Patent Publication Number: US-6987363-B1

Title: Emergency ballast for compact fluorescent lamp with battery heater

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application is a continuation in part of, and claims benefit of, U.S. patent application Ser. No. 10/427,462, file May 1, 2003, issuing as U.S. Pat. No. 6,753,651, to be issued Jun. 22, 2004; and U.S. Provisional Application Ser. No. 60/376,864, filed May 1, 2002; and all of which are hereby incorporated in their entirety by reference. 

   STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
   Not Applicable 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention relates to emergency lighting, and particularly to fluorescent lighting wherein a fluorescent lamp is connected to a source of electrical energy other than normal AC line current in the event that the normal AC current fails. 
   Emergency lighting is required in commercial, industrial, and institutional buildings just as fire extinguishers, smoke alarms and other safety equipment. Three types of emergency lighting are common in such installations: unit equipment, engine generators and central battery systems. Unit equipment falls into two principle types: fluorescent and incandescent. 
   The fluorescent emergency units are customarily combined with and within a conventional fluorescent lighting unit by merely adding the emergency ballast consisting of a battery, a battery charger, inverter and sensing circuitry adjacent the standard fluorescent AC ballast. The sensing circuit of the emergency ballast observes the interruption of normal AC power to the lamp unit and immediately switches on the emergency ballast to power individual lamp(s) or the light fixture for the required period which, under most state safety codes, is a period of at least ninety (90) minutes, a standard called out in the National Electrical Code, NFPA Article 70, and NFPA Article 101 Light Safety Code. 
   2. General Background of the Invention 
   U.S. Pat. No. 5,004,953 entitled Emergency Lighting Ballast for Compact Fluorescent Lamps with Integral Starters, assigned to the assignee of the present invention is illustrative of the general fluorescent type of emergency lighting with a ballast and also illustrates a compact fluorescent lamp. It is common in the installation of emergency fluorescent lighting that an emergency ballast is added to a conventional fluorescent fixture or provided integrally in a fixture having internal regular and emergency ballast installed. When main AC power fails, voltage sensing circuitry instantly connects DC current from a battery (in the emergency ballast) to an inverter which produces high frequency, high voltage power to illuminate the emergency fluorescent lamp(s) for the required period. 
   The present invention is directed to fluorescent lighting fixtures which are likely to be exposed to extreme low temperatures wherein the battery which supplies the power for lighting when main AC power fails is apt to freeze. Until now, emergency lighting has been utilized in such as commercial an governmental buildings wherein it is unlikely that power will be out for such a long period of time that the batteries for providing the back-up power will freeze. The state of the art units typically are recommended for temperature ranges of about 0° C. to about 50° C. Unit contained emergency fluorescent lighting is now so reliable and common that it is being considered for such as smaller out buildings, garages, outside staircases and warehouses where the building (or fluorescent unit) is unheated, or if subjected to prolonged power outage during winter, the internal environment may cool to 0° C. or lower. After a prolonged time at below freezing temperatures, the battery internal to the emergency ballast is likely to freeze. The problem arises when normal AC power is restored and the battery charging circuit of the unit attempts to recharge the battery. With the inclusion of the present invention, emergency fluorescent lighting may be extended to an operating range of about −20° C. to about 50° C. 
   Emergency fluorescent lighting has now advanced to the state of art wherein compact lamps as well as conventional (large) fluorescent lamps are finding application in extreme low temperature sites, particularly those where operation of the lamp, as well as the emergency ballast, are disadvantageously effected. Compact Fluorescent lamps present special issues when operated in low power ranges, and operation of such lamps in colder than normal settings causes permanent and rapid deterioration of the lamp. Among the observed problems are cathode instability including sputtering and the deposit of a pink haze on the glass envelope of the lamp. 
   Compact fluorescent lamps are designed to be operated on a-c current and at rated power, i.e., about 42 Watts. In emergency operation in conjunction with an emergency ballast, all fluorescent lamps are operated at power levels that are considerably below rated, and in the instance of the compact lamp, anywhere between about 7 to about 12 Watts, depending upon the particular lamp. Likewise, the emergency operating current is supplied by a battery in the ballast, and is a variety of a pulsating d-c current except compact lamps operate more efficiently with AC current. It has become evident that the degree of heating generated by the normal AC current at a level of around 7–12 Watts of output is nowhere close to the level in emergency mode for generating sufficient heat energy to sustain a satisfactory continuing operation for a compact lamp in a severely low temperature environment. 
   It is likewise known that rechargeable batteries such as the nickel-cadmium type typically used in fluorescent emergency lighting systems have difficulties in charging when frozen. Charging may be erratic, and at times at rates much higher than the rate recommended by manufacturers for safe operation. There is also a danger that during the charging process that volatile gasses, particularly hydrogen, may build-up and pose the threat of explosion. The present invention provides a heating mechanism for the rechargeable battery which keeps it at a suitable charging temperature during normal operation whether the installation site building is heated or not, enabling the use of the unit in unheated or lesser heated facilities. Further, the heater circuit addition includes means for connecting the charging circuit to a dummy load while the battery comes up to suitable temperature for charging, while keeping the appropriate relays connected so that upon the resumption of AC power, the normal fluorescent lighting may be powered by the AC main power. Once the battery temperature is sensed to be at a sufficient level for safe charging, the charging circuit is switched to the battery from the dummy load so as to fully recharge the battery. In conjunction with these improvements useful for standard or large sized fluorescent lamps, the present invention related to compact fluorescent lamps includes providing an additional cathode heating current to at least one of the filaments of the compact lamp, which filament is provided with a current (a-c, preferably or d-c) at a level of about 3 to 4 volts. The heating current may be supplied from a separate battery or the battery supplying the current to illuminate the fluorescent lamp during emergency operation 
   Those skilled in the art will recognize that alternative approaches to the preferred embodiments of the present invention disclosed herein may be made without departing from the scope of the present invention. 
   SUMMARY OF THE INVENTION 
   The present invention is directed to an emergency ballast for operation of a compact fluorescent lamp in extreme temperature conditions where the battery powering the emergency ballast and emergency fluorescent lamp becomes frozen and requires heating to a recognized minimum temperature before safe recharging may be initiated. 
   The primary objective of the present invention is to ensure stable operation of the compact lamp while operating in the emergency mode. Extremely cold temperatures affect operation of the lamp during the low power operation in the emergency phase, causing, among other problems, cathode sputtering and the deposition of a pink haze on the interior of the glass envelope of the lamp. 
   Another one of the objectives of the present invention is to cause the internal battery of the compact fluorescent emergency ballast to remain in its normal operating temperature range during the time that main AC power is supplied to the compact fluorescent lamp. 
   A further objective of the present invention is to delay the recharging of the battery in the emergency ballast after a loss of main AC power during extreme cold wherein the internal temperature of the battery has dropped below the recommended operating temperature, or has frozen, and the battery is heated to a permissible operating range before recharging current is applied. 
   A further objective of the present invention is the inclusion of the described delay in energizing the battery when its internal temperature is below recommended, and the inclusion of enabling circuitry to cause the fluorescent fixture to illuminate on the return of main AC power, irrespective of the ambient temperature. 
   A further objective of the present invention is the inclusion of a delay of the operation of the normal ac ballast for the lamp after line voltage has been restored to the circuit. 
   These and other objectives will be evident from the detailed descriptions of the preferred embodiments provided below. 

   
     DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a circuit diagram of a preferred embodiment of an emergency ballast according to the present invention. 
       FIG. 2  is an alternative embodiment of an emergency ballast according to the present invention. 
       FIG. 3  is a further aspect of an emergency ballast according to the present invention, showing the power line connection. 
       FIG. 4  is a further alternative embodiment of an emergency ballast according to the present invention however, having a supplemental battery for cathode heating. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The invention is illustrated in the context of a conventional fluorescent lamp including an emergency ballast for standby lighting during a period when the main AC power fails.  FIG. 1  illustrates the circuit diagram of an emergency ballast according to the present invention which is connected to a conventional compact fluorescent ballast (not shown—see  FIG. 3 ) for providing emergency lighting in the event of main AC power failure. 
   The circuitry for an emergency ballast B is illustrated in  FIG. 1 , as adapted with the components for meeting the objectives stated above. If a standard compact fluorescent ballast be shown, its output would be connected to the fluorescent lamp LAMP, in parallel with the output of the emergency ballast I o and through its K1C and K2C relay contacts . This system includes an input/charging circuit I n  which provides charging current to the battery BT 1  and disables the emergency operation mode, i.e., places it in standby during the period that AC power is being supplied. The input/charging circuit has first and second input terminals J- 1  and J- 2 , respectively, connectable to standard AC voltage sources such as 120 AC and 277 volts AC. Inclusion of alternative voltage connections enables the system to be selectively connected to either standard commercial voltage AC (277 volts AC) or normal residential voltage (120 volts AC). Common, or ground potential, connector J- 3  completes the A.C. power connections to the system input. 
   The two A.C. supply voltage terminals J- 1  and J- 2  and the common terminal J- 3  are connected to the AC inputs of a rectifier D 1  (which in the preferred embodiment is a full wave rectifier), the high voltage (277 v. AC) input terminal J- 2  being connected by means of a series arrangement of a first circuit composed of a capacitor, C 1 , and a resistor, R 17 , and a second circuit composed of a capacitor, C 2 , and a resistor, R 18 . The lower voltage (e.g. 120 volts AC) terminal is connected to rectifier D 1 , only via the second circuit including C 2  and R 8 . The capacitors in the circuits serve to limit the charging current supplied to rectifier D 1  to a level consistent with the requirements for a charging current to battery BT 1 . The resistors are included as a safety measure to limit the discharge of power from the capacitors after the A.C. power is removed from the circuits. 
   In a first embodiment ( FIG. 1 ), the DC output from rectifier D 1  is supplied to battery BT 1  through the coils of two relays, K 1 A and K 2 A, and a diode D 4 . A resistor R 19  is connected in parallel with coils K 1 A and K 2 A to assure proper current flowing through the K 1 A and K 2 A relay coils. A resistor R 18  is connected in series with an LED indicator to show the charging status of the emergency ballast B. 
   In an alternative embodiment illustrated in  FIG. 2 , the output from rectifier D 1  is supplied to battery BT 1  through coils of three relays, K 4 A, K 1 A and K 2 A. Current limiting resistor R 29  is connected in series with light emitting diode indicator LED to show the charging status of emergency battery BT 1 . Relay coil K 4 A operates contacts K 4  which are in the AC supply for the AC ballast ( FIG. 3 ) when the AC power is reestablished such that the emergency ballast ceases supplying current to the lamp LAMP, the transient AC load on contacts K 1 B, K 1 C and K 2 C is removed, thereby prolonging their life by reducing the arcing which occurs on the opening of the contacts. As shown in  FIG. 3 , the AC ballast is connected to the building AC supply in series with a conventional wall switch W. Relay K 4  interrupts the AC supply to the ac ballast as described below when the battery BTR 1  is sensed as being outside its operating limits. 
   Battery BT 1  may be composed of, for example, a high temperature nickel-cadmium battery. In the described embodiment, battery BT 1  in the embodiment of  FIG. 1  is comprised of four D cells providing 4.8 volts and the battery BT 1  in the embodiment of  FIG. 2  is comprised of seven C cells and provides nominal voltage of 8.4 volts. Alternate battery configurations are possible, dictated by the power requirements of load LAMP and size of the battery space available in the emergency ballast. 
   As should be appreciated, the output circuit I o  of the embodiment illustrated in  FIG. 1  includes a secondary transformer winding S for powering the lamp LAMP, (from a primary winding P, a feedback winding F on the inverter side of the transformer T) and a supplemental secondary winding S 1  for providing a cathode heating current to stabilize the illumination output of the compact fluorescent lamp when operating in emergency mode. The output circuit I o  also provides switching by switches K 1 B and K 1 C and K 2 C between normal lamp operation (K 1 A and K 2 A coils energized) and the emergency ballast mode (K 1 A and K 2 A coils de-energized) during which time the AC power is not available. The output circuit I o  in this embodiment is composed of a capacitor C 7  connected in series with the secondary winding S and the Lamp and capacitors C 4  and C 5  connected in parallel. As may be observed by those skilled in the art, the output circuit I o  is remarkably simple in that the output circuit of the emergency ballast B provides only that current limiting and cathode heating necessary to keep the compact fluorescent lamp within a stable operating range in extreme cold temperatures so as to provide for a maximized operating cycle during the emergency mode. An alternative embodiment of the invention illustrated in  FIG. 1  may include a time delay circuit Td to allow the K 1 B, K 1 C and K 2 C relay contacts to open before allowing the AC ballast to power the lamp LAMP. In the illustrated embodiment, the provided delay is in the order of five seconds, however the length of time may be more or less, depending on particular lamp characteristics and operating choice. 
   The output circuit I o  illustrated in the alternative embodiment of  FIG. 2  includes a secondary winding S of transformer T having a primary winding P and a feedback winding F on the inverter circuit I v  side of transformer T. Output circuit I o  provides current limiting to the fluorescent lamp load LAMP only to the degree that is necessary to keep the lamp within its normal operating limits. The output I o  circuit also provides switching by switches K 1 B and K 1 C and K 2 B between normal lamp operation (K 1 A and K 2 A energized) and the emergency ballast mode (K 1 A and K 2 A de-energized) during which the AC power is not available. The output circuit I o  is composed of a capacitor, C 6 , connected in series with the output of the secondary winding, S, of transformer T 1 . Capacitors C 7  and C 8  are connected across the secondary winding of T 1  (to provide a load upon the inverter I v  in the unusual event no other load be present, and in series with the fluorescent lamp LAMP which the output circuit I o  powers. 
   The embodiment illustrated in  FIG. 4  discloses a separate battery system for providing cathode heating current, should a particular compact lamp application be improved by the addition of the resource. 
   Referring now to  FIG. 1 , in emergency mode, emergency power is supplied to load LAMP by battery BT 1  through the operation of inverter circuit Iv and I o . The operation of the inverter circuit I v  is placed in operation enabling the oscillation of switching transistors Q 1  and Q 2 . Those familiar with fluorescent lighting will recognize that an application of an initial voltage of about 100 to as much as approximately 600 volts (depending upon lamp size) may be required to initiate the ignition of the gasses in the standard compact fluorescent lamp. Immediately after ignition, as battery BT 1  through coil L 1  and resistors R 17  and R 18  supplies base current to Q 1  and Q 2 , as later discussed, the current regulating capacitors C 4  or C 5  in the output circuit I o  regulate the current level to that required to operate the fluorescent lamp at reduced illumination typical of fluorescent emergency lamps. 
   The inverter I v  constitutes a current-fed, self-resonant, switch-mode converter supply, also known as a push-pull converter which includes primary P and feedback F windings of transformer T 1 , the transformer having an inductance setting gap in its core. Transformer T 1  is composed of a center tapped primary winding P, a feedback winding F and a high-voltage secondary winding S, composed of a large number of turns of fine magnet wire. Secondary winding S 1  is composed of a low number of turns, i.e., three turns in the illustrated embodiment, and of similar 25 gauge wire for this application. Two transistors, Q 1  and Q 2 , are connected so that the emitter/collector pad of each is connected between a respective end of the primary winding P and feedback winding F and the negative terminal battery BT 1  as shown. A low-voltage feedback winding, F, of transformer T 1  is connected between the bases of transistors Q 1  and Q 2  to provide positive feedback from winding F to cause Q 1  and Q 2  to alternately switch the battery current through primary winding P 1  creating the alternating current in secondary winding S. 
   Battery heater H is connected to main AC supply J 1  or J 2  and common J 3  and in the illustrated embodiment is composed of a sequential line of heater resistors R (R 1  through R  10 ), physically disposed over an area above which the battery BT 1  is positioned such that the heat dissipated by the AC current flowing through the heater resistors R rises to warm battery BT 1 . Included in series with heater resistors R is heater switch HS 1 , which in the illustrated embodiment is a simple bimetallic switch, such as a Phillips/Air Pak 67LO40, which operates to control the flow of current through the heater resistors R 1  to R 10  so that when the ambient temperature at the switch reaches a level where heating of e battery BT 1  will extend its operating range, as in event the temperature around the fluorescent fixture should drop below the recommended operating limits for the battery. In the illustrated embodiment, heater switch HS closes at about 25° C. initiating AC current flow and opens at about 40° C., suspending heater H operation. As will be understood by those skilled in the art, should main AC power fail, there will be no functioning of the heater H, irrespective of the open or closed position of heater switch HS. 
   Charge control circuit C regulates charging of battery BT 1  to occur only during those periods when the battery BT 1  is at a suitable temperature to be safely and effectively charged. Inclusion of control circuit C enables the utilization of fluorescent emergency ballasts in environments not previously considered suitable for effective operation of the emergency ballasts. Control circuit C includes diode D 2  (a 7–15 V Zener diode, depending upon the battery BT 1  voltage) across the output of rectifier D 1  to limit potentially damaging high voltage when the K 3 A contacts are switching. Control circuit including resistor R 16 , relay coil K 3 B, charge activation switch Q 5 , and temperature sensor and controller TC 1  and precision resistor R 15  (for setting the temperature value for activation). Relay coil K 3 B activates switch K 3 A when current flows through coil K 3 B by virtue of temperature controller TC 1  activating switch Q 5  to close the circuit to rectifier D 1 . Battery BT 1  is then connected to rectifier D 1  so that the charging current will flow and recharge the battery BT 1 . In the illustrated embodiment, temperature sensor and controller TC 1  is physically located on the ballast circuit board (not shown) which is under the battery BT 1  package. TC 1  is disposed adjacent the battery BT 1  in order to sense the temperature of the battery BT 1 . As previously described, heater H operates (so long as AC power is being supplied to ballast B) when switch S 1  is below 40° C. to bring battery BT 1  to a safe charging temperature. TC 1  senses the battery BT 1  temperature and actuates when heat generated in heater H has raised the temperature of battery to a safe charging level (around 0° C.) thereby causing transistor Q 5  to conduct and cause a current to flow through relay coil K 3 B and activate switch K 3 A to connect the charging current of rectified D 1  to battery BT 1 . Since rectifier D 1 , upon return of main AC current, will only be connected to battery BT 1  by switch K 3 A when the temperature of the battery BT 1 , as measured by TC 1  adjacent the battery, charging will only occur when battery BT 1  is at a temperature for safe and effective charging. 
   In the embodiment described above and illustrated in the  FIG. 1 , the following components were utilized: 
   
     
       
         
             
             
             
           
             
                 
             
             
               Designator 
               Description 
               Component value/description 
             
             
                 
             
           
          
             
               C1 
               capacitor 
               4.0 uF/3.3 uF 
             
             
               C2 
               capacitor 
               6.0 uF/4.4 uF 
             
             
               C3 
               capacitor 
               220 uF/25 VDC 
             
             
               C4 
               capacitor 
               0.1 uF/100 VDC 
             
             
               C5 
               capacitor 
               220 pF/2 kV 
             
             
               C6 
               capacitor 
               220 pF/2 kV 
             
             
               C7 
               capacitor 
               470 pF/3 kV 
             
             
               C8 
               capacitor 
               390 uF/3 kV 
             
             
               R1–R10 
               resistor 
               150Ω/2 W 
             
             
               R11 
               resistor 
               10MΩ/0.25 W 
             
             
               R12 
               resistor 
               10MΩ/0.25 W 
             
             
               R13 
               resistor 
               180Ω/0.25 W 
             
             
               R14 
               resistor 
               10kΩ/0.25 W 
             
             
               R15 
               resistor 
               107KΩ/0.25 W (1%) 
             
             
               R16 
               resistor 
               620Ω/0.25 W (1%) 
             
             
               R17–R18 
               resistor 
               180Ω/0.5 W 
             
             
               R19 
               resistor 
               110Ω/1 W 
             
             
               R21 
               resistor 
               10KΩ/0.25 W 
             
             
               R22 
               resistor 
               4.7Ω/0.25 W 
             
             
               D1 
               diode bridge 
               1 A, 600 V 
             
             
               D2 
               Zener diode, 
               10 V/5 W 
             
             
               D3, D4 
               diode, 1N9005 
               1 A, 600 V 
             
             
               K1A, K2A 
               DPDT relay 
               3 V, 166 mA coil 
             
             
               K3 
               SPDT relay 
               5 V, 370Ω coil 
             
             
               K4 
               DPDT relay 
               5 V, 90 ma coil 
             
             
               Q1, Q2 
               transistor ZTX-851 
               60 V, 5.0 A 
             
             
               Q5 
               mosfet VN2222 
               60 V, 0.15 A 
             
             
               BT 
               nickel-cadmium battery 
               4.8 V, 4 D cell 
             
             
               BT2 
               nickel-cadmium battery 
               3.6 V, 700 mAh (KR-AAH) 
             
             
               HS1 
               thermostat switch 
               Phillips/AirPax 67LO40 
             
             
               TC1 
               temperature control 
               TC622EPA 
             
             
               T1 
               E187 inverter transformer: 
             
          
         
         
             
             
             
             
             
          
             
                 
               Winding Wire 
                 
               Number 
                 
             
             
                 
               Description 
               GA 
               of Turns 
             
             
                 
               Secondary 
               35 
               650 
             
             
                 
               Secondary 1 
               25 
               3 
             
             
                 
               Primary 
               23 
               4 
             
             
                 
               Primary 
               23 
               4 
             
             
                 
               Feedback 
               25 
               2 
             
             
                 
                 
             
          
         
       
     
   
   The disclosed embodiment is to be considered in all respects as illustrative and not restrictive. Several embodiments are described and illustrated and suggest that there are others within the scope of the invention which meet particular requirements of an application which do not depart from the scope of the invention. The output of the disclosed embodiments is an AC current for driving compact fluorescent lamps, as compared to a variable DC illustrated in the related patent. These are matters of design choice prompted by the characteristics of the lamp being driven. The scope of the invention is to be defined by the appended claims rather than the foregoing descriptions and other embodiments which come into the meaning and range of equivalency of the claims are therefore intended to be included within the scope thereof.