Note: Descriptions are shown in the official language in which they were submitted.
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There is provided a ballast circuit for thermal regula-
tion of at laast one gaseous discharge lamp~ More particularly
there i~ provided a ballast including a capacity clrcuit which
may ~e switched ~xom one capacitance level to another ~apacitance
level in response to a temperaturel change.
In the fluorescent ballast art, it i~ de~irable to
operate at ca~e temperatures no gr~ater than 90 C. Temperature~
much greater than thiS cause reduced life, ~ometimes cause noise,
and may cause other problems related to exce~sive temperature~.
Several means have been employed to provide thermal
protection for ballasts. One of these is kn~wn as a single
shot end of life thermal protector. This protector could be
placed in a circuit relationship with the core and coil and/or
the ballast capacitor so that if the temperature of the ballast
or its surroundings became too high ~hen the ballast would be
taken out of the line. That is, the cir~uit would be open.
~owever, once the circuit i5 opened the ballast is generally
removed permanently from the line.
Recycling protector3 also have been used and are
widely u~ed in the motor industry~ They allow the circuit to
open during a temperature overload and reclose after the
temperature lowers. However, these types of devices are less
reliable than the 3ingle shot technique and are more expensive.
Furthermore, recycling protectors cause the lamp to switch off
thereby darkening the room and also shortening lamp life.
When a new building is under construction, a lighting
system is one o~ the flrst things to be installed in~ide the
building so that the workmen can see to do their work. Quite
often the lighting system employes gaseous discharge lamps~
e.g. fluore~cent type, which require ballasts. These in~talla-
; tions usually occur long before the air conditioning or other
ventiliation systems are actuated. Under these conditions it
is not uncommon for the combination of the ballast heat, the
58-BV-6Z27
~IL0~9~
fixture heat and the air in the ~naircondltioned room to cauRe
ballaqt ca~e temp~ratures to exceed 110 C wherea~ ~luorescent
ballasts ~hould normally operate between 90 and 95 C. ~rhi~
would cause a ~ingle shot protectc~r to trigger and the ballast
would have to ba replaced~ It i~ therefore desirable to provide
a thermal regulation mean~ whereby the ballast case temperature
is thermally regulated rather than taken out of the line when the
temperature exceeds a predetermined value.
U~ing ballasts operating ~luore~cent lamp~ on an average
lighting fixutureO only about 20% of the input power i~
di~sipated in the ballast it3elf. Approximately 10% of the power
i~ liberated as visible lightO The remaining 70% of the input
power appears as heat liberated by the lamp within the ~ixture.
~herefore the primary source of balla~t case heat and fixture
heat comes from the lamps themselves. m e most ef~ective means,
therefore, for controlling the ballast thermal environment i5 to
control the power dissipated in the lamp80 One might be~ieve
that to reduce the power in a lamp would cause the light output
of the lamp to also be reduced. However, between certain
temperature ranges, thi~ is not true.
FIG. 7 shows a curve relating the light output o a
typical fluorescent lamp to the ambient temperature. It can be
; seen that it is a characteristic o this fluorescent lamp having
- fixed input power to operate at maximum light output near 25~ C
ambient and at lower light outputs on either side of the 25 C
point. It follows, therefore, that if a decrea~e in ambient
temperature around the lamp from 70 C to 25 C results in a
20% increase in light output, then the light losses caused ~y
the lowering of lamp power a certain percentage could nearly
be compensated for because of the lamp characteristic.
One ~f the ob~ects of the invention is to provide
a thermally-regulated ballast circuit.
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Another object is to provide a ballast circuit having
a capacity circuit whereby the capacitance sub~tantially changes
in re~pon~e to a change in ambient temperature.
Anothsr obj~ct i~ to provide a ballast circuit having
a capacity circuit for lncreasing the ballast c~rcuit impedance
in respon~e to an increa~e in ambient temperature with little
effect on light output.
Still another object is to provide a thermally regulated
ballast operating near normal temperatures for providing a long
balla~t life.
In accordance wit~ one form of this invention there
i5 provided a ballast circuit for regulating the curr~nt through
at least one gaseous discharge lamp over a range of ambient
temperatures. A pair o input leads connect the baLlast circuit
to a source of operating power. A transf~rmer i9 connected to
the i~put leads. A capacity circuit including a power
capacitance is connected between the tran~former and at least
one lamp. ~he capacity circuit fur~her includes a m~ans for
varying the total effective capacitance of the capacity circuit
responsive to the ambient temperature whereb~ lamp power i5
substantially decreased in response to an increase in ambient
temperature.
~he subject matter which is regarded as the inven~ion
is ~et forth in t~e appended claLms. The invention itself,
however, together with further ob~ects and advantages thereo
may be better understood by reference to the following
description taXen in conjunction with the accompanying drawings
in which:
FIG. 1 is a schematic circuit diagram of a ballast
circuit showing a capacity circuit in block form.
FIG. 2 is a schematic circuit diagram of one embodiment
of the capacity circuit as shown in FIG. 1.
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FIG. 3 is a Ychematic circuit diagram o~ another
embodiment of the capacity circuit shown in FIG. 1.
FIG. 4 is a schematic ci.rcuit diagram of ~till another
embodiment of the capacity circuit: shown in FI&. 1.
FI~. 5 is a schematic circuit diagram o~ still ~nother
embodiment of the capacity circuit: shown in FIG. 1.
FIG~ 6 is a schematic circuit diagram of still another
embodiment of the capacity circuit shown in FIG. 1. ~ ;
FIG. 7 is a graph showing the ~lationship between ~:
light output and ambient temperature near a fluorescent lamp.
FIG. 8 is a graph showing the relationship between
the capacitanc~ and ambient temperature of a capacity
compensation circuit.
Re~erring n~w to FIGo 1~ there is provided input
terminals 1 and 2 adapted to receive input power for operating
the ballast circuit. Input terminals 1 and 2 are ~urther conneted
across primary winding 3 which is a part of tran ~ormer 4.
Transformer 4 further includes secondary winding 5. Secondary
winding 5 i5 connected to capacity circuit 7 at terminal 8.
Terminals 8 and 11 are shown for ilLustrative purpos~s. Capacity
circuit 7 includes a p~wer capacitance for aiding in ballasting
a pair of gaseous di~charge l~mps 9 and 10. Capacity circui~ 7
also includes a means ~or substantially changing the e~fective
capacitance of the capacity circuit 7 in re~ponse to a ~hange in
temperature. This provides for thermal reg~lation of the
ballast circuit.
Th2 ef~activa capacitance i3 the capacitance across
texminals 8 and 11. This e~fective capacitance will substantially
decrease as the temperature aroun~ capacity circuit 7 increases. :~
Thi decrease in capacitance w~ll result in an increase in net
impedance of ~he ballast circuit~ The increase o~ impedance
results in lass power consumed by the lamps 9 and 10. Since
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9~
70% of the input power i~ di~sipated by the lamps, a sub tantial
decrea~e in power will re~ult in al substantial decrea~e in
ambient temperature. A~ shown in FIG. 7, a decrease in t~mp~ra-
ture toward 25 C will result in highar light output at a fixed
lamp power dissipation. The net re~ult i9 that the light
output will remain nearly constant: while the temperature i~
lowered.
~he capacity circuit may include, but is not limited
to, any of the circuits shown in FIGS. 2-6. It furthermore may
only include a power capacitance means itself having the
characteri tic of a reduction in capacitance as the ambient
temperature increases. In order for this circuit to be extremely
effective the decrea~e in capacitance should be approximately 15
to 20 percent for a change in tempsrature between 25 C to 70 C,
however les~er changes in capacitance would be al~o advantageous,
e.g. greater than about 7 percent.
The graph in FIG. 8 ~how.s illu~tratively how the
- capacitance o~ the capacity circuit may decrea3e nearly 20
percent bekween 25 C and 70 C. This decrease in capacitance
and the re~ultLng increase in impsdance will not substantially
effect the light oukput of a fluore~cent type lamp. Again the
grap~ in FIG. 7 illu~trates this. A ~luorescent lamp whose
ambient i~ at 70 C will generate less light than a fluorescent
lamp whose ambi~nt i~ 25 C) as~uming the power input is
constant. By using thi~ khermal regulation technique the power
dissipated by the lamp will decrease because o~ the increase
; in impedance in the balla3k circuit. However, as the lamp
power is decreased the temperature of the ambient around the
lamp will also begin to decrease and the lighk oukput should
remain abouk the same.
The remainder of the circuit of FIG. 1 includes
gasaou~ di~charge lamp 9 cvnnected to capacity circuit 7 at
point ll~ Gaseous discharge lamp 9 has ~ilaments 12 and 13.
_ 5 _
Sfl-BD-6227
10~ L98
Filament 12 i8 connected to filament winding 14. Filament
winding 14 is magnetically coupled to primary winding 3 to
provide pre-hea~ for filament 12~ Filament ~3 i~ connected to
filament winding 15. Filament winding 15 is ~ so magnetically
coupled to primary winding 3 to provide filament pre-heat
filament 13. Starting capacitor 16 i~ connected across lamp 9
at filaments 12 and 13. Lamp 10 includes filamant~ 17 and 18.
Filament 17 is also coupled to ~ilament 13 of lamp 9 and to
filament winding 15 for providing pre heat. Filament 18 of
gaseous discharge lamp 10 is connected to filament winding 6
for providing pre-heat for lamp 12. Secondary windlng 6 is
connected to prlmary winding 3.
The circuit of FIG. 2 shows one embodiment of the
capacity circuit which may be connected to the circuit of FIG. 1
across terminals 8 and 11. Power capacitance means 19 is
connected between terminals 8 and 11 to help provide ballasting
for lamps 9 and 10 and ~urther to provide power factor
cvrrection. Circuit branch 20 is connected in parallel with
power capacitance means 19. ~nis circuit branch 20 includes
thermistor 21 which is a positive temperature coefficient
resistor (PTC) well known to those skilled in the art. The
second capacitor 22 is connected to the thermiskor 21 and is
al~o included in circuit branch 20. Thermistor 21 may be of the
type which either gradually increases its resistance as the
temperature incxeases or undergoes an abrupt re~istance change
whereby the capacitance means 22 is abruptly switched out of a
circuit relationship with capacitor 19 when the temperature
exceeds a predetermined value. With normal operating temperature ~ ;
of fluorescent ballast cases (90-95 C), capacitance means 22 is
in a circuit relation with capacitance means 19 whereby the
effective capacitance is relatively high.
The circuit of FIG. 3 is another capacity circuit and
shows a power capacitor 19 having a variable ceramic capacitor
.i . ,. . :
.~ : -: .
58-BD-6227
~IO~LZ~9~
23 connected thereacro~s. C~ramic capacltor 23 may also b~ a
non-variable t~pe. Ceramic capacitors have been deslgned to
undaryo a capacitance change of UE~ to 60 percent between 25 C
and 100 C. By placing the ceramic capacitor 23 in parallel with
the power capacitor l9 a reductiorl in lamp current of nearly lO
percent between a temperature range of 24 C and 67 C has been
measured. '~he po~er dissipated by tne lamp and the temperature
are then lowared.
The circuit of FIG. 4 1~ still another capacity circuit
and shows power capacitor 19 connected in parallel with a series
combination of bimetal switch 24 and capacitor 25. Switch
24 may also be made of a non-metal material which is temperature
sensitive. Switch 24 will be closed during low tamperatures
and will be opened during high temperatures.
The embodiment shown in FIG. 5 shows power capacitor
l9 connectQd in parallel with the ~eries combination of electr~nic
switch 26, which in this embodiment is ~rRlAc~ and capacitor 27.
A thermal responsive resistor 28 is connected to the gate of
TRIAC 26 so as to switch on the TRI~C 26 at a predetermined low
temperature level. When capacitor 27 is switched into the
parallel circuit the overall capacitanca between leads 8 and
11 increa~es. TRIAC 26 turns off at zero ~urrent cros~ing, then
switching capacitor 27 out o~ the parallel circuit. '~his cause~
the overall capacitance to decrease~ Thermistor 28 may be a
well known thermal responsive switch such as a P~rc resistor.
The embodiment shown in FIG~ 6 shows power capacitor
l9 connected in series with a second capacitor 29. An electronic
switch, which is in this embodiment TRIAC 30, is connected
across se~ond capacitor 29. A thermal responsive switch 31 is
connected to the gate of TRIAC 300 When a predatermined
temperature is sensed by thermal resistor ~witch 31 TRIAC 30
turns on. This e~fectively ~witches capacitor 29 out of the
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~ 5~-~D-6227
1(~4~498
circuit. Other types of capaci-ty circuits may be utilized.
For example, the power capacitor alone may be utilized whereby
the internal structure of the power capacitance is made so that
its capacity increases as the temperature around it decreases.
A paper-askarel capacitor has been used in the prior
art which undergoes, at the most, a 3~ decrease in capacitance
for a temperature rise between 25 C and 70 C. This small
change, however, was deemed insubstantial. This is, its
effect on thermal regulation was insignificant.
la An askarel-filled polypropylene film dielectric capaci-
tor has been developed which undergoes a seven or eight percent
decrease in capacitance when the temperature around it goes from
25 C to 70 C. This film capacitor may be used as a power
capacitor. While this drop in capacitance was helpful in
decreasing the overall temperature of the ballast and lamp,
it is further helpful in that a savings in materials for the
ballast may be realized. If one is willing to leave the
temperature at a fairly hiyh point, smaller than normal sized
transformer wire may be used. Seemingly this would cause the
2Q temperature to in¢rease but it would be compensated or by the
capacity circuit. Furthermore-, dif~erent types and less
expensive core materials may be used which allow the ballast to
heat up but again the capacity circuit would compensate for this
temperature increase.
One of the most desirahle ranges for thermal regulation
is a 15% to 2Q~ change in capacitance. With a 15% to 20% droop,
a ballast operating with an undesirable 110 C case may be
regulated back to 90-95 C ~Yithout a significant change in light
output. Another one of the benefits of a 15% to 20% reduction
in capacitance is that the ballast and lamp may be operated
at least within 95 percent of its normal unre~ulated light output
hetween 7Q C and 25 C ambient. This, again, takes advantage
58-BD-6227
498
of the light output to temperature phenomena illu~trated in
the graph shown ln FI~. 7 whereby the light output increaseY as
the temperature decrease~ between 70 C and 25 C. It has
been shown by tests on the various circuit~ shown in FIGS~ 2-6
that this 95 percent light output may be achieved in ~ome
environments even though the capacitance has decreased between
15 and 20 percent.
The circuit shown in FIG. 1 and incorporating t~e
spacific capacity circuit of FIG. 2 operates in the following
manner: input power is received across terminals 1 and 2. Fila-
ment winding 6, 14 and 15 are energized to pre-heat the lamp
filaments. me voltage on primary winding 3 is ~tepped up
acro s secondary winding 5 and, the primary winding. Starting
capacitor 16 is charged through power capacitor 19 and gaseous
discharge lamps 9 and lO (in this example fluorescent lamps~ are
started. A current flows from input terminal l through secondary
winding 5 and power capacitance l9 and further through the
filaments of lamps 9 and 10 bacX to other side of prim~ry
winding 3 and input terminal 2. As the ambient temperature
around and i the balla~t and ~ixture begins to rise, thermistor
21, shown in FIG. 2, begi~s to show more resistance. This
particular thermistor switches, i~e. 50 ohms at 25 C and 105
ohms at 100~ C. merefore capacitox 22 is switched out of
electrical parallel with powex capacitor l9. The capacity
circuit therefore has less capacitance between terminal~ 8
and ll at a high t2mperature than it does at a relatively low
temperature~ This decrease in capacitance results in an
increase in o~erall circuit impedance. Capacitance i~ related
to impedance by the ~ormula Z - ~ . Since the impedance is
increased, the current through the lamps and therefore the
power di~sipated by the lamps is decreased. With less power
being dissipated by the lamps the overall temperature in the
fixture and near the ballast will begin to ~ecrease. Thi5
58--BV--6227
9~
combined decrea3e ln lamp power and decrease in ambiant
temperature will allow the light output to remaln nearly
constant. A~ the temperaturs decrea~es sufficiently, the
thermistor 21 will ~ense that the temperature i8 decreasing and
~witch capacitor 22 bacX into the capacity circuit. Thi~
switching of capacitor 22 in or out of the capacity circuit
results in the thermal regulation of the ballast circuit.
A circuit has been built with the components shown
in FIGS. 1 and 2 having the following set of value3:
Capacitor 19 - 3.4 MFd
Capacitor 22 - 0.4 MFd
Capacitor 16 - O.05 MFd
PTC Resistor 21
R25OC - 50 Ohms.
Rl0ooc - 105 Ohms .
Primary Winding 3 - 823T, dia~ .0169"
Secondary Winding 5 - 1442T, dia. .0164"
Filament Winding 6 - 28T, dia. .0169"
Filament Winding 14 - 28T, dia~ .0169"
Filament Winding 15 - 28T, diaO .0169"
Lamp 9 ~ 40W rapid start fluore cent
Lamp 10 ~ 40W rapid start fluorescent
From the foregoing description of the lllustrative
embodiments of the invention, it will be apparent that many :: :
modification~ may be made therein. For example, varlous type~
~: of capacity circuits may be used.w~ereby the thermal character- .
istics of the ballast circuit are substantially regulated. It
will be understood, therefore, that the e embodiments of the
invention are intended as an exemplification of tha invention
- 30 only and that this invention is not limited thereto. It is
also understood, therefore, that it is intended in the appended
claims to cover all modifications that fall within the true
spirit and scope o* ~his invention.
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