US3333150A

US3333150A - Multi-level ballast circuit including an isolation transformer for series circuit connection with a fluorescent lamp

Info

Publication number: US3333150A
Application number: US400447A
Authority: US
Inventors: Franklin P Eppert
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1964-09-30
Filing date: 1964-09-30
Publication date: 1967-07-25
Anticipated expiration: 1984-07-25

Description

y 1967 F. P. EPPERT 3,333,150

MULTI-LEVEL BALLAST CIRCUIT INCLUDING AN ISOLATION TRANSFORMER FOR SERIES CIRCUIT CONNECTION WITH A FLUORESCENT LAMP Filed Sept. 30, 1964 2 Sheets-Sheet 1 INVENTOR. flan/W0? PIE gnarl:

BULL? United States Patent 3,333,150 MULTILEVEL BALLAST CIRCUIT INCLUDING AN ISOLATION TRANSFORMER FOR SERIES CIRCUIT CONNECTION WITH A FLUORES- CENT LAP/l1 Franklin P. Eppert, Danville, Ill., assignor to General Electric Company, a corporation of New York Filed Sept. 30, 1964, Ser. No. 400,447 7 Claims. (Cl. 315-97) This invention relates to an improved ballast circuit for use with fluorescent lamps. More specifically, it relates to a ballast circuit arrangement which provides two-level operation of fluorescent lamps.

In present commercial practice when using two-level ballasts with parallel connected fluorescent lamps it is necessary to include in the lamp circuits a separate pair of switching contacts for each ballast. If the separate switching contacts are not provided it has been found that unbalanced lamp operating levels result, with one lamp burning brighter than the others. Also, with a single switch in series with several parallel connected lamps it is impossible to uniformly control the lamp currents at lower levels.

It is an object of this invention to provide an improved ballast circuit useful for operating fluorescent lamps at two levels of output.

It is an object of this invention to provide a ballast circuit arrangement wherein the impedances of several ballasts, each of which is connected in series with one of several parallel connected fluorescent lamps, can be changed by the operation of a single pair of switching contacts.

It is a further object of this invention to provide a ballast circuit arrangement wherein two levels of operation of fluorescent lamps are provided with uniform output of the lamps at each level.

These objects are accomplished in accordance with this invention, in one form thereof, by including one Winding of an isolation transformer in series with each fluorescent lamp. A switch is connected in series with the other windings of the isolation transformers, which are connected in parallel if more than one is used. The windings may be open-circuited or short-circuited by the switch. When the contacts are operated to short circuit the windings, the impedances of the windings in series with the lamps are reduced, thereby raising the output levels of the lamps.

Other objects and further details of that which is believed to be novel will be clear from the following description and claims taken with the accompanying drawings wherein:

FIGURE 1 is a schematic circuit diagram of a ballast circuit for several parallel connected fluorescent lamps including the improved circuitry of this invention.

FIGURE 2 is a schematic circuit diagram of a ballast circuit for a single fluorescent lamp including the improved circuitry of this invention.

FIGURE 1 shows a first embodiment of the subject invention in which three fluorescent lamsp L L and L are connected in parallel. A transformer T is provided with a primary winding P which is energized by an AC power source having terminals 1 and 2. A capacitor 3 is connected in parallel with the primary winding P for power factor correction. Transformer T has four secondary windings, S 8 S and S These secondary windings are used to heat the cathodes in lamps L L and L Secondary winding S is used to heat one of the cathodes in each of the three lamps, while windings 8 S and S are used to heat the other cathodes in lamps L L and L respectively. One cathode of each of the three lamps is connected to terminal 1 of the AC power supply by lead 4.

3,333,150 Patented July 25, 1967 Isolation transformers T T and T are provided with primary windings P P and P respectively, all of which are connected to terminal 2 of the AC power supply by leads 5. The other terminals of the primary windings P P and P are connected to one of the terminals of ballast reactors R R and R respectively. The other terminals of the reactors R R and R are connected to the second terminals of the lamps L L and L respectively, by leads 6, 7, and 8, respectively. Each of the isolation transformers T T and T is provided with a secondary winding S S and S respectively. Corresponding terminals of the three secondary windings are connected to each other and the parallel connected secondary windings are also connected in parallel with contacts of an on-01f switch 9.

With the switch 9 in the off position, as shown, the reactances of the primaries P P and P of transformers T T and T are large. Therefore, the lamps L L and L operate at a low level as the power supplied to each lamp is limited by the reactances of a transformer primary winding and a ballast reactor.

With the switch 9 in the on position, the reactances of the primary windings P P and P are reduced according to well-known transformer principles, and therefore increased power is supplied to the lamps L L and L Thus, with switch 9 in the on position the lamps are operated at a higher output level than with the switch 9 in the oil? position. Without the physical interruption of the three parallel circuits, each including in series a ballast reactor, a transformer primary winding and a lamp, it is possible to alter the impedance of each of the three parallel circuits by closing or opening the contacts of switch 9.

The turns ratios of the isolation transformer windings are chosen such that the current in the secondary winding and the voltage developed across it are compatible with the voltage and current ratings of the switch 9.

With the control circuit shown in FIGURE 1, the operating level of each of the three lamps is controlled by a single switch 9', but the failure of an individual isolation transformer, reactor, or lamp, afiects only its circuit, the remainder of the lamps continue to operate in a normal manner with the switch 9 continuing to control their output level.

It can easily be seen that a greater number of parallel lamp circuits could be added to this ballast circuit, with the operating level of all of the lamps being controlled by a single switch 9. The cathodes of these additional lamps could be energized by transformer T or a separate transformer could be provided for each additional group of three lamps. In either case, the secondary windings of the isolation transformers whose primaries are each connected in series with one of the lamps would all be connected in parallel, whereby the switch 9 would control the operating level of all of the lamps.

Similarly, two or more lamps connected in series could replace each of the lamps L L and L to increase the number of lamps controlled by the single switch 9. If two or more lamps were connected in series, additional ballast reactance would also be required, and could be obtained by connecting an additional reactor in series with each isolation transformer primary.

By reference to FIGURE 2, it will be seen that a single fluorescent lamp L is energized by a ballast transformer T5. This transformer has a primary P which is connected by lines 10 and 11 to the terminals of an AC power supply. The transformer T has a main magnetic core 12, and also a bridging core portion 13 which provides a high leakage reactance between the primary winding P and a secondary winding S It will be understood, of course, that various other arrangements for providing leakage flux paths or shunts between the primary winding P and the secondary winding S may be employed. Depending upon the design of the particular ballast transformer, either air leakage paths, inserted shun-ts, or shunts integrally formed on the magnetic core 12 may be employed.

Transformer T is also provided with two additional secondary windings S and S which are used to heat the cathodes of lamp L Winding S is connected to one of the cathodes of lamp L; by leads 14 and 15, while winding S is connected to the other cathode of tube L; by

leads

16 and 17. The cathode of lamp L, which is connected to secondary winding S is also connected to one side of the primary winding P and therefore to terminal 11 of the AC power supplied by lead 18. One terminal of the secondary winding S is connected to a terminal of the primary winding P and to terminal 9 of the AC power supply by lead 19. An isolation transformer T is provided with a primary winding R; which is connected in series with the secondary winding S and the lamp L, by

leads

20 and 21, respectively. The contacts of an on-oil switch 22 are connected to a second-ary winding S on transformer T; by

leads

23 and 24. The operation of this ballast circuit is similar to that shown in FIGURE 1. With the switch 22 in the off position, as shown, the reactance of the primary winding P of the transformer T is large, and therefore the lamp L operates at a low level. The power supplied to the lamp L being limited by the reactances of the transformer windings S and P With the switch 22 in the on position, the reactance of a primary winding P is reduced according to well-known transformer principles, and therefore increased power flows to the lamp L with the output of lamp L thereby being increased.

While particular embodiments of the invention have been shown, other embodiments of the invention, such as the use of two or more isolation transformers in series with each lamp to give multilevel lamp operation, will be apparent to those skilled in the art, and it is intended to cover .by the appended claims all embodiments falling within the scope thereof.

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

1. A ballast circuit for varying the output level of a hot cathode fluorescent lamp energized by an alternating current source, said circuit comprising:

(a) a first transformer having a primary winding and a plurality of secondary windings, (b) a capacitor connected to said transformer for correcting the power factor of said circuit, (c) means for connecting said secondary windings to heat the cathodes of the lamp,

(d) an isolation transformer having a primary and a secondary winding,

(e) a reactor for limiting current to the lamp during operation,

(f) means for connecting said isolation transformer primary winding and said current limiting reactor in series between the lamp and the source,

(g) a bilaterally conducting switch connected to said secondary winding whereby with said switch closed said secondary winding is short circuited during successive half cycles of applied voltage and said lamp operates at a higher level, and with said switch open, said lamp operates at a lower level.

2. A ballast circuit for varying the output level of a fluorescent lamp energized by an alternating current source, said circuit comprising:

(a) a transformer having a first winding, and a high reactance secondary winding,

(b) means for connecting said first winding to the alternating current source,

(-c) an isolation transformer having a primary and a secondary winding,

(d) means for connecting said high reactance secondbetween the lamp and the source,

(e) bilaterally conducting switch means connected to I said secondary winding whereby with said switch means in a closed condition said secondary winding is short circuited during successive half cycles of applied voltage and said lamp operates at a higher level, and with said switch means in an open condition, said lamp operates at a lower level.

3. A ballast circuit for varying the output level of a hot cathode fluorescent lamp energized by an alternating current source, said circuit comprising:

(a) a transformer having a first winding, a high reactance secondary winding, and additional secondary windings,

(b) means for connecting said first winding to the alternating current source,

(c) means for connecting each of said additional secondary windings to heat one of the cathodes of the lamp,

(d) an isolation transformer having a primary and a secondary winding,

(e) means for connecting said high reactance secondary winding and said primary winding in series between the lamp and the source,

(f) a switch connected to said secondary winding whereby with said switch closed said secondary winding is short circuited during successive half cycles of applied voltage and said lamp operates at a higher level, and with said switch open, said lamp operates .at a lower level.

4. Arballast circuit useful for operating fluorescent lamps at two output levels from an alternating current source, said circuit comprising:

'(a) isolation transformers, each having a primary and a secondary winding,

(b) means for connecting each of said primary windings in series with one of the lamps,

(c) means for connecting all of said second-ary windings in parallel with each other,

(d) switch means connected in parallel with said secondary windings, whereby with said switch means in a closed condition said secondary windings are short-circuited and said lamps operate at a higher level, and with said switch means in an open condition, said lamps operate at a lower level.

5. A ballast circuit useful for operating fluorescent lamps at two output levels from an alternating current source, said circuit comprising:

(a) ballast reactors, and means for connecting each ballast reactor in series with one of the lamps,

(b) isolation transformers, each having a primary and a secondary winding,

(c) means for connecting each of said primary windings in series with one of the lamps, f

(d) means for connecting all of said secondary Win-dings connected in parallel with each other,

(e) switch means connected in parallel with said secondary windings, whereby with said switch means in a closed condition said secondary windings are short-circuited and said'lamps operate at .a higher level, and with said switch means in an open condition, said lamps operate at,a lower level.

6. A bal last'circuit useful for operating rhot cathode fluorescent lamps at two output levels from an alternating current source, said circuit comprising:

(a) a transformer having a first winding and several secondary windings, p

(-b) means for connecting said first Winding to the alternating current source,

(c) means for connecting one of said secondary windings to heat one of the cathodes in each of the lamps,

(d) means for connecting each of said other secondary 5 windings to heat the other cathode in one of the lamps,

(e) isolation transformers, each having a primary and a secondary winding,

(f) means for connecting each of said primary windings in series with one of the lamps,

(-g) means for connecting all of said secondary windings in parallel with each other,

(h) a switch connected in parallel with said secondary windings, whereby with said switch closed said secondary windings are short-circuited and said lamps operate at a higher level, and with said switch open, said lamps operate at a lower level.

7. A ballast circuit useful for operating hot cathode fluorescent lamps at two output levels from an alternating current source, said circuit comprising:

(e) ballast reactors, and means for connecting each ballast reactor with one of the lamps,

(f) isolation transformers, each having a primary and a secondary winding,

(-g) means for connecting each of said primary windings in series with one of the lamps,

(h) means for connecting all of said secondary windings in parallel with each other,

(i) a switch connected in parallel with said secondary windings, whereby with said switch closed said secondary windings are short-circuited and said lamps operate at a higher level, and with said switch open, said lamps operate at a lower level.

References Cited UNITED STATES PATENTS 1,926,423 9/1933 Barclay 315-255 2,665,394 1/1954 Arvidsson et al. 315-97 2,774,917 12/1956 Passmore 315-97 2,961,579 1-1/1960 Roney et al. 315-170 3,070,743 12/1962 Harper 323-86 X 3,182,249 5/1965 Pahlavan 323-50 X JAMES W. LAWRENCE, Primary Examiner.

C. R. CAMPBELL, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,333,150 July 25, 1967 Franklin P. Eppert It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below Column 6, line 2, after "reactor" insert in series Signed and sealed this 24th day of September 1968.

(SEAL) Attest:

EDWARD J. BRENNER Edward M. Fletcher, Jr.

Commissioner of Patents Attesting Officer

Claims

1. A BALLAST CIRCUIT FOR VARYING THE OUTPUT LEVEL OF A HOT CATHODE FLUORESCENT LAMP ENERGIZED BY AN ALTERNATING CURRENT SOURCE, SAID CIRCUIT COMPRISING: (A) A FIRST TRANSFORMER HAVING A PRIMARY WINDING AND A PLURALITY OF SECONDARY WINDINGS, (B) A CAPACITOR CONNECTED TO SAID TRANSFORMER FOR CORRECTING THE POWER FACTOR OF SAID CIRCUIT, (C) MEANS FOR CONNECTING SAID SECONDARY WINDINGS TO HEAT THE CATHODES OF THE LAMP, (D) AN ISOLATION TRANSFORMER HAVING A PRIMARY AND A SECONDARY WINDING, (E) A REACTOR FOR LIMITING CURRENT TO THE LAMP DURING OPERATION, (F) MEANS FOR CONNECTING SAID ISOLATION TRANSFORMER PRIMARY WINDING AND SAID CURRENT LIMITING REACTOR IN SERIES BETWEEN THE LAMP AND THE SOURCE,