CA1110319A - Every half cycle ignited discharge lamp operating circuit - Google Patents

Abstract

TITLE OF THE INVENTION:

DISCHARGE LAMP OPERATING SYSTEM

ABSTRACT OF THE DISCLOSURE:

A discharge lamp is ignited in every half cycle in its operating system including a discharge lamp operating circuit provided with a low frequency alternating current power source, a single winding type current limiter. The discharge lamp which is connected to the power source through the current limiter and a series circuit includ-ing a high voltage output generator which is connected in parallel to the discharge lamp. The high voltage out-put generator operates at least during the lamp operation for reigniting the discharge lamp. The voltage of the low frequency alternating current power source is set to less than the required reignition voltage of the discharge lamp during its operation, whereby the lamp current stabilizer is minimized. Further, a filament preheating circuit is arranged to use current derived from the high voltage gen-erator. The filament preheating circuit is combined with this operating circuit and so is a time delay for assuring a stable operation.

Description

~ L03~

1 The present application is related to my Canadian Patent Number: 1,065,007, granted on: October 23, 1979. This invention relates to a discharge lamp operating system wherein the discharge lamp means is ignited by a high voltage in every half cycle of an a.c. power source in its continued operation. More particularly, the invention relates to a combination of a single choke ballast and an electronic preheating circuit forming part of the "every half cycle" ignited system.
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In recent years, energy optimization and the saving of energy resources have been the prime targets of technology. ~ ~;
The present so-called "every hal~ cycle" ignited discharge lamp operating system intends to find a solution for the saving of energy in the field of illumination. For example, in an article "An Investigation of Minimized Ballast Upon ~very-Half-Cycle Ignited Discharge Lamp Operating System with ~nalogue Computer Simulation" published in the Journal of Light and Visual Envlronment (Vol. 1, No. 1, 1977) by the Illuminating Engineering Institute of Japan, there are dis-closed theoretically estimated improvements in the powex J
loss and the weight reduction. The power loss is reduced to one third and even up to one fourth, as compared to the rapid -~
start type. The weight reduction is to one fourth and even ~
to only one eleventh compared to those of conventional glow ~`
or rapid-start discharge lamp operating devices. Thus, a substantial miniaturization of such device has been realized according to said article.

To facilitate the understanding of how the current limiting choke, which is used in the "every half cycle ignited discharge -lamp operating system" of the present invention, is miniaturized, ~ 2 3:~

1 the function of the conventional discharge lamp operating system be explained first. As shown in U. S. Patents 3,665,243;
3,753,073; 3,866,088; and 3,942,069, a conventional fluore-scent lamp operating device is constructed, for instance of a circuit shown in Fig. 1, wherein the discharge lamp FL is ;~
connected in series with the current limiting choke CH, which acts as a current limiting device, and to an a.c. Power source AC and the oscillation circuit or oscillator Rl is connected ;
to the lamp FL in parallel. When the power source AC is turned on, the oscillator Rl starts oscillation and hence heating the filaments fa and fc of the lamp FL by its oscillation current. ~
The oscillation output voltage which is higher than the re- -;
quired starting voltage Est, is applied across the filaments of the lamp. When the filaments fa and fc are sufficiently heated and the required starting voltage for the lamp FL becomes lower than Est, the lamp is ignited by the above described oscil-lation output and begins a lag-phase operation. Once the lamp is lit, the terminal voltage vT, i.e., the lamp voltage of the discharge lamp FL corresponds to about one half of the source voltage. Hence, the osci]lator Rl can no longer continue to oscillate, and the discharge lamp FL is operated by the voltage supplied from the power source AC through the current limiting choke CH.

Fig. 2 (A), (B), and (C) show the waveforms of the source vol-tage "e", the lamp voltage vT and the lamp current iT respec-tively obtained from observation of the lamp under operation.
Fig. 2 (D) shows the product of the terminal voltage vCH of the current limiting choke CH which does not contain a resis-tive component, and the lamp current iT. Fig. 2 (E) shows the 3~L~

1 energy Se stored in the choke at each respective instant.
As seen from these waveforms, for the period (tl - t2) in which the source voltage e is higher than the lamp voltage vT, the energy Sel = C (e = vT)iTdt increase monotonically Vtl and is stored in the current limiting choke CH. For the per-iod (t2 - t3) in which ~e source voltage e is lower than the lamp voltage vT, the stored energy is releasecl and the released energy is expressed by Se2 = ~ ~e - vT)iTdt. The size of ~ t2 the current limiting choke CH is determined by the maximum value of the stored energy Se shown in Fig. 2 (E). Thus, the capacity of the choke CH must be so selected as to endure the maximum amplitude Semax of the stored energy.
-, In the just described case, the required reignition voltage Erst of the dischargelamp FL must be lower than the source voltage e at the reignltio~ instant. In other words,the peak value vTP of the lamp voltage vT must not exceed the source voltage e. Since in the conventional discharge lamp the effective value VT of the lamp voltage is set at about 1/2 of that oE the source voltage e, the effective value VCH
of the terminal voltage of the current limiting choke is set higher than the 1/2 of the source voltage. ---`, '~ ~'~ '-My copending Canadian Patent Number 1,065,007, granted on October 23, 1979, proposes an "every half cycle ignited discharge lamp operating system", and present Fig. 3 shows one example of such operating circuits for a fluorescent lamp. In Fig. 3 the current limiting choke CH and the discharge lamp FL, connected in a series circuit, are connected to an a.c. power source AC. The current limiting choke is provided with a secondary winding W20 which superposes the oscillation output 3~9 1 of the booster circuit as a high voltage generating means, on the power souree voltage, and one end of the secondary ;
winding 1~0 is connected to a junction jl of the filament fa of the discharge lamp ~L. The other end of the winding W20 is connected to the booster circuit or booster R.

The booster R is a series connection of an intermittently oscillating capacitor Cl and an oscillator Rl which is con-nected in a parallel circuit of an oscillation capacitor C
and a series connection of a bidirectional diode thyristor S
and a backswing voltage generating or boosting inductor L.
One end of the booster circuit R is connected to the other ~
end of the seeondary winding W20. The other end of the .
booster R is conneeted to a junetion j2 of the filament fe of the diseharge lamp FL. In addition~ the booster R may be, so far as it operates as a high frequeney oseillator, replaeed by a circuit whieh employs a gated t;ype thyristor sueh as a TRIAC or by an invertor or a high voltage generating circuit ;

whieh employs a pulse generator.
;:
The above eireuit operates as follows. When the power source AC is turned on, the source voltage e is applied to the dis charge lamp FL through the current limiting ehoke CH and to the booster R through the secondary winding W20. In the booster R the souree voltage e is applied to the thyristor S ;;
through the intermittently oscillative capacitor C1, then the !
oscillator Rl starts oscillation in order to break over the thyristor. Without the intermittently oscillating capacitor Cl the oseillation would continue once generated, but in the cir-euit shown here due to the eapaeitor Cl, the oseillation oeeurs repeatedly at every half cycle in the leading portion of the 3~

1 source voltage e.~ After the oscillator Rl starts oscillation, the capacitor Cl is charged with such polarity that it cancels the source voltage e. Thus, as the terminal voltage VCl rises and the voltage difference of the terminal and the source vol-tage e becomes insufficient relative to the break-over voltage VB0 of the thyristor S, the latter assumes the off-state, hence the oscillator Rl ceases to oscillate. Therefore, the terminal voltage vcl of the capacitor Cl remains constant and the oscil-lator Rl is in the non-oscillating state during the later per-~; 10 iod of the just described half cycle. In the next half cycle, ~ ;~
where the source voltage e is reversed compared to the preced- ;~
ing half cycle, the summed up voltage of the source and the terminal voltage vcl which charged the capacitor Cl during the preceding half cycle, is impressed on the oscillator Rl, which causes the break-over of the thyristor and hence again an os-~. .
cillation. However, from the moment when the oscillationstarts again, the intermittently oscillatingr capacitor Cl begins to be charged to compensate the source voltage e again and the polar-ity of the terminal voltage vcl of the capacitor Cl is rapidly reversed. In the meantime the oscillator Rl again stops oscil-lating. The oscillator Rl~ therefore, operates exclusively during the period of the inversion of the voltage of the inter-mittently oscillation capacitor Cl. Thus, the current flows from the source AC to the oscillator Rl through the primary W10 and the secondary winding W20 of the ballast choke CH solely during this period. Such operational mode is repeated in the same way in every following half cycle. Fig. 4 (A) is a voltage-current waveform showing the above described operation, wherein e is the source voltage and vcl is the terminal voltage of the intermittently oscillating capacitor C1. As seen from this 3 1~ ~

1 figure, the current icl flows to the capacitor Cl in the period of the rapid inversion of the terminal voltage~ and just in this period also appears the oscillation output vR of ;~
the high frequency high voltage across both ends of the boos-ter R.

The above described oscillation output vR is blocked by the primary winding W10 and the secondary winding W20 of the cur~
rent limiting choke CH. The terminal voltage of the primary ;~
winding W10 is superposed on the source voltage e, and the summed up voltage is impressed on the discharge lamp FL and the filament preheating circuit PRH. Thus, in the filament preheating circuit PRH the voltage is impressed on the thyristor SP through the high frequency blocking inductor NL, then the - thyristor SP is driven to conduct by the sudden ehange effect : (dV/dt effeet) of the voltage. Therefore, at the end of the ` intermittently oscillative phase, the current flows from the souree AC through the filament fa, the thyristor SP, the in-i ductor NL and the filament fc, so as to initiate the preheating of the filaments fa and fc. Each time when the oscillation out-put vR of the booster R is applied to the preheating eircuit PR~
the t~hyristor SP is driuen to conduct and the preheating is re- ;
peated during this period by the eurrent flow from the source AC
to the filaments fa and fc.

When the filaments fa and fc are sufficiently preheated and the vol.tage required to start the discharge lamp FL becomes the starting voltage Est, the discharge lamp FL is triggered to start by the oseillation output vR from the booster cireuit R.
After the diseharge lamp FL is lit, the intermittent oscilla-tion energy flows mainly through the conducting discharge lamp FL

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1 and the remaining energy is absorbed by the high frequency blocking inductor NL. By setting the break-over voltage VB0 of the thyristor SP sufficiently high above the peak voltage vTP of the lamp voltage, the thyristor does not conduct. In addition, in the case where the break-over voltage of the `
thyristor is set considerably high, if required, the high frequency blocking inductor NL can be omitted. After the lamp is lit, the filament preheating does not occur, hence, the discharge lamp FL is ignited by the oscillation outputvR -at every half cycle of the power source AC and operated sole-ly by the source voltage e as referred to in Fig. 4 (B). In :~
addition, the preheating circuit PRH of Fig. 3 may be replaced by a rilament preheating transformer.

Fig. 5 shows the waveforms o~ each instant observed in the experiment using the circuit of Fig. 3, wherein the high ~
frequency component is neglected. As seen from Fig. 5 (B), ~;
the lamp voltage vT is a nearly rectangular waveform having a pause period due to the intermittently oscillating period. `
Thus, the effective value VT of the lamp voltage is about 90 - 95% of the convenfional lighting system. The discharge lamp FL is ~eignited at the step-up portion of every half cycle by thehigh voltage oscillation output vR in the follow-ing way. As the intermittent current icl originating from the booster circuit flows through the secondary winding W20, the corresponding terminal voltage of the winding is applied through the coupling with the primary winding W10 as a rapidly rising low frequency voltage, to the discharge lamp FL, whereby a sufficient quantity of ions are generated in the lamp, which is helpful for its easy breakdown, thus, resulting in the arc 3~L~

1 discharge of the lamp. Further in this case~ the lamp current ~ -iT remains constant in the step-up, in spite of the change of the source voltage e, and as the lamp current iT increases, the above current icl decreases due to the encroachment of the edge of the lamp current waveform into the next half cycle.
Hence3 the initial value of the lamp current is controlled to be rather low by the rapidly growing low frequency voltage.
Conse~uently, the fluctuation of the lamp current of the every half cycle ignited operating system is excellent regardless of the decrease in the stabilizing impedance.
~ :`
The lamp current from the power source AC to the discharge lamp FL flows, for the most part, during the period (t2 - t4) outside of the oscillation period, as shown in Fig. 5 (C).
During the periods (tl - t2) and(t4 - t5), the current icl flows from the source AC to the booster R. The waveform icl is shown in Figo 5 (D). This current flows both through the primary winding W10 and the secondary winding W20, which are coupled together by the current llmiting choke CH in a mag-netlsm increasing manner or direction. The exciting or ener-gizing effect can generally be varied by the winding ratio of the primary ~10 to the secondary wlnding W20. Figs. 5 (E) and ~i~
(F) show the waveforms of the stored energy Se and the pro~
duct (vCH.i~ of the voltage of the current limiting choke CH
calculated from the above described waveforms of the lamp voltage vT, the lamp current iT, the current icl which flows into the booster R and the source voltage e. Fig. 5 (E) shows the voltage-current product of the current limiting choke CH
caused by the voltage difference between the source voltage e and the oscillation output vR or the lamp voltage vT. The _ g _ .

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1 total stored energy Sel due to the current icl is given by ( ~t2 ~ Sel = ~ (e - vR)Kicldt~ , wherein K is a constant deter-mined from the winding ratio of the primary W10 and the secondary winding W20. The stored energy Se2 for the period, where the source voltage e is higher than the lamp voltage vT~ ;

is given by ~ Se2 = 5 (e - vT)iTdt3 .
t2 On the other hand, during the period (t3 - t4), where the lamp voltage vT is higher than the source voltage e, the stored energy is released and the total released energy Se3 is given ~
(` ft4 _ ~ :
by ~ Se3 =~ (e - vT)iTdt . Consequently, the energy,which is stored in the current limiting choke CH, is varied as shown ~:
in Fig. 5 (F). The relation Sel + Se2 - Se3 applies to the waveforms shown in Fig. 5.

The calculations of the stored energy in the ballast of the conventional operating system and in the every half cycle operating system, are based onthe waveforms shown in Fig. 2 and ~ig. 5 respectively. I'he following relation is obtained, ~ ~.
for instance, for the cases when a lamp of the 40T12 type is ~;
operated by the former conventional system with a 200v line~
voltage and the same lamp is operated by the latter in an "every half cycle system" with a 100v line-voltage. The results may be compared as follows:

(The maximum of every half cycle operated Sel + Se2 + Se3 1 and The maximum of conventionally operated Sel + Se2 Inductance of every half cycle system<l }
lnductance of conventional system 5 3~ ~

l Thus, the current limiting choke CH of the latter can be reduced in impedance and in size accordingly. .

Substantial advantages may thus be obtained from an "every half cycle ignited operating system" which is the aim of the invention so far described. However, still some problems re~
main to be solved. Namely, presently there are few discharge lamp types which have the lamp voltage equal to the source voltage. Therefore, an appropriate voltage difference exists in the conventional type discharge lamps. In another aspect, since drawing out of the intermediate top o~ the choke coil CH
is necessary, such a structure imposes an unfavorable condition on its fully automated production.

Another problem is seen in that the preheating circuit means are rather complicated which also causes an economical dis-advantage when one or more discharge lamps with filaments are to be operated. For instance~ where a plurality of discharge lamps are to be employed in series, a preheating means which meets the requirements o~ small size~ light weight and low cost cannot be realized satisfactorily with conventional pre-heating means employing the secondary windings of a heatingtransformer connected on the power source side of the discharge lamp means.

It has also been found to be somewhat diff`icu]t to maintain a stable operation in every half cycle due to the variation of the source voltage and/or the ambient temperature. The source voltage usually varies + 10% at its maximum. Further, thelamp voltage of the discharge lamp means varies according to the variation of the lamp current and ambient temperatures. For instance, as the ambient temperature falls or rises the lamp i3~

1 voltage goes down and it may happen that if the source voltage e goes up it reaches a value more than twice as high as the lamp voltage vT. On this occasion the discharge lamp may operate not accordin~ to the"every half cycle operational :
mode" but according to a conventional operational mode as illustrated in Fig. l and the discharge lamp operational mode shifts back and forth between these two modes, resulting in a :
flickering light output and a greater stress on the current limiting means.

OBJRCTS OF THE INVENTION~
~ .

In view of the above it is the aim of the invention to achieve the following objects, singly or in combination:

to eliminate the above described problems, and to provide an every half cycle discharge lamp operating system having practical and economical advantages and to employ as current limiting means a single winding type choke coil or a : single winding leakage type autotransformer;
. ;, to provide a discharge lamp operating system having a simplified filament preheating device which is a so-called :-electronic preheating means for operating discharge lamps of the hot cathode type;

to provide an every half cycle discharge lamp operating system employing time delay means to stabilize the operation against fluctuations of the source voltage : and/or of the ambient temperatures; and ! ~

~1i331~) 1 to provide the above described discharge lamp operatir.g system with sequentially operating starting means, including high voltage output generating means or switching means where a plurality of discharge lamps are operated in series.
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SUMMARY OF THE IN~ENTION-According to the invention there is provided a discharge lamp operating system, wherein the discharge lamp is connected to the low frequency a.c~ power source through a single winding current limiting device such as a single choke or a single leakage transformer and the booster circuit is connected in parallel to the discharge lamp and operates at least during the lamp operation and which supplies the reignition energy ~ `
required for the lamp operation once the lamp is started. In other words, when the booster circuit is removed, the discharge lamp employed in the operating circu:lt of the present invention is extinguished. ~ ;~

According to another aspect of this invention a discharge lamp operating system employing a single winding type current limit-ing means is combined with a booster as a high frequency, highvoltage output generating means which acts as an initial ignitor for the first ignition and as a repetitive ignitor for the sec-ond and further ignition functions. In this case a standard a.c. power source voltage which energizes and operates the dis-charge lamp and high voltage output generating or booster means, `
is set to a value below the reignition voltage or second ignition voltage of the discharge lamp. To this end, timing means are combined with the high voltage output generating means fordeter-.

3~1~

1 mining the timing of the high voltage generation at a definite phase in every half cycle of the a.c. power source during the discharge lamp operation.

Where one or more discharge lamp means are provided with preheatable filaments, the invention avoids the use o~ fila- ~-ment preheating transformers and uses instead an electronic filament preheating circuit which uses current from and into the booster of the high voltage generating means. The elec-tronic preheating circuit is so constructed that one or more oscillation capacitors or a series circuit of a boosting in-ductor and a -thyristor are connected to the filaments of the discharge lamp means on the side opposite of the a.c. source.
When the high voltage generating means or both the oscillation capacitor and the series circuit are connected to the opposite side of the source, the filament is preheated only by the in-put current of this circuit, hence the preheating effect is insufficient. However, if only the capacitor or the series circuit is connected to the side opposite of the source, a much greater preheating effect is achieved by a circular cur-rent which is produced hy amplifying the input current. In other words, notwithstanding a small input current, the pre-heating circuit gives a greater amplified preheating - current due to the function of an impedance conversion effect of the high voltage generating means. According to the third aspect of this invention, means is added for regulating the timing for activating the booster of the high voltage gener-ating means prior to the reignition of the discharge lamp means.
Thus, the present discharge lamp operating system assures the activation phase of the high voltages generating means prior , ~ , . , ~ .

3~ :

1 to the ignition phase of the discharge lamp means by time delay means connected between the current limiting means and the discharge lamp means. In the fourth aspect of this invention, a lamp operating device is disclosed which oper-ates sequentia]ly a plurality of discharge lamp means con-nected in series, whereby the same effect is achieved as by the time delay means. This is accomplished by one or mGre bi~directional, two terminal thyristors as switching rneans for the high voltage output generating means and setting their effective break-over voltage below the lamp voltage of the discharge lamp means.

~ , BRIEF FI~URE DESCRIPTION: ~`

In ordér that the invention may be clearly understood, it will now be described, by way ov example, with reference to the accompanying drawings, wherein:

Fig. 1 is a circuit diagram of a conventional discharge lamp operating device of a well-known system;

Figs. 2(A) to

2(E) show the waveforms of the circuit of Fig. l; `~

20Fig. 3 is a circuit diagram of a discharge lamp operating device of an 'revery half cycle ignited system" as disclosed in the above mentioned parent case;

Figs. 4(A~, 4(B) show waveforms of the circuit of Fig. 3 for and 5(A) to 5(F) the explanation of the "every half cycle ignited system;
,~ .
~:~
~ 15 ~
.. ..
.: ., , .: ... . .
, :, . :, .
,,:

3~1 ' 1 Fig. 6 is a circuit diagram of a basic embodiment of a discharge lamp operating device of the "every hal~ eyele ignited system" aecording to this ,nvention; ~

Fig. 7 shows the waveforms obtained when the ;- - -circuit of Fig. 6 is operated in a first ~`~
operational mode; -~
; ' Fig. 8 shows the waveforms obtained when the - ~
circuit of Fig. 6 is operated in a second `;
operational mode;

Fig. 9 is a circuit diagram of a praetiea] embodi-ment according to this invention, which is suited for operation in the f'irst operational mode using an oseillation output;

Fig. 10 is a cireuit diagram of another prae~ieal ~`;
embodiment aeeording to this invention, whieh lS suited for operation in the second oper-ational mode using a pulse output, - -Fig. 11 is a cireuit diagram of a further praetieal modifieation of Fig. 5, in whieh a single leakage transformer is used as a eurrent ~
limiting means, and two diseharge lamps in ~-series eonneetion are operated in the first operatlonal mode;

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1 Fig. 12 is a circuit diagram of another basic embodiment according to this in~ention, in which a preheating circuit is employed;
.
Fig. 13 is a circuit diagram of a modification of Fig. 12, in which a double oscillator booster is used as a high voltage generating means;

Fig. 14 is a circuit diagram of another modification of Fig. 12 in which a high frequency filament transformer is employed;
:. ' Fig. 15 is a circuit diagram of a modification of - Fig. 14 for operating two discharge lamps; and :' Fig. 16 is a circ~lit diagram of a further embodiment for operating a cold cathode discharge lamp according to this invention.

:
DETAILED DESCRIPTION OF PREFERRED EXAMPLE EMBODIMENTS: -~
':
Fig. 6 shows a basic circuit diagram of this invention. A
fluorescent discharge lamp FL is connected to the low fre~
quency a.c. power source AC~ such as a standard or commer-cial power supply network, through a single choke SCH, and a series circuit of an intermittently oscillating capacitor Cl. ;~
An oscillator Rl of the construction as shown in Fig. 3, lS
connected in parallel to the discharge lamp FL. The winding of the single winding choke SCH is so designed that it is approx-imately the same as the sum of the primary W10 and the second-ary winding W20 of the choke coil SCH in the previously pro-posed "every half cycle operating system" as shown in present 3~,9 1 Fig. 3. According to the present improvement, the source voltage e is so close to the lamp voltage vT that, if the oscillator Rl is removed, the operation of the discharge lamp FL cannot continue. The fluctuation characteristic of the lamp is thus further improved.

~ ' Figs. 7 and 8 show the waveforms of each instant portion in the operation of the present invention. The first operational mode will now be explained with reference to Fig. 7. The first operational mode or "pattern I" is approximately the same as explained above with reference to the circuit of Fig. 3 and the waveforms of Figs. 4 and 5. Since, as viewed from the ~-single choke SCH, the discharge lamp FL and the booster cir-cuit R are connected in parallel when the source AC is turned on, the voltage e is applied to the discharge lamp FL and to the booster circuit R through the single choke SCH. The thyristor S, which serves as a switching means for the oscil-lator Rl, breaks over in response to the source voltage e, and then the oscillator Rl begins to oscillate. The oscillation output vR is derived intermittently from the booster R due to the intermittently oscillating capacitor Cl, and is impressed on the discharge lamp FL immediately after every pause period of every half cycle of the lamp voltage vT or the lamp cur-rent iT. As described above, the inductance value of the single choke SCH is so designed, with ~reference to the inter-mittently oscillating capacitor Cl, as to generate the inter-mittent oscillation. It is therefore required that the lamp current must not flow through the single choke coil SCH in the early period of the oscillation when it would be super- ~-~
posed on the input current; thus, the input current icl must exist prior to starting of the discharge lamp FL.

3~L~

1 The second operational mode or "pattern II" will now be described with reference to Fig. 8, whereby the break-over voltage ~B0 of the thyristor S is selected to be lower than in the"pattern I" operation of ~ig. 7. Consequently, when the source AC is turned on, the thyristor S breaks over even if the source ~roltage e is comparatively low. Hence, the operating phase of the oscillator Rl is expedited compared to the "pattern I" of Fig. 7. This means that when thethyristor S
of the oscillator Rl is in the conduction state, a residual . ~
current iT (not zero~ exists in the single choke, therefore, the inductance of this single choke SCH decreases. Therefore, the oscillation condition changes and the high frequency os-cillation stops. At t,he phase or point of the ignition of the booster R, the lamp current iT decreases rapidly close to the zero level, then immediately, the input current i of the booster R begins to flow rapidly. Therefore, a pulse type high voltage is generated across the single choke SCH by the energy stored therein, which is expressed by e = - LlddiT
wherein Ll is the inductance of the single choke SCH. This pulse type voltage is impressed on the discharge lamp FL and enables its continuous operation. Consequently, in case of the "pattern II" operation once the discharge lamp FL starts, the high frequency high voltage cannot be obtained from the booster R, and the reignition energy for the discharge lamp FL
is then provided ln the form of a high voltage pulse. Hence the "pattern II" as compared to the l'pattern I", is still advantageous even though the stability may be poor, because the high frequency oscillation ceases to operate once the dis- -~
charge lamp FL is started, high frequency noiseis thus reduced.

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1 In addition, according to the invention the phase angle -~
is more advanced in the "pattern I" operation than in the "pattern II" operation described above. ;

According to an example of the present invention, because the difference between the source voltage and the lamp vol-tage is slight, the choke coil employed as a current limit-ing device can be a single winding type, which realizes an ;~
extremely simple as well as a low cost production of the choke coil.

Fig. 9 shows the electrical circuit diagram of another embod-iment of the present invention, which is well suited for operating in accordance with "pattern I". Fig. 9 is substan-tially similar as the circuit of Fig. 6, except that a delay-ing inductor DL is connected between the booster R and the discharge lamp FL. This circuit is used for operating a rel-atively high power lamp, for instance, a llOW fluorescent dis- -`
charge lamp. The filaments fa and fc are each preheated by filament windings Wf of the heater transformer HT. In addi-tion, two thyristors Sl and S2 are connected in series as -~
switching means for the oscillator Rl to set the break-over voltage or capacity high. Also, a resistor r2 for promoting the starting is connected in parallel to one of the thyristors, namely, S2. Moreover, the stabilizing resistor rl is connected in parallel to the boosting inductor L and the capacitor C1.
If necessary, a capacitor CP for advancing phase is connected as shown in the circuit of Fig. 9.

The delaying inductor DL is employed for this discharge lamp operating device to be operated in the "pattern I~' operational mode. Thus, the source voltage e is applied to the booster R

3:1~

1 through the single choke SCH, and to the discharge lamp FL
also through the single choke SCH and through the delaying inductor DL which delays the ignition phase of the discharge lamp FL relative to the booster R. Thus, the booster R must operate before the discharge lamp FL starts. Hence,a stable "pattern I" operation is achieved.
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Fig. 10 is an electrical circuit diagram of afurther embod-iment of this invention, which is well suited for the "pattern II" operational mode. This circuit is used, for instance, to operate a discharge lamp having a low starting voltage. A preheating transformer HT which is connected to the a.c. power source AC has a primary winding W30, filament windings Wf and a tertiary winding W30. The output voltage of the tertiary winding W~ is applied to the booster circuit R, and since it has a voltage multiplying function, a voltage higher than the source voltage is applied to the booster R.
; This ~eature is there~ore equivalent to substantially lowering the break-over voltage of the thyristor S of the booster. It is to be understood that the "pattern II" operational mode is realized in that the ignition phase angle of the thyristor S
is advanced as compared to the source voltage. In addition, the delaying inductor as in the Fig. 9 can be omitted in this embodiment. However, in this circuit, the capacitor C, as shown in Fig. 6, may be connected in parallel to the series circuit of the boosting inductor L and the thyristor S, or the delaying inductor DL, as shown in the Fig. 9, may be con-nected in series with the capacitor Cl or C and the filament fa.

Fig. 11 is an electrical circuit diagram of another embodiment of this invention, which is well suited ~or "pattern I" oper-: , . , .. ,....... . ~ ,;

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l ational mode~ except for the following differences. Thesingle leakage transformer ALT is used in place of the single choke SCH, and the inductance between the primary and the secondary windings is so selected as to be approximately the same as that of the single choke SCH. It is characteristic for this embodiment, that the leakage inductance value is very large compared to that used in the case of ~he basic circuit. Thus, whether it is a one lamp or a two lamps operating system, when the source voltage and the lamp vol-tage are substantially the sameg the secondary winding W20which is used in the conventional circuit, can be eliminated by the use of a single leakage transformer. By the way, there must exist some dif~erence between the source voltage and the lamp voltage to increase the current limiting inductance in the circuit using a conventional choke. This is the advantage of using the single leakage transformer according to the in-~ention. In the circuit, two discharge lamps FLl and FL2 are connected in series. Moreover, a noise suppressing capacitor CNl is connected in parallel to the delaying inductor DL, and another noise suppressing capacitor CN2 is connected in par-allel to the series circuit of the discharge lamps FLl and FL2. -A further capacitor Cs is connected in parallel to the discharge lamp FL2. The capacitor CNl is used, in cooperation with the delaying inductor DL, in order to make this circuit anti-re-sonant at, for instance, 150KHz, to thereby suppress a radia-tion noise. The capacitor Cs is used to start the discharge lamps FLl and FL2 consecutively.

It is easily understood that the operation of this circuit is based on the same principle as that of Fig. 9. In this case, 3~

1 however, when the high frequency high voltage from the booster R is superposed by the source voltage and supplied to the discharge lamps FLl and FL2 at the starting instant, the discharge lamp FLl starts first and then the discharge lamp FL2 starts, due to the presence of the sequential oper-ating capacitor Cs. If only one discharge lamp is used in the operating circuit of Fig. 11, the same effect as described here is achieved.

Although the booster R or the oscillator Rl is employed as a -;
high voltage generating means in the above-described examples, these means may be replaced by other high voltage generating circuit components. Moreover, in this case the first and the second ignition are used in common, but the same effect can be obtained when these are separately provided.

Fig. 12 shows a basic discharge lamp operating circuit accord-ing to the invention which improves the filament preheating effect of the circuit of Fig. 6. The circuit construction and the operational mode of "pattern I" are basically the same as that explained with reference to Figs. 6and 7. Therefore, du-plicating explanations are omitted here, but the characteris-tics are that the current generated by the oscillator Rl o~
the booster R operating as high voltage generating means, pre-heats the filaments fa and fc of the discharge lamp FL. The current generated by the oscillator Rl is employed to preheat ~ filaments fa and fc in the following three practical embodi-; ments.

In the first embodiment or mode, for instance, the oscillator Rl is connected to the filaments on the side opposite of the voltage source as shown in the circuit of Figo 6, and the input . .

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1 current is employed for preheating also during the activation of the oscillation circuit. The preheating current of this mode is comparatively small and therefore used only for a limited type of discharge lamps.

The second and third operational modes, in the filament preheating, are that one oscillation capacitor C and the series circuit of the inductor L and the thyristor S are connected to the side opposite of the voltage source and the other oscillation capacitor C2 is connected to the voltage source side of the filaments fa, fc of the discharge lamp means, and the filament preheating current is thus amplified.
The oscillation capacitance comprises two capacitors C and C2. ~, When C is replaced by C2, maximum preheating current is obtained. ~; -A high frequency current from the oscillation output vR produced ~ ~-by the booster R flows into the capacitor C2 through the filaments fa and fc, whereby a suff:icient preheating of the filaments is achieved. Here, the capacitor CP is employed for the purpose of improving the power f'actor or as a filter~ ~
and by changing one of the funGtions from the primary side to ;
the secondary side the capacitor becomes protected against destruction and thus a low cost type capacitor may be used.

.
Figo 13 is a circuit diagram of another example of this in-vention which is suited to a discharge lamp operating system requiring a greater preheating current for the discharge lamp.
The oscillation circuit means comprise a first and a second oscillation circuit, or oscillators Rl and R20 forming, in effect, a double oscillating circuit. Each oscillator heats its filament fa or fc individually. The high frequency cur-rent flows through the filaments and is considerably ampli-- 2LI _ ~

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1 fied by an increased capacitance of the capacitors C and C20 connected in series. Moreover, a leading activation of the booster R is achieved before the ignition of the discharge lamp FL due to the resistor r connected in parallel to the thyristor S20 in the second oscillator R20. The characteris-tics of the circuit of Fig. 13 are similar to those of the circuit shown in Fig. 12. In this embodiment the capacitorCP
for the improvement of the pcwer factor is connected across the power source AC, and the bias coils BC and BC20 are also added to the boosting inductors L and L20 for obtaining a consolidated output vR. The details and constant values of each component are as follo~s:

FL --- hot-cathode type 110-~ fluorescent discharge lamp;
AC --- 200 V source voltage of 50/60Hz;
SCH --- single winding choke coil;
CP --- 3.5~ F preferably connected in parallel to a discharge resistor lM~;
C --- 0.047 ~ F;
C20 --- 0.049 ~ F;

Cl --- 3.3 ~ F (may be used with a discharge resistor lM Q in parallel connection);
L --- 280 turns of which four turns form a bias coil;
L20 --- 250 turns of which two turns form a bias coil;
S,S20 --- KlV12 type having VB0 of 110 ~ 125V; and r --- lOK ~ resistance.

The capacitances of C and C20 have different values to prevent a beat oscillat,ion.

.... .
': , ~ !. ~., 3~

1 Another practical circuit employing a current originating from the high voltage generating means, as a preheat current may be realized in that the filaments of the discharge lamps are preheated by the output of the secondary windings of a ~;
high frequency insulating transformer provided within the closed circuit of the oscillation booster circuit R for ~ .
generating a high frequency high voltage output. Fig. 14 is an electrical circuit diagram showing one of the practical embodiments using such a high frequency insulating transformer.
The construction and the operation is similar to the embodi-ment of Fig. 6, hence,a detailed explanation is omitted here.
The difference resides in that the booster R is connected to the source side, and the capacitor Cl is provided within the oscillator Rl as compared to Fig. 6. The booster circuit may be connected to the opposite side of the source~ and, in addi~
tion, the intermittently oscillating capacitor Cl may be serially connected to the oscillator Rl, as shown in Fig. 6.

The characteristics of this operating system reside in that the filamen~ transformer FT is provided within the booster R
and the primary winding W10 is connected between the inductor L
and the thyristor S. This transformer FT is constructed by winding the primary winding W10 around a ferromagnetic core such as a ferrite core, to which the secondary windings, i.e., the filament windings Wf are coupled. The filament windings are connected to the respective filaments fa and fc of the discharge lamp FL. In operation, during the period when the oscillator Rl is activated, the oscillation output vR is ap-plied to the discharge lamp FL and at the same time induced within the filament windings W~ of the filament trans~ormer FT

~: .

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1 which preheats the filaments fa and fc of the discharge lamp.
Thus, both filaments are sufficiently preheated by the cur-rent which is greater than the input current of the booster circuit R. When the filaments fa and fc are sufficiently preheated, the discharge lamp FL is started or ignited by the oscillation output vR.

:' Fig. 15 is an electrical circuit of a modification of Fig. 14 of this invention, wherein the two discharge lamps FLl andFL2 ~-are connected in series and operated sequentially. The fila-ments flc and f2a of the two discharge lamps FLl and FL2 are connected in series as shown or they may be arranged in par-allel connection. In any event flc and f2a are connected to the secondary winding Wf of the filament transformer FT. In addition, a capacitor Cs for the sequential ignitlon is also provided at this connection.
;~:

The oscillation capacitor C is connected to the source side of a series circuit of the discharge lamps FLl and FL2, while a series circuit of the intermittently oscillating capacitor Cl, the backswing boosting inductor L and the thyristor S is con- ;
nected to the opposite side of the discharge lamps. In this circuit of a closed booster R or the oscillator Rl and primary winding W10 of the filament transformer FT is connected in series to the boosting inductor L. In operation, when the source AC is switched on, the source voltage e is applied to the booster R, and the booster R is activated so as to gener-ate a high voltage oscillation output vR and to impress the output on the series circuit of the discharge lamps FLl and FL2. When the thyristor S is in the non-conducting state, the capacitor C is charged, and when the thyristor S goesinto ~. . : , : ,, ~ , , - ,, : . .: , .;

3~L~

1 the conducting state, the electrical charge flows through the following circuif: capacitor C - filament f2c - :
thyristor S - primary winding of the filamert transformer FT - ~ .
boosting inductor L - intermittently oscillating capacitor Cl - filament fld - capacitor C. Therefore, the filaments fla and f2c are rapidly heated by the superposed current of a low frequency current from the source AC and a high fre- ~:
quency current originated by the discharge current of the capacitor C.

Meanwhile, during the oscillation period a high frequency voltage is induced inthe primary winding W10 of the filament trans:~ormer FT which is a high frequency insulating trans-former, provided in the closed booster circuit R with the filament winding Wf. The filaments flc and r2a which are ~ ;
located at the connection of the two discharge lamps FLl and FL2, are thus preheated in series by the high frequency cur~
rent induced in the secondary winding Wf of said filament transformer FT.

Therefore~ the discharge lamps FLl and FL2 are sequentially ignited by the function of the capacitor Cs. The discharge lamp FLl fires first and then follows the other discharge lamp FL2. The filaments fla and f2c are preheated by a cur-rent resulting from the superposition of the low frequency ~:
power source current and the high frequency current of the oscillator R1. Therefore, a large size power transformer for the filamert preheating as shown in Figs. 9 to 11, is not required in Fig. 15. Thus, miniaturization, one of the advan-tages of every half cycle discharge lamp operating systems is easily realized, resulting in a low cost production. In ad-- 28 - .

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1 dition, the sequential igniting capacitor Cs of the above described circuit of Fig. 15 may be eliminated.

When the high frequency transformer is connected to all fila-- ments, the base-pin current of the discharge lamp is divided into two parts during lamp operation, thus achieving a simpli-fication of the base pin construction. In this case the fila-ments flc and f2a are connected in series to the secondary winding Wf of the filament transformer FT, however, they may be connected in parallel, if desired.

In order to stabilize the ignition, delaying means or other means assuring precedence of the activation of the booster -circuit prior to ignition of a discharge lamp is connected between the current limiting means and the discharge lamp means, regardless whether it is a hot-cathode type or a cold-cathode type to regulate the ignition sequence in the dis-charge lamp operating system of the present invention. For instance, when time delay means are employed~ the source a.c.
voltage e activates the booster R first, then follows the ignition of the discharge lamp FL due to the high voltage output vR and the source voltage from the current limiting means delayed by the delaying means. That is, the ignition of the discharge lamp always follows after the booster cir-cuit ignition in every half cycle of the source voltage e, and even when the source voltage e becomes twice as high as the lamp voltage, the booster R is activated at first.

Therefore, a stable "every half cycle igniting operation" is assured prior to the lamp ignition. The following components may be used as time delay means, an unsaturated inductor, a saturable inductor, a combined circuit of an unsaturated in-ductor and a noise preventing capacitor, or a four terminal '~:

- :, , ~, .

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1 circuit network composed o~ two coils arranged to compensate the generated voltage by a series connection or a delaying circuit employing semiconductor means may al~o be used. For instance, when SSS is employed as a delay means, the ignition time delay is determined by its break-over voltage. The ~unction o~ such time delay means is to regulate the ignition sequence of the booster circuit and the discharge lamp means so that the booster circuit is activated earlier which is equivalent to delaying the reignition of the discharge lamp.
mherefore, or instance, when two booster circuits as shown ~-in Fig. 13 are employed and sequentially activated, it func-tions as a regulating means of the ignition sequence.

Fig. 16 is a circuit diagram of a futher embodiment o~ the present invention containing such tlme delay means. The construction is similar to that o~ the practical circuits described above, but in Fig. 16 a cold cathode type discharge lamp FL is connected to the booster R through a blocking or delaying inductor DL. A bias coil BC which is activated by the current o~ the oscillator Rl is magnetically coupled to this blocking inductor DL. The bias coil BC which is connected ~-- :.
in series to the intermittently oscillative capacitor Cl~ is positively biased and increases the inductance of the blocking inductor DL when activated.
,.~ .

In operation, when the source ~C is switched on, the source voltage e is applied to the booster R through a single winding type choke coil SCH and the oscillation circuit be-gins to oscillate. On the other hand, the source voltage e to the discharge lamp FL is blocked by the delaying inductor DL.

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1 Now as current flows through the bias coil BC due to the input current of the oscillator Rl~ an increase in the effect of the delaying inductor DL results. The blocking -~
of the oscillation output vR due to the delaying inductor `
DL becomes more effective and the start or the ignition of ~;; `
the discharge lamp FL is delayed. In this context it will ~
be appreciated that the miniaturization of the delay in- ;
ductor DL has been achieved. According to this circuit, a very stable operation of the discharge lamp is assured due to 1~the every half cycle ignited system", even if variations of the lamp voltage occur due to the variation of the source voltage and of the ambient temperatures. ;~

Although the invention has been described with reference to specific example embodiments, it will be appreciated, that it is intended to cover all modifications and equivalents within the scope of the appended claims.

:
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Claims (14)

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

1. A discharge lamp operating system for sustaining the lit condition of discharge lamp means, comprising an electrical a.c. power source having a given low frequency, lamp current limiting means connecting said a.c. power source to said discharge lamp means for establishing light-ing conditions for said discharge lamp means, and reignition means connected across said discharge lamp means, said reignition means comprising oscillator circuit means (R1) and an intermittently oscillating capacitor (C1) supplying an intermittent output, having a frequency higher than said given low frequency, directly to the discharge lamp means immediately after every pause period of every half cycle whereby the reignition means sustain said lit condition by the intermittent output current of said oscillator circuit means which sustains a constant reignition voltage even if the a.c. power source should supply a varying vol-tage, whereby the oscillator circuit means constitute a self-oscillating independent high frequency output power source, said current limiting means comprising a single winding current limiter, wherein the voltage of said a.c.
power source is established below the required reignition voltage of said discharge lamp means during its operation, whereby said discharge lamp means is reignited by supply ing an initial discharge lamp current value as an input current to said reignition means in every half cycle of said a.c. power source, so that the lit condition is sub-stantially independent of the effective voltage of said a.c. power source.

2. The operating system of claim 1, wherein said oscillator circuit means of said reignition means comprises an oscillation capacitor (C) and a series circuit of a switching means and a boosting inductor in parallel con-nection with said oscillation capacitor (C), and wherein said reignition means is energized by said power source to generate an intermittently high frequency high voltage out-put, at a point of time just prior to ignition of said dis-charge lamp means.

3. The operating system of claim 2, wherein said switching means comprises one or more bi-directional two terminal thyristors having an effective break-over voltage higher than the lamp voltage of said discharge lamp means and lower than the voltage of said power source.

4. The operating system of claim 1, wherein said single winding current limiter is a choke coil having end terminals only.

5. The operating system of claim 1, wherein said single winding current limiter is a leakage inductance of a transformer.

6. The operating system of claim 1, wherein said discharge lamp means comprise a plurality of discharge lamps serially connected and sequentially ignited in oper-ation.

7. The operating system of claim 2, wherein time delay means are connected between said discharge lamp means and said current limiting means whereby the ignition phase of said reignition means is controlled at every half cycle of said power source prior to the ignition of said discharge lamp means.

8. The operating system of claim 7, wherein said time delay means include an inductor and means for changing the inductance of said inductor in response to the activa-tion of said reignition means.

9. The operating system of claim 8, wherein said means for changing the inductance is a bias coil which is energized by the current flowing through said reignition means and at the same time acts as a bias winding by a magnetic coupling with said inductor.

10. The operating system of claim 2, wherein said discharge lamp means is a hot-cathode type discharge lamp having a filament, and further comprising a preheating circuit for said filament, said preheating circuit including said filament located within said reignition means so as to flow current through said filament.

11. The operating system of claim 10, wherein said preheating circuit includes a high frequency insulating transformer located within the closed circuit of said reignition means, said insulating transformer supplying a part of the energy output from said reignition means to said filament of said discharge lamp.

12. The operating system of claim 11, wherein a plurality of discharge lamps are employed in series con-nection, and wherein at least a part of the oscillation energy output of said reignition means is supplied to said filaments of said series connected discharge lamps by said high frequency insulating transformer.

13. The operating system of claim 10, wherein said reignition means comprises two oscillators in series con-nection, each of said filaments of said discharge lamp means being located within each of said oscillators so as to promote the preheating of said filaments.

14. The operating system of claim 10, wherein one of said oscillators includes sequentially operating means for the activation of said oscillators.