Abstract:
Disclosed is a wireless power receiver to transfer power wirelessly received from a wireless power transmitter to a load. The wireless power receiver includes a first reception induction coil coupled with a reception resonant coil to receive AC power; a first rectifying diode to rectify the AC power received through the first reception induction coil; a second reception induction coil connected to the first reception induction coil and coupled with the reception resonant coil to receive the AC power; and a second rectifying diode to rectify the AC power received through the second reception induction coil, wherein the wireless power receiver changes a transferring path of the power provided to the load according to a polarity variation of the AC power received through the first and second reception induction coils.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit under 35 U.S.C. §119 of Korean Patent Application No. 10-2012-0027978, filed Mar. 19, 2012, which is hereby incorporated by reference in its entirety. 
       BACKGROUND 
       [0002]    The disclosure relates to a wireless power transmission technology. In more particular, the disclosure relates to a wireless power receiver and a wireless power transferring method capable of maximizing the power transmission efficiency by using resonance. 
         [0003]    A wireless power transmission or a wireless energy transfer refers to a technology of wirelessly transferring electric energy to desired devices. In the 1800&#39;s, an electric motor or a transformer employing the principle of electromagnetic induction has been extensively used and then a method for transmitting electrical energy by irradiating electromagnetic waves, such as radio waves or lasers, has been suggested. Actually, electrical toothbrushes or electrical razors, which are frequently used in daily life, are charged based on the principle of electromagnetic induction. The electromagnetic induction refers to a phenomenon in which voltage is induced so that current flows when a magnetic field is varied around a conductor. Although the commercialization of the electromagnetic induction technology has been rapidly progressed around small-size devices, the power transmission distance is short. 
         [0004]    Until now, wireless energy transmission schemes include a remote telecommunication technology based on resonance and a short wave radio frequency in addition to the electromagnetic induction. 
         [0005]    Recently, among wireless power transmitting technologies, an energy transmitting scheme employing resonance has been widely used. 
         [0006]    In a wireless power transmission system employing resonance, since an electrical signal generated between the wireless power transmitter and the wireless power receiver is wirelessly transferred through coils, a user may easily charge electronic appliances such as a portable device. 
         [0007]    However, according to the related art, there is a limitation to reduce the power loss caused while AC power is converted into DC power in the wireless power receiver that receives power using resonance. 
       BRIEF SUMMARY 
       [0008]    The disclosure provides a method capable of maximizing the efficiency of the power transmission by using resonance in a wireless power transmission technology. 
         [0009]    The disclosure provides a method capable of improving rectifying efficiency by reducing the power loss caused while AC power is converted into DC power in a wireless power receiver that receives power using resonance. 
         [0010]    The disclosure provides a method capable of reducing the cost and the size of a circuit by reducing a number of rectifying diodes that convert AC power into DC power in a wireless power receiver that receives power using resonance. 
         [0011]    According to one embodiment, there is provided a wireless power receiver to transfer power wirelessly received from a wireless power transmitter to a load. The wireless power receiver includes a first reception induction coil coupled with a reception resonant coil to receive AC power; a first rectifying diode to rectify the AC power received through the first reception induction coil; a second reception induction coil connected to the first reception induction coil and coupled with the reception resonant coil to receive the AC power; and a second rectifying diode to rectify the AC power received through the second reception induction coil, wherein the wireless power receiver changes a transferring path of the power provided to the load according to a polarity variation of the AC power received through the first and second reception induction coils, 
         [0012]    wherein either the first rectifying diode or the second rectifying diode rectify the AC power according to the polarity variation of the AC power, and 
         [0013]    wherein the first rectifying diode is turned on to transfer the power to the load when a polarity of the AC power is positive, and the second rectifying diode is turned on to transfer the power to the load when the polarity of the AC power is negative. 
         [0014]    The wireless power receiver transfers the power to the load through a first loop and a second loop. The first loop is a power transferring path extending through the first reception induction coil, the first rectifying diode and the load, and the second loop is a power transferring path extending through the second reception induction coil, the second rectifying diode and the load. 
         [0015]    One terminal of the first reception induction coil is connected to one terminal of the second reception induction coil. 
         [0016]    The first and second reception induction coils are wound in a same direction. 
         [0017]    The first rectifying diode includes a first anode connected to an opposite terminal of the first reception induction coil and a first cathode connected to the one terminal of the load, the second rectifying diode includes a second cathode connected to the first cathode and a second anode connected to an opposite terminal of the second reception induction coil, the one terminal of the first reception induction coil and the one terminal of the second reception induction coil are connected to an opposite terminal of the load, and the opposite terminal of the load is grounded. 
         [0018]    The embodiments have the following effects. 
         [0019]    First, the efficiency of the power transmission between a transmission side and a reception side can be maximized by using resonance. 
         [0020]    Second, the rectifying efficiency can be improved through the configuration of a reception side which can reduce a power loss caused while AC power is converted into DC power. 
         [0021]    Third, a number of rectifying diodes for converting AC power into DC power can be reduced, so that the cost can be reduced and the entire size of a circuit can reduced. 
         [0022]    Meanwhile, any other various effects will be directly and implicitly described below in the description of the embodiment. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]      FIG. 1  is a view showing a wireless power transmission system according to one embodiment; 
           [0024]      FIG. 2  is a circuit diagram showing an equivalent circuit diagram of a transmission induction coil according to one embodiment; 
           [0025]      FIG. 3  is a circuit diagram showing an equivalent circuit of the power source and the wireless power transmitter according to one embodiment; 
           [0026]      FIG. 4  is a circuit diagram showing an equivalent circuit of the wireless power receiver according to one embodiment; 
           [0027]      FIG. 5  is a circuit diagram showing a wireless power receiver according to one embodiment; 
           [0028]      FIG. 6  is a circuit diagram illustrating a scheme through which a wireless power receiver according to the embodiment transfers power to the load when a positive AC current of a half-cycle duration is applied to the rectifying unit; 
           [0029]      FIG. 7  is a circuit diagram illustrating a scheme through which a wireless power receiver according to the embodiment transfers power to the load when a negative AC current of a half-cycle duration is applied to the rectifying unit; 
           [0030]      FIG. 8  is a circuit diagram showing a wireless power receiver according to another embodiment; 
           [0031]      FIG. 9  is a circuit diagram illustrating a scheme through which a wireless power receiver according to another embodiment transfers power to the load when a positive AC current of a half-cycle duration is applied to the first and second reception induction coils; 
           [0032]      FIG. 10  is a circuit diagram illustrating a scheme through which a wireless power receiver according to another embodiment transfers power to the load when a negative AC current of a half-cycle duration is applied to the first and second reception induction coils; and 
           [0033]      FIG. 11  is a flowchart showing a wireless power transmitting method of a wireless power receiver according to one embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0034]    Hereinafter, the exemplary embodiments will be described with reference to accompanying drawings in detail so that those skilled in the art can easily realize the embodiments. 
         [0035]      FIG. 1  a circuit diagram showing a resonance-type wireless power transmission system  1000  according to the embodiment. 
         [0036]    Referring to  FIG. 1 , the wireless power transmission system may include a power source  100 , a wireless power transmitter  200 , and a wireless power receiver  300 . 
         [0037]    The wireless power transmitter  200  may include a transmission induction coil  210  and a transmission resonant coil  220 . 
         [0038]    The wireless power receiver  300  may include a reception resonant coil  310 , a reception induction coil  320 , and a rectifying circuit  330  and a load  340 . 
         [0039]    Both terminals of the power source  100  are connected to both terminals of the transmission induction coil  210 . 
         [0040]    The transmission resonant coil  220  may be spaced apart from the transmission induction coil  210  by a predetermined distance. 
         [0041]    The reception resonant coil  310  may be spaced apart from the reception induction coil  320  by a predetermined distance. 
         [0042]    Both terminals of the reception induction coil  320  are connected to both terminals of the rectifying circuit  330 , and the load  340  is connected to both terminals of the rectifying circuit  330 . According to one embodiment, the load  340  may not be included in the wireless power receiver  300 , and may be separately configured. 
         [0043]    The power generated from the power source  100  is transmitted to the wireless power transmitter  200 . The power received in the wireless power transmitter  200  is transmitted to the wireless power receiver  300  that makes resonance with the wireless power transmitter  200  due to a resonance phenomenon, that is, has the resonance frequency the same as that of the wireless power transmitter  200 . 
         [0044]    Hereinafter, the power transmission process will be described in more detail. 
         [0045]    The power source  100  may be an AC power source for supplying AC power having a predetermined frequency. 
         [0046]    AC current flows through the transmission induction coil  210  by electric power provided from the power source  100 . If the AC current flows through the transmission induction coil  210 , the AC current is induced to the transmission resonant coil  220  physically spaced apart from the transmission induction coil  210  due to the electromagnetic induction. Thereafter, the power received in the transmission resonant coil  220  is transmitted to the wireless power receiver  300 , which makes a resonance circuit with the wireless power transmitter  200 , through resonance. 
         [0047]    Power can be transmitted between two LC circuits, which are impedance-matched with each other, through resonance. The power transmitted through the resonance can be farther transmitted with higher efficiency when comparing with the power transmitted by the electromagnetic induction. 
         [0048]    The reception resonant coil  310  receives power from the transmission resonant coil  220  through the resonance. The AC current flows through the reception resonant coil  310  due to the received power. The power received in the reception resonant coil  310  is transmitted to the reception induction coil  320 , which is inductively coupled with the reception resonant coil  310 , due to the electromagnetic induction. The power received in the reception induction coil  320  is rectified by the rectifying circuit  330  and transmitted to the load  340 . 
         [0049]      FIG. 2  is a circuit diagram showing an equivalent circuit of the transmission induction coil  210  according to the one embodiment. 
         [0050]    As shown in  FIG. 2 , the transmission induction coil  210  may include an inductor L 1  and a capacitor C 1 , and a circuit having a desirable inductance and a desirable capacitance can be constructed by the inductor L 1  and the capacitor C 1 . 
         [0051]    The transmission induction coil  210  may be constructed as an equivalent circuit in which both terminals of the inductor L 1  are connected to both terminals of the capacitor C 1 . In other words, the transmission induction coil  210  may be constructed as an equivalent circuit in which the inductor L 1  is connected to the capacitor C 1  in parallel. 
         [0052]    The capacitor C 1  may include a variable capacitor, and impedance matching may be performed by adjusting the capacitance of the capacitor C 1 . The equivalent circuits of the transmission resonant coil  220 , the reception resonant coil  310  and the reception induction coil  320  may be the same as the equivalent circuit shown in  FIG. 2 . 
         [0053]      FIG. 3  is a circuit diagram showing an equivalent circuit of the power source  100  and the wireless power transmitter  200  according to one embodiment. 
         [0054]    As shown in  FIG. 3 , the transmission induction coil  210  and the transmission resonant coil  220  may be constructed by using inductors L 1  and L 2  and capacitors C 1  and C 2  having predetermined inductances and capacitances, respectively. 
         [0055]      FIG. 4  is a circuit diagram showing an equivalent circuit of the wireless power receiver  300  according to one embodiment. 
         [0056]    As shown in  FIG. 4 , the reception resonant coil  310  and the reception induction coil  320  may be constructed by using inductors L 3  and L 4 , and capacitors C 3  and C 4  having predetermined inductances and capacitances, respectively. 
         [0057]    The rectifying circuit  330  may include a diode D 1  and a rectifying capacitor C 5  and may output the DC power by converting the AC power into the DC power. In detail, the rectifying circuit  330  may include a rectifier and a smoothing circuit. The rectifier may include a silicon rectifier. The smoothing circuit can output smooth DC power. 
         [0058]    Although the load  340  is denoted as a DC power source of 1.3V, the load  340  may be a predetermined rechargeable battery or a device requiring the DC power. However, the DC power source of 1.3V is only one example. 
         [0059]    The configuration of the wireless power receiver  400  and the power transmission scheme of transferring power to the load  440  thereof according to the embodiment will be described with reference to  FIGS. 5 to 7 . 
         [0060]      FIG. 5  is a circuit diagram showing the wireless power receiver  400  according to another embodiment. 
         [0061]    Referring to  FIG. 5 , the wireless power receiver  400  may include a reception resonant coil  410 , a reception induction coil  420 , the rectifying unit  430 , and a load  440 . 
         [0062]    In the embodiment, the load  440  may not be included in the wireless power receiver  400 , but may be configured as a separate element. The load  440  may be an apparatus, such as a battery, into which power is charged, but the embodiment is not limited thereto. 
         [0063]    The reception resonant coil  410  receives power from a transmitting side through resonance in a non-radiation scheme. The power received in the reception resonant coil  410  may include AC power. 
         [0064]    The reception resonant coil  410  may include an inductor L 3  having a predetermined inductance value and a capacitor C 3  having a predetermined capacitance value. The inductor L 3  may be connected in series to the capacitor C 3 . 
         [0065]    The reception induction coil  420  may wirelessly receive power from the reception resonant coil  410  through electromagnetic induction. 
         [0066]    The reception induction coil  420  may include an inductor L 4  having a predetermined inductance value and a capacitor C 4  having a predetermined capacitance value. The inductor L 4  may be connected in series to the capacitor C 4 . 
         [0067]    The rectifying unit  430  may convert the AC power received in the reception induction coil  420  into DC power. 
         [0068]    The rectifying unit  430  may include a rectifier  431  and a smoothing circuit  432 . 
         [0069]    The rectifier  431  may include at least one diode. According to the embodiment, the diode may be a silicon diode, but the embodiment is not limited thereto. 
         [0070]    According to one embodiment, although the rectifier  431  may perform a rectifying function by using one diode, the rectifier  431  may preferably include at least one diode. As shown in  FIG. 5 , the rectifier  431  may include bridge diodes. The diode bridge is a circuit structure in which four diodes are connected to each other to perform a rectifying function. 
         [0071]    The rectifier  431  performs a rectifying function of converting received AC power into DC power. According to the embodiment, since the power is proportional to voltage or current, it is assumed that power, voltage, and current have the same concept for the convenience of explanation. The rectifying function refers to a function allowing current to flow only in one direction. In other words, the forward resistance of the rectifier  431  is low, and the reverse resistance of the rectifier  431  is sufficiently great, so that current may flow in one direction. 
         [0072]    The smoothing circuit  432  may output the stable DC current by removing a ripple component from the DC output power of the rectifier  431 . 
         [0073]    The smoothing circuit  432  may include a capacitor for smoothing. 
         [0074]    The current power output from the smoothing circuit  432  may be transferred to the load  440 . 
         [0075]      FIG. 6  is a circuit diagram illustrating a power transferring scheme of a wireless power receiver  400  according to the embodiment when a positive AC current of a half-cycle duration is applied to the rectifying unit  430 . 
         [0076]    Hereinafter, it is assumed in the following description that the AC current applied to the rectifying unit  430  has a sine waveform. The sine waveform is only one example. 
         [0077]    As one example, the rectifier  431  is a diode bridge including a first rectifying diode  431   a,  a second rectifying diode  431   b,  a third rectifying diode  431   c  and a fourth rectifying diode  431   d.    
         [0078]    Referring to  FIG. 6 , line ‘A’, that indicates a direction in which current flows while the positive AC current corresponding to the half-cycle duration is applied to the rectifying unit  430 , is depicted in  FIG. 6 . 
         [0079]    If the positive AC current of the half-cycle duration is applied to the rectifying unit  430 , such as the AC current direction line A, the AC current flows through the first rectifying diode  431   a,  the smoothing circuit  432 , the load  440  and the second rectifying diode  431   b.    
         [0080]    If it is assumed that the voltage of 5V is applied to the rectifying unit  430  and the voltage of 0.7V is applied to each rectifying diode of the rectifier  431 , since the voltage applied to the first and second rectifying diodes  431   a  and  431   b  is 1.4V, the voltage applied to the load  440  may be 3.6V. 
         [0081]      FIG. 7  is a circuit diagram illustrating a scheme through which a wireless power receiver  400  according to the embodiment transfers power to the load  440  when a negative AC current is applied to the rectifying unit  430 . 
         [0082]    If the negative AC current of the half-cycle duration is applied to the rectifying unit  430 , such as the AC current direction line B, the AC current flows through the third rectifying diode  431   c,  the smoothing circuit  432 , the load  440  and the fourth rectifying diode  431   d.    
         [0083]    If it is assumed that the voltage of 5V is applied to the rectifying unit  430  and the voltage of 0.7V is applied to each rectifying diode of the rectifier  431 , since the voltage applied to the third and fourth rectifying diodes  431   c  and  431   d  is 1.4V, the voltage applied to the load  440  may be 3.6V. 
         [0084]    Hereinafter, a power transferring scheme of a wireless power receiver  400  according to another embodiment will be described with reference to  FIGS. 8 to 10 . 
         [0085]      FIG. 8  is a circuit diagram showing a wireless power receiver  400  according to still another embodiment. 
         [0086]    Referring to  FIG. 8 , the wireless power receiver  400  may include a reception resonant coil  410 , a reception induction coil unit  450 , the rectifying unit  460 , and a load  440 . 
         [0087]    In the embodiment, the load  440  may not be included in the wireless power receiver  400 , but may be configured as a separate element. The load  440  may be an apparatus, such as a battery, into which power is charged, but the embodiment is not limited thereto. 
         [0088]    The reception resonant coil  410  may include an inductor L 3  having a predetermined inductance value and a capacitor C 3  having a predetermined capacitance value. The inductor L 3  may be connected in series to the capacitor C 3 . 
         [0089]    The reception induction coil unit  450  may include a first reception induction coil  451  and a second reception induction coil  452 . 
         [0090]    The first reception resonant coil  451  may include an inductor L 4  having a predetermined inductance value and a capacitor C 4  having a predetermined capacitance value. The inductor L 4  may be connected in series to the capacitor C 4 . 
         [0091]    The second reception resonant coil  452  may include an inductor L 5  having a predetermined inductance value and a capacitor C 5  having a predetermined capacitance value. The inductor L 5  may be connected in series to the capacitor C 5 . 
         [0092]    The rectifying unit  460  may include a first rectifying diode  461 , a second rectifying diode  462  and a smoothing circuit  432 . 
         [0093]    The inductor L 4  has one terminal connected to one terminal of the capacitor C 4  and the opposite terminal connected to one terminal of the inductor L 5 . 
         [0094]    The opposite terminal of the capacitor C 4  may be connected to a first anode of the first rectifying diode  461 . 
         [0095]    The inductor L 5  has one terminal connected to the opposite terminal of the inductor L 4  and the opposite terminal connected to one terminal of the capacitor C 5 . 
         [0096]    The opposite terminal of the capacitor C 5  may be connected to a second anode of the second rectifying diode  452 . 
         [0097]    A first cathode of the first rectifying diode  461  may be connected to one terminal of a smoothing capacitor C and a second cathode of the second rectifying diode  462 . 
         [0098]    The one terminal of the smoothing capacitor C may be connected to one terminal of the load  440 , the first cathode of the first rectifying diode  461  and the second cathode of the second rectifying diode  452 , and the opposite terminal of the smoothing capacitor C may be grounded. 
         [0099]    The opposite terminal of the load  440  may be connected to the opposite terminal of the inductor L 4  and one terminal of the inductor L 5 . 
         [0100]    The reception resonant coil  410  receives power from a transmitting side through resonance in a non-radiation scheme. The power received in the reception resonant coil  410  may include AC power. 
         [0101]    The reception induction coil unit  450  may transfer the power received from the reception resonant coil  410  through electromagnetic induction to the rectifying unit  460 . 
         [0102]    The first and second reception induction coil  451  and  452  may receive the power from the reception resonant coil  410  through electromagnetic induction. 
         [0103]    The rectifying unit  460  transfers the power received from the reception induction coil unit  450  to the load  440 . 
         [0104]    The first rectifying diode  461  may allow AC current to pass therethrough or may block the AC current according to a polarity of the AC current applied to the first reception induction coil  451 . Due to property of a rectifying diode, the current flows in one direction according to the polarity of the AC power. 
         [0105]    For example, when the polarity of the AC current applied is to the first rectifying diode  461  is positive, the first rectifying diode  461  allows the current to flow therethrough. In addition, when the polarity of the AC current applied to the first rectifying diode  461  is negative, the first rectifying diode  461  blocks the current. When the current is blocked due to a polarity change, the resistance value of the rectifying diode is increased so that the rectifying diode is operated as if a circuit is open. 
         [0106]    Like the first rectifying diode  461 , the second rectifying diode  462  allows AC current to flows through or be blocked according to the polarity of the AC current applied to the second reception induction coil  452 . 
         [0107]    The smoothing circuit  432  may output the stable DC current by removing a ripple component from the DC output power of the rectifying unit  460 . 
         [0108]    The smoothing circuit  432  may include the smoothing capacitor C. 
         [0109]    The DC power outputted from the smoothing circuit  432  may be transferred to the load  440 . 
         [0110]    When compared with the power loss of the wireless power receiver  400  depicted in  FIG. 5 , the power loss of the wireless power receiver  400  depicted in  FIG. 8  may be more reduced, which will be described below in detail. 
         [0111]      FIG. 9  is a circuit diagram illustrating a scheme through which a wireless power receiver  400  according to another embodiment transfers power to the load  440  when a positive AC current of a half-cycle duration is applied to the first and second reception induction coils  451  and  452 . 
         [0112]    As shown in  FIG. 9 , dots are depicted at one terminal of the inductor L 3  and one terminal of the inductor L 4 . The dots represent that the coils of the inductors L 4  and L 5  are wound in the same direction. That is, this signifies that voltages (currents) are applied to the inductors L 4  and L 5  in the same direction. 
         [0113]    Hereinafter, it is assumed in the following description that the AC current applied to the first and second reception induction coils  451  and  452  has a sine waveform. The sine waveform is only one example. 
         [0114]    Further, it is assumed that the applied voltage is 0.7 when the current flows through the first and second rectifying diodes  461  and  462 . The voltage of 0.7V is only one example. 
         [0115]    When a positive AC voltage of a half cycle is applied to both terminals of the inductor L 4 , the same positive AC voltage may be applied to both terminals of the inductor L 5 . Referring to  FIG. 9 , the positive AC voltage of the half cycle applied to both terminals of the inductor L 4  and both terminals of the inductor L 5  is marked with plus (+) and minus (−) signs. 
         [0116]    In this case, the first rectifying diode  461  allows the positive AC current to pass therethrough during one half-cycle, but the second rectifying diode  462  prohibits the positive AC current from passing therethrough during the other half-cycle. 
         [0117]    Referring to  FIG. 9 , a line F 1  that represents a direction in which current flows while the positive AC current corresponding to a half cycle duration is applied to both terminals of the inductor L 4  and both terminals of the inductor L 5 , is depicted. The current direction line F 1  represents the direction in which the AC current flows in the wireless power receiver  400 . 
         [0118]    If the positive AC current of the half-cycle duration is applied to both terminals of the inductor L 4  and both terminals of the inductor L 5 , such as the AC current direction line F 1 , the AC current flows through the inductor L 4 , the capacitor C 4 , the first rectifying diode  461 , the smoothing capacitor C and the load  440 . 
         [0119]    The AC current may be applied to the second rectifying diode  462  in the forward bias direction so that the flowing of current may be blocked. That is, the second rectifying diode  462  is operated as an open circuit. 
         [0120]    If it is assumed that the voltage of 5V may be applied to both terminals of each inductor L 4  and L 5 , although 0.7V is applied to the first rectifying diode  461 , a voltage is not applied to the second rectifying diode  462 , so that the voltage applied to the load  440  may be 4.3V. 
         [0121]    Different from the case of  FIG. 6  where the current passes through the rectifying diode two times since a diode bridge is used as the rectifying unit  430 , the wireless power receiver  400  according to the embodiment of  FIG. 8  provides the power to the load  440  through only one rectifying diode, so that the transferred power may be increased. 
         [0122]    The wireless power receiver  400  according to the embodiment shown in  FIG. 9  may reduce the power loss by a half as compared with the power loss of the wireless power receiver  400  according to the embodiment shown in  FIG. 6 . 
         [0123]    If the rectifying efficiency of the wireless power receiver according to the embodiment of  FIG. 6  is about 90%, the rectifying efficiency of the wireless power receiver according to the embodiment of  FIG. 9  is about 95%. That is, the power loss may be reduced from 10% to 5%. The rectifying efficiency may signify the ratio of the power applied from the reception induction coil to the rectifying circuit to the power transferred to the load  440 . 
         [0124]    Although the wireless power receiver according to the embodiment of  FIG. 6  uses four rectifying diodes, the wireless power receiver according to the embodiment of  FIG. 9  uses two rectifying diodes so that the cost may be reduced and the size of the entire circuit may be reduced. 
         [0125]      FIG. 10  is a circuit diagram illustrating a power transferring scheme of a wireless power receiver  400  according to another embodiment when a negative AC current of a half-cycle duration is applied to the first and second reception induction coils  451  and  452 . 
         [0126]    Referring to  FIG. 10 , a line F 2  that represents a direction in which current flows while the negative AC current corresponding to a half cycle duration is applied to both terminals of the inductor L 4  and both terminals of the inductor L 5 , is depicted. The current direction line F 2  represents the direction in which the AC current flows in the wireless power receiver  400 . 
         [0127]    If the negative AC current of the half-cycle duration is applied to both terminals of the inductor L 4  and both terminals of the inductor L 5 , such as the AC current direction line F 2 , the AC current flows through the inductor L 4 , the capacitor C 4 , the first rectifying diode  461 , the smoothing capacitor C and the load  440 . 
         [0128]    The negative AC current may be applied to the second rectifying diode  462  in the forward bias direction so that the flowing of current may be blocked. That is, the first rectifying diode  461  is operated as an open circuit. 
         [0129]    If it is assumed that the voltage of 5V may be applied to both terminals of each inductor L 4  and L 5 , although 0.7V is applied to the second rectifying diode  462 , a voltage is not applied to the first rectifying diode  461 , so that the voltage applied to the load  440  may be 4.3V. 
         [0130]    Thus, even if the negative AC current is applied to the first and second reception induction coils  451  and  452 , the efficiency described in  FIG. 9  may be obtained. 
         [0131]      FIG. 11  is a flowchart showing a wireless power transmitting method of a wireless power receiver according to one embodiment. 
         [0132]    The configuration of the wireless power receiver  400  is the same as that depicted in  FIG. 8 . 
         [0133]    First, in step S 101 , the reception resonant coil  410  receives power from the wireless power transmitter  200  by using resonance. The received power may be in a type of an AC power. 
         [0134]    Then, in step S 103 , the reception induction coil unit  450  receives the AC power from the reception resonant coil  420  through electromagnetic induction. In the embodiment, the received power may be in a type of an AC power. 
         [0135]    If the received power is a positive AC voltage in step S 105 . The wireless power receiver  400  transfers the power to the load through a first loop during one half-cycle in step S 107 . In the embodiment, the first loop may signify a loop having a configuration in which the inductor L 4 , the capacitor C 4 , the first rectifying diode  461  and the load  440  are connected to each other along the AC current direction line F 1  depicted in  FIG. 9 . 
         [0136]    If the received power is a negative AC voltage in step S 105 . The wireless power receiver  400  transfers the power to the load  440  through a second loop during the other half-cycle in step S 109 . In the embodiment, the second loop may signify a loop having a configuration in which the inductor L 5 , the capacitor C 5 , the second rectifying diode  462 , the smoothing capacitor C and the load  440  are connected to each other along the AC current direction line F 2  depicted in  FIG. 10 . 
         [0137]    Different from the case of  FIG. 6  where the current passes through the rectifying diode two times since a diode bridge of the rectifying unit  430  is used as the rectifying unit  430 , the wireless power receiver  400  provides the power to the load  440  through only one rectifying diode, so that the transferred power may be increased. That is, the diode voltage drop occurs once, so that the power loss caused while the AC power is converted into the DC power is reduced, so the rectifying efficiency may be improved. 
         [0138]    Further, the wireless power transferring scheme of the wireless power receiver  400  uses two rectifying diodes so that the cost may be reduced and a size of the entire circuit may be reduced. 
         [0139]    The wireless power receiver  400  may be mounted on a mobile terminal such as a portable phone, smart phone, a laptop computer, a digital broadcasting terminal, a PDA (Personal Digital Assistants), a PMP (Portable Multimedia Player), or a navigation terminal. 
         [0140]    In addition, it shall be easily understood by those skilled in the art that the configuration according to the embodiment described in the disclosure may be applicable to a fixed terminal such as a digital TV or a desktop computer as well as a mobile terminal. 
         [0141]    Although embodiments have been described with reference to a number of illustrative embodiments thereof, it should be understood that numerous other modifications and embodiments can be devised by those skilled in the art that will fall within the spirit and scope of the principles of this disclosure. More particularly, various variations and modifications are possible in the component parts and/or arrangements of the subject combination arrangement within the scope of the disclosure, the drawings and the appended claims. In addition to variations and modifications in the component parts and/or arrangements, alternative uses will also be apparent to those skilled in the art.