High-pressure discharge lamp with an auxiliary ignition electrode as well as circuitry and process for operation

Abstract

The invention relates to a switching arrangement and a method for operating a high-pressure discharge lamp, and to a lighting system comprising a high-pressure discharge lamp and its operating circuit. The switching arrangement comprises a voltage transformer (T1, T2), preferably a push-pull voltage transformer; a transformer (TR1) connected to the output of the voltage transformer; a pulse-operated ignition device and a load circuit designed as a series resonant circuit (L1, C1) into which the high-pressure discharge lamp (LP) is connected. The transformer (TR1) has at least two secondary windings (w1c, w1d), of which the first secondary winding (w1c) is connected to the load circuit and the second secondary winding (w1d) is connected to the voltage input of the pulse-operated ignition device. The ignition voltage output of the pulse ignition device is connected to the ignition auxiliary electrode (ZE) of the high-pressure discharge lamp (LP). à

Description

The invention relates to a switching arrangement and a method for operating a high-pressure discharge lamp, as well as to a lighting system comprising a high-pressure discharge lamp and its operating circuit. The switching arrangement comprises - a voltage converter that produces alternating voltage, - a transformer connected to the voltage converter, - a pulsed ignition circuit for the high-pressure discharge lamp, which pulsed ignition circuit has a voltage input and an ignition voltage output, - a load circuit designed as a series resonant circuit, into which the high-pressure discharge lamp is connected, and which comprises at least one inductance and at least one capacitor. The invention relates in particular to a circuit arrangement for a low-power, metal halide, high-pressure discharge lamp, for example used in motor vehicle headlights, which has a nominal power of typically about 35 W, and to a lighting system comprising a low-power, metal halide, high-pressure discharge lamp and an operating circuit adapted thereto. The high-pressure discharge lamp has a quartz glass discharge vessel, which is sealed gas-tight with molybdenum foil inserts and is surrounded by an outer cover. Two gas discharge electrodes extend into the discharge space, which are electrically connected to the external current supply lines by molybdenum foil inserts. The ionizable charge of this lamp, which is sealed in the discharge space, consists of xenon and metal halides. The operating circuit for operating the high-pressure discharge lamp used in the headlights of motor vehicles, or the switching arrangement located in the operating circuit, is usually supplied with electrical energy by the vehicle's electrical system. This means that the switching arrangement is supplied with a low-voltage voltage source, typically 12 V or 24 V DC. The switching arrangement must transform the DC voltage supplied by the vehicle's electrical system to meet the requirements for the operation of the lamp. For example, a few kilovolts are required to ignite a high-pressure discharge lamp in a cold state, while an ignition voltage of approximately 20 kV is required to re-ignite the same high-pressure discharge lamp when it is still hot. After ignition, the operating voltage of the high-pressure discharge lamp, i.e. the voltage drop required in the discharge section to maintain the arc discharge, is still approximately 80-100 V. EP 0 294 604 describes a circuit arrangement for operating a high-pressure discharge lamp with a low-voltage voltage source, in particular for operating a 35 W metal halide high-pressure discharge lamp with a 12 V vehicle network. This circuit arrangement includes a self-oscillating push-pull voltage converter which comprises two alternately switched power transistors and two transformers. One transformer is part of the control circuit of the power transistors, while the other transformer serves to transfer the medium-frequency oscillation of the push-pull voltage converter to a series resonant circuit. The high-pressure discharge lamp or the discharge section of the high-pressure discharge lamp is connected in a parallel circuit with the capacitor of the series resonant circuit.The primary winding of the transformer of the control circuit is connected in series with the secondary winding of the transformer supplying the series resonant circuit, in order to adapt the control of the push-pull voltage converter to the lamp to be operated. The circuit arrangement also includes a circuit for changing the time constants of the control circuits of the push-pull voltage converter, in order to stabilize the lamp power in the event of changes in the operating voltage, and to provide an increased starting current during the warm-up phase of the high-pressure discharge lamp. To ignite the high-pressure discharge lamp, a sinusoidal alternating voltage with a frequency of 45 kHz and an amplitude of about 18 kV is generated by resonant voltage boosting across the capacitor of the series resonant circuit, which ignites the lamp within a time interval of 6 ms. US Patent No. 5,036,256 describes a circuit arrangement for a high-pressure discharge lamp, which can be used, for example, in a motor vehicle headlight. This circuit arrangement includes a push-pull voltage converter supplied from a low-voltage voltage source and comprising two switching transistors and a transformer. The transformer of the push-pull voltage converter transfers the high-frequency output voltage of the voltage converter to the load circuit in which the high-pressure discharge lamp is connected. The frequency of this output voltage is approximately 20 kHz. The high-frequency induction voltage on the secondary winding of the transformer of the push-pull voltage converter is converted by a bridge rectifier into a direct voltage required for the direct current operation of the high-pressure discharge lamp.For igniting the high-pressure discharge lamp, the circuit arrangement comprises a pulsed ignition circuit which comprises a spark gap, a surge capacitor and a pulse transformer and which generates ignition voltage pulses of up to 30 kV at the main electrodes through the discharge section of the high-pressure discharge lamp. The secondary windings of the pulse transformer are connected in series with the discharge section of the high-pressure discharge lamp, so that after the lamp has been ignited, the entire operating current flows through the secondary windings of the pulse transformer. The circuit arrangement described in the above-mentioned US patent specification further comprises a voltage multiplier consisting of a plurality of diodes and capacitors, after which a storage capacitor is connected in order to provide the transfer energy required for a reliable transition from the glow discharge to the arc discharge. The object of our invention is to provide an improved circuit arrangement for operating a high-pressure discharge lamp. The first two of this circuit arrangement HU 221 364 Bl must enable flicker-free operation of a high-pressure discharge lamp installed in a motor vehicle headlight and must ensure reliable cold and hot ignition of this lamp and a rapid and safe transition from glow discharge to arc discharge. This object is achieved according to the invention in that the transformer has at least two secondary windings, of which the first secondary winding is connected to the load circuit, and the second secondary winding is connected to the voltage input of the pulse ignition circuit, and the ignition voltage output of the pulse ignition circuit is connected to the ignition auxiliary electrode of the high-pressure discharge lamp. The circuit arrangement according to the invention thus comprises a voltage converter which produces an alternating voltage; a transformer which is connected to the voltage converter and which transfers the alternating voltage produced by the voltage converter to the load circuit of the high-pressure discharge lamp which is designed as a series resonant circuit; and it further comprises a pulsed ignition circuit for the high-pressure discharge lamp. The transformer connected to the voltage converter has at least two secondary windings, of which the first secondary winding is connected to the load circuit and the second secondary winding is connected to the voltage input of the pulsed ignition circuit. The ignition voltage output of the pulsed ignition circuit is connected to the ignition auxiliary electrode of the high-pressure discharge lamp.The supply of voltage to the pulsed ignition circuit and the load circuit from the two secondary windings of the transformer connected to the voltage converter allows the ignition circuit to be separated from the load circuit, in which the series resonant circuit and the high-pressure discharge lamp are connected, so that after the lamp is ignited, the operating current of the high-pressure discharge lamp does not have to flow through the ignition circuit. The design of the ignition circuit can therefore be much more compact, since the elements of the ignition circuit do not have to withstand the relatively high amperage of the operating current during the starting phase and during the burning operation of the lamp. During the ignition phase and subsequent start-up phase of the high-pressure discharge lamp, the series resonant circuit, using the method of resonant voltage increase on the capacitor, provides the high-pressure discharge lamp with the transfer energy required for the transition from glow discharge to arc discharge.The separation of the ignition circuit and the load circuit as described above according to the invention is particularly advantageous in circuit arrangements for high-pressure discharge lamps used in vehicle headlights, since these lamps carry a particularly high current during the start-up phase, so that the start-up phase is shorter. The term start-up phase is understood here to mean the time interval from the ignition of the lamp until a quasi-stationary operating state is reached, in which operating state a stable arc discharge has been established in the lamp. In the case of a metal halide high-pressure discharge lamp with an electrical power of 35 W, which is usually used in vehicle headlights, an alternating voltage of between 500 and 1550 V with a resonance-increased voltage is preferably provided on the capacitor for the transition from the glow discharge to the arc discharge in the start-up and start-up phases. A push-pull voltage converter consisting of two switching transistors is preferably used as the voltage converter, which, together with a transformer connected to its output, enables the high-pressure discharge lamp to be operated from a low-voltage voltage source. This is particularly important when the high-pressure discharge lamp is used in vehicle headlights. The push-pull voltage converter and the transformer are used to transform the low-voltage voltage - for example the supply voltage of the vehicle network, which is typically 12 V or 24 V direct voltage - into a medium-frequency alternating voltage, the voltage amplitude of which on the secondary side of the transformer is approximately 500 V. The frequency of this alternating voltage is preferably greater than 200 kHz and preferably between 500 kHz and 3 MHz.In this advantageous frequency range, particularly flicker-free operation is possible for low-power, high-pressure discharge lamps used in motor vehicles. Furthermore, in this frequency range, sufficient interference suppression of the switching arrangement can still be achieved with acceptable effort. The transformer connected to the push-pull voltage converter has two primary windings, through which the supply current flows alternately during the switching cycle of the push-pull voltage converter. A capacitor is preferably connected in parallel with the primary windings of this transformer, which forms a resonant circuit with the primary windings of the transformer. The capacitance of this capacitor is preferably matched to the inductance of the transformer in such a way that a sinusoidal voltage is generated across this capacitor at a high switching frequency of the push-pull voltage converter. This significantly reduces the switching losses on the transistors of the push-pull voltage converter. In order to prevent longitudinal acoustic vibrations occurring in the discharge medium from disturbing the operation of the lamp, the alternating voltage generated by the voltage converter for the high-pressure discharge lamp is frequency modulated. The center frequency or carrier frequency of the frequency-modulated alternating voltage is preferably more than 300 kHz, and more preferably between 500 kHz and 2.9 MHz. The frequency step is preferably between 10 kHz and 100 kHz, and the modulation frequency is preferably between 100 Hz and 5 kHz. The object is achieved according to the invention in that the lighting system comprises a high-pressure discharge lamp and an associated operating circuit. The operating circuit comprises a switching arrangement. This switching arrangement comprises a voltage converter which converts an alternating voltage into a HU 221 364 Bl; a transformer connected to the voltage converter, which transfers the alternating voltage generated by the voltage converter to the load circuit of the high-pressure discharge lamp; a pulsed ignition circuit for the high-pressure discharge lamp and a series resonant circuit, the resonant capacitance of which is connected in parallel with the discharge section of the high-pressure discharge lamp. The transformer connected to the voltage converter has at least two secondary windings, of which the first secondary winding is connected to the series resonant circuit, the second secondary winding is connected to the voltage input of the pulsed ignition circuit. The high-pressure discharge lamp of the lighting system according to the invention has, in addition to the electrodes arranged in its discharge vessel, an additional ignition auxiliary electrode which is connected to the ignition voltage output of the pulsed ignition circuit and receives high-voltage pulses for the purpose of igniting the high-pressure discharge lamp. The ignition auxiliary electrode is preferably arranged outside the discharge vessel, so that the ignition pulses are capacitively coupled into the lamp. The ignition auxiliary electrode is preferably formed by a conductive layer which is applied to a lamp vessel, preferably to the outer shell of the high-pressure discharge lamp surrounding the discharge vessel. In high-pressure discharge lamps used in motor vehicle headlights, this conductive layer is also preferably designed as an optical aperture for producing a low beam. Our invention is described in more detail in relation to its two exemplary embodiments with the help of our figures, of which the Figure 1 is a schematic representation of the circuit arrangement according to the invention, Figure 2 is a schematic side view of a high-pressure discharge lamp equipped with an auxiliary ignition electrode and operated with the switching arrangement according to the invention, the Figure 3 is a schematic representation of a second embodiment of the switching arrangement according to the invention. Figure 1 shows a schematic diagram of the circuit principle of a circuit arrangement according to the invention for operating a metal halide high-pressure discharge lamp with an electrical power consumption of approximately 35 W. This circuit arrangement comprises a push-pull voltage converter, a load circuit and a pulsed ignition circuit for the high-pressure discharge lamp. The input of the push-pull voltage converter is supplied from a 12 V DC voltage source U. The high-pressure discharge lamp to be operated is connected to the load circuit. The push-pull voltage converter essentially consists of two field-effect transistors TI and T2, their control circuit A and a transformer TR1. The transformer TR1 has two primary windings wla, wlb and two secondary windings wlc, wld. The grounded negative pole of the DC voltage source U is connected to the source terminal of the two field-effect transistors TI and T2. The The positive terminal of the DC voltage source U is connected via a center tap M to the first terminal of the first primary winding of the transformer TR1, wla, on the one hand, and to the first terminal of the second primary winding of the transformer TR1, wlb, on the other hand. The second terminal of the first primary winding, wla, is connected to the drain terminal of the first field-effect transistor TI, and the second terminal of the second primary winding, wlb, is connected to the drain terminal of the second field-effect transistor T2. The first secondary winding, wlc, of the transformer TR1 is connected to the load circuit, while its second secondary winding, wld, is connected to the ignition circuit. In addition to the secondary winding wlc, the load circuit also contains an inductance L1, a capacitor Cl and two terminals for the LP high-pressure discharge lamp to be operated. The inductance L1 and the capacitor Cl form a series resonant circuit, which is supplied with medium-frequency alternating voltage by the secondary winding wlc of the transformer TR1. The metal halide LP high-pressure discharge lamp is connected to the load circuit in such a way that the discharge section defined by the electrode El, E2 is connected in parallel with the capacitor Cl. One terminal of the first secondary winding, wlc, is connected via the inductance L1 and the branch point VI to one terminal of the capacitor Cl and the electrode El of the LP high-pressure discharge lamp. The other terminal of the first secondary coil, wlc, is connected via the branch point V2 to the other terminal of the capacitor Cl and to the electrode E2 of the high-pressure discharge lamp LP. The pulse ignition circuit consists of a spark gap FS, a surge capacitor C3, a pulse transformer TR2, a rectifier diode Dl, an ohmic resistor R1, a field-effect transistor T3 and the second secondary winding wld of the transformer TR1. The first terminal of the second secondary winding wld is connected to the cathode of the rectifier diode Dl. The anode of the rectifier diode Dl is connected via the V3 branch point to the first terminal of the spark gap FS and to the first terminal of the primary winding w2a of the pulse transformer TR2. The second terminal of the primary winding w2a is connected via the V4 branch point to the first terminal of the secondary winding w2b of the pulse transformer TR2 and to one of the terminals of the surge capacitor C3. The other terminal of the surge capacitor C3 is connected to the second terminal of the spark gap FS and the ohmic resistor R1 via the branch point V5. The branch point V5 is at the same electrical potential as the branch point V2.The ohmic resistor R1 is connected to the second secondary winding wld of the transformer TR1 through the source-sink section of the field-effect transistor T3. The second terminal of the secondary winding w2b of the pulse transformer TR2 forms the ignition voltage output of the pulse ignition circuit and is connected to the ignition auxiliary electrode ZE of the high-pressure discharge lamp LP. The LP high-pressure discharge lamp shown in Figure 2 is a metal halide LP high-pressure discharge lamp with a single end and an electrical power consumption of approximately 35 W. HU 221 364 Β1 discharge lamp. This lamp, together with the control circuit coordinated with it, which includes the circuit arrangement shown in Figure 1, forms a lighting system that can be used in the headlights of motor vehicles. The LP high-pressure discharge lamp has a quartz glass discharge vessel 1, in which a gas-tight ionizable charge is enclosed. The ionizable charge contains xenon and metal halide compounds. The two ends of the discharge vessel 1, la and lb, are sealed with a molybdenum foil fusion 2a, 2b. Inside the discharge vessel 1, there are two electrodes, El and E2, between which a discharge arc is created during operation of the lamp, which produces light emission. The electrodes El and E2 are electrically connected to one of the current supplies 3a or 3b of the lamp head 4 by a molybdenum foil fusion 2a or 2b. The discharge vessel 1 is surrounded by a glass outer envelope 5. A detailed description of this LP high-pressure discharge lamp can be found, for example, in the publication EP 0 696 046.The auxiliary ignition electrode ZE is formed in this embodiment of the invention by a thin metal coating layer on the outer surface of the outer bulb 5. The thin metal coating layer is in the form of a long strip and extends from the end of the outer bulb 5 close to the lamp head 4 to approximately the height of the center of the discharge vessel 1, so that the end of the auxiliary ignition electrode ZE remote from the lamp head 4 is approximately the same distance from the two electrodes E1 and E2. The field-effect transistors TI and T2 controlled by the control circuit A alternately switch with a switching frequency of approximately 800 kHz, so that - without taking into account the capacitor C2 - the primary windings wla, wlb of the transformer TR1 are alternately connected to the 12 V DC voltage source U. An alternating current therefore flows through the primary windings wla, wlb whose frequency is the same as the switching frequency of the push-pull voltage converter. The capacitance of the capacitor C2 is matched to the inductance of the primary windings wla, wlb in such a way that the primary windings wla, wlb and the capacitor C2 form a resonant circuit at the frequency of the switching frequency of the push-pull voltage converter consisting of the field-effect transistors TI, T2, with the help of which the switching losses occurring in the field-effect transistors TI, T2 can be reduced. The voltage across the capacitor C2 is approximately sinusoidal.The voltage waveform on the primary windings wla, wlb describes a sinusoidal half-wave, the peak value of which is approximately 24 V due to the resonant voltage increase. The two primary windings, wla, wlb are inductively coupled to the two secondary windings, wlc, wld, of the transformer TR1. The primary windings wla, wlb have three turns each, the secondary windings wlc, wld have forty turns each, so that the alternating voltage produced by the push-pull voltage converter consisting of the field-effect transistors TI, T2 is transferred to the load circuit by the first secondary winding, wlc, and to the pulse-operated ignition circuit by the second secondary winding, wld, with a ratio of approximately 13:1. The peak voltage induced in the secondary windings wlc and wld is approximately 500 V. The frequencies of the induced voltages in the load circuit and the ignition circuit are the same as the frequency of the alternating voltage produced by the push-pull voltage converter consisting of the field-effect transistors TI, T2. To ignite the LP high-pressure discharge lamp, the pulse ignition circuit is activated by means of the field-effect transistor T3 (switching transistor). For this purpose, the control electrode of the field-effect transistor T3 is controlled by an integrated circuit (not shown), preferably a timing circuit. In the switched state of the field-effect transistor T3, the surge capacitor C3 is charged via the rectifier diode Dl and the primary winding 2a of the pulse transformer TR2, and then is discharged in a pulsed manner when the breakdown voltage of the spark gap FS is reached. The pulsed discharge currents of the shock capacitor C3 flow through the primary winding w2a of the pulse transformer TR2, and these currents are converted into high-voltage pulses by the secondary winding w2b, which are fed to the ignition auxiliary electrode ZE of the halogen-metal vapor LP high-pressure discharge lamp and capacitively coupled into the LP high-pressure discharge lamp.These high-voltage ignition pulses transmitted from the secondary coil w2b to the ignition auxiliary electrode ZE are unipolar and their polarization is positive in this embodiment. They reach peak values ​​of about 30 kV. Since the shock capacitor C3 and the primary coil w2a are designed as an oscillating circuit, each discharge of the shock capacitor C3 not only produces an ignition voltage pulse, but also triggers a whole series of high-voltage pulses for the ignition auxiliary electrode ZE. The first secondary winding, wlc, of the transformer TR1 supplies an input voltage of approximately 500 V to the load circuit, which contains the inductance L1 and the capacitor Cl of the resonance circuit and the connections for the LP high-pressure discharge lamp. The resonance circuit achieves a resonant voltage increase of approximately 500 to 1500 V of this input voltage. The energy stored in the resonance circuit is made available to the LP high-pressure discharge lamp as transfer energy immediately after ignition in order to ensure a rapid start-up of the lamp and, in particular, a rapid transition from glow discharge to arc discharge. The inductance L1 and the capacitor Cl of the resonance circuit are dimensioned in such a way that the available energy is optimally tuned to the LP high-pressure discharge lamp to be operated.In the embodiment discussed here, in the case of a 35 W metal halide LP high-pressure discharge lamp, the capacitance of the capacitor Cl is 330 pF, the inductance of the inductor L1 is 50 μΗ, so that the resonant frequency of the resonant circuit is 1.2 MHz. The supply voltage of the LP high-pressure discharge lamp, i.e. the voltage at the electrodes El, E2, is frequency modulated already in the ignition and start-up phase of the lamp. The carrier frequency and frequency step, as well as the modulation frequency, are chosen so that the available receiving energy is optimally tuned to the LP high-pressure discharge lamp to be operated. The metal halide LP high-pressure discharge lamp is operated with frequency modulated alternating voltage after the ignition and starting phase is completed5. HU 221 364 Β1. The carrier frequency or center frequency of this frequency-modulated alternating voltage is about 800 kHz and the frequency jump is about 100 kHz, so that the operating voltage of the lamp varies periodically between 700 kHz and 900 kHz. The modulation frequency is about 1.5 kHz. The modulation signal is triangular in shape. Through the modulation, a flicker-free, stable discharge arc is created. The frequency modulation of the alternating voltage is carried out by a frequency generator, not shown, belonging to the control circuit A. Since the control circuit A is not essential for the understanding of the present invention, it is not discussed in more detail here. The control circuit A can be implemented, for example, by an integrated circuit, the output of which is connected to the control terminals of the field-effect transistors TI, T2, and which controls the time course of all processes in the entire circuit arrangement. The control circuit A usually also allows the power control of the high-pressure discharge lamp LP by means of pulse-width modulation of the control signal for the field-effect transistors TI, T2 of the push-pull voltage converter. The control circuit A can, however, also be an additional transformer, as is described, for example, in the patent specifications EP 0 294 604 and EP 0 294 605. Figure 3 shows a second embodiment of the circuit arrangement according to the invention. This second embodiment differs from the first embodiment only in the inductance in the load circuit. This inductance is formed in the second embodiment by two equally large inductances, Ll', Ll'. For this reason, identical elements in Figures 1 and 3 are designated by identical reference numerals. In the second embodiment, the inductances Ll', Ll' and the capacitor Cl of the series resonant circuit are symmetrical to the electrodes El, E2 of the lamp. This means that the first terminal of the first inductance, Ll' is connected to the first terminal of the first secondary winding, wlc, of the transformer TR1, while its second terminal is connected via the branch point VI to the first electrode El of the lamp and to the first terminal of the capacitor Cl.Similarly, the first terminal of the second inductor, L1", is connected to the second terminal of the first secondary coil, wlc, and its second terminal is connected via the branch point V2 to the second electrode, E2, of the lamp and the second terminal of the capacitor Cl. In this way, primarily during the start-up phase of the LP high-pressure discharge lamp - in which the transition from the glow discharge to the arc discharge occurs - the energy stored in the series resonance circuit is coupled into the LP high-pressure discharge lamp via the two electrodes El, E2 of the lamp. The structure and mode of operation of the second embodiment are identical in all other respects to the structure and mode of operation of the first embodiment. The invention is not limited to the embodiments described in more detail above. For example, a high-frequency filter can also be connected between the DC voltage source U and the input of the push-pull voltage converter, which suppresses radio interference in the circuit arrangement according to the invention and significantly reduces the feedback of the high- or medium-frequency oscillations generated by the push-pull voltage converter on the voltage source. Another voltage converter can also be used instead of the push-pull voltage converter. Instead of the spark gap FS, the ignition circuit can contain another automatic switch, for example a four-layer diode, a triac or another semiconductor element designed as a threshold switch. In addition, the field-effect transistor (switching transistor) of the ignition circuit T3 can be replaced by a relay. However, it is also possible to connect the field-effect transistor T3 between the diode Dl and the junction point V3 in the ignition circuit, and then the polarity of the diode Dl is such that its anode is connected to the secondary winding wld and its cathode to the drain terminal of the field-effect transistor T3. The junction point V5 is then connected to the secondary winding wld through the resistor R1. The ignition auxiliary electrode ZE of the high-pressure discharge lamp can also have different embodiments. The ignition auxiliary electrode ZE can be formed, for example, as a thin metal coating layer on the inside of the outer bulb or on the outside of the discharge vessel 1. The strip-shaped ignition auxiliary electrode ZE shown in FIG. 2 can also be widened on the outside of the outer bulb 5 and can be designed in such a way that it can simultaneously serve as an optical aperture or a shielding element for producing a low beam. Finally, it is possible to make the ignition auxiliary electrode ZE from a wire that is parallel to the longitudinal axis of the lamp, inside or outside the outer bulb 5, or is twisted around the discharge vessel 1. The lighting system consisting of the LP high-pressure discharge lamp and the circuit arrangement according to the invention does not necessarily have to be part of a vehicle headlight, but can be used for other applications, for example in projection lamps or in the photo-optical field. In this case, the DC voltage source U is not the electrical network of a vehicle. The supply voltage can also be the AC voltage of an AC voltage source.

Claims

PATENT CLAIMS 1. Switching arrangement for operating a high-pressure discharge lamp, comprising - a voltage converter generating an alternating voltage, - a transformer (TR1) connected to the voltage converter, - a pulsed ignition circuit for the high-pressure discharge lamp, which pulsed ignition circuit has a voltage input and an ignition voltage output, - a load circuit designed as a series resonant circuit, into which the high-pressure discharge lamp (LP) is connected and which contains at least one inductance (Ll) and at least one capacitor (Cl), characterized in that - the transformer (TR1) has at least two secondary windings (wlc, wld), of which the first secondary winding (wlc) is connected to the load circuit, and the second secondary winding (wld) is connected to the is connected to the voltage input of a pulsed ignition circuit,and - the ignition voltage output of the pulse ignition circuit is connected to the ignition auxiliary electrode (ZE) of the high-pressure discharge lamp (LP)., 2. The switching arrangement according to claim 1, characterized in that the frequency of the alternating voltage produced by the voltage converter exceeds 200 kHz.

3. The switching arrangement according to claim 2, characterized in that the frequency of the alternating voltage produced by the voltage converter is between 500 kHz and 3 MHz.

4. The switching arrangement according to claim 1, characterized in that the resonant frequency of the unloaded series resonant circuit exceeds 200 kHz.

5. The circuit arrangement according to claim 4, characterized in that the resonant frequency of the unloaded series resonant circuit is between 500 kHz and 3 MHz.

6. A circuit arrangement according to claim 1, characterized in that the pulsed ignition circuit comprises a surge capacitor (C3), a pulse transformer (TR2) and an automatic switch.

7. Switching arrangement according to claim 6, characterized in that the automatic switch is formed by a spark gap (FS).

8. A switching arrangement according to claim 6, characterized in that the automatic switch is formed by a semiconductor element designed as a threshold switch.

9. The circuit arrangement according to claim 1, characterized in that the ignition circuit comprises a rectifier (e.g. diode (D1)).

10. The switching arrangement according to claim 1, characterized in that the voltage converter is a push-pull voltage converter.

11. The switching arrangement according to claim 10, characterized in that - the push-pull voltage converter has two field-effect transistors (TI, T2), - the push-pull voltage converter transformer (TR1) has two primary windings (wla, wlb) and each of these has two terminals, - the first terminal of the first primary winding is connected to the first terminal of the second primary winding (wlb) via a center tap (M), - the second terminal of the first primary winding (wla) is connected to the first field-effect transistor (TI), - the center tap is used for connecting to the positive pole of a DC voltage source (U), - the second terminal of the second primary winding (wlb) is connected to the second field-effect transistor (T2), - the push-pull voltage converter has at least one capacitor (C2), and one terminal of the at least one capacitor (C2) is connected to the first terminal of the first primary winding (wla),the other terminal of the at least one capacitor (C2) is connected to the second terminal of the second primary winding (wlb), 12. Lighting system, which consists of a high-pressure discharge lamp and an operating circuit, preferably a circuit arrangement according to claim 1, and the high-pressure discharge lamp has a discharge vessel with electrodes arranged therein, between which a gas discharge occurs during operation of the lamp, characterized in that the high-pressure discharge lamp (LP) has an ignition auxiliary electrode (ZE), which is electrically connected to the ignition voltage output of the pulsed ignition circuit.

13. Lighting system according to claim 12, characterized in that the ignition auxiliary electrode (ZE) is arranged outside the discharge vessel (1).

14. Lighting system according to claim 12, characterized in that the ignition auxiliary electrode (ZE) is formed by a current-conducting layer which is applied to a lamp vessel of the high-pressure discharge lamp (LP).

15. Lighting system according to claim 14, characterized in that the high-pressure discharge lamp (LP) has a discharge vessel (1) and an outer envelope (5) which partially or completely surrounds the discharge vessel (1), and the lamp vessel is formed by the outer envelope (5).

16. The lighting system according to claim 14, characterized in that the current-conducting layer is designed as an optical aperture.

17. The lighting system according to claim 12, characterized in that the high-pressure discharge lamp (LP) is a metal halide high-pressure discharge lamp (LP) having an electrical power consumption of less than or equal to 100 W.

18. Operating method for a lighting system according to claim 12, characterized in that - for igniting the high-pressure discharge lamp (LP), high-voltage pulses are applied to the ignition auxiliary electrode (ZE) of the high-pressure discharge lamp (LP), - in the ignition phase of the high-pressure discharge lamp (LP) and in the subsequent transition phase from glow discharge to arc discharge, an alternating voltage is generated for the high-pressure discharge lamp (LP) by resonant voltage increase on the capacitor (Cl) of the series resonance circuit.

19. The operating method according to claim 18, characterized in that the frequency of the alternating voltage is greater than 200 kHz.

20. The operating method according to claim 18, characterized in that the frequency of the alternating voltage is greater than 500 kHz.

21. Operating method according to claim 18, characterized in that the high-pressure discharge lamp (LP) is a metal halide high-pressure discharge lamp (LP) with an electrical power consumption of less than or equal to 100 W, and the alternating voltage generated by resonant voltage boosting on the capacitor (Cl) of the series resonant circuit is between 500 V and 1.5 kV. HU 221 364 Bl 22. Operating method according to claim 18, characterized in that the high-pressure discharge lamp (LP) is operated with a frequency-modulated alternating voltage after the transition phase from glow discharge to arc discharge is completed.

23. The operating method according to claim 22, characterized in that the carrier frequency of the frequency modulated alternating voltage is above 300 kHz.

24. The operating method according to claim 23, characterized in that the carrier frequency of the frequency modulated alternating voltage is between 500 kHz and 2.9 MHz.

25. The operating method according to claim 22, characterized in that the frequency swing of the frequency modulated alternating voltage is between 10 kHz and 100 kHz.

26. The operating method according to claim 22, characterized in that the modulation frequency of the alternating voltage is between 100 Hz and 5 kHz.

27. Operating method according to claim 18, characterized in that the switching arrangement is powered by a low voltage voltage source.

28. The operating method according to claim 27, characterized in that the low voltage voltage source is a DC voltage source.

29. The operating method according to claim 28, characterized in that the DC voltage source is a vehicle battery.

30. The operating method according to claim 27, characterized in that the supply voltage of the low voltage voltage source 15 is less than 50 V.