EP0824761B1 - Process for operating a discharge lamp - Google Patents

Description

The invention relates to a method for operating discharge lamps according to the preamble of claim 1.

The method particularly relates to the operation of low-pressure noble gas discharge lamps, such as in automotive engineering can be used for signal and display purposes.

From DE-U-89 04 853 is a fluorescent lamp operated with AC voltage known. Be inside the discharge vessel of the lamp spiral-shaped glow electrodes and one from the inside of the discharge space metallic element separated by a dielectric. By means of the heated spiral electrodes becomes one inside the discharge vessel Discharge generated. In addition, the metallic element is in operation put a tension. In this way, the metallic element acts as Capacitor plate on the discharge such that the electrical resistance of the discharge plasma is increased, locally the more, the larger the current density is. The aim is to use the capacitor plate to control the lamp current and consequently spatially homogenize the luminance of the lamp as well as to increase the efficiency of the lamp.

EP-A-0 550 047 describes a flat one operated with AC voltage Fluorescent lamp disclosed, the discharge vessel formed by flat plates is. On the inside of the plates is a pair of flat, with dielectric glass layers covered electrodes arranged. additionally the lamp has a pair of galvanic electrodes inside. Both Electrode pairs are either different or high-frequency operated at the same frequency, in the latter case 90 ° out of phase. The sheet-like electrodes capacitively generate a plasma that is stable and is spatially uniform. The galvanic electrodes generate a low pressure discharge with high luminous efficacy, but spatially uneven is. Both discharges complement each other to form a flat light source high luminance and good uniformity. Because of this and because of it The flat geometry makes the lamp particularly suitable for backlighting of liquid crystal displays.

From EP-A 700 074 an elongated lamp is known with a tubular discharge vessel which is hermetically sealed at both ends and contains neon as the filling gas. The inner wall of the discharge vessel is optionally provided with a phosphor layer, in particular with Y ₃ Al ₅ O ₁₂ : Ce. In the interior, the discharge vessel has two unheated electrodes that face each other and are connected to power supplies.

1. Eine sinusähnliche Wechselspannung, z.B. mit einer Frequenz von 60 kHz dient der Erzeugung einer Entladung innerhalb des Entladungsgefäßes, wobei elektromagnetische Strahlung vorwiegend im roten und infraroten Spektralbereich mit geringen VUV- bzw. UV-Anteilen emittiert wird. In dieser Betriebsart hat die Lampe im wesentlichen eine rote Lichtfarbe und eignet sich daher z.B. für den Einsatz in einer Kfz-Bremsleuchte. Üblicherweise wird in diesem Fall auf eine Leuchtstoffschicht verzichtet.

2. Eine pulsförmige Spannung, z.B. mit einer Frequenz von 12 kHz und typischen Pulsdauern im µs-Bereich dient der Erzeugung einer Entladung innerhalb des Entladungsgefäßes, die ebenfalls elektromagnetische Strahlung im roten und infraroten Spektralbereich emittiert, im Unterschied zur Betriebsart 1 allerdings mit einem deutlich erhöhten VUV-bzw. UV-Anteil. Die VUV- bzw. UV-Strahlung regt den Leuchtstoff Y₃Al₅O₁₂:Ce an, der im gelben Spektralbereich fluoresziert (mittlere Wellenlänge: 556 nm, Halbwertsbreite: 103 nm). Dadurch hat die Lampe in dieser Betriebsart im wesentlichen eine gelbe Lichtfarbe und eignet sich folglich z.B. für den Einsatz in einer Kfz-Blinkleuchte.

The lamp can be operated in two ways:

1. A sinusoidal alternating voltage, for example with a frequency of 60 kHz, serves to generate a discharge within the discharge vessel, electromagnetic radiation being emitted predominantly in the red and infrared spectral range with low VUV or UV components. In this operating mode, the lamp has essentially a red light color and is therefore suitable, for example, for use in a motor vehicle brake light. A phosphor layer is usually dispensed with in this case.

2. A pulse-shaped voltage, for example with a frequency of 12 kHz and typical pulse durations in the µs range, is used to generate a discharge within the discharge vessel, which likewise emits electromagnetic radiation in the red and infrared spectral range, but in contrast to operating mode 1 with a significantly increased one VUV respectively. UV component. The VUV or UV radiation excites the phosphor Y ₃ Al ₅ O ₁₂ : Ce, which fluoresces in the yellow spectral range (medium wavelength: 556 nm, half-width: 103 nm). As a result, in this operating mode the lamp has essentially a yellow light color and is therefore suitable, for example, for use in a blinking motor vehicle.

In the case of pulsed operation of the lamp, the power supply lines which are led outwards at the ends of the discharge vessel, a consequence of voltage pulses. The voltage pulses are different from each other separated by relatively long breaks (low duty cycle). The break times are required for setting the desired color location of the lamp.

Since the ionization decreases rapidly during the pulse pauses, relatively high pulse voltages are required to re-ignite the discharge, particularly in the case of long lamps with correspondingly large electrode spacings. However, the level of the pulse voltages also increases the electromagnetic interference emitted by the lamp and the operating circuit. Thereby can be influenced (EMI = e lectro m agnetic nterference i) electronic circuits. In order to prevent this, a correspondingly complex shield is required, particularly in a safety-relevant environment, for example when used in automotive technology. Another disadvantage results from the high pulse voltages of operating mode 2. For suitable operating devices, voltage-proof and therefore expensive components are required.

An object of the invention is to provide a method for pulsed operation of discharge lamps with which the spectral distribution of the radiation specifically emitted by the discharge lamps and the required amount of voltage pulses compared to conventional Procedure can be reduced.

This object is achieved by the characterizing features of claim 1 solved. Further advantageous features are in the subordinate claims directed thereon.

The basic idea of the invention is - in addition to the conventional pulsed discharge between the lamp electrodes of a discharge lamp - A dielectric barrier discharge in the discharge vessel too produce. Through this measure, the spectral distribution of the Discharge lamp specifically affects the radiation emitted and the required Voltage pulses in comparison to conventional methods reduced.

Dielectric-barrier discharges differ from conventional ones (unhindered) discharges by either an electrode (one-sided dielectric discharge) or both electrodes (two-sided dielectric barrier discharge) by means of a dielectric layer of the discharge is or are separated. The dielectric layer in Shape of an at least partial covering of at least one electrode be realized. The dielectric layer can also pass through the wall of the discharge vessel itself by the electrode (s) outside of the discharge vessel, is arranged approximately on the surface (are). For the sake of simplicity, such electrodes are referred to below as "dielectric electrodes". To distinguish this from the following electrodes, which are immediate, i.e. without intermediate dielectric Interface, adjacent to the discharge, shortening as "galvanic Electrodes ".

The method according to the invention provides - in addition to that for generation the consequence of the dielectric unimpeded pulsed discharge of voltage pulses - the use of a time-varying voltage to generate the dielectric barrier discharge. As time-varying Voltages are suitable e.g. AC voltages and in particular Sequences of voltage pulses, the individual voltage pulses each are separated from each other by breaks.

For the voltage pulses, both to generate the unhindered as well the dielectric barrier discharge, is in principle a variety of Suitable pulse shapes, e.g. triangular and rectangular. The pulse width is typically in the range between 0.1 µs and 50 µs. Essential for an efficient Radiation generation is that the pulses are separated by pauses. typical Pulse-pause ratios are in the range between 0.001 and 0.1. The pulse sequences disclosed in WO 94/23442 are also particularly suitable.

The optical spectrum of the radiation emitted by the lamp is through the ratio of the conventional (dielectric free) or the dielectrically impeded discharge coupled medium electrical Achievements can be influenced. The reason for this is the different Particle kinetics of both types of discharge. Hence the spectral composition of the radiation emitted differently. Depending on The ratio of the coupled electrical power changes accordingly also the radiation components of the respective spectral components of both Discharge types on the total radiation of the discharge lamp and consequently also the entire spectrum or the color locus.

The ratio of the services is determined by the pulse train (s), in particular the Time periods and amplitudes of the pulses and pauses or, if applicable, the frequency the AC voltage, the electrode configurations as well as type and pressure affects the lamp filling. Typical electrical power ratios from unhindered unloading to disabled unloading lie in the Range between 0.01 and 100, preferably in the range between 0.5 and 10.

The influencing of the color locus can be done by using a suitable one Phosphor are supported. For this is the inner wall of the discharge vessel provided with a fluorescent layer, which the UV or VUV radiation of the discharge converted into light.

The selection of the ionizable filling and possibly the phosphor layer depends on the application. Noble gases are particularly suitable, e.g. Neon, argon, krypton and xenon as well as mixtures of noble gases. However, other fillers can also be used, e.g. all those who are usually used in light production, in particular Hg and rare gas-Hg mixtures as well as rare earths and their halides.

Unhindered discharges result in a relatively broadband excitation of the atoms of the filling, ie atomic states of various excitation levels are occupied. In the case of neon, this excitation includes, for example, the neon lines in the red area of the optical spectrum. In contrast to this, the use of the dielectric barrier discharge and particularly the use of the pulsed dielectric barrier discharge permits selective coupling of the energy in such a way that essentially only the resonance level and a few levels in the immediate vicinity of the resonance level are excited. As a result of further collisions, the atoms in metastable states very efficiently form short-lived, excited molecules, so-called excimers, in the case of neon, for example, Ne ₂ ^* . When the excimers decay, molecular band radiation arises. Noble gas excimers emit in the UV and VUV range of the spectrum. For example, Ne ₂ ^{* has} an intensity maximum at approximately 85 nm. This short-wave invisible radiation can be converted into visible radiation, in the aforementioned example in the yellow spectral range, by phosphors, for example Y ₃ Al ₅ O ₁₂ : Ce.

This effect is achieved with phosphors with high excitability in the area of Excimer emission particularly clear. This creates a new, independent Possibility to set the color location opened.

In the event that the dielectric barrier discharge as well as the unobstructed Discharge is operated pulsed, the two pulse trains synchronized with each other in order to ensure that lamp operation is uniform over time to ensure. In a simplified variant, this is achieved by that the same sequence of voltage pulses both for generating the dielectrically disabled as well as the dielectrically unimpeded discharge is used.

In a preferred embodiment of the method, the pulsed dielectric disabled unloaded unloaded unloading in time upstream that enough starting electrons for the unhindered Unloading be provided. This way, the disabled Discharge - in addition to the advantage of independent adjustability the spectral distribution of the emitted radiation - necessary for the operation of the required voltage can be reduced.

A permanent lowering of the necessary voltage pulses for the Unhindered discharge can be achieved by the fact that the dielectric pulses applied to those of the galvanic electrodes Lead electrodes in time. However, this requires either two synchronizable supply devices or a specific measure, around the two pulse sequences in the desired manner to postpone.

This disadvantage is caused in a preferred variant of the method avoided that firstly the same sequence of voltage pulses both for Generation of the dielectrically handicapped as well as the unhindered discharge is used. Second, the electrode configurations are targeted chosen so that the ignition voltage of the dielectric barrier discharge is smaller than that of the unhindered discharge. To meet the The first requirement is the current supply of a galvanic and a dielectric electrode electrically contacted with each other. The second condition requires a sufficiently short distance between the dielectrically handicapped electrodes compared to the unhindered. In the case of tubular discharge vessels with longitudinally arranged ones This can be easily accomplished by galvanic electrodes, for example two electrodes on the outer wall of the vessel transverse to be ordered.

Through these measures it is achieved that first a dielectric barrier Discharge uses, which on the one hand efficiently stimulates fluorescent UV or. VUV radiation generated and on the other hand the operating voltage of the unhindered discharge reduced.

The invention, for the operation according to the invention explained above Discharge lamp suitable method shows in the simplest Only one version apart from the two galvanic electrodes additional third electrode. A first of the two galvanic electrodes takes on two functions in this case. For one, it serves how usual, together with the second galvanic electrode of the generation conventional unhindered unloading. On the other hand, it serves together with the additional third electrode generating a one-sided dielectric barrier discharge. For this purpose the third Electrode must necessarily be a dielectric electrode. Moreover it is also advantageous in accordance with the teaching of WO 94/23442 Anode potential with respect to the corresponding unobstructed counter electrode connected.

If the luminance distribution of the lamp and consequently also symmetrical discharge conditions within the discharge vessel if desired, an additional fourth electrode is advantageous. The fourth, dielectric electrode then also serves together with the third dielectric electrode generating a double-sided dielectric disabled discharge. Another advantage of the arrangement with two dielectric and two galvanic electrodes there is the possibility the mean power coupling of both discharges independently of one another to be able to choose. This results in an even greater freedom in the Setting the spectral distribution or the color locus.

The shape of the dielectric electrodes is advantageously based on the shape of the Discharge vessel adapted. Suitable for tubular discharge vessels there are, for example, strip-shaped metallic electrodes that run along the Lamp longitudinal axis are arranged.

In a low-cost version, the dielectric electrode (s) is (are) arranged on the outer wall of the discharge vessel, e.g. as applied metal strip or vapor-deposited thin strip-like metal layer (s). The advantage of this solution is that additional gas-tight Bushings and dielectric layers can be omitted. As A conventional lamp can serve as the starting point. In a more elaborate one The variant is (are) the metal strips in the outer wall of the discharge vessel embedded or embedded or completely in included the wall of the discharge vessel. Through these measures the metal strips are fixed with the discharge lamp. The disadvantage is an increased manufacturing effort and thus higher costs.

In a variant of this embodiment, the dielectric electrodes are included one of the current leads of the galvanic electrodes is connected. The Advantage compared to separate power supply for the electrodes is that only a single supply device is required for both discharges is. On the other hand, a separate supply for the galvanic or dielectric electrodes the possibility of the respective supply device to the special requirements of the type of discharge in question optimize.

In the case of a single dielectric electrode, it is particularly suitable a metal strip tapered on one side. The metal strip is advantageous connected to the galvanic electrode of which the tapered End pointing away. This will make one along the entire strip and almost in the direction of the corresponding galvanic counter electrode uniform unilaterally dielectric discharge guaranteed.

In one embodiment of the lamp for automotive engineering, a tubular discharge vessel contains neon with a filling pressure in the range between approximately 1 kPa and 200 kPa, preferably between approximately 5 kPa and 50 kPa. The inner wall of the discharge vessel is provided with a VUV-stimulable phosphor, for example Y ₃ Al ₅ O ₁₂ : Ce. The galvanic electrodes are realized by two mutually opposite electrodes, in particular cold cathodes, which are arranged within the discharge vessel. At least one metal electrode, in particular at least one metal strip, is attached as the dielectric electrode (s) on the outer wall of the discharge vessel. When operated according to the method according to the invention, the lamp lights up yellow and serves as a flashing light.

Fig. 1

eine rohrförmige Leuchtstofflampe mit galvanischen Elektroden gemäß dem Stand der Technik sowie ein Betriebsgerät zum Betreiben dieser Lampe,

Fig. 2

eine erfindungsgemäße rohrförmige Leuchtstofflampe mit galvanischen Elektroden und zwei damit verbundenen dielektrischen Elektroden,

Fig. 3

wie Figur 2, aber mit voneinander elektrisch getrennt versorgten galvanischen bzw. dielektrischen Elektroden,

Fig. 4

wie Figur 2, aber mit nur einem als dielektrische Elektrode wirkenden einseitig verjüngten Metallstreifen,

Fig. 5

einen Vergleich der Farbkoordinaten der Lampe aus Figur 4 bei unterschiedlichen Betriebsweisen.

The invention is explained in more detail below with the aid of a few exemplary embodiments. Show it

Fig. 1

a tubular fluorescent lamp with galvanic electrodes according to the prior art and an operating device for operating this lamp,

Fig. 2

a tubular fluorescent lamp according to the invention with galvanic electrodes and two dielectric electrodes connected thereto,

Fig. 3

as in FIG. 2, but with galvanic or dielectric electrodes supplied separately from each other,

Fig. 4

like FIG. 2, but with only one metal strip tapering on one side as a dielectric electrode,

Fig. 5

a comparison of the color coordinates of the lamp from FIG. 4 with different operating modes.

In Figure 1, a tubular fluorescent lamp 1 according to the prior art and a ballast 2 for operating this lamp is shown schematically. The fluorescent lamp 1 consists of a circular cylindrical discharge vessel 3 closed on both sides, the inner wall of which is coated with a fluorescent layer 4 made of Y ₃ Al ₅ O ₁₂ : Ce, and two metallic electrodes 5, 6 ("galvanic electrodes") arranged inside the discharge vessel 3. The length of the discharge vessel 3 made of tempered glass is approximately 315 mm, the inner diameter approximately 3 mm and the thickness of the vessel wall approximately 1 mm. Within the discharge vessel 3 there is neon with a filling pressure of approx. 13.3 kPa. The two cup-shaped electrodes 5, 6 are oriented in the direction of the lamp longitudinal axis and face each other at a distance of about 305 mm. The electrodes 5, 6 are each connected to a power supply 7, 8, which are guided gas-tight from the ends of the discharge vessel 3 to the outside. The ballast 2 consists of a generator 9 and a high-voltage transformer 10. The secondary winding 11 of the high-voltage transformer 10 is connected to the electrodes 5, 6 via the current leads 7, 8.

In the figures explained below, the same reference numbers are used same features and are therefore not explicitly described again.

Figure 2 shows an embodiment of a tubular according to the invention Fluorescent lamp in a schematic representation. In contrast to The fluorescent lamp 12 in FIG. 2 additionally has the prior art in FIG. 1 two dielectric electrodes 13, 14. The dielectric electrodes 13, 14 each consist of a metal strip and are diametrical to each other and each parallel to the lamp's longitudinal axis on the outer wall of the discharge vessel 3 applied. The width of the metal strip is approx. 2 mm. The metal strips 13, 14 are provided with power leads 15, 16 connected, which in turn each with a power supply 7 or 8 of the galvanic electrodes are contacted. The metal strips 13, 14 extend each of the electrodes 5, 6 connected to them and via a Partial length of the discharge vessel 3. These measures ensure adequate Distances between metal strips 13, 14 and galvanic electrodes 6.5 with opposite potential. This way you become unwanted parasitic discharges between metal strips 13, 14 and galvanic Electrodes 6.5 prevented. Burns as desired within the Discharge vessel 3 along both sides dielectrically impeded discharge of the entire area in which the metal strips 13, 14 face each other directly. Consequently, the phosphor layer 4 is almost over Entire length of the discharge vessel 3 excited to luminescence.

In Figure 3 is another embodiment of an inventive tubular fluorescent lamp shown schematically. In contrast to Fluorescent lamp 12 in FIG. 2 is for fluorescent lamp 19 in FIG. 3 the dielectric electrodes 17, 18 not with the galvanic electrodes 5,6 connected, but with the secondary coil 20 of an additional ballast 21. The ballast 21 for the dielectric electrodes 17, 18 is with the ballast 2 for the galvanic electrodes 5.6 over the Synchronization line 22 synchronized.

Figure 4 shows an embodiment of a tubular according to the invention Fluorescent lamp 23 with only one dielectric electrode 24. The dielectric Electrode 24 consists of a metal strip tapered on one side, which is glued to the outer wall of the discharge vessel 3. The trapeze-like at its corners rounded metal strip 24 is in common with a first galvanic electrode 6 with one pole of the secondary coil 11 of the high-voltage transformer 2 connected. The metal strip 24 is parallel oriented to the longitudinal axis of the lamp 23, the tapered end 24a away from the first galvanic electrode 6 and to the second galvanic Electrode 5, the counter electrode shows. The second galvanic electrode 5 is connected to the other pole of the secondary coil 25. In this way is achieved that a unilaterally dielectric discharge between Metal strip 24 and second galvanic electrode 5 burns in the longitudinal direction distributed almost evenly.

The benefit of the invention using the example of use as a flashing light in automotive engineering is clear from FIG. 5 with regard to the adjustability of the color location and from the table with regard to the reduction in the voltage pulses. FIG. 5 shows the color coordinates of the lamp from FIG. 4, measured during operation in accordance with the method according to the invention (measuring point A), ie with unimpeded and additionally dielectrically impeded discharge. In comparison, measuring point B shows the color coordinates measured during operation according to the conventional method, ie only with unimpeded discharge. In order to implement the conventional method, the current leads 15, 16 of the two dielectric electrodes 13, 14 of the fluorescent lamp 12 are cut. The measuring point C finally marks the case of the purely dielectric impeded discharge, the current leads 7, 8 of the two galvanic electrodes 5, 6 of the fluorescent lamp 12 being disconnected. In the examples shown, one and the same ballast 9 is used for all three operating methods. The ballast 9 supplies unipolar, negative, half-sine-like voltage pulses with pulse widths of approximately 1 µs and pauses of 50 µs. The SAEJ578 and ECE coordinates are also shown, which define the requirements for the color locus of automotive flashing lights for the US and European markets. It can be clearly seen how, with the help of the invention, the color locus is specifically shifted in the direction of the ECE color area. With the same power input (40 W), approximately the same luminous flux (approx. 390 lm) is achieved for measuring points A and B. At the same time, the required voltage pulse size is reduced from approx. 8.5 kV to 5.2 kV. As a result, the effort for shielding electromagnetic interference radiation can be considerably reduced. Furthermore, the high-voltage transformer and the switching elements of the ballast 9 can be dimensioned correspondingly smaller, which above all offers cost advantages. For the purely dielectric impeded discharge, only 10 W are coupled in at pulse voltages of approx. 6 kV and the luminous flux reaches 70 lm when using the phosphor Y ₃ Al ₅ O ₁₂ : Ce. The values mentioned are summarized in the table below for all three operating methods. Comparison of some operating data for the measuring points shown in FIG. 5. measuring point A B C operating procedures unhindered + dielectric disabled (according to the invention) unhindered (conventional) Dielectric. with special needs pulse height 5.2 kV 8.5 kV 6 kV elec. power 40 W. 40 W. 10 W. Luminous flux 391 lm 390 lm 70 lm

Claims (9)

1. Method for operating discharge lamps (12; 19; 23) having a discharge vessel (3), a dielectrically unimpeded pulsed discharge being generated by means of a train of voltage pulses inside the discharge vessel (3), characterized in that inside the discharge vessel (3) a dielectrically impeded discharge is additionally generated and, as a result, the spectral distribution of the radiation emitted by the discharge lamp (12; 19; 23) is specifically influenced, and the level of the voltage pulses which is required for the dielectrically unimpeded pulsed discharge is reduced in such a way that the required level is lower with an additional, dielectrically impeded discharge than without an additional, dielectrically impeded discharge.
2. Method according to Claim 1, characterized in that the dielectrically impeded discharge is generated by a train of voltage pulses, the individual voltage pulses respectively being separated from one another by dead times.
3. Method according to Claim 2, characterized in that the pulse width is in the region of between 0.1 µs and 50 µs, and the pulse/dead time ratio is in the region of between 0.001 and 0.1.
4. Method according to Claim 2, characterized in that the train of voltage pulses for generating the unimpeded discharge is synchronized with the train of voltage pulses for generating the dielectrically impeded discharge.
5. Method according to Claim 4, characterized in that the train of voltage pulses for generating the dielectrically impeded discharge is positioned in time ahead of the train of voltage pulses for generating the unimpeded discharge.
6. Method according to Claim 2, characterized in that the same train of voltage pulses is used for generating both the dielectrically impeded and the dielectrically unimpeded discharges.
7. Method according to Claim 1, characterized in that the ratio of the electric powers coupled into the unimpeded and impeded discharges is in the region of between 0.01 and 100.
8. Method according to Claim 7, characterized in that the ratio is preferably in the region of between 0.5 and 10.
9. Method according to Claim 1, characterized in that the discharge vessel (3) is provided with a fluorescent coating (4) in order thereby to support the influencing of the spectral distribution of the radiation emitted by the discharge lamp (12; 19; 24), and/or the colour locus of the discharge lamp (12; 19; 24).

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