Abstract:
An integral emergency lighting system which utilizes the same branch circuit wiring as main alternating current (AC) power to selectively supply emergency power to light fixtures during an emergency condition such as during an interruption or unavailability of main power from the AC source. The system includes line detection circuitry at the lighting fixtures to enable switching from main AC operation to emergency DC power and also the energizing of the associated egress lighting regardless of the on/off switch settings connected to the branch circuitry. Upon the restoration of main power, the DC battery source automatically switches off and a built-in time delay circuit allows line detection circuitry to stabilize into AC input condition before AC power re-energizes the branch circuit (i.e., switches into the main power mode).

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims benefit to provisional Application Ser. No. 60/200,506, filed Apr. 28, 2000. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is directed generally to an emergency lighting system for supplying emergency power to a lighting device. More particularly, the present invention is directed to an emergency lighting system which selectively energizes a lighting device upon the occurrence of a power interruption and includes a branch circuit relay at the lighting panel comprising a plurality of relays for directing alternating current (AC) power to the branch circuit during normal operation, and direct current (DC) power to the branch circuit during emergency power operations. In addition, the system includes a time delay circuit in which, upon restoration of AC power to the branch circuit, allows line detection circuitry to stabilize before switching from an emergency mode to the normal mode. 
     2. Description of Related Art 
     Emergency lighting is utilized in buildings to provide light for egress and to direct occupants toward the exits in case of a loss of main power to a building. In related art systems, this is generally accomplished by installing exit and emergency lighting fixtures having self-contained batteries or battery powered inverters mounted internal to fluorescent lighting fixtures within these buildings. The self-contained exit and emergency lighting fixtures utilize small batteries which are kept charged in case of main power failure. In the case of the loss of main alternating current (AC) power, the self-contained exit fixture switches power from the lamps within the unit (which function off of main AC power) to a set of direct current (DC) powered lamps which are powered by an internal battery within the exit fixture. In a situation resulting in the loss of main AC power, the self-contained emergency light senses the loss of power and, in response thereto, energizes a set of DC powered lamps from the internal battery within the emergency light fixture. Internal battery powered inverters mounted within fluorescent fixtures operate similarly to self-contained batteries in that they also operate to sense a loss of main power and ignite and hold selected fluorescent lamps in response thereto. 
     There are several disadvantages to having these many independent battery operated fixtures throughout the buildings. For instance, because the emergency components operate in a very hostile environment as a result of being mounted within the fixture, they expose the batteries to undue heat. In addition, over time, because the batteries are maintained at a constant charge, they deteriorate in their ability to provide the rated output required by code to allow safe egress from the building in which they are installed. Furthermore, the required maintenance and testing of the fixtures is commonly ignored, and thus, the safety of the system is compromised. Additionally, leakage from the batteries commonly results in damage to both the fixtures and the surrounding environment. 
     Larger buildings are generally provided with emergency lighting devices which utilize central battery systems for powering exit and emergency fixtures. The central battery system is advantageous in that it can keep the batteries maintained at full charge, monitor the lifetime of the batteries, provide a single location for maintenance, and be equipped to alarm the building in the event of a sensed abnormal condition. The central battery system is disadvantageous in that it utilizes separate wiring for the main AC system and the emergency DC system. This redundancy adds obvious additional cost to new installations which may also be inconvenient to install. In addition, central battery systems are usually not an option for existing buildings which require the installation of a new emergency lighting system, and thus, requires the installation of new conduit and wiring dedicated to the emergency lighting system, which is often impractical due to costs or esthetic reasons. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing, it is an object of the present invention to overcome obviate the disadvantages in the related art in providing an emergency lighting system which detects a power interruption in the main lighting system. 
     It is a second object of the present invention to provide an emergency lighting system which controls the operation of main and emergency lighting fixtures within a building or structure. 
     It is a third object of the present invention to provide an emergency lighting system which utilizes existing wiring for controlling the operation of main and emergency lighting fixtures. 
     It is a fourth object of the present invention to provide an emergency lighting system which automatically switches from the AC power source to a DC power source upon the detection of a power interruption in the main power source regardless of an on/off switch position of the light branch circuit. 
     It is a fifth object of the present invention to provide an emergency lighting system which stabilizes the lighting circuitry upon switching from emergency power to main power. 
     These and other objects are achieved in the present invention by providing an central battery emergency lighting system that allows the sharing of the main AC branch circuit wiring for both the main and emergency power distribution within a building or structure. The sharing of the branch circuit wiring is accomplished by introducing a branch circuit relay at the lighting panel connected to a DC central battery system. Accordingly, during circumstances in which the main AC voltage is not present due to an interruption in power (i.e., an outage or shortage), a line detection circuit detects the loss of the AC voltage and the branch circuit relay switches the line to thereby provide a source of emergency power to the branch circuit from the voltage from the DC central battery system. Additionally, line detection circuits are provided in the lighting fixtures for actuating and operating an emergency lamp. Upon detecting the loss of AC voltage, the line detection circuit automatically switches power to a dedicated emergency lamp within the lighting fixture. Upon the restoration of main power, the lighting fixture resets to the AC voltage lamps to allow the resumption of normal operations. 
     The central battery emergency lighting system also includes switch sensing to allow DC power to be transmitted to an emergency fixture regardless of the position of the main AC lighting switch position. The switch sensing allows for the main AC wiring of the lighting system with appropriate light switches within the building, and bypasses the switches during emergency DC operation regardless of the switch position. In addition, the system utilizes an automatic time delay circuit for delaying re-energizing the line with AC power to allow stabilization of the switch circuits between emergency and normal modes. 
     In accordance with an embodiment of the invention, the line detection circuits are installed in predetermined locations, and preferably, are located within any type of normal lighting fixture. For example, fluorescent lay-in lighting fixtures are equipped with a line detection circuit mounted within or adjacent to the ballast chamber to thereby direct main AC power to the fluorescent ballast and emergency backup power to the dedicated emergency lamps. In addition, the line detection circuits will actuate and hold the lamp in an emergency operation mode. For recessed incandescent lamps, the line detection circuits are modified for mounting within a junction box adjacent to the light fixture to direct the main AC power to the light fixture and the emergency DC power to an appropriate local emergency lighting fixture. Exit fixtures equipped with both AC and DC powered lamps may also be provided with a line detection circuit for directing power to the appropriate lamps. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A complete understanding of the invention is obtained from the following descriptions whereby the objects and advantages of this invention become more apparent and readily appreciated from the following detailed description taken in conjunction with the accompanying drawings demonstrating the exemplary embodiments of the invention, of which: 
     FIG. 1 a  is a block diagram of an exemplary embodiment of the invention wired into a typical lighting branch circuit; 
     FIGS. 1 b  and  1   c  are circuit diagrams illustrating an emergency lighting branch circuit according to second and third embodiments of the present invention; 
     FIG. 2 is a block diagram illustrating the logic and switching of circuit diagram illustrated in FIG. 1 a ,  1   b  or  1   c ; and 
     FIG. 3 is a detailed schematics of the illustrative embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 a  depicts a block diagram of an exemplary embodiment of the invention wired into a typical lighting branch circuit. As shown, a branch circuit with a line switch feeding a series of four standard fluorescent fixtures  100 ,  200 ,  300  and  400 . FIGS. 1 b  and  1   c  depict two separate embodiments of the invention. In FIG. 1 b , a ballast  13  and a DC detector and ballast (mod- 0 )  4  are shown electrically connected to a standard fluorescent fixture  100  and having a branch switch K 3  terminating at the fluorescent fixture  100 . In FIG. 1 c , the ballast  13  DC detector is shown with a ballast (mod- 1 )  41  electrically connected to the standard fluorescent fixtures  200 ,  300  and  400 , however, without a branch switch K 3 . As shown in FIG. 3, the DC detector and ballast (mod- 0 )  4  differs from the DC detector and ballast (mod- 1 )  41  due to it having a relay  9  removed and a jumper wire installed between a first junction (J 1 )  39  and a second junction (J 2 )  40 . 
     FIG. 2 depicts a block diagram of an illustrative embodiment of the invention. During the loss of main power (for example, 110V (AC)), power relays  2 ,  3  de-energize so that an emergency power of 24V from a DC battery  51  is provided to the lighting branch circuit K 3  through the normally closed contact of power relay  2  contacts  2   a - 2   b ,  2   c - 2   d  and normally closed contacts of power relay  3  contacts  3   a - 3   c ,  3   d - 3   f . In a normal state, 110V (AC), 60 Hz power is provided to the light branch circuit K 3  through the normally open contact of power relay  3  contacts  3   a - 3   b ,  3   d - 3   e  while power relay  3  is energized. As shown in FIG. 2, an event causing the interruption of power from the main power source causes the de-energizing of the relays  2 ,  3  so that emergency power is activated from the emergency power source to thereby supply 24V (DC) to the light branch circuit K 3  through normally closed contacts  2   a - 2   c ,  2   d - 2   f ,  3   a - 3   c  and  3   d - 3   f  of relays  2 ,  3  respectively. 
     Power relay  3  is a timed closed instant open (TCIO) relay provided to ensure that the DC circuitry in mod- 0  and mod- 1  is stabilized before restoring main power of 110V (AC), 60 Hz back to the lighting branch circuit. Power relay  2  is an instant open instant closed (IOIC) relay, and is provided for removing the standby or emergency power of 24V (DC) from the emergency battery source  51  when main power of 110V (AC), 60 Hz is restored. When main power is restored, the branch light circuit K 3  loses all power for the time it takes the power relay  3  to energize. This time period is designed to give relays in the DC detector and ballast circuit  4 ,  41  time to stabilize and also to ensure that no contact bounce occurs when main power is returned to the lighting branch circuit K 3 . 
     The DC detector and ballast  9  illustrated in FIG. 2 is designed to monitor the lighting branch circuit and detect when emergency power of 24V (DC) is present, and thereby switches the emergency power of 24V (DC) to a DC/AC inverter ballast circuit  8 , which, in turn, drives a light fixture  12 , such as a 40 W fluorescent lamp. When the DC detector and ballast  9  detects emergency power of 24V (DC), a relay  11  energizes and interrupts the normal feed to lamp  12  from the standard ballast  13 , through relay contacts  11   a - 11   c  and  11   d - 11   f , and supplies lamp  12  with the inverter ballast  8  output of main power (120V (AC), 20 KHz) through relay contacts  11   a - 11   b  and  11   d - 11   e . Preferably, the DC detector and ballast  9  comprises a positive half wave rectifier  5 , a negative half wave rectifier  6 , and a voltage divider network including resistors  15 ,  16 , and transistor  7 . 
     As shown in FIG. 2, when the DC detector and ballast  9  detects a power amount from the main power source, such as 110V (AC), the output of each rectifier  5 ,  6  is equal and opposite in polarity to one another, and the values of resistors  15 ,  16  are such that the voltage presented at the base of the transistor  7  is held negative, thus, biasing the transistor  7  to an off state. When the lighting branch circuit switches from main power (i.e., 110V (AC), 60 Hz) to the backup or emergency power of 24V (DC), the positive half wave rectifier  5  passes the 24V (DC). In this event, the base of the transistor  7  goes positive and biases the transistor  7  to saturation, drawing current through coils of relays  9 ,  10  and  11 , thereby causing each relay  9 ,  10  and  11  to energize. 
     Preferably, relay  9  is only present for mod- 0  type DC detector and ballast  4  where a given light fixture has a branch switch circuit K 3  coming into the fixture. In accordance with the present invention, the branch lighting circuit switch K 3  is bypassed in an off position to provide emergency lighting to the branch lighting circuit if it incorporates an emergency lighting circuit. The possibility exists that a branch lighting circuit may be off, even though that circuit is needed for egress lighting. In such an event and where main power is lost, the designated emergency lighting will automatically energize to provide for egress lighting. In the event of a loss of main power (i.e., 110V AC, 60 Hz), relay  9  energizes when 24V (DC) is detected and, in turn, will close contact  9   a - 9   b . This closure will short the light branch circuits on/off switches and extend the 24V (DC) to the remaining lighting fixtures in the circuit. Relay  10  routes 24V (DC) through normally open contacts  10   a - 10   b  and  10   d - 10   e  to the inverter ballast upon the loss of main power (i.e., 110V AC, 60 Hz). Upon the presence of main power at the light branch circuit, contact  10   a - 10   c  and  10   d - 10   f  will route main power (i.e., 110V (AC), 60 Hz) to the input of the standard light fixture ballast. Lamp  14  is a DC lamp illuminated while main power is present and mounted in the fixture of the emergency light to signify that the fixture contains emergency egress lighting. 
     FIG. 3 illustrates a detailed schematic of an illustrative embodiment of a DC detector and ballast circuit  50  in accordance with the present invention and includes a negative half wave rectifier and filter comprising a diode  17 , resistors  19 ,  20  and filter capacitor  18 . A third resistor  21  and a zener diode  22  are provided to establish a negative reference voltage of 5.1V (DC) for comparison to the same components which establishes a positive reference voltage of 5.1V (DC). These components include a diode  24 , resistors  25 ,  26  and a filter capacitor  23 . The positive 5.1V DC voltage and the negative 5.1V DC voltage are connected to a voltage dividing network  15 ,  16 . Preferably, the value of network  15  is approximately 2 times the value of that of network  16 , and therefore, will drop twice the voltage of network  16 . As a result, this maintains the junction of network  15 ,  16  at a minus 1.83V which, in turn, biases the transistor  7  in the off state. The biasing of the transistor  7  when the lighting branch circuit is supplied with main power (i.e., 110V (AC), 60 Hz) ensures that relays  9 ,  10  and  11  remain de-energized. Accordingly, the light fixture (fluorescent lamp) is supplied with the standard ballast output through normally closed contacts  11   d - 11   f  of relay  11 . 
     At the DC detector and ballast circuit, positive 24V (DC) is present at the cathode of diode  17  and the anode of diode  24 , with 24V (DC) return now becoming the circuit ground. At this point, the diode  17  now blocks current flow and the diode  24  will thereby conduct. With the conduction of diode  24 , 24V (DC) is coupled to the voltage divider comprising resistors  25 ,  26 , thereby providing 12V (DC) to the voltage reference circuit of the resistor  27  and the zener diode  28 . The zener diode  28  maintain a 5.1V (DC) reference at the voltage divider circuit of resistor  15 . The other side of the voltage divider resistor  16  no longer has negative 5.1V (DC) with the absence of main power (i.e., 110V (AC), 60 Hz), but the negative half wave rectifier does complete the current path for the voltage divider of resistors  15 ,  16  through resistors  20 ,  21 . This current flow will put the junction of resistors  15 ,  16  to a positive voltage and coupled to the base of the transistor  7  will forward bias the transistor  7  to saturation. Upon conduction, the transistor  7  provides ground to relays  9 ,  10  and  11 , causing each relay  9 ,  10  and  11  to energize. While relay  9  is energized, normally open contacts  9   a - 9   b  close, in turn, shorting any on/off switches that might be off keeping power to the lights. The closure of these contacts will route positive 24V (DC) to relay contact  10   d  of relay  10 . Relay  10  also is in the energized state and will route positive 24V (DC) to the inverter ballast circuit through its normally open contact  10   d - 10   e . In addition, 24V (DC) return is coupled to the inverter ballast circuit through the normally open contacts  10   a - 10   b  of relay  10 . 
     The inverter circuit is designated to convert 24V (DC) to a high voltage AC signal at approximately 20 KHz. The voltage level and frequency are selected to be compatible with several fluorescent lamp types. Transistors  29 ,  30  begin conducting when 24V (DC) is applied through relay  10 . Since there can never be a perfect balance one will conduct harder than the other. As the dominant transistor conducts toward saturation, the feedback winding of transformer  32  at secondary winding S 2  aides the harder conducting transistor and at the same time bias the other off. This continues until transformer  32  primary P 1  saturates and no more magnetic flux coupling occurs in transformer  32 . At this point, base current stops flowing, thereby negating conduction of the conducting transistor. Current stops flowing to the transformer  32  primary P 1  and the magnetic field collapses causing current reversal in secondary S 2 . The current of opposite polarity will bias the transistor that was bias off first in the forward direction. At this time, the same action occurs with this transistor turning on to saturation and biasing the opposite transistor to cut off. This transition repeats and sets up a square wave oscillation at a frequency determined by the transformer values and transistor operating characteristics. Capacitor  31  is to reduce transformer ringing when push pull transistor is switched on and off. 
     The secondary S 1  winding of transformer  32  is stepped up from the primary P 1  to produce the desired voltage needed to start and operate the selected fluorescent lamp. Coupled to the secondary winding S 1  of transformer  32  is an impedance matching circuit consisting of diodes  34 ,  35  and capacitors  36 ,  37 . The lamp drive voltage from transformer  32  secondary S 1  is coupled to fluorescent lamp  4 ,  38  through diode  34  and normally open contacts  11   e - 11   d  of relay  11  and through diode  34  and normally open contacts  11   a - 11   b  of relay  11 . 
     It will be apparent that any modifications and variations may be effected without departing from the spirit and scope of the novel concepts set forth in the present invention.