Electric lamp and discharge devices: systems – Current and/or voltage regulation
Reexamination Certificate
1999-03-22
2001-05-01
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Current and/or voltage regulation
C315S246000, C315S260000, C313S607000
Reexamination Certificate
active
06225758
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. 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 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, essentially, the pulse shape, in particular steep rises, as well as the time durations 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 on the nature and the thickness of the dielectric.
PRIOR ART
The document DE 195 48 003 A1 has already disclosed such a circuit arrangement for producing pulsed-voltage sequences having 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). In addition, all of the energy consumption required for each discharge pulse is taken entirely from the pulse circuit, for which reason it must be designed appropriately.
DESCRIPTION OF THE INVENTION
The object of the present invention is to avoid the said disadvantages and to provide a method that produces a pulse sequence which ensures more efficient energy provision for the discharge, which is operated in a pulsed manner and is impeded dielectrically. A further aspect is to produce less EMI.
A further object of the present invention is to provide a circuit arrangement for implementing this method.
Finally, it is an object of the present invention to provide a corresponding lighting system.
The basic idea of the invention is to replace some of the pulse peak values required for pulsed discharges which are impeded dielectrically, by an offset DC voltage component, a portion of the electrical real power injected into the discharge(s) predominantly throughout the duration of the voltage pulses also being injected on the basis of the offset DC voltage component.
To do this, at least one offset DC voltage and a sequence of voltage pulses are additively superimposed to form a total voltage, in such a manner that the offset DC voltage component virtually forms the “base” of the total voltage on which the sequence of voltage pulses is placed. In this way, the peak values of the total voltage result from the sum of the value of the offset DC voltage and of the peak values of the voltage pulses. In consequence, with the aid of the superimposition according to the invention, voltage pulses with lower peak values than those without superimposition are sufficient to achieve the required level of effective peak values.
The total amplitude of the offset DC voltage is in this case deliberately chosen to be at most sufficiently high that the discharge(s) can be extinguished after each voltage pulse. This requirement must be satisfied in order to provide the efficient method of operation described in WO 94/23442.
The individual pulses of the sequence of voltage pulses can be unipolar as well as bipolar. The term “bipolar pulse” means that, within such a pulse, the time-dependent voltage changes the sign once or several times. By superimposing a sequence of bipolar pulses on an offset DC voltage it is possible to produce also a bipolar overall voltage.
In addition, the invention provides a source which supplies the offset DC voltage and which is suitable for providing a portion of the electrical real power injected into the discharge(s) predominantly throughout the duration of the voltage pulses. This has the advantage that the pulse source has to supply only the remaining portion of the power required for the discharge which is operated in a pulsed manner and is impeded dielectrically, and is therefore designed only for correspondingly lower power levels.
The method according to the invention for producing pulsed-voltage sequences for the operation of discharge lamps by means of (a) pulsed discharge(s) which is(are) impeded dielectrically provides the following method steps.
At least one offset DC voltage is provided, in which case the total amplitude of the offset DC voltages is in this case deliberately chosen to be at most sufficiently high that the discharge(s) can be extinguished after each voltage pulse and undesirable restriking between the individual voltage pulses is prevented.
A sequence of voltage pulses, which are separated from one another by pauses, is provided, the polarity of the sequence being opposite the polarity of the offset DC voltage with respect to a common potential.
The at least one offset DC voltage and the sequence of voltage pulses are superimposed to form a total voltage in such a manner that the peak values of the total voltage result from the sum of the magnitude of the offset DC voltage and of the magnitude of the peak values of the voltage pulses (additive superimposition of magnitudes).
The total voltage produced in this way is applied to the electrodes for use according to the invention.
Owing to the lower required pulse level of the sequence of voltage pulses, it is sufficient to design the pulse circuit for lower peak values, and this results in a number of further significant advantages. First of all, a lower transformation ratio is sufficient for the pulse transformer which is normally present in the pulse circuit, or it may be possible to dispense with the pulse transformer completely. In either case, steeper pulse flanks can be achieved, which results in an increase in the efficiency of the useful radiation production. Furthermore, the reduction in the level of the voltage pulses also achieves a reduction in the EMI and in the current in the primary circuit of the pulse transformer.
The circuit arrangement according to the invention for producing pulsed-voltage sequences according to the method described above comprises a pulse circuit and a DC voltage circuit, each having two output poles.
One of the two output poles of the pulse circuit is connected to the output pole of opposite polarity of the DC voltage circuit. The connection of the two said output poles defines the reference-earth potential with respect to the two free output poles of the two series-connected circuits. In this way, the difference signal of the two partial signals which are in each case prese
Hitzschke Lothar
Vollkommer Frank
Alemu Ephrem
Bessone Carlo S.
Patent-Treuhand-Gesellschaft Fuer Elektrische Gluehlampen MBH
Wong Don
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