Apparatus for remote ballasting of gaseous discharge lamps

Abstract: Remote ballasting apparatus adapted for insertion between a high frequency power source and one or more gaseous discharge lamps. The ballasting apparatus includes an isolation transformer having a primary winding adapted for connection to the high frequency power source, a low capacitance power transmission line having an output end adapted for connection to the one or more gaseous discharge lamps, and current limiting means, such as an inductor or a capacitor or a series resonant circuit connected between the secondaries of the isolation transformer and the input end of the low capacitance power transmission line.

Description: The present invention relates to a remote ballasting apparatus comprising an isolation transformer including a primary winding and secondary arranged in a center tapped secondary configuration and having a first secondary winding and a second secondary winding, a current limiting means connected to said isolation transformer, a low capacitance power transmission cable including a first conductor and a second conductor adapted for connecting said first secondary winding and said second secondary winding with a gaseous discharge lamp, said remote ballasting apparatus being adapted for connection to a high frequency power supply for energizing said primary winding of said isolation transformer. The operation of gaseous discharge lamps at high frequency is well known and the benefits of this operation have been listed in part in the literature. Most balast equipments currently available supplied for the high frequency operation of the lamps have either explicit in their instructions or implicit in their use that the ballast be located within approximately 10 feet, (3 m), of the lamp. In many applications, such as drying of printing ink, outdoor lighting, explosion proof environments, water treatment and portable lamps, it is not convenient to locate the ballast near to the lamp. In addition, using present means of connecting, even at shorter distances, large amounts of electrical noise interference are generated that cause erratic operation of other nearby electronic equipment. Finally, existing ballasts do not allow monitoring with ground fault interrupter equipments to reduce the hazard of electric shock to persons as the capacitive leakage currents generated by the high frequencies trip ground fault interrupters. In GB-A-1,054,794 a monochromatic light source is disclosed which includes a tube containing an ionizable gas. The ends of the tube are surrounded by identical windings which are connected through a solenoid, the mid-point of which is grounded. The two windings on the end portions of the tube are connected to the first secondary winding and the second secondary winding, respectively, of a remote isolation transformer, the primary winding of which is connected to a high frequency power supply. The center tap of the first secondary winding and the second secondary winding is grounded. A further monochromatic light source arrangement disclosed in GB-A-1,054,794 comprises a tube which is surrounded at its tube ends by windings, connected in series with a timing capacitor. A coaxial cable, whose outer conductor is grounded, has its single inner conductor connected to a high frequency power supply, one of whose terminals is grounded. The inner conductor is connected to the end of a first turn of one of the two windings surrounding the tube. The outer conductor of the coaxial cable is connected to the extreme terminals of the windings surrounding the lamp tube. The timing capacitor is so adjusted that the circuit with the inductance of the said windings is tuned to the frequency of the remote high frequency power supply. The last mentioned light source arrangement does not comprise an isolation transformer of the aforesaid type. A gaseous discharge lamp energized through an inverter which is in turn energized from a standard household alternating current voltage source is disclosed in U.S.-5,053,681. The inverter has a low voltage, low current, high frequency output and includes a step-down transformer with a single secodary winding which is connected by means of a small gauge jacket wire conductor with a primary winding of step-up transformer located remote from the inverter. The step-up transformer is located in proximity to the gaseous discharge lamp and is connected at its secondary with a gaseous discharge lamp. It is an object of the invention to provide a safe, efficient, non-interfering remote balasting apparatus having simple circuit arrangement. Starting from a device with the features of the precharacterizing clause of claim 1 the invention is characterized in- that said power transmission cable includes an outer sheathing conductor surrounding said first conductor and said second conductor, and insulation means for insulating said outer sheathing conductor from said first conductor and said second conductor, and in that said outer sheathing conductor has an input end connected to the center tap of said first secondary winding and said second secondary winding. The remote ballasting apparatus according to the present invention for starting and operating a gaseous discharge lamp may be used for the operation of a lamp at frequencies in excess of 10 kilohertz and at a predetermined distance (wherein the predetermined distance is dependent on the use of the apparatus and in a preferred embodiment, when operating the lamp remotely of the ballast apparatus, the predetermined distance being greater than 10 feet (or 3 m)) from the power supply. Said windings of said isolation transformer are preferably wound to minimize interwinding capacitance. According to a preferred embodiment of the invention, the sheathing conductor has an output end adapted for connection to said gaseous discharge lamp. According to a preferred embodiment, said current limiting means include a series resonant circuit. The current limiting means may include a first current limiting inductor through which said first conductor of said low capacitance power transmission cable is connected to said first secondary winding of said isolation transformer. Preferably, said current limiting means include a second current limiting inductor through which said second conductor of said low capacitance power transmission cable is connected to said second secondary winding of said isolation transformer. Another preferred embodiment of the invention is characterized in that said first conductor has an input end connected to said current limiting means and an output end adapted for connection to a first end of a first gaseous discharge lamp, that said second conductor has an input end connected to said current limiting means and an output end adapted for connection to a first end of a second gaseous discharge lamp, and that said low capacitance power transmission cable includes a third conductor extending within said outer sheathing conductor and having an input end connected to the center tap of said first secondary winding and said second secondary winding of said isolation transformer and an output end adapted for connection to a second end of the first gaseous discharge lamp and a second end of the second discharge lamp. According to a further embodiment of the invention said current limiting means are connected to said primary winding. A preferred embodiment of the invention is described with reference to figure 1 in the following. Figure 1 is a schematic view of a preferred embodiment of the invention. With reference to Figure 1 there is shown a device schematically of one embodiment of the invention. The device consists of three principal parts: the first, an isolation transformer as shown in the box 101; the second a current limiting means, for example an inductor or a capacitor or a series resonant circuit shown in box 102; and the third, a low capacitance power transmission line shown in box 103. High frequency power, typically 31.2 Khz, at 125 volts RMS, is connected to each of the ends of primary winding 1, typically 63 turns #22 AWG, of transformer 101, built on an RM14 core. The marked end of secondary winding 3, typically 56 turns #24 AWG, is connected to inductor 2 which, in turn, connects to node 6 and capacitor 10. Similarly, the unmarked end of secondary 5 is connected to inductor 4 which, in turn, connects to node 7 and capacitor 11. The other side of capacitors 10 and 11 are connected, along with the unmarked end of secondary 3, the marked end of secondary 5, conductor 14 and sheath conductor 9, to node 8. The input end of transmission cable 103, for example 40 feet, (12 m), of cable manufactured by Belden (as described in their product catalogue at catalogue number 9365), is connected with conductor 12 to node 6, conductor 13 to node 7, conductor 14 to node 8 and sheath conductor 9 to node 8. The output end of transmission line 103 is connected with conductors 12 and 14 to lamp 18, (F96T12 fluorescent lamp), and conductors 13 and 14 to lamp 15 (F96T12 fluorescent lamp). Inductors 2 and 4, typically 2 millihenry, and capacitors 10 and 11, typically 12000 picofarads, along with the distributed capacitance of transmission line conductor 12 between nodes 6-16 and 14 between nodes 8-11 and conductor 13 between nodes 7-17 and 14 between nodes 8-11, typically 1000 picofarads, form series resonant circuits which resonate at approximately 31.2 Khz. This resonance will produce an adequate voltage (600 to 800 volts) to initiate conduction in lamps 18 and 15 and then act as near resonant current limiters to maintain a voltage of approximately 200 volts to keep the lamps running. This configuration as shown in Figure 1 is a low noise generating balanced load with very small electrical noise radiation inasmuch as any electrical noise generated by minor component imbalances are returned via the shield conductor to the common node 8. For greater noise reduction node 8 can also be grounded.

Claims: A remote ballasting apparatus comprising: an isolation transformer (101) including a primary winding (1), and a secondary arranged in a center tapped secondary configuration and having a first secondary winding (3) and a second secondary winding (5), a current limiting means (102) connected to said isolation transformer (101), a low capacitance power transmission cable (103) including a first conductor (12) and a second conductor (13) adapted for connecting said first secondary winding (3) and said second secondary winding (5) with a gaseous discharge lamp (15, 18), said remote ballasting apparatus being adapted for connection to a high frequency power supply for energizing said primary winding (1) of said isolation transformer (101), characterized in that said power transmission cable (103) includes an outer sheathing conductor (9) surrounding said first conductor (12) and said second conductor (13) and insulation means for insulating said outer sheathing conductor (9) from said first conductor (12) and said second conductor (13), and in that said outer sheathing conductor (9) has an input end connected to the center tap of said first secondary winding (3) and said second secondary winding (5). A remote ballasting apparatus according to claim 1, characterizing by said windings (1, 3, 5) of said isolation transformer (101) are wound to minimize interwinding capacitance. A remote ballasting apparatus according to claim 1 or 2, characterized in that said sheathing conductor has an output end adapted for connection to said gaseous discharge lamp. A remote ballasting apparatus according to claim 1, 2 or 3, characterized by said current limiting means (102) including a series resonant circuit (2/10, 4/11). A remote ballasting apparatus according to claim 1, 2, 3 or 4, characterized by said current limiting means (102) including a first current limiting inductor (2) through which said first conductor (12) of said low capacitance power transmission cable (103) is connected to said first secondary winding (3) of said isolation transformer (101). A remote ballasting apparatus according to claim 5, characterized by said current limiting means (102) including a second current limiting inductor (4) through which said second conductor (13) of said low capacitance power transmission cable (103) is connected to said second secondary winding (5) of said isolation transformer (101). A remote ballasting apparatus according to one of the claims 1 - 6, characterized by said first conductor (12) having an input end connected to said current limiting means (102) and an output end adapted for connection to a first end of a first gaseous discharge lamp (18), said second conductor (13) having an input end connected to said current limiting means (102) and an output end adapted for connection to a first end of a second gaseous discharge lamp (15), and said low capacitance power transmission cable (103) including a third conductor extending within said outer sheathing conductor (9) and having an input end connected to the center tap of said first secondary winding (3) and said second secondary winding (5) of said isolation transformer (101) and an output end adapted for connection to a second end of the first gaseous discharge (18) lamp and a second end of the second discharge lamp (15). A remote ballasting apparatus according to claim 1, 2 or 3, characterized in that said current limiting means are connected to said primary winding.

Inventors: GIBSON J ALAN, GIBSON, J. ALAN
Applicants: TROJAN TECHN INC, TROJAN TECHNOLOGIES INC.
Application year: 1993
Main classification: H05B41
IPC codes: H05B41