Patent Application
20090085491
The invention relates to a device for operating or igniting a high-pressure discharge lamp in accordance with the precharacterizing clause of patent claim 1, a lamp base and a lighting system having such a device and a method for operating a high-pressure discharge lamp.
Such a device has been disclosed, for example, in WO 98/18297. This laid-open specification describes a pulse ignition device for a high-pressure discharge lamp, which has been provided with an auxiliary ignition electrode, in particular for a vehicle headlight high-pressure discharge lamp. This pulse ignition device has, as the essential components, a spark gap, an ignition capacitor and an ignition transformer. In order to ignite the gas discharge in the high-pressure discharge lamp, the ignition capacitor is charged in order to then be discharged via the spark gap and via the primary winding of the ignition transformer when the breakdown voltage of said spark gap is reached, so that high voltage pulses are induced in the secondary winding of the ignition transformer which are injected into the high-pressure discharge lamp via the auxiliary ignition electrode and result in the gas discharge in the high-pressure discharge lamp being ignited. Once the gas discharge has been ignited, the high-pressure discharge lamp is operated with a high-frequency current of alternating polarity, whose frequency is in the megahertz range. The above-described ignition circuit is DC-isolated from the operating circuit of the high-pressure discharge lamp. The operating circuit and the ignition circuit are both supplied with energy by the same push-pull inverter. For the DC isolation between the ignition circuit and the operating circuit and for the coupling to the inverter, a transformer is used having two secondary windings, of which in each case one is arranged in the ignition circuit and in the operating circuit. Once the gas discharge in the high-pressure discharge lamp has been ignited, the ignition circuit or ignition device is deactivated by means of a controllable semiconductor switch.
The object of the invention is to provide a device of the generic type having a simplified design. This object is achieved according to the invention by the features of patent claim 1. Particularly advantageous embodiments of the invention are described in the dependent patent claims.
The device according to the invention for operating or igniting a high-pressure discharge lamp, which has been provided with an auxiliary ignition electrode, has a voltage-dependent switching means for applying the ignition voltage for the high-pressure discharge lamp to the auxiliary ignition electrode, the switching threshold voltage of the voltage-dependent switching means being greater than or equal to the ignition voltage required for igniting the gas discharge in the high-pressure discharge lamp. In this context, the ignition voltage is understood to mean the voltage required between the auxiliary ignition electrode and the associated main electrode which is necessary for igniting the gas discharge in the high-pressure discharge lamp. As a result, an ignition device for a high-pressure discharge lamp, which has been equipped with an auxiliary electrode, can be realized which manages to produce the ignition voltage pulses without the use of an ignition transformer. In addition, the controllable semiconductor switch for deactivating the ignition device once the gas discharge in the high-pressure discharge lamp has been ignited and the transformer for DC-isolating the ignition circuit and the operating circuit can also be dispensed with. The device according to the invention therefore has a simpler design than the device in accordance with the prior art.
In order to be able to produce such high voltages as are required for igniting the gas discharge in a high-pressure discharge lamp which has been provided with an auxiliary electrode, the voltage-dependent switching means preferably comprises at least one spark gap. The switching threshold voltage, i.e. the breakdown voltage of the spark gap, can be adjusted to the desired value or to a value which is greater than or equal to the ignition voltage of the high-pressure discharge lamp by changing the distance between its electrodes or by changing the pressure of the filling gas used.
Alternatively, instead of one spark gap it is also possible for a plurality of series-connected spark gaps or a spark gap which can be triggered externally with an additional ignition electrode to be used. However, instead of spark gaps it is also possible to use other voltage-dependent switching means, for example thyristors or voltage-dependent resistors or a combination of the abovementioned component parts.
Preferably, a charge storage means which can be charged to the switching threshold voltage is provided in the device according to the invention in order to provide the energy for the breakdown of the voltage-dependent switching means. The abovementioned charge storage means is preferably one or more capacitors, which are designed for high voltages.
In accordance with the preferred exemplary embodiments of the invention, the charge storage means is preferably charged to the switching threshold voltage of the voltage-dependent switching means with the aid of a resonant circuit or a voltage multiplication circuit or a piezo transformer or a combination thereof. The required high voltages of several kilovolts can be produced in a relatively simple manner by means of a resonant circuit, which is operated close to its resonance during the ignition phase, or by means of a voltage multiplication circuit. The voltage multiplication circuit can be supplied with energy, for example, via a transformer, which has been connected into the lamp circuit, or a resonant circuit.
Advantageously, a voltage convertor is provided in order to ensure the voltage supplied to the voltage-dependent switching means during the ignition phase of the high-pressure discharge lamp and to ensure the supply of current of alternating polarity to the high-pressure discharge lamp, from the system voltage, for example from the 230 volt low-voltage AC system, or from the on-board electrical system voltage of a motor vehicle. Different operating modes can be realized with the aid of the voltage convertor in order to meet the different requirements of the high-pressure discharge lamp during its ignition phase and during lamp operation once the ignition phase has come to an end. Preferably, by means of the voltage convertor, during the ignition phase of the high-pressure discharge lamp a first supply voltage is generated for the voltage-dependent switching means and, once the gas discharge in the high-pressure discharge lamp has been ignited, a second supply voltage is generated for the purpose of producing a lamp current with alternating polarity.
The voltage convertor is therefore preferably in the form of an inverter or AC voltage convertor, which can be operated at different clock or switching frequencies. For the purpose of producing the abovementioned first and second supply voltage, the inverter is preferably operated at switching frequencies from different frequency ranges. As a result, it is possible to ensure in a simple manner that, once the gas discharge in the high-pressure discharge lamp has been ignited, now only a lower voltage is present at the voltage-dependent switching means than its switching threshold voltage and therefore no further ignition voltage pulses are generated.
The device according to the invention only comprises a few components and can therefore be accommodated in the lamp base of a high-pressure discharge lamp. Therefore, the device according to the invention can be used particularly advantageously in metal-halide high-pressure discharge lamps for motor vehicle headlights which have been provided with an auxiliary ignition electrode, in particular also in mercury-free metal-halide high-pressure discharge lamps for motor vehicle headlights.
The invention will be explained in more detail below with reference to a plurality of preferred exemplary embodiments. In the drawing:
In order to ignite the gas discharge in the high-pressure discharge lamp 18, the voltage convertor 10 is operated at a switching frequency which is close to the resonant frequency of the series resonant circuit comprising the component parts 11a and 12. In the secondary winding section 11b of the autotransformer 11, a high voltage is thus induced which is sufficient for charging the capacitor 15, via the rectifier diode 13 and the resistor 14, to the breakdown voltage of the spark gap 16. If the voltage at the capacitor 15 reaches the breakdown voltage of the spark gap 16, it is discharged via the spark gap 16, and high voltage pulses are applied to the auxiliary ignition electrode 181 which results in the gas discharge in the high-pressure discharge lamp 18 being ignited.
Once the gas discharge in the high-pressure discharge lamp 18 has been ignited, the resonant capacitor 12 is bridged by the conductive discharge path of the high-pressure discharge lamp and the series resonant circuit is damped, so that there is no sufficiently high voltage induced in the secondary winding 11b to charge the capacitor 15 to the breakdown voltage of the spark gap 16. The ignition device is therefore automatically deactivated once the gas discharge has been ignited. In addition, the spark gap 16 therefore provides DC isolation of the auxiliary ignition electrode 181 from the device once the gas discharge has been ignited. The auxiliary ignition electrode 181 is free of potential once the ignition phase has come to an end and therefore does not cause any sodium migration, which would result in a sodium loss in the discharge vessel of the high-pressure discharge lamp 18 and therefore in premature failure of the high-pressure discharge lamp 18.
Once the ignition phase of the high-pressure discharge lamp 18 has come to an end, the switching frequency of the voltage convertor 10 is selected by means of its driving device in such a way that the high-pressure discharge lamp 18, in the case of a mercury-containing metal-halide high-pressure discharge lamp, is operated with a running voltage of approximately 85 volts and, in the case of a mercury-free metal-halide high-pressure discharge lamp, is operated with a running voltage of approximately 40 volts. The high-pressure discharge lamp 18 is fed an alternating current whose frequency is above 100 kHz. Once the ignition phase has come to an end, the capacitor 15 is charged to a voltage which is below the breakdown voltage of the spark gap 16.
In order to ignite the gas discharge in the high-pressure discharge lamp 28, the voltage convertor 20 is operated at a switching frequency which is close to the resonant frequency of the series resonant circuit comprising the component parts 21a and 22. As a result, a high voltage is induced in the secondary winding 21b of the transformer 21 which is increased by the abovementioned voltage doubling circuit by a factor of two, so that the capacitors 251, 252 are charged to the breakdown voltage of the spark gap 26. If the voltage at the capacitors 251, 252 reaches the breakdown voltage of the spark gap 26, said capacitors are discharged via the spark gap 26, and high voltage pulses are applied to the auxiliary ignition electrode 281 which result in the gas discharge in the high-pressure discharge lamp 28 being ignited. Once the gas discharge in the high-pressure discharge lamp 28 has been ignited, the resonant capacitor 22 is bridged by the conductive discharge path of the high-pressure discharge lamp, and the series resonant circuit is damped, so that no sufficiently high voltage is induced in the secondary winding 21b for charging the capacitors 251, 252 to the breakdown voltage of the spark gap 26. The ignition device is therefore automatically deactivated once the gas discharge has been ignited. In addition, the spark gap 26 as a result ensures DC isolation of the auxiliary ignition electrode 281 from the device once the gas discharge has been ignited.
Once the ignition phase of the high-pressure discharge lamp 28 has come to an end, the switching frequency of the voltage convertor 20 is selected by means of its driving device in such a way that the high-pressure discharge lamp 28, in the case of a mercury-containing metal-halide high-pressure discharge lamp, is operated with a running voltage of approximately 85 volts and, in the case of a mercury-free metal-halide high-pressure discharge lamp, is operated with a running voltage of approximately 40 volts. The high-pressure discharge lamp 28 is fed a virtually square-wave alternating current having a frequency of 400 hertz. Once the ignition phase has come to an end, the capacitors 251, 252 are charged to a voltage which is below the breakdown voltage of the spark gap 26. The exemplary embodiment which is explained further below and is depicted in
During the ignition phase of the high-pressure discharge lamp 48, a sufficiently high voltage is induced in the secondary winding 41b of the transformer to charge the capacitor 45, via the rectifier diode 43 and the resistor 44, to the breakdown voltage of the spark gap 46. If the voltage at the capacitor 45 reaches the breakdown voltage of the spark gap 46, said capacitor is discharged via the spark gap 46, and high voltage pulses are applied to the auxiliary ignition electrode 481 which result in the gas discharge in the high-pressure discharge lamp 48 being ignited.
Once the ignition phase of the high-pressure discharge lamp 48 has come to an end, the switching frequency of the voltage convertor 40 is selected by means of its driving device in such a way that the high-pressure discharge lamp 48, in the case of a mercury-containing metal-halide high-pressure discharge lamp, is operated with a running voltage of approximately 85 volts and, in the case of a mercury-free metal-halide high-pressure discharge lamp, is operated with a running voltage of approximately 40 volts. The high-pressure discharge lamp 48 is fed an alternating current whose frequency is above 100 kHz. Once the ignition phase has come to an end, the capacitor 45 is now only charged to a voltage which is below the breakdown voltage of the spark gap 46.
The high-pressure discharge lamp 18, 28, 38, 48, which is illustrated schematically in
This high-pressure discharge lamp La has a discharge vessel 1 consisting of quartz glass, in which an ionizable filling is enclosed in a gas-tight manner. The ionizable filling contains xenon and metal-halide compounds, preferably iodides of the metals sodium, scandium, zinc and indium, and the ionizable filling preferably does not contain any mercury. The xenon coldfilling pressure is approximately 10 bar. The two ends 1a, 1b of the discharge vessel 1 are in each case sealed off by means of a molybdenum foil fuse seal 2a, 2b. Two electrodes E1, E2 are located in the interior of the discharge vessel 1 and the discharge arc responsible for the light emission is formed between said electrodes during lamp operation. These main electrodes E1, E2 are each electrically conductively connected to a power supply line 3a, 3b, which is passed out of the discharge vessel 1, via one of the molybdenum foil fuse seals 2a, 2b. The discharge vessel 1 is enveloped by a vitreous outer bulb 5. The auxiliary ignition electrode ZE, which in
The diodes 53a and 53b are designed for voltages of up to 25 kV and are, for example, of the type BY724. The capacitor 15 has a capacitance of 220 pF and is designed for a voltage of up to 15 kV. The resistor 57, which is illustrated by dashed lines in
In order to ignite the gas discharge in the high-pressure discharge lamp 58, the voltage convertor 50 is operated at a switching frequency which is close to the resonant frequency of the piezoelectric transformer, and in the process a high voltage is produced at its output which is rectified and increased again by the voltage doubler circuit at its output so that it is sufficient to charge the capacitor 55, via the resistor 54, to the breakdown voltage of the spark gap 56. If the voltage at the capacitor 55 reaches the breakdown voltage of the spark gap 56, it is discharged via the spark gap 56, and high voltage pulses are applied to the auxiliary ignition electrode 581 which result in the gas discharge in the high-pressure discharge lamp 58 being ignited. The component parts 51 and 52 of the series resonant circuit are in this case dimensioned such that they are close to the resonant frequency of the piezo transformer, likewise at resonance, and thus, owing to the excitation of the piezo transformer, during the ignition a sufficiently high voltage is produced between the two main electrodes of the gas discharge lamp with an amplitude of, for example, 1200 volts, and therefore the ignition of a discharge between the two main electrodes of the gas discharge lamp is made possible by the voltage pulse at the auxiliary ignition electrode 581.
Once the ignition phase of the high-pressure discharge lamp 58 has come to an end, the switching frequency of the voltage convertor 50 is selected in such a way that the high-pressure discharge lamp 58, in the case of a mercury-containing metal-halide high-pressure discharge lamp, is operated with a running voltage of approximately 85 volts and, in the case of a mercury-free metal-halide high-pressure discharge lamp, is operated with a running voltage of approximately 40 volts. The high-pressure discharge lamp 58 is fed an alternating current whose frequency is above 100 kHz. Owing to the changed frequency, the piezoelectric transformer no longer produces an output voltage which is as high, which ultimately results in the capacitor 55, once the ignition phase has come to an end, being charged to a voltage which is below the breakdown voltage of the spark gap 56.
| Number | Date | Country | Kind |
|---|---|---|---|
| 05008228.8 | Apr 2005 | EP | regional |
| 10 2005 023 798.3 | May 2005 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/DE2006/000657 | 4/12/2006 | WO | 00 | 5/30/2008 |
