Patent Publication Number: US-2010127630-A1

Title: Lamp lighting device and projector type picture display device using same

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a lamp lighting device and a projector type picture display device using such a lamp lighting device, in particular, a lamp lighting device for lighting up a selected one of a plurality of discharge lamps, and a projector type picture display device using such a lamp lighting device. 
     2. Description of the Background Art 
     Conventionally, there is a liquid crystal projector having one power source, two halogen lamps, and a switching circuit. In the liquid crystal projector, one of the two halogen lamps and the power source are connected to each other by the switching circuit. When the halogen lamp is dead, the switching circuit connects the other halogen lamp to the power source. Thus, in the liquid crystal projector, the halogen lamps can be switched readily and promptly (for example, see Japanese Patent Laying-Open No. 4-104583). 
     In recent years, in liquid crystal projectors, halogen lamps are being replaced with discharge lamps such as high pressure mercury lamps. This is because a discharge lamp, which employs arc discharge, provides higher brightness, consumes less power, and has a longer life than a halogen lamp, which employs a filament. Also in such a liquid crystal projector employing discharge lamps, two discharge lamps and a switching circuit are desirably provided to achieve easy and prompt switching between the discharge lamps, as with the above-described patent document. 
     However, a discharge lamp is provided with a trigger electrode for applying a pulse of high voltage to start discharge, and a main electrode for applying an alternating-current voltage to maintain the discharge. In order to provide a high voltage to a selected one of two discharge lamps, a switching circuit with high breakdown voltage needs to be used. This may result in upsizing, increased cost, and decreased reliability of the switching circuit. 
     SUMMARY OF THE INVENTION 
     In view of this, a main object of the present invention is to provide a small, low-cost, and highly reliable lamp lighting device capable of lighting up a selected one of a plurality of discharge lamps, and a projector type picture display device using such a lamp lighting device. 
     A lamp lighting device according to the present invention serves to light up a selected discharge lamp of a plurality of discharge lamps each having a trigger electrode and a main electrode, and includes: a pulse generating circuit outputting a starting pulse voltage; a plurality of step-up circuits, respectively provided corresponding to the plurality of discharge lamps and each having an output terminal connected to a trigger electrode of a corresponding discharge lamp, and each stepping up a voltage received at its input terminal and outputting the voltage to the output terminal; an alternating-current power source outputting an alternating-current voltage; and a switching circuit providing the starting pulse voltage output from the pulse generating circuit, to an input terminal of a step-up circuit corresponding to the selected discharge lamp, and providing the alternating-current voltage output from the alternating-current power source, to a main electrode of the selected discharge lamp. 
     Preferably, the switching circuit includes a plurality of relays provided corresponding to the plurality of discharge lamps respectively. Each of the relays has a first switch, which is connected between an output terminal of the pulse generating circuit and an input terminal of its corresponding step-up circuit and becomes conductive when its corresponding discharge lamp is selected; and a second switch, which is connected between an output terminal of the alternating-current power source and a main electrode of its corresponding discharge lamp and becomes conductive when its corresponding discharge lamp is selected. 
     Further, a projector type picture display device according to the present invention includes: the above-described lamp lighting device; the plurality of discharge lamps; and picture display unit displaying a picture on a screen using light from the selected discharge lamp. 
     In the lamp lighting device according to the present invention, the output terminals of the plurality of step-up circuits are respectively connected to the trigger electrodes of the plurality of discharge lamps, and the switching circuit is provided to provide the input terminal of the step-up circuit corresponding to the selected discharge lamp with the starting pulse voltage output from the pulse generating circuit, and provide the main electrode of the selected discharge lamp with the alternating-current voltage output from the alternating-current power source. As such, each step-up circuit is provided at a stage coming after the switching circuit, and a switching circuit with low breakdown voltage can be therefore used, thus achieving downsizing, reduced cost, and improved reliability of the device. 
     The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a circuit block diagram showing a configuration of a lamp lighting device according to one embodiment of the present invention. 
         FIG. 2  is a block diagram showing a configuration of a lamp voltage generating circuit shown in  FIG. 1 . 
         FIG. 3  shows a major portion of a liquid crystal projector including two high pressure mercury lamps and the lamp lighting device shown in  FIG. 1 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  is a circuit block diagram showing a configuration of a lamp lighting device  1  according to one embodiment of the present invention. In  FIG. 1 , lamp lighting device  1  includes a power source circuit  2 , a lamp voltage generating circuit  3 , a control circuit  4 , relays  5 ,  6 , and step-up transformers  7 ,  8 , and serves to light up a selected one of two high pressure mercury lamps  9 ,  10 . 
     High pressure mercury lamp  9  includes a luminous tube having mercury and argon gas filled therein, a trigger winding  9   a  wound around the luminous tube, and a pair of main electrodes  9   b,    9   c  provided to opposite to each other in the luminous tube. Similarly, high pressure mercury lamp  10  includes a luminous tube, a trigger winding  10   a,  and a pair of main electrodes  10   b,    10   c.  When a high voltage is applied to trigger windings  9   a,    10   a,  glow discharge is started in the luminous tube. When an alternating-current voltage is applied between the pair of main electrodes  9   b,    9   c  or between the pair of main electrodes  10   b,    10   c,  the glow discharge is shifted to arc discharge and light resulting from the arc discharge is emitted from the luminous tube. 
     Power source circuit  2  is controlled by control circuit  4 , and converts a commercial alternating-current voltage to a direct-current voltage VDC 1  of 300-400 V. Lamp voltage generating circuit  3  is controlled by control circuit  4 , and outputs a starting pulse voltage VP for starting discharge of high pressure mercury lamps  9 ,  10 , and an alternating-current voltage VAC for maintaining the discharge. 
     More specifically, as shown in  FIG. 2 , lamp voltage generating circuit  3  includes a down-converter circuit  11 , an inverter circuit  12 , a starting pulse generating circuit  13 , an external signal detecting circuit  14 , a constant power control circuit  15 , a lighting signal output circuit  16 , and output terminals  3   a - 3   d.    
     Down-converter circuit  11  is controlled by constant power control circuit  15 , and steps down the direct-current voltage generated by power source circuit  2 , to generate a direct-current voltage VDC 2  (lamp voltage) of 50-120 V. Inverter circuit  12  generates a pulse voltage VP 0  of 210-230 V and provides it to starting pulse generating circuit  13 , and converts voltage VDC 2  output from down-converter circuit  11  into alternating-current voltage VAC (rectangular wave) for driving a lamp, and outputs alternating-current voltage VAC between output terminals  3   c,    3   d.  In response to pulse voltage VP 0  from inverter circuit  12 , starting pulse generating circuit  13  generates starting pulse voltage VP, and outputs starting pulse voltage VP between output terminals  3   a,    3   b.    
     External signal detecting circuit  14  detects a signal φ 1  supplied from control circuit  4  to instruct turning on/off of a lamp, and a signal φ 2  supplied from control circuit  4  to set a power of the lamp, and provides constant power control circuit  15  with signals φ 1 , φ 2  thus detected. 
     Upon lighting up high pressure mercury lamps  9 ,  10 , the lamp voltage varies greatly and characteristics thereof also vary greatly with passage of time. To accommodate this, constant power control circuit  15  detects lamp voltage VDC 2 , receives from inverter circuit  12  information indicating the lamp current, and controls down-converter circuit  11  to maintain a fixed power consumption of the lamp even when lamp voltage VDC 2  varies. In addition, constant power control circuit  15  outputs a signal φ 3  indicating whether or not the lamp is lit up, a power, a voltage, and the like. Lighting signal output circuit  16  sends signal φ 3  to control circuit  4  or the like. Thus, whether or not the lamp is lit up, the power, the voltage, and the like can be monitored. 
     Referring to  FIG. 1  again, control circuit  4  controls power source circuit  2 , lamp voltage generating circuit  3 , and relays  5 ,  6 . Relay  5  controlled by control circuit  4  includes switches  5   a,    5   b.  Relay  6  controlled by control circuit  4  includes switches  6   a,    6   b.  Step-up transformer  7  includes a primary winding  7   a  and a secondary winding  7   b.  Step-up transformer  8  includes a primary winding  8   a  and a secondary winding  8   b.  Each of step-up transformers  7 ,  8  steps up starting pulse voltage VP of 210-230 V and outputs a high voltage pulse VPH of 7-10 KV. 
     Output terminal  3   a  of lamp voltage generating circuit  3  is connected to the input terminal of primary winding  7   a  of step-up transformer  7  and the input terminal of primary winding  8   a  of step-up transformer  8 . Output terminal  3   b  of lamp voltage generating circuit  3  is connected to the common terminal of windings  7   a,    7   b  of step-up transformer  7  via switch  5   a  of relay  5 , and is connected to the common terminal of windings  8   a,    8   b  of step-up transformer  8  via switch  6 a of relay  6 . The output terminal of secondary winding  7   b  of step-up transformer  7  is connected to trigger winding  9   a  of high pressure mercury lamp  9 , and the output terminal of secondary winding  8   b  of step-up transformer  8  is connected to trigger winding  10   a  of high pressure mercury lamp  10 . 
     Output terminal  3   c  of lamp voltage generating circuit  3  is connected to main electrode  9   b  of high pressure mercury lamp  9  via switch  5   b  of relay  5 , and is connected to main electrode  10   b  of high pressure mercury lamp  10  via switch  6   b  of relay  6 . Output terminal  3   d  of lamp voltage generating circuit  3  is directly connected to main electrode  9   c  of high pressure mercury lamp  9 , and is directly connected to main electrode  10   c  of high pressure mercury lamp  10 . 
     Next, operations of lamp lighting device  1  will be described. When high pressure mercury lamp  9  is selected from high pressure mercury lamps  9 ,  10 , switches  5   a,    5   b  of relay  5  become conductive, and switches  6   a,    6   b  of relay  6  become non-conductive. Starting pulse voltage VP generated by lamp voltage generating circuit  3  is provided to primary winding  7   a  of step-up transformer  7  via switch  5   a  of relay  5 , to generate high voltage pulse VPH at secondary winding  7   b.  When high voltage pulse VPH is applied to trigger winding  9   a  of high pressure mercury lamp  9 , high pressure mercury lamp  9  starts to discharge. Meanwhile, alternating-current voltage VAC generated by lamp voltage generating circuit  3  is applied between main electrodes  9   b,    9   c  of high pressure mercury lamp  9  via switch  5   b  of relay  5 . This maintains the discharge of high pressure mercury lamp  9 , and light resulting from the discharge is emitted accordingly. 
     On the other hand, when high pressure mercury lamp  10  is selected from high pressure mercury lamps  9 ,  10 , switches  6   a,    6   b  of relay  6  become conductive and switches  5   a,    5   b  of relay  5  become non-conductive. Starting pulse voltage VP generated by lamp voltage generating circuit  3  is provided to primary winding  8   a  of step-up transformer  8  via switch  6   a  of relay  6 , to generate high voltage pulse VPH at secondary winding  8   b.  When high voltage pulse VPH is applied to trigger winding  10   a  of high pressure mercury lamp  10 , high pressure mercury lamp  10  starts to discharge. Meanwhile, alternating-current voltage VAC generated by lamp voltage generating circuit  3  is applied between main electrodes  10   b,    10   c  of high pressure mercury lamp  10  via switch  6   b  of relay  6 . This maintains the discharge of high pressure mercury lamp  10 , and light resulting from the discharge is emitted accordingly. 
     In this embodiment, one of two high pressure mercury lamps  9 ,  10  can be lit up selectively. Hence, when for example, high pressure mercury lamp  9  currently used is dead, high pressure mercury lamp  9  can be readily and promptly switched to new high pressure mercury lamp  10 . 
     Further, step-up transformers  7 ,  8  are provided at stages coming after relays  5 ,  6 . Hence, relays  5 ,  6  with low breakdown voltage can be used. Thus, small and low-cost relays  5 ,  6  can be used, and are not broken by high voltage nevertheless. In this way, downsizing, reduced cost, and improved reliability of the device can be achieved. 
     It should be noted that this embodiment deals with the case of lighting up high pressure mercury lamps  9 ,  10 , but the present invention is applicable to a case of lighting up discharge lamps such as extra high pressure mercury lamps, metal halide lamps, and xenon lamps, each of which has a trigger winding (or trigger electrode, auxiliary electrode) and main electrodes. 
     It should be also noted that a selected one of two high pressure mercury lamps  9 ,  10  is lit up in this embodiment but the present invention is applicable to a case of lighting up a selected one of three or more high pressure mercury lamps. In this case, a step-up transformer and a relay are provided for each high pressure mercury lamp. 
       FIG. 3  shows a major portion of a liquid crystal projector having two high pressure mercury lamps  9 ,  10 , and lamp lighting device  1  shown in  FIG. 1  and  FIG. 2 . In  FIG. 3 , beams of light emitted from high pressure mercury lamp  9  are converted by a reflector  21  into substantially parallel light beams and enter a mirror unit  23 . Likewise, beams of light emitted from high pressure mercury lamp  10  are converted by a reflector  22  into substantially parallel light beams and enter mirror unit  23 . 
     In mirror unit  23 , a mirror  23   a  is rotatably provided. When lamp  9  is used, mirror  23   a  is rotated to lead the beams of light from lamp  9  to a fly&#39;s-eye integrator  24 , whereas when lamp  10  is used, it is rotated to lead the beams of light from lamp  10  to fly&#39;s-eye integrator  24 .  FIG. 3  shows a case where lamp  9  is used. 
     The beams of light from lamp  9  pass through fly&#39;s-eye integrator  24 , and enter a PBS (polarization beam splitter) array  25  and a condenser lens  26 . Fly&#39;s-eye integrator  24  includes two fly-eye&#39;s lenses constituted by a group of lenses in the form of a fly&#39;s eye, and provides an optical effect to the beams of light from lamp  9  to attain uniform distribution in the amount of light when the beams enter liquid crystal panels  31 ,  37 ,  46 . 
     In PBS array  25 , a plurality of PBSs and ½ wave plates are provided in the form of an array. PBS array  25  aligns, in one direction, the polarization directions of the beams of light having come from fly&#39;s-eye integrator  24 . Condenser lens  26  provides a beam gathering effect to the beams of light having come from PBS array  25 . The beams of light having passed through condenser lens  26  enter a dichroic mirror  27 . Dichroic mirror  27  only permits passage of light beams in the wavelength range of blue color (hereinafter, referred to as “B light beams”) among the beams of light from condenser lens  26 , and reflects light beams in the wavelength range of red color (hereinafter, referred to as “R light beams”) and light beams in the wavelength range of green color (hereinafter, referred to as “G light beams”). The B light beams having passed through dichroic mirror  27  are reflected by mirror  28  and enter a condenser lens  29 . 
     Condenser lens  29  provides an optical effect to the B light beams to convert them into substantially parallel light beams and allow them to enter liquid crystal panel  31 . The B light beams having passed through condenser lens  29  enter liquid crystal panel  31  through an incoming side polarizing plate  30 . Liquid crystal panel  31  is driven according to a blue color picture signal to modulate the B light beams. The B light beams thus modulated by liquid crystal panel  31  enter a dichroic prism  33  through an outgoing side polarizing plate  32 . 
     The R light beams and G light beams reflected by dichroic mirror  27  enter a dichroic mirror  34 . Dichroic mirror  34  only permits passage of the R light beams of the beams of light from dichroic mirror  27 , and reflects the G light beams. The G light beams thus reflected by dichroic mirror  34  enter a condenser lens  35 . 
     Condenser lens  35  provides an optical effect to the G light beams to convert them into substantially parallel light beams and allow them to enter liquid crystal panel  37 . The G light beams having passed through condenser lens  35  enter liquid crystal panel  37  through an incoming side polarizing plate  36 . Liquid crystal panel  37  is driven according to a green color picture signal to modulate the G light beams. The G light beams thus modulated by liquid crystal panel  37  enter dichroic prism  33  through an outgoing side polarizing plate  38 . 
     The R light beams having passed through dichroic mirror  34  enter a condenser lens  39 . Condenser lens  39  provides an optical effect to the R light beams to convert them into substantially parallel light beams and allow them to enter liquid crystal panel  46 . The R light beams having passed through condenser lens  39  travel in an optical path constituted by relay lenses  40 ,  42 ,  44  for adjusting the length of the optical path as well as two mirrors  41 ,  43 , and enter liquid crystal panel  46  via an incoming side polarizing plate  45 . Liquid crystal panel  46  is driven according to a red color picture signal to modulate the R light beams. The R light beams thus modulated by liquid crystal panel  46  enter dichroic prism  33  through an outgoing side polarizing plate  47 . 
     Dichroic prism  33  combines the colors of the beams of light, i.e., the B light beams, G light beams, and R light beams respectively modulated by liquid crystal panels  31 ,  37 ,  46 , and causes the combined beams of light to enter a projector lens  48 . Projector lens  48  includes a group of lenses for joining the projected beams of light onto a projection target surface, and an actuator for displacing a part of the group of lenses in the direction of the optical axis to adjust zoom and focus states of the projected picture. The beams of light resulting from the color combination by dichroic prism  33  are enlarged and projected by projector lens  48  onto a screen (not shown). 
     When high pressure mercury lamp  9  is dead, lamp lighting device  1  lights up high pressure mercury lamp  10 , and mirror  23   a  is rotated to the lamp  10  side. Thus, the lamps can be switched readily and promptly. Further, when high pressure mercury lamp  9  is not dead but lamp  9  has been used longer than a predetermined period of time, lamp  9  may be switched to lamp  10 . 
     Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the scope of the present invention being interpreted by the terms of the appended claims.