US3701925A

US3701925A - Instantaneous starting system for discharge lamp

Info

Publication number: US3701925A
Application number: US117935A
Authority: US
Inventors: Shunichi Nozawa; Hisashi Kuroi; Masamichi Hatada; Shunsaku Fukuyama
Original assignee: Blackwell Electronics Ind Co Ltd
Current assignee: Blackwell Electronics Ind Co Ltd
Priority date: 1970-02-28
Filing date: 1971-02-23
Publication date: 1972-10-31
Anticipated expiration: 1989-10-31
Also published as: DE2109556B2; FR2079119A5; DE2109556A1; GB1352399A

Abstract

A system for the instantaneous starting of a fluorescent lamp includes a circuit connected across the lamp having a start compensation device to apply a half-sinusoidal wave derived from a commercial power supply and oscillatory means to provide a high frequency oscillation across the lamp. The oscillatory means may include a symmetrical silicon switch (SSS) or an inversely blocking two-terminal thyristor and an oscillation adjusting inductance and capacitor. The start compensation device may be a start compensation winding wound on the same core as a current limiting winding in series with the lamp, and a start compensation diode may be connected in series with the start compensation winding. Alternatively, the diode alone may serve as the start compensation device. A thermistor having a positive characteristic may be connected in the circuit across the lamp.

Description

United States Patent Nozawa et al.

[54] INSTANTANEOUS STARTING SYSTEM FOR DISCHARGE LAMP [72] lnventors: Shunichi Nozawa, Akashi; Hia'ashi Kuroi; Masamichi Hatada', both of Kyoto; Shunsaku Fukuyama, Amagasaki, all of Japan [73] Assignee: Blackwell Electronics Ind. Co., Ltd.,

Shimogyo-ku, Kyoto, Japan 221 Filed: I Feb. 23, 1971 21] Appl.No.:117,935

[30] Foreign Application Priority Data [58] Field oiScarch....315/92, 93, 94, 101, 103, 104, 315/105,106,107,182,192,199, 239,156, 158, DIG. 2, DIG. 5

[56] References Cited UNITED STATES PATENTS 3,476,976 11/1969 Morita et al. ..3l5/10l 3,249,806 5/ l 966 Genuit ..3 l SIDlG. 2

[151 3,701,925 [451 Oct. 31, 1972 Primary Examiner-Stanley T. Krawczewicz Attorney-Raphael Semmes [57] ABSTRACT A system for the instantaneous starting of a fluorescent lamp includes a circuit connected across the'lamp having a start compensation device to apply a half-sinusoidal wave derived from a commercial power supply and oscillatory means to provide a high frequency oscillation across the lamp. The oscillatory means may include a symmetrical silicon switch (SSS) or an inversely blocking two-terminal thyristor and an oscillation adjusting inductance and capacitor. The start compensation device may be a start compensation winding wound on the same core as a current limiting winding in series with the lamp, and a start compensation diode may be connected in series with the start compensation winding. Alternatively, the diode alone may serve as the start compensation device. A thermistor having a positive characteristic may be connected in the circuit across the lamp.

17 Claims, 14 Drawing Figures PAIENTEUUBISI I972 3.701.925

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' SHEET 5 BF 5 INV ENTORS SHUN l CHI AWA HISASHI K OI MASAMICHI HATADA SHUNSAKU FUKUYAMA INSTANTANEOUS STARTING SYSTEM FOR DISCHARGE LAMP FIELD OF THE INVENTION The invention relates to an instantaneous starting system for a fluorescent discharge lamp.

BACKGROUND OF THE INVENTION starting system achieves the starting within 0.1 second or thereabouts, but involves severe loss of the cathode oxide of a fluorescent lamp, which is not economical.

SUMMARY OF THE INVENTION Therefore, it is an object of the invention to provide an instantaneous starting system for a fluorescent lamp which permits the starting to be effected within a time interval comparable to that of an incandescent lamp, i.e., on the order of 0.1 to 0.2 second with minimized loss of the cathode oxide, that is, in a manner such that the influence of the cathode oxide loss during starting on the life of the fluorescent lamp is substantially negligible.

It is another object of the invention to provide an instantaneous starting system for a fluorescent lamp vwhich is simple in circuit arrangement, compact and of low cost and high reliability and which therefore can be commercialized on an economic basis.

It is a further object of the invention to provide an instantaneous starting system for a fluorescent lamp of the kind described which has as its major advantage little radio interference.

Briefly, the instantaneous starting system of the present invention contemplates the provision of current control means between a supply of alternating current power and a discharge lamp having two cathodes and circuit means connected between ,the cathodes across the lamp including start compensation means for applying a half-sinusoidal wave derived from the supply and oscillatory means to provide a high frequency oscillation across the lamp, the oscillation growing and decaying after reaching an amplitude substantially greater than the amplitude of the half-sinusoidal wave so that a relatively low starting voltage provides sufficient preceding ionization in the lamp to promote rapid establishment of a main discharge therein. In several embodiments, the current control means and the start compensation means are windings wound on a common saturable magnetic path with opposite polarity. The oscillatory means includes a symmetrical contactless switch, such as a symmetrical silicon switch (SSS),or an inversely blocking two-terminal thyristor and may include an oscillation adjusting inductance in series with the switch and an oscillation adjusting capacitor in parallel to the series path including the switch and inductance.

A start compensation diode may be connected in series with the start compensation winding and may, in one embodiment, replace the winding as the start compensation means. A thermistor having a positive characteristic may be connected in series with the switch.

The above and other objects, features and advantages of the invention and the manner in which the same are accomplished will become more readily apparent upon consideration of the following detailed description of the invention when taken in conjunction with the accompanying drawings, which illustrate preferred and exemplary embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 and 2 are wiring diagrams of two embodiments of the invention;

FIG. 3 shows the waveform of the voltage across the lamp occurring when starting the fluorescent lamp with the circuits shown in FIGS. 1 and 2;

FIG. 4 shows the waveform of pulse voltage at the time of starting;

FIG. 5 is a graph showing the starting time as a function of the preheat current;

FIGS. 6 to 12 are wiring diagrams of various other embodiments of the invention; and

FIGS. 13 and 14 are wiring diagrams of two other embodiments illustrating the application of the system according to the invention to a discharge lamp of relatively low wattage.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, there is shown a fluorescent lamp 1 of the preheat starting type which has a pair of cathodes 2 and 2'. A lamp current control winding 3 is connected between one of the cathodes 2 and an alternating current power supply indicated at 12. A start compensation winding 4 is provided on the same magnetic path 5 as the lamp current control winding 3. A symmetrical contactless switch 6, which may, for example, be a silicon symmetrical switch (hereafter abbreviated as SSS), also known in the art as a diac, a bidirectional diode thyristor, or a bilateral trigger diode, is connected in series with the start compensation winding 4 and an oscillation adjusting inductance 7 across the cathodes 2 and 2', the inductance 7 being free from magnetic coupling with the magnetic path 5. An oscillation adjusting capacitor 8 is connected across the series connection of the winding 4, SSS 6 and the inductance 7. A thermistor 9 having a positive characteristic (hereafter referred to as VIII) is connected in series with the SSS 6 in the circuit across the cathodes 2 and 2'. It is desirable to have both the lamp current control winding 3 and the start compensation winding 4 on thesame magnetic path 5 with opposite polarities. It is also desirable that the magnetic path 5 is saturable. A capacitor 10 is connected, for the purpose of preventing noises, in series with a power switch 11 across the power supply 12.

In operation, when the supply voltage reaches the breakover voltage V of SSS 6, the latter becomes conductive. By suitable choice of the oscillation adjusting inductance 7 and the oscillation adjusting capacitor 8 to meet a required oscillation condition, the current controlled negative resistance of SSS 6 causes an increase in current in this circuit by producing a growing sinusoidal oscillation or progressively growing quasirelaxation oscillation. Then SSS 6 shifts into a region of positive resistance, thereby producing a decaying sinusoidal oscillation. As a result, a high frequency alternating field, as depicted in FIG. 3, is applied across the

cathodes

2, 2. Subsequently, at the time of heating or at the phase of preheat operation, the start compensation winding 4 causes a field of a half-sinusoidal commercial wave to be applied; and when the preheat current reduces to the holding current level 1,, of SSS 6, the latter turns off, whereupon the lamp is applied with the supply voltage of the next cycle. By the use of a high frequency alternating voltage which alternately effects, as shown in FIG. 4, similar processes as mentioned above, a low start voltage is sufficient to produce preceding ionization with little environmental dependency, and the half-sinusoidal commercial frequency voltage applied across the lamp from the start compensation winding 4 assures the preceding discharge within the lamp which matures into the main discharge by the supply voltage across the lamp at the pause phase or turnover phase of SSS in each half cycle. When the current flow increases to a value which causes the voltage across the lamp to decrease below the V of SSS, the latter is turned off, whereupon the current rapidly reaches the level determined by the ballast choke, thus completing the starting operation.

In order to utilize the negative current-controlled resistance of SSS 6 to produce a growing sinusoidal oscillation, it is necessary to provide an oscillation adjusting inductance 7 that is not magnetically coupled with the start compensation winding 4 and the lamp current control winding 3, in addition to the provision of the oscillation adjusting capacitor 8 and the start compensation winding 4. This applies equally when using a ballast having as its core conventional silicon steel plate which involves much loss in high frequency operation, or when the core of the ballast comprises a ferrite core for high frequency use.

' By suitably choosing the inductance value of the oscillation adjusting inductance 7 and the capacitance of the oscillation adjusting capacitor 8, it is possible to produce a sinusoidal high frequency voltage having an amplitude of several hundred volts across the oscillation adjusting capacitor 8 or across the lamp 1.

A series resonance circuit may be constituted by the oscillation adjusting capacitor 8, oscillation adjusting inducatance 7 and SSS 6 alone by connecting the oscillation adjusting capacitor in the circuit so as to exclude the start compensation winding 4 from the loop. However, this results in an increase in radio interferences as compared with the arrangement including .,the start compensation winding in the loop, and hence it is more practical to connect the start compensation winding in the loop.

' Satisfactory characteristics for practical purposes are also obtained when one or both of the cathodes and PTH are also included in the loop of the series resonance circuit.

Where a core is used which involves a small amount of iron loss in high frequency operation, the stray capacitance of the lamp current control winding alone may be sufficient to serve as the oscillation adjusting capacitor; and in such an instance, the oscillation capacitor may be omitted.

I Since in accordance with the invention, the occurrence of ionization preceding the main discharge relies on a high frequency alternating field, the required amplitude may be half the value which would be the case if a unidirectional single pulse field or unidirectional repeated pulse field were used. This has been confirmed by experiments. The starting pulse voltage generated in accordance with the invention can be regarded as equivalent to a sustained sinusoidal wave of the oscillation frequency that is amplitude modulated by the envelope of the pulses, so that the deviation of the side band waves is extremely narrow. For example, for an oscillation frequency of 30 KHz, both-sideband waves remain within several KHz at most. Thus the start pulse itself can be considered as completely free from inducing radio interference. The only noise would be caused by the transients when SSS turns off by decay of the current flow therethrough below 1,, at the end of the preheat phase, whereby radio interferences are substantially reduced. An example of measurements made on the intensity of interference waves produced during the starting is given below.

The general average amounts to only 38 dB, which is nearly comparable to the noises emitted by the existing various fluorescent lamps during their lighting, which are on the order of 33 dB t 9 dB at 1,000 KHz.

With respect to the problem of possible destruction of the SSS, it is pointed out that according to the invention, the current flow through the SSS at the start pulse generating phase is approximately sinusoidal or square of cosine, so that the time derivative of the current is very low, thereby effectively preventing the destruction of the SSS and increasing the reliability of the circuit according to the invention.

Denoting the time during which the preheat current is passed to the

cathode filaments

2 and 2 to produce cathode arcs for facilitating the starting by t, the preheat current by i,(t) and the resistance of the cathode filament by rf(t), it has been confirmed by experiments that the following relationship applies:

i, (t) t constant,

so that it follows that the time required for the starting is inversely proportional to the square of the cathode preheat current. However, as indicated by a graph shown in FIG. 5 which depicts the result of measurement conducted on a FCL-ZO lamp, for a preheat current in excess of 1.5 times the upper limit of its rating, secondary delay in the temperature rise of the cathode oxide becomes appreciable to limit the starting time to the order of 0.1 second, and an extreme increase in the preheat current produces little additional effect.

In accordance with the invention, instantaneous starting can be effected by connectingthe start compensation winding in opposite polarity to the tube current control winding during preheat and by establishing the preheat current at a level substantially in excess of the upper limit of its rating. In order to use such a large preheat current and nevertheless avoid the use of a large ballast, it is only necessary to use an overcurrent control element, such as a thermistor having a positive characteristic, which provides a suitable thermal time constant to allow the ballast to be designed at the instantaneous rating for such value of preheat current. To prevent re-breakdown of the SSS when the supply voltage through the start compensation winding is excessively high, it is ideal to use an arrangement including a ballast that is non-saturable by the lamp current during lighting and that is saturable by the preheat current. By choosing the preheat current substantially in excess of the upper limit of its rating, it is possible to provide a ballast that is saturable during the preheat period.

With the arrangement mentioned above, the invention achieves a starting time that is comparable to instantaneous starting, i.e., from 0.1 to 0.2 second for a FCL-ZO lamp, and also minimizes the ion bombardment experienced by the cathodes upon starting. In a test, the durability proved to well exceed one million times of switching on and off, which is by two orders of magnitude greater than the durability of lamps of common rapid start systems which lies on the order of ten thousand times. Therefore, the loss of cathode oxide during the starting can be neglected for practical purposes.

Furthermore, since the invention eliminates the influence of the start pulse voltage upon radio interferences, the start pulse voltage may be increased for an added margin for starting. The use of a high frequency alternating field serves to provide a reduction of the required starting voltage and also of environmental dependency, and the start compensation winding causes the preceding discharge to proceed into the tube. All these contribute to assure a reliable starting of fluorescent lamps of the preheat-starting type which are known to have various starting voltages varying with environment and from lamp to lamp. I

Thus, the invention provides a highly practical lighting system for a discharge lamp capable of starting fluorescent lamps of the preheat-starting type rapidly enough to compare, in effect, with the lighting of incandescent lamps and which is compact in the circuit arrangement.

FIG. 6 shows an embodiment in which PTH 9 is included in the closed oscillation circuit so as to be in series circuit relationship with SSS 6. FIG. 7 shows another embodiment in which the oscillation adjusting capacitor 8 is removed. FIG. 8 shows a further embodiment in which the start compensation winding is removed out of the closed oscillation circuit. All of these embodiments are able to achieve the above objects of the invention.

FIG. 9 shows an arrangement which differs from the systems described thus far in that a start compensation diode 13 is connected in series with the series circuit comprising the oscillation adjusting inductance 7, SSS 6 and the start compensation winding 4. With this arrangement, the start compensation diode additionally assures that the preceding discharge caused within the tube by the half-sinusoidal commercial frequency field across the lamp proceeds into the lamp.

As shown in FIG. 10, the start compensation winding may be eliminated, and the lamp current control device 14 may comprise a passive element such as an inductor or resistor or an active element. Start compensation diode 13 will serve as the start compensation means in this embodiment.

As shown in FIG. 11, where a ballast 16 is of a leakage transformer type, involving a high saturation of the magnetic path by the d.c. component, the start compensation diode 13 can be substituted for the start compensation winding to effect the preheat operation based on a saturable magnetic path.

In the embodiments as illustrated in FIGS. 9 to 11, a

high voltage is not applied across SSS 6,and start compensation diode 13 therefore need only be able to block an inverse supply voltage. In such an instance, SSS 6 and diode 13 may be replaced by an inversely blocking two-terminal thyristor such as PNPN diode 15, as shown in FIG. 12, thereby simplifying the arrangement.

FIG. 13 shows en embodiment in which PTI-I 9, SSS 6 and start compensation winding 4 are connected in series across both

cathodes

2, 2. Such an arrangement can be used with lamps of lower wattage less than 10 watts.

FIG. 14 shows another embodiment for a lamp of further low wattage. Such an arrangement, comprising a simple connection of SSS 6 and start compensation winding 4 in series across the

cathodes

2, 2, can be used, provided the use of a somewhat larger ballast is acceptable, to provide an instantaneous starting of a discharge lamp within a time interval on the order of 0.1 second comparable to that for an incandescent lamp, that is, the time required for an incandescent lamp rated 100 V and I00 W to reach percent of the full luminous flux.

It should be understood that in the arrangements shown in FIGS. 13 and 14, the start compensation winding 4 is provided on the same magnetic path 5 as the lamp current control winding 3 in opposite polarity relationship thereto, and that the preheat current for the cathodes are at levels above the upper limit of the preheat current rating for all practical voltage fluctuations.

We claim:

1. An instantaneous starting system for a discharge lamp of the preheat type having a pair of cathodes, comprising:

a supply of alternating current power;

current control means in series between said supply of power and said cathodes for limiting current to said cathodes; and

circuit means connected between said cathodes across said lamp, said circuit means including start compensation means for applying a half-sinusoidal wave derived from said supply and oscillatory means including a resonant circuit and contactless switch means, said contactless switch means becoming conductive when said alternating current power reaches the breakover voltage of said switch means, and, upon becoming conductive, having a current controlled negative resistance for causing the production of said high frequency oscillation as a growing sinusoidal oscillation in said circuit means, said switch means then shifting into a region of positive resistance for causing said sinusoidal oscillation to decay, said high frequency oscillation attaining an amplitude substantially greater than the amplitude of said half sinusoidal wave whereby a relatively low starting voltage will provide sufficient preceding ionization in the lamp to promote rapid establishment of a main discharge therein.

.a common magnetic path.

4. An instantaneous starting system according to claim 3, wherein said magnetic path is a saturable path and said windings are wound thereon with opposite polarity.

5. An instantaneous starting system according to claim 3, wherein said contactless switch means comprises a symmetrical contactless switch and said resonant circuit includes an oscillation adjusting inductance in series with said start compensation winding and an oscillation adjusting capacitor connected across the series circuit formed by said start compensation winding, symmetrical switch, and oscillation adjusting inductance. 6. An instantaneous starting system according to claim 5, wherein said circuit means further comprises a thermistor having a positive characteristic in series with said symmetrical switch.

7. An instantaneous starting system according to claim 3, wherein said magnetic path comprises a core having a small high frequency loss and wherein said contactless switch means comprises a symmetrical contactless switch and said resonant circuit includes an oscillation adjusting inductance in series with said start compensation winding.

8. An instantaneous starting system according to claim 7, wherein said circuit means further comprises a thermistor having a positive characteristic in series with said symmetrical switch.

9. An instantaneous starting system according to claim 3, wherein said circuit means further comprises a start compensation diode connected in series with said start compensation winding.

12. An instantaneous starting system according to claim 11, wherein said contactless switch means comprises a symmetrical contactless switch and said resonant circuit comprises an oscillation adjusting inductance in series with said start compensation winding and start compensation diode and an oscillation'adjusting capacitor connected across the series circuit formed by said start compensation winding, start compensation diode, symmetrical switch, and oscillation adjusting inductance.

13. An instantaneous starting system according to claim 3, wherein said contactless switch means comprises an inversely blocking two-terminal thyristor and said resonant circuit comprises an oscillation adjusting inductance in series with said start compensation winding and an oscillation adjusting capacitor connected across the series circuit formed by said start compensation winding, thyristor, and inductance.

14. An instantaneous starting system according to claim 13, wherein said circuit means further comprises a thermistor having a positive characteristic in series with said thyristor.

15. An instantaneous starting system according to claim 3, wherein said contactless switch means comprises a symmetrical contactless switch and said circuit means further comprises a thermistor having a positive characteristic, said start compensation winding, switch, and thermistor being connected in series between said cathodes.

16. An instantaneous starting system according to claim 3, wherein said contactless switch means comprises a symmetrical contactless switch connected in series with said start compensation winding between said cathodes.

17. An instantaneous starting system according to claim 2, wherein said start compensation means comprises a start compensation diode.

Claims

1. An instantaneous starting system for a discharge lamp of the preheat type having a pair of cathodes, comprising: a supply of alternating current power; current control means in series between said supply of power and said cathodes for limiting current to said cathodes; and circuit means connected between said cathodes across said lamp, said circuit means including start compensation means for applying a half-sinusoidal wave derived from said supply and oscillatory means including a resonant circuit and contactless switch means, said contactless switch means becoming conductive when said alternating current power reaches the breakover voltage of said switch means, and, upon becoming conductive, having a current controlled negative resistance for causing the production of said high frequency oscillation as a growing sinusoidal oscillation in said circuit means, said switch means then shifting into a region of positive resistance for causing said sinusoidal oscillation to decay, said high frequency oscillation attaining an amplitude substantially greater than the amplitude of said half sinusoidal wave whereby a relatively low starting voltage will provide sufficient preceding ionization in the lamp to promote rapid establishment of a main discharge therein.

2. An instantaneous starting system as recited in claim 1, wherein said current control means and said circuit means are so constructed that said lamp, during a preheat period, is provided with a preheat current substantially greater than the upper limit of the preheat current rating of the lamp for all practical supply voltage fluctuations.

3. An instantaneous starting system according to claim 2, wherein said start compensation means comprises a start compensation winding and said current control means comprises a current control winding on a common magnetic path.

5. An instantaneous starting system according to claim 3, wherein said contactless switch means comprises a symmetrical contactless switch and said resonant circuit includes an oscillation adjusting inductance in series with said start compensation winding and an oscillation adjusting capacitor connected across the series circuit formed by said start compensation winding, symmetrical switch, and oscillation adjusting inductance.

6. An instantaneous starting system according to claim 5, wherein said circuit means further comprises a thermistor having a positive characteristic in series with said symmetrical switch.

9. An instantaneous starting system according to claim 3, wherein said contactless switch means comprises a symmetrical contactless switch and said resonant circuit comprises an oscillation adjusting inductance In series with said start compensation winding and an oscillation adjusting capacitor connected across the series circuit formed by said symmetrical switch and said oscillation adjusting inductance.

10. An instantaneous starting system according to claim 9, wherein said circuit means further comprises a thermistor having a positive characteristic in series with said symmetrical switch.

11. An instantaneous starting system according to claim 3, wherein said circuit means further comprises a start compensation diode connected in series with said start compensation winding.

12. An instantaneous starting system according to claim 11, wherein said contactless switch means comprises a symmetrical contactless switch and said resonant circuit comprises an oscillation adjusting inductance in series with said start compensation winding and start compensation diode and an oscillation adjusting capacitor connected across the series circuit formed by said start compensation winding, start compensation diode, symmetrical switch, and oscillation adjusting inductance.