Abstract:
In the related art, the measurement error due to the internal resistance of the battery is not considered in the battery balance method, such that the battery balance is not accurate, or the battery balance process is frequently started and stopped. In exemplary embodiments of the invention, detecting battery voltage and balancing battery voltage are performed in different time, such that the difference of charge current/discharge current among the batteries due to the battery voltage balance process do not affect the battery voltage detecting.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the priority benefit of China application serial no. 201010146528.1, filed on Apr. 13, 2010. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The invention generally relates to a battery voltage balance apparatus and a battery charge apparatus. More particularly, the invention relates to a battery voltage balance apparatus and a battery charge apparatus which perform the battery voltage detecting and the battery voltage balancing in different time. 
         [0004]    2. Description of Related Art 
         [0005]    With the development of portable electronic products, the requirement for chargeable battery is gradually increased. The type of chargeable battery is classified into the conventional nickel-cadmium (NiCd) battery, the advanced nickel-metal hydride (NiMH) battery and lithium ion (Li-ion) battery, and the modern Li-Polymer battery. The voltages provided by the different type of chargeable batteries are different, and the operation voltages of the portable electronic products are also different. Accordingly, the manufacturer may couple a plurality of batteries in series as a battery module to provide the desired voltage depending on the operation voltage of the portable electronic product. 
         [0006]    When the energy of the batteries in the battery module has been depleted, a battery charger is needed to charge the battery module for next usage. However, the battery capacities of the batteries in the battery module may be different depending on manufacture and usage. For example, a 7.4V Li battery module is formed by two 3.7V Li batteries coupled in series. Before the two batteries are dispatch from the factory, the battery capacities thereof are respectively 80% and 70%. Because over charging will damage the Li battery, the Li battery charger may stop charging the Li battery module when any of the batteries has been fully charged. At this time, the battery capacities of the two batteries may respectively be 100% (the maximum) and 90%. During usage, when any of the battery capacities has fallen down to 0% (the minimum), the battery module can not be used any more. Accordingly, when the battery capacities of the two batteries have respectively fallen down to 10% and 0%, the battery module must be charged before usage. 
         [0007]    As known from above, when the battery capacities of the batteries in the battery module are different, the practical electric power of the battery module for usage is determined according to the battery having the lower battery capacity. Besides, when the battery is not used, the battery may self-discharge. In the condition that the self-discharge rate of each battery is different, the battery capacities thereof will be gradually unbalanced, so that the practical electric power of the battery module for usage also gradually decreases as the time goes on, thereby lowering the efficiency of the battery module and shortening the battery life thereof. 
         [0008]    Referring to  FIG. 1 , it shows a digital battery balance controller which is disclosed in the datasheet of ISL9208 by Intersil. A digital battery balance controller  10  includes a battery balance microcontroller  5  and transistor switches S 1 -S 7 . The transistor switches S 1 -S 7  are respectively parallel with batteries BAT 1 -BAT 7  through resistors R 1 -R 7 . The voltages of the batteries BAT 1 -BAT 7  are converted to digital signals through A/D converters. According to the digital signals corresponding to the batteries BAT 1 -BAT 7 , the battery balance microcontroller  5  determines the battery having the highest voltage by an algorithm built inside, and further, turns on the parallel transistor switch corresponding to the battery having the highest voltage. Accordingly, the charge current of each battery can be adjusted based on the voltage of each battery to achieve the function of charge balance. 
         [0009]    However, each battery has internal resistance, and when the charge balance is performed, the charge currents of the batteries are different, i.e. the charge current of the battery having the higher battery voltage is smaller. Accordingly, the measurement for battery voltages is not correct. Especially, for the battery module having the larger battery capacity or charging by fast charging technology, the charge currents are relatively large, such that the measurement errors of battery voltages are also larger. 
       SUMMARY OF THE INVENTION 
       [0010]    Accordingly, in the related art, the measurement error due to the internal resistance of the battery is not considered in the battery balance method, such that the battery balance is not accurate, or the battery balance process is frequently started and stopped. In exemplary embodiments of the invention, detecting battery voltage and balancing battery voltage are performed in different time, such that the difference of charge current/discharge current among the batteries due to the battery voltage balance process do not affect the battery voltage detecting. 
         [0011]    An embodiment of the invention provides a battery voltage balance apparatus including a timing control unit, a balance determining unit, and a battery voltage balance unit. The timing control unit alternately determines a detecting timing and a balance timing, wherein the detecting timing and the balance timing do not overlap with each other. The balance determining unit is coupled to a plurality of battery units coupled in series and the timing control unit. The balance determining units detects battery voltages of the battery units during the detecting timing to determine whether to start a battery voltage balance process. The battery voltage balance unit is coupled to the battery units, the balance determining unit, and the timing control unit. When the battery voltage balance process starts, the battery voltage balance unit controls at least one of a charging rate and a discharging rate of the battery unit having a highest battery voltage and at least one of a charging rate and a discharging rate of the battery unit having a lowest battery voltage to have a difference, such that battery voltage difference between any two of the battery units is decreased to within a first predetermined value or a first predetermined percentage. 
         [0012]    Another embodiment of the invention provides a battery charge apparatus adapted to charge a battery module. The battery module includes a plurality of battery units coupled in series. The battery charge apparatus includes a charge control unit, a timing control unit, and a balance determining unit. The charge control unit is coupled to a power supply and the battery module and controls the power supply to provide a charge current to charge the battery module. The timing control unit alternately determines a detecting timing and a balance timing, wherein the detecting timing and the balance timing do not overlap with each other. The balance determining unit is coupled to a plurality of battery units and the timing control unit. The balance determining units detects battery voltages of the battery units during the detecting timing to determine whether to start a battery voltage balance process. The battery voltage balance unit is coupled to the battery units, the balance determining unit, and the timing control unit. When the battery voltage balance process starts, the battery voltage balance unit controls a charging rate a of the battery unit having a highest battery voltage and a charging rate of the battery unit having a lowest battery voltage to have a difference, such that battery voltage difference between any two of the battery units is decreased to within a first predetermined value or a first predetermined percentage. 
         [0013]    It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed. In order to make the features and the advantages of the invention comprehensible, exemplary embodiments accompanied with figures are described in detail below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
           [0015]      FIG. 1  shows a digital battery balance controller which is disclosed in the datasheet of ISL9208 by Intersil. 
           [0016]      FIG. 2  is a schematic block diagram of a battery charge apparatus according to an embodiment of the invention. 
           [0017]      FIG. 3  is a schematic circuit diagram of a battery voltage balance apparatus according to a first embodiment of the invention. 
           [0018]      FIG. 4  is a schematic circuit diagram of a battery voltage balance apparatus according to a second embodiment of the invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0019]      FIG. 2  is a schematic block diagram of a battery charge apparatus according to an embodiment of the invention. Referring to  FIG. 2 , the battery charge apparatus includes a charge control unit  140 , a balance determining unit  110 , a battery voltage balance unit  120 , and a timing control unit  130 . The battery charge apparatus is used to charge a battery module BAT. Herein, the battery module BAT includes a plurality of battery units coupled in series, and the balance determining unit  110 , the battery voltage balance unit  120 , and the timing control unit  130  form a battery voltage balance apparatus. In the present embodiment, the battery module BAT including the battery units Cell 1 , Ce 112 , and Ce 113  is exemplary. 
         [0020]    The charge control unit  140  is coupled to a charge switch  145  coupled with a power source VCC and the battery module BAT, and controls the charging and discharging of the battery module BAT by the charge switch  145 . Accordingly, the charge control unit  140  determines whether to provide a charge current Ich from the power source VCC to the battery module BAT to charge the battery module BAT. The timing control unit  130  alternately generates a first timing signal t 1  and a second timing signal t 2  to the balance determining unit  110  and the battery voltage balance unit  120 , so as to control their operation. That is, the first timing signal t 1  and the second timing signal t 2  respectively represents a detecting timing and a balance timing. Moreover, the detecting timing and the balance timing do not overlap with each other, such that the timing of the balance determining unit  110  detecting the battery units Cell 1 , Ce 112 , and Ce 113  and the timing of the battery voltage balance unit  120  balancing the battery units Cell 1 , Ce 112 , and Ce 113  do not overlap with each other. 
         [0021]    The balance determining unit  110  is coupled to the battery module BAT and the timing control unit  130 . When receiving the first timing signal t 1 , the balance determining unit  110  determines whether to perform a battery voltage balance process according to battery voltage detecting signals DET 1 , DET 2 , and DET 3  of the battery units Cell 1 , Ce 112 , and Ce 113 . When the voltage difference between any two of the battery units Cell 1 , Ce 112 , and Ce 113  is higher than a predetermined percentage or a predetermined voltage difference, the balance determining unit  110  generates a balance start signal BC to start the battery voltage balance process. The balance start signal BC is used to inform the battery voltage balance unit  120  of the conditions of the battery units in the battery module BAT. Accordingly, the balance start signal BC may be a single signal or a combination of many signals according to the number of the battery units in the battery module BAT. 
         [0022]    The battery voltage balance unit  120  is coupled to the balance determining unit  110 , the battery module BAT, and the timing control unit  130 . When receiving the balance start signal BC and the second timing signal t 2 , the battery voltage balance unit  120  performs the battery voltage balance process. The battery voltage balance unit  120  determines which one of the battery units in the battery module BAT has the highest battery voltage or which one of the battery units in the battery module BAT has the lowest battery voltage, so as to control a charging rate and/or a discharging rate, i.e. the charge current and/or the discharge current, of the battery unit having the highest battery voltage and a charging rate and/or a discharging rate, i.e. the charge current and/or the discharge current, of the battery unit having the lowest battery voltage to have a difference. Accordingly, the voltage difference of the highest battery voltage and the lowest battery voltage is gradually decreased, and when the voltage difference of any two of the battery units in the battery module BAT decreases to within a predetermined stopping voltage difference or a predetermined stopping voltage difference percentage, the balance determining unit  110  stops the battery voltage balance process. 
         [0023]    Accordingly, when the battery voltage balance unit  120  performs the battery voltage balance process, and thereby the currents of the battery units in the battery module BAT are different, the balance determining unit  110  stops detecting the battery voltages of the battery units to avoid an inaccurate detecting due to the different value of the currents flowing through internal resistors Ri 1 , Ri 2 , and Ri 3  of the battery units Cell 1 , Ce 112 , and Cell 3 . When the battery voltage balance unit  120  stops performing the battery voltage balance process, the currents of the battery units in the battery module BAT are identical due to that the battery units are connected in series (charge state) or the battery units stays in open-circuit state (non-charge state). At this time, the balance determining unit  110  detects the battery voltages of the battery units to obtain accurate battery voltages, so as to determine whether to start or maintain the battery voltage balance process based on the accurate battery voltages. Therefore, in the present embodiment, by alternately performing battery voltage detecting and battery voltage balancing in different time, the issue of detecting inaccurate battery voltages due to internal battery resistance in the related art could be avoided. 
         [0024]      FIG. 3  is a schematic circuit diagram of a battery voltage balance apparatus according to a first embodiment of the invention. Referring to  FIG. 3 , the battery voltage balance apparatus includes a balance determining unit  210 , a battery voltage balance unit  220 , and a timing control unit  230 . The timing control unit  230  includes a first timing generating circuit  232  and a second timing generating circuit  234 . The first timing generating circuit  232  generates a first timing signal t 1  to represent a detecting timing by a detecting timing capacitor Cde. The second timing generating circuit  234  generates a second timing signal t 2  to represent a balance timing by a balance timing capacitor Cba. When the detecting timing capacitor Cde is charged to a predetermined level by the first timing generating circuit  232 , the first timing generating circuit  232  stops generating the first timing signal t 1 , and further generates a first reset signal Re 1  and releases the charge stored in the detecting timing capacitor Cde. The second timing generating circuit  234  is triggered by the first reset signal Re 1 , and thereby generates the second timing signal t 2 , and charges the balance timing capacitor Cba. When the balance timing capacitor Cba is charged to a predetermined level, the second timing generating circuit  234  stops generating the second timing signal t 2 , and further releases the charge stored in the balance timing capacitor Cba and generates a second reset signal Re 2  to trigger the first timing generating circuit  232  to generate the first timing signal t 1 . 
         [0025]    The balance determining unit  210  includes a detecting circuit  212  and a reference voltage generating circuit  214 . The reference voltage generating circuit  214  generates a reference voltage signal Vr, and the reference voltage signal Vr may be an average battery voltage of the battery units in the battery module BAT. The detecting circuit  212  is coupled to the first timing generating circuit  232 , the reference voltage generating circuit  214 , and the positive ends and the negative ends of the battery units to receive the reference voltage signal Vr and battery voltage detecting signals DETi, wherein the value i represents the number of the battery units and is an integer larger than 1. Accordingly, the detecting circuit  212  determines whether to start the battery voltage balance process, When receiving the first timing signal t 1  and determining the voltage difference between any two of the battery units is higher than a predetermined percentage or a predetermined voltage difference, the detecting circuit  212  generates the balance start signal BC to start the battery voltage balance process. 
         [0026]    The battery voltage balance unit  220  includes a balance control circuit  222  and a battery voltage balance circuit  224 . The battery voltage balance circuit  224  includes a plurality of transistor switches (not shown) which are respectively parallel to the battery units in the battery module. The battery voltage balance circuit  224  discharges the battery unit having the higher voltage (including the highest voltage) (non-charge state) or decreases the charge current of the battery unit having the higher voltage (charge state). The balance control circuit  222  determines the transistor switch(es) which must be conducted while the battery voltage balance process is preformed according to the balance start signal BC. Next, when receiving the second timing signal t 2 , the balance control circuit  222  generates a control signal Sj to conduct which transistor switch(es) in the battery voltage balance circuit  224  to adjust the charge or discharge rate of the battery units. Herein, the value j represents the number of the transistor switches in the battery voltage balance circuit  224  and is an integer larger than 1. 
         [0027]    By releasing the power stored in the battery unit having the higher voltage or decreasing the charge current of the battery unit, the battery voltage balance apparatus shown in  FIG. 3  gradually decreases the voltage differences among the battery units until the voltage difference of any two of the battery units is decreased to within the predetermined stopping voltage difference or the predetermined stopping voltage difference percentage. However, in this case, the power is consumed, and even the temperature of the battery module is inappropriately increased. Accordingly, the battery voltage balance apparatus can adopt a battery voltage balance unit having an energy storage circuit, such that the power is stored in the energy storage circuit, substituted for consuming power. Furthermore, the power stored in the energy storage circuit can charge the battery module. Hence, it reduces the power consumption in the battery voltage balance process. It will be described in detail as follows. 
         [0028]      FIG. 4  is a schematic circuit diagram of a battery voltage balance apparatus according to a second embodiment of the invention. Referring to  FIG. 4 , the battery voltage balance apparatus includes a balance determining unit  310 , a battery voltage balance unit  320 , and a timing control unit  330 . The balance determining unit  310  includes a detecting circuit  312  and a reference voltage generating circuit  314 . The battery voltage balance unit  320  includes a balance control circuit  322 , a battery voltage balance circuit  324 , and an energy storage circuit  326 . The timing control unit  330  includes a timing generating circuit  332  and a time capacitor Ct. 
         [0029]    The timing generating circuit  332  is coupled to the balance determining unit  310  and the battery voltage balance unit  320 . The timing generating circuit  332  determines the period of the detecting timing according to the time capacitor Ct and the period of the balance timing according to a current detecting signal Isei of the battery voltage balance unit  320 . In order to cooperate with the battery module in charge process or at a specific time to perform the battery voltage balance process, the timing generating circuit  332  can simply start to determine the detecting timing and the balance timing and correspondingly generates the first timing signal t 1  and the second timing signal t 2  after receiving a start signal EN. During the detecting timing, the timing generating circuit  332  generates the first timing signal t 1 . When the detecting circuit  312  receives the first timing signal t 1  and determines the voltage difference between any two of the battery units is higher than a predetermined percentage or a predetermined voltage difference according to the battery voltage detecting signals DETi and the reference voltage signal Vr generated by the reference voltage generating circuit  314 , the detecting circuit  312  generates the balance start signal BC to start the battery voltage balance process. 
         [0030]    When the time capacitor Ct is charged to a predetermined level by the timing generating circuit  332 , the timing generating circuit  332  stops generating the first timing signal t 1 , and further generates the second timing signal t 2  and releases the charge stored in the time capacitor Ct. The balance control circuit  322  determines to perform the battery voltage balance process according to the balance start signal BC. When receiving the second timing signal t 2 , the balance control circuit  322  generates a control signal Sj to conduct the transistor switch(es) in the battery voltage balance circuit  324 . Therefore, the power of the battery unit having the higher voltage is transmitted to and stored in the energy storage circuit  326  through the transistor switch(es) in the battery voltage balance circuit  324 , and then the power stored in the energy storage circuit  326  is released to charge the battery unit having the lower voltage. The current detecting signal Isei represents the value of the current flowing through the transistor switch(es) in the battery voltage balance circuit  324 . When the current detecting signal Isei is smaller than a predetermined value, it means the process of the energy storage circuit  326  charging the battery unit having the lower voltage is going to be finished. Accordingly, the timing generating circuit  332  would stop generating the second timing signal t 2  to stop the balance timing and further generate the first timing signal t 1  later or at the same time. 
         [0031]    In the present embodiment, the timing control unit  330  determines the state of the battery voltage balance process performed by the battery voltage balance unit  320  according to the current detecting signal Isei, and accordingly determines the period of the balance timing. Therefore, in the present embodiment, the timing control unit  330  can cooperate with the battery voltage balance unit  320  according to the practical state, such that the battery voltage balance process is more effectively performed. Moreover, as the timing control unit  230  shown in  FIG. 3 , the timing control unit  330  may also set the periods of the detecting timing and the balance timing to be constant. 
         [0032]    In addition, the battery voltage balance circuit  324  may be a DC-DC converting circuit, such as a DC-DC step-up converter, a DC-DC step-down converter, a DC-DC SEPIC converter, a low dropout regulator (LDO), and a converting circuit capable of converting voltage. The battery voltage balance circuit  324  is used to buck or boost the voltage of at least one of the battery units and store the power to the energy storage circuit  326 . For example, when the battery voltage balance circuit  324  is a converting circuit capable of boosting voltage, the battery voltage balance circuit  324  can convert the voltage of the battery unit having the highest voltage into a voltage higher than the voltage of the battery module, i.e. the total voltage of the battery units coupled in series, in the balance timing, for storing the power in the energy storage circuit  326 . Then, the stored power is releases to charge the battery module. When the battery voltage balance circuit  324  is a converting circuit capable of bucking voltage, the battery voltage balance circuit  324  can convert the voltage of the battery unit having the highest voltage or the battery module into a voltage higher than the battery unit having the lowest voltage in the balance timing for storing the power in the energy storage circuit  326 . Then, the stored power is releases to charge the battery unit having the lowest voltage. 
         [0033]    Furthermore, the battery units are frequently charged and/or discharged in the battery voltage balance process, such that the maximum battery capacity or the discharge capability of the battery units is reduced due to memory effect. Accordingly, the balance determining unit can simply generate the balance start signal BC to start the battery voltage balance process when the voltages of the battery units are all within a predetermined battery voltage range or higher than a predetermined battery voltage, wherein the battery units within the predetermined battery voltage range or higher than the predetermined battery voltage have slighter memory effect. 
         [0034]    As the above description, the invention completely complies with the patentability requirements: novelty, non-obviousness, and utility. It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the invention without departing from the scope or spirit of the invention. In view of the foregoing descriptions, it is intended that the invention covers modifications. and variations of this invention if they fall within the scope of the following claims and their equivalents.