Electric lamp and discharge devices: systems – Current and/or voltage regulation – Automatic regulation
Reexamination Certificate
1996-07-02
2001-01-16
Kinkead, Arnold (Department: 2817)
Electric lamp and discharge devices: systems
Current and/or voltage regulation
Automatic regulation
C315S291000, C315S082000, C307S010800
Reexamination Certificate
active
06175200
ABSTRACT:
STATE OF THE ART
The invention is based on a device for operating a gas discharge lamp of the type having an energy supply circuit which provides an alternating-current voltage or an alternating current normally having a predetermined period in order to feed the gas discharge lamp with a predetermined power defined in the main claim. A circuit arrangement for operating a gas discharge lamp is known from DE-A 41 36 486 which includes a voltage transformer that converts the energy provided by a direct current source into an alternating-current voltage of suitable height and frequency. The voltage transformer includes a DC/DC converter and a downstream bridge circuit, in whose diagonal the gas discharge lamp is disposed. The DC/DC converter increases the voltage provided by a direct current source, which is configured as a battery, to a value sufficient to operate the gas discharge lamp. The bridge circuit operates as an inverse rectifier, and converts the direct-current voltage into a corresponding alternating-current voltage. The known circuit arrangement provides that, directly after ignition of the gas discharge lamp, the bridge circuit still does not operate as an inverse rectifier, and therefore acts upon the gas discharge lamp with the direct-current voltage generated by the DC/DC converter. Depending on a signal of a status determination device that emits a signal when the gas discharge lamp has ignited successfully, and depending on the time predetermined by a delay device, the inverse rectifier is controlled in such a way that the gas discharge lamp is acted upon by the provided alternating-current voltage. The previously observed extinguishing of the gas discharge lamp directly after ignition during the first zero crossings of the alternating current of the lamp is prevented by the known measure.
In subsequent operation with the alternating-current voltage, an instantaneous power reduction which can lead to a short-time reduction in the light arc, even in this operating state, occurs in the gas discharge lamp during each pole-reversal process. A sufficiently high operating frequency, an example of which would be a few hundred Hertz, ensures that the light arc is not completely extinguished during the brief zero crossing of the current. The voltage necessary to keep the light arc operating at normal rating after the pole-reversal process corresponds to the normal arc drop voltage of the gas discharge lamp. A reduction in the electrical power supplied to the gas discharge lamp leads to the occurrence of a complete breakdown of the light arc during the pole-reversal process. The energy supply circuit must therefore be capable of applying the necessary re-ignition voltage following the pole-reversal process. A reduction in the electrical power supplied to the gas discharge lamp is therefore possible to the extent that the energy supply circuit is capable of applying the re-ignition voltage.
It is therefore the object of the invention to provide a device for operating a gas discharge lamp that assures reliable operating of the gas discharge lamp in an operating phase with reduced power.
The object is accomplished by the features disclosed in the main claim.
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, having an energy supply circuit which provides an alternating-current voltage or an alternating current normally having a predetermined period in order to feed the gas discharge lamp with a predetermined power, and circuit means responsive to a reduction of the average lamp power with respect to operation at normal rating, for causing an extension of the period of the lamp alternating-current voltage or the lamp alternating current.
The device according to the invention has the advantage that an increase in the output voltage is not necessary in order to achieve a higher re-ignition voltage. In accordance with the invention, it is provided that an extension of the period of the alternating-current lamp voltage or the alternating lamp current is provided when a reduction in the average lamp power occurs with respect to operation at normal rating. The reduction in re-ignition voltage through a lowering of the operating frequency could be attributed to the fact that a more intense heating of the lamp electrodes takes place, which leads to an increased electron emission.
Advantageous modifications and embodiments of the device of the invention ensue from the dependent claims.
An advantageous embodiment provides that the extension of the period is performed for each half-period. This measure results in a particularly simple embodiment of the device according to the invention, because only the operating frequency of the lamp is to be reduced. A change in a possibly predetermined mark-space ratio with an assumed rectangular voltage need not be undertaken.
Another advantageous embodiment provides that the amount of the extension of the period is a function of the amount of the provided reduction in power.
An advantageous modification relates to the energy supply circuit, which preferably includes a DC/DC converter that provides a direct-current voltage at its output which is converted into an alternating-current voltage in a subsequent bridge circuit in whose diagonal the gas discharge lamp is disposed.
An embodiment of this modification provides that the DC/DC converter is fed by a battery.
The modifications of the energy supply circuit provided in accordance with the invention permit the embodiment of a highly-efficient DC/DC converter that can have a significantly higher clock frequency internally that the alternating-current voltage acting upon the gas discharge lamp. The comparably low-frequency alternating-current voltage having a frequency of, for example, a few hundred Hertz is generated by corresponding actuation of the bridge circuit.
The device of the invention is particularly suited for operating a metal-doped, high-pressure gas discharge lamp, which is critical with respect to the consumption of a re-ignition voltage after the undesired extinguishing of the light arc. A preferred use of the high-pressure gas discharge lamp, particularly of the metal-doped, high-pressure gas discharge lamp, is in a headlight of a motor vehicle.
Further advantageous modifications and embodiments of the device of the invention for operating a gas discharge lamp ensue from further dependent claims and the following description.
REFERENCES:
patent: 5498935 (1996-03-01), Nakamura
patent: 4136486 (1993-05-01), None
Kinkead Arnold
Kunitz Norman N.
Robert & Bosch GmbH
Venable
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