Abstract:
A lighting apparatus of the present invention includes a discharge lamp incorporating a detecting element having a predetermined electrical characteristic, a detector circuit to discriminate the electrical characteristic of the detecting element and a lighting circuit to light the discharge lamp according to the output from the detector circuit. According to the lighting apparatus of the present invention, it is possible to detect whether a discharge lamp mounted in the socket is an adapted lamp without necessity for lighting the discharge lamp.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a lighting apparatus for lighting a discharge lamp. 
     2. Description of the Related Art 
     The technique to detect wattage of a discharge lamp by detecting an electrical characteristic of the discharge lamp when it is lighted in order to prevent the erroneous mounting of a discharge lamp having a different rated lamp voltage in a socket has been disclosed in Japanese Published Unexamined Patent Application JP-A No, 7-106088. 
     This type of lamp base has become commonly used for different kinds of lamps in recent years because different kinds of lamps may be erroneously mounted in different kinds of lamp sockets. 
     However, in the conventional technology disclosed in the Published Unexamined Patent Application JP-A No. 7-106088, there is a problem that even the same type lamps have different wattage ratings, it is not possible to prevent erroneous mounting of these high pressure discharge lamps and incandescent lamps. 
     Further, in the above-mentioned conventional technique, in order to detect that a lamp mounted in a socket is properly adapted from the viewpoint of its type and rated power, the mounted lamp must be lighted. Therefore, if a high pressure discharge lamp that has a lower rated lamp power is lighted in a high pressure discharge lamp lighting apparatus, this lamp receives an overcurrent and may possibly burst. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a lighting apparatus capable of detecting whether a lamp mounted in a socket is a adapted lamp without necessity of lighting it 
     The lighting apparatus of the present invention is composed of a discharge lamp incorporating a detecting element having a predetermined electrical characteristic, a detector circuit for discriminating the electrical characteristic of the detecting element and a lighting circuit for lighting the discharge lamp according to the output from the detector circuit. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a circuit diagram showing a first embodiment of a lighting apparatus of the present invention; 
     FIG. 2 is a plan view showing a high pressure discharge lamp that is a adapted lamp in the lighting apparatus shown in FIG. 1; 
     FIG. 3 is a graph for explaining the action of the lighting apparatus shown in FIG. 1; 
     FIG. 4 is a circuit diagram showing a second embodiment in the lighting apparatus of the present invention; 
     FIG. 5 is a circuit diagram showing a third embodiment in the lighting apparatus of the present invention; 
     FIG. 6 is a circuit diagram showing a fourth embodiment in the lighting apparatus of the present invention; and 
     FIG. 7 is a plan view showing a high pressure discharge lamp that is a adapted lamp in the lighting apparatus shown in FIG.  6 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, several embodiments of the lighting apparatus of the present invention will be described with reference to the attached drawings. 
     FIG. 1 is a circuit diagram of a lighting apparatus showing a first embodiment of the present invention and is for direct current. 
     In the lighting apparatus, a lighting circuit  3 , a starting circuit  4 , a lamp mounting detector circuit  5  and a high pressure discharge lamp  6  are connected to the power line of a DC power source  2  as shown in FIG.  1 . 
     The lighting circuit  3  comprises a driving circuit  11  which drives the high pressure discharge lamp  6  to light and a controlling circuit  12  which controls the driving circuit  11 . 
     The driving circuit  11  comprises a switching element  13 , a transformer  14  of which secondary side winding is connected to the base side of the switching element  13   f  a choke coil  15 , a diode  16 , etc. When square wave is input to the primary side winding of the transformer  14 , the switching element  13  is turned. ON/OFF to drive the high pressure discharge lamp  6  to light. 
     The controlling circuit  12  comprises switching elements  21  and  22  to turn ON/OFF electric power supplied to the primary side winding of the transformer  14 , a comparator  23  of which an output side is connected to the gate sides of the switching elements  21  and  22 , an oscillator  24  of which an output side is connected to the inversion input terminal of the comparator  23 , etc. At triangle wave pulse which is output from the oscillator  24  is compared with a prescribed reference voltage in the comparator  23  and the output corresponding to the result of this comparison is output to the switching elements  21  and  22  from the comparator  23 . By the turn-on/off of the switching elements  21  and  22 , the output corresponding to the duty ratio of square wave that is applied to the transformer  14  is supplied from the driving circuit  11  to the high pressure discharge lamp  6 . 
     The starting circuit  4  comprises a capacitor  31  connected between the power lines, a pulse transformer  32 , a capacitor  33  of which one side is connected to the minus side of the power line and the other side is connected to the primary side winding of the pulse transformer  32 , a thyristor  34  of which anode side is connected to the primary side winding of the pulse transformer  32  and the cathode side is connected to the minus side of the power line, a diode AC switch  35  connected to the charging side of the capacitor  31  and the gate side of the thyristor  34 , etc. When electric energy more than the fixed level is accumulated in the capacitor  31 , the diode AC switch  35  triggers the thyristor  34  and the charge current flows from the capacitor  33  to the primary side winding of the pulse transformer  32  repetitively. By repeating this operation, starting pulses are applied to the high pressure discharge lamp  6  from the secondary side winding of the pulse transformer  32 . 
     The discharge lamp  6  is, for instances a metal halide lamp, and an arc tube  41  and a detecting element  42  are connected in parallel. More definitely, the high pressure discharge lamp  6  comprises an outer bulb  43  and the arc tube  41 , which is suspended in the outer bulb  43 . The outer bulb  43  has a screw base  44  for coupling to a socket (not shown) at its one end. A detecting element  42  is incorporated in the outer bulb  43  and is connected between wires  45  and  46  which supply electric power to the arc tube  41  as shown in FIG.  2 . The detecting element  42  is a resistance for divided voltage detecting in this embodiment. The detecting element  42  has a temperature coefficient of resistance more than 500 ppm/° .C Further, a resistance value of the detecting element  42  is larger than an equivalent resistance value of the arc tube  41  when it is lighted. 
     The lamp mounting detector circuit  5  is equipped with comparators  51  and  52 , and the non-inversion input terminal of the comparator  51  and the inversion input terminal of the comparator  52  are connected to the plus side of the power supply line to the high pressure discharge lamp  6 . The inversion input terminal of the comparator  51 . and the non-inversion input terminal of the comparator  52  are connected to reference voltage sources, respectively. That is, the voltage at the plus side of the power supply line is compared with the reference voltages of these reference voltage sources. The output terminals of the comparators  51  and  52  are connected with each other and the combined output voltage of both comparators is input to the oscillator  24 . 
     A resistor  53  used for detecting a divided voltage in this embodiment divided voltage. The resistor  53  is connected together with a switch  54  in series between the emitter and the collector of the switching element  13  and is able to apply current to the power line bypassing the switching element  13 . 
     Next, the operation of the lighting apparatus  1  will be described. 
     When the switch  54  is closed, the current flows to the high pressure discharge lamp  6  bypassing the switching element  13 . At this time, as the starting circuit  4  and the lighting circuit  3  are not in operation, the arc tube  41  is not ON and DC current flows to the detecting elements  53  and  42  which are connected with each other in series. As a result, a divided voltage corresponding to a size of resistance value of the high pressure discharge lamp  6 , that is, the detecting element  42  is applied to the comparators  51  and  52 . Both of the comparators  51  and  52  output minus voltages only when the divided is within the range of fixed numerical values corresponding to reference voltages input to these comparators, respectively. 
     When a resistance value of the high pressure discharge lamp  6 , that is, a resistance value of the detecting element  42  is in a range of fixed numerical values, a lamp mounted in the socket of the lighting apparatus  1  is judged to be a lamp adaptable to the lighting apparatus  1 . The combined voltage of minus voltages output from the comparators  51  and  52  at that time is usable as the starting signal to drive the lighting apparatus J. 
     When describing definitely, if a metal halide lamp for 250 watt is adaptable to the lighting apparatus  1 , a metal halide lamp outputs the driving start signal as an adapted lamp if the detecting element  42  of which resistance is in the range of fixed numerical values is connected to a 250 watt metal halide lamp. A resistance value in this range of fixed numerical values is, for instance, 200 kΩ. On the contrary, if the lamp mounted in the lighting apparatus  1  is a metal halide lamp of other rated lamp power (70 watt, 150 watt, etc.) or another kind of lamp, for instance, an incandescent lamp, as this mounted lamp has a different resistance value (as there is a filament in an incandescent lamp, current flows but a resistance value of this filament is small), it can be detected that the lamp mounted in the socket is the wrong type lamp without lighting the lamp. 
     Further, by detecting whether a resistance value of the detecting element  42  is within the range of fixed numerical values, it is possible to judge if a mounted lamp, after being turned OFF is in the state ready to be lighted again. That is, the higher the lamp temperature, the higher a resistance of the detecting element  42  becomes. Thus, it may not be possible to light the lamp again even when a starting pulse is given. Therefore, to light a lamp again, it is possible to prevent the supply of starting pulses until the lamp temperature drops to a lower level by stopping the starting circuit  4 . 
     In this case, it is desirable to make the upper limit value of resistance in the range of fixed numerical values below a value b that is considered to be the upper limit value able to light the high pressure discharge lamp  6  and above a resistance value at the normal temperature (about 25° C.). 
     Further, as a temperature coefficient of resistance is above 500 ppm/° C., it is preferred that the inclination of resistance value to the lamp temperature change can be made sufficiently large. 
     As described above, when a lamp mounted in the socket is judged to be a lamp adaptable to the lighting apparatus  1  and the lighting apparatus drive starting signal is output to the oscillator  24  of the controlling circuit  12 , the controlling circuit  12  drives the driving circuit  11 . When the driving circuit  11  is driven, the starting circuit  4  is also driven and a starting pulse is given to the high pressure discharge lamp  6 , which is an adapted lamp, and the high pressure discharge lamp lights. 
     Further, as a resistance value of the detecting element  42  is set at larger than an equivalent resistance value when the arc tube  41  is turned on, the power loss when electric power is applied to the detecting element  42  can be made relatively small. 
     Furthermore, as the detecting element  42  is connected to the wires  45  and  46  as described above, it contributes to improve the mounting strength of the arc tube  41 . 
     Next, a second embodiment of the present invention will be described. 
     FIG. 4 is a circuit diagram of a lighting apparatus  60  showing the second embodiment of the present invention and is for alternate current. 
     In FIG. 4, the circuit elements assigned with the same reference numerals as in FIGS. 1 and 2 are the same as those in the first embodiment of the present invention and therefore, the detailed explanations thereof will be omitted. 
     As shown in FIG. 4, the lighting apparatus  60  is equipped with a lighting circuit  63  comprising a DC—DC converter  61  and an inverter circuit  62 . 
     The DC—DC converter  61  is composed of a switching element  64 , a choke coil  65 , a diode  66 , etc. and a signal voltage is applied to the gate of the switching element  64  from a controlling circuit  75 . 
     The inverter circuit  62  is a full-bridge circuit comprising four switching elements  71 ,  72 ,  73  and  74 . The switching elements  71 ,  72 ,  73  and  74  are turned on/off to drive the high pressure discharge lamp  6  by alternate current. 
     A controlling circuit  75  turns on/off the switching element  64  by outputting signals having different duty ratios. 
     The lighting apparatus  60  is provided with a plurality of stages of the lamp mounting detector circuit  5  ( 3  stages in this embodiment), and in each of the lamp mounting detector circuits  5 , various reference voltages are set for the comparators  51  and  52 . 
     Next, the operation of the lighting apparatus  60  will be described. 
     As the lighting apparatus  60  is provided with a plurality of stages of the lamp mounting detector circuits  5  ( 3  stages in this embodiment) and in each of the lamp mounting detector circuits  5 , various reference voltages are set for the comparators  51  and  52 . Thus, it is possible to set divided voltage in various ranges of different fixed numerical values according to size of resistance of the high pressure discharge lamp  6 , that is, the detecting element  42 , that can be detected in each of the lamp mounting detector circuits  5 . 
     Then, each of the different fixed numerical value ranges is brought to correspond to a plurality of kinds of rated lamp power (for instance, 70, 150 and 250 watts) of the high pressure discharge lamp  6 . It is therefore possible to judge whether the type of the lamp is proper or whether its rated power is proper according to whether a signal is output from lamp mounting detector circuit  5 . 
     When no signal is input to the controlling circuit  75  from any lamp mounting detector circuit  5 , the switching element  64  is not turned on/off. Therefore, as the lighting circuit  63  is not driven, a lamp mounted in the socket is judged to be not adaptable. Accordingly, that lamp is an adapted lamp (an incandescent lamp, etc.) and does not light. 
     When a signal is input to the controlling circuit  75  from one of the lamp mounting detector circuits  5 , the ON time ratio of the switching element  64  is changed according to the lamp mounting detector circuit  5  from which that signal is output. According to this change in ON time ratio, the rated lamp power of a mounted lamp that is an adapted lamp is judged and the output corresponding to that rated lamp power is output from the DC—DC converter  61 . 
     Next, a third embodiment of the present invention will be described. 
     FIG. 5 is a circuit diagram of a lighting apparatus  80  showing the third embodiment of the present invention. In this FIG. 5, the circuit elements assigned with the same reference numerals as those shown in FIGS. 1 and 2 are the same as those in the first embodiment of the present invention and therefore, the detailed explanations thereof will be omitted. 
     The lighting apparatus  80  is the lighting apparatus  1  added with a pulse generation deactive circuit  81 . 
     The pulse generation deactive circuit  81  is composed of a switching element  82  comprising the capacitor  31  with an emitter and a collector connected to its two sides, a timer  83  connected to the gate side of the switching element  82  for turn on/off the switching element  82 , a DC power source  84 , etc. The DC power source  84  supplies the electric power to the timer  83  to drive it when the starting circuit  4  is operated. 
     Next, the operation of the lighting apparatus  80  will be described. 
     When the switch  54  is closed, a lamp mounted in the socket is judged as to whether it is an adapted lamp, the first embodiment. When the lamp is judged to be an adapted, the starting circuit  4  generates the starting pulse and tries to start the lamp. 
     The timer  83  starts the counting for a preset fixed amount of time. When this fixed time is over, the voltage is output from the timer  83  to the gate side of the switching element  82  and the switching element  82  is turned on. When the switching element  82  is turned on, the circuit between the switching element  82  and the capacitor  31  is short-circuited and the charging of the capacitor  31  is interrupted and therefore, the starting circuit  4  stops the subsequent operation. 
     To turn on the high pressure discharge lamp  6  when it is not sufficiently cooled down after it was turned off, the lamp mounting detector circuit  5  may not be able to judge a mounted lamp to be an adapted lamp due to the temperature characteristic of the detecting element  42  in some cases. When a mounted lamp was sufficiently cooled down and the lamp mounting detector circuit  5  judges it to be an adapted lamp, the starting circuit  4  starts to generate the starting pulse. Then, interlocking with the start of the starting circuit  4 , the timer  83  is also energized and begins the counting for a fixed time. Even when the high pressure discharge lamp  6  is pulled out of the socket or becomes defective during this period, it is tried to start the lamp for the fixed time when the timer  83  is counting and then, the starting circuit  4  is stopped. Therefore, the useless pulse generation is prevented and the dielectric breakdown of the base of a lamp mounted in the socket and adverse effects to other electric/electronic equipment will never be caused. 
     Then, a fourth embodiment of the present invention will be described. 
     FIG. 6 is a circuit diagram of a lighting apparatus  90  showing the fourth embodiment of the present invention. In FIG. 6, the circuit elements assigned with the same reference numerals as those shown in FIGS. 1 and 2 are the same as those in the first embodiment of the present invention and therefore, the detailed explanations thereof will be omitted. 
     The lighting apparatus  90  is equipped with a lighting circuit  93  comprising a DC—DC converter  91  and a driving circuit  92 . The DC—DC converter  91  is composed of a switching element  94 , a choke coil  95 , a diode  96 , a smoothing capacitor  97 , etc. 
     The driving circuit  92  is connected to the gate of the switching element  94  and turns the switching element  94  on/off at a fixed ON time ratio. 
     The resistor  53  is connected to the output line at the minus side of the DC—DC converter  91  and the switch  54  is connected so as to by-pass the switching element  94  without passing through the resistor  53 . 
     A lamp lighting detector circuit  101  is connected in parallel with a lamp mounted in the socket and detects the lighting of the mounted lamp according to fluctuation of divided voltage of the mounted lamp. 
     A timer  105  starts the counting for a fixed time and when it was not lighted until the counting time was over, the timer  105  outputs a signal to a controlling circuit  103 . Upon receipt of this signal, the controlling timer  103  outputs a drive stopping signal to the driving circuit  92  and the starting circuit  4 . 
     The lamp mounting detector circuit  5  starts the counting for a fixed time by a timer  104  when judging that a lamp mounted in the socket is an adapted lamp. When this counting is completed, the controlling circuit  103  sends a signal to the driving circuit  92  which in turn drives the DC—DC converter  91 . 
     In the high pressure discharge lamp  6 , a thermally-actuated element  106  such as a bimetal switch is connected to turn off the power supplied to the detecting element  42  according to temperature rise. The thermally-actuated element  106  is arranged near the arc tube  41  so as to be able to perceive heat of the arc tube  41  sufficiently as shown in FIG.  7 . 
     Next, the operation of the lighting apparatus  90  will be described. 
     When the high pressure discharge lamp  6  which is an adapted lamp is mounted in the state where the switch  54  is closed and no lamp is mounted in the lighting apparatus  90 , the lamp mounting detector circuit  5  judges the mounted lamp to be an adapted lamp according to the divided voltage of the detecting element  42 . According to this judgment, the controlling circuit  103  outputs a control signal to drive the lighting circuit  93  and in addition, the starting circuit  4  is driven to light the high pressure discharge lamp  6 . Therefore, it is possible to automatically light a lamp only when an adapted lamp is mounted. 
     In this case, the lamp mounting detector circuit  5  does not light a lamp immediately after detecting an adapted lamp but waits until a time set on the timer  104  is over. Accordingly, it is possible to wait the start of lighting a lamp until the mounting work of an adapted lamp in the socket is completely finished and since it is prevented to supply the starting pulse to the lamp after the lamp mounting in the socket, the safety can be enhanced. 
     Further, when the starting circuit  4  operates, the timer  105  starts the counting and the lamp lighting detector circuit  101  detects the lighting of an adapted lamp and when the adapted lamp does not light until the counting time is over, a signal is output to the controlling circuit  103  and a drive stopping signal is output to the starting circuit  4 . Accordingly, even when an adapted lamp becomes defective and does not light, the output of useless pulse is prevented and the dielectric breakdown of the base of a lamp mounted in the socket and adverse effects to other electric/electronic equipment will never be caused. 
     When a lamp did not light within the counting time by the timer  105  and thereafter, a mounted lamp was exchanged, the lamp mounting detector circuit  5  judges again whether the exchanged lamp is an adapted lamp and if it is an adapted lamp, after the waiting time of the timer  104 , the controlling circuit  103  outputs a signal to the driving circuit  92  and the automatic lighting is tried as in the above. 
     Further, when the adapted lamp  6  lights and after a while, the lamp temperature rises, the power to the detecting element  42  is turned off by the thermally- actuated element  106  and thus, the power loss by the detecting element  42  is prevented.