Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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CIRCUIT FOR STARTING AND OPERATING FLUORESCENT LAMPS
This invention is in the field of circuits for starting
and operating fluorescent lamps from low frequency a-c power.
In particular, this invention is an improvement over that
invention described in the United States Patent No. 4,399,391.
Various circuits have been devised for starting and
operating fluorescent lamps, and for heating or preheating their
cathodes. U.S. patent No. 4,185,323 to Riesland, Hammer and
Lemmers discloses a circuit in which cathodes of fluorescent
lamps are heated by a transformer, and U.S. patent No. 4,207,497
to Capewell et al discloses a high frequency lamp operating
circuit in which the cathodes are heated by a transformer having
a primary winding connected in series with a capacitor to the
a-c power source, the primary winding and/or ballast inductor in
combination with the capacitor, being resonant at or near the
frequency of the a-c power source; the transformer is connected
to provide constant cathode voltages during the high frequency
lamp operation and dimming. U.S. patent 3,611,021 to Wallace
and 4,207,497 to Kornumpf also disclose high-frequency circuits
for starting and operating fluorescent lamps, and employ a
resonant circuit tuned to a single individual harmonic of the
high-frequency (20 kilohertz) operating current source to aid in
starting the lamps.
Other fluorescent lamp circuits have been devised which
turn off the cathode heating power while the lamps are
operating. For example, U.S. patent Nos. 2,330,312 to Raney,
4,009,412 to Latassa, and 4,146,820 to Bessone disclose circuits
having magnetically operated switches which open to disconnect
the cathode heating circuit when the lamps are operating; U.S.
patent Nos. 2,354,421 to Pennybacker, 2,482,335 to Reinhardt,
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and 4,097,779 to Latassa disclose thermostatic cathode heating
disconnect switches; and U.S. patent No. 4,010,39~ to Bessone
discloses solid state switches for the same purpose.
In some cases, the primary coil is subject to
undesirable high temperatures if one or both of the lamps should
rectify the high temperature sometimes causing damage to the
coil and ballast.
In the circuit of U.S. Patent 4,399,391, a single
switch 21 is utilized which is preferably a voltage actuated
bidirectional diode such as SIDAC. Although the utilization of
a single SIDAC in the circuit of the '391 patent did result in
satisfactorily operating the circuit, it has been found that it
is preferable to stack a plurality of the SID~CS in series.
Objects of the invention are to provide improved and
low-cost circuits for starting and operating fluorescent lamps
from a low frequency (such as 60 Hz) power source, and to
conserve electrical energy.
The invention comprises, briefly and in a preferred
embodiment, circuits for starting and operating fluorescent
lamps from an a-c low frequency power source. The circuit
comprising reactive ballast means connected to ballast the lamps
and having a non-linear characteristic for producing a plurality
of harmonics of the power source frequency, and a capacitor and
a cathode heating transformer connected in series and connected
to receive power from said ballast means and resonant in a
frequency range encompassing a plurality of said harmonics.
This resonant voltage is applied across the lamps to aid the
starting of their discharge and thereafter the lamps operate at
the a-c power source frequency. Thus, the lamps are started
with the aid of a peaked higher voltage waveform (lag circuit)
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or a harmonically enriched non-linear waveform (lead circuit)
than is normally present in their operating frequency. The
aforesaid resonance frequency range preferably is broad enough
to encompass several harmonics of the power source frequency,
for example the third through the ninth harmonics (180 to 540 Hz
for a source frequency of 80 Hz~. Preferably a switch is
connected in series with the capacitor and cathode heating
transformer for opening the cathode heating circuit when the
lamps are operating. This switch may be a bidirectional diode
such as a SlDAC, triac-diac combination, or equivalent voltage
sensitive solid state switch, which switches on and off during
each half cycle of the lamp starting time period and thus
contributes to the harmonic content of the starting voltage
waveform.
This invention consists in the construction, arrange-
ments and combination of the various parts of the device,
whereby the objects contemplated are attained as hereinafter
, more fully set forth, specifically pointed out in the claims,
and illustrated in the accompanying drawings, in which:
Figures 1-7 are reproductions of the drawings of U.S.
Patent 4,399,391; and
Figure 8 is an electrical schematic diagram of the
approved circuit.
In Figure 1, a pair of fluorescent lamps 11 and 12 are
connected electrically in series and to the output of a circuit
having input terminals 13 and 14 for connection to a source of
low-frequency a-c electrical power, for example 120, 240, or 277
volts, at a given frequency of for example 80 Hz. The lamps 11
and 12 respectively comprise envelopes ll'and 12' of glass or
other suitable material containing electron emissive cathodes
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lla, llb and 12a, 12b, respectively near the ends thereof.
These cathodes may comprise coiled tungsten wire filaments
coated with an electron emissive material. The lamp envelopes
contain mercury and an inert fill gas such as argon. krypton.
neon, or mixtures thereof. The cathodes llb and 12a are
connected electrically in parallel, thus connecting the lamps 11
and 12 in electrical series. An inductive ballast reactor 18 is
connected between the power input terminal 13 and an end the
cathode lla, and the power input terminal 14 is connected to an
end the cathode 12b. A series connected combination of a
capacitor 17, a primary winding 18 of a cathode heating
transformer 19, and switch 21 is connected between the power
input terminal 14 and a point 22 at the lamp end of the ballast
reactor 16. Alternatively, the latter connection can be to a
tap 23 on the ballast 16 as indicated by dashed line 24. The,
cathode heating transformer 19 comprises a first secondary
winding 26 connected across the cathode lla, a second cathode
heating winding 27 connected across the parallel cathode llb and
12a, and a third secondary winding 28 connected across the
cathode 12b. A starting capacitor 29 is connected across the
lamp 11 in conventional manner, through which electrical energy
passes to aid in starting the electrical discharge in lamp 12,
whereupon the lamp 11 readily starts.
The ballast reactor 16 is designed so as to be
non-linear due to partial magnetic saturation when current flows
through it, thereby generating harmonics of the frequency of the
input power to terminals 13 and 14, for example discernible
harmonic frequencies up to or beyond the 10th harmonic of the
input power frequency and of varying amplitudes, for example as
shown in Figure 7.
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In accordance with the invention, the reactance values
of the inductors 16 and 18, and of the capacitor 17 are chosen
so these components are broadly tuned to be resonant over a
frequency range which encompasses two or more of the aforesaid
harmonic frequencies. They may be broadly tuned so as to
encompass several harmonics such as the second through ninth
harmonics . This is illustrated in Figure 7, in which the
vertical axis 51 represents amplitude and the horizontal axis 52
represents frequency. In measurements made on the circuit of
Figure 5, the 60 Hz input ~MS voltage 53 at terminals 13, 14 was
120; of the several RMS harmonic voltages shown, measured across
switch 21 and inductor 18, the second harmonic 54 was 0.1 volt,
the third harmonic 55 was 41 volts, the fourth 56 was 0.5 volt,
the fifth ~7 was 9.4 volts, the sixth 58 was 0.5 volt, the
seventh 59 was 4.7 volts, the eighth 80 was l.o volt, and the
ninth 81 was 10 volts. The dashed curve 62 is an idealized
representation of the resonance curve of capacitor 17a and
inductors 18, 42 which in this example is sufficiently broad to
encompass the second through ninth harmonics 54 to 61. As is
well known, in a capacitor-inductor series resonant circuit, the
voltage produced across each of the capacitive and inductive
components of the circuit is considerably greater than the total
voltage applied across the resonant circuit, and these voltages
are substantially out of phase with respect to each other.
Although theoretically the greatest peak value of starting
voltage for the lamps 11, 12 could be obtained across the
capacitor 17 only, it has been found that enhanced peaked
starting voltage can be obtained across various parts of the
tuned resonant circuit. For example, in a ballasting circuit
built according to Figure 1, with the starting voltage for the
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lamps 11, 12 taken from between the points 14 and 22 of the
circuit and with the resonant circuit 17, 18 inoperative, the
peak value of starting voltage was approximately 350 volts when
the input voltage at terminals 13 and 14 was 240 RMS volts at 60
Hz; and with the resonant circuit comprising components 16, 17,
and 18 operative in the harmonic 30 frequency spectrum, the
harmonically induced resonant peak voltage was about 420 volts
which substantially improved lamp starting. The voltage curves
in Figure 6 have been traced from photographs of an oscilloscope
display and show starting voltage 31 (solid curve) and lamp
operating voltage 32 (dashed line). The peak values 33 of the
starting voltage 31, which occur during each half-cycle of the
60 Hz power input frequency, in this example, has a value of
about 420 peak volts for a power supply input voltage of 240 RMS
volts at input terminals 13, 14, this peak value 33 being
considerably higher than the peak voltage without the resonant
effect and being produced due to the resonant circuits 16, 17,
and 18 being tuned to some harmonic or harmonics of the power
input frequency. After the lamps 11, 12 start and are
operating, the operating voltage 32 has a peak value of 200
volts at the peaks 34 thereof, and has 175 volts RMS value. In
starting the lamps, the peak 33 voltage value of the starting
voltage 31 is an important criteria, whereas in operating the
lamps the RMS value of the operating voltage 32 is the more
important criteria. Starting of the lamps 11, 12 is facilitated
by the increased starting voltage value due to the enhanced
magnitude of the peaks 33 produced by the resonant starting
circuit, but also because the lamps start more easily, as the
harmonic frequency content of the starting voltage waveform is
increased. The peaks 33 of the starting voltage 31, which
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contain harmonic frequency components of the power input
frequency, and which are superimposed on the 60 Hz frequency,
are in effect such a higher frequency, and thus enhance lamp
starting in addition to their being an increased voltage value
with respect to the power input voltage of the circuit. Thus
improving the starting of the lamps 11, 12, it is found feasible
in some instances to eliminate the conventional starting stripes
in the lamps, thus reducing the cost thereof. As is well known,
the starting of the lamps is effected not only by the peak
voltage applied thereacross, but also by electrostatic or
electromagnetic coupling of the starting voltage between the
outer ends of the lamp combination, (i.e., the ends at cathodes
lla and 12b) and the metal or otherwise electrically conductive
light fixture in which the lamps are mounted.
Contrary to the above-referenced Wallace and Xornrumpf
patents, which teach the use of a high-frequency square-wave
inverter (producing square waves at a high frequency of 20
kilohertz, for example, and inherently having high values of
harmonic amplitude content), and a tuned circuit resonant at a
single harmonic frequency for aiding the, starting of
fluorescent lamps, the present invention is based on the
unexpected discovery that fluorescent lamp starting can be aided
in a low frequency (60 hertz, for example) sine-wave powered
circuit with simultaneously generated cathode voltage by
producing harmonics of the sine wave, by means of a non-linear
ballast inductor (which harmonics have considerably lower
amplitude than the harmonics contained in square waves of the
prior art), and providing a tuned circuit that is resonant over
a relatively broad frequency band which includes, and
encompasses, several of the harmonics thereby providing a
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sufficiently harmonically enriched starting voltage which can
aid the starting of the lamps.
Further in accordance with the invention, the switch
21, which is a closed switch during starting of the lamps, opens
the circuit to the primary winding 18 after the lamps 11, 12
have started and while they are operating, thereby turning off
the cathode, heating power source and conserving this electrical
power while the lamps are operating. The cathode heating
current is not required while the lamps are operating, because
during operation electrons are emitted, from a small area on
each of the cathodes, which are called "hot spots", and which
remain hot enough during operation to sustain the required
ability of the cathodes to emit the electrons to support the
electrical gas discharge in the lamps. The switch 21 may be of
any suitable type such as voltage actuated, current actuated, or
thermally actuated from heat of the lamps 11 or 12. The
preferred switch 21, as shown, is a voltage actuated
bidirectional diode such as a SlDAC. Such a device is disclosed
in U.S. Patent No. 3,866,088 to Kaneda, which is incorporated
herein by reference thereto. This type of switch is conductive
when a voltage thereacross is above a certain value, and is open
or non-conductive when the the voltage thereacross is below a
given value. For example, the switch 21 becomes conductive when
the voltage thereacross is relatively high, such as when the
power input voltage from terminals 13, 14 is applied thereto
during starting of the lamps 11, 12, and the switch becomes open
and non-conductive when the voltage applied thereto is
relatively below this value, due to the lamps 11, 12 operating
and conducting current which causes a voltage drop across the
lamps 11 and 12, which thus reduces the voltage applied across
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the switch 21. When this voltage-actuated switch is conductive
during lamp starting, in reality it turns on and off during each
half-cycle of the 60 Hz voltage, which advantageously adds
harmonic frequency content into the resonant aircuit. Such a
switch also increases lamp life by reducing cathode sputter
damage during starting as compared to a flow switch type start.
The circuit of Figure 2, the commonly referred to as a
~leadn circuit, is similar to that of Figure 1, except that the
starting voltage is obtained across only the primary winding 18
of the cathode heating transformer 19 which is achieved by
connecting the cathode lla to the junction 36 of the capacitor
17 and primary winding 18. The circuit has improved starting
characteristics similar to that described for the circuit of
Figure 1 and the capacitor 17 of Figure 1 is designated 17a in
Fig. 2 because, in addition to functioning in the resonant
starting circuit, it also functions as a power capacitor during
operation of the lamps 11, 12 in well known manner. The circuit
of Fig. 3 is a nleadn circuit similar to that of Fig. 2 except
that the dual functions of capacitor 17a in Fig. 2 are performed
by individual capacitors 17b and 17c in Fig. 3. Capacitor 17b
is the power capacitor, connected between the ballast 16 and
cathode lla in normal manner, and capacitor 17c is connected to
the junction 22' of capacitor 17b and cathode lla and functions
like capacitor 17 in Fig. 1. Capacitor 17c has a considerably
lower value of capacitance than does 17b, and therefore, a
considerably higher peak value of resonant voltage is produced
across it than across power capacitor 17b, to aid in starting
the lamps.
In the circuits shown in the drawing, the positions of
the resonant circuit capacitor 17 or 17c and primary winding 18
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can be interchanged and the lamps 11, 12 can be connected to
obtain the harmonically peaked starting voltage from across the
capacitor 17. Also, the switch 21 can be moved to other
positions in the series circuit 11, 18. The circuits of Figures
4 and 5 are generally similar too, and function the same as, the
circuits of Figures 1 and 2. respectively, except that in
Figures 4 and 5 the ballast reactor is in the form of an auto
transformer. The auto transformer comprises a primary winding
41 connected across the input terminals 13, 14, and a secondary
winding 42 magnetically coupled to the primary 41 and having one
end thereof connected to an end 43 of the primary winding 41, or
to a tap 44 on the primary winding 41, as is disclosed in the
above referenced patent to Riesland et al, which is incorporated
here and by reference thereto. The auto transformer 4D has a
turns ratio of secondary 42 to primary 41 so as to increase the
voltage with respect to the input voltage terminals 13, 14. The
secondary winding 42 also functions as the reactive ballast for
operating the lamps 11, 12, and also contributes inductive
reactance in the starting resonant circuit comprising winding
42, capacitor 17, and winding 18. The lead type circuits of
Figs. 2 and 5 may also exhibit an increased higher frequency
harmonic content of the non-linear starting voltage waveform.
If desired, in the circuits of Figs. 1 and 4 the
resonant circuit components 17 and 18 can be connected to the
tap on the ballast impedance 16 or 42, such as a tap 23
connected by a dashed line 24, as shown in Figure 1 instead of
to the point 22 at an end of the ballast, so that the impedance
value of the ballast inductance in the resonant circuit is less
than the value thereof that functions for ballasting the lamps.
Thus, this ballast inductance provides two different values for
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the two different functions.
The invention achieves a relatively simple and
inexpensive lamp starting and operating circuit, which improves
starting of the lamps in the manner described above, which can
also permit eliminating the conventional starting stripes in
the lamps, thereby reducing the cost of the lamps, and the
invention further reduces operating costs of the lamps, by
switching the cathode heating transformer out of the circuit
when the lamps are operating, thereby conserving about ten
percent of the system input electrical energy, for example a
saving of about 5 to 6 watts in a 60 watt system having a pair
of 27 watt lamps.
Figure 8 illustrates the improved circuit of this
invention and is essentially the same as that previously
described except for two very important modifications thereof.
In Figure 8, a PTC thermistor 100 is utilized in series with the
filament transformer primary winding 102. Further, the PTC
thermistor is a Nichicon PTC thermistor, part number PDB-49A50-2
(TBD part number 73B140376-6) in the e~rent that one or both of
the bulbs in the circuit should rectify, the thermistor 100 will
switch from a low impedance to a high impedance to prevent the
winding 102 from being subjected to damaging currents and
temperatures.
Another very important feature of the improved circuit
is the stacking of a plurality of SIDACS 104, 106 and 108 series
with the thermistor 100 and the winding 102 as seen in Figure
8. The SIDACS are preferably a voltage actuated bidirectional
diode such as disclosed in U.S. Patent No. 3,866,088 to Kaneda,
which is incorporated herein by reference thereto. This type of
switch is conductive when a voltage thereacross is above a
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certain value, and is open or non-conductive when the voltage
thereacross is below a given value. The SIDACS 104, 106 and 108
function identically to the SIDAC 21 in '391 patent except for
the stacking of the same in series. During the operation of the
SIDACS, it is important that the switching resistance (Rs) be
adequate to insure proper switching of the SIDACS. A switching
resistance of approximately 3.5 K Ohms is needed for the entire
stack of SIDACS 104, 106 and 108 to resolve any possible
switching problem.
Thus it can be seen that an improved circuit has been
provided which achieves all of its stated objectives.
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