JP2014053122A - Method of driving discharge lamp, and projector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve problems with a composite driving method that alternately supplies a high frequency AC current and a low frequency square wave alternating current.SOLUTION: A method of driving a discharge lamp 500 having electrodes 610, 710 oppositely arranged in a cavity part 512 encapsulating a discharge medium supplies a current having a frequency higher than 1 kHz between the electrodes 610, 710 over a startup period following power input, supplies an AC current switching between frequencies including a high frequency and a low frequency between the electrodes 610, 710 over a rated period subsequent to the startup period, and supplies the low frequency AC current at the start of the rated period.

Description

  The present invention relates to a driving technique for a discharge lamp that is lit by discharge between 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 of the discharge lamp, there is also a driving method for supplying an alternating current (direct current 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

By the way, in the driving method for supplying a high-frequency alternating current, 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. To spread. On the other hand, according to the driving method for supplying a low-frequency DC alternating current, the discharge lamp main body is blackened, devitrified, etc., and the life of the discharge lamp is reduced.
For this reason, a driving method that combines the supply of a high-frequency alternating current and the supply of a low-frequency direct current alternating current has been attempted. However, various problems also occur in this combined driving method.
One of the objects of some embodiments of the present invention is to provide a discharge lamp driving method and a projector for solving various problems in the case of combining a high-frequency alternating current supply and a low-frequency alternating current supply. Is to provide.

  In the method for driving a discharge lamp according to one aspect of the present invention, a method for driving a discharge lamp having a first electrode and a second electrode arranged to face each other in a cavity in which a discharge medium is enclosed, An alternating current having a frequency higher than 1 kHz is supplied between the first electrode and the second electrode over a first period after power-on, and the first electrode and the second electrode are supplied over a second period after the first period. An alternating current switched at a frequency including a high frequency and a low frequency is supplied between the two electrodes, and the low frequency alternating current is supplied at the start of the second period. According to this driving method, for example, electrode deformation is suppressed over a first period after the power is turned on, and then the operation shifts to driving (combination driving) at a frequency including a high frequency and a low frequency. Furthermore, since the first combination drive is low-frequency drive, the combination drive starts with the shape of the protrusions adjusted. As a result, both the maintenance of the distance between electrodes and the prevention of blackening are achieved, and the life of the discharge lamp is extended. Can be achieved.

  In the above aspect, it is preferable that the AC current supplied at the start of the second period is a DC alternating current and has a frequency of 1 kHz or less. Further, the DC alternating current is preferably supplied for a period of 1 to 1000 for a cycle or 1 to 10 milliseconds for a time.

  In one example of a projector according to another aspect of the invention, a light source device, a modulation device that modulates light emitted from the light source device based on a video signal, and light modulated by the modulation device A projection device for projecting, wherein the light source device includes a discharge lamp having a first electrode and a second electrode arranged to face each other in a cavity in which a discharge medium is sealed, the first electrode, and the first electrode. A driving device for supplying an alternating current between the two electrodes, the driving device having an alternating current having a frequency higher than 1 kHz between the first electrode and the second electrode over a first period after power-on. And an alternating current switched at a frequency including a high frequency and a low frequency is supplied between the first electrode and the second electrode over a second period after the first period, and the second period At the start And supplying an alternating current of the low frequency. According to this projector, the life of the discharge lamp can be extended.

It is a figure which shows the light source device with which the drive method of the discharge lamp which concerns on embodiment is applied. It is principal part sectional drawing of the discharge lamp in the light source device. It is a figure which shows the electric constitution of the light source device. It is a figure which shows the current waveform of a high frequency drive and a low frequency drive. It is a figure for demonstrating the combination drive in the light source device. It is a flowchart which shows the control of the combination drive in the light source device. It is a figure which shows the deformation | transformation etc. of the electrode in the same discharge lamp. It is a figure which shows the drive method of the discharge lamp which concerns on embodiment in order of a time series. It is a flowchart which shows the operation | movement after power activation of the light source device. It is a flowchart which shows another operation | movement after power activation of the light source device. It is a figure which shows the comparison result of an Example and a comparative example. 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, an example of a light source device to which a discharge lamp driving method according to an embodiment of the invention is applied will be described.

FIG. 1 is a diagram illustrating a structure of a light source device. As shown in this figure, the light source device 1 includes a light source unit 110 including a discharge lamp 500 and a driving device 200 that drives 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 inside. The sub-reflecting mirror 520 is disposed with its reflecting surface facing the main reflecting mirror 112 and is adhered to the discharge lamp main body 510 with an adhesive 522 so as to be disposed at a predetermined interval. In addition, the reflecting surface of the sub-reflecting mirror 520 is 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, xenon, and the like. Examples of the gas that contributes to the above include mercury, vaporized metal halides, 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 electrodes 610 and 710 are attached so that the tip portions thereof are separated from each other by a predetermined distance in the cavity portion 512 of the discharge lamp main body 510 and 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 potential becomes relatively high and the anode The function is switched alternately between when it becomes low and when it becomes relatively low and becomes the cathode.

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 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 for convenience of explanation.
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 the electrodes 610 and 710, for example, a refractory metal material such as tungsten can be used.

  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 when the discharge lamp 500 is lit even once by the arc discharge AR, the main body portion Protrusions 618 and 718 are formed at the tips of 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 a diagram illustrating an example of 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 constant current source 31, switches Sw <b> 1 to Sw <b> 4, a control unit 33, a voltmeter 35, and a time measurement unit 36.
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. The time measuring unit 36 measures the time according to an instruction from the control unit 33, and supplies the measured time to the control unit 33.

In this driving device 200, when the control unit 33 controls the set of the switches Sw1 and Sw4 to be in the on state and the set of the switches Sw2 and Sw3 is controlled to be in the off state, the constant current is transferred from the electrode 610 to the electrode 710. It flows toward. 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 710 toward the electrode 610. For this reason, when the control unit 33 alternately switches on and off the switch Sw1 and Sw4 and the switch Sw2 and Sw3, an alternating current flows between the electrodes 610 and 710, and an alternating voltage is applied. Will be.
In this description, the current (or voltage) flowing between the electrodes 610 and 710 is positive when flowing from the electrode 610 to the electrode 710, and conversely when flowing from the electrode 710 to the electrode 610. Let be a negative value. 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.

By the way, when the electrodes 610 and 710 operate as anodes, the temperature becomes higher than when they operate as cathodes. Here, as shown in FIG. 4 (a), according to the high frequency driving in which a high frequency current having a current frequency of 1 kHz or more is supplied to the discharge lamp 500, the temperature change within one cycle becomes small, and therefore blackening occurs. The chemical reaction for suppressing / recovering is stabilized, and blackening and devitrification associated therewith 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.
The frequency of the high-frequency current may be 1 kHz or more from the viewpoint of suppressing blackening, but if it exceeds 10 GHz, the power efficiency is lowered and the cost of the power supply is increased.

On the other hand, as shown in FIG. 4B, according to the low frequency driving in which the DC alternating current having a current frequency lower than 1 kHz is supplied to the discharge lamp 500, the electrodes 610 and 710 are turned on when the discharge lamp is lit. A protrusion is formed at the tip of the electrode, and the protrusion grows by repetition of melting and solidification, so that a state in which the distance between the electrodes is narrow 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, as shown in FIG. 5, a combination drive has been proposed in which high-frequency drive and low-frequency drive are combined and switched alternately.
Specifically, first, an upper limit value and a lower limit value 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.
Secondly, for example, the voltage between the electrodes is measured while supplying a high frequency current, and when the measured voltage reaches the upper limit value, the high frequency driving is switched to the low frequency driving. Note that when switching to low frequency driving, as shown in FIG. 5, 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, the low frequency drive is switched to the high frequency drive. 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.

FIG. 6 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 apparatus 200 sets a cycle for alternately switching on and off states for the set of switches Sw1 and Sw4 and the set of switches Sw2 and Sw3 to a cycle of high-frequency driving (step Sa101). As a result, a high-frequency current flows through the electrodes 610 and 710 of the discharge lamp 500.
The control unit 33 acquires the inter-electrode voltage measured by the voltmeter 35 (step Sa102), and determines whether or not the voltage has reached the upper limit value (step Sa103). If the voltage has not reached the upper limit value (if the determination result in step Sa103 is “No”), the processing procedure is returned to step Sa102 again. However, when the high frequency current is supplied to the discharge lamp 500, the distance between the electrodes increases, so that the voltage between the electrodes eventually reaches the upper limit value.

  When the voltage between the electrodes reaches the upper limit value (when the determination result in Step Sa103 is “Yes”), the control unit 33 is in an on / off state with respect to the set of the switches Sw1 and Sw4 and the set of the switches Sw2 and Sw3. Is switched to a low-frequency driving cycle (step Sa104). Thereby, the current flowing through the electrodes 610 and 710 of the discharge lamp 500 is switched from the high frequency current to the low frequency current. The control unit 33 acquires the voltage between the electrodes measured by the voltmeter 35 (Step Sa105), and determines whether or not the voltage has reached the lower limit (Step Sa106). If the voltage has not reached the lower limit value (if the determination result in step Sa106 is “No”), the processing procedure is returned to step Sa105 again. However, when the low frequency current is supplied to the discharge lamp 500, the distance between the electrodes is narrowed, so that the voltage between the electrodes eventually reaches the lower limit value. When the voltage between the electrodes reaches the lower limit value (when the determination result in Step Sa106 is “Yes”), the processing procedure is returned to Step Sa101 again. Thereby, the current flowing through the electrodes 610 and 710 of the discharge lamp 500 is switched from the low frequency current to the high frequency current.

  According to this combination driving, the distance between the electrodes is maintained in a range from a distance corresponding to the lower limit value of the voltage between the electrodes to a distance corresponding to the upper limit value, and not only blackening does not occur during high frequency driving. In some cases, blackening that occurs when a low-frequency current is supplied is also recovered. For this reason, both maintenance of the distance between electrodes and prevention of blackening were expected.

By the way, when the discharge lamp is used as a light source for a projector or the like, the power is turned on (turned on) and turned off (shut off) many times.
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, in the rated state 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 to the rated state after the power is turned on, it is necessary to supply the discharge lamp 500 with a current close to the rating or equivalent to the steady state after the power is turned on. However, since a large heat load is applied to the electrodes 610 and 710 after the power is turned on, the protrusions 618 and 718 formed at the tips are deformed or blackening due to electrode sublimation occurs.

In particular, in the above combination driving, the high frequency driving and the low frequency driving are alternately switched, and therefore the following points need to be considered. That is, of the combination driving, the projection 618 (718) on the electrode 610 grows as shown in FIG. 7A by the low frequency driving, and then the projection 618 is changed to the high frequency driving by FIG. 7B. Decrease as shown. When the power supply is cut off in this state, the electrode 610 is solidified in the state shown in FIG. 5B, so that the shape shown in FIG. , (B) almost the same shape. When the power is turned on in this state, the protrusion 618 formed on the electrode 610 does not have a shape (design shape) assumed in position, thickness, etc., as shown in FIG. Deform. If the combination driving is continued in this deformed shape, the deformation of the projection 618 further proceeds, and as a result, normal combination driving cannot be performed. Specifically, for example, as shown in FIG. 5E, the shape of the protrusion 618 may collapse in the electrode 610.
Although the case where the power supply is interrupted in the middle of the high frequency driving in the combination driving is shown here, the normal combination driving cannot be performed even when the power supply is interrupted in the middle of the low frequency driving. Specifically, among the combination driving, the protrusion 618 on the electrode 610 is reduced as shown in FIG. 5B by high-frequency driving, and thereafter, the protrusion 618 is changed to low-frequency driving in FIG. Grows as shown. When the power supply is cut off in this state, the electrode 610 is hardened in the state shown in FIG. When the power is turned on in this state, not only the protrusion 618 that has grown to a certain extent is deformed, but the inter-electrode voltage may soon reach the lower limit value. When the combination driving is continued in a state where the protrusion 618 is deformed and grown, the protrusion 618 eventually collapses and the combination driving fails.
As described above, when combination driving is started with the discharge lamp 500 cooled when the power is turned on, the normal combination is obtained regardless of whether the driving is ended with high frequency driving or low frequency driving immediately before use. There is a possibility that driving cannot be continued.

  Therefore, in the present embodiment, as shown in FIG. 8, high-frequency driving is intentionally executed instead of the combination driving in the start-up period (first period) immediately after power-on. Thereby, the shape change of the electrodes 610 and 710 at the time of start-up is suppressed and blackening is prevented. Next, combination driving is executed in the rated period (second period) next to the start-up period to achieve both maintenance of the distance between the electrodes and prevention of blackening. At this time, in combination driving, low frequency driving is performed first. Thereby, since the shape of the projection is adjusted, the combination driving can be continued.

Note that it is preferable that the high-frequency current during the start-up period immediately after power-on is limited to be equal to or less than the current value of the combined drive during the rated period. Further, the frequency of the high-frequency current immediately after the power is turned on is preferably higher than 1 kHz.
On the other hand, in the first low frequency driving in the rated period, it is preferable that the frequency is a DC alternating current having a frequency of 1 kHz or less. The direct current alternating current is preferably about 1 to 1000 cycles when the current flowing between the electrodes 610 and 710 becomes a positive value and immediately after it becomes a negative value. When the frequency is as low as about 200 Hz, the time is preferably set to about 1 to 10 milliseconds.

Note that, in the first low-frequency driving in the rated period, the purpose is to prioritize adjusting the shape of the protrusions. Therefore, in the present embodiment, the first period of the rated period is set as the specific period, and the control is performed in the specific period. The unit 33 ignores the voltage from the voltmeter and forces the low frequency drive. However, since the voltage between the electrodes is increased by the high frequency drive at the time of start-up (the distance between the electrodes is widened), the voltage between the electrodes hardly reaches the lower limit by the first low frequency drive during the rated period. it is conceivable that.
Further, the frequency of the first low frequency drive in the rated period and the frequency of the low frequency drive after the high frequency drive may be different as long as the frequency is lower than 1 kHz.

FIG. 9 is an example of a flowchart showing the operation after the power is turned on. The end of the start-up period is when a predetermined time has elapsed.
When the light source device 1 is instructed to turn on the power, the control unit 33 first sets the frequency for alternately switching on and off the switch Sw1, Sw4 and the switch Sw2, Sw3 to 2 kHz or higher. At the same time, a value equal to or less than the rated period is designated as a constant current value for the constant current source 31 (step Sa11). As a result, a high-frequency current limited to a steady period or less flows through the electrodes 610 and 710 of the discharge lamp 500 at the time of startup after the current is supplied.

Next, the control unit 33 instructs the time measurement unit 36 to measure time (step Sa12). Thereby, the time measuring unit 36 starts measuring time and supplies the measured time to the control unit 33.
The control unit 33 determines whether or not a predetermined time has elapsed since the measurement was instructed, that is, after the high frequency current was supplied after the power was turned on (step Sa13). Here, as the predetermined time, an appropriate value is appropriately selected within a range of 1 to 60 minutes, for example.

  If the predetermined time has not elapsed (if the determination result in step Sa13 is “No”), the processing procedure returns to step Sa13. Therefore, when the predetermined time has elapsed, the determination result of step Sa13 becomes “Yes”, and the combination drive process (step Sa100a) is executed until the power is shut off in the next step Sa104 and subsequent steps. In this case, the combination drive process (step Sa100a) is the low frequency drive (steps Sa104 to Sa106) first, then the high frequency drive (steps Sa101 to Sa103), and the first specific period of the rated period. Except for the point that the voltage measured by the voltmeter 35 is ignored and the low frequency driving is performed in 1 to 100 cycles, it is as described in FIG. For this reason, after the specific period has elapsed, switching to high-frequency driving is performed, and thereafter, switching between low-frequency driving and high-frequency driving is alternately performed according to the voltage between the electrodes until the power is shut off.

  According to this embodiment, the high-frequency driving in the start-up period until the elapse of a predetermined time immediately after the power is turned on suppresses the shape change of the electrodes 610 and 710 and prevents blackening. Next, since the shape of the protrusion is adjusted by the low frequency driving in the first specific period of the rated period, the subsequent combination driving can be stably continued.

  In the flowchart shown in FIG. 9, when the predetermined time has elapsed from the power-on instruction at the end of the start-up period (the start of the rated period), the inter-electrode distance is set to a threshold value (upper limit) after power-on. Value), it may be done.

FIG. 10 is an example of a flowchart illustrating an operation in the case where the end of the start-up period is performed when the distance between the electrodes reaches a threshold value.
When the power supply to the light source device 1 is instructed, first, the control unit 33 is the same as FIG. 6 in that the high-frequency current limited to the steady state or less is supplied to the discharge lamp 500 (step Sa11).
Next, the control part 33 acquires the voltage between electrodes measured by the voltmeter 35 (step Sb12), and discriminate | determines whether the said voltage has reached the threshold value (step Sb13). If the voltage acquired from the voltmeter 35 has not reached the threshold value (if the determination result in step Sb13 is “No”), the control unit 33 returns the processing procedure to step Sb12 again. However, if the high frequency driving is continued, the distance between the electrodes increases, so that the voltage between the electrodes eventually reaches the threshold value.

  When the voltage between the electrodes reaches the threshold value, the determination result in step Sb13 is “Yes”, and the combination drive process in step Sa100a is executed until the power is turned off. This driving process (step Sa100a) is the same as the combination driving process in FIG.

  Here, the upper limit value in the combination driving is used as the threshold value, but it may be a value lower than the upper limit value or an upper value. In any case, if the inter-electrode distance reaches the threshold at the end of the start-up period, the shape change of the electrodes 610 and 710 can be suppressed and the blackening can be prevented after the power is turned on. Can be continued stably.

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. The driving conditions of this embodiment are as follows.

<Example>
Rated power of discharge lamp 500: 200W
Current during start-up period: 2.86 A
Frequency during start-up period: 5 kHz (high frequency)
Combined drive (rated period) current: 2.86 A
Current waveform of combination drive (specific period): DC alternating current Frequency of combination drive (specific period): 200 Hz (1 cycle: 5 milliseconds)
Combination drive (rated period) frequency: 150 Hz, 5 kHz
Voltage control range of combination drive: 5V (difference between upper limit and lower limit)
That is, in the embodiment, the current at the start-up and the current in the combination drive are set to the same value, and the first low frequency drive in the rated period is set to the DC alternating current, and the frequency and the frequency after the high frequency drive are set. The frequency of the low frequency drive is different.

<Comparative Example 1>
The comparative example 1 is a low frequency of 280 Hz in the start-up period in the examples.

<Comparative example 2>
Comparative Example 2 is an example in which the current at startup is 3.2 A. That is, in Comparative Example 2, the current during the startup period is made larger than the current during the rated period.

<Comparative Example 3>
In Comparative Example 3, the first driving frequency in the rated period is set to 150 Hz until the lower limit is reached.

<Evaluation>
For each of the examples and comparative examples 1 to 3, the continuous operation time (Hour) until the combined drive failed was measured. The result is shown in FIG. Of these results, when comparing the example and the comparative example 1, it can be seen that the high-frequency driving in the example is better than the low-frequency driving in the comparative example 1 during the start-up period. Further, comparing the example and the comparative example 2, it can be seen that it is not preferable to set the current during the start-up period to be larger than the current during the rated period. Further, comparing the example and the comparative example 3, it can be seen that it is better to limit the DC alternating current time to about 5 mm in the first low-frequency driving in the rated period.
In addition, the order of the longest time is Example, Comparative Example 1, Comparative Example 2, and Comparative Example 3. As indicated by *, Comparative Examples 1 to 3 are started up immediately after the power is turned on. The occurrence of blackening has been confirmed.
Therefore, according to the example, it can be seen that, compared with Comparative Examples 1 to 3, good results are obtained with respect to the time until the combined drive fails and the suppression of the occurrence of blackening.

<Projector>
Next, an example of a projector to which the light source device 1 described above is applied will be described.
FIG. 12 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. 13 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 compared to 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 the loss.

The projector 2100 is supplied with video signals corresponding to the respective colors 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.
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 at 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.

  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.

DESCRIPTION OF SYMBOLS 1 ... Light source device, 200 ... Drive apparatus, 500 ... Discharge lamp, 610, 710 ... Electrode, 618, 718 ... Protrusion, 31 ... Constant current source, 33 ... Control part, 35 ... Voltmeter, 36 ... Time measurement part, 2100 …projector.

Claims (11)

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,
In a first period after turning on the power, a first alternating current having a frequency higher than 1 kHz is supplied between the first electrode and the second electrode,
Supplying an alternating current having a plurality of frequencies between the first electrode and the second electrode in a second period after the first period;
The alternating currents of the plurality of frequencies include a second alternating current having a frequency higher than 1 kHz and a third alternating current having a frequency of 1 kHz or less,
The method for driving a discharge lamp, wherein the second period starts from the third alternating current. In the driving method of the discharge lamp of Claim 1,
In the second period, the second alternating current and the third alternating current are alternately and repeatedly supplied. The method for driving a discharge lamp according to claim 1 or 2,
The method for driving a discharge lamp, wherein the third alternating current supplied at the start of the second period is a direct current alternating current. In the driving method of the discharge lamp of Claim 3,
The method of driving a discharge lamp, wherein the third alternating current is supplied in a cycle of 1 to 1000 or a time of 1 to 10 milliseconds. In the driving method of the discharge lamp in any one of Claims 1 thru | or 4,
In the first period, the maximum value of the current flowing from the first electrode to the second electrode is
The discharge lamp driving method according to claim 1, wherein the current is equal to or less than a maximum value of a current flowing from one of the first electrode and the second electrode to the other in the second period. In the driving method of the discharge lamp in any one of Claims 1 thru | or 4,
The discharge lamp driving method characterized in that the amplitude of the first alternating current is smaller than the amplitude of the second alternating current and smaller than the amplitude of the third alternating current. The method for driving a discharge lamp according to any one of claims 1 to 6,
The discharge lamp driving method according to claim 1, wherein the first period ends when a predetermined time has elapsed since power-on. The method for driving a discharge lamp according to any one of claims 1 to 6,
Furthermore, a voltage value between the first electrode and the second electrode when a predetermined current value in the first alternating current is applied is measured,
The discharge lamp driving method according to claim 1, wherein the first period ends when the voltage value reaches a predetermined threshold value. The method for driving a discharge lamp according to any one of claims 1 to 6,
The method of driving a discharge lamp, wherein the first alternating current is a direct current alternating current. In the driving method of the discharge lamp according to claim 9,
In the first period, an alternating voltage is applied between the first electrode and the second electrode by the first alternating current,
The discharge lamp driving method according to claim 1, wherein the first period ends when the amplitude of the AC voltage becomes equal to or greater than a predetermined determination value. A light source device;
A modulation device that modulates light emitted from the light source device based on a video signal;
A projection device that projects the light modulated by the modulation device,
The light source device
A discharge lamp having a first electrode and a second electrode disposed in a cavity in which a discharge medium is enclosed;
A driving device for supplying an alternating current between the first electrode and the second electrode,
The driving device includes:
In the first period after power-on, an alternating current having a frequency higher than 1 kHz is supplied between the first electrode and the second electrode,
Supplying an alternating current having a plurality of frequencies between the first electrode and the second electrode in a second period after the first period;
The alternating currents of the plurality of frequencies include a second alternating current having a frequency higher than 1 kHz and a third alternating current having a frequency of 1 kHz or less,
The projector according to claim 1, wherein the second period starts from the third alternating current.

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