EP2119323B1 - Ignition transformer for a discharge lamp - Google Patents

Abstract

An ignition transformer for a discharge lamp is provided having a transformer core whose material and dimensions are selected in such a manner that the Curie temperature of the material after the ignition which is achieved by means of the ignition transformer can be achieved by a voltage drop across a secondary winding of the ignition transformer.

Description

Technical area

The invention is based on an ignition transformer for igniting a discharge lamp, preferably high-pressure gas discharge lamp, by means of pulse ignition, whereby after the ignition a high-frequency lamp operation takes place on an electronic ballast.

State of the art

One in the publication WO2005 / 011338 reproduced circuit arrangement for a high-pressure discharge lamp has an operating part with a DC voltage source and an ignition part with pulse source and a mercury-free metal halide high-pressure discharge lamp. In the ignition part, the discharge lamp and a secondary winding of an ignition transformer are connected in series. The primary winding of the ignition transformer is controlled by a pulse source. As material for the ignition transformer core, a particularly low-loss material is preferred. After ignition of the discharge lamp via pulse source and ignition transformer, the secondary winding with the discharge lamp in the operating circuit is in series.

Since the lamp current flows through the secondary winding during operation of the discharge lamp, this secondary winding has an unwanted inductance during lamp operation. A partial compensation of the inductance of the secondary winding can be achieved according to the above-mentioned document be connected in series with the secondary winding, a capacitor.

Patent JP 2005340060 (Toshiba) describes a transformer for filament heating, wherein the transformer core is formed so that the Curie temperature is reached after the ignition of the lamp.

In a high-frequency lamp operation, however, using the aforementioned capacitor remains the inductance of the secondary winding in the lamp circuit, so that both losses occur in the ignition transformer and in the high-frequency lamp current supplying converter.

Presentation of the invention

The object of the present invention is to provide an ignition transformer for a discharge lamp, in which the losses during high-frequency lamp operation are reduced and a low circuit complexity is required, as well as to provide a compact lamp cap.

This object is achieved by the ignition transformer for the discharge lamp according to claim 1 and a lamp cap according to claim 9.

Particularly advantageous embodiments can be found in the dependent claims.

According to the invention, an ignition transformer for a discharge lamp is provided with a transformer core whose material, power and structure are chosen in such a way that the Curie temperature of the material can be achieved by a voltage drop across a secondary winding of the ignition transformer after the ignition caused by the ignition transformer , The heating up to the ignition temperature takes place with the at the secondary winding applied energy, wherein after reaching the Curie temperature, the secondary winding of the ignition transformer is practically ineffective and only a small power and absorption from the lamp circuit is necessary to keep the transformer core to the Curie temperature.

It is preferred that the material of the transformer core has a Curie temperature in the range of 60 ° C to 400 ° C, especially between 100 ° C and 220 ° C, thereby overheating the transformer core possibly due to materials in the environment the transformer core could have a negative impact is avoided.

The Curie temperature in the range between 100 ° C and 220 ° C is preferred, since with increasing Curie temperature, the efficiency decreases due to heat losses, on the other hand, the Curie temperature must be above the ambient temperature in any case to ensure proper functioning can.

Further, the transformer core is preferably configured such that the magnetic length and the magnetic effective cross-section of the transformer core are minimized in such a way that sufficient magnetic ignition between the primary and secondary windings for ignition in the cold state of the ignition transformer. Thus, a quick ignition can take place while the secondary winding is virtually ineffective during lamp operation.

In a particular embodiment, the transformer core has a ring shape, since with a high-frequency lamp current less electromagnetic interference than an open geometry such as a rod core.

Furthermore, it is preferred if the ignition transformer is formed thermally isolated to keep the transformer core at a lower power to be supplied and thus higher efficiency of the entire assembly to Curie temperature and to make the secondary winding virtually ineffective.

The transformer core is preferably encapsulated for thermal and electrical insulation, whereby this can be produced economically favorable.

Alternatively, the transformer core may be provided in a sealed housing, thereby preventing the convection of air and the associated increased cooling.

The ignition transformer is provided in particular for a high-pressure discharge lamp. In this case, a compact design with good luminous efficacy can be achieved especially in automotive headlamps.

Furthermore, a lamp cap for a discharge lamp is provided with an ignition transformer having the properties described above, wherein due to the small volume of the transformer core, a compact design of the lamp assembly can be implemented.

In a further development, the discharge vessel of the lamp is provided in the hole of the ignition transformer in the lamp base at least partially protruding. In this way, the large axial dimension of the discharge lamps can be to provide the transformer core in the vicinity of the discharge vessel of the discharge lamp.

Brief description of the drawings

Fig. 1

Eine Schaltungsanordnung für eine Entladungslampe mit einem Zündtransformator entsprechend der vor- liegenden Erfindung,

Fig. 2

Eine schematische Ansicht eines Lampensockels mit Zündtransformator, Impulsquelle und Entladungslam- pe entsprechend der vorliegenden Erfindung,

Fig. 3

Eine Perspektivansicht eines Transformatorkerns mit Spalt für einen Zündtransformator entsprechend der vorliegenden Erfindung,

Fig. 4

Eine graphische Darstellung der Abhängigkeit der Anfangspermeabilität von der Temperatur bei einem Material für den Transformatorkern entsprechend der vorliegenden Erfindung,

Fig. 5

Den Aufbau der Impulsquelle zur Ansteuerung eines Zündtransformators entsprechend dem ersten Ausfüh- rungsbeispiel der Erfindung,

Fig. 6

Den Aufbau einer Impulsquelle für einen Zündtrans- formator entsprechend dem zweiten Ausführungsbei- spiel der Erfindung, und

Fig. 7

Eine graphische Darstellung der Spannung an der Sekundärwicklung und am Kondensator entsprechend dem zweiten Ausführungsbeispiel.

Fig. 8

Eine Schaltungsanordnung für eine Entladungslampe unter Verwendung einer symmetrischen Zündung ent- sprechend dem dritten Ausführungsbeispiel.

Fig. 9

zeigt eine Abwandlung eines Transformatorkerns mit beispielhaften Maßen.

In the following, the invention will be explained in more detail with reference to exemplary embodiments. The figures show:

Fig. 1

A circuit arrangement for a discharge lamp with an ignition transformer according to the present invention,

Fig. 2

A schematic view of a lamp base with ignition transformer, pulse source and discharge lamp according to the present invention,

Fig. 3

A perspective view of a transformer core with gap for an ignition transformer according to the present invention,

Fig. 4

A graph of the dependence of the initial permeability of the temperature on a material for the transformer core according to the present invention,

Fig. 5

The structure of the pulse source for driving an ignition transformer according to the first embodiment of the invention,

Fig. 6

The structure of a pulse source for an ignition transformer according to the second embodiment of the invention, and

Fig. 7

A graph of the voltage at the secondary winding and the capacitor according to the second embodiment.

Fig. 8

A circuit arrangement for a discharge lamp using a symmetrical ignition according to the third embodiment.

Fig. 9

shows a modification of a transformer core with exemplary dimensions.

Preferred embodiment of the invention

A circuit arrangement 1 with ignition transformer 2 according to the present invention is shown in FIG FIG. 1 shown.

A primary winding 4 of the ignition transformer 2 is fed by a pulse source 6 and an ignition voltage U2. The secondary winding 8 of the ignition transformer 2 is connected in series with the discharge lamp 10 and is fed by an operating voltage U _Q. The discharge lamp used is preferably a high-pressure gas discharge lamp, for example a mercury-containing metal halide lamp of the "OSRAM HQI" type.

In FIG. 2 a discharge lamp 10 is shown in a lamp cap 12. The lamp cap 12 has the Impulsqüelle 6, through which the primary winding 4 of the ignition transformer 2 is fed. The ignition transformer 2 is, as in FIG. 2 shown, preferably annular and has a transformer core 14, as in FIG. 3 shown has an air gap 15. On the transformer core 14, the secondary winding 8 is applied, which is surrounded by the primary winding 4.

As already in FIG. 1 As shown, a terminal 16 of the discharge lamp 10 is connected to one end of the secondary winding 8, while another terminal 18 of the discharge lamp 10 is supplied with the operating voltage U _Q via the lamp cap. As already in FIG. 1 shown, the pulse source 6 is supplied with the ignition voltage U2. The lamp base 12 is preferably filled with a potting compound, such as silicone, so that a high voltage insulation is present around the ignition transformer and at the same time a thermal insulation of the transformer core 14 is provided. It is a casting with a foam structure or a hollow body filling conceivable. Alternatively, the core may be provided in a sealed housing, which prevents convection of the air and thus prevents cooling.

The connections for the ignition voltage U2 and the operating voltage Ü _Q are led out of the lamp base as electrical connections to the operating device.

The discharge vessel 20 of the discharge lamp 10 is immersed in a central hole in the ignition transformer 2, whereby, as already in the published patent application DE 19610385 set out, a small-volume gas discharge lamp with short power supplies can be implemented in an integrated design. In addition to the advantageous compact design losses in the ignition voltage can be kept low due to this compact design.

In FIG. 3 the exemplary perspective view of the transformer core 14 is shown with an air gap 15.

The core material used is a ferrite. In this example, material N30 from manufacturer Epcos having an outer diameter of 25mm, an inner diameter of 15mm, a height of 3.8mm and an air gap of 3.5mm is used. The material for the transformer core is chosen in such a way that the Curie temperature directly after ignition is achieved by utilizing a portion of the energy provided by the transducer to heat the transformer core. When the transformer core has at least partially reached the Curie temperature, the secondary winding of the transformer is substantially ineffective, but low power absorption from the lamp circuit is required to maintain the transformer core or parts of the transformer core at the Curie temperature.

In the prior art, a high Curie temperature was sought so that the magnetic device can be operated at a high power. In contrast, in the present invention, a Curie temperature is preferably sought in the range between 60 ° C and 400 ° C of the material, since from the viewpoint of the prior art due to poor ferrite properties of the desired effect in the secondary winding already occurs at an early stage ,

While in the prior art with regard to desired low losses, a large cross-section of the transformer core was advantageous, in the present invention, a particularly small core cross-section is desired. In addition, the magnetic length should be kept low. As a result, the energy required to heat the transformer core can be low being held. In summary, it can thus be said that a small core volume is advantageous for the present invention. However, the transformer core is to be chosen so large that the transformer can perform its functions, ie in the cold state allows sufficient magnetic coupling between the primary and the secondary winding.

As core form is particularly the in FIG. 3 shown ring shape, since at such a temperature and high-frequency lamp currents less electromagnetic interference than in a rod core caused, which occurs especially at temperatures near or at the Curie temperature.

Out FIG. 4 It can be seen that the permeability reaches a value of about 1 at a temperature of about 143 ° C, the Curie temperature, with the core material N30 used. If now, during operation after ignition, the temperature of the transformer core is kept close to 143 ° C or slightly above that temperature, the transformer core loses its ferrimagnetic properties and shows only paramagnetic properties, whereby the secondary winding is effectively ineffective.

In the first and second embodiments described below, a transformer core made from the material N30 as described above is used.

FIG. 5 shows a pulse source 26 according to the first embodiment, instead of the pulse source 6 from FIG. 1 is used.

The secondary winding 8 has 30 turns of Teflon-insulated wire and has an impedance of 39μH at 20 ° C. The primary winding has two turns. The middle turns of both the primary winding 4 and the secondary winding 8 are arranged on the transformer core 14 with respect to the air gap. The transformer core is insulated by vacuum encapsulation by means of silicone heat and high voltage. The primary winding 4 is connected in series via a resistor 28 of 100 kΩ and a spark gap 30 with a switching voltage of 2 kV. A capacitor 32 of 27nF is connected in parallel via the resistor 28 to the ignition voltage U2. The ignition voltage U2 is 2.5kV.

Subsequently, the operation of an ignition transformer with the pulse source 26 from FIG. 5 described.

As long as an ignition voltage U2 is applied, 8 pulses with peak voltage of 21kV are generated by the ignition transformer 2 to the secondary winding. This leads to the ignition of the FIG. 5 Discharge lamp 10, not shown, is a mercury-containing metal halide lamp of the "OSRAM HQI" type with a nominal power of 35W.

After the ignition of the discharge lamp 10, the ignition voltage U2 is switched off, so that no further ignition pulses are generated via the ignition transformer 2. Corresponding FIG. 1 An operation of the discharge lamp 10 via the operating voltage U _Q with a frequency of 2 MHz. The discharge lamp 10 is operated with an operating current of 400mA, thereby initially an ohmic-inductive voltage drop across the secondary winding 8 of about 200V occurs. Due to this voltage drop, the transformer core 14 is heated. The lamp voltage is initially 20V.

When the temperature of the transformer core 14 comes close to the Curie temperature of about 143 ° C, it decreases accordingly FIG. 4 the inductance drastically, so that the voltage drop across the secondary winding sets to about 40V. By means of suitable thermal insulation and a corresponding design of the circuit, the core temperature reaches a value close to the Curie temperature in the same time range as the ramp-up of the lamp. In practice, this period may be a few seconds to a few minutes. During this time, the lamp voltage increases from initially 20V to 85V. Due to the reduced voltage drop across the secondary winding 8 only a low operating voltage U _{Q is} necessary.

A regulation of the lamp power is now carried out by increasing the frequency, for example from 2.5MHz to 3.5MHz. This regulation of the lamp power and the stabilization of the discharge via the remaining residual inductance of the secondary winding 8. This residual inductance depends on the inductance of the air coil formed by the secondary winding 8, and the temperature conditions during steady-state operation. This residual inductance is preferably adjusted so that the resulting impedance in the range of _^1/5 is up to five times the impedance of the discharge lamp. In the first embodiment, the residual inductance has been 8μH. Under the impedance of the discharge lamp should Here, the quotient of the two of the two RMS values of lamp voltage and current at rated power are understood.

In FIG. 6 a pulse source 46 according to the second embodiment is shown. This pulse source 26 of the first embodiment has a spark gap 50 and a capacitor 52. A resistance comparable to the resistor 28 in the first embodiment is not provided in the second embodiment. The capacitor 52 has a capacitance of 70nF and the spark gap has a switching voltage of 800V.

In FIG. 7 In the upper diagram, the voltage generated by the secondary winding 8 is shown, while in the lower diagram the voltage across the capacitor 52 can be seen.

The operation subsequent to the ignition of the lamp is the same as that in the circuit arrangement according to the first embodiment. By the circuit arrangement according to the first and second embodiments can be achieved for a lamp operation after ignition, a low inductance of the secondary winding and lower losses during operation of the discharge lamp.

The discharge lamps are preferably used for video projection, in the motor vehicle headlight and for general lighting. Compared to that in the WO2005 / 011338 In the case of a circuit arrangement for the operation of a discharge lamp according to the present invention, there is no additional component, such as the partial compensation capacitor, for example from this mentioned document necessary. As a result, with the present invention, a good overall efficiency can be achieved in the circuit arrangement.

In the embodiments shown so far, an asymmetrical ignition arrangement has always been considered, in which the ignition transformer has only one secondary winding. The FIG. 8 shows a circuit arrangement 54 according to the third embodiment wherein a symmetrical ignition is realized by the two secondary windings 8a and 8b. As the core material, a ferrite having a Curie temperature of only about 109 ° C and a maximum initial permeability of only 2500 is used, as opposed to about 143 ° C and 5400 μm FIG. 4 in the two previous embodiments. Furthermore, in Fig. 8 a pulse source 56 and a driver 58 which provides the voltages U2 and UQ. The connections for the power supply (eg 12 V DC or 230 V AC are designated 60. The circuit 54 is located in the lamp base

The geometric dimensions of the core, which has no gap, shows FIG. 9 , The two secondary windings 8a and 8b are wound on the two 30mm long core sides. In a further step, the primary winding was wound in half over the secondary windings 8a and down on the two long core sides.

The transformer is encapsulated in the lamp socket together with the pulse source and the operating device. Parts of the control gear which are particularly hot during operation were thereby be arranged, such as power semiconductors, in close proximity to the ignition transformer to use their waste heat to heat the transformer core can. During operation, therefore, very little energy must be removed from the lamp circuit in order to keep the transformer core close to the Curie temperature.

An ignition transformer for a discharge lamp with a transformer core is provided. The material and dimension of the transformer core are selected in such a manner that the Curie temperature of the material after ignition by the ignition transformer is achievable by a voltage drop across a secondary winding of the ignition transformer. In this way, only one residual inductance remains for the secondary winding. Furthermore, a lamp base for a discharge lamp is provided with such an ignition transformer, the discharge vessel of the lamp preferably protruding at least in sections into the center hole of the ignition transformer in the lamp base, resulting in a compact lamp base with discharge lamp.

Claims (10)

1. Ignition transformer (2) for a discharge lamp having a transformer core (14), characterized in that whose materials and dimensions are chosen in such a manner that the Curie temperature of the material after the ignition which is achieved by means of the ignition transformer (2) can be achieved by a voltage drop across a secondary winding (8) of the ignition transformer.
2. Ignition transformer according to Claim 1, with the Curie temperature of the material being in the range from 60°C to 400°C.
3. Ignition transformer according to Claim 1 or 2, with the magnetic length and the magnetically effective cross section of the transformer core (14) being minimized in such a manner that magnetic coupling which is sufficient for ignition occurs between the primary and secondary winding (4, 8) in the cold state of the ignition transformer.
4. Ignition transformer according to one of the preceding claims, with the transformer core being annular.
5. Ignition transformer according to one of the preceding claims, with the ignition transformer being thermally insulated.
6. Ignition transformer as clamed in Claim 5, with the transformer core (14) being encapsulated for thermal and/or electrical insulation.
7. Ignition transformer as claimed in Claim 5, with the transformer core (14) being provided in a closed housing, by means of which convection of air is reduced.
8. Ignition transformer as claimed in one of the preceding claims, which ignition transformer is intended for a highpressure discharge lamp.
9. Lamp cap (12) for a discharge lamp, characterized in that an ignition transformer (14) as claimed in one of the preceding claims.
10. Lamp cap as claimed in claim 9, with the discharge vessel (20) of the lamp projecting at least partially into the center hole of the ignition transformer in the lamp cap (12).

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