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
  • H05B41/292—Arrangements for protecting lamps or circuits against abnormal operating conditions
• • 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
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S315/00—Electric lamp and discharge devices: systems
  • Y10S315/05—Starting and operating circuit for fluorescent lamp

Definitions

• the invention relates to a circuit arrangement for operating a high pressure discharge lamp with a current having successive pe ⁇ ods of opposite pola ⁇ ty, which lamp is provided with at least two mam electrodes being placed on an electrode distance from each other, the circuit arrangement comp ⁇ smg: -input terminals for connecting a supply source, -output terminals for connecting the high pressure discharge lamp, and -means, coupled to the input terminals, for supplying the lamp current to the high pressure discharge lamp of which the successive pe ⁇ ods have a predetermined shape
• Such a circuit a ⁇ angement is known from the Ame ⁇ can Patent 5,608,294
• the known circuit a ⁇ angement provides a measure to suppers flicke ⁇ ng of a high pressure discharge lamp and is in particular suitable for operating a high pressure discharge lamp in a projection system like a projection television apparatus
• the lamp is supplied with a cu ⁇ ent of successive block shaped pe ⁇ ods of opposite pola ⁇ ty
• the suppression of flicke ⁇ ng is reached by supplying to pe ⁇ ods of the lamp cu ⁇ ent an additional cu ⁇ ent pulses with the same pola ⁇ ty at the end of a predetermined fraction of such a pe ⁇ od of the lamp cu ⁇ ent
• the temperature of the electrode is raised to a relatively high value, which high temperature increases the stability of the discharge arc, because the discharge arc o ⁇ ginates from the same place on the electrode in each cathodic phase and so flicke ⁇ ng is substantially suppressed
• the additional cu ⁇ ent pe ⁇ od the temperature of the electrode is raised to
• each electrode of the lamp alternatingly functions as a cathode and as an anode during successive periods of the lamp current. During these periods the electrode is said to be in the cathodic phase and the anodic phase respectively. Electrode material, that is removed from the electrode in the anodic phase, returns to the electrode as a stream of ions in the cathodic phase.
• the invention aims to provide a circuit a ⁇ angement for operating a high pressure discharge lamp in a way which substantially overcomes the mentioned drawback and simultaneously is maintaining the substantially suppression of flickering of the lamp during its operation.
• a circuit a ⁇ angement of the kind mentioned in the opening paragraph is for this purpose characterized in that that the circuit a ⁇ angement is provided with
• circuit a ⁇ angement further comprises:
• the first parameter is formed by the lamp voltage, preferable averaged over several pe ⁇ ods.
• the lamp voltage du ⁇ ng each successive pe ⁇ od is providing for the second parameter.
• Use of the lamp voltage for forming the second parameter has as advantage that for first and second parameter the same quantity is used This simplifies the circuit arrangement
• the shape of the lamp voltage du ⁇ ng each pe ⁇ od is detected and used for forming the second parameter Preferable this is realized by means in the circuit a ⁇ angement which measure the lamp voltage at selected intervals du ⁇ ng such a pe ⁇ od and compare the thus found values with each other.
• the second parameter is the value of the lamp voltage in successive pe ⁇ ods at a fixed moment du ⁇ ng each pe ⁇ od, preferably at a moment of a constant lamp current, which are detected
• this is preferable realized by means measu ⁇ ng the lamp voltage at a moment close to the end of each pe ⁇ od and compa ⁇ ng the outcome of consecutive pe ⁇ ods having the same pola ⁇ ty
• the second parameter is formed by the luminous output of the lamp, for instance by means of optical detectors placed around a display area of a projection system, for instance at the edge of the display area
• Fig 1 shows an embodiment of a circuit a ⁇ angement according to the invention
• Fig 2 shows control means of an embodiment of a circuit arrangement according to the invention in accordance with fig 1;
• Fig 3 shows control procedure as prosecuted by the embodiment according to Fig. 4 shows a flicker control loop forming part of the control procedure according to fig 3, and
• Kl and K2 denote input terminals for connection to a supply voltage source supplying a supply voltage.
• I coupled to Kl and K2, are means for generating a DC supply current.
• Output terminals of means I are connected to respective input terminals of commutator II.
• Output terminals of commutator II are connected by the high pressure discharge lamp La, which lamp is provided with at least two main electrodes being placed on an electrode distance from each other.
• Ill are control means to control the shape of successive periods of opposite polarity of the cu ⁇ ent supplied to the lamp by way of controlling the means I and incorporate both means for detecting a first parameter indicative for the electrode distance and forming a first signal dependent on the first parameter and means for adapting the lamp cu ⁇ ent in dependence of the thus formed first signal.
• Means I and means II together constitute means A, coupled to the input terminals, for supplying the lamp cu ⁇ ent to the high pressure discharge lamp of which lamp cu ⁇ ent the successive periods have a predetermined shape.
• the operation of the circuit a ⁇ angement shown in Fig. 1 is as follows.
• means I When input terminals K1,K2 are connected to a voltage supply source, means I generate a dc supply cu ⁇ ent from the supply voltage supplied by the voltage supply source. Commutator II converts this dc cu ⁇ ent into an alternating cu ⁇ ent having successive periods of opposite polarity. By control means III the shape of the successive periods of the current thus formed and supplied to the lamp La is controlled.
• the means I are formed by a rectifier bridge followed by a switch mode power circuit, for instance a Buck or down converter.
• Commutator II preferably comprises a full bridge circuit. Lamp ignition circuitry is preferably incorporated also in the commutator means II.
• the control means III for controlling means I are shown in more detail.
• the control means III comprise an input 1 for detecting the lamp voltage, for instance the voltage over the terminals L1,L2 connected to the lamp forming a signal representing the lamp voltage.
• the lamp voltage representing signal is formed by detecting a voltage at a connection point L3, as the thus detected voltage is a dc voltage which will not be disturbed by ignition voltage generated in the lamp ignition circuitry.
• Control means III further comprises an input 2 for detecting of the current through inductive means L of the converter forming the switch mode power circuit of the means I, which converter has at least a switch, and an output terminal 3 for switching the switch of the switch mode power circuit periodically in a conducting and. a non-conducting state thus controlling the current through the induction means L of the converter.
• Input 1 is connected to connection pin PI of a microcontroller MC.
• a connection pin P3 of the microcontroller is connected to an input 4 of a switching circuit SC.
• Input 2 is connected to an input 5 of the switching circuit SC, of which an output O is connected to output terminal 3.
• the microcontroller MC are forming means for detecting a first parameter indicative for the electrode distance and forming a first signal dependent on the first parameter as well as means for detecting a second parameter indicative for the occu ⁇ ence of lamp flicker and forming a second signal dependent on the detected second parameter.
• the switching circuit forms means for reshaping of the periods of the lamp current in dependence of the thus formed first signal and means for further adjustment of the shape of the successive periods in dependence of the thus formed second signal.
• the operation of the circuit arrangement shown in Fig. 2 with the converter being a Buck or down converter is as follows.
• the microcontroller MC is provided with software for prosecution procedures as further explained herebelow with reference to figures 3 and 4.
• the procedures result in a converter peak cu ⁇ ent value which is fed to switching circuit SC at input 4 and used as reference for comparison for the detected cu ⁇ ent at input 2 which is also fed to the switching circuit SC, at input 5.
• the switching circuit Based on this cu ⁇ ent values comparison the switching circuit generates a switching off signal at output O, which switches the switch of the down converter in the non- conducting state when the detected current equals the peak cu ⁇ ent value.
• the cu ⁇ ent through the inductive means will decrease.
• the converter switch is kept in the non-conductive state until the cu ⁇ ent through the inductive means L becomes zero.
• the switching circuit SC On detecting the converter cu ⁇ ent becoming zero the switching circuit SC generates at its output O a switch on signal that renders the switch of the down converter conductive.
• the cu ⁇ ent through the inductive means L now starts to increase until it reaches the peak cu ⁇ ent value.
• Such switching circuit SC is for instance known from WO97/14275.
• the value of the peak cu ⁇ ent is refreshed as outcome of the procedures as prosecuted by the microcontroller MC.
• the detection of the lamp voltage is done with a frequency depending on the shape of the cu ⁇ ent to be realized through the lamp and is controlled by a built in timer of the microcontroller MC.
• Taking the lamp voltage as lamp parameter for detection has as an advantage that it makes possible to have a wattage control of the lamp inherently incorporated in the microcontroller software.
• a wattage control would not only require an additional detection of the lamp voltage, but also an additional control procedure in the microcontroller.
• the down converter operates in a favourable embodiment at a frequency in the range of 45kHz to 75kHz.
• Fig. 3 shows control procedure as prosecuted by the microcontroller MC of the control means III according to fig 2.
• a shown voltage control loop NC is started on a regular time basis, for instance once per minute from a flicker control loop FC. From a start SV the driver detects at AA whether the lamp voltage is outside a preferred range. The lamp voltage as supplied via input 1 to connection pin PI thus forms the first parameter. If the first parameter is not outside the preferred range the control procedure returns to the flicker control loop FC which is explained in detail below. If the lamp voltage is detected at AA to be below a minimum level U- the shape of the successive periods of opposite polarity forming the lamp cu ⁇ ent, further called mode of operation, is established as stored at B.
• Too low a lamp voltage indicates that the electrode distance has become too small due to electrode tip growth.
• the control switches at BI to a next shape of periods from a look up table I which counteracts electrode growth or even promotes electrode distance increase.
• the new selected shape is stored in B. Then the control procedure returns to loop FC. If the lamp voltage detected at AA is above a maximum level U+ the mode of operation detected at C is switched at CII to a next mode according to a look up table II and the control procedure returns to loop FC.
• the new selected mode is stored at C. Too high a lamp voltage indicates that the electrode distance has become too large and so the new selected mode is a mode which promotes electrode tip growth.
• Preferable look up table II is the inverse of look up table I.
• the detected voltage values are in case of the described embodiment values of the lamp voltage taken at a fixed moment of each successive period, preferably at the moment .75tp, but at least at a moment that the lamp voltage tends to be stable.
• the flicker control loop FC is illustrated. From a start S the driver detects at F whether flicker is occurring. If so the mode of operation is switched at Fill to a next one according to a look up table HI. After a delay period D to let the lamp operation stabilize the control procedure switches to the voltage control loop VC. If no flicker is detected at F it is determined at T if lamp operation is free of flicker for a period > T. If not the control procedure returns to S. Is however the lamp operating flicker free for a period > T than the control procedure forces at FIV the switching over to a next mode of operation according to the look up table IV. After a delay period D to let the lamp operation stabilize the control procedure switches to the voltage control loop VC.
• Preferable look up table IV is the inverse of look up table III.
• This mode provides for flicker free operation and also for growth of the electrode tips and so reduction of the electrode distance.
• fig 6 is shown the lamp cu ⁇ ent of an alternative mode of operation in which the cu ⁇ ent over the first part of the period is held constant at the value which allows for a diffuse stable attachment of the discharge to the electrodes, herewith defined as themionic emission of the electrode. Therefore the mean value of the current over this first part Ie is at most equal to the maximum cu ⁇ ent that could be supplied by the electrodes through thermionic emission.
• This mode provides for flicker free operation and also for growth of the electrode tips and so reduction of the electrode distance.
• the resulting cu ⁇ ent is shown in fig 7.
• the cu ⁇ ent II at the start of the period is higher than Ie.
• this mode provides for flicker free operation and also for growth of the electrode tips and so reduction of the electrode distance.
• fig 8 is shown a graph of the cu ⁇ ent according to another mode of operation in which the lamp cu ⁇ ent is provided with a pulse of the same polarity at the end of the period with a value 13.
• t3 is the pulse width.
• the value of 13 is 1.61m. From experiments it has been deduced that 13 is preferable chosen in the range 1.6 ⁇ I3/Im ⁇ 3.
• t2 is the time lapse between start of the pe ⁇ od and start of the additional cu ⁇ ent pulse.
• a cu ⁇ ent shape as shown in fig 10 in which an additional current pulse of opposite pola ⁇ ty is applied, is also suitable for causing lamp voltage increase.
• the necessary relation to be fulfilled are:
• a practical embodiment of a circuit arrangement as shown m Fig. 1 has been used for the operation of a high pressure discharge lamp of the type UHP, make Philips.
• the lamp had a nominal power consumption of 100 Watt and an electrode distance of only 1.4 mm, was operated with two different modes of operation defining different shapes of successive pe ⁇ ods forming the lamp cu ⁇ ent.
• a first mode of operation the successive pe ⁇ ods of opposite pola ⁇ ty are shaped as shown in fig 9.
• the value of the cu ⁇ ent in this mode co ⁇ esponding to II is regulated by way of a wattage control incorporated in the microcontroller software to a nominal value of 1 06A
• the maximum value for 13 is fixed at 2 5A
• the lamp ⁇ oltage having a nominal value of 85V
• the cu ⁇ ent 13 is fixed at 2 5A
• the pe ⁇ ods are reshaped by the means A in that the cu ⁇ ent 13 is stepped down in 3 steps to the value of II, after which the means A sw itch over to a second mode of operation in which the supplied lamp cu ⁇ ent is formed by pe ⁇ ods which are shaped as rectangular blocks with a value controlled with the same wattage control as mentioned for the
• the thus detected lamp voltage is also forming the second parameter.
• the found values of successive pe ⁇ od of equal pola ⁇ ty are compared for detecting occu ⁇ ence of discharge attachment on the electrodes tending to become unstable and used as defining lamp flicker.
• a value of >1V occurring more than once over a time span of 2 minutes is set in the software as threshold for the occu ⁇ ence of lamp flicker.
• the detection of occu ⁇ ence of lamp flicker is based on comparison of the found voltage differences of the detected voltages with 3 different thresholds each connected to a separate repetition rate as to detect both lamp flicker of high and of low frequency with high accuracy.
• the values of the thresholds and co ⁇ esponding repetition rate is given in a table.

Landscapes

• Circuit Arrangements For Discharge Lamps (AREA)
• Lock And Its Accessories (AREA)
• Selective Calling Equipment (AREA)
• Inductance-Capacitance Distribution Constants And Capacitance-Resistance Oscillators (AREA)

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Publications (1)

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Cited By (12)

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Citations (5)

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• 1999
  • 1999-12-01 KR KR1020007008930A patent/KR100664337B1/ko not_active Expired - Fee Related
  • 1999-12-01 TW TW088120985A patent/TW490998B/zh not_active IP Right Cessation
  • 1999-12-01 CN CNB998028363A patent/CN1155300C/zh not_active Expired - Lifetime
  • 1999-12-01 EP EP99959373A patent/EP1057376B1/en not_active Expired - Lifetime
  • 1999-12-01 DE DE69912102T patent/DE69912102T2/de not_active Expired - Lifetime
  • 1999-12-01 JP JP2000589008A patent/JP4508425B2/ja not_active Expired - Lifetime
  • 1999-12-01 WO PCT/EP1999/009352 patent/WO2000036882A1/en not_active Ceased
  • 1999-12-01 AT AT99959373T patent/ATE252309T1/de active
  • 1999-12-15 US US09/464,006 patent/US6232725B1/en not_active Expired - Lifetime

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