U.S. patent application number 15/501614 was filed with the patent office on 2017-08-10 for discharge lamp lighting device.
This patent application is currently assigned to USHIO DENKI KABUSHIKI KAISHA. The applicant listed for this patent is USHIO DENKI KABUSHIKI KAISHA. Invention is credited to Minoru FUKUDA, Shigeyoshi MATSUMOTO, Kosuke SAKA, Shoichi TERADA.
Application Number | 20170231074 15/501614 |
Document ID | / |
Family ID | 55399407 |
Filed Date | 2017-08-10 |
United States Patent
Application |
20170231074 |
Kind Code |
A1 |
SAKA; Kosuke ; et
al. |
August 10, 2017 |
DISCHARGE LAMP LIGHTING DEVICE
Abstract
A discharge lamp lighting device includes a control unit adapted
to control a frequency of the AC electric current supplied to a
discharge lamp by a feeding unit, in different manners within a
first term and a second term which are alternately repeated, the
control unit is adapted to control the frequency of the AC electric
current such that, within the first term, the frequency of the AC
electric current becomes at least one frequency out of plural set
frequencies, and is further adapted to control the frequency of the
AC electric current, based on a predetermined frequency and an
electric current within the previous first term, such that, within
the second term, the frequency of the AC electric current becomes a
frequency lower than this predetermined frequency.
Inventors: |
SAKA; Kosuke; (Himeji-shi,
JP) ; FUKUDA; Minoru; (Himeji-shi, JP) ;
MATSUMOTO; Shigeyoshi; (Himeji-shi, JP) ; TERADA;
Shoichi; (Himeji-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
USHIO DENKI KABUSHIKI KAISHA |
Tokyo |
|
JP |
|
|
Assignee: |
USHIO DENKI KABUSHIKI
KAISHA
Tokyo
JP
|
Family ID: |
55399407 |
Appl. No.: |
15/501614 |
Filed: |
August 5, 2015 |
PCT Filed: |
August 5, 2015 |
PCT NO: |
PCT/JP2015/072154 |
371 Date: |
February 3, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01J 61/0732 20130101;
H01J 61/04 20130101; H01J 61/00 20130101; H01J 61/12 20130101; H01J
61/822 20130101; H01J 61/26 20130101; Y02B 20/202 20130101; H05B
41/2886 20130101; Y02B 20/00 20130101; H05B 41/2887 20130101; H05B
41/36 20130101 |
International
Class: |
H05B 41/36 20060101
H05B041/36 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 28, 2014 |
JP |
2014-173906 |
Claims
1. A discharge lamp lighting device comprising: a feeding unit
adapted to supply an AC electric current to a discharge lamp having
a pair of electrodes placed to oppose each other within a discharge
container which encloses a predetermined gas; and a control unit
adapted to control a frequency of the AC electric current supplied
to the discharge lamp by the feeding unit, in different manners
within a first term and a second term which are alternately
repeated; wherein the control unit is adapted to control the
frequency of the AC electric current such that, within the first
term, the frequency of the AC electric current becomes at least one
frequency out of plural set frequencies, and is further adapted to
control the frequency of the AC electric current, based on a
predetermined frequency and an electric current within the previous
first term, such that, within the second term, the frequency of the
AC electric current becomes a frequency lower than this
predetermined frequency.
2. The discharge lamp lighting device according to claim 1, wherein
the control unit is adapted to control the frequency of the AC
electric current such that the frequency of the AC electric current
becomes a predetermined frequency out of plural set frequencies,
within the first term.
3. The discharge lamp lighting device according to claim 1, wherein
the control unit is adapted to control the frequency of the AC
electric current such that, within the first term, the frequency of
the AC electric current becomes at least two frequencies out of the
plural set frequencies, and is further adapted to control the
frequency of the AC electric current, based on an electric current
and a frequency having a largest time ratio within the previous
first term, such that, within the second term, the frequency of the
AC electric current becomes a frequency lower than this
frequency.
4. The discharge lamp lighting device according to claim 1, wherein
the control unit is adapted to control the frequency of the AC
electric current such that, within the first term, the frequency of
the AC electric current becomes at least two frequencies out of the
plural set frequencies, and is further adapted to control the
frequency of the AC electric current, based on an electric current
and a lowest frequency within the previous first term, such that,
within the second term, the frequency of the AC electric current
becomes a frequency lower than this frequency.
5. The discharge lamp lighting device according to claim 1, wherein
the plural frequencies to be set within the first term are set to
be respective frequencies provided by multiplying a highest
frequency out of the plural frequencies by the inverses of
respective natural numbers, and the frequency within the second
term is set to be a frequency provided by multiplying the highest
frequency by the inverse of a natural number.
6. The discharge lamp lighting device according to claim 1, wherein
the control unit is adapted to control the frequency of the AC
electric current in such a way as to alternately repeat a basic
term and a lower-frequency term, the basic term being provided for
controlling the frequency of the AC electric current in different
manners within the first term and the second term which are
alternately repeated, and the lower-frequency term being provided
for controlling the frequency of the AC electric current such that
the frequency of the AC electric current becomes a frequency lower
than a lowest frequency within the previous basic term.
7. The discharge lamp lighting device according to claim 6, wherein
the control unit is adapted to control the frequency of the AC
electric current, based on an electric current and a predetermined
frequency within the previous basic term, such that the frequency
of the AC electric current becomes a frequency lower than the
predetermined frequency, within the lower-frequency term.
8. The discharge lamp lighting device according to claim 6, wherein
the plural frequencies to be set within the first term are set to
be frequencies provided by multiplying a highest frequency out of
the plural frequencies by the inverses of respective natural
numbers, the frequency within the second term is set to be a
frequency provided by multiplying the highest frequency by the
inverse of a natural number, and the frequency within the
lower-frequency term is set to be a frequency provided by
multiplying the highest frequency by the inverse of a natural
number.
Description
TECHNICAL FIELD
[0001] The present invention relates to a discharge lamp lighting
device for supplying an AC electric current to discharge lamps
having a pair of electrodes placed to oppose each other within a
discharge container enclosing a predetermined gas.
BACKGROUND ART
[0002] Conventionally, as discharge lamps, there have been known
discharge lamps that include a discharge container enclosing a
halogen gas and a pair of electrodes placed to oppose each other
within the discharge container. Further, as a discharge lamp
lighting device for lighting such discharge lamps, there have been
known a discharge lamp lighting device for supplying an AC electric
current to discharge lamps (refer to Patent Document 1, for
example).
[0003] When such a discharge lamp is lighted, the electrodes reach
a higher temperature and are evaporated. Then, the evaporated metal
bonds to the halogen gas enclosed within the discharge container
and, thus, returns to the electrodes again without being adhered to
the inner surface of the discharge container. This effect is
referred to as a halogen cycle.
[0004] On the other hand, the discharge lamp lighting device
according to Patent Document 1 is adapted to supply, to a discharge
lamp, an AC electric current having two different frequencies
independent of data about operations of the discharge lamp (voltage
value, electric current value, luminance, distance between the
electrodes, temperature and the like). By doing this, a shape of
the electrodes can be preferably maintained at the beginning of
lighting, but it has been difficult to maintain the shape of the
electrodes (particularly, their protruding portions) as the
lighting time period is increased. This has made the life of the
discharge lamp shorter.
PRIOR ART DOCUMENTS
Patent Documents
[0005] Patent Document 1: JP-A-2006-156414
SUMMARY OF THE INVENTION
Technical Problems
[0006] Therefore, in view of the aforementioned circumstance, it is
an object of the present invention to provide a discharge lamp
lighting device capable of elongating a life of a discharge
lamp.
Solution to the Problems
[0007] According to the present invention, there is provided a
discharge lamp lighting device, which includes:
[0008] a feeding unit adapted to supply an AC electric current to a
discharge lamp having a pair of electrodes placed to oppose each
other within a discharge container which encloses a predetermined
gas; and
[0009] a control unit adapted to control a frequency of the AC
electric current supplied to the discharge lamp by the feeding
unit, in different manners within a first term and a second term
which are alternately repeated;
[0010] wherein the control unit is adapted to control the frequency
of the AC electric current such that, within the first term, the
frequency of the AC electric current becomes at least one frequency
out of plural set frequencies, and is further adapted to control
the frequency of the AC electric current, based on a predetermined
frequency and an electric current within the previous first term,
such that, within the second term, the frequency of the AC electric
current becomes a frequency lower than this predetermined
frequency.
[0011] According to the discharge lamp lighting device of the
present invention, the feeding unit supplies the AC electric
current to the discharge lamp having the pair of electrodes placed
to oppose each other within the discharge container which encloses
predetermined gasses. The control unit controls the frequency of
the AC electric current supplied to the discharge lamp from the
feeding unit, in the different manners, within the first terms and
the second terms which are alternately repeated.
[0012] At first, within the first terms, the control unit controls
the frequency of the AC electric current such that the frequency of
the AC electric current becomes one frequency out of the plural set
fixed frequencies. On the other hand, the positions on the
electrodes to which the metal evaporated from the electrodes
returns depend on the temperature of the electrodes. Further, the
temperature of the electrodes depends on the frequencies within the
first terms and the electric current within the first terms.
[0013] Therefore, within each of the second terms, the control unit
controls the frequency of the AC electric current, based on the
electric current and the predetermined frequency within the
previous first term, such that the frequency of the AC electric
current becomes the frequency which is lower than the predetermined
frequency. Consequently, the positions on the electrodes to which
the evaporated metal returns within the previous first terms are
accurately figured out. Accordingly, within the second terms, it is
possible to supply the AC electric current with a frequency
suitable thereto, to the discharge lamp. Therefore, even when the
discharge lamp is lighted for a longer time period, it is possible
to maintain the shape of the electrodes (particularly, the
protruding portions). This can elongate the time period for which
the shape of the electrodes can be maintained.
[0014] Also, the discharge lamp lighting device according to the
present invention may have a configuration in which:
[0015] the control unit is adapted to control the frequency of the
AC electric current such that the frequency of the AC electric
current becomes a predetermined frequency out of plural set
frequencies, within the first term.
[0016] Also, the discharge lamp lighting device according to the
present invention may have a configuration in which:
[0017] the control unit is adapted to control the frequency of the
AC electric current such that, within the first term, the frequency
of the AC electric current becomes at least two frequencies out of
the plural set frequencies, and is further adapted to control the
frequency of the AC electric current, based on an electric current
and a frequency having a largest time ratio within the previous
first term, such that, within the second term, the frequency of the
AC electric current becomes a frequency lower than this
frequency.
[0018] Also, the discharge lamp lighting device according to the
present invention may have a configuration in which:
[0019] the control unit is adapted to control the frequency of the
AC electric current such that, within the first term, the frequency
of the AC electric current becomes at least two frequencies out of
the plural set frequencies, and is further adapted to control the
frequency of the AC electric current, based on an electric current
and a lowest frequency within the previous first term, such that,
within the second term, the frequency of the AC electric current
becomes a frequency lower than this frequency.
[0020] Also, the discharge lamp lighting device according to the
present invention may have a configuration in which:
[0021] the plural frequencies to be set within the first term are
set to be respective frequencies provided by multiplying a highest
frequency out of the plural frequencies by the inverses of
respective natural numbers, and
[0022] the frequency within the second term is set to be a
frequency provided by multiplying the highest frequency by the
inverse of a natural number.
[0023] Also, the discharge lamp lighting device according to the
present invention may have a configuration in which:
[0024] the control unit is adapted to control the frequency of the
AC electric current in such a way as to alternately repeat a basic
term and a lower-frequency term, the basic term being provided for
controlling the frequency of the AC electric current in different
manners within the first term and the second term which are
alternately repeated, and the lower-frequency term being provided
for controlling the frequency of the AC electric current such that
the frequency of the AC electric current becomes a frequency lower
than a lowest frequency within the previous basic term.
[0025] Also, the discharge lamp lighting device according to the
present invention may have a configuration in which:
[0026] the control unit is adapted to control the frequency of the
AC electric current, based on an electric current and a
predetermined frequency within the previous basic term, such that
the frequency of the AC electric current becomes a frequency lower
than the predetermined frequency, within the lower-frequency
term.
[0027] Also, the discharge lamp lighting device according to the
present invention may have a configuration in which:
[0028] the plural frequencies to be set within the first term are
set to be frequencies provided by multiplying a highest frequency
out of the plural frequencies by the inverses of respective natural
numbers,
[0029] the frequency within the second term is set to be a
frequency provided by multiplying the highest frequency by the
inverse of a natural number, and
[0030] the frequency within the lower-frequency term is set to be a
frequency provided by multiplying the highest frequency by the
inverse of a natural number.
Effect of the Invention
[0031] As described above, the discharge lamp lighting device
according to the present invention provides the excellent effect of
elongating the life of the discharge lamp.
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] FIG. 1 is a schematic view of an image projection device
having a discharge lamp lighting device according to an embodiment
of the present invention.
[0033] FIG. 2 is a schematic cross-sectional view of a discharge
lamp which is supplied with an AC electric current from the
discharge lamp lighting device according to the same
embodiment.
[0034] FIG. 3 is an enlarged view of main parts of the discharge
lamp, in FIG. 2, according to the same embodiment.
[0035] FIG. 4 is a block diagram of the discharge lamp lighting
device according to the same embodiment.
[0036] FIG. 5 is a view illustrating electric current waveforms in
the discharge lamp lighting device according to the same
embodiment.
[0037] FIG. 6 is a view illustrating the relationship between a
voltage (an electric current) and a multiplying factor for the
frequency within variation terms, in the discharge lamp lighting
device according to the same embodiment.
[0038] FIG. 7 is an enlarged view of main parts of the discharge
lamp, which is a view for illustrating an effect of the discharge
lamp lighting device according to the same embodiment.
[0039] FIG. 8 is a view illustrating the relationship between the
time period for which the discharge lamp is lighted and the time
period of fixation terms, according to the same embodiment.
[0040] FIG. 9 is a view illustrating the relationship between the
voltage (the electric current) and the multiplying factor for
frequencies within lower-frequency terms, in the discharge lamp
lighting device according to the same embodiment.
[0041] FIG. 10 shows a graph for illustrating an effect of the
discharge lamp lighting device according to the same
embodiment.
[0042] FIG. 11 is a view illustrating an electric current waveform
in a discharge lamp lighting device according to another embodiment
of the present invention.
[0043] FIG. 12 is a view illustrating an electric current waveform
in a discharge lamp lighting device according to yet another
embodiment of the present invention.
[0044] FIG. 13 is a view illustrating a relationship between a
voltage and a multiplying factor for frequencies within variation
terms, in a discharge lamp lighting device according to yet another
embodiment of the present invention.
[0045] FIG. 14 is a view illustrating a relationship between a
voltage and a multiplying factor for frequencies within
lower-frequency terms, in a discharge lamp lighting device
according to yet another embodiment of the present invention.
DESCRIPTION OF EMBODIMENTS
[0046] Hereinafter, an embodiment of a discharge lamp lighting
device according to the present invention will be described with
reference to FIGS. 1 to 9. Note that, throughout the drawings, the
dimensional ratios in the drawings are not necessarily coincident
with the actual dimensional ratios. Further, the discharge lamp
lighting device according to the present embodiment is used in an
image projection device (for example, a projector).
[0047] As illustrated in FIG. 1, an image projection device 100
includes a light source device 101 for emitting light, and a
projection-device main body 102 which creates light images with the
light emitted from the light source device 101 and projects them
onto a screen 104. Further, the image projection device 100
includes an optical fiber 103 connected at its respective end
portions to the light source device 101 and to the
projection-device main body 102, in order to enter the light
emitted from the light source device 101 to the projection-device
main body 102.
[0048] The light source device 101 includes a discharge lamp 10 for
emitting light, and a discharge lamp lighting device 1 for
supplying an AC electric current to the discharge lamp 10. Note
that, although not illustrated, the light source device 101
includes an optical system such as a convergence lens or a
collimator lens.
[0049] Although not illustrated, the projection-device main body
102 includes an image optical system for creating light images by
receiving the light emitted from the light source device 101, and a
projection optical system (for example, a projection lens) for
receiving the light images emitted from the image optical system
and for projecting them onto the screen 104. Further, the image
optical system includes an optical system, such as a spatial
modulation element, for modulating light into light images.
[0050] As illustrated in FIGS. 2 and 3, the discharge lamp 10
includes a hollow-shaped discharge container 11, and a pair of
electrodes 12, 12 which are placed to oppose each other within the
discharge container 11. The discharge lamp 10 includes sealing
portions 13, 13 placed at the opposite end portions of the
discharge container 11, metal foils 14 embedded in the sealing
portions 13, and outer leads 15 connected to the metal foils
14.
[0051] The discharge container 11 is formed to have a spherical
shape. The discharge container 11 is translucent and radiates light
generated therein toward the outside. In the present embodiment,
the discharge container 11 is formed integrally with the sealing
portions 13 and is formed from quartz glass. The material of the
discharge container 11 and the sealing portions 13 is not limited
to quartz glass, and they may be formed from a different
material.
[0052] The electrodes 12 include a head portion 12a housed in the
discharge container 11, and a shaft portion 12b which is formed to
have a smaller diameter than that of the head portion 12a and is
secured to the discharge container 11. The electrodes 12 include a
protruding portion 12c at the tip end of the head portion 12a. The
protruding portion 12c is formed from the electrode material which
has been aggregated at the tip end of the electrode 12 during
lighting of the discharge lamp 10, as will be described later.
[0053] The pair of electrodes 12 (the head portions 12a, 12a) are
placed to oppose each other in such a way as to interpose,
therebetween, an extremely small interval which is equal to or less
than 2 mm, for example. In the present embodiment, the electrodes
12 are formed from tungsten. The material of the electrodes 12 is
not limited to tungsten, and they may be formed from a different
material.
[0054] The metal foils 14 are formed from a conductive material
made of, for example, molybdenum and are embedded in an airtight
manner within the sealing portions 13 using shrink sealing, for
example. The metal foils 14 are bonded, at their one end portions,
to the other end portions of the shaft portions 12b of the
electrodes 12. The other end portions of the metal foils 14 are
bonded to one end portions of the outer leads 15.
[0055] In the discharge lamp 10, a light-emitting gas, a halogen
gas and an inert gas are enclosed within the discharge container
11. The light-emitting gas is for providing radiated light and is
constituted by mercury in the present embodiment. The halogen gas
is for increasing the life of the discharge lamp 10 which utilizes
a halogen cycle and is constituted by iodine in the present
embodiment. The inert gas is for improving lighting startability
and is constituted by argon in the present embodiment. The
respective gases enclosed therein are not limited to the
aforementioned gases and may be constituted by other gases.
[0056] The mercury is for providing radiated light with a necessary
visible light wavelength, such as a wavelength in the range of 360
to 780 nm, for example. The mercury is enclosed in an amount of
0.20 mg/mm3 within the discharge container 11, for example. This
amount of mercury enclosed therein, which may be varied depending
on temperature conditions, is for achieving a higher vapor
pressure, as an internal pressure in the discharge container 11
during lighting, which is equal to or higher than 200 atm. Further,
by enclosing a larger amount of mercury therein, it is possible to
fabricate the discharge lamp 10 which contains a higher mercury
vapor pressure, that is, the mercury vapor pressure during lighting
is equal to or higher than 250 atm or equal to or higher than 300
atm. Thus, it is possible to realize a light source more suitable
for a projector as the mercury vapor pressure is higher.
[0057] The halogen gas is enclosed within the discharge container
11, in the state of being combined with mercury or other metals.
The halogen gas is enclosed within the discharge container 11, in
an amount selected from the range of 1.times.10-6 .mu.mol/mm.sup.3
to 1.times.10-2 .mu.mol/mm.sup.3. The largest reason for the
enclosure of halogen therein is to elongate the life of the
discharge lamp 10 which utilizes the halogen cycle. Further, in
cases where the discharge lamp 10 has an extremely smaller size and
a higher lighting vapor pressure, it is also possible to provide an
effect of preventing devitrification of the discharge container
11.
[0058] When the electrodes 12, 12 are energized, the electrodes 12
are incandesced to reach a higher temperature, so that the tungsten
forming the electrodes 12 is sublimated. The sublimated tungsten
bonds to the halogen gas enclosed therein to form a tungsten
halide, in the inner wall surface area of the discharge container
11 which is a portion at a relatively lower temperature. The
tungsten halide has a relatively higher vapor pressure and,
therefore, moves again to the vicinities of the tip ends of the
electrodes 12, in a gaseous state.
[0059] Further, by being heated again at the vicinities, the
tungsten halide is separated into halogen and tungsten. Out of
them, the tungsten returns to the tip ends of the electrodes 12 and
is aggregated thereat, while the halogen is restored as a halogen
gas within the discharge container 11. This phenomenon is called a
halogen cycle. Further, the aggregated tungsten adheres to the
vicinities of the tip ends of the electrodes 12 to form the
protruding portions 12c.
[0060] As an example of the discharge lamp 10, it is possible to
exemplify a discharge lamp 10 with a rated electric power (AC) of
250 W, wherein the discharge container 11 has a largest outer
diameter of 9.4 mm, the distance between the electrodes 12, 12 is
1.0 mm, and the discharge container 11 has an internal volume of 55
mm.sup.3.
[0061] As illustrated in FIG. 4, the discharge lamp lighting device
1 according to the present embodiment includes a feeding unit 2 for
supplying an AC electric current to the discharge lamp 10 through
the outer leads 15, in order to light the discharge lamp 10.
Further, the discharge lamp lighting device 1 includes a control
unit 3 for controlling the AC electric current supplied to the
discharge lamp 10 from the feeding unit 2.
[0062] The feeding unit 2 includes a step-down chopper unit 21 for
reducing a supplied DC voltage to a desired DC voltage, and a DC/AC
conversion unit 22 for converting the DC voltage resulted from the
voltage reduction by the step-down chopper unit 21 into an AC
voltage with a desired frequency. The feeding unit 2 includes a
starter unit 23 for raising the AC voltage supplied from the DC/AC
conversion unit 22 and for supplying the raised voltage to the
discharge lamp 10, at the time of starting (lighting) the discharge
lamp 10.
[0063] The control unit 3 includes an electric-power control unit
31 for controlling the step-down chopper unit 21 to control the
value of the electric power supplied to the discharge lamp 10 such
that the value of the electric power is constant. The control unit
3 includes a pulse generating unit 32 for outputting pulse signals
to the DC/AC conversion unit 22, and a frequency control unit 33
for controlling the frequency of the AC electric current supplied
to the discharge lamp 10. The frequency control unit 33 controls
the frequency of pulses generated by the pulse generating unit
32.
[0064] The circuit structure in the discharge lamp lighting device
1 according to the present embodiment will be described in detail.
Note that the circuit structure in the discharge lamp lighting
device 1 according to the present invention is not limited to this
structure and may be a different circuit structure.
[0065] The step-down chopper unit 21 includes a switching element
Qx, a reactor Lx, a diode Dx, a smoothing capacitor Cx, and a
resistance Rx.
[0066] The switching element Qx is connected, at its one end, to a
positive-side power-supply terminal, which is supplied with a DC
voltage Vdc. The other end of the switching element Qx is connected
to one end of the reactor Lx. The diode Dx is connected, at its
cathode terminal, to the point of connection between the switching
element Qx and the reactor Lx, and is connected to a negative-side
power-supply terminal at its anode terminal. The smoothing
capacitor Cx is connected, at its one end, to an output-side
terminal of the reactor Lx. The other end of the smoothing
capacitor Cx (its negative-side terminal) is connected to an
output-side terminal of the resistance Rx. The resistance Rx is
connected between the negative-side terminal of the smoothing
capacitor Cx and the anode terminal of the diode Dx, and realizes
an electric current detecting function.
[0067] The switching element Qx is driven by a gate signal Gx which
is outputted from the electric power control unit 31. Depending on
the duty of the gate signal Gx, the step-down chopper unit 21
reduces the input DC voltage Vdc to a voltage corresponding to this
duty and outputs the reduced voltage to the DC/AC conversion unit
22 in the subsequent stage.
[0068] The DC/AC conversion unit 22 includes switching elements Q1
to Q4 which are connected to each other in a bridge shape (a
full-bridge circuit).
[0069] The switching element Q1 is driven by a gate signal G1 which
is outputted from a driver 22a. Similarly, the switching element Q2
is driven by a gate signal G2, the switching element Q3 is driven
by a gate signal G3, and the switching element Q4 is driven by a
gate signal G4. The driver 22a outputs the gate signals to the
combination of the switching elements Q1 and Q4 and the combination
of the switching elements Q2 and Q3 which are placed diagonally, in
such away as to alternately turn them on and off. Thus, an AC
voltage with a rectangular wave shape is generated, between the
point of connection between the switching elements Q1 and Q2 and
the point of connection between the switching elements Q3 and
Q4.
[0070] The starter unit 23 includes a coil Lh and a capacitor Ch.
At the time of starting the discharge lamp 10, the DC/AC conversion
unit 22 applies, thereto, an AC voltage having a switching
frequency (for example, several hundreds kHz) which is close to the
resonance frequency of the LC serial circuit including the coil Lh
and the capacitor Ch, thereby creating a high voltage necessary for
starting the discharge lamp 10 in the secondary side of the starter
unit 23. Thus, the high voltage is supplied to the discharge lamp
10. Further, after the discharge lamp 10 has been lighted, the
frequency of the AC voltage supplied from the DC/AC conversion unit
22 is shifted to a normal frequency (for example, 1 Hz to 1000 Hz),
thereby performing normal lighting.
[0071] Further, in the aforementioned circuit, the frequency of the
AC voltage supplied to the starter unit 23 can be successfully
changed by adjusting a cycle of switching between turning on and
off the combination of the switching elements Q1 and Q4 and the
combination of the switching elements Q2 and Q3 in the DC/AC
conversion unit 22. Further, the peak value of the AC voltage
supplied to the starter unit 23 can be successfully changed by
adjusting the operation duty of the switching element Qx in the
step-down chopper unit 21.
[0072] Namely, the switching element Qx in the step-down chopper
unit 21 is turned on and off at a switching frequency corresponding
to the duty of the gate signal Gx which is outputted from the
electric power control unit 31, thereby changing the electric power
supplied to the discharge lamp 10. For example, when the electric
power supplied to the discharge lamp 10 is increased, the electric
power control unit 31 performs control for decreasing the duty of
the gate signal Gx in such a way as to attain a desired electric
power value.
[0073] The structure of the discharge lamp lighting device 1
according to the present embodiment is as described above. Next,
with reference to FIGS. 5 to 9, the discharge lamp lighting device
1 according to the present embodiment will be described, regarding
control thereof and effects provided thereby.
[0074] As illustrated in FIG. 5, the control unit 3 controls the
frequency of the AC electric current supplied to the discharge lamp
10 from the feeding unit 2, in predetermined control manners.
Overall, the control unit 3 performs control in different manners,
within basic terms T10 (T10a, T10b, T10c, . . . ) and
lower-frequency terms T20 (T20a, T20b, . . . ) which are
alternately repeated. Further, within the basic terms T10 (in FIG.
5, T10b is illustrated), the control unit 3 performs control in
different manners, within fixation terms (also referred to as
"first terms" in the present invention) T1 (T1a, T1b, T1c, T1d, . .
. ) and variation terms (also referred to as "second terms" in the
present invention) T2 (T2a, T2b, T2c, T2d, . . . ) which are
alternately repeated.
[0075] At first, with reference to FIGS. 5 to 8, the control within
the basic terms T10 including fixation terms T1 and variation terms
T2, which are alternately repeated, will be described.
[0076] Within the fixation terms (the first terms), the control
unit 3 controls the frequency of the AC electric current such that
the frequency of the AC electric current becomes a predetermined
single frequency out of plural set fixed frequencies f1. Namely,
within the fixation terms T1, the control unit 3 controls the
frequency of the AC electric current, in such a way as to select a
predetermined single frequency out of the plural set fixed
frequencies f1. Accordingly, within the respective fixation terms
T1a to T1d, the fixed frequencies f1 are set to be respective ones
of the fixed frequencies f1a to f1d.
[0077] In the present embodiment, four frequencies are set as the
plural fixed frequencies f1. More specifically, the first to fourth
fixed frequencies f1a to f1d are set to be 960 Hz, 480 Hz, 240 Hz
and 120 Hz, respectively. Note that the fixed frequency f1 is
varied for each fixation terms T1, based on data independent of
data about operations of the discharge lamp 10 (the voltage value,
the current value, the luminance, the distance between the
electrodes, the temperature and the like), such as data which has
been preliminarily obtained from experiments and the like.
[0078] Further, in the present embodiment, the fixed frequencies f1
(f1a to f1d) within the fixation terms T1 (T1a to T1d) are
continuously varied, such that they are made gradually smaller.
More specifically, when the fixed frequency f1 within a certain
fixation term T1 (T1a) is the first fixed frequency f1a, the fixed
frequency f1 within the next fixation term T1 (T1b) is the second
fixed frequency f1b. Here, a certain fixed frequency f1 can be
successively continued through two or more fixation terms T1. For
example, when the fixed frequency f1 within a certain fixation term
T1 (T1a) is the first fixed frequency f1a, the fixed frequency f1
within the next fixation term T1 (T1b) may be, again, the first
fixed frequency f1a.
[0079] Further, within each of the variation terms (the second
terms) T2, the control unit 3 controls the frequency of the AC
electric current, based on the electric current and the fixed
frequency f1 within the previous fixation term T1, such that the
frequency of the AC electric current becomes a varied frequency f2
which is smaller than this fixed frequency f1. More specifically,
as illustrated in FIG. 6, the control unit 3 sets the varied
frequency f2 within each variation term T2 to be the result of
calculation on the fixed frequency f1 within the previous fixation
term T1 with a multiplying factor based on the electric current
within the previous fixation term T1.
[0080] Note that, as the electric current within the previous
fixation term T1, it is possible to employ, for example, an average
electric current, an initial electric current within the fixation
term T1, and a last electric current within the fixation term T1,
and the like. Further, in the present embodiment, instead of the
electric current within the previous fixation term T1, it is also
possible to employ the voltage within the previous fixation term
T1, which correlates with this electric current. This is because
the discharge lamp 10 is controlled with constant electric power.
In FIG. 5, the voltage within each of the fixation terms T1a to T1d
is set to be 85 V, and each of varied frequencies f2a to f2d is set
to be a frequency which is 1/3 time the fixed frequency f1a, f1b,
f1c or f1d within the previous fixation terms T1a to T1d, as
illustrated in FIG. 6.
[0081] On the other hand, the areas in the electrodes 12 from which
the metal is evaporated and the positions on the electrodes 12 to
which the evaporated metal is returned depend on the temperature of
the electrodes 12. For example, the temperature of the electrodes
12 which permits the metal to evaporate therefrom is about 3000 K,
and the temperature of the positions on the electrodes 12 to which
the evaporated metal is returned is about 2500 K. Further, the
temperature of the electrodes 12 depends on the electric current
and the frequency of the AC electric current supplied to the
discharge lamp 10.
[0082] Within the fixation terms T1, the electric current is hardly
changed during these fixation terms T1. Therefore, as the frequency
decreases, the positions on the electrodes 12 which reach a
predetermined temperature (for example, 2500 K) get closer to the
base ends. For example, as illustrated in FIG. 7, in the case of
the first fixed frequency (960 Hz) which is a higher frequency, the
position on the electrode 12 to which the metal returns are P1. In
the case of the fourth fixed frequency (120 Hz) which is a lower
frequency, the positions on the electrodes 12 to which the metal
returns are P2, which are apart from the protruding portion
12c.
[0083] Further, within the variation terms T2, similarly, in cases
where the electric current is constant, as the frequency decreases,
the areas in the electrodes 12 which reach a predetermined
temperature (for example, 3000 K) are spread to get closer to the
base ends. More specifically, in the case of the first varied
frequency (320 Hz) f2a which is a higher frequency, the positions
on the electrodes 12 from which the metal can evaporate are limited
to P1. In the case of the fourth varied frequency (40 Hz) f2d which
is a lower frequency, the positions on the electrodes 12 from which
the metal can evaporated are P1 and P2 and, namely, are spread up
to the positions of P2.
[0084] Accordingly, within the fixation terms T1, the fixed
frequency f1 is varied for each fixation term T1, based on data
independent of data about operations of the discharge lamp 10.
Consequently, the metal evaporated from the electrodes 12 is
allowed return to desired positions on the electrodes 12. Further,
within each of the variation terms (the second terms) T2, since the
varied frequency f2 is set to correspond to the electric current
and the fixed frequency f1 within the previous fixation term T1,
evaporating, again, the metal returned during the previous fixation
term T1 is allowed. Thus, the shape of the electrodes 12 can be
maintained.
[0085] Further, as illustrated in FIG. 8, the time periods of the
fixation terms T1 are varied. More specifically, the time periods
of the fixation terms T1 are varied with the time period for which
the discharge lamp 10 is lighted. In the present embodiment, along
with the time period for which the discharge lamp 10 is lighted, a
term within which the time periods of the fixation terms T1 are
shorter, a term within which the time periods of the fixation terms
T1 are gradually made longer, and a term within which the time
periods of the fixation terms T1 are gradually retuned to be
shorter are repeated.
[0086] Since the time periods of the fixation terms T1 are varied,
as described above, the frequency of evaporation of the metal from
the electrodes 12 is varied. More specifically, the terms within
which the time periods of the fixation terms T1 are shorter make
the frequency of the variation terms T2 larger and, therefore,
mainly function as terms for evaporating the metal from the
electrodes 12. On the other hand, the terms within which the time
periods of the fixation terms T1 are varied (made longer) make the
frequency of the variation terms T2 smaller and, therefore, mainly
function as terms for returning the metal to the electrodes 12.
Consequently, the terms within which the metal evaporates from the
electrodes 12 and the terms within which the metal returns to the
electrodes 12 are distinctive, which enables effectively performing
the halogen cycle.
[0087] On the other hand, if the time periods of the fixation terms
T1 are abruptly varied (made longer), the metal simultaneously
returns to the electrodes 12, thereby making it impossible to
sufficiently evaporate the metal from the electrodes 12. On the
contrary, in the present embodiment, the time periods of the
fixation terms T1 are gradually varied (made longer), which causes
the metal to gradually return to the electrodes 12, while gradually
evaporating the metal from the electrodes 12. Consequently, the
halogen cycle is more effectively performed.
[0088] The time periods of the fixation terms T1 may be set to be
constant. Further, the time periods of the variation terms T2 are
preferably set such that the variation frequencies f2 provide at
least one period. Further, the time periods of the variation terms
T2 can be set such that the variation frequencies f2 provide a
constant period. Also, the time periods of the variation terms T2
can be set to be either a constant time period or varying time
periods.
[0089] Next, with reference to FIGS. 5 and 9, the control of
lower-frequency terms T20, which are repeated alternately with the
basic terms T10, will be described.
[0090] As illustrated in FIG. 5, within each lower-frequency term
T20, the control unit 3 controls the frequency of the AC electric
current such that the frequency of the AC electric current becomes
a frequency f20 which is lower than the lowest frequency within the
previous basic term T10. More specifically, as illustrated in FIG.
9, the control unit 3 sets the frequency f20 within each
lower-frequency term T20 to be the result of calculation on the
lowest fixed frequency f1 within the fixation terms T1 in the
previous basic term T10, in which the calculation is made with a
multiplying factor based on the electric current within the
previous basic term T10.
[0091] In the present embodiment, instead of the electric current
within the previous basic term T10, it is also possible to employ
the voltage within the previous basic term T10, which correlates
with this electric current. This is because the discharge lamp 10
is controlled with constant electric power. In FIG. 5, the voltage
within each basic term T10a to T10c is set to be 85 V, and the
frequency f20a, f20b in each lower-frequency term T20a, 20b is set
to be a frequency which is 1/12 time the lowest fixed frequency f1
within the fixation terms T1 in the previous basic term T10a, T10b,
as illustrated in FIG. 9.
[0092] With this structure, the frequency f20 within each
lower-frequency term T20 is lower than the lowest frequency within
the previous basic term T10. This enables evaporating, from the
electrodes 12, even the metal returned to positions on the
electrodes 12 from which the metal can not be evaporated within the
variation terms T2 in the basic terms T10, namely the base end
portions of the electrodes 12 (for example, the positions closer to
the base ends than the position of P2 in FIG. 7).
[0093] The time periods of the lower-frequency terms T20 are
preferably set such that the frequencies f20 provide at least one
period. Further, the time periods of the lower-frequency terms T20
can be set such that the frequencies f20 provide a constant period.
Also, the time periods of the lower-frequency terms T20 can be set
to be either a constant time period or varying time periods.
[0094] The varied frequencies f2a to f2d are set to be frequencies
provided by multiplying the fixed frequencies f1a to f1d by the
inverse of a natural number. Further, the frequencies f20 within
the lower-frequency terms T20 are set to be frequencies provided by
multiplying the fixed frequencies f1a to f1d by the inverses of
natural numbers.
[0095] On the other hand, the plural fixed frequencies f1a to f1d
to be set within the fixation terms T1 are set to be respective
frequencies provided by multiplying the highest frequency f1a out
of these plural fixed frequencies f1a to f1d by the inverses of
respective natural numbers. More specifically, the fixed
frequencies f1a to f1d are 960 Hz, 480 Hz, 240 Hz and 120 Hz,
respectively, which are 1/1 time, 1/2 time, 1/4 time and 1/8 time
the highest fixed frequency f1a, respectively.
[0096] This means that the varied frequencies f2a to f2d and the
frequencies f20 in the lower-frequency terms T20 are set to be
frequencies provided by multiplying the highest frequency f1a by
the inverses of respective natural numbers. As described above, all
the frequencies f1, f2 and f20 are set to be frequencies provided
by multiplying the highest frequency f1a by the inverses of
respective natural numbers, which makes it easier to synchronize
signals of the projection-device main body 102 (for example,
vertical synchronization signals) and signals of the light source
device 101 (for example, polarity inversion signals), with each
other.
[0097] Next, effects of the discharge lamp lighting device 1
according to the present embodiment will be describe with reference
to FIG. 10.
EXAMPLES
Examples and Comparative Examples 1 to 2
[0098] An example is the discharge lamp lighting device 1 according
to the aforementioned embodiment illustrated in FIGS. 1 to 9.
[0099] A comparative example 1 is a discharge lamp lighting device
adapted to control the frequency of the AC electric current, using
fixation terms having a single fixed frequency, and lower-frequency
terms.
[0100] A comparative example 2 is a discharge lamp lighting device
adapted to control the frequency of the AC electric current, using
fixation terms having plural fixed frequencies.
<Methods for Experiments>
[0101] Tests for lighting of the discharge lamp 10 were conducted,
using the discharge lamp lighting devices according to the example
and the respective comparative examples. As the lighting tests, a
short-arc type discharge lamp with a rated electric power of 250 W
was lighted for 5000 hours. While the lamp is lighted, the lamp
voltage in the discharge lamp 10 was measured.
<Results of Experiments>
[0102] In the case of the discharge lamp 10 according to the
comparative example 1, the lamp voltage was 70 Vat the beginning of
lighting. Further, the lamp voltage was 90 V when the lighting time
period reached 3000 hours, and the lamp voltage was 130 V when the
lighting time period reached 5000 hours.
[0103] In the case of the discharge lamp 10 according to the
comparative example 2, the lamp voltage was 70 Vat the beginning of
lighting. Further, the lamp voltage already had exceeded 90 V when
the lighting time period reached 3000 hours, and the lamp voltage
was 127 V when the lighting time period reached 5000 hours.
[0104] On the contrary, in the case of the discharge lamp 10
according to the example, the lamp voltage was 70 V at the
beginning of lighting. Further, the lamp voltage was 84 V even when
the lighting time period reached 5000 hours.
[0105] As described above, in the respective comparative examples,
as the lighting time period was increased, the electrodes 12
changed in shape and, therefore, the lamp voltage was made
significantly larger. On the contrary, in the example, even when
the lighting time period was made longer, the electrodes 12 were
maintained in shape, which inhibited the lamp voltage from being
made larger. Accordingly, in the example, it was possible to
elongate the time period for which the electrodes 12 could be
maintained in shape, thereby elongating the life of the discharge
lamp 10.
[0106] As described above, with the discharge lamp lighting device
1 according to the present embodiment, the feeding unit 2 supplies
the AC electric current to the discharge lamp 10 having the pair of
electrodes 12 placed to oppose each other within the discharge
container 11 which encloses predetermined gasses. The control unit
3 controls the frequency of the AC electric current supplied to the
discharge lamp 10 from the feeding unit 2, in the different
manners, within the fixation terms (the first terms) T1 and the
variation terms (the second terms) T2 which are alternately
repeated.
[0107] At first, within the fixation terms (the first terms) T1,
the control unit 3 controls the frequency of the AC electric
current such that the frequency of the AC electric current becomes
one fixed frequency f1 out of the plural set fixed frequencies f1a
to f1d. On the other hand, the positions on the electrodes 12 to
which the metal evaporated from the electrodes 12 returns depend on
the temperature of the electrodes 12. Further, the temperature of
the electrodes 12 depends on the fixed frequencies f1 within the
fixation terms (the first terms) T1 and the electric current within
the fixation terms (the first terms) T1.
[0108] Therefore, within each of the variation terms (the second
terms) T2, the control unit 3 controls the frequency of the AC
electric current, based on the electric current and the fixed
frequency f1 within the previous fixation term (the first term) T1,
such that the frequency of the AC electric current becomes the
varied frequency f2 which is lower than the fixed frequency f1.
Consequently, the positions on the electrodes 12 to which the
evaporated metal returns within the previous fixation terms (the
first terms) T1 are accurately figured out.
[0109] Accordingly, within the variation terms (the second terms)
T2, it is possible to supply the AC electric current with a
frequency suitable thereto, to the discharge lamp 10. Therefore,
even when the discharge lamp 10 is lighted for a longer time
period, it is possible to maintain the shape of the electrodes 12
(particularly, the protruding portions 12c). This can elongate the
time period for which the shape of the electrodes 12 can be
maintained.
[0110] The discharge lamp lighting device of the present invention
is not limited to the configuration of the embodiment described
above, and the effects are not limited to those described above. It
goes without saying that the discharge lamp lighting device of the
present invention can be variously modified without departing from
the scope of the subject matter of the present invention. For
example, the constituents, methods, and the like of various
modified examples described below may be arbitrarily selected and
employed as the constituents, methods, and the like of the
embodiments described above, as a matter of course.
[0111] In the discharge lamp lighting device 1 according to the
aforementioned embodiment, the control unit 3 is structured to
control the frequency of the AC electric current such that the
frequency of the AC electric current becomes a predetermined single
frequency out of the plural set frequencies f1a to f1d, within the
fixation terms (the first terms) T1. However, the the discharge
lamp lighting device 1 according to the present invention is not
limited to this structure. For example, in the the discharge lamp
lighting device 1 according to the present invention, the control
unit 3 can be also structured to control the frequency of the AC
electric current such that the frequency of the AC electric current
becomes predetermined two frequencies out of the plural set
frequencies f1a to f1d, within the fixation terms (the first terms)
T1, as illustrated in FIGS. 11 and 12.
[0112] According to the control method in FIG. 11, within each of
the variation terms (the second terms) T2, the control unit 3
controls the frequency of the AC electric current, based on the
fixed frequency f1a having a largest time ratio within the previous
fixation term (the first term) T1 and based on the electric current
within this fixation term T1, such that the frequency of the AC
electric current becomes a varied frequency f2 which is lower than
this frequency f1a. Referring to FIG. 11, the time period Tf1a of
the first fixed frequency f1a is longer than the time periods Tf1b
to Tf1d of the other fixed frequencies f1b to f1d. Further, the
calculation of the varied frequency f2 can be also the same as the
calculation according to the aforementioned embodiment (see FIG.
6).
[0113] With this control method, within the fixation terms T1, the
metal returns in a larger amount to the positions on the electrodes
12 to which the metal returns at the first fixed frequency f1a.
Accordingly, within the variation terms T2, it is possible to
supply the AC electric current with a frequency suitable to these
positions. Accordingly, even when the discharge lamp 10 is lighted
for a longer time period, it is possible to maintain the shape of
the electrodes 12 (particularly, the protruding portions 12c). This
can elongate the time period for which the shape of the electrodes
12 can be maintained.
[0114] Further, referring to FIG. 12, within each of the variation
terms (the second terms) T2, the control unit 3 controls the
frequency of the AC electric current, based on the lowest fixed
frequency f1d within the previous fixation term (the first term) T1
and based on the electric current within this fixation term T1,
such that the frequency of the AC electric current becomes a varied
frequency f2 which is lower than this frequency f1d. Referring to
FIG. 12, the frequency of the fourth fixed frequency f1d is longer
than those of the other fixed frequencies f1a to f1c. Further, the
calculation of the varied frequency f2 can be also the same as the
calculation according to the aforementioned embodiment (see FIG.
6).
[0115] According to this control method, within the fixation terms
T1, at the fourth fixed frequency f1d, the metal returns to
positions on the electrodes 12 which are closest to the base ends
(apart from the protruding portions 12c). Accordingly, within the
variation terms T2, it is possible to supply the AC electric
current with a frequency suitable to these positions. Accordingly,
even when the discharge lamp 10 is lighted for a longer time
period, it is possible to maintain the shape of the electrodes 12
(particularly, the protruding portions 12c). This can elongate the
time period for which the shape of the electrodes 12 can be
maintained.
[0116] Further, the discharge lamp lighting device 1 according to
the aforementioned embodiment is structured such that the plural
fixed frequencies f1a to f1d to be set within the fixation terms
(the first terms) T1 are set to be respective frequencies provided
by multiplying the highest frequency f1a out of these plural fixed
frequencies f1a to f1d by the inverses of respective natural
numbers. However, the discharge lamp lighting device 1 according to
the present invention is not limited to this structure.
Furthermore, the number of plural set fixed frequencies is not
limited to four and can be also two, three, five or more.
[0117] Further, the discharge lamp lighting device 1 according to
the aforementioned embodiment is structured such that the varied
frequencies f2 within the variation terms (the second terms) T2 are
set to be frequencies provided by multiplying the highest frequency
f1a out of the plural fixed frequencies f1a to f1d to be set within
the fixation terms (the first terms) T1 by the inverses of natural
numbers. However, the discharge lamp lighting device 1 according to
the present invention is not limited to this structure. For
example, in the discharge lamp lighting device 1 according to the
present invention, as illustrated in FIG. 13, the control unit 3
can be also structured to set the varied frequency f2 within each
of the variation terms (the second terms) T2 to be the result of
calculation on the fixed frequency f1 within the previous fixation
term T1 with a multiplying factor based on the electric current
within the previous fixation term T1.
[0118] Further, the discharge lamp lighting device 1 according to
the aforementioned embodiment is structured such that the
frequencies f20 within the lower-frequency terms is set to be
frequencies provided by multiplying the highest frequency f1a out
of the plural fixed frequencies f1a to f1d to be set within the
fixation terms (the first terms) T1 by the inverses of natural
numbers. However, the discharge lamp lighting device according to
the present invention is not limited to this structure. For
example, in the discharge lamp lighting device 1 according to the
present invention, as illustrated in FIG. 14, the control unit 3
can be also structured to set the frequency f20 within each of the
lower-frequency terms T20 to be the result of calculation on the
lowest fixed frequency f1 within the fixation terms T1 within the
previous basic term T10 with a multiplying factor based on the
electric current within the previous basic term T10.
[0119] Further, the discharge lamp lighting device 1 according to
the aforementioned embodiment is structured to vary the fixed
frequency f1 selected for each fixation term T1, based on data
independent of data about operations of the discharge lamp 10,
within the fixation terms T1. However, the discharge lamp lighting
device according to the present invention is not limited to this
structure. For example, the discharge lamp lighting device
according to the present invention can be also structured to vary
the fixed frequency f1 selected for each fixation term T1, based on
data which depends of data about operations of the discharge lamp
10 (the voltage value, the electric current value, the luminance,
the distance between the electrodes, the temperature and the like),
within the fixation terms T1.
[0120] Further, the discharge lamp lighting device 1 according to
the aforementioned embodiment is structured to alternately repeat
the basic terms T10 and the lower-frequency terms T20. For example,
the discharge lamp lighting device according to the present
invention can be also structured to insert, through interruption,
the lower-frequency terms T20 into the basic terms T10 or to
insert, through overwriting, the lower-frequency terms T20 into the
basic terms T10, through control programs.
[0121] Further, the discharge lamp lighting device 1 according to
the aforementioned embodiment is structured to alternately repeat
the fixation terms (the first terms) T1 and the variation terms
(the second terms) T2. For example, the discharge lamp lighting
device according to the present invention can be also structured to
insert, through interruption, the variation terms (the second
terms) T2 into the fixation terms (the first terms) T1 or to
insert, through overwriting, the variation terms (the second terms)
T2 into the fixation terms (the first terms) T1, through control
programs.
DESCRIPTION OF REFERENCE SIGNS
[0122] 1 Discharge lamp lighting device [0123] 2 Feeding unit
[0124] 3 Control unit [0125] 10 Discharge lamp [0126] 11 Discharge
container [0127] 12 Electrode [0128] 12a Head portion [0129] 12b
Shaft portion [0130] 12c Protruding portion [0131] 13 Sealing
portion [0132] 14 Metal foil [0133] 15 Outer lead [0134] 21
Step-down chopper unit [0135] 22 DC/AC conversion unit [0136] 22a
Driver [0137] 23 Starter unit [0138] 31 Electric power control unit
[0139] 32 Pulse generating unit [0140] 33 Frequency control unit
[0141] 100 Image projection device [0142] 101 Light source device
[0143] 102 Projection-device main body [0144] 103 Optical fiber
[0145] 104 Screen [0146] T1 First term (fixation term) [0147] T2
Second term (variation term) [0148] T10 Basic term [0149] T20
Lower-frequency term
* * * * *