US2821661A

US2821661A - Apparatuses and circuits for dimming gaseous discharge devices

Info

Publication number: US2821661A
Application number: US435170A
Authority: US
Inventors: Arthur L Bastian
Original assignee: Ward Leonard Electric Co
Current assignee: Ward Leonard Electric Co
Priority date: 1954-06-08
Filing date: 1954-06-08
Publication date: 1958-01-28
Anticipated expiration: 1975-01-28

Description

Jan. 28, 1958- A. BASTIAN 2,

APPARATUSES AND CIRCUITS FOR DIMMING GASEOUS DISCHARGE DEVICES Filed June 8, 1954 :57 4 I) INVENTOR.

l'Jnited States Patent Oflice APPARATUSES AND CIRCUITS FOR DIMMING GASEOUS DISCHARGE DEVICES Arthur L. Bastian, Yonkers, N. Y., assignor to Ward Leonard Electric Company, a corporation of New York Application June 8, 1954, Serial No. 435,170 12 Claims. (Cl. 315-98) This invention relates to electrical circuits operating gaseous discharge devices such as fluorescent lamps and particularly to circuits for adjusting the intensity of illumination of the lamp.

Electrical discharge lamps, such as fluorescent lamps, contain ionizable gas which presents a high impedance when the gases are substantially un-ionized and a low impedance when the gases are ionized. A high voltage is required across the electrodes of the lamp to cause the gases to ionize. Once .the gases have ionized the voltage required to force the electrons through the gas is substantially lowered and as the current increases the impedance of the tube generally decreases since with more current more ions are formed and the conductivity of the tube increases. The current is limited by the external circuit. The intensity of the illumination of the phosphoric coating is dependent of the energy impressed on the electrodes since the voltage of the lamp across the lamp electrodes is substantially constant during ionization. The intensity of illumination is controlled by the amount of current supplied to the lamp. As the current decreases the intensity of illumination decreases and as the current increases the intensity of illumination increases. The difliculty encountered in operating a lamp at low intensities with conventional ballasts is that it becomes unstable and will deionize and the arc becomes extinguished. In reducing the current supplied to the lamp the intensity of illumination is slowly reduced but before there is a substantial reduction in brilliance of the lamp the arc is extinguished. Correlative with this is that the lamp cannot be started at the low intensity levels.

The circuits controlling such lamps should provide a high voltage to force current through the high impedance and provide a means to limit the current through the lamp in view of the aforementioned negative impedance characteristic of the lamp.

ln changing the intensity of illumination of fluorescent lamps it is desirable that the illumination may be smoothly and evenly changed from full brilliance to dim-out and from dim-out to full brilliance without any intermediate conditions of instability or a reversal of change of illumination. The change should be continuous and uniform throughout the entire range of illumination. It is also desirable that at lower illumination the lamp remains lit and does not abruptly extinguish itself. Another requirement is that the lamp can be instantaneously started at any degree of illumination. A further desirable requirement is to limit the voltages in the circuit and lamp fixtures to safe values so as to prevent undue hazard from electrical shock.

The present invention is applicable to the conventional fluorescent lamp having a cylindrical glass envelope with a phosphor or fluorescent coating along the entire length of the inner surface of the envelope and with heated coated cathodes at each end of the glass envelope. The ends of the envelope are sealed. The envelope contains a gaseous atmosphere comprising a rare gas, such as argon, at a pressure of a few millimeters of mercury and a small quantity of mercury which during the operation of the lamp has a low pressure in the order of 6 to 10 microns of mercury. On ionization of the argon and mercury by the application of a voltage across the heated electrodes the fluorescent coating is excited to emit light by the radiation from the are through the ionized gases.

An object of this invention is to provide a circuit to vary the intensity of illumination of fluorescent lamps.

Another object of the invention is to provide a circuit to vary the intensity of illumination of fluorescent lamps smoothly and evenly without discontinuity over the range of illumination.

Another object of the invention is to provide a circuit for controlling the illumination of fluorescent lamps that comprises a minimum of components.

Another object of the invention is to provide a circuit for controlling illumination of fluorescent lamps that is inexpensive and reliable under all conditions of operation.

Another object of the invention is to provide a circuit and apparatus that varies the intensity of illumination and also starts the fluorescent lamp and limits the arc current therethrough.

A further object of the invention is to provide a circuit for controlling the intensity of illumination of fluorescent lamps that will start the lamp at all degrees of illumination and under all conditions of operation.

A still further object is to provide a circuit operating at voltages safe from the hazard of electrical shock that adjust the intensity of illumination of the lamp.

Other and further objects will appear from the following specification taken in connection with the accompanying drawings in which:

Fig. 1 shows a circuit diagram illustrating the invention.

Fig. 2 illustrates a modification of the ballast.

The fluorescent lamp 10 has a sealed cylindrical glass envelope with a fluorescent or phosphor coating 12, such as a zinc beryllium silicate and magnesium tungstate mixture, on the inner surface of the envelope. The coating radiates light in a visible spectrum on energization by the radiation from the ionized gas contained within the sealed envelope. The gas may comprise a rare gas, such as argon, at a pressure of about 3.5 mm. of mercury, and a small quantity of mercury at a low pressure of the order of 6 to 10 microns. Filaments or

electrodes

13 and 14 positioned inside of and at a respective end of the glass envelope lit and may be of the oxide coated type, preferably in the form of coiled tungsten wire activity with alkaline earth metal oxides. In the case of a 48-inch fluorescent lamp the application of a voltage in the order of 300 to 400 volts across the

electrodes

13, 14 ionized the gases and a current is conducted between the electrodes energizing the gas and causing it to radiate. The radiation of the gas in turn excites the fluorescent coating which radiates visible light. As an example of a given lamp when it is conducting, the voltages across the lamp has a range of to volts and the current through the lamp has a range from .0005 to .5 ampere.

The fluorescent lamp is supplied with an alternating current and voltage through autotransformer 15 from terminals 17, 18 connected to a suitable alternating current supply. The current passes through a path provided by the conducting wire 19 connected to the electrode 14 through the lamp and from the electrode 13 through the conducting wire 20 through the coil 21 and Wire 22 to the slider 44 of the transformer 15. The coil 23 is connected to the autotransformer 15 by the

lines

19 and 24. The coil 23 is wound on a magnetic core 26 which comprises legs 27, 28 and 29. The coil 23 is Wound on leg 27 and on passage of current through the coil 23 provides flux passing through legs 28 and 29. The core 26 consists of a laminated ferro-mag- Patented Jan. 28, 1953 netic metal. The leg 28 has an air gap and the leg 29 has small cross-section with high permeability at low flux values so that on application of a sinusoidal flux to the legs the leg 29 carries the initial fluxes which saturate the leg and that the remaining flux is carried by the leg 23. The constricted leg 29 has a higher permeability than the leg 28 with an air gap 30 at the low values of flux created by the coil 23 and becomes saturated at these low fluxes. Thus during the small portion of the periodic flux cycle generated by coil 23 the greater portion of the flux passes through the constricted path of leg 29. During the larger and longer portion of the periodic flux cycle generated by coil 23 during which the instantaneous flux value is relatively low the greater portion of the flux passes through the path provided by the leg 28 with the gap 30. The constricted path provided by the leg 29 is magnetically saturated and therefore the additional flux must pass through the air gap 30. The leg 29 is magnetically separated from the core 31 so that the flux passing through leg 29 J is not shunted around coil 21 through the leg 34. The coil 21, conducting the arc current passing through the lamp 10, is Wound around leg 32 of the ferro-magnetic core 31 and the leg 29 of the ferromagnetic core 26. The flux created by the coil 21 passes through the

legs

32, 33, 34, 35. The elfect of the small amount of flux created by coil 23 passing through the constricted leg 29 and coupled with the coil 21 is to generate a peak voltage wave in coil 21. A sinusoidal alternating current supplied to the terminals 17, 18. The peaked voltage occurs at the maximum value of the voltage. A voltage peak occurs for each half cycle of all values of current passing through the lamp.

The peaked voltage is created very rapidly which provides it with a very steep slope. This'peaked voltage or high voltage pipexists for a very short duration of time and does not appreciably increase the R. M. S. value of the sinusoidal voltage. This peaked voltage preferably has a value of approximately 170 volts which is added to the amplitude of the voltage supplied through lines 19 and 20 with the sum appearing across lamp 10 under; starting conditions. The amplitude and the steep wave front of the peaked voltage is conducive to ionization of the gases in the lamp 10. The high rate of voltage change of the steep wave front is particularly conducive tov producing an instantaneous ionization of the gases. The peak voltage also declines at a very rapid rate after reaching the peak value so that there is relatively little energy in the voltage. Its function is to. provide a starting potential across the electrodes of the lamp 10. The peaks occur on each half of the sinusoidal voltage wave and are uniform in amplitude. When the lamp is conducting a high are current the waveform of the voltage across the lamp changes to a rather irregular. periodic wave and the sharp peak voltage is eliminated by virtue of regulation. As the arc current is reduced in value to lower the brilliance of the lamp the, impedance of the lamp increases with the decrease in ionization of the lamp. correspondingly the eifect ofregulation on. the peaking. is reduced and the peak voltage. produced in. the. coil 21 increases and is added to the, lowered voltage. across the lamp 10 and coil 21 thereby maintaining the are through thev lamp.

The

cores

26 and 31 are spaced from one another by non-magnetic members 47, 48 secured to the cores so that the legs 29;, 32 are provided with non-magnetic separation 38 to prevent the flux which passes through the. constricted leg' 29. and: threading coil 22 from having an, alternate path through the legs. 33, 34, of core' 31 and thus vitiating the elfect of inducing a peakvoltage in coil 21. The core 31 preferably comprises 1aminations of ferro-magnetic material.

The coil 21 serves two purposes. One purpose is as a current limiting means and the other purpose as a 4 starter means. As a current limiting means it functions as a reactor 01' ballast to create a voltage so that the voltage across the lamp 10 is a value in the range of to volts for conventional lamps. The other purpose is to create a starting voltage as described in detail hereinbefore.

The coil 23 is coupled with the windings 4%, 4-1 which supply the

electrodes

13 and 14, respectively, with a steady alternating current for heating the cathodes.

The transformer 15 has windings 42 and 43. The coil 23 is connected across the winding 43 by the

conductive wires

19 and 24 and is supplied from the winding 43 with a steady alternating current. The coil 21 and lamp 113 are connected in series across the winding 42 and the winding 43 through the slider 44. One end of the coil 21 is connected to the slider 44 slideably engaging the turns of the winding 42 and the other end of the coil 21 is connected to the winding 43 through the line 20, lamp 10 and line 19, so that when the slider is at the terminal A end of the winding 42 the full voltage across the terminals 17, 18 is applied across the coil 21 and the electrodes 13 14- of the lamp 10, and when the slider is at the terminal B end the voltage of the winding 43 is impressed across the coil 21, lamp 16. Thus the current supplied to the lamp 10 may be varied. The voltage across

electrodes

13, 14 remains generally constant and the voltage across the coil 21 changes in accordance with the current or the changes of the voltage between terminal C and the slider 22. With a 48-inch, 40 watt lamp as an example 230 volts are impressed across the terminals 17, 18. This voltage is apportioned across windings 42, 43 with winding 43 having a voltage of approximately 85 volts and the winding 43 has a voltage of volts. The voltage may be varied across the coil 21 and lamp 10 from 85 volts to 230 volts.

When the slider 44 is at the terminal A end the lamp 10 is at full brilliance. As the slider is moved toward the terminal B end the voltage across the coil 21 and lamp 10 is reduced and the current through the lamp 10 is correspondingly reduced. The energy that is sup plied to the arc is lessened and the radiation of the arc drops and therefore the fluorescent coating 12 does not receive suflicient radiation to hold it at full brilliance and the radiation correspondingly declines. Thus as the voltage is reduced the radiation supplied to the coating 12 is reduced and over-all illumination declines. Conversely, as the current is increased when the slider 4-4 is moved towards the terminal A end, more energy is supplied to the lamp and the radiation from the fluorescent coating correspondingly increases in intensity. At the lower intensities when the tube would normally blackout, the high voltage peak occurs across the

electrodes

13 and 14 to refire the arc and maintain the lamp illuminated. Even when the lamp is at its, lowest intensity the peak voltage is applied across the

electrodes

13, 14 to maintain the arc. Therefore the tube also starts at these low intensiies. The full range ofvoltage available across windings 42, 43 of the transformer 15 is not needed to dim the lamp. The portion between terminal A and terminal B is sufficient to reduce the lamp to a dim-out condition.

The core 31 may be modified by reducing the crosssection. of the flux path through one of the legs of the core. For example, the leg 34 may have an opening 46. Such a magnetic constriction modifies the impedance of the coil 21 and the core 31 with respect to the current level. The size and shape of the hole or constriction can be varied and the net effect is to alter the normal impedance or B--H curve of the combination of coil and core. The transformer 15 illustrates a typical source of fixed and variable alternating voltage for the control system. Other types of variable and fixed A. C. supplies may be used with appropriate phase. relationships. A single autotransformer 15 may control a plurality of fluorescent lamps, the number of lamps depending upon the rating of the autotransformer utilized.

The

lines

50, 51, 52 may be extended to connect to other lamps and ballasts such as the ballast shown in Fig. 1. Each lamp has a ballast similar to the one in Fig. 1 and is similarly connected.

It is thus seen from the above description that there are many advantages in the invention. It is capable of starting at any point or degree of illumination. The starting circuit is built into the ballast limiting the current through the lamp and does not have any movable elements that require replacement. Smooth dimming can be obtained over a wide range of lamp intensities without the necessity of extensive and complicated equipment. The only additional piece of equipment required is an adjustable transformer.

Small condensers 47 and 48 are connected across the

electrodes

13, 14 and the coil 21, respectively, for the purpose of suppressing radio interference and reduce striations in the luminous column of the fluorescent lamp.

Although the invention has been described as varying the intensity of illumination of a particular fluorescent lamp, it may also be adapted to vary the radiation of similar gaseous discharge lamps such as ultraviolet lamps and other types of fluorescent lamps.

Various other modifications and changes may be made without departing from the scope of the invention as set forth in the appended claims.

I claim:

1. Apparatus for starting a gaseous discharge lamp comprising electromagnetic means adapted to be connected in series with a gaseous discharge lamp to limit the arc current therethrough and electromagnetic means for producing high voltage pips of short duration in said first means for starting a gaseous discharge lamp.

2. Apparatus for adjusting the intensity of illumination of a gaseous discharge lamp comprising means adapted to be connected in series with a gaseous discharge lamp to limit the arc current therethrough, means coupled with said first means for producing high voltage pips of short duration in said first means for starting a gaseous discharge lamp, and voltage adjusting means for connection across said first means and a gaseous discharge lamp to vary the potential thereacross for dimming the lamp.

3. A circuit for adjusting the intensity of illumination of a fluorescent gaseous discharge lamp comprising a gaseous discharge lamp, a ballast in series with said lamp, means for forming high voltage pips of short duration in said ballast for igniting said lamp and means for supplying a voltage adjustable over a range connected across said ballast and said lamp to vary the intensity of illumination of said lamp. v

4. A laminated ferromagnetic core with a portion having a high permeability at low flux values and saturating at higher flux values, means for supplying an alternating flux to said core, a second ferromagnetic core having a winding around said second core and said portion to couple said flux of said portion with said coil to produce high voltage pips of short duration in said winding on creation of an alternating flux in said first core.

5. A starting ballast for a gaseous discharge lamp comprising a laminated ferromagnetic core having a constricted leg, a second leg having a permeability lower than said first leg at low flux values and a third leg, a first coil wound around said third legfor providing electromagnetic flux to said constricted leg to saturate said leg at low flux values, a second laminated ferromagnetic core magnetically separated from said constricted leg, a second coil wound around said second core and said constricted leg to provide an impedance limiting current therethrough and creating high voltage pips of short duration across the output of said second coil.

6. Apparatus for starting a gaseous discharge lamp and adjusting the intensity of illumination comprising a laminated ferromagnetic core having a constricted leg, a

second leg having a permeability lower than said first leg at low flux values and a third leg, a first coil wound around said third leg for providing electromagnetic flux to said constricted leg at low flux values, a second laminated ferromagnetic'core spaced from said constricted leg, a second coil for connection in series with a gaseous discharge lamp and wound around said second core and said constricted leg to provide an impedance for limiting the arc current through a gaseous discharge lamp and creating high voltage pips of short duration for starting a gaseous discharge lamp and a variable transformer for connection across a gaseous discharge lamp and said second coil in series for varying the potential thereacross.

7. Apparatus as claimed in'claim 6 wherein said second core has a leg with a constriction therein.

8. Apparatus for-starting a gaseous discharge lamp comprising means adapted to be connected in series with a gaseous discharge lamp to limit the arc current therethrough and means having a separate electromagnetic iron core spaced from said first means, said first means coupled with magnetic flux through said means for producing high voltage pips of short duration in said first means and for starting a gaseous discharge lamp.

9. Apparatus for starting and maintaining the ionization of a gaseous discharge lamp over a range of voltages applied for controlling the intensity of illumination of the lamp and comprising a reactor core and a winding around said core for passing current to a gaseous discharge lamp and having an impedance limiting the maximum current passing through the Winding, reactor means having a first flux path of high permeability and a second flux path of a reluctance higher than the first flux path and a higher flux capacity, means for supplying flux to said paths, said first flux path passing through said first Winding and magnetically separate from said reactor core, said first flux path having a low flux capacity and rapidly saturating to create a high voltage pip of short duration additively superimposed on the alternating current across a discharge lamp to start and maintain the ionization of a gaseous discharge lamp.

10. Apparatus for starting and maintaining the ionization of a gaseous discharge lamp over a range of voltages applied for controlling the illumination of the lamp and comprising reactor means having a winding adapted to be connected in series with a gaseous discharge lamp to limit the maximum alternating current therethrough, a second reactor means having a high permeability and a low flux capacity fiuX path and a second flux path having a higher flux capacity and a higher reluctance than said first path, a winding coupled to both of said paths and creating a flux therein, said first path coupled through the winding of said reactor means to produce high voltage pips of short duration in said reactor winding and said second means passing the remainder of the flux of said second winding, the alternating voltage applied to I said first winding and said voltage pip being in timed relation so that said voltage pip is additively superimposed on each half cycle of the voltage across the lamp to produce a total voltage suificient to ionize a gaseous discharge lamp.

11. Apparatus for starting and maintaining the ionization of a gaseous discharge lamp and comprising a ferromagnetic core and a winding forming a reactor for having an impedance limiting the current supplied to a gaseous discharge lamp, a second ferromagnetic means having one flux path of a high permeability and low flux capacity, and a second parallel flux path having a higher reluctance and a higher flux capacity than said first flux path, a

winding coupled to said first and second flux paths to provide flux thereto and said first flux path passing through said first winding to create a sharp voltage pip of short duration in said first winding in timed relation with the alternating voltage applied to said winding to superimpose said voltage pip of short duration on said applied voltage to create a voltage sufiicient to ionize a gaseous discharge lamp.

12. Apparatus for starting and maintaining the ionization of a gaseous discharge lamp and comprising a reactor core and a Winding around said core for passing alternating current to a gaseous discharge lamp and having an impedance that varies inversely to the current through the lamp and having a value limiting the maximum current passing through the Winding, reactor means having a first flux path of high permeability and low flux capacity and a second flux path of a reluctance higher than the first flux path and with a higher flux capacity, means for supplying flux to said paths to pass the flux through the first flux path, said first flux path passing through said first Winding and magnetically spaced from said ferromagnetic core to create a voltage of short duration additive to each half cycle of the alternating voltage across a gaseous discharge lamp and increasing in value as the current through said Winding decreases so that the total voltage is sufficient to ionize the discharge lamp.

References Cited in the file of this patent UNITED STATES PATENTS 1,835,209 Dowling Dec. 8, 1931 2,298,589 Reitherrnan et a1. Oct. 13, 1942 2,598,617 Stirnler May 27, 1952 2,650,326 Williams Aug. 25, 1953 2,665,394 Arvidsson et a1. Jan. 5, 1954 U. S. DEPARTMENT OF COMMERCE PATENT OFFICE CERTIFICATE OF CORRECTION Patent Non 2,821,661 January 28, 1958 Arthur Lo Bastian It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

(301mm 1, line 31, for "dependent of" read dependent on line 57.5, for "reversal of" read reversal or column 2, line 44, for "13 and 14" read 13 and 14 are w line 47, for -"activity" read activated line 56, for' hazs a range" read have a range column 3, line 5, for

"and that the read and the column 4, line 22, for "electrodes l3 14" read

electrodes

13, 14 column 5, line 46, strike out "fluorescent" Signed and sealed this 18th day of March 1958.,

(SEAL) Atteet:

KARL Ho AXLINE ROBERT C. WATSON Atteeting Officer Cunnissioner of Patents 1 U. S. DEPARTMENT OF COMMERCE PATENT OFFICE CERTIFICATE OF CORRECTION Patent Noo 2,821,661 January 28, 1958 Arthur L,, Bastian It is hereby certified that error appears. in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1, line 31, for "dependent of" read dependent on line 5.5, for "reversal of" read 1- reversal or column 2, line 44, for "13 and 14" read l3 and lAYare line 47, for "activity" read activated =5 line 56, for fihas a range" read have a range column 3, line 5 for "and that the read and the column 4, line 22, for "electrodes l3 14" read me electrodes l3, 14 as; column 5, line 46, strike out "f.l1.1orescent Signed and sealed this 18th day of March 1958,

(SEAL) Attest:

KARL AXLINE ROBERT c. WATSON Atteeting Officer Commissioner of Patents