US3467886A - Ballast apparatus for starting and operating arc lamps - Google Patents

Description

Sept. 16, 1969 R. P. ALLEY 3,467,886

BALLAST APPARATUS FOR STARTING AND OPERATING ARC LAMPS Filed Feb. 24, 1966 2 Sheets-Sheet 1 50 as I .2 l0 2 A? /4 2a i W I I i 2/ 54 I I as I I a/ I //5 van rs 60mm: I 26 I 4/ I t:- ---Z? I y I I .J I I I 2 I I 24 I I Eli/V sin/27' I I I I 40 I 5 25% 60 I I I I I I I a Fig.4?

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Sept. 16, 1969 R. P. ALLEY 3,467,836

I BALLAST APPARATUS FOR STARTING AND OPERATING ARC LAMPS Filed Feb. 24, 1966 2 Sheets-Sheet 2 I N VE NTOR. iaerz, P141163,

United States Patent 01 fice 3,467,886 BALLAST APPARATUS FOR STARTING AND OPERATING ARC LAMPS Robert P. Alley, Danville, Ill., assignor to General Electric Company, a corporation of New York Filed Feb. 24, 1966, Ser. No. 529,862 Int. Cl. H05b 41/04 U.S. Cl. 315-163 12 Claims ABSTRACT OF THE DISCLOSURE A ballast circuit for starting and operating arc lamps includes a full wave rectifier in series with an adjustable resistor and a reactor across the terminals of an A-C supply. An arc lamp may be connected across the output terminals of the rectifier to receive its operating current therefrom which operating current is essentially controlled by the setting of the resistor and the reactance of the reactor. A circuit for providing starting current comprises a pair of storage capacitors connected to the primary winding of a pulse transformer to discharge through that transformer to provide a starting pulse higher in amplitude than the operating current when a switch is moved from a run to a start position.

The invention relates to an improved ballast apparatus for operating arc lamps.

Arc lamps, such as electric discharge lamps utilizing a metal halide filling in a quartz tube, impose severe operating and starting requirements on the ballast apparatus. For example, a typical metal halide lamp requires a start or breakdown voltage of approximately 10,000 volts to strike an arc. An intermediate voltage of approximately 300 volts is then needed to cause cathode spots to form on the two electrodes. After the cathode spots are formed, the lamp can be operated with an applied voltage of approximately 40 volts.

The metal halide arc lamp has an operating resistance characteristic which, while positive (i.e., the lamp current does not run away), is relatively flat. It will be apparent that a small increase in applied lamp voltage causes a relatively large increase in lamp current, or a small decrease in applied lamp voltage causes a relatively large decrease in lamp current. Therefore, it is desirable if not necessary to operate such are lamps with a stabilized or ballasted current.

An inherent difiiculty encountered in starting metal halide lamps is that the lamp voltage during the start-up condition varies over a relatively wide range. The ballast apparatus must effectively control the current supplied to the lamp during the starting condition to prevent possible damage to the electrodes or seals.

Applications for which the metal halide lamps are particularly suited are projection lighting systems. It is expected that such lighting systems will not only be used in classrooms or theatres, but will also be used in homes. It is therefore desirable that the lamp circuit or ballast apparatus be operable from a conventional 115 volt, 60 cycle alternating supply and that it be safe and relatively simple to operate.

Accordingly, an object of the invention is to provide a new and improved lamp ballast apparatus for starting and operating metal halide lamps.

It is another object of the invention to provide a lamp ballast circuit for starting and operating an arc lamp of the metal halide type.

A further object of the invention is to provide an improved ballast apparatus for operation from a conventional alternating current power source wherein the current supplied to the lamp is effectively limited during the starting period.

3,467,886 Patented Sept. 16, 1969 Another object of the invention is to provide an improved ballast apparatus that provides starting and operating functions from conventional alternating current power, and that has a readily adjustable operating characteristic.

In accordance with one form of my invention I have provided improved ballast apparatus for starting and operating an arc lamp, such as for example, a metal halide lamp. The improved ballast apparatus includes a full wave rectifying means, such as a bridge rectifier, having an alternating input and a direct current output, a power supply circuit, a lamp operating circuit and a lamp starting circuit. According to an important aspect of my invention, the power supply circuit includes a reactive ballasting device and circuit means connecting the reactive ballasting device and alternating input of the full wave rectifying means in series circuit relation across the alternating source to form an alternating current supply loop wherein the current supplied to the input of the full wave rectifying means is limited by the reactive ballasting device. The lamp operating circuit includes the direct current output of the full wave rectifying means, terminals for connection to at least one arc lamp and circuit means connecting the terminals and the direct current output of the full wave rectifying means in a lamp operating loop for supplying direct current to the arc lamp connected across the terminals in the lamp operating loop. During operation, the direct current supplied to operate the arc lamp is essentially limited by the current flow in the alternating current supply loop.

According to another aspect of the invention, the electrical energy required to provide the starting pulse for the arc lamp is obtained by discharging a start capacitor through an autotransformer having its primary and secondary in the lamp operating loop to provide reactance in the operating loop for smoothing the rectified voltage. Further, at least one capacitor is coupled with the full wave rectifying means to provide a voltage doubler circuit to step up the charge level on the start capacitor. Preferably, the lamp starting circuit may also include a means for supplying the arc lamp with electrical energy at a predetermined intermediate level to insure that sufficient volt-amperes are supplied to the arc lamp after the arc is struck.

An important ad'Jantage of the improved ballast apparatus results from the improved arrangement for regulating lamp current wherein the operating direct current supplied to the lamp is ballasted on the alternating current side of a bridge. With this arrangement it was found that a lamp electrode damage was effectively minimized since the starting inrush current is effectively limited over a relatively wide range of lamp voltage variations. For the metallic iodide lamp used in the exemplifications of my invention, it was necessary to limit the starting inrush current to 200 or 300 percent of the operating current which was about 7% amperes. It will be appreciated that a cold metal iodide lamp has a voltage between 10-15 volts as it just starts up. As the lamp warms up, the voltage increases to a value ranging from 37.5-42.5 volts. Despite this voltage variation across the lamp during the starting condition, the ballast apparatus must effectively limit the starting inrush current in order to prevent damage to the lamp electrodes or seals. With the improved ballasting circuit arrangement, a vector relationship is achieved between the reactor and supply line voltage such that as the lamp voltage varies the reactor current and consequently the lamp current do not appreciably vary beyond the limit at which the lamp electrodes might be damaged.

The invention is particularly pointed out in the claims. The invention may be better understood from the following description given in connection with the accompanying drawings, in which:

FIGURE 1 is a schematic circuit diagram of one embodiment of the invention wherein a start switch is utilized to connect and disconnect the starting circuit from the are lamp;

FIGURE 2 is a schematic circuit diagram of another embodiment of my invention wherein a thermistor is employed in the lamp operating circuit; and

FIGURE 3 is a schematic circuit diagram of an embodiment of the invention wherein a relay is employed to selectively uncouple the starting circuit from the lamp operating circuit.

Referring now more specifically to the drawings, I have employed in FIGURES 1 through 3 the same reference numerals in all of the figures to identify the corresponding circuit elements thereof that are functionally similar. In FIGURES 1, 2, and 3, the ballast apparatuses are generally identified by the reference numerals7, 8, and 9 respectively. The main input terminals 10, 11 are provided for connection to a 60 cycle, alternating current source. Power is applied to ballast apparatus 7 by actuating switch 12 connected to the terminal to its on position. It will be noted that ballast apparatus 7 of FIGURE 1 is connected to an adjustable or variable resistor 13 and to a reactor or a ballasting element 14.

The reactor 14 is. coupled to one alternating current bridge inputterminal 15 of a full wave rectifier bridge 16. The other alternating current bridge input terminal 17 of the rectifier bridge 16 is connected to the other main input terminal 11. The rectifier bridge 16 comprises four diodes or rectifiers connected in conventional bridge fashion, each diode or rectifier being provided with transient suppressing capacitors C C C and C Direct current is derived from the bridge rectifier 16 at the output terminals 18, 19, terminal 18 connected to line 20 being the positive output terminal and terminal 19 connected to line 5 being the negative terminal of the bridge rectifier 16. A pair of capacitors 21, 22 connected in series across the line 20 and junction 24 function as a voltage doubling circuit. Two parallel connected capacitors 26 and 27 serve as an intermediate energy storage circuit.

Preferably, the energy storage capacitor 26 has a relatively large capacitive value (1800 microfarads) as compared with capacitor 27 (2 microfarads). Capacitor 27 with the lesser capacitive value makes a pulse of energy available with a very short time delay.

A start circuit including a charging resistor 30 and a start capacitor 31 is connected in series across the positive and negative direct current output terminals 18, 19 of the rectifier bridge 16. A pulse transformer 32 as a primary winding 33 connected in series between the junction of resistor 30 and capacitor 31 and a start contact of switch 40. The secondary winding 34 of pulse transformer 32 has one end connected in circuit with the positive output terminal 18 and the other end is connected with one of the lamp electrodes. Secondary winding 34 of the pulse transformer 32 is magnetically coupled with the primary winding 33 on a magnetic core and is provided with a bypass capacitor 35. It will be noted that rotatable switch arm of the switch is connected to the negative output terminal 19 while the run contact of switch 40 is connected to junction 24. The arm of the switch 40 normally engages the run contact, but may be moved manually to the start position. After release, the arm of switch 40 is biased by a spring 60 to the run position.

Referring specifically to FIGURE 1, I will now more fully describe the operation of the ballast apparatus 7 illustrated therein. To energize the ballast apparatus 7 the on-off switch 12 is first closed so as to provide current to the rectifier bridge 16. The voltage doubling capacitors 21, 22 receive a charge that produces a direct current voltage across line 20 and junction 24. The intermediate energy storage capacitors 26, 27 also receive a charge, and start capacitor 31 is charged through the resistor 30. After these capacitors are charged to their normal level (about one second in the illustrated embodiment of my invention) the ballast apparatus is ready for operation, and the start switch 40 may be manually or automatically actuated to the start position thereby causing the start capacitor 31 to discharge a pulse of current through the primary winding 33. This pulse of current induces a voltage (depending on the turns ratio between the primary winding 33 and the secondary winding 34) in the secondary winding 34. At the instant that the arc is struck, energy from the intermediate capaci-.

tors 26, 27 begins to flow through the secondary winding 34, the lamp 41, and the resistor 23.

The resistor 23 is selected or provided with a value to limit the discharge current from capacitors 26, 27 to the desired level to prevent the intermediate capacitors 26, 27 from discharging too rapidly. These capacitors 26, 27 continue to provide current to the lamp 41 for at least as long as necessary to enable the rectifier 16 to supply lamp. If the arc inthe lamp 41 is struck just as current-voltage of an alternating current cycle is passing through Zero, the rectifier 16 is not able to supply the requisite energy to form the cathode spots on the lamp electrodes and maintain the arc. Thus, the intermediate energy capacitors 26, 27 provide this requisite energy until the rectifier 16 takes over the operation of the lamp 41. After the arc is struck, the start switch 40 is released and its movable arm then engages the run contact. The lamp 41 then receives energy, if there is any remaining, from the intermediate energy capacitors 26, 27 and from the rectifier 16, and the arc is maintained during operation by a current, the magnitude of which is essentially controlled by reactance of the reactor 14 and the resistance setting on the adjustable resistor 13.

Referring now to FIGURE 2, I have illustrated therein another embodiment of a ballast apparatus 8 for providing the starting, intermediate, and operating power requirements to a lamp 41. The circuit components of FIG- URE 2 have been given the same reference numerals at their corresponding components of FIGURE 1 where they essentially perform the same function. The circuit of FIGURE 2 includes the ballasting reactor 14, but it wil be noted that an adjustable resistor 13 is not employed. The rectifier bridge 16 produces direct current across the voltage doubler capacitors 21, 22. A pair of intermediate energy capacitors 26, 27 are used, but the capacitor 27 of lesser capacitance is not connected through the current limiting resistor 23 so its discharge current is not limited during starting. The pulse transformer 32 is an autotransformer and thereby provides a voltage pulse which combines the primary winding voltage and the secondary winding voltage. The start capacitor 31 is charged through the primary winding 33 and the resistor 30. Also, a thermistor 42 is provided in series with the lamp 41 for the purpose of limiting start inrush current while the arc lamp is cool.

In order to initiate operation of ballast apparatus 8 of FIGURE 2, the on-off switch 12 is closed. The voltage doubler capacitors 21, 22, the intermediate storage capacitors 26, 27, and the start capacitor 31 are charged. When switch 40 is operated to the start position, the start capacitor 31 discharges through the primary winding 33. This provides a voltage pulse in the secondary winding 34 to strike an arc in the lamp 41. The intermediate capacitor 27 supplies current through this arc, and the intermediate capacitor 26 also supplies current through the limiting resistor 23. This intermediate supply of energy insures that the necessary cathode spots are maintained so that the rectifier 16 may take over and provide an operating current limited by the reactor 14. When the switch 40 is released, the movable arm engages the run contact, the lamp 41 is operated at its normal operating level, and the charge on the capacitors are restored.

In FIGURE 3, the ballasting reactor 14' includes four parallel windings L L L and L rather than a single winding, and automatic starting is provided by means of a relay 62. The relay 62 includes a Winding RA and associated contacts RA-l, RA-2, RA-3, and RA-4. In the unenergized condition of the winding RA, contacts RA-l and RA-4 are normally closed and contacts RA-2 and RA-3 are normally open. When the Winding RA is energized, the contacts RA-1 and RA-4 are open, and the contacts RA2 and RA-3 are closed.

The relay 62 is-operated through a cycling circuit comprising a charging resistor 50, a diode rectifier 51, and an operating capacitor 52 that are connected across the rectifier bridge direct current output terminals 18, 19. A capacitor 53 is also coupled across the diode rectifier 51. In this embodiment of the invention only a single intermediate energy storage capacitor 26 is provided along with its current limiting resistor 23 and a tuning or filtering inductor 54. This inductor is provided as an energy storage device to supplement the energy of the capacitor 26 rather than to use an additional capacitor. It will be noted that a bleeder resistor 56 is also provided for the capacitor 26.

In the exemplification of my invention illustrated in FIGURE 3, the start capacitor 31 has a charging resistor 30 and the pulse transformer 32 has its primary and secondary windings 33, 34 connected in autotransformer relation. The normally closed relay contact RA-l connects the junction of the charging resistor 23 and the intermediate energy storage capacitor 26 to line 20 connected to the positive terminal 18, and the normally open relay contacts RA2 when closed cause the starting capacitor 31 to be discharged through the primary winding 33 to provide the pulse of electrical energy required to strike the arc.

The lower terminal of the lamp 41 is connected to the direct current output terminal 19 through a start current limit resistor 55 which is shunted by the normally closed contacts RA4. It will be seen that the normally open contacts RA-3 are connected to the junction of resistor 50 and rectifier 51, and the negative output terminal 19. These contacts RA-3 cause the relay 62 to cycle until the lamp 41 is conducting.

When the on-ofi switch 12 is closed, the rectifier 16 charges the capacitors 21, 22, 26, 31, 52, and 53. The resistor 50 has a resistance such that the relay capacitor 52 is the last capacitor to reach its predetermined charge level at which level it will energize the relay winding RA When the relay capacitor 52 is so charged, the voltage doubler capacitors 21, 22, the intermediate storage capacitor 26, and the start capacitor 31 are fully charged.

When the capacitor 52 reaches the predetermined charge level, the relay winding RA is then energized to close the contacts RA-2 and RA-3, and to open the contacts RA-l and RA-4. The start capacitor 31 then supplies current through the primary winding 33 to provide a voltage pulse to strike an arc in the lamp 41 connected across terminals 70 and 71. At the same time, the closed contacts RA-3 prevent further charge from being placed on the capacitor 52. The intermediate storage capacitor 26 also supplies energy to the lamp, this energy being limited by the start current limit resistor 55 which is now operative since the contacts RA-4 are open, and by the current limiting resistor 23, which is now operative since the contacts RA-l are open.

If the lamp 41 is started properly, the voltage across the direct current output terminals 18, 19 is reduced to a level such that the charge on capacitor 52 is not sufficient to cause the relay winding RA to be energized. Thus, during the operating condition of the lamp 41 the relay winding RA is not energized, and contacts RA-l and RA-4 close again while contacts RA-2 and RA-3 open again. The circuit then functions with the lamp 41 being supplied with the proper voltage limited or ballasted by the reactor 14 in the alternating power supply circuit.

However, if the lamp 41 does not start, the voltage doubler circuit produces suiiicient voltage which, after a predetermined time delay, charges the capacitor 52 to again energize the relay winding RA. The relay winding RA when so energized again causes the start circuit to function and attempt to start the lamp 41 again. In this manner, the relay 60 is cycled until the lamp 41 starts.

A ballast apparatus shown in FIGURE 3 has been successfully built and operated with components having the following values or characteristics:

Ballast reactor 14' 30 millihenries. Capacitor 21 8.0 microfarads, 250 volts. Capacitor 22 8.0 microfarads, 250 volts. Resistor 50 15,000 ohms, 12 watts. Capacitor 52 60 microfarads, 350 volts. Capacitor 53 0.01 microfarad, 1000 volts. Resistor 23 25 ohms, 25 watts. Capacitor 26 1500 microfarads, 400 volts. Resistor 56 47,000 ohms, 2 watts. Resistor 30 22,000 ohms, 2 watts. Capacitor 31 2.0 microfarads, 400- volts. Resistor 55 4 ohms. Pulse transformer 32 Copper foil layer wound on E-E laminated core. Primary winding 6 turns of .002." x 1%."

copper foil. Secondary winding turns of .002" x 1% copper foil.

From the foregoing description it will be apparent that the improved apparatus includes a power supply circuit consisting of a reactor 14, a bridge rectifier 16, and a pair of input terminals 10, 11 for connection to an alternating current supply. When the terminals 10, 11 are connected to the alternating supply, the reactor 14, the alternating input terminals 15, 17 and the power supply are operated in a closed loop when the on-off switch 12 is in the on position. The lamp operating circuit includes the transformer 32 and lamp supply terminals 70, 71 for connection to an arc lamp, all of which form a second or lamp operating loop with both the primary and secondary windings 33 and 34, respectively, connected in the lamp operating loop to provide a maximum series inductance in the lamp operating loop. Preferably, sufficient inductance is provided for smoothing or filtering the rectifier direct current used to operate the lamp 41. It was found that with this improved arrangement for ballasting the arc lamp it was possible to effectively limit the lamp current in a given application for relatively a wide range of lamp voltage variations.

It will be understood that the various ballast apparatuscs described herein are intended as illustrative examples of the invention and that the invention is not limited to such embodiments thereof. Further, it will be apparent that many modifications of the particular embodiments of the invention described herein may be made. It is to be understood, therefore, that I intend by the appended claims to cover all such modifications that fall within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A ballast apparatus for starting and operating an arc lamp from an alternating source, said ballast apparatus comprising: a full wave rectifying means having an alternating input and direct current output; a power supply circuit including a reactive ballasting device and circuit means for connecting said reactive ballasting device and alternating current input of said full wave rectifying means in series circuit relation across the alternating source to form an alternating current supply loop wherein the current supplied to the input of the full wave rectifying means is limited by said reactive ballasting device; a lamp operating circuit including said direct current output of said full wave rectifying means, terminals for connection to at least one are lamp, and circuit means connecting said terminals and said direct current output of said full wave rectifying means in a lamp operating loop for supplying direct current to the arc lamp; means limiting said direct current in the lamp operating loop of the lamp during operation by the current flow in said alternating current supply loop; and a lamp starting circuit coupled with the lamp operating loop for introducing an electrical energy pulse to strike the arc of the arc lamp.

2. The ballast apparatus set forth in claim 1 wherein said lamp starting circuit includes a means for supplying the arc lamp with electrical energy at a predetermined intermediate level to maintain the cathode spots on the arc lamp after the arc is struck.

3. The ballast apparatus set forth in claim 1 wherein said full wave rectifying means is a bridge rectifier comprised of four diodes and at least one capacitor is connected across the bridge rectifier to produce a voltage doubling action at said output.

4. The ballast apparatus set forth in claim 1 wherein an autotransformer is connected in said lamp operating loop to couple said lamp starting circuit with the lamp operating loop to introduce therein the electrical energy pulse for striking the arc of the lamp.

5. The ballast apparatus set forth in claim 1 wherein an electric relay selectively connects said lamp starting circuit to introduce said electrical energy pulse into the lamp operating loop when the arc lamp is not ignited.

6. The ballast apparatus set forth in claim 1 wherein a thermistor is connected in the lamp operating loop to limit inrush current to the arc lamp during the starting condition. I

7. The ballast apparatus set forth in claim 1 wherein the reactive ballasting device is a reactor comprised of a magnetic core having wound thereon a plurality of turns of conductor wire, said winding being connected in series circuit with said alternating input of the full wave rectifying means.

8. A ballast apparatus for starting and operating an arc lamp of the metal halide type from an alternating source, said ballast apparatus comprising: a full wave bridge rectifier having an alternating current input and direct current output; an alternating power circuit including a pair of terminals for connection to an alternating current source, a ballast reactor, and said alternating current input of said full wave bridge rectifier, said ballast reactor, alternating current input and terminals being connected in a closed loop when terminals are energized from the alternating source; a lamp operating circuit including an autotransformer, said direct current output of said bridge rectifier, lamp terminals for connection to the metal halide lamp, said autotransformer, said direct current output of the full wave bridge rectifier and lamp terminals being connected in a lamp operating loop; and means coupled with the primary winding of the autotransformer for supplying a high voltage pulse to strike the arc of the metal halide lamp.

9. The ballast apparatus set forth in claim 8 wherein at least one capacitor is connected across said bridge rectifier to produce a voltage doubling action at the output thereof.

10. The ballast apparatus set forth in claim 8 wherein said ballast means is comprised of a reactor including a winding wound on a magnetic core and connected in series circuit relation with said input of the rectifier bridge.

11. A ballast apparatus for starting and operating a direct current arc lamp from a source of alternating current comprising: first and second main input terminals for connection with the alternating current source; a full wave rectifier circuit having first and second alternating current bridge input terminals and first and second direct current bridge output terminals; a linear reactor connected between said first main input terminal and said first bridge input terminals; means connecting said second main input terminal to said second bridge input terminal; a start capacitor connected between said first and second bridge output terminals; a pulse transformer having a primary Winding and a secondary winding coupled thereto to produce a steppedup voltage in response to current flow through said primary winding; lamp supply terminals; means serially connecting said secondary winding and said lamp supply terminals between said first and second bridge output terminal; and switching means for selectively connecting said start capacitor to said primary winding for energizing said primary winding by discharging said start capacitor, and for selectively disconnecting said start capacitor from said primary winding.

12. The ballast apparatus set forth in claim 11 and further comprising means for repetitively causing said switching means to connect said start capacitor to said primary winding and to disconnect said start capacitor from said primary winding until the voltage across said lamp supply terminals falls below a predetermined value.

References Cited UNITED STATES PATENTS 3,156,826 11/1964 Mutschler 250-199 3,213,840 10/1965 Corfield et al 123l48 3,235,769 2/ 1966 Wattenbach 315176 3,323,012 5/1967 Seib 315-174 3,334,270 8/1967 Nuckolls 315-171 JOHN W. HUCKERT, Primary Examiner SIMON BRODER, Assistant Examiner US. Cl. X.R.

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