Abstract:
A plurality of lamps are connected in series. A plurality of burnout detector mechanisms are provided where one of the burnout detector mechanisms from the plurality is connected across a corresponding lamp of the plurality of serially connected lamps. When a lamp in the series enters a failure state, the burnout detector mechanism is activated providing an indication as to the burned out lamp. Depending upon the values provided in the burnout detector mechanism and the type of lamps, the remaining lamps will either enter an OFF state, or a low-light glow state.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to lamp lighting circuits, and more particularly to a circuit which indicates a failure of a lamp within a lighting system where the lamps are connected in series. 
     Environments exist where it is desirable to implement lamps wired in series. Such situations may include having a low voltage lamp which provides better performance than a higher voltage equivalent lamp, or when a higher voltage lamp is not practical or feasible due to wire size limitations or for other parameter requirements. For example, in the United States the standardized input power line is 120-volt a.c. However, a high-efficiency quartz halogen lamp has not be designed for efficient operation at the 120-volt a.c. input line. Rather, quartz halogen lamps operate most efficiently with a low-voltage coil or filament, in order to obtain a high lumen-per-watt efficiency output. Therefore, to operate a low-voltage lamp (e.g. a 40-watt quartz halogen lamp) it is necessary to provide a ballast for each lamp to limit the 120-volt a.c. input to an appropriate lamp operating voltage. However, ballasts are at times bulky and add economic cost to lamp lighting systems. 
     A manner in which low-voltage lamps may be operated without the implementation of a ballast is by placing the lamps in series. For example, if 120-volt a.c. input line is considered as being standard, placing three 40-volt lamps in series allows each lamp to operate at its normal rated voltage. 
     A significant obstacle to wiring lamps in series however, is that when a lamp in the series fails, the entire circuit is broken and all lamps in the series are deactivated. In this situation, replacing the failed lamp requires a pick-and-choose solution, where lamps are randomly replaced to determine whether a selected lamp has failed. This requires the lamp system to be deactivated. Next, a lamp is randomly selected and removed from the system, a new lamp is inserted to replace the removed lamp, and the lighting system is supplied with power. If the replaced lamp is not the failed lamp, the process is repeated until the failed lamp is found. 
     This process is tedious and inefficient and discourages the practice of placing lamps in a series arrangement, even when such a configuration would be otherwise beneficial. 
     Therefore, it has been considered desirable by the inventors to develop a mechanism which provides a clear indication of which lamp in a series of lamps has failed, in order to provide an efficient manner of replacing the failed lamp. 
     SUMMARY OF THE INVENTION 
     A plurality of lamps are connected in series. A plurality of burnout detector mechanisms are provided where one of the burnout protection mechanisms from the plurality is connected across a corresponding lamp of the plurality of serially connected lamps. When a lamp in the series enters a failure state, the burnout detector mechanism is activated providing an indication as to the burned out lamp. Dependant upon the values provided in the burnout detector mechanism and the type of lamps, the non-failed lamps will either enter an OFF state, or a low-light glow state when a burnout detection mechanism is active. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic diagram of a plurality of lamps configured in a series with each other, and including a burnout detector mechanism associated with each of the lamps; 
     FIG. 2 shows the burnout detector mechanisms located within a socket or connector designed to hold a lamp; 
     FIG. 3 illustrates the burnout detector mechanism located within the lamp in an integrated fashion; and 
     FIG. 4 is a block diagram of a detector mechanism using an audible indicator. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 is a schematic diagram of a lighting system  10  according to the teachings of the present invention. Lighting system  10  includes a first input line  12 , and a second input line  14 , supplied by a a.c. source  16 . The a.c. source  16  may be any value appropriate for the powering of lighting system  10 . In the United States, the standard lighting supply is a 120-volt a.c. source and in Europe it is a 220-volt a.c. source. 
     System  10  illustrates a lamp lighting system having three lamps  18 - 22  connected to each other in a series configuration. It is to be appreciated however, that the present invention may be used in connection with other numbers of lamps such as two, or more than three, as long as there is a sufficient voltage supply to operate the lamps of the system. 
     The present invention will function with lamps of many varieties, including quartz-halogen high-efficiency lamps, neon lamps, xenon lamps, krypton lamps, incandescent lamps, or other low-voltage lamps known in the industry. For example, if operating in North America, the 120-volt a.c. input lamp fixtures could include five 24 low-voltage a.c. lamps in the series. In Europe where the input standardized voltage is 220-volts a.c., it would be possible to operate the two 120-volt a.c. voltage lamps in series, or nine 24-volt a.c. lamps, or eighteen 12-volt a.c. lamps. 
     As noted, lamps  18 ,  20  and  22  are wired in a series arrangement with each other. More particularly, lamp  18  has a first end  24  connected to first input  12 . A second end  26  of lamp  18  is connected to a first end  28  of lamp  20 . A second end  30  of lamp  20 , is connected to a first end  32  of lamp  22 , and the second end  34  of lamp  22  is connected to the second input line  14 . 
     Burnout detector mechanism  36 ,  38  and  40  are connected across respective lamps  18 ,  20  and  22 . Burnout detector  36  is connected across lamp  18  by connection at a first end to node  42 , which connects to input line  12 , and at a second end at node  44  which in turn connects between second end  26  of lamp  18  and first end  28  of lamp  20 . Node  44  also connects burnout detector  36  to a first end of burnout detector  38 . A second end of burnout detector  38  is connected to burnout detector  40  at node  46 , which also connects between second end  30  of lamp  20  and first end  32  of lamp  22 . A second end of burnout detector  40  is connected at node  48  to the input line  14 , and also the second end  34  of lamp  22 . 
     In this embodiment each burnout detector  36 ,  38  and  40  is configured by a resistor  50  and light-emitting diode (LED)  52 . In this embodiment the resistors and LEDs for each burnout detector will be of substantially equal value. It is to be understood that burnout detector mechanisms  36 ,  38  and  40  may be configured other than with resistor  50  and LED  52 . For example, LED  52  may be replaced with a neon lamp or other low wattage light source. Further components other than a resistor may be used to drop the voltage for the detector mechanism. 
     During normal operation, when all lamps  18 ,  20  and  22  are functional and power has been applied to the system, the lamps are in an operational state. At this time sufficient current is flowing through filaments of coils  54 ,  56  and  58  of respective lamps  18 ,  20  and  22 . During this period, burnout detector mechanisms,  36 ,  38  and  40  are non-functional. When one of the lamps, such as lamp  20 , enters a failed state (i.e. filament  56  fails to a burn out condition), a high, substantially infinite impedance exists in lamp  20 . This causes current flow to be diverted through burnout detection mechanism  38 , wherein resistor  50  of burnout mechanism  38  generates a sufficient voltage to cause LED  52  of mechanism  38  to light. At the same time, there will be insufficient current flow through lamp  18  and lamp  22  such that these lamps have a cold filament whereby minimal resistance exists within the lamps and the filament acts as a short. 
     Due to the insufficient voltage and current flow through lamps  18  and  22 , they are in a non-active state. Therefore no lamps within lighting system  10  are operational except for LED  52 . This allows a user to identify which one of lamps  18 ,  20 ,  22  is in a failure mode. A user may then remove the power source  16  deactivating the circuit. Lamp  20  can then be removed and replaced with a new lamp. Once the new lamp has been inserted into lamp system  10 , and power has been restored, lamp  18 , new lamp  20  and lamp  22  will again be activated and the LED indicating lamp  52  of burnout mechanism  38  will be deactivated. 
     Thus, burnout detector mechanisms  36 ,  38 ,  40  will immediately indicate when a lamp with which it is associated becomes non-functional. This configuration eliminates the inconvenience of all lights of a system deactivating, without an indication as to which lamp in the series has failed. The present invention provides immediate and continuous identification of the failed lamp. 
     When burnout detector mechanism  38  is operational, lamps  18  and  22  have cold filaments. These are described as cold filaments when there is insufficient current through the filaments to light the lamp. In this manner, the corresponding burnout detector mechanisms  36  and  40  will not light. 
     In a situation where two or more of the lamps in a system are in a failure mode (burned out), each of the associated burnout detection mechanisms will be active. 
     Resistance  50  in burnout detector mechanisms  36 ,  38 ,  40  are selected such that they will drop the system voltage to a level that non-failed lamps are no longer able to stay active. In the embodiment where lamp  20  has failed, the path of the current is through lamp  18  which acts substantially as a short, and therefore minimal resistance, the current then flows through resistor  50  of mechanism  38  which is the current limiting resistor for LED  50 . Resistor  50  in this embodiment will limit the current down to a few milli-amps thereby lighting LED  52 . The current then passes through the cold filament of lamp  22  which again has very low resistance. 
     In an embodiment using a 120v a.c. input to light LED  52 , it is desirable to draw approximately 10 milli-amps. To draw 10 milli-amps, resistor  50  will be approximately 120K ohms (ohms law −120 volts a.c. ÷10 milli-amps). The indicator, LED  52 , needs to be sized with an appropriate peak inverse voltage (PIV) protection to ensure against breakdown of the diode. In this example, an acceptable peak inverse voltage rating would be 40 volts (where peak inverse voltage is determined by 120-volt input for three 40volt lamps). 
     In an another embodiment, burnout detection mechanisms  36 ,  38  and  40  may be configured with a resistance  50  of a value smaller than in the foregoing embodiment. This resistance may be selected such that the current drawn down to the selected burnout detection mechanism does not cause the filaments of the remaining lamps to turn entirely cold. Thus there will be, in this embodiment, sufficient current within the remaining good lamps to provide at least a low-level glow light output from these non-failed lamps. 
     Turning to FIG. 2, illustrated is an embodiment where lamps  18 ,  20  and  22  are inserted within corresponding sockets  60 ,  62  and  64 . Each socket has an internally connected burnout detector mechanism  36 ,  38  and  40 . The wiring of these burnout detectors within the sockets correspond to the wiring diagram of FIG.  1 . Thus in this embodiment, upon insertion of the lamps  18 ,  20  and  22  into the corresponding sockets  60 ,  62  and  64 , burnout detectors  36 ,  38  and  40  are placed across a corresponding lamp of the plurality of lamps connected in series. More particularly, when considering lamp  18 , upon insertion into socket  60 , ends of lamp  18  connect with electrical connectors  66  and  68 . A burnout detector mechanism  36  is connected to the electrical connectors  66  and  68  in a configuration such that the mechanism  36  is placed in parallel across lamp  18  in a manner similar to that discussed in connection with FIG.  1 . 
     Sockets  60 ,  62 ,  64  are designed such that an aperture  70  exists, wherein the indicator (e.g. LED  52 ) of detectors  36 ,  38 ,  40  is able to transmit light  72  through these openings when detectors  36 ,  38 ,  40  are activated. 
     In a further embodiment, as illustrated in FIG. 3, each burnout detector  36 ,  38  and  40  may be configured within base  80  of lamps  18 ,  20  and  22 . In this embodiment, burnout detector mechanisms  36 ,  38  and  40  are inserted within base  80  and connected at a first end  82  to a first lead  84  and at a second end  86  to a second lead  88  of lamps  18 ,  20  and  22 . Base  80  also includes an aperture or window portion  90  to allow the passage of light from burnout detector mechanisms  36 ,  38  and  40  upon activation. 
     While the present invention has been disclosed where the indication mechanism is a light-emitting mechanism, such as an LED, neon lamp, or other low-wattage light source, it is to be appreciated that other indicators may be used. For example, as shown in FIG. 4, the indicator may be a sound indicator  92  such as a small amplifier circuit emitting a predetermined tone. 
     While the invention has been described with respect to specific embodiments by way of illustration, modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as which fall within the true scope and spirit of the invention.