Classifications

• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
  • H05B41/00—Circuit arrangements or apparatus for igniting or operating discharge lamps
  • H05B41/14—Circuit arrangements
  • H05B41/26—Circuit arrangements in which the lamp is fed by power derived from dc by means of a converter, e.g. by high-voltage dc
  • H05B41/28—Circuit arrangements in which the lamp is fed by power derived from dc by means of a converter, e.g. by high-voltage dc using static converters
  • H05B41/288—Circuit arrangements in which the lamp is fed by power derived from dc by means of a converter, e.g. by high-voltage dc using static converters with semiconductor devices and specially adapted for lamps without preheating electrodes, e.g. for high-intensity discharge lamps, high-pressure mercury or sodium lamps or low-pressure sodium lamps
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
  • H05B41/00—Circuit arrangements or apparatus for igniting or operating discharge lamps
  • H05B41/14—Circuit arrangements
  • H05B41/26—Circuit arrangements in which the lamp is fed by power derived from dc by means of a converter, e.g. by high-voltage dc
  • H05B41/28—Circuit arrangements in which the lamp is fed by power derived from dc by means of a converter, e.g. by high-voltage dc using static converters
  • H05B41/288—Circuit arrangements in which the lamp is fed by power derived from dc by means of a converter, e.g. by high-voltage dc using static converters with semiconductor devices and specially adapted for lamps without preheating electrodes, e.g. for high-intensity discharge lamps, high-pressure mercury or sodium lamps or low-pressure sodium lamps
  • H05B41/292—Arrangements for protecting lamps or circuits against abnormal operating conditions
  • H05B41/2928—Arrangements for protecting lamps or circuits against abnormal operating conditions for protecting the lamp against abnormal operating conditions

Definitions

• This invention relates to arc discharge lamps and, more particularly, to methods and apparatus for operating very high pressure short arc mercury discharge lamps primarily used for projection applications.
• Very high pressure discharge lamps include an arc tube containing an inert gas, mercury vapor, and two electrodes positioned at opposite ends of the arc tube. An arc discharge is established in the arc tube by supplying an electrical current to the electrodes.
• the very high pressure discharge lamp is typically utilized for projection applications, where the optical system requires point-like light sources. To achieve such optical performance, the arc length must be on the order of 1.0-1.5 millimeters.
• the lamps typically include an arc tube constructed of heat resistant and optical transparent material such as quartz, tungsten electrodes, mercury vapor and an inert starting gas.
• the electrodes are constructed of a tungsten rod with a tungsten coil attached to one end.
• the electrode tip in very high pressure discharge lamps reaches temperatures close to or even above the melting point of tungsten. This is necessary to prevent movement of the point of arc attachment to the electrode, also called the arc root.
• the molten tip solidifies and collapses to a relatively flat surface.
• the arc attachment becomes unstable, leading to sudden arc movement or jumping.
• the distance between electrodes increases, thereby reducing the performance of the light collecting optics.
• the electrodes become too hot, the molten region increases, leading to a meltback condition where the distance between electrodes increases, thereby reducing the performance of the light collecting optics.
• increased amounts of tungsten are evaporated from the electrodes and deposited on the arc tube walls, leading to poor lamp maintenance. Therefore, the operation of very high pressure discharge lamps needs to be optimized in order to achieve the most beneficial electrode temperature.
• a problem in establishing the optimal temperature for the two electrodes of a discharge lamp may arise when the lamp current is varied. Such a situation occurs as the lamp voltage increases.
• prior arc ballast circuitry reduces the lamp current.
• the tip temperature of one electrode is reduced such that the tip starts to solidify.
• the tip of the electrode diminishes, leading to a larger arc gap and therefore, a larger lamp voltage.
• the current supply to the lamp decreases and the electrode tip temperature is further reduced. The process continues until the electrode surface becomes flat. Arc instability may then occur.
• a very high pressure discharge lamp is usually mounted in a reflector, which changes the thermal environment of the arc tube.
• One end of the lamp, and thus one electrode, may be hotter than the other end.
• very high pressure discharge lamps are operated with forced air cooling, which is usually directed to both sides of the lamp or to the upper side of the lamp.
• forced air cooling which is usually directed to both sides of the lamp or to the upper side of the lamp.
• different lamp performance is achieved.
• the structure of the electrodes may change due to tungsten transport from the tip of the electrode.
• the flattening process may accelerate, leading to early lamp failure.
• Using preshaped electrodes cannot compensate for most of these asymmetries, because they are unpredictable. Different electrode shapes require additional devices to permit proper mounting of the lamp in the system in which it is employed.
• a method for operating a high pressure discharge lamp.
• the method comprises controlling an alternating lamp current supplied to the lamp at a constant RMS value, and adjusting the lamp current to a new RMS value to prevent power supplied to the lamp from exceeding an upper power limit.
• the lamp current is maintained constant at the new RMS value.
• a lamp system comprises a high pressure discharge lamp, a power circuit for supplying alternating current to the lamp, and a controller configured to control the lamp current at a constant RMS value and to adjust the lamp current to a new RMS value to prevent power supplied to the lamp from exceeding an upper power limit.
• the lamp current is maintained constant at the new RMS value.
• a method for operating a high pressure discharge lamp including an arc tube.
• the method comprises controlling an alternating current supplied to the lamp at a constant RMS value, and adjusting lamp cooling to maintain a wall temperature of the arc tube below a softening temperature.
• a lamp system comprises a high pressure discharge lamp including an arc tube, a power circuit for supplying alternating current to the lamp, a cooling source directed at the lamp, and a controller configured to control the lamp current at a constant RMS value and to adjust the cooling source to maintain a wall temperature of the arc tube below a softening temperature.
• a method for operating a high pressure discharge lamp.
• the method comprises controlling an alternating lamp current supplied to the lamp at a constant RMS value, and adjusting the lamp current to a new RMS value to maintain lamp power between an upper power limit and a lower power limit.
• the lamp current is maintained constant at the new RMS value.
• a lamp system comprises a high pressure discharge lamp, a power circuit for supplying alternating current to the lamp and a controller configured to control the lamp current at a constant RMS value and to adjust the lamp current to a new RMS value to maintain lamp power between an upper power limit and a lower power limit.
• the lamp current is maintained constant at the new RMS value.
• a method is provided for operating a high pressure discharge lamp. The method comprises controlling an alternating lamp current supplied to the lamp at a constant RMS value! and increasing the lamp current to a new RMS value in response to a prescribed value of lamp voltage and maintaining the lamp current constant at the new RMS value.
• a lamp system comprises a high pressure discharge lamp; a power circuit for supplying alternating lamp current to the lamp; and a controller configured to control the lamp current at a constant RMS value, to increase the lamp current to a new RMS value in response to a prescribed value of lamp voltage and to maintain the lamp current constant at the new RMS value.
• Fig. 1 is a schematic block diagram of a lamp system in accordance with a first embodiment of the invention!
• Fig. 2 illustrates an electrode condition for stable arc root attachment
• Fig. 3 illustrates a flat electrode tip which exhibits flicker conditions
• Fig. 4A is a graph of lamp power, lamp voltage and lamp current as a function of time and illustrates current control in accordance with embodiments of the invention!
• Fig. 4B is a flow chart of a process for lamp control in accordance with embodiments of the invention!
• Fig. 5 is a graph of relative light output (RLO) of a discharge lamp as a function of time for flicker and flicker-free operation!
• Fig. 6 is a graph of lamp power, lamp voltage and lamp current as a function of time and illustrates current control in accordance with embodiments of the invention!
• Fig. 7 is a schematic block diagram of a prior art lamp reflector and forced air cooling assembly!
• Fig. 8 is a schematic block diagram of a lamp system in accordance with a second embodiment of the invention.
• Fig. 9A is a graph of cooling rate, lamp power, lamp voltage and lamp current as a function of time and illustrates current control and cooling control in accordance with embodiments of the invention!
• Fig. 9B is a flow chart of a process for lamp control in accordance with embodiments of the invention!
• Fig. 10 is a graph of lamp voltage and lamp power as a function of time in accordance with a prior art constant power control technique;
• Fig. 11 is a graph of lamp voltage and lamp power as a function of time in accordance with embodiments of the invention
• ' and Fig. 12 is a graph of lamp voltage and lamp power as a function of time in accordance with embodiments of the invention.
• FIG. 1 A schematic block diagram of a lamp system in accordance with a first embodiment of the invention is shown in Fig. 1.
• the lamp system includes a very high pressure discharge lamp 10 and an electronic power supply 20.
• Discharge lamp 10 is mounted in a reflector 12.
• One end 22 of discharge lamp 10 is secured in a neck 24 of reflector 12.
• the reflector 12 is enclosed by a transparent member 26.
• Very high pressure discharge lamps typically include an arc tube 30 constructed of a heat resistant and optically transparent material, such as quartz.
• Tungsten electrodes 32 and 34 are mounted at opposite ends of arc tube 30, and the interior volume of arc tube 30 contains mercury vapor and an inert starting gas.
• Each of electrodes 32 and 34 includes a tungsten rod 40 having a tungsten coil 42 attached to one end, as shown schematically in Figs. 2 and 3. Electrodes 32 and 34 are separated by an electrode distance, called the arc length. To achieve a desired optical performance, the arc length is on the order of 1.0-1.5 millimeters.
• the electrodes are affixed to opposite ends of arc tube 30 by press pinching. The electrodes are connected by appropriate electrical wiring to respective output terminals Ol and 02 of electronic power supply 20.
• Electronic power supply 20 includes a power circuit 50, an ignition circuit 52 and a controller 54.
• power circuit 50 When input terminals Il and 12 of electronic power supply 20 are connected to an AC voltage supply, power circuit 50 generates an alternating current having successive periods of alternate polarity and of predetermined shape.
• the alternating current may be a square wave.
• Ignition circuit 52 ensures lamp starting.
• Controller 54 senses the operation of discharge lamp 10 and controls lamp current in accordance with embodiments of the invention.
• the controller 54 includes a lamp current sensor 60, a lamp voltage sensor 62 and a control circuit 64.
• Lamp current sensor 60 senses a lamp current value and provides outputs to power circuit 50 and control circuit 64.
• Lamp voltage sensor 62 senses a lamp voltage value at the output of power circuit 50 and provides a voltage value to control circuit 64.
• Control circuit 64 controls power circuit 50 in this embodiment.
• Control circuit 64 computes lamp power and maintains lamp power within specified limits as described below.
• Power circuit 50 maintains a constant value of RMS lamp current, with changes to new constant values of RMS lamp current in response to changes in lamp operation.
• the lamp current is an alternating current, having successive periods of alternate polarity and of predetermined shape.
• the RMS (root mean square) value of the alternating current is maintained constant over extended periods of time, its value depending on lamp operation as described below.
• the tips of electrodes 32 and 34 typically reach temperatures close to or even above the melting point of tungsten. Such operating temperatures are necessary to prevent movement of the point of arc attachment to the electrode, also called the arc root.
• the arc root 72 of arc 74 remains at a fixed position. However, if the electrode temperature becomes too low, the molten tip solidifies and collapses to a relatively flat surface 80 as shown in Fig. 3. Then, arc root 72 may move on flat surface 80, causing the lamp to flicker.
• a controlled constant RMS value of lamp current Ii mp it is possible to substantially preserve the round shape of the electrode tip over an extended period of time, regardless of lamp voltage changes.
• Fig. 4A illustrates a lamp control routine in accordance with embodiments of the invention.
• Lamp power P lm p, lamp voltage V lm p and lamp current Ii mp are plotted as a function of time in Fig. 4A.
• the lamp current I lm p is controlled at a constant RMS value Ihnpi.
• the lamp RMS current can be changed to a new constant RMS value.
• the lamp current increases to a prescribed value of Vi m p2
• the lamp current is increased to a level Ii mp 2 and is maintained at a constant RMS value of I lm p2 until a further change in lamp conditions.
• This routine ensures the electrode tips are maintained in a molten state with a rounded tip.
• lamp voltage and electrode spacing increase with time.
• the prescribed value of Vi mp 2 at which the RMS current is increased may be defined by equation (l) below, but is not limited to this value.
• Pimp hi upper power limit, typically 120% of rated lamp power
• Pimp nom nominal lamp power
• the electrical power supplied to the lamp is substantially the product of the RMS values of lamp voltage and lamp current.
• the lamp RMS current is decreased proportionally to maintain the lamp power constant. Consequently, the electrode tip temperature decreases and the molten tip region starts to solidify and contract.
• the electrode surface becomes flat and the arc root attachment becomes unstable, leading to lamp flicker.
• the flicker and flicker-free modes of lamp operation may be assessed by measuring lamp relative light output (RLO).
• RLO lamp relative light output
• a photodiode positioned in front of the lamp reflector was utilized to quantify the light output. Typical signal traces are illustrated in Fig. 5. Large fluctuations of the RLO are indicative of arc jumping or flicker.
• an upper power limit Pimp hi typically 180 watts for 150 watts nominal lamp power or 120% of the rated lamp power
• lamp current is decreased to a new constant RMS level Ii mp 3, such that the lamp power does not exceed the upper power limit for the lamp.
• the upper power limit Pi mp hi may be specified relative to the rated lamp power.
• an upper power limit of 180 watts is 120% of the rated lamp power or 30 watts above the rated lamp power.
• lamp control routine as shown in Fig. 4A, if the lamp power decreases to a lower power limit Pi mp i 0 , typically 120 watts for 150 watts nominal lamp power or 80% of the rated lamp power, lamp current is increased to a new constant RMS level Ilmp4 so that the lamp power does not decrease below the lower power limit for the lamp.
• a lower power limit Pi mp i 0 typically 120 watts for 150 watts nominal lamp power or 80% of the rated lamp power
• control circuit 64 preferably implements a delay following a change in RMS current before another change in RMS current can occur.
• the delay permits the discharge lamp to stabilize in response to the new operating conditions.
• the delay may be on the order of 25 to 50 hours, for example.
• step 82 lamp current limp is controlled at a constant RMS value. Initially, the lamp current may be controlled at a nominal value.
• step 84 the lamp voltage Vi mp is compared with a prescribed value Vi mp 2, such as the value given by equation (l) above.
• the prescribed value Vim P 2 of lamp voltage is typically higher than the nominal lamp voltage and indicates that the electrode spacing has increased over its nominal value. If the lamp voltage Vi mp exceeds the prescribed value Vi mp 2, the lamp current Ii mp is increased to a new RMS value Iimp2 in step 86.
• the process then returns to step 82 and the lamp current limp is maintained constant at the new RMS value.
• the reaction of the discharge lamp to changes in RMS current is typically relatively slow. Accordingly, the controller 54 may implement a delay on the order of 25 to 50 hours before another comparison of lamp voltage Vi mp with the prescribed value Vi m p2.
• step 88 the lamp power Pimp is compared to the upper power limit Pimp-hi. If the lamp power Pi mp is equal to or greater than the upper power limit, the lamp current Ii mp is decreased to lamp current Ii m p3 in step 90. The process then returns to step 82 and the lamp current is maintained constant at the new RMS value Iim P 3-
• step 92 the lamp power Pimp is compared with the lower power limit Pimp io. If the lamp power Pimp is less than or equal to the lower power limit, the lamp current limp is increased to a new RMS value Ii mp 4 in step 94. The process then returns to step 82 and the lamp current is maintained constant at the new RMS value Ii mp 4. In the case where the lamp voltage does not exceed the prescribed value Vi mp 2 and the lamp power remains between the upper and lower power limits, the lamp current is maintained constant at the present RMS value in step 82.
• FIG. 6 A further embodiment of the lamp control routine is illustrated in Fig. 6, where lamp power, lamp voltage and lamp current are plotted as a function of time.
• the lamp current When the lamp voltage increases to a level Vi mp 5, which corresponds to the upper power limit Pimp hi, typically 180 watts for 150 watts nominal lamp power or 120% of the rated lamp power, the lamp current is decreased to a new constant RMS level Ii mp 5, such that the lamp operates within a desired range of the rated power.
• the lamp current may be adjusted (increased or decreased) from one constant RMS value to a new constant RMS value continuously or in one or more steps.
• the lamp current is adjusted in increments of 1 ⁇ 2% of the lamp current to avoid an abrupt change in light output.
• the lamp current is adjusted, based on known characteristics of the lamp, to bring the lamp power from the upper or lower power limit to or near the rated lamp power.
• FIG. 8 A block diagram of a lamp system incorporating lamp cooling control in accordance with a further embodiment of the invention is shown in Fig. 8. Like elements in Figs. 1 and 8 have the same reference numerals. Cooling devices 100 and 102 are controlled by drive circuits 110 and 112, respectively, which in turn are controlled by control circuit 64. The amount of controlled cooling is adjusted such that the maximum wall temperature of the arc tube 30 is maintained below the softening temperature of the arc tube material. This softening temperature is defined as the temperature at which a solid material starts losing its rigidity and starts transforming into a plastic or liquid state.
• FIG. 9A A lamp control routine in accordance with a further embodiment of the invention is illustrated in Fig. 9A.
• Lamp cooling rate, lamp power, lamp voltage and lamp current are plotted as a function of time.
• the cooling rate is increased.
• the cooling rate is increased, the lamp voltage drops and the lamp power thus drops, as shown in Fig. 9A.
• the critical temperature is not to exceed the devitrification point. This temperature is lower than the softening temperature and is the temperature at which quartz starts becoming opaque and loses optical transmission, typically around 1000° C.
• step 200 the lamp current limp is controlled at a constant RMS value. Initially, the lamp current may be controlled at a nominal value.
• step 202 the lamp power Pimp is compared with an upper power limit Pimp hi and a lower power limit Pimp-io. If the lamp power is between the upper and lower power limits, lamp cooling by cooling devices 100 and 102 (Fig. 8) is maintained at its present value in step 204. If the lamp power Pimp is determined in step 206 to be less than or equal to the lower power limit Pimp-io, the lamp cooling is decreased in step 208.
• step 212 determines whether the lamp cooling is at maximum value. If the lamp cooling is not at maximum value, lamp cooling is increased in step 214, by controlling cooling devices 100 and 102. If lamp cooling is determined in step 212 to be at maximum value, the lamp current I lm p is decreased to a new RMS value in step 216. Following steps 204, 208, 214 and 216, the process returns to step 200 and the lamp current I lm p is maintained at a constant RMS value.
• the control process shown in Fig. 9B and described above has a relatively slow time constant, since the lamp system is relatively slow to react to changes in lamp cooling and lamp current.
• Fig. 10 illustrates experimental graphs of the lamp voltage and lamp power versus time in accordance with the prior art technique of constant power. As the lamp voltage increases or decreases with time, lamp power is maintained constant near lamp nominal power (typically within 1-2%).
• Fig. 11 illustrates experimental graphs of the lamp voltage and lamp power versus time in accordance with embodiments of the invention.
• lamp current RMS value As the lamp voltage increases or decreases and lamp current RMS value is maintained constant and, because the electrical power supplied to the lamp is substantially the product of RMS values of lamp voltage Vi mp and lamp current I lm p, lamp power increases or decreases accordingly. However, lamp power is not permitted to drop below 120W (for a 150W nominal lamp power) or 80% of the rated lamp power.
• Fig. 12 illustrates experimental graphs of the lamp voltage and lamp power versus time in accordance with embodiments of the invention.
• lamp power increases accordingly. However, lamp power is not permitted to exceed 180W (for a 150W nominal lamp power) or 120% of the rated lamp power.

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• 2005
  • 2005-10-25 WO PCT/JP2005/019961 patent/WO2007049358A1/en active Application Filing
  • 2005-10-25 JP JP2008518549A patent/JP2009512120A/ja active Pending
  • 2005-10-25 DE DE602005027912T patent/DE602005027912D1/de active Active
  • 2005-10-25 CN CN2005800519489A patent/CN101297608B/zh not_active Expired - Fee Related
  • 2005-10-25 EP EP05799139A patent/EP1925189B1/de not_active Expired - Fee Related

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