Abstract:
A power system includes one or more notification circuits for powering notification devices, a backup power source, and a plurality of primary power supplies. The primary power supplies are configured to provide a combined current to the notification circuits. Each primary power supply regulates its output current to equal a highest output current provided by one of the primary power supplies so that each contributes approximately the same current to the load. The primary power supplies also include boost regulator circuits for boosting the voltage of the backup power supply.

Description:
BACKGROUND 
       [0001]    The current invention is related to powering notification appliance circuits (NACs), and in particular to a system and method for providing boost voltage and load-sharing for a plurality of NACs. 
         [0002]    Emergency systems, such as fire systems, often contain one or more NACs. These NACs provide power to several emergency notification devices such as, but not limited to, strobe lights and sirens. Each notification device has a specified working voltage and current. Regulations require these NACs to continuously provide a proper working voltage and current in order to ensure continuous, uninterrupted operation of the emergency notification devices. Therefore, a power source must supply enough power to the one or more NACs to provide a working voltage and current to each notification device, taking into account any voltage drops such as those caused by wiring impedances and power switches. 
         [0003]    Traditionally, NACs have been powered through the use of a single power supply. The power supply often contains an AC power source that is converted from AC to DC power. If this power supply malfunctions, the NACs are powered entirely by a backup power source. The backup power source usually consists of a backup battery. Batteries can only operate at a given voltage for a limited amount of time before the voltage of the battery drops. Once the voltage of the battery falls below the required working voltage of the NAC, the notification devices will fail to function as specified. 
       SUMMARY 
       [0004]    A system and method that provides a working voltage and current to one or more notification appliance circuits (NACs) includes a plurality of primary power supplies, and a backup power source, which provide power to the one or more NACs. Each primary power supply regulates its output voltage so that each supply sources an approximately equal current to the one or more NACs. Each primary power supply consists of an AC source, an AC-DC converter, a switching network, a load-sharing controller, and a boost regulator circuit. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]      FIG. 1  is a block diagram of an embodiment of the present invention. 
           [0006]      FIG. 2  is a block diagram of an embodiment of a primary power supply of the present invention. 
           [0007]      FIG. 3  is a flow chart illustrating a method of providing load-sharing and boosted voltage for one or more NACs according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0008]    The present invention describes an electrical power system that provides a working voltage and current to one or more notification appliance circuits (NACs). In particular, the system contains a plurality of primary power supplies, and one or more backup power sources. Each primary power supply contains an AC power source, an AC-DC converter, a boost regulator circuit, a load-sharing controller, and a switching network. The backup power source provides power to each of the primary power supplies in the event that a primary power supply&#39;s AC power source is unavailable or malfunctioning. The boost regulator circuit of each primary power supply boosts the voltage supplied to the respective primary power supply from the backup power source when the backup power source&#39;s voltage is no longer sufficient for the power system to supply a working voltage and current to the one or more NACs. 
         [0009]      FIG. 1  is a block diagram illustrating an embodiment of electrical power system  10  for providing power to one or more NACs  16   a - 16   n.  System  10  includes primary power supplies  12   a - 12   n,  backup power source  14 , load-sharing bus  18 , and power supply path  20 . Each of the NACs  16   a - 16   n  contain notification devices  22   a - 22   n.  Notification devices  22   a - 22   n  may be any notification device such as a siren or a strobe light. While illustrated schematically as a single backup power source, a plurality of backup sources may be used, such that each primary power supply  12   a - 12   n  has its own dedicated backup power source  14 . Backup power source  14  may comprise one or more batteries. 
         [0010]    The combination of primary power supplies  12   a - 12   n  provide load-sharing for NACs  16   a - 16   n.  Load-sharing is used in electrical power systems to provide a current to a load using multiple power sources in parallel. The circuit is designed such that each power source provides an approximately equal fraction of the total current of the system. This configuration provides redundancy and reliability, and eliminates the need for a single power source to provide large output currents to one or more loads. 
         [0011]    Load-sharing in system  10  consists of providing a combined current from primary power supplies  12   a - 12   n  to NACs  16   a - 16   n  such that each primary power supply  12   a - 12   n  provides an approximately equal current, and the combined current is greater than the current provided by any single primary power supply. For example, if NACs  16   a - 16   n  require 30 amperes, each primary power supply  12   a - 12   n  will regulate its output such that the current is approximately equal to 30/n amperes. If there are three primary power supplies, each source will provide a current that is approximately 10 amperes. 
         [0012]    Load-sharing bus  18  is used to provide each primary power supply  12   a - 12   n  with a voltage proportional to the highest current provided by any of primary power supplies  12   a - 12   n.  Each primary power supply  12   a - 12   n  may then compare the voltage on load-sharing bus  18  with a voltage representative of its own output current. If the voltage on load-sharing bus  18  is greater than the voltage representative of its own output current, the respective primary power supply will adjust its output voltage such that it outputs an approximately equal current to that communicated on load-sharing bus  18 . If the voltage on load-sharing bus  18  is not greater than the voltage of the respective primary power supply, the respective primary power supply will not adjust its output current. 
         [0013]    If one of primary power supplies  12   a - 12   n  fails to operate correctly, backup power source  14  will provide power in place of the unavailable primary power supply. For example, if there are three primary power supplies, all supplying 10 amperes of current, and one of the power supplies becomes unavailable, backup power source  14  will supply sufficient voltage to provide 10 amperes of current in place of the unavailable primary power supply. 
         [0014]    In an alternate embodiment, backup power source  14  may take over and supply power in place of all primary power supplies  12   a - 12   n  in the event that any one of primary power supplies  12   a - 12   n  is unavailable or malfunctioning. In the example above, if one of the three primary power supplies becomes unavailable, all three primary power supplies will stop providing power, and backup power source  14  will take over and provide all 30 amperes to NACs  16   a - 16   n.    
         [0015]      FIG. 2  is a block diagram of a primary power supply  12 . Primary power supply  12  includes AC power source  30 , AC-DC converter  32 , switching network  34 , boost regulator circuit  36 , backup power source input  38 , load-sharing controller  40 , diode  42 , output  44 , load-sharing output path  46 , load-sharing input path  48 , and load-sharing control path  50 . Backup power source input  38  receives power from backup power source  14 . AC power source  30  may be any readily available electrical power source and is typically AC mains power provided by a power utility company. AC-DC converter  32  converts the output of AC power source  30  to a DC output for supplying NACs  16   a - 16   n  with a working voltage and current. 
         [0016]    Switching network  34  is used to select between the output of AC-DC converter  32 , and the output of boost regulator circuit  36 . Switching network  34  selects the output of AC-DC converter  32  when AC power source  30  is operational. If AC power source  30  is unavailable or malfunctioning, switching network  34  selects the output of boost regulator circuit  36 . 
         [0017]    Boost regulator circuit  36  operates to boost the voltage from backup power source  14  when a respective AC power source  32  is unavailable and backup power source  14  is not supplying enough voltage for power system  10  to provide a working voltage and current to NACs  16   a - 16   n.  When the voltage of backup power source  14  falls below the voltage needed for system  10  to provide a working voltage and current to NACs  16   a - 16   n,  respective boost regulator circuit  36  of each unavailable primary power supply  12   a - 12   n  boosts the voltage from backup power source  14  such that a sufficient voltage for system  10  to provide a working voltage and current to each of the NACs  16   a - 16   n  is provided. 
         [0018]    For example, if two out of three primary power supplies are malfunctioning, and NACs  16   a - 16   n  require a total of 30 amperes of current to operate, backup power source  14  must supply a sufficient voltage to each of the two unavailable primary power supplies to produce the missing 10 amperes of current. If the voltage necessary to produce the 10 amperes of current for each unavailable primary power supply is 22.5 volts, then each boost regulator circuit  36  of the unavailable primary power supplies will operate when the backup voltage source  14  is producing a voltage less than 22.5 volts on respective backup source input  38 . If no primary power supply is operating on backup power, boost regulator circuit  36  may operate to charge backup power source  14 . 
         [0019]    Load-sharing controller  40  operates to regulate the output current on output  44 . Load-sharing controller  40  senses the current on output  44  and communicates to load-sharing output path  46  a reference voltage proportional to the output current. This reference voltage is communicated to load-sharing bus  18  through diode  42 . Diode  42  acts to diode OR the reference voltages of each of primary power supplies  12   a - 12   n.  Therefore, the reference voltage is only communicated onto load-sharing bus  18  if the reference voltage is higher than the reference voltage that is already on load-sharing bus  18 . This ensures that load-sharing bus  18  will always contain the reference voltage of the primary power supply that is producing the greatest output current. 
         [0020]    Load-sharing controller  40  uses load-sharing control path  50  to regulate the current on output  44  based upon the reference voltage on load-sharing bus  18 . If the reference voltage produced by load-sharing controller  40  is lower than the reference voltage on load-sharing bus  18 , load-sharing controller  40  will regulate the output voltage from AC-DC converter  32  or boost regulator circuit  36 , depending on which is selected, such that the output current on output  44  produces a reference voltage approximately equal to that of the reference voltage on load-sharing bus  18 . 
         [0021]      FIG. 3  is a flowchart illustrating a detailed method  60  of providing load-sharing and boosted voltage for one or more NACs  16   a - 16   n.  At step  62 , all primary power supplies  12   a - 12   n  are functional. At step  64 , output voltages of each primary power supply are regulated such that each primary power supply provides approximately equal current to NACs  16   a - 16   n.  At step  66 , it is determined if all primary power supplies  12   a - 12   n  are operational. If one of the primary power supplies  12   a - 12   n  is unavailable then power system  10  proceeds to step  68 . If all primary power supplies are operational, then power system  10  returns to step  64  and continues to regulate the output voltage of each primary power supply. At step  68 , switching network  34  of the primary power supply that is unavailable selects power from backup power source  14 . At step  70 , it is determined if backup power source  14  is supplying a sufficient voltage to provide a working voltage and current to NACs  16   a - 16   n.  If backup power source  14  is not supplying a sufficient voltage, then power system  10  proceeds to step  72 . If backup power source  14  is supplying sufficient voltage, then power system  10  returns to step  64  and continues to regulate the output voltage of each primary power supply. At step  72 , boost regulator circuit  36  of the primary power supply that is unavailable boosts the voltage of backup power source  14  to a voltage that is sufficient to provide NACs  16   a - 16   n  with a working voltage and current. After step  72 , power system  10  returns to step  64  and continues to regulate the output voltage of each primary power supply, including those primary power supplies providing output voltage from backup power source  14 . 
         [0022]    In this way, the present invention describes an electrical power system that provides a working voltage and current to one or more notification appliance circuits (NACs). Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.