A HIGH INTENSITY DISCHARGE LAMP BALLAST

Abstract: A ballast for lighting a high intensity discharge lamp having a power factor correction scheme. False triggering of the power factor correction scheme when attempting to ignite the lamp is substantially eliminated by a bypass capacitor (66) which diverts a false triggering signal away from the switching device. The ballast also includes an optional auxiliary light source for illumination when the HID lamp is not lit. By diverting the false triggering signal away from the switching device, the auxiliary light source is substantially free from flicker and/or being turned OFF prior to starting of the HID lamp.

Description: A high intensity discharge lamp ballast. This invention relates generally to a high intensity discharge (HID) lamp ballast and, more particularly, to an HID lamp ballast having a power factor correction scheme with optional auxiliary lighting. An HID lamp generally refers to a family of lamps including high pressure mercury, high pressure sodium, metal halide and low pressure sodium. A conventional ballast for powering an HID lamp often includes a capacitive power factor correction scheme which is responsive to and employed when the HID lamp is lit. The power factor correction scheme, should not be used when the HID lamp is not lit. Otherwise, a relatively high current level can be drawn by the ballast prior to the lamp being lit. The relatively high level of current can limit the number of power factor correction ballasts which can be connected to a branch utility power line (i.e. protected by a circuit breaker). HID lamps also are often difficult to ignite and especially difficult to re- ignite immediately. Typically, up to about fifteen minutes may be required for the lamp to sufficiently cool prior to attempting re-ignition. Auxiliary lighting responsive to the unlit HID lamp provides light during the initial period for ignition or re-ignition of the HID lamp or whenever the HID lamp otherwise fails to light. The responsiveness of the power factor correction and auxiliary lighting schemes to the HID lamp status (i.e. lit or not lit) can be provided by a switching device, the switching device being turned ON and OFF based on the HID lamp status. The switching device (e.g. a thyristor), however, can be subject to false triggering when attempting to ignite the HID lamp. False triggering can result in the power factor correction scheme being turned ON when the HID lamp is not lit. Undesirably high current levels drawn by the ballast can result. False triggering also can result in the auxiliary lamp flickering or being turned OFF prior to lamp ignition. Accordingly, it is desirable to provide an improved HID ballast having a more reliable power factor correction scheme. A more reliable optional auxiliary lighting scheme also should be provided. The power factor correction and auxiliary lighting schemes, in particular, should be substantially free from false triggering when attempting to ignite the HID lamp. Generally speaking, in accordance with a first aspect of the invention, ballast for a HID lamp, comprising: - control means for producing a switching signal; switching means for providing an interruptible conductive path on the switchi signal; corrective means responsive to the establishment of the interruptible conducti path for improving the power factor. The invented ballast is characterized in that the ballast comprises bypass means for diverti a portion of a certain type of the switching signal away from the switching means such th the switching means is non responsive to the certain type of switching signal. The certain type of switching signal includes, but is not limited to, volt pulses of a frequency of about 120 Hz or greater produced when attempting to start the ballast. False triggering of the power factor correction device prior to successful ignition o the lamp is substantially eliminated. More particularly, false triggering of the power factor correction device is avoided by the bypass device diverting voltage pulses which can turn the switching device away from the switching device when attempting to ignite the lamp. Accordingly, undesirable high current levels drawn by a capacitive power factor correctio scheme of an HID ballast prior to ignition of an HID lamp are substantially eliminated. In the preferred embodiment of the invention, the control device is a choke (i.e., inductor). The switching signal, which is produced from a tap of the choke, represents the flow of current through a first portion of the choke. Ignition pulses produce by a starting circuit across a second portion of the choke induce voltage pulses across the first portion of the choke. The induced voltage pulses result in the certain type of switchin signal which is diverted by the bypass device. The switching device is generally a triac. T bypass device preferably includes a capacitor which is connected to a gate of the triac. In accordance with a second aspect of the invention, a ballast for lighti a first lamp and a second lamp includes a control device for controlling current flow throu the first lamp and for producing a switching signal representing the flow of current throug portion of the control device. A switching device is operable for substantially short circuiti the second lamp based on the switching signal. The ballast further includes a bypass devic for diverting a certain type of switching signal away from the switching device such that t switching device is non-responsive to the production of the certain type of switching signal by the control device. The certain type of switching signal which is diverted has a frequency greater than a predetermined level (e.g. at or above 120 Hz). In accordance with this second aspect of the invention, the first lamp is of the HID type. The second lamp provides auxiliary lighting when the first lamp is not lit. The ballast also includes power factor correction means for improving the power factor of the ballast during the time the second lamp is substantially short circuited. The switching device (including an inductor for suppressing high inrush currents) and second lamp are preferably connected in parallel to form a parallel connection which in turn is serially connected to the power factor correction device. In accordance with a third aspect of the invention, a ballast for lighting a high intensity discharge lamp includes a ballast controller for controlling current flow through the lamp and for producing a switching signal reflecting the voltage developed across at least a portion of the ballast controller. The ballast also includes a switching device for providing an electrically conductive path therethrough based on the switching signal and a power factor correction device responsive to establishment of an electrically conductive path through the switching device for improving the power factor of the ballast. The ballast further includes a bypass device for diverting a certain type of switching signal away from the switching device such that the switching device is non-responsive to the production of the certain type of switching signal by the ballast controller. In accordance with a fourth aspect of the invention, a method for operating a ballast for powering a high intensity discharge lamp includes the steps of producing a switching signal representing the flow of current through at least a portion of a ballasting element during and after starting of the lamp, diverting the switching signal away from a switching device during lamp starting, establishing only after starting of the lamp an electrically conductive path through the switching device based on the switching signal and correcting the power factor of the ballast once the electrically conductive path has been established. Accordingly, it is an object of the invention to provide an improved HID ballast having a more reliable power factor correction scheme. It is another object of the invention to provide an improved power factor corrected HID ballast having a more reliable auxiliary lighting scheme. It is yet another object of the invention to provide an improved HID ballast in which the power factor correction scheme taken singly or in combination with an auxiliary lighting scheme is substantially free from false triggering when attempting to ignite an HID lamp. Still other objects and advantages of the invention, will, in part, be obvious, and will, in part, be apparent from the specification. The invention accordingly comprises several steps in the relation of on more such steps with respect to each of the others, and the device embodying features of construction, combination of elements and arrangements of parts which are adapted to eff such steps, all is exemplified in the following detailed disclosure, and the scope of the invention will be indicated in the claims. For a fuller understanding of the invention, reference is had to the following description taken in connection with the accompanying drawing in which FIG. a lighting system in accordance with the invention. As shown in FIG. 1, a lighting system 10 includes an A.C. source 20 connected to a pair of input terminals 33 and 36 of a ballast 30, an HID lamp 40 and an optional auxiliary lamp 50. Ballast 30 also includes a first pair of output terminals 39 and to which HID lamp 40 is connected. Auxiliary lamp 50, which can be but is not limited t incandescent type, is connected to a second pair of output terminals 45 and 48 of ballast Although auxiliary lamp 50 is shown connected to output terminals 45 and 48, it is to be understood that auxiliary lamp 50 can be disconnected from ballast 30 without adversely affecting operation of ballast 30. Auxiliary lamp 50 serves to provide light when power is supplied by source 20 to ballast 30 and HID lamp 40 is not lit. Ballast 30 further includes a power factor correction capacitor 53 connected in parallel with a discharge resistor 54. This parallel combination is connected one end to input terminal 36 and at its other end to output terminal 48. A first main termi MT1 of a triac 56 (or other suitable switching device) is connected to one end of an indu 57. The other end of inductor 57 is connected to a junction joining together input terminal 33, output terminal 45, a ballast reactor 65 and a bypass capacitor 66. A second main terminal MT2 of triac 56 is connected to a junction joining together capacitor 53, resistor and output terminal 48. The serial combination of inductor 57 and triac 56 is connected in parallel with auxiliary lamp 50. A gate G of triac 56 is connected through a switching controller 60 to tap point 73 of ballast reactor 65 in providing a switching signal for turning ON and OFF triac 56. Switching controller 60 can be, but is not limited to, a resistor for limiting the current level of the switching signal supplied to gate G of triac 56. The portion of ballast reactor 65 between input terminal 33 and tap point 73 will hereinafter be referred to as a winding portion 74. The point at which ballast reactor 65 is tapped to switching controller 60 is chosen, in part, so as to minimize the power consumed by switching controller 60. Capacitor 66 is also connected to gate G of triac 56. As described below, capacitor 66 serves to bypass/divert a certain type of switching signal. False triggering of triac 56 based on this type of switching signal is thereby avoided. Ballast reactor 65, which serves to limit/control the level of current flowing through lamp 40 when the latter is lit is also connected at a tap point 76 to one end of a SIDAC 89. The other end of ballast reactor 65 is connected to output terminal 39 and to a capacitor 92. The portion of ballast reactor 65 connected between tap point 76 and capacitor 92 is hereinafter referred to as an ignitor winding 79. SIDAC 89 and capacitor 92 are also connected to one end of a resistor 95. The other end of resistor 95 is connected to the junction joining together capacitor 53, resistor 54, input terminal 36 and output terminal 42. Ignitor winding 79, SIDAC 89, capacitor 92 and resistor 95 serve in combination as an ignitor (i.e., starting circuit) 80. Lighting system 10 operates as follows. Power is supplied from A.C. source 20 to input terminals 33 and 36 of ballast 30. The voltage produced by A.C. source 20 is insufficient to ignite/start lamp 40, the latter of which requires one or more supplemental starting pulses. The one or more pulses are provided by ignitor 80. More particularly, capacitor 92 based on the RC time constant of capacitor 92 and resistor 95 charges to the breakover voltage of SIDAC 89. Once the breakover voltage is reached, SIDAC 89 switches from its previous off-state to its on-state. A rapid flow of current now passes through and results in a voltage pulse produced across ignitor windings 79. The voltage pulse can be sufficient to ignite lamp 40. For example, when lamp 40 is of a metal halide type, nominally rated at 400 watts, 135 volts with SIDAC 89 having a breakover voltage of about 240 volts, a voltage pulse of about 240 volts is developed across ignitor winding 79. Through transformer action (i.e. , ballast reactor 65 acting as an autotransformer) a voltage of about 1800 to 3500 volts is developed across output terminals 39, 42. In the event lamp 40 does not start, the cycle of charging capacitor 92 until reaching the SIDAC breakover voltage resulting in the generation of a high voltage pulse applied to lamp 40 is repeated until lamp 40 ignites/starts. Once lamp 40 is lit, the voltage across ignitor 80 will drop down to abo 135 volts, that is, below the SIDAC breakover voltage of 240 volts. The voltage across ignitor 80 is now insufficient to produce a voltage pulse across ignitor winding 79. In othe words, as long as lamp 40 remains lit, ignitor 80 will produce no additional voltage pulses. Prior to and until lamp 40 reaches a predetermined level of illumination auxiliary lamp 50 is lit, (e.g. triac 56 is in its open state). Lamp 50 is nominally rated at about 120 volts and when lit is serially connected to capacitor 53 (i.e. triac 56 being turne OFF). Capacitor 53 serves to limit the flow of current through lamp 50. When HID lamp is initially lit (i.e. reaches at least a predetermined lev of illumination), current flows through ballast 65. The level of current flowing through lam 40 is controlled by ballast reactor 65. A switching signal representing/reflecting the flow o current through at least a portion of ballast reactor 65 is produced at tap 73 of winding portion 74. The switching signal is supplied to gate G by switching controller 60 whereby triac 56 is turned ON (i.e., provides an electrically conductive path therethrough). A substantially short circuit formed by inductor 57 and triac 56 effectively turns OFF auxiliar lamp 50. Inductor 57 serves to suppress high inrush currents which can damage triac 56. Power factor correction capacitor 53 with triac 56 turned ON draws a relatively large level of capacitive current thereby improving the power factor of ballast 30 (referred to hereinaft as the power factor correction scheme). Whenever HID lamp 40 is turned OFF through, for example, a momentary or longer lasting power interruption, the level of the switching signal produced by switch controller 60 will be insufficient to turn ON triac 56 or maintain triac 56 in its conductive state. Triac 56 will now switch to its open/off state. Once power returns to inp terminals 33, 36 and prior to lamp 40 being relit, light is provided by auxiliary lamp 50. During the period of time that power is not being supplied to input terminals 33, 36, resist 54 provides a path for discharge of capacitor 53. The impedances of capacitor 53 and lamp 50 are chosen such that whenever triac 56 is turned OFF sufficient current will flow throu lamp 50 to light the latter. In accordance with the invention, the power factor correction scheme when not being employed to offset the inductive component of current flowing through lam 40 (i.e. when triac 56 is turned OFF) results in less current being drawn from A.C. source 20 than may be otherwise drawn by a power factor correction scheme in which a capacitor always connected across A.C. source 20. Consequently, as compared to such conventional ballasts, a greater number of ballasts in accordance with the invention can be connected to branch utility power line. As can now be readily appreciated, switching controller 60 controls when the power factor correction scheme is employed by ballast 30 and when auxiliary lamp 50 is turned ON and OFF. As can also be readily appreciated, other types of ballast configurations including a high reactance type autotransformer ballast can be used in lieu of ballast reactor 65. The conditions under which triac 56 is turned ON and OFF are of particular importance and specifically addressed by the invention. Capacitor 53 should be placed across the mains voltage (i.e. connected between input terminals 33, 36) by turning triac 56 ON for power factor correction when lamp 40 is lit. When lamp 40 is not lit, capacitor 53 should be disconnected from the mains voltage by turning triac 56 OFF. Otherwise, current drawn by capacitor 53 can greatly exceed total line current thereby limiting the number of lamps which can operate on a given circuit breaker. In starting/igniting lamp 40, a series of voltage pulses at a frequency of about 120 Hz for about 2 to 3 seconds is typically developed across ignitor winding 79 of ignitor 80. A series of voltage pulses induced across winding portion 74 of reactor ballast 65 results. The induced voltage across winding portion 74 can result in a switching signal being produced by winding portion 74 sufficient to turn ON triac 56. A switching signal formed from such induced voltage pulses can result in the false triggering of triac 56. To avoid such false triggering, which can result in auxiliary lamp 50 being turned OFF and power factor correction capacitor 53 being placed across the mains voltage prior to a HID lamp 40 being lit, that portion of the switching signal based on the ignition pulses is substantially diverted away from gate G of triac 53 by bypass capacitor 66. In other words, triac 56 is non- responsive to the switching signal prior to lamp ignition, that is, non-responsive to the switching signal which is based on the ignition pulses (i.e. , the switching signal produced during starting of lamp 40). In accordance with the preferred embodiment of the invention, A.C. source 20 produces an A.C. voltage of about 277 volts. Capacitor 53 is nominally rated at about 20 microfarads. Auxiliary lamp 50 is nominally rated at about 250 watts, 120 volts and is of the quartz incandescent type. Switching controller 60 is a resistor (or other suitable impedance) nominally rated at about 300 ohms, 5 4 watts. Resistors 95 and 54 are nominally rated at 19,000 ohms, 7 watts and 470,000 ohms, 'Λ watt, respectively. Ballast reactor 65 is a one and one-half El lamination, 400 watt metal halide reactor ballast having total turns of 468 with tap points 73 and 76 at about the 36th and 453th turn, respectively. Triac 56 is nominally rated at 15 amps, 800 volts and is available from Teccor Inc. of Hurd, Texas as Part No. Q8015L5. SIDAC 89 is available from Shindengen Electric Mfg. Co., Ltd. of Tokyo, Japan as Part No. K1V26 and has a nominally rated breakover voltage of about 24 volts. Capacitor 92 is nominally rated at about 0.15 microfarads. Lamp 40 is a high intensit discharge type, such as but not limited to, a 400 watt, 135 volt metal halide type. Inductor 57 is nominally rated at .06 millihenries. Capacitors 66 and 92 are nominally rated at 5.6 microfarads and 0.1 microfarads, respectively. As now can be readily appreciated, the invention provides an improved ballast scheme in which false triggering of triac 56 during the starting of lamp 40 is eliminated. An optional auxiliary light source (i.e. lamp 50) is turned ON whenever the primary/main light source (i.e. lamp 40) has not reached a predetermined level of illumination. When this predetermined level of illumination is reached, triac 56 in combination with inductor 57 substantially short circuits auxiliary lamp 50 whereby lamp 5 is effectively turned OFF. At the same time (i.e. when lamp 50 is substantially short circuited), the power factor of power drawn by ballast 30 is increased by substantially balancing the capacitive and inductive components of current drawn from A.C. source 20. The gate current provided to gate G of triac 56 by switching controller 60 reflects/represent the flow of current through ballast reactor 65 and lamp 40. It will thus be seen that the objects set forth above and those made apparent from the preceding description, are efficiently obtained and since certain changes may be made in the above construction without departing from the spirit and scope 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. It is also to be understood that the following claims are intended to cove all the generic and specific features of the invention hereindescribed, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetwee

Claims: CLAIMS 1. A ballast for a HID lamp, comprising: control means for producing a switching signal; switching means for providing an interruptible conductive path on the switching signal; corrective means responsive to the establishment of the interruptible conductive path for improving the power factor; characterized in that the ballast comprises bypass means for diverting a portion of a certain type of the switching signal away from the switching means such that the switching means is non responsive to the certain type of switching signal. 2. The ballast of Claim 1 , wherein said certain type of switching signal has a frequency of about 120 Hz or greater. 3. The ballast of Claim 1 or 2, further including starting means for producing ignition pulses, said certain type of switching signal being produced by said control means based on said ignition pulses. 4. The ballast of Claim 1 of 3, wherein a device exhibiting inductive characteristics serves as said control means. 5. The ballast of Claim 4, wherein said device is an inductor having a first portion for producing said switching signal and a second portion included within said starting means. 6. The ballast of Claim 1 , 2, 3, 4 or 5, wherein said switching means includes a triac having a gate and further including switching control means connected between said control means and said gate for supplying said switching signal to said switching means. 7. The ballast of Claim 1 , 2, 3, 4, 5 or 6, wherein said bypass means includes a capacitor. 8. A ballast according to one or more of the previous claims, comprising a second lamp which is substantially short circuited by the switching means based on the switching signal. 9. The ballast of Claim 8, wherein the second lamp is of the incandescent type. 10. The ballast of Claim 8 or 9, wherein said switching means and second lamp are connected in parallel to form a parallel connection, the parallel connection being serially connected to said power factor correction means.

Inventors: DANIEL EDMOND, DROHO JOSEPH S, DANIEL, EDMOND, DROHO, JOSEPH, S.
Applicants: PHILIPS ELECTRONICS NV, PHILIPS NORDEN AB, PHILIPS ELECTRONICS N.V.
Application year: 1995
Main classification: H05B41
IPC codes: H05B41