Electric lamp and discharge devices: systems – Periodic switch in the supply circuit – Silicon controlled rectifier ignition
Reexamination Certificate
1999-03-17
2001-11-27
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Periodic switch in the supply circuit
Silicon controlled rectifier ignition
C315S219000, C315S291000, C315SDIG007, C315S276000
Reexamination Certificate
active
06323600
ABSTRACT:
TECHNICAL FIELD
The invention relates to an electrical circuit arrangement for producing pulsed-voltage sequences for the operation of discharge lamps. The invention further relates to the method in accordance with which the circuit arrangement produces the pulsed-voltage sequences.
To be more precise, the circuit arrangement according to the invention is used to operate discharge lamps or radiators in which at least the electrodes of one polarity are impeded dielectrically, by means of unipolar or at least substantially unipolar voltage pulses, such as those described in WO 94/23442, for example. This method of operation uses a sequence, which is in principle unlimited, of voltage pulses which are separated from one another by pauses. The critical factors for the efficiency of the wanted radiation production are, essentially, the pulse shape as well as the time durations of the pulse and pause times. Typical duty ratios are in the range between about 1:5 to 1:10. The peak value of the high-voltage pulses depends on the design of the respective lamp, for example the number of electrodes, the flashover distance and the nature and thickness of the dielectric, and is typically between 1 kV and 5 kV. The pulse repetition frequency is also dependent on the geometry of the lamp and is in the range from about 25 kHz to about 80 kHz. Conventional methods of operation for such lamps in contrast use sinusoidal AC voltages.
In contrast to conventional discharges, as are normally used for discharge lamps, discharges which are impeded dielectrically have a dielectric which is arranged between the interior of the discharge space and the electrode or electrodes of one polarity (impeded dielectrically on one side) or else all the electrodes, that is to say the electrodes of both polarities (impeded dielectrically on both sides). Such electrodes are also called electrodes which are impeded dielectrically. The charge carrier transportation from an electrode which is impeded dielectrically to the ionized gas in the discharge path thus takes place by means of a displacement current rather than by means of a conduction current. This results in a capacitive component in the electrical equivalent circuit for such a discharge. In consequence, the circuit arrangement has to be suitable for injecting the energy capacitively into the lamp.
PRIOR ART
DE 195 48 003 A1 (Huber et al., U.S. Pat No. 5,581,394) discloses an electrical circuit arrangement for producing pulsed-voltage sequences, in particular for the operation of discharges which are impeded dielectrically. This circuit arrangement has a charge circuit which is fed from an input voltage and has a charge capacitor, a discharge and pulse circuit having a fast controllable switch which is connected to a pulsed drive circuit, and a pulse transformer with a load connected to it, as well as a feedback circuit with a feedback electrical valve and a buffer capacitor which is connected in parallel with the input of the charge circuit. During the phases when the switch is switched on, the electrical energy stored in the charge capacitor is always transmitted to the load via the pulse transformer. The oscillating energy returning from the load and the pulse transformer passes through the feedback circuit, is fed into the feedback point, and is absorbed by the buffer capacitor. Thus, during the reverse oscillation phases, the potential of the secondary winding is clamped to the potential of the input voltage. In addition, the energy fed back is in this way also used for the charging phase of the charge capacitor. The disadvantages of this solution are the high pulsed load on the pulse transformer and on the switch, the relatively poor efficiency, as well as the not inconsiderable component complexity. In addition, the specific design of the pulse transformer has a critical effect on the operation of the circuit. Furthermore, the optimum design of the pulse transformer can be determined only by experiment.
DESCRIPTION OF THE INVENTION
The object of the present invention is to provide a circuit arrangement with whose aid largely unipolar pulsed-voltage sequences can be produced, with low circuit losses. In addition, it is intended to be possible to produce pulsed-voltage sequences with pulse shapes that are as smooth as possible on loads which act in a predominantly capacitive manner. A further aspect of the invention is to provide a relatively simple circuit with as few components as possible.
A further object of the invention is to provide a method of producing the above mentioned pulsed-voltage sequences.
The basic idea of the invention is explained in the following text with reference to a simplified block diagram in FIG.
1
. Fed from an energy supply source
1
, an inductive energy reservoir
3
is first of all cyclically charged up during the switched-on phase of a controllable switch
2
. After the charging-up phase, that is to say as soon as the switch
2
switches off, the magnetic energy stored in the inductive energy reservoir
3
is transmitted to a capacitive energy reservoir
4
. In consequence, a first voltage half-cycle of a roughly sinusoidal oscillation is produced on the inductive energy reservoir
3
, while a similar voltage half-cycle, but in antiphase, is produced on the capacitive energy reservoir
4
. This first voltage half-cycle is used as a voltage pulse for the lamp
5
—which is coupled either to the inductive energy reservoir
3
or to the capacitive energy reservoir
4
. After this, the energy is fed back from the capacitive energy reservoir
4
, via the inductive energy reservoir
3
, into the energy supply source
1
, which advantageously contains an additional feedback reservoir (not illustrated). In this case, the voltage on the capacitive energy reservoir
4
is clamped to the voltage which is dropped across the open electrical valve
6
. In consequence, during this process, the voltage on the inductive energy reservoir
3
is equal to the supply voltage. This process is repeated cyclically after a time which can be predetermined. The timing is controlled via a signal transmitter
7
which is connected to the controllable switch
2
.
In this way, a sequence of essentially half-sinusoidal voltage pulses in the same phase is produced at the lamp electrodes, the individual voltage pulses being separated from one another by pauses, that is to say times during which the voltage at the electrodes is largely constant and is considerably less than the peak value of the voltage pulses, preferably being close to zero.
This idea of the invention is in essence achieved by the series circuit formed by a controllable switch and an inductance which is used, inter alia, as an inductive energy reservoir and is also referred to in the following text, for short, as a tuned circuit inductance, the switch having connected in parallel with it the electrical valve and a capacitance which is used as the capacitive energy reservoir—also referred to as a tuned circuit capacitance in the following text, for short.
The width of the voltage pulses, inter alia, can be influenced by the specific values of the tuned circuit inductance and the tuned circuit capacitance. Typical values for the operation of radiation sources of the type mentioned in the introduction are in the range between about 500 &mgr;H and 10 &mgr;H for the tuned circuit inductance, and about 100 pF and 1 &mgr;F for the tuned circuit capacitance.
A capacitor may be used, for example, as the tuned circuit capacitance, or alternatively the actual intrinsic capacitance of a discharge arrangement which is provided with electrodes which are impeded dielectrically. If the switch is provided by a controllable semiconductor switch, for example by a bipolar transistor, IGBT (Insulated Gate Bipolar Transistor) or MOSFET (Metal Oxide Semiconductor Field Effect Transistor), the depletion layer capacitance of the semiconductor switch can also be used as the tuned circuit capacitance, since the tuned circuit capacitance—as will be shown later—is significant to the operation of the circuit arrangemen
Ertl Bernhard
Statnic Eugen
Veser Alwin
Bessone Carlo S.
Patent-Treuhand-Gesellschaft Fuer Elektrische Gluehlampen MBH
Vo Tuyet T.
Wong Don
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