Patent Publication Number: US-2011050180-A1

Title: Charging Control Circuit

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to a charging control circuit, and more particularly to a charging control circuit capable of effectively charging a plurality of series-connected rechargeable batteries. 
     2. The Related Art 
     A charging control circuit used to charge a rechargeable battery often has a control function for preventing the battery from being overcharged. That is to say, in the process of charging the battery, if the voltage of the battery is raised to a default value, then the charging control circuit will cut off a switch unit to terminate the charging process. Therefore the battery can avoid being damaged caused by overcharging. 
     However, when the above-mentioned charging control circuit is used to charge a plurality of series-connected rechargeable batteries, if the remained power in each battery differs from one another, then the battery having a more remained power therein will be charged to easily make the voltage thereof raised to the default value firstly. At this time, the charging control circuit will cut off the switch unit so as to protect the corresponding battery from being overcharged that prevents the charging control circuit from charging other batteries. Therefore, although the charging process is completed, some batteries are not fully charged to the default value that reduces the effectiveness of the batteries. Therefore, a charging control circuit capable of overcoming the foregoing problems is required. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a charging control circuit adapted for charging a plurality of rechargeable batteries. The charging control circuit includes a plurality of connecting terminals series-connected, a current-restraining unit, a switch unit, a charging unit and a control unit. Each of the connecting terminals includes a positive connecting point and a negative connecting point adapted for connecting one battery therebetween. The current-restraining unit and the switch unit are connected between the positive connecting point and the corresponding negative connecting point of each connecting terminal. The charging unit is adapted for charging the batteries connected with the connecting terminals. The control unit is adapted for detecting the voltage of each connecting terminal so as to judge whether the connecting terminal disconnects with the battery or not and whether the battery is fully charged or not according to the detected voltage signal, and then control a switch state of the corresponding switch unit to adjust the flow direction of a charge current from the charging unit according to the judged result, wherein when all of the batteries are detected to be fully charged, the control unit will control the corresponding switch units to be connected to divide the charge current through the corresponding current-restraining units for making only a trickle current flow through the fully charged batteries, or the control unit will directly control the charging unit to adjust the charge current into a trickle current for the fully charged batteries. 
     Another object of the present invention is to provide a charging control circuit adapted for charging a plurality of rechargeable batteries. The charging control circuit includes a plurality of connecting terminals series-connected with one another, a current control circuit, a charging unit and a control unit. Each of the connecting terminals includes a positive connecting point and a negative connecting point adapted for connecting one battery therebetween. The current control circuit is connected between the positive connecting point and the corresponding negative connecting point of each of the connecting terminals. The charging unit is adapted for charging the batteries connected with the connecting terminals. The control unit is adapted for detecting the voltage of each connecting terminal so as to judge whether the connecting terminal disconnects with the battery or not and whether the battery is fully charged or not according to the detected voltage signal, and then control the corresponding current control circuit to adjust the flow direction of a charge current from the charging unit according to the judged result, wherein when all of the batteries are detected to be fully charged, the control unit will control the corresponding current control circuits to divide the charge current for making only a trickle current flow through the fully charged batteries, or the control unit will directly control the charging unit to adjust the charge current into a trickle current for the fully charged batteries. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be apparent to those skilled in the art by reading the following description, with reference to the attached drawings, in which: 
         FIG. 1  is a circuitry view of a charging control circuit according to a first embodiment of the present invention; 
         FIG. 2  is a concrete circuitry of the charging control circuit of  FIG. 1 ; 
         FIG. 3  is a circuitry view of the charging control circuit of  FIG. 2 , wherein each of connecting terminals is connected with one rechargeable battery for executing a charge process; 
         FIG. 4  is a circuitry view of the charging control circuit of  FIG. 2 , wherein there is one of the connecting terminals unconnected with the rechargeable battery; 
         FIG. 5  is a circuitry view of the charging control circuit of  FIG. 2 , wherein there is one rechargeable battery connected with the corresponding connecting terminal fully charged; 
         FIG. 6  is a circuitry view of the charging control circuit of  FIG. 2 , wherein all of the rechargeable batteries connected with the connecting terminals are fully charged; 
         FIG. 7  is a circuitry view of the charging control circuit of  FIG. 2 , wherein all of the connecting terminals are unconnected with the rechargeable batteries; and 
         FIG. 8  is a circuitry view of a charging control circuit according to a second embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With reference to  FIG. 1  and  FIG. 2 , a charging control circuit according to a first embodiment of the present invention is shown. The charging control circuit includes a charging unit  10 , a plurality of connecting terminals  30  series-connected with one another, and a control unit  20 . Each of the connecting terminals  30  includes a positive connecting point P 1 /P 3 /P 5  . . . P 2   n - 1  and a corresponding negative connecting point P 2 /P 4 /P 6  . . . P 2   n . The charging unit  10  is connected between the outmost positive connecting point P 1  and the control unit  20 . The outmost negative connecting point P 2   n  is connected to ground. A plurality of rechargeable batteries  40  can be respectively connected to the corresponding connecting terminals  30  for being charged by the charging control circuit. 
     The positive connecting point P 1 /P 3 /P 5  . . . P 2   n - 1  of each connecting terminal  30  is on one hand directly connected to the control unit  20  for transmitting a voltage signal to the control unit  20 , and on the other hand, connected to the corresponding negative connecting point P 2 /P 4 /P 6  . . . P 2   n  through a current-restraining unit  21  and a switch unit  22  successively. The switch unit  22  is further connected with the control unit  20 . The charging unit  10  can transmit a current signal to the control unit  20 . The control unit  20  can judge whether the connecting terminal  30  disconnects with the rechargeable battery  40  or not and whether the rechargeable battery  40  is fully charged or not according to the voltage signal and the current signal, and then control a switch state of the corresponding switch unit  22  to adjust the flow direction of a charge current from the charging unit  10  according to the judged result so as to ensure each rechargeable battery  40  fully charged and further prevent the rechargeable battery  40  from being over-charged. If all of the rechargeable batteries  40  are detected to be fully charged, then the control unit  20  will control the corresponding switch units  22  to be connected to divide the charge current through the corresponding current-restraining units  21  for making only a trickle current flow through the fully charged batteries  40 , or the control unit  20  will directly control the charging unit  10  to adjust the charge current into a trickle current for the fully charged batteries  40 . 
     The current-restraining unit  21  can be a resistance element, a constant current circuit or a limited current circuit etc. The switch unit  22  can be a power MOS, a relay, an FET or an IGBT etc. In the first embodiment, the current-restraining unit  21  is a resistance element and the switch unit  22  is an N-channel FET having the drain connected with the current-restraining unit  21 , the source connected with the corresponding negative connecting point P 2 /P 4 /P 6  . . . P 2   n , and the grid connected with the control unit  20 . The grid of the switch unit  22  is further connected to ground through a resistor  23 . 
     Referring to  FIGS. 2-7 , the charge process of utilizing the charging control circuit to charge the rechargeable battery  40  will be described as follows, wherein the charging control circuit has three connecting terminals  30 , namely three pairs of the positive and negative connecting points P 1 -P 6 . 
     Referring to  FIG. 2  and  FIG. 3 , when each of the three connecting terminals  30  is connected with one rechargeable battery  40 , the control unit  20  will control the charging unit  10  to provide a charge current for the three rechargeable batteries  40 . Simultaneously, the control unit  20  will control each of the switch units  22  to be disconnected to make the charge current successively flowed through the three rechargeable batteries  40  so as to charge the rechargeable batteries  40 . 
     Referring to  FIG. 2  and  FIG. 4 , if there is the connecting terminal  30  unconnected with the corresponding rechargeable battery  40 , such as the positive connecting point P 3  and the corresponding negative connecting point P 4  without the rechargeable battery  40  connected therebetween, then the control unit  20  will control the corresponding switch unit  22 , which is connected between the positive and the negative connecting points P 3 , P 4 , to be connected. At this time, the charge current from the charging unit  10  will successively flow through the rechargeable battery  40  connected between the positive connecting point P 1  and the negative connecting point P 2 , the current-restraining unit  21  and the switch unit  22  connected between the positive connecting point P 3  and the negative connecting point P 4 , and the rechargeable battery  40  connected between the positive connecting point P 5  and the negative connecting point P 6 . 
     Referring to  FIG. 2  and  FIG. 5 , if the rechargeable battery  40  is fully charged, for example, the rechargeable battery  40  connected between the positive connecting point P 3  and the corresponding negative connecting point P 4  is fully charged, then the control unit  20  will control the corresponding switch unit  22  to be connected to make the charging current, which flows through the rechargeable battery  40  connected between the positive connecting point P 1  and the negative connecting point P 2 , divided into two branches. One of the two branches of currents which is restrained by the current-restraining unit  21  connected with the positive connecting point P 3  successively flows through the current-restraining unit  21  and the corresponding switch unit  22 , and the other branch of current is acted as a trickle current to flow through the fully charged rechargeable battery  40  so as to protect the rechargeable battery  40  from being over-charged. Then the restrained current and the trickle current are converged to flow through the rechargeable battery  40  connected between the positive connecting point P 5  and the negative connecting point P 6 . So the rechargeable batteries  40  not yet been fully charged will keep on being charged even if some of the rechargeable batteries  40  are fully charged. 
     Referring to  FIG. 2  and  FIG. 6 , if each of the rechargeable batteries  40  connected with the three connecting terminals  30  is fully charged, then the control unit  20  will control all of the switch units  22  to be connected to divide the charge current for making only the trickle current flow through the rechargeable batteries  40 , or the control unit  20  will control the charging unit  10  to directly provide a trickle current for the rechargeable batteries  40 . So the fully charged rechargeable batteries  40  can avoid being over-charged. In the first embodiment, if each of the rechargeable batteries  40  is fully charged, then the control unit  20  will control the charging unit  10  to directly provide the trickle current for the rechargeable batteries  40 . 
     Referring to  FIG. 2  and  FIG. 7 , if all of the rechargeable batteries  40  are withdrawn out of the corresponding connecting terminals  30 , then the control unit  20  will control all of the switch units  22  to be disconnected, or the control unit  20  will control the charging unit  10  to stop working. In the first embodiment, if all of the rechargeable batteries  40  are withdrawn out of the corresponding connecting terminals  30 , then the control unit  20  will control all of the switch units  22  to be disconnected. 
     Referring to  FIG. 8 , a charging control circuit according to a second embodiment of the present invention is shown and has a similar circuit to the first embodiment. The difference is that both the current-restraining unit  21  and the corresponding switch unit  22  connected with each of the connecting terminals  30  in the first embodiment are replaced by a current control circuit  50  in the second embodiment. The current control circuit  50  can be a constant current circuit or a limited current circuit. The charge process of utilizing the charging control circuit of the second embodiment to charge the rechargeable battery  40  is same to the charge process in the first embodiment, so it will not be described any more. 
     As described above, the charging control circuit of the present invention utilizes the control unit  20  to accurately control the charging unit  10  and the switch units  22  or the current control units  50  according to the voltage signal and the current signal so as to further control the charging current through each rechargeable battery  40 . So each rechargeable battery  40  connected in the charging control circuit can be charged completely and efficiently, and further can avoid being over-charged.