Abstract:
A light emitting device includes a set of light source units including multiple types of solid state light emitting elements having different light colors, each of the light source units comprising the same type of the solid state light emitting elements connected in series and; and an information storage unit which stores information about electrical characteristic of the set of light source units. The information stored in the information storage unit represents a relationship between a light output and a drive current in the set of light source units.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a light emitting device using a solid state light emitting element as a light source, and an illumination apparatus using the light emitting device. 
     BACKGROUND OF THE INVENTION 
     In recent years, there have been provided various light emitting devices and illumination apparatuses using a solid state light emitting element such as a light emitting diode and an organic electroluminescence (EL) element as a light source. In Japanese Patent Application Publication No. 2011-9233, for example, there is disclosed an illumination apparatus in which a plurality of light emitting modules (light emitting devices) are connected in parallel to a constant current source. 
     In the light emitting module, a resistor, a transistor and one or more light emitting diodes are connected in series between a pair of main terminals, and a resistor for outputting connection information (information output resistor) is connected between a joint of the light emitting diode and one of the main terminals and an information output terminal. The information output resistors of the light emitting modules all are set to substantially the same resistance value. 
     The constant current source includes a pair of output terminals connected to the pair of main terminals of the light emitting module, an input terminal to which the connection information outputted from the information output terminal is inputted, a variable constant current source whose output current is variable, and a control unit for varying the current outputted from the variable constant current source according to the connection information. 
     With the technology disclosed in Japanese Patent Application Publication No. 2011-9233, the control unit of the constant current source determines the number of the light emitting modules connected between the main terminals on the basis of a voltage inputted to the input terminal, and varies the output current of the variable constant current source according to the number of the light emitting modules connected such that a predetermined current flows in each of the light emitting modules. Accordingly, despite changes in the number of the light emitting modules connected between the main terminals of the constant current source, a predetermined current (e.g., a rated current) can flow constantly in each light emitting module. 
     Also, there has been provided an illumination apparatus having a dimming function of varying light intensity and a toning function of changing light color. In this case, the light emitting module is composed of three types of light emitting diodes including, e.g., red light emitting diodes, green light emitting diodes and blue light emitting diodes, and luminous color can be changed by individually driving the light emitting diodes. 
     However, the solid state light emitting element such as a light emitting diode tends to have a large variation in light output due to a difference in the use environment or the production lot compared with other light sources such as fluorescent lamps. For example, in case of light emitting diodes, there is a variation in the magnitude of forward current flowing when the same forward voltage is applied, thereby resulting in variations in the light output. 
     SUMMARY OF THE INVENTION 
     In view of the above, the present invention provides a light emitting device capable of suppressing a variation of light output due to individual differences in solid state light emitting elements, and an illumination apparatus using the same. 
     In accordance with a first aspect of the present invention, there is provided a light emitting device which includes a set of light source units including multiple types of solid state light emitting elements having different light colors, each of the light source units comprising the same type of the solid state light emitting elements connected in series and; and an information storage unit which stores information about electrical characteristic of the set of light source units, wherein the information stored in the information storage unit represents a relationship between a light output and a drive current in the set of light source units. 
     In the light emitting device, the information storage unit may include one or more resistive elements having a resistance value corresponding to the information. 
     Preferably, the information storage unit includes the resistive elements; and switch elements which separately switches on and off conduction of the resistive elements. 
     In accordance with a second aspect of the present invention, there is provided an illumination apparatus including one of the above described light emitting devices; a power supply unit which individually supplies a drive current to each of the light source units of the light emitting device; and an adjusting unit which obtains the information stored in the information storage unit, and adjusts the drive current supplied from the power supply unit to each of the light source units based on the obtained information. 
     With the present invention, it is possible to suppress variations in light output between light emitting devices due to individual variations among the light emitting diodes included therein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The objects and features of the present invention will become apparent from the following description of embodiments, given in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a block diagram showing a light emitting device and an illumination apparatus in accordance with a first embodiment of the present invention; 
         FIG. 2  is a plan view of the light emitting device shown in  FIG. 1 ; 
         FIG. 3  is a circuit diagram illustrating a specific configuration of an information storage unit shown in  FIG. 1 ; 
         FIG. 4  is a block diagram partially showing a light emitting device and an illumination apparatus in accordance with a second embodiment of the present invention; 
         FIG. 5  is a diagram for explaining operation in accordance with the second embodiment of the present invention; and 
         FIG. 6  is a block diagram partially showing another configuration of a lighting unit in the second embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Hereinafter, a light emitting device and an illumination apparatus using a light emitting diode as a solid state light emitting element in accordance with embodiments of the present invention will be described in detail. However, the technical concept of the present invention can be applied to a light emitting device and an illumination apparatus using a solid state light emitting element such as an organic electroluminescence (EL) element other than the light emitting diode, without being limited to those using the light emitting diode. 
     First Embodiment 
     Referring to  FIG. 1 , an illumination apparatus in accordance with a first embodiment of the present invention includes a light emitting device  1 , a lighting unit  2 , and terminal blocks  3 A,  3 B and  3 C. The light emitting device  1  includes three light source units  10 A,  10 B and  10 C and an information storage unit  11 . The light source unit  10 A includes a plurality of red light emitting diodes connected in series. The light source unit  10 B includes a plurality of green light emitting diodes connected in series. The light source unit  10 C includes a plurality of blue light emitting diodes connected in series. 
     Further, red light, green light and blue light emitted from the light source units  10 A,  10 B and  10 C are mixed to produce a color of light, e.g., white light, depending on a ratio of the amounts of the red, green and blue lights. Further, both ends of the light source units  10 A,  10 B and  10 C are connected to the terminal blocks  3 A,  3 B and  3 C, respectively. 
     The information storage unit  11  is formed of, e.g., resistive elements, which is set to a resistance value corresponding to a rank to which a group including the light source units  10 A,  10 B and  10 C belongs, as will be described later. Further, both ends of the information storage unit  11 , i.e., both ends of the resistive element, are connected to one end of the terminal block  3 A connected to a positive terminal of the light source unit  10 A and a terminal block  3 D. 
     On the other hand, the lighting unit  2  includes a power supply unit  20 , an adjusting unit  21 , a filter circuit  22 , a rectifier circuit  23  and the like. An AC voltage and current supplied from a commercial AC power source  100  is filtered by the filter circuit  22 , rectified by the rectifier circuit  23 , and inputted to the power supply unit  20 . The power supply unit  20  includes, e.g., a step-up chopper circuit for power factor improvement, three step-down chopper circuits for stepping down a DC voltage outputted from the step-up chopper circuit and outputting the stepped-down voltage, and four drive circuits for driving the step-up chopper circuit and the three step-down chopper circuits respectively. 
     Output terminals of the three step-down chopper circuits are connected the terminal blocks  3 A,  3 B and  3 C in a one-to-one manner, so that a drive current is individually supplied to each of the light source units  10 A,  10 B and  10 C from each step-down chopper circuit. Further, the drive circuits of the step-down chopper circuits perform pulse-width modulation (PWM) control on switching elements constituting the step-down chopper circuits, and vary the light amount of each of the light source units  10 A,  10 B and  10 C by increasing or decreasing the drive current supplied to each of the light source units  10 A,  10 B and  10 C. Herein, since a circuit configuration of the power supply unit  20  is conventionally well known, detailed illustration and explanation of the circuit configuration will be omitted. 
     The adjusting unit  21  adjusts the drive current of each of the light source units  10 A,  10 B and  10 C by controlling the power supply unit  20  to produce a desired light color (e.g., white). That is, the adjusting unit  21  outputs a dimming signal (PWM signal) to the drive circuit of each of the step-down chopper circuits of the power supply unit  20 . Each drive circuit performs PWM control on the step-down chopper circuit according to the dimming signal, so that a target drive current can be supplied to each of the light source units  10 A,  10 B and  10 C. 
     Further, the adjusting unit  21  obtains the information stored in the information storage unit  11  of the light emitting device  1  through the terminal block  3 D, and adjusts the drive current supplied to each of the light source units  10 A,  10 B and  10 C from the power supply unit  20  based on the obtained information. In addition, the adjusting unit  21  may be realized, e.g., by executing a program for adjustment of the drive current in a microcomputer. 
     Hereinafter, there will be described a method in which a rank is given to a set of three types of the light source units  10 A,  10 B and  10 C having a different emission color from each other. For example, in case of mixing colors into white, a percentage of the light amount emitted from each of the red light source unit  10 A, the green light source unit  10 B and the blue light source unit  10 C is uniquely determined, and it is possible to determine a target value of the drive current flowing into each of the light source units  10 A,  10 B and  10 C according to the percentage. 
     Further, since the magnitude of the drive current is adjusted by the dimming signal applied to the drive circuit of the step-down chopper circuit, the dimming signal corresponding to the target value of the drive current is applied to each drive circuit and the drive current flowing into each of the light source units  10 A,  10 B and  10 C is measured. Then, the rank is determined in five steps based on an error between the sum of the target values of the drive currents for the light source units  10 A,  10 B and  10 C and the sum of the measured drive currents (=Sum of Measured values÷Sum of Target Values×100%). 
     For example, if the error is in the range of +1 to +3%, it is determined that the light emitting device is in rank  1 , if the error is in the range of +3 to +5%, it is determined that it is in rank  2 , and, if the error is in the range of −3 to −1%, it is determined that it is in rank  3 . Further, if the error is in the range of −5 to −3%, it is determined that it is in rank  4 , and if the error is in the range of −1 to +1%, it is determined that it is in rank  5 . Then, there is provided the information storage unit  11  formed of a resistive element having a different resistance value corresponding to each of the ranks  1  to  5 . 
     Next, the operation of the adjusting unit  21  in this embodiment will be described in more detail. First, when the AC power source  100  is turned on after the light emitting device  1  is connected to the lighting unit  2  via the terminal blocks  3 A to  3 D, the power supply unit  20  and the adjusting unit  21  of the lighting unit  2  start to operate. When the power supply unit  20  starts to operate, a DC current flows through the information storage unit  11  via the terminal block  3 A, and a voltage drop according to the resistance value of the information storage unit  11  is inputted to the adjusting unit  21  through the terminal block  3 D. The adjusting unit  21  obtains the information (the rank of the light emitting device  1 ) stored in the information storage unit  11  based on the voltage drop inputted through the terminal block  3 D. 
     Then, the adjusting unit  21  adjusts the drive current supplied to each of the light source units  10 A,  10 B and  10 C from the power supply unit  20  according to the rank of the light emitting device  1 . For example, if the light emitting device  1  that is connected is in the rank  1 , the adjusting unit  21  applies the dimming signal to each drive circuit to flow the drive current 3% less than the target value of the drive current flowing into each of the light source units  10 A,  10 B and  10 C. If the light emitting device  1  that is connected is in the rank  4 , the adjusting unit  21  applies the dimming signal to each drive circuit to flow the drive current 5% more than the target value of the drive current flowing into each of the light source units  10 A,  10 B and  10 C. 
     As described above, the light emitting device  1  of this embodiment includes the information storage unit  11  storing the information about the electrical characteristics of the light source units  10 A,  10 B and  10 C, i.e., the information representing the relationship between the drive current and the light output in each of the light source units  10 A,  10 B and  10 C. When the light emitting device  1  is connected to the lighting unit  2 , the adjusting unit  21  of the lighting unit  2  adjusts the drive current supplied to each of the light source units  10 A,  10 B and  10 C from the power supply unit  20  based on the information obtained from the information storage unit  11 . Therefore, it is possible to suppress variations in light output between light emitting devices  1  due to individual variations among the light emitting diodes included therein. 
     However, the method of determining the rank of the set including the light source units  10 A,  10 B and  10 C is not limited to that described above. For example, after measuring the drive currents actually flowing when the dimming signals corresponding to the target values of the drive currents of the respective light source units  10 A,  10 B and  10 C are applied to the respective drive circuits, the rank may be determined on the basis of differences in the target values and the measured values of the drive currents between the respective light source units  10 A,  10 B and  10 C. 
     In this case, when one of the ranks  1  to  5  as described above is given to each of light source units, total  125  ranks can be given to a set of light source units. Further, since the drive circuit supplied to each light source unit is controlled independently, it is possible to obtain the accurate target color of light. Alternatively, the rank may be determined using a deviation in chromaticity coordinates between the target light color and the light color that is obtained when the dimming signal corresponding to the target value of the drive current for each of the light source units  10 A,  10 B and  10 C is applied to each drive circuit. 
     Here, as shown in  FIG. 2 , the light emitting device  1  may be configured such that the light source units  10 A,  10 B and  10 C are mounted on a main substrate  12  having a substantially elliptical shape, and a mounting substrate  13  having the information storage unit  11  thereon is disposed in a rectangular opening  12 A provided at the center of the main substrate  12 . With this configuration, it is easy to replace the information storage unit  11  storing the information about the rank. Further, there is an advantage of simplifying a manufacturing process of the light emitting device  1 . 
     In addition, the information storage unit  11  may be configured with a plurality of resistive elements. For example, it is possible to identify four ranks by using at least one of the resistive element of 500Ω and the resistive element of 1 kΩ. Alternatively, as shown in  FIG. 3 , the information storage unit  11  may be constituted by a plurality of resistive elements Rj (four resistive elements R 1 , R 2 , R 3  and R 4  in the illustrated example) and four switch elements Sj to separately switch on and off the conduction of each of resistive elements Rj (j=1, 2, 3, 4). A desired number of ranks can be identified by appropriately combining a plurality of resistive elements each having a specific resistance value. 
     Second Embodiment 
     In the first embodiment, the adjusting unit  21  of the lighting unit  2  is connected to the information storage unit  11  of the light emitting device  1  via the dedicated terminal block  3 D. In this embodiment, as shown in  FIG. 4 , a resistive element R 1  as the information storage unit  11  is connected in parallel with the terminal block  3 A connected to one of the light source units (e.g.,  10 A), which eliminates the need for the dedicated terminal block  3 D. In the following description, since a basic configuration of this embodiment is almost the same as that of the first embodiment, the same reference numerals are assigned to the same components as the first embodiment, and illustration and description thereof will be omitted. 
     As shown in  FIG. 4 , the power supply unit  20  includes a step-up chopper circuit  20 A, three (only one shown) step-down chopper circuits  20 B and their drive circuits  20 C. Further, the light source units  10 B and  10 C, the step-down chopper circuits and drive circuits therefor, the filter circuit and rectifier circuit are not illustrated in  FIG. 4 . 
     The step-down chopper circuit  20 B includes a series circuit of a diode D 1  and a switching element Q 1 , and a choke coil L 1 . The series circuit of the diode D 1  and the switching element Q 1  is connected across an electrolytic capacitor C 1  for smoothing an output of the step-up chopper circuit  20 A. Further, the choke coil L 1  is connected between an anode of the diode D 1  and a negative terminal of the terminal block  3 A (i.e., the terminal connected to a cathode of the light emitting diode in the light source unit  10 A). Herein, since the operation of the step-down chopper circuit  20 B is conventionally well known, a detailed description thereof is omitted. 
     In the lighting unit  2 , a series circuit of a capacitor C 2 , a resistor R 2  and a switch SW 1  is connected between the negative terminal of the terminal block  3 A and the ground. The adjusting unit  21  performs switching control of the switching element Q 1  of the step-down chopper circuit  20 B through the drive circuit  20 C, and turns on the switch SW 1  when the switching element Q 1  is off (when the step-down chopper circuit  20 B is stopped). 
     If the switch SW 1  is turned on, a voltage caused by charges charged in the electrolytic capacitor C 1  is applied to the terminal block  3 A, the voltage applied to the terminal block  3 A is V DC ×R 1 /(R 1 +R 2 ) when a voltage across the electrolytic capacitor C 1  is VDC. Further, if the voltage V DC  is higher than a forward voltage V LED  of the light source unit  10 A (the sum of forward voltages of the light emitting diodes which are connected in series), the discharge current from the electrolytic capacitor C 1  flows through the resistor R 1  of the information storage unit  11  to charge the capacitor C 2 . 
     At this time, the potential of a connection point between the capacitor C 2  and the resistor R 2  is represented by VDC×R 2 /(R 1 +R 2 ), and decreases with decrease in the voltage VDC across the electrolytic capacitor C 1  (see  FIG. 5 ). Further, a decreasing rate (time constant) of the potential of the connection point between the capacitor C 2  and the resistor R 2  varies depending on the resistance value of the resistor R 1  (e.g., see curves A to D in  FIG. 5 ). 
     Thus, the potential of the connection point between the capacitor C 2  and the resistor R 2  is monitored by the adjusting unit  21 , and the ranks represented by the resistance value of the resistor R 1  can be determined based on the potential at the time point when a certain time T 1  has elapsed from the time point (t=0) when the switch SW 1  is turned on. In addition, the ranks (curves A to D) may also be determined based on the elapsed time until the potential of the connection point between the capacitor C 2  and the resistor R 2  reaches a predetermined value since turning-on of the switch SW 1 . 
     On the other hand, as shown in  FIG. 6 , one end of the light emitting device  1  (one end of the cathode side of the light source units  10 A,  10 B and  10 C) may be connected to the ground. In this case, the arrangement of the switching element Q 1  and the diode D 1  in the step-down chopper circuit  20 B is opposite to that of  FIG. 4 , and the series circuit of the resistor R 2 , the capacitor C 2  and the switch SW 1  is connected between a positive terminal of the terminal block  3 A and a terminal of the high potential side of the electrolytic capacitor C 1 . 
     Thus, the adjusting unit  21  can monitor the potential of the connection point between the resistors R 1  and R 2 , and determine the rank (curves A to D) represented by the resistance value of the resistor R 1  based on the potential at the time point when a certain time T 1  has elapsed from the time point (t=0) when the switch SW 1  is turned on. Instead of the potential of the connection point between the resistors R 1  and R 2 , the adjusting unit  21  may monitor the potential of the connection point between the resistor R 2  and the capacitor C 2 . 
     While the invention has been shown and described with respect to the embodiments, it will be understood by those skilled in the art that various changes and modification may be made without departing from the scope of the invention as defined in the following claims.