Abstract:
A lithium polymer (LiPo) battery pack having LiPo battery cells is provided which includes battery protection circuitry, charging circuitry, cell balancing circuitry, and control and communication circuitry. The batteries can be charged while in use by an internal charger. Battery charging and discharging are accomplished in a controlled and protected manner to avoid overcharging and overdischarging conditions. The novel battery pack has built-in safeguards against dangerous LiPo battery conditions and is implemented in a small, portable unit which contains the battery cells, control and protection circuitry, internal charger and display gauge. The battery pack is useful for powering an intravenous fluid warmer or other medical or electrical devices and equipment.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of co-pending U.S. patent application Ser. No. 12/820,094, filed Jun. 7, 2011, which is a continuation of U.S. patent application Ser. No. 11/593,456, filed Nov. 6, 2006, which claims benefit of U.S. provisional patent application Ser. No. 60/734,108, filed Nov. 7, 2005. Each of the aforementioned related patent applications is herein incorporated by reference in their entireties. 
     
    
     FIELD 
       [0002]    This invention is generally related to battery-operated fluid warmers and, in particular, to fluid warmers running on batteries including lithium polymer rechargeable cells. 
       BACKGROUND OF THE INVENTION 
       [0003]    Intravenous (IV) fluid warmers have traditionally been powered by an AC power source because of the high power required to heat IV fluids. Battery powered IV fluid warmers have heretofore had poor performance because of the battery sources which have been available. 
         [0004]    The battery requirements for IV fluid warmers include the following:
       1. Small size and weight for easy portability,   2. Extremely high discharge rates (very low impedance),   3. Protection from overcharging,   4. Protection from overdischarging,   5. Capability to heat at least four liters of IV fluids, and   6. Battery “gas gauge” (Battery Condition Indicator) to monitor battery charge status.       
 
         [0011]    A known battery powered IV fluid warmer is called the Thermal Angel and is produced by Estill Medical. Thermal Angel uses a 12 volt lead acid battery which is heavy, weighing about 7 pounds, limiting its portability. The battery requires an external charger and thus requires an extra piece of equipment for operational use Thermal Angel has a low heating capacity of less than 2 liters of room temperature IV fluid. It cannot be charged while the fluid warmer is in use. It has a long charge time of about 12 hours and cannot be fast charged. In addition, the device has only a minimal gas gauge which is only accurate when the battery is not in use. 
         [0012]    Lithium polymer (LiPo) batteries have extremely low internal impedance and are particularly suitable for high current applications. They have very high energy density, do not exhibit memory effects, and in addition, are environmentally safe. However, such batteries can be dangerous if overcharged or overdischarged and in such circumstances the batteries can explode or catch fire. 
       SUMMARY OF THE INVENTION 
       [0013]    In accordance with the present invention, lithium polymer (LiPo) battery cells are employed in a portable unit which includes battery protection circuitry, charging circuitry, cell balancing circuitry, and control and communication circuitry. The batteries can be charged while in use by an internal charger. Battery charging and discharging are accomplished in a controlled and protected manner to avoid overcharging and overdischarging conditions. The novel battery pack has built-in safeguards against dangerous LiPo battery conditions and is implemented in a small, portable unit which contains the battery cells, control and protection circuitry, internal charger and display gauge. The battery pack or the battery cells may be enclosed in an enclosure resistant to fire and/or explosion 
         [0014]    An embodiment of the present invention is described herein for powering a fluid warmer for intravenous or similar fluids. It is contemplated that the present invention may also be employed as a power source for powering other medical equipment or electrical equipment more generally. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    Further aspects of the invention will be apparent upon consideration of the following detailed description, taken in conjunction with the accompanying drawings, in which like reference characters refer to like parts throughout, and in which: 
           [0016]    FIG.  1 —A fluid warmer assembly according to a first embodiment of the present invention. 
           [0017]    FIG.  2 A—A fluid warmer heating and control circuit, part 1 of 2, according to the first embodiment of the present invention. 
           [0018]    FIG.  2 B—The fluid warmer heating and control circuit, part 2 of 2, according to the first embodiment of the present invention. 
           [0019]    FIG.  3 —A fluid warmer heating and control circuit according to a second embodiment of the present invention. 
           [0020]    FIG.  4 —A charger circuit according to the second embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    The fluid warmer assembly of the present invention is useful for powering an IV fluid warmer used in military and civilian emergency settings, such as a battlefield or civilian medical facility. DC power for charging the fluid warmer assembly can be provided from a vehicle or other battery source operating over a typical voltage range of 12-36 volts DC. An interconnecting cable can provide an electrical connection between an external DC power source and the fluid warmer assembly. In one embodiment, a hermaphrodite cable may be provided so that only a single cable having associated connectors is necessary to make a connection between the fluid warmer assembly and a power source. Such hermaphrodite connectors have no “wrong end” and either connector end can be plugged into the fluid warmer assembly and the power source. 
         [0022]    The fluid warmer assembly according to the present invention provides a unitary device which contains the battery cells, control and monitoring circuitry and charging circuitry needed for reliable and safe operation without a need for auxiliary or additional equipment. The fluid warmer assembly may have a replaceable heater cartridge inside the fluid warmer. The replaceable heater cartridge includes a case through which an intravenous fluid line or a tube extends. Components in contact with the fluid may optionally be of a single-use design considering a convenient use or medically hazardous conditions. The fluid warmer assembly is capable of an intelligent power control within safe operating limits of the exemplary LiPo cells. 
         [0023]    Data from the fluid warmer assembly can typically represent the following parameters:
       1. Nominal voltage,   2. Battery capacity and amp/hours,   3. Maximum current draw, and   4. Low voltage cut out level.       
 
         [0028]    Battery temperature is monitored to determine the proper load or charging parameters. An audible alarm can be provided in the fluid warmer assembly to signify a fully discharged state and/or a hazard state. Multicolor LEDs can be included to show, for example, a change from red to green to indicate the state of charge. 
         [0029]      FIG. 1  illustrates a fluid warmer assembly  100  according to a first embodiment of the present invention. A fluid warmer  105  has a fluid warmer cover  101  and a fluid warmer cover  103 . The arrows above the fluid warmer cover  101  and the fluid warmer cover  103  show the respective bidirectional capability of movement. The fluid warmer cover  101  and the fluid warmer cover  103  include a switch (not shown) that generates a fluid warmer cover closure signal  244 , described below, indicating whether the fluid warmer covers  101 ,  103  are open or closed. 
         [0030]    A unitary housing includes the fluid warmer  105 , monitoring and control electronics, and the rechargeable cells. Specifically, the fluid warmer  105  is disposed on a fluid warmer heating and control circuit  107 , which includes a group of rechargeable Lithium Polymer cells, namely, LiPo cells  110 ,  112 ,  114 , and  116 . In a preferred embodiment, the fluid warmer assembly  100  has a removable cartridge  105   a  to which a fluid line is attached and through which fluid is caused to flow. The cartridge is typically for a single use and is disposed of after use with a patient. The fluid warmer assembly  100  is typically usable for a period of time that the battery pack is capable of being recharged. However, a person having an ordinary skill in the art would appreciate that there could be several variations to a structural relationship between the various components of the fluid warmer assembly  100  described above. 
         [0031]      FIGS. 2A and 2B  describe a fluid warmer heating and control circuit  200  according to the first embodiment of the present invention.  FIGS. 2A and 2B  connect at points A, B, pack(+)  240  and pack(−)  242 . 
         [0032]    The fluid warmer heating and control circuit  200  is capable of sensing a hazardous condition inside one or more individual cells, such as LiPo cell  210 , of battery pack  262 . Further, the fluid warmer heating and control circuit  200  permits a magnetic or other isolating coupling of power from a charger  232  to Pack(+)  240 . The fluid warmer heating and control circuit  200  has a novel structure that does not permit a conduction of electric power from the battery pack  262  through the charger  232  by including a battery discharge switch  230 . That is, electric power from the battery pack  262  to a load does not pass through the charging circuit. 
         [0033]      FIG. 2A  shows that external power is connected through terminals labeled as external power(+)  202  and external power(−)  206 . A power path controller logic  221 , akin to steering logic, controls two switches, namely, an external power switch  208  and the battery discharge switch  230  such that based on a need of the fluid warmer assembly  100  or of the battery pack  262 , power may be directed from external power or the battery pack  262 . 
         [0034]    External power(+)  202  is also connected to a low voltage power supply  220  which delivers power to all circuits of the fluid warmer assembly  100  except a heater  226 . The heater  226  includes a heating element, adapted to heat a fluid to be administered to a living body in an efficient manner. The heater  226  is controlled by a heater control switch  228  operated by a fluid warmer microcontroller  222 . 
         [0035]    The heater  226  is powered via a thermal fuse  224  connected to a fluid warmer overtemperature protection circuit  218  and to a second order battery protection circuit  252  shown on  FIG. 2B . On sensing a temperature of the fluid warmer  105  exceeding a predetermined limit, the fluid warmer overtemperature protection circuit  218  electrically heats and melts the thermal fuse  224  to prevent an overheating condition. To improve protection, the second order battery protection circuit  252 , independent of other protection measures, has been included. On sensing a potentially damaging condition in any of the components of the battery pack  262 , the second order battery protection circuit  252  electrically heats and melts the thermal fuse  224  to prevent a furtherance of the potentially damaging condition. A common damaging condition is an excessive voltage across the components of the battery pack  262 , namely, LiPo cells  210 ,  212 ,  214 , and  216  shown on  FIG. 2B . Though the second order battery protection circuit  252  is shown connected to the voltage sensor  256 , other sensor(s) may also be connected to the second order battery protection circuit  252 . 
         [0036]    The fluid warmer microcontroller  222  may operate the heater control switch  228  based on a range of conditions stemming from personal safety and circuit operation considerations. A spread spectrum oscillator  204  is included in the fluid warmer heating and control circuit  200  for at least two purposes. A first purpose is to provide for an improved electromagnetic compatibility (EMC) performance. A second purpose is to facilitate, via the fluid warmer microcontroller  222 , a pulse width modulation of the charger  232  to control the output voltage or regulate the current of the charger  232 . The charger  232  is connected to the battery pack  262  via pack(+)  240 . In an alternative embodiment, suitable circuitry included either in the spread spectrum oscillator  204  or the charger  232  may permit a direct connection between the spread spectrum oscillator  204  and the charger  232  for controlling the output voltage or regulating the current of the charger  232 . In such an embodiment, charger  232  is connected to battery condition indicator and controller  248  described below. 
         [0037]      FIG. 2B  also illustrates some additional monitoring and control blocks to facilitate charging and discharging of the battery pack  262 . A battery condition indicator and controller  248  may interface with, as shown in  FIG. 2B , a first order battery protection circuit  250 , a current sensor  264 , a fluid warmer cover closure signal  244 , and a fluid warmer microcontroller  222 . In some embodiments, the battery condition indicator and controller has an electromagnetic interface. In some embodiments, the electromagnetic interface is an electrical interface. In some embodiments, the electromagnetic interface is an optical interface. The battery condition indicator and controller  248  is connected to a first order battery protection circuit  250 . The battery condition indicator and controller  248  together with the first order battery protection circuit  250  provide a first-level protection to the LiPo cells, indicate the battery capacity, charge the LiPo cells in a balanced manner, facilitate “sleep” or “wake”-style activation of the LiPo cells, and communicate with external circuits as needed. The operation of the battery condition indicator and controller  248  is activated when a fluid warmer cover closure signal  244  is received. That is, the fluid warmer cover closure signal  244  is generated when the fluid warmer covers  101 ,  103  operate as shown on  FIG. 1 . As an example, heating of a fluid in fluid warmer  105  begins when the fluid warmer covers  101 ,  103  are closed. 
         [0038]    The first order battery protection circuit  250  accepts inputs from several sensors to operate a battery disconnect switch  246 . These sensors are: voltage sensor  256 , temperature sensors  258  and  260 , current sensor  264 , and strain/pressure sensor  266 . These sensors may be connected to one or more of the LiPo cells  210 ,  212 ,  214 , and  216 . Though only four LiPo cells  210 ,  212 ,  214 , and  216  are shown, more or fewer LiPo cells may be employed based on a given application by making simple changes in the fluid warmer heating and control circuit  200  appreciated by a person having an ordinary skill in the art. In addition to a voltage sensor  256  and a current sensor  264 , the first order battery protection circuit  250  also accepts a temperature sensor  258  and a temperature sensor  260 . Based on a structure or a layout of the fluid warmer assembly  100  of  FIG. 1 , the temperature sensor  258  and the temperature sensor  260  may be located at different points on the battery pack  262  to provide a better monitoring, in a distributed manner, of the overall temperature of the battery pack  262 . Though not shown on  FIGS. 2A and 2B , additional temperature sensors may be provided, for example, to monitor an ambient temperature or a body temperature. 
         [0039]    The current sensor  264  is also connected to the battery condition indicator and controller  248  to permit a control of the first order battery protection circuit  250  and facilitate the battery condition indicator and controller  248  to function as a “battery gas gauge.” It may also be noted that  FIGS. 2A and 2B  show the fluid warmer microcontroller  222  and the battery condition indicator and controller  248  as separate blocks but these two may be combined in a single controller. 
         [0040]    The first order battery protection circuit  250  is connected to a cell balance circuit  254 . The cell balance circuit  254  block monitors various parameters, such as charging/discharging current and terminal voltage. Cell balancing is accomplished by shunting current around one or more of the LiPo cells  210 ,  212 ,  214 , and  216  in an intelligent manner. That is, current is shunted around a cell which has a higher voltage to an adjacent cell during charging. 
         [0041]    The first order battery protection circuit  250  is also connected to a strain/pressure sensor  266  via a diode  268  at a point where the temperature sensor  260  is connected. The diode  286  pulls the temperature sensor  260  low. The strain/pressure sensor  266  is attached to the battery pack  262  in such a manner that the strain/pressure sensor  266  detects a change in a stress or a strain or a pressure relevant to the battery pack  262  or any of the constituent LiPo cells, such as the LiPo cells  210 ,  212 ,  214 , and  216 . Such changes, as well a change in a dimension of the battery pack  262  or any of the constituent LiPo cells, such as the LiPo cells  210 ,  212 ,  214 , and  216 , may herald a potentially harmful condition inside the battery pack  262 . An example of change in dimension is a swelling or expansion of an individual cell or the battery pack  262 . The first order battery protection circuit  250  operates in response to the signal of the strain/pressure sensor  266 , to generate suitable alarms(s) and disconnects the batteries via switch  246 . 
         [0042]    The fluid warmer heating and control circuit  200  shown in  FIGS. 2A and 2B  conditions external power to make it usable by the low voltage supply  220 , performs pulse width modulation for an intelligent performance of the charger  232 , improves the EMC performance, monitors the battery pack  262 , via several sensors, for a safe operation, includes a back-up battery protection and a fluid warmer overtemperature protection via the thermal fuse  224 . These functions are performed while also sensing the dimensions of the LiPo cells, or the battery pack  262 , for a potential structural failure and not permitting a load current from the battery pack  262  to pass through the charger  232  circuitry. 
         [0043]    Various circuits or blocks of  FIGS. 2A and 2B  may be implemented by several commercially available integrated circuits. The spread spectrum oscillator  204  can be based on LTC6908 of the Linear Technology Corporation. A pulse width modulator, to control the charger  232 , can be implemented by the MCP1630 of the Microchip Technology, Inc. The battery condition indicator and controller  248  and the first order battery protection circuit  250  can be implemented by the bq20z70 and the bq29330 chipset of Texas Instruments. The second order battery protection circuit  252  can be implemented by the bq2941x family of Texas Instruments. 
         [0044]    The fluid warmer heating and control circuit  200 , including the battery pack  262 , may be enclosed in a fire- and/or explosion-resistant enclosure ( 150  depicted in  FIG. 1 ). Alternatively, such an enclosure can contain only the LiPo cells  210 ,  212 ,  214 , and  216  ( 152  depicted in  FIG. 1 ). Such enclosure may be rigid or flexible, and composed of a fire- and/or explosion-resistant material such as Kevlar®. A commercially available envelope sold under the brand Liposack is also useful for such an enclosure. 
         [0045]      FIG. 3  illustrates a fluid warmer heating and control circuit  300  according to a second embodiment of the present invention. As an illustration, eight LiPo cells, namely,  310 ,  312 ,  314 ,  316 ,  310 A,  312 A,  314 A, and  316 A, are connected in series and included in a battery pack  362 . Each of the LiPo cells is connected to a first order battery protection circuit  350 , a second order battery protection circuit  352  and a cell balance circuit  354 . The first order battery protection circuit  350  and the cell balance circuit  354  are connected to a fluid warmer controller  322  which also receives temperature information from a temperature sensor  358  and from an ambient temperature sensor  372 . The fluid warmer controller  322  is in communication with a charger  332 . The fluid warmer controller  322  communicates with a controller of an IV fluid warmer system (not shown) via a data input/output  341 . A UART included in the fluid warmer controller  322  can be used for data transfer. The fluid warmer controller  322  is also coupled to an array of LEDs, constituting a battery condition indicator  370 , which indicates battery charge and also a warning of a hazardous condition. The battery condition indicator  370  may include a display and an annunciator  371 . A push-to-test switch  374  is provided for actuation of the battery condition indicator  370 . 
         [0046]    The LiPo cells  310 ,  312 ,  314 ,  316 ,  310 A,  312 A,  314 A, and  316 A are connected via a current sensor  364  to the negative output terminal labeled Pack(−)  342 . The positive output of the stack is connected via a thermal fuse  324  and a pair of MOSFET P  380  and MOSFET P  382  to the positive output terminal labeled Pack (+)  340 . The reference numerals  376  and  378  indicate the body diodes inherent with the structure of the respective MOSFET P  380  and MOSFET P  382 . The charge and discharge states of the LiPo cells  310 ,  312 ,  314 ,  316 ,  310 A,  312 A,  314 A, and  316 A are continuously monitored by the first order battery protection circuit  350  and the second order battery protection circuit  352  and the charge status is provided to the fluid warmer controller  322 . The fluid warmer controller  322  provides control signals to the cell balance circuit  354  operative to adjust the charging and discharging current to LiPo cells  310 ,  312 ,  314 ,  316 ,  310 A,  312 A,  314 A, and  316 A within a safe operating range. In the event of an undesirable condition, such as an abnormally high voltage or a high current or a high temperature, the fluid warmer controller  322  in response to inputs from the first order battery protection circuit  350  and the second order battery protection circuit  352  and/or cell balance circuit  354  and/or from temperature sensor  358  and ambient temperature sensor  372 , causes one or both of MOSFET P  380  and MOSFET  382  to turn off and thereby shut off the supply of current from the LiPo cells  310 ,  312 ,  314 ,  316 ,  310 A,  312 A,  314 A, and  316 A. 
         [0047]    The second order battery protection circuit  352  is operative to monitor charge and discharge states of the LiPo cells  310 ,  312 ,  314 ,  316 ,  310 A,  312 A,  314 A, and  316 A and in the event of a fault condition provide an output current to melt the thermal fuse  324  to disconnect the LiPo cells  310 ,  312 ,  314 ,  316 ,  310 A,  312 A,  314 A, and  316 A before a dangerous condition can occur. 
         [0048]    The charger  332  is internal to the fluid warmer assembly  100  of  FIG. 1  and eliminates a need for a separate or external charger. In addition, the charger  332  can be operative while the fluid warmer assembly  100  is in use if the fluid warmer assembly  100  is connected to an external charging power source. DC power can be provided to the fluid warmer assembly  100  for operating the charger  332 . 
         [0049]    The fluid warmer controller  322  provides an identification information via the data input/output  341  to the fluid warmer assembly  100  such that the fluid warmer assembly  100  recognizes an appropriate power source for powering the fluid warmer assembly  100 . 
         [0050]      FIG. 4  illustrates a charger circuit  432  according to the second embodiment of the present invention. Though  FIG. 4  shows only one LiPo cell  410 , there could be more such LiPo cells based on a specific application. 
         [0051]    Similar to the feature of the first embodiment, the charger circuit  432  directs a discharge load current on a path separate from a path of charging current. Specifically, a switch including MOSFET P  480  and MOSFET P  482  connects the LiPo cell  410  to pack(+)  440 , via a thermal fuse  424 , away from the charging circuitry of charger circuit  432 . 
         [0052]    When pack(+)  440  and pack(−)  442  are supplied with less than the LiPo cell  410  voltage, a step up conversion is provided by MOSFET N  484 , MOSFET N  486 , inductor  488  and diode  496 . The step up conversion is accomplished under the fluid warmer controller  322  management by holding MOSFET N  484  on and pulsing MOSFET N  486 . While MOSFET N  486  is on, current rises in inductor  488 , and when MOSFET N  486  turns off, the voltage across inductor  488  reverses polarity and discharges from the pack+  440  terminal through diode  496  into the battery. 
         [0053]    When pack(+)  440  and pack(−)  442  are supplied with battery voltage greater than that of the LiPo cell  410 , a step down conversion is provided by MOSFET N  484 , MOSFET N  486 , inductor  488 , diode  496  and diode  494 . The fluid warmer controller  322  causes pulsing of both MOSFET N  484  and MOSFET N  486 . Current rises in inductor  488  while MOSFET N  484  and MOSFET N  486  are on. When MOSFET N  484  and MOSFET N  486  turn off, the voltage across inductor  488  reverses polarity and discharges through diode  496  into the LiPo cell  410  and from the LiPo cell  410  through diode  494 . Alternatively, the diodes  494  and  496  may be replaced with an active switch, such as a MOSFET, for a higher efficiency. Charge current is controlled by measuring the voltage drop across a current sensor  464  and varying the duty cycle of MOSFET N  484  and MOSFET N  486 . The reference numerals  476 ,  478 ,  490 , and  492  indicate the body diodes inherent with the structure of the respective MOSFET P  480 , MOSFET P  482 , MOSFET N  484 , and MOSFET N  486 . 
         [0054]    The embodiment described above employs a buck-boost converter. A SEPIC converter (Single-ended Primary Inductance Converter) may also be included in the charger circuit  432  in place of the buck-boost converter. 
         [0055]    As discussed in relation to  FIG. 3 , the second order battery protection circuit  352  can interrupt power using the thermal fuse  424  in the event of a major failure such as failure of the MOSFET P  480  or MOSFET P  482 , or of the first order battery protection circuit  350 . 
         [0056]    Though the above description has generally been oriented to powering an IV fluid warmer, a person having an ordinary skill in the art will appreciate that the fluid warmer assembly  100  can also be used for heating other liquids or substances with suitable modifications or enhancements. The invention is not limited to heating IV or other fluids, but is applicable to powering other electrical devices and equipment including other medical devices and equipment.