EP2119323A1

EP2119323A1 - Ignition transformer for a discharge lamp

Info

Publication number: EP2119323A1
Application number: EP08708820A
Authority: EP
Inventors: Bernhard Siessegger; Manfred RÖHL
Original assignee: Osram GmbH
Current assignee: Osram GmbH
Priority date: 2007-02-13
Filing date: 2008-02-08
Publication date: 2009-11-18
Anticipated expiration: 2028-02-08
Also published as: US8339060B2; DE102007017338A1; TW200850069A; JP5069321B2; WO2008098881A1; CN101578922B; ATE472928T1; JP2010518650A; DE502008000877D1; CN101578922A; EP2119323B1; US20100045199A1

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

description

Ignition transformer for a discharge lamp

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

A reproduced in the document WO2005 / 011338 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.

However, in the case of a high-frequency lamp operation, the inductance of the secondary winding in the lamp circuit also remains using the above-mentioned capacitor, so that both losses occur in the ignition transformer and in the converter supplying the high-frequency lamp current.

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 kundärwicklung 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 ⁰ C to 400 ⁰ C, in particular between 100 ° C and 220 ⁰ C, whereby an excessive heating of the transformer core, which may be due to materials in the environment the transformer core could have a negative impact is avoided.

It is the Curie temperature in the range between 100 ⁰ C and 220 ° C preferred because 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.

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

In a particular embodiment, the transformer core ring shape, as in 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 cast for thermal and electrical insulation, which makes it economically producible economically.

Alternatively, the transformer core can be provided in a closed housing, whereby the convection of air and the associated increased cooling can be prevented.

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 use lamps for providing the transformer core in the vicinity of the discharge vessel of the discharge lamp.

Brief description of the drawings

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

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

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

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

4 is a graph showing the dependence of initial permeability on temperature on a material for the transformer core according to the present invention;

5 shows the structure of the pulse source for controlling an ignition transformer according to the first embodiment of the invention,

Fig. 6 shows the construction of a pulse source for an ignition transformer according to the second embodiment of the invention, and Fig. 7 is a graph of the voltage across the secondary winding and the capacitor according to the second embodiment.

Fig. 8 shows 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.

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.

FIG. 2 shows a discharge lamp 10 in a lamp base 12. The lamp base 12 has the pulse source 6, through which the primary winding 4 of the ignition transformer 2 is fed. As shown in FIG. 2, the ignition transformer 2 is preferably of annular design and has a transformer core 14, which has an air gap 15 as shown in FIG. On the transfor- Matorkern 14, the secondary winding 8 is applied, which is surrounded by the primary winding 4.

As already shown in FIG. 1, 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 UQ via the lamp base. As already shown in FIG. 1, the pulse source 6 is supplied with the ignition voltage U2. The lamp cap 12 is preferably provided with a potting compound, such as a potting compound. Silicone, filled 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 U _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 stated in the published patent application DE 19610385, a small-volume gas discharge lamp with short power supply 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.

FIG. 3 shows the exemplary perspective view of the transformer core 14 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 using a portion of the energy provided by the converter 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 portions 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 ⁰ C and 400 ⁰ C of the material, as this occurs from the perspective of the prior art due to poor ferrite properties of the desired effect in the secondary winding 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 a core shape, the ring shape shown in FIG. 3 is particularly suitable, since at such a temperature and high-frequency lamp currents less electromagnetic interference is caused than in a rod core, which occurs especially at temperatures near or at the Curie temperature.

It can be seen from FIG. 4 that the permeability reaches a value of approximately 1 at a temperature of approximately 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 exhibits only paramagnetic properties, effectively rendering the secondary winding 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 which is used instead of the pulse source 6 of FIG. 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 10OkQ and a spark gap 30 with a switching voltage of 2kV. 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.

The operation of an ignition transformer with the pulse source 26 of Figure 5 will be described below.

As long as an ignition voltage U2 is applied, 8 pulses with peak voltage of 2IkV are generated by the ignition transformer 2 to the secondary winding. This leads to the ignition of the discharge lamp 10 (not shown in FIG. 5). The discharge lamp used 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. According to FIG. 1, the discharge lamp 10 is operated via the operating voltage U _Q with a frequency of 2 MHz. The discharge lamp 10 is operated with an operating current of 40 ohms, whereby 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, as shown in Figure 4, the inductance decreases drastically, so that the voltage drop across the secondary winding is set 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 UQ 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 takes place 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, as well as the temperature conditions during steady-state operation. This residual inductance is preferably set so that the resulting impedance is in the range of yζ 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 nominal power are understood.

FIG. 6 shows a pulse source 46 in accordance with the second exemplary embodiment. 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 7OnF and the spark gap has a switching voltage of 800V.

In Figure 7, the voltage generated by the secondary winding 8 is shown in the upper graph, while in the lower illustration, 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. The circuit arrangement according to the first and second exemplary embodiment makes it possible to achieve a low inductance of the secondary winding and also lower losses during operation of the discharge lamp for lamp operation after ignition.

The discharge lamps are preferably used for video projection, in the motor vehicle headlight and for general lighting. Compared to the prior art shown in WO2005 / 011338, in a circuit arrangement for the operation of a discharge lamp according to the present invention, no additional component, such as the capacitor for partial grain compensation from this document is 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. FIG. 8 shows a circuit arrangement 54 according to the third exemplary embodiment, wherein a symmetrical ignition is realized by the two secondary windings 8a and 8b. As the core material is a ferrite having a Curie temperature of only about 109 ⁰ C and a maximum initial permeability of 2500 is used only, in contrast to about 143 ° C and 5400 according to Figure 4 in the two previous embodiments. Also shown in FIG. 8 is 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, Figure 9 shows 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 the dimension of the transformer core are chosen in such a way that the Curie temperature of the material after the ignition effected by means of the ignition transformer can be achieved 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 projecting 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

claims

An ignition transformer (2) for a discharge lamp having a transformer core (14) whose material and dimensions are selected in such a manner that the Curie temperature of the material after ignition by the ignition transformer (2) is caused by a voltage drop across a secondary winding (8) of the ignition transformer is accessible.

2. Ignition transformer according to claim 1, wherein the Curie temperature of the material in the range of 60 ⁰ C to 400 ⁰ C.

3. ignition transformer according to claim 1 or 2, wherein the magnetic length and the magnetically active cross section of the transformer core (14) is minimized in such a way that sufficient for the ignition magnetic coupling between the primary and secondary windings (4, 8) in cold condition of the ignition transformer is present.

4. Ignition transformer according to one of the preceding claims, wherein the transformer core is formed annular.

5. Ignition transformer according to one of the preceding claims, wherein the ignition transformer is formed thermally insulated.

6. ignition transformer according to claim 5, wherein the transformer core (14) is cast for thermal and / or electrical or electrical insulation.

7. Ignition transformer according to claim 5, wherein the transformer core (14) is provided in a sealed housing, through which a convection of air is reduced.

8. Ignition transformer according to one of the preceding claims, which is provided for a high-pressure discharge lamp.

9. lamp base (12) for a discharge lamp with an ignition transformer (14) according to one of the preceding claims.

10. Lamp base according to claim 9, wherein the discharge barrel (20) of the lamp projects into the center hole of the ignition transformer in the lamp base (12) at least in sections.