Abstract:
A method and system for standby lighting uses a power supply module and a standby lamp in conjunction with an HID lamp. The power supply module has a processor with smart trigger circuitry, soft start capability, overlap timer, and an advanced current sense algorithm. The power supply module continuously monitors the electronic ballast current to the HID lamp. If the current drops for a period of time, the power supply module supplies DC current to turn on the standby lamp gradually over a couple of seconds. The standby lamp is kept on while the processor checks for a rise in the electronic ballast current to a threshold current level for more than two seconds. Then, an overlap timer starts to count down for the time it takes for HID lamp to reach full intensity, approximately fifteen minutes. The standby lamp is turned off at the end of the count down.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates to high intensity discharge (“HID”) lamps, and more particularly, to standby lamps used in conjunction with HID lamps in the event of momentary power loss, and even more particularly, to a power supply module for supplying power to the standby lamps when a momentary power loss occurs to provide standby lighting.  
       BACKGROUND OF THE INVENTION  
       [0002]     High intensity discharge lamps are typically used when high levels of light are required over large areas and when energy efficiency and/or long life are desired. These areas include gymnasiums, large public areas, warehouses, manufacturing facilities, outdoor activity areas, roadways, parking lots, and pathways. Like fluorescent lamps, HID lamps require a ballast which provides the necessary circuit conditions for starting and maintaining their operation. When HID lamps are initially turned on, it takes anywhere from five to fifteen minutes, depending upon the particular HID lamp, for the normal light intensity level to be reached. When a momentary interruption of the line voltage occurs, the same time period is required to restore the HID lamp to its normal intensity level. For situations where the lack of light for this time period is unacceptable, standby lamps (also referred to as auxiliary lamps) are typically incorporated into the lighting system. Usually, the conventional ballasts for the HID lamps have provided a voltage supply and trigger circuitry to turn on the auxiliary lamps until the HID lamps reach their normal intensity level. Then, the auxiliary lamps are turned off by the circuitry.  
         [0003]     Conventional ballasts can operate over wide standard input voltages, typically 208-277 volts AC, which can normally be preset by the end user. The auxiliary lamps used in conjunction with HID lamps typically only operate at 120 volts AC. Conventional ballasts typically provide a transformer for the auxiliary lamp. Trigger circuitry for the auxiliary lamp is actuated by an electromechanical relay where the coil is connected in series to the HID lamp and the relay contacts are connected in series to the auxiliary lamp. When the HID lamp breaks down, such as occurs with a temporary loss of line voltage, the full voltage is presented on the coil, the relay contacts close, and the auxiliary lamp turns on.  
         [0004]     Conventional ballasts are being rapidly being replaced with electronic ballasts which do not provide a voltage supply and trigger circuitry for systems that require auxiliary lamps. There is thus a need in the art to supply such a system. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]      FIG. 1  shows a wiring diagram for a typical application of an embodiment of the power supply module for a standby lamp, used in conjunction with an HID lamp, of the present invention.  
         [0006]      FIG. 2  shows an electronic schematic diagram of an embodiment of the power supply module for a standby lamp, used in conjunction with an HID lamp, of the present invention.  
         [0007]      FIG. 3  shows a block flow diagram of the method of utilizing a power supply module with a standby lamp, used in conjunction with an HID lamp, of the present invention.  
         [0008]      FIG. 4  shows oscilloscope traces of the feedback signal from the voltage sensor module which is proportional to the line voltage in the apparatus and method for standby lighting of the present invention.  
         [0009]      FIG. 5  shows oscilloscope traces of the output waveform from the processor module to the power switching module in the apparatus and method for standby lighting of the present invention.  
         [0010]      FIG. 6  shows oscilloscope traces of the chopped rectified voltage output waveform of the bipolar signal transistor within the power switching module in the apparatus and method for standby lighting of the present invention.  
         [0011]      FIG. 7  shows oscilloscope traces of the voltage between the output terminals for the auxiliary lamp in the apparatus and method for standby lighting of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0012]     Referring now to the Figures, in which like reference numerals and names refer to structurally and/or functionally similar elements thereof,  FIG. 1  shows a wiring diagram for a typical application of an embodiment of the power supply module for a standby lamp, used in conjunction with an HID lamp, of the present invention. Referring now to  FIG. 1 , Standby Lamp Module  100  has a three wire input: Neutral Terminal  102 , Ground  104 , and Phase which is made up of Phase In Terminal  106  and Phase Out Terminal  108 . Two Output Terminals  110 ,  112  supply  120  volts DC to Auxiliary Lamp  114 . Phase Out Terminal  108  is connected to Phase Input Terminal  116  of Electronic Ballast  118 , and Neutral Terminal  102  is connected to Neutral Input Terminal  128  of Electronic Ballast  118 . Line Voltage Supply  120  supplies between 200 to 300 volts AC to Standby Lamp Module  100  and Electronic Ballast  118 . Electronic Ballast  118  has two Output Terminals  122 ,  124  which supply HID Lamp  126  with the 200 to 300 volts AC. Electronic Ballast  118  also has Neutral Input  128  and Ground  130 .  
         [0013]      FIG. 2  shows an electronic schematic diagram of an embodiment of the power supply module for a standby lamp, used in conjunction with an HID lamp, of the present invention. Referring now to  FIG. 2 , Standby Lamp Module  100  provides a regulated power supply and trigger circuitry in a single module. In a phase control mode technique, two silicon controlled rectifiers (“SCR&#39;s”) connected back to back could be used to reduce the voltage supplied to Auxiliary Lamp  114 . Even though the resulting voltage is 120 volts true root mean square (“trms”), the voltage peaks are very high for typical incandescent auxiliary lamps and is not recommended.  
         [0014]     One embodiment of the invention reduces these high voltage peaks by employing a switching mode technique instead of a phase control mode technique. A twenty-five KHz carrier frequency is used along with a metal oxide semiconductor field effect transistor (“MOSFET”), or an insulated gate bipolar transistor (“IGBT”), as a power switching device and power inductor in series with Auxiliary Lamp  114 . The MOSFET embodiment is shown in  FIG. 2 . Consequently, a rectified sine waveform is supplied to Auxiliary Lamp  114 .  
         [0015]     One skilled in the art will recognize that one of the relevant changes to prior art practice provided by Standby Lamp Module  100  is that 120 volts DC, instead of 120 volts AC, is supplied to Auxiliary Lamp  114 . Because Auxiliary Lamp  114  is typically a quartz incandescent type lamp, it can operate with either AC or DC voltage. Some incandescent lamps however are very sensitive to pulsed current. This is due to the vibration caused to the filament, which can greatly reduce the life of the filament. Such lamps often have constraints regarding the ratio of root mean square current to average current that precludes the use of a phase controlled 60 Hz approach. The twenty-five KHz chopping frequency utilizing in the present invention eliminates audible noise and reduces the filter component sizes. Thus, Standby Lamp Module  100  can operate with a wide input voltage ranging between 200 to 300 volts AC, and provide a constant voltage of 120 volts DC to Auxiliary Lamp  114  of the incandescent variety that is sensitive to pulsed current.  
         [0016]     Standby Lamp Module  100  has several circuit modules that provide the overall functionality as described above and herein below. Overvoltage Protection Module  202  has a varistor to protect Standby Lamp Module  100  against surge peaks and overvoltage. Individual components of Overvoltage Protection Module  202  include: polarized capacitors C 1  and C 21 , metal oxide varistor MOV 1 , and a Fuse. In one embodiment of the invention, the components of Overvoltage Protection Module  202  have the following values: C 1  and C 21  are 0.33 μF; MOV 1  is a ZNR P7210-ND varistor available from Panasonic; and the Fuse is a 4 ampere 250V AC.  
         [0017]     EMI Filter Module  204  reduces the Electro Magnetic Interference (“EMI”) conducted emissions to the AC line generated by Standby Lamp Module  100 . Individual components of EMI Filter Module  202  include: polarized capacitors C 2 , C 3 , C 4 , C 5 , C 6 , and C 7  and inductors L 1  and L 2 . In one embodiment of the invention, the components of EMI Filter Module  204  have the following values: C 2 , C 3 , C 5 , and C 6  are 4.7 nF, C 4  is 1.0 μF, C 7  is 0.33 μF, L 1  is 2.0 mH, and L 2  is 148.0 μH.  
         [0018]     Rectification Module  206  provides a suitable DC voltage for Power Switching Module  210  using a diode bridge. Individual components of Rectification Module  206  include: full wave bridge rectifier BR 1  and polarized capacitors C 10  and C 11 . In one embodiment of the invention, the components of Rectification Module  206  have the following values: C 10  is 100.0 nF and C 11  is 2700.0 pF. Polarized capacitors C 10  and C 11  serve to reduce high frequency.  
         [0019]     Logic Power Supply Module  208  regulates the voltage for the MOSFET driver circuitry. In one embodiment of the invention, the regulated voltage is  12  volts DC. Individual components of Logic Power Supply Module  208  include: resistors R 20 , R 21 , and R 22 ; polarized capacitors C 12  and C 13 ; and zener diode DZ 2 . In one embodiment of the invention, the components of Logic Power Supply Module  208  have the following values: R 20  and R 21  are 39.0 k Ohms, R 22  is 100.0 k Ohms, C 12  is 100.0 μF  16 V, C 13  is 0.1 μF, and DZ 2  is a MMSZ4699T1 12 V SOD-123 available from ON Semiconductor®.  
         [0020]     Power Switching Module  210  has an inductor placed in series to the load and MOSFET switching at high frequency to reduce the output voltage. Individual components of Power Switching Module  210  include: low side MOSFET driver MC 3 ; polarized capacitors C 14  and C 15 ; resistors R 23 , R 24 , and R 25 ; inductor L 3 ; bipolar signal transistor Q 1 ; and diode D 3 . In one embodiment of the invention, the components of Power Switching Module  210  have the following values: low side MOSFET driver MC 3  is an MIC4416BM4 available from Micrel Inc., C 14  is 2700.0 pF, C 15  is 1.8 μF 250 V, R 23  is 10.0 k Ohms, R 24  is 62.0 Ohms, R 25  is 10.0 Ohms, L 3  is 820.0 mH, bipolar signal transistor Q 1  is an IRFB16N60L 600 V Single N-Channel HEXFET Power MOSFET available from International Rectifier, and D 3  is an 8ETH06 600 V 8 A HyperFast Discrete Diode also available from International Rectifier.  
         [0021]     Inductor L 3  is placed in series in order to get the effect of dynamic impedance (high frequency=high impedance, low frequency=short circuit). Polarized capacitor C 14  and resistor R 25  act as a snubber to reduce noise.  FIG. 6  shows oscilloscope traces of the Chopped Rectified Voltage Output  602  of bipolar signal transistor Q 1 . After being smoothed by polarized capacitor C 15 ,  FIG. 7  shows oscilloscope traces of the Constant Voltage Output  702  between Output Terminals  110  and  112  for Auxiliary Lamp  114 .  
         [0022]     Logic Power Supply Module  212  regulates the voltage for the microcontroller and its peripherals. In one embodiment of the invention, the regulated voltage is 3.3 volts DC. Individual components of Logic Power Supply Module  212  include: resistors R 1  and R 2 ; zener diode DZ 1 ; polarized capacitors C 8  and C 9 ; microcontroller MC 2 ; and control circuit DC bus VCC for sensing and regulating circuits. In one embodiment of the invention, the components of Logic Power Supply Module  212  have the following values: R 1  and R 2  are 24.0 k Ohms, DZ 1  is an MMSZ4689T1 5.1 V SOD-123 available from ON Semiconductor®, C 8  is 100.0 μF 14 V, C 9  is 0.1 μF, and MC 2  is a TPS79733 10 mA 3.3 V Micro-Power Low-Dropout (“LDO”) Voltage Regulator in SOD-123 available from Texas Instruments.  
         [0023]     Voltage Sensor Module  214  senses the input signal, which is proportional to the line voltage that is used to maintain constant output voltage, which is accomplished by adjusting the switching frequency. Individual components of Voltage Sensor Module  214  include: resistors R 8 , R 9 , R 10 , and R 11  and polarized capacitors C 16  and C 17 . In one embodiment of the invention, the components of Voltage Sensor Module  214  have the following values: C 16  is 0.01 μF, C 17  is 3.3 pF, R 8  and R 9  are 1.0 M, R 10  is 21.0 k Ohms, and R 11  is 100.0 k Ohms.  FIG. 4  shows oscilloscope traces of the Feedback Signal  402  from Voltage Sensor Module  214  which is proportional to the line voltage.  
         [0024]     Processor Module  216  has the central processing unit, which generates the appropriate switching duty cycle and frequency to maintain constant output voltage based upon the input signals it receives. Individual components of Processor Module  216  include: polarized capacitor C 18 ; resistor R 12 ; VCC; and Microcontroller MC 1  which may be one of many types of suitable microcontrollers. In one embodiment of the invention, the components of Processor Module  216  have the following values: C 18  is 3.3 μF, R 12  is 5.1 k Ohms, and microcontroller MC 1  is an ATtiny15L 8-bit Microcontroller with 1K Byte Flash available from Atmel Corporation.  FIG. 5  shows oscilloscope traces of the Switching Frequency Output  502  from Processor Module  216  to Power Switching Module  210  which is a twenty-five KHz switching frequency.  
         [0025]     Auxiliary Lamp  114  is in series with inductor L 3 , which acts like a voltage divider. Therefore, in order to maintain a constant voltage output for Auxiliary Lamp  114  the characteristics of inductor L 3  are adjusted. If the input voltage increases, the voltage in both inductor L 3  and Auxiliary Lamp  114  will increase. A constant switching frequency of twenty-five KHz is maintained, and to compensate for the change in line voltage Processor Module  216  modifies the duty cycle according to the line voltage, which may range between 200-300 volts AC. For example, if the input line voltage is 200 volts AC, then the duty cycle will be 60% on and 40% off. If the input line voltage is 300 volts AC, the duty cycle will be adjusted to 30% on and 70% off. Processor Module  216  monitors the voltage level from Voltage Sensor Module  214 . The signal received from Voltage Sensor Module  214  has been smoothed by resistor R 11  and polarized capacitor C 17 . Microcontroller MC 1  within Processor Module  216  has a lookup table to compare the input line voltage, and find a reload value for updating the duty cycle of the switching output to obtain a constant output voltage.  
         [0026]     Current Sensor Module  218  senses the current from Electronic Ballast  118  and amplifies it. Individual components of Current Sensor Module  218  include: transformer T 1 ; resistors R 13 , R 14 , R 15 , R 16 , R 17 , R 18 , and R 19 ; polarized capacitors C 19  and C 20 ; amplifiers MC 4  and MC 5 ; and switching diodes D 1  and D 2 . In one embodiment of the invention, the components of Current Sensor Module  218  have the following values: transformer T 1  is a CSE187-L low frequency current sense transformer available from Gopher Electronics, R 13  is 100.0 k Ohms, R 14  and R 15  are 1.0 k Ohms, R 16  is 39.0 k Ohms, R 17  and R 18  are 100.0 k Ohms, R 19  is 10.0 k Ohms, C 19  and C 20  are 3.3 μF, amplifiers MC 4  and MC 5  are LM2904D single supply dual operational amplifiers available from ON Semiconductor®, and switching diodes D 1  and D 2  are CMOD6001 surface mount ULTRAmini™ low leakage silicon switching diodes available from Central™ Semiconductor Corp.  
         [0027]     Processor Module  216  of Standby Lamp Module  100  has smart trigger circuitry that includes a soft start feature, overlap timer, and an advanced current sense algorithm. Processor Module  216  continuously monitors the electronic ballast current for HID Lamp  126 . If the current drops below one ampere for a period of time, typically about one to two seconds, then Standby Lamp Module  100  supplies direct current to turn on Auxiliary Lamp  114  in a gradual fashion, typically from off, or no current, to on, or total current, in about one to two seconds. This soft start feature reduces the inrush of current to Auxiliary Lamp  114  and helps prolong the bulb life of Auxiliary Lamp  114  as well as Standby Lamp Module  100  itself.  
         [0028]     Auxiliary Lamp  114  is kept on until the electronic ballast current rises to a threshold current level, typically about one ampere, for more than two seconds, then an overlap timer starts to count down for a predetermined period of time, about fifteen minutes. This time may vary depending upon the individual characteristics of the HID lamp used. This count down time will vary, more or less, depending upon the characteristics of HID Lamp  126 . At the point where the electronic ballast current rises to the threshold current level and stabilizes, HID Lamp  126  starts to work properly, but the brightness is only about  20 % of normal. The brightness level will increase slowly during the next fifteen minutes until 100% brightness is reached. Auxiliary Lamp  114  will be turned off when the overlap timer has count down fifteen minutes, and HID Lamp  126  has reached 100% brightness. Should the electronic ballast current drop again prior to reaching the fifteen minute count down, Processor Module  216  resets the overlap timer, and the fifteen minute count down begins again.  
         [0029]      FIG. 3  shows a block flow diagram of the method of utilizing a power supply module with a standby lamp, used in conjunction with an HID lamp, of the present invention. Referring now to  FIG. 3 , the method begins in step  302  when power is initially supplied to Standby Lamp Module  100 . The programs stored in the various microcontrollers initialize themselves in preparation for operation, setting ports, clocks, timers, and certain program variables.  
         [0030]     In step  304 , Processor Module  216  begins monitoring the current being supplied to Electronic Ballast  118  by Line Voltage Supply  120 . Processor Module  216  continually checks in Step  306  for a drop in current below one ampere. When a drop in current is detected, then step  308  determines if the drop in current is sustained for a predetermined period of time, typically about one to two seconds. If the drop in current is less than the predetermined time, control returns to Step  304  where Processor Module  216  resumes checking for a drop in current. If step  308  determines that the drop in current exceeds the predetermined time, then in step  310  Standby Lamp Module  100  supplies current to soft start Auxiliary Lamp  114  in a gradual fashion over a predetermined period of time, typically in about one to two seconds.  
         [0031]     In step  312 , Processor Module  216  resumes monitoring the current being supplied to Electronic Ballast  118  by Line Voltage Supply  120 . In step  314  Processor Module checks for a rise in current to a threshold current level, typically about one ampere. When the threshold current level is detected, then step  316  determines if the threshold current level is sustained for a predetermined period of time, typically for more than two seconds. If the threshold current level is held less than the predetermined time, control returns to Step  312  where Processor Module  216  resumes continually checking for a rise in current to a threshold current level. If step  316  determines that the threshold current level is sustained for the predetermined period of time, then in step  318  Processor Module  216  starts an overlap timer count down for an approximate fifteen minute period of time.  
         [0032]     In step  320 , Processor Module  216  resumes monitoring the current being supplied to Electronic Ballast  118  by Line Voltage Supply  120 . Processor Module  216  checks in step  322  for a drop in current, typically below one ampere. If no drop in current of the predetermined amount is detected, then control flows to step  326 . When a drop in current is detected, then step  324  determines if the drop in current is sustained for a predetermined period of time, typically about one to two seconds. If the drop in current is less than the predetermined time, then control flows to step  326 . If step  324  determines that the drop in current exceeds the predetermined time, then control returns to step  318  where Processor Module  216  resets the overlap timer to begin again the approximate fifteen minute count down.  
         [0033]     Step  326  determines if the count down has been completed. If not, then control returns to step  320  where Processor Module  216  continues to check for a drop in current until the count down is completed.  
         [0034]     When step  326  determines that the count down has been completed, then in step  328  Processor Module  216  turns off the current that has been supplying Auxiliary Lamp  114 , and in step  330  resets the overlap timer. In step  332 , if Standby Lamp Module  100  is still in service, control returns to step  304  for continuation of the method, and if not, the method of the present invention ends.  
         [0035]     Having described the present invention, it will be understood by those skilled in the art that many changes in construction and circuitry and widely differing embodiments and applications of the invention will suggest themselves without departing from the scope of the present invention.