CA1156302A - System for energizing and dimming gas discharge lamps - Google Patents

System for energizing and dimming gas discharge lamps

Info

Publication number
CA1156302A
CA1156302A CA000341249A CA341249A CA1156302A CA 1156302 A CA1156302 A CA 1156302A CA 000341249 A CA000341249 A CA 000341249A CA 341249 A CA341249 A CA 341249A CA 1156302 A CA1156302 A CA 1156302A
Authority
CA
Canada
Prior art keywords
output
lamps
circuit
capacitor
high frequency
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired
Application number
CA000341249A
Other languages
French (fr)
Inventor
Joel S. Spira
Dennis Capewell
David G. Luchaco
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Lutron Electronics Co Inc
Original Assignee
Lutron Electronics Co Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from US05/966,601 external-priority patent/US4207497A/en
Priority claimed from US05/966,604 external-priority patent/US4207498A/en
Priority claimed from US05/966,643 external-priority patent/US4210846A/en
Application filed by Lutron Electronics Co Inc filed Critical Lutron Electronics Co Inc
Application granted granted Critical
Publication of CA1156302A publication Critical patent/CA1156302A/en
Expired legal-status Critical Current

Links

Classifications

    • HELECTRICITY
    • H05ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05BELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B41/00Circuit arrangements or apparatus for igniting or operating discharge lamps
    • H05B41/14Circuit arrangements
    • H05B41/36Controlling
    • H05B41/38Controlling the intensity of light
    • H05B41/39Controlling the intensity of light continuously
    • H05B41/392Controlling the intensity of light continuously using semiconductor devices, e.g. thyristor
    • H05B41/3921Controlling the intensity of light continuously using semiconductor devices, e.g. thyristor with possibility of light intensity variations

Abstract

ABSTRACT OF THE DISCLOSURE

An illumination control system for gas discharge lamps which can be dimmed is provided in which a central inverter produces an output voltage at a high frequency which can be about 23 kHz. The amplitude of the inverter output is adjustable to dim the lamps. A
transmission line consisting of spaced wires having respective thick insulation sheaths distributes the high frequency power to remotely located assemblies of ballasts and lamps. The ballasts consist of passive linear components. A high power factor rectifier network is disclosed for providing a d-c input to the inverter from the 50/60 Hz mains.

Description

SYSTEM FOR ENERGI~ING AND DIMMING GAS
DISCHARGE LAMPS

BACKGROUND OF THE INVENTION

This invention relates to the energization of gas discharge lamps, and more specifically relates to novel energy conservation circuits for eneTgizing and controlling the illumination output of gas-filled lamps and high intensity discharge lamps.
To conser~e energy in lighting applications using gas discharge lamps, it is known that the lamps should be energized from a relatively high frequency source, and that the lamps should be dimmed if their output light is greater than needed under a given situation. For fluorescent lamps, the use of a fre-quency of about 20 kHz-will reduce energy consumption by more than about 20~, as compared to energization at 60 Hz. For high intensity discharge lamps, such as those using mercury vaporj metal halide and sodium, the saving in energy exis~s ~ut is somewhat less than for a fluorescent lamp. Numerous publications deal with the desirability of high frequency energization of gas discharge lamps, inciuding, for example:

: -.,.. :.. .

Federal Construction Council, High-Frequency Lighting, Technical Report No. 53, National Academy of Sciences Publication No. 1610, 1968, p. 6-30;
Campbell, J.H., New Parameters for High Frequency Lighting Systems. Illuminating Engineering, V. 55, May 1960, p. 247-254; discussion, p. 254-256;
Campbell, J. H., Schultz, H.E., and Schlick, J. A., A New 3000-Cycle Fluorescent-Lighting System.
IEEE Transactions on Industry and ~eneral Applications, Vol. IGA-l, Jan.-Feb. 1965, p. 19-24;
Campbell, J. H. Schultz, H. E. and Schlick, J. A., Characteristics of a New 300Q-CPS System for Industrial and Commercial Use. Illuminating Engineering, ~. 60, March 1965, p. 148-152;
Dobras, Q. D., ~tatus of High Frequency Lighting. General Electric Architects and Engineers Conference, April 1963, p. 17-24;
Northern Illinois ~as Company, High Frequency Lighting at our General Office, June 1970; and Wolfframm, B. M., Solid State Ballasting of Fluorescent and Mercury Lamps. IEEE Conference Record of 4th Annual Meeting of the Industry ~ General Applications Group, October 12-16, 1969, p. 381-386.
Energy saved by dimming gas discharge lamps depends on the degree of dimming which is permitted in a gi~en situation. The iight output of a lamp is roughly proportional to the power expended. Thus, at 50%
; light output, only about ~Q% of the full rated power is expended.
Many applications exist where it is accept-~ able or desirable to decrease the amount of light from ¦ a lamp. For example, light in a building might be decreased uniformly or locally in the presence of ~unlight coming through a window to maintain a constant ~1¦ 35 or acceptable illumination a~ a work surface. Thus, during 8 normal work day, an energy saving of about 50g may be experienced. Light might also be decreased . .' ,' during non-working hours and maintained at a low level for security purposes. Light output might also be decreased, either from local controls or from signals from a generating station during periods of overload on the utility lines.
Energy savings may also be obtained by dimming lamp output when the lamps are new and have a light output much higher at a given input power than at the end of their life. Since a lighted area must be properly illuminated at the end of lamp life, energy can be saved by dimming the lamps when they are new, and then reducing the dimming as the lamps age. Energy saYings of 15% for fluorescent lamps and 2Q% to 3Q~ for high intensity discharge lamps can be obtained in this fashion.
One system used at the present time to obtain the benefits of high frequency energization of gas discharge lamps distributes power at low frequency C60 Hz~ to each of the fixtures of a lighting system. Each fixture could commonly contain several lamps in parallel or series connection. Each fixture is also provided with an inverter to produce the high frequency energiz-ing power and contains the necessary ballast circuits for the lamp. Circuits used in the individual fixture for the above type circuit are typically shown in United States Patents 3,422,309, 3,61~,~16; 3,731,142;
25 and 3,824,428, each in the names o Spira and Licata;
and 3,919,592 in the name of Gray, each of which is assigned to the assignee of the present invention.
i Systems of this type are aYailable from the Lutron Electronics Co., Inc. of Coopersburg, Pennsylvania under the trademark Hi-Lume.
While the above arrangement performs well, a complete inverter circuit and controls therefor must be placed in each fixture. Thus, the system is costly and the reliabilit~ problem is repeated for each fixture.
Since esch fîxture receives the co~plete inverter " --circui~, designers and users are hesitant to use complex and expensive circuits and control schemes because of cost and reliability. Furthermore, each circuit exists in the relatively hot environment of the lamp fixture. The scheme also requires that four leads go to each fixture; two for power and two for the dimming signal. A further problem is that it is difficult to proYide a good 5Q Hz to ~Q Hz power factor in each fixture since the power factor correction devices are bulky and expensive.
In another known system, a single source of high frequency is used and provides energy for a rela-tively short distance over relati~ely short power lines. Dimming is obtained by changing the inverter frequency to a capacitiYe ballast. An arrangement of this kind is shown in the publication Federal Con-struction Council, High-Frequency Lighting, Washington, D.C.; National Academy of Sciences, 1~68, referred to above.
This arrangement has several disadYantages.
First it provides relatively poor dimming. The lamps used in the system require separate filament trans-formers since, if high frequency is used to power the filaments, it is difficult to keep the filamen~ vol~age constant with variable frequency. The separate fila-ment transformers are costly and further complicate thesystem. It is also difficult to change the inverter frequency and requires costly and complex controls. A
further problem of these systems is that the load on the in~erter îs capacitive so that the high frequency power factor is poor. Thus, excessiYe current flows in the wires between the in~erter and ballast, creating additional energy loss.
Other arrangements are known in which 50 Hz to ~0 Hz power is supplied from a local source directly to the lamps and theîr ballasts, and dimming is obtained by changing the current amplitude through the use of an auto-transformer or thyristor control circuit. While .

.

t 156302 this system obviously does not have the advantage of high frequency excitation for the lamps, it is also true that bulky components are needed in this fixture and a good 50/60 Hz power factor is hard to obtain.

In accordance with the present invention, a novel arrangement is provided wherein a central high frequency inverter is provided to energize a plurality of remote ballasts and associated gas discharge lamps with an a-c output wave form which may or may not be symmetrical. Circuits of any desired sophistication are provided for control of the central inverter and dimming is obtained by varying the amplitude of the in~erter output. The connection from the in~erter to the ballasts and lamps and remote fixtures is preferably by a novel low-loss transmission line consisting of a pair of spaced conductors which are each insulated by a very thick insulating sheath which minimizes their capacitive coupling to one another and to the grounded Z0 conduit in which they are located. It also minimizes magnetic field coupling to an iron or ferrous material conduit, and thus the iron losses in the conduit.
Moreover, the structure permits use of a ferrous metal ', conduit. Furthermore, magnetic coupling proximity 1 25 effect losses are minimized by the no~el heavily ¦ insulated transmission line.
The ballasts used with the lamps are those ' which preferably use passive and linear components, but ! they could be active and/or non-linea~. A passive ¦ 30 ballast is defined herein as one using only resistors, ¦ inductors, transformers and capacitors. An active ballast is one using amplifier components such as transistors, thyristors, magnetic ampli~iers, and the li~e. A linear component is one having a ~airly linear relationship between input and output.

' .
, 11~6302 The output current wave shape of the inverter of the invention is preferably sinusoidal but, in general, it is a substantially continuous periodic wave form. By a substantially continuous periodic wave form is meant a wave form which has an alternating component and may or may not have a d-c component. By substantially continuous wave form is also meant one ~hich has no significant interYal of "zero" curTent during each cycle of the high frequency output, as is present in some pulsed sources or in a phase controlled thyristor circult. However, a continuous wave form shall include wave forms such as sinusoids; triangular wave forms; square or rectangular wave forms, each with or without d-c components. The output amplitude of the inverter may be controlled by:
(a~ Phase control;
(b~ Pulse width modulation with a filtering ballast; or ~ cl D-c input voltage.
In each of the above, there will always be con-ti~nuously flowing current. By pulse width modulator aboveis meant fixed frequency and variable pulse width or fixed pulse width and variable frequency, or combinations thereof.
In order to maintain a high power factor, the recti~ier network used i~n converting the frequency at the mains (5Q Hz to ~Q Hz~ to a d-c input or the high frequency inverter has a novel structure. Moreover, the ballast circuits used in the f~xtures have a novel configuration.
Pinally, while any deslred high frequency inverter circuit 3~ can be used, a novel preferred inverter to be described is particularly use~ul with this ;nven~ion.

With the in~erter of this invention, the use of the single inverter permits it to be designed with many features with high reliability at low cost. Thus, all complexIty is confined to a single unit rather than being repeated over many fixtures. The single inverter can be located to enjoy full air circulation and may be easily cooled. When dimming with a single inverter, all lamps track in intensity. Since dimming is obtained by inverter output amplitude control, simple, low cost and highly reliable equipment can be used in the fixture. Thus, the fixture for lamp and ballast has only a small number of small, low loss, highly reliable capacitive and inductive and transormer components.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a block diagram showing the essential components o the present invention.
Figure 2 is a cross-sectional view of a pre-ferred transmission line for connecting the output of the in~erter to the ballasts and lamps in Figure 1.
Figure 3 is a circuit diagram of a preferred inverter which can be used in the diagram of Figure 1.
Figure 4 is a circuit diagram of a ballast and lamp structure wh~ch can be used in the block diagram o~ Pigure 1.
Pigure 5 is a circuit diagram o a power supply rectifier which can be used with the present invention.
~igure 6 is a block diagram of a novel inverter circui~t arrangement which can be used in the present invention.

-DETAILED DESCRIPTION OF THE DRAWINGS

Referring first to Figure 1, there is shown a relatively low frequenc~ (for example, from 25 to 60 Hz) source 20 which is connected to a rectifier network 21 which produces rectified output power for a single central inverter 22. Source 20 and network 21 can be replaced by any appropriate d-c supply or can be driven from the d-c battery of an emergency battery which is charged or energized from a power line. In addition, although the use of a d-c supply powering an inverteT
is most suitable, it is also possible to use a frequency converter in a manner similar to that shown in U.S.
Patent 3,731,142 dated May 1, 1973, in the names of 30el Spira and Joseph Licata where, for example, a-c voltage or an unfiltered rectified d-c voltage is fed directly to a frequency con~erter. RectifieT network 21 may be of the type shown in Figure 5 which will be later described, and which has high power factor characteristics. Inverter 22 will be later described in connection with Figure 3 and produces a sinusoidal a-c output wave shape at a frequency of about 23 kHz.
. The output of inverter 22 is preferably higher than about 20 kHz to be above the audio range, and can be as high as permitted by semiconductor switching losses, ~ 25 component losses, and the.like which increase with ¦ higher fre~uencies. Note that if the apparatus is installed in an area where audio noise is not important, ' the in~erter output need be h~gher than only about an ;~ order of magnitude greater than the input line fre-quency.
n inverter output amplitude control circuit 23 is connected t~ i~verter 22 and, under the influence ~ ~ of a signal from dimming sign~l cont~ol deYice 24, will .~ ~ ~ increase or ~educe the 'a.mpi~tude of the' wave shape o the high'fre~uency outp~t of~in~ertex' 22~ The control device 24 can be a ~BnuBl contrsl or can be derived .
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l 156302 from such devices as photocell controls, time clocks, and the like which apply some desired condition respon-sive and/or temporal responsive control to inverter 22.
The output of inverter 22 is then connected to two leads 30 and 31 of a transmission line which is particularly well adapted to distribute the high fre-quency power output of inverter 22 over relatively long distances with relatively low loss. By way of example, the lines 30 and 31 could have a length of about 100 feet, and could supply power to about twenty-five discrete spaced fixtures which each might contain two lamps. In this use, 1850 watts must be provided to the system with a power factor of about 0.9.
Note that this installation could consist of fifty 40-watt fluorescent lamps which require 2500 watts at 60 Hz. Only 1850 watts are needed at the higher frequency and with the novel system of the invention for the same ligh~ output.
Note further that only two wires are needed to carry power to lamp fixtures with the present inven-tion as contrasted to the need for four wires in fixtures which locally contain inverter circuits and are connected to easily transmitted low frequency (50/60 Hz) power.
Pigure 2 shows a preferred form of the novel transmission line of the invention for distribution of high frequency high power energy, as contrasted to well known arrangements for the distribution of high fre-quency, low power signalling voltages. In Pigure 2, `
lines 30 znd 31 are formed of respective central con-ductors 32 and 33, respectively, which each consist ofnineteen strands of copper wire having diamete~s of 0.014 inch. The outer diameter o the bundle of strands is about 0.070 inch. ~ach o~ conductors 32 and 33 are covered with dielectr~c sheaths 34 and 35, respectively, 3~ which may be o~ any suitable conYentional insulation.
Each of sheaths 34 and 3~ ha~e diameters of 0.235 inch and are preferably at least about three times the . , .
~;

llS6302 diameter of their respective central conductor. Strands 30 and 31 are then contained in a grounded steel con-duit 36 which may be a so-called 3l4 inch conduit which has an inner diameter of about 0.825 inch and an outside diameter of about 0.925 inch. The transmission lines 30 and 31 are confined in conduit 36 for a major portion of their lengths, as needed by the particular installa-tion.
Note that the dimensions given above are only typical and that other dimensions could be selected.
By using relatively thick insulation sheaths 34 and 35, the capacitive coupling and thus losses between con-ductors 32 and 33 and from the conductors 32 and 33 to conduit 36 are minimized. Thus the transmission line will have low loss qualities, even if it extends long distances. Note that any desired connection can be used if the distance from inverter 22 to its loads is short.
By using maximum thickness insulation sheaths 34 and 35 which can still be conveniently drawn th~ough conduit 36, the electric field intensity is reduced, thereby to reduce bulk loss resistivity. In the past, it was believed necessary to use a minimum dielectric thickness to minimize dielectric volume and thus di-electric loss. The present invention departs from this conventional approach in order to reduce the shunt capacitive losses between the wires and from the wires i to the conduit.
The relatively thick insulation sheaths 34 and 35 also minimize magnetic field losses incurred by coupling with the ferrous metal conduit. The lower magnetic loss is due to the greater distance of the conductoss 32 and 33 from the ferrous metal conduit.
Thb magnet'ic field raries inversely as the distance `; from a conductor. Ener:gy losses due to the presence of ' 35 fer'rous'~et'al in a magnetic 'field vary di~ectly as a ; ~ s~uare o the~magnetic~fiel'd;intensity. Therefore, it ~ ~s seen tha`t thes'e'losses vary inver'sely as the square ~J~
'., ' of the distance between the conductors and the ferrous metal conduit. This permits use of ferrous conduits, rather than aluminum or other non-ferrous materials.
Preferably, the characteristic impedance of the trans-mission line should be matched to that of the load toreduce the V~R loss and variation in voltage along the line.
The transmission line conductors 30 and 31 extend through a building or along a roadway, or the like, and are connected to one or more remote fixtures.
Two fixtures 40 and 41 are shown for illustration purposes, but any number can be used. Fixtures 40 and 41 each contain ballasts 42 and 43, respectively, and associated gas discharge lamps 44 and 45, respectively.
A typical ballast and lamp assembly will be later described in connection with Figure 4. Lamps 44 and 45 may be fluorescent OT high intensity gas discharge lamps or any other desired type of gas discharge lamp.
Ballasts 42 and 43 preferably use passive linear com-ponents such as reactors (of relatively small sizebecause of the relati~ely high frequency applied to the ballast) and capacitors which are reliable and inex-pensive. Note that in a prior high efficiency 60 H2 ballast, there was a ballast loss of about 12 watts in the fixture so that the ~ixture is quite hot. With the present invention, the ballast loss in the fixture is less than 1 watt. Thus the components in the ballast are not subject to high temperature.
In operation, high frequency power (abore 30 about 20 kHz) is trans~itted from inverter 22 over the I transmission lines 30-31 with relatively lo~ loss and ; is distributed to the plurality of remotely located and simple and reliable ballasts 42 and 43 and their asso-ciated lamps 44 and 45J reSPeCtiYe1Y.
In ~rder to dim the output of all the lamps 44 and 4~ in an identical manner, a signal from signal source 24 Cwhich can be a manual control, a clock control, a control from the electric utility to control utility loading, a sunlight intensity responsive control, or the like) causes the inverter output amplitude contTol circuit to reduce the output amplitude of the 5 a-c output of inverter 22. The light output of lamps 44 and 45 will then decrease roughly proportionally to the reduction in power from inverter 22.
Any desired inverter circuit having a variable a-c output can be used for the inverter 22. Pigure 3 shows a novel inverter circuit which can be used with the present invention. A circuit similar to that of Figure 3 is shown in the pulication An ~mproved Method of Resonant Current Puise Modulation for Power Converters, Francisc C. Schwarz, IEEE Transactions, Vol.
IEC 1-23, No. 2, May, 1976; and are also shown in U.S.
Patent 3,663,940 to Francisc Schwarz. That circuit, however, does not obtain variable amplitude adjustment with constant fre~uency as is the case of Figure 3.
In Figure 3, the d-c output of rectifier 21 is applied between-d-c positive bus 50 and the negative or ground bus 51 which are connected ac~oss series-connected, high speed thyristors 52 and 53. Thyristors 52 and 53 ha~e turn-on speeds of less than about 1 microsecond and turn-off speeds of about 2 to 3 micro-seconds. The junction between thysistors 52 and 53 isconnected to series-connected capacitor 54, inductor 55, the primary winding 56 of a step-up transformer 57 and the ground bus 51. Trans$ormer 57 has a high voltage secondary winding 58 which delivers a high frequency sinusoidal output voltage of about 2S5 volts a-c for a d-c input voltage o about 320 volts.
Suitable bypass diodes 59 and 60 may be con-nected across thyristors 52 ~nd 53~ respectively. Ca-pacitoT 54 and inductor 55 have values chosen to be resonant-~t about~23 kHz. Thus, capacitos ~4 ~ay have a~Yalue of ~33 mic~ofarads and inductor 55 may have a value of about 130 microhenrys.
' ,..,..,, .. ~ ... ..

A~plitude control circuit 23 provides timed output gate pulses to thyristors 52 and 53 to control their operation, and these pulses are phase-controlled by the dimming signal.
In operation, and to start the inverter, consider that both thyristors 52 and 53 are off. A
gate pulse from control 23 first turns on thyristor 52 to create a current path through components 50, 52, 54, 55, 56 and 51. The gate pulse to thyristor 52 is removed after a few microseconds and when conduction o~
thyristor 52 is fully established. Since capacitor 54 and inductor 55 are resonant at about 23 kHz, the current in the above circuit goes through a half cycle at the resonant frequency and, when it comes close to zero, thyristor 52 is commutated off, and the current reverses and flows through the path 51, 56, 55, 54, 59 and 50.
At this point, a pulse from control 23 turns on thyristor 53 so that the resonant current (and energy stored in the resonant circuit) can now reverse and flow through the circuit including components 53, 56, 55 and 54 in a resonant half cycle. The triggering pulse from circuit 23 is removed after conduction is established in thyristor 53. Thus, when the current at the end of this negative half cycle approaches zero, the thyristor 53 is commutsted off and the current re~erses into the positive half cycle and flows through components 60, 54, 55 and 56. The next pulse from control Z3 turns on thyristor 52 as the resonant current swings into its positive half cycle to complete a full ; cycle of operation.
Obviously, a high output ~oltage is induced into output winding 58 during this operation which is subsequently applied to the transmission line consisting o~ conductoss 30:and 31.
Amplitude variation is obtained by delaying the application of the firing signal to thyristors 52 ~ , .

~ , ......

~ 14 .
and 53 and th~s varying the duty cy~le of the in~e~ter.
Thus, the conduction time of t~e th~ristors, during the half cycle, is reduced and less voltage ;s applied to the prlmary wind~ng 56. ~o~ever, the voltage to winding 56 is sinusoidal due to t~e resonsnce of capacitor 54 and in-ductor 55. Thus the voltage fed to ballasts 42 and 43 (Figure 1) is also sinusoîdal. Ampl~tude variation may be obtained by var;a61e delar of t~e firing signal to either or both thyristor switches.
As will be later described, the ballasts 42 and 43 are tuned to the output frequency of inverter 22. The sinusoidal wave form reduces inefficiency due to harmonics and also reduces production of electromagnetic inter-ference. However, as mentioned previously, non-sinusoidal wave forms can also be used with the invention.
Note that any desired inverter circuit and con-trol could be used in place of inverter 22 including arrange-ments for varying the voltage at bus SO; pulse width modulation techniques; transistorized circuits; and the use of a high frequency variable ratio transformer, or other circuits using similar controllably conductive devices.
While some aspects of the particular inverter circuit of Figure 3 are known, it was never previously used for gas discharge lamp control purposes. This is because in ordinary lamp applications, the lamps would go out if the voltage input is reduced. However, in the present in-vention, the lamps stay on and dim as input voltage amplitude is decreased because the lamps are operated at high freguency and are provided with a special and suit-1 30 able passiYe linear ballast.
i A novel ballast arrangement such as that shown ¦~ in Figure 4 is pro~ided for each of ballasts 42 and 43.
~j~ The ballast o~ Figure 4 is used for two series lamps 70 and 3-1~ 71 (equi~alent ~o lamps 44 in fixture 40 of Pigure 1), where lamps 70 and 71 are rapid-start fluorescent lamps which are ~'i véry suita61e for dimming. Other gas discharge lamps ! could have been used.
~s :i: :

, - 15 ~
The ~allast circui"t for th~ lam~s 7Q and 71 in-cludes capacitors 72 and 73, transformer 75 and inductor 76.
A winding tap 77 i~s connected to filament 78 of tu~e 70. A
wi`nding tap 79 i~s connected to fi~aments 8Q and 81 of tubes 70 and 71, respectively. A winding 82 is connected to fila-ment 83 of tube 71. Transformer 75 has a primary winding of about 235 turns. Taps 77 and 79 and ~inding 82 may be about 9.5 turns. A conventional thermally responsive switch 84 which opens, for example, at 105C is in series with capacitor 72.
The values of capacitors 72 and 73 and inductor ?6 are chosen to ~e resona~t at about 32 kHz while capacitor 72 and inductor 76 resonate close to about 12 kHz. Therefore, the reactive impedance of inductor 76 is greater than that of capacitor 72 at 23 kHz. By way of example, capacitor 72 is Q.033 microfarad; capacitor 73 is about 0.0047 micro-farad; and inductor 76 is about 5.1 millihenrys.
- An important feature of t~e ballasts of the inven-tion ~s that they only need to provide filament heater power.
- 20 Moreover, the ~allast inductors and capacitors can be con-tained in the same can or housing, thus contributing to small size and economy for the ballast. The use of a common housing also simplifies the installation of the ballast since it is not necessary to handle many separate parts.
The ballast circuit described above has the follo~ing desirable characteristics:
~ 1. It will not be damaged by accidental appli-¦ cation of 50 Hz to 60 Hz power.
2. The inverter 22 will not be shorted if any one ballast component fails. Thus, the short circuit can ¦ be located more easily sînce the lamps in unshorted fixtures are still on.
3. The circuit exhib~ts a good power factor to ~! the inverter 22 and transmission lines 30-31.
4. T~ere ls a relat~vely constant filament voltage ¦ over the dim~ing range to a~oid damage to lamps.
~- 5. T~e starting voltage is sufficiently high to strike the lamps under specified conditions but is , .. , . , , . . .. . . , . .. , .. . . ~ ... . ... .. . .

-not so high that the lamps can be damaged.
6. The ballast is small and efficient because the ballast transformer only handles the filament power of the lamps.
The operation of the circuit of Figure 4 is ~s follows: When a-c power is applied to lines 30 and 31, the 23 kHz power causes components 72, 73 and 76 to partially resonate at their resonant frequency of 32 kHz. The increase in current flow due to this par-tiai resonance causes the voltage on capacitor 73 to rise high enough to start lamps 20 and 21. The partial resonance is important since it affords suffi-cient but not excessive starting voltage which might damage lamps 70 and 71. Once lamp 71 starts, capacitor 73 is essentially shorted,so that capacitor 72 and inductor 76 are resonant below the inverter frequency.
During'operation, capacitor 72 blocks low frequency voltage of from 50 Hz to 60 Hz, if that vol-tage is accidentally applied to lines 30 and 31. Thus, accidental destruction of the ballast by low frequency power is prevented. Also, since impedance components including capacitors 72 and 73, transformer 75 and inductor 76 are connected in series, the failure of any one component will not appear as a short on the inverte~
22. Thus, all lamps of all fixtures are not extinguished and the faulty component can be easily located.
, Good power factor is ob,tained wit,h the circuit of Figure 4 by making the impedance of capacitor 72 close to that of inductor 76 a~ 23 kHz. `Since the ' reactive impedances of components'72 and 76 subtract, , the ~esultant is small compared,to the series resist'ance of lamps 70 and 71, Thus, the reactiVe component of the load is small so that good power factor is o~tained.
A relati~ely constant filament voltage for ' ' 3S ~i,1aments 78j 80, 81 and 83 is assured s~ce the ', primaTy winding of transo~mer' 75 is -connected ac~oss i lamp 70. The ~oltage drop across this lamp is rela-1 ~ ~

, .

tively constant even as the lamp is dimmed. Thus, the filament voltages remain approximately constant. Note, however, that as the amplitude of the input voltage from lines 30 and 31 is varied, the current in lamps 70 and 71 varies and the light output of the lamps varies.
The inductor 76, in addition to being a component of the power factor network, has a larger reactive impedance than capacitor 72, and thus acts as a ballasting impedance to limit current in lamps 70 and 71.
Although the arrangement of Figure 4 shows the invention in connection with fluorescent lamps, it should be understood that the invention can be applied to the energization and dimming o any gas discharge lamp. Indeed, the invention can be used to operate and dim incandescent lamps if desired to give a user of the circuit flexibility of application. If one or more incandescent lamps are used in place of lamps 70 and 71, the ballast circuit can, of course, be eliminated.
Lamps 70 and 71 in Figure 4 could be replaced by conventional high intensity discharge lamps, such as mercury ~apor, metal halide, and high and low pressure sodium lamps. These lamps do not have filaments and are relatively immune to damage from too high a striking 25 voltage. Thus, the ballast of Figure 4 can be modified to remove the transformer 75 and its filament heater windings when applied to a high.intensity discharge lamp.
The circuit of Figuse 4 can also be modified to place the inductor 76 across the lamp terminals in a well known.circuit arrangement. With the transformer . 7~ remo~ed, the capacitor 72 is designed to block 60 Hz power and to prevent shut-down of the system in case of ~a shorted co~ponent. Resonance is established between the inducto.r 76.and..the capacitors in series therewith near the d~iving freq-uency of the inverter 22. Thus, be`fore the ~.-I.D. lamp strikes,.the circuit has a high ., -.

~~

Q and a large voltage builds up across the lamp. This pro-vides sufficient voltage to strike the lamp arc~ and the lamp becomes a lower impedance, more nearly matched to the ballast. The ballast then regulates the lamp arc current as a function of the ballast input voltage.
Any suitable ballast circuit could be used with the H.I.D. lamp where, however, the ballast is subject to an energy-conserving dimming operation.
Figure 5 shows a rect~fier network circuit 21 ~hich can be used with the present invention, and which has the adYantage of haY~ng a high power factor so as not to place an unnecessarily high current drain on the 50~6~ ~z wiring leading to the rectifier network 21.
The circuit consists of a resonant circuit ~nclud~ng inductor ~0 and capacitor Ql connected be-tween the input low frequency a-c source and the single phase, bridge-connected rectifier 92. The d-c output of rectifier Q2 is then connected to an output capacitor ~3, which ma~ be an electrolytic capacitor, and to the positive bus 5Q and ground bus 51. The values of i~nductor 9Q and capacitor Qi are critical and are 30 millihen~s and 10 microfarads, respectiYely.
In opération, the LC circuit QQ-~l in front of rect~fier ~2 causes the current drawn from the S0/60 Hz in-put to flow for a longer time during each half cycle and tohave a better phase relationship with the ~oltage. The in-ductor QQ and capacitor Ql are resonant at a period of about one-fourth of the period of the input circuit frequency : .

~: . ... . . .. . . .. ... . . .. . . . .. . ... .
.,, . . . ~ .:

.

(usually 5~ Hz to 60 Hz). At one point in the cycle, the voltage on capacitor 93 exceeds the voltage on capacitor 91. This back-biases rectifier 92 so that line current will surge into capacitor 91 rather than cutting-off. The surging of current into capacitor 91 during reverse-biasing of rectifier 92 causes inductor 90 and capacitor 91 to resonate, thereby causing more uniform current flow from the a-c mains over each half -cycle, and thereby substantially improving power factor.
It is understood that the system shown herein can also be realized with inverter 22 as a multi-phase inverter such as a three-phase inverteT. In this case, the high frequency power will be distributed to ballasts and lamps by means of multi-conductor transmission line, lS e.g. three conductors for three-phase power. The ballasts and lamps would be connected conductor-to-conductor, or conductor to neutral, if a neutral is provided. Likewise, the low frequency 50/60 Hz supply 20 in Figure 1 can be a multi-phase supply, e.g. three phase.
An important feature of this invention is the use of a single central inverter transformer 57 to supply the proper starting voltage to the lamps. This feature improves the efficiency of the system. In the conven-tional system, a transformer is contained in each fixture to supply proper starting voltage. It is well known to transformer designers that for a given volt-ampere size, one large transformer is more efficient than a number of smaller transformers.
The inverter transformer 57 supplies the proper starting voltage and the transfo~mers 75 in the fixture ballasts ~Figure 4~ does not have to carry full lamp powes, but only carries filament power. ~11 lamp powe'r is sup~lied rom the single inverteT transformer 57 of Pigu~e 3 which'is more 'efficient than an aggregate of smaller transformer's for each'ballast and for the same total volt amper'es rating. Thus higher system ~ 2Q -efficiency is ~btained.
Furthermore, since the ballast transfoTmers 75 only carr~ filament power, the f~xture ~allasts are smaller, cooler, lig~ter, more e~ficient, less complex and thus more relia~le than ~allast transformers which must carry the full lamp power.
The ballast will generate appToximately an ordeT
of magnitude less heat t~an those in which lamp volt amperes must be ~andled by the ballast transformer.
Therefore the fixture temperature is considerably lower.
When fluorescent lamps are run at this resultant cooler temperature, their lig~t output for a given input power ~efficacy~ increases. This effect can save an approximate additional 5~ in power in a given system.
lS In addition to the gain in efficiency by the use of a central transformer 57, the heat produced by the lamp power volt-amperes is dissipated in the central inverter transformer 57 rather than in the individual fixtures.
The central inverter transformer 57 can be efficiently cooled since it ~ill be in a convenient and accessible location, and any desired cooling can be used.
One inverter or converter structure which generally follows the concepts of the arrangement shown in Figure 3 is shown in ~lock diagram form in Figure 6. In Figure 6 controls are provided for the circuit of Figure 3 which enable the circuit to be uniquely applicable to a variable power output type of system such as a lamp dimming system ~here the inverter is the central high frequency supply for a plurality of lamp loads which are connected to the supply over a transmission line or the like.
The inverter to be described in Figure 6 will satisfy the ollowing criteria:
The converter output will be a sine wave 3~ w~ich îs believed to ~e th~ ~est for the lowest trans-mission line loss.

.,;,. :

~156302 2. The output amplitude of the sine wave output of the converter is variable in ordeT to obtain dimmlng.
3. The inverter operates with high efficiency, thereby to save energy.
4. The output frequency of the inverter can be greater than about 20 kHz and above the audio range so that the converter will not generate annoying audible noise when used in an environment susceptible to an audio noise problem.
5. The converter can be reliably started up and turned of with the switching devices of the inverter being immediately operated in order to insure proper converter operation and to insure proper lamp striking.
6. The inverter sine wave output has low distortion even though there is a relatively large change in the load current due, for example, to dimming or a change in the number of lamps in the system which are conducting load current.
7, The conYerter is protected against fault load current and is turned o~f and requires an intentional operation by t~e user to turn it back on if a load fault is developed.
8. The converter is internally protected with automaticall~ reset means for temporarily turn~ng off the converter upon the occurrence of an internal converter fault and then automatically returning the converter to duty.
In Figure 6, input power at lines 50-51 are connected to the block 52-53 labeled CONYERTER POWER
SWITCHI~G ELEMENTS. These power switching elements could be the thyristor switching devices 52 and 53 of Pigure 3 ~and their associated diodes 5~ and 6Q, respectively) or could be anr other desired type of switching element including transistors and the like.

The circuit including switching elements 52 to 53 contains a converter fault detector circuit lO0 which is operable to produce an output signal in response to a fault within the converter. By way of example the fault detector lO0 could consist of a current transformer whose output winding is connected to a load resistor which produces a suitable output to a shut-down circuit system 103.
The main current carrying circuit next contains the sine wave filter 54-55 consisting of previously described components 54 and 55 and which insures that the sqllare wave input from the converter power swi~ching elements 52 and 53 is con~erted to a sine wave with low distortion. This is obtained because, at the fundamental frequency, the sum of the impedances of inductor 55 and of capacitor 54 is zero, so that the fundamental frequency of the square wave is unattenuated. However, the total impedance of the tuned circuit 54-55 is different from zero for other frequency components which form the input 2Q square wave and these frequency components are greatly attenuated. Consequently, a relatively low distortion sine wave output is produced by the converter circuit in view of the tuned circuit including capacitor 54 and inductor 55. Moreover, the fre~uency of this circuit is chosen aboYe the audible range and preferably is greater than 20 kHz so that both criterion 1 and 4 above are met.
The load circuit in Figure 6 is next connected through a phase-sensitive zero crossing detector circuit llQ which is operable to time the operation of a syn-3~ chronizing circuit 111. The phase-sensitive zero crossing detector can consist of any desired type of circuit. The circuit could consist of a saturable core transformer whi~ch is saturated during most of the positive and negative hal~ c~cles and is unsaturated only for a short time during each current zero interval. Thus, an output voltage pulse is produced on a secondary winding and ~ , ~
-.. , . ,, . , ~ , . . ... ..
~:`.

across a load resistor each time the main converter current passes through zero.
The main load current circuit also includes a load fault detector circuit 120 which may include a load current transformer having a secondary winding which has an output connected to a suitable shut-down circuit system 123.
The main load circuit next includes a load buffer network 130 which can consist of a-Yoltage transformer and a capacitor which tends to overpower large values of resistance which might appear due to a very light load, and preserves the sine wave configuration of the output.
Thus, in the circuit of Figure 3, which does not contain the abo~e-mentioned capacitor, if the load resistance becomes too large, the circuit becomes over-damped and the voltage across the load is no longer a sine wave and the resonance of members 54 and 55 ceases. The load buffer capacitor presents an added resonating component which is in parallel with the load and is used to preserYe criteria ~ listed above.
The block diagram of Figure 6 contains con-sIderable control circuitry which can ~e conYeniently constructed and adjusted for use with a single central inverter and which would be Yery expensive to reproduce at each fixture of a fluorescent lamp system. Thus, the circuit of Figure 6 includes a variable amplitude control circuit 14Q) whic~ receives an input from the synchronizing circuit 111. The variable amplitude control circuit is used to change the switching point of the power switching elements 52 and 53 (to obtain phase control) and is con-trolled from several inputs. These include the shut-down circuit lQ3 which is operated from the conYerter fault detector and the shut-down circuit 123 which is operated from the load fault detector 12Q. Circuit 140 is also controlled by a lamp striking sequence circuit 15Q or from a manual control input 151 which operates through the lamp : ~

striking sequence circuit 150. A start-up and shut-down sequence control circuit 152 is also provided.
Although the present invention has been described in connection with a preferred embodiment thereof, many variations and modifications will now become apparent to those skilled in the art. It is preferred, therefore, that the present invention be limited not by the specific disclosure herein, but only by the appended claims.

:"
~ ... . . . .. .. .......
~, ~,,, ~,

Claims (15)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:-
1. An energy-conserving illumination control system consisting of:
a plurality of passive linear ballasts and respective gas discharge lamps therefor;
a single high frequency power source which is connected to a power input line and which has an output frequency of greater than about 20 kHz; said high frequency power source output being connected to each of said plurality of passive linear ballasts and lamps;
the output wave shape of said high frequency power source being a substantially continuous periodic wave form; and control circuit means connected to said high frequency power source for varying the amplitude of at least one of the current or voltage wave shapes of the output of said high frequency power source, thereby to vary the light intensity of each of said lamps;
the energy consumed by said illumination control system being functionally related to the output light intensity from said plurality of lamps.
2. The system as set forth in claim 1 wherein said wave shape is at least approximately sinusoidal.
3. The system substantially as set forth in claim 1 which includes a high frequency power trans-mission line for coupling the output of said high frequency power source to each of said plurality of passive linear ballasts.
4. The system substantially as set forth in claim 3 wherein said transmission line includes first and second elongated conductors for coupling the output of said high frequency power source to each of said plurality of passive linear ballasts; each of said first and second conductors being covered with an insulation sheath of substantial thickness.
5. The system substantially as set forth in claim 4 wherein said first and second conductors are disposed within a ferrous metal conduit for at least a portion of their length.
6. The system as set forth in claim 4 wherein the diameter of said insulation sheath for each of said conductors is at least three times the diameter of their respective conductor.
7. The system of claim 1 wherein said high frequency power source includes a series inverter comprising first and second series-connected controllably conductive devices each poled in the same direction and rectifier means for connecting rectified power from said relatively low frequency power source to said series-connected controllably conductive devices; said first controllably conductive device being connected in closed circuit relation with a capacitor, an inductor and transformer means; said capacitor and inductor being resonant at about the frequency of said high power source; and inverter output amplitude control means coupled to the resonant current of said capacitor and inductor for switching said first and second con-trollably conductive devices on in synchronism with said resonant frequency of said capacitor and inductor;
said transformer means being connected to said ballasts.
8. The illumination control system of claim 1 wherein said high frequency power source includes a d-c converter for rectifying the input from said power input line and producing a d-c output; and an a-c converter for converting said d-c output into a high frequency output in excess of about 20 kHz.
9. The system of claim 8 wherein said d-c converter circuit includes:
a tuned circuit comprising an inductor and a capacitor having respective values which are tuned to resonate at a frequency which is higher by less than about one order of magnitude than the frequency of said power input line;
coupling means for connecting said power input line to said tuned circuit;
a rectifier means having a-c input means con-nected to said tuned circuit and having a d-c output circuit means; said inductor being connected in series with said rectifier means; said capacitor being con-nected in shunt with said rectifier means and having one terminal connected to the junction between said inductor and said rectifier means;
and an output capacitor connected to said d-c output circuit means.
10. The system of claim 9 wherein said rectifier means comprises a single phase, full-wave bridge-connected rectifier; and wherein said coupling means includes connection wires for connecting said power input line to said inductor and capacitor respec-tively.
11. The system of claim 9 wherein said coupling means includes a second rectifier means.
12. The energy-conserving illumination control system of claim 1 wherein each of said ballasts contains a single ballast transformer for providing only filament power to its respective lamp.
13. The energy-conserving illumination system of claim 12 wherein said single high frequency power source includes a main ballast transformer for said lamps and for handling the volt amperes of all of said ballasts and lamps in said system.
14. The energy-conserving illumination system of claim 13 wherein said single ballast trans-formers provide the start-up voltage for their respec-tive lamps.
15. The system of claim 1 wherein said high frequency power source includes a series inverter comprising at least one controllably conductive device and a diode connected in anti-parallel relationship with said at least one controllably conductive device;
a capacitor and an inductor connected to one another and forming a resonant circuit which is resonant at about the frequency of said high power source; said at least one controllably conductive device connected in closed circuit relation with said capacitor and said inductor; transformer means connected in circuit rela-tion with said resonant circuit; discharge circuit means connected to said capacitor; and inverter output amplitude control means for switching said at least one controllably conductive device on in synchronism with said resonant frequency of said capacitor and inductor;
said transformer means being connected to said ballasts.
CA000341249A 1978-12-05 1979-12-05 System for energizing and dimming gas discharge lamps Expired CA1156302A (en)

Applications Claiming Priority (6)

Application Number Priority Date Filing Date Title
US05/966,601 US4207497A (en) 1978-12-05 1978-12-05 Ballast structure for central high frequency dimming apparatus
US966,601 1978-12-05
US966,604 1978-12-05
US05/966,604 US4207498A (en) 1978-12-05 1978-12-05 System for energizing and dimming gas discharge lamps
US05/966,643 US4210846A (en) 1978-12-05 1978-12-05 Inverter circuit for energizing and dimming gas discharge lamps
US966,643 1992-10-26

Publications (1)

Publication Number Publication Date
CA1156302A true CA1156302A (en) 1983-11-01

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CA (1) CA1156302A (en)
DE (1) DE2948938A1 (en)
FR (1) FR2469082A1 (en)
GB (1) GB2038571B (en)

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2132751A (en) * 1982-12-23 1984-07-11 Menvier Ambient light control for artificial lighting
DE4231286A1 (en) * 1992-09-18 1994-03-24 Bosch Gmbh Robert Device for igniting gas discharge lamps
EP1800522A4 (en) * 2004-10-13 2010-08-18 Osram Sylvania Inc Frequency modulation method and device for high intensity discharge lamp

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GB661705A (en) * 1949-04-22 1951-11-28 Gen Electric Co Ltd Improvements in electric circuit arrangements for operating electric discharge lamps
US3116438A (en) * 1961-06-01 1963-12-31 Gen Electric High frequency lighting systems and ballast circuits therefor
US3514668A (en) * 1967-05-17 1970-05-26 Rollie C Johnson Controllable intensity illumination system and method
US3824428A (en) * 1969-07-23 1974-07-16 Lutron Electronics Co High frequency fluorescent tube lighting circuit and a-c driving circuit therefor
US3663940A (en) * 1970-05-21 1972-05-16 Nasa Controllable, load insensitive power converters
US3753071A (en) * 1972-06-15 1973-08-14 Westinghouse Electric Corp Low cost transistorized inverter
US3919592A (en) * 1973-11-19 1975-11-11 Lutron Electronics Co High intensity discharge mercury vapor lamp dimming system
JPS5843880B2 (en) * 1976-02-18 1983-09-29 三菱電機株式会社 discharge lamp dimmer

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GB2038571A (en) 1980-07-23
FR2469082A1 (en) 1981-05-08
GB2038571B (en) 1983-05-05
FR2469082B1 (en) 1983-08-26
JPS63196599U (en) 1988-12-19
DE2948938A1 (en) 1980-06-26
DE2948938C2 (en) 1991-05-29

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