Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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The present invention relates to ligh-t control sys-
tems ~or illumi\nation purposes and the like
Because the problems associated with conventional
lighting systems using fluorescent lamps are not always ~ully
understood, a brief description of such systems and the nature
of fluorescent lamps in particular will be conside~ed by way of
background It should be noted that some of this discussion
will be continued below after the invention has been 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 "fluoresces"
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 phenomena which lack simple definition, As dis- ;
cussed hereinbelow, the current in the arc discharge region
; of operation will continue to increase to disastrous levels
unless limited by e~ternal meaDS In order to proYide this
current limiting, devices commonly known as ballasts are
employed. In general, for AC operation, inductive ballasts
are used, while for DC operation, resistive ballasts are
generally employed. Transistor ballasts can be also used but
these are impractical for most applications as is explained in
more detail below. Further, and more generally resistive
ballasting requires a substantial increase in voltage over
that required ~y the lamp and system employing such ballast-
ing are highly dissipative and energy ine~ficient.
A further problem associated with lamps such as are
being discussed is that of providing adjustment of 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
~hich are specifically designed to enable adjustment of the
arc current
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 electrodes. 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 windingsO Another
type of fluorescent lamp is the "pre-heat" lamp which has a
switch mechanism in the ballast circuit that momentarily closes
or is closed upon energization so that a curreDt flows through
the lamp cathode and the inductor The switch then opens, aDd
due to the stored inductive energy, a voltage transien* 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 firing, preheat 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
deleterious material from collecting on the cathodes.
A third group of lamps are the so-called "instant
start" lamps. The cathodes of these lamps are designed for
cold starting and the ballast circuit simply provides a
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suf~iciently high starting voltage to cause conduction to be
initiated by w~at is called arc bombardment. Once the lamp is
started the rated arc current k~eps the cathodes hot enough to
provide emission and to boil o~ any contaminating materials
It is noteworthy that neither the instant start nor prehe~t
lamps can be dimmed because these lamps are designed to require
the rated arc current in order to keep their cathodes at a
"liveable" temperatureO ~hen these lamps are used in a dimming
mode, the cathode temperature is lowered and the lamp ends are
blackened by material sputtering off the cathode so that, fin-
ally, the cathode is used up and the lamp ceases to function.
A further problem associated with fluorescent lamps
is that of the ~ecline 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 associated 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 with 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), 4,012,663 (Soileau) and 3,909,666 (Tenen) the
latter of which is discussed below
In accordance with the invention, a light control
system for fluorescent and like lamps is provided which af~ords
very substantial eDergy savings According to one aspect of
the invention a system is pro~ided which enables the lumen
output of the fluoresGent lamps to be controlled so as to pro-
vide a minimum level of room light and to be adjusted inversely
proportional to the amount of light present ~rom other sources,
including daylightO Thus, according to this aspect o~ the in-
vention, a system is provided wherein light is the controlled
variable rather than lamp currentO
According to a ~urther aspect o~ the invention,
fluorescent lamps are driven from a voltage supply which is
intentionally poorly regulated so that the supply voltage is
reduced in a non-dissipative manner simultaneously with the
reduced 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 for the lamps whereby the voltage
supply is more closely matched to the lamp requirements. This
combination minimizes the amount of power dissipated by the
ballasting transistor while operating in the active region
thereof and also provides intrinsic current limiting wh0n 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
(ballast transistor) connected in the arc current path of the
lamps. A light sensing means is provided ~or sensing the le~el
of ambient light in the area of the lamps, this total includ-
ing the light output o~ the lamps and the ambient light pro~
duced by any other light sources including sunlight. A feed-
back means connected between the electronic de~ice and the
light sensing means controls the conduction of said electronic
device and thus the current ~low in the arc current path in
accordance with the output of the light sensing means so as to
--5--
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maintain the total ambient light substantially constant, The
poorly regulated voltage supply comprises a voltage multiply-
ing circuit utilizing diodes and capaeitors, An ionizing sup-
ply cireuit is also provided which supplied the starting or
firing voltage for the lamps and which automatically provides
a negligible low voltage when the lamps are fired. The ion-
izing supply circuit also comprises a voltage multiplying cir-
euit employing diodes and capacitors.
In aecordance with a second embodiment o-f the inven-
tion, a transistor ballasting and control circuit similar to
that described above is ineorporated in lighting systems which
ineludes an induetive ballast, It will be appreeiated that
millions of sueh inductively ballasted lighting systems are
presently in existenee, and the inelusion of the transistor
ballasting and eontrol eircuit in eombination with the indue-
tive ballast provides substantial energy savings, The two ~`
ballasts are operable selectively and automatieally, with the
transistor ballast being the operating eurrent limiting bal-
last over the dynamie range of current eontrol from a given
~0 minimum up to a design eurrent maximum and being automatieally
supereeded by the induetive ballast at that eurrent maximum,
More speeifieally, the ballast transistor saturates at the
eurrent maximum and the induetive ballast serves its eonven-
tional ~unetion of current limiting only at this time ? i.e,,
with the transistor saturated, The induetive ballast also
provides a high firing voltage during "start up" as well as
the sustaining operating voltage, The presenee of the in-
duetive ballast also prevents the transistor from having to
piek up and dissipate all o~ the power assoeiated with the
exeess voltage resulting from the negative volt-ampere ehara-
eteristies o~ the lamps, Beeause the transistor operates as
the eurrent limiter during most of the "on" time of the lamps,
;
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~?s~
$he I R losses of the inductive ballast are substantially re-
duced and consèquently the life of the ballast is greatly
extended.
Other features and advantages of the invention will
be set forth in, or apparent from, the detailed description of
the preferred embodiments found hereinbelow.
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Brief Description of the Drawings
_
Figure 1 is a graph plotting light output as a function
of hours in use for a fluorescent lamp;
Figure 2 is a graph illustrating the operating char-
acteristics of ~ixed arc current declining light output light-
ing systems;
; Figure 3 is a graph illustrating the operating char-
acteristics of a constant light output lighting system in ac-
cordance 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 resistive ballast;
Figure 6 is a highly schematic block circuit diagram
of a prior art lamp system 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 con-
- 20 taining Fig. 5)
Figure 9 is a schematic circuit diagram ~f a lamp
lighting 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 o~ drawings con~
taining 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) and
Figure 12 is a schematic circuit diagram of a further : :
embodiment of the invention adapted for use with a pre-existing
. inductive ballasting system.
7 ~.
6~
Before considering the preferred embodiments of the
invention~ somè of the points raised in the ~oregoing background
discussion of the invention will be consi~ered in more detail.
Thus, as stated above, because of the phosphor decay problems
associated with fluorescent lamps, a design criteria that
establishes the need for, eOg , seventy foot candle (70FC)
lighting 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 o~ 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 the 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 F40~12 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 consumption. Over time, while the
arc current, with its related power consumption, remains reason-
ably constant, the light output declines as is shown graphically
in Figure 2. As e~plained hereinafter, one aspect of the
present invention concerns control o~ the arc current as a
function of a referenced ~evel of the ambient or room light.
8~
Thus, referring to Figure 3, this type o~ control is illus-
trated graphically for a constant li~ht level over time of
70 FC with a starting arc current of 200 ma. Now as the phos-
phor decays (and the phosphor will decay more slowly at the
lower arc level because of the lower UV and ion interaction
level associated with the lower arc level), the provided con-
trol advances the arc current so as to maintain the ~ight con-
stant at the referenced level of 70 FC. 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 relationahip to the level of its arc current.
: Because 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 point the current has reached only 360
ma (with the average current ~rom zero to 24,000 hours being
285 ma) as opposed to 430 ma in the case of Figure ~. Thus,
in addition to having the ability to adjust the referenced
level of light and then hold this level constant over time,
this approach permits immediate evaluation and variation in
different areas to meet varying requirements. Before proceed-
ing further, it should be pointed out that the light decline
in Figure 2 and the curreDt 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 ~o those
actually found in practice
As stated above, the arc control capability provided
by the invention is a function of the room or ambient light
level Accordingly, if the room referred to in the e~ample
has an outdoor window, daylight would enter the room at certain
times of the day so that less light would be required from the
g _
. . ~
lamps to maintain the relative 70 FC level, Thus, an even
lower arc currènt would be required resulting in further, and
even more substantial power savings, As mentioned, and as is
explained in more detail hereinbelow, the system of the present
invention possesses the arc control capabilities discussed and
thus provides the advantages which have been re~erred to,
Before discussing the combination of artificial and
daylight and the manner in which the present invention takes
advantage of the combination, some brief comments on "daylight-
ing" might be helpful, Daylight illumination is made of twocomponents, 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
wiDdow as if it were a piece of opal diffusing glass li~hted
by varying light sources on the outside, The illumination from
the source or combination of sources will vary from zero during
the night period up to several thousant lumens per square foo$
of window area in the day period, 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 up-
wardly as the daylight declines, The average arc over the time
of a 12 hour day period with daylight available would be re-
duced to less than half required without such auxiliary light-
ing, on most days,
Another area which was cusorily explored above and
which will be considered in somewhat more detail DOW iS that
of the difficulty of controlling fluorescent lamps, The im~
portant problems iD this area were mentioned above, The first
is that the mercury within the lamp must be ionized, thereby,
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$~
among other effects, lowering the resistance between the lamp
electrodes from a virtually infinite level to a level where
electron conduction is permitted through the ionized gas and
hence the lamp is turned on The second and most difficult
problem to deal with is the phenomena that occurs in the con-
duction of electricity through gas that occurs upon firing of
the lamp. In this regard, it is stated by Condon and Odishaw
in the text Handboo~ on Physics, at page ~-174 that the phen-
omena associated with the conduction of electricity through gas
defies rigorous definition. Figure 4 is adapted from the same
page of the text and shows a model of the volt-ampere character-
istics of a gas discharge lamp It will be seen that when the
arc is struck the arc current, starting close to zero, trav-
erses through the various discharge regions. The last region
is where gas discharge lamps used for lighting generally opera~e
Of significance is that the arc discharge region, shown in Fig-
ure 4, does not follow Ohm's law. In fact, the voltage de-
creases, rather than increases, with an increase in current.
This explains why fluorescent lamps are said to ha~e negative
resistance characteristics and means that if the lamp was
energized with a voltage source and current conduction reached
the arc discharge region, the current would continue to rise to
a disastrous level.
If the commonly available AC power was provided as a
fixed current-voltage compliant source, a fluorescent lamp
might be connected and operated directly 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 positi~e resistance of the load, a
fluorescent lamp requires a means for stabilizing the arc
current. Such a means is commonly referred to as a ballast
as noted previously.
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... ..
Most fluorescent lamps are operated with AC through
one or more la~ps connected in series with an inductor as the
ballast element therefor, The reactance of the inductor be-
comes the limiting impedance and limits the amount of current
in the series circuit, Except ~or second order ef~ec-ts, an
inductive reactance ballast can be ~onsidered a non-dissipative
current limiter. Capacitive reactance can also be employed as
a non-dissipative ballast at high AC frequencies. However, at
60 Hertz the stored energy in the capacitors would discharge
into the lamp as a highly peaked current due to the volt-
ampere characteristics of the lamps unless the current is
limited in some other way,
Direct current operation of fluorescent 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 mu~h or more power than the lamp
consumes in its lumen generating process, There are exceptions
to this statement 9 as example being disclosed in U,S. Patent
Re ~8,044 (Widmayer) where a choke is used as a volt second
integrator with other controls,
Referring to Figures 5 and 6, two embodiments of a
DC ballast are illustrated, The emobidment 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 com-
plies to a level more or less equ~l to the source voltage ES
minus the fluorescent lamp voltage EL drop at current equili-
brium, divided by the ballast resistance R ~ ES - EL/R)3 ,
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 di~ference
-12_
between the embodiments of Figures 5 and 6 is that a transis-
tor ballast is ùsed in Figure 6. The transistor ballast is
formed by a transistor T which is controlled by a control cir-
cuit CC It should be noted that the embodiment of Figure 6
is not practical principally because in order to be an effec-
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 fluorescent arc levelsO Of course, 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, howevPr, specially designed
ballast circuits that permit some manual adjustment of the arc
current. The more common types include thyratrons, adjustable
voltage transformers and adjustable reactor circuits, among
others, which vary the arc current amplitude and/or the current
on-off time within the AC half 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 of a prior art
DC resistive ballast network is illustrated Figure 7 is
adapted from the drawing in U.S. Patent No~ 3,909,606 (Tenen)
and is of particular interest in that the input voltage cir-
cuit bears some resemblance to that of the invention. The
Tenen patent describes the capacitors Cl to C4 and diodes D
13-
to D4 as forming a voltage quadrupler circuit. The patent
states that wh~n the switch arm o~ switch S is mov~d to the
high or low position, the voltage output between terminals T
and T2 is four times the pea~ input potential and that when
fluorescent bulf FB ingnites, most of the resulting increased
current ~lows through lower impedance capacitors Cl and C2 so
that the vol~age increasing ef~ect o~ trigger capaci~ors
C3 and C4 becomes negligible The current through bulb FB is
limited by ballast resistor Rl and dimmer resistor R2.
The voltage input circuit of the Tenen patent 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
~vaveform of the supply voltage at load would generally corres-
pond to that shown in Figure 8, wherein the positive half-wave
provides the voltage indicated at (a), the minus half-wave pro-
vides voltage (b) and the voltages (c) and (d) result from the
outputs of the one-half doubler circuit as added to the plus
and minus supply voltages, respectively, It is important to
note that because of the nature of the half doublers the wave-
forms (c) and (d) are out of phase. This is important since
these voltages are used in building up the no load ionizing
voltage which is required only momentarily in order to fire
the lamps. H~nce, one of the waveforms (c) or (d), and thus
the components which produce that waveform, are unnecessary.
It is also noted that a F13T5WW lamp is fired without pre-
heating and thus may account for the use of four times the line
peak (640 VDC no load) to fire a lamp that requires a start-
ing voltage of 176 volts and an operating voltage of 95 volts
(based on page 4 of the Westinghouse Fluorescent Lamp Service
Manual 7/68 A-8072). Again, high voltage cold cathode firing
of a pre-heat lamp is not practical when the lamp is to provide
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light for other than the short term.
The circuit o~ Figure 7 clearly illustrates the need
for dropping a considerable voltage across the resistors Rl
and R2 since, in the speci~ic example given, the line voltage
is in excess of the 95 volt operating level the majority of the
time in a given cycle, and the DC voltage is substantially in
excess of the line voltage. It is interesting to note that if
the 15 watt rated lamp were operated at the DC equivalent of
the 160 ma RMS current, the 400 Ohm resistor Rl would drop 64
volts which equates to lQ wattsO 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, of course, proportional to the current equabed,
Hence, the power dissipated at ra$ed 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 of speci~ic embodiments
of the invention, the overall system of the invention can per-
haps be best understood by examining each of the four inter-
related sub-systems making up the overall system, viz., the
ionizing power supply, the arc current power supply, the load
; devices, i.e. t~e fluorescent l~mps used in the specific embodi- ment under consideration, and the control sub-system
Referring to Figure 9, in the specific example illus-
trated, three fluorescent lamps, lOa, lOb, and lOc~ collective- ;
ly denoted 10, are to be ionized so an electrical discharge can
be struck and a few hundred micro-amperes of current permitted
to flow. The ionîzing power supply, which is indicated by
dashed line block 12, and the arc current power supply, which
--15-
s
36~3~
is indicated by dashed line block 14, will be described here-
inbelow.
The lamps 10 are of the heated cathode type having
filaments which are independently heated via the multiple secon-
dary windings 16a, 16b, 16c, and 16d of a transformer 16 In-
dependent heating of the electron emitters of the lamps 10 is
provided for 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 transformer
winding, in what is probably a preferable design the adjacent
lamp filaments would be connected in parallel
-15a_
One end cf the lamp series 10, designated as point H,
is connected to a system neutral line N ~hrough a diode ~2 and
a diode 24 and a transistor 26 of a control sub-system (trans-
istor ballast) generally denoted 20, The other end of the lamp
series 10 is connected to point C o~ the arc current power supply
14. Point H of the lamp series 10 is also connected through a
zener diode 28 to ionizing power supply 12,
Briefly consid0ring the make-up of 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 38,
and 40 and 42, are connected as shown. Further capacitors 44
and 46 are connected to neutral line N from the junctions between
the two pairs of diodes.
Similarly, arc current supply 14 includes a series of
three diodes 48, 50 and 52 as well as a capacitor 54 connected
between supply line 34 and the ~unction between diodes 48 and 50.
Another capacitor 56 is connected across diodes 48 and 50 while
a further capacitor 58 is connected between the junction between
diodes 50 and 52 and neutral line N.
Considering the operation of the system as described
thus far, the 115 VAC current-compliant voltage source, whose
output appear~ on line 34, is first converted into a voltage
compliant source which more or less matches the volt-ampere
characteristics of the fluorescent lamps 10 during operation
of lamps 10 in the arc discharge region of current conduction,
Specifically, a voltage compliant source is provided wherein
t~e 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 multip]ier. The capacitors 54, 56 and 5$
of arc current supply circuit 14 are sized so that a low current
loading the DC voltage is substantially higher than the ~C line
peak voltage so as to provide a reasonable voltage compliance
range, With this arrangement, the DC voltage
-- 16 --
lowers non-dissipatively in a manner somewhat analagous to
the changing voltage requirement of the lamps 10 in the arc
discharge region The poorly regulated voltage source pro-
vided by arc current supply circuit 149 acting in combination
with the transistor control provi~ed 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 capacitor
58 form a half-wave recti~ier bridge circuit, v~ith capacitor
58, in the speci~ic example under consideration, being ¢harged
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 and is identified as
component B in Figure 10. Finally, diode 48 and capacitor 56
"~ill in" the positive DC voltage waveform by adding the remain-
ing phase related sinusoidal component C as is illustrated in
Figure 10. Thus, the AC line voltage multiplying arc current
supply circuit 14 provides a nominal 490 VDC poorly regulated
voltage source, with diode 52 and capacitor 58 forming a 160
volt DC supply and diodes 50 and 48, together with capacitors
54 and 56, forming an AC line voltage multiplier circuit that
adds approximately 320 VDC to the -~160 VDC half wave supply.
In an exemplary circuit, 240 MFD capacitors were used which
permitted lamp operation up to 700 ma of arc current.
Before the lamp current can be controlled~ the lamps
10 must, of course, be ignited and ioniæing supply 12 is pro-
vided for this purpose. Ionizing supply 12 basically comprisesa half wave rectifier circuit and a full AC lil~e voltage multi-
plying rectifier circuit, similar to the positive voltage
.
-16A-
source previously discussed, together with one half of another
AC line voltage multiplying rectifier circuit. The specific
components of ionizing supply 12 were described above9 and
referring *o the Figures 9 and 10 together, the negative half
wave circuit formed by diode 36 and capacitor 44 provides the
no load voltage component D of the waveform shown in Figure 10,
The no load voltage components E and F are provided by the full
AC line voltage multiplier circuit formed by diode 38 and capa-
citor 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 nom-
inally 800 volt peak DC supply is provided. This voltage, in
conjunction with the positive low ripple 490 AC volts produced
by the arc current supply 14 provide adequate voltage to ionize
the mercury in lamps 10 so that the lamps can be started.
Capacitors 30, 32, 44 and 46 are very small, e,g.,
,005 MFD in a specific example, so that as soon as the lamps .
10 fire the negative voltage drops back essentially to the
negative half wave of the AC line, with at most a few micro~
amperes of average current flowing iD the negative supply.
Zener diode 28 is employed so that with the voltage drop there-
of, in combination with the poor regulation of 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 star-
ting current path9 which is identified by *he dotted line in
Figure 9, shares the arc discharge current path, which is indi~
cated by the cha~n line in Figure 9, where the two lines run
~17~ ~:
r~-~
. ~
. . . , ~ .. , : :
parallel but that the transistor controlled lamp current never
flows in the ne~gative starting circuit, i,e,, in ionizing
supply circuit 12, and hence diodes 36, 38, 40, 42 and 28 need
only be rated ~or 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 ~ 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 with a 1,000 PIV
rating, transistor 26 and a companion transistor 60 are pro-
tected because diode 22 is back biased when point H is negative
and can only conduct when point H is pulled positive, Diode 24,
which could be replaced by a simple one ohm resistor, is em-
ployed in the collector circuit of transistor 26 to insure that
there is sufficient voltage between the emitter and collector
of transistor 60 to permit its proper operation when, and if,
transistor 26 is saturated,
Transistors 26 and 60 are connected to a further
20 transistor 62 in a high current gain configuration. The base
drive for transistor 62 is provided by circuitry including a
potentiometer 64 connected to a 6VDC bus 66. The tap 64a of
potentiometer 64 is connected through a resistor 68 to a sum-
ming point 70, A second potentiometer 72 is also connected to
summing point 70, with a tap 72a of potentiometer 72 being
connected to a photo-diode 74, A capacitor 76 is connected
across potentiometer 72 between the base of transistor 62
and neutral line N, It is evident that transistors 26 aDd
60 will have to have a su~iciently 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 re-
.'
. --1~-.
spect to neutral line N, the collector-to-emitter voltage
withstand rating thereo~ only needs to be a few volts. The
three transistors 26, 60 and 62 are, as noted, essen-tially
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 of the
signal input transistor 62 does not turn the transistors on
until the base signal voltage is one or more volts above the
emitter voltage of transistor 26. This signal must be higher
than the sum of the voltage drops across the emitter-base
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 68,
could be tied directly to the bus 66 in certain systems In
operation, the current signal of flows from the plus 6 VDC
bus 66 through resistor 68 into the base of transistor 62 to
thereby turn on transistor 62 and transistors 60 and 26~ Thus,
a controlled current, other than the miniscule 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 con-
tinue to flow through potentiometer 17 to neutral. The voltage
level above neutral at the junction 70 between resistor 68 and
potentiometer 72 must b0 greater than the emitter-base diode
drops of transistors 26, 60 and 62 for a base current to flow
into transistor 62. Once current begins to flow in the lamps
10, light is generated and photodiode 74 (which can be replaced
--19--
':
.. . ~.
by any suitable configured photosensitive device) receives
some o~ the la~p generated light J together with whatever light
is produced by other sources, so as to permlt more o~ the re~-
erence signal current to ~low therethrough to neutral line N
rather than flow into the base of transistor 26 Thus, a
closed feedback loop is provided and the current through lamps
10 is dependent on the light received by photodiode 74.
Considering some of the secondary features of cir-
cuit 20, capaci~or 76 serves to average abrupt changes in light
levels as detected by the light feedback photodiode 78 Pho~o-
diode 78 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 78
The 6 volt supply provided by bus 66 is derived by
using a 6 volt zener diode 78 ha~ing 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 si~ed so that the
6 V bus can supply at least 10 ma o~ current to transistor 62
and potentiometer 64 when the actual voltage provided by 160
VDC bus is reduced under maximum load. The 6 volt bus can
also be generated by con~ecting resistor 82 to the 115 VAC
line 34 to form another hal~ wave DC supply. In this embodi
ment, a blocking diode (not shown) would be inserted in series
with resistor 82 to preveDt discharge o~ capacitor 80 during
the negative half o~ 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
declines. For example, i~ the temperature is reduced, the light
output for the same lamp current will be less due to a reduc-
tion in the mercury ion population. Likewise, the light output
-20-
is reduced as ~he internal phosph~r coating "wears", thereby
resulting in lèss 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 result-
ing in an increased base drive for transistor 26 and a corres-
ponding increase in the lamp currentO Hence, again within the
design limits of the s~stem, the control sub-system 20 continu-
ously adjusts the lamp current so as to hold the light output
constant in relation to the input signal reference, Thus, the
system of the invention can be said to differ from prior art
systems in that light rather than current is the controlled
variable.
Referring to Figure ll, a further embodiment of the
invention is illustrated. The embodiment of Figure ll is very
similar to that of Figure 9 and like elements have been given
the same number with primes attached, The embodiment of Figure
ll differs from that of Figure 9 in th~t four rapid start
fluorescent lamps are emplo~ed. The fourth lamp is denoted lOd
and the cathodes and heater transformers have been left out for
purposes of clarity. The four lamp system of Figure ll will,
of course, require more voltage than the three lamp system of
Figure 9 and rather than choosing to increase the plus 490 VDC
.~ .,: . .
supply, the transistor ballast and control system 201 is dis-
connected from neutral line N~ and reconnected to the miDUS
160 bus provided at point D' in ionizing circuit 121. 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 5B~,
The remaining high voltage negative supply has been found suf-
ficient for starting purposes.
Referring to Figure 12, a further embodiment of the
-21-
8~
invention is illustrated. As explained hereinbe~ore, 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 reflected in savings
in peak lighting (35% in a specific example) as well as off-peak
lighting (30% in the same example), in air conditioning energy,
ln reduced demand charges and in additional heating energy
charges
In Figure 12, the transistor ballast (control sub-
system) of Figure 9 is utilized in combination with a convention-
al inductive ballast 100. The transistor ballast is connected
in a full wave AC diode bridge formed by diodes 92, 94, 96 and
98 and is formed by components which are similar to those des-
cribed above in connection with the transistor ballast of Figure
9 and which are given the same reference numerals with double
primes attached. As illustrated, the junction between diodes ;
92 and 94 is connected to neutral line N " while the collector
of transistor 62~ is connected to a 6 volt bus provided by a
6 volt Zener diode 78'~, resistor 81~l and a ~urther diode 91
being connected to the 115 volt AC line 90 as shown
Inductive ball~st 100 is a standard two lamp,
; rapid start, series sequence ballast and includes the requisite
lamp wiring for a pair of lamps Ll and L2.
In operation, the transistor ballast o~ Figure 11
limits the ballast current more or less to a controlled ampli-
tude square wave AC current so as to produce a correspondlng
light input. The current ~low through the system alternates
between two paths. Specifically, during a first AC half cycle,
the current flows through diode 92, diode 24 ~ transistors 2B~l
and 60~ and diode 98. On the other hand~ during the alternate
-22_
~ ,~,
i
6~3~
AC half cycle, the current will reverse and flow through diode
96, diode 24~ transistor 26~ and 60~ and diode 9~.
It will be unders-tood tha-t the system of Figure 12,
similarly to those described above, provides DC control to con-
trol the output of the lamps, this being accomplished by
locating the transistor ballast and feedback current within a
full wave diode bridge (formed by diodes 92, 94, 96 and 98)
connected in series with one side of the AC line 90 which feeds
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 o~ 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, L2 as well as for
heating the lamp filaments. Once the lamps Ll, L2 are fired,
the current is limited by the control transistor 26~ which then
operates in the active region thereof. On the other hand, when-
ever transistor 26'~ is saturated, the inductive reactance of
the ballast 100 provides the required current limiting Thus,
the transistor circuit acts as the system ballast over the
dynamic range of current control, i.e., for minimum arc current
up to a design current maximum, with the voltage across tran-
sistor 26~ decreasing with increasing arc current flow there-
through until saturation occurs At this point, i e., at the
current design ]imit, the transistor ballast is ineffective
i.e., ceases to function, and, for the first time, the induc-tive
ballast 100 provides the system current limitingt Hence, the
function of the inductive ballast is changed from one of current
limiting throughout the entire operating cycle to one of pro-
viding a cost effective voltage source ~or ~iring the lamps
and providing the necessary sustaining voltage. It wlll be
. -23-
-
appreciated that the power losses associated with the inductive
ballast 100 are greatly decreased with the incorporation of the
transistor ballast o~ the invention in that, with transistor
ballasting, the normal current peaking characteristics o~ the
inductive ballast are eliminated and since the inductive react-
ance ballast power losses in question are I2R losses, the re-
actance ballast runs cooler and its operating life is hence ex-
tended.
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
fallof~ may occur due to ion migration to one end of the lamp
10. Such falloff will depend OD the lamp array, the length of
the gas column (and hence the lamp length), the arc current
density and the lamp on-time interval, If such light falloff
occurs, it can be dealt with by a periodic reversal of point H
to point C and vice versa, This can be accomplished with a
simple polarity reversing relay such as a Potter Brom~ield
~0 GM-ll which per~orms the switching ~unction as soon as the sys- -
tem is turned o~,
It will be understood that arc current control pro-
vided in the embodiments of Figures 9, 11 and 12 di-~fers 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 o~ the invention
described above, minimum power is dissipated in the transistor
ballast when the lamp current is highest because the transistor
is then saturated on, As the lamp and transistor current in-
creases the emitter-collector voltage across the control trans-
istor decreases do~n to its saturation voltage of less than one
volt at which time the system becomes intrinsically ballasted
- -24-
$~
by being voltage limited In Gther dissipative hallasts,
maximum power i~ dissipated at high arc current levels.
It will be understood that while the speci~ic circuits
discussed above provide certain advantages, other circuitry
could also be employed For example, other solid state power
supplies could obviously be used for the transistor ballast
control circuit and the control circuit could also use opera-
tional amplifiers and photo voltaic or photo-resistive compon-
ents as well as other components in other configurations.
Typically, a 30 or 40 or more milliampere constant current could
be generated and steered either to the base of the control
transistor or the neutral or minus bus as a function of a refer-
ence signal and the light level. Similarly, other forms of
ionizing circuitry could be employed.
As was briefly discussed above, in all o~ the system
embodiments, the sensed ligh$ can be either that produced by
the lamps themselves and/or that from other sources such as
daylight. The daylight or "other source" light in effect will
generate a downturn signal Stated differently, as the inten-
sity of other optically coupled light sources increases, thesystem arc current will be turned down. If the intensity of
other source light is sufficiently high the controlled arc
current will go to zero On the other hand, the arc current
automatically increases as the light from that source declines
The nature of the systems of Figures 9 and 11 is essentially
non--dissipative when the ballast transistor is saturated and
minimally dissipative, in a declining fashion, when the trans-
istor is operating in thP 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 th~ lamp current
-25-
.
~J~
increases since this decline reduces the power that the trans-
istor ballast must dissipate Thus, a more efficient energy
conserving light system is made possible For exarnple, in an
instance where external source light is sufficiently high to
turn down the controlled arc current to zero, the power consump-
tion would be reduced about 90% from what it would have been
with the design maximum arc current. The quiescent power is,
of course, required for the ionizing supply, the lamp heater
transformer and the control power supply.
Referring again specifically to the embodiment of
Figure 9, the polarities of 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 from ground would be higher
and the controlled arc current path would have to flow through
the ionizing supply which would require that more expensive com-
ponents be used in the ionizing supply.
Although the present invention is particularly appli-
cable to illuminating light, the inven$ion would also be use~ul
in many photographic and other technical or scientific appli-
cations where light control is of a definite advantage, As
stated, a simple yet highly efficient energy conserving system
is provided in accordance with the invention which controls the
level of light from a fluorescent lamp(s) and which has appli-
cations for con$rolling 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 oper-
3~ ating range. The acutal savings which can be realized would
amount to millions of barrels of oil where the principles of
the invention were utilized on a sufficiently widespread basis.
-26- :
`
Although the invention has been described relative
to exemplary embodiments $hereo~ t will be understood that
other variations and modifications can be effected in these
embodiments without departing from the scope and spirit of the
invention.
~0
- ~:
