Abstract:
A ballast (e.g. a fluorescent light ballast) includes a primary ballast for powering the lamp from a power supply (e.g., utility line power) and an battery powered ballast for powering the lamp from a battery when the primary power supply is not energized by the power supply. When power supply power is restored to the ballast, the ballast shuts down the battery powered ballast and a switch circuit operably connects the lamp to the primary ballast. The ballast toggles the switch circuit such that the primary ballast detects replacement of a lamp and resets any fault detection or protection circuits (e.g., an end of lamp life circuit) that may have been triggered during the transition from battery power to power from the power supply.

Description:
BACKGROUND 
       [0001]    A ballast provides power to a lamp and regulates the current and/or power provided to the lamp. When a lamp (e.g. a fluorescent lamp) nears the end of its usable life or breaks, the resistance of the lamp increases as seen by the ballast. The increased resistance requires the ballast to output higher voltages in order to maintain the current or power transferred to the lamp. Thus, the ballast develops very high voltages (e.g., voltages in excess of 500 volts AC) as the resistance continues to increase. The high voltage poses an electrocution hazard to a technician who needs to replace the old lamp because the increased voltage increases the risk that the electricity will arc to earth ground through the technician as he attempts to replace the lamp. Therefore, some ballasts are equipped with a protection circuit (e.g., an end of lamp life circuit) that detects output voltages in excess of a threshold and shuts down the high voltage output of the ballast. These ballasts also have a circuit for detecting when a lamp has been replaced and restarting the high voltage output of the ballast in order to light the new lamp (e.g., by resetting the end of lamp life circuit). 
         [0002]    A ballast may receive power from multiple sources. For example, ballasts used in commercial buildings commonly receive power from a utility line supply and from a battery. Such ballasts include a primary ballast for powering a lamp from the utility line supply and an battery powered ballast for powering the lamp from the battery. The primary ballast is configured to power two lamps in a single fixture while the battery powered ballast is configured to only power one of the lamps. Generally, the primary ballast is providing power to both lamps whenever utility line power is available to the ballast and the light is switched on, and the battery powered ballast powers one lamp from the battery when the light is switched on but there is no utility line power available to the ballast such as during a fire or utility power outage. 
         [0003]    A problem can occur in these existing ballasts when switching power sources, for example, when switching from battery power to utility line power after an interruption in utility line power to the ballast. That is, when utility line power is restored to the ballast, the ballast switches operation from the battery powered ballast to the primary ballast by shutting down the battery powered ballast and reconfiguring the connection between the ballast and the lamps such that the lamps can be powered by the primary ballast instead of the battery powered ballast. However, due to timing delays in the primary and battery powered ballasts, the primary ballast may fail to properly power to the lamps due to timing delays in the primary and battery powered ballasts. That is, due to timing delays or rebound action in the switches that reconfigure the lamp to ballast connection, the end of lamp life circuit of the primary ballast may erroneously detect that the lamps are broken or end the end of their useful lives and shut down the output of the primary ballast. These timing delays may also cause other protection circuits to trigger. 
         [0004]    To overcome these timing delays, one prior art solution disclosed in U.S. Pat. No. 6,339,296 is to delay supplying power from the utility line to the primary ballast for a period of 5 to 10 seconds in order to allow adequate time for the switches that determine the lamp to ballast connection to reconfigure the connection and other transients in the ballast to settle. Thus, when the primary ballast receives power, the end of lamp life circuit (and other protection circuits) is not falsely triggered because the lamps have been connected to the primary ballast output for a number of seconds. One problem with this solution is that delaying power to the primary ballast introduces a relatively long wait time when switching between power sources (e.g. when switching from battery power to utility line power). 
       SUMMARY 
       [0005]    In one embodiment of the invention, a ballast having a relamping circuit includes a primary ballast for supplying power to a lamp from a power supply (e.g. utility line power), and an battery powered ballast for supplying power to a lamp from a battery. When power from the power supply is restored to the ballast after an interruption, the ballast provides the power from the power supply to the primary ballast, de-energizes a lamp driver circuit of the battery powered ballast, and reconfigures the connection between the ballast and the lamp so that the lamp is operably connected to the primary ballast. A relamping circuit of the battery powered ballast then toggles a switch circuit that determines the connection configuration between the lamp and the ballast to disconnect the lamp from the primary ballast and then reconnect the lamp to the primary ballast. In operation, a protection circuit (e.g., an end of lamp life circuit) of the primary ballast detects that a lamp has been replaced, and the protection circuit resets, enabling an inverter of the primary ballast to supply power to the lamp from the power supply. 
         [0006]    In another embodiment of the invention, a method is provided for transitioning a lamp from power from a battery to power from a power supply in response to a power restoration event. The power restoration event occurs when the power supply energizes the primary ballast following a period during which the power supply was not energizing the power supply. The transition is preformed by a ballast including a primary ballast for powering the lamp from the power supply when the primary ballast is energized by the power supply and an battery powered ballast for powering the lamp from a battery when the primary power supply is not energized by the power supply. In response to the power restoration event, the ballast disables a lamp driver circuit of the battery powered ballast and actuates a switch circuit of the battery powered ballast. The switch circuit has a first state in which the lamp is operably connected to the battery powered ballast, and a second state in which the lamp is operably connected to the primary ballast. In response to the power restoration event, the switch circuit is actuated to the second state so that the primary ballast, when energized by the power supply, can provide power from the power supply to the lamp. The ballast toggles the switch circuit between the second state and the first state in response to the power restoration event. That is, the ballast places the switch circuit in the first state, and then returns the switch circuit to the second state. In one embodiment, toggling the switch circuit causes a protection circuit (e.g., an end of lamp life circuit) in the primary ballast to detect a lamp replacement which in turn causes the protection circuit to reset so that the primary ballast provides power to the lamp. 
         [0007]    This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. 
         [0008]    Other features will be in part apparent and in part pointed out hereinafter. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a block diagram of a ballast for receiving power from a battery and a power supply and for powering one or more lamps according to one embodiment of the invention. 
           [0010]      FIG. 2  is a timing diagram of voltages in a power supply, a first switch circuit, and a second switch circuit according to one embodiment of the invention. 
           [0011]      FIG. 3  is a schematic diagram of a relamping circuit for use with the ballast of  FIG. 1  according to one embodiment of the invention. 
           [0012]      FIG. 4  is a flow chart of a method for transitioning a lamp from power from a battery to power from a power supply according to one embodiment of the invention. 
       
    
    
       [0013]    Corresponding reference characters indicate corresponding parts throughout the drawings. 
       DETAILED DESCRIPTION 
       [0014]    Referring to  FIG. 1 , a ballast  100  powers a first lamp  102  from a battery  104  or power supply  106  according to one embodiment of the invention. The ballast includes a primary ballast  110  for providing power to the first lamp  102  from the power supply  106 , and a battery powered ballast  112  for providing power to the first lamp  102  from the battery  104 . In operation, when the power supply  106  is supplying power to the ballast  100 , the ballast  100  powers the first lamp  102  and a second lamp  108 . When the power supply  106  is not providing power to the ballast  100 , the ballast  100  powers only the first lamp  102 . In one embodiment, the power supply  106  is utility line power (e.g., 120Vrms AC, 60 Hz). 
         [0015]    When the power supply  106  is supplying power to the ballast  100 , the power supply  106  energizes a first switch circuit  118 , a second switch circuit  114 , and the primary ballast  110 . In one embodiment, the primary ballast  110  is a program start electronic ballast and rapid start electronic ballast. The second switch circuit  114  operably connects the power supply  106  to the primary ballast  110  and the power supply  106  energizes the primary ballast  110 . An inverter  116  of the primary ballast  110  converts power from the power supply  106  into a relatively high voltage signal (e.g., 700-800 volts) having a frequency approximately equal to the resonant frequency of the lamps  102 ,  108 . The first switch circuit  118  is energized via a relamping circuit  122  of the battery powered ballast  112  which places the first switch circuit  118  in a second state wherein the lamps  102 ,  108  are operably connected to the inverter  116  such that the inverter  116  can provide the high voltage signal to the lamps  102 ,  108 . Thus, the ballast  100  is providing power to the lamps  102 ,  108  from the power supply  106 . 
         [0016]    When the power supply  106  ceases to provide power to the ballast  100  (e.g., in the event of a utility power outage), the second switch circuit  114  is de-energized, and defaults to a state wherein the power supply  106  is not operably connected to the primary ballast  110 . The first switch circuit  118  is also de-energized and defaults to a first state wherein the lamp  102  is operably connected to a lamp driver circuit  120  of the battery powered ballast  112  and the lamp  102  is operably disconnected from the inverter  116  of the primary ballast  110 . The lamp driver circuit  120  provides power from the battery  104  to the lamp  102  through the first switch circuit  118  at a voltage and frequency such that the lamp  102  gives off light. Thus, the ballast  100  provides power to the lamp  102  from the battery  104  when the power supply  106  is not providing power to the ballast  100 . 
         [0017]    A power restoration event occurs when the power supply  106  energizes the ballast  100  following a period during which the power supply  106  was not energizing the ballast  100 . One example of a power restoration event is utility line power being restored following a power outage. In response to a power restoration event, the second switch circuit  114  is energized by the power supply  106 , connecting the power supply  106  to the primary ballast  110  such that the power supply  106  also energizes the primary ballast  110 . The first switch circuit  118  is also energized via the relamping circuit  122 , placing the first switch circuit  118  in the second state and operably connecting the lamps  102 ,  108  to the inverter  116  of the primary ballast  110 . The second switch circuit  114  disables the lamp driver circuit  120  of the battery powered ballast  112  in response to the power restoration event so that the lamp driver circuit  120  discontinues generating a high voltage signal from power from the battery  104 . 
         [0018]    Additionally, the relamping circuit  122  of the battery powered ballast  112  toggles the first switch circuit  118  between the second state and the first state of the first switch circuit  118  in response to the power restoration event. Referring to  FIG. 2 , before time t 0  the ballast  100  is powering the lamp  102  with power from the battery  104 , and at time t 0 , the power restoration event occurs. Thus, at time t 0 , the second switch circuit  114  is energized and actuated by the power supply  106  after a nominal delay (due to capacitance in the ballast  100 ) as shown in  FIG. 2 . The first switch circuit  118  is also energized, placing the first switch circuit  118  in the second state after a nominal delay (due to capacitance in the ballast  100 ) as shown in  FIG. 2 . The first switch circuit  118  remains energized for 1 second, and at time t 1 , the relamping circuit  122  toggles the first switch circuit  118 . That is, the relamping circuit  122  de-energizes the first switch circuit  118  for 1 second, placing the first switch circuit in the first state, and then re-energizes the first switch circuit, returning the first switch circuit  118  to the second state. Generally, the effect of toggling the first switch circuit  118  is to electrically disconnect at least one lamp (e.g., lamp  102 ) from the primary ballast  110  to cause the primary ballast  110  to reset any protection circuits (e.g., an end of lamp life circuit) that detected a fault while transitioning the lamp  102  from power from the battery  102  to power from the power supply  106 . It is also contemplated that the relamping circuit  122  may toggle the first switch circuit  118  in response to the initial application of power to the ballast  100  from the power supply  106  (i.e., that the initial application of power to the ballast  100  front the power supply  106  is a power restoration event). 
         [0019]    In one embodiment of the invention, the first switch circuit  118  is toggled exactly once in response to a power restoration event, but in other embodiments of the invention, the relamping circuit  122  toggles the first switch circuit  118  at least twice as shown in  FIG. 2 . That is, at time t 2 , the relamping circuit  122  de-energizes the first switch circuit  118 , placing the first switch circuit  118  in the first state for 1 second, and re-energizes the first switch circuit  118  returning it to the second state thereafter. It is contemplated that in some embodiments of the invention, the relamping circuit  122  may place the first switch circuit  118  in a given state for a time period other than 1 second (e.g., 0.5 seconds or 2 seconds) when toggling the first switch circuit  118 . 
         [0020]    One skilled in the art will recognize that the second switch circuit  114  and the first switch circuit  118  may be configured in a variety of alternative ways. For example, in one embodiment, the first switch circuit  118  connects lamp  102  to the lamp driver circuit  120  when it is energized and connects lamps  102 ,  108  to the inverter  116  of the primary ballast  110  when it is de-energized. Similarly, in one embodiment, the second switch circuit  114  connects the power supply  106  to the primary ballast  110  when it is de-energized, and enables the lamp driver circuit  120  when it is energized. The first and second switch circuits  114 ,  118  may also be energized with any voltage signal. For example, the first and second switch circuits  114 ,  118  may be actuated by 3, 5, or 12 volts DC, or 120Vrms AC, and the two switch circuits may be actuated by different voltage signals. Additionally, the ballast  100  may be configured to only power one lamp  102 , regardless of whether the ballast  100  is providing power from the power supply  106  or the battery  104 . Conversely, the ballast  100  may be configured to power both lamps  102 ,  108  regardless of the source of the power. 
         [0021]    Referring to  FIG. 3 , one embodiment of the relamping circuit  122  is shown. The power supply  106  energizes the relamping circuit  122  with a 120Vrms, 60 Hz power signal. The relamping circuit  122  includes a clock  306  for receiving the power signal and providing a clock signal. The clock  306  includes a half wave rectifier driving a transistor  308  which produces the clock signal. A timer circuit  310  receives the clock signal and provides a two pulse waveform. The timer circuit  310  includes a first timer  302  for receiving the clock signal and driving a second timer  304  for providing the two pulse waveform. In one embodiment, the first timer  302  is a monostable 555 timer, and the second timer  304  is an astable 555 timer. In another embodiment of the invention, the timer circuit  310  comprises a 556 timer dual monostable multivibrator for generating the 2 pulse waveform. The two pulse waveform is provided to a transistor  312  which interrupts power to the first switch circuit  118  in order to toggle it between the second state and the first state. 
         [0022]    Referring to  FIG. 4 , a method of transitioning a lamp from power from a battery to power from a power supply is shown according to one embodiment of the invention. The method begins at  402  in response to a power restoration event, and at  404 , a lamp driver circuit of an battery powered ballast is disabled and a primary ballast is energized. At  406 , a switch circuit (e.g., first switch circuit  118 ) is actuated, and the switch circuit is toggled at  408 . At  410 , the switch circuit is toggled a second time and the method ends at  412  with the lamp being powered with power from the power supply. 
         [0023]    The order of execution or performance of the operations in embodiments of the invention illustrated and described herein is not essential, unless otherwise specified. That is, the operations may be performed in any order, unless otherwise specified, and embodiments of the invention may include additional or fewer operations than those disclosed herein. For example, it is contemplated that executing or performing a particular operation before, contemporaneously with, or after another operation is within the scope of aspects of the invention. 
         [0024]    Embodiments of the invention may be implemented with computer-executable instructions. The computer-executable instructions may be organized into one or more computer-executable components or modules. Aspects of the invention may be implemented with any number and organization of such components or modules. For example, aspects of the invention are not limited to the specific computer-executable instructions or the specific components or modules illustrated in the figures and described herein. Other embodiments of the invention may include different computer-executable instructions or components having more or less functionality than illustrated and described herein. 
         [0025]    When introducing elements of aspects of the invention or the embodiments thereof, the articles “a,” “an,” “the,” and “said” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. 
         [0026]    Having described aspects of the invention in detail, it will be apparent that modifications and variations are possible without departing from the scope of aspects of the invention as defined in the appended claims. As various changes could be made in the above constructions, products, and methods without departing from the scope of aspects of the invention, it is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.