Abstract:
An electronic circuit is shown to initiate and sustain conduction in a gaseous discharge light. A breakover device and snubber network, isolation network, and self-adjusting symmetrical high voltage pulse generator are incorporated into a standard gaseous discharge light assembly typically composed of a power source, gaseous discharge lamp ballast apparatus, and gaseous discharge lamp. The electronic circuit is used (1) for initiating and sustaining conduction of electrical current through gaseous discharge lamps, (2) to provide active suppression of transient voltages both within and external to the gaseous discharge lighting apparatus, and (3) to provide significant attenuation of the propagation of undesirable conducted and radiated radio frequency interference from the gaseous discharge lamp and the overall associated ballast apparatus.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Applicant&#39;s invention relates to an electrical apparatus and more particularly to devices normally employed as part of a gaseous discharge lighting system. The invention provides an electronic circuitry for initiating of electrical current through gaseous discharge lamps, sustaining conduction of electrical current through gaseous discharge lamps when such conduction of electrical current would otherwise cease, providing active suppression of electrical transient voltages within the apparatus normally employed with gaseous discharge lamps for their operation, providing active suppression of electrical transient voltages from sources internal and external to the gaseous discharge lighting apparatus, providing significant attenuation to the propagation of undesirable conducted radio frequency interference emissions back into the power line mains supplying power for the operation of gaseous discharge lighting equipment, and providing significant attenuation to radiated radio frequency interference emissions from the gaseous discharge lighting equipment. 
     2. Background Information 
     The typical gaseous discharge lamp can experience startup delays due to various problems. It is known that gaseous discharge lamps themselves present particular problems with regard to 1) starting at low ambient temperatures, 2) peculiarities intrinsic to the various types and sizes or power ratings of gaseous discharge lamp construction, 3) extended hot re-strike times if extinguished even very briefly due to external causes, such as loss of supplying power, and internal causes, such as age, during normal operation, and 4) changing their characteristics to beyond that which the associated ballasting apparatus can sustain conduction of electrical current through the particular gaseous discharge lamp. For example, if low pressure sodium lamps go out, the lamp will typically not relight for 20 minutes. This can cause safety and/or security problems depending on the location of the lamp. 
     Another significant disadvantage to present gaseous discharge lighting systems is high EMI/RFI interference from the lamp itself. It is known that during the operation of gaseous discharge lamps, various nonlinear effects intrinsic to the operation of gaseous discharge lamps commonly and inadvertently couple significant and undesirable radio frequency interference back into the power line mains supplying the power necessary for the operation of the overall gaseous discharge lighting apparatus and equipment as well as radiate significant and undesirable radio frequency interference energy into the environment from the lamps themselves. The standard gaseous discharge lighting system cannot be used in many countries due to strict regulations on electromagnetic noise pollution. A third problem with the existing gaseous discharge lighting systems is that there is no means by which to accurately set the breakover voltage of overvoltage protection devices into the system. 
     The present invention alleviates the problem of delayed starts by incorporating a self adjusting symmetrical high voltage pulse generator. The self-adjusting symmetrical high voltage pulse generator generates a series of pulses to restart the lamp whenever the lamp goes out or low temperature conditions prevent starting. Presently, it is well-known that a significantly higher than normal operating voltage must be applied to the lamps in order to initiate conduction of an electrical current through the active volume of the lamps. However it is not known in the prior art to apply such high voltage in a series of pulses from a self-adjusting symmetrical high voltage pulse generator. 
     The symmetry of the generator is also important in the reduction of EMI/RFI interference. The present invention allows the modification of existing gaseous discharge lighting systems for use in other countries that regulate electromagnetic noise pollution. The third benefit of the present invention is the incorporation of a precision electronic crowbar to provide a momentary short to protect the high voltage circuits from transient overvoltages. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a novel electrical device and method that initiates conduction of electric current through gaseous discharge lamps. 
     Another object of the present invention is to provide a novel electrical device and method that sustains conduction of electric current through gaseous discharge lamps. 
     Still another object of the present invention is to provide a novel electrical device and method that sustains conduction of electric current through gaseous discharge lamps when such conduction would otherwise cease. 
     It is yet an object of the present invention to provide a novel electrical device and method that actively suppresses electrical transient voltages within apparatus normally employed in the operation of gaseous discharge lamps. 
     It is still an object of the present invention to provide a novel electrical device and method that actively suppresses electrical transient voltages from sources external to the gaseous discharge lighting apparatus. 
     Another object of the present invention is to provide novel electrical device and method that provides significant attenuation to the propagation of undesirable conducted radio frequency interference emissions back into the power line mains supplying power for the operation of gaseous discharge lighting equipment. 
     Still another object of the present invention is to provide a novel electrical device and method that provides significant attenuation to radiated radio frequency interference emissions from the gaseous discharge lighting equipment. 
     In satisfaction of these and related objectives, Applicant&#39;s present invention provides for a gaseous discharge lighting system and method that incorporates a breakover device and snubber network, isolation networks, and self-adjusting symmetrical high voltage pulse generator to a system composed of a gaseous discharge lamp ballast apparatus and gaseous discharge lamp. The incorporation of these various components into a known gaseous discharge lighting assembly allows for the instant restart of the gaseous discharge lamp if the lamp goes out. In addition, the present invention allows for the reduction of the EMI/RFI noise pollution from the lamp. And last, the embodiment of the present invention allows for transient voltage suppression through the system by the use of a precision crowbar. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram of an electrical schematic for the present invention. 
     FIG. 2 is a detailed electrical schematic for the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1, a block diagram of the electrical schematic for the present invention is shown. Alternating current (AC) main power line supply  10  is connected to gaseous discharge lamp  12  by way of gaseous discharge lamp ballast apparatus  11 , breakover device and snubber network  13 , isolation network  14  and self adjusting symmetrical high voltage pulse generator  15 . The AC main power line supply  10  is the utility electric source from which electric current is obtained. The present invention was designed to accommodate voltage from AC main power line supply  10  and can be from 95 volts to 550 volts and from approximately 45 cycles to approximately 66 cycles. 
     The AC main power line supply  10  feeds into the gaseous discharge lamp ballast apparatus  11 . The gaseous discharge lamp ballast apparatus  11  operates as an inductor, the function of which is to limit and control the current of intrinsically unstable operation of the gaseous discharge lamp  12 . Gaseous discharge lamps have a negative resistance characteristic (i.e. when current is increased through the lamp the voltage across the lamp decreases). Without some means of limiting and controlling the current, the current would otherwise increase without limit. Gaseous discharge lamp ballast apparatus  11  opposes any change in the current to limit and control the current. The gaseous discharge lamp ballast apparatus  11  used with the present invention can be of any type. In current practice, gaseous discharge lamp  12  is connected directly to gaseous discharge lamp ballast apparatus  11 . However, in the present invention additional electrical components are added between gaseous discharge lamp  12  and gaseous discharge lamp ballast apparatus  11  to provide several benefits over the current practice. 
     In the preferred embodiment of the present invention, the gaseous discharge lamp ballast apparatus  11  is connected to a breakover device and snubber network  13 . An AC voltage flows out of gaseous discharge lamp ballast apparatus  11  and into breakover device and snubber network  13 . This AC voltage can be higher or lower than the power line voltage and may be in various wave forms. The breakover device portion of breakover device and snubber network  13  provides transient voltage protection and is activated by either the actual value of the voltage across it or the rate at which the voltage across it changes. This typically occurs under abnormal conditions. The typical breakover device is a triac and can be triggered by either its intrinsic properties or by external properties. The typical snubber would be a resistor and capacitor in series across the triac. The snubber network is designed to permit the triac to commutate to its off state when the line transients or load switching disturbances are no longer present. 
     From the breakover device and snubber network  13  is an isolation network  14 . The function of the isolation network  14  is to disconnect or isolate the self-adjusting symmetrical high voltage pulse generator  15  and gaseous discharge lamp  12  from the gaseous discharge lamp ballast apparatus  11  which is essential to the operation of the EMI/RFI suppression characteristics of the present invention. Functionally the isolation network  14  acts as a very low impedance short circuit to high frequency currents or high frequency voltages. Isolation network  14  is connected to a self-adjusting symmetrical high voltage pulse generator  15 , providing electrical power for its operation. 
     The function of the self-adjusting symmetrical high voltage pulse generator  15  is to generate high voltage starter pulses to initiate conduction through the gaseous discharge lamp  12 . Gaseous discharge lamps typically require a high voltage to initiate conduction through the volume of the active material within the inner arc tube or glow tube of the gaseous discharge lamp  12 ; this high voltage can be a single or preferably a series of multiple pulses. The self-adjusting symmetrical high voltage pulse generator  15  operates, in the case of low pressure sodium lamps, when the lamp is extinguished due to a momentary power outage or when the lamp is very cold. The self-adjusting symmetrical high voltage pulse generator  15  is then connected to the gaseous discharge lamp  12 . The gaseous discharge lamp  12  can be low pressure sodium, high pressure sodium, mercury vapor, metal halide, or other gaseous discharge lamps operating in either the low pressure glow or high pressure arc regimes. 
     FIG. 2 illustrates a detailed electrical schematic for the present invention. In the present invention alternating current is delivered from the AC main power line supply  10  (See FIG.  1 ). The current first flows through a gaseous discharge lamp ballast apparatus  11  (See FIG. 1) and into a breakover device and snubber network  13 . The AC voltage can be higher or lower than the power line voltage and may be in various wave forms. The breakover device portion of breakover device and snubber network  13  provides transient voltage protection and is activated by either the actual value of the voltage across it or the rate at which the voltage across it changes. This typically occurs under abnormal conditions. The typical breakover device is a triac and it can be triggered by either its intrinsic properties or by extrinsic properties. The typical snubber network would be a resistor and capacitor in series across the triac. The snubber network is designed to allow the triac to commutate to its off state whenever the abnormal conditions are no longer present. 
     In the breakover device and snubber network  13  is a thermistor  41  which exhibits electrical resistance that varies with temperature and has a low value during normal operation, preferably being approximately 1 ohm. The function of thermistor  41  is as a self-resetting fuse. Thermistor  41  is preferably ceramic to alleviate any hysteresis effecting intrinsic to alternatives such as polymeric plastic thermistors. If a short occurs downstream from thermistor  41 , it will get hot and the circuit will not function nor be damaged or present in hazard due to the several orders of magnitude increase in the resistance of thermistors. When the power is turned OFF or the short is removed, thermistor  41  will cool down and the circuit return to normal function. 
     Within breakover device and snubber network  13  and past thermistor  41  are terminals  42  and  43 . Connected between terminals  42  and  43  is a series string of resistors  44 ,  45 ,  46 , and  47 . Resistor  44  is connected across gate main terminal  1  connections triac  51 . This resistor  44  is of a low value, preferably in the range of 10 ohms. The function of resistor  44  is to bypass inadvertent unwanted currents from gate to main terminal  1  of triac  51 . Resistors  45 , 46 , and  47  are connected in series with respect to each other and in parallel respectively with SIDAC devices  48 ,  49 , and  50 . Resistors  45 ,  46 , and  47  are high value resistors the function of which are to make the voltages that appear across SIDAC&#39;s  48 ,  49 , and  50  balanced and exactly the same and within the non-breakover voltage of SIDAC&#39;s  48 , 49  and  50 . The breakover voltage for the SIDACs is the minimum voltage required to cause the SIDAC to break down and conduct. The SIDAC&#39;s used in the preferred embodiment are preferably rated from 270 to 330 volts normal breakover voltage. Triac  51  is turned ON by the action of SIDAC&#39;s  48 ,  49 , and  50  acting in conjunction with resistors  45 ,  46 , and  47  if the low frequency power line voltage or a surge from a lamp flicking out exceed their breakover voltage. Once triac  51  is turned ON it short circuits the pulse and commutates OFF when the transient overvoltage level or rate of voltage rise across triac  51  are no longer present. 
     For fast rising transient pulses that may be due to a broken weld, loose socket, or bad connection, triac  51  will turn ON due to its intrinsic characteristics at gate main terminal  1  since applying sudden voltage to a triac will turn it ON. A capacitor exists between gate main terminal  1  and gate main terminal  2  of triac  51  that upon application of a sudden voltage to gate main terminal  2  will capacitively couple sufficient current into the gate to forward bias the gate-main terminal  1  junction and the triac  51  will turn ON. Typically this is not desired; however, it is beneficial to the present invention. The breakover voltage for triac  51  is preferably 800 volts, but typically triggered at 750 volts. Triac  51  is also connected in series with themistor  52 . 
     Thermistor  52  has an electrical resistance that varies with temperature and, in conjunction with capacitor  19 , acts as a snubber network to suppress the voltage change over time to ultimately allow the commutated turn OFF triac  51 . 
     From breakover device and snubber network  13  is isolation network  14 . The function of the isolation network  14  is to disconnect or isolate the self-adjusting symmetrical high voltage pulse generator  15  and gaseous discharge lamp  12  from the gaseous discharge lamp ballast apparatus  11  which is essential to the EMI/RFI suppression characteristics of the present invention. Functionally isolation network  14  acts as a short circuit at high frequencies. 
     To accomplish this within isolation network  14 , capacitor  19  is connected in series with resistor  20 . Capacitor  19  is a short circuit at high frequencies and an open circuit at low frequencies i.e. power line frequencies. Its value is preferably large on the order of approximately 0.1 microfarad. Resistor  20  is a very low value resistor which function is as a fuse. If capacitor  19  short circuits, resistor  20  blows up to prevent damage downstream. Downstream from capacitor  19  and resistor  20  are transformers  16  and  17 . Transformers  16  and  17  are closed magnetic path transformers with ferrite cores of any closed magnetic path configuration such as toroid, E-core, El-core, L-core, C-core, or closed magnetic path wound with ordinary Class H magnet wire. The windings of transformers  16  and  17  are impregnated using standard vacuum techniques with a 100% solid system silicone based resin. This resin provides environmental resistance to moisture penetration, atmospheric pollution, decay, and pests. 
     Transformer  16  is phased, or connected, on the same side such that at high radio frequencies it functions as close as practicable to a short circuit. Transformer  17  is physically connected and built the same as transformer  16 . However, transformer  17  is phased, or connected, on opposite sides such that at high radio frequencies it operates as an open circuit. The construction of both transformer  16  and transformer  17  is such that they have no effect in power line frequency. Both transformers  16  and  17  are more effective with progressively higher harmonic frequencies of the nonlinear operations that are intrinsic to a gaseous discharge lamp. At low frequencies transformers  16  and  17  do nothing. Located between transformers  16  and  17  and across terminals  31 A and  30 A is capacitor  18 . Capacitor  18  functions as a short circuit at high frequencies and as an open circuit at low frequencies. In addition, capacitor  18  assists in keeping the high frequencies from getting back into the gaseous discharge lamp ballast apparatus  11  and power line. 
     The connection of transformers  16  and  17  across terminals  31 A and  30 A results in a 42 dB decrease in the radiated EMI/RFI from gaseous discharge lamp  12  and a 40 dB decrease in the conducted EMI/RFI back into the gaseous discharge lamp ballast apparatus  11  and powerline. 
     Connected to the isolation network  14  is self adjusting symmetrical high voltage pulse generator  15 . The function of the self adjusting high voltage pulse generator  15  is to generate a high voltage starter pulses to initiate conduction through the gaseous discharge lamp  12 . Gaseous discharge lamp typically require a high voltage to initiate conduction through the volume of active material within the inner arc tube of the gaseous discharge lamp  12  which can be a pulse or multiple pulses. The self-adjusting symmetrical high voltage pulse generator  15  operates in the case of a low pressure sodium lamp when the lamp is extinguished due to a momentary power outage or when the lamp is cold to restart the lamp. It will also automatically generate sustaining “pilot-light” pulses to maintain conduction through the lamp  12  after the end of its normal operating lifetime. 
     Within self adjusting symmetrical high voltage pulse generator  15  and connected in series across terminals  30 A and  31 A are thermistor  26 , capacitor  28 , and fixed resistor  27 . The fixed resistor  27  is a base fixed value and thermistor  26  is a ceramic positive temperature coefficient thermistor. Thermistor  26  is used to make a constant current flow between terminals  30 A and  31 A and automatically adjusts the circuit for the applied voltage over a range of approximately 90 to 550 RMS volts. The current flowing between terminals  30 A and  31 A is needed to charge capacitor  28 . Capacitor  28  has constant impedance with respect to the combination thermistor  26  or fixed resistor  27  such that an essentially constant portion of power line frequency voltage appears across terminals  29  and  32  of capacitor  28  charging it up. When the power line frequency voltage across terminals  29  and  32  reaches the breakover voltage of SIDAC  25 , SIDAC  25  turns from an open circuit to a short circuit. SIDAC  25  then dumps the charge from capacitor  28  into primary winding  23  of pulse transformer  21 . 
     Pulse transformer  21  is a tall ratio transformer which lies across terminals  33  and  34 . The number of turns on primary winding  23  is significantly less than the number of turns on secondary winding  22 . The ratio is anywhere from 60:1 to 1500:1. The core  24  of pulse generator  21  is preferably a rod shaped slug of ferrites or powdered iron. The magnetic path of core  24  in pulse transformer  21  is open from end to end. 
     Self adjusting symmetrical high voltage pulse generator  15  is designed to generate a multitude of high voltage pulses, preferably 5 to 50, per alternate half cycle of the power line voltage. For example, for a 60 cycle/second power line, there could be as few as 10 or as many as 6000 pulses per second. This could be higher for some specialized applications with high pressure sodium and metal halide lamps. 
     Once the charge is dumped into primary winding  23  a very high voltage appears across terminals  33  and  34 . In order to keep the power line voltage out of the secondary winding  22  to keep the secondary winding  22  from fusing together, a symmetrical set of resistors and capacitors are connected in series with terminals  33  and  34  going up to terminal  31 B and down to terminal  30 B. More particularly, resistor  35  is connected in parallel with capacitor  36 . This parallel network is connected from terminal  34  to the wire that is connected to terminal  31 B. Similarly, resistor  37  is connected in parallel with capacitor  38 . This second parallel network is connected from terminal  33  to the wire that is connected to terminal  30 B. The value for capacitors  36  and  38  is preferably on the order of 10 nanofarads (nF) and the value for resistors  35  and  37  is preferably on the order of 1 megaohms to 5 megaohms. Resistors  35  and  37  provide voltage stress equalization while the system is active and safely discharge capacitors  36  and  38  when power is not available. 
     The approximately 10 to 6,000 pulses per second are coupled into the bus connected to terminals  30 B and  31 B of block  15  by way of capacitors  36  and  38 . At high frequencies the current is delivered to that bus. Gaseous discharge lamp  12  and transformer  17  are also connected across this bus. As mentioned, transformer  17  acts as an open circuit and therefore there is no current flowing through transformer  17 . Therefore there is no where else for the current to go other than into gaseous discharge lamp  12 . Gaseous discharge lamp  12  is connected across terminals  39  and  40  and can include low pressure sodium, high pressure sodium, mercury vapor, metal halide lamps, or other gaseous discharge lamps, operating in the low pressure glow or high pressure arc regimes. The current is used to get gaseous discharge lamp  12  turned ON in low temperature conditions or in situations where the lamp has gone out and it has not had time to cool off to restart itself as well as initiate conduction as normally required for certain types of gaseous discharge lamps as a requirement for their normal operation. 
     Self adjusting symmetrical high voltage pulse generator  15  is also designed to be symmetrical with isolation network  14  which, although not necessary for the operation of the gaseous discharge lamp  12 , is necessary for the reduction of the EMI/RFI. The present embodiment reduces electromagnetic noise pollution coming from and through the gaseous discharge lamp  12  by a factor of 40 dB. 
     The present invention is also useful in brownout conditions. Assume low pressure sodium lamps are being used along a street, which lamps normally operate at 480 volts AC. Typically, these lamps have a 10% tolerance or will normally operate between approximately 440 volts AC and 520 volts AC. Typically, low pressure sodium lamps will operate a little further outside the tolerance on the high side than they will on the low side. 
     In the present invention, during brownout conditions, the lamp  12  is maintained ON because of the current flow through the positive temperature coefficient thermistor  26  and fixed resistor  27  maintains essentially a constant current through primary coil  23  of transformer  21 . This constant current causes a relatively constant rate of pulses being generated by SIDAC  25 , even during normal operating conditions. In other words, high voltage pulse generator  15  continues to generate pulses even during normal operation when the lamp  12  is continuously lit. While the energy level of the pulses will be relatively small when the lamp  12  is lit, the pulses are continually present and act as a pilot light to keep the lamp  12  lit. Therefore, when the line voltage drops in a brownout condition, the constant triggering pulses will cause the lamp  12  to stay lit to a much lower voltage level than would otherwise be the case. For example, assuming lamp  12  is a low pressure sodium lamp that would normally operate at approximately 480 volts AC, lamp  12  would operate in a brownout condition down to approximately 200 volts AC or somewhere within the 30 percentile range. Certainly, lamp  12  would be sustained in the ON position to well below 50% of normal operating voltage. During such brownout conditions, lamp  12  would give off less light, but would remain ON. Therefore, the pulses from the high voltage pulse generator  15  would sustain lamp  12  in the ON position during brownout conditions. 
     As lamps get older, the voltage requirements for the lamps increase over time. For example, if 100 volts were required to sustain the lamp  12  in the ON condition, as the lamp gets older, it might require up to 150 volts to maintain lamp  12  in the ON condition. Currently, as a lamp gets old, the lamp will ignite and burn for a period of time and then flick OFF. As the gas inside the tube cools down, the lamp will reignite and come back ON. This can be seen in streetlights that go OFF for a period of time and, after cooling, come back ON. The lamp is towards the end of its life cycle. In the present invention, due to the continuous firing of pulses caused by the current flow through thermistor  26  and fixed resistor  27 , in combination with capacitor  28  and SIDAC  25  firing the primary winding  23  of the transformer  21 , a continual series of pulses are being received across the lamp  12  from secondary winding  22 . The series of pulses tend to sustain the lamp  12  in the ON condition, even though lamp  12  has deteriorated over time. The high voltage pulses being delivered to the lamp  12 , as it nears the end of its life cycle, continue to keep the lamp  12  ON. Therefore, the high voltage pulses from the secondary winding  22  sustain lamp  12  in the ON condition as it nears the end of its normal life. This prevents flickering of the lamp  12  from the ON to the OFF condition and then back ON as the gases inside of the lamp  12  cool. 
     Although the invention has been described with reference to specific embodiments, this description is not meant to be construed in a limited sense. Various modifications of the disclosed embodiments, as well as alternative embodiments of the inventions will become apparent to persons skilled in the art upon the reference to the description of the invention. It is, therefore, contemplated that the appended claims will cover such modifications that fall within the scope of the invention.