DE102007054330A1 - Ballast with DBD lamp - Google Patents

Abstract

The invention relates to a lighting system comprising a DBD lamp (DBD) and an electronic ballast having a square-wave converter (S1-S4) and a charging inductance (L1, L2).

Description

Technical area

The The invention relates to a lighting system with a combination from an electronic ballast and a DBD lamp, ie lamp for dielectrically impeded discharges (DBD: Dielectric Barrier Discharge).

State of the art

For dielectrically impeded discharges designed lamps, hereinafter short DBD lamps, are intensified for several years in development and application. This applies, for example, relatively large-format, very flat lamps, for example for monitor backlighting, which are referred to below as flat radiator, or also line-shaped DBD lamps. In addition to classic lamps that over Phosphors generate visible light, DBD lamps are included in various designs also used as UV lamps, for example for sterilization, for technical processes, such as plastic hardening, or for office automation.

DBD lamps are basically using electronic ballasts controlled and operated, because only so the necessary ignition voltages and Operating voltages can be generated. It will be short power injection pulses of relatively high frequency of typically coupled to some 10 kHz, each a single Discharge process in the DBD lamp. The single ones Discharge processes are by the internal Gegenpolarisation stopped due to the charging of the dielectric layers, wherein the individual discharge processes by discharge-free Intermediate phases are separated.

For corresponding ballasts are already different Transducer topologies have been used, in particular class E converter and flux transformers with connected transformers. These ballasts have fulfilled the requirements placed on them in principle, However, they are relatively expensive and their efficiency definitely still capable of improvement. In the design of such ballasts must pay particular attention to the strong capacitive nature of DBD lamps Be considered.

The EP 1 753 272 A2 shows a comparison with this prior art already improved converter topology, namely constructed of switching transistors half bridges and full bridges with charging inductances, but without transformers. Thus, the ballasts have already been significantly simplified and improved efficiencies can be achieved.

Presentation of the invention

Of the Invention is the technical problem underlying this state of Improve technology.

The The invention relates to a lighting system with an electronic Ballast and a DBD lamp, the electronic Ballast comprises: a square wave converter for outputting a Transducer output potential at a lamp terminal by clocked Switching between two converter input potentials, the converter at least two switching transistors for the clocked switching and switched terminals of the switching transistors galvanically connected to one pole of the lamp terminal are connected, and a lamp-serial charging inductance between a pole of the lamp connection and a switched connection of one of the Switching transistors, characterized in that the switching transistors in the opened state unidirectionally bridged by diodes are so that the diodes each between one on the switching transistor applied transducer input potential and the converter output potential lie, and the lighting system because of a relative to the lamp sufficiently small charging inductance value so damped is that in the fired continuous operation the amplitude of the first current overshoot peak after the Main current peak is at most a third of this.

preferred Embodiments of this lighting system are in the dependent Claims specified.

As already mentioned at the beginning, DBD lamps are also used for generating invisible light, in particular UV light. Thus, with the term "lighting system" is also a UV illumination meant. The term refers to operable Combinations of electronic ballasts and DBD lamps in the General.

The basic idea of the invention is that of the prior art EP 1 753 272 A2 known schalttransistoreriellen diodes, there referred to as "current valves" to save. Instead, the switching transistors should be bypassed in the open state in one direction, either by additional parallel-connected diodes or by transistor intrinsic diodes (body diodes of FETs). This bridging should be provided in fact Lich without current valves in the corresponding transformer branch, the bridging diodes should therefore lie between a transducer input potential and the converter output potential. The invention should therefore not include the use of FETs in the cited prior art, because there the Bodydioden the switching transistors not between Transducer input potential and converter output potential bypass, because of the respective flow control valves.

The in the prior art provided function of the flow control valves, an excessive back swing from energy through by charging inductance and capacitive Lamp to avoid formed resonant circuit is inventively characterized realizes that the charging inductance value is relatively small is measured. This results in a corresponding attenuation of the resonant circuit and thus limitation of the return oscillation of energy in the converter branches. Quantitatively, this is how it should be be dimensioned that in the current / time diagram of the lamp current the the first main current peak following first overshoot point with inverse polarity at most one third of the Amplitude of the main current peak is. Preferably the current peak ratio even less than 1: 4. there should pass through the swinging lamp current until the next Discharge ignition defined current serve as a reference.

The Substitute circuit diagram of a DBD lamp can in simplified form as Parallel connection of a series connection of a first capacitor and an ohmic resistor on the one hand and a second capacitor on the other hand be written. The second capacity describes the capacitive character of the lamp in the unfired state.

Of the capacitive character increases during and after ignition, because free charge carriers are generated in the discharge space. Therefore, the first capacity is in series with the ohmic Resistance then effective when the lamp is ignited and is. It therefore essentially corresponds to the capacity of the discharge plasma.

Of the ohmic resistance is temporally variable, namely before ignition practically infinite, and falls significantly during the ignition process. After fading away the discharge increases this resistance again. Even while The actual discharge process can not be of one in the strict sense time constant ohmic resistance in the equivalent circuit diagram become. For understanding but is an equivalent circuit diagram a classic constant ohmic resistance during the actual discharge process helpful.

at the explanation of the embodiment will illustrated that starting from this simplified image the damping of the oscillation with increasing value of the charging inductance and decreasing value of lamp capacitance and ohmic Replacement resistance decreases. So for a given lamp can by a sufficiently small charging inductance a relative high attenuation can be ensured.

to Explanation should be noted that because of the earlier than second Capacity also referred to capacitive effect of the lamp in the unfired state already before the ignition an LC resonant circuit exists. However, the first capacity is significantly larger than the second for DBD lamps, so that in the ignited state the simplified image of a through ohmic losses in the ohmic resistance of the equivalent circuit diagram damped LC resonant circuit the essential part of Reality describes.

The Charge inductance can, of course, as already in mentioned in the prior art, from more than be constructed a single component. The previous statements refer to the inductance value sum. Furthermore The charging inductance is the replacement for one Transformer saved according to the invention shall be. Accordingly, in positive terms, between switched terminals of the switching transistors and a pole of the lamp terminal of the converter a galvanic Connection exist.

advantageously, the charging inductance is for reasons of symmetrization distributed over a plurality of components. In particular, it may be two charging inductances symmetrical to both sides of the lamp act.

The Invention thus has the advantage of the current valve diodes as components to be able to save. Furthermore, she leaves by the Abandonment of these diodes a back swing basically to. This can be, for example, late or non-igniting Lamps are relevant. In the described prior art rocks by the blocking effect of the flow valves that of the converter Energy pumped into and out of the resonant circuit In particular, the lamp voltage increases theoretically unlimited. If the lamp does not light in time, can there are problematic surges.

at This behavior is significantly less in the present invention critical, because the rectifying effect of the flow control valves is missing. Thus, the converter can certainly by resonance peaks is higher voltages in the resonant circuit, however, is he does not insist on a theoretically unchecked increase in tension because the energy is flowing back can. On the other hand, by the sufficient damping in normal operation too much energy swinging back avoided and thus ensured a very good efficiency become.

In the prior art are transistor Half bridges and full bridges mentioned. Also in the present invention form transistor full bridges a particularly preferred embodiment of the converter according to the invention. Another preferred embodiment is multilevel inverters, especially those of the "cascaded cell type".

When General term for the eligible converter is used here the term of the "square-wave converter", of course also includes half bridges, namely all converters by switching clocking of switching transistors with switched connections to supply potentials one approximately rectangular converter output potential value produce. Under a switched connection is here by the way a connection of the switched path of the transistor understood, about a source or drain terminal in a FET or an emitter or collector terminal in a bipolar transistor.

there Preferably only the extreme values of the converter output potential values are to be used be accepted, so no intermediate stages. This applies in particular the Cascaded Cell multilevel inverter, which also works with intermediate stages the transducer output potential values can work. (Naturally Here, in a simplified image, it becomes firmer and more constant over time Converter output potential values argued. Of course it works just for the qualitative behavior.)

In spite of Waiver of the transformer remain as a result of resonance peaks by excitation of the LC resonant circuit with respect to the voltage significantly increased lamp voltages between the supply potentials readily possible, however, can be with a transformer in principle, larger voltage translations achieve. Therefore, an inventive requires Circuit compared to transducer topologies equipped with transformers u. U. higher supply voltages of the converter.

Preferably if these are provided in a DC link, wherein the intermediate circuit voltage by a power factor correction circuit is produced. In particular, a boost converter comes into consideration. This can be in a simple way DC link voltages, for example on the order of 1 kV, so that it is not crucial to a high transformation ratio arrives. In particular, converter input potentials are preferred 0.6 kV, more preferably above 0.7 kV or 0.8 kV.

Of the required for the increased DC link voltage But effort is by the way very simple converter topology justified without further ado. In particular, the waiver means on a transformer the accessibility also very low Operating frequencies, if desired, and the omission of Isolation problems and iron or copper losses in the magnetic Components. Also, the voltage rise rates can be at the lamp, which are important for the lamp efficiency, Favorable through targeted choice of charging inductances optimize. Here would be stray inductances of a Transformers disturb. Cost and volume reduction come So to add benefits.

In The described prior art mentions that depending on the dielectric strength of the available switching transistors in each converter branch, ie between converter input potential and converter output potential, each also a plurality of transistors can be connected in series. This applies to the present invention as well. Preferred are however, topologies with only one switching transistor per Wandlerast.

Prefers is also on additional ignition aids such as Ignition electrodes u. Ä. to give up and the through the LC resonant circuit possible resonance peak to use the lamp voltage.

Furthermore is the application of the invention to flat radiator, so relative large lamps with relatively large capacities, very particularly preferred.

Brief description of the drawings

in the Below is an embodiment for illustration explained the invention, wherein the individual features as well in other combinations may be essential to the invention. As a precaution, it should be noted that the previous and following Implicit implicit also on a procedure for operating a DBD lamp, a ballast and a built-up Lighting system relates.

1 shows a simple schematic diagram of an embodiment of the invention.

2 shows an equivalent circuit diagram of a DBD lamp 1 ,

3 shows a current / time history and a voltage / time history to the circuit diagram 1 ,

Preferred embodiment the invention

In 1 is left symbolically as a DC voltage source, a known step-up converter as a power factor correction circuit for generating a DC link voltage shown. The DC link voltage, which is represented by the DC voltage source, is about 0.9 kV. she lies between a in 1 lower and upper horizontal branch, wherein between the branches a full bridge of four switching transistors S1-S4 is located. In this case, the switching transistors S1 and S2 on the one hand and S3 and S4 on the other hand in each case in series with each other and between the two branches. Between the center tap between S1 and S2 on the one hand and the center tap between S3 and S4 on the other hand is the converter output voltage.

Between these center taps, a dielectrically impeded discharge lamp designated by the reference symbol DBD is accordingly connected. This is a flat radiator with 32 '' diagonal and about 0.28 m ² surface, which is offered by the OSRAM GmbH, Munich, under the brand "Planon".

The DBD lamp is connected to the two center taps each intermediate charging inductances L1 and L2 of each 6 μH connected. Both inductors form together have an effective total charging inductance of 12 μH, but is distributed for symmetrization on two components.

2 shows the already mentioned above equivalent circuit diagram of the DBD lamp with a first inductance C1 and a second inductance C2 and a time-varying ohmic resistance R1. The equivalent circuit diagram of the lamp used concretely here has a second capacitance C2 of approximately 200 pF which is effective in the non-ignited state of the lamp and an approximately one order of magnitude greater first capacitance C1 of 2200 pF in series with the ohmic resistance. The standing for the power losses in the discharge resistance R1 during discharge is a little 242 Ω, this value is time variable, so again increases as the discharge dies, between the individual discharge pulses practically infinitely large and also somewhat depends on the performance, with the lamp is operated. DBD lamps are dimmable over a certain range, with the ohmic resistance decreases slightly with a constant lamp, increasing the average lamp power. At the given data, the lamp is operated at about 135 W, with the total power consumption of an experimental setup being about 150W.

In the simple image of an LC resonant circuit dominated by the first capacitance C1, that is to say neglected in the ignited state of the second capacitance C2, the following results for a supercritical damping of the LC resonant circuit: L1 + L2 <(R1 2 × C1) / 4

In the present case, this means that the sum of L1 and L2 for supercritical damping should be less than 32.2 μH, which is obviously true. However, this is only a roughly approximated quantitative assessment. In fact, the in 3 illustrated current and voltage / time course diagrams of the lamp current i _lamp and v _lamp after the respective main peaks - in 3 denoted by i _max or v _max - still slight overshoot peaks to the opposite polarity. These are in the amplitude ratio here on the order of one fifth to one sixth of the current and one fifth of the voltage.

At the in 1 drawn switching transistors S1-S4 are in this embodiment, IGBTs, which, such as 1 shows antiparallel diodes D1-D4 are switched on. If, for example, FET were used here, this function could be achieved by the intrinsic body diode. Accordingly, it may be in the 3 shown backward swing, namely the polarity inverse peak in the time courses come. This in 3 At 50% duty cycle can in principle have other values.

Compared to the cited prior art EP 1 753 272 A2 It should be noted that there is achieved by the flow control valves a "damping" of the Rückschwingverhaltens. The actual "ohmic" throttling of the LC resonant circuit is weaker there. So is for the embodiment in the local 4 a total charging inductance of 208 μH is given for comparable DBD lamp.

The Effect of the flow control valves is in the EP document u. a. in paragraph 0018 explained. The rising currents described there and voltage values are based on the blocking effect of the local current valve diodes. In the present case, these flow control valves are deliberately omitted and instead designed the charging inductance much smaller. The Advantages of this procedure have already been explained. Furthermore However, the explanations in the EP document apply mutatis mutandis, for the present invention.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - EP 1753272 A2 [0005, 0010, 0041]

Claims (10)

Lighting system with an electronic ballast and a DBD lamp (DBD), wherein the electronic ballast comprises: - a rectangular converter (S1-S4) for outputting a Wandlerausgangspotentials at a lamp terminal by clocked switching between two converter input potentials, wherein the converter at least two switching transistors (S1 -S4) for the clocked switching and switched terminals of the switching transistors (S1-S4) are galvanically connected to one pole of the lamp terminal, and - a lampenserielle charging inductance (L1, L2) between a pole of the lamp terminal and a switched terminal of one of the switching transistors ( S1-S4), characterized in that the switching transistors (S1-S4) are unidirectionally bypassed in the open state by diodes (D1-D4), so that the diodes (D1-D4) are each connected between one on the switching transistor (S1-S4) applied transducer input potential and the converter output potential Because of a charge inductance value (L1 + L2) sufficiently small in relation to the lamp, the illumination system is so attenuated that in continuous firing operation the amplitude of the first current overshoot peak after the main current peak is at most one third of that. Lighting system according to claim 1, wherein the lamp (DBD) symmetrical between two forming the charging inductance Inductances (L1, L2) is connected. Lighting system according to claim 1 or 2, wherein the square-wave converter (S1-S4) has a transistor full-bridge is. Illumination system according to claim 3, wherein the rectangular converter (S1-S4) is designed so that the converter output potential is switched between its extreme values without intermediate steps. Illumination system according to one of the preceding claims with a power factor correction circuit for generating converter input potentials. Lighting system according to claim 5, wherein the power factor correction circuit is a boost converter. Lighting system according to claim 5 or 6, wherein the voltage between the converter input potentials at least 0.6 kV. Illumination system according to one of the preceding claims, wherein each transducer branch is between a transducer input potential and a converter output potential, only one switching transistor at a time (S1-S4). Illumination system according to one of the preceding claims, which is designed to the DBD lamp (DBD) only by resonance peaking without to ignite additional aids. Illumination system according to one of the preceding claims, where the DBD lamp (DBD) is a flat radiator.