CA1128605A - Energy conserving automatic light output system - Google Patents

Abstract

ENERGY CONSERVING AUTOMATIC LIGHT
OUTPUT SYSTEM

Abstract of the Disclosure An energy conserving lighting system is provided wherein a plurality of fluorescent lamps are powered by a poorly regulated voltage supply which provides a decreasing supply voltage with increasing arc current so as to generally match the volt-ampere characteristics of the lamps. A transistor ballast and control circuit connected in the arc current path controls the arc current, and hence the light output, in accordance with the total ambient light, i.e., the light produced by the lamps together with whatever further light is produced by other sources such as daylight. In another embodiment, a transistor ballast is utilized in combination with an inductive ballast. The transistor ballast provides current control over a wide dynamic range up to a design current maximum at which maximum the transistor is saturated and the inductive ballast takes over the current limiting function. An operational amplifier is preferably connected in the base biassing circuit of the control transistor of the transistor ballast. In an embodiment wherein two sets of lamps with separate inductive ballasts are provided, the arc currents for the two ballasts are scaled or matche to provide the desired light output.

Cross-Reference to Related Applications This application is a continuation-in-part of my co-pending U.S. Patent Application Serial No. 849,427, filed on November 7, 1977 and entitled "Energy Conserving Automatic Light Output System".

Description

~ ~lf~ 5 The present iDvention relates to light con~rol systems for illumination purposes and the li~e.
Because the problems associated with conventional lighting systems using fluorescent lamps are not always fully understood, a brief description of such systems and the nature of fluorescent lamps in particular will be considered by way of background. It should be noted -that some of this discussion will be continued below after the invention has becn summarized because the points raised are best explained in connection with a drawing.
A fluorescent lamp, in contrast to the incandescent lamp, is an area source rather than a point source, In terms of light output, for a given amount of electrical power, the fluorescent lamp is three or four times more efficient than the incandescent lamp. The name "fluorescent" lamp is derived from the fact that an electric arc conducting through mercury gas within the lamp emits ultraviolet photons which impinge on an ; interior coating of phosphor that then radiates or "flouresces"
longer wave length visible light photons.
Critical to the operation referred to is the conduc-tion of electricity through the mercury vapor~ The volt-ampere characteristics of this conduction are determined by a number of complex phonemena which lack simple definition. As discus-sed hereinbelow, the current in the arc discharge region of ; operation will continue to increase to disastrous levels unless limited by external meansO In order to provide this current limiting, devices commonly known as ballasts are employed In general, for AC operation, inductive ballasts are used, while ~or DC operation, resistive ballasts are generally employed Transistor ballasts can be also used but th0se are impractical for most applications as e~plained in more detail below. Fur-ther, and more generally9 resistive ballasting requires a `_2-6~

substantial increase in voltage over that required by the lamp and systems em~loying such ballasting are highly dissipative and energy inefficient, A ~urther problem associated with lamps such as are being discussed is that of providing adjustment o~ the light level in an effective, practical way, In general, both induc-tive and resistive ballasts simply limit the current to a design value although, as discussed below, there are ballast circuits which are specifically designed to enable adjustment of the arc currentO
Another operational problem associated with fluores-cent lamps is starting the lamps In essence, the mercury with-in a fluorescent lamp must be ionized before conduction can occur This can be accomplished by momentarily applying a high voltage to the electrodesO If the lamps have heated electrodes, the ionizing or starting voltage is reduced, For this reason, the more common "rapid start" lamps have cathodes which are excited by separate transformer windings Another type of fluorescent lamp is the "pre-heat" lamp which has a switch ~0 mechanism in the ballast circuit that momentarily closes or is closed upon energization so that a current flows through the lamp cathode and the inductor. The switch then opens, and due to the stored inductive energy, a voltage transient is also generated~ The voltage transient coupled with the hot cathodes causes the lamp arc to conduct Since the preheated electrodes are not heated after firingJ pre-heat lamps are designed so that once the lamp is ~ired the rated arc current keeps the electrodes hot enough to emit electrons and to keep deleteri-ous material from collecting on the cathodes.
A third group o~ lamps are the so-called "instant start" lamps. The cathodes o~ these lamps are designed for - cold starting and the ballast circuit simply provides a suP-~ .
"t ~r3 s~

ficiently high starting voltage to cause conduction to be initiated by wh~at is called arc bombardement. Once the lamp is started the rated arc current keeps the cathodes hot enough to provide emission and to boil o~ any contaminating materials.
~t is noteworthy that neither the instant start nor preheat lamps can be dimmed because these lamps are designed to require that rated arc current in order to keep their cathodes at a "liveable" temperature. When these lamps are used in a dimming ~ode, the cathode temperature is lowered and the lamp ends are blackened by material sputtering off the cathode so that, finally, the cathode is used up and the lamp cease~ to function.
A further problem associated with ~luorescent lamps is that of the decline in lumen output with usage This decline is primarily caused by phosphor wear or coating. Changes in temperature will also affect the lumen output. As explained ` in more detail hereinbelow, because of the phosphor decay problem, lighting systems are characteristically designed to initially overlight the associate area so that sufficient minimum light is provided as the light output decreases with lamp use This approach results in a very substantial waste of energy. This problem, and other aspects thereof, as well as other problems associated wi-th fluorescent lamps, are also considered below.
Patents of interest in this general field include some of my earlier patents, viz , 3,422,310 (Widmayer), 3,781,598 (Widmayer), 3,876,907 (Widmayer), as well as 3,531,684 (Nuckolls), 3,609,451 (Edgerly, Jr et al), 3,801,867 (West et al), 4,01~ 7 6ff3 (Soileau) and 3,909,666 (Tenen) the latter of which is discussed below In accordance with the invention, a light control system for fluoresecnt and like lamps is provided which affords very substantial energy savings According to one aspect of -~ _4_ , the invention, a system is provided which enables the lumen output of the f~uorescent lamps to be controlled so as to provide a minimum level of room light and to be adjusted inver-sely proportional to the amount of light present from other sources, including daylightO Thus, according to this aspect of the invention, a system is provided wherein light is the controlled variable rather than lamp current.
According to a further aspect of the invention, lluorescent lamps are driven ~rom a voltage supply which is in-tentionally poorly regulated so that the supply voltage is re-duced in a non-dissipative manner simultaneously with the re-duced voltage requirements of the lamps when operating in the arc discharge region. This voltage supply, in combination with a transistor ballast and control circuit, serves as a voltage-compliant current source ~or the lamps whereby the voltage supply is more closely matched to the lamp requirements. This combina-tion minimizes the amount of power dissipated by the ballast-ing transistor while operating in the active region thereof and also provides intrinsic current limiting when the ballast transistor is saturated, In a first embodiment of the invention, the poorly regulated voltage supply referred to above is utilized in combination with a solid state electronic control device ~bal-last transistor) connected in the arc current path of the lamps. A light sensing means is provided ~or sensing the 7evel o~ ambient light in the area of the lamps, this total including the light output of the lamps and the ambient light produced by any other light sources including sunlight. A feedback means connected between the electronic device and the light sensing means controls the conduction o~ said electronic device and thus the current ~low in the arc current path in accordance with the output o~ the light sensing means so as - . , to maintain the total ambient light substantially constant.
The poorly regùlated voltage supply comprises a voltage multiplying circuit utilizing diodes and capacitors. An ion-izing supply circuit is also provided which supplies the starting or firing voltage for the lamps and which automatic-ally provides a negligible low vol-tage when the lamps are fired, The ionizing supply circuit also comprises a voltage multiply-ing circuit employing diodes and capacitors.
In accordance with a second embodiment of the inven-tion~ a transistor ballasting and control circuit similar to that described above is incorporated in lighting systems which include an inductive ballastD It will be appreciated that millions of such inductively ballasted lighting systems are presently in existence, and the inclusion of the transistor ballasting and control circuit in combination with the induc-tive ballast provides substantial energy savings, The two ballasts are operable selectively and automatically, with the transistor ballast being the operating current limiting bal-last over the dynamic range of current control from a given minimum up to a design current maximum and being automatically superseded by the inductive ballast at that current maximum.
More specifically, the ballast transistor saturates at the current maximum and the inductive ballast serves its conven-tional function of current limiting only at this time, i.e., with the transistor saturated~ The inductive ballast also provides a high firing voltage during "start up" as well as the sustaining operating voltageO The presence of the induc-tive ballast also prevents the transistor from having to pick up and dissipate all of the power associated with the excess voltage resulting from the negative volt-ampere characteristics of the lamps, Because the transistor operates as the current limiter during most of the "on" time of the lamps, the I R

,, losses of the inductive ballast are substantially reduced ~nd consequently, t~e life of the ballast is gre~tly extended In accordance with a preferred embodiment of the in-vention as applied to lighting system including a conventional ballast, an operational ampli~ier is connected in the biassing circuit of the control transistor of the transistor ballast One input of the operational amplifier is connected to receive a light feedback signal while another is connected to variable voltage supply such as potentiometer or a programmed voltage input. In addition, a mînimum biassing signal is preferably provided for the control transistor, In accordance with a further embodiment of the in-vention, a system is provided wherein at least first and second sets of lamps are used, each having an individual reactive ; ballast associated therewith. The system includes a control unit sueh as discussed above in combination with a follower eireuit arrangement whieh provides for matehing or sealing of the are eurrents flowing in two ballasts so as to eontrol the .~ , light output as desired. The follower eireuit arrangement ~O ineludes resistors connected in the emitter circuits of the eontrol transistor of the eontrol unit as well as a contro~
transistor eonneeted to the seeond ballast. In a preferred embodiment, an operational amplifier arrangement is provided whieh affords preeise eontrol of the are eurrent flow for eaeh of the two ~or more) ballasts Other features and advantages of the invention will be set forth in, or apparent from, the detailed deseription of the preferred embodiments found hereinbelow, Figure 1 is a graph plotting light output as a fun~
etion of hours in use for a fluoreseent lamp;
Figure 2 is a graph illustrating the operating ehar-aeteristies of fixed are eurFent deelining ligh~ output light-6~

ing systems;
Figu~e 3 is a graph illustrating the operating char-acteristics o~ a constant light output lighting system in accordance -7a-. ~ :
.

3~;

with the invention;
Figure 4 is a graph illustrating the volt-ampere char-acteristics of a fluorescent (arc discharge) lamp;
Figure 5 is a highly schematic block circuit of a prior art lamp system employing a resi.stive ballast;
Figure 6 is a highly schematic block circuit diagram of a prior art lamp sys-tem employing a transistor ballast;
Figure 7 is a schematic circuit diagram of a further prior art lamp supply system employing resistive ballasting;
Figure 8 is a diagram of a waveform associated with the circuit of Figure 7; (shown on the sheet of drawings containing Fig, 5) Figure 9 is a schematic circuit diagram of a lamp light-ing control system in accordance with a first embodiment of the invention;
Figure 10 is a diagram of a waveform associated with the circuit of Figure 9; (shown on the sheet of drawings containing Fig, 5) Figure 11 is a schematic circuit diagram of a lamp lighting control system in accordance with a further embodiment of the invention; (shown on the sheet of drawings containing Fig. 7) Figure 12 is a schematic circuit diagram of a further embodiment of the invention adapted for use with a pre-existing inductive ballasting system;
Figure 13 is a schematic circuit diagram of a further embodiment of the invention which is of the type shown in Figure 12;
Figure 14 is a schematic circuit diagram of yet another embodiment of the invention, as used with at least two separate sets of lamps and at least two separate ballasts; and Figure 15 is a schematic circuit diagram of a further ~: ''.'.,:
,, embodiment of the system o~ Figure 14.
Description of the Preferred Embodiments Before considering the preferred embodiments of the invention, some of the points raised in the foregoing background ~0 - 8a -, discussioD of the inventi~n will be considered in more detail.
Thus, as state3 above, because of the phosphor decay problem associated with fluorescent lamps, a design criteria that es-tablishes the need for, e.g , seventy foot candle (70FC) light-ing must be designed to initially over-light the area in order to meet the design criteria by taking into consideration -the aging effects that occur before lamp replacement. Referring to Figure 1, which is adapted from a graph used in the sales literature of a leading fluorescent manufacturer and which therefore perhaps minimizes the problem, the light depreciation over time of typical fluorescent lamps is shown Two major causes of this depreciation or decline relate directly to the density of the arc currentO Specifically, an increase in arc current increases the amount of $he deleterious 185 nanometer wavelength radiation impinging on the phosphors as well as the interaction between the mercury ions in the gas column and the phosphor molecules.
It will be appreciated that any light over that which is required, i e~, any lumen output in excess of 70FC, can be said to waste electrical power. To further illustrate this point, it will be assumed that a room is of such a size that a four lamp F40T12 fixture which, when operating with new lamps, will give 140 starting foot candles at some point. The lamps are driven by the standard 430 ma ballasts which provide a more or less fixed power consumptioD. Over time, while the arc current, with its related power consumption, remains reasonably constant, the light output declines as ls shown graphically in Figure 2. As explained hereinafter, one aspect of the present invention concerns control of the arc current as a function of a referenced level of the ambient or room light. Thus, re-ferring to Figure 3, this type of control is illustrated graphi-cally for a constant light level over time of 70FC with a ..~,. _g_ ,"~

starting arc curren~ of 200 ma Now as the phosphor decays (and the phosph~r will decay more slowly at the lower arc level because of the lower UV and ion interaction level associ-ated with the lower arc level), the provided control advances the arc current so as to maintain the light constant at the re~erenced level of 70FC. Finally, it is noted that when the lamp is fully aged, the arc current has advanced more than that of the ballasted lamp example shown in Figure 2 The electrical power consumed by a given fluorescent lamp bears a relationship to the level of its arc current.
Because of the lower average arc current illustrated in Figure 3, both the power consumed and the phosphor deterioration is less than for the technique illustrated in Figure 2, Figure 3 shows that at the 24,000 hour poin$ the current has reached only 360 ma (with the average current from zero to 24,000 hours being 285 ma) as opposed to 430 ma in the case of Figure 2 Thus, in addition to having the ability to adjust the referenced level of light and then hold this level constant over time 9 this approach permits immediate evaluation and variation in different areas to meet v~rying requirements. Before proceeding further, it should be pointed out that the light decline in Figure 2 and the current increase in Figure 3 are shown as being linear for purposes of clarity of illustration but that the same general relations hold true for curves closer to those actually found iD practice.
As stated above, the arc control capability provided by the invention is a function of the room of ambient light level, Accordingly, if the room referred to in the example has an outdoor window, daylight would enter the room at certain times of the day so that less light would be required from the lamps to maintain the relative 70 FC level. Thus, an even lower arc current would be required resulting in further, and ,~

.~

even more substantial power savingsO As mentione~, and as is explained in mo\ e detail hereinbelow, the ~ystem o~ the present invention possesses the arc control capabilities discussed and thus provides the advantages which have been referred to.
Before discussing the combination of arti~icial and daylight and the manner in which the present invention takes advantage of the combination, some brie~ comments on "daylight-ing" might be helpful. Daylight illumination is made of two ~omponents, viz , (i) illumination direct from the sun and, (ii) indirect solar illumination due to skylight, Rather than consider the actual sources it is probably simpler to view a window as if it were a piece of opal diffusing glass lighted by varying light sources on the outside. The illumination ~rom the source or combination of sources will vary from zero during the night period up to several thousand lumens per square foot of window area in the day period3 This wide variation is a function of the direct and indirect components which vary with weather conditions, the time of day and the season of the year, In any event, with arc control of the fluorescent lamp related to the room light level, the arc current is turned downwardly -as the daylight increases and the arc current is turned upward-ly as the daylight declinesO The average arc over the time of a 12 hour day period with daylight available would be reduced to less than half required without such auxiliary lighting, on most days.
Another area which was cursorily explored above and which will be considered in somewhat more detail now is that of the difficulty of controlling fluorescent lamps. The impor-tant problems in this area were mentioned aboveO The first is that the mercury within the lamp must be ionized, thereby, among other effects, lowering the resistance between the lamp electrodes from a virtually in~inite level to a le~el where electron conduction is permit-ted through the ionized gas and hence the lamp is turned on. The second and most di~icult problem to deal with is the phenomena in the conduction o~
electricity through gas that occurs upon ~iring o~ the lamp.
In this regard, it is stated by Condon and Odishaw in the text Handbook on Physics, at page 4-174 that the phenomena associ-ated with the conduction of electricity through gas defies rigorous definitionO Figure 4 is adapted from the same page of the text and shows a model of the volt-ampere characteristic lo of a gas discharge lamp It will be seen that when the arc is struck the arc current, starting close to zero, traverses through the various discharge regions The last region is where gas discharge lamps used ~or lighting generally operate O~
signi~icance is that the arc discharge region, shown in Figure 4, does not follow Ohm~s law. In ~act, the voltage decreases, rather than increases, with an increase in current This ex-plains why fluorescent lamps are said to have negative resis-tance characteristics and means that if the lamp was energized with a voltage source and current conduction reached the ar~
~O discharge region, the current would continue to rise to a dis-astrous level.
If the commonly available AC power was provided as a fixed current-voltage compliant source, a -fluorescent lamp might be connected and operated directlyO However~ because wall outlet or electrical distribution systems provide a fixed voltage-current compliant source, i e., a source wherein the current adjusts to the positive resistance o~ the load, a ~luorescent lamp requires a m0ans ~or stabili~ing the arc cur-rent. Such a means is commonl~ re~erred to as a ballast as noted previously.
Most ~luorescent lamps are operated with AC through one or more lamps connected in series with an inductor as the -12_ , , ~ ~

ballast element therefor The reactance of the inductor be-comes the limiting impedance and limits the am~un-t of cu~rent in the series circuit. Except ~or second order e~ects, an inductive reactance ballast can be considered a non-dissipative current limiter. Capacitive reactance can also be employed as a non-dissipative ballast at high AC frequencies Ho~ever, at 60 Hertz the stored energy in the capacitors would discharge into the lamp as a highly peaked eurrent due to the volt-ampere characteristics of the lamps unless the current is limited in some other way Direct current operation of ~luorescent lamps is possible and such systems usually employ a resistance ballast at a higher operation voltage. Such a ballast is dissipative and will often dissipate as much or more power than the lamp consumes iD its lumen generating process. There are except-ions to this statement, an example being disclosed in U.S. Pat-ent Re 28,044 (Widmayer) where a choke is used as a volt sec-ond integrator with other controls.
Re~erring to Figures 5 and 6, two embodiments of a DC ballast are illustrated The embodiment of Figure 5 in-cludes a lamp L connected across a fixed voltage source VS with a starting circuit SC connected between lamp L and source VS as shown. A resistor R is employed as the ballast. In this ; embodiment, the lamp L is fired and the current complies to a level more or less equal to the source voltage ES minus the fluorescent lamp voltage EL drop at current equilibrium, divid-ed by the ballast resistance r CI=ES - EL/R)~ ~
The embodiment of Figure 6 is similar to that of Figure 5, and like elements are given the same designations with primes attached. As will be evident, the only difference between the embodiments of Figures 5 and 6 is that a transis-tor ballast is used in Figure 6 The transistor ballast is '' ~ -13 ,.~, ~ ~ r?~$~

formed by a transistor T which is controlled by a con~rol circuit CC It~ should be noted that the embodiment of Figure 6 is not practical principally because in order to be an e~fec--tive ballast, transistor T would have to operate in the linear region. The problem with such operation is that due to the negative volt-ampere characteristics of the lamp, the transis-tor T, acting as a control device, would have a rising current and an increasing collector-emitter voltage which would be clearly beyond the power dissipation capabilities of a transis-tor at practical ~luorescent arc levels. Of course9 a collec-tor resistor (not shown) could be added to relieve the transis-tor T of some of the excess volts but such an approach would defeat the purpose of using a transistor and thus a variable resistance might just as well be used.
In general, both inductive and resistive ballasts simply limit the current to a design level and provide no light level adjustment. There are, however, specially designed bal- ;
last circuits that permit some manual adjustment of the arc current. The more common types include thyratrons, adjustable voltage trans~ormers and adjustable reactor circuits, among others, which vary the arc current amplitude and/or the current on-off time within the AC hal~ wave so as to provide an appar- -ent light change due to the averaging effect perceived by human vision~
Referring to Figure 7, an example o~ a prior art DC
resistive ballast network is illustrated. Figure~7 is adapted from the drawing in U.SO Patent No. 3,909,606 ~TenaD) and is of particular interest in that the input voltage circuit bears some resemblance to that of the invention. The Tenan patent describes the capacitors Cl to C4 and diodes Dl to D4 as forming a voltage quadrupler circui-t, The patent states that when the switch arm o~ switch S is moved to the high or low ,,, 1~--. } ~

~ , ~

position, the voltage output between terminals Tl and T2 is four times the peak input potential and that when fluorescent bulb FB ignites, most of the resulting increased current ~lows through lower impedance capacitors Cl and C2 so that the vol-tage increasing ef~ect of trigger capacitors C3 and C4 becomes negligible. The current through bulb FB is limited by ballast resistor Rl and dimmer resistor R2 The voltage input circuit o~ the Tenan paten~ is perhaps best understood as providing a plus and minus half-wave rectified DC voltage source wherein one half of a doubler out-put is added, (with the appropriate sign) to each wave. The waveform of the supply voltage at load would generally corres-pond to that shown in Figure 8, wherein the positive half-wave provides the vo~tage indicated at (a), the minus half-wave provides voltage (b) and the voltages (c) and (d) result from the outputs of the one-hal~ doubler cir~uit as added to the plus and minus supply voltages, respectively. It is impOrtaDt to note that be2auce o~ the nature of the half doublers the waveforms (c) and (d) are out of phase. This is important since these voltages are used in building up the no load ion-izing voltage which is required only momentarily in order to fire the lamps. Hence, one of the waveforms (c) or (d), and thus the components which produce that wave~orm, are unneces-sary. It is also noted that a F13T5WW lamp is fired without preheating and thus may account ~or the use of four times the line peak (640 VDC no load) to fire a lamp that requires a starting voltage of 176 volts and an operating voltage of 95 volts (based on page 4 of the Westinghouse Fluorescen~ Lamp ` Service Manual 7/68 A-8072). Again, high voltage cold cathode firing o~ a pre-heat lamp is not practical when the lamp is to provide light for other than the short term.
The circuit of Figure 7 clearly illustrates the need -15_ ~ '`"i $~

~or dropping a considerable voltage across the resistors Rl and R2 since, i~ the specific example given, the line voltage is in excess o~ the 95 volt operatiDg level the majority o~ the time in a given cycle, and the DC ~oltage is substantially in excess of the line voltage. It is interesting to note that i~
the 15 watt rated lamp were operated at the DC equivalent oP
the 160 ma RMS current, the 400 Ohm resistor Rl would drop 64 volts which equates to 10 watts However, the dissipation is actually much higher because the DC current in this circuit will necessarily have a high ripple content and the power dis~
sipated is, o~ course, proportional to the current squared.
Hence, the power dissipated at rated RMS current will exceed the 15 lamp watts. In any event, it will be clear that the resistive ballasting provided requires a substantial increase in voltage over that required by the lamp and that, more gener-ally, such resistive ballasting systems are highly dissipative and energy inefficient.
Turning now to a consideration o~ specific embodiments of the invention, the overall system of the invention can perhaps be best understood by examining each o~ the our inter-related sub-systems making up the overall system, viz., the ionizing power supply, the arc current power supply, the load devices, i~e , the fluorescent ~amps used in the specific em-bodiment under consideration, and the control sub-system Re~erring to Figure 9, in the specific example illus-trated, three fluorescent lamps, 10a, 10b, and 10c, collective-ly denoted 10, are to be ionized so an electrical discharge can be struck and a few hundred micro-amperes o~ current per-mitted to ~low. The ionizing po~er supply, which is indicated by dashed line block 12, and the arc current power supply 9 which is indicated by dashed line b~ock 14, will be described hereinbelow, . ~ .
,, The lamps 10 are o~ the heated cathode type having ~ilaments which are independently heated via the multiple secondary windings 16a, 16b, 16c, and 16d of a tr~ns~ormer 16.
Independent heating of the electron emit-ters of the lamps 10 is provided ~or the reasons set forth in the general discussion above. Further, although the adjacent lamp heaters are shown as being connected in series with the associated trans~ormer winding, in what is probably a preferable design the adjacent lamp Eilaments would be connected in parallel.
One end of the lamp series 10) designated as point H, is connected to a system neutral line N through a diode 22 and a diode 24 and a transistor 26 of a con-trol sub-system (transis-tor ballast) generally denoted 200 The other end of the lamp series 10 is connected to point C of the arc current power sup-ply 14 Point H of the lamp series 10 is also connected through a zener diode 28 to ionizing power supply 12 Brie~ly considering the make-up o~ the supply sub-systems, the ionizing supply 12 includes capacitors 30 and 32 connected with the 115 V AC input line 34 Diodes 36 and 389 and 40 and 42, are connected as shown. Further capacitors 44 and 46 are connected to neutral line N Erom the junctions between the two pairs of diodes.
Similarly, arc current supply 14 includes a series oE three diodes 48, 50 and 52 as well as a capacitor 54 con-.
nected between supply line 34 and the junction between diodes 48 and 50 Another capacitor 56 is connected across diodes 48 and 50 while a ~urther capacitor 58 is connected between the junction between diodes 50 and 52 and neutral line N
Considering the operation o~ the system as described thus :Ear, the 115 VAC current~compliant voltage source, whose output appears on line 34, is first converted into a voltage compliant source which more or less matches the volt-ampere -~7-.

characteristics o~ the ~luorescent lamps 10 during operation of lamps 10 iM the arc discharge region of current conductionO
Specifically, a voltage compliant source is provided wherein the lower the arc current the higher the supply voltage This is accomplished by the arc current supply circuit 14 which acts as an AC line voltage multiplier The capacitors 54, 56 and 58 of arc current supply circuit 14 are sized so that a low current loading the DC voltage is substantially higher than the AC line peak voltage so as to provide a reasonable voltage compliance range With this arrangement, the DC voltage lowers non-dissipatively in a manner somewhat analogous to the chang-ing voltage requirement of the lamps 10 in the arc discharge region. The poorly regulated voltage source provided by arc current supply circuit 14, acting in combination with the tran-sistor control provided by transistor ballast circuit 20, in effect provides the lamps 10 with a controlled DC current source.
Considering the operation of arc current supply cir-cuit 14 in more detail, functionally diode 52 and capaeitor 58 form a half-wave rectifier bridge circuit, with capacitor 58, in the specific example under consideration, being charged to the AC line peak of 160 VDC above the neutral line N, This voltage appears at point A in the Figure 9 and is represented as voltage component A in Figure 10. Diode 50 and capacitor 54 add a full 115 VAC peak to peak sinusoidal DC voltage to ;
the 160 VDC which appears at point B in Figure 9 and is identi-fied as component B in Figure 10. Finally, diode 48 and capa-citor 56 "fill in" the positive DC voltage waveform by adding the remaining phase related sinusoidal component C as is illus-trated in Figure 10. Thus, the AC line voltage multiplying arc current supply circuit 14 provides a nominal 490 VCD
poorly regulated voltage source~ with diode 52 and capacitor - 18_ 58 forming a 160 volt DC supply and diodes 50 and 48, to-gether with capacitors 54 and 56, :Eorming an AC line volta~e multiplier circuit that adds appro~imately 320 VDC to the +160 VDC half wave supplyO In an exemplary circuit, 240 MFD
capacitors were used which permitted lamp operation up to 700 ma o~ arc current.
Be~ore the lamp current can be controlled, the lamps lO must, o~ course, be ignited and ionizing supply 12 is pro-vided for this purpose. Ionizing supply 12 basically comprises lO a half wave recti~ier circuit and a full AC line voltage multi-plying recti~ier circuit, similar to the positive voltage source previously discussed, together with one half o~ another AC
line voltage multiplying rectifier circuit. The specific com-ponents of ionizing supply 12 were described above, and refer-ring to the Figures 9 and lO together, the negative half wave circuit formed by diode 36 and capacitor 44 provides the no load voltage component D of the wave~orm shown iD Figure lO.
The no load voltage components E and F are provided by the ~ull AC line voltage multiplier circuit formed by diode 38 and `
20 capacitor 30 and diode 40 and capacitor 46 Finally, component G is provided by the half AC line voltage multiplier circuit formed by diode 42 and capacitor 32, Thus, in the specific embodiment under consideration, a negative-going no load nominally 810 volt peak DC supply is provided. This voltage, in conjunction with the positive low ripple 490 AC volts pro-duced by the arc current supply 14 provide adequate voltage ~
to ionize the mercury in lamps lO so that the lamps can be -started.
Capacitors 30, 32, 44 and 46 are very small, e~g., 30 .005 MFD in a specific example, so that as soon as the ~amps lO fire the negative voltage drops back essentially to the negative hal~ wave o~ the AC line, with at most a ~ew micro---19- ~

- -, . . . . . . .

~ 2~

amperes of average current flowing ln the negative supply, Zener diode 28 is employed so that with the voltage drop there-of, in combination with the poor regulation o~ the negative supply, there is insufficient voltage for the system to "run away", It is noted that a small one or two megohm resistor used in place of the zener diode 28 would serve the same pur-pose by limiting the current in the negative supply circuit to a few micro-amperes, It is important to note that the micro-ampere start-ing current path~ which is identified by the dot and dash lineFigure 9, shares the arc discharge current path, which is indi-cated by -the double dot and dash line in Figure 9, where the two lines run parallel but that the transis~or controlled lamp current never flows in the negative starting circuit, i,e,, in ionizing supply circuit 12, and hence diodes 36, 38, 40, 42 and 28 need only be rated for micro-ampere currents, Turning now to the transistor ballast and current control circuit 20, because point H is pulled strongly negative until the lamps 10 are ignited, the collector of transistor 26 must be protected~ Point H swings positive as soon as the lamps 10 are fired since the lamps drop less voltage than the +490 VDC supply. Hence, by providing diode 22 ~ith a 1,000 PIV rating, transistor 26 and a companion transistor 60 are protected because diode 22 is back biased when point H is nega-tive and can only conduct when point ~ is pulled positive.
Diode 24, which could be replaced by a simple one ohm resistor, is employed in the collector circuit of transistor 26 to insure that there is sufficient voltage between the emitter and col-lector of transistor 60 to permit its proper opera-tion when . 30 and if, transistor 26 is saturated, .~ Transistor 25 and 60 are connected to a ~urther transistor 62 in a high current gain configuration, The base .

' d '~ 20-~, , : . . .

drive for transistor 62 is provide~ by circuitry including a potentiometer 6~ connected to a 6VDC bus 66 The tap 64a of potentiometer 64 is connected through a resistor 68 to a summing point 70. A second potentiometer 72 is also connected to s~lmming point 7Q, with the tap 72a of potentiometer 72 ;
being connected to a photo-diode 74 A capacitor 76 is con-nected across potentiometer 72 between the base of transistor 62 and neutral line N. It is evident that transistors 26 and 60 will have to have a sufficiently high collector-to-emitter voltage rating to withstand the positive voltage remaining after the lamp voltage drop. Because the collector of trans-istor 62 is connected to the positive 6 VDC bus 66 with respect to neutral line N, the collector-to-emitter voltage withstand rating thereof only needs to be a few volts. The three trans-istors 26, 60 and 62 are, as noted, essentially connected in a high current gain configuration with a nominal overall beta of 5,000 or more Transistors 26, 60 and 62 are deliberately chosen as NPN transistors so that the base o~ the signal in-put transistor 62 does not turn the transistors on until the base signal voltage is one or more volts above the emit~er voltage of transistor 260 This signal must be higher than the sum of the voltage drops across the emitter-b~se diodes of transistors 26, 60 and 62. With the configuration shown, the single plus 6 VDC control supply bus 66 serves to generate both the reference and feedback signals as will now be explained.
Summing mode resistor 68 derives a signal from the reference signal potentiometer 64 It will be appreciated that an adjustable resistance is not actually required and an appropriately valued resistor, corresponding to resistor 6B, could be tied directly to the bus 66 in certain svstems. In operation, the current signal of potentiometer 84 ~lows from the plus 6 VDC bus 66 through resistor 6~ into the base of :

'''' .

6~5 transistor 62 to thereby turn on transistor 62 and transistors 60 and 26, Thu~s, a controlled current, other than the mini-scule starting current, is allowed to flow through the lamps 10. It is noted that all of current flowing in resistor 68 does not go into the base of -transistor 62, in that some of the current will continue to flow through potentiometer 72 to neutral, The voltage level above neutral at the junction 70 between resistor 68 and potentiometer 72 must be greater than the emitter-base diode drops of transistors 26, 60 and 62 ~or a base current to ~low into transistor 62. Once current begins to flow in the lamps 10, light is generated and photodiode 74 (which can be replaced by any suitable configured photosensi-tive device) receives some o~ the lamp generated light, toget-her with whatever light is produced by other sources, so as to permit more of the re~erence signal current to flow therethrough to neutral line N rather than flow into the base of transistor 26. Thus, a closed ~eedback loop is provided and the current through lamps 10 is dependent on the light received by photo-diode 74.
Considering some of the secondary features of circuit 20, capacitor 76 serves to average abrupt changes in light levels as detected by the light feedback photodiode 74. Photo- -~
diode 74 is connected to the wiper arm 72a of potentiometer 72 to provide a feedback signal gain adjustment which may be re-quired depending on the positioning of the photodiode 74.
The 6 volt supply provided by bus 66 is derived by using a 6 volt zener diode 78 having a capacitor 80 connected in shunt therewith. Zener diode 78 is connected through a ~urther resistor 82 to the plus 160 volt bus provided at point A in arc supply circuit 14. Resistor 82 is siæed so that the 6 V bus can supply at least 10 ma of current to transistor 62 and potentiometer 64 when the actual voltage is provided by -22~

~; ~

. . . ~

160 VDC bus is reduced under maximum load. The 6 volt bus can also be gen\erated by connecting resistor 82 to the 115 VAC
line 34 to form another half wave DC supply, In this embodi-ment, a blocking diode (not shown) would be inserted in series with resistor 82 to prevent discharge of capacitor 80 during the negative half of the AC line cycle, Under the circumstances described with the system operating with the lamps on, the controlled lamp current will increase as long as the light incident on the photodiode 74 declinesO For example~ i~ the temperature is reduced, the light output for the same lamp current will be less due to a reduction in the mercury ion population. Likewise, the light output is reduced as the internal phosphor coating "wears", thereby resulting in less photons being emitted, In either or both of these instances, and within the systems design limits, the light feedback photodiode 74 receives less light, thus resulting in an increased base drive for transistor 26 and a corresponding increase in the lamp current. Hence,again within the design limits of the system, the control sub-system 20 continuously adjusts the lamp current so as to hold the light -output constant in relation to the input signal re~erence.
Thus, the system of the invention can be said to differ from prior art systems in that light ra-ther than current is the controlled variable.
Referring to Figure 11, a further embodiment of the invention is illustrated. The embodiment of Figure 11 is very similar to that of Figure 9 and like elements have been given the same number with primes attached, The embodiment of Figure 11 differs from that of Figure 9 in that four rapid start , 30 fluorescent lamps are employed. The ~ourth lamp is denoted lOd and the cathodes and heater trans~ormers have been left out for purposes o~ clarity. The four lamp system o~ Figure :. , ,~ , .

~f~
11 will, of course, require more voltage than the three lamp system o~ Figure 9 and rather than choosing to increase the plus 490 VDC supply, the transistor ballast and con-trol system 20~ is disconnected ~rom neutral line N' and reconnected to the minus 160 bus provided at point D~ in ionizing circuit 12'.
With this arrangement, diode 36' and capacitor 44' become part of the control current voltage source supply so the diode 36' must be capable of handling the controlled arc current.
Capacitor 44' would have the same rating as capacitors 54', 56~ and 58~. The remaining high voltage negative supply has been ~ound su-~icient for starting purposes.
Referring to Figure 12, a ~urther embodiment of the invention is illustrated, As explained hereinbelow, millions of ~luorescent lamp ~ixtures are presently in operation which ; already include ballasts. In accordance with this aspect of the invention, additional ballasting is combined with the already existing ballast so as to provide a very significant energy savings. In brief, these savings would be re~lected in savings in peak lighting (35% in a speci~ic example) as well as off-peak lighting (30% in the same example), iD air conditioning energy, iD reduced demand charges and in addition~-al heating energy charges. ~ ;
In Figure 12, the transistor ballast (control sub-system) of Figure 9 is utilized in combination with a conven-tional inductive ballast 100. The transistor ballast is con-nected in a ~ull wave AC diode bridge ~ormed by diodes 92, 94, 96 and 98 and is ~ormed by components which are similar to those described above in connection with the transistor bal-last o~ Figure 9 and which are given the same reference numer-` 30 als with double primes attached As illustrated, the junction ;~ between dlodes 92 and 94 is connected to neutral line N while the collector o~ transistor 62" is connected to a 6 volt bus -24_ ' e~3.
`` ' ` ~; ' , pro~ided by a 6 volt Zener diode 78", resistor 82" and a further dio~e 9~ being connected to the 115 volt AC line 90 as shown Inductive ballast 100 is a standard two lamp, rapid start, series sequence ballast and includes the requisite lamp wiring for a pair of lamps Ll and L2O
In operation, the transistor ballast of Figure 11 limits the ballast current more or less to a controlled ampli-tude square wave AC current so as to produce a corresponding light input The current flow through the system alternates between two paths Specifically, during a first AC hal.~ cycle, the current flows through diode 92, diode 24", transistors 26"
and 60" and diode 98. On the other hand, during the alternat~
AC half cycle, the current will reverse and flow through diode 96, diode 24", transistors 26" and 60" and diode 94 It will be understood that the system of Figure 12, similarly to those described above, provides DC control to control the output of the lamps, this being accomplished by locating the transistor ballast and feedback current within a ~ull wave diode bridge (formed by diodes 92, 94, 96 and 98) connected in series with one side of the AC line 9~ which ~eeds inductive ballast 100. Moreover~ considering the operation further, it is very important to note that when the lamps Ll ::
and L2 are not conducting at the beginning and end of each AC
half cycle, the nature of the ballasting system is such that control transistor 26" is saturated on. Thus~ apart for sec ~ -ond order effects, the inductive ballast 100 provides the full open circuit voltage for firing the lamps Ll and L2 as well as for heating the lamp filaments Once the lamps Ll, L~ are fired, the current is limited by the control transistor 26"
whi~ch then operates in the active region thereo~. On the ; other hand, whenever transistor 26" is saturated, the lnduc-_25-}

.
, Aq, ~ 2 ~663Ç ~

tive reactance of the ballast 100 provides the required cur-rent limiting. Thus, the transistor circuit acts as the sys-tem ballast over the dynamic range of current control, i e., for minimum arc current up to a design current maximum, with the voltage across transis-tor 26" decreasing with increasing arc current flow therethrough until saturation occurs At this pointJ i e , at the current design limit, the transistor ballast is ineffective i e , ceases to function, and, ~or the first time, the inductive ballast 100 provides the system current limiting~ Hence, the function o~ the inductive bal-last is changed from one of current limiting throughout the entire operating cycle to one of providing a cost effective voltage source for firing the lamps and providing the neces-sary sustaining voltage, It will be appreciated that the power losses associated with the inductuve ballast 100 are greatly decreased with the incorporation of the transistor ballast of the invention in that, with transistor ballasting, the normal current peaking characteristics o~ the inductive ballast are eliminated and since the inductive reactance ballast power losses in question are I R losses, the reactance ballast runs cooler and its operating life is hence extended.
It is noted that minor additions to the circuits de-scribed may be necessary or help~ul in improving the operation.
Thus, because in the circuit of Figure 9 the current through the lamp series 10 is direct current noticeable lamp end light falloff may occur due to ion migration to one end o~ the lamps 10. Such falloff will depend on the lamp array, the length of the gas column tand hence the lamp length), the arc current density and the lamp on-time interval. If such light fallof~
occurs, it can be dealt with by a periodic reversal o~ pvint H
to point C and vice versa, This can be accomplished with a simple polarity reversing relay such as a Potter Bromfield , ` _~6-,, . . ~ .:

GM-ll which per~orms the switching function as soon as the system is turne~d of~.
It will be understood that arc current control pro~
vided in the embodiments of Figures 9, 11 and 12 di~ers from that provided by a resistive ballast in that, inter alia, the maximum power is dissipated in a resistive ballast when the lamp current is highest In all embodiments of the invention described above, minimum power is dissipated in the transistor ballast when the lamp current is highest because the transistor is then saturated onO As the lamp and transistor current in-creases the emitter-collector voltage across the control trans-istor decreases down to its saturation voltage of less than one volt at which time the system becomes intrinsically ballas-ted by being voltage limitedO In other dissipative ballasts, maximum power is dissipated at high arc current levelsO `
It will be understood that whil~ the specific circuits discussed above provide certain advantages, other circuitry could also be employed. For example, other solid state power supplies could obviously be used for the transistor ballast control circuit and the control circuit could also use operat-ional amplifiers and photo-voltaic or photo-resistive compon-ents as well as other components in other configurations.
Typically, a 30 or 40 or more milliampere constant current could be generated and steered either to the base o~ the con-trol transistor or to the neutral or minus bus as a function of a reference signal and the light levelO Similarly, other forms of ionizing circuitry could be employed.
As was brie~ly discussed above, in all o~ the system embodiments, the sensed light can be either that produced by the lamps themselves and/or that ~rom other sources such as daylight. The daylight or "other source" light in ef~ect will - generate a downturn signal, Stated differently, as the inten-27~

sity of other optically coupled light sources increases, the system arc current will be turned downO I~ the intensity o~
other source light is sùfficiently high the controlled arc cur-rent will go to zero. On the other hand, the arc current auto-matically increases as the light from that source declines~
The nature of the systems of Figures 9 and ll is essentially non-dissipative when the ballast transistor is saturated and minimally dissipative, in a declining fashion, when the trans-istor is operating in the linear control region Except for its initial turn on charge, the transistor ballast takes power from the AC line in relation to the lamp current density. Of particular importance in a DC embodiment is the fact that the voltage source declines as the lamp cur-rent increases since this decline reduces the power that the transistor ballast must dissipate. Thus, a more efficient energy conserving light system is made possible For example, in an instance where external source light is sufficiently high to turn down the controlled arc current to zero, the power consumption would be reduced about 90~ from what i$ would have been with the design maximum arc current. The quiescent power is, of course, required ~or the ionizing supply, the lamp heater transformer and the control power supply.
~eferring again specifically to the embodiment of . Figure 9, the polarities o~ the voltage source and the ionizing supply 12 could, of course, be reversed with an accompanying use of PNP type transistors in the control sub-system 20.
Alternatively, the ionizing and arc current supplies could be a single circuit located on one side of neutral, However, in such a configuration the voltage ~rom ground would be higher and the controlled arc current path would have to flow through the ionizing supply which would re~uire that more expensive -~ components be used in the ionizing suppl~.

, Referring to Figure 13, an embodiment is illus~rate~
wherein t~e bas~c arc control circuit discussed above is altered so as to use an operational ampli~ier and a trans~ormer power supply as was suggested previously, In Figure 13, those elements which are similar to those of Figure 12 are assigned to the same reference number with a prime (t) or a triple prime (~') attached thereto while new components are assigned new reference numerals, In this manner the similarities and depar-tures between the embodiment of Figure 12 and the embodiment of Figure 13 can easily be seen, Considering the power supply portion o~ Figure 13, a trans~ormer 102 steps down the line voltage (which may be 116 VACJ 277 VAC or other available line voltages) to a 10 VAC
voltage appearing on the isolated secondary winding thereof, A diode 104 acts as a half wave rec-tifier so as to permit the positive half circle of the secondary voltage to charge a capacitor 108 connected across the secondary to a level approxi-mately 14 VDC above the voltage o~ the common bus, re~erred to hereinafter as the signal common, This voltage level will ~0 hereinafter be referred to as the plus or positive supply~ A
further diode 106 permits the negative half cycle o~ the 10 VAC secondary voltage to charge a capacitor 110 to a level approximately 14 VDC below signal common, which level will hereinafter be referred to as the minus supply. A resistor 82'~ is connected in series combination with a zener diode 78't~, with zener diode 78'~ being connected to the signal common bus and resistor 82'~ to the plus supply, as shown, in order to provide a regulated voltage above the signal com-mon voltage above ~or signal generation purposes, The use of a plus and minus power supply is desir-able, (although a single sided supply can be employed) J when an operational amplifier 116 is substituted in place of the sum point transistor 62' shown in Figure 120 The employment of such an oper~tional amplifier, whether used in an in.verting or non-inverting virtual ground summing mode or a di~feren~ial input configuration, has numerous advantages including the exceedingly high gain attributes of most operational amplifiers, Figure 13 shows operational amplifier 116 connected in a non-inverting differential input configuration, The setting o~ a potentiometer 64 " ' provides a reference signal at the plus in-put of operational amplifier 116, A light controlled variable resistance photocell 74 "', which is connected to a resistor 112 and a resistor 114 as shown, is connected to the minus in-put, Before proceeding, it should be noted that the func-tion of potentiometer 641l~ can also be replaced by a remote program signal, signal generator or the like in an application requir-ing remote adjustment of the reference signal, When photocell 74 " ~ and resistor 112 are connected in a circuit between signal common and the plus regulated bus9 they act as a voltage divider wherein the amplitude of the voltage at their junction node 113 will vary from almost zero '~ 20 volts ~with photocell 74 " ' in darkness) to almost that of the plus regulated bus ~in bright light). As noted above, junction node 113 is connected to the minus input of operational ampli-fier 116 through resistor 114, Resistor 11~ is part of an RC
time constant network that further includes a capacitor 118.
This network helps to prevent abrupt changes in the output of the system where this is desirable. Alternatively, for a faster response system, the RC networ~ might be modified to different component values or be removed with the minus input of operational amplifier 116 can be connected directly to the junction of photocell 74~t and resistor 112.
The output of operational amplifier 116 is connected to the plus and minus supplies and to a further diode 120.
.

;30- : :

t,~,``'~ ;
: `' ` '` ` . ' ' ` ' " ': ` ' The latter is also connected to a diode 122 whose anode is al~o connected ~to the junction of a pair o~ voltage divider resistors 124 and 126~
The values of resis-tors 124 and 126 are selected such that the junction voltage, i.e., the voltage on the anode of diode 122, provides a minimum "onl' signal through diode 122 to a transistor 60'~'o Hence, transistor 60~ " is "on" at some minimal level related to the voltage division ~f resis-tors 124 and 126 whenever the system has AC line power Transistor 60 " ' drives a control transistor 26~'~
via a resistor 128 which acts as a current source to minimize component thermal drifts and the like. Transistor 26~ norm-ally operates in the active (transition) region, thereby limit-ing the current in the ballast primary only when the lamps are ignited However, transistor 26~ is effectively saturated "on" during the "lamps o~f" portion of the AC cycle so full magnetizing and lamp filament current is provided at least up to lamp ignition. To reiterate, it is important to understand that, except for the minor losses in $he bridge across and ~0 saturated transistor 26?ll, the full line voltage is applied to the ballast 100' until the lamps ignite Hence, the ballast 100' is provided with magneti~ing current and the lamps have their rated cathode current when applicable The bridge diodes 92~, 94~, 96~ and 98~ recti~y the AC o~ the ballast 100~ and transis$or 26~', being located in the DC leg, permits the previously described DC control techniques to be employed~
When the lamps Ll and L2 ignite, the load applied to the secondary (not shown) of the inductive ballast 100~ is reflected to the primary (not shown) and an increase in primary current is demanded by the lamps. The base drive set by the light loop, determines the amount o~ collector current that is allowed to ~low through transistor 26'~. There~ore, when the current demand of the lamps is not satisfied by transistor 26 " ', the voltage across the primary o~ the ballast 100' ~alls.
At the same instant in time, this drop in ballast primary voltage is applied to the collector-emitter circuit of transis-tor 26~l. This voltage when added to the ballast primary vol-tage, equals the line voltage until the lamps are extinguished further on in the half cycle. At this later time, the voltage from the collector to emitter of transistor 26~t is reduced to a minimum and transistor 26~ll therefor reverts to a saturated condition The signal information for the closed loop is thus generated at a 120Hz rate for a 60~z system and a lOOHz rate for a 50Hz system, and in approximately 6 millisecond bursts from the lamps for a 60Hz system and in 8 milliseconds bursts for a 50Hz systsm. These bursts of light are averaged by the time constant circuit associated with operational amplifier 116. :
Briefly considering the operation of the embodiment of Figure 13, when the system is energized with either 116 VAC
or other line voltages, current flows through the primary of ballast 100' and two of the diodes 92', 94', 96', and 98', depending on the polarity of half cycle of the AC input Fur-ther, transistor 26ll~ is conducting, transistor 26 " ' being "saturated on" by the reference signal derived from potentio- ;
meter 64l~l, providing that this reference is sufficient to drive the output of operational amplifier 116 to a voltage level sufficient to back bias diode 122. Alternatively, i~
the output voltage o~ operational amplifier 116 is insufficient to back bias diode 122, the minimum signal provided by diode - 122 will back bias diode 120, with diode 122 providing a mini-mum signal from voltage divider resistors 124 and 126 to transistor 60'l~. The signal from diode 120 or diode 122 turns : on transistor 60~' through resistor 128 and transistor 26 : -32-. ~
.. . . . ............. . . . . . .
... . . ..

~ 2~

is saturated "on" as long as ~he lamps have no~ ignited It is noted that a~transistor is saturated "on" when that trans-istor has sufficient minorit~ carriers in the base region so as not to limit any current which would flow through the col-lector. Expressed another way, the collector current o~ the transistor is now unlimited and will remain so to the extent o~ the availability of minority base region carriers.
For this saturated condition of transistor 26~', the ballast primary of ballast 100' essentially receives the full line voltage and the saturated transistor 26lll conducts the magnetizing current of ballast 100l (together with the load current of the lamp heaters if rapid start lamps are used).
After the cathodes in lamps Ll and L2 are heated, and the hal~-wave AC lamp voltage rises to a ~iring level, the lamps ignite Current through lamps Ll and L2 then rises to a level dependent on base drive of transistor 26 " ', as explained hereinabove.
Once this current level is reached, the transistor 26 " ' comes out of saturation and the current flow is now limited. At this time, the circuit voltages adjust due to the fact that the change in circuit current ceases. In particular, as the AC
halfwave ballast primary voltage ~alls, the difference between the line voltage and this ballast primary voltage appears ac-ross transistor 26~ This adjustment iD voltage continues such that the sum of ballast primary voltage and transistor voltage equals the line voltage until the lamps extinguish, This occurs each time the AC halfwave declines to a nonsus-taining arc level. At this time the circuit current will be-gin to be less than the regulated value and transistor 26 " ~
then resaturates and the collector-emit-ter voltage ~eaches a saturation minimum~ The ballast primary voltage is then once again equal to the line ~oltage minus the small saturation voltage o~ the saturated transistor-diode bridge combination.

-33~
' ~ .

86~;

The operation o~ the circuit o~ Figure 13 described above is repeated during a part o~ each hal~ cycle of the line voltage depending on the duration o~ the current limiting period The base drive or regulated collector current o~ transistor 26l~ is set by the closed loop completed through lamps Ll and L2 and photocell 74 " ~. The loop response is slowed down by the RC network ~ormed by resistor 114 and capacitor 118 such that fast changes in light level are averaged over a several second time periodO However, as noted above, the loop can also have a fast response by providing adjustmen~s to, or the elimin-ation of, the RC network.
The value o~ current limiting provided in response to a related light level is set by setting the tap or wiper o~
potentiometer 64'~' to produce the desired output voltage.
Feedback is provided by sensing the light output from the lamps Ll and L2 and/or some other light components via a light col-lecting lens CL attached to a bundle o~ fiber optics F0 to transmit a measure of the ambient light level at a given loca-tion to photocell 74~' generally located with the control cir-cuitry within a lamp fixture without using electrical conduc-tors. This insures that the selected lamp current will be limited to a level related to the reference signal level. In operation, the feedback light produces a voltage at the junc-tion of photocell 74 ~ ~ and resistor 1120 Assuming that light is falling on photocell 74 " ', this voltage increases until it is virtually equal to the potentiometer voltage at the positive input of operational amplifier 116. The almost zero di~ference voltage referred to constitutes the signal which produces the regulated current through lamps Ll, L2. The light output o~
the lamps Ll, L2 may be increased or decreased by changing the reference level signal provided by potentiometer 64 " ' within the bounds of the lower limit set by the voltage at the junction .~ .

6~S
of resistors 124 and 126 and the upper level set by the current limiting of the balla~t 100' Whenever the current limit of ballast 100' is rea~hed, transisto~ 26''' is ag~in sa~urated "on".
It is noted that in the embodiments described previ-ously the minimum level signal is established by adjustment of the reference or command signal potentiometer (element 64) so as to establish a minimum reference signal level at the trans-istor summing point To summarize, a key -feature ~ the system of the invention in all illustrated embodiments thereof, is that the control transistor is saturated "on" for the period of time during each AC half cycle that the lamps are not ignited. There-fore, firing of the lamps is not iDhibited and once the lamps fire, the control transistor then operates in a new unsaturated linear range up to the point that the ballast limits the current.
Further, with the use of a sufficient input reference signal, the ballast will provide limiting and the control transistor is again saturated with lamps "on". This sequence may repeat it-self each half cycle.
Before considering the embodiment of Figure 14, cer-tain background consîderations should be examined In most instances in the commercial lighting field each pair of lamps in a fixture has an AC inductive ballast; in fact, many fix~
tures contain four lamps with two ballasts in the ballast com-partment of the fixture. While an individual sys~em could be used for each ballast, substantial savings might be realized if two or more ballasts could be operated from a single control system. However, in actual practice two ballasts cannot be operated in parallel ~rom a single system because the lamp pairs, iD effect, act in a manner somewhat analagous to zener diodes. Specifically, one pair inevitably ignites and there-after, while the other pair may subsequently ~gnite, this pair will operate in a low uncontrolled current region so that only .

, the pair that first reaches the arc discharge region is con-trolled. This ~ehaviour of paralleled ballasts is due to the arc-discharge phenomena and is a substantial obstacle to real-izing the economies referred to above One simple but unique solution to this problem is illustrated in Figure 140 Generally speaking, apart ~rom the circuitry used in providing the solution in question, Figure 14 corresponds to Figure 13 with addition of a second pair o~ pairs lamps L3 and L4 and an associated ballast, and the same refer-ence numerals are used for common components. In accordance with this solution referred to, another four diode bridge formed by diodes 134, 13~, 138 and 140, a control transistor 141, and a pair of emitter resistors 130 and 132, are connected as shown in Figure 14 It is noted that one of these emitter resistors, vizo, emitter resistor 130, is added in the emitter leg o~
transistor 26~l and the base lead o~ transistor 141 is connec-ted to the junction between resistor 128 and transistor 26l~1.
I~ it is assumed, -~or example, that when the lamps Ll and L2 connected to the ballast 100' ignite, the s~stem (and the as-sociated lamp pair) proceed to a current limited mode set by the collector-emitter current o~ transistor 26 "' it will be seen that the collector-emitter current will generate a voltage across resistor 130 tending to reduce the base drive for transistor 26l'~ relative to transistor 141. This will happen unless there is a similar current flow in ballast -transistor 141 whereby a matching voltage would be developed across emitter resistor 132 There~ore, the collector-emit$er currents o~ transistor 26 " ' and 141 would tend towards matching due to the "emitter degeneration" caused by the emitter resistors 130 and 132. It will also be appreciated that the value of resistor 128 must be reduced so as to provide the extra current to drive the additional transistor ~or the second ballast - ~ .
: .

This concept, with appropriate modification, could also be extended to include ~dditional ballasts in other ~ix-tures. The ~ixture with the sensing and reference signal cir-cuitry will hereinafter be referred to as the "master unit" and the second ballast and/or other fixtures with other ballast(s), together with their full wave bridges and control transistors with e~itter resistors~ will hereinafter be referred to as "follower units", The power supply, as well as transistor 60'~' of the master unit, must be suitably rated to provide suffic-ient signal levels to accommodate the needs of a plurali-ty of control transistors, Electro-optical devices can also be em-ployed to eliminate wiring used in conductive coupling between master and follower units, Referring to Figure 15, another embodiment of the master-follower concept is illustrated, Figure 15 is similar to Figure 14 and like elements have been given the same refer-ence numerals. The advantage of the embodiment of Figure 15 over that of Figure 1~ is that the currents ~lowing in the primaries of the one or more follower ballasts are more precise-ly matched or scaled, In addition to the components added inFigure 14, a further transistor 602 and further operational amplifier 116' are also incorporated in the follower circuit, The reference signal supplied to the plus input of operational amplifier 116' is derived from the voltage generated across emitter resistor 130 and the feedback or minus base input to operational amplifier 11~2 is derived from the voltage generat-ed across emitter resistor 132, With a rated forward gain of 50,000, operational amplifier 1162 provides maximum output for less than a millivolt of differential signal input, Because of this, the embodiment o~ Figure 15 provides precise current matching or scaling of a plurality of ballast currents, The transistor currents can be scaled by providing an appropriate ratio between the values o~ the respective emitter resistors.
As discussed above, follower units could be provided for many ballasts with interconnecting signal wiring ~rom the master unit or optical coupling devices Alternatively, by using the AC line as a carrier, signals can be coded and trans-mitted and thereafter received and decoded at selected fixtures.
The current matching capability of the circuit of Figure 15 is so precise that the full wave bridge formed by diodes 134, 136, 138 and 140 and the second ballast 142 could be eliminated and the collector of transistor 141 connected directly to the col-lector of transistor 26~ so as to increase the current capa-city of the master unitO This would be particularly useful with the higher current ballasts employed with higher current arc discharge lamps or as a simple method for connecting a plural-ity of output stage transistors in parallel to provide a unique high current source capable of handling up to a hundred or more amperes Returning again to commercial lighting systems, an-other problem related to energy savings is what might be termed the light turn on/turn off problem. This occurs, for example, when someone forgets to turn off the lights when leaving an area and/or when maintenance personnel turn lights on after - -hours for longer than necessary Some buildings are DOW ~.
equipped with light turn-on and turn-off programs and many software programs and/or sensors are available for doing the same thingO However, the cost of the magnetic contactors, housings, power handling wiring and other power switching pro-blems inhibit the provision of automatic programming for light systems. However, with a system in accordance with the pre-sent invention in place, a computer signal delivered to any master or single unit could shut of~ the lights controlled thereby by the addition of simple circuitry which would serve ... .

., . . . ~ .. -to pull the base of transistor 60~' in Figure 15 negative to the point of pr`oviding shut o~f In a simple example illus-trated in Figure 15, a photo-transistor or other optical device, denoted 144, is connected to the base o~ transistor 60~ and to a resistor 146 connected to the minus 15 volt power supply bus, With this arrangement, the software program referred to above would, at the appropriate time, energize a light emitting diode (not shown) to switch the photo-transistor 144 "on", thereby pulling the base of transistor 60'l~ negative to the point of cut off. This would of course turn o~f transistor 26~ and terminate flow of the ballast magnetizing currents and hence cut off power to the lamps.
Although the present invention is particularly appli-cable to illuminating light, the invention would also be useful in many photographic and other technical or scientific appli-cations where light control is of a definite advantage. As stated, a simple yet highly efficient energy conserving system is provided in accordance with the invention which controls the level of light from a fluorescent lamp(s) and which has appli ~0 cations for controlling the quantity and other characteristics of the outputs of gaseous arc discharge lamps in general, as well as special purpose load devices, over a wide dynamic operating range The actual savings which can be realized ; would amount to millions of barrels of oil where the principles of the in~ention were utilized on a sufficiently widespread basisO ~' -38a-. . .

: :

It will be appreciated that although an inductive ballast is shown in the specific embodiments illustra-ted, other ballasts can be employed and that the term "reactive ballast" as used in this application refers to inductive, capacitive and resistive ballasts.
Although the invention has been described relative to exemplary embodiments thereof, it will be understood that other variations and modifications can be effected in these embodiments without departing from the scope and spirit of the .invention.

Claims (27)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In a fluorescent lamp lighting system comprising at least one fluorescent lamp and an AC supply for supplying energy to said at least one lamp through an inductive ballast, an automatically and relatively operative transistor ballast comprising:
rectifying means connected to the AC supply;
control transistor means connected to said rectifying means for controlling the arc current through said at least one lamp by limiting and controlling the arc current supplied to the at least one lamp during at least a part of the portion of a half wave of the AC supply during which said at least one lamp is ignited and for providing substantially no current limiting during those portions of a half wave of the AC supply when said at least one lamp is extinguished, said control transistor means including a control transistor having a base biasing circuit and an operational amplifier connected in the base biasing circuit of said control transistor said inductive ballast being connected to provide current limiting when said control transistor is providing substantially no current limit-ing and said control transistor providing a series current path for all of the current flowing in said inductive ballast at all times during which current flows in said ballast; and means responsive to the light output of the at least one lamp for controlling said control transistor means so as to control the arc current supplied to the at least one lamp at least partially in accordance with the light output of said at least one lamp.

2. A system as claimed in Claim 1 wherein said rec-tifying means comprises a full wave rectifying bridge connec-ted in series with the reactive ballast and said control trans-istor is connected in said bridge.

3. A system as claimed in Claim 2 wherein said light responsive means further includes a photoelectric means for receiving light and for producing an output in accordance therewith and means for connecting the output of said photo-electric means to one input of said operational amplifier.

4. A system as claimed in Claim 3 wherein control transistor means further comprising a variable voltage supply means for supplying a predetermined input voltage to the other input of said operational amplifier,

5. A system as claimed in Claim 4 wherein said vari-able voltage supply means comprises a potentiometer for supply-ing a fixed input voltage to said operational amplifier in accordance with the voltage setting of said potentiometer.

6. A system as claimed in Claim 1 wherein said base biasing circuit further comprises means for supplying a further biasing voltage to said control transistor for providing a minimum biasing signal for maintaining said control transistor in the "on" state when the at least one lamp is not ignited.

7. A system as claimed in Claim 6 wherein control transistor means includes a further transistor connected to the base of said control transistor and means for providing a regulated power supply, said means for providing a minimum biasing signal including a resistive voltage divider connected to said regulated power supply and a diode connected between the output of said voltage divider and the base of said further transistor.

8. A system as claimed in Claim 1 further comprising means connected to said AC supply for providing positive and negative DC supply voltages for said operational amplifier.

9. A system as claimed in Claim 1 wherein said control transistor is biased into operation in the active region of the operating characteristics thereof when the lamps are ignited and which is biased into saturation when the arc current exceeds a predetermined level.

10. A fluorescent lamp lighting system powered from an AC supply, said system comprising:
a first plurality of fluorescent lamps;
a first reactive ballast for said first plurality of lamps;
a second plurality of fluorescent lamps;
a second reactive ballast for said second plurality of lamps;
rectifying means connected to said AC supply;
a control transistor connected to said rectifying means for controlling the arc current supplied to said first plurality of lamps;
a single control unit for controlling the arc current through said first and second plurality of lamps including feedback means responsive to the output of said lamps for pro-ducing an arc current control signal related to the output of said lamps;
means for supplying said arc current control signal to said first control transistor; and follower circuit means, connected between control unit and said second ballast and including a second control transistor connected to the output of said control unit, for controlling the arc current supplied to said second plurality of lamps and including means for relating the arc current control signals applied to said first and second control transistors so that currents flowing in said first and second ballasts are in a desired relationship.

11. A fluorescent lamp lighting system as claimed in Claim 10 wherein said means for relating the arc current signals provides scaling of the currents flowing in said first and second ballasts,

12. A fluorescent lamp lighting system as claimed in Claim 10 wherein said means for relating said arc current signals provides matching of the currents flowing in said first and second ballasts.

13. A fluorescent lamp lighting system as claimed in Claim 10 wherein said means for relating the arc current signals comprises a resistance connected in the emitter cir-cuit of each said first and second control circuits.

14. A fluorescent lamp lighting system as claimed in Claim 13 wherein said follower circuit means includes an operational amplifier connected to said second control trans-istor.

15. A fluoreseent lamp lighting system as claimed in Claim 14 wherein one input to said operational amplifier is connected to the emitter of the first control transistor and the second input of said operational amplifier is connected to the emitter of said second control transistor.

16. A fluorescent lamp lighting system as claimed in Claim 15 wherein said single control unit includes a further operational amplifier and a first biasing signal transistor connected to the output of said further operational amplifier and to the base of the first control transistor, and said follower circuit means includes a second biasing signal trans-istor connected between the output of the first-mentioned operational amplifier and the base of said second control trans-istor,

17. A fluorescent lamp lighting system as claimed in Claim 10 wherein said first and second control transistors act to limit and control the are currents supplied respectively to said first and second plurality of lamps during at least a part of the portion of a half wave of said AC supply when said lamps are ignited and provide substantially no current limiting for values of arc current above a predetermined level.

18. A fluorescent lamp lighting system comprising:
means for providing an AC supply voltage;
a first set of fluorescent lamps;
a first ballast connected to said first set of lamps;
at least one further set of fluorescent lamps;
a further ballast connected to said at least one further set of lamps;
first control means connected to said first ballast for controlling the arc current through said first set of fluorescent lamps, said first control means including a first control transistor which is fully saturated on (i) for arc currents below a predetermined level and (ii) subsequent to extinguishment of said first set of lamps and prior to ignit-ion of said first set of lamps, and which is biased such as to operate in the active region of the operating characteris-tics thereof subsequent to the ignition of the first set of lamps and up to said predetermined arc current level;
second control means connected to said second bal-last for controlling the arc current through said second set of fluorescent lamps, said second control means comprising a second control transistor which is fully saturated on (i) for arc currents below a predetermined level and (ii) subsequent to extinguishment of said second set of lamps and prior to ignition of said second set of lamps, and which is biased to operate in the active region of the operating characteristics thereof subsequent to the ignition of the second set of lamps and up to said predetermined arc current level;
a single feedback control unit for sensing the light output of said lamps for generating a control signal for controlling said first and second control transistors; and means, including first and second resistors connec-ted to the respective emitter circuits of said first and sec-one control transistors, for providing a desired relationship between the arc currents flowing in said first and second ballasts.

19. A system as claimed in Claim 18 wherein said feedback control unit includes a first operational amplifier connected therein, said system further comprising a second operational amplifier connected to the base of said second control transistor.

20. A system as claimed in Claim 18 wherein a point on the junction between the first resistor and the emitter of the first control transistor is connected to one input of said second operational amplifier.

21. A system as claimed in Claim 1 further comprising fiber optic means for guiding light from at least one of the lamps to said light responsive means.

22. A system as claimed in Claim 21 wherein the rectifying means, control transistor means and light respon-sive means are disposed in control unit located within a light fixture containing said at least one lamp from which light is guided by said fiber optic means.

23. A system as claimed in Claim 20 further compris-ing fiber optic means for guiding light from at least one of the lamps to said light responsive means,

24. A system as claimed in Claim 23 wherein the rectifying means, control transistor means and light respon-sive means are disposed in control unit located within a light fixture containing said at least one lamp from which light is guided by said fiber optic means.

25. A light regulation system for controlling the output of at least one lamp in a follower fixture in accordance with the light output of a master fixture containing at least one lamp, said lamps comprising arc discharge lamps and said lamp units each comprising a ballast for the at least one lamp and a control circuit connected to the ballast for con-trolling the light output of the at least one lamp, said system comprising optical-electrical transducer means connected in the control circuit of said follower fixture for controlling the output of the control circuit of the follower fixture in ac-cordance with the light input received thereby, and light col-lecting and coupling means for collecting the light output of the at least one master lamp and for coupling the said output of said at least one master lamp to said optical-electrical transducer means of said follower fixture.

26. A fluorescent lamp light system powered from an AC supply and adapted for use with higher current ballasts employed with higher current arc discharge lamps, said system comprising:
a plurality of said arc discharge lamps;
a said reactive ballast for said plurality of lamps;
rectifying means connected to said AC supply, a first control transistor connected to said recti-fying means for controlling the arc current supplied to said lamps through said ballast;
a control unit for controlling the conduction said control transistor including feedback means responsive to the output of said lamps for producing an arc current control sig-nal related to the output of said lamps and for supplying said arc current control signal to said control transistor; and means for increasing the arc current supplied to said lamps including at least one further control transistor and means for substantially matching the current flow through the first control transistor and said at least one further control transistor comprising a first resistor connected in the emitter circuit of said first control transistor, a second resistor connected in the emitter circuit of said at least one further control transistor and having a resistance value sub-stantially equal to the resistance value of said first resistor, and an operational amplifier having an output connected to the base of the at least one further control transistor, a first input connected to a junction between said first resistor and the emitter of said first control transistor, and a second input connected to a junction between said second resistor and the emitter of the said at least one further control transistor

27. A system as claimed in Claim 26, further com-prising means for directly connecting collector of the said at least one further control transistor to the collector of said first control transistor.