Patent Publication Number: US-2013241477-A1

Title: Wireless Charging System and Method for Controlling the Same

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a wireless charging system and a method for controlling the wireless charging system, and more particularly, to a wireless charging system which can dynamically adjust a coupling voltage and a method fir controlling the wireless charging system. 
     2. Description of the Related Art 
     Various kinds of electronic devices have emerged with the advancement of technology; in the meantime, these electronic devices have created more demands for electricity. Due to different charging interfaces of electronic devices, it is troublesome for a user to charge his/her devices when there&#39;s no available adapter. Therefore, a prior art technique is proposed to implement a wireless charging method through magnetic induction. 
     However, in the prior art wireless charging technique, the charging terminal would keep transmitting a coupling voltage to a rechargeable device without knowing the load and the required voltage value of the rechargeable device and could waste a considerable amount of power. On the other hand, if it is necessary to increase the transmitting power, the coupling circuit and the power characteristics of the rechargeable device must be also taken into consideration in addition to increasing the voltage or current. Therefore, in prior art techniques, the voltage level of the coupling voltage is limited for lower manufacturing cost since building a circuit which can sustain high voltage is not cost effective. 
     Therefore, it is necessary to propose a new wireless charging system and a method for controlling the new wireless charging system to overcome the deficiencies of prior art techniques. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a wireless charging system which can dynamically adjust a coupling voltage. 
     It is another object of the present invention to provide a method for controlling the wireless charging system. 
     In order to achieve the above object, the present invention discloses a wireless charging system for charging a rechargeable device. The wireless charging system comprises a charging circuit, a power supply module, a power switching module, a power sensing terminal, and a comparison module. The power supply module is used for providing a DC power signal on the charging circuit. The power switching module is electrically connected to the power supply module and converts the DC power signal to an AC power signal based on a switching frequency. The power sensing terminal is disposed on the charging circuit and used for sensing a coupling voltage according to the AC power signal to charge the rechargeable device. The comparison module is electrically connected with the power sensing terminal for comparing the coupling voltage with a default value, wherein the default value is set by the power switching module according to the switching frequency; when the coupling voltage is less than the default value, the comparison module controls the power switching module to increase the switching frequency. 
     The present invention also provides a method for controlling a wireless charging system to charge a rechargeable device. The method comprises the following steps: providing a dc power signal; converting the dc power signal into an AC power signal based on a switching frequency; sensing a coupling voltage according to the AC power signal to charge the rechargeable device; comparing the coupling voltage with a default value, wherein the default value is set according to the switching frequency; and when the coupling voltage is less than the default value, increasing the switching frequency to increase the AC power signal. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a structural view of a wireless charging system of the present invention; 
         FIG. 2  illustrates a circuit diagram of an embodiment of the present invention; 
         FIG. 3  illustrates a flow chart of a method controlled by the wireless charging system of the present invention; and 
         FIG. 4  illustrates a flow chart of an embodiment of the wireless charging system of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The advantages and innovative features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
     Please refer to  FIG. 1  for a structural view of a wireless charging system of the present invention. 
     The present invention provides a wireless charging system  1  for charging a rechargeable device  2  through wireless charging. The wireless charging system  1  comprises a charging circuit C, a power supply module  10 , a power switching module  20 , a power sensing terminal  30 , and a comparison module  40 . The above modules can be implemented by hardware structures; however, they can be implemented by firmware or software structures as well. The power supply module  10  can be a battery module disposed on the charging circuit C for providing a dc power signal. The power switching module  20  is electrically connected with the power supply module  10  for converting the dc power signal into an AC power signal. The power sensing terminal  30  is disposed on the charging circuit C for sensing a coupling voltage according to the AC power signal and for charging the rechargeable device  2  through magnetic induction. The power switching module  20  determines the current and the voltage value of the AC power signal according to the switching frequency; therefore, when the switching frequency of the power switching module  20  increases, the coupling voltage of the power sensing terminal  30  increases, which can be used to charge the rechargeable device  2  having a heavy load/power demand. On the other hand, when the rechargeable device  2  does not have a large power demand, the switching frequency of the power switching module  20  is also low. 
     The comparison module  40  is electrically connected with the power sensing terminal  30  and the power switching module  20  for comparing the coupling voltage with the default value, wherein the default value is set by the power switching module  20  according to its switching frequency. Since the coupling voltage of the power sensing terminal  30  corresponds to the switching frequency set by the power switching module  20 , the power switching module  20  can obtain the coupling voltage based on the switching frequency. Consequently, the power switching module  20  dynamically sets the default value based on the current switching frequency; when the switching frequency changes, the power switching module  20  changes the default value. When the rechargeable device  2  is having a heavy load, which means the rechargeable device  2  requires a larger current, thereby causing the coupling voltage to drop. When the coupling voltage is less than the default value, the comparison module  40  controls the power switching module  20  to increase the switching frequency and to increase the coupling voltage to meet the power demand of the rechargeable device  2 . 
     Please refer to  FIG. 2  for a circuit diagram of an embodiment of the present invention. 
       FIG. 2  illustrates a preferred embodiment of the present invention; however, the wireless charging system  1   a  can be implemented by other circuit structures. In this embodiment, the charging circuit C of the wireless charging system  1   a  also comprises a first switch module  21 , a second switch module  22 , and a resistor  51 . The power switching module  20  is electrically connected with the first switch module  1  and the second switch module  22 . The first switch module  21  and the second switch module  22  can be formed by Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs) or any other suitable transistors. The first switch module  21  and the second switch module  22  are both disposed on the charging circuit C; the power switching module  20  controls the ON/OFF of the first switch module  21  and the second switch module  22  according to the switching frequency to convert the dc power signal into the AC power signal. It is noted that the mechanism of converting the dc power signal into the AC power signal is well known in art, it will not be further described. In addition, the present invention can use other circuit implementations other than that shown in  FIG. 2  to convert the dc power signal. 
     The resistor  51  is disposed on the charging circuit C. The resistor  51  comprises a first end  51   a  and a second end  51   b , wherein the second end  51   b  is cascaded with the power sensing terminal  30 . The first end  51   a  and the second end  51   b  of the resistor  51  comprises a first voltage value VR 1  and a second voltage value VR 2  respectively. In this embodiment, the comparison module  40  is further electrically connected with the first comparator  41  and the second comparator  42 . The first comparator  41  compares the first voltage value VR 1  with a first reference value V 1 ; the second comparator  42  compares the second voltage value VR 2  with a second reference value V 2 . Similar to the default value, the first reference value V 1  and the second reference value V 2  are set by the power switching module  20  according to the switching frequency and are not fixed values. Since the resistor  51  is cascaded with the power sensing terminal  30 , the same current flow through the resistor  51  and the power sensing terminal  30 . Consequently, the present invention can project the relationship between the coupling voltage and the default value by comparing the first voltage value VR 1  and the second voltage value VR 2  with the first reference value V 1  and the second reference value V 2  respectively. 
     For example, when the wireless charging system  1   a  is charging the rechargeable device  2  having a heavy load, the increased current causes the coupling voltage to drop; therefore, the voltage difference between the first voltage value VR 1  and the second voltage value VR 2  becomes larger. At this moment the second voltage value VR 2  will drop below the second reference value V 2 . So when the second comparator  42  compares that the second voltage value VR 2  is less than the second reference value V 2 , and the first comparator  41  finds out that the first voltage value VR 1  is still larger than the first reference value V 1 , the comparison module  40  determines that the wireless charging system  1   a  needs to increase the coupling voltage. Thereafter, the comparison module  40  controls the power switching module  20  to increase the switching frequency. 
     On the other hand, when the rechargeable device  2  is removed or out of order, a considerable amount of power could accumulate at the power sensing terminal  30  to cause the first voltage value VR 1  to rise above the first reference value V 1 . Therefore, when the first voltage value VR 1  increases from less than the first reference value V 1  to larger than the first reference value V 1 , the comparison module  40  controls the power switching module  20  to decrease the switching frequency to stop transmitting the coupling voltage. Later, when the second comparator  42  finds out that the second voltage value VR 2  is less than the second reference value V 2 , the comparison module  40  can controls the power switching module  20  to increase the switching frequency again. 
     Consequently, through continuous comparing process, the wireless charging system  1   a  can dynamically adjust the outputted coupling voltage. The power sensing terminal  30  can adjust the coupling voltage according to the load of the rechargeable device  2  and does not need to output a fixed coupling voltage, thereby preventing unnecessary power consumption. On the other hand, the wireless charging system  1   a  can adjust the coupling voltage in a stepwise manner by comparing the first voltage value VR 1  and second voltage value VR 2  to avoid changing the coupling voltage frequently. It is noted that the above process is only for illustration, there can be other method or process to control the power switching module  20  to achieve the same object. 
     Please refer to  FIG. 3  for a flow chart of a method controlled by the wireless charging system of the present invention. It is noted that the although the method is controlled by the wireless charging system  1   a  to achieve the object of the present invention, the method can be applied in other circuit to serve its purpose. 
     First the method goes to step  301 : providing a dc power signal. 
     When the wireless charging system  1   a  is going to charge the rechargeable device  2 , at first the power supply module  10  of the wireless charging system  1   a  provides the dc power signal. 
     Then the method goes to step  302 : converting the dc power signal into an AC power signal based on a switching frequency. 
     In an embodiment of the present invention, the power switching module  20  turns on the first switch module  21  and the second switch module  22  on the charging circuit C respectively based on the switching frequency to convert the dc power signal into the AC power signal. In the step  302 , the power switching module  20  can convert the dc power signal based on a low switching frequency. 
     Then the method goes to step  303 : sensing a coupling voltage according to the AC power signal to charge the rechargeable device. 
     Then the power sensing terminal  30  senses the coupling voltage according to the received AC power signal to charge the rechargeable device  2  though wireless charging. 
     Then the method goes to step  304 : determining whether the coupling voltage is less than a default value. 
     Then the comparison module  40  compares the coupling voltage with the default value to determine whether the coupling voltage is less than the default value. 
     If the coupling voltage is less than the default value, then the method goes to step  305 : increasing the switching frequency to increase the AC power signal. 
     If so, then it is determined that the rechargeable device  2  requires a higher current, so the comparison module  40  controls the power switching module  20  to increase the switching frequency to boost the coupling voltage, thereby providing enough power to the rechargeable device  2 . 
     If the coupling voltage is not less than the default value, then the step goes to step  306 : maintaining the switching frequency. 
     If the coupling voltage is not less than the default value, it is determined that the coupling voltage can meet the power requirement of the rechargeable device  2 ; therefore, the comparison module  40  controls the power switching module  20  to maintain the same switching frequency. 
     The step  304  of determining whether the coupling voltage is less than a default value is further explained in  FIG. 4 , which illustrates a flow chart of an embodiment of the wireless charging system of the present invention. It is noted that other method or steps can be used for determining whether the coupling voltage is less than a default value. 
     First the method goes to step  401 : providing a resistor cascaded with the power sensing terminal. 
     The resistor  51  is disposed on the charging circuit C and cascaded with the power sensing terminal  30 . The resistor  51  comprises a first end  51   a  and a second end  51   b ; the first end  51   a  and the second end  51   b  of the resistor  51  comprises a first voltage value VR 1  and a second voltage value VR 2  respectively. 
     Then the method goes to step  402 : comparing the first voltage value with a first reference value; and comparing the second voltage value with a second reference value. 
     The first comparator  41  compares the first voltage value VR 1  with the first reference value V 1 , the second comparator  42  compares the second voltage value VR 2  with the second reference value V 2  to obtain a change of the coupling voltage. The first reference value V 1  and the second reference value V 2  are set by the power switching module  20  according to the switching frequency. Since the first reference value V 1  and the second reference value V 2  are set by the power switching module  20  according to the switching frequency, they are not fixed values. 
     Based on the results of comparing the first voltage value VR 1  with the first reference value V 1  and comparing the second voltage value VR 2  with the second reference value V 2 , different embodiments can be implemented. For example, in step  403 : when the first voltage value is larger than the first reference value and the second voltage value is less than the second reference value, increasing the switching frequency. 
     When the second comparator  42  learns that the second voltage value VR 2  is less than the second reference value V 2 , and the first comparator  41  finds out that the first voltage value VR 1  is still larger than the first reference value V 1 , the comparison module  40  determines that the comparison module  40  determines that the wireless charging system  1   a  needs to increase the coupling voltage. Thereafter, the comparison module  40  controls the power switching module  20  to increase the switching frequency. 
     Or the method goes to step  404 : when the first voltage value changes from less than the first reference value to larger than the first reference value, decreasing the switching frequency to stop sensing the coupling voltage. 
     When the first voltage value VR 1  changes from less than the first reference value V 1  to larger than the first reference value V 1 , it is possible for the power sensing terminal  30  to experience a high voltage level of coupling voltage due to short circuit; therefore, the comparison module  40  controls the power switching module  20  to decrease the switching frequency to stop transmitting the coupling voltage. 
     Then the method goes to step  405 : generating an alert signal. 
     At this time the wireless charging system  1   a  can use a light emitting module (not shown in figure) to generate the alert signal to inform the user any abnormal conditions. 
     Finally the method goes to step  406 : when the second voltage value is less than the second reference value, increasing the switching frequency again. 
     When the second comparator  42  learns that the second voltage value VR 2  drops below the second reference value V 2  again, the comparison module  40  controls the power switching module  20  to increase the switching frequency again. 
     It is noted that the method is not limited to the order of the steps disclosed herein, and the method can have another order of steps as long as the object of the present invention is fulfilled. 
     Therefore, the wireless charging system  1   a  of the present invention can dynamically adjust the coupling voltage according to the condition of the rechargeable device  2 , and can also adjust the coupling voltage in a stepwise manner by comparing the voltage values at both ends of the resistor to avoid changing the voltage frequently. 
     It is noted that the above-mentioned embodiments are only for illustration, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents. Therefore, it will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention.