1. A power supply apparatus for obtaining a direct current voltage from an alternating voltage source, comprising:
a rectification smoothing unit electrically connected to the alternating voltage source for rectifying and smoothing an alternating current voltage from the alternating voltage source;
a first DCDC converter for converting the direct current voltage from the rectification smoothing unit and outputting a first direct current voltage;
a second DCDC converter, receiving the first direct current voltage from the first DCDC converter, for outputting a second direct current voltage lower than the first direct current voltage through switching operation of a switching unit; and
a transit unit for making a transit to a state in which an output voltage of the first DCDC converter decreases from the first direct current voltage to a third direct current voltage lower than the second direct current voltage and the switching unit of the second DCDC converter is driven in a continuously-conducting state.
2. A power supply apparatus according to claim 1, wherein the transit unit includes a differential amplifier, detecting the output voltage of the first DCDC converter, for performing feedback, resistors for dividing at least one of a reference voltage of the differential amplifier and the detected voltage, and a unit for switching between the resistors, and wherein the transit unit changes the output voltage of the first DCDC converter from the first direct current voltage to the third direct current voltage by using the unit for dividing.
3. A power supply apparatus according to claim 1, wherein the transit unit includes a unit for controlling the first DCDC converter such that the output voltage of the second DCDC converter settles on the third direct current voltage.
4. A power supply apparatus according to claim 1, wherein the first DCDC converter is constructed in an RCC-type power supply apparatus having a start-up resistor, and
wherein the power supply apparatus further comprises a unit for switching the start-up resistor to change the output voltage of the first DCDC converter to the third direct current voltage lower than the second direct current.
5. A power supply apparatus according to claim 1, further comprising a load switch for supplying and checking the first direct current voltage, which is the output voltage of the first DCDC converter, to a load, wherein
after the load switch is turned off to check the first direct current voltage to the load, the output voltage of the first DCDC converter is reduced to the third direct current voltage.
6. A power supply apparatus according to claim 1, further comprising a load switch for supplying and checking the first direct current voltage, which is the output voltage of the first DCDC converter, to a load, wherein
when the load switch is to turn on, the output voltage of the first DCDC converter is returned to the first direct current voltage and the load switch is then turned on.
7. An image forming apparatus comprising:
a driving part driven to form an image;
a control part for controlling operation of the driving part; and
a power supply part for obtaining a direct current voltage from an alternating voltage source to operate the driving part and the control part, the power supply part including:
a rectification smoothing unit electrically connected to the alternating voltage source for rectifying and smoothing an alternating current voltage from the alternating voltage source;
a first DCDC converter for converting the direct current voltage from the rectification smoothing unit and outputting a first direct current to the driving part;
a second DCDC converter, receiving the first direct current from voltage the first DCDC converter, for outputting to the control part a second direct current voltage lower than the first direct current voltage through switching operation of a switching unit; and
a transit unit for making a transit to a state in which an output voltage of the first DCDC converter decreases from the first direct current voltage to a third direct current voltage lower than the second direct current voltage and the switching unit of the second DCDC converter is driven in a continuously-conducting state, when the image forming apparatus is brought into an energy-saving mode in response to a command from the control part.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
What is claimed is:
1. A projection display, comprising:
a light source unit which comprises a light source and a reflector;
an illumination optics unit for converting a light beam emission from the light source unit into approximately parallel light rays;
a video display device for generating an optical image by modulating a light beam emission from the illumination optics unit in accordance with a video signal;
a projection unit for projecting image light which is received from the video display device; and
a variable aperture having at least a first state in which the light beam emission is blocked in accordance with the visibility angle characteristic of the video display device and a second state in which the aperture is maximized, and making a plurality of image brightnesscontrast combinations selectable.
2. The projection display according to claim 1, further comprising:
an aperture status detector which detects the status of said variable aperture;
a cooling fan for cooling the interior of said projection display; and
an adjustment circuit which makes electrical characteristics adjustments of said video display device, including a color temperature characteristic, gamma characteristic, or color irregularity correction,
wherein either or both the revolving speed of said cooling fan and said adjustment circuit are controlled in accordance with the results of detection by said aperture status detector.
3. The projection display according to claim 2, wherein said cooling fan is controlled to increase the revolving speed when said variable aperture is maximized and decrease the revolving speed when said variable aperture is reduced.
4. The projection display according to claim 1, further comprising:
an aperture status setting unit which sets the status of said variable aperture;
a cooling fan for cooling the interior of said projection display; and
an adjustment circuit which makes electrical characteristics adjustments of said video display device, including a color temperature characteristic, gamma characteristic, or color irregularity correction,
wherein either or both the revolving speed of said cooling fan and said adjustment circuit are controlled in accordance with a setting selected by said aperture status setting unit.
5. The projection display according to claim 4, wherein said cooling fan is controlled to increase the revolving speed when said variable aperture is maximized and decrease the revolving speed when said variable aperture is reduced.
6. The projection display according to claim 4, wherein said variable aperture comprises an electrical light beam block device.
7. The projection display according to claim 1, wherein said illumination optics unit comprises an array lens group which comprises a first array lens and a second array lens, a polarization changer device for aligning light rays in a specified polarization direction, and a condensing lens for condensing light rays, and wherein said variable aperture is positioned at a location between said light source unit and said first array lens, between said first array lens and said second array lens, between said second array lens and said polarization changer device, or between said polarization changer device and said condensing lens.
8. The projection display according to claim 1, wherein said variable aperture lies between said light source unit and said first array lens, and comprises a reflection mirror for reflecting light rays from said light source unit.
9. The projection display according to claim 8, wherein said reflector is shaped like a paraboloid of revolution.
10. The projection display according to claim 1, wherein said variable aperture is either in a first shape which results when the size of a light beam is reduced from the periphery in accordance with the visibility angle characteristic of said video display device or in a second shape which is substantially similar to said first shape and different from said first shape in area.
11. The projection display according to claim 1, wherein said variable aperture is in a first shape, in a second shape, or in a third shape, and wherein said first shape results when the size of a light beam is reduced from the periphery in accordance with the visibility angle characteristic of said video display device; said second shape is substantially similar to said first shape and different from said first shape in area; and said third shape results when said variable aperture is maximized.
12. A projection display, comprising:
a light source unit which comprises a light source and a reflector;
an illumination optics unit for converting a light beam emission from the light source unit into approximately parallel light rays;
a video display device for generating an optical image by modulating a light beam emission from the illumination optics unit in accordance with a video signal;
a projection unit for projecting image light which is received from the video display device; and
a plurality of variable apertures having at least a first state in which said light beam emission is blocked in accordance with the visibility angle characteristic of said video display device and a second state in which the aperture is maximized, and making a plurality of image brightnesscontrast combinations selectable.
13. The projection display according to claim 11, further comprising:
an aperture status setting unit which sets the status of said variable aperture;
a cooling fan for cooling the interior of said projection display; and
an adjustment circuit which makes electrical characteristics adjustments of said video display device, including a color temperature characteristic, gamma characteristic, or color irregularity correction,
wherein either or both the revolving speed of said cooling fan and said adjustment circuit are controlled in accordance with a setting selected by said aperture status setting unit.
14. The projection display according to claim 12, wherein said cooling fan is controlled to increase the revolving speed when said variable aperture is maximized and decrease the revolving speed when said variable aperture is reduced.
15. The projection display according to claim 12, wherein said variable aperture comprises an electrical light beam block device.
16. The projection display according to claim 12, wherein said illumination optics unit comprises an array lens group which comprises a first array lens and a second array lens, a polarization changer device for aligning light rays in a specified polarization direction, and a condensing lens for condensing light rays, and wherein said plurality of variable apertures are positioned at a plurality of different locations between said light source unit and said first array lens, between said first array lens and said second array lens, between said second array lens and said polarization changer device, or between said polarization changer device and said condensing lens.
17. The projection display according to claim 12, comprising at least a first variable aperture and a second variable aperture, wherein said first variable aperture is positioned between said light source unit and said first array lens; said second variable aperture is positioned between said first array lens and said second array lens; and said first variable aperture has a larger opening area than said second variable aperture.
18. A projection display, comprising:
a light source unit which comprises a light source and a reflector;
an illumination optics unit for converting a light beam emission from the light source unit into approximately parallel light rays;
a video display device for generating an optical image by modulating a light beam emission from the illumination optics unit in accordance with a video signal;
a projection unit for projecting image light which is received from the video display device;
a variable aperture having at least a first state in which said light beam emission is blocked in accordance with the visibility angle characteristic of said video display device and a second state in which the aperture is maximized; and
a photoelectric conversion device for detecting the amount of light,
wherein the status changeover of said variable aperture is controlled in accordance with the amount of light detected by the photoelectric conversion device.
19. The projection display according to claim 18, further comprising a cooling fan for cooling the interior of said projection display, wherein the revolving speed of the cooling fan is controlled in accordance with the amount of light detected by said photoelectric conversion device.
20. The projection display according to claim 18, wherein said variable aperture comprises an electrical light beam block device.