Electric lamp and discharge devices: systems – Periodic switch in the supply circuit – Periodic switch in the primary circuit of the supply...
Reexamination Certificate
2001-02-26
2003-02-18
Vu, David (Department: 2821)
Electric lamp and discharge devices: systems
Periodic switch in the supply circuit
Periodic switch in the primary circuit of the supply...
C315S224000, C315S276000
Reexamination Certificate
active
06522082
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an operating method and a corresponding electronic ballast for a discharge lamp. In this case, the operating method and the ballast relate to a specific type of discharge lamp, in which so-called dielectrically impeded discharges are utilized to generate light. In order to produce such discharges, a dielectric layer is situated between at least one of the discharge electrodes and the discharge medium of the discharge lamp. The technology of discharge lamps with dielectrically impeded discharges is not discussed in detail here and, in this regard, reference is made to the prior art.
PRIOR ART
Technical development in this field has principally been concerned heretofore with the discharge lamp as such. One exception to this is an earlier patent application in respect of a relevant operating method with pulsed active power coupling into the discharge lamp. In this respect, reference is made to WO 94/23442, whose disclosure content is incorporated here by reference. The operating method presented therein forms the foundation for the invention described below.
In this case, the present invention is concerned with converting the operating procedure which is described in principle in the cited prior art into an operating method which is particularly advantageous in terms of electrical engineering, and an associated electronic ballast. When developing such an operating method and ballast, the aim generally is to fulfil various quality criteria in an overall compromise which is as favorable as possible. Firstly, an electronic ballast should be operated as power-efficiently as possible in order to obtain, together with the efficiency of the lamp, a good overall efficiency of an illumination system comprising discharge lamp and ballast.
A second aspect concerns the electronic ballast having a compact and lightweight design made possible by a corresponding operating method, which ballast, in this respect, is also suitable for installation in the case of confined space conditions or weight restrictions. This has a significant part to play precisely in the areas of application which are of particular interest with regard to discharge lamps with a dielectrically impeded discharge. Examples are backlighting systems for flat screens or copying lamps, which will be discussed further on in the description.
Finally, economic advantages with regard to mass production costs and service life and frequency of failure are intended to be attained.
SUMMARY OF THE INVENTION
The invention is based on the technical problem, proceeding from the technical teaching of WO 94/23442, of specifying a particularly favorable operating method using a ballast, and an illumination system and ballast designed for this.
For this purpose, the invention provides an operating method for a discharge lamp having a dielectric layer between at least one electrode and a discharge medium using a ballast having a power-supplied primary circuit, a secondary circuit containing the discharge lamp, and also a transformer which connects the primary circuit to the secondary circuit, in which method a voltage pulse is impressed on the secondary circuit from the primary circuit via the transformer, which voltage pulse leads to an external voltage U
L
effecting an ignition across the discharge lamp L and to an internal counterpolarization in the discharge lamp, characterized in that, by means of the ballast, afterward the charge effecting the external voltage across the discharge lamp is withdrawn from the discharge lamp and, in this way, the discharge lamp is led to effect a back ignition by the remaining internal counterpolarization.
Furthermore, the invention relates to an illumination system having a discharge lamp and a ballast which is designed for the operating method according to the invention.
Finally, the invention also relates to a particular design of a ballast which is suitable for the operating method, namely in the form of a forward converter.
The various dependent claims relate to preferred refinements of the invention.
The invention thus provides an operating method for a discharge lamp of the type already described, in which a ballast is used. For the purposes of this invention, this ballast, which is preferably an electronic ballast, comprises a primary circuit which is supplied with power in a manner that is of no further interest here, and a secondary circuit into which the lamp is intended to be connected or is connected. The primary circuit and the secondary circuit are coupled via a transformer via which power can be coupled into the secondary circuit from the primary circuit.
Provision is now made for coupling a voltage pulse into the secondary circuit via the transformer, which voltage pulse leads to an external voltage across the discharge lamp. The subsequent behavior of the discharge lamp itself is of importance for the concept underlying the invention. Specifically, it has been found that, in the discharge lamps with dielectrically impeded discharges which are considered here, a counterpolarization occurs in the discharge lamp as a dielectric reaction to the external voltage and as a result of a discharge ignited by an external voltage.
To be precise, after the ignition voltage has been reached, discharges are formed in the discharge medium, as is described in more detail in the foundation application pertaining to the operating method, to which reference has already been made. As a consequence, charge carriers move to the dielectric layer on one of the electrodes and accumulate to an increasing extent on the dielectric layer. This creates an internal counterpolarization relative to the external field which increases until an overall field is no longer present in the discharge medium, which also means that current can no longer flow through the lamp. As a result, the discharge medium has changed from a behavior acting as an ohmic load—although with time-variable resistance—to an electrical behavior manifested as capacitance.
Added to this is the fact that further capacitances are connected in series with the discharge medium, to be precise in particular through one or a plurality of dielectric layers on the electrodes.
Proceeding from this physical behavior of the discharge lamp, the fundamental concept of the invention consists, then, in not interpreting this internal counterpolarization as a disturbing effect, but rather integrating it functionally into the operating method and also into the functional principle of the associated ballast. In this sense, the operating method according to the invention provides for the external voltage across the discharge lamp, which originally caused the counterpolarization just described, to be withdrawn again from the discharge lamp sufficiently rapidly in order to have the internal counterpolarization lead to a further ignition in the opposite direction after the first ignition effected by the external voltage. This second ignition is in this case designated as back ignition and is not attributed, at any rate not completely, to an external voltage but rather, at any rate at least partly, to the internal counterpolarization.
In this application, for the sake of clarity of explanation, it is thus argued that the external voltage across the discharge lamp or the internal counterpolarization effects an ignition. For the sake of completeness, however, this must also be expanded by stating that the ignition behavior of the lamp depends on a number of further parameters. In particular, the edge steepness or the dissipation when building up a voltage across the lamp or a field in the lamp has a significant part to play. This means that, for example, an ignition on account of an external voltage across the discharge lamp takes place at smaller voltage values if said external voltage is built up very rapidly. This basically empirical result can probably be explained by the fact that the electrodes can follow the field rise more poorly, possibly also by the fact that with a steeper voltage rise and thus a larger proportion of high-
Hitzschke Lothar
Vollkommer Frank
Wammes Klaus
Bessone Carlo S.
Patent-Treuhand-Gesellschaft fuer Elektrische Gluehlampen mBH
Vu David
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