JP2014060094A - Apparatus and method for driving discharge lamp, light source device, and projector - Google Patents

Abstract

[Object] To suppress blackening and devitrification while extending the life of a discharge lamp.
A light source device includes a discharge lamp having a pair of electrodes and a driving device. The drive device 200 includes a supply unit 30 that supplies an interelectrode current to the pair of electrodes 610 and 710, and a control unit 33. In the low frequency driving, the control unit 33 is in the first state where the interelectrode current is positive, in the second state where the interelectrode current is negative, and during the state transition between the first state and the second state. The supply unit 30 is controlled so as to be in a third state where the current between the electrodes is constant.
[Selection] Figure 3

Description

  The present invention relates to a technique for driving a discharge lamp that is lit by discharge between a pair of electrodes.

As a light source of an image display device such as a projector, a discharge lamp such as a high-pressure mercury lamp or a metal halide lamp is used. This discharge lamp is driven by, for example, a driving method for supplying a high-frequency alternating current. According to this driving method, discharge stability can be obtained, so-called blackening or devitrification of the discharge lamp body can be prevented, and a reduction in the life of the discharge lamp can be suppressed (for example, Patent Document 1). ).
As another driving method for the discharge lamp, there is a driving method for supplying an alternating current having a rectangular waveform at a low frequency. According to this driving method, when the discharge lamp is lit, a projection is formed and grows at the tip of the pair of electrodes, so that a state where the distance between the electrodes is narrow can be maintained (for example, Patent Document 2).

JP 2007-115534 A JP 2010-1114064 A

However, in the driving method for supplying an alternating current of high frequency, the electrode becomes hot due to arc discharge generated between the pair of electrodes when the discharge lamp is lit, and the distance between the electrodes gradually increases due to melting of the electrodes. There is a problem that the life of the discharge lamp is shortened. On the other hand, according to the driving method for supplying a low-frequency alternating current, there is a problem that the light amount is reduced due to blackening or devitrification of the discharge lamp body, and the life of the discharge lamp is shortened.
The present invention has been made in view of the circumstances described above, and solves the problem of suppressing blackening and devitrification while extending the life of the discharge lamp when combining high frequency driving and low frequency driving. And

One aspect of the drive device according to the present invention drives a discharge lamp having a first electrode and a second electrode arranged in a cavity in which a discharge medium is sealed, and the drive device includes the first electrode and the second electrode. A first alternating current is supplied between one electrode and the second electrode, and the first alternating current includes a first section having a constant current value and a second current having a constant current value. A second section that is a value, the first section and the second section are alternately and repeatedly set, and provided between the first section and the second section, and the current value is constant, And a third section of a third current value, which is a current value between the first current value and the second current value, and provided between the second section and the first section. And a fourth section that is the third current value.
The distance between the electrodes is shortened by the growth of the electrode protrusions, and the temperature change of the electrodes affects the growth rate. When the third section and the fourth section are provided in the alternating current, the electrodes that have become hot in the first section and the second section are cooled in the third section and the fourth section and tend to be slightly solidified. The protrusion grows faster by repeating a state of low viscosity (high temperature) and a state of high viscosity (low temperature) due to temperature change, rather than continuing the melted state. According to one aspect of the driving device, since the alternating current including the third section and the fourth section is generated, the growth rate of the protrusion is compared with the case where the alternating current including only the first section and the second section is generated. Can be expedited.

In one aspect of the driving device described above, a second alternating current is supplied between the first electrode and the second electrode, and the second alternating current includes the first section, the second section, and the third section. Including the section and the fourth section, wherein the first alternating current has a frequency of 1 kHz or less, the second alternating current has a frequency higher than 1 kHz, and the first alternating current and the second alternating current Are preferably set alternately and repeatedly.
According to one aspect of the present invention, the low-frequency first alternating current and the high-frequency second alternating current are alternately repeated. In this case, when the third and fourth sections are provided in the low-frequency first alternating current, the protrusions are accelerated by repeating the low viscosity state (high temperature) and the high viscosity state (low temperature) due to temperature changes. Since it grows, the period of low frequency driving can be shortened. As a result, it is possible to extend the life of the discharge lamp while increasing the proportion of the high-frequency driving period and suppressing blackening and opaqueness.

  In one aspect of the driving device described above, the third section and the fourth section in the first alternating current are the first period having the same length, and the third section and the fourth section in the second alternating current are the same. Preferably, the section is a second period having the same length, and the first period is longer than the second period. According to one aspect of the present invention, the third and fourth sections of the low-frequency drive are longer than the third and fourth sections of the high-frequency drive. Driving can be completed in a short time. As a result, it is possible to extend the life of the discharge lamp while increasing the proportion of the high-frequency driving period and suppressing blackening and opaqueness.

In one aspect of the driving device described above, the third alternating current further has an amplitude smaller than that of the first alternating current and includes the first section, the second section, the third section, and the fourth section. And a fourth alternating current having a smaller amplitude than the second alternating current, and before the rated period in which the first alternating current and the second alternating current are alternately and repeatedly set, A low power period in which alternating current and the fourth alternating current are alternately and repeatedly set is set, and the third section and the fourth section in the first alternating current are the first period of the same length, The third section and the fourth section in the third alternating current are a third period having the same length, and the third period is longer than the first period.
In the low power period, blackening and devitrification are more problematic than the rated period. However, according to one aspect of the present invention, the third period of the third alternating current that is driven at a low frequency in the low power period is the rated period. Since it becomes longer than the first period of the first alternating current that is driven at a low frequency, the growth rate of the protrusions can be further increased. As a result, it is possible to extend the life of the discharge lamp by suppressing blackening and devitrification in a low power state.

In one aspect of the driving device described above, a second alternating current is supplied between the first electrode and the second electrode, and the second alternating current is alternately in the first section and the second section. The first alternating current has a frequency of 1 kHz or less, the second alternating current has a frequency higher than 1 kHz, and the first alternating current and the second alternating current are alternately repeated. It is preferable that it is set. In this case, the third and fourth sections are provided only for the first AC current of low frequency driving to accelerate the growth of the protrusions, while the second AC current of high frequency driving is driven by a binary DC alternating current. can do.
In the aspect of the driving device described above, it is preferable that the third current value is zero. In this case, since a large temperature change can be applied to the first electrode and the second electrode, the protrusions can be efficiently grown and the low frequency driving can be completed in a short time.

  Next, one aspect of the photoelectric device according to the present invention includes the above-described driving device, and a discharge lamp having a first electrode and a second electrode disposed in a cavity in which a discharge medium is enclosed. Features. According to this aspect of the light source device, it is possible to improve the reliability of the device by suppressing blackening and devitrification while extending the life of the discharge lamp.

  Next, one aspect of the projector according to the present invention includes the light source device described above, a modulation device that modulates light emitted from the discharge lamp based on image information, and a projection that projects light modulated by the modulation device. And a device. According to one aspect of the projector, since the blackening and devitrification are suppressed while extending the life of the discharge lamp, a stable image can be displayed for a long time.

Next, one aspect of a method for driving a discharge lamp according to the present invention is a method for driving a discharge lamp having a first electrode and a second electrode disposed in a cavity in which a discharge medium is enclosed, A first alternating current is supplied between the first electrode and the second electrode, and the first alternating current has a first section in which the current value is a first current value, and a second section in which the current value is constant. A second section that is a current value, the first section and the second section are alternately and repeatedly set between the first section and the second section, and the current value is constant. And a third interval of a third current value, which is a current value between the first current value and the second current value, and a current value provided between the second interval and the first interval. Is controlled so as to include a fourth section having the third current value.
According to one aspect of this driving method, since an alternating current including the third section and the fourth section is generated, by repeating a state where the viscosity is low (high temperature) and a state where the viscosity is high (low temperature) due to temperature change, Protrusions grow faster. For this reason, compared with the case where the alternating current which consists only of a 1st area and a 2nd area is produced | generated, the growth rate of protrusion can be sped up.

Moreover, in one aspect of the driving method of the discharge lamp described above, a second alternating current is supplied between the first electrode and the second electrode, and the second alternating current is supplied between the first section and the second section. Including a section, the third section, and the fourth section, wherein the first alternating current has a frequency of 1 kHz or less, the second alternating current has a frequency higher than 1 kHz, and the first alternating current and The second alternating current is alternately and repeatedly set, the third section and the fourth section in the first alternating current are the same length of the first period, and the third alternating current is in the third alternating current. Preferably, the section and the fourth section are the second period having the same length, and the first period is longer than the second period.
In one aspect of this driving method, the low-frequency first alternating current and the high-frequency second alternating current are alternately repeated. In this case, the third and fourth sections of the low-frequency first alternating current are longer than the third and fourth sections of the high-frequency second alternating current. Therefore, the protrusion grows quickly due to the first alternating current, so that the period of low frequency driving can be shortened. As a result, it is possible to extend the life of the discharge lamp while increasing the proportion of the high-frequency driving period and suppressing blackening and opaqueness.

It is a figure which shows the light source device which concerns on 1st Embodiment. It is principal part sectional drawing of the discharge lamp in the light source device. It is a figure which shows the electrical structure of the drive device used for the light source device. It is a figure which shows the outline | summary of the combination drive in the light source device. It is a flowchart which shows the content of the combination drive process in the light source device. It is a figure which shows the waveform of the interelectrode current of the combination drive in the light source device. It is a figure which shows the growth of the protrusion in a low frequency drive. It is a bluff which shows the measurement result of the Example of the same embodiment, and a comparative example. It is a figure which shows the waveform of the interelectrode current of the combination drive in the light source device which concerns on 2nd Embodiment. It is a figure which shows the waveform of the interelectrode current of the combination drive of the light source device. It is a bluff which shows the measurement result of the Example of the same embodiment, comparative example 1, and comparative example 2. It is a figure which shows the waveform of the interelectrode current of the low frequency drive which concerns on a modification. It is a figure which shows the projector using the light source device. It is a figure which shows the optical structure of the projector.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. First, a light source device to which a discharge lamp driving method according to an embodiment of the invention is applied will be described.

<First Embodiment>
FIG. 1 is a diagram illustrating an example of the structure of a light source device. As shown in this figure, the light source device 1 includes a light source unit 110 having a discharge lamp 500 and a driving device 200 for driving the discharge lamp 500. The discharge lamp 500 receives electric power from the driving device 200 and discharges it to emit light.
The light source unit 110 includes a discharge lamp 500, a main reflecting mirror 112 having a concave reflecting surface, and a collimating lens 114 that makes emitted light substantially parallel. The main reflecting mirror 112 and the discharge lamp 500 are bonded by an adhesive 116. Further, the main reflecting mirror 112 has a surface (inner surface) on the discharge lamp 500 side as a reflecting surface, and this reflecting surface forms a spheroidal surface in the illustrated configuration.

  The shape of the reflecting surface of the main reflecting mirror 112 is not limited to a spheroid, and may be a rotating paraboloid, for example. If the reflecting surface of the main reflecting mirror 112 is a paraboloid, the collimating lens 114 can be omitted if the light emitting part of the discharge lamp 500 is arranged at the so-called focal point of the paraboloid.

  The discharge lamp 500 includes a discharge lamp main body 510 and a sub-reflecting mirror 520 having a concave reflecting surface. The discharge lamp main body 510 and the sub-reflecting mirror 520 are disposed so that the sub-reflecting mirror 520 faces the main reflecting mirror 112 and the concave reflecting surface is disposed at a predetermined interval from the discharge lamp main body 510. As shown in FIG. Further, in the sub-reflecting mirror 520, the inner surface on the discharge lamp 500 side is a reflecting surface, and this reflecting surface forms a spherical surface in the illustrated configuration.

A central portion of the discharge lamp main body 510 is a hollow portion 512 that is sealed with a discharge medium sealed therein. The discharge lamp main body 510 is made of a light transmissive material such as quartz glass or light transmissive ceramics. The discharge medium is, for example, a discharge start gas or a gas that contributes to light emission. Among these, examples of the discharge start gas include noble gases such as neon, argon, and xenon. Examples of the gas that contributes to light emission include mercury, vaporized metal halide, and the like.
The discharge lamp main body 510 is provided with a pair of electrodes 610 and 710, a pair of conductive connection members 620 and 720, and a pair of electrode terminals 630 and 730. The electrodes 610 and 710 are attached to the cavity 512. Specifically, the tips of the electrodes 610 and 710 are attached to the cavity 512 of the discharge lamp main body 510 so as to be separated from each other by a predetermined distance and to face each other. Among these, the electrode (first electrode) 610 and the electrode terminal 630 are electrically connected to each other by the connection member 620. Similarly, the electrode (second electrode) 710 and the electrode terminal 730 are electrically connected to each other by a connection member 720. The electrode terminals 630 and 730 are each connected to the output terminal of the driving device 200.

  The driving device 200 supplies an AC current (AC power) described later to the electrode terminals 630 and 730. For this reason, in the electrode 610 connected to the electrode terminal 630 via the connection member 620 and the electrode 710 connected to the electrode terminal 730 via the connection member 720, the positive electrode having a relatively high potential, The polarity is alternately switched between the relatively lower negative electrode and the negative electrode.

When an alternating current is supplied to the electrode terminals 630 and 730, an arc discharge is generated between the tips of the electrodes 610 and 710 in the cavity 512, and the discharge medium emits light. Light generated by the arc discharge is radiated in all directions from the arc generation position (discharge position). Of the radiated light, the light radiated in the direction of the electrode 710 is mainly reflected by the sub-reflecting mirror 520. Reflected toward the reflecting mirror 112. For this reason, the light radiated | emitted in the direction of the electrode 710 can be utilized effectively.
In the present embodiment, the discharge lamp 500 includes the sub-reflecting mirror 520, but the discharge lamp 500 may be configured not to include the sub-reflecting mirror 520.

FIG. 2 is an example of a cross-sectional view of a main part of the discharge lamp 500. In FIG. 2, the sub-reflecting mirror 520 in FIG. 1 is omitted.
As shown in FIG. 2, the electrode 610 includes a core rod 612, a coil portion 614, and a main body portion 616. The electrode 610 is formed by winding a wire rod of an electrode material around a core rod 612 to form a coil portion 614 and heating and melting the formed coil portion 614 in a stage before being enclosed in the discharge lamp main body 510. Is done. As a result, a body portion 616 having a large heat capacity is formed on the tip side of the electrode 610. The electrode 710 also includes a core rod 712, a coil portion 714, and a main body portion 716, and is formed in the same manner as the electrode 610.
In addition, as a constituent material of each electrode 610,710, high melting point metal materials, such as tungsten, etc. are mentioned, for example.

  In the state where the discharge lamp 500 has never been lit, the main body portions 616 and 716 are not formed with the protrusions 618 and 718, but the discharge lamp 500 is lit even once by the arc discharge AR as will be described later. Then, protrusions 618 and 718 are formed at the tip portions of the main body portions 616 and 716, respectively. The protrusions 618 and 718 are maintained while the discharge lamp 500 is turned on, and are also maintained after the lamp is turned off.

FIG. 3 is an example of a diagram illustrating an electrical configuration of the light source device 1, particularly the driving device 200. As shown in this figure, the driving device 200 includes a supply unit 30 that supplies an alternating current to the discharge lamp 500, a control unit 33 that controls the supply unit 30, and a voltmeter that measures the interelectrode voltage of the discharge lamp 500. 35.
Further, the supply unit 30 includes switches Sw <b> 1 to Sw <b> 4 that are bridge-connected to the constant current source 31. The constant current source 31 controls the current value returning from the positive electrode output terminal (+) to the negative electrode output terminal (−) to be constant at a value designated by the control unit 33.
The switches Sw1 to Sw4 are respectively controlled to be in an on (closed) state and an off (open) state by the control unit 33, and among these, the switches Sw1 and Sw4 are controlled to be in the same state, and the same The switches Sw2 and Sw3 are paired and controlled to be in the same state. However, the set of the switches Sw1 and Sw4 and the set of the switches Sw2 and Sw3 are not simultaneously turned on, but are controlled to be turned on exclusively.
The switch Sw1 is electrically inserted between the positive electrode output terminal (+) of the constant current source 31 and the electrode terminal 630 of the discharge lamp 500, and the switch Sw2 is the negative electrode output terminal of the electrode terminal 630 and the constant current source 31. It is electrically inserted between (-). The switch Sw3 is electrically inserted between the positive electrode output terminal (+) of the constant current source 31 and the electrode terminal 730 of the discharge lamp 500, and the switch Sw4 is the negative electrode output terminal of the electrode terminal 730 and the constant current source 31. It is electrically inserted between (-).
The voltmeter 35 measures the voltage between the positive electrode output terminal (+) and the negative electrode output terminal (−) of the constant current source 31 and supplies the measured value to the control unit 33.

  In this driving device 200, when the set of switches Sw1 and Sw4 is controlled to be in the on state by the control unit 33, and when the set of switches Sw2 and Sw3 is controlled to be in the off state, a constant current is applied from the electrode terminal 630 to the electrode terminal. It flows toward 730 (first state). On the contrary, when the set of the switches Sw1 and Sw4 is controlled to be in the off state and the set of the switches Sw2 and Sw3 is controlled to be in the on state, a constant current flows from the electrode terminal 730 toward the electrode terminal 630 (second State). For this reason, when the control unit 33 alternately switches on and off states with respect to the set of switches Sw1 and Sw4 and the set of switches Sw2 and Sw3, an alternating interelectrode current flows between the electrodes 610 and 710, and the on, If the switching cycle of the off state is shortened, the frequency of the alternating current is increased.

  In this description, regarding the current (or voltage) flowing between the electrodes 610 and 710, the case where the current flows from the electrode 610 toward the electrode 710 is a positive value (positive polarity), and conversely from the electrode 710 to the electrode 610 A negative value (negative polarity) is defined for the case of flowing toward. However, the voltage measured by the voltmeter 35 is the absolute value (positive value) of the voltage between the electrodes 610 and 710 regardless of the direction of the current flowing through the electrodes 610 and 710.

  In the present embodiment, the first state is a state in which an interelectrode current having a first predetermined value with positive polarity is flown, and the second state is a state in which an interelectrode current having a second predetermined value is flowed with a negative polarity. A third state in which the interelectrode current is zero is provided in the middle of the state transition between the state and the second state. In the third state, the switches Sw1, Sw2, Sw3, and Sw4 are all turned off. In particular, in the low frequency drive, the period of the third state is determined as described later from the viewpoint of shortening the period of the low frequency drive.

An alternating current supplied from the driving device 200 to the discharge lamp 500 will be described. In the present embodiment, the discharge lamp 500 is driven by a combination of high-frequency driving that supplies an alternating current of a predetermined frequency or higher to the discharge lamp 500 and low-frequency driving that supplies a low-frequency current of less than a predetermined frequency to the discharge lamp 500. . That is, as shown in FIG. 4, in combination driving, high frequency driving and low frequency driving are alternately repeated.
According to the high frequency driving, the stability of the discharge can be obtained as described above, and the temperature change in the discharge lamp 500 including the electrodes 610 and 710 is small, so that the chemical reaction for suppressing and recovering the blackening is stable. Thus, blackening and accompanying devitrification can be prevented. For this reason, the lifetime reduction of the discharge lamp is suppressed.
However, in the high frequency driving, because the arc discharge generated between the electrodes 610 and 710 causes the electrodes 610 and 710 to melt at a high temperature, the distance between the electrodes gradually increases. When the distance between the electrodes increases, not only the light use efficiency decreases, but also the impedance changes between the electrodes, resulting in an increase in reactive power, resulting in a decrease in efficiency.

On the other hand, according to the low-frequency driving for supplying an alternating current to the discharge lamp 500, when the discharge lamp is lit, a protrusion is formed at the tip of the electrodes 610 and 710, and the protrusion is caused by repetition of melting and solidification. Therefore, a narrow state between the electrodes can be maintained.
However, in the driving method of supplying a low-frequency current to the discharge lamp 500, the temperature change in the discharge lamp 500 is large, so that the chemical reaction for suppressing blackening becomes unstable, and blackening, devitrification, etc. occur. There is a problem that the life of the discharge amount is reduced.

Therefore, in the present embodiment, as shown in FIG. 4, a combination drive in which high frequency drive and low frequency drive are combined and switched alternately is adopted.
Specifically, first, an upper limit value Vmax and a lower limit value Vmin are preset for the voltage between the electrodes 610 and 710. As described above, since the driving device 200 supplies a constant current to the electrodes 610 and 710, the voltage between the electrodes 610 and 710 increases as the distance between the electrodes increases. Therefore, the interelectrode voltage indicates the distance between the electrodes 610 and 710.
Second, for example, the inter-electrode voltage is measured while supplying a high-frequency inter-electrode current, and when the measured voltage reaches the upper limit value Vmax, the high-frequency driving is switched to the low-frequency driving. Note that when switching to low frequency driving, as shown in FIG. 4, the voltage between the electrodes decreases, and the distance between the electrodes gradually decreases. On the other hand, blackening is unavoidable.
Third, when the measured voltage reaches the lower limit value Vmin, the low frequency driving is switched to the high frequency driving. When switching to high frequency driving, as shown in the figure, the interelectrode voltage gradually increases and the interelectrode distance gradually increases. On the other hand, blackening generated by low frequency driving is caused by the above chemical reaction. May recover.

  According to this combination driving, the distance between the electrodes is maintained in a range from a distance corresponding to the lower limit value Vmin of the interelectrode voltage to a distance corresponding to the upper limit value Vmax, and blackening does not occur during high frequency driving. In addition, blackening that occurs when a low-frequency interelectrode current is supplied may be recovered. For this reason, it is possible to achieve both maintenance of the distance between the electrodes and prevention of blackening. The predetermined frequency that becomes the boundary between the high frequency driving and the low frequency driving may be determined from the viewpoint of keeping the distance between the electrodes within a predetermined range and suppressing blackening, and in this example, 1 kHz is adopted. Further, the frequency of the low frequency drive is preferably 10 Hz or more and less than 1 kHz, and the frequency of the high frequency drive is preferably 1 kHz or more and less than 10 GHz.

FIG. 5 is an example of a flowchart showing the combination driving process, and is executed by the driving device 200.
First, the control unit 33 in the driving device 200 sets the cycle for switching on / off of the switches Sw1 to Sw4 to high-frequency driving (step S10). As a result, a high-frequency inter-electrode current flows through the electrodes 610 and 710 of the discharge lamp 500.
Next, the control part 33 acquires the voltage between electrodes measured by the voltmeter 35 (step S11), and discriminate | determines whether the said voltage has reached the upper limit value Vmax (step S12). If the voltage has not reached the upper limit value Vmax (if the determination result in step S12 is “NO”), the control unit 33 returns the processing procedure to step S11 again. However, in the high-frequency driving in which a high-frequency inter-electrode current is supplied to the discharge lamp 500, the inter-electrode distance increases, so that the inter-electrode voltage eventually reaches the upper limit value Vmax.

  When the voltage between the electrodes reaches the upper limit value Vmax (when the determination result in step S12 is “YES”), the control unit 33 sets the cycle of switching on / off of the switches Sw1 to Sw4 as the cycle of the low frequency drive. (Step S13). Thereby, the interelectrode current flowing in the electrodes 610 and 710 of the discharge lamp 500 is switched from a high frequency to a low frequency. The control unit 33 acquires the interelectrode voltage measured by the voltmeter 35 (step S14), and determines whether or not the voltage has reached the lower limit value Vmin (step S15). If the voltage has not reached the lower limit value Vmin (if the determination result in step S15 is “NO”), the control unit 33 returns the processing procedure to step S14 again. However, when the low-frequency interelectrode current is supplied to the discharge lamp 500, the interelectrode distance is reduced, so that the interelectrode voltage eventually reaches the lower limit value Vmin. When the voltage between the electrodes reaches the lower limit value Vmin (when the determination result of step S15 is “YES”), the control unit 33 returns the processing procedure to step S10 again. Thereby, the interelectrode current flowing through the electrodes 610 and 710 of the discharge lamp 500 is switched from the low frequency to the high frequency.

  FIG. 6 shows an example of waveforms of a high-frequency interelectrode current and a low-frequency interelectrode current. In both high-frequency driving and low-frequency driving, the first state is in the first section T1, the second state is in the second section T2, and the third state is in the third section T3 and the fourth section T4. In the first state (first section T1), the switch Sw1 and the switch Sw4 are turned on, the switch Sw2 and the switch Sw3 are turned off, and in the second state (the second section T2), the switch Sw1 and the switch Sw4 are turned off. The switch Sw2 and the switch Sw3 are turned on, and in the third state (the third section T3 and the fourth section T4), the switches Sw1 to Sw4 are turned off. That is, the control unit 33 controls the supply unit 30 so that the interelectrode current is in the first state, the second state, and the third state in the low frequency driving and the high frequency driving.

  By the way, there is a problem that blackening and devitrification occur in low frequency driving. For this reason, it is desirable that the low frequency drive period be as short as possible. On the other hand, the low frequency drive has a function of increasing the distance between the electrodes shortened by the high frequency drive. When the distance between the electrodes gradually decreases and reaches a predetermined distance, the low frequency drive is switched to the high frequency drive. Therefore, if the speed at which the distance between the electrodes is increased can be increased, the low frequency drive period can be shortened.

  Here, an example of the shape change of the electrode in the low frequency drive is shown in FIG. In this example, the electrode 610 is shown, but the shape of the electrode 710 is similarly changed. First, in a state where high frequency driving is completed and low frequency driving is started, there are almost no protrusions 618 on the electrode 610. As the low frequency driving proceeds, the protrusion 618 grows, and when the predetermined length is reached, the high frequency driving ends. The growth of the protrusion 618 is affected by a change in heat load. That is, in the anode and the cathode, the anode is hotter than the cathode. In the low-frequency driving, since the cycle in which the cathode and the anode are interchanged becomes long, the temperature of the electrode 610 that has become the cathode is lowered, and the electrode 610 that is melted at a high temperature tends to be slightly hardened. It is considered that the protrusion 618 grows by repeating a state where the viscosity is low (high temperature) and a state where the viscosity is high (low temperature) due to a temperature change, rather than continuing the melted state.

  In the present embodiment, the growth speed of the protrusion 618 is increased by managing the time of the third state in the low frequency driving. As described above, the interelectrode current is zero in the third state. Therefore, in the third state, the temperature of both electrodes 610 and 710 can be lowered. For this reason, in the third state, the viscosity of both the electrodes 610 and 710 is increased, and the growth of the protrusions 618 and 718 can be promoted.

  In the low frequency drive, by providing the third state (the third section T3 and the fourth section T4), there is no third state, and only the first state and the second state (the first section T1 and the second section T2). Compared to driving, the growth rate of the protrusions 618 and the protrusions 718 can be increased. As a result, the target inter-electrode distance can be reached in a short time, and the low frequency drive period can be shortened.

  More specifically, the time ta (first period) in the third state in the low frequency driving is set to be longer than the time tb (second period) in the third state in the high frequency driving. The third state in the high-frequency driving mainly has an effect of preventing the through current from flowing due to the combination of the switches Sw1 and Sw2 or the combination of the switches Sw3 and Sw4 being simultaneously turned on. On the other hand, the third state in the low frequency drive has an action of promoting the growth of the protrusions 618 and 718 as described above. For this reason, the time ta in the third state in the low frequency driving is set longer than the time tb in the third state in the high frequency driving.

Next, examples of the present invention will be described in comparison with comparative examples.
Here, the embodiment is the light source device 1 shown in FIGS. 1 and 3, and the discharge lamp 500 shown in FIG. 2 is used.

<Example>
Material of the discharge lamp body: Quartz glass Inclusion in the discharge lamp body: Argon, mercury, methyl bromide
Pressure at lighting in the discharge lamp body: 200 atm
Electrode constituent material: Tungsten Electrode distance: 1.1 mm
Rated power: 200W
AC current value (average): 2.9 A
Low frequency current frequency: 135 Hz (rectangular wave, 50% duty ratio)
High frequency current frequency: 5 kHz every 4 cycles
Upper limit voltage between electrodes: 80V
Lower limit voltage between electrodes: 70V
Time of the third state in high frequency driving: 1 μs
Time of the third state in low frequency driving: 10 μs

<Comparative example>
Time of the third state in high frequency driving: 1 μs
Time of the third state in low frequency driving: 1 μs
Other conditions are the same as the example

<Evaluation>
About the Example and the comparative example, the growth of the protrusions 618 and 718 in the low frequency driving was measured. FIG. 8 shows the measurement results. The interelectrode voltage reveals the distance between the electrodes. As shown in the figure, in the example, the time to reach 70V is about 12 minutes, while in the comparative example, the time to reach 70V is about 24 minutes. Therefore, it can be seen that the growth rate of the protrusions 618 and 718 is faster in the example than in the comparative example.
Furthermore, when it was driven for 1000 hours under the conditions of the example and the comparative example, in the comparative example, faint blackening was observed at the root portion. On the other hand, blackening was not recognized in the Example. This is because the growth rate of the protrusions 618 and 718 in the example is faster than that in the comparative example, so the period of low frequency driving is shortened, and as a result, blackening is suppressed.

Second Embodiment
In the first embodiment described above, the low frequency driving in the so-called rated period has been described. On the other hand, the light source device 1 of the second embodiment relates to low frequency driving in a low power period in which power is reduced compared to the rated period, and the amplitude of the interelectrode current in the low power period compared to the rated period. The configuration is the same as that of the light source device 1 of the first embodiment, except that the time of the third state in the low frequency driving is switched between the rated period and the low power period.

  The driving in the low power period is executed, for example, in the start-up period immediately after turning on the power. The electrode temperature of the discharge lamp 500 is approximately room temperature when a sufficient time has elapsed from the previous use state, and the pressure of the cavity 512 is low. On the other hand, during the rated period of the discharge lamp 500, the temperature of the electrodes 610 and 710 of the discharge lamp 500 is extremely high (1000 ° C. or higher), and the pressure of the cavity 512 is also high (50 atm or higher). For this reason, in order to quickly shift the discharge lamp 500 between the time when the power is turned on and before the rated period, it is necessary to supply the discharge lamp 500 with a current close to the rating or equivalent to the rating after the power is turned on. However, a great heat load is applied to the electrodes 610 and 710 after the power is turned on. For this reason, when driving in the rated state during the start-up period, the protrusions 618 and 718 are deformed or blackening due to electrode sublimation occurs. Therefore, in the start-up period, it is driven in a low power state.

FIG. 9 shows a waveform of the interelectrode current in the light source device of the second embodiment. As shown in this figure, during the low power period, the amplitude x of the interelectrode current (third AC current) is smaller than the amplitude y of the interelectrode current (first AC current) during the rated period. In addition, the time tc (third period) in the third state in the low-frequency driving in the low power period is longer than the time tb (first period) in the third state in the low-frequency driving in the rated period. For this reason, in the low frequency driving in the low power period, the growth rate of the protrusions 618 and 718 is faster than in the low frequency driving in the rated period, and the period of the low frequency driving can be shortened. Therefore, blackening and devitrification in a low power period can be suppressed.
The switching between the rated period and the low power period is performed by the control unit 33 controlling the output current of the constant current source 31.

  In this example, the time of the third state in the low frequency drive during the rated period is set equal to the time tb of the third state in the high frequency drive during the rated period. However, as shown in FIG. The time of the third state in the high-frequency drive in the third state and the low power period is “tb”, the time of the third state in the low-frequency drive in the rated period is “ta”, and in the low-frequency drive in the low power period When the time of the third state is “tc”, tc> ta> tb may be satisfied.

<Example>
Material of the discharge lamp body: Quartz glass Inclusion in the discharge lamp body: Argon, mercury, methyl bromide
Pressure at lighting in the discharge lamp body: 200 atm
Electrode constituent material: Tungsten Electrode distance: 1.1 mm
Power: 140W
AC current value (average): 2.9 A
Low frequency current frequency: 135 Hz (rectangular wave, 50% duty ratio)
High frequency current frequency: 5 kHz every 4 cycles
Upper limit voltage between electrodes: 75V
Lower limit voltage between electrodes: 65V
Time of the third state in high frequency driving: 1 μs
Time of the third state in low frequency driving: 10 μs

<Comparative Example 1>
Power: 200W
Upper limit voltage between electrodes: 80V
Lower limit voltage between electrodes: 70V
Time of the third state in high frequency driving: 1 μs
Time of the third state in low frequency driving: 1 μs
Other conditions are the same as the example

<Comparative example 2>
Time of the third state in high frequency driving: 1 μs
Time of the third state in low frequency driving: 1 μs
Other conditions are the same as the example

<Evaluation>
For the example, comparative example 1 and comparative example 2, the growth of the protrusions 618 and 718 in low frequency driving was measured. FIG. 8 shows the measurement results. The interelectrode voltage reveals the distance between the electrodes. Comparative Example 1 is driving during the rated period, and Comparative Example 2 and Example are driving during the low power period. Since the amount of evaporation of mercury as a discharge medium is small during the low power period, the voltage between the electrodes is reduced compared to the rated period. In Comparative Example 2, the distance between the electrodes is slower than Comparative Example 1. This is because the low power period has less temperature fluctuation than the rated period, and the protrusions are less likely to extend. Further, the distance between the electrode electrodes is narrower in the example than in the comparative example 2. This is because by increasing the time tc of the third state, a large temperature change is applied to the electrodes 610 and 710, and the growth rate of the protrusions 618 and 718 is increased.

<Modification>
The present invention is not limited to the first embodiment and the second embodiment described above, and for example, various modifications described below are possible. Moreover, each embodiment and each modification can be combined suitably.

(1) In each of the embodiments described above, the interelectrode current in the third state is zero, but the present invention is not limited to this, and the interelectrode current changes from a positive current value X1 to a negative current. It may be a constant size in the range up to the value X2. For example, as shown in FIG. 12A, in the third section T3 and the fourth section T4 that are in the third state, the interelectrode current may be a current value X3 lower than the amplitude center Ic. In addition, as shown in FIG. 12B, in the third section T3 and the fourth section T4 in the third state, the interelectrode current may be a current value X4 higher than the amplitude center Ic. Furthermore, as shown in FIG. 12C, the current value X5 of the interelectrode current in the third section T3 that is in the third state may not match the current value X6 of the interelectrode current in the fourth section T4. .
Specifically, the control unit 33 of the driving device 200 has a first state in which the interelectrode current is positive and has a first predetermined value (for example, a current value X1), and the interelectrode current is negative and has a second predetermined value ( For example, the second state where the current value is X2), provided in the middle of the state transition between the first state and the second state, the inter-electrode current is constant in the range from the first predetermined value to the second predetermined value. What is necessary is just to control the supply part 30 so that it may become the 3rd state used as current value (for example, current value X3, X4, X5, X6).

(2) In each of the above-described embodiments and modifications, the supply unit 30 of the driving device 200 is configured by a bridge circuit. However, the present invention is not limited to this, and can supply a step-like interelectrode current. As long as it is, any circuit configuration may be used. For example, a push-pull type current amplifying device may be used.

(3) Although the inter-electrode current for high-frequency driving includes the third state, the present invention is not limited to this, and the inter-electrode current for high-frequency driving is composed of the first state and the second state. May be. In this case, the control unit 33 of the driving device 200 controls the supply unit 30 so that the frequency becomes a predetermined frequency or higher in high-frequency driving and generates an interelectrode current composed of the first state and the second state. When the supply unit 30 is configured as a bridge type as in the embodiment, the through current becomes a problem. However, if a high-speed transistor is used as the switches Sw1 to Sw4, the through current can be reduced. Further, if the supply unit 30 is configured by a push-pull type current amplifying device, the through current does not pose a problem.

(4) The first embodiment described above is characterized in that the time of the third state of the low-frequency drive is longer than the time of the third state of the high-frequency drive. Although the description has been made with the feature that the time of the third state of driving is longer than the time of the third state of low frequency driving in the rated period, the present invention is not limited to these, and in the low frequency driving, the control unit 33 should just be what controls the supply part 30 so that the interelectrode current containing a 3rd state may be produced | generated. Even in this case, in the low frequency driving, the growth speed of the protrusions 618 and 718 can be increased as compared with the case where the third state is not included. And the life of the discharge lamp 500 can be extended.

<Projector>
Next, an example of a projector to which the light source device 1 described above is applied will be described.
FIG. 13 is a diagram showing an external configuration of the projector. As shown in this figure, the projector 2100 is a stationary type, and a projection lens 2114 for projecting an image is provided in front of the projector 2100, and a push-on type for instructing power on / off on the top plate. A switch 38 is provided.

FIG. 14 is a plan view showing an example of the optical configuration of the projector 2100.
As shown in this figure, the projector 2100 is a so-called three-plate type using transmissive liquid crystal light valves 100R, 100G, and 100B.
Inside the projector 2100, the above-described light source device 1 is provided, an alternating current is supplied from the driving device 200 to the discharge lamp 500, white light is emitted from the discharge lamp 500, and an optical element such as a main reflector. It is injected in the direction of 3 o'clock in the figure by the member. The emitted white light is separated into three primary colors of R (red), G (green), and B (blue) by three mirrors 2106 and dichroic mirrors 2108 and 2109 arranged inside, and corresponds to each primary color. Are incident on the liquid crystal light valves 100R, 100G, and 100B, respectively. More specifically, the dichroic mirror 2108 transmits light in the R wavelength region out of white light incident from the 9 o'clock direction in the drawing, and reflects the remaining light in the G and B wavelength regions in the 6 o'clock direction. The dichroic mirror 2109 transmits light in the B wavelength region out of light in the G and B wavelength regions incident from the 12 o'clock direction, and reflects light in other G wavelength regions in the 3 o'clock direction. Since B has a longer optical path than R and G, B is guided through a relay lens system 2121 including an incident lens 2122, a relay lens 2123, and an exit lens 2124 in order to prevent loss.

The projector 2100 is supplied with video signals corresponding to the respective colors of R, G, and B from upper circuits not shown, and the liquid crystal light valves 100R, 100G, and 100B are respectively supplied to the R, G, and B, respectively. Driven by the corresponding video signal. As a result, light incident on the liquid crystal light valves 100R, 100G, and 100B is emitted with its transmittance modulated for each pixel. That is, the liquid crystal light valves 100R, 100G, and 100B function as a modulation device that modulates the light emitted from the discharge lamp 500 based on the video signal (image information).
The lights modulated by the liquid crystal light valves 100R, 100G, and 100B are incident on the dichroic prism 2112 from three directions. In the dichroic prism 2112, R and B light is refracted by 90 degrees, while G light travels straight. Therefore, after the modulated lights of the respective colors are combined, a color image is projected onto the screen 2120 by the projection lens 2114. These optical systems function as a projection device that projects light modulated by the liquid crystal light valves 100R, 100G, and 100B, respectively.

  Since light corresponding to each of R, G, and B is incident on the liquid crystal light valves 100R, 100G, and 100B by the dichroic mirror 2108, a color filter is not provided as in the direct view type. Further, the transmission images of the liquid crystal light valves 100R and 100B are projected after being reflected by the dichroic prism 2112, whereas the transmission image of the liquid crystal light valve 100G is projected as it is, so that the horizontal scanning by the liquid crystal light valves 100R and 100B is performed. The direction is opposite to the horizontal scanning direction by the liquid crystal light valve 100G, and a horizontally reversed image is created.

Further, as a modulation device, a DLP (Digital Light Processing) type projector may be configured by using a DMD (Digital Mirror Device) which is an assembly element of micromirrors instead of the liquid crystal light valves 100R, 100G and 100B. DMD is a panel in which a large number of fine micromirrors are formed. Each of these micromirrors is mounted so that it can be tilted by about ± 10 degrees. For example, one mirror reflects incident light from the discharge lamp 500 in the direction of the projection lens when tilted at +10 degrees corresponding to one pixel, and does not reflect in the direction of the projection lens when tilted at −10 degrees. To act on. Accordingly, the DMD that has received the digital signal of the display image changes the inclination angle of each mirror to turn on / off the light emitted from the light source lamp. Since the tone can be controlled, it can be configured as a projector capable of obtaining a clear image without color unevenness. Further, the DLP projector may have a color wheel and a single DMD.
Note that the electronic device using the light source device 1 is not limited to a projector, and includes a lighting device and a device that requires a high-luminance light source.

  DESCRIPTION OF SYMBOLS 1 ... Light source device, 30 ... Supply part, 31 ... Constant current source, 33 ... Control part, 35 ... Voltmeter, Vmax ... Upper limit value, Vmin ... Lower limit value, 200 ... Drive apparatus, 500 ... Discharge lamp, 610, 710 ... Electrode, 100R, 100G, 100B ... Liquid crystal light valve, 2100 ... Projector.

Claims (10)

A drive device for driving a discharge lamp having a first electrode and a second electrode disposed in a cavity portion in which a discharge medium is enclosed,
The driving device supplies a first alternating current between the first electrode and the second electrode,
The first alternating current is:
A first interval in which the current value is a constant first current value;
A second section in which the current value is a constant second current value,
The first section and the second section are set alternately and repeatedly,
A third section of a third current value that is provided between the first section and the second section, has a constant current value, and is a current value between the first current value and the second current value. When,
A fourth section provided between the second section and the first section, the current value of which is the third current value;
A drive device comprising: The drive device according to claim 1,
Furthermore, a second alternating current is supplied between the first electrode and the second electrode,
The second alternating current includes the first section, the second section, the third section, and the fourth section,
The first alternating current has a frequency of 1 kHz or less,
The second alternating current has a frequency higher than 1 kHz;
The drive device, wherein the first alternating current and the second alternating current are alternately and repeatedly set. The drive device according to claim 2, wherein
The third section and the fourth section in the first alternating current are a first period of the same length;
The third section and the fourth section in the second alternating current are the second period of the same length,
The driving apparatus characterized in that the first period is longer than the second period. The drive device according to claim 2, wherein
A third alternating current having a smaller amplitude than the first alternating current and including the first section, the second section, the third section, and the fourth section;
Supplying a fourth alternating current having an amplitude smaller than that of the second alternating current;
Before the rated period in which the first alternating current and the second alternating current are alternately and repeatedly set,
A low power period in which the third alternating current and the fourth alternating current are alternately and repeatedly set is set,
The third section and the fourth section in the first alternating current are a first period of the same length;
The third section and the fourth section in the third alternating current are a third period of the same length;
The driving device characterized in that the third period is longer than the first period. The drive device according to claim 1,
Furthermore, a second alternating current is supplied between the first electrode and the second electrode,
In the second alternating current, the first section and the second section are alternately and repeatedly set,
The first alternating current has a frequency of 1 kHz or less,
The second alternating current has a frequency higher than 1 kHz;
The drive device, wherein the first alternating current and the second alternating current are alternately and repeatedly set. The drive device according to any one of claims 1 to 5,
The drive device characterized in that the third current value is zero. A driving device according to any one of claims 1 to 6,
A discharge lamp having a first electrode and a second electrode disposed in a cavity in which a discharge medium is enclosed;
A light source device comprising: The light source device according to claim 7;
A modulator that modulates light emitted from the discharge lamp based on image information;
A projection device for projecting light modulated by the modulation device;
A projector characterized by comprising: A method for driving a discharge lamp having a first electrode and a second electrode disposed in a cavity in which a discharge medium is enclosed,
Supplying a first alternating current between the first electrode and the second electrode;
The first alternating current is:
A first interval in which the current value is a constant first current value;
A second section in which the current value is a constant second current value,
The first section and the second section are set alternately and repeatedly,
A third section of a third current value that is provided between the first section and the second section, has a constant current value, and is a current value between the first current value and the second current value. When,
A fourth section provided between the second section and the first section, the current value of which is the third current value;
A method for driving a discharge lamp, comprising: In the driving method of the discharge lamp according to claim 9,
Furthermore, a second alternating current is supplied between the first electrode and the second electrode,
The second alternating current includes the first section, the second section, the third section, and the fourth section,
The first alternating current has a frequency of 1 kHz or less,
The second alternating current has a frequency higher than 1 kHz;
The first alternating current and the second alternating current are alternately and repeatedly set,
The third section and the fourth section in the first alternating current are a first period of the same length;
The third section and the fourth section in the second alternating current are the second period of the same length,
The method for driving a discharge lamp, wherein the first period is longer than the second period.

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