Abstract:
A controller allows use of a battery protection circuit that limits electrical current to a safe level regarding short circuits and hazardous locations as well as determining each battery configuration having a voltage-temperature profile associated with that enhances cold weather operation; high battery temperatures are also detected and then rectified by the controller.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The present invention is related to battery powered lanterns and lights and more specifically to an electronic control module for a lithium-ion battery powered lantern. 
     2. Background 
     It is the goal of every designer of battery-powered devices to prolong battery discharge life as much as possible. Battery life is particularly important in lanterns and other lighting devices used by firefighters and other emergency personal. Use of such battery powered lights in emergency environments is further complicated by the effect of increased or decreased temperatures in which the lights are used. 
     Li-ion batteries have a higher energy to weight ratio than any other commercially available rechargeable batteries. This makes them very desirable as a power source for portable devices. For safety, most Li-ion battery packs must have a safety circuit to protect them from over voltage, under voltage and over-discharge conditions. This presents some limitations for viable applications of Li-ion batteries. Namely, desired high discharge currents may not be possible because the battery protection circuit will not allow them. This controller safely allows high discharge currents from a Li-ion battery pack by controlling current to the main lamp. It prevents high currents from activating the safety circuit. It is possible to use a safety circuit that would allow higher currents, but this would also allow high currents during undesirable conditions such as a short circuit at the external charging contacts on the lantern. A high current short across these external contacts may result in an unsafe condition during use in hazardous locations. 
     At lower temperatures, the voltage is depressed. At higher temperatures the voltage is elevated. 
     Since low temperatures depress the voltage of Li-ion cells, application of a high power load further drops the cell voltage to the point that the protection circuit may activate and disconnect the load due to a low-voltage condition. This effect is further increased as the ratio of the size of the load to the capacity of the battery is increased. 
     In a typical lantern, main lamp is of the incandescent type, and can be of low power or high power. While a high power lamp produces more light, it draws much more current from the battery. As is well known, higher currents cause the battery to discharge rapidly and thus reduce the useful life of the battery charge. In addition to the nominal current drain resulting from the lamp in the “ON” condition, there is an initial spike of current that is many times the nominal. Further, because of the potential presence of in ignitable vapors, dust or other chemicals, the powering-up sequence of such lights must be carefully controlled as not to create a spark or other harmful electrical discharge. This “turn on” current spike can be large enough to cause a safety circuit, if present, to disconnect the battery from the load or appear as a short. 
     It is therefore a goal of manufacturers and users of battery powered lanterns to provide control over battery discharge that minimizes battery depletion and provides regulation of the start-up charge to maximize the safe operation of the lanterns in potentially hazardous environments. It is further goal to maximize battery depletion based on the temperature of the battery. 
     SUMMARY OF INVENTION 
     The inventive controller allows use of a battery protection circuit that limits electrical current to a safe level regarding short circuits and hazardous locations, and still run a high-power load such as a very bright lamp in this case. Because of this, a lantern is provided that is lighter, smaller and brighter than prior art systems and still be safety listed for use in hazardous locations by third party agencies. 
     In the program for the controller, each battery configuration has a voltage-temperature profile associated with it. In addition, this controller can identify which of three battery configurations is installed in the lantern, a four, six, or eight-cell battery pack When controller identifies which pack is installed and uses this voltage-temperature information to activate a low battery LED indicator. This indicator alerts the end user that limited run time remains before the lamp goes out. 
     Another advantage of this controller is the enhancement of cold weather operation. Based on cell temperature, the controller will automatically reduce the power available to the lamp to prevent the cell voltage from reaching the low voltage cutoff point prematurely. As the cells are discharged, even at this lower power setting, heat is generated internally in the cells. This heat increases cell voltage faster than discharging it decreases it. The controller continuously monitors cell temperature, and indirectly the cell voltage, and slowly increases the load on the battery until full lamp power is achieved. This feature allows use of a relatively high power lamp with a small capacity Li-ion battery at low ambient temperatures. High battery temperatures are also detected and then rectified by the controller 
     The controller is also capable of flashing the four high-brightness signaling LEDs at various rates to make the end user highly visible to others in emergency situations. This is very beneficial during smoky conditions encountered by firefighters, first responders to nighttime automotive accidents or any disaster relief workers. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Specific embodiments of the invention have been chosen for purposes of illustration and description, and are shown in the accompanying drawings, forming a part of the specification wherein: 
         FIG. 1  is a circuit diagram of the battery controller of the instant invention; 
         FIG. 2A  is a flow diagram of the hardware initialization procedure for the battery controller of the instant invention; 
         FIG. 2B  is a flow diagram of the main program loop and temperature measurement sub-procedure for the battery controller of the instant invention; 
         FIG. 2C  is a flow diagram of the battery type determination sub-procedure for the battery controller of the instant invention; 
         FIG. 2D  is a flow diagram of the shut off procedure for the battery controller of the instant invention; 
         FIG. 2E  is a flow diagram of the short detection and handling procedure for the battery controller of the instant invention; 
         FIG. 2F  is a flow diagram of the low battery measurement procedure for the battery controller of the instant invention; 
         FIG. 2G  is a flow diagram of the warm-up procedure for the battery controller of the instant invention; and 
         FIG. 2H  is a flow diagram of the interrupt handler procedure for the battery controller of the instant invention; 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     It shall be understood that reference to the term “lantern” herein shall also include, but not be limited to, flashlights, spotlights and similar illumination devices known in the art. 
     Hardware 
     Referring now to the schematic of  FIG. 1 , the inventive controller  10  is coupled to the appurtenant parts of a battery powered lantern. Show here is lithium-ion battery  60 , with battery protection circuit  62  and thermister  64 , switch  70 , main lamp  80  and low battery indicator led  90 . Also shown, are signal LEDs (light emitting diodes)  100 , that may or may not be provided. In one embodiment, four LEDs are provided and are connected internally into two separate groups of two. The two groups of LEDs can be of different or the same color and they can be programmed to flash in a predetermined sequence or to remain “on” any time the lantern is turned on. The LEDs are high intensity and are intended to be visible at a great distance. It should be noted that the controller could be coupled to additional lantern features not described herein. Further, the structure and operability any of the lantern components described herein with some specificity are but just one embodiment for illustration purposes and be substituted with other relevant components and/or characteristics that are known in the art. 
     Lithium-ion battery  60  is generally composed of a set 4, 6 or 8 lithium-ion battery cells connected in series-parallel to generate 7.2 volts nominally. Such cells are rated at 3.7 volts and 2200 mAh. The battery protection circuit  62 , in connection with the controller  10  as described below, prevents the battery  60  from overcharging, over discharging and from an external short. Further, the battery protection circuit  62  disconnects the load from the battery when one of the aforementioned conditions is detected. The thermister  64  is also used by the controller  10  to measure the temperature of the battery pack, allowing the controller to regulate the battery based on the detected temperature. 
     Battery Controller and Operation 
     In general operation, when the user activates the ON-OFF-ON  70  switch to either of the on positions, the battery voltage will be connected to the battery control electronics  62 , preferably a microprocessor. The microprocessor control  62  then monitors the ambient temperature and type of battery pack before turning on a Field Effect Transistor (FET) to apply battery voltage to the incandescent lamp. The microprocessor monitors the temperature, battery voltage and tests for shorted lamps on a continuous basis as long as the ON-OFF-ON switch is in either ON position. Now will be described in detail the various functions and routines performed by battery controller  62 . 
     A) Hardware Initialization and Soft Start 
     When power is first applied to the microprocessor  10 , the internal registers are automatically initialized to predetermined states. These states must be modified in order to make the peripherals within the microcontroller work as desired in the application. This hardware initialization does the following:
         Selects either input or output function for all I/O (input/output) pins;   Initializes an A/D (analog to digital) converter by selecting the I/O pins that are to be used for analog inputs;   Selects the clock to be used to run the A/D converter and then enable the A/D converter module;   Erases all locations in SRAM (static random access memory);   Applies battery voltage to the lamp  80 ;   Initializes the timer  0  parameters so that it will cause an interrupt every millisecond; and   Enables the interrupts.       

     After the registers and peripherals inside the microcontroller have been initialized and power has been applied to the incandescent lamp the firmware performs a “soft start” operation in which the current to the lamp is allowed to build slowly. The soft start procedure prevents a large turn on current from flowing into the lamp. By keeping the turn on current low, the service life of the lamp filament is increased and the safety circuit inside the battery pack will not be triggered. 
     The soft start procedure alternately turns the lamp ON for a fixed period of time then it turns the lamp OFF for an amount of time that will be reduced to zero as the lamp warms up. This ON/OFF cycle is repeated multiple times and in each cycle the OFF time is reduced a small amount. When the off time is nearly zero, the lamp is turned ON continuously and the main program loop is entered. 
       FIG. 2A  sets forth one embodiment of the specific steps for such initialization and soft start with  FIG. 2H  describing the steps of the interrupt handling procedure. 
     B) Main Program Loop 
     1) Low Battery Test 
     Referring now to  FIGS. 2B ,  2 C and  2 F, the first task in the main program loop is to obtain a new A/D sample for the battery voltage and average it with a running average. Then, the average value of the battery voltage is compared to the value that requires that the battery be disconnected from the lamp. If the battery voltage is less than the smallest voltage allowable, the firmware will branch to a loop where it continues to monitor the battery voltage for a short while and if after that period of time the battery voltage is still to low to use, the lamp will be turned off and the firmware will remain in a tight loop continuously monitoring battery voltage. If the battery voltage rises above the minimum then the lamp will be turned on again and the firmware will branch to the beginning of the main loop once again. 
     This monitoring of battery voltage is to make sure that the battery is not over discharged. This will enhance battery life. 
     If the battery temperature rises, the battery voltage will also rise and if it rises high enough so that the battery voltage is larger than the minimum, the lamp will once again be turned on and the program will branch to the beginning of the main loop. 
     2) Blink Test and Enable 
     Again referring to  FIG. 2A , after the low battery test, the ON-OFF-ON position of switch  70  is checked by the firmware to determine if the LEDs should flash. If so then a program control flag is set which causes the interrupt handler to evoke blinking. 
     3) Shorted Lamp Test 
     Following the blink test the firmware tests to see if the incandescent lamp is shorted, as is shown in  FIG. 2E . If a shorted lamp is detected, the lamp  80  is turned OFF and the battery voltage is measured. The program monitors the battery voltage continuously until the battery voltage has recovered from the short. Once the battery  60  has recovered, the lamp  80  is turned on again and the short test is performed again. If a short is still present the lamp is turned off and the firmware branches to a tight loop where it remains until power is removed. If the short is removed, the program branches to the beginning of the main loop. 
     4) Battery Temperature 
     As is illustrated in second and third branches the main flow diagram of  FIG. 2B , after the shorted lamp test, the battery pack temperature is measured. The battery temperature will be used as an index in a look up table to determine what the “low battery voltage” should be. For all temperatures greater than 122° F. the index should be the same. As such, for all temperatures greater than 122° F., the index will be equal to 122. 
     Next, a test is made to see if the battery temperature is less than 15° F. If it is, the program branches to a battery pack warm up routine, illustrated in  FIG. 2G . Otherwise, the program will proceed to look up the low battery voltage value based on which battery pack is present, illustrated in  FIG. 2C , and described below. 
     5) Low Battery Voltage Test 
     Once the battery temperature is known and the battery type is known the low battery voltage value is obtained from the table for the type of battery that is present. The low battery voltage value is then compared to the present battery voltage. If the battery voltage is less than the low battery voltage value obtained from the table then a counter is started. When the counter reaches its maximum value the low battery test is made again. If the battery voltage is still too low then the low battery LED will be turned ON. Otherwise the counter is stopped and cleared. After this test the program branches to the beginning of the main loop of  FIG. 2B . 
     6) Warm Up 
     If the battery temperature is less than 15° F. then a warm up procedure may be required. The exception to this is the 8-cell battery pack that does not require a warm up cycle. 
     If the battery pack is a 4 or 6 cell type then a warm up rate is calculated for the type of battery pack that is present based on the measured battery temperature. The warm up procedure takes advantage of the fact that when the lamp is on, the current flowing in the lamp also flows in the internal resistances of the batteries and this results in I*I*R heating of the battery. At low temperatures the amount of current that can be drawn from the batteries is reduced but even the reduced amount causes internal heating in the battery. As the battery heats up the allowable load current increases until at 15° F. full load current is permitted. The flow-path of battery warm up procedure is set forth in  FIG. 2G . 
     The warm up cycle is basically an ON/OFF cycle in which the ON time is fixed and the OFF time is reduced as the battery heats up. Once the battery temperature reaches 15° F. the program branches to the beginning of the main loop after turning on the lamp and fully enabling the interrupt handler, as previously described. 
     Utilizing the aforementioned procedures, as is further detailed in  FIGS. 2A-2H , voltage from the battery  60  is continuously monitored, as is temperature. If low voltage is detected by the controller  10 , the low battery indicator  90  will be turned on and if below the voltage cut-off set point, the lantern power will be turned off to protect the battery  60  from over discharge. Similarly, if temperature is below a set point when the lantern is turned on, the power will be regulated and slowly ramped up based on temperature feedback from the battery  60  (via thermister  64 ) until full power is reached. 
     In addition to the structures, sequences, and uses immediately described above, it will be apparent to those skilled in the art that other modifications and variations can be made the method of the instant invention without diverging from the scope, spirit, or teaching of the invention. As one such example, portable Li-ion powered device such as cell phones and laptop computers can benefit from employing a warm-up routine to enhance cold weather operation. Therefore, it is the intention of the inventors that the description of instant invention should be considered illustrative and the invention is to be limited only as specified in the claims and equivalents thereto.