Reexamination Certificate
2001-10-30
2003-05-27
Philogene, Haissa (Department: 2821)
C315S268000, C315S276000, C315S284000, C315S224000
Reexamination Certificate
active
06568774
ABSTRACT:
The present invention relates to an operating method for what is termed a silent discharge lamp. This is understood as a type of discharge lamp in which what are termed dielectrically impeded discharges are employed to generate light. The discharge is dielectrically impeded owing to a dielectric layer between the discharge medium of the discharge lamp and at least one of the electrodes. Silent discharge lamps per se are prior art and will not be explained here in detail.
The present invention is based on an operating method, developed by the same inventors, for pulsed coupling of active power into a quiet discharge lamp. Reference is made in this regard to WO94/23442, whose disclosure content is hereby incorporated by reference. The operating method described there forms the basis of the invention described below. It is of paramount importance that what are termed dead times without substantially coupling active power are inserted between individual pulses if active power is coupled into the discharge lamp, and the length of these dead times is dimensioned up to a new pulse which couples active power such that a specific type of discharge described in the cited application and having a particularly high discharge efficiency is formed. The dead times may not be too long for this purpose, because each active-power pulse is then to be evaluated as a new ignition, as it were, and the absence of a connection between the individual active-power pulses renders it impossible to achieve good efficiency, a sufficient lamp power or else good temporal and spatial stability. If the dimensions of the dead times between the active-power pulses are, on the other hand, too short, filamentous discharges form which exhibit poor efficiency and, moreover, a poor temporal and spatial stability.
An invention of the same inventors already filed as an application proposed an operating method and a ballast for a silent discharge lamp with the aid of which the outlined pulsed operating method of WO94/23442 can be implemented particularly effectively. The associated patent application with the file reference 198 39 329.6 has not yet been published at the application date of the present invention, but forms a technical basis for the invention explained below. The disclosure content of this second prior application is therefore also referred to completely.
In particular, it was proposed in this prior application to use a ballast in accordance with the forward converter principle, in which a voltage pulse is impressed from a primary circuit via a transformer into a secondary circuit containing the discharge lamp, and leads to an ignition (termed forward ignition below) in the discharge lamp. The operating method is designed in this case such that after the forward ignition in the discharge lamp an oscillation is set up in the secondary circuit by means of which the charge effecting the external voltage across the discharge lamp, which has previously effected the forward ignition, is removed from the discharge lamp. Thereupon, the remaining internal counterpolarization can lead to a back ignition in the discharge lamp. Reference may be made to the cited application for the details of this basic principle.
In particular, it has already been described in the cited application as a preferred case that the temporal spacing between forward ignition and back ignition is so short that it is not to be regarded as dead time in the meaning of the pulsed operating method. Thus, the abovementioned dead times occur between in each case a back ignition and the forward ignition following thereupon, but not between this forward ignition and the back ignition following thereupon. The following also proceeds on this basis. The operating method described in the second cited application had been developed with the aim of achieving a favorable overall compromise with regard to the power efficiency, the overall volume and overall weight of the associated ballast, and the production costs, service life and failure frequency.
SUMMARY OF THE INVENTION
The present invention is based overall on the technical problem of further improving the described operating method according to the forward converter principle. In particular, it is to be possible to operate with the highest possible lamp powers in conjunction with small overall volume and overall weight and good efficiency.
According to the invention, it is provided for this purpose in accordance with claim 1 that in the described operating method an inductance governing the temporal variation in a current through the transformer is varied temporally within a period including a forward ignition and a back ignition such that the altered inductance is substantially larger in an initial phase of the impression of the voltage pulse which leads to the forward ignition than in at least a portion of the back ignition phase, in which the charge is removed from the discharge lamp after the forward ignition and the back ignition is performed.
The invention likewise aims at a ballast designed for this operating method, and at an illuminating system comprising such a ballast and a silent discharge lamp.
The following findings are fundamental in this case: the temporal behavior of the change in the external voltage across the discharge lamp is important for the physical nature, and thus also the efficiency of the silent discharge in the discharge lamp. In particular, it has emerged in this case that excessively large pulse widths should not be selected for ignition in the pulsed operating method. The special efficiency of the pulsed operating method is based, rather, on the fact that a dead time starts again after a relatively short pulse in the coupling of active power.
Consequently, the voltage pulse across the lamp, and therefore also the associated primary current pulse in the transformer must be relatively short.
In particular, the back ignition leads to a more efficient and more complete conversion of the energy stored in the secondary circuit the faster the secondary circuit swings back in the case of the half wave leading to the back ignition and during the back ignition, that is to say after the reignition as a consequence of the internal counter polarization. The aim is therefore to select the natural frequency or speed of the secondary circuit to be as high as possible. The inductance given in the secondary circuit by the transformer plays a substantial role in this speed.
On the other hand, however, it has also emerged that the discharge physics of the forward ignition can, in turn, be unfavorably influenced by excessively steep rising edges of the voltage at the start of a pulse leading to a forward ignition, and thus also by excessively steep rising edges at the start of the primary current rise. Evidently, the situation is that the occurrence of the discharge right at the beginning of the field build-up should favorably still be allowed sufficient time to prepare an optimum form of the discharge structures rendered possible by the pulsed operating method. An excessively low transformer inductance could give rise here to unfavorably steep rising edges. This, in turn, could worsen the efficiency of the discharge. If it is ensured by a sufficiently large primary circuit inductance that the forward ignition has a basic physical form suitable for very high efficiency, there will be no further fundamental subsequent change in this basic fact owing to the speed of the voltage rise in the primary and/or secondary circuit. Specifically, the still remanent residual ionization of the last back ignition is then preimpressed suitably for the new ignition by the electric fields building up.
However, the inductances caused by the transformer in the primary circuit and in the secondary circuit cannot in principle be selected entirely independently of one another. Consequently, the invention provides a temporal variation in at least one of the inductances governing the currents through the transformer.
In particular, the aim in this case is that no excessively low inductance be present in the prim
Hitzschke Lothar
Vollkommer Frank
Clark Robert F.
Patent-Treuhand-Gesellschaft fuer Elektrische Gluehlampen mBH
Philogene Haissa
Vo Tuyet T.
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