Patent Document

CROSS-REFERENCES TO RELATED APPLICATIONS 
   The present application is a continuation of U.S. application Ser. No. 10/888,241 filed Jul. 8, 2004 now U.S. Pat. No. 6,995,523 which claims priority from Japanese application serial no. P2004-050740, filed on Feb. 26, 2004, the contents of which are hereby incorporated by reference in their entirety for all purposes. 

   BACKGROUND OF THE INVENTION 
   The present invention relates to a discharge lamp lighting device for a projection-type display apparatus such as a liquid-crystal projector. 
   Metal-halide lamps, high-pressure mercury lamps, or other high-pressure discharge lamps are used as light sources for projection-type display apparatus such as a liquid-crystal projector, because they have high conversion efficiency and are easily available as light sources close to a point light source in terms of characteristics. 
   Special discharge lamp lighting devices for supplying the voltage and electric current required are used to light up high-pressure discharge lamps. 
   Additionally, as disclosed in Japanese Patent Application Laid-Open No. Hei 8-8076 and 2002-110379, schemes in which a microcomputer is used to control a discharge lamp lighting device have been proposed in recent years. 
   BRIEF SUMMARY OF THE INVENTION 
   It is possible, by mounting a microcomputer in a discharge lamp lighting device, to control the lighting sequence and electric power of a high-pressure discharge lamp very accurately and to control various anti-error protecting functions. Consequently, an added value of the discharge lamp lighting device can be enhanced. However, since microcomputer processing typically progresses in accordance with the programs previously recorded on a ROM, various actions of the discharge lamp are controlled in accordance with ROM-recorded sets of setup data. To modify these settings, the contents of the ROM need to be updated. Although a flash ROM can be easily updated in contents, modifying a mask ROM in contents requires creating its new version and is thus a time-consuming and expensive task. In addition, even a flash ROM does not permit its internal setup data to be modified during the operation of the discharge lamp lighting device. 
   To solve the above problems, the present invention makes various sets of setup data modifiable by assigning an external communication function to a microcomputer designed to control a discharge lamp. 
   In the present invention, a UART (Universal Asynchronous Receiver Transmitter) can be used for communication between the microcomputer of a discharge lamp lighting device and an external device and hence to perform operations such as setting the internal inverter frequency of the discharge lamp lighting device and setting the permission/prohibition of external synchronization. 
   The present invention is effective in that it can provide a discharge lamp lighting device enhanced in added value. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a block diagram showing a first embodiment of a discharge lamp lighting device which applies the present invention; 
       FIG. 2  is a block diagram of a projector applying a discharge lamp lighting device according to the present invention; 
       FIG. 3  is a diagram explaining how an output voltage changes from the lighting start of a discharge lamp to stable lighting thereof in the first embodiment of the discharge lamp lighting device applying the present invention; 
       FIG. 4  is a timing chart explaining the operation of the present invention; 
       FIG. 5  is a diagram explaining the UART communication conducted according to the present invention; 
       FIG. 6  is a timing chart explaining the external synchronizing operation of the present invention; 
       FIG. 7  is a block diagram showing a second embodiment of a discharge lamp lighting device which applies the present invention; 
       FIG. 8  is a diagram explaining a memory map of an EEPROM used in the second embodiment; 
       FIG. 9  is a diagram that explains 1-byte writing during UART communication in the second embodiment; 
       FIG. 10  is a diagram that explains 1-byte reading during UART communication in the second embodiment; 
       FIG. 11  is a diagram that explains multiple-byte writing during UART communication in the second embodiment; 
       FIG. 12  is a diagram that explains multiple-byte reading during UART communication in the second embodiment; and 
       FIG. 13  is a block diagram showing a third embodiment of a discharge lamp lighting device which applies the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Embodiments of the present invention are described below using the accompanying drawings. 
   First Embodiment 
     FIG. 1  is a block diagram showing a first embodiment of a discharge lamp lighting device which applies the present invention. 
   The discharge lamp lighting device is applied to, for example, a projection-type display shown in  FIG. 2 . Referring to  FIG. 2 , a reflector  77  and a high-pressure discharge lamp  78  constitute a light source that irradiates light from the rear of an image display device  76 . The light, after being passed through the image display device  76 , is projected onto a screen  74  through optics  75 . The image display device  76  is, for example, a liquid-crystal display element, and is driven by an image display device driver  79  and thus displays an image, whereby a large-screen image can be obtained on the screen  74 . A discharge lamp lighting device  80  controls starting up and lighting up the high-pressure discharge lamp  78 . 
   Referring back to  FIG. 1 , symbol  1  denotes a power supply input terminal;  2 , an MOS-FET;  3 , a diode;  4 , a choke coil;  5 , a capacitor;  6 ,  7 , resistors;  8 ,  9 ,  10 ,  11 , MOS-FETs;  12 , a resistor;  13 , a discharge lamp;  14 , an igniter circuit;  15 , an arithmetic processing circuit;  16 ,  17 , low-pass filters (LPFs);  18 , a PWM controller;  19 , an ON/OFF signal input terminal of the PWM controller  18 ;  20 , a control voltage input terminal of the PWM controller  18 ;  21 , a driver of the MOS-FET  2 ;  22 , a driver of the MOS-FETs  8 ,  9 ,  10 ,  11 ;  23 , an ON/OFF signal input terminal of the driver  22 ;  24 ,  25 , input terminals of the driver  22 ;  26 , a lamp-on signal input terminal;  27 , a low-power mode signal input/serial data receiving terminal (hereinafter, referred to as RXD); and  28 , a serial data transmitting terminal (hereinafter, referred to as TXD). 
   The MOS-FET  2 , the diode  3 , the choke coil  4 , the capacitor  5 , the driver  21 , and the PWM controller  18  constitute a power control circuit  30 . The MOS-FETs  8 ,  9 ,  10 ,  11 , and the driver  22  constitute an alternating-current (AC) conversion circuit  31 . The igniter circuit  14  generates high-voltage pulses and starts the high-pressure discharge lamp  13 . 
   The arithmetic processing circuit  15  is constructed of, for example, a microcomputer. The arithmetic processing circuit  15  includes a bi-directional communication unit which conducts bi-directional communications with an exterior of the discharge lamp lighting device  80 , and is adapted to control the discharge lamp lighting device  80  in accordance with a required command received via the bi-directional communication unit. One embodiment of a bi-directional communication unit is a unit using UART communication. The circuit  15  detects an output voltage from a voltage divided in the resistors  6 ,  7 , and further detects an output current from a voltage generated in the resistor  12 . In accordance with detection results on the above-mentioned output voltage and output current, the arithmetic processing circuit  15  also computes the output voltage and then controls this voltage by applying a limiting voltage to the control voltage input terminal  20  of the PWM controller  18  to ensure a constant output voltage. Additionally, the arithmetic processing circuit  15  compares the above-described detection results with limit values LV 1  and LV 2  determined inside the processing circuit  15 . Here, LV 1  signifies an output voltage limit value and LV 2  signifies an output current limit value. If the above-detected output voltage is in excess of LV 1 , a signal is transmitted to both the ON/OFF signal input terminal  19  of the PWM controller  18  and the ON/OFF signal input terminal  23  of the driver  22  to stop the discharge lamp lighting device. If the above-detected output current is in excess of LV 2 , a control voltage is applied to the control voltage input terminal  20  of the PWM controller  18  so that the output current will be limited by a current value determined by LV 2 . In both cases, the PWM controller  18  is thus controlled. 
   Next, the basic operation of a typical discharge lamp lighting device is described below. 
   First, the way the high-pressure discharge lamp  13  is started up is described referring to  FIG. 3 .  FIG. 3  is a timing chart explaining how an output voltage changes from the time the discharge lamp lighting device receives an input from the lamp-on input terminal  26 , to the time the discharge lamp enters a stable lighting state. In  FIG. 3 , “Lamp-on signal” denotes a change in a lamp-on signal received from the lamp-on input terminal  26 . 
   At a time “t 0 ”, when the lamp-on signal is received and enters an active Hi (high) state (see  FIG. 3 ), a maximum voltage V 3  is output as an output voltage of the power control circuit  30  since the lamp  13  is not on. When a high-voltage pulse from the igniter circuit  14  is further superimposed on the above-mentioned voltage V 3 , a voltage V 4  is applied to the high-pressure discharge lamp  13 , thus starting up the lamp. Next, at a time “t 1 ”, high-voltage small-current glow discharge is started, and this state further changes to high-voltage small-current arc discharge at a time “t 2 ”. The lamp voltage increases with increases in a temperature of the lamp. At a time “t 3 ”, the AC conversion circuit  31  starts operating and the high-pressure discharge lamp  13  changes to an AC lighting mode. After this, when a stationary voltage V 4  is reached at a time “t 4 ”, the power control circuit  30  supplies constant electric power to the high-pressure discharge lamp  13  by activating constant-power control. The frequency of a rectangular wave from “t 3 ” onward is generally called the inverter frequency. 
   Operation modes of the discharge lamp after it has been lit up (i.e., after “t 4 ” in  FIG. 3 ) are described next. There are typically four operation modes of the discharge lamp: (1) an “off” mode in which the lamp is off, (2) a stationary power mode in which the lamp is normally on, (3) a low-power mode in which the lamp is lit up with power suppressed below that of the stationary power mode, and (4) an extremely-low-power mode in which, when the stationary power mode or the low-power mode is changed to the “off” mode, the lamp is lit up with the power reduced to, for example, about 30% of its original level and this state is maintained. 
   In the low-power mode, effects such as noise reduction can be obtained since it is possible, by lighting up the lamp with the power suppressed to, for example, about 80% of the power level used in the stationary power mode, to suppress power consumption and thus extend lamp life and to reduce a rotating speed of a lamp fan. 
   It is understood that in the extremely-low-power mode, when the lamp changes from its “on” state to an “off” state, power is temporarily maintained at a very low level, not immediately changed to a power level of 0, for reduced electrode deterioration and hence for longer lamp life. 
   A timing chart of the above operation modes is shown in  FIG. 4 . In  FIG. 4 , operation starts from the “off” mode, and then changes to the stationary power mode on lighting, and after temporarily changing to the low-power mode, returns to the stationary power mode. Finally, the operation mode changes to the “off” mode. 
   The four modes of the lamp are each identified by a combination of two bits, one for a lamp-on signal entering the input terminal  26  of the arithmetic processing circuit  15 , and the other for a low-power mode signal entering the input terminal  27 . (Hereinafter, for the sake of convenience in description, these signals are referred to as the signals  26 ,  27 .) More specifically, as listed in  FIG. 4 , when the combination of the lamp-on signal  26  and the low-power mode signal  27  is (Low, Hi), this denotes the “off” mode. Likewise, (Hi, Hi) denotes the stationary power mode, (Hi, Low) the low-power mode, and (Low, Low) the extremely-low-power mode. 
   When operation changes from the stationary power mode or the low-power mode to the extremely-low-power mode, the power level momentarily changes, for example, from 100% (or 80%) to 30%, and this change is likely to cause electrode deterioration. 
   Therefore, as indicated by the dotted-line arrow in the lamp power level transition diagram of  FIG. 4 , a change period of about several seconds may be provided for power to be reduced gently when operation changes from the stationary power mode or the low-power mode to the extremely-low-power mode. A further life-extending effect can be obtained as a result. Hereinafter, the mode during such a change period is referred to as a slow extremely-low-power mode. 
   The basic operation of the discharge lamp lighting device has been described heretofore. 
   Next, description is given of the UART communication control featuring the present embodiment. UART communication is full-duplex communication during which data can be transmitted and received simultaneously. It is an asynchronous communication scheme in which data is transmitted with a start bit and a stop bit appended to the front and rear, respectively, of the data. The RS-232C communication using a personal computer is a typical example.  FIG. 5  shows an example of a UART communication command format, in which RXD denotes command data sending and TXD denotes command data receiving. In both cases, one command is constituted of 1 start bit, 1 stop bit, 8 data bits, and 1 parity bit. The RXD and TXD here are equivalent to the low-power mode signal RXD  27  and TXD  28  shown in  FIG. 1 . 
   The use of RXD requires care since it is also used as a low-power mode signal. For UART communication, when a command is not yet transmitted, both RXD and TXD need to be at a “Hi” level as in  FIG. 5 . Therefore, although UART communication is possible in the stationary power mode and “off” mode where the low-power mode signal RXD  27  becomes “Hi”, the UART communication is not possible in the low-power mode and extremely-low-power mode where the low-power mode signal RXD  27  becomes “Low”. 
   Next, such control functions as listed in Table 1 below are assigned to different types of command data. Commands  30 H to  33 H, where H stands for hexadecimal notation, set the inverter frequency to predefined values. The command  30 H, for example, activates the arithmetic processing circuit  15  to control the AC conversion circuit  31  so that the inverter frequency is 150 Hz. Since the inverter frequency can be arbitrarily changed in this manner, a life-extending effect can be obtained by, for example, optimizing the inverter frequency according to a particular usage time of the lamp. 
   
     
       
             
             
             
             
           
             
             
             
             
           
         
             
                 
               TABLE 1 
             
             
                 
                 
             
             
                 
               Command 
               Name 
               Description of control 
             
             
                 
                 
             
           
           
             
                 
             
           
        
         
             
               1 
               30H 
               Inverter frequency 1 
               Sets the inverter 
             
             
                 
                 
                 
               frequency to 150 HZ. 
             
             
               2 
               31H 
               Inverter frequency 2 
               Sets the inverter 
             
             
                 
                 
                 
               frequency to 170 HZ. 
             
             
               3 
               32H 
               Inverter frequency 3 
               Sets the inverter 
             
             
                 
                 
                 
               frequency to 190 HZ. 
             
             
               4 
               33H 
               Inverter frequency 4 
               Sets the inverter 
             
             
                 
                 
                 
               frequency to 210 HZ. 
             
             
               5 
               34H 
               Slow extremely-low- 
               Permits the use of slow 
             
             
                 
                 
               power ON 
               extremely-low-power 
             
             
                 
                 
                 
               transition mode. 
             
             
               6 
               35H 
               Slow extremely-low- 
               Prohibits the use of 
             
             
                 
                 
               power OFF 
               slow extremely-low- 
             
             
                 
                 
                 
               power transition mode. 
             
             
               7 
               36H 
               External 
               Permits external 
             
             
                 
                 
               synchronization ON 
               synchronization. 
             
             
               8 
               37H 
               External 
               Prohibits external 
             
             
                 
                 
               synchronization OFF 
               synchronization. 
             
             
                 
             
           
        
       
     
   
   For a command  34 H, the arithmetic processing circuit  15  controls power so that before operation changes to the extremely-low-power mode mentioned above, the operation enters a slow extremely-low-power transition mode. 
   Next, the ON/OFF operation of external synchronization using commands  36 H and  37  H is described. External synchronization means causing the inverter frequency and power superimposition to be synchronized with respect to a trigger signal received from an exterior of the discharge lamp lighting device.  FIG. 6  shows how the external synchronization is established. In general, the external trigger signal is superimposed on the lamp-on signal and input to the discharge lamp lighting device. When the lamp is on (i.e., in the stationary power mode or low-power mode of  FIG. 4 ), the lamp-on signal is “Hi”, and when the synchronization is established, the lamp changes to “Low” (i.e., a lamp-on signal A in  FIG. 6  is generated). The arithmetic processing circuit  15  controls the AC conversion circuit  31  so that an AC driving function operates at the falling edge of the lamp-on signal A. 
   However, malfunction results if the lamp-on signal A in  FIG. 6  is used intact to identify the operation mode. More specifically, during a superimposing period of the external trigger, the lamp-on signal is maintained at a “Low” level and the “off” mode persists as the operation mode. To avoid the inconvenience, the LPF  17  is inserted on a route of the lamp-on signal and the results obtained by filtering with the LPF are integrated, whereby a signal of a substantially “Hi” level, such as a lamp-on signal B of  FIG. 6 , can be obtained. Thus, malfunction can be avoided by using this lamp-on signal B for mode identification. 
   The same also applies to the low-power mode signal RXD  27 . Using the low-power mode signal RXD  27  intact for mode identification causes malfunction since, when a command is transmitted, there exists a period during which the signal becomes “Low”. To avoid this, the LPF  16  is inserted on a route of the low-power mode signal RXD  27  and the results obtained by filtering with the LPF are integrated. 
   As described above, according to the present embodiment, inverter frequency setting, slow extremely-low-power control, external synchronization control, and the like can be performed by conducting UART communication control of the discharge lamp lighting device. 
   Second Embodiment 
   Next, an example of circuit composition according to a second embodiment of the present invention is shown in  FIG. 7 . The present embodiment is characterized in that multiple lamps can be lit up with one discharge lamp lighting device by providing an involatile memory such as an EEPROM, storing multiple sets of setup data in the memory, and modifying desired sets of setup data according to a difference in the types of lamps to be connected. Additionally, it is possible to accommodate sudden changes in design and to improve development efficiency, by making the internal setup data of the EEPROM modifiable. 
   In  FIG. 7  that shows the circuit composition according to the second embodiment of the present invention, the same symbol is assigned to each of sections equivalent to those of  FIG. 1  which shows an example of the circuit composition according to the first embodiment. The composition in  FIG. 7  differs in that an EEPROM  32  and a DIP switch  33  that allows “Hi”/“Low” output selection are provided. Description of all other sections is omitted since each is the same as in the first embodiment. 
   The EEPROM  32  is connected to an arithmetic processing circuit  15  by a three-wire serial bus or the like, and is capable of reading out and writing in data. Further, various sets of setup data likely to require modification according to lamp types or during a development and design phase are saved in a split form in multiple internal regions of the EEPROM  32 .  FIG. 8  shows one such example, in which two types of setup data regions,  32 A and  32 B, are provided. For example, when a lamp manufactured by company A is to be used as a lamp  13 , data is read in from the setup data region  32 A, and when a lamp manufactured by company B is to be used, data is read in from the setup data region  32 B. The DIP switch  33  is used to select either of the setup data regions. When an output of the DIP switch  33  is “Hi”, data is read in from setup data region  32 A, and when the output of the DIP switch  33  is “Low”, data is read in from setup data region  32 B. If three or more setup data regions are to be set, the number of bits in the output of the DIP switch  33  can be increased according to the number of setup data regions desired. 
   Next, a specific example of setup data is shown in Table 2 below. The setup data in Table 2 is a specific example of data settings in one setup data region. The settings are: (1) a load current limit value, (2) a slow extremely-low-power duration, (3) an inverter frequency, (4) an extremely-low-power level value, (5) an overvoltage limit value, (6) a low-voltage limit value, (7) an overpower limit value, (8) a temperature limit value, (9) an input voltage limit value, (10) a pulse-superimposing height ratio, and (11) a pulse-superimposing width. Details of these settings are as shown in Table 2, and further detailed description of the settings is omitted. 
   
     
       
             
             
             
             
           
             
             
             
             
             
           
             
             
             
             
           
             
             
             
             
             
           
             
             
             
             
           
             
             
             
             
             
           
         
             
               TABLE 2 
             
             
                 
             
             
                 
                 
               Description 
               Set 
             
             
               No. 
               Name 
               of the value 
               value 
             
             
                 
             
           
           
             
                 
             
           
        
         
             
               1 
               Load current 
               Maximum current 
               4 
               A 
             
             
                 
               limit value 
               value when lamp 
             
             
                 
                 
               is ON 
             
             
               2 
               Slow extremely- 
               Time required for 
               1 
               sec 
             
             
                 
               low-power duration 
               a change to slow 
             
             
                 
                 
               extremely-low- 
             
             
                 
                 
               power mode 
             
             
               3 
               Inverter 
               AC operating 
               178 
               Hz 
             
             
                 
               frequency 
               frequency of AC 
             
             
                 
                 
               conversion 
             
             
                 
                 
               circuit 31 
             
             
               4 
               Extremely-low- 
               Power value in 
               60 
               W 
             
             
                 
               power level value 
               extremely-low- 
             
             
                 
                 
               power mode 
             
             
               5 
               Overvoltage 
               Maximum output 
               150 
               V 
             
             
                 
               limit value 
               voltage value of 
             
             
                 
                 
               power control 
             
             
                 
                 
               circuit 30 
             
             
               6 
               Low-voltage 
               Minimum output 
               10 
               V 
             
             
                 
               limit value 
               voltage value of 
             
             
                 
                 
               power control 
             
             
                 
                 
               circuit 30 
             
             
               7 
               Overpower 
               Maximum power 
               200 
               W 
             
             
                 
               limit value 
               value of power 
             
             
                 
                 
               control circuit 30 
             
           
        
         
             
               8 
               Temperature 
               Maximum operating 
               117° C. 
             
             
                 
               limit value 
               temperature of 
             
             
                 
                 
               the discharge lamp 
             
             
                 
                 
               lighting device 
             
           
        
         
             
               9 
               Input voltage 
               Maximum input 
               300 
               V 
             
             
                 
               limit value 
               voltage value of 
             
             
                 
                 
               power control 
             
             
                 
                 
               circuit 30 
             
           
        
         
             
               10 
               Pulse-superim- 
               Superimposing ratio 
               136% 
             
             
                 
               posing height 
               of power = 
             
             
                 
               ratio 
               (amount of pulse 
             
             
                 
                 
               superimposition + 
             
             
                 
                 
               stationary value)/ 
             
             
                 
                 
               stationary value 
             
           
        
         
             
               11 
               Pulse-superim- 
               Pulse-superimposing 
               778 
               μsec 
             
             
                 
               posing width 
               period of power 
             
             
                 
             
           
        
       
     
   
   In the present embodiment, setup data within the EEPROM can be read/written from an exterior of the discharge lamp lighting device via UART communication. Table 3 below an exemplifies UART commands associated with EEPROM data reading/writing.  FIGS. 9 to 12  each show an example of a UART communication protocol 
   
     
       
             
             
             
             
           
             
             
             
             
           
         
             
                 
               TABLE 3 
             
             
                 
                 
             
             
                 
               Command 
               Name 
               Description of control 
             
             
                 
                 
             
           
           
             
                 
             
           
        
         
             
               1 
               50H 
               1-byte write 
               Writes 1-byte data into EEPROM. 
             
             
               2 
               51H 
               Multiple-byte write 
               Writes multiple-byte data into 
             
             
                 
                 
                 
               EEPROM. 
             
             
               3 
               B0H 
               1-byte read 
               Reads 1-byte data from EEPROM. 
             
             
               4 
               B1H 
               Multiple-byte read 
               Reads multiple-byte data from 
             
             
                 
                 
                 
               EEPROM. 
             
             
                 
             
           
        
       
     
   
     FIG. 9  shows an example of a protocol for 1-byte data writing into the EEPROM. First, a command  50 H is transmitted from an external device to the discharge lamp lighting device. The arithmetic processing circuit  15  of the discharge lamp lighting device receives the command and returns the same command  50 H to the external device. Next, the arithmetic processing circuit  15  receives an address and data, and similarly to the above, returns the same address and the same data. After this, the arithmetic processing circuit  15  writes the data into a specified address of the EEPROM  32 , thus completing the operation. 
     FIG. 10  shows an example of a protocol for 1-byte data reading from the EEPROM. First, a command B 0 H is transmitted from the external device to the discharge lamp lighting device. The arithmetic processing circuit  15  of the discharge lamp lighting device receives the command and returns the same command B 0 H to the external device. Next, the arithmetic processing circuit  15  receives an address and similarly to the above, returns the same address. After this, the arithmetic processing circuit  15  reads data from a specified address of the EEPROM  32  and stores the data. Finally, the arithmetic processing circuit  15  receives a data request command  00 H and returns the stored data. 
     FIGS. 11 and 12  show examples of protocols for respectively writing and reading multiple bytes of data. The operation in these figures is substantially the same as that of  FIGS. 9 and 10 , except that a command specifying the number of sets of data to be read/written is transmitted after an address has been transmitted and received. Data as much as there actually are bytes in the above command is transmitted and received. The transmitted address is a starting address of the data. The address is incremented by 1 with each additional set of data. 
   The DIP switch  33  may be a slide switch or a rotary switch or may be merely set by means of resistor wiring. 
   Third Embodiment 
   Next, an example of circuit composition according to the third embodiment of the present invention is shown in  FIG. 13 . The present embodiment is characterized in that an operating state of a discharge lamp lighting device can be inquired about via UART communication. 
   In  FIG. 13  that shows the circuit composition according to the third embodiment of the present invention, the same symbol is assigned to each of sections equivalent to those of  FIG. 1  which shows an example of the circuit composition according to the first embodiment. The composition in  FIG. 13  differs in that a frequency-measuring circuit  35  is provided. Description of all other sections is omitted since each is the same as in the first embodiment. 
   Table 4 below exemplifies a command associated with inquiry from an external device. For example, when a command A 0 H is transmitted from the external device to the discharge lamp lighting device, an arithmetic processing circuit  15  returns an inverter frequency currently being used. When a command A 1 H is transmitted, the frequency-measuring circuit  35  measures an output, so-called chopper frequency, of a PWM controller  18  provided in a power control circuit  30 , and the arithmetic processing circuit  15  receives frequency measurement results and returns the results to the external device. The frequency-measuring circuit  35  is constructed of, for example, a counter circuit, and when the number of pulses during a period of one second is counted, this count denotes the frequency. When a command  82 H is transmitted, the arithmetic processing circuit  15  returns a present state of the discharge lamp lighting device. If an error is not occurring, a command  00 H is returned. If an error is occurring, a command associated with the error is returned. For example, even after an “off” mode has been set as an operation mode, if the power control circuit  30  generates an output voltage, a command  0 EH is returned since a lamp voltage error is judged to have occurred. When the operation mode is a stationary power mode or a low-power mode, if lamp power exceeding a limit value is supplied, a command  0 FH is returned since a lamp overpower is judged to have occurred. 
   
     
       
             
             
             
             
             
           
             
             
             
             
             
           
         
             
                 
               TABLE 4 
             
             
                 
                 
             
             
                 
               Command 
                 
               Command 
               Description of the 
             
             
                 
               sent 
               Name 
               returned 
               command returned 
             
             
                 
                 
             
           
           
             
                 
             
           
        
         
             
               1 
               A0H 
               Inverter 
               00H-FFH 
               Inverter frequency value 
             
             
                 
                 
               frequency 
                 
               is returned. 
             
             
               2 
               A1H 
               Chopper 
               00H-FFH 
               Chopper frequency value 
             
             
                 
                 
               frequency 
                 
               is returned. 
             
             
               3 
               82H 
               State inquiry 
               00H 
               No error 
             
             
                 
                 
                 
               0EH 
               Lamp OFF or lamp voltage 
             
             
                 
                 
                 
                 
               error 
             
             
                 
                 
                 
               0FH 
               Lamp overpower 
             
             
                 
             
           
        
       
     
   
   The above inquiry command is only an example, and the command may be extended when any other state of the discharge lamp lighting device is to be examined. 
   While the second and third embodiments have heretofore been described assuming the use of the EEPROM  32  as an involatile memory, the present invention is not limited by these embodiments and a flash ROM or the like may be used instead. Further, although the UART scheme has been used for communication, three-wire serial communication or other communication schemes may be used instead. 
   As described above, the discharge lamp lighting device of the present invention can be improved in added value by, during operation, modifying various data settings, and confirming states of the discharge lamp lighting device, by means of UART communication control. 
   In addition, multiple lamps can be lit up with one discharge lamp lighting device by providing an involatile memory such as an EEPROM, saving multiple sets of setup data in the memory, and modifying desired sets of setup data according to a difference in the types of lamps to be connected.

Technology Category: 5