 of FIG. 2 is only an embodiment of the present invention, the concept of the present invention is not limited to FIG.

Hereinafter, the operation of the wireless power transmission system 10 according to an embodiment of the present invention will be described with reference to FIG. The resonance circuit 110 may receive electric power from the power transmission device 101 using a resonance phenomenon to generate an alternating current. The power transmission device 101 and the resonance circuit 110 may include one or more inductors and one or more capacitors for power transmission using resonance and may include a power transmission device 101 that is not physically connected, Wireless power transmission is achieved through power transfer through resonant frequency matching of the power supply 110.

The rectifying circuit 120 can rectify the alternating current generated by the resonant circuit 110 to convert it into a direct current and output the converted current to the load 140. [ Accordingly, the resonance circuit 110 can be connected to the input terminal of the rectifier circuit 120 and the load 140 can be connected to the output terminal of the rectifier circuit 120. The current output from the rectifier circuit 120 flows to the power transmission device 101 are consumed.

The frequency control circuit 130 can adjust the output voltage by changing the resonance frequency in accordance with the variation of the load 140. [ In general, the load 140 can be referred to as no load, light load, overload, etc., depending on the magnitude (referred to as " load size ") of the current required by the load under constant voltage driving. No load refers to a state in which a load is removed so that both ends of the load are opened and no current flows in the lower end (that is, the impedance of the load is infinite), and a state in which the current hardly flows close to the no load (Ie, the impedance of the load is large enough to be close to infinity), and the overload is a state in which the load is large (ie, the impedance of the load is very small) in which excessive current flows due to excessive load or light load, . When the load 140 is reduced in size and becomes unloaded or lightly loaded, for example, when the load 140 is suddenly removed, both ends of the load 140, that is, the voltage at the output terminal of the rectifying circuit 120, As described above. In this case, the frequency control circuit 130 can prevent the resonance from occurring by changing the resonance frequency of the resonance circuit 110, thereby blocking the generation of the current in the resonance circuit 110. In addition, when it is determined that the load 140 is normalized again, the frequency control circuit 130 can restore the resonance frequency of the resonance circuit 110 to restore the resonance frequency.

Specifically, when the size of the load 140 is out of the predetermined range, for example, the frequency control circuit 130 becomes smaller than a predetermined level and becomes a no-load or light load state (that is, when the magnitude of the impedance of the load is a certain level Or more), the resonance frequency of the resonance circuit 110 can be changed. The change in the resonance frequency can be achieved by changing the equivalent capacitance value of the resonance circuit 110, for example. Here, the size of the load 140 can be calculated based on both ends of the load 140, that is, the voltage of the output terminal of the rectifying circuit 120. Through the resonance current generation interruption by the resonance frequency conversion, it is possible to prevent the energy loss and the life of the device from being reduced.

3 is a circuit diagram of a wireless power transmission system according to an embodiment of the present invention. The wireless power transmission system 20 of FIG. 3 embodies the wireless power transmission system 10 of FIG. 2, represented in block diagram form. The wireless power transmission system 20 of FIG. 3 may include a power receiving device 200 and a power transmitting device 201. The power receiving apparatus 200 includes a resonant circuit 210, a rectifying circuit 220 and a voltage adjusting circuit 230 for transmitting the power transmitted from the power transmitting apparatus 201 to the load 240 . However, the wireless power transmission system 20 of FIG. 3 is only an embodiment of the present invention, and therefore, the concept of the present invention is not limited to FIG. 3, and description overlapping with FIG. 2 will be omitted below. .

The resonant circuit 210 may include an inductor L21 and capacitors C21 and C22. The resonance frequency of the resonance circuit 210 is determined according to the size of the inductor L21 and the capacitors C21 and C22 and thus the resonance frequency is changed by adjusting the size of the inductor L21 and the capacitors C21 and C22 .

The rectifier circuit 220 may be implemented in various forms, but may include a bridge rectifier circuit having a plurality of diodes D21, D22, D23, and D24 as a representative example. A rectifying capacitor C23 may be connected between both ends of the output side of the bridge rectifying circuit. Due to the operation of the bridge rectifying circuit and the rectification capacitor C23, a DC current is output from the output terminal of the rectifying circuit 220. Since the detailed operation principle of such a rectifying circuit 220 is obvious to a person skilled in the art, The detailed description will be omitted. The load 240 may be connected between the output ends of the rectifying circuit 220, that is, in parallel with the rectifying capacitor C23. As shown in FIG. 3, one end of the load 240, .

The frequency control circuit 230 may include a measurement resistor and a control block 231 connected in parallel with the load 240. In addition, the frequency control circuit 230 may include switches S21 and S22. 3, the switch S21 may be connected between one end of the inductor L21 and ground, and the switch S22 may be connected between the other end of the inductor L21 and the ground.

First, the resistance for measurement may be realized by two resistors R21 and R22 having a size larger than a predetermined value and connected to each other in series. The control block 231 can also calculate the voltage across the load 240 by measuring the potential of the node between the two resistors R21 and R22. That is, the two resistors R21 and R22 serve as a voltage divider. Since the two resistors R21 and R22 are used for the purpose of voltage measurement and it is not preferable that the current flows to the two resistors R21 and R22, the resistance values of the two resistors R21 and R22 are sufficiently large May be required.

The control block 231 switches the switches S21 and S22 to the ON state when the voltage applied to the load 240 reaches the upper limit of the predetermined range and when the voltage applied to the load 240 reaches the predetermined range The switches S21 and S22 can be switched to the OFF state. Hereinafter, the operation of the control block 231 will be described in more detail.

When the voltage applied to the load 240 is within the predetermined range, the switches S21 and S22 are basically set to the OFF state, and accordingly, the resonance circuit 210 can generate the alternating current normally. However, if the load 240 suddenly becomes an unloaded state or a light load state and the voltage applied to the load 240 also increases to reach the upper limit of the preset range, the control block 231 controls the switch S21, and S22 can be turned on. In this case, since both ends of the inductor L21 are grounded and electrically isolated from the other configurations of the power receiving apparatus 200, the inductors L21 and C22 are equivalent to the inductors L21 and C22, The resonance frequency does not fluctuate due to a change in the capacitance, so that the generation of the current is cut off, and the voltage across the load 240 can be stabilized within a predetermined range.

On the other hand, when the load 240 is normalized, the charge stored in the rectification capacitor C23 is discharged through the load 240, so that the voltage across the load 240 is reduced. When the voltage across the load 240 continues to decrease to reach the lower limit of the predetermined range, the control block 231 may cause the switches S21 and S22 to be turned off again, . A control block 231 for controlling this series of processes may be implemented including a comparator.

As described above, according to the present embodiment, the power receiving apparatus 200 can be safely protected even when the load 240 enters an unstable state with no load or light load. Particularly, since a method of interrupting the generation of current is adopted, there is no problem that causes energy loss and device life reduction due to existence of current even when current is unnecessary.

4A and 4B are diagrams for comparing the current in the resonant circuit according to the prior art and the current in the resonant circuit according to the embodiment of the present invention. 4A, it can be seen that, in the case of the resonance circuit 4 of the prior art, the magnitude of the current generated even in the no-load state hardly changes. However, referring to FIG. 4B, in the case of the resonant circuit 210 according to the embodiment of the present invention, the magnitude of the current generated in the no-load state is greatly reduced as compared with the steady state. Therefore, according to an embodiment of the present invention, it is possible to prevent an energy loss and a device life reduction by blocking current generation unlike the prior art.

According to the present embodiment, the frequency control circuit 230 can be implemented by simple elements such as a resistor, a capacitor, and a comparator to stabilize the voltage across the load 240, so that a bulky additional element such as a DC- . Therefore, according to the present embodiment, the configuration can be simplified, the circuit can be downsized and integrated, and power consumption by additional devices can be reduced, thereby improving the efficiency of the device.

5 is a circuit diagram of a wireless power transmission system to which a field effect transistor is applied as a switch of a resonant circuit, according to an embodiment of the present invention. The wireless power transmission system 30 of FIG. 5 may include a power receiving device 300 and a power transmitting device 301. The power receiving apparatus 300 includes a resonant circuit 310, a rectifying circuit 320, and a voltage adjusting circuit 330 for transmitting the power transmitted from the power transmitting apparatus 301 to the load 340 . However, since the wireless power transmission system 30 of FIG. 5 is only an embodiment of the present invention, the concept of the present invention is not limited to FIG. 5, and a description overlapping with FIGS. Can be omitted.

Referring to FIG. 5, it can be seen that the transistors Q31 and Q32 can be used as a switch for grounding both ends of the inductor L31. Such a transistor may be, for example, a field effect transistor. The frequency control circuit 330 can control ON and OFF of the transistors Q31 and Q32 by applying control signals to the gates of the transistors Q31 and Q32. By using the transistor as a switch in this way, the integration and miniaturization of the wireless power transmission system 30 including the power reception device 300 can be achieved.

6 is a circuit diagram of a wireless power transmission system including a bridge rectifier circuit according to an embodiment of the present invention in which a bridge rectifier circuit is applied with a cross-occlusion scheme. The wireless power transmission system 40 of FIG. 6 may include a power receiving device 400 and a power transmitting device 401. The power receiving apparatus 400 includes a resonant circuit 410, a rectifying circuit 420 and a voltage adjusting circuit 430 for transmitting the power transmitted from the power transmitting apparatus 401 to the load 440 . However, since the wireless power transmission system 40 of FIG. 6 is only an embodiment of the present invention, the concept of the present invention is not limited to FIG. 6, and a description overlapping with FIGS. Can be omitted.

According to this embodiment, all or a part of the diodes of the bridge rectifier circuit included in the rectifier circuit 420 can be implemented through a pair of field effect transistors connected in a cross-coupled manner. Referring to FIG. 6, it can be seen that two diodes at the lower end of the diode of the bridge rectifier circuit are implemented as a pair of field effect transistors Q41 and Q42 connected in a cross-coupled manner. More specifically, it can be seen that the gates of the transistors Q41 and Q42 are electrically connected to each other's drains. When the diodes are replaced with the transistors Q41 and Q42 connected in a cross-over manner, the efficiency of the wireless power transmission system 40 is increased due to the characteristics of the transistors Q41 and Q42 having lower voltage drop characteristics than the diode .

7 is a circuit diagram of a wireless power transmission system using a field effect transistor including a bridge rectifier circuit and a built-in diode in a bridge rectifier circuit, in accordance with an embodiment of the present invention. The wireless power transmission system 50 of FIG. 7 may include a power receiving apparatus 500 and a power transmitting apparatus 501. The power receiving apparatus 500 includes a resonant circuit 510, a rectifying circuit 520 and a voltage adjusting circuit 530 for transmitting the power transmitted from the power transmitting apparatus 501 to the load 540 . However, since the wireless power transmission system 50 of FIG. 7 is only an embodiment of the present invention, the concept of the present invention is not limited to FIG. 7, and a description overlapping with FIGS. Can be omitted.

According to the present embodiment, all or a part of the diodes of the bridge rectifier circuit included in the rectifier circuit 520 are implemented through a field effect transistor having a gate and a source shorted to each other and having an intrinsic diode . Referring to FIG. 7, two diodes at the upper end of the diode of the bridge rectifier circuit are implemented with field effect transistors Q51 and Q52 having gates and sources shorted to each other and having intrinsic diodes Can be confirmed. In this case, since the gate and the source are short-circuited, the transistors Q51 and Q52 are cut off and do not pass the current, and therefore, can be thought of as substantially the same as those connected in parallel with the transistors Q51 and Q52. . As a result, the transistors Q51 and Q52 can perform a rectifying operation by operating as a diode. When the diode is replaced with a field effect transistor (Q51, Q52) having a gate and a source shorted together and having an intrinsic diode, the diode is advantageous in downsizing and integration compared to the case of using a diode, The amount is also reduced, which is advantageous in terms of efficiency.

8 is a circuit diagram of a wireless power transmission system capable of selectively converting a resonant frequency according to an embodiment of the present invention. The wireless power transmission system 60 of FIG. 6 may include a power receiving device 600 and a power transmitting device 601. The power receiving apparatus 600 includes a resonant circuit 610, a rectifying circuit 620 and a voltage adjusting circuit 630 for transmitting the power transmitted from the power transmitting apparatus 601 to the load 640 . However, since the wireless power transmission system 60 of FIG. 8 is only an embodiment of the present invention, the concept of the present invention is not limited to FIG. 8, and a description overlapping with FIGS. Can be omitted.

Referring to FIG. 8, the resonant circuit 610 may include an inductor L61 and capacitors C61, C62, C63, and C64. The capacitor C61 and the capacitor C63 may be connected in series to one end of the inductor L61 and the capacitor C62 and the capacitor C63 may be connected in series to each other to be connected to the other end of the inductor L61 . The node between the capacitor C61 and the capacitor C63 and the node between the capacitor C62 and the capacitor C64 may be connected through switches, e.g., field effect transistors Q61 and Q62, respectively.

Comparing the wireless power transmission system 60 of this embodiment with the wireless power transmission system 30 of the embodiment of FIG. 3, the inductor L61 is connected to the inductor L21, the capacitors C63 and C64 are connected to the capacitors C21 and C22 , And transistors Q61 and Q62 may correspond to switches S21 and S22. That is, the wireless power transmission system 60 of this embodiment is basically the same as the wireless power transmission system 30 of FIG. 3 except that a capacitor C61 and a capacitor C62 are added to both ends of the inductor.

According to the wireless power transmission system 60 of the present embodiment, there is a voltage dispersion effect by the addition of the capacitors C61 and C62. Accordingly, the degree of the resonance frequency conversion becomes smaller than that of the wireless power transmission system 30 of FIG. 3, but the voltage across the transistors Q61 and Q62 becomes smaller than the voltage across the switches S21 and S22. In general, in a system in which resonance occurs due to resonance frequency matching, it is possible to prevent resonance from occurring substantially even if the resonance frequency is shifted only by a certain threshold value. That is, if the degree of resonance frequency conversion exceeds a certain threshold, even if the degree of conversion is increased, the effect of resonance blocking is substantially the same. Therefore, according to the present embodiment, by setting the values of the capacitors C61, C62, C63, and C64 appropriately and setting the degree of resonance frequency conversion to a level sufficient for resonance blocking, by reducing the voltage across the transistors Q61 and Q62 It is possible to implement the wireless power transmission system 60 with a transistor having a low breakdown voltage.

The above description is merely illustrative of the technical idea of the present invention, and various modifications and changes may be made by those skilled in the art without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present invention are intended to illustrate rather than limit the scope of the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments. The scope of protection of the present invention should be construed according to the following claims, and all technical ideas within the scope of equivalents thereof should be construed as falling within the scope of the present invention.

100: Power receiving device
101: Power transmitting device
110: resonant circuit
120: rectifying circuit
130: Frequency control circuit
140: Load

Claims (12)

A power receiving apparatus comprising:
A resonance circuit that receives electric power from a power transmission device using a resonance phenomenon to generate an alternating current;
A rectifying circuit rectifying the alternating current and outputting the alternating current to a load connected to the power receiving device; And
By calculating the magnitude of the impedance of the load when the rectified current is supplied to the load and by changing the resonance frequency of the resonance circuit when the magnitude of the impedance of the calculated load is out of a predetermined range, And a frequency control circuit for interrupting the generation of the alternating current in the resonant circuit by the power transmission and the power transmission,
Wherein the frequency control circuit changes a resonant frequency of the resonant circuit by changing an equivalent capacitance value of the resonant circuit,
Wherein the rectifying circuit includes a rectifying capacitor connected in parallel to the load,
Wherein the resonant circuit includes an inductor for generating the alternating current,
Both ends of the inductor are respectively connected through one end having a lower potential than the other end and the first switch and the second switch when a current flows through the load,
Wherein the frequency control circuit switches the first switch and the second switch to the ON state when the voltage applied to the load reaches the upper limit of the predetermined range, The first switch and the second switch are switched to the OFF state
Power receiving device. The method according to claim 1,
The frequency control circuit calculates the magnitude of the impedance of the load using the voltage across the load
Power receiving device. 3. The method of claim 2,
The frequency control circuit
Control block; And
And a measurement resistor connected in parallel with the load,
Wherein the measurement resistor includes a first resistor and a second resistor having a size greater than a predetermined value and connected in series to each other,
Wherein the control block calculates a voltage across the load by measuring a potential at a node between the first resistor and the second resistor and changes the resonant frequency of the resonant circuit based on the voltage across the load
Power receiving device. delete delete delete delete The method according to claim 1,
The rectifier circuit includes a bridge rectifier circuit having a plurality of diodes
Power receiving device. 9. The method of claim 8,
All or some of the diodes of the bridge rectifier circuit are implemented through a pair of field effect transistors connected in a cross coupled fashion
Power receiving device. 9. The method of claim 8,
All or part of the diodes of the bridge rectifier circuit are implemented through a field effect transistor in which the gate and the source are shorted together and have an intrinsic diode
Power receiving device. The method according to claim 1,
The resonant circuit further includes a first capacitor, a second capacitor, a third capacitor, and a fourth capacitor,
Wherein the first capacitor and the second capacitor are connected in series to each other and connected to one end of the inductor, the third capacitor and the fourth capacitor are connected in series to each other and connected to the other end of the inductor,
And a node between the first capacitor and the second capacitor and a node between the third capacitor and the fourth capacitor are connected to each other when a current flows to the load by the rectifying circuit at both ends of the load, And a second switch connected between the first switch and the second switch,
Wherein the frequency control circuit switches the first switch and the second switch to the ON state when the voltage applied to the load reaches the upper limit of the predetermined range, The first switch and the second switch are switched to the OFF state
Power receiving device. delete
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