Electric lamp and discharge devices: systems – Pulsating or a.c. supply
Reexamination Certificate
1999-04-12
2001-01-09
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Pulsating or a.c. supply
C315S250000
Reexamination Certificate
active
06172467
ABSTRACT:
TECHNICAL FIELD
The invention relates to a method for producing pulsed-voltage sequences for the operation of discharge lamps by means of a pulsed discharge, which is impeded dielectrically, according to the precharacterizing clause of claim
1
. The invention also relates to an electrical circuit arrangement for producing pulsed-voltage sequences according to this method. Finally the invention also relates to a lighting system according to the precharacterizing clause of the claim focused thereon with this circuit arrangement.
The term “discharge lamp” is also intended to cover those radiation sources which, in addition to electromagnetic radiation in the visible spectral band, that is to say light, also or even predominantly emit radiation in the UV or VUV bands.
The pulsed-voltage sequence can in principle be both unipolar and bipolar and is used for operating discharge lamps or radiators in which at least the electrodes of one polarity are impeded dielectrically, as is described, for example, in WO 94/23442. This method of operation uses a sequence, which is in principle unlimited, of voltage pulses during which predominantly electrical real power is injected, and which are separated from one another by pauses. The critical factors for the efficiency of the useful radiation production are, in principle, the pulse shape, in particular steep rises, as well as the time duration of the pulse times and pauses. The required peak values of the voltage pulses are typically one to several kilovolts—depending, inter alia, on the flash-over distance, on the nature and the pressure of the filling gas, as well as the nature and the thickness of the dielectric.
1. Prior Art
At present, these high voltage peaks in the kV region cannot reliably be switched and produced by means of a switching transistor. A pulse transformer is normally required for this purpose, and is connected into the output of the pulsed-voltage source.
The document DE 195 48 003 A1 has already disclosed such a circuit arrangement for producing pulsed-voltages sequences having one, and only one, pulse circuit. This pulse circuit essentially comprises a capacitor, a transistor and a pulse transformer. During the phase when the transistor is switched on, the energy stored in the capacitor is transferred to the pulse transformer. In the process, the pulse transformer transforms the pulsed voltage to the required peak values, although a number of disadvantages are associated with this. Firstly, the pulse transformer must be designed for the peak value of the pulsed-voltage sequence and is thus relatively large and expensive. In addition, the pulse load on the pulse transformer is relatively large and the winding capacitances, which are likewise relatively large, have an adverse effect on the pulse shape. A further disadvantage is that the full peak value of the pulsed-voltage sequence occurs on the supply leads of the secondary winding of the pulse transformer. The parasitic capacitances to the environment which are always present result in relatively high interference signals, so-called EMI (Electromagnetic Interference).
2. Description of the Invention
The object of the present invention is to avoid the said disadvantages and to provide a method according to the precharacterizing clause of claim
1
, which produces less EMI.
This object is achieved by the characterizing features of claim
1
. Particularly advantageous refinements are contained in the claims that are dependent on claim
1
.
A further object of the present invention is to provide a circuit arrangement for carrying out this method. This object is achieved by the features of the independent claim which relates to the circuit arrangement. Further, particularly advantageous refinements are contained in the claims that are dependent thereon.
Finally, it is an object of the present invention to provide a lighting system according to the precharacterizing clause of the independent claim which relates to the lighting system and does not have the disadvantages mentioned. This object is achieved by the characterizing features of this claim.
The basic idea of the invention is that the pulsed-voltage sequence is composed of two partial voltage sequences in such a manner that the peak values of each partial voltage sequence are less than the peak values of the resultant pulsed-voltage sequence, for example only half as large. This has the advantage that correspondingly less EMI is generated when the partial voltage sequences are produced. In addition, one of the two partial voltage sequences contains positive rising flanks with respect to a reference-earth potential, and the other partial voltage sequence contains negative rising flanks with respect to this reference-earth potential. One of the two partial voltage sequences is preferably the inverse, with respect to the reference-earth potential, of the other partial voltage sequence. Ideally, the EMI produced by the two partial voltage sequences is completely compensated for at least locally. The higher peak values which are required for the discharge which is impeded dielectrically and, in consequence, the relatively severe EMI, are produced only where high peak voltages are actually required, namely at the load, that is to say between the electrodes of the radiation source itself.
According to the invention, this basic idea is implemented in the following method. Two partial sequences of voltage pulses are produced which are each separated from one another by pauses—also referred to in the following text as partial voltage sequences, for short—the two partial sequences having rising flanks with mutually opposite gradients with respect to a common reference-earth potential, for example earth. The two partial sequences are superimposed in such a manner that a difference sequence is produced. If required, the two partial sequences are synchronized to one another in such a manner that the peak values of the difference sequence are greater than the peak values of each of the two individual partial sequences of voltage pulses.
The individual pulses in the partial sequences may be either unipolar or bipolar. The term “bipolar pulse” means that the time-dependent voltage changes its mathematical sign once or more within such a pulse. Finally, according to the abovementioned method, this results in unipolar or bipolar difference sequences. The only critical factor in this case is that the corresponding pulses in the two partial sequences have (with respect to the common reference potential) rising flanks with mutually opposite gradients. In the bipolar case, the electrodes carry out both the role of the anode and the role of the cathode, depending on the phase of the pulse.
When defining the critical gradient of the rising flanks of the respective pulses, the intention is to ignore signal distortion, which frequently occurs in practice and in some cases is even unavoidable, such as overshoots or undershoots, noise components and the like which, however, generally make only an insignificant contribution (<50%) to the real power coupled to the lamp. The important factor for this analysis is, in fact, those time periods of the pulses during which the major real power inputs (>50%) take place.
In a preferred variant for the production of a difference sequence, one partial sequence of voltage pulses is formed by inverting the other partial sequence of voltage pulses. Synchronization is carried out in such a manner that the peak values of the difference sequence are the sum of the peak values of the partial sequences.
In a further variant, at least one of the two partial sequences of voltage pulses and/or the difference sequence have/has an offset DC voltage additively superimposed on them/it as an additional method step, the total offset DC voltage being chosen such that the discharge(s) can be extinguished after each voltage pulse, and undesirable restriking between the individual voltage pulses is avoided. Specifically, in this way, a relevant voltage element can be provided by the DC voltage. This has the advantage tha
Hitzschke Lothar
Vollkommer Frank
Bessone Carlo S.
Patent-Treuhand-Gesellschaft Fuer Elektrische Gluehlampen MBH
Tran Chuc D
Wong Don
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