U.S. patent number RE33,057 [Application Number 07/034,436] was granted by the patent office on 1989-09-12 for high frequency supply system for gas discharge lamps and electronic ballast therefor.
This patent grant is currently assigned to Brigham Young University. Invention is credited to John C. Clegg, Ariel R. Davis.
United States Patent |
RE33,057 |
Clegg , et al. |
September 12, 1989 |
**Please see images for:
( Certificate of Correction ) ** |
High frequency supply system for gas discharge lamps and electronic
ballast therefor
Abstract
The invention is both a system for supplying high frequency
alternating current to gas discharge lamps, such as fluuorescent
lamps, and the like and a unit that can be placed in or adjacent to
a lighting fixture to convert a direct current supply into high
frequency AC and also provide the ballast needed for operation of
the gas discharge lamps. This unit contains a symmetrical, class B,
push-pull current-limited, tuned-collector, sinusoidal oscillator
which is self starting, highly efficient and stable over a wide
range of input voltage, with or without load. The number of parts
is a minimum and the parts are relatively low cost, the power
losses are very low and the system operates at high power factor
with low acoustic and radio noise and low flicker. The system may
derive the current from a commercially available source at any
voltage and phase but preferably three phase primary of a building
transformer can convert this into six phase at the output terminals
which can be converted to DC of low ripple even without filtering.
From the central building supply, it is possible to send AC at
suitable voltage to subcenters in the building for rectification,
inversion and use in lighting fixtures but preferably there is a
single rectifier adjacent to the main transformer and the DC at
proper voltage is distributed to the fixtures where the ballast
unit is installed in a fixture to supply the lamps in it with the
high frequency AC. However, one ballast unit can serve, in many
instances, more lamps than a single fixture holds and it is
necessary in such instances to supply the high frequency AC from
one fixture to another and this can be done with only two wires.
The invention also provides means for dimming the lights, for
supplying heating current to lamp filaments at high voltage at the
start and much reduced voltage after the arc has been struck in the
lamps served by the ballast unit, and this reduction in filament
current takes place automatically without switches, resistsors or
other expensive and energy consuming means. The transformers used
in the practice of the invention may also be used to supply the
building with AC for customary appliances, incandescent lighting,
and the like.
Inventors: |
Clegg; John C. (Provo, UT),
Davis; Ariel R. (Provo, UT) |
Assignee: |
Brigham Young University
(Provo, UT)
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Family
ID: |
26710938 |
Appl.
No.: |
07/034,436 |
Filed: |
April 2, 1987 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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161914 |
Jun 23, 1980 |
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Reissue of: |
373994 |
May 3, 1982 |
04508996 |
Apr 2, 1985 |
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Current U.S.
Class: |
315/224; 315/206;
315/219; 315/250; 315/288 |
Current CPC
Class: |
H05B
41/282 (20130101); Y02B 20/183 (20130101); Y02B
20/00 (20130101) |
Current International
Class: |
H05B
41/28 (20060101); H05B 41/282 (20060101); H05B
037/02 () |
Field of
Search: |
;307/157 ;361/377
;315/184,288,324,244,201,97 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2260218 |
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Aug 1975 |
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FR |
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2052896 |
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Jan 1981 |
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GB |
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Other References
J H. Campbell & B. D. Bedford, Fluorescent Lamp Operation at
Frequencies above 60 Cycles, 1947, Proceedings of Natn'l
Electronics Conf., vol. 3, pp. 480-493. .
John H. Campbell, High Frequency Operation of Fluorescent Lamps,
Illuminating Engineering, vol. 43, No. 2, Feb. 1948, pp. 125-140.
.
John H. Campbell, Special Circuits for Fluorescent Lamps, Apr.
1950, Illuminating Engineering, vol. 45, No. 4, pp. 235-241. .
John H. Campbell, Characteristics & Applications of High
Frequency Fluorescent Lighting, Feb. 1953, Illuminating
Engineering, vol. 48, No. 2, pp. 95-103. .
John H. Campbell, Elements of High Frequency Fluorescent Lighting,
Jul. 1957, Illuminating Engineering, vol. 52, No. 7, pp. 337-342.
.
John H. Campbell, New Parameters for High Frequency Lighting
Systems, May 1960, Illuminating Engineering, vol. 55, No. 5, pp.
247-256. .
John H. Campbell, Characteristics of a New 3000-CPS System for
Industrial and Commercial Lighting, Mar. 1965, Illuminating
Engineering, vol. 60, No. 3, pp. 148-156. .
Funke and Oranje, Gas Discharge Lamps, 1951, Phillips'
Gloeilampenfabrieken. .
Zwikker, Fluorescent Lighting, 1952, Philips Technical Library, pp.
73-143. .
D. E. Spencer, Frequency and Fluorescent Lamps, 1953, Electrical
Engineering, vol. 72, No. 12, pp. 1066-1071. .
Shelly Krasnow, Converter Equipment, 1957, Illuminating
Engineering, vol. 52, No. 7, pp. 353-356. .
George Gilleard, Fluorescent Lighting Systems from Gas-Driven
Turbines, 1964, Illuminating Engineering, vol. 58, No. 3, pp.
163-169. .
John H. Campbell, from a paper presented to the National Technical
Conf. of the Illuminating Engineering Society in San Francisco, CA,
1959, pp. 560-562. .
J. J. Ebers & J. L. Moll, Large-Signal Behavior of Junction
Transistors, 1954, Proceedings of the Institute of Radio Engineers,
vol. 42, pp. 1754-1772. .
John L. Moll, Large-Signal Transient Response of Junction
Transistors, 1954, Proceedings of the Institute of Radio Engineers,
vol. 42, pp. 1773-1784. .
George C. Uchrin & Wilfred O. Taylor, a New Self-Excited Square
Wave Transistor Power Oscillator, 1955, Proceedings, Institute of
Radio Engineers, vol. 43. .
R. L. Bright, Junction Transistors used as Switches, 1955, AIEE
Transactions, vol. 74, pp. 111-121. .
G. H. Royer, a Switching Transistor DC to AC Converter Having an
Output Frequency Proportional to the DC Input Voltage, 1955, AIEE
Transactions, vol. 73, pp. 322-326. .
C. J. Yarrow, Transistor Converters for the Generation of
High-Voltage Low-Current DC Supplies, 1959, Proceedings,
Institution of Electrical Engineers, vol. 106, pp. 1320-1324. .
W. H. Johnson, J. L. Winpisinger & J. F. Roesel, Jr., a New
High Frequency Power Source for Fluorescent Lighting, 1959,
Illuminating Engineering, vol. 54, pp. 43-50. .
W. H. Johnson, Progress in Static Converters for High Frequency
Fluorescent Lighting, 1961, Illuminating Engineering, vol. 56, pp.
379-383. .
Robert J. Haver, the Verdict is in: Solid State Fluorescent
Ballasts are Here, 1976, Electronic Design News, pp. 65-68. .
Charles Cohen, Transistor Ballast Cuts Power Loss, 1979,
Electronics. .
Chester L. Dawes, a Course in Electrical Engineering, vol. II,
1947, Alternating Currents, 4th Ed., McGraw Hill Book Co., pp.
534-587..
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Primary Examiner: Britton; Howard W.
Assistant Examiner: Powell; Mark R.
Attorney, Agent or Firm: Workman Nydegger Jensen
Parent Case Text
INTRODUCTION
This application is a continuation-in-part of our prior application
Ser. No. 161,914 filed June 23, 1980, now abandoned.
The present invention relates to an electrical system for supplying
high frequency alternating current to gas discharge lamps. The
system is adapted to be connected to commercially available
alternating current supply lines, preferably a three-phase current
supply. The system comprises means to rectify the alternating
current to a relatively smooth direct current at a safe voltage for
transmission over ordinary building wiring and electronic means to
invert the direct current to high frequency alternating current,
e.g. 20 to 30 KHZ, and suitable voltage adapted to supply gas
discharge lamps, without or with filament heating means, and to
control the current through the lamps. The invention also relates
to said electronic means referred to herein as electronic or solid
state ballast.
BACKGROUND OF THE INVENTION
It is well known to utilize high frequency (20 kHz or above) in the
operation of fluorescent lamps for the purpose of eliminating
standard 60 cycle noise and reducing power loss via lengthy
transmissions within a relatively large building complex.
In the most common prior practice, 60 Hz single phase power has
been distributed to be rectified at each fixture. In a large
building this necessitates many rectifiers, and large, usually
electrolytic, condensers or capacitors and perhaps large inductors.
Inductors used for such purposes are inefficient, costly and noisy
while electrolytic capacitors are unreliable, temperature sensitive
and have limited lifetimes. Capacitor filters used alone lead to a
very low power factor for the system and consequently to large
power transmission losses.
Prior proposed systems to obtain the benefit of high frequency
operation of the lamps by rectifying AC to provide DC to high
frequency inverters and to operate at the necessary high power
factor, high efficiency and low noise have either been
prohibitively costly or have made unacceptable compromises in
performance and reliability. No one has succeeded in providing a
system which has found acceptance in the market place, which has
been affordable, and has the advantages of the present, safe,
economic, reliable, efficient and flexible system and ballast for
operating at frequencies in the range of about 20 to 30 kHz or
higher.
The present invention satisfies this long felt need.
SUMMARY OF THE INVENTION
The present invention comprises a system for supplying high
frequency alternating current, preferably from a source of low
frequency alternating current by rectifying means and inverting
means, to a large number of gaseous discharge lamps, usually
fluorescent lamps, e.g., fixtures for all the lamps in a large
building, optionally with means for dimming the lamps, and
electronic means frequently referred to herein as electronic or
solid state ballast, for use in the system (a) for providing the
necessary starting voltage for the lamps when the resistance to
current flow is comparatively high, (b) for limiting the current
flow in the lamp circuit during lamp operation when the resistance
to current flow is comparatively low, and (c) for optionally
supplying current to heat the filaments or electrodes in the lamps,
preferably at a comparatively high level to start operation of the
lamp and at a much lower level during operation.
The system comprises a distribution center in which there is
usually a single central transformer adapted to be connected to the
commercially available AC power source, preferably three-phase
current, with its primary winding designed to accept the power from
the supply at the line voltage, which is usually too high for safe
distribution in the building, and with its secondary designed to
supply the building distribution center with current at suitable
building voltage. If the available current supply is at suitable
voltage for distribution through the building, then a central
transformer is not necessary. The building distribution system
comprises a plurality of subcenters, e.g., one for each floor, if
not too extensive an area, or several if the floor area is too
extensive for a single subcenter to suffice for efficient
distribution. From the subcenter the usual building needs may be
supplied by means of a transformer having its primary designed for
the voltage of distribution from the center and its secondary
designed for connection to convenience outlets and the like (not
shown) which usually are supplied by 110-130 volt lines. At the
subcenter a rectifier is provided at strategic locations on the
floor to convert the AC to DC to supply a plurality of inverters
near the lamps. Preferably the transformer in the subcenter has its
primary windings connected in delta configuration and its secondary
windings connected in star or Y-configuration with the common
connection serving as a terminal for a neutral or ground line.
Preferably the secondary windings include not only the usual three
windings but an additional three windings wound in the manner
described hereinafter so as to supply six-phase current to the
rectifiers. Six-phase current has a relatively small ripple which
makes rectification to an almost smooth direct current relatively
simple and inexpensive. The rectifier preferably comprises a
six-phase diode bridge providing direct current as a positive and
at a negative terminal for connection to positive and negative
lines, which, with the natural or ground line mentioned above form
a DC distribution system for supplying the inverters. There is an
inverter for each fixture or group of adjacent fixtures, depending
upon the number of lamps per fixture. The inverters of the
invention are capable of supplying one to four or even a few more
lamps without overloading. One skilled in the art can readily
determine the number of lamps and fixtures to be supplied by each
inverter from the ratings of the lamps and inverters.
The inverter includes means to convert the direct current it
receives from the system described above into high frequency
alternating current, e.g., 20 to 30 kHz, a transformer for this
high frequency AC to convert the voltage generated in the
conversion means into proper voltage to operate the lamps, and, if
desired, to heat the filaments thereof. Means to smooth out the DC
before it is converted to AC may be incorporated, if deemed
necessary or desirable. Further, means to facilitate starting the
lamps may be provided as well as means to limit the current flow
through the lamps after they begin to conduct current. The inverter
and associated means constitute the electronic or solid state
ballast of the invention.
Claims
Having thus described and illustrated the invention, what is
claimed is:
1. An electrical system for supplying a high frequency AC voltage
to gas discharge lamps, said system comprising:
(a) rectifier means for converting an AC voltage to a rectified DC
voltage,
(b) inverter means having a pair of input terminals and a pair of
output terminals, said inverter means coupled to the output of said
rectifier means for converting said rectified DC voltage appearing
across said pair of input terminals to a high frequency AC voltage
across said pair of output terminals, said inverter means
comprising:
(1) oscillator means comprising first and second switching
transistors, each of said transistors having a base, collector and
emitter, the emitters of said transistors connected to one of said
pair of input terminals,
(2) tuned circuit means, said tuned circuit means comprising a
transformer having first and second series-connected inductive
windings respectively connected to the output terminals and
connected with the collectors of said transistors, a .[.feed
back.]. .Iadd.feedback .Iaddend.winding connecting the bases of
said transistors,
(3) inductor means connected between the other one of said pair of
input terminals and a junction point intermediate said first and
second inductive windings for limiting the current in the
collectors of said first and second transistors during the time
period of simultaneous conduction of said transistors, and
(4) capacitor means coupled between said junction point and said
feedback winding for increasing the switching .Iadd.speed
.Iaddend.of said first and second transistors by decreasing base
current of the transistor that is turning off and increasing base
current of the transistor that is turning on; and
(c) means coupling at least one gas discharge lamp to the pair of
output terminals of said inverter means.
2. An electrical system for supplying a high frequency AC voltage
to gas discharge lamps, said system comprising:
(a) rectifier means for converting an AC voltage to a rectified DC
voltage,
(b) inverter means having a pair of input terminals and a pair of
output terminals, said inverter means coupled to the output of said
rectifier means for converting said rectified DC voltage appearing
across said pair of input terminals to a high frequency AC voltage
across said pair of output terminals, said inverter means
comprising:
(1) oscillator means comprising first and second switching
transistors, each of said transistors having a base, collector and
emitter, the emitters of said transistors connected to one of said
pair of input terminals,
(2) transformer means comprising a pair of primary windings
connected in series between the collectors of said transistors, a
first feedback loop winding connecting the bases of said first and
second transistors, and a second feedback loop winding connected by
way of a pair of forward diodes to the base of each of said
transistors, and
(3) inductor means connected between the other one of said pair of
input terminals and a junction point intermediate said pair of
primary windings for limiting the collector current of said first
and second transistors during the time period of simultaneous
conduction of said transistors; and
(c) means coupling at least one gas discharge lamp to the pair of
output terminals of said inverter means.
3. The system as claimed in claim 2 further comprising a
combination of a third winding in series with a resistor, said
third winding-resistor combination being connected between one of
the input terminals and an intermediate point of said second
feedback loop winding. .Iadd.
4. A high frequency AC lighting system for gas discharge lamps
comprising:
a plurality of electrical fixtures for removably holding gas
discharge lamps, each said fixture being distributed throughout an
area which is to be lighted by said lamps;
one or more subcenters for receiving commercial AC power at
available voltage and phase;
means at each said subcenter for rectifying said received AC power
into DC power for distribution from said one or more subcenters to
said plurality of lighting fixtures;
wiring means for distributing said DC power from said one or more
subcenters to said fixtures; and
a plurality of inverting means for receiving said DC power at input
terminals thereof and inverting said DC into high frequency AC at
output terminals thereof, each of said inverting means being
located at one of said fixtures, and being electrically connected
at said output terminals to a plurality of said lamps, and each
said inverting means comprising a semiconductor switching means in
electrical connection with a transformer. .Iaddend. .Iadd.
5. A system as set forth in claim 4 in which each said fixture
comprises a ballast means electrically connected to said lamps held
in said fixture, and in which each said inverting means is
electrically connected to said ballast means of its own and a
plurality of adjacent fixtures. .Iaddend. .Iadd.6. A system as set
forth in claim 5 in which each said inverting means is connected to
one or more ballast means of adjacent fixtures by
two load-carrying wires. .Iaddend. .Iadd.7. A system as set forth
in claims 5 or 6 in which said ballast means comprises an inductor.
.Iaddend. .Iadd.8. A system as set forth in claims 5 or 6 in which
said ballast means comprises a capacitor. .Iadd.9. A system as set
forth in claims 5 or 6 in which said ballast means comprises an
inductor and a capacitor. .Iaddend. .Iadd.10. A system as set forth
in claims 5 or 6 in which each said inverter means further
comprises a pair of transistors in push-pull
connection with a collector transformer. .Iaddend. .Iadd.11. A
system as set forth in claim 10 in which each said fixture holds at
least one gas discharge lamp comprising one or more filaments, and
in which each said inverter means further comprises heater windings
on said transformer, said heater windings being adapted to make
electrical connection with said filaments of one or more said
lamps. .Iaddend. .Iadd.12. A system as set forth in claim 11 in
which said means for electrically connecting said output terminals
of said inverter means comprises a separate magnetic core
transformer and wherein said heater windings derive induction from
said separate magnetic core. .Iaddend. .Iadd.13. A system as set
forth in claim 4 further comprising energy-saving transformer means
for deriving lamp filament voltage from, and proportional to, lamp
arc voltage so as to reduce lamp filament power after arc voltage
drops as said lamps turn
fully on. .Iaddend. .Iadd.14. A system as set forth in claim 4 in
which each said fixture holds at least one of said gas discharge
lamps and each lamp comprises a filament, and in which each said
inverting means is situated in a first fixture and is electrically
connected to a second fixture, said second fixture comprising
transformer means for heating the filament of each lamp in said
second fixture, and said second fixture further comprising ballast
means for each lamp in said second fixture. .Iaddend. .Iadd.15. A
system as set forth in claim 4 in which the DC is delivered to each
said inverting means by a two-wire circuit. .Iaddend. .Iadd.16. A
system as set forth in claim 4 in which the DC is delivered to each
said inverting means by a balanced three-wire circuit.
.Iaddend.
.Iadd.17. A system as set forth in claim 4 further comprising
voltage transforming means for inputting said AC power to said
rectifying means, and said voltage transforming means also
comprising means for transforming said commercial AC to proper
voltage for conventional AC facilities comprising at least one of
(a) single phase output terminals, (b) three phase output
terminals, and (c) six phase output terminals. .Iaddend.
.Iadd.18. A high frequency AC lighting system system for gas
discharge lamps comprising:
one or more subcenters for receiving commercial AC power at
available voltage and phase;
means at said subcenter for rectifying said received AC power into
DC power for distribution from said one or more subcenters;
a plurality of electrical fixtures for removably holding gas
discharge lamps each comprising one or more filaments;
wiring means for distributing said DC power from said one or more
subcenters to said fixtures;
inverting means associated with at least one said fixture, and
receiving said DC power at input terminals thereof and inverting
said DC into high frequency AC at output terminals thereof for
connection to said lamp, said inverting means comprising a
semiconductor switching means in electrical connection with a
transformer; and
energy saving transformer means in parallel electrical connection
across at least one said lamp, for deriving lamp filament voltage
from, and proportional to, lamp arc voltage so as to reduce lamp
filament power after arc voltage drops as said lamp turns fully on.
.Iaddend.
Description
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
The invention, its features and advantages, will be described in
conjunction with the several views of the drawings in which:
FIG. 1 is a block diagram of the system of the invention showing
the commercial power source of three-phase current, a transformer
for reducing the high supply voltage to a voltage suitable for
distribution from the central transformer for the building to
subcenters where the AC is rectified to DC, preferably a three wire
transmission system, to supply a plurality of inverters which
supply the desired high frequency power to operate the lamps;
FIG. 2 is a schematic diagram of the secondary of the transformer
in the rectifier with associated parts to provide three-wire direct
current for the inverters;
FIG. 3 represents the primary of the transformer of FIG. 2;
FIG. 4 represents an additional secondary for the transformer in
the central power room or the transformer in the inverter to obtain
single-phase AC for use in convenience outlets, for driving motors
of air-conditioning equipment and the like;
FIG. 5 is a similar diagram to FIG. 4 showing means .[.to obtain
single-phase.]. current at 120/.[.208.]. .Iadd.240 .Iaddend.volts,
.[.single or three-phase.].;
FIG. 6 is a circuit diagram of an inverter circuit suitable for use
in the system of FIG. 1;
FIG. 7 shows a circuit diagram of a portion of a transistorized
inverter of the prior art;
FIG. 8 is a modification of a portion of the circuit of FIG. 6
showing how to operate multiple rapid start fluorescent lamps in
series;
FIG. 9 is a circuit diagram of a portion of the circuit of FIG. 6
modified to provide for flashing of fluorescent lamps;
FIG. 10 illustrates a further modification of a portion of the
circuit of FIG. 6 to provide means to reduce the power supplied to
the electrodes of the lamps after starting;
FIG. 11A is a diagram of a circuit which supplies filament heating
current to both filaments or electrodes of a fluorescent lamp at
two levels, (1) full heating current at the start of operation of
the lamp and (2) greatly reduced filament current, e.g., about
one-third of the normal filament power, during operation of the
lamps;
FIG. 11B is a diagram of the right portion of FIG. 11A modified to
supply constant heating power to the filaments of the lamp;
FIG. 11C is a further modification of the right portion of FIG. 11A
to achieve the same result but with slightly different connections
to the transformer.
FIG. 12 illustrates ways for connecting a plurality of lamps across
the high-frequency, high-voltage lines from an inverter using both
capacitor and inductor ballasts so as to obtain a favorable power
factor in the high frequency supply lines;
FIG. 13A is a circuit diagram of an inverter circuit similar to
that of FIG. 6 but with modified means to supply the bases of the
two transistors;
FIG. 13B is a diagram of a portion of the circuit of FIG. 13A
modified by the addition of a diode in the line connecting each
collector of the transistors with the transformer;
FIGS. 14 and 15 each show a different connection of the anode of
the zener diode of FIG. 13A into the circuit;
FIG. 16 is a diagram of the circuit connecting the inverter to two
pairs of series connected fluorescent lamps with means for heating
the filaments of all lamps and utilizing both capacitor and
inductor ballasts for high power factor at the inverter output.
FIG. 17 is a diagram of the circuit connecting the inverter to four
lamps in parallel with means for heating the filaments of all the
lamps and utilizing both capacitor and inductor ballasts for high
power factor at the inverter output.
FIG. 18 is a diagram of the circuit of FIG. 16 with the addition of
starting aids for the pairs of series connected lamps; and
FIG. 19 is a diagram of the connection of the inverter to a
plurality of lamps in series and parallel across the lines from the
high-frequency, high-voltage secondary of the transformer and
including a saturable reactor for dimming lamps.
DETAILED DESCRIPTION OF THE INVENTION
As stated in the summary of the invention above, the present
invention comprises a system for supplying high-frequency
alternating current to a plurality of fixtures for gaseous
discharge lamps, usually fluorescent lamps. The preferred system
will now be described which is adapted to receive low-frequency (50
to 60 Hz) alternating current from a commercially available source
at whatever voltage the source happens to provide, transform it, if
necessary, to a voltage suitable for distribution and transmitting
it to rectifying means which produces a three-wire direct current
circuit which supplies power to the inverting means for converting
the DC into high-frequency, high-voltage alternating current. Each
inverter supplies the high-frequency (20 to 30 kHz or higher)
current to at least one fixture adapted to hold at least one
fluorescent lamp. The fixture wiring connects the filaments or
electrodes of the lamps to the high-frequency, high-voltage lines
from the inverter. The invention is not limited to this preferred
embodiment, however, but contemplates a system which derives the
current for operating lamps in the fixtures of the circuit of the
invention from a DC source instead of, or as an emergency adjunct
to, the AC source mentioned above, as will be described in greater
particularity hereinafter.
THE PREFERRED SYSTEM
Referring first to FIG. 1, the system obtains its power from a
commercially available source (not shown) to which connection is
made by terminals 1a, 1b and 1c of the primary of a transformer 2.
In most countries of the world commercially sold power is generated
and transmitted as low-frequency (50 to 60 Hz) alternating current
and, in order to minimize I.sup.2 r losses in transmission, it is
stepped up by transformers to a much higher voltage than the output
of the generator and then stepped down, usually in a succession of
voltage reductions, to voltages deemed safe for the various parts
of the transmission system from the main transmission line to the
entrance to the customer's premises. Sometimes this supply voltage
is in the 110 to 240 volt range, which is considered a safe voltage
for distribution in a building occupied by humans, such as a home,
barn, shop, store, Church, place of entertainment, etc. In many
cases, particularly in recent years, the power is brought to the
customer's premises at a much higher voltage, especially where the
building to be supplied is a Church, a school, a commercial
structure, of the like. It is usual practice in such cases to
provide in the building a central transformer room to house the
transformer necessary to reduce the supplied voltage to a voltage
suitable for the building through which it will be distributed.
Transformer 2 represents such a central transformer and its primary
winding would be insulated to operate safely at the high supply
voltage. The secondary winding would have the right number of turns
in relation to the number of turns in the primary winding to step
the voltage down to the building distribution voltage and make it
available for connection to the building distribution system by
output leads or terminals 3a, 3b and 3c. The primary windings for a
three-phase circuit may be connected delta or Y, as may the
windings of the secondary also be connected.
The building distribution system shown is a three-wire circuit from
the transformer 2 and it is represented by lines 4, 5 and 6 which
are connected to the terminals 3a, 3b and 3c.
The lines 4, 5 and 6 are connected to a plurality of rectifying
means 7 at subcenters in the distribution system. For such
rectifying means are illustrated in FIG. 1 by way of example and
they are designated as 7a, 7b, 7c and 7d for ease of reference in
FIG. 1 but the general designation 7 is used in the illustration
thereof in FIGS. 2 and 3 and the following description thereof. In
general each floor of a large building would have at least one
subcenter and if the floor area is larger than a single subcenter
can efficiently supply, a floor might have two or more
subcenters.
If commercial power is available at the premises of a building at
suitable building voltage, transformer 2 would not be necessary and
the building distribution system would then start with lines 4, 5
and 6 which would connect directly to the source of power but there
still would be a need for a building center to receive the power
and distribute it to the lines going to the subcenters.
Each rectifying means 7 receives the low-frequency alternating
current at the building voltage on its input side and delivers the
power from its output side as three-wire direct current to lines 8,
9 and 10.
Referring now to FIGS. 2 and 3, each rectifying means 7 comprises a
transformer having an iron core (not shown) and primary and
secondary windings. The primary 11 (FIG. 3) has three windings 12,
13 and 14 in delta connection providing terminals 15, 16 and 17 to
which lines 4, 5 and 6 are connected as shown.
The secondary, 18 (FIG. 2) of the rectifier transformer comprises
six windings 19, 20, 21, 22, 23 and 24 having a common central
connection 25 forming one terminal 26 on the output side of the
rectifying means 7. Terminal 26 may be grounded, as illustrated at
27, and it is sometimes referred to herein as the common, neutral
or grounded terminal. Line 9, which FIG. 1 shows to be connected to
terminal 26 of rectifying means 7a, is also sometimes referred to
herein as the neutral, common or grounded line.
The current delivered by the rectifying means 7a to lines 8, 9 and
10 and the voltages across these lines are relatively smooth. When
the EMF of each winding is plotted against time, the envelope of
the successive positive peaks has a maximum variation of 13.3%,
i.e., taking the peak or maximum EMF across center connection 25
and the end terminals 28, 29, 30, 31, 32 and 33 of the six windings
of the secondary as unity, the minimum EMF is 0.867. By the
optional use of a smoothing inductance and/or capacitance in the
load line, as hereafter mentioned for the circuits of the
invention, the ripples in the load current become still smaller
that they may be neglected without serious error.
Each said end terminal 28 through 33 of each secondary winding 19
through 24 is connected to the mid point of a bifurcated line
having in one leg an outwardly oriented diode 34 and in the other
leg an inwardly oriented diode 35. The cathode of each diode 34 is
connected to a common line 36, and the anode of each diode 35 is
connected through its leg of the bifurcated line to a different
outer end of a secondary winding 19 through 24. Similarly the
anodes of each of the six diodes 35 are connected to a common line
37 and the cathodes are each connected through its leg of the
bifurcated end to a different outer end of a secondary winding 19
through 24. Common line 36 is connected to terminal 38 and common
line 37 to terminal 39 on the output side of the rectifier 7. It is
to terminal 38 that line 8 is connected and to terminal 39 that
line 10 is connected, as shown in FIGS. 1 and 2. The voltage
between terminals 26 and 38 is the same, except for polarity, as
the voltage between terminals 26 and 39 and the voltage between
terminals 29 and 38 is double that, as shown in FIG. 2. What these
voltages are is a matter of design of the secondary windings with
respect to the primary windings. In practice it is satisfactory if
the peak voltage across a secondary winding is 170 volts,
therefore, the DC voltage across terminals 26 and 38 and across
terminals 26 and 39 will also be approximately 170 volts; the
voltage across terminals 38 and 38 is double that or 340 volts.
The rectifier transformer may also be used to supply AC power to
energize AC loads such as convenience outlets and AC motors. It is
popular practice at present to distribute power to large buildings
at 277/480 volts, three-phase AC and to energize the lighting
systems directly from this source. The convenience outlets and
other loads require 120 (110 to 130) volts and it is present
practice to use numerous dry-type transformers throughout the
building to convert 480 volt, three-phase current to 120/208 volts.
The transformer used in the rectifier shown in FIG. 2 will supply
120 volt single phase current to a load, if the load is connected
either to terminal 28, 30 or 32 and to neutral point 25, as shown
schematically in FIG. 4, or to terminals 29, 31 and 33 and neutral
point 25, or three phase current to a load if the load is connected
to terminals 28, 30 and 32, or single phase 208 volt current to a
load if the load is connected to terminals 28 and 30, or 28 and 32,
or 30 and 32. Furthermore, single-phase outputs of 120/240 volts
can be obtained from terminals 28 and 31 and neutral point 25, in a
three-wire system, as shown schematically in FIG. 5, or equally
well from terminals 29 and 32, or 30 and 33 and neutral point 25.
The output terminals for the circuits of FIGS. 4 and 5 will be
located in the output side of the rectifier 10 (although they are
not rectified and not shown in FIG. 1) and have been given the
designations 28, 30 and 32, and 28, 25 and 31, respectively for
convenience of reference. The rectifier of FIG. 2 incorporates a
three-phase transformer such as is utilized in modern building
power distribution systems to furnish power for 120, 208, or 240
volt AC loads. By making combined use of the same transformer in
the DC power supply system of the invention, lower cost of the
total system is achieved than in prior art high-frequency lighting
systems.
If desired, DC output voltages other than plus and minus 170 volts
can be obtained from the rectifier of FIG. 2. Thus, lower voltages
may be obtained merely by connecting the twelve diodes 34 and 35 to
taps (not shown) on secondary windings 19 to 24, inclusive, and
higher voltages may be obtained by providing extensions (not shown)
to the said windings. DC outputs of plus and minus 120 volts are
especially desirable because of previously established standards of
potential use in appliances other than the present lighting
system.
The three-wire DC distribution system has the advantage over a
two-wire DC system that smaller wires may be used, the secondary
windings 19 through 24 are more fully utilized, with each
conducting twice each cycle, no direct current flows in any of
these windings nor in the neutral line 25 if the DC loads are equal
on the positive and negative lines 36 and 37, and the positive DC
power supply may continue to operate in the event of failure of the
negative supply, and vice versa.
In the operation of the illustrated rectifier each of the six
secondary windings 19 through 24 produces a sinusoidal alternating
voltage varying over a cycle from minus 170 to plus 170 volts.
Because of the three-phase excitation of the primary 11 of the
transformer, the voltages of the outer terminals 28 through 33 of
the six secondary windings will reach their positive peaks at
different successive times equally spaced within a cycle of the
low-frequency current. At any instant, one of the terminals 28, 29,
30, 31, 32 or 33 will be more positive than all of the other
terminals in this group and approximately 170 volts more positive
than the neutral point 25. The diode 34 connected to the more
positive terminal connects it to conductor 36. The remaining five
diodes are in non-conducting states at this instant. As time
progresses, each of he other five diodes 34 conducts in turn, one
at a time, to connect the most positive winding to conductor 36.
Thus, conductor 36 remains at all times approximately 170 volts
more positive than the neutral point 25 and the AC transformer
voltages have been rectified to DC voltage. The six diodes 35
operate in a similar manner one by one to connect the most negative
terminal from the group 28 through 33 to conductor 37 which remains
approximately 170 volts more negative than neutral point 25. The
rectifier of FIG. 2 produces a good, low-ripple DC output of about
4.5% ripple while preserving a high power factor of about 95.5% in
the three-phase supply circuit 4, 5, 6.
The three-wire DC lines 8, 9 and 10 supplied from terminals 38, 26
and 39, respectively, of rectifying means 7a are connected to a
plurality of balanced loads cross lines 8 and 9 for one load
circuit and across lines 9 and 10 for another load circuit. Each
load is an inverting means 40 connected to fluorescent lamps 67 in
various numbers and arrangements. Six such inverting means are
shown by way of example in FIG. 1. They are given letter
designations a through f for ease of reference but in the following
description of the inverting means illustrated in FIG. 6 the
general designation 40 is used and the description of the circuit
of FIG. 6 applies to each inverting means 40a through 40f.
Inverting means 40a, 40c and 40e are in parallel across lines 8 and
9 while 40b, 40d and 40f are in parallel across lines 9 and 10.
While a total of six inverting means is given by way of example,
the invention contemplates any desired number thereof in the output
circuit of a single rectifying means 7 from one to as many as the
rating of the rectifying means permits. Any person skilled in this
art can readily determine the maximum number of inverting means
which the rating of the rectifying means 7b, 7c and 7d also has a
load circuit similar to the load circuit described and illustrated
for rectifying means 7a.
The fluorescent lamps 67 in FIG. 1 have been given postscripts
identifying them with the particular inverting means 40a, 40b, 40c,
40d, 40e and 40f which supplies them with high-frequency
alternating current. Thus, the lamps supplied from inverter 40a are
designated 67a1 and 67a2 which are in series, 67a3 and 67a4 which
are in parallel, 67a5 and 67a6, each being supplied individually.
Similarly the lamps supplied from inverter 40b are designated 67b1
and 67b2, each supplied individually, and 67b3 and 67b4 in
parallel. Likewise lamps supplied from inverter 40c are designated
67c1, 67c2 and 67c3, all supplied individually; lamps supplied from
inverter 40d are designated 67d1 and 67d2, each supplied
individually; lamps supplied from inverter 40e are designated 67e1
and 67e2 and are arranged in parallel; and the lamp supplied from
inverter 40f is designate 67f.
THE INVERTING MEANS
Referring now to FIG. 6, the inverting means 40 comprises a
positive input terminal 41 and a negative input terminal 42. These
terminals, 41 and 42, are adapted to be connected to the direct
current lines from the rectifying means 7, e.g., across lines 8 and
9 or across lines 9 and 10. In the event a source of direct current
other than the rectifying means 7 is used, which the invention
contemplates as mentioned above, terminals 41 and 42 would be
connected to whatever source is to be used, e.g., battery circuit
for emergency use or use remote from a commercial source of power,
a solar cell, a fuel cell, or the like. On the output side of the
inverting means 40 are two terminals 43 and 43a for the
high-frequency current generated in the inverting means 40 by the
means now to be described in detail. The entire circuit from input
terminals 41 and 42 to the output terminals 43 and 43a comprises
each inverting means 40a, 40b, 40c and 40d.
The inverter means 40 further comprises two transistors 44 and 45
which are the active elements of a high-power, push-pull, class-B,
tuned-collector, current-driven oscillator. An oscillator of this
sort, intended to produce a large amount of AC power from a DC
source, is commonly denominated in this art as an inverter and that
name is generally used herein for such elements of the circuit of
the invention. Transistor 44 has a base 46, a collector 47 and an
emitter 48. Transistor 45 has a base 49, a collector 50 and an
emitter 51. The tuned circuit comprises inductors or windings 52
and 53 of an inverter transformer 54 which has a magnetic core 55,
e.g., a ferrite core. Windings 52 and 53 have a common center
terminal 57 and end terminals 58 and 59. A capacitor 60 is
connected to the end terminals 58 and 59 which in turn are
connected to collectors 47 and 50 by lines 65 and 70, respectively.
This circuit is tuned to oscillate or resonate at a frequency of at
least 20 kHz in order (1) to enhance the efficiency of fluorescent
lamps, (2) to be inaudible and (3) to make possible the utilization
of small and practically loss-free circuit components. Collector
inductors 52 and 53 are wound on the magnetic core 55 of
transformer 54, along with other windings which are described
hereafter. In operation, a high AC voltage of sinusoidal waveform
appears across the end terminals 58 and 59 of inductors 52 and 53.
A feedback winding 61 is provided on core 55 and by transformer
action a much smaller voltage is induced in it than in windings 52
and 53 because of the small number of turns it has. The end
terminals of feedback winding 61 are connected respectively to
bases 46 and 49 of the transistors 44 and 45. The polarity of the
feedback voltage is selected to provide positive feedback from
collectors to bases as required to maintain or sustain oscillation.
The transistors operate in an efficient alternate switching mode,
one being turned off completely at one instant while the other is
saturated at which time it is turned fully on and is equivalent to
a closed switch. The feedback signal to the bases causes switching
from one state to the other. The transistor with the more positive
base voltage is saturated or in the "on" state. The transistor with
the more negative base voltage is in the "off" state. A brief
transitional interval is required to complete switching from one
state to the other.
Direct current flowing into the inverting means 40 from the
rectifying means 7, or other power source as described above,
enters at the positive terminal 41 which is connected by conductor
62 to the center terminal 57 of windings 52 and 53 through a fuse
63, a diode 64 and an inductor or winding 76 on a magnetic core 66.
At the central terminal junction point 57 the current must take one
of two alternate paths. One path comprises inductor or winding 52,
terminal 58, line 68, collector 47, emitter 48 of transistor 44,
line 68 and line 69 which returns current to the rectifying means 7
or other source through terminal 42. The current takes this path
when transistor 44 is in conducting mode. The other path which the
current takes, when transistor 44 turns off and transistor 45 turns
on, comprises winding 53, terminal 59, line 70, collector 50,
emitter 51 of transistor 45, line 69 and terminal 42, thus
returning the current to the rectifying means 7 or other source
along this second path. Current flowing alternately through
windings 52 and 53 of transformer 54 produces an alternating
voltage in every winding on the core 55, which is the desired
result of the action of inverting means 40.
Transistors can generally turn on more quickly than they can turn
off. Consequently, one transistor will turn on before the other
transistor has turned completely off. This results in an actual
short circuit across the terminals 58 and 59 of the windings 52 and
53 for a brief interval at each switching time. This short circuit
is rendered harmless because inductor 76 maintains an essentially
constant current through itself and associated parts of the circuit
and thus prevents the transistor collector currents from rising
appreciably during the short circuit or conduction overlap period.
The transistors thus start and complete their switching actions
under ideal conditions of practically zero collector voltage and
externally limited collector current.
Resistor 71 in line 72, which connects conductor 62, e.g., at the
junction of adjacent terminals of diode 64 and inductor 80, with
the midpoint of feedback winding 61 conducts a small current from
the positive DC input terminal 41 and conductor 62 to the bases 46
and 49, respectively, of the two transistors 44 and 45 by way of
feedback winding 61. This is the only source of base current when
the inverter is first turned on and is essential for reliable
starting. As oscillations build up, most of the base current comes
from voltage induced in the feedback winding 61, as will be
described in more detail hereafter.
Diode 64 is optional and, when used, prevents the blowing of fuse
63 if the input terminals 41, 42 are connected to the DC supply
lines 8,9 or 9,10 of wrong polarity.
Diode 73 connects the base 46 of transistor 44, and diode 74
connects the base 49 of transistor 45, the line 69 through resistor
75.
The difference in the operation of the circuit of the invention
over the typical prior art base connection arrangement may be
clearly understood by comparing FIG. 7 with FIG. 6. In FIG. 7
comparable parts have the same reference numbers used in FIG. 6
with a postscript a.
The typical prior art base connection arrangement comprises two
transistors 44a and 45a, a single diode 73a connected in series
with inductor 80a and resistor 75a, and this combination connects
the center tap of feedback winding 61a to the emitters 48a and 51a
of both transistors 44a and 45a. The purpose of this circuit is
efficiently to provide a large DC component of base current by
rectifying the low voltage of the feedback winding 61a. The
base-emitter junctions of the transistors provide the rectifying
action, and the inductor 80a maintains base current in at least one
transistor during the switching instants when the alternating
feedback voltage passes through zero. Diode 73a merely prevents the
draining away of the small starting component of base current from
resistor 71a. Neither base can rise more than about 0.8 volt above
the emitters because of the transistor characteristics. This
requires that most of the feedback voltage across winding 61a will
show up as negative voltage at the base of the "off" transistor,
whichever that may be at any given time. Also, the center tap of
winding 61a will be driven negative twice each cycle at the one
time each cycle when each base goes negative. As the center tap
goes negative, current flows upward through diode 73a, inductor 80a
and resistor 75a and continues into the base of whichever
transistor is turned on. This current is largely responsible for
turning the transistors on. As stated previously, the inductor 80a
keeps the current through itself substantially constant, providing
a steady source of current for one or the other of the bases.
With this prior art circuit, the maximum voltage across the
feedback winding 61a is necessarily only a few volts, as limited by
the peak reverse voltage rating of the emitter-base junctions of
the transistors. A significant portion of this voltage is lost in
diode 73a and in the emitter-base junctions of the transistors.
Thus, when feedback voltage is reduced because of low-line voltage,
as may be experienced during a "brown-out" and at other times, the
base drive voltage becomes unreliably small, and a condition of
intermittent oscillation known as "squegging" can occur. In
particular, the transistors may not saturate but conduct current
while a large voltage exists from collector to emitter, increasing
power dissipation which may quickly damage the transistors.
With the present invention, as shown in FIG. 6, two diodes 73 and
74 are connected one at each end of the feedback winding 61, rather
than having a single diode at the center tap as shown in the prior
art circuit in FIG. 7. This doubles the voltage available for
rectification and allows stable operation down to such low input
line voltages that the transistors are adequately protected for all
low voltage conditions.
Inductor 80 is not always required in FIG. 6. However, when used,
it can reduce peak base current and reduce the power dissipated in
resistor 75a (FIG. 7) or resistor 75 (FIG. 6). A more economical
way to implement the equivalent inductor 80a in FIG. 7, if such is
desired, is to substitute for inductor 80a a few turns of wire 80
around the core 66 of inductor 76, as shown in FIG. 7, connected in
series with resistor 75. This causes current to flow from diodes 73
and 74 through resistor 75, line 81, winding 80 and line 82 to line
69 in the circuit of FIG. 6. Transformer action from the main
inductor winding 76 then induces the same voltage in these few
turns 80 that inductor 80a would ideally have, but without the
expense of an additional magnetic core and bobbin. Winding 80 adds
an AC voltage at the bottom of resistor 75 equal to the AC
component of voltage from feedback winding 61 at the top of
.[.resister.]. .Iadd.resistor .Iaddend.75, leaving only a DC
voltage across resistor 75, resulting in the same constant base
current provided in prior art by the additional inductor 80a.
A small capacitor 83 is preferably connected between the junction
of collector windings 52 and 53 and the feedback winding 61. This
capacitor helps speed the switching action by drawing base current
away from the base of whichever transistor is turning off at the
proper time and by adding base current to the turning-on transistor
a moment later.
Diode 84 and Zener diode 85, when used, are arranged in series with
each other and across inductor 76, as shown, to limit the maximum
positive voltage that can be applied to the transistor circuit. A
dangerous voltage capable of destroying the transistors can
otherwise occur during the transient condition when the inverter is
first switched on to the low-impedance voltage source from the
central rectifier 7.
A diode 86 may be placed across the DC input lines. This diode
conducts only for an instant when the DC input power is switched
off. It provides a controlled path for decay of the current stored
in inductor 76 when that current can no longer flow through the
input line 62. Diode 86 also reduces arcing at the switch (not
shown) which turns off the DC input voltage. Diodes 84 and 86,
Zener diode 85 and capacitor 83 comprise transient suppression
circuitry.
In the preferred embodiment shown, the several windings are placed
on transformer core 55. This avoids the use of two more costly
individual transformers, as are commonly used in the prior art.
The AC output of the inverter can be used in many ways. FIG. 6
illustrates how three, or more, "rapid start" fluorescent lamps
67a5, 67a6 and 67a7 can be driven. These lamps have electrodes in
the form of filaments at each end thereof, which must be heated by
a flow of current produced by means of a low voltage. For ease of
description, the filaments in lamp 67a5 are designated 90a5 and
91a5, those in lamp 67a6 are designated 90a6 and 91a6, and those in
lamp 67a7 are designated 90a7 and 91a7, respectively. The heater
voltage for the filaments 90a5, 90a6 and 90a7 is obtained from low
voltage heater windings 92 on magnetic core 55. Filaments 91a5,
91a6 and 91a7 at the opposite end of each lamp require separate
heater windings 93, 94 and 95 on the same core, as shown.
Fluorescent and other gas discharge lamps have a negative impedance
characteristic which makes direct parallel operation impractical.
Each lamp requires a ballast impedance in series with it to limit
the current. Either inductors or capacitors can perform the ballast
function without wasting energy. Capacitors 96, 97 and 98 are shown
as ballasts in FIG. 6. Windings 52 and 53 constitute a sinusoidal
high voltage, high-frequency power supply for the lamps. The
voltage of these windings is determined almost completely by the DC
input voltage to the inverter, but the voltage applied to the lamps
can be selected independently by tapping one or both of the
windings 52 and 53 as shown at tap 99 for lower voltage. A higher
voltage can be obtained by extending either or both windings with
additional turns (not shown) beyond the points where the transistor
collectors connect.
An entirely separate winding (not shown) on core 55, of any desired
voltage, can be used for the lamps and with full transformer
isolation, if necessary or desirable.
Other loading arrangements are possible and more (or fewer) than
three lamps can be accommodated by the system of FIG. 6 as shown in
FIG. 1 and described above. This parallel system of operation
permits removal of part of the lamps from the fixture to adjust
light intensity without appreciable effect on the remaining lamps.
Lamps can also be operated in series or series-parallel,
particularly if there are an even number of lamps. Such an
arrangement reduces the number of ballast capacitors needed and
makes dimming by adjusting ballast capacitance entirely
feasible.
Many fluorescent and other gas discharge lamps do not require
separately heated filaments, and if such lamps are used, the heater
windings 92, 93, 94 and 95 would not be needed.
FIG. 8 shows that portion of the circuit of FIG. 6 that may be
modified for series operation of two rapid start lamps 101 and 102.
Parts in the circuit of FIG. 8 that correspond to parts in the
circuit of FIG. 6, are given the same reference number with the
postscript b and need not be further discussed at this point.
Voltage greater than that between the transistor collectors is
obtained by adding one or two extension windings 103 and 104 to the
core 55b. Windings 92b, 106, and 110 then provide heating power for
the lamp filaments, 105, 107, 108 and 109. A single capacitor 111
provides current limiting or ballasting for both lamps.
DIMMING
Rapid start fluorescent lamps are readily dimmed by lowering the
capacitance of the ballast capacitor 111 in FIG. 8. One simple
means is to make capacitor 111 from a number of separate capacitors
which can be switched manually or remotely into the circuit in
various combinations .[.be.]. .Iadd.by .Iaddend.conventional switch
means (not shown). Another means adaptable to adjustable zone
lighting is to plug in different values of capacitor 111 in
accordance with a desired lighting level. Dimming by adjustment of
the ballast capacitor allows for full starting voltage at all
levels and is superior therefore to voltage reduction methods. The
preferred dimming method described keeps filament voltages
constant, as is usually desired when dimming.
Dimming is also readily achieved by the circuit illustrated in FIG.
19 as fully described hereinafter.
FLASHING
The inverter 40 is readily adapted to utilize electronic control
for flashing. This requires only a modification of a portion of the
circuit of FIG. 6. Such a modified portion of the circuit shown in
FIG. 9 in which parts comparable to parts in FIG. 6 have been given
the same reference numbers with a postscript c and need no further
description here. A separate transformer 112 having a magnetic core
113, a primary winding 114 with terminals 115 and 116 adapted to
connect the primary to an AC source of any frequency, and a series
of secondary coils 92c, 93c, 94c and 95c for heating the filaments
of lamps 67a5c, 67a6c and 67a7c, operating independently of the
inverter keeps the filaments always heated, so that filament
windings from the inverter itself are not needed. DC power into the
inverter is controlled by transistor 114 which can be turned on and
off by a low-level signal (less than 1 volt) between the base 115
and ground 116. This method of switching is superior to and easier
to accomplish switching in an AC circuit. A mechanical switch could
replace transistor 114 if desired.
FILAMENT CONTROL
FIG. 10 shows a modified form of the circuit of FIG. 8 in which
comparable parts have been given the same reference numbers with a
postscript d. The filaments of lamps 101d and 102d are supplied
from a transformer .[.54b.]. .Iadd.54d .Iaddend.instead of directly
from the constant-voltage inverter transformer 54 of FIGS. 6 and 8.
The primary 52d of transformer 54d receives its input from the lamp
voltage. Before the arc strikes in the lamps, there is little
voltage drop in the ballast capacitor 111d and practically the full
inverter voltage is applied to the primary of the transformer 54d.
This results in a relatively high output of transformer 54d to heat
the filaments rapidly. As soon as the arc strikes, the lamp arc
voltage drops substantially, lowering the voltage on all windings
of transformer 54d and specifically reducing the heater voltages on
windings 92d, 106d and 110d. Reduced heater voltage means that less
power is consumed and the circuit operates more efficiently than it
would otherwise do. No switches are needed to accomplish heater
power reduction, in contrast to the practice in some prior art
systems. Placing the heater windings on transformer 54d simplifies
the design of already complicated transformer 54. Because of the
high frequency used, transformer 54d can be very small,
inexpensive, and free from power loss. Note that the heaters are
not shut off entirely since this would be harmful to the life of
some filaments. The greatest damage to filaments normally occurs
during starting when they are bombarded by heavy ions before the
reach proper operating temperature. The control offered by
transformer 54d shortens this time of bombardment and assures
increased lamp life as well as improved operating energy
efficiency.
FIG. 11A depicts a circuit which is capable of supplying a high
current to the filaments of a heated filament fluorescent lamp when
the lamp is first turned on at the start of a lighting cycle and
automatically reducing the current flow through the filaments as
soon as stable operation is achieved. The circuit comprises an
inverter illustrated by the block 120, which may have the same
circuit described above or it may have any other circuit which will
accomplish the same function, a ballast represented by the block
122, which may be any electronic component serving this function
such as an inductor or capacitor, an electric connection 124
between the inverter and the ballast, a line 125 from the ballast
122 to a load 126 to be described more fully hereunder, and a
return connection 128 to the inverter 120. The load illustrated
comprises an autotransformer 130 having one terminal connected to
line 125 and the other terminal connected to line 128, a
fluorescent lamp 132 having a filament 134 at one end and a
filament 136 at the other end. The current for filament 134 is
supplied from one end of the autotransformer 130 by a tap 138 just
a turn or so from that end while the current for filament 136 is
supplied from the other end of the autotransformer by a tap 140
just a turn or two from said other end.
After the inverter 120 has been turned on and before the arc has
been struck between the cathodes or filaments 134 and 136 of the
lamp or tube 132, very little electric current flows through the
lamp and ballast circuit. Accordingly there is little voltage drop
in the ballast impedance 122, and essentially all the voltage from
the inverter 120 appears across the entire winding of the
autotransformer 130. Voltages suitable for quickly heating the
filaments or cathodes 134 and 136 are induced in the end turns of
the autotransformer beyond taps 138 and 140, respectively. After a
short period of heating, sufficient electrons are emitted by the
cathodes or filaments 134 and 136 to permit an arc to be
established between the cathodes. A large electric current then
flows through the lamp and ballast, and a large voltage drop occurs
in the ballast. The voltage remaining across the lamp terminals
(between the filaments or cathodes) drops to a much lower value,
e.g., about half its former value, more or less. This lamp voltage
is applied to the autotransformer, so the voltage in every part of
the autotransformer winding drops to the lower value. In
particular, the voltage in the heater turns beyond taps 138 and 140
drops and reduces the cathode heating voltage to the said lower
value. The direct heating power for the cathodes depends on the
square of the voltage, so the heating power drops to substantially
less than half its former value. Typically 2/3 of the energy used
for direct cathode heating can be saved by this means. Note that no
switches, electronic or otherwise, are needed and that the
lamp-ballast filament transformer circuits are connected to the
inverter by only two conductors. Thus, the circuit is inexpensive
and convenient for use in a lamp fixture separate from the one
containing the inverter As such, a system including several
one-lamp or two-lamp fixtures can be operated from a common
inverter which for economy should be loaded to its full
capacity.
Not only does the autotransformer 130 allow energy saving, but it
does so without the disadvantage of certain prior-art ballasts
which turn the heaters off completely. A definite voltage
maintained across the length of each cathode encourages the
intercathode arc to form first between the ends of the cathodes
where the voltage difference is greatest. A hot spot forms there
where most of the electron emission takes place. As the
electron-emitting oxide is burned away from one end of each
cathode, the hot spot moves to an adjacent spot having the next
highest voltage and in this manner progresses in an orderly way
along the entire filament throughout the useful life of the lamp.
If a definite voltage is not provided across the filament, the hot
spot may wander out of control and may never reach some portions of
the cathode still having good oxide coatings. Premature cathode
failure results.
In summary, one feature of the present invention provides means to
maintain sufficient voltage across each cathode to promote orderly
hot spot migration while saving 2/3 of the cathode heater
power.
One filament transformer similar to 130 but with additional
filament windings, some of which are not conductively connected
together as in an autotransformer but isolated as in a conventional
transformer, can serve two or more lamps connected in series in a
straight-forward extension of the circuit described above.
In applications not needing to conserve heater power, the heaters
can be energized in this system, as in prior-art, directly from
additional windings not shown, on the main inverter transformer or
from one or more intermediate transformers with primary windings
connected to the inverter output ahead of the ballast
impedances.
FIG. 11B illustrates a modification of the circuit of FIG. 11A
which provides constant heater power. In this figure, parts which
are the same as comparable parts in FIG. 11A have been given the
same reference numbers and need not be described again for the
circuit of FIG. 11B. The significant difference in the circuit of
FIG. 11B over the circuit of FIG. 11A is the filament transformer
130a is connected across lines 124a and 128a between the terminals
12 and 144 from an inverter (not shown), e.g., such as 120, and the
ballast 122a. This means that the voltage across the transformer
does not change substantially with current flow so that the voltage
supplying current to the filament 134a and 136a remains practically
constant during operation of the lamps. The high-frequency
transformer 130a is preferably a transformer having a magnetic
core, e.g. ferrite core, 148.
FIG. 11C depicts a further circuit modified from that of FIG. 11A
which also has such comparable parts numbered with the
corresponding part number in FIG. 11A. The difference is that the
autotransformer 130b has taps 138b and 140b a few turns from the
ends of the winding connected to lines 125b and 128b and the leads
to the filaments 134b and 136b connect to the end terminals of the
transformer rather than the taps on the winding. The operation of
the circuits of FIGS. 11B and 11C is essentially the same as
described for the circuit of FIG. 11A.
FIG. 12 illustrates a number of circuits for providing heating
current to lamp filaments from the high frequency AC output lines
124c and 128c from an inverter, e.g., such as 120 in FIG. 11A.
The first circuit 150 in FIG. 12 comprises a pair of fluorescent
lamps 152 and 154 in parallel across lines 124c and 128c through
various means for heating the cathodes 156 and 158 in lamp 152 and
the cathodes 160 and 162 in lamp 154. The heating means for
filament 156 comprises an inductance winding 160 connected at one
end to one end of the filament 156 and at the other end to a line
162 which connects at one end to the other end of the aforesaid
filament 156 and at the other end to the junction of the connection
of the winding 160 to it and one terminal of a capacitor 164. The
other terminal of capacitor 164 is connected by line 166 to line
124c. Filament 158 of lamp 152 has one end connected directly to
line 128c by a line 168. The other end of filament 158 is connected
to one end of an inductance winding 170 by a line 172. The other
end of winding 170 is connected to line 168. Filament 162 of lamp
154 is connected at one end by a line 174 to line 172 and at the
other end by line 176 to line 128c. Filament 160 of lamp 154 has
the same connections to line 124c as filament 156 of lamp 152
except that an inductance 182 replaces capacitor 164 and winding
178 replaces winding 160, parts 164 and 182 serving as ballast for
the lamps. The mixing of capacitor and inductor ballasts maintains
high power factor at the output of the inverter. Windings 160, 170
and 178 are all on the main inverter transformer and supply
constant heating power. This circuit is adapted to supply full line
voltage of lines 124c and 128c across both lamps 152 and 154 at the
start of lamp operation (as do the circuits of FIGS. 11A and 11C),
but to reduce the voltage substantially during operation by the
voltage drops across ballast capacitor 164 and ballast inductor
182.
The second circuit 184 comprises a single fluorescent lamp 186
having a filament 188 at one end and a filament 190 at the other
end. It receives constant filament power from an intermediate
autotransformer 192 connected across lines 124c and 128c by lines
194 and 196, respectively. Filament 188 is supplied with heating
current by a transformer 198 having a high frequency core 200,
e.g., ferrite. One end of the autotransformer winding 192 forms the
primary of transformer 198. The secondary is a winding 202
connected at one end to one end of the filament 188 and at the
other end to a line 204 which is connected at one end to the other
end of the filament 188 and at the other end to the junction of
said connection of winding 202 to line 204 and one terminal of a
ballast capacitor 206. The other terminal of capacitor 206 is
connected by line 208 to line 124c. Filament 190 has one end
connected by line 210 to line 196 and the other end connected by
line 212 to a tap 214 on autotransformer winding 192.
The third circuit 216 bears the same reference numbers to parts
corresponding to circuit 184 with postscript a and is the same as
the second circuit 184, except that the separate transformer 198 is
eliminated by using a few turns of the autotransformer circuit at
both ends, e.g., by connecting the one end of filament 188a to a
tap 202 on the winding 192a a few turns from the end. The filaments
of lamp 186a receive variable power from this circuit, i.e., the
filament voltage is reduced after the lamp arc strikes.
The fourth circuit 218 is the same as circuit 216 except that the
ballast capacitor 206a is replaced by a ballast inductance 206b.
Other parts bear the same reference numbers as the corresponding
parts in circuits 184 and 216 with a postscript b and need not be
further described. The combination of capacitor 206a for ballast in
circuit 216 with inductor 206b for ballast in circuit 218 gives
high power factor.
The circuits 184, 216 and 218, as is true of all of the circuits,
operate in essentially the same way, providing full voltage of the
inverter to which lines 124c and 128c are connected across the lamp
at the start and a much reduced voltage after it is operating
steadily. In circuit 184, full voltage is applied to the filaments
at all times, whereas in circuits 216 and 218, the voltage applied
to the filaments is automatically reduced when the voltage across
the lamps decreases.
The fifth circuit 220 comprises two fluorescent lamps 222 and 224
in series across lines 124c and 128c and are served by a single
filament transformer 192c. Lamp 222 has one filament 226 connected
at one end to a tap 202c on autotransformer winding 192c, as in
circuit 216, and at the other end to the end of transformer winding
192c, and through capacitor 206c and line 208c to line 124b.
Filaments 190c at one end of tube 228c is connected at one end to
tap 214c on transformer winding 192c a few turns from the end, and
at the other end by lines 210c and 196c to line 128c. The adjacent
end filaments 227 and 228 of lamps 222 and 224, respectively, are
connected in parallel across the terminals of a short winding 230
forming a secondary of a transformer of which the primary is
winding 192c. Optionally, a small capacitor 232 (or inductor)
connected across lamp 224 (or across lamp 222 instead) may be used
to aid starting and reduce the need for higher voltage for good
operation.
The sixth circuit 234 is the same as circuit 220 except that
capacitors 206c and 232 are replaced by inductances 206d and 232d,
respectively. Other parts of circuit 234 have the same reference
numbers as the corresponding parts of circuit 220 with the
postscript d and need not be further described.
Circuits 220 and 234 operate in essentially the same manner as
circuits 216 and 218 except that there are two lamps in series in
circuits 220 and 234 instead of a single lamp in circuits 216 and
218.
FIG. 12 shows the great versatility of the circuits of the
invention to modification without changing the principle of
operation to operate with constant filament voltage or to achieve
voltage reduction, across the filaments of lamps, with consequent
reduction of heating current during operation after a maximum
voltage start up, and with high power factor.
FIG. 13A depicts a circuit for an inverter similar to the inverter
circuit shown in FIG. 6, showing only parts necessary to understand
the circuit and its operation, but with a modified means to supply
the bases of transistors 44 and 45. The parts of the circuit of
FIG. 13A which correspond to parts of the circuit of FIG. 6 are
given the same numbers with a postscript b and need not be
described further.
A small electric current enters the circuit at terminal 41b and
flows through line 72b and resistor 71b into the base of either
transistor 44b or 45b or both. Resistor 71b has a high resistance,
e.g., about 100 kilohms, so that the current flowing through it is
a very small initial bias current to assure reliable starting. At
least one of the transistors turns on and allows current to flow
from terminal 41b through inductor 76b, center tap 57b and
alternately through the primary windings 52b and 53b of the main
inverter transformer 54b. A voltage is thus applied to coil 52b,
53b, and this induces a voltage in the low-voltage feedback winding
61b on the same core 55b (although not shown in the same location
in FIG. 13A). One terminal of winding 61b is connected to base 46b
of transistor 44b. The other terminal of winding 61b is connected
to base 49b of transistor 45b, preferably through a resistor 240.
Polarity of the feedback is such as to reinforce whatever the
transistors are doing. That is, if 44b initially conducts more
heavily than 45b, the feedback signal will tend to turn 44b on
still more, and 45b will be turned off. Capacitor 60b resonates
with 52b, 53b, and causes the voltage polarity to reverse
periodically in all of the windings on 54b. First one transistor
conducts and then the other. Winding 76b maintains a constant
current through itself; therefore, the sum of the two transistor
collector currents must be constant. In the transition interval
when switching from one transistor to the other, and when both
transistors are partly turned on and winding 52b, 53b is shorted,
76b assures that excessive current will .[.now.]. .Iadd.not
.Iaddend.flow.
Voltage is induced also in the feedback windings 79 and 79a, also
on core 55b, and when oscillations build up enough that this
voltage can turn on diodes 73b and 74b, most of the transistor base
current is supplied from this new source. It is far more efficient
to obtain base current from two turns on 79 and 79a than from the
120 volt input source. Only about 1.2 mA of base current flows
through resistor 71b, while about 80 mA comes from 79 and 79a. This
arrangement saves about 9 watts. Diodes 73b and 74b have other
important functions. They, of course, force the starting current
from 71b to flow into the transistor bases instead of being drained
away from resistor 75b. Diodes 73b and 74b also connect both
relatively high voltage feedback windings 79 and 79a between both
bases at the switching time to provide a large feedback signal to
assure fast switching and very rapid turn off for one transistor
and rapid turn on for the other. Diodes 73b and 74b are slow diodes
having a longer charge storage time than the transistors 44b and
45b. Thus while one diode conducts normally, the other will conduct
backward for a short time until the transistor to which it is
connected is fully turned off. However, before the base is driven
too far negative, that diode will cease to conduct, and the base
can drop only as far as allowed by the low-voltage feedback winding
61b, (e.g., to about -4.5 volts.).
The voltage at point D, the common junction of windings 79 and 79a
with resistor 75b has a negative DC component of about 4.5 volts
with respect to point B (or terminal 42b) and an AC component
consisting of a train of half-sine waves. It turns out that the AC
component at point D has the same waveform as that at point C, the
center tap 57b, except for polarity and amplitude. The AC component
at point C appears across winding 76b. By adding a second winding
78, of very few turns on the same core 66b, and connecting it as
shown, the AC component of voltage at point E (between resistor 75b
and winding 78) can be made almost exactly the same as that at
point D. The potential across resistor 75b is therefore almost a
pure 4.5 V DC voltage, and a constant current of about 80 mA flows
up through resistor 75b and into one base or the other of
transistors 44b and 45b. Since the sum of the collector currents is
held constant by inductance 76b, it is proper and efficient to have
the sum of the base currents constant also.
If the voltage at point C ever rises sufficiently far .[.about.].
.Iadd.above .Iaddend.point B, Zener diode 85b turns on and prevents
further rise to protect the .[.transitors.].
.Iadd.transistors.Iaddend.. Abnormally high voltage can occur at
point C for a few cycles at turn on. Diode 84b prevents 85b from
conducting when the voltage at C drops below that at A as happens
in normal operation.
Diode 86b functions only at turn off to allow a discharge path for
current in winding 76b.
Capacitor 81b helps to reduce radio noise conducted back into the
DC supply line. Inductance 76b is also very effective in this
regard although that is not its main function.
The main output terminals are 43b and 43ab at the ends of secondary
winding 237a of transformer 54b. If desired, auxiliary output
terminals 238 and 239 may be provided at the remote or outer ends
of windings 52b and 53b.
Lamps may be connected to terminals 43b and 43ab, or alternatively
to terminals 238 and 239, in the circuit of FIG. 13 in essentially
the same manner shown for lamps 67 in FIG. 6, using either ballast
capacitors or inductances or both.
Each lamp or pair of lamps operates independently from the others
and each has its own ballast inductor or capacitor. By using both
inductors and capacitors, the reactive effects cancel so far as the
inverter is concerned. The load power factor is therefore high, and
the inverter frequency is relatively independent of the load in
case some of the lamps are removed.
Air gaps are used with both inductors or transformers 54b and 76b
and also with the ballast inductors. A DC input voltage of about
120 V was selected because of the commercial availability of
switches and circuit breakers of this rating, and this also permits
incandescent lamps to be run from the same circuit.
Lamp filaments can be powered in the circuit of FIG. 13 from 1-turn
windings on the core of transformer 54b, the same as in FIG. 6. One
winding can serve one end of all the lamps which may be connected
together, but individual windings are needed at the ballast ends.
Alternatively, one or more separate filament transformers can be
used to reduce the number of wires to lamps not contained in the
same fixture with the inverter.
FIG. 13B is a circuit diagram of a portion of the circuit of FIG.
13A in which parts common to both circuits are numbered with the
same numbers used in FIG. 13A but with postscripts c. The circuit
of FIG. 13B is modified from that of FIG. 13A by the addition of a
diode 235 in line 65c and a diode 236 in line 70c which serve to
assure the absence of any reverse flow of current in lines 65c and
70c.
FIGS. 14 and 15 are circuit diagrams of inverter circuits similar
to the inverter circuit depicted in FIG. 13A in which parts
comparable to those in the circuit of FIG. 13A bear the same
reference numbers with postscripts d and e, respectively. One
difference between the circuits of FIGS. 13A, 14 and 15 is the
connection of the anode of the Zener diode into the circuit. This
diode is designated 85b in FIG. 13A, 85d in FIG. 14 and 85e in FIG.
15. In the circuit of FIG. 13A the connection of the anode of Zener
diode 85b into the circuit is to line 72b through diode 84b. In the
circuit of FIG. 14 the connection of the anode Zener diode 85d is
to the bases of the transistors either directly to base 46d of
transistor 44d or through winding 61d and resistor 240d to the base
49d of transistor 45d. In the circuit of FIG. 15 the connection of
the anode of Zener diode 85e is directly to line 69e. The
connection in the circuit of FIG. 13A of line 62b to line 72d
through Zener diode 85b and 84d causes the input DC voltage (120 V)
to be added to the conduction voltage of Zener diode 85b which
should be designed to conduct at about 120 V for the required 240
volts maximum at point C. In the circuits of FIGS. 14 and 15 diodes
85d and 85e must conduct at about 240 volts. Diode 84b in the
circuit of FIG. 13A prevents Zener diode 85b from conducting when
the cathode of diode 85b drops below 120 volts as it
.[.periodiclly.]. .Iadd.periodically .Iaddend.does in normal
operation. The direct connection of the anode of Zener diode 85e to
the negative input terminal 42e, as in the circuit of FIG. 15, is
the most straightforward alternative, but requires a higher
combination of voltage and current in diode 85e than do the
connections of FIGS. 13A and 14.
The circuit of FIG. 14 has an additional difference from the
circuits of FIGS. 13A and 15 as illustrated. This difference is the
presence in the circuit of FIG. 14 of two additional diodes 299 and
300. The cathode of diode 299 is connected to collector 47d of
transistor 44d and its anode is connected to the junction of the
anode of diode 73d and feedback winding 79d. Similarly the cathode
of diode 300 is connected to collector 50d of transistor 45d and
its anode is connected to the junction of the anode of diode 74d
and feedback winding 79ad. With diodes 299 and 300 in the circuit,
the resistance rating of resistor 75d can be selected to provide
all the base current needed to drive very low gain transistors, and
the excess base current not needed by transistors of normal or high
gain is shunted by diodes 299 and 300 (hence catching diodes) away
from the base to the collector of either transistor as that
transistor approaches saturation. The result is .[.than.].
.Iadd.that .Iaddend.the transistors do not quite saturate and can
be turned off more quickly that if allowed to saturate heavily.
Diodes 299 and 300 may, therefore, serve as well to adjust the
inverter to accommodate transistors differing greatly in current
gain. While diodes 299 and 300 are shown only in the circuit of
FIG. 14, they may also be used in the circuits of FIGS. 13A, 13B
and/or 15 if the benefits described by reason of their presence in
the circuit of FIG. 14 are desired in any one or more of these
circuits.
The operation of the circuit of FIGS. 13A, 14 and 15 will be
described by reference to the circuit of FIG. 14. Connection of the
anode of Zener diode 85d to the base of either transistor 44d or
45d causes at least one of these transistors to turn on heavily
when diode 85d turns on. Current flowing through the collectors of
the transistors 44d and 45d can limit their collector voltages as
effectively as current through Zener diode 85d but with the
advantage that the transistors 44d and 45d are capable of
conducting much larger currents than the Zener diode 85d needs to
conduct in this situation. Thus by using the Zener diode 85d to
turn on the transistors 44d and 45d, a relatively low-current and
inexpensive Zener diode may be used.
The drive circuit for the transistors 44d and 45d represents a
significant improvement over circuits known in the prior art. Two
independent feedback windings 79d and 79ad of the main inverter
transformer 54d are used to satisfy conflicting requirements in an
optimum way. It is desirable to have a large feedback voltage
during the switching time to turn one transistor off and the other
on with a minimum of overlap time when both transistors are
partially on. However, a sufficiently large feedback voltage for
this purpose causes too much reverse base voltage for the
turned-off transistor between switching events.
A small current from the +DC source 41d flows through resistor 71d
to supply a very small amount of bias current for the bases of the
transistors 44d and 45d. This is sufficient to cause the
transistors to begin to oscillate in the conventional way, i.e.,
the outputs of the collectors of both transistors are connected to
transformer 54d by windings 52d and 53d which in turn are coupled
magnetically to the transistor bases 46d and 49d by way of the
low-voltage feedback winding 61d on the core of the same
transformer. Feedback polarity is such as to reinforce and sustain
an oscillating condition, with each transistor in turn causing
current to flow from the positive DC voltage source 41d through
inductor 76d, line 62d and then through either winding 52d or 53d
of transformer 54d, and returning to the negative power supply
terminal 42d.
When the amplitude of oscillation increases sufficiently, diodes
73d and 74d are turned on and off alternatively by voltage induced
in high-voltage feedback winding 79d or 79ad. Base current is
increased very substantially by current from winding 79d or 79ad
and the bases are driven efficiently at this time primarily from
this source. Although the voltage of windings 79d and 79ad is high
compared to the voltage of winding 61d, it is still small compared
to the input voltage at terminals 41d and 42d, which means that
base current is obtained more efficiently from windings 79d and
79ad than from the high-resistance dropping resistor 71d.
Diodes 73d and 74d are inexpensive, low-voltage slow diodes which
have a larger charge storage time than the transistor bases 46d and
49d. This means that when the anode of either diode 73d or 74d goes
negative with respect to the cathode, that diode will not
immediately turn off but will conduct backward and withdraw all of
the stored charge in the base of the transistor connected
.[.threreto.]. .Iadd.thereto.Iaddend.. The other diode has already
turned on .[.oven.]. .Iadd.even .Iaddend.sooner. Thus, during this
critical switching time, the high voltages of feedback windings 79d
and 79ad are connected directly to both bases through very
low-impedance diodes 73d and 74d, and the low-voltage winding is
effectively isolated by the relatively higher resistance of
resistor 240d. Before the voltage of the base of the turning-off
transistor drops below a safe value, the associated diode runs out
of stored charge (while also driving current through resistor 240d)
and turns off. The peak negative base voltage is therefore
determined only by the low-voltage winding 61d, as desired. Current
flowing through the collectors 47d and 50d of the transistors 44d
and 45d, respectively, can limit their collector voltages as
effectively as current through Zener diode 85d but with the
advantage that the transistors are capable of conducting much
larger currents than the Zener diode 85d needs to conduct in this
circuit. Thus by using the Zener diode 85d to turn the transistors
on, a relatively low current and inexpensive Zener diode may be
used.
FIG. 16 depicts a circuit connecting essential parts of an inverter
to two pairs of series connected fluorescent lamps with means for
heating the filaments of all lamps and using both capacitor and
inductor ballasts for high power factor. Terminal 241 connects the
inverter to the positive terminal and terminal 242 connects it to
the negative terminal of a power supply line (not shown). Current
flowing into the inverter from terminal 241 flows through winding
243, which is analogous to winding 76 in the circuit of FIG. 6, to
the center tap 244 of the two windings 245 and 246 of the primary
of a transformer 247 having a magnetic core, e.g., a ferrite core
248. The transformer 247 has a main secondary winding 249 and a
number of short winding secondaries later to be described. The free
end terminal of winding 245 connects with line 250 and the free end
terminal of winding 246 connects to a line 251. A capacitor 252,
analogous to capacitor 60 in FIG. 6, is connected at one terminal
to line 250 and at the other terminal to line 251. Line 250 also
connects through diode 253 to transistor 255. Similarly line 251
connects through diode 254 to transistor 256. Transistor 255 has a
base 257, a collector 258 to which diode 253 is connected, and an
emitter 259. Transistor 256 has a base 260, a collector 261 to
which diode 254 is connected, and an emitter 262. The bases are fed
by a low voltage secondary 263 on core 248 of transformer 247,
i.e., they are feedback windings of a very few turns, e.g., two
turns. Emitters 259 and 262 are connected together to the negative
terminal 242 referred to above.
Lamps 264 and 265 are connected in series in the output circuit of
the .[.inventer.]. .Iadd.inverter .Iaddend.as also are lamps 266
and 267. A short secondary winding 268 on the core 248 of
transformer 247 supplies heating current for filament 269 at a
first end of lamp 264. Ballast for lamps 264 and 265 is provided by
inductor 270 which is connected at one terminal to one terminal of
secondary winding 249 and at the other terminal to the line
connecting winding 268 to filament 269, as shown. Another short
secondary winding 271 on core 248 supplies filament heating current
to filament 272 at the second end of lamp 264 and to filament 273
at a first end of lamp 265. A still further short winding secondary
274 on core 248 supplies filament heating current to filament 275
at the second end of lamp 266 and the filament 276 at the first end
of lamp 267. An additional short winding secondary 277 on core 248
supplies filament heating current to the filament 278 at the first
end of tube 266. Lamps 266 and 267 have a capacitor ballast 279
which is connected at one terminal to the line connecting winding
277 to filament 278 and at the other terminal to the same terminal
of secondary 249 as inductor 270. A final short winding secondary
280 connected at one end to the other terminal of secondary winding
249 and at the other end to filament 281 at the second end of lamp
267 and to filament 282 at the second end of lamp 265, putting
these two filaments in parallel across the lines from winding 280.
The operation of this circuit is clear in the light of the
explanation of other inverter output circuits hereinabove and need
not be repeated. The combination of inductor and capacitor ballasts
in the circuit provide high power factor in the inductor output
circuit.
The circuit illustrated in FIG. 17 is similar to the circuit of
FIG. 16 just described except that the four lamps are in parallel
instead of two pairs in series. Parts in the circuit of FIG. 17
which are comparable to parts in the circuit of FIG. 16 are given
the same reference numbers with a postscript a. The inverter
components and their connections to each other are the same as the
components of the inverter in the circuit of FIG. 16. One terminal
of secondary winding 249a is connected in parallel (a) through a
ballast inductor 270a to the line connecting short winding
secondary 268a to filament 269a at the first end of lamp 264a, (b)
through a ballast capacitor 279a to the line connecting short
winding secondary 271a with filament 273a at the first end of lamp
265a, (c) through a ballast inductor 283 to the line connecting
short winding secondary 274a to the filament 276a at the first end
of lamp 266a, and (d) through a ballast capacitor 284 to the line
connecting short winding secondary 277a to the filament 278a at the
first end of lamp 267a. Short winding secondary 280a has one
terminal connected to the second terminal of secondary winding 249a
and the two lines from winding 280a are connected in parallel to
the filaments 272a, 282a, 288a and 275a at the second ends of tubes
264a, 265, 266a and 267a, respectively. Operation of this circuit
is obvious from the descriptions of output circuits of inverters
hereinabove. Again the combination of inductor and capacitor
ballasts in the inverter output circuit for the tubes, as shown and
described, assures high power factor in the output circuit.
FIG. 18 shows a modification of the circuit of FIG. 16 with the
addition of starting aids for the two pairs of series connected
fluorescent lamps. The inverter circuit of FIG. 18 is the same as
the inverter circuit of FIG. 16 and the parts in the circuit of
FIG. 18 corresponding to parts in the inverter circuit of FIG. 16
bear the same reference numbers with a postscript b. The output
circuit of the inverter of FIG. 19 is the same as the output
circuit of the inverter of FIG. 16 with the addition of the
starting aids 285 and 286 and the reference numbers are the same in
FIG. 19 as in FIG. 16 with the addition of postscripts b. The
starting aid 285 is a capacitor having one terminal connected (a)
to the line from short winding 268b to filament 269b and (b) to the
inductor 270b and the other terminal connected to the line
connecting short winding 271b with filaments 272b and 273b. The
starting aid 286 is a capacitor having one terminal connected (a)
to the line from short winding 277b to filament 277b and (b) to the
capacitor 279b and the other terminal connected to the line
connecting short winding 277b to filament 268b. These starting aids
have the characteristic of reducing the starting voltage required
to strike the arc between the cathodes (filaments) at the first and
second ends of the lamps.
FIG. 19 .[.despicts.]. .Iadd.depicts .Iaddend.a circuit comprising
an inverter like the inverter of FIG. 16 and an inverter output
circuit. Components in the circuit of FIG. 19 have been given the
same reference numbers as .[.corresponsing.]. .Iadd.corresponding
.Iaddend.parts in the circuit of FIG. .[.1161.]. .Iadd.16
.Iaddend.with a postscript c. The output circuit of FIG. 19
includes three fluorescent lamps 264c, 265c and 266c, 264c and 265c
being connected in series and then connected in parallel with lamp
265c across the terminals of secondary winding 249c of the inverter
transformer 247c. The series connected lamps have a capacitor
ballast 279c between the line connecting short winding 268c with
filament 278c and the terminal of secondary winding 249c. The short
windings 268c, 274c and 280c have voltage induced in them from
primary 287 which receives voltage from winding 249c of the
inverter transformer 247c. An auxiliary circuit 289 comprising in
series a primary winding 290 of a saturable reactor 291 having a
magnetic core, e.g., ferrite, and a .[.resister.]. .Iadd.resistor
.Iaddend.293 connected to the DC terminals 241c and 242c. The
secondary of reactor 291 is a short winding 294 having one terminal
connected by line 295 to one terminal of inverter transformer 247c
and by line 296 to a capacitor 297 connected to the line connecting
short winding 268c with filament 278c, and to an inductor 298 on
core 292 connected to the line connecting short winding 277c with
filament 278c.
Ballast capacitor 279c and ballast inductor 284 conduct small
currents to their respective lamps for very dim operation.
Additional current flows through ballast capacitor 297 and ballast
inductor 298 by way of the saturable reactor windings 294 for
brighter operation. The amount of additional current is controlled
by the DC current in winding 290 of the saturable reactor which DC
current, in turn, is controlled manually or automatically by means
of the variable resistor 293. In this manner, the light
.[.internsity.]. .Iadd.intensity .Iaddend.may be changed in
response to varying needs.
The circuits of the invention, and in particular the electronic
ballast circuits have great benefit to the utility industry because
of its efficiency which make it possible to save capital
investment. The invention has great value also to users of electric
power for lighting because of great savings that can be made in
consumption of electric power.
Fluorescent lamps operate more efficiently on high frequencies than
they do on commercially available AC of 50 to 60 Hz., a fact that
the art has recognized for many years, as the discussion of the
prior art hereinabove states. Despite this recognition there is not
available on the market either a system having the advantages of
the present affordable, safe, economic, reliable, efficient and
flexible system for operating at high frequencies, e.g., in the
range of 20 to 30 kHz or higher, nor a ballast that combines safe,
economic, reliable, efficient and flexible use in present
fluorescent installations and particularly as part of a system
powered from a three-phase source. The system and ballast of the
invention make use of the enhanced efficiency allowed by high
frequency in the range of 20 to 30 kHz, keep the power loss to a
practical minimum in the inverter and ballast, keep the costs low,
obtain high power factor (e.g., at least 90%), provide reliability
by avoiding the use of components like electrolytic capacitors and
by using a minimum number of parts, obtain low acoustic noise, low
radio noise and low flicker.
The inverter may be described as a symmetrical, class B, push-pull,
current-limited, .[.turned-collector.].
.Iadd.tuned-collector.Iaddend., sinusoidal oscillator. It is self
starting, highly efficient and stable over a wide range of input
voltage without squegging at any voltage, with or without load.
While the system and ballast have been described and illustrated
with many modifications and embodiments, those skilled in the art
will recognize that further modifications and embodiments may be
made within the ambit of the disclosure and claims without
departing from the principles of the invention disclosed.
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