Electric lamp and discharge devices: systems – Current and/or voltage regulation – Automatic regulation
Reexamination Certificate
1997-05-05
2001-01-09
Kinkead, Arnold (Department: 2817)
Electric lamp and discharge devices: systems
Current and/or voltage regulation
Automatic regulation
C315S291000, C315S082000, C307S010800
Reexamination Certificate
active
06172469
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention is based on a device for operating a gas discharge lamp having a power supply circuit which makes available an alternating voltage or an alternating current of a predetermined period duration for the supply of the gas discharge lamp with a predetermined power. From DE-A 37 15 162.2, a circuit arrangement for operating a gas discharge lamp is known comprising a voltage transformer that converts the energy made available by a direct current source to an alternating voltage of appropriate level and frequency. At control inputs, the voltage transformer receives control signals derived from the lamp voltage and from the lamp current to supply the gas discharge lamp with a predetermined electrical power. During the pole-changing process of the alternating voltage, an instantaneous power reduction occurs in the gas discharge lamp, which power reduction can lead to a short-time reduction of the arc. A sufficiently high operating frequency, which may be, for example, at a few 100 Hertz, ensures that the arc does not go out entirely during the short current zero. The required voltage after the pole-changing process for the maintenance of the arc during operation at normal rating corresponds to the normal burning voltage of the gas discharge lamp. A reduction of the electrical power supplied to the gas discharge lamp results in a total interruption of the arc during the pole-changing process. The power supply circuit must be able to come up with the necessary reignition voltage after the pole-changing process. A reduction of the electrical power supplied to the gas discharge lamp is therefore possible to the same extent that the power supply circuit is able to come up with the reignition voltage.
It is the object of the invention to provide a device for operating a gas discharge lamp which ensures a reliable operation of the gas discharge lamp in an operating phase with reduced power.
SUMMARY AND ADVANTAGES OF THE INVENTION
The above object generally is achieved according to the present invention by a device for operating a gas discharge lamp, including a power supply circuit which makes available an alternating voltage or an alternating current of a predetermined period duration for the supply of the gas discharge lamp with a predetermined power, wherein upon a desired reduction of the mean lamp operating power rating compared to the operation at normal power rating, an increase of the instantaneous power is provided within a half period duration immediately prior to the pole change of the alternating voltage or alternating current supplied to the lamp.
The device according to the invention offers the advantage that an increase of the output voltage of an existing power supply circuit is not necessary in order to accomplish a higher reignition voltage. The invention provides that, during a reduction of the mean lamp rating compared to the operation at normal rating, an increase of the instantaneous power is provided within a half period duration immediately prior to the pole change of the alternating voltage. The short-time increase of the instantaneous power prior to the pole-changing process has the effect that the necessary reignition voltage after the pole-changing process is not considerably higher compared to the operation at normal rating.
Advantageous modifications and configurations of the device according to the invention ensue from the dependent claims.
An advantageous feature provides that the increase of the instantaneous power prior to the pole-changing process corresponds to the power during operation at normal rating. In this design, a power reserve of the power supply circuit is not necessary.
In another advantageous configuration, wherein the power supply circuit can supply a power which is above the rated power, it is provided that the short-time instantaneous power is above the rated power. This measure ensures a reignition of the gas discharge lamp after the pole-changing process in all conceivable operating conditions, also taking ageing of the gas discharge lamp into account.
According to an advantageous modification, it is provided that the increase of the instantaneous power within a half period duration prior to the pole change of the alternating voltage is provided in each half period of the alternating voltage. This measure further increases the reliability of the reignition of the gas discharge lamp after the pole-changing process.
A further advantageous modification provides that the increase of the instantaneous power is implemented, in particular, by increasing the current, with the current intensity being predetermined. The current intensity determines the ionization conditions in the gas discharge lamp and therefore is an essential characteristic quantity which is of importance particularly for a pole-changing process.
A modification of the device according to the invention provides that the increase of the instantaneous power takes place a predetermined time prior to the pole-changing process, which time is a function of the period duration of the alternating voltage. This advantageous modification allows an adaptation to a different operating frequency of the gas discharge lamp.
A further modification relates to the power supply circuit which is preferably configured as voltage transformer supplying a direct voltage at its output, which direct voltage is converted to an alternating voltage in a subsequent bridge circuit in whose diagonal the gas discharge lamp is disposed.
A feature of this modification provides that the voltage transformer is a DC/DC converter fed by a battery.
The modifications of the power supply circuit which are provided according to the invention allow the realization of a highly-efficient voltage transformer which, internally, may have a considerably higher clock frequency than the alternating voltage that is supplied to the gas discharge lamp. The comparatively low-frequency alternating voltage having a frequency of, for example, a few 100 Hertz, is generated in the bridge circuit.
The device according to the invention is particularly suited for operating a metal-doped high-pressure gas discharge lamp which is critical with respect to the need for reignition after the arc has gone out. A preferred application of the high-pressure gas discharge lamp, particularly of the metal-doped high-pressure gas discharge lamp, is the use in a headlight of a motor vehicle.
Further advantageous modifications and features of the device according to the invention for operating a gas discharge lamp ensue from further dependent claims and from the following description.
REFERENCES:
patent: 5498933 (1996-03-01), Nakamura
Kinkead Arnold
Kunitz Norman N.
Robert & Bosch GmbH
Venable
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