Abstract:
A wireless charging circuit for power bank and a power bank thereof are provided in the present invention. The wireless charging circuit includes a boost DC to DC converter, a unidirectional conductive element and a wireless power converter. The input terminal of the boost DC to DC converter is coupled to the battery to receive the battery voltage. The output terminal of the boost DC to DC converter outputs a converted DC voltage. The first terminal of the unidirectional conductive element is coupled to the battery to receive the battery voltage, wherein the direction of the current flow is from the first terminal of the unidirectional conductive element to the second terminal of the unidirectional conductive element. The input terminal of the wireless power converter is coupled to the second terminal of the unidirectional conductive element. When the wireless charging circuit performs the detection for the wireless power receiver, the wireless power converter disables the boost DC to DC converter.

Description:
[0001]    This application claims priority of No. 102148710 filed in Taiwan R.O.C. on Dec. 27, 2013 under 35 USC 119, the entire content of which is hereby incorporated by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of Invention 
         [0003]    The present invention relates to the wireless power transmission and feedback technology, and more particularly to a wireless charging circuit adapted for a mobile power bank and a mobile power bank using the same. 
         [0004]    2. Related Art 
         [0005]    Wireless charging technology is a technology for charging device by electromagnetic field without any wire. Wireless charging technology is evolved from the wireless power transmission technology to use the magnetic resonant to transmit the electrical charge from charger to device to resonate coil and capacitor between the charge and device to achieve a high efficient power transmission. The wireless charger is more safer, no exposed connections, no leakage current. Thus, a lot of problems in wired charger is prevented. 
         [0006]    Due to the development of the wireless charging technology, Wireless Power Consortium is established because of the situation. One of accomplishments of Wireless Power Consortium is to promote Qi standard. With the standardization, wireless charging technology is more widely adopted. 
         [0007]    Additionally, since the mobile power bank is widely used, many manufacturers want to launch a product combining the wireless charging circuit and mobile power bank. The mobile power bank adopts the battery to be the main power source. Generally, the battery supplies 3.7V. However, the wireless charging circuit needs 5V input voltage to operate. Thus, between the wireless charging circuit and the battery, it must design a DC to DC converter.  FIG. 1  illustrates a circuit diagram depicting a wireless charging circuit according to a conventional art. Referring to  FIG. 1 , in this circuit diagram, a boost DC to DC converter  103  is implemented between the battery  101  and the wireless charging circuit  102 . When the wireless charging circuit  102  detects whether a wireless power receiver is disposed on the wireless charging circuit  102  or not, the boost DC to DC converter  103  must be enabled so that the detection can be performed. Thus, if an external object is disposed on the wireless charging circuit, the boost DC to DC converter  103  would be enabled. It causes the conversion loss and then the usage time of the power bank is decreased. 
       SUMMARY OF THE INVENTION 
       [0008]    It is therefore an objective of the present invention to provide a wireless charging circuit adapted for a mobile power bank and a mobile power bank using the same such that the power consumption from the detection of the external object can be reduced and the life time of the power bank can be extended. 
         [0009]    To achieve the above-identified or other objectives, the present invention provides wireless charging circuit, which is adapted for a power bank, wherein the power bank includes a battery. The wireless charging circuit includes a boost DC to DC converter, a unidirectional conductive element, and a wireless power converter. The boost DC to DC converter includes an input terminal and an output terminal, wherein the input terminal of the boost DC to DC converter is coupled to the battery to receive a battery voltage, wherein the output terminal of the boost DC to DC converter is for outputting a converted DC voltage. The unidirectional conductive element includes a first terminal and a second terminal, wherein the first terminal of the unidirectional conductive element is coupled to the battery to receive the battery voltage, wherein a current direction is from the first terminal of the unidirectional conductive element to the second terminal of the unidirectional conductive element. The wireless power converter is coupled to the second terminal of the unidirectional conductive element and the output terminal of the boost DC to DC converter. When the wireless charging circuit determines whether an external object is disposed on the wireless power converter or not, the wireless power converter disables the boost DC to DC converter. When the wireless charging circuit determines that an external object is disposed on the wireless power converter, the wireless power converter enables the boost DC to DC converter. 
         [0010]    In the wireless charging circuit according to the preferred embodiment of the present invention, the wireless power converter includes a low voltage pulse width modulation (PWM) circuit, a resonant circuit and a control circuit. The low voltage PWM circuit includes an input terminal and an output terminal, wherein the input terminal of the low voltage PWM circuit is coupled to the second terminal of the unidirectional conductive element, and the output terminal of the low voltage PWM circuit outputs a PWM detecting signal. The resonant circuit includes a first input terminal, wherein the first input terminal is coupled to the output terminal of the low voltage PWM circuit. The control circuit is coupled to the enable terminal of the boost DC to DC converter. When the wireless charging circuit determines whether an external object is disposed on the wireless power converter or not, the control circuit controls the boost DC to DC converter to disable the boost DC to DC converter. Furthermore, in a preferred embodiment, the low power PWM circuit includes a first upper switch and a first lower switch, wherein the first upper switch and the first lower switch is composed of a half bridge converter controlled by the battery voltage. 
         [0011]    In the wireless charging circuit according to the preferred embodiment of the present invention, the wireless power converter further includes a high voltage pulse width modulation (PWM) circuit and a driving circuit. The high voltage PWM circuit is coupled to the output terminal of the boost DC to DC converter for outputting a driving PWM signal to the resonant circuit. The driving circuit is coupled to the high voltage pulse width modulation circuit, the boost DC to DC converter and the control circuit. When the wireless charging circuit determines that an external object is disposed on the wireless power converter, the control circuit enables the boost DC to DC converter and the control circuit enables the driving circuit to drive the high voltage PWM circuit. 
         [0012]    In the wireless charging circuit according to the preferred embodiment of the present invention, the high voltage PWM circuit includes a second upper switch and a second lower switch. The control terminal of the second upper switch is coupled to the driving circuit, and the first terminal of the second upper switch is coupled to the output terminal of the boost DC to DC converter. The control terminal of the second lower switch is coupled to the driving circuit, the first terminal of the second lower switch is coupled to the second terminal of the second upper switch and the first input terminal of the resonant circuit, and the second terminal of the second lower switch is coupled to a common voltage. In another preferred embodiment, the high voltage PWM circuit is a full bridge converter, and the resonant circuit further includes a second input terminal. Thus, the high voltage PWM circuit further includes a third upper switch and a third lower switch. The control terminal of the third upper switch is coupled to the driving circuit, and the first terminal of the third upper switch is coupled to the output terminal of the boost DC to DC converter. The control terminal of the third lower switch is coupled to the driving circuit, the first terminal of the third lower switch is coupled to the second terminal of the third upper switch and the second input terminal of the resonant circuit, and the second terminal of the third lower switch is coupled to the common voltage. Further, when the high voltage PWM circuit is the full bridge converter, the wireless charging circuit further includes a detection switch. The control terminal of the detection switch is coupled to the control circuit, the first terminal of the detection switch is coupled to the second input terminal of the resonant circuit, and the second terminal of the detection switch is coupled to the common voltage. When the wireless charging circuit determines whether an external object is disposed on the wireless power converter or not, the control circuit controls to connect the first terminal of the detection switch and the second terminal of the detection switch. 
         [0013]    The present invention further provides a mobile power bank. The mobile power bank includes a battery and a wireless charging circuit. The wireless charging circuit includes a boost DC to DC converter, a unidirectional conductive element and a wireless power converter. The boost DC to DC converter includes an input terminal and an output terminal, wherein the input terminal of the boost DC to DC converter is coupled to the battery to receive a battery voltage, wherein the output terminal of the boost DC to DC converter is for outputting a converted DC voltage. The unidirectional conductive element includes a first terminal and a second terminal, wherein the first terminal of the unidirectional conductive element is coupled to the battery to receive the battery voltage, wherein a current direction is from the first terminal of the unidirectional conductive element to the second terminal of the unidirectional conductive element. The wireless power converter is coupled to the second terminal of the unidirectional conductive element and the output terminal of the boost DC to DC converter. 
         [0014]    When the wireless charging circuit determines whether an external object is disposed on the wireless power converter or not, the wireless power converter disables the boost DC to DC converter. When the wireless charging circuit determines that an external object is disposed on the wireless power converter, the wireless power converter enables the boost DC to DC converter. 
         [0015]    The spirit of the present invention is to disable the DC to DC converter when the wireless charging circuit determines whether an external object is disposed on the wireless power converter or not. Instead, when the wireless charging circuit determines whether an external object is disposed on the wireless power converter or not, the battery voltage is supplied to the wireless charging circuit without conversion to perform the detection of external object. When the wireless charging circuit determines that an external object is disposed on the wireless power converter, the wireless power converter enables the boost DC to DC converter. Thus, when the detection of an external object is performed, there is no extra power consumption from the DC to DC converter. Meanwhile, the power consumption of the detection of an external wireless power receiver can be also reduced. 
         [0016]    Further scope of the applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention. 
           [0018]      FIG. 1  illustrates a circuit diagram depicting a wireless charging circuit according to a conventional art. 
           [0019]      FIG. 2  illustrates a circuit diagram depicting a mobile power bank according to a preferred embodiment of the present invention. 
           [0020]      FIG. 3  illustrates a circuit diagram depicting a mobile power bank according to a preferred embodiment of the present invention. 
           [0021]      FIG. 4  illustrates a circuit diagram depicting a mobile power bank according to a preferred embodiment of the present invention. 
           [0022]      FIG. 5  illustrates a circuit diagram depicting a mobile power bank according to a preferred embodiment of the present invention. 
           [0023]      FIG. 6  illustrates a circuit diagram depicting a mobile power bank according to a preferred embodiment of the present invention. 
           [0024]      FIG. 7  illustrates a circuit diagram depicting a mobile power bank according to a preferred embodiment of the present invention. 
           [0025]      FIG. 8  illustrates a circuit diagram depicting a mobile power bank according to a preferred embodiment of the present invention. 
           [0026]      FIG. 9  illustrates a circuit diagram depicting a mobile power bank according to a preferred embodiment of the present invention. 
           [0027]      FIG. 10  illustrates a circuit diagram depicting a mobile power bank according to a preferred embodiment of the present invention. 
           [0028]      FIG. 11  illustrates a circuit diagram depicting a mobile power bank according to a preferred embodiment of the present invention. 
           [0029]      FIG. 12A  illustrates a circuit diagram depicting a current detection circuit according to a preferred embodiment of the present invention. 
           [0030]      FIG. 12B  illustrates a circuit diagram depicting a current detection circuit according to a preferred embodiment of the present invention. 
           [0031]      FIG. 12C  illustrates a circuit diagram depicting a current detection circuit according to a preferred embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0032]    The present invention will be apparent from the following detailed description, which proceeds with reference to the accompanying drawings, wherein the same references relate to the same elements. 
         [0033]      FIG. 2  illustrates a circuit diagram depicting a mobile power bank according to a preferred embodiment of the present invention. Referring to  FIG. 2 , the mobile power bank includes a battery  201 , a unidirectional conductive element  202  and a wireless charging circuit  203  of the present embodiment of the present invention. The wireless charging circuit  203  includes a boost DC to DC converter  204 , a control circuit  205  and a wireless power converter  206 . The boost DC to DC converter  204  is used for converting 3.7V supplied from the battery  201  to 5V which is required by the wireless power converter  206 . The wireless power converter  206  includes a half bridge converter  207 , a resonant circuit  208  and a driving circuit  209 . The half bridge converter  207  includes a upper switch M 1  and a lower switch M 2 . 
         [0034]    The operation of the control circuit  205  depends on the 3.7V supplied by the battery  201 . The operation of the driving circuit  209  depends on the 5V outputted from by the boost DC to DC converter  204 . In addition, the control circuit  205  is used for controlling whether the boost DC to DC converter  204  is enabled or not. Moreover, although the resonant circuit  208  is implemented by a resonant coil L 21  and a resonant capacitor C 21 , people having ordinary skill in the art should know that the number of the resonant coil L 21  and the resonant capacitor C 21  can be changed according to different design, and the coupling relationship of the resonant coil L 21  and the resonant capacitor C 21  can be changed, such as interchanging the resonant coil L 21  with the resonant capacitor C 21 . Thus, the present invention is not limited thereto. 
         [0035]    When the wireless charging circuit  203  begins to detect a wireless power receiver (or an external object), the boost DC to DC converter  204  and the driving circuit  209  is disabled. Instead, the control circuit  205  directly outputs the control signals G 1  and G 2  to control the gates of the switch elements M 1  and M 2  of the half bridge converter  207  to output a low voltage pulse width modulation (PWM) signal, whose amplitude is about 3.7V, to the resonant circuit  208 . Then, the control circuit  205  begins to detect the current of the resonant circuit  208 . Generally, the control circuit  205  would detect the voltage Vsense from the current sensing resistor R 21  to serve as the means for detecting the current of the resonant circuit  208 . When the current flowing through the current sensing resistor R 21  is increased, it represent that there is an object being disposed on the resonant coil L 21 . At this time, the control circuit  205  enables the boost DC to DC converter  204 , and controls the driving circuit  209  to drive the half bridge converter with 5V to output a high voltage PWM signal whose amplitude is about 5V, to attempt establishing a wireless connection with the object. 
         [0036]    Further, in order to prevent the 5V outputted from the boost DC to DC converter  204  returning to the battery  201 , in the abovementioned embodiment, the unidirectional conductive element  202  is coupled between the battery  201  and the output terminal of the boost DC to DC converter  204 . Thus, the 5V outputted from the boost DC to DC converter  204  would not feed back to the battery  201 . In the abovementioned embodiment, since the amplitude of the control signal outputted from the control circuit  205  is about 3.7V, the control signal is insufficient to drive the gate of the upper switch M 1  if the boost DC to DC converter  204  is enabled. Thus, the driving circuit  209  is with a function of level shift for converting the 3.7V amplitude of the driving signal to the 5V amplitude of the driving signal. In addition, the terminals of the control circuit  205  and the terminals of the driving circuit  209  are coupled to the half bridge converter  207 . In order to prevent the driving signal outputted from the driving circuit  209  to interfere the operation of the control circuit  205 , a resistor or a diode can be selectively coupled between the control circuit  205  and the gates of the switching elements M 1  and M 2  of the half bridge converter  207 . 
         [0037]    Moreover, although the unidirectional conductive element  202  in this embodiment is implemented by a diode, people having ordinary skill in the art should know that the unidirectional conductive element  202  also can be implemented by a electrical switch or a diode-connected transistor. Thus, the present invention is not limited thereto. 
         [0038]      FIG. 3  illustrates a circuit diagram depicting a mobile power bank according to a preferred embodiment of the present invention. Referring to  FIG. 2  and  FIG. 3 , in this embodiment, the wireless charging circuit  203  includes the boost DC to DC converter  204 , a control circuit  205  and the wireless power converter  206 . The wireless power converter  206  includes a first half bridge converter  301 , the resonant circuit  208 , the driving circuit  209  and a second half bridge converter  302 . The first half bridge converter  301  includes a upper switch M 1  and a lower switch M 2 . The second half bridge converter  302  includes an upper switch M 3  and a lower switch M 4 . 
         [0039]    Similarly, the operation of the control circuit  205  depends on the 3.7V supplied by the battery  201 . The operation of the driving circuit  209  depends on the 5V outputted from by the boost DC to DC converter  204 . In addition, the control circuit  205  is used for controlling whether the boost DC to DC converter  204  is enabled or not. Moreover, although the resonant circuit  208  is implemented by a resonant coil L 21  and a resonant capacitor C 21 , people having ordinary skill in the art should know that the number of the resonant coil L 21  and the resonant capacitor C 21  can be changed according to different design, and the coupling relationship of the resonant coil L 21  and the resonant capacitor C 21  can be changed, such as interchanging the resonant coil L 21  with the resonant capacitor C 21 . Thus, the present invention is not limited thereto. 
         [0040]    In this embodiment, a low voltage pulse width modulation circuit, which is the half bridge converter  301 , is used to replace the unidirectional conductive element  202 . When the wireless charging circuit  203  begins to detect the wireless power receiver (or an external object), the boost DC to DC converter  204 , the driving circuit  209  and the second half bridge converter  302  are disabled. Instead, the control circuit  205  controls the first half bridge converter  301  to output a low voltage PWM signal, whose amplitude is about 3.7V, to the resonant circuit  208 . The control circuit then starts to detect the current flowing through the resonant circuit  208 . Generally, the control circuit  205  would detect the voltage Vsense from the current sensing resistor R 21  to serve as the means for detecting the current of the resonant circuit  208 . When the current flowing through the current sensing resistor R 21  is increased, it represent that there is an object being disposed on the resonant coil L 21 . At this time, the control circuit  205  enables the boost DC to DC converter  204 , and controls the driving circuit  209  to drive the half bridge converter with 5V to output a high voltage PWM signal whose amplitude is about 5V, to attempt establishing the connection with the object. 
         [0041]    According to the abovementioned embodiment, people having ordinary skill in the art should know that the boost DC to DC converter  204  is disabled during the wireless charging circuit detecting an external object. Thus, the energy waste causing by the efficiency of the boost DC to DC converter  204  can be saved. Beside, when the boost DC to DC converter  204  starts to operate, since the upper switch M 1  of the first half bridge converter  301  is coupled to the battery voltage and the upper switch M 3  of the second half bridge converter  302  is coupled to 5V outputted from the boost DC to DC converter  204 , the operation of the first half bridge converter  301  and the operation of the second half bridge converter  302  would not interfere each others. Also, the 5V outputted from the boost DC to DC converter  204  will not feed back to the battery  201 . 
         [0042]      FIG. 4  illustrates a circuit diagram depicting a mobile power bank according to a preferred embodiment of the present invention. Referring to  FIG. 3  and  FIG. 4 , the difference between the circuit in  FIG. 4  and the circuit in  FIG. 3  is that the unidirectional conductive element  401  is coupled between the upper switch M 1  of the first half bridge converter  301  and the battery  201 .  FIG. 5  illustrates a circuit diagram depicting a mobile power bank according to a preferred embodiment of the present invention. Referring to  FIG. 3  and  FIG. 5 , the difference between the circuit in  FIG. 5  and the circuit in  FIG. 3  is that the unidirectional conductive element  501  is coupled between the upper switch M 1  of the first half bridge converter  301  and the upper switch M 3  of the second half bridge converter  302 . The unidirectional conductive element  501  would block the output voltage Vo outputted from the boost DC to DC converter  204  to feed back to the battery  201 . 
         [0043]      FIG. 6  illustrates a circuit diagram depicting a mobile power bank according to a preferred embodiment of the present invention. Referring to  FIG. 3  and  FIG. 6 , the difference between the circuit in  FIG. 6  and the circuit in  FIG. 3  is that the control circuit  205  samples the voltage of the node N 60  coupled to the resonant coil L 21  and the resonant capacitor C 21  instead of the voltage Vsense of the current sensing resistor R 21 . 
         [0044]      FIG. 7  illustrates a circuit diagram depicting a mobile power bank according to a preferred embodiment of the present invention. Referring to  FIG. 6  and  FIG. 7 , the difference between the circuit in  FIG. 7  and the circuit in  FIG. 6  is that the unidirectional conductive element  701  is coupled between the node N 70  and the node N 71 . Since the current of the unidirectional conductive element  701  only can flow from the battery  201  to the second half bridge  302 , the output voltage Vo of the boost DC to DC converter  204  would not affect the battery  201 . 
         [0045]      FIG. 8  illustrates a circuit diagram depicting a mobile power bank according to a preferred embodiment of the present invention. Referring to  FIG. 3  and  FIG. 8 , the difference between the circuit in  FIG. 8  and the circuit in  FIG. 3  is that the second half bridge converter  302  is replaced by the full bridge converter  801 . The full bridge converter  801  includes a first upper switch M 5 , a first lower switch M 6 , a second upper switch M 7  and a second lower switch M 8 . Thus, the control circuit  205  must output six gate control signals G 1 , G 2 , G 3 ′ ˜G 6 ′. And the driving circuit  209  must output four gate control signals G 3 ˜G 6  to respectively drive the first upper switch M 5 , the first lower switch M 6 , the second upper switch M 7  and the second lower switch M 8 . The operation concept of the circuit in  FIG. 8  is essentially the same as the operation concept of the circuit in  FIG. 3 . The detail description is omitted. 
         [0046]      FIG. 9  illustrates a circuit diagram depicting a mobile power bank according to a preferred embodiment of the present invention. Referring to  FIG. 8  and  FIG. 9 , the difference between the circuit in  FIG. 9  and the circuit in  FIG. 8  is that the circuit in  FIG. 9  has extra unidirectional conductive element  901 . Since the current of the unidirectional conductive element  901  only can flow from the battery  201  to the full bridge converter  801 , the output voltage Vo of the boost DC to DC converter  204  would not affect the battery  201 . 
         [0047]      FIG. 10  illustrates a circuit diagram depicting a mobile power bank according to a preferred embodiment of the present invention. Referring to  FIG. 8  and  FIG. 10 , the difference between the circuit in  FIG. 9  and the circuit in  FIG. 8  is that the circuit in  FIG. 10  has an extra switch M 9 . And the control circuit also has an extra control terminal G 7  coupled to the gate of the switch M 9 . Similarly, when the wireless charging circuit  203  in this embodiment begins to detect the wireless power receiver (or an external object), the boost DC to DC converter  204  and the driving circuit  209  are disabled. Instead, the control circuit  205  output the control signals G 1  and G 2  to control the gates of the switch M 1  and M 2  of the first half bridge converter  301  to output the low voltage PWM signal, whose amplitude is about 3.7V, to the resonant circuit  208 . Meanwhile, the control circuit  205  controls the gate G 7  of the switch M 9  to turn switch M 9  on such that the resonant circuit  208  is grounded. 
         [0048]    Next, the control circuit then starts to detect the current flowing through the resonant circuit  208 . Generally, the control circuit  205  would detect the voltage Vsense from the current sensing resistor R 21  to serve as the means for detecting the current of the resonant circuit  208 . When the current flowing through the current sensing resistor R 21  is increased, it represent that there is an object being disposed on the resonant coil L 21 . At this time, the control circuit  205  enables the boost DC to DC converter  204 . Meanwhile, the control circuit  205  controls the gate G 7  of the switch M 9  to turn the switch M 9  off. Further, the control circuit  205  then controls the driving circuit  209  to drive the four switch M 5 , M 6 , M 7  and M 8  of the full bridge converter  801  to output a high voltage PWM signal to the resonant circuit to attempt establishing the connection with the object, wherein the amplitude of the high voltage PWM signal is about 5V. 
         [0049]    Moreover, in order to prevent the 5V outputted from the boost DC to DC converter  204  returning to the battery  201 , in the abovementioned embodiment, there is no electrical connection between the output terminal of the boost DC to DC converter  204  and the first half bridge converter  301 . Thus, the 5V outputted from the boost DC to DC converter  204  would not feed back to the battery  201 . In the abovementioned embodiment, since the amplitude of the control signal outputted from the control circuit  205  is about 3.7V, the control signals are insufficient to drive the switches M 5 , M 6 , M 7  and M 8  of the full bridge converter  801 . Thus, the driving circuit  209  is with a function of level shift for converting the 3.7V amplitude of the driving signal to the 5V amplitude of the driving signal. 
         [0050]      FIG. 11  illustrates a circuit diagram depicting a mobile power bank according to a preferred embodiment of the present invention. Referring to  FIG. 10  and  FIG. 11 , the difference between the circuit in  FIG. 11  and the circuit in  FIG. 10  is that the resistor R 21  is removed. The control circuit  205  samples the voltage Vr of the node N 11  of the resonant circuit  208  to serve as the means for detecting the current of the resonant circuit  208 . The node voltage Vr of the node N 11  is proportional to the current flowing through the resonant circuit  208 . Thus, the control circuit  205  can obtain the current flowing through the resonant circuit  208  by detecting the voltage Vr of the node N 11 . 
         [0051]      FIG. 12A  illustrates a circuit diagram depicting a current detection circuit according to a preferred embodiment of the present invention.  FIG. 12B  illustrates a circuit diagram depicting a current detection circuit according to a preferred embodiment of the present invention.  FIG. 12C  illustrates a circuit diagram depicting a current detection circuit according to a preferred embodiment of the present invention. Referring to  FIG. 12A , the current detection circuit can be coupled between the control circuit  205  and the node N 11  of the resonant circuit  208  in  FIG. 11  or be coupled between the control circuit  205  and the node N 60  in  FIG. 6 . The current detection circuit may also be coupled between the current sensing resistor R 21  and the control circuit  205 . Assuming the current detection circuit is applied to the circuit in  FIG. 11 , the resistor R 121  is coupled between the node N 11  of the resonant circuit and the capacitor C 121 . The resistors R 122  and R 123  are used for dividing the voltage of another terminal of the capacitor C 121 . Afterward, the divided voltage is sampled by the quasi-peak detector implemented by the diode D 121 , the capacitor C 122  and the resistor R 124 . The control circuit  205  detects the DC voltage VDC to determine the magnitude of the current flowing through the resonant circuit  208 . 
         [0052]    Similarly, referring to  FIG. 12B , assuming the current detection circuit is applied to the circuit in  FIG. 11 , the diode D 122  is coupled between the node N 11  of the resonant circuit  208  and the resistor R 125 . The resistors R 125  and R 126  are used for dividing the voltage of the cathode D 122  and then outputting the divided voltage to the capacitor C 123 . The control circuit  205  detects the DC voltage VDC to determine the magnitude of the current flowing through the resonant circuit  208 . Analogously, referring to  FIG. 12C , assuming the current detection circuit is applied to the circuit in  FIG. 11 , the resistor R 127  is coupled between the node N 11  of the resonant circuit  208  and the diode D 123 . The resistors R 128  and R 129  are used for dividing the voltage of the cathode of the diode D 123  to output the divided voltage to the capacitor C 124 . The control circuit  205  detects the DC voltage VDC to determine the magnitude of the current flowing through the resonant circuit  208 . 
         [0053]    In summary, the spirit of the present invention is to disable the DC to DC converter while the wireless charging circuit determines whether an external object is disposed on the wireless power converter or not. Instead, when the wireless charging circuit determines whether an external object is disposed on the wireless power converter or not, the battery voltage is supplied to the wireless charging circuit without conversion to perform the detection of external object. When the wireless charging circuit determines that an external object is disposed on the wireless power converter, the wireless power converter enables the boost DC to DC converter. Thus, when the detection of an external object is performed, there is no extra power consumption from the DC to DC converter. Meanwhile, the power consumption of the detection of an external wireless power receiver can be also reduced. 
         [0054]    While the invention has been described by way of examples and in terms of preferred embodiments, it is to be understood that the invention is not limited thereto. To the contrary, it is intended to cover various modifications. Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications.