Abstract:
An apparatus for improving protection of a battery pack when the battery pack is in a very low power state, the battery pack including a plurality of battery cells coupled to present an output voltage at a battery potential locus and a protection device for providing a plurality of safeguards to protect the battery pack, affects operation of the protection device to control at least one safeguard and includes a current sensing unit coupled with the plurality of battery cells and with the protection device. The current sensing unit senses a battery traversing current associated with at least one battery cell. The current sensing unit generates an alerting signal when the battery traversing current exceeds a predetermined value. The protection device enables the at least one safeguard in response to the alerting signal.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention is directed to protection for a battery pack, and especially to improving operation of a protection device associated with a battery pack in a very low power state.  
         [0002]     A battery pack may be in a very low power state for one of several reasons. For example, a battery pack may be in a very low power state because it is nearly fully spent or drained. A battery pack may be in a very low power state because it is a new battery pack that has never been charged up.  
         [0003]     Yet another reason that a battery pack may be in a very low power state is because its protection mechanism or system (i.e., electronics circuitry associated with and usually integrally housed with a battery pack) has been ordered into such a low power state. Battery packs typically have a number of different power states, such as a NORMAL state which is extant during normal operations of a unit powered by a battery pack. Another power state often used with a battery pack is a SLEEP state. A SLEEP state is usually employed after no operation of the device powered by the battery pack is noted for a predetermined time.  
         [0004]     An example of such a situation is there not having been any key strokes entered to a laptop computer for a given time interval so the laptop computer orders its battery pack to a SLEEP state or mode. In such a SLEEP state the laptop battery pack powers fewer functions of the laptop and thereby conserves battery power for later availability when the laptop is being used. This is a way to extend useful battery life for a battery-powered device. It is typical that safeguards are still in place to protect the battery pack when a laptop orders the battery pack into a SLEEP state. Representative safeguards include, by way of example and not by way of limitation, protection against over-voltage, under-voltage, overload, over-current and short-circuit.  
         [0005]     Another power state into which a battery pack may be placed is known as a SHIP state (sometimes referred to as a SHUTDOWN state). A SHIP power state is a sort of extended sleep mode that is generally employed for extending shelf life of a battery pack or for conserving battery power during other lengthy dormant periods such as when the battery pack is in shipment. When a battery pack is in a SHIP state or mode it is in a very low power mode (or, ultra-low power mode) during which power is conserved to a great degree by denying of power to various functions, including by way of example and not by way of limitation, the “gas gauge” function for relating amount of power used and safety FET (field effect transistor) control. Safety FETs are provided to isolate the battery pack from voltage or current that exceeds the safe operating parameters of the battery chemistry to the point of rendering the cells unusable and un-repairable.  
         [0006]     There is a need for an apparatus for improving protection of a battery pack when the battery pack is in a very low power state.  
       SUMMARY OF THE INVENTION  
       [0007]     An apparatus for improving protection of a battery pack when the battery pack is in a very low power state, the battery pack including a plurality of battery cells coupled to present an output voltage at a battery potential locus and a protection device for providing a plurality of safeguards to protect the battery pack, affects operation of the protection device to control at least one safeguard and includes a current sensing unit coupled with the plurality of battery cells and with the protection device. The current sensing unit senses a battery traversing current associated with at least one battery cell. The current sensing unit generates an alerting signal when the battery traversing current exceeds a predetermined value. The protection device enables the at least one safeguard in response to the alerting signal.  
         [0008]     It is, therefore, an object of the present invention to provide an apparatus for improving protection of a battery pack when the battery pack is in a very low power state.  
         [0009]     Further objects and features of the present invention will be apparent from the following specification and claims when considered in connection with the accompanying drawings, in which like elements are labeled using like reference numerals in the various figures, illustrating the preferred embodiments of the invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  is a schematic diagram illustrating the preferred embodiment of the present invention.  
         [0011]      FIG. 2  is a schematic diagram illustrating a first alternate embodiment of the present invention.  
         [0012]      FIG. 3  is a schematic diagram of the preferred embodiment of the current sensing device used for the present invention.  
         [0013]      FIG. 4  is a schematic diagram illustrating a second alternate embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0014]      FIG. 1  is a schematic diagram illustrating the preferred embodiment of the present invention. In  FIG. 1 , a battery pack  10  includes a battery cell array  12  and a protective system  13 . Battery cell array  12  includes a plurality of batteries, represented by battery cells  14   1 ,  14   2 ,  14   3 ,  14   n  coupled together to present an output voltage at a battery potential locus  20 . The indicator “n” is employed to signify that there can be any number of battery cells  14   n  in battery cell array  12 . The inclusion of four battery cells  14   1 ,  14   2 ,  14   3 ,  14   n , in  FIG. 1  is illustrative only and does not constitute any limitation regarding the number of battery cells that may be included in battery cell array  12 . Battery cells  14   1 ,  14   2 ,  14   3 ,  14   n  are connected in series between battery potential locus  20  and a ground locus  22  via a resistor  24 . Resistor  24  is proximate with ground locus  22 .  
         [0015]     A charging potential (not shown in  FIG. 1 ) may be applied at a charging locus  30  for charging battery cell array  12 . Charging locus  30  is coupled with battery cell array  12  via a charge FET (field effect transistor)  32  and a discharge FET  34  coupled in series. A control logic unit  40  is coupled with charge FET  32  and discharge FET  34  to control their operation and thereby control connection of charging locus  30  with battery cell array  12 . Control logic unit  40  is coupled with a protective device  50 . Protective device  50  is also coupled across each respective cell  14   1 ,  14   2 ,  14   3 ,  14   n  in battery cell array  12 . Protective device  50  is illustrated in  FIG. 1  as a single unitary protective device. However, protective device  50  may be embodied in a plurality of individual protective devices (not shown in  FIG. 1 ), each of which individual protective devices is connected across a respective battery cell  14   1 ,  14   2 ,  14   3 ,  14   n .  
         [0016]     A current sensor device  52  is coupled across resistor  24 . Current sensor device  52  has an alert signal output locus  51 . Protective device  50  has an alert signal input locus  49  that is coupled with alert signal output locus  51  (connection not shown in  FIG. 1 ). Whenever battery pack  10  is in a very low or an ultra-low power state and current through resistor  24  is greater than a predetermined amount current sensor device  52  generates an ALERT signal at alert signal output locus  51 . Protective device  50  receives the ALERT signal at alert signal input locus  49  and responds to the ALERT signal by enabling predetermined safeguards that are disabled because battery pack  10  is in an ultra-low power state.  
         [0017]     Another current sensor device  54  is coupled with charging locus  30  and battery potential locus  20 . Current sensor device  54  has an alert signal output locus  53 . Alert signal output locus  53  is coupled with alert signal input locus  49  (connection not shown in  FIG. 1 ). Whenever battery pack  10  is in a very low or an ultra-low power state and current between charging locus  30  and battery potential locus  20  is greater than a predetermined amount current sensor  54  generates an ALERT signal at alert signal output locus  53 . Protective device  50  receives the ALERT signal at alert signal input locus  49  and responds to the ALERT signal by enabling predetermined safeguards that are disabled because battery pack  10  is in an ultra-low power state.  
         [0018]     Whenever battery pack  10  is in an ultra-low power state most protection features or safeguards provided by protection device  50  are disabled to conserve power. In such an ultra-low power state, FETs  32 ,  34  are also usually turned off. Prior art battery packs only permit exiting the ultra-low power state by applying a voltage to charging locus  30  that is greater than potential at battery potential locus  20 . This operation is typically accomplished using a battery charger unit connected with charging locus  30 .  
         [0019]     However, if a short circuit occurs that causes a fault manifested by excessive current flow between charging locus  30  and battery potential locus  20 , then an over-current or overload condition could occur. An example of a circumstance in which such a fault may occur is if one of FETs  32 ,  34  is damaged when using a charging unit attached with charging locus  30  and a resulting reverse current from charging locus  30  to battery potential locus  20  is great enough to overcome one of FETs  32 ,  34 . Protective device  50  cannot protect against an over-current or overload condition because safeguards protecting against such conditions are disabled while battery pack  10  is in the ultra-low state. As a result, battery pack  10  may be damaged beyond use or repair.  
         [0020]     The apparatus of the present invention equips battery pack  10  to sense current draw that would occur in the circumstance of applying a voltage to charging locus  30  with either of FETs  32 ,  34  damaged. Protective device  50  is structured to respond to the current sensing (i.e., responds to the ALERT signal from either of current sensors  52 ,  54 ) to enable appropriate safeguards to be exercised by protective device  50  to keep battery pack  10  safe. In contrast, prior art battery protection systems typically employ a voltage sensor in place of current sensor  54 , and typically have no structure similar to current sensor  52 .  
         [0021]      FIG. 2  is a schematic diagram illustrating a first alternate embodiment of the present invention. In  FIG. 2 , a battery pack  100  includes a battery cell array  112  and a protective system  113 . Battery cell array  112  includes a plurality of batteries, represented by battery cells  114   1 ,  114   2 ,  114   3 ,  114   n  coupled together to present an output voltage at a battery potential locus  120 . The indicator “n” is employed to signify that there can be any number of battery cells  114   n  in battery cell array  112 . The inclusion of four battery cells  114   1 ,  114   2 ,  114   3 ,  114   n  in  FIG. 2  is illustrative only and does not constitute any limitation regarding the number of battery cells that may be included in battery cell array  112 . Battery cells  114   1 ,  114   2 ,  114   3 ,  114   n  are connected in series with resistors  124   1 ,  124   2 ,  124   3 ,  124   n . Resistor  124 , is coupled between battery cells  114   1 ,  114   2 .  
         [0022]     Resistor  124   2  is coupled between battery cells  114   2 ,  114   3 . Resistor  124   3  is coupled between battery cells  114   3 ,  114   n . Resistor  124   n  is coupled between battery cells  114   n  and ground locus  122 . The indicator “n” is employed to signify that there can be any number of resistors  124   n  in battery cell array  112 . The inclusion of four resistors  124   1 ,  124   2 ,  124   3 ,  124   n  in  FIG. 2  is illustrative only and does not constitute any limitation regarding the number of resistors that may be included in battery cell array  112 . It is preferred but not required that the number of resistors  124   n , equal the number of battery cells  114   n .  
         [0023]     A charging potential (not shown in  FIG. 2 ) may be applied at a charging locus  130  for charging battery cell array  112 . Charging locus  130  is coupled with battery cell array  112  via a charge FET (field effect transistor)  132  and a discharge FET  134  coupled in series. A control logic unit  140  is coupled with charge FET  132  and discharge FET  134  to control their operation and thereby control connection of charging locus  130  with battery cell array  112 . Control logic unit  140  is coupled with a protective device  150 . Protective device  150  is also coupled across each respective cell  114   1 ,  114   2 ,  114   3 ,  114   n  in battery cell array  112 . Protective device  150  is illustrated in  FIG. 2  as a single unitary protective device. However, protective device  150  may be embodied in a plurality of individual protective devices (not shown in  FIG. 2 ), each of which individual protective devices is connected across a respective battery cell  114   1 ,  114   2 ,  114   3 ,  114   n .  
         [0024]     A current sensor device  152  is coupled across each resistor  124   n . Current sensor device  152  has an alert signal output locus  151 . Protective device  150  has an alert signal input locus  149  that is coupled with alert signal output locus  151  (connection not shown in  FIG. 2 ). Whenever battery pack  100  is in a very low or an ultra-low power state and current through resistor  124  is greater than a predetermined amount current sensor device  152  generates an ALERT signal at alert signal output locus  151 . Protective device  150  receives the ALERT signal at alert signal input locus  149  and responds to the ALERT signal by enabling predetermined safeguards that are disabled because battery pack  100  is in an ultra-low power state. Current sensor device  152  is illustrated in  FIG. 2  as a single unitary current sensor device. However, current sensor device  152  may be embodied in a plurality of individual protective devices (not shown in  FIG. 2 ), each of which individual protective devices is connected across a respective resistor  124   1 ,  124   2 ,  124   3 ,  124   n .  
         [0025]     Another current sensor device  154  is coupled with charging locus  130  and battery potential locus  120 . Current sensor device  154  has an alert signal output locus  153 . Alert signal output locus  153  is coupled with alert signal input locus  149  (connection not shown in  FIG. 2 ). Whenever battery pack  100  is in a very low or an ultra-low power state and current between charging locus  130  and battery potential locus  120  is greater than a predetermined amount current sensor  154  generates an ALERT signal at alert signal output locus  153 . Protective device  150  receives the ALERT signal at alert signal input locus  149  and responds to the ALERT signal by enabling predetermined safeguards that are disabled because battery pack  100  is in an ultra-low power state.  
         [0026]     Whenever battery pack  100  is in an ultra-low power state most protection features or safeguards provided by protection device  150  are disabled to conserve power. In such an ultra-low power state, FETs  132 ,  134  are also usually turned off. Prior art battery packs only permit exiting the ultra-low power state by applying a voltage to charging locus  130  that is greater than potential at battery potential locus  120 . This operation is typically accomplished using a battery charger unit connected with charging locus  130 .  
         [0027]     However, if one of FETs  132 ,  134  is damaged when using a charging unit attached with charging locus  130  or if reverse current from charging locus  130  to battery potential locus  120  is great enough to overcome one of FETs  132 ,  134 , then an over-current or overload condition could occur. Protective device  150  cannot protect against an over-current or overload condition in such circumstances because safeguards protecting against such conditions are disabled while battery pack  100  is in the ultra-low state. As a result, battery pack  100  may be damaged beyond use or repair.  
         [0028]     The apparatus of the present invention equips battery pack  100  to sense current draw that would occur in the circumstance of applying a voltage to charging locus  130  with either of FETs  132 ,  134  damaged, shorted, overcome or otherwise breached. Protective device  150  is structured to respond to the sensing (i.e., responds to the ALERT signal from either of current sensors  152 ,  154 ) to enable appropriate safeguards to be exercised by protective device  150  to keep battery pack  100  safe.  
         [0029]      FIG. 3  is a schematic diagram of the preferred embodiment of the current sensing device used for the present invention. In  FIG. 3 , a current sensing device  200  is embodied in a differential comparator  210  having a non-inverted input locus  212  and an inverted input locus  214 . A reference signal REF is received at a reference locus  216 . An output ALERT signal is presented at an output locus  218  whenever the difference between signals at input loci  212 ,  214  is greater than reference signal REF. Connecting input loci  212 ,  214  across a resistor, such as resistor  124   n  ( FIGS. 1, 2 ; shown in phantom in  FIG. 3  for exemplary purposes) permits differential comparator to operate as a current sensing device without introducing significant impedance into a battery cell array (e.g., battery cell arrays  12 ,  112 ;  FIGS. 1, 2 ).  
         [0030]      FIG. 4  is a schematic diagram illustrating a second alternate embodiment of the present invention. In  FIG. 4 , a battery pack  300  includes a battery cell array  312  and a protective system  313 . Battery cell array  312  includes a plurality of batteries, represented by battery cells  314   1 ,  314   2 ,  314   3 ,  314   n  coupled together to present an output voltage at a battery potential locus  320 . The indicator “n” is employed to signify that there can be any number of battery cells  314   n  in battery cell array  312 . The inclusion of four battery cells  314   1 ,  314   2 ,  314   3 ,  314   n  in  FIG. 4  is illustrative only and does not constitute any limitation regarding the number of battery cells that may be included in battery cell array  312 . Battery cells  314   1 ,  314   2 ,  314   3 ,  314   n  are connected in series with resistors  324   1 ,  324   2 ,  324   3 ,  324   n . Resistor  324 , is coupled between battery cells  314   1 ,  314   2 . Resistor  324   2  is coupled between battery cells  314   2 ,  314   3 . Resistor  3243  is coupled between battery cells  314   3 ,  314   n . Resistor  324   n  is coupled between battery cells  314   n  and ground locus  322 . The indicator “n” is employed to signify that there can be any number of resistors  324   n  in battery cell array  312 . The inclusion of four resistors  324   1 ,  324   2 ,  324   3 ,  324   n  in  FIG. 4  is illustrative only and does not constitute any limitation regarding the number of resistors that may be included in battery cell array  312 . It is preferred but not required that the number of resistors  324   n , equal the number of battery cells  314   n . A charging potential (not shown in  FIG. 4 ) may be applied at a charging locus  330  for charging battery cell array  312 . Charging locus  330  is coupled with battery cell array  312  via a charge FET (field effect transistor)  332  and a discharge FET  334  coupled in series. A control logic unit  340  is coupled with charge FET  332  and discharge FET  334  to control their operation and thereby control connection of charging locus  330  with battery cell array  312 . Control logic unit  340  is coupled with a protective device  350 . Protective device  350  is also coupled across each respective cell  314   1 ,  314   2 ,  314   3 ,  314   n  in battery cell array  312 . Protective device  350  is illustrated in  FIG. 4  as a single unitary protective device. However, protective device  350  may be embodied in a plurality of individual protective devices (not shown in  FIG. 4 ), each of which individual protective devices is connected across a respective battery cell  314   1 ,  314   2 ,  314   3 ,  314   n .  
         [0031]     A plurality of current sensor devices  352   n  are coupled across resistors  324   1 ,  324   2 ,  324   3 ,  324   n . Current sensor device  352 , is coupled across resistor  3241 . Current sensor device  352   2  has an alert signal output locus  3511 . Whenever battery pack  300  is in a very low or an ultra-low power state and current through resistor  324   1  is greater than a predetermined amount current sensor device  352   1  generates an ALERT signal at alert signal output locus  351   1 . Current sensor device  352   2  is coupled across resistor  324   2 . Current sensor device  352   2  has an alert signal output locus  351   2 . Whenever battery pack  300  is in a very low or an ultra-low power state and current through resistor  324   2  is greater than a predetermined amount current sensor device  352   2  generates an ALERT signal at alert signal output locus  351   2 . Current sensor device  352   3  is coupled across resistor  324   3 . Current sensor device  352   3  has an alert signal output locus  351   3 . Whenever battery pack  300  is in a very low or an ultra-low power state and current through resistor  324   3  is greater than a predetermined amount current sensor device  352   3  generates an ALERT signal at alert signal output locus  351   3 . Current sensor device  352   n  is coupled across resistor  324   n . Current sensor device  352   n  has an alert signal output locus  351   n . Whenever battery pack  300  is in a very low or an ultra-low power state and current through resistor  324   n  is greater than a predetermined amount current sensor device  352   n  generates an ALERT signal at alert signal output locus  351   n .  
         [0032]     The indicator “n” is employed to signify that there can be any number of current sensor devices  352   n  in battery pack  300 . The inclusion of four current sensor devices  352   1 ,  352   2 ,  352   3 ,  352   n  in  FIG. 4  is illustrative only and does not constitute any limitation regarding the number of current sensor devices that may be included in battery pack  300 . It is preferred but not required that the number of current sensor devices  352   n , equal the number of battery cells  314   n .  
         [0033]     Protective device  350  has an alert signal input locus  349  that is coupled with alert signal output loci  351   1 ,  351   2 ,  351   3 ,  351   n  (connections not shown in  FIG. 4 ). Whenever battery pack  300  is in a very low or an ultra-low power state and current through a resistor  324   n  is greater than a predetermined amount, a respective current sensor device  352   n  generates an ALERT signal at a respective alert signal output locus  351   n . Protective device  350  receives at least one of the ALERT signals at alert signal input locus  349  from an alert signal output locus  351   n  and responds to receiving at least one of the ALERT signals by enabling predetermined safeguards that are disabled because battery pack  300  is in an ultra-low power state. Current sensor devices  352   n  are illustrated in  FIG. 4  as differential comparators (e.g., differential comparator  210 ;  FIG. 3 ). However, current sensor devices  352   n  may be embodied other current sensing devices connected across a respective resistor  324   1 ,  324   2 ,  324   3 ,  324   n .  
         [0034]     Another current sensor device  354  is coupled with charging locus  330  and battery potential locus  320 . Current sensor device  354  is illustrated in  FIG. 4  as being embodied in a differential comparator (e.g., differential comparator  210 ;  FIG. 3 ) and has an alert signal output locus  353 . Alert signal output locus  353  is coupled with alert signal input locus  349  (connection not shown in  FIG. 4 ). Whenever battery pack  300  is in a very low or an ultra-low power state and current between charging locus  330  and battery potential locus  320  is greater than a predetermined amount current sensor  354  generates an ALERT signal at alert signal output locus  353 . Protective device  350  receives the ALERT signal at alert signal input locus  349  and responds to the ALERT signal by enabling predetermined safeguards that are disabled because battery pack  300  is in an ultra-low power state.  
         [0035]     Whenever battery pack  300  is in an ultra-low power state most protection features or safeguards provided by protection device  350  are disabled to conserve power. In such an ultra-low power state, FETs  332 ,  334  are also usually turned off. Prior art battery packs only permit exiting the ultra-low power state by applying a voltage to charging locus  330  that is greater than potential at battery potential locus  320 . This operation is typically accomplished using a battery charger unit connected with charging locus  330 .  
         [0036]     However, if one of FETs  332 ,  334  is damaged when using a charging unit attached with charging locus  330  or if reverse current from charging locus  330  to battery potential locus  320  is great enough to overcome one of FETs  332 ,  334 , then an over-current or overload condition could occur. Protective device  350  cannot protect against an over-current or overload condition in such circumstances because safeguards protecting against such conditions are disabled while battery pack  300  is in the ultra-low state. As a result, battery pack  300  may be damaged beyond use or repair.  
         [0037]     The apparatus of the present invention equips battery pack  300  to sense current draw that would occur in the circumstance of applying a voltage to charging locus  330  with either of FETs  332 ,  334  damaged, shorted, overcome or otherwise breached. Protective device  350  is structured to respond to the sensing (i.e., responds to the ALERT signal from either of current sensors  352 ,  354 ) to enable appropriate safeguards to be exercised by protective device  350  to keep battery pack  300  safe.  
         [0038]     It is to be understood that, while the detailed drawings and specific examples given describe preferred embodiments of the invention, they are for the purpose of illustration only, that the apparatus and method of the invention are not limited to the precise details and conditions disclosed and that various changes may be made therein without departing from the spirit of the invention which is defined by the following claims: