EP1869951A1

EP1869951A1 - Pulsed igniting device comprising a piezoelectric transformer for a high-pressure discharge lamp

Info

Publication number: EP1869951A1
Application number: EP06722774A
Authority: EP
Inventors: Bernhard Siessegger
Original assignee: Patent Treuhand Gesellschaft fuer Elektrische Gluehlampen mbH
Current assignee: Osram GmbH
Priority date: 2005-04-14
Filing date: 2006-04-11
Publication date: 2007-12-26
Also published as: US20090039798A1; CA2606187A1; WO2006108394A1

Abstract

The invention relates to a device for igniting the gas discharge in a high-pressure discharge lamp (La). Said igniting device is embodied as a pulsed igniting device (C, FS, Tr1) while a piezoelectric transformer (PT) is provided for supplying the pulsed igniting device (C, FS, Tr1) with voltage.

Description

HIGH-PRESSURE GAS DISCHARGE LAMP PULSE TURNING DEVICE WITH PIEZOELECTRIC TRANSFORMER

The invention relates to an ignition device according to the preamble of patent claim 1 and a corresponding method.

I. State of the art

Such an ignition device is disclosed, for example, in WO 98/18297. This document describes a circuit arrangement for operating a high-pressure discharge lamp with a voltage converter designed as an inverter, a load circuit fed by the inverter, which is provided with connections for a high-pressure discharge lamp and with a throttle for limiting the lamp current, and a pulse ignition device for igniting the gas discharge the high pressure discharge lamp has. The circuit also has a transformer for galvanic isolation of the inverter from the load circuit and the Impulszündvorrichtung. The pulse ignition device comprises a spark gap, a firing capacitor which is charged during the ignition of the gas discharge in the high-pressure discharge lamp to the breakdown voltage of the spark gap, and an ignition transformer, via the primary winding of the ignition capacitor discharges after the breakthrough of the spark gap and the secondary winding high voltage pulses to ignite the gas discharge are generated in the high pressure discharge lamp. The power supply of this pulse ignition device is generated by means of the inverter and the aforementioned, the galvanic isolation transformer.

EP-A 1 496 725 discloses an ignition device for a high pressure discharge lamp equipped with a piezoelectric transformer. The primary side of the piezoelectric transformer is energized to ignite the gas discharge in the high pressure discharge lamp with an AC voltage whose frequency corresponds to a resonant frequency of the piezoelectric transformer. On the secondary side of the piezoelectric transformer, a high voltage is thereby produced. neriert, which is supplied to a Zündhilfselektrode the high pressure discharge lamp to ignite the gas discharge in the high pressure discharge lamp.

IL illustration of the invention

It is an object of the invention to provide an improved pulse ignition device for a high pressure discharge lamp which is suitable for operation of the high pressure discharge lamp with a high frequency lamp current, i.e. at a frequency greater than 0.1 MHz, or at low supply voltage of the pulse ignition device

This object is achieved by the features of claim 1. Particularly advantageous embodiments of the invention are described in the dependent 10 claims.

The ignition device according to the invention is designed as a pulse ignition device and to its power supply, a piezoelectric transformer is provided. Through the use of a piezoelectric transformer for supplying voltage to the pulse ignition device, an ignition device can be used in the pulse ignition device.

15 transformer can be used with a much lower voltage translation ratio, as can be realized by means of the piezoelectric transformer already large voltage translation ratios, and thus the waiting on the secondary side of the piezoelectric transformer supply voltage for the pulse igniter against the voltage applied to its primary side

20 voltage is significantly increased and only the difference between the ignition voltage of the high pressure discharge lamp and the supply voltage of the pulse ignition of the pulse ignition transformer must be generated in order to ignite the gas discharge in the high pressure discharge lamp.

Especially advantageous is the use of the piezoelectric transformer to _25th Power supply of a pulse ignition device, when the high-pressure discharge lamp with a high-frequency lamp current, that is, with a frequency greater than 0.1 MHz, operated because thereby the turns number ratio of Secondary to primary winding and the secondary inductance of the ignition transformer of the pulse ignition device and thus the voltage drop across the secondary winding of the ignition transformer through which the high-frequency lamp current flows can be reduced. Otherwise, the efficiency of the entire system would suffer during the lamp operation after ignition of the gas discharge under the high inductance of the secondary winding of the ignition transformer, because even after the ignition of the gas discharge would still occur a high voltage drop at the traversed by the high-frequency lamp current secondary winding of the ignition transformer. Therefore, only relatively small numbers of turns of the ignition transformer of less than 20 are permissible, otherwise the number of turns of the primary winding becomes very small, for example equal to 1, and thus poor magnetic coupling of the primary and secondary windings of the ignition transformer, a high current through the primary winding during ignition with heavy use of the components of the pulse ignition device and only an inefficient high voltage generation is effected. If, nevertheless, high ignition voltages of approximately 20 kV are to be generated, then a switching means with a higher blocking voltage than the usual 350 V to 800 V in the pulse ignition device must be used. Accordingly, the requirement arises to supply the pulse ignition device with a higher voltage than that in a lamp operation according to the prior art. This is achieved particularly advantageously with the ignition device according to the invention or the operating device according to the invention.

Advantageously, the ignition transformer has a design in which the magnetic flux largely in the magnetic material, such as ferrite or iron, the transformer core runs to ensure good electromagnetic compatibility and minimizing the losses caused by the magnetic field outside of the ignition transformer. The ignition transformer therefore preferably has an almost closed core, for example a toroidal core or pot core with an air gap. The use of the piezoelectric transformer for supplying power to a pulse ignition device is also particularly advantageous if the pulse ignition device is only available with a relatively low supply voltage, ie less than 500 V, since this is generated, for example, from the vehicle electrical system voltage.

Advantageously, a voltage doubling circuit or a cascade circuit is connected downstream of the voltage output of the piezoelectric transformer in order to further increase the supply voltage for the pulse ignition device.

According to the preferred exemplary embodiments, the pulse ignition device according to the invention comprises a switching means, for example a voltage-dependent switching means with a switching threshold voltage, a charge storage means which can be charged to the switching threshold voltage of the voltage-dependent switching means, and an ignition transformer for generating the ignition voltage required for igniting the gas discharge of the high-pressure discharge lamp. The components of the ignition device are preferably arranged in the interior of the lamp base of the high-pressure discharge lamp. In addition, the piezoelectric transformer is preferably also accommodated in the lamp base of the high-pressure discharge lamp.

III. Description of the preferred embodiments

The invention will be explained in more detail with reference to several preferred embodiments. Show it:

Figure 1 is a circuit diagram of the ignition device and the operating device of the high pressure discharge lamp according to the first embodiment of the invention

Figure 2 is a circuit diagram of the ignition device and the operating device of the high-pressure discharge lamp according to the second embodiment of the invention Figure 3 is a circuit diagram of the ignition device and the operating device of the high pressure discharge lamp according to the third embodiment of the invention

Figure 4 is a circuit diagram of the ignition device and the operating device of the high-pressure discharge lamp according to the fourth embodiment of the invention

Figure 5 is a circuit diagram of the ignition device and the operating device of the high pressure discharge lamp according to the fifth embodiment of the invention

Figure 6 is a circuit diagram of the ignition device and the operating device of the high-pressure discharge lamp according to the sixth embodiment of the invention

Figure 7 is a circuit diagram of the ignition device and the operating device of the high-pressure discharge lamp according to the seventh embodiment of the invention

Figure 8 is a circuit diagram of the ignition device and the operating device of the high pressure discharge lamp according to the eighth embodiment of the invention

Figure 9 is a circuit diagram of the ignition device and the operating device of the high-pressure discharge lamp according to the ninth embodiment of the invention

Figure 10 is a circuit diagram of the ignition device and the operating device of the high-pressure discharge lamp according to the fourth embodiment of the invention with partial compensation of the input capacitance of the piezoelectric transformer see FIG. 1 schematically shows the circuit diagram of a pulse ignition device and an operating device for a high-pressure discharge lamp according to the first exemplary embodiment of the invention.

The pulse igniting device comprises a starting capacitor C, a spark gap J FS, or any other voltage-dependent switching means, for example comprising a DIAC or a combination of a DIAC and a thyristor, which is activated or deactivated upon reaching a certain switching threshold voltage, and an ignition transformer Tri Primary winding Lp and secondary winding Ls. The series circuit of spark gap FS and primary winding Lp is

10 connected in parallel to the ignition capacitor C. To power the pulse ignition device serve an AC voltage source Ul, a piezoelectric transformer PT and a voltage doubling circuit, which is formed by the diodes Dl, D2 and the ignition capacitor C. After ignition of the gas discharge in the high-pressure discharge lamp La, the lamp La by means of

/ 5 AC voltage source U2 operated, which generates a current flowing through the secondary winding Ls of the ignition transformer Tri lamp current. For igniting the gas discharge in the high-pressure discharge lamp La, the piezoelectric transformer PT is excited on its primary side by means of the alternating voltage source U1 with an alternating voltage frequency which is close to a resonance frequency of the piezoelectric transformer.

20 zoelektrischen transformer PT is located. As a result, a high voltage is generated on its secondary side, which is rectified by means of the diodes D1, D2 of the voltage doubler circuit, so that the ignition capacitor C is the rectified, double output peak voltage of the piezoelectric transformer PT. When the piezoelectric transformer PT by means of the Wechselspan-

25 voltage source Ul is excited with one of its resonant frequencies, the ignition capacitor C is a voltage available, which is sufficient for the breakthrough of the spark gap FS, so that the ignition capacitor C intermittently with a Zündwiederholfrequenz of about 100 Hz over the spark gap FS and the primary winding Lp of the ignition transformer Tri discharges. As a result, in the secondary winding

30 hung Ls of the ignition transformer Tri high voltage pulses induced, which the Ignite gas discharge in the high-pressure discharge lamp La. After ignition of the gas discharge in the high-pressure discharge lamp La, the AC voltage source U1 is either deactivated or the frequency of its AC voltage changed so that it has sufficient distance from the resonance frequencies of the piezoelectric transformer to avoid excitation of the piezoelectric transformer PT or to prevent charging of the ignition capacitor C to the breakdown voltage of the spark gap FS.

FIG. 9 schematically shows the circuit diagram of a pulse ignition device and an operating device for a high-pressure discharge lamp according to the ninth exemplary embodiment of the invention. It differs from the first exemplary embodiment only in that, instead of the switching-dependent switching means FS, any other switch S, for example a thyristor, an IGBT, a MOSFET or a triggerable spark gap with trigger electrode is used. The switch S is to be provided with a sequence of drive pulses which corresponds to the ignition repetition frequency of the pulse ignition device. It should be ensured that before the arrival of a corresponding drive pulse, the capacitor C is charged to a sufficiently high voltage.

FIG. 2 schematically shows the circuit diagram of a pulse ignition device and of an operating device for a high-pressure discharge lamp according to the second exemplary embodiment of the invention. It differs from the first embodiment only in that a single, common AC voltage source U1 is provided for supplying voltage to the piezoelectric transformer PT with downstream pulse ignition device and the high-pressure discharge lamp La, so that the voltage source U2 is dispensed with. In all other details, the first and second embodiments are the same. Therefore, the same reference numerals have been used in Figures 1 and 2 for identical components. The AC voltage source U1 is preferably a voltage converter U1 which generates a high-frequency AC voltage for igniting and operating the high-pressure discharge lamp La from the vehicle electrical system voltage of the motor vehicle. The high pressure discharge lamp La is in all embodiments Preferably, a metal halide high-pressure discharge lamp with an electrical power consumption of about 35 W, which is provided as a light source in a vehicle headlight. To ignite the high-pressure discharge lamp La, an alternating voltage whose frequency is close to a resonance frequency of the piezoelectric transformer PT to excite the piezoelectric transformer PT is generated by the voltage converter or by the voltage source U1. The alternating voltage generated on the secondary side of the piezoelectric transformer PT is rectified and doubled by means of the diodes D1, D2, so that the starting capacitor C is charged to the rectified, double output voltage of the piezoelectric transformer PT which is greater than the breakdown voltage of the spark gap FS is. As a result, the ignition capacitor C discharges via the spark gap FS and the primary winding Lp of the ignition transformer Tri. In the secondary winding Ls of the ignition transformer Tri, therefore, high-voltage pulses are induced, which lead to the ignition of the gas discharge in the high-pressure discharge lamp La. After ignition of the gas discharge in the high-pressure discharge lamp La, the frequency of the alternating voltage generated by the voltage transformer or the voltage source Ul is varied so that it has a sufficient distance to the resonance frequencies of the piezoelectric transformer PT, not to stimulate this or a charge of the ignition capacitor C to avoid the breakdown voltage of the spark gap FS. For example, the AC voltage source U1 can be realized as a DC-DC converter (eg boost converter) with a downstream inverter (eg full-bridge inverter). The switching frequency of the full bridge is selected during the ignition phase close to a resonant frequency of the piezoelectric transformer PT to about 100 kHz and reduced to about 400 Hz after ignition. Alternatively, the switching frequency of the full bridge, during the ignition phase of the high pressure discharge ^• lamp La also be for example only one fifth of the resonance frequency of the piezoelectric transformer PT, to the piezoelectric transformer PT with a contained in the signal of the voltage source Ul harmonic, such as the 5th harmonic to stimulate. But if a high-frequency lamp operation is desired, so for example, a piezoelectric transformer PT with a Resonant frequency of, for example 400 kHz are used, which is excited to ignite the gas discharge in the high-pressure discharge lamp La with an AC voltage of about 400 kHz. After completion of the ignition phase, the frequency of the AC voltage for the further lamp operation, for example, increased to 2 MHz in order not to further stimulate the piezoelectric transformer PT and to operate the high pressure lamp La above their acoustic resonances. A regulation of the lamp power is carried out, for example, by means of a variation of the frequency of the alternating voltage, since in this way the frequency-dependent reactance of the secondary winding Ls through which the lamp current flows is changed accordingly. The secondary winding Ls serves, similar to a throttle, to stabilize the discharge of the high-pressure discharge lamp La.

If the frequency of the alternating voltage generated by the voltage source U1 always lies above the resonance frequency of the piezoelectric transformer PT, an amplitude modulation is advantageously used to excite the piezoelectric transformer PT, the modulation frequency being equal to the resonance frequency of the piezoelectric transformer PT. For example, in a piezoelectric transformer PT having a resonance frequency of 100 kHz, an amplitude-modulated AC voltage having a carrier frequency of 4 MHz and a modulation frequency of 100 kHz is used to excite the piezoelectric transformer PT during the ignition phase of the high-pressure discharge lamp La. After completion of the ignition phase, the modulation is either switched off or the modulation frequency and / or the degree of modulation varied so that the voltage generated by the piezoelectric transformer PT no longer leads to the breakthrough of the spark gap FS. After completion of the ignition phase, an amplitude modulation of the AC voltage generated by the voltage converter Ul is maintained, for example, in order to achieve a straightening of the discharge arc of the high-pressure discharge lamp La curved by the convection in the discharge plasma, by exciting acoustic resonances in the discharge plasma by means of the amplitude modulation. FIG. 3 schematically shows the circuit diagram of a pulse ignition device and an operating device for a high-pressure discharge lamp according to the third exemplary embodiment of the invention. This exemplary embodiment differs from the second exemplary embodiment only in that the alternating voltage source U1 is designed as a one-transistor voltage converter by means of which the voltages required for igniting and operating the high-pressure discharge lamp La are generated from the vehicle electrical system voltage U _{B of} the motor vehicle. The one-transistor voltage converter has a clocked switching means, preferably a field effect transistor Ql (for example, a power MOSFET) whose switching clock determines the frequency of the AC voltage generated by the voltage converter Ul, and a capacitor Cs connected in parallel to the switching path of the switching means Ql and a transformer Tr2 whose Primary winding connected in series with the parallel circuit consisting of the switching means Ql and the capacitor Cs. The secondary winding of the transformer Tr2 is connected in parallel to the input of the piezoelectric transformer PT and to the series circuit consisting of the secondary winding Ls of the ignition transformer Tri and the discharge path of the high-pressure discharge lamp La. The voltage at the secondary winding of the transformer Tr2 is used during the ignition phase for power supply or excitation of the piezoelectric transformer PT and after ignition of the gas discharge fertilg to the power supply of the high pressure discharge lamp La. As already explained above, the frequency of the alternating voltage generated by the voltage converter and thus also the switching frequency of the switching means Q1 during the ignition phase and after completion of the ignition phase is different.

FIG. 4 schematically shows the circuit diagram of a pulse ignition device and an operating device for a high-pressure discharge lamp according to the fourth exemplary embodiment of the invention. The fourth embodiment differs from the third embodiment only in that the parallel connected to the switching means Ql capacitor Cs (Figure 3) according to the fourth embodiment (Figure 4) is replaced by the input capacitance of the piezoelectric transformer PT and the secondary winding of the transformer Tr2 parallel to the series - circuit of capacitor CK, secondary winding Ls of the ignition transformer Tri and discharge path of the high-pressure discharge lamp La is connected. The capacitor CK is optional and serves to partially compensate the inductance of the secondary winding Ls during lamp operation after completion of the ignition phase. The switching means S and the diode D connected in parallel with the switching means S correspond to the field-effect transistor Q1 and its body diode in FIG. The input capacitance of the piezoelectric transformer PT, as well as the capacitor Cs in the embodiment three, a zero voltage switching operation (zero volta- ge switching) of the switching means safely. If the input capacitance of the piezoelectric transformer PT should be too small for the voltage converter operation, a further capacitor can be connected in parallel with the input of the piezoelectric transformer PT and the switching means S in the circuit arrangement according to FIG. If the input capacitance of the piezoelectric transformer PT for the voltage converter operation should be too large, can be connected in series to the input of the piezoelectric transformer PT in the circuit Maßmaß 4 a capacitor, which together with the input capacitance of the piezoelectric transformer PT, a capacitive voltage divider forms. Alternatively, as shown in FIG. 10, if the input capacitance of the piezoelectric transformer PT is too large, a partial compensation of its input capacitance can be achieved by the parallel connection of a choke L _{κ pτ} to the input of the piezoelectric transformer. In order to prevent in this case a short circuit of the input voltage source Ug via the primary winding of the transformer Tr2 and the throttle added for partial compensation, a blocking capacitor C _{βpτ of} sufficient magnitude is to be connected in series with this choke, and this series circuit is connected in parallel with the input to connect the piezoelectric transformer. The blocking capacitor C _Bpτ prevents a direct current through the inductor L _KPT , it leaves the AC _{behavior of} the described arrangement, however, largely unaffected. In Figures 3 and 4, the same reference numerals have been used for identical components of the two embodiments. The operation of the fourth embodiment corresponds to the second and third embodiments. FIG. 5 schematically shows the circuit diagram of a pulse ignition device and a high-pressure discharge lamp control device according to the fifth exemplary embodiment of the invention. The fifth exemplary embodiment differs from the second or fourth exemplary embodiment only in that a current-fed push-pull converter is used as the AC voltage source or voltage converter U 1 instead of the one-transistor voltage converter. The power supply during lamp operation after ignition of the gas discharge in the high-pressure discharge lamp is ensured by the input inductor Lin, through which then flows an approximately constant current. The current-supplied active clock converter (FIG. 5) consists of two alternating switching switching means S1, S2, which are preferably designed as field-effect transistors (power MOSFET) with integrated body diode D1, D2, from the inductance Lin, the input capacitance of the piezoelectric transformer PT and the transformer Tr3. The transformer Tr3 has two primary windings which are connected so that when the switch S1 is closed the current can flow from the positive pole of the battery U _B via the first primary winding to the ground terminal and with the second switch S2 closed across the second primary winding of the transformer Tr3 to the ground terminal can flow. The switching clock of the switching means Sl and S2 determines the frequency of the alternating voltage which is available at the input of the piezoelectric transformer PT, and the frequency of the alternating voltage which is generated at the secondary winding of the transformer Tr3 for supplying power to the load circuit connected thereto. The input capacitance of the piezoelectric transformer PT, analogous to the fourth embodiment, a zero-voltage switching operation (zero voltage switching) of the two switches Sl and S2 safe. The load circuit consists of the series connection of capacitor Ck, secondary winding Ls of the ignition transformer Tri and the discharge path of the high-pressure discharge lamp La. Connected to the voltage output of the piezoelectric transformer PT is the voltage doubler circuit consisting of the diodes D1, D2 and the firing capacitor CFS, so that the rectified double output peak voltage of the piezoelectric transformer PT is applied to the firing capacitor CFS. The piezoelectric transformer PT and the voltage transformer Double-circuit-fed igniter of the high-pressure discharge lamp La consists of the ignition capacitor CFS, the spark gap FS and the ignition transformer Tri with its primary winding Lp and its secondary winding Ls. During the ignition phase of the high pressure discharge lamp La, the switching frequency of the switching means Sl, S2 is set so that the piezoelectric transformer PT is excited with an alternating voltage whose frequency corresponds to one of its resonance frequencies. As a result, the firing capacitor CFS is charged to the breakdown voltage of the spark gap FS, in order then to discharge via the primary winding Lp of the ignition transformer Tri and the spark gap FS. In the secondary winding Ls of the ignition transformer Tri, therefore, high-voltage pulses are induced, which lead to the ignition of the gas discharge in the high-pressure discharge lamp La. After completion of the ignition phase, the switching frequency of the switching means S 1, S2 is varied, so that the piezoelectric transformer PT is no longer excited and the voltage drop across the firing capacitor CFS is no longer sufficient to break the spark gap FS. The high-pressure discharge lamp La is supplied with energy via the secondary winding of the transformer Tr3. The secondary winding Ls of the ignition transformer Tri, through which the lamp current flows, acts as a choke for limiting the lamp current. The optional capacitor CK serves, in particular in the case of a high-frequency lamp current, for the partial compensation of the inductance of the secondary winding Ls of the ignition transformer Tri.

If the input capacitance of the piezoelectric transformer PT for the operation of the push-pull converter Sl, S2, Tr3 should be too small, may be connected in parallel with the input of the piezoelectric transformer PT, a capacitor with a suitably selected capacity. In contrast, if the input capacitance of the piezoelectric transformer PT for the operation of the push-pull converter S l, S2, Tr3 should be too large, can be connected in series with the input of the piezoelectric transformer PT, a capacitor with suitably selected capacity. Alternatively, if the input capacitance of the piezoelectric transformer PT is too large, a partial compensation of its input capacitance can be achieved by the parallel connection of a choke to the input of the piezoelectric transformer. In contrast for execution according to embodiment four, a blocking capacitor is not required here.

FIG. 6 schematically shows the circuit diagram of a pulse ignition device and an operating device for a high-pressure discharge lamp according to the sixth exemplary embodiment of the invention. It differs from the first embodiment in that the high pressure discharge lamp La has a Zündhilfs- electrode ZE, which is acted upon by the Impulszündvorrichtung during the ignition phase of the high pressure discharge lamp La with the high voltage pulses to ignite the gas discharge in the lamp La. The pulse injection apparatus according to FIG. 6 comprises a starting capacitor C, a spark gap FS, or any other voltage-dependent switching means which is activated or deactivated when a specific switching threshold voltage is reached, and an ignition transformer Tri with primary winding Lp and secondary winding Ls. The series circuit of spark gap FS and primary winding Lp is connected in parallel to the ignition capacitor C. An alternating voltage source U1, a piezoelectric transformer PT and a voltage doubler circuit, which is formed by the diodes D1, D2 and the ignition capacitor C, serve for voltage supply to the pulse ignition device. After ignition of the gas discharge in the high-pressure discharge lamp La, the lamp La is operated by means of the alternating voltage source U2 and the series resonant circuit LRes, CRes, which generate an alternating current over the discharge path of the high-pressure discharge lamp La. For igniting the gas discharge in the Hochdruckentladuiigslampe La, the frequency of the AC voltage source U2 is selected so that at the series resonant circuit LRes, CRes a sufficiently high voltage is generated, which is applied between the two main electrodes of the high pressure discharge lamp La and an ignition of the discharge via the auxiliary ignition electrode ZE allows or supports. Furthermore, the piezoelectric transformer PT on its primary side by means of _. AC voltage source Ul excited with an AC voltage frequency which is close to a resonance frequency of the piezoelectric transformer PT. As a result, a high voltage is generated on its secondary side, by means of the diodes Dl, D2 the voltage doubler circuit is rectified, so that the rectified capacitor C, the rectified, double output peak voltage of the piezoelectric transformer PT is applied. If the piezoelectric transformer PT is excited by means of the AC voltage source U1 with one of its resonant frequencies, a voltage is available at the ignition capacitor C, which is sufficient for the breakthrough of the spark gap FS, so that the ignition capacitor C intermittently on the spark gap FS and the primary winding Lp of the ignition transformer Tri unloads. As a result, high voltage pulses are induced in the secondary winding Ls of the ignition transformer Tri, which are supplied to the auxiliary ignition electrode ZE and are capacitively coupled by means of the auxiliary ignition ZE in the discharge medium of the high pressure discharge lamp La to ignite the gas discharge in the high pressure discharge lamp La. After ignition of the gas discharge in the high-pressure discharge lamp La, the AC voltage source Ul is either deactivated or the frequency of its AC voltage changed so that it has sufficient distance from the resonant frequencies of the piezoelectric transformer to avoid excitation of the piezoelectric transformer PT or a charge of the ignition capacitor C to prevent the breakdown voltage of the spark gap FS. The lamp operation after completion of the ignition phase is performed by means of the AC voltage source U2 and the series resonant circuit LRes, CRes.

FIG. 7 schematically shows the circuit diagram of a pulse ignition device and a high-pressure discharge lamp control device according to the seventh exemplary embodiment of the invention. It differs from the sixth embodiment in that the second alternating voltage source U2 is dispensed with and the ignition and the operation of the high-pressure discharge lamp La are performed with only one alternating voltage source U1. The capacitor CK is optional and serves for the partial compensation of the inductance LGes during lamp operation after completion of the ignition phase. The inductance LGes denotes the entire inductance of the autotransformer, where LRes denotes only the inductance of the first winding section connected to the voltage source U1 and the Input of the piezoelectric transformer PT is connected. In addition, the ignition transformer Tri of the pulse ignition device according to Figure 7 in contrast to the embodiment of Figure 6 is designed as autotransformer. To ignite the high-pressure discharge lamp La, an alternating voltage whose frequency is close to a resonance frequency of the piezoelectric transformer PT in order to excite the piezoelectric transformer PT is generated by the voltage converter or by the voltage source U1. The excitation can also take place by means of a harmonic contained in the signal of the voltage source U1. The series resonant circuit LRes, CRes is dimensioned such that a sufficiently high voltage is generated at it, which is applied between the two main electrodes of the high-pressure discharge lamp La and enables ignition of the discharge via the auxiliary starting electrode ZE or supported. The function of the capacitor CRes may optionally be taken over by the input capacitance of the piezoelectric transformer PT. Therefore, the component CRes is shown in dashed lines in FIG. The alternating voltage generated on the secondary side of the piezoelectric transformer PT is rectified and doubled by means of the diodes D1, D2, so that the starting capacitor C is charged to the rectified, double output voltage of the piezoelectric transformer PT, which is greater than the breakdown voltage of the spark gap FS. As a result, the ignition capacitor C discharges via the spark gap FS and the primary winding Lp of the ignition transformer Tri. In the secondary winding Ls of the ignition transformer Tri high-voltage pulses are thus induced se, with which the auxiliary ignition electrode ZE of the high-pressure discharge lamp La is acted upon to ignite the gas discharge in the high-pressure discharge lamp La. After ignition of the gas discharge in the high-pressure discharge lamp La, the frequency of the alternating voltage generated by the voltage converter or the voltage source U1 is varied so that it has a sufficient distance from the resonance frequencies of the piezoelectric transformer PT so as not to excite it or charge it of the ignition capacitor C to avoid the breakdown voltage of the spark gap FS. The high-pressure discharge lamp La is operated after the ignition phase by means of the series resonant circuit LRes, CRes at the AC voltage source U1. The electrical power consumption of High-pressure discharge lamp La is regulated by varying the frequency of the alternating voltage U1. In particular, the high-pressure discharge lamp La can be operated immediately after the ignition phase, in the so-called start-up phase, by means of the LGES and CK series resonant circuit at a multiple of their rated power in order to achieve a rapid evaporation of the discharge medium, for example the metal halides. The inductor LRes also limits the lamp current and thus ensures the stabilization of the discharge.

FIG. 8 schematically shows the circuit diagram of a pulse ignition device and an operating device for a high-pressure discharge lamp according to the eighth exemplary embodiment of the invention. It differs from the seventh embodiment in that in the eighth embodiment, the AC voltage source Ul is formed as a single-transistor voltage converter and the ignition transformer Tri is not designed as an autotransformer. The alternating voltage for supplying voltage to the piezoelectric transformer PT and the high-pressure discharge lamp La is generated from the vehicle electrical system voltage U _{B of} the motor vehicle by means of the controllable switching means S, the diode D connected in parallel thereto, the capacitor Cs connected in parallel with the switching means S and the transformer Tr2. The switching means S and the diode D are preferably designed as a field-effect transistor with an integrated body diode, as shown in FIG. The switching clock of the switching means S determines the frequency of the AC voltage generated by the voltage converter. The secondary winding of the transformer Tr2 supplies the series resonant circuit LRes, CRes with energy. The input or the primary side of the piezoelectric transformer PT and the discharge path of the high-pressure discharge lamp La are each connected in parallel to the resonant capacitor CRes. For igniting the gas discharge in the high-pressure discharge lamp La, the switching frequency of the switching means S and thus the frequency of the alternating voltage generated by the one-transistor voltage converter is tuned to a resonant frequency of the piezoelectric transformer PT. In addition, the series resonant circuit formed of LRes, CRes and the input capacitance of the piezoelectric transformer PT is excited, so that between the two main electrodes of the high-pressure discharge lamp La, a peak voltage of about 800 V is formed during ignition. The output voltage of the piezoelectric transformer PT is rectified and doubled by means of a voltage doubler circuit Dl, D2, C, so that the rectified capacitor C of the pulse igniter C, FS, Tri the rectified double output voltage of the piezoelectric transformer PT, which upon excitation of the piezoelectric transformer PT sufficient with its resonant frequency for the breakthrough of the spark gap FS, so that the ignition capacitor C discharges via the spark gap FS and the primary winding Lp of the ignition transformer Tri. In the secondary winding Ls of the ignition transformer Tri thereby high voltage pulses are induced with which the auxiliary ignition electrode ZE of the high pressure discharge lamp La is acted upon to ignite the gas discharge in the high pressure discharge lamp La. After ignition of the gas discharge, the switching frequency of the switching means S is changed, so that no excitation of the piezoelectric transformer PT and no breakthrough of the spark gap FS more. The voltage provided by the secondary winding of the transformer Tr2 then serves to supply the series resonant circuit LRes, CRes and the high-pressure discharge lamp La. As already described above in the seventh embodiment, the power consumption of the high-pressure discharge lamp La is controlled by varying the switching frequency of the switching means S and thus by varying the AC voltage frequency. In stationary operation, the high pressure discharge lamp La has a burning voltage in the range of about 40 V to 90 V.

Claims

claims

1. ignition device for igniting the gas discharge in a high-pressure discharge lamp (La), wherein the ignition device is designed as a pulse ignition device (C, FS, Tri), characterized in that a piezoelectric transformer (PT) for supplying power to the pulse ignition device (C, FS, Tri) is provided.

2. Ignition device according to claim 1, wherein the pulse ignition device comprises a switching means (FS), a charge storage means (C), and an ignition transformer (Tri) for generating the ignition voltage required for igniting the gas discharge of the high-pressure discharge lamp (La).

3. Ignition device according to claim 1 or 2, wherein the voltage output of the piezoelectric transformer (PT) a voltage doubling circuit (Dl, D2, C) is connected downstream.

4. Ignition device according to claim 2, wherein the switching means (FS) is a voltage-dependent switching means.

5. Ignition device according to claim 2, wherein the switching means (FS) has a switching threshold voltage greater than 800 V.

6. Ignition device according to claim 2, wherein the ignition device is supplied with a supply voltage of less than 500 volts.

7. Ignition device according to claim 2, wherein the ignition of the lamp takes place by means of a Zündhilfselektrode (ZE).

An igniter according to claim 1, 2 or 7, wherein the input capacitance of the piezoelectric transformer (PT) is part of a resonant circuit which is excited during ignition to produce a sufficiently high voltage between the main electrodes of the lamp.

9. Ignition device according to claim 8, wherein a capacitor (CK) in series with the inductance (LGes) of the resonant circuit, which ensures a sufficiently high voltage between the main electrodes of the lamp during ignition, is arranged and after the ignition to a partial compensation of the inductance (LGes) serves.

10. Ignition device according to one or more of the preceding claims, wherein components of the ignition device (C, FS, Tri) or or and the piezoelectric transformer (PT) in the lamp base of the high-pressure discharge lamp (La) are housed.

1 1. Control gear for a high pressure discharge lamp (La) with a pulse ignition device (C, FS, Tri) and a piezoelectric transformer (PT) for supplying power to the pulse ignition device (C, FS, Tri).

12. Operating device according to claim 1 1, which supplies the high-pressure discharge lamp with a lamp current whose frequency is greater than 0.1 MHz.

13. Operating device according to claim 1 1, wherein the input capacitance of the piezoelectric transformer (PT) is a functional part of the voltage converter, which supplies the lamp (La) with energy.

14. Operating device according to claim 13, wherein the input capacitance of the piezoelectric transformer (PT) is used for switching discharge of one or more of the semiconductor switches used.

15. A method for operating a high-pressure discharge lamp, wherein for igniting the gas discharge in the high-pressure discharge lamp (La), as a pulse ignition device (C, FS, Tri) formed ignition device, characterized in that the voltage supply of the Impulszündvor- direction (C, FS, Tri ) by means of a piezoelectric transformer (PT).

16. The method according to claim 15, wherein the shutdown of the pulse ignition device (C, FS, Tri) takes place in that at the voltage output of the piezoelectric transformer (PT), a supply voltage for the pulse ignition device (C, FS, Tri) is provided, not for switching a voltage-dependent switching means (FS) of the pulse ignition device

(C, FS, Tri) is sufficient.

17. The method according to any one of claims 15 to 16, wherein the shutdown of the pulse ignition device takes place in that the frequency spectrum of the piezoelectric transformer (PT) exciting voltage is changed so that at the voltage output of the piezoelectric transformer (PT) a supply voltage for the pulse ignition device ( C, FS, Tri) is generated, which is not sufficient for switching a voltage-dependent switching means (FS) of the pulse ignition device (C, FS, Tri).

18. The method according to claim 15, wherein the excitation of the piezoelectric transformer (PT) is effected by an amplitude-modulated signal.

19. The method of claim 15, wherein the excitation of the piezoelectric transformer is effected by a harmonic of one of its resonant frequencies, which is included in the frequency spectrum of the voltage applied to the voltage input of the piezoelectric transformer (PT) voltage.