Abstract:
The present invention describes an apparatus and methods for operating one or more gas arc lamps or metal vapor, wherein a rectified multiphase voltage is directly used by an electronic ballast device without intermittently connecting any active component, so as to achieve an efficient control of a gas arc lamp with a reduced interference radiation, wherein the power factor is inherently higher than 0.95.

Description:
FIELD OF THE INVENTION 
   The present invention relates to apparatus and methods for operating a gas arc lamp and, in particular, relates to light equipment in which gas arc lamps are operated by means of an electronic ballast device. 
   BACKGROUND OF THE INVENTION 
   The employment of gas arc lamps and especially of fluorescent lamps is common practice in many industrially and economically oriented fields due to their higher efficiency when compared to filament lamps and due to illumination characteristics that are widely variable by selecting the fluorescent coating. In particular, for applications in which not only high efficiency but also a stable, i.e. flicker-free, illumination or a continual adjustment of the luminescence of a gas arc lamp is required, electronic ballast devices are often used that enable an operation of the gas arc lamp at high frequencies in the range of approximately 20 kHz to 50 kHz. Consequently, the flicker may be avoided or is no longer perceivable contrary to gas arc lamps that are merely operated at the grid frequency by means of a choke, wherein an appropriate control of the electronic ballast device enables the variation of the illumination intensity within a wide range. 
   The increasing employment of electronic ballast devices, however, entails an increased transmission of interfering signals that are generated by the switched operation of the switching elements—mostly MOSFETs- or bipolar transistors—used in the electronic ballast device. Moreover, the application of electronic ballast devices causes a significant non-sinusoidal current extraction from the grid, which leads to a remarkable supply of upper harmonic waves into the grid, thereby resulting in an undue loading of the grid. Consequently, legislators have issued corresponding guidelines with respect to the creation of upper harmonic waves of electronic ballast devices, especially in the power range up to 1000 W, which may not be exceeded. For this reason, a multiplying boost converter precedes the electronic ballast device, which is also referred to as a “power factor regulator,” so as to maintain the power factor at approximately 1, i.e., to extract the current from the grid in a substantially sinusoidal form and in phase with the grid voltage. 
   The power factor regulator generally requires a further switching element and an inductor, thereby causing a significant increase in the number of circuit elements. Furthermore, with reasonable effort typically an efficiency of the power factor regulator of 95% at most is achievable, so the total efficiency of the system comprised of the power factor regulator, the electronic ballast device and the gas arc is reduced. The boost converter used in the power factor regulator operates in a switched mode and contributes to a further increase of the interference radiation, thereby requiring great effort to filter the interference radiation and necessitating expensive metal housings. 
   SUMMARY OF THE INVENTION 
   In view of the problems identified above, it is an object of the present invention to provide a technique for reducing the expense in terms of circuit elements, thereby at the same time assuring the required degree of electromagnetic compatibility (EMC) and reduced amount of harmonic waves. 
   According to one aspect of the present invention, this object is solved in that an apparatus is provided for controlling the illumination of a gas arc lamp and/or a metal vapor lamp, the apparatus comprising: a multiphase full-wave rectifier that is at the input side connected to a multiphase voltage source, and a controlled switch device that is connected with its input side to the output of the multiphase full-wave rectifier and that is connected with its output side to a resonant circuit to which the gas arc lamp or the metal vapor lamp may be connected. Moreover, the apparatus comprises a control circuit for driving the switch device in accordance with an externally supplied control signal so as to control the energy coupled into the gas arc lamp or the metal vapor lamp, wherein the power factor of the apparatus is greater than 0.95 due to the rectified multiphase voltage. 
   By rectifying the multiphase AC voltage by means of the full-wave rectifier, a DC voltage that exhibits a reduced waviness is obtained at the output of the rectifier. For example, in the European three-phase grid, the waviness of a six-phase circuit is only approximately 10% at a frequency corresponding to six times the grid frequency. This rectified voltage may be directly supplied to the electronic ballast device, thereby eliminating the necessity for the complex power factor regulator. Because of the reduced waviness in connection with the higher frequency of the voltage waviness, only slight variations in the illumination of the gas arc lamp or the metal vapor lamp occur. Due to the higher ripple frequency, these variations are imperceivable to the human eye. Excellent illumination characteristics are thereby obtained. Especially in applications requiring a higher power and a control of the average illumination, such as in a solarium and devices for sterilization of rooms and objects in medical fields and the like, the present invention may be most advantageous, since in these applications usually a three-phase terminal is provided anyway and the direct usage of the rectified multiphase voltage without a power factor regulator significantly increases efficiency. Different voltages in different countries (USA and Japan 220V, Europe 380V, outer conductor voltage) may be taken into consideration by a correspondingly adapted resonant circuit, wherein the high rectified voltage of approximately 560V to 600V (Europe) is advantageous for igniting the gas arc lamp. 
   In a further embodiment, a buffer capacitor is provided at the output side of the multiphase full-wave rectifier. Thus, a short break-down of the voltage caused during the switching of the half-bridge may substantially be avoided. Owing to the direct employment of the rectified multiphase voltage, the capacity of the buffer capacitor may be selected relatively small, since this capacitor does not have to smooth the waviness of the rectified DC voltage; rather the capacitor merely has to buffer the voltage during the switch events occurring at the high operating frequency. Hence, expensive, bulky and unreliable electrolyte capacitors may be omitted. 
   In a further embodiment, the apparatus further comprises a pre-control that modulates the external control signal inversely with respect to the residual waviness of the rectified multiphase voltage. In this way, even the minor variations of the illumination may be substantially compensated for should these minor variations adversely affect certain applications. 
   In a further embodiment, a resonant capacitor that is provided in parallel to the gas arc lamp is directly provided at the gas arc lamp. 
   In this way, the number of leads connecting to the gas arc lamp may be reduced. Especially if a plurality of gas arc lamps are provided, the provision of the respective resonance capacitors directly at the respective gas arc lamp assures that only one lead for each lamp and a common return line is necessary, wherein the required monitoring for the individual gas arc lamps may be performed without additional connections. Preferably, the external resonant capacitor is accommodated within the starter housing. 
   According to a further aspect of the present invention, a controller is provided for a plurality of gas arc lamps and/or metal vapor lamps. It comprises an electronic wired board, a multiphase full-wave rectifier installed on the electronic board and connectable to a multiphase AC voltage source, and a plurality of electronic ballast devices installed on the electronic board, wherein each of the electronic ballast devices is connected with its input side to the multiphase full-wave rectifier and is connected with its output side to one of the plurality of gas arc lamps and/or metal vapor lamps. As already explained, due to the direct employment of the rectified multiphase AC voltage corresponding power factor regulators and corresponding filter capacitors may be avoided, thereby providing the possibility of supplying a plurality of gas arc lamps and/or metal vapor lamps by a single electronic board in spite of the high power required, since the circuitry may be designed in a compact manner and without additional power factor regulators, which would generate heat that would have to be dissipated. This is especially advantageous in applications in which a plurality of gas arc lamps and/or metal vapor lamps have to be operated within a restricted space. 
   One or more of the electronic ballast devices may be controllable in such a way that the illumination of the lamps, either individually or in groups or as a whole, is adjustable. 
   According to a further aspect of the present invention, a controllable illumination apparatus is provided. It comprises a three-phase bridge rectifier; a buffer capacitor having a capacity in the range of approximately 0.1 μF to 1 μF that is arranged at the output side of the three-phase full-wave bridge rectifier; an electronic ballast device having a control input, wherein the electronic ballast device is connected to the buffer capacitor without any intermediate active components; and a gas arc lamp or metal vapor lamp connected to the electronic ballast device. 
   By means of the direct rectification of the three-phase voltage by using a buffer capacitor having a small capacity, costs with respect to material and fabrication may be reduced, wherein at the same time an excellent EMC and a high power factor are achieved. 
   According to a further aspect of the present invention, a method for controlling an illumination or lighting equipment is provided, wherein the illumination equipment comprises a multiphase AC voltage source, a multiphase full-wave rectifier, an electronic ballast device and a gas arc lamp or a metal vapor lamp. The method comprises the steps of: rectifying the multphase AC voltage, supplying the rectified voltage to the electric ballast device, generating a control signal that serves the adjustment of the gas arc lamp or metal vapor lamp, and feeding the control signal to the electronic ballast device so as to control the illumination of the gas arc lamp or metal vapor lamp, wherein the power factor is equal to 0.95 or higher. 
   The operation of the illumination equipment may be carried out in accordance with the present invention so as to significantly reduce the expense at the material side and to provide an increased efficiency compared to the prior art. Hence, for example, a solarium, sterilization equipment and medical devices for treatment in the form of a light therapy and the like may be operated in a significantly increased economical manner, wherein the EMC is within the legal limits at a minimum expense owing to the omission of one or more power factor regulators. 
   In a further embodiment, the generation of the control signal is based on one or more of the following parameters: a duration of the intended emission of radiation of the gas arc lamp or metal vapor lamp, a current illumination of the gas arc lamp, an illumination integrated over a predefined time interval, an operating age of the gas arc lamp, a physical and/or biological effect on a specified object of the radiation emitted, an operating temperature of the gas arc lamp and an operating temperature of a specified portion of the electronic ballast device. 
   By means of the parameter-dependent control of the illumination equipment, a controlled adjustment of the illumination within a wide control range is achievable, wherein it is only necessary to adapt the ballast device to the desired power control range due to the missing power factor regulator. Thus effort, in terms of material and costs, is low compared to a conventional apparatus. The generation of the control signal may then occur in an application-specific manner by means of appropriate. parameters. For example, when using the illumination equipment in a solarium, the problem arises that the radiation should be emitted only within a certain frequency range and with a predefined intensity. By providing appropriate sensor elements, the radiation emitted may be monitored and a signal output by the sensors may be used as the parameter for generating the control signal. A corresponding sensor output signal may indicate, for example, that a maximum current radiation intensity and/or a maximum or desired integrated intensity is exceeded. 
   In one embodiment, the controlling may be performed as a controlled operation by means of a target value and an actual value, so that one or more appropriate parameters may be selected for the specific application, wherein the associated parameter values are read out in a continuous or step-wise manner and used for the generation of the control signal. Hence, for example, the solarium mentioned before may be effectively controlled without any risk with respect to the health of the user, when for instance the current illumination is controlled in accordance with a predefined target value. Especially, in combination with an apparatus as previously discussed, wherein a plurality of gas arc lamps and/or metal vapor lamps are controllable by means of a single electronic board, a compact, energy-efficient and cost-effective possibility for controlling the illumination equipment is achieved on a large scale. 
   Alternatively or additionally, appropriate parameter values for the control or regulation of the illumination equipment, especially for medical devices for treatment by means of light and radiation, may be obtained from corresponding predefined models of the illumination process or by means of other tools. For instance, by knowing a specific type of skin, a respective mode of operation in the solarium may be determined so as to set corresponding parameters, such as intensity and duration of treatment. The corresponding parameter values may be determined in real time or provided, for instance, in the form of a table. 
   Similarly, other parameters may be determined, such as the effect of the radiation on certain objects, such as skin areas, micro organisms, specific materials that have to be examined and the like, wherein these parameters may then be used for the control and/or regulation of the irradiation process. Thereby, the effect may be measured and/or determined by models or data. For instance, from previous measurements or calculations, the effects on specific micro organisms with respect to a specified type of radiation may be known so that the illumination may then be appropriately adapted to obtain the desired results, for instance, a specified effect of sterilization. In this respect, it is advantageous that the direct employment of the rectified multiphase grid voltage allows to obtain an efficient and sensitive control for adjustment of the illumination. 
   Further embodiments are described in the appended claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the following, a plurality of exemplary embodiments will be described with reference to the accompanying drawings in which: 
       FIG. 1   a  illustrates a circuit diagram of a first exemplary embodiment; 
       FIG. 1   b  shows a variant of the embodiment illustrated in  FIG. 1   a , wherein the resonant capacitor is provided outside of the circuit board directly at the gas arc lamp; 
       FIG. 2  schematically illustrates an embodiment in which a plurality of electronic ballast devices is combined on a single electronic board; 
       FIG. 3  schematically shows an embodiment in which a transformer is provided in the resonant circuit for matching the gas arc lamp or the metal vapor lamp to the circuit; and 
       FIG. 4  schematically represents an arrangement in which a gas arc lamp or a metal vapor lamp is controlled by using signals directly obtained from sensor elements and/or by using externally determined parameters. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1   a  schematically shows an apparatus  100  for controlling a gas arc lamp or a metal vapor lamp  106 , which may be provided in the illustrated embodiments in the form of a fluorescent lamp. The apparatus  100  comprises a three phase full-wave rectifier  101  rectifying a three phase AC voltage R, S, T. According to the European standard, the voltage across two phases is approximately 380 volts so that the voltage at the output side of the rectifier  101  is approximately 560 volts, wherein the residual ripple or waviness of the rectified voltage is approximately 10%. Due to the sixth-pulse circuit arrangement of the rectifier  101  the waviness exhibits a frequency that is six times the frequency of the input AC voltage. 
   At the output side of the rectifier  101  a buffer capacitor  102  may be provided, the capacity of which may be, however, relatively low, for instance 0.1 μF to 1 μF, since the capacitor  102  does not need to smooth the residual waviness of the rectified voltage, but buffers the voltage during the high frequency switch events. At the output side of the rectifier  101  a filter  103  may be provided that enhances the electromagnetic compatibility (EMC) of the apparatus  100 . Also connected to the output side of the rectifier  101  is a switch device in the form of a half-bridge  104 , which comprises in the embodiments illustrated herein two MOSFET transistors T 1  and T 2 , a common terminal of which is connected to an inductor  105  having an inductance L R . The other terminal of the inductor  105  is connected with a terminal of the gas arc lamp  106 , the other electrode of which is connected to a capacitor  107  having a capacity C R . A control circuit  108  is configured so as to provide gate signals for the transistors T 1  and T 2 . Moreover, the control circuit  108  comprises a control input  109  for receiving a control signal for adjusting the illumination of the gas arc lamp  106 . For the sake of simplicity, further circuit elements required, for instance, to preheat the electrodes of the gas arc lamp  106 , or various protective means for avoiding excess currents and excess voltages are not shown. It should further be noted that a plurality of circuit variants regarding the switching device  104  are known. For instance a full bridge may be used instead of the half bridge or a single switching element may be used as a (resonance) boost converter. 
   During the operation of the apparatus  100  the AC voltage RST is rectified by means of the rectifier  101 , wherein conventional rectifier bridges may be used or, if desired, fast switching diodes having a short reverse recovery time. Due to the direct rectification of the three-phase AC voltage, the rectified voltage exhibits merely a slight waviness of approximately 10%–12% so that contrary to conventional electronic ballast devices this voltage is directly usable without requiring a regulation of the power factor by means of an additional power factor regulator. The control circuit  108  generates the gate control signal for the transistors T 1  and T 2  in response to an externally supplied or an internally generated control signal at a frequency and/or duty cycle corresponding to the control signal. The resonant circuit formed by the inductor  105 , the gas arc lamp  106 , and the capacitor  107  is excited by the frequency determined by the externally generated or internally generated control signal so that the gas arc lamp  106  is ignited and radiates. A typical operating frequency is in the range of 20–60 KHz, wherein the minor variations in the illumination caused by the residual waviness of the rectified AC voltage is hardly perceivable or even unperceivable due to the increased frequency that is six times the frequency of the input AC voltage. As already explained, the capacity of the buffer capacitor  102  may advantageously be selected so that during the switch events of the transistor T 1  and T 2  the voltage remains substantially constant; hence, a value of 0.1 μF or more preferably from 0.1 μF to 0.67 μF is sufficient. Moreover, the residual waviness may be compensated for by a corresponding pre-controller (not shown), wherein the control circuit  108  receives the rectified AC voltage, for instance from a voltage divider, so that a variation in the illumination caused by the residual waviness may be substantially compensated for. 
   Of course, a buffer capacitor  102  having a high capacity may be provided so as to smooth the residual waviness at the bridge rectifier, which would then, however, require the employment of a bulky electrolyte capacitor that is dimensioned with respect to the expected output current. 
     FIG. 1   b  shows an embodiment that is identical to the embodiment of  FIG. 1   a  with respect to driving the gas arc lamp  106 . Identical components are thus denoted with the same reference signs and the description of these components is omitted. 
   In  FIG. 1   b  an inductor, such as the inductor  105  of  FIG. 1   a , is connected in series with a coupling capacitor (not shown) having a capacity C K , which may be in the range of, for example, 50–200 nF. The resonance capacity  107  having a capacitance of C F  is directly provided at the gas arc lamp  106  outside of the arrangement for the apparatus  100  in this embodiment. Moreover, a resistor  121 , which may be comprised of two or more individual resistors, may be provided in a parallel manner with respect to the resonance capacitor  107  C F . In this embodiment, merely two supply lines to the gas arc lamp  106  are required, wherein nevertheless monitoring of the lamp heating filament as well as a corresponding monitoring of the lamp are possible. For the sake of simplicity, in this embodiment the corresponding supply lines (four terminals per arc lamp in total) are not shown. The resonance capacitor  107  and, if provided, the resistors  121  may be accommodated within the starter housing. Thus, existing light equipment may also be used with the present invention. 
   Moreover, a plurality of arc lamps  106  may be driven with respective associated resonance capacitors within the starter housing, wherein only one single common ground line and only one single supply line from a corresponding half bridge  104  is required. In this way, savings in terms of material as well as in terms of effort with respect to installation are achieved compared to a conventional device. 
   In a further embodiment, which is not shown, the three-way full-wave rectifier  101  and the capacitor are, possibly in combination with additional filter elements, provided on a separate wiring board, which may supply a plurality of half-bridge circuits  104 , located on one or more different wiring boards. 
     FIG. 2  schematically illustrates a further embodiment, in which an apparatus  200  for controlling a plurality of gas arc lamps or metal vapor lamps  206  comprises a rectifier  201 , again configured as a three-phase full-wave rectifier, an optional buffer capacitor  202  at the output side of the rectifier  201  and a plurality of electronic ballast devices  204 , including respective control inputs  209 . Due to the omission of power factor regulators required for conventional lamp controls, a plurality of electronic ballast devices may be arranged on a single electronic board in a compact fashion. Due to the omission of the power factor regulators, which would generate additional heat, a moderately large amount of power is controllable by means of a relatively compact control unit. Moreover, alternatively or additionally, an EMC filter may be provided. 
     FIG. 3  schematically illustrates a further embodiment of an apparatus  300  for operating a gas arc lamp or a metal vapor lamp  306 . At the output side of a three-phase full-wave rectifier  301 , a buffer capacitor  302  having a capacity in the range of 0.1 μF to 1 μF is provided. A half-bridge circuit  304  is connected to a resonant circuit, including an inductor  305  with an inductance L R , and a capacitor  307  with a capacity C R , and a transformer  310  for matching the voltage to the gas arc lamp  306 . Furthermore, a diode half-bridge  311 ,  312  is provided so as to clamp the capacitor voltage. At the secondary side of the transformer  310 , a rectifier  313  in combination with an output capacitor  314  is provided. 
   During the operation, the half-bridge  304  is driven via a drive circuit, which is not shown, at a frequency that is below the resonant frequency (F R =1/(2π√{square root over (L R C R )})). Upon turning on the upper bridge transistor, a sinusoidal current half-wave is generated, wherein the transformer  310  merely serves as a current source having a voltage that corresponds to the output voltage at the capacitor  314  and thus the voltage at the gas arc lamp  306 , which is transformed back to the primary side. In order to assure an optimum energy transfer during this half-wave, preferably the ratio of the windings of the transformers  310  is selected so as to obtain approximately half the bridge voltage at the primary side of the transformer  310  during the rated operation. When the sinusoidal resonant current returns to zero, the capacitor  307  is charged to approximately the bridge output voltage and the resonant current remains at zero, so that the upper bridge transistor may be switched off without any loss. 
   A corresponding behavior is obtained during the turning on of the lower transistor, where the capacitor  307  is discharged by the sinusoidal resonant current, so as to transfer energy to the gas arc lamp  306 . After elapse of the half-wave period, the lower transistor may also be turned off without loss. Because of this arrangement, extremely high switch frequencies may be achieved due to the significantly reduced switching losses, so that the elements determining the resonant frequency may be of very low volume and thus may be inexpensive. Especially the stray inductance of the transformer  310  may be used as the inductance L R , thereby eliminating the necessity for an additional inductor  305 . 
   The energy transfer to the gas arc lamp  306  may be readily controlled by varying the switching frequency of the bridge  304 . Due to the reduced switching losses, a significantly improved EMC behavior is achieved, thereby eliminating the necessity for an EMC filter or at least reducing the volume and thus the cost of the filter. By means of this arrangement, switching frequencies in the range of 20 to 1000 kHz may be obtained at a high level of efficiency. 
     FIG. 4  schematically depicts a further apparatus  400  for operating a gas arc lamp or a metal vapor lamp  406 , wherein a three-phase full-wave rectifier  401  is connected to an electronic ballast device  404 , connected to which is the gas arc lamp  406 . The electronic ballast device  404  includes an external or an internal control or drive circuit  408 , which in turn is connected to a parameter generating unit  409  and/or to one or more sensor elements  420 , for instance, configured as a light-sensitive sensor, a current sensor, a temperature sensor, and the like. The apparatus  400  may represent a lighting equipment that may be used in a solarium, in an equipment for light therapy, in applications requiring the sterilization of rooms or objects or medical devices, and the like. Because of the direct usage of the rectified three-phase voltage, a control of the illumination of the gas arc lamp  406  may be achieved in a compact and energy-efficient fashion. Thereby, the control of the illumination may be performed on the basis of parameters, the values of which are determined, for instance, on the basis of signals delivered by the sensor elements  420 . For example, the sensor element  420  may detect the spectral distribution and/or the intensity of the presently emitted radiation and may supply a corresponding signal to the control circuit  408 . The control circuit may, for instance, comprise an integrator so as to additionally determine the illumination integrated over a predefined time interval. From the currently prevailing and/or the averaged illumination, a control signal may then be established for the desired illumination. 
   Furthermore, alternatively or additionally, signals may be taken into consideration during the generation of the control signals, which may be supplied from corresponding current sensor elements and/or corresponding temperature sensor elements that monitor, for instance, the temperature of sensitive device portions of the electronic ballast device. 
   For many applications, it is not only important that the gas arc lamp  406  is controllable in a reliable and energy-saving fashion; of comparable importance is the fact that the control may be performed with respect to important parameters that represent the effect of the radiation output by the gas arc lamp. To this end, the parameter generation unit  409  may comprise respective means so as to establish the control signal in conformity with corresponding parameter values. For instance, the unit  409  may contain corresponding limiting values for the illumination and the duration for operating the gas arc lamp  406  in the form of a table that corresponds to a defined type of skin. This is especially advantageous in a solarium, wherein prior to the beginning of the treatment the type of skin may be determined and then the illumination is performed in relation to the corresponding allowable maximum values or the maximum duration of the illumination. 
   Additionally, the physical or biological effects on, for example, micro organisms and certain materials may be stored in the unit  409  or may be calculated therein, so as to perform the control of the gas arc lamp  406  with respect to a desired effect of the emitted radiation. For instance, for sterilizing or treating a material or for a medical treatment, a specific illumination or irradiation procedure may be required to obtain an optimum result. 
   In a preferred embodiment, a feedback loop is provided so that the target value and an actual value of a corresponding manipulated parameter, for instance, the illumination, is obtained, and the actual value is continuously adapted to the target value. A corresponding determination of target values and actual values and of parameter values may be accomplished by means of a micro computer and/or an external source, for instance, in the form of a personal computer and corresponding storage means. 
   While the present invention is described with reference to individual embodiments, a plurality of variations are within the scope of the invention. For instance, the control and regulation methods and any means required therefore may be implemented in each of the described embodiments.