Patent Publication Number: US-2011057616-A1

Title: Battery Charging Circuit

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to a battery charging circuit, and more particularly to a battery charging circuit capable of effectively charging a plurality of series-connected rechargeable batteries. 
     2. The Related Art 
     A battery charging circuit used to charge a rechargeable battery often has a control function for preventing the rechargeable battery from being overcharged. That is to say, in the process of charging the rechargeable battery, if the voltage of the rechargeable battery is raised to a default value, the battery charging circuit will turn off a switch unit so as to terminate the charge process. Therefore the rechargeable battery can avoid being damaged by overcharging. 
     However, when the above-mentioned battery charging circuit is used to charge a plurality of series-connected rechargeable batteries, if the remained power in each of the rechargeable batteries differs from one another, then the rechargeable 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 battery charging circuit will turn off the switch unit so as to protect the corresponding rechargeable battery from being overcharged that prevents the battery charging circuit from charging other rechargeable batteries. Therefore, when the charge process is terminated, some rechargeable batteries are not charged completely to be raised to the default value that will reduce the time of supplying power of the rechargeable batteries and speed up aging the rechargeable battery. Therefore, a battery charging circuit capable of overcoming the foregoing problems is required. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a battery charging circuit adapted for charging a plurality of series-connected rechargeable batteries. The battery charging circuit includes a plurality of charging units, a control module and a power input unit for supplying power to the charging units and the control module. Each of the charging units includes a connecting port for connecting one battery, an electromagnetic coil and a switch module connected between the connecting port and the electromagnetic coil. The connecting ports of the charging units are series-connected with one another. The control module is used for monitoring the voltage of the batteries and then controlling a work state of the switch modules by means of comparing a voltage variance between any two of the batteries with a specific data set in the control module so as to make the battery with a greatest voltage discharged to produce a discharge current for secondarily charging the other batteries by means of the electromagnetic coils when the voltage variance is greater than the specific data. So that retards the ageing of the batteries and further ensures each of the batteries charged completely and effectively. 
    
    
     
       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 of a battery charging circuit of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With reference to  FIG. 1 , a battery charging circuit  100  according to the present invention is shown. The battery charging circuit  100  includes a power input unit  1 , a control module  2  and a plurality of charging units. In this embodiment, there are four of the charging units respectively designated as a first charging unit  31 , a second charging unit  32 , a third charging unit  33  and a fourth charging unit  34 . The power input unit  1  is connected with an external power supply (not shown) so as to supply power to the control module  2  and the charging units  31 ˜ 34 . 
     The control module  2  has a monitoring and control function for the charging units  31 ˜ 34 . A Vcc port of the control module  2  is connected with the power input unit  1  for gaining a working voltage from the power input unit  1 , and a Vss port thereof is connected to ground. The control module  2  further has a plurality of monitoring ports and control ports. In the embodiment, the monitoring ports include a first monitoring port V 1 , a second monitoring port V 2 , a third monitoring port V 3  and a fourth monitoring port V 4 ; the control ports have four groups each including a first control port designated as PWM 1 ˜PWM 4 , a second control port designated as Poo 1 ˜Poo 4  and a third control port designated as EMF 1 ˜EMF 4 . 
     The first charging unit  31  includes a connecting port for connecting a first rechargeable battery  101 , a π filter, a switch module and an electromagnetic coil M 1 . The a filter includes two parallel capacitors C 1 , C 5  one of which is connected to the connecting port and a series inductance L 1 . The connecting port includes a positive connecting point p 12  connected to the first monitoring port V 1  of the control module  2  through a first resistor R 5  and a negative connecting point p 11  connected to ground, so the voltage of the first rechargeable battery  101  can be monitored by the first monitoring port V 1  of the control module  2 . The switch module includes a diode D 1 , a resistance element R 1 , a first switch element Q 1 , a second switch element Qp 1  and a third switch element Qe 1 . In the embodiment, the first switch elements Q 1  and the third switch element Qe 1  are an N-channel FET respectively, and the second switch element Qp 1  is a P-channel FET. The sources of the first switch element Q 1  and the third switch element Qe 1  are connected with the negative connecting point p 11 . The drain of the first switch element Q 1  is on one hand connected to the drains of the second switch element Qp 1  and the third switch element Qe 1  through the electromagnetic coil M 1 , and on the other hand, connected to the source of the second switch element Qp 1  through the diode D 1 . The grid of the first switch element Q 1  is connected with the first control port PWM 1  of the control module  2 , and the grid of the third switch element Qe 1  is connected with the third control port EMF 1  of the control module  2 , so the switch state of the first and third switch elements Q 1 , Qe 1  can be respectively controlled by the first and third control ports PWM 1 , EMF 1 . The source of the second switch element Qp 1  is further on one hand connected to the positive connecting point p 12  through the inductance L 1 , and on the other hand, connected to the grid thereof through the resistance element R 1 . The grid of the second switch element Qp 1  is further connected with the second control port Poo 1  of the control module  2 , so the connection and the disconnection of the second switch element Qp 1  can be controlled by the second control port Poo 1 . 
     The second, third and fourth charging units  32 ˜ 34  each has the same circuitry as the first charging unit  31 , and includes a connecting port which includes a positive connecting point designated as p 22 , p 32 , p 42  and a corresponding negative connecting point designated as p 21 , p 31 , p 41 , a π filter which includes two capacitors designated as C 2  and C 6 , C 3  and C 7 , C 4  and C 8  and an inductance designated as L 2 , L 3 , L 4 , a switch module and an electromagnetic coil designated as M 2 , M 3 , M 4 . Each of the switch modules of the second, third and fourth charging units  32 ˜ 34  includes a diode designated as D 2 , D 3 , D 4 , a resistance element designated as R 2 , R 3 , R 4 , a first switch element designated as Q 2 , Q 3 , Q 4 , a second switch element designated as Qp 2 , Qp 3 , Qp 4 , and a third switch element designated as Qe 2 , Qe 3 , Qe 4 . The connecting ports of the second, third and fourth charging units  32 ˜ 34  are respectively used to connect a second rechargeable battery  20 , a third rechargeable battery  30  and a fourth rechargeable battery  40 . The positive connecting points p 22 , p 32 , p 42  are respectively connected to the second, third and fourth monitoring ports V 2 , V 3 , V 4  of the control module  2  through a second, third and fourth resistor R 6 , R 7 , R 8 . The connecting ports of the charging units  31 ˜ 34  are series-connected with one another, and the outmost positive connecting point p 42  of the fourth charging unit  34  is connected with the power input unit  1 . The grids of the first switch elements Q 2 , Q 3 , Q 4  of the second, third and fourth charging units  32 ˜ 34  are respectively connected with the first control ports PWM 2 , PWM 3 , PWM 4  of the control module  2 , the grids of the second switch elements Qp 2 , Qp 3 , Qp 4  thereof are respectively connected with the second control ports Poo 2 , Poo 3 , Poo 4 , and the grids of the third switch elements Qe 2 , Qe 3 , Qe 4  thereof are respectively connected with the third control ports EMF 2 , EMF 3 , EMF 4 . The electromagnetic coils M 1 ˜M 4  of the charging units  31 ˜ 34  are wound around only one core (not labeled) in the same direction for strengthening the magnetic field intensity when there is current flowed therethrough. 
     When the battery charging circuit  100  charges the series-connected rechargeable batteries  101 ,  20 ,  30 ,  40 , the control module  2  controls all of the switch modules of the four charging units  31 ˜ 34  off. At the same time, the control module  2  utilizes the monitoring ports V 1 ˜V 4  to respectively monitor the voltage of the corresponding rechargeable batteries  101 ,  20 ,  30 ,  40 . When the voltage variance between any two of the rechargeable batteries  101 ,  20 ,  30 ,  40  is monitored by the control module  2  to be greater than a specific data set in the control module  2 , the working principle of the battery charging circuit  100  is described hereinafter. Now take description to the working principle of the battery charging circuit  100  provided that the first rechargeable battery  101  has a highest voltage. At this moment, the control module  2  controls the switch module of the first charging unit  31  to be in a discharging state, that is to say, the first control port PWM 1  controls the first switch element Q 1  continually connected and disconnected, the second control port Pool controls the second switch element Qp 1  connected and the third control port EMF 1  controls the third switch element Qe 1  disconnected so as to make the first rechargeable battery  101  discharged by means of the electromagnetic coil M 1 . Simultaneously, the control module  2  controls the switch modules of the second, third and fourth charging units  32 ˜ 34  to be in a secondary charging state, namely the first switch elements Q 2 ˜Q 4  and the second switch elements Qp 2 ˜Qp 4  being disconnected and the third switch elements Qe 2 ˜Qe 4  being connected so as to make the second, third and fourth rechargeable batteries  20 ,  30 ,  40  charged by means of the corresponding electromagnetic coils M 2 ˜M 4 . 
     When the first rechargeable battery  101  is discharged to produce a discharge current, the discharge current will substantially flow in the following direction: the positive connecting point p 12 →the second switch element Qp 1 →the electromagnetic coil M 1 →the first switch element Q 1 →the negative connecting point p 11 . As a result, the discharge current is partially transformed into magnetic energy through the electromagnetic coil M 1 , then the magnetic energy is newly transformed into electrical energy by means of the electromagnetic coils M 2 ˜M 4  so as to charge the second, third and fourth rechargeable batteries  20 ,  30 ,  40  through the corresponding diodes D 2 ˜D 4  and the corresponding third switch elements Qe 2 ˜Qe 4  respectively until the voltage variance between the first rechargeable battery  101  and each of the second, third and fourth rechargeable batteries  20 ,  30 ,  40  is re-monitored by the control module  2  to be smaller than the specific data. At this time, the control module  2  re-controls all of the switch modules of the charging units  31 ˜ 34  to be disconnected to make the rechargeable batteries  101 ,  20 ,  30 ,  40  continuatively charged by the power input unit  1 . 
     The working principle of the control module  2  controlling the second, third and fourth charging units  32 ˜ 34  is the same as the one of controlling the first charging unit  31 , so it will not be described any more. When all of the series-connected rechargeable batteries  101 ,  20 ,  30 ,  40  are fully charged, the charge process of the battery charging circuit  100  is stopped by the control module  2 . 
     As described above, the battery charging circuit  100  of the present invention utilizes the control module  2  to control the work state of the switch modules of the charging units  31 ˜ 34  according to the compared result of the voltage variance between the any two of the series-connected rechargeable batteries  101 ,  20 ,  30 ,  40  and the specific data, and then utilizes the electromagnetic coils M 1 ˜M 4  to transfer the electrical energy of the rechargeable battery with the greatest voltage to the other rechargeable batteries so that retards the ageing of the rechargeable battery and further ensures each of the rechargeable batteries  101 ,  20 ,  30 ,  40  charged completely and effectively.