JP6278255B2 - Discharge lamp lighting device - Google Patents

Description

  The present invention relates to a discharge lamp lighting device preferably used for a light source such as a projector.

  A discharge lamp with a high mercury vapor pressure is used as a light source of the projector apparatus. Such a high-pressure mercury lamp can obtain light in the visible wavelength region with high output by increasing the mercury vapor pressure.

  The discharge lamp has a substantially spherical light emitting portion formed by a discharge vessel, and a pair of electrodes are arranged in the light emitting portion so as to face each other at an extremely small interval of, for example, 2 mm or less.

  When such a discharge lamp is lit for a long time in the same state, a plurality of minute protrusions may be formed at a high temperature, or minute irregularities may be generated on the tip surface portion of the electrode. These micro-protrusions and irregularities are formed by agglomeration of the compound formed by melting the material constituting the electrode (for example, tungsten) and combining with the gas sealed in the light emitting part. The shape of the surface part of the is changed. Along with this, the starting point of the arc moves, the discharge position becomes unstable, and there is a problem that flickering of projection light called so-called flicker occurs.

  In order to solve such a problem, the following Patent Document 1 supplies a current of a pulse wave P1 having a predetermined frequency (fundamental frequency) to the discharge lamp and a current of a pulse wave P2 having a frequency lower than the fundamental frequency. A discharge lamp lighting method is disclosed that is intermittently or periodically inserted into the pulse wave of the fundamental frequency (see FIG. 10).

  By setting the frequency of the pulse wave to a low frequency, the period during which one electrode is fixed to the anode and the other electrode to the cathode, that is, the period during which a high voltage is applied between the two electrodes is lengthened. As a result, the degree of heating of the electrode is increased, and heat can be transmitted not only to the tip of the electrode but also to a location away from the tip. Therefore, while a low-frequency pulse wave is applied, heat is also transmitted to a location away from the tip of the electrode, and the minute protrusions and irregularities generated at the location can be melted and evaporated. Thereby, protrusions and irregularities other than the electrode tip that may adversely affect can be eliminated, and the bright spot of the arc can be stabilized.

JP 2006-59790 A

  According to the technique described in Patent Document 1, an effect of suppressing flicker when the discharge lamp is turned on can be obtained. However, according to the diligent research of the present inventors, when the discharge lamp is arranged inside the concave reflecting mirror and the light emitted from the discharge lamp is condensed and projected at a predetermined position, flickering of the projected light occurs. Confirmed to do. The present inventors infer the reason why this phenomenon occurs as follows.

  FIG. 11 is a diagram schematically showing the configuration when the discharge lamp 10 is arranged inside the concave reflecting mirror 60 together with the optical path of the discharge light. The discharge lamp 10 has a pair of electrodes 20a and 20b, and is discharged by applying a voltage between the electrodes. Here, as described above with reference to FIG. 10, since the discharge lamp 10 is driven to be lit by an alternating current, the electrode 20a becomes a cathode or the electrode 20b becomes a cathode depending on the polarity of the current. Discharging is sustained by applying a high electric field to the cathode and continuing to supply electrons from the cathode toward the anode. At this time, the tip portion of the cathode to which the highest electric field is applied shines brightest. That is, the position of the brightest spot (bright spot) in the discharge lamp 10 differs depending on whether the cathode is the electrode 20a or the electrode 20b.

  FIG. 11 shows a case where the light from the discharge lamp 10 is taken into the irradiation region 62 using the concave reflecting mirror 60 and the optical element 61. The light rays 73, 74, and 74 are used as light rays when the electrode 20a is a cathode. 75, and light rays 76, 77, 78, 79 are illustrated as light rays when the electrode 20b is a cathode.

  When the electrode 20a, that is, the electrode arranged on the opening region side of the concave reflecting mirror 60 is a cathode, each light beam 73, 74, 75 reflected by the concave reflecting mirror 60 is condensed at the condensing position 70a. On the other hand, when the electrode 20b, that is, the electrode disposed on the side opposite to the opening area of the concave reflecting mirror 60 is a cathode, each light beam 76, 77, 78 reflected by the concave reflecting mirror 60 is focused on the condensing position 70a. Are condensed at different condensing positions 70b. Further, when the electrode 20b is a cathode, there is also a light beam 79 that is not incident on the reflecting surface of the concave reflecting mirror 60 and is emitted to the outside of the concave reflecting mirror 60.

  The inventors of the present invention change the amount of light irradiated to the irradiation region 62 as a result of the difference in the amount of light reflected by the concave reflecting mirror 60 and the condensing position depending on whether the cathode is the electrode 20a or the electrode 20b. The light intensity in the irradiation region 62 is different at the timing when the polarity of the current supplied to the discharge lamp 10 is reversed, and it is assumed that this phenomenon can be visually recognized as flicker.

  In the case of the driving method as described with reference to FIG. 10, the discharge lamp 10 has a lighting period (period T1 in FIG. 10) based on the pulse wave P1 having the fundamental frequency and a pulse wave P2 having a frequency lower than that. It has a lighting period based on (period T2 in FIG. 10). In particular, in the period T2, since the period during which the polarity is maintained is long, the change in the light amount is easily visually recognized at the timing when the polarity is reversed. On the other hand, in the period T1, since the polarity is reversed in a very short time, the change in the light intensity due to the change in the polarity may not be visually recognized. However, when the difference in the light intensity is large, the change in the light intensity is visually recognized. It is also assumed that.

  In view of the above consideration, in the case of driving a discharge lamp with an alternating current, the present invention suppresses the occurrence of a light intensity difference due to polarity inversion, and flickering of light output from the discharge lamp (flicker) is more than conventional. It aims at providing the lighting device which is controlled.

The discharge lamp lighting device of the present invention,
A power feeding unit for supplying an alternating current to a discharge lamp in which a pair of electrodes are arranged to face each other in a discharge vessel in which a predetermined gas is sealed;
A power control unit that outputs a signal related to a control power value to the power supply unit;
A pulse generation unit that outputs a pulse wave to the power supply unit.

And the said electric power feeding part is the structure which converts the supplied DC voltage into the alternating current according to the frequency of the said pulse wave, and the said control electric power value, and supplies it to the said discharge lamp,
The power control unit is configured so that the average light intensity of the discharge lamp and the pulse wave are negative during the period in which the pulse wave is positive, compared to the case where the control power value is the same regardless of the polarity of the pulse wave. The control power value is controlled to be different between the period in which the pulse wave is positive and the period in which the pulse wave is negative in the direction in which the difference from the average light intensity of the discharge lamp is reduced during the positive period.

  Conventionally, control is performed so that the same power is supplied from the power supply unit to the discharge lamp regardless of the polarity of the pulse wave. The difference in the light intensity in the irradiation region depending on the polarity of the pulse wave, that is, which side of the pair of electrodes constitutes the cathode, is described above in the section “Problems to be solved by the invention”. Street.

  It is considered that the above problem is caused by the fact that the position of the bright spot moves due to the change in polarity as the cathode side forms the brightest bright spot. The discharge lamp lighting device according to the present invention intentionally varies the power value supplied from the power supply unit to the discharge lamp according to the polarity of the pulse wave based on the control from the power control unit. More specifically, compared to the case where the power value supplied from the power supply unit to the discharge lamp is equal regardless of the polarity of the pulse wave, the power for each polarity is reduced so that the difference in average light intensity between the two polarities is reduced. The values are different. Thereby, the light intensity difference between the polarities as described above is reduced, and flicker is suppressed.

  When lighting is driven by a conventional method, the position of the electrode provided in the discharge lamp, the lamp position, and the like, whether the light intensity is high when the pulse wave is positive or negative Since it depends on the positional relationship of the optical system, it is not generally determined. According to the above method, the flicker is suppressed regardless of whether the pulse wave is viewed with high light intensity or viewed with low light intensity during the positive wave period compared with the negative wave period. Effect can be obtained.

  Further, in the above configuration, the power control unit has an average light intensity of the discharge lamp during a period in which the pulse wave is positive, compared to a case where the control power value is the same regardless of the polarity of the pulse wave. And the period when the pulse wave is negative and the period when the pulse wave is negative so that the difference between the average light intensity of the discharge lamp and the pulse wave during the period when the pulse wave is negative is within ± 2%. The control power value may be controlled differently.

  As described later in the section “DETAILED DESCRIPTION OF THE INVENTION”, when the pulse wave suppresses the difference in average light intensity between the positive polarity period and the negative polarity period within ± 2%, it is visually recognized as flicker. The possibility can be made very low.

  Further, in the above configuration, the power control unit stores in advance information related to a ratio between the control power value during a period when the pulse wave is positive and the control power value during a period when the pulse wave is negative. Based on the stored information, the control power value may be controlled to be different between the period in which the pulse wave is positive and the period in which the pulse wave is negative.

  Here, in the stage before shipping the lighting device and the discharge lamp, the control power value is made constant regardless of the polarity of the pulse wave, the average light intensity in the period of each polarity of the pulse wave is measured, and based on the result In order to reduce the difference between the two, it is possible to determine the ratio of the input power in each period and store the value in the control power value. The power control unit outputs a control power value based on the stored information to the power feeding unit in each of the positive polarity period and the negative polarity period of the pulse wave, and the power feeding unit is determined based on this value. Power is supplied to the discharge lamp. As a result, the difference in average light intensity between the period in which the pulse wave is positive and the period in which the pulse wave is negative is reduced, and the visual recognition of flicker is suppressed.

In the above configuration,
The pulse generator repeats a cycle of outputting a first pulse wave over a first period and then outputting a second pulse wave having a frequency lower than that of the first pulse wave over a second period shorter than the first period. Configuration,
The power control unit may perform control to vary the control power value within the second period.

  As described above, when the discharge lamp is driven with a high-frequency first pulse wave and a lower-frequency second pulse wave, flickering of the projection light accompanying the movement of the bright spot of the arc on the electrode is suppressed. The However, the period during which the second pulse wave is applied (second period) is longer than the period during which the first pulse wave is applied (first period). As a result, when there is a difference in the light intensity depending on the polarity of the pulse wave, it is easily recognized as flicker.

  According to the above configuration, the flicker suppression effect can be reduced because the light intensity difference between the polarities can be reduced in the second period in which the flicker is particularly easily recognized due to the difference in the light intensity according to the polarity of the pulse wave. Is expensive.

  In addition to the above configuration, the power control unit may perform control to vary the control power value not only in the second period but also in the first period.

  According to the lighting device of the present invention, it is possible to suppress the occurrence of a light intensity difference associated with polarity reversal, and to suppress flickering (flicker) of light output from the discharge lamp as compared with the conventional case.

It is a cross-sectional schematic diagram of a discharge lamp. It is the cross-sectional schematic diagram which expanded the electrode tip vicinity of the discharge lamp. It is a circuit block diagram which shows typically the structure of a discharge lamp lighting device. It is a figure which shows an example of the lamp current waveform supplied from a discharge lamp lighting device. It is a figure which shows an example of a lamp current waveform and a waveform of light intensity. It is a typical drawing explaining the setting method of control electric power value. It is a graph which shows the relationship between a light intensity difference and a flicker level. It is a figure which shows another example of a lamp current waveform and a waveform of light intensity. It is a figure which shows another example of a lamp current waveform and a waveform of light intensity. It is a figure which shows another example of a lamp current waveform and a waveform of light intensity. It is a figure which shows an example of the conventional lamp current waveform. It is the figure which showed typically the structure at the time of arrange | positioning a discharge lamp inside a concave reflective mirror with the optical path of discharge light.

  An embodiment of a discharge lamp lighting device of the present invention will be described with reference to the drawings. Here, prior to the description of the configuration of the lighting device, the configuration of a discharge lamp to which an alternating current is supplied by the lighting device will be described with reference to the drawings. In each figure, the dimensional ratio in the drawing does not necessarily match the actual dimensional ratio.

[Lamp configuration]
1A and 1B are schematic cross-sectional views of a discharge lamp. FIG. 1B is a schematic cross-sectional view enlarging the vicinity of the electrode tip of FIG. 1A.

  The discharge lamp 10 has a substantially spherical light emitting portion 11 formed by a discharge vessel made of quartz glass. The material of the discharge vessel is not limited to quartz glass, and may be made of other materials.

  In the light emitting unit 11, a pair of electrodes 20a and 20b are disposed to face each other at an extremely small interval of, for example, 2 mm or less.

  Further, sealing portions 12 are formed at both ends of the light emitting portion 11. A conductive metal foil 13 made of molybdenum or the like is hermetically embedded in the sealing portion 12 by, for example, a shrink seal. The shaft portions of the electrodes 20a and 20b are joined to one end of the metal foil 13, and the external lead 14 is joined to the other end of the metal foil 13, and power is supplied from the discharge lamp lighting device of the present invention described later. .

  Mercury, rare gas, and halogen gas are sealed in the light emitting portion 11 of the discharge lamp 10.

Mercury is used to obtain a necessary visible light wavelength, for example, radiation having a wavelength of 360 to 780 nm, and in terms of specific values, 0.20 mg / mm ³ or more is enclosed. Although the amount of sealing varies depending on the temperature condition, a high vapor pressure of 200 atm or more is realized as the pressure inside the light emitting unit during lighting. In addition, by enclosing more mercury, it is possible to make a discharge lamp with a high mercury vapor pressure of mercury vapor pressure of 250 atm or higher and 300 atm or higher when the lamp is turned on. it can.

  As the rare gas, for example, argon gas is sealed at about 13 kPa. Its function is to improve the lighting startability.

As the halogen gas, iodine, bromine, chlorine, etc. are enclosed in the form of a compound with mercury or other metals. The amount of halogen encapsulated is selected from the range of 10 ⁻⁶ μmol / mm ³ to 10 ⁻² μmol / mm ³ . The biggest reason for enclosing the halogen is to extend the life of the discharge lamp using a so-called halogen cycle. Further, when the discharge lamp 10 is extremely small and has a very high lighting vapor pressure, the effect of preventing devitrification of the discharge vessel can be obtained by enclosing the halogen. Devitrification means that crystallization proceeds from a metastable glass state and changes to an aggregate of crystal grains grown from many crystal nuclei. If such a phenomenon occurs, light is scattered at the grain boundaries of the crystal and the discharge vessel becomes opaque.

  In addition, as long as the same function is realizable, the gas enclosed with the light emission part 11 is not limited to the said gas.

As an example of the discharge lamp 10, the maximum outer diameter of the light emitting part is 9.4 mm, the distance between the electrodes is 1.0 mm, the inner volume of the discharge vessel is 55 mm ³ , the rated voltage is 70 V, and the rated power is 180 W. It can be set as a structure.

In addition, when it is assumed that a discharge lamp 10 is built in and used in a projector that has been miniaturized in recent years, the discharge lamp 10 is required to be extremely small as a whole size, and on the other hand, a high light emission amount is also required. . For this reason, the thermal influence in the light emitting part is extremely severe, and the lamp wall load value of the lamp is 0.8 to 2.5 W / mm ² , specifically 2.4 W / mm ² . As described above, the discharge lamp 10 having a high mercury vapor pressure and a tube wall load value is mounted on a presentation device such as a projector or an overhead projector, thereby providing the presentation device with emitted light having good color rendering properties. be able to.

[Shape of electrode tip]
As shown in FIG. 1B, the electrode 20a includes a head portion 29a and a shaft portion 30a, and the electrode 20b includes a head portion 29b and a shaft portion 30b. Each of the electrode 20a and the electrode 20b has a protrusion 21 at the tip. The protrusion 21 is formed by agglomerating molten electrode material at the electrode tip when the lamp is turned on. In the present embodiment, the electrode 20a and the electrode 20b are described as both made of tungsten, but the material is not limited to this.

  When the electrode 20a and the electrode 20b are energized, the electrode 20a and the electrode 20b are heated to a high temperature, and tungsten constituting them is sublimated. The sublimated tungsten is combined with the enclosed halogen gas in the inner wall surface region of the light emitting portion 11 which is a relatively low temperature portion to form tungsten halide. Since the vapor pressure of tungsten halide is relatively high, it moves again in the vicinity of the tips of the electrodes 20a and 20b in the gas state. When heated again at this point, the tungsten halide is separated into halogen and tungsten. Among these, tungsten returns to the tips of the electrodes 20 a and 20 b and aggregates, and the halogen returns as the halogen gas in the light emitting unit 11. This corresponds to the “halogen cycle” described above. The agglomerated tungsten adheres to the vicinity of the tips of the electrode 20a and the electrode 20b, whereby the protrusion 21 is formed.

[Configuration of lighting device]
FIG. 2 is a circuit block diagram schematically showing the configuration of the discharge lamp lighting device of the present invention. As shown in FIG. 2, the lighting device 1 includes a power feeding unit 3 and a control unit 4. The control unit 4 includes a pulse generation unit 41, a power control unit 42, and a frequency control unit 43, and a pulse wave P having a frequency determined based on a signal from the frequency control unit 43 is supplied from the pulse generation unit 41 to the power supply unit. 3 is supplied. And the electric power feeding part 3 is alternating current based on the signal (corresponding to the gate signal Gx in FIG. 2) regarding the control electric power value output from the electric power control part 42, and the pulse wave P output from the pulse generation part 41. A current is generated and supplied to the discharge lamp 10. The discharge lamp 10 lights up when this alternating current is supplied.

<Power supply unit 3>
The power feeding unit 3 includes a step-down chopper unit 31, a DC / AC conversion unit 32, and a starter unit 33.

  The step-down chopper unit 31 steps down the supplied DC voltage Vdc to a desired low voltage and outputs it to the DC / AC conversion unit 32 at the subsequent stage. In FIG. 2, as a specific configuration example, the step-down chopper unit 31 includes a switching element Qx, a reactor Lx, a diode Dx, a smoothing capacitor Cx, a resistor Rx, and a voltage dividing resistor Vx.

  Switching element Qx has one end connected to the + side power supply terminal to which DC voltage Vdc is supplied and the other end connected to one end of reactor Lx. The diode Dx has a cathode terminal connected to a connection point between the switching element Qx and the reactor Lx, and an anode terminal connected to the negative power supply terminal. The smoothing capacitor Cx has one end (+ side terminal) connected to the output side terminal of the reactor Lx and the other end (− side terminal) connected to the output side terminal of the resistor Rx. The resistor Rx is connected between the negative terminal of the smoothing capacitor Cx and the anode terminal of the diode Dx, and realizes a current detection function. In addition, the voltage dividing resistor Vx is connected between the − side terminal and the + side terminal of the smoothing capacitor Cx to realize a voltage detection function.

  The switching element Qx is driven by a gate signal Gx output from the power control unit 42. Based on the duty of the gate signal Gx, the step-down chopper unit 31 steps down the input DC voltage Vdc to a voltage corresponding to the duty and outputs it to the DC / AC conversion unit 32 at the subsequent stage.

  The DC / AC conversion unit 32 converts the input DC voltage into an AC voltage having a desired frequency, and outputs the AC voltage to the subsequent starter unit 33. In FIG. 2, as a specific configuration example, the DC / AC converter 32 is configured by switching elements Q1 to Q4 connected in a bridge shape (full bridge circuit).

  The switching element Q1 is driven by a gate signal G1 output from the driver 35. Similarly, the switching element Q2 is driven by the gate signal G2, the switching element Q3 is driven by the gate signal G3, and the switching element Q4 is driven by the gate signal G4. The driver 35 outputs a gate signal to alternately repeat on / off for the pair of switching elements Q1 and Q4 and the pair of switching elements Q2 and Q3 arranged diagonally. Thereby, a rectangular wave AC voltage is generated between the connection point of the switching elements Q1 and Q2 and the connection point of the switching elements Q3 and Q4.

  The starter unit 33 is a circuit unit for boosting the AC voltage supplied from the DC / AC unit 32 when starting the discharge lamp and supplying the boosted voltage to the discharge lamp 10. In FIG. 2, as a specific configuration example, the starter unit 33 is configured by a coil Lh and a capacitor Ch. When the discharge lamp is started, an AC voltage having a high switching frequency (for example, several hundred kHz) in the vicinity of the resonance frequency of the LC series circuit including the coil Lh and the capacitor Ch is applied from the DC / AC unit 32, whereby the secondary of the starter unit 33 is applied. On the side, a high voltage required for starting the discharge lamp is generated and supplied to the discharge lamp 10. In addition, after the discharge lamp is lit, the frequency of the AC voltage supplied from the DC / AC unit 32 is shifted to a steady frequency (for example, 60 to 1000 Hz), and a steady lighting operation is performed. This steady frequency corresponds to the frequency of a pulse wave P1 described later.

  In the above circuit, the change in the frequency of the AC voltage supplied to the starter unit 33 is the on / off switching cycle of the set of the switching elements Q1 and Q4 and the set of the switching elements Q2 and Q3 in the DC / AC unit 32. It can be achieved by adjusting. Further, the change of the peak value of the AC voltage supplied to the starter unit 33 can be achieved by adjusting the operation duty of the switching element Qx in the step-down chopper unit 31.

  That is, the switching element Qx of the step-down chopper unit 31 is turned on / off at a switching frequency corresponding to the duty of the gate signal Gx output from the power control unit 42, thereby changing the power supplied to the discharge lamp 10. For example, when it is desired to increase the power supplied to the discharge lamp 10, the power control unit 42 performs control to increase the duty of the gate signal Gx so that a desired power value is obtained.

<Control unit 4>
As described above, the control unit 4 includes the pulse generation unit 41, the power control unit 42, and the frequency control unit 43. The pulse generation unit 41 outputs the generated pulse signal P to the driver 35 of the DC / AC unit 32. As described above, switching control for the switching elements Q1 to Q4 of the DC / AC unit 32 is performed based on the pulse signal.

  The pulse generator 41 generates a pulse signal having a frequency specified by the frequency controller 43. The frequency control unit 43 may be configured by a microcomputer or the like together with the power control unit 42 described above.

  The pulse wave P generated from the pulse generator 41 will be described with reference to FIG. FIG. 3 is a diagram showing an example of the waveform of the pulse signal P output from the pulse generator 41, that is, the lamp current waveform of the discharge lamp 10. As shown in FIG. The pulse wave P generated from the pulse generator 41 outputs a pulse wave P1 having a fundamental frequency f1 (corresponding to the “first pulse wave”) for a predetermined period T1, and then a pulse wave having a frequency f2 lower than the fundamental frequency. The cycle of outputting P2 (corresponding to “second pulse wave”) for a predetermined period T2 shorter than that is repeated. This is the same as the content described above with reference to FIG. 3 and 10, for the sake of explanation, there is no significant difference between the lengths of the period T1 and the period T2, but actually the length of the period T1 is sufficiently longer than the length of the period T2. It doesn't matter if it is long.

  However, in the present embodiment, the peak value of the period in which the pulse wave P (P1, P2) exhibits positive polarity is set lower by ΔP than the peak value of the period in which the pulse wave P exhibits negative polarity. That is, the power control unit includes a period during which the pulse wave P exhibits positive polarity (hereinafter referred to as “positive polarity period”) and a period during which the pulse wave P exhibits negative polarity (hereinafter referred to as “negative polarity period”). The value of the control power value designated from 42 to the power feeding unit 3 is varied. In this example, the gate signal Gx is supplied from the power control unit 42 to the switching element Qx so that the power value in the positive polarity period is lower than the power value in the negative polarity period. More specifically, in the positive polarity period, the power supply to the discharge lamp 10 in the positive polarity period is lower than in the negative polarity period by reducing the duty ratio of the gate signal Gx compared to the negative polarity period.

  The power control unit 42 appropriately changes the duty ratio of the gate signal Gx based on the value of the current flowing through the resistor Rx of the power supply unit 3 and the voltage value indicated by the voltage dividing resistor Vx, and sets the input power value as a target power value ( Feedback control for maintaining the control power value). Further, when the control unit 4 receives a signal related to the timing of switching the polarity of the pulse wave P, the power control unit 42 changes the control power value based on the signal. The power control unit 42 changes the duty ratio of the gate signal Gx so that the power value input by the feedback control matches the set control power value. In addition, about the information regarding the control power value in the positive polarity period and the negative polarity period, the power control unit 42 may store the information in advance. At this time, information regarding the control power value itself in each of the positive polarity period and the negative polarity period may be stored, or information regarding the ratio of the control power value between one period and the other period may be stored. It does not matter as long as it is.

  The frequency control unit 43 outputs information related to the frequency of the pulse wave P to the pulse generation unit 41 at a predetermined timing so that the pulse wave P exhibits frequency fluctuation as shown in FIG. For example, the frequency control unit 43 includes a timer that measures an elapsed time since the output of the pulse wave P is started, a frequency f1 of the pulse wave P1, a continuous output time T1 of the pulse wave P1, a frequency f2 of the pulse wave P2, And a memory storing information on the continuous output time T2 of the pulse wave P2. At this time, the frequency determination unit 43 determines the frequency of the pulse wave P based on the information about the elapsed time given from the timer and the information stored in the memory, and outputs the determined frequency to the pulse generation unit 41. The pulse generator 41 outputs a pulse wave P having a frequency determined based on a control signal from the frequency controller 43 to the power feeder 3.

  For example, the frequency determination unit 43 first sets the pulse generation unit 41 to output a pulse wave having the frequency f1 at the start of pulse generation. Next, when the elapse of time T1 is detected by the timer, the frequency determination unit 43 reads information related to the frequency f2 of the pulse wave P2 from the memory and sets the pulse wave of the frequency f2 to be output. Further, when the elapse of time T2 is detected by the timer, information related to the frequency f1 of the pulse wave P1 is read from the memory, and the pulse wave of the frequency f1 is set to be output again. The frequency control unit 43 repeats such control below.

  When the frequency determination unit 43 includes a timer as described above, the frequency determination unit 43 may output a signal related to the timing at which the polarity is inverted to the power control unit 42.

  The frequency (fundamental frequency) of the pulse wave P1 corresponds to the fundamental frequency when the discharge lamp 10 is steadily turned on, and is one frequency selected from the range of 60 to 1000 Hz, for example. The pulse wave P2 is a low frequency that is intermittently inserted after the lapse of the period T1, and the frequency is a frequency that is lower than the fundamental frequency, for example, selected from a range of 5 to 200 Hz.

  In the example of FIG. 3, the period T2 during which the pulse wave P2 is output is set to one period of the pulse wave P2. That is, in this period T2, the pulse generation unit 41 is configured to output the positive and negative pulse waves P2 once each. However, the output form of the pulse wave P2 is not limited to such a form.

  For example, after the pulse generator 41 outputs the pulse wave P1 for a predetermined period T1, the low-frequency pulse wave P2 is output for a half cycle length T2, and further, the pulse wave P1 is output for a time T1, and then the pulse wave P2 is output. You may employ | adopt the structure which changes only polarity as before and outputs only half cycle length T2. Further, the low-frequency pulse wave P2 included in the pulse signal output from the pulse generation unit 41 may be included over a period of one cycle or more, such as 1.5 cycles of the pulse wave P2. However, if the application time of the low-frequency pulse wave P2 is excessively extended, the shape of the protrusion 21 serving as the arc starting point may change due to excessive heating of the electrode. It is preferable to keep P2 within one period.

[Action]
FIG. 4 is a graph showing changes in the light intensity of the projection light in accordance with the lamp current waveform shown in FIG. 4A is a waveform of the same lamp current as that in FIG. 3, and FIG. 4B is a waveform showing a change in the light intensity of the projection light.

  As described above with reference to FIG. 3, in the lighting device 1 of the present embodiment, the input power from the power supply unit 3 to the discharge lamp 10 is less than the negative polarity period of the pulse wave P by the control from the power control unit 42. The positive polarity period of the pulse wave P is set to be lower. As a result, as shown in FIG. 4B, the steady value W2 of the light intensity in the positive polarity period of the pulse wave P is lower by ΔW than the steady value W1 of the light intensity in the negative polarity period of the pulse wave P. Yes.

  As described above with reference to FIG. 11 in the section “Problems to be Solved by the Invention”, the light intensity varies depending on which of the electrode 20a and the electrode 20b is a cathode, and as a result, it may be visually recognized as flicker. Arise. As an example, according to the pulse current shown in FIG. 4 above, in the situation where the same power is input regardless of the polarity, the light intensity is higher in the period in which the pulse wave P is positive than in the period in which the pulse wave P is negative. When it becomes high, the light intensity difference between polarities can be suppressed. Thereby, it is visually recognized as light of substantially the same output over both the positive polarity period and the negative polarity period, and flicker is less visible.

[Setting Method in Power Control Unit 42]
As described above, the power control unit 42 stores the control power values in the positive polarity period and the negative polarity period in advance. Hereinafter, an example of a method for setting the control power value will be described. The setting of the control power value may be performed at a stage before the lighting device 1 and the discharge lamp 10 are shipped.

  FIG. 5 is a schematic diagram for explaining a control power value setting method. The light from the projection device 51 including the discharge lamp 10 and the optical system is irradiated toward the light detection unit 53 including a high-sensitivity sensor and the time change of the light intensity detected by the light detection unit 53 is changed to an oscilloscope. 54. At this time, the lighting device 1 first supplies current to the discharge lamp 10 in a state where the control power value is constant in both the positive polarity period and the negative polarity period. The oscilloscope 54 obtains the light intensity change mode under this state, and calculates the average light intensity of each of the positive polarity period and the negative polarity period by calculation.

  Then, in either one or both of the positive polarity period and the negative polarity period, the same process as described above is performed while changing the input power from the lighting device 1 to the discharge lamp 10, and the difference between the average light intensities is a predetermined threshold value. Find conditions that are within. Then, the value of the input power when such a condition is satisfied is stored in the power control unit 42.

Here, the “predetermined threshold value” is preferably within ± 2%, and more preferably within ± 1%. FIG. 6 is a graph showing the relationship between the light intensity difference and the flicker level. Here, the main horizontal axis (lower horizontal axis) is the difference in light intensity, and is a value calculated by the following (Equation 1).
(Equation 1)
Light intensity difference = (average light intensity during positive polarity period−average light intensity during negative polarity period) / average light intensity over both periods

  The vertical axis indicates the flicker level, which is a numerical value of the degree of flickering of the screen at a frequency that can be seen by a person. Here, “minor flicker” refers to a level that may be viewed as flicker depending on the person or environment to be viewed, and “severe flicker” refers to a level that is viewed as flicker regardless of the person or environment that has been viewed. Point to. Further, “no flicker” refers to a level that is not visually recognized as flicker regardless of the visually recognized person or environment.

  According to FIG. 6, it can be seen that when the light intensity difference exceeds ± 2%, the level is such that many viewers can visually recognize flicker (severe flicker). On the other hand, by keeping this difference in light intensity within ± 2%, the probability of being visually recognized as flicker can be reduced, and by keeping it within ± 1%, it is possible to make it completely invisible as flicker. it can.

  Control the input power value in each period so that the difference in average light intensity between the positive polarity period and the negative polarity period is within ± 2% by the above method at the stage before shipment. The power value is stored in the power control unit 42 as a power value. According to the lighting device 1 in the state in which such a setting is made in the power control unit 42, almost the same light intensity can be realized regardless of which of the electrodes 20 a and 20 b constitutes the cathode. Flickering of the light intensity at the spot illuminated by 10 (illumination area 62) is suppressed.

[Another embodiment]
Hereinafter, another embodiment will be described.

  <1> In the above-described embodiment, the case where the control is performed in the power control unit 42 so as to lower the input power in the positive polarity period than in the negative polarity period has been described (see FIG. 4). However, depending on the arrangement positions of the electrodes 20a and 20b, the average light intensity may be lower in the positive period than in the negative period when the input power is constant. In such a case, contrary to the case of FIG. 4, the power control unit 42 may perform control so that the positive power period is higher than the negative power period (see FIG. 7).

  <2> In the above-described embodiment, the case where the power control unit 42 performs control to lower the input power in the positive polarity period than in the negative polarity period in both the period T1 and the period T2 has been described (FIG. 4). However, since the flicker caused by the difference in light intensity is easily visible in the period T2 where the period fixed by one polarity is long, the above control may be performed only during the period T2 (see FIG. 8). ).

  In this case, the power control unit 42 can be configured to receive a signal related to the switching timing of the period T1 and the period T2 from the control unit 4 in addition to the polarity inversion timing of the pulse wave P. More specifically, the signal related to the timing of switching between the period T1 and the period T2 can be supplied from the frequency control unit 43.

  Also in this alternative embodiment, when the input light is constant and the average light intensity is lower in the positive polarity period than in the negative polarity period, the power control unit 42 sets the positive polarity period in the period T2. Control may be performed so that the input power is higher than in the negative polarity period.

  Furthermore, the power control unit 42 may perform control to change the ratio of input power in the positive polarity period and the negative polarity period in the period T1 and the period T2 (see FIG. 9). For example, in the example of FIG. 9B, the steady value W2 of the light intensity in the positive polarity period of the pulse wave P is lower by ΔW1 than the steady value W1 of the light intensity in the negative polarity period of the pulse wave P in the period T1. Thus, in the period T2, the steady value W3 of the light intensity in the positive polarity period of the pulse wave P becomes lower by ΔW2 than the steady value W1 of the light intensity in the negative polarity period of the pulse wave P.

  <3> In the above-described embodiment, it has been described that the discharge lamp 10 is driven by alternately supplying the pulse wave P1 having a high frequency and the pulse wave P2 having a frequency lower than that. However, the present invention is not limited to the case where the discharge lamp 10 is driven using the pulse wave P having a different frequency as described above, but can also be used when the discharge lamp 10 is driven by the pulse wave P having a constant frequency. .

  <4> In the above-described embodiment, the projection device 51 including the discharge lamp 10 directly irradiates the light detection unit 53 with projection light, and the light intensity is detected by the oscilloscope 54, whereby the positive polarity of the pulse wave P is detected. It demonstrated as what determines the control electric power value in a period and a negative polarity period. However, this method is merely an example, and any method may be used as long as the average light intensity of the positive polarity period and the negative polarity period of the pulse wave P can be calculated.

  For example, the discharge lamp 10 controlled to be lit by the lighting device 1 is arranged inside the integrating sphere, the light intensity of a partial region of the outer wall of the integrating sphere is detected by the light detection unit 53, and the detection result is sent to the oscilloscope 54. It is good also as a structure to output. The magnitude of the light intensity output from the discharge lamp 10 can be calculated by the ratio of the area of the region that can be detected by the light detection unit 53 and the surface area of the integrating sphere. The oscilloscope 54 can calculate the average light intensity of the positive and negative periods of the pulse wave P by multiplying the light intensity obtained by the light detection unit 53 by the ratio.

  The means for calculating the average light intensity in the positive polarity period and the negative polarity period of the pulse wave P based on the information on the light intensity detected by the light detection unit 53 is not limited to the oscilloscope 54, and has the same function. Any device can be used as long as it can be realized.

  <5> In the above-described embodiment, the timing of changing to the pulse wave P2 after continuously outputting the pulse wave P1 has been described as being fixed. When the discharge lamp 10 is driven to light while switching between the pulse wave P2 and the pulse wave P1, the timing for switching from the pulse wave P1 to the pulse wave P2 may be appropriately changed. In addition, in the case where the timing for inserting the pulse wave P2 is fixed, the configuration may be such that the pulse wave P1 of about one to two cycles is inserted exceptionally at the timing for inserting the pulse wave P2. This is for the following purpose, for example.

  As shown in FIG. 2, when the AC / DC unit 32 is a full-bridge inverter circuit, a power source for driving the high-side switches Q1 and Q4 is required. As this power source, for example, a bootstrap circuit can be used, and when the high-side switches Q1 and Q4 are OFF, a bootstrap capacitor (not shown) is charged. However, if the charging amount of this capacitor is insufficient, the switches Q1 and Q4 cannot be driven ON because the power supply voltage is insufficient. For this reason, for the purpose of charging the capacitor, the pulse wave P1 having about one to two cycles may be inserted exceptionally.

  Another object relates to a case where a light source including the lighting device of the present invention is used in, for example, a DLP (registered trademark) projector. In a DLP projector, control is usually performed to invert the polarity according to the movement of the color wheel so that the projected image is not adversely affected, and the capacitor is charged at the time of polarity inversion. For the same reason as described above, when the elapsed time from the start of lighting becomes long and the amount of charge to the capacitor becomes insufficient, an exceptionally 1 is set for the purpose of charging the capacitor during the output of the pulse wave P2. A configuration may be adopted in which a pulse wave P1 having a period of about 2 cycles is inserted.

DESCRIPTION OF SYMBOLS 1: Lighting device 3: Power supply part 4: Control part 10: Discharge lamp 11: Light emission part 12: Sealing part 13: Metal foil 14: External lead 20a, 20b: Electrode 21: Protrusion 22: Discharge arc 23: Minute protrusion 29a 29b: Electrode head 30a, 30b: Electrode shaft 31: Step-down chopper 32: DC / AC converter 33: Starter 35: Driver 41: Pulse generator 42: Power controller 43: Frequency controller 51 : Projector 53: Photodetector 54: Oscilloscope 60: Concave reflector 61: Optical element 62: Irradiation area 70a, 70b: Condensing position 73, 74, 75, 76, 77, 78, 79: Light beam

Claims (4)

A power feeding unit for supplying an alternating current to a discharge lamp in which a pair of electrodes are arranged to face each other in a discharge vessel in which a predetermined gas is sealed;
A power control unit that outputs a signal related to a control power value to the power supply unit;
A pulse generation unit that outputs a pulse wave to the power supply unit;
The power feeding unit is configured to convert a supplied DC voltage into an alternating current corresponding to the frequency of the pulse wave and the control power value and supply the alternating current to the discharge lamp,
The power control unit is configured so that the average light intensity of the discharge lamp and the pulse wave are negative during the period in which the pulse wave is positive, compared to the case where the control power value is the same regardless of the polarity of the pulse wave. In the direction in which the difference from the average light intensity of the discharge lamp in the sexual period is reduced, the peak value of the pulse wave is different between the period in which the pulse wave is positive and the period in which the pulse wave is negative. It is configured to perform control to vary the control power value ,
The power control unit stores in advance information related to a ratio between the control power value during a period in which the pulse wave is positive and the control power value in a period in which the pulse wave is negative, and the stored information is stored in the stored information. The discharge lamp lighting device according to claim 1, wherein the control power value is controlled to be different between a period in which the pulse wave is positive and a period in which the pulse wave is negative .   The power control unit is configured so that the average light intensity of the discharge lamp and the pulse wave are negative during the period in which the pulse wave is positive, compared to the case where the control power value is the same regardless of the polarity of the pulse wave. The control power value between the period in which the pulse wave is positive and the period in which the pulse wave is negative is such that the difference from the average light intensity of the discharge lamp within a positive period is within ± 2%. 2. The discharge lamp lighting device according to claim 1, wherein control is performed to make the difference between the two. The pulse generator repeats a cycle of outputting a first pulse wave over a first period and then outputting a second pulse wave having a frequency lower than that of the first pulse wave over a second period shorter than the first period. Configuration,
The power control unit, a discharge lamp lighting device according to claim 1 or 2, characterized in that the control for varying the control power value in said second time period. 4. The discharge lamp lighting device according to claim 3 , wherein the power control unit performs control to vary the control power value within the first period. 5.

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