Patent Publication Number: US-2010109606-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 rechargeable battery units of a pile formed by the series-connection of the battery units. 
     2. The Related Art 
     A charging control circuit used to charge a rechargeable battery often has a protecting function for preventing the battery from being overcharged and over-discharged. That is to say, in the process of charging the battery, when the voltage of the battery is raised to a predefined data (namely a protecting voltage for preventing the battery from being overcharged), the charging control circuit cuts off a protecting switch so as to terminate the charging process; in the process of discharging the battery, when the voltage of the battery goes down to another predefined data (namely another protecting voltage for preventing the battery from being over-discharged), the charging control circuit cuts off the protecting switch so as to terminate the discharging process. Therefore the battery can be protected from being damaged on account of the overcharging and over-discharging. 
     However, when the above-mentioned charging control circuit is used to charge a pile formed by the series-connection of a plurality of rechargeable battery units, if the remained power in each battery unit differs from each other, then the battery unit having a more remained power therein will be charged to easily make the voltage thereof raised to the predefined data firstly. At this time, the charging control circuit will cut off the protecting switch so as to protect the corresponding battery unit from being overcharged (namely the charging control circuit is disconnected) that prevents the charging control circuit from charging other battery units of the pile. Therefore, when the process of charging the pile is terminated, some battery units of the pile are not charged completely to be raised to the predefined data that reduces the time of supplying power of the pile. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a charging control circuit which is connected with a charging power supply for charging a pile formed by a series-connection of a plurality of battery units. The charging control circuit includes a protecting circuit, a charging circuit and a control circuit. The protecting circuit has a plurality of monitoring ports and control ports. The monitoring ports are connected with two terminals of the corresponding battery units for monitoring the voltage of the battery units. The charging circuit includes a plurality of diffluent circuits respectively parallel-connected to the corresponding battery units. Each diffluent circuit has a controlled switch element and a diffluent resistance element connected with each other in series. The controlled switch element has a switch control terminal connected to the respective control port of the protecting circuit. The control circuit includes two parallel branches connected between the charging power supply and the pile. One of the two branches has a third resistance element. The other branch has a fourth resistance element and a third switch element connected with each other in series. The third switch element has a third control terminal connected to the charging circuit. Wherein the protecting circuit controls a switch state of the controlled switch element of the charging circuit according to the voltage of the respective battery unit, the charging circuit controls connection or disconnection of the third switch element according to the switch state of the controlled switch element. So the charging current of the charging control circuit can be regulated to ensure each battery unit of the pile charged completely and efficiently. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be apparent to those skilled in the art by reading the following description of a preferred embodiment thereof, with reference to the attached drawings, in which: 
         FIG. 1  is a circuitry of a charging control circuit according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With reference to  FIG. 1 , a charging control circuit according to the present invention is shown. The charging control circuit is connected with a charging power supply  10  for charging a pile  20  formed by the series-connection of a plurality of rechargeable battery units. In this embodiment, the pile  20  is formed by the series-connection of a first battery unit  21  and a second battery unit  22 . The charging power supply  10  has a positive terminal  11  and a negative terminal  12 . The charging control circuit includes a protecting circuit  30 , a charging circuit  40  and a control circuit  50 . The anode of the first battery unit  21  is connected to the positive terminal  11  of the charging power supply  10  via the control circuit  50 , and the cathode of the second battery unit  22  is connected to the negative terminal  12  of the charging power supply  10  via a protecting switch assembly  60  which will be described in detail later on. 
     The protecting circuit  30  is a chip, such as an OZ890 type of chip, having a protecting, monitoring and control function. A Vcc port of the protecting circuit  30  is connected with the anode of the first battery unit  21  for supplying a working voltage to the protecting circuit  30  and a Vss port thereof is connected to ground. The protecting circuit  30  has a plurality of monitoring ports and control ports. In the embodiment, the monitoring ports include a first monitoring port  31 , a second monitoring port  32  and a third monitoring port  33 ; the control ports include a first control port  36 , a second control port  37 , a third control port  38  and a fourth control port  39 . The anode of the first battery unit  21  is connected to the first monitoring port  31  and the cathode thereof is connected to the second monitoring port  32 . The anode of the second battery unit  22  is connected to the second monitoring port  32  and the cathode thereof is connected to the third monitoring port  33 . So the voltage of the first battery unit  21  and the second battery unit  22  can be monitored by the protecting circuit  30 . 
     The charging circuit  40  includes a first diffluent circuit  41  and a second diffluent circuit  44 . The first diffluent circuit  41  has a first resistance element  42  and a first switch element  43 . The second diffluent circuit  44  has a second resistance element  45  and a second switch element  46 . In the embodiment, the switch elements  43 ,  46  are an N-channel FET respectively. One terminal of the first resistance element  42  is connected with the anode of the first battery unit  21  and the other terminal thereof is connected with the drain of the first switch element  43 . The source of the first switch element  43  is connected with the cathode of the first battery unit  21  and the grid thereof is connected to the first control port  36  of the protecting circuit  30 , so the connection and the disconnection of the first switch element  43  are controlled by the first control port  36 . One terminal of the second resistance element  45  is connected with the anode of the second battery unit  22  and the other terminal thereof is connected with the drain of the second switch element  46 . The source of the second switch element  46  is connected with the cathode of the second battery unit  22  and the grid thereof is connected to the second control port  33  of the protecting circuit  30 , so the connection and the disconnection of the second switch element  46  are controlled by the second control port  37 . 
     The charging circuit  40  further includes two photo-couplers  47  each having a light-emitting diode (LED)  47   a  and a photosensitive triode  47   b.  The positive electrode of one of the two LEDs  47   a  is connected with the anode of the first battery unit  21  and the negative electrode thereof is connected with the drain of the first switch element  43 . The positive electrode of the other LED  47   a  is connected with the anode of the second battery unit  22  and the negative electrode thereof is connected with the drain of the second switch element  46 . The collector of each of the photosensitive triodes  47   b  is connected to a regulated power supply  80  via a first voltage-dividing resistance  49  for supplying a working voltage to the corresponding photosensitive triode  47   b.  The emitter of each of the photosensitive triodes  47   b  is connected to ground. The connection and the disconnection of the photosensitive triode  47   b  are controlled by the corresponding LED  47   a.    
     The control circuit  50  has two branches. One of the two branches includes a third resistance element  51  having one terminal connected with the positive terminal  11  and the other terminal connected with the anode of the first battery unit  21 . The other branch includes a fourth resistance element  52  and a third switch element  53 . In the embodiment, the third switch element  53  is a P-channel FET. The source of the third switch element  53  is connected with the positive terminal  11  and the drain thereof is connected with one terminal of the fourth resistance element  52 . The other terminal of the fourth resistance element  52  is connected with the anode of the first battery unit  21 . The grid of the third switch element  53  is connected to the positive terminal  11  via a second voltage-dividing resistance  54  on one hand, and on the other hand connected to ground via a third voltage-dividing resistance  55  and a control switch  56 . In the embodiment, the control switch  56  is a NPN triode. One terminal of the third voltage-dividing resistance  55  is connected with the grid of the third switch element  53  and the other terminal thereof is connected with the collector of the control switch  56 . The emitter of the control switch  56  is connected to ground and the base thereof is connected with the collector of each of the photosensitive triodes  47   b  of the charging circuit  40 . So the photo-couplers  47  can control the connection and the disconnection of the control switch  56  for further controlling the connection and the disconnection of the third switch element  53 . 
     The protecting switch assembly  60  includes a first protecting switch  61  preventing the pile  20  from being over-discharged and a second protecting switch  62  preventing the pile  20  from being overcharged. In the embodiment, the protecting switches  61 ,  62  are respectively an N-channel FET. The drain of the first protecting switch  61  is connected with the drain of the second protecting switch  62 . The source of the first protecting switch  61  is connected with the cathode of the second battery unit  22 , and the source of the second protecting switch  62  is connected with the negative terminal  12 . The grid of the first protecting switch  61  is connected to the third control port  38  of the protecting circuit  30 , and the grid of the second protecting switch  62  is connected to the fourth control port  39 . So the connection and the disconnection of the protecting switches  61 ,  62  are controlled by the protecting circuit  30  so as to protect the pile  20  from being damaged on account of the over-discharging and overcharging. 
     The process of utilizing the above-mentioned charging control circuit to charge the pile  20  is described as follows. 
     In the process of charging the pile  20 , when the voltage difference between the first battery unit  21  and the second battery unit  22  is monitored by the protecting circuit  30  to be smaller than a specific data (such as 0.02˜0.01V), the first switch element  43  and the second switch element  46  are respectively disconnected by the first control port  36  and the second control port  37  of the protecting circuit  30 . At this time, the photo-couplers  47  are disconnected, the regulated power supply  80  supplies a voltage to the base of the control switch  56  so as to make the positive terminal  11 , the second voltage-dividing resistance  54 , the third voltage-dividing resistance  55 , the control switch  56  and ground to form a circuit. As a result, the potential of the source of the third switch element  53  is higher than the potential of the grid thereof that makes the third switch element  53  connected. So the total resistance is reduced and the charging current is increased because of the parallel-connection of the third resistance element  51  and the fourth resistance element  52  that improves the charging efficiency to the pile  20 . 
     When the voltage difference between the first battery unit  21  and the second battery unit  22  is monitored by the protecting circuit  30  to be greater than the said specific data, the first switch element  43  is connected by the first control port  36  of the protecting circuit  30  if the first battery unit  21  has a higher voltage, on the contrary, the second switch element  46  is connected by the second control port  37  if the second battery unit  22  has a higher voltage. Now take description to the working principle of the charging control circuit provided that the first battery unit  21  has a higher voltage. When the voltage of the first battery unit  21  is higher, the first switch element  43  is connected by the first control port  36  of the protecting circuit  30  so as to make the charging current divided by the first resistance element  42  and reduce the charging current to the first battery unit  21 . Simultaneously, the LED  47   a  emits light to make the corresponding photosensitive triode  47   b  connected. So the regulated power supply  80 , the first voltage-dividing resistance  49 , the corresponding photosensitive triode  47   b  and ground form a circuit for disconnecting the control switch  56 . As a result, the connection of the positive terminal  11 , the second voltage-dividing resistance  54 , the third voltage-dividing resistance  55 , the control switch  56  and ground is disconnected that makes the third switch element  53  disconnected. At this time, the charging power supply  10  charges the pile  20  only through the third resistance element  51  that makes the total resistance increased and the charging current reduced. Moreover the first resistance element  42  has a current-dividing function to the charging current that further reduces the charging current to the first battery unit  21 . Thereby the charging current is greater in the second battery unit  22  than in the first battery unit  21  that ensures the second battery unit  22  charged efficiently until the voltage difference between the first battery unit  21  and the second battery unit  22  is smaller than the said specific data. 
     When the voltage of the first battery unit  21  or the second battery unit  22  is monitored by the protecting circuit  30  to be raised to a predefined data (namely a protecting voltage for preventing the pile  20  from being overcharged), the second protecting switch  62  is disconnected by the fourth control port  39  of the protecting circuit  30  so as to terminate the process of charging the pile  20 . In the process of discharging the pile  20 , when the voltage of the first battery unit  21  or the second battery unit  22  is monitored by the protecting circuit  30  to go down to a predefined data (namely a protecting voltage for preventing the pile  20  from being over-discharged), the first protecting switch  61  is disconnected by the third control port  38  so as to terminate the process of discharging the pile  20 . Therefore the pile  20  can be protected from being damaged on account of the overcharging and over-discharging. 
     As described above, the charging control circuit of the present invention utilizes the protecting circuit  30  to control a switch state of the first switch element  43  and the second switch element  46  of the charging circuit  40  according to the voltage difference between the first battery unit  21  and the second battery unit  22 , and then utilizes the photo-coupler  47  of the charging circuit  40  to control connection or disconnection of the third switch element  53  of the control circuit  50  according to the said switch state so as to regulate the charging current for ensuring the first battery unit  21  and the second battery unit  22  be charged completely and efficiently.