Patent Publication Number: US-2010109537-A1

Title: Led lighting circuit and illuminating apparatus using the same

Description:
TECHNICAL FIELD 
     The present invention relates to an LED lighting circuit and an illuminating apparatus using the LED lighting circuit, and more particularly, to a technique for uniformizing currents of a plurality of LEDs arranged in parallel. 
     BACKGROUND ART 
     When many LEDs (light-emitting diodes) are used to obtain required light output as in the case where the LEDs are used for the illuminating apparatus, or even when a chip is fragmented to obtain the same light output because LEDs with low currents have high efficiency, an exorbitant power supply voltage is required to connect the plurality of LEDs in series and light up the LEDs. On the other hand, when the many LEDs are connected parallel to each other and lit up, an exorbitantly high current is required. Therefore, an appropriate serial/parallel configuration that fits the application is actually adopted. However, in the case of blue LEDs, an ON voltage Vf thereof is on the order of 3 to 3.5 V, has a great variation and combining the LEDs in series or parallel results in a problem that differences are likely to occur in split ratio among serial circuits arranged parallel to each other, that is, differences are likely to occur in brightness among the serial circuits. 
     More specifically, light outputs from the LEDs are said to depend on flowing current values, and from this standpoint, the flowing current values in the serial configuration remain the same even if there are variations in ON voltages Vf of the individual LEDs, and so the variations in light outputs of the individual LEDs are also small. In contrast, in the case of a parallel configuration, when the sum of LED ON voltages Vf in the series configuration differs, currents flowing to the series circuits from a collective output of the lighting circuit (power supply circuit) are concentrated on a circuit with a low ON voltage Vf and the light outputs vary a great deal from one series circuit to another. 
       FIG. 29  is a block diagram showing a configuration of a typical LED lighting circuit  1  of a prior art. This prior art is disclosed in Patent Document 1. In this LED lighting circuit  1 , an LED module  2  is constructed of LED load circuits u 1  to u 3  connected in parallel, each LED load circuit being made up of many serially connected LED loads. The LED module  2  is given a DC voltage VDC resulting from converting a voltage Vac from a commercial power supply  3  to DC through a noise cut capacitor c 1  and a rectification bridge  4  and converting the DC to a voltage through a DC-DC converter  5 . 
     The DC-DC converter  5  is constructed of a voltage boosting chopper circuit provided with a switching element q 0  that switches the DC output voltage of the rectification bridge  4 , a choke coil  1  that stores/discharges the excitation energy resulting from the switching, a diode d and a smoothing capacitor c 2  that rectify and smooth the output current from the choke coil  1 , a resistor r 1  for converting the current flowing through the switching element q 0  to a voltage and a control circuit  6  that controls the switching of the switching element q 0 . 
     On the other hand, constant current circuits q 1  to q 3  for equalizing values of currents flowing through the LED load circuits u 1  to u 3  are inserted in series respectively. The applied voltages (load voltages) of the constant current circuits q 1  to q 3  are compared with a reference voltage Vref from a reference voltage source  8  by a comparison circuit  7 , the comparison results are given to the control circuit  6  and the control circuit  6  controls the constant voltage output of the DC-DC converter  5  so that the applied voltages of the respective constant current circuits q 1  to q 3  become smaller than the sum of the ON voltages Vf of the series LEDs. This suppresses losses at the respective constant current circuits q 1  to q 3 . However, this prior art has a problem that the overall light output level varies as the variations in the LED ON voltages Vf increase and losses at the constant current circuits q 1  to q 3  also increase. 
       FIG. 30  is a block diagram showing a configuration of an LED lighting circuit  11  of another prior art. This prior art is disclosed in Patent Document 2. This LED lighting circuit  11  is configured to convert a total value of currents flowing to the respective LED load circuits u 1  to u 3  to a voltage and detect the voltage by a resistor r 2 , compare the voltage with a reference voltage Vref by a comparator  17  and control a DC-DC converter  15  through a PWM control circuit  16  so that the comparison result is kept to a constant value. The DC-DC converter  15  is constructed of a one-transistor flyback converter that switches a voltage Vdc from a DC power supply  13  by a switching element q 0  and gives the voltage Vdc to the primary side of a transformer t, gives a DC voltage VDC resulting from rectifying/smoothing the secondary side output by a rectification smoothing circuit  14  to the respective LED load circuits u 1  to u 3  and thereby insulates the power supply side from the load side. In this LED lighting circuit  11 , constant current circuits d 1  to d 3  are also connected in series to the respective LED load circuits u 1  to u 3  respectively. 
       FIG. 31  is an electric circuit diagram showing a specific example of the constant current circuit d 1  to d 3 . This constant current circuit d 1  to d 3  is configured by including a transistor q 11  and a resistor r 11  connected in series to the LED load circuit u 1  to u 3 , a resistor r 12  that connects the collector and the base of the transistor q 11  and a Zener diode dz inserted between the base and the emitter of the transistor q 11 . The collector current of the transistor q 11  is kept to a constant current under a condition that the sum of a voltage drop of the resistor r 11  and a base-emitter voltage Vbe of the transistor q 11  substantially matches the Zener voltage of the Zener diode dz. 
     Thus, the currents of the respective LED load circuits u 1  to u 3  are individually kept to a constant current and the collective output current of the DC-DC converter  15  is also controlled to a constant current and it is thereby possible to significantly suppress variations in the light outputs due to variations in the LED ON voltages Vf. However, there is a problem that this constant current circuit d 1  to d 3  has greater loss than the simple constant current circuit q 1  to q 3  made up of an FET source-follower circuit. 
     Thus, the present inventor has proposed an LED lighting circuit  21  as shown in  FIG. 32  in Patent Document 3. According to this prior art, transistors q 21  and q 22 , and resistors r 21  and r 22  are connected in series to LED load circuits u 1  and u 2  respectively and a transistor q 20  configuring a current mirror circuit with the transistors q 21  and q 22  is inserted between the terminals of the DC power supply  23  via resistors r 23 , r 24 , r 20 , and the like. A reference current determined by the voltage VDC from the DC power supply  23  and resistors r 23 , r 24  and r 20  flows to the transistor q 20 , the currents flowing through the transistors q 21  and q 22  are balanced with the reference current and variations in the light outputs are thereby suppressed. The resistor r 24  is short-circuited by a bypass switch sw provided parallel to one resistor (r 24  in this example) so as to increase the reference current and also increase the light output. 
     However, although the above described method using a mirror circuit is convenient for balancing currents between the LED load circuits u 1  and u 2 , the method also involves a problem that the reference current varies due to a variation of the power supply voltage VDC and losses are produced at the resistors r 23 , r 24 , r 20  that create the reference current and the transistor q 20 . 
     Patent Document 1: Japanese Patent Laid-Open No. 2002-8409 
     Patent Document 2: Japanese Patent Laid-Open No. 2004-319583 
     Patent Document 3: Japanese Patent Laid-Open No. 2004-39290 
     DISCLOSURE OF THE INVENTION 
     It is an object of the present invention to provide an LED lighting circuit capable of uniformizing light outputs of many LEDs with low loss and an illuminating apparatus using the LED lighting circuit. 
     The LED lighting circuit of the present invention provides control elements configuring a current mirror circuit in series to a plurality of LED circuits arranged parallel to each other, uses a circuit having the highest voltage drop by LED currents including the respective LED ON voltages as a reference, allows the control element in the circuit to have a diode structure and causes flowing current values of the control elements of the remaining circuits to be interlocked through control terminals of the control element. Such a configuration allows the current mirror circuit to uniformly control current balance between the parallel LEDs, and can thereby uniformize light outputs from many LEDs. Furthermore, since a circuit having the highest voltage drop by the LED currents including the ON voltages is used as the circuit that creates a reference current for the current mirror circuit, such a configuration does not require the circuit that creates only a reference current and can eliminate circuit loss accordingly. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram showing a configuration of an LED lighting circuit according to Embodiment 1 based on a first viewpoint of the present invention; 
         FIG. 2  is a block diagram showing a configuration of another mode of the DC power supply in the LED lighting circuit according to Embodiment 1 based on the first viewpoint of the present invention; 
         FIG. 3  is a block diagram showing a configuration of a further mode of the DC power supply in the LED lighting circuit according to Embodiment 1 based on the first viewpoint of the present invention; 
         FIG. 4  is a block diagram showing a configuration of a still further mode of the DC power supply in the LED lighting circuit according to Embodiment 1 based on the first viewpoint of the present invention; 
         FIG. 5  is a block diagram showing a configuration of an LED lighting circuit according to Embodiment 2 based on the first viewpoint of the present invention; 
         FIG. 6  is a block diagram showing a configuration of an LED lighting circuit according to Embodiment 1 based on a second viewpoint of the present invention; 
         FIG. 7  shows a state when wire breakage has occurred in one LED; 
         FIG. 8  is a block diagram showing a configuration of another mode of the DC power supply in the LED lighting circuit according to Embodiment 1 based on the second viewpoint of the present invention; 
         FIG. 9  is a block diagram showing a configuration of a further mode of the DC power supply in the LED lighting circuit according to Embodiment 1 based on the second viewpoint of the present invention; 
         FIG. 10  is a block diagram showing a configuration of a further mode of the DC power supply in the LED lighting circuit according to Embodiment 1 based on the second viewpoint of the present invention; 
         FIG. 11  is a block diagram showing a configuration of an LED lighting circuit according to Embodiment 1 based on a third viewpoint of the present invention; 
         FIGS. 12A  to C show examples of the impedance element in the lighting circuit shown in  FIG. 11 ; 
         FIG. 13  is a block diagram showing another configuration example of the LED lighting circuit according to Embodiment 1 based on the third viewpoint of the present invention; 
         FIG. 14  is a block diagram showing a configuration of an LED lighting circuit according to Embodiment 2 based on the third viewpoint of the present invention; 
         FIG. 15  is a block diagram showing a configuration of the Vf detection circuit and the switching control circuit in the lighting circuit shown in  FIG. 11 ; 
         FIG. 16  is a block diagram showing a configuration of an LED lighting circuit according to Embodiment 3 based on the third viewpoint of the present invention; 
         FIG. 17  is a block diagram showing a configuration of an LED lighting circuit according to Embodiment 4 based on the third viewpoint of the present invention; 
         FIG. 18  is a block diagram showing a configuration of an LED lighting circuit according to Embodiment 1 based on a fourth viewpoint of the present invention; 
         FIGS. 19A  and B show configuration examples of the splitting circuit in the lighting circuit shown in  FIG. 18 ; 
         FIG. 20  is a block diagram showing a configuration of an LED lighting circuit according to Embodiment 2 based on the fourth viewpoint of the present invention; 
         FIG. 21  is a block diagram showing a configuration of an LED lighting circuit according to Embodiment 3 based on the fourth viewpoint of the present invention; 
         FIG. 22  is a block diagram showing a configuration of an LED lighting circuit according to Embodiment 1 based on a fifth viewpoint of the present invention; 
         FIG. 23  is a block diagram showing another example of the wire breakage detection circuit in the LED lighting circuit shown in  FIG. 22 ; 
         FIG. 24  is a block diagram showing a further example of the wire breakage detection circuit in the LED lighting circuit shown in  FIG. 22 ; 
         FIG. 25  is a block diagram showing a configuration of the LED lighting circuit according to Embodiment 2 based on the fifth viewpoint of the present invention; 
         FIG. 26  is a block diagram showing a configuration of an LED lighting circuit according to Embodiment 3 based on the fifth viewpoint of the present invention; 
         FIG. 27  is a block diagram showing a configuration of an LED lighting circuit according to Embodiment 4 based on the fifth viewpoint of the present invention; 
         FIG. 28  is a block diagram showing another configuration of the LED lighting circuit according to Embodiment 4 based on the fifth viewpoint of the present invention; 
         FIG. 29  is a block diagram showing a configuration of an LED lighting circuit according to a typical prior art; 
         FIG. 30  is a block diagram showing a configuration of an LED lighting circuit according to another prior art; 
         FIG. 31  is an electric circuit diagram showing a specific example of the constant current circuit in the LED lighting circuit shown in  FIG. 30 ; and 
         FIG. 32  is a block diagram showing a configuration of an LED lighting circuit according to a further prior art. 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     Hereinafter, an embodiment of the present invention will be explained with reference to the accompanying drawings. Configurations assigned the same reference numerals among the drawings indicate the same configurations and explanations thereof will be omitted 
     Embodiment 1 Based on First Viewpoint 
       FIG. 1  is a block diagram showing a configuration of an LED lighting circuit  31  according to Embodiment 1 based on a first viewpoint of the present invention. In this LED lighting circuit  1 , an LED module  32  is configured with three LED load circuits U 1  to U 3  connected in parallel, each LED load circuit being made up of many serially connected LEDs D 1 . The number of series LED loads in each LED load circuit U 1  to U 3  is arbitrary and each LED load circuit may also be constructed of a single LED. 
     Each LED load circuit U 1  to U 3  is configured such that the LEDs D 1  are mounted on and bonded to a common heat sink and a fluorescent substance for wavelength conversion and a light diffusion lens and the like are also mounted. The LED module  32  and LED lighting circuit  31  are used as an illuminating apparatus, and emit blue or ultraviolet light as the LED load, convert, in wavelength, the light from the LED load using the fluorescent substance and emit the light as white light. The number of parallel circuits of the LED load circuits U 1  to U 3  is also arbitrary and a technique for obtaining white light by combining light emitted in three primary colors RGB, for example, is also arbitrary. 
     A DC voltage VDC resulting from converting a voltage Vac from a commercial power supply  33  to DC through a noise cut capacitor C 1  and a rectification bridge  34  and converting the DC to a voltage via a DC-DC converter  35  is added to the LED module  32 . The DC-DC converter  35  is constructed of a voltage boosting chopper circuit configured by including a switching element Q 0  that switches the DC output voltage of the rectification bridge  34 , a choke coil L that stores/discharges excitation energy through the switching, a diode D and a smoothing capacitor C 2  that rectify and smooth the output current from the choke coil L, a resistor R 1  that converts a current flowing through the switching element Q 0  to a voltage for detection and a control circuit  36  that controls the switching of the switching element Q 0 . 
     The current that flows from the DC-DC converter  35 , which is a DC power supply, to the LED module  32  is converted to a voltage value by a current detection resistor R 2 , compared with a reference voltage Vref from a reference voltage source  38  by a comparison circuit  37  and the comparison result is fed back to the control circuit  36 . The control circuit  36  controls the switching frequency and duty of the switching element Q 0  in response to the detection results of the resistors R 1  and R 2 . Constant voltage control over the voltage VDC and constant current control over the current that flows to the LED module  32  are performed in this way. 
     What should be noted is that according to the present embodiment, in the respective LED load circuits U 1  to U 3 , control elements Q 1  to Q 3  configuring a current mirror circuit are arranged in series to equalize values of currents flowing through the LED load circuits U 1  to U 3 , and using a circuit (U 1  in  FIG. 1 ) with the highest voltage drop by the LED currents including the sum of the LED ON voltages Vf in the corresponding LED load circuits U 1  to U 3  in the control elements Q 1  to Q 3  as a reference, the control element in the circuit (Q 1  in the example of  FIG. 1 ) is to have a diode structure, the flowing current values of the control elements (Q 2  and Q 3  in the example of  FIG. 1 ) of the remaining circuits (U 2  and U 3  in the example of  FIG. 1 ) are interlocked through the control terminals and the LED load circuits U 1  to U 3  are thereby balanced. 
     To be more specific, when the control elements are transistors as shown in  FIG. 1 , the base and collector, which are the control terminals, are short-circuited for the control element Q 1  and the bases of the control elements Q 1  to Q 3  are commonly connected. On the other hand, when the control terminals are MOS type transistors, the gate and drain, which are the control terminals, are short-circuited for the control element Q 1  and the gates of the control elements Q 1  to Q 3  are commonly connected. 
     Therefore, the currents flowing from the DC-DC converter  35  to the respective LED load circuits U 1  to U 3  are controlled through collective constant current control based on the detection result of the resistor R 2  so that the sum of the flowing current values is kept constant and the current balance between the respective LED load circuits U 1  to U 3  is uniformly controlled through the current mirror circuit, and it is thereby possible to uniformize light outputs from the many LEDs D 1 . Furthermore, since the LED load circuit (U 1  in the example of  FIG. 1 ) having the highest voltage drop by the LED currents including the sum of the ON voltage Vf is used for the circuit (Q 1  in the example of  FIG. 1 ) that creates a reference current of the current mirror circuit, the circuit that creates only a reference current is not necessary and circuit loss can be eliminated accordingly. Furthermore, one of the control elements Q 1  to Q 3  such as transistors is to have a diode structure and is only configured into a mirror circuit, and therefore the circuit can be realized in a low-cost configuration. 
     For example, when the number of LED load circuits is assumed to be three; U 1  to U 3 , each LED load circuit U 1  to U 3  is constructed of five LEDs D 1  and the variation of the ON voltage Vf is assumed to be ±5%, if only collective constant current control is performed based on the detection result of the resistor R 2 , that is, when the control elements Q 1  to Q 3  are not provided, the current variation between the LED load circuits U 1  to U 3  is 17.5 to 22.71 mA (current value of the collective constant current control is 60 mA), whereas when the control elements Q 1  to Q 3  are provided and other control elements Q 2  and Q 3  are allowed to perform mirror operation using the control element Q 1  corresponding to the LED load circuit U 1  having the maximum sum of ON voltages Vf as a reference, the current variation can be suppressed to 20.0 to 20.1 mA. Similarly, when a variation in the ON voltages Vf is assumed to be ±10%, the current variation can be suppressed to 15.2 to 25.8 mA only through collective constant current control and 20.0 to 20.1 mA by allowing the control elements Q 2  and Q 3  to perform mirror operation. 
       FIG. 2  to  FIG. 4  are block diagrams showing configurations of LED lighting circuits  41 ,  51  and  61  with DC power supplies in different configurations. In the configurations in  FIG. 2  to  FIG. 4 , configurations similar or corresponding to those shown in aforementioned  FIG. 1  are assigned the same reference numerals and explanations thereof will be omitted. In the configurations in  FIG. 2  to  FIG. 4 , the configuration of the LED module  32  made up of LED load circuits U 1  to U 3  is the same. However, while the control elements Q 1  to Q 3  connected in series to the LED load circuits U 1  to U 3  in  FIG. 1  to  FIG. 3  are N-type transistors, control elements Q 1 ′ to Q 3 ′ in  FIG. 4  are P-type transistors. However, in the example of this  FIG. 4 , the U 1  is assumed to be the circuit having the maximum sum of LED ON voltages Vf out of the respective LED load circuits U 1  to U 3 , and the corresponding control element Q 1 ′ has a diode structure and the values of currents flowing through the remaining circuits U 2  and U 3  are interlocked through the control elements Q 2 ′ and Q 3 ′. 
     The LED lighting circuit  41  shown in  FIG. 2  is configured such that the total value of currents flowing to the respective LED load circuits U 1  to U 3  is converted to a voltage and detected by a resistor R 2 , the voltage is compared with a reference voltage Vref by a comparator  47  and a DC-DC converter  45  is controlled via a PWM control circuit  46  so that the comparison result is kept to a constant value. The DC-DC converter  45  is constructed of a one-transistor flyback converter that switches a voltage Vdc from a DC power supply  43  by a switching element Q 0 , given to the primary side of a transformer T, a DC voltage VDC resulting from rectifying/smoothing the secondary side output through a rectification smoothing circuit  44  is given to the respective LED load circuits U 1  to U 3  so as to insulate the power supply side from the load side. This LED lighting circuit  41  is similar to the LED lighting circuit  11  shown in the aforementioned conventional example in  FIG. 30 . 
     In an LED lighting circuit  51  or  61  shown in  FIG. 3  or  FIG. 4 , a voltage Vdc from a DC power supply  43  is boosted or lowered by a DC-DC converter  55 , rectified by a full-wave or half-wave rectifier  56 , smoothed by a smoothing capacitor C 3  and the DC voltage VDC is then given to the LED module  32 . The total value of currents flowing to the respective LED load circuits U 1  to U 3  is converted to a voltage and detected by the resistor R 2 , the voltage is compared with a reference voltage Vref from the reference voltage source  38  by the comparator  37  and the PWM control circuit  6  controls the DC-DC converter  55  so that the comparison result is kept to a constant value. 
     Here, Table 1 shows details of losses at the control elements Q 1  to Q 3  in the case where the DC-DC converter  35 , which is a DC power supply, performs only constant current control based on the detection result of the resistor R 2  using the current mirror circuit according to the present embodiment and in the case where only constant voltage control over the voltage VDC is performed as shown in the conventional example in  FIG. 30 . Furthermore, Table 1 also shows details of losses in the case where the constant current circuits d 1  to d 3  shown in conventional examples in  FIG. 30  and  FIG. 31  are used and when constant current control is performed and when constant voltage control is performed. Suppose conditions of test calculations are such that the current flowing through the LED load circuit U 1  to U 3 , that is, rated current of the LEDs D 1  is 20 mA, ON voltage Vf of the LED D 1  is 3.2 V, and the variation thereof is ±10%, and hfe of the control element (transistor) Q 1  to Q 3  is 100. 
     
       
         
           
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 TABLE 1 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                   
                 CONSTANT CURRENT CONTROL 
               
            
           
           
               
               
               
            
               
                   
                 NO Vf VARIATION 
                 MAXIMUM Vf VARIATION 
               
               
                   
               
               
                 C 
                 ⋄CONSTANT CURRENT CONTROL 
                 ⋄CONSTANT CURRENT CONTROL 
               
               
                 M 
                  VALUE: 60 mA 
                  VALUE: 60 mA 
               
            
           
           
               
               
               
            
               
                   
                 ⋄LOSS OF TRANSISTORS Q1 TO Q3 
                 ⋄TOTAL Vf . . . REFERENCE CIRCUIT 17.6 v 
               
            
           
           
               
               
               
            
               
                   
                  •Ic = 20 mA 
                 OTHER CIRCUIT 14.4 v 
               
            
           
           
               
               
               
            
               
                   
                  •Ib = 0.2 mA 
                   POTENTIAL DIFFERENCE 3.2 v 
               
               
                   
                  •Vbe ≈ 0.6 V 
                 ⋄P Q1  ≈ 20 mA × 0.6 v = 12 mW 
               
               
                   
                  ∴P Q1~Q3  = 20 mA × 0.6 = 12 mW × 3 
                 ⋄ p   Q2~Q3  ≈ 20 mA × (3.2 + 0.6) v  = 76 mW × 2 
               
               
                   
                  TOTAL LOSS: 36 mW 
                  TOTAL LOSS: 164 mW 
               
            
           
           
               
               
               
            
               
                 CONSTANT 
                 ⋄CONSTANT CURRENT CONTROL 
                 ⋄CONSTANT CURRENT CONTROL 
               
               
                 CURRENT 
                  VALUE: 60 mA 
                  VALUE: 60 mA 
               
               
                 CIRCUIT 
                 ⋄CONSTANT DESIGN 
                 ⋄SAME AS LEFT 
               
            
           
           
               
               
               
            
               
                   
                  •RESISTOR r11 . . . 200 Ω 
                  TOTAL LOSS: 368 mW 
               
               
                   
                  •dz . . . 2.4 V (0.1 mA) 
               
               
                   
                  •RESISTOR r12 = 5 kΩ 
               
               
                   
                 ⋄LOSS CALCULATION 
               
               
                   
                  •P r11  ≈ (20 mA) 2  × 200 = 80 mW × 3 
               
               
                   
                  •P r12  ≈ (0.3 mA) 2  × 5k = 0.45 mW × 3 
               
               
                   
                  •P dz  = 2.4 V × 0.1 mA = 0.24 mW × 3 
               
               
                   
                  •P q11  ≈ 20 mA × (0.3 m × 5k + 0.6 v) = 42 mW × 3 
               
               
                   
                  TOTAL LOSS: 368 mW 
               
               
                   
                   
               
            
           
           
               
               
               
            
               
                   
                 CONSTANT VOLTAGE CONTROL 
                   
               
            
           
           
               
               
               
               
            
               
                   
                   
                 NO Vf VARIATION 
                 MAXIMUM Vf VARIATION 
               
               
                   
                   
               
               
                   
                 C 
                 ⋄CONSTANT VOLTAGE CONTROL 
                 ⋄CONSTANT VOLTAGE CONTROL 
               
               
                   
                 M 
                  VALUE: 19 V 
                  VALUE: 19 V 
               
            
           
           
               
               
               
            
               
                   
                  (SERIES 40 Ω ADDED FOR STABILITY 
                  (SERIES 40 Ω ADDED FOR STABILITY 
               
               
                   
                  OF OPERATION) 
                  OF OPERATION) 
               
               
                   
                 ⋄P Q1~Q3  = 20 mA × 0.6 = 
                  ⋄TOTAL Vf . . . REFERENCE CIRCUIT 17.6 v 
               
            
           
           
               
               
               
            
               
                   
                   12 mW × 3 
                 OTHER CIRCUIT 14.4 v 
               
            
           
           
               
               
               
            
               
                   
                 ⋄LOSS OF ADDITIONAL RESISTOR 40 Ω 
                   POTENTIAL DIFFERENCE 3.2 v 
               
               
                   
                  P R1~R3  = (20 mA) 2  × 40 Ω = 
                 ⋄ P Q1  ≈ 20 mA × 0.6 V = 
               
               
                   
                  16 mW × 3 
                  12 mW 
               
               
                   
                  TOTAL LOSS: 84 mW 
                 ⋄ P Q2~Q3  ≈ 20 mA × 3.8 v = 
               
            
           
           
               
               
            
               
                   
                  76 mW × 2 
               
               
                   
                 ⋄LOSS OF ADDITIONAL RESISTOR 40 Ω 
               
               
                   
                   P R1~R3  ≈ (20 mA) 2  × 40 Ω = 
               
               
                   
                   16 mW × 3 
               
               
                   
                  R = (19 − 17.6 − 0.6) v ÷ 20 mA = 
               
               
                   
                  40 Ω 
               
               
                   
                   TOTAL LOSS: 21.2 mW 
               
            
           
           
               
               
               
               
            
               
                   
                 CONSTANT 
                 ⋄CONSTANT VOLTAGE CONTROL 
                 ⋄CONSTANT VOLTAGE CONTROL 
               
               
                   
                 CURRENT 
                  VALUE: 23.7 V 
                  VALUE: 23.7 V 
               
               
                   
                 CIRCUIT 
                 ⋄LOSS CALCULATION 
                 ⋄CONSTANT VOLTAGE SET VALUE 
               
            
           
           
               
               
               
            
               
                   
                  •ΣVf = 3.2 × 5 = 16 v 
                  •ΣVf: 17.6 v(max) 
               
            
           
           
               
               
               
            
               
                   
                  • CONSTANT CURRENT CIRCUIT 
                 14.4 v(min) 
               
            
           
           
               
               
               
            
               
                   
                   VOLTAGE DROP = 23.7 − 16 = 
                  •Vf = 17.6 v(max) 
               
               
                   
                   7.7 V 
                   V R  = 20 mA × 200 Ω = 4 v 
               
               
                   
                  •LED CURRENT 20 mA 
                   V Q  = 2.1 v 
               
               
                   
                  ∴ 7.7 v × 20 mA = 154 mW × 3 
                 ∴CONSTANT VOLTAGE VALUE 23.7 v 
               
               
                   
                  TOTAL LOSS: 462 mW 
                 ⋄LOSS CALCULATION 
               
            
           
           
               
               
            
               
                   
                  •ΣVf = 14.4 v(min) 
               
               
                   
                  •CONSTANT CURRENT CIRCUIT 
               
               
                   
                   VOLTAGE DROP = 
               
               
                   
                   23.7 − 14.4 = 9.3 v 
               
               
                   
                  •LED CURRENT 20 mA 
               
               
                   
                  ∴9.3 v × 20 mA = 186 mW × 3 
               
               
                   
                  TOTAL LOSS: 558 mW 
               
               
                   
                   
               
            
           
         
       
     
     As is apparent from Table 1, according to the current balance control using the current mirror circuit of the present embodiment, loss is smaller when there is no variation in the ON voltage Vf, but it is understandable that constant current control produces less loss than constant voltage control regardless of the presence/absence of a variation in the ON voltage Vf. On the other hand, with the current balance control using the constant current circuits d 1  to d 3  shown in  FIG. 30  and  FIG. 31  in the aforementioned conventional examples, constant current control also produces less loss than constant voltage control regardless of the presence/absence of a variation in the ON voltage Vf, but since the total amount of current is limited in constant current control, it is understandable that loss is the same irrespective of whether or not there is a variation in the ON voltage Vf. Therefore, constant current control is preferable for current balance control by the current mirror circuit of the present embodiment and it is understandable that loss can be drastically reduced in securing the current balance under both conditions compared to the case where the constant current circuits d 1  to d 3  are used. 
     In the above explanations, the emitter area ratios of the control elements (transistors) Q 1  to Q 3 , that is, the rated currents of the LEDs D 1  in the LED load circuits U 1  to U 3  are the same, but the emitter area ratios may also be configured to be different from each other, and in that case, the control elements Q 1  to Q 3  perform control so as to maintain the different set current ratios. Furthermore, an organic EL (organic LED) is also applicable to the LEDs D 1  of the present invention. 
     Embodiment 2 Based on First Viewpoint 
       FIG. 5  is a block diagram showing a configuration of an LED lighting circuit  71  according to Embodiment 2 based on the first viewpoint of the present invention. In the LED lighting circuit  71 , parts similar and corresponding to those of the aforementioned LED lighting circuit  31  will be assigned the same reference numerals and explanations thereof will be omitted. What should be noted is that in the LED lighting circuit  71 , an LED module  72  is constructed of n LED load circuits U 1 ′, U 2 ′, . . . , Un′ connected in series and the respective LED load circuits U 1 ′, U 2 ′, . . . , Un′ are configured by including a plurality of LEDs D 11 , D 12 , . . . , D 1   m ; D 21 , D 22 , . . . , D 2   m ; . . . ; Dn 1 , Dn 2 , Dnm arranged parallel to each other and control elements Q 11 , Q 12 , . . . , Q 1   m ; Q 21 , Q 22 , Q 2   m ; . . . ; Qn 1 , Qn 2 , Qnm connected in series thereto and configuring current mirror circuits. 
     Using the LEDs (D 11 , D 2   m , . . . , Dn 2  in  FIG. 5 ) with the highest ON voltages Vf in the respective LED load circuits U 1 ′ to Un′ as a reference, the control elements (Q 11 , Q 2   m , . . . , Qn 2  in  FIG. 5 ) corresponding to the LEDs D 11 , D 2   m , . . . , Dn 2  are to have a diode structure and the flowing current values of the control elements of the remaining LEDs D 12 , . . . , D 1   m ; D 21 , . . . , D 2   m −1; . . . ; Dn 1 , Dn 3 , . . . , Dnm in the same LED load circuits U 1 ′ to Un′ are interlocked through the control terminals. 
     Such a configuration also allows light outputs from many LEDs D 11  to Dnm to be uniformized. Furthermore, since the LEDs (D 11 , D 2   m , . . . , Dn 2  in the example of  FIG. 5 ) with the highest ON voltages Vf are used for the circuits (Q 11 , Q 2   m , . . . , Qn 2  in the example of  FIG. 5 ) for creating a reference current of the current mirror circuit are used, a circuit to create only a reference current is not necessary and circuit loss can be eliminated accordingly. 
     Summary of First Viewpoint 
     As described above, the LED lighting circuit based on the first viewpoint of the present invention is an LED lighting circuit that causes a current to flow from a DC power supply to an LED module made up of a plurality of LEDs arranged parallel to each other, including control elements each of which being arranged in series to each of the parallel LED circuits configuring a current mirror circuit, in which a circuit with the highest voltage drop by LED currents including ON voltages of the LEDs is used as a reference, the control element in the circuit is to have a diode structure and the flowing current values of the control elements of the remaining circuits are interlocked through control terminals of the control elements. 
     Furthermore, the LED lighting circuit based on the first viewpoint of the present invention is an LED lighting circuit that causes a current to flow from a DC power supply to an LED module made up of a plurality of LED load circuits arranged parallel to each other, each LED load circuit being made up of one or a plurality of serially connected LEDs, preferably including control elements arranged in series to the LED load circuits configuring a current mirror circuit, in which a circuit with the highest voltage drop by LED currents including the sum of the LED ON voltages in the LED load circuits is used as a reference, the control element in the circuit is to have a diode structure and the flowing current values of the control elements of the remaining circuits are interlocked through control terminals of the control elements. 
     According to the above described configuration, in an LED lighting circuit to be used for an illuminating apparatus and the like, when a current is caused to flow from a DC power supply to an LED module with one or a plurality of LED load circuits made up of serially connected LEDs arranged parallel to each other, including control elements arranged in series to the LED load circuits configuring a current mirror circuit, in which a circuit with the highest voltage drop by the LED currents including the sum of the LED ON voltages in the LED load circuits is used as a reference, the control elements in the circuit is to have a diode structure and the flowing current values of the control elements of the remaining circuits are interlocked through control terminals of the control elements and the LED load circuits are thereby balanced. To be more specific, when the control elements are transistors, the base and collector, which are control terminals, are short-circuited and the bases are connected commonly. On the other hand, when the control elements are MOS type transistors, the gate and drain, which are control terminals, are short-circuited and the gates are connected commonly. 
     Therefore, since the current balance among the LED load circuits is uniformly controlled by the current mirror circuit, light outputs from many LEDs can be uniformized. Furthermore, since the LED load circuit with the highest sum of the ON voltages Vf is used for the circuit for creating the reference current of the current mirror circuit, a circuit to create only a reference current is not necessary and circuit losses can be reduced accordingly. 
     Furthermore, the LED lighting circuit based on the first viewpoint of the present invention is an LED lighting circuit that causes a current to flow from a DC power supply to an LED module made up of a plurality of LEDs, in which the LED module is preferably made up of a plurality of LED load circuits connected in series, each LED load circuit being made up of a plurality of LEDs connected parallel to each other and the LEDs are provided with control elements configuring a current mirror circuit arranged in series, and an LED with the highest ON voltage in the LED load circuits is used as a reference, the control element corresponding to the LED is to have a diode structure and the flowing current values of the control elements of the remaining LEDs in the LED load circuits are interlocked through control terminals. 
     According to the above described configuration, in an LED lighting circuit to be used for an illuminating apparatus and the like, when a current is allowed to flow from a DC power supply to an LED module made up of a plurality of LEDs, if the LED module is constructed of a plurality of serially connected LED load circuits, each being made up of a plurality of LEDs connected parallel to each other, control elements configuring a current mirror circuit are arranged in series to the LEDs, an LED with the highest ON voltage Vf in the LED load circuits is preferably used as a reference and the control element corresponding to the LED is to have a diode structure and the flowing current values of the control elements of the remaining LEDs in the same LED load circuit are interlocked through the control terminals and the LEDs are thereby balanced in the LED load circuit. To be more specific, when the control elements are transistors, the base and collector, which are control terminals, are short-circuited and the bases are connected commonly. On the other hand, when the control elements are MOS type transistors, the gate and drain, which are control terminals, are short-circuited and the gates are connected commonly. Since the respective LED load circuits are connected in series, the flowing currents are the same. 
     Therefore, the current balance in the LED load circuits is uniformly controlled by the current mirror circuit and it is thereby possible to uniformize light outputs from many LEDs. Furthermore, since an LED load circuit with the highest sum of ON voltages Vf is used for the circuit to create a reference current of the current mirror circuit, a circuit to create only a reference current is not necessary and circuit loss can be eliminated accordingly. 
     Furthermore, in the LED lighting circuit based on the first viewpoint of the present invention, the DC power supply is preferably a DC-DC converter and configured by including current detection means ectively detecting currents flowing through the LED module, a reference voltage source and a comparator for comparing the detection result from the current detection means and control means for controlling the DC power supply through feedback so that the sum of values of currents flowing to the LED module becomes a predetermined value according to the output of the comparator. 
     According to the above described configuration, the sum of values of currents flowing from the DC power supply to the LED load circuits is detected and the DC power supply is collectively subjected to constant current control through feedback based on the detection result so that the sum of the flowing current values becomes a predetermined value, and therefore losses at the control elements are smaller compared to constant voltage control, and losses can thereby be reduced. 
     Furthermore, the illuminating apparatus based on the first viewpoint of the present invention preferably uses the above described LED lighting circuit. According to the above described configuration, it is possible to uniformize light outputs from many LEDs and also realize a low loss illuminating apparatus. 
     Embodiment Based on Second Viewpoint 
       FIG. 6  is a block diagram showing a configuration of an LED lighting circuit  131  according to Embodiment 1 based on a second viewpoint of the present invention. This LED lighting circuit  131  is similar to the LED lighting circuit  31  shown in aforementioned  FIG. 1  and corresponding parts will be shown assigned the same reference numerals. In this LED lighting circuit  131 , an LED module  32  is also configured by connecting three LED load circuits U 1  to U 3  in parallel, each being made up of many serially connected LEDs D 1 . The number of serially connected LED loads in each LED load circuit U 1  to U 3  is arbitrary and can also be constructed of a single LED. 
     In each LED load circuit U 1  to U 3 , LEDs D 1  are mounted on and bonded to a common heat sink, and configured with a fluorescent substance for wavelength conversion and a light diffusion lens and the like attached. The LED module  32  and LED lighting circuit  31  are used as an illuminating apparatus, emit blue or ultraviolet light as the LED load, convert, in wavelength, the light from the LED load using the fluorescent substance and emit the light as white light. The number of parallel circuits of the LED load circuits U 1  to U 3  is also arbitrary and a technique for obtaining white light by combining light emitted in three primary colors RGB, for example, is also arbitrary. 
     A DC voltage VDC resulting from converting a voltage Vac from a commercial power supply  33  to DC through a noise cut capacitor C 1  and a rectification bridge  34  and converting the DC to a voltage via a DC-DC converter  35  is added to the LED module  32 . The DC-DC converter  35  is constructed of a voltage boosting chopper circuit configured by including a switching element Q 0  that switches the DC output voltage of the rectification bridge  34 , a choke coil L that stores/discharges excitation energy through the switching, a diode D and a smoothing capacitor C 2  that rectify and smooth the output current from the choke coil L, a resistor R 1  that converts a current flowing through the switching element Q 0  to a voltage for detection and a control circuit  36  that controls the switching of the switching element Q 0 . 
     What should be noted is that according to the present embodiment, in the LED load circuits U 1  to U 3 , control elements Q 1 ′ to Q 3 ′, which are P-type transistors configuring a current mirror circuit are arranged in series to equalize values of currents flowing through the LED load circuits U 1  to U 3 , a circuit (U 1  in  FIG. 6 ) with the highest voltage drop by the LED currents including the sum the LED ON voltages Vf in the corresponding LED load circuits U 1  to U 3  in the control elements Q 1 ′ to Q 3 ′ is used as a reference, the control element in the circuit (Q 1 ′ in the example of  FIG. 6 ) is to have a diode structure, the flowing current values of the control elements (Q 2 ′ and Q 3 ′ in the example of  FIG. 1 ) of the remaining circuits (U 2  and U 3  in the example of  FIG. 6 ) are interlocked through control terminals and the LED load circuits U 1  to U 3  are thereby balanced. 
     To be more specific, when the control elements are transistors as shown in  FIG. 6 , the base and collector, which are the control terminals, are short-circuited for the control element Q 1 ′ and the bases of the control elements Q 1 ′ to Q 3 ′ are commonly connected. On the other hand, when the control elements are MOS type transistors, the gate and drain, which are the control terminals, are short-circuited for the control element Q 1 ′ and the gates of the control elements Q 1 ′ to Q 3 ′ are commonly connected. 
     Furthermore, the current flowing from the DC-DC converter  35 , which is the DC power supply, to the LED module  32  is converted to a voltage value by a current detection resistor R 2  inserted in the circuit (U 1  in the example of  FIG. 6 ) that serves as the reference, compared with a reference voltage Vref from a reference voltage source  38  by a comparison circuit  137  and the comparison result is fed back to the control circuit  36 . In response to the detection result of the resistors R 1  and R 2 , the control circuit  36  controls the switching frequency and duty of the switching element Q 0 . Constant voltage control over the voltage VDC and constant current control over the current that flows to the LED module  32  are performed in this way. 
     Therefore, since the current balance among the LED load circuits U 1  to U 3  is uniformly controlled by the current mirror circuit, light outputs from many LEDs D 1  can be uniformized. Furthermore, since an LED load circuit (U 1  in the example of  FIG. 6 ) with the highest voltage drop by the LED currents including the sum of the ON voltages Vf is used for the circuit (Q 1 ′ in the example of  FIG. 6 ) for creating a reference current of the current mirror circuit, a circuit to create only a reference current is not necessary and circuit loss can be eliminated accordingly. Furthermore, the values of currents flowing from the DC-DC converter  35  to the LED load circuits U 1  to U 3  are controlled to be constant by the constant current control based on the detection result of the resistor R 2 , and therefore losses at the control elements Q 1 ′ to Q 3 ′ can be reduced compared to a case where only constant voltage control to keep the voltage VDC constant is performed. Furthermore, one of the control elements Q 1 ′ to Q 3 ′ of transistors and the like is to have a diode structure and simply configured into a mirror circuit, and therefore the present embodiment can be implemented in a low-cost configuration. 
     Furthermore, by inserting the current detection resistor R 2  in the circuit (U 1  in the example of  FIG. 6 ) that serves as a reference as described above, even if wire breakage occurs in the LEDs D 1  in circuits other than the circuit that becomes a reference (U 3  in the example of  FIG. 6 ) as shown in  FIG. 7 , the remaining circuits (U 1  and U 2  in the example of  FIG. 6 ) can continue lighting with the current value remaining constant (without becoming overcurrent). 
       FIG. 8  to  FIG. 10  are block diagrams showing configurations of LED lighting circuits  141 ,  151  and  161 , the DC power supply of which has a different mode. In the configurations in  FIG. 8  to  FIG. 10 , parts similar or corresponding to those shown in aforementioned  FIG. 6  are assigned the same reference numerals and explanations thereof will be omitted. In the configurations in  FIG. 8  to  FIG. 10 , the configuration of the LED module  32  made up of LED load circuits U 1  to U 3  is the same. However, as opposed to  FIGS. 6 ,  8  and  9  where control elements Q 1 ′ to Q 3 ′ connected in series to the LED load circuits U 1  to U 3  are P-type transistors, control elements Q 1  to Q 3  in  FIG. 10  are N-type transistors. However, also in the example of  FIG. 10 , a circuit with the highest sum of LED ON voltages Vf of the LED load circuits U 1  to U 3  is assumed to be the U 1  and the corresponding control element Q 1  has a diode structure and the flowing current values of the remaining circuits U 2  and U 3  are interlocked through the control elements Q 2  and Q 3 . 
     The LED lighting circuit  141  shown in  FIG. 8  is configured such that the value of a current flowing to the LED load circuit U 1  is converted to a voltage and detected by a resistor R 2 , the voltage is compared with a reference voltage Vref from a reference voltage source  38  by a comparator  147  and a DC-DC converter  45  is controlled via a PWM control circuit  46  so that the comparison result is kept to a constant value. As described above, the DC-DC converter  45  is constructed of a one-transistor flyback converter that switches a voltage Vdc from a DC power supply  43  by a switching element Q 0  and gives the voltage Vdc to the primary side of a transformer T, gives a DC voltage VDC resulting from rectifying/smoothing the secondary side output by a rectification smoothing circuit  44  to the LED load circuits U 1  to U 3  so as to insulate the power supply side from the load side. The LED lighting circuit  141  is also similar to the LED lighting circuit  11  shown in aforementioned conventional example in  FIG. 30 . 
     In the LED lighting circuits  151  and  161  shown in  FIG. 9  and  FIG. 10 , a voltage Vdc from a DC power supply  43  is boosted or lowered by a DC-DC converter  55 , rectified by a full-wave or half-wave rectifier  56 , smoothed by a smoothing capacitor C 3  and the resulting DC voltage VDC is given to the LED module  32 . The value of the current flowing to the LED load circuit U 1  is converted to a voltage and detected by the resistor R 2 , the voltage is compared with a reference voltage Vref by a comparator  147  and the PWM control circuit  46  controls the DC-DC converter  55  so that the comparison result is kept to a constant value. 
     In the explanations above, the emitter area ratios of the control elements (transistors) Q 1 ′ to Q 3 ′; Q 1  to Q 3 , that is, rated currents of the LEDs D 1  in the LED load circuits U 1  to U 3  are the same, but the emitter area ratios may also be configured to be different from each other and in such a case, the control elements Q 1 ′ to Q 3 ′; Q 1  to Q 3  perform control so as to maintain different set current ratios. Power consumption by a current detection resistor R 2  can be reduced to a minimum by making such a setting that the sum of LED ON voltages Vf in an LED load circuit with the least current value becomes the highest. Furthermore, an organic EL (organic LED) is also applicable to the LEDs D 1  in the present invention. 
     Summary of Second Viewpoint 
     As described above, the LED lighting circuit based on the second viewpoint of the present invention is an LED lighting circuit that causes a current to flow from a DC power supply to an LED module made up of a plurality of LED load circuits arranged parallel to each other, each LED load circuit being made up of one or a plurality of serially connected LEDs, detects a value of the current flowing from the DC power supply to the LED module and controls the DC power supply through feedback based on the detection result so that the flowing current value is kept to a predetermined value, in which control elements configuring a current mirror circuit are preferably arranged in series to the LED load circuits, a circuit with the highest voltage drop by LED currents is used as a reference including the sum of LED ON voltages in the LED load circuits, the control element in the circuit is to have a diode structure, and the flowing current values of the control elements of the remaining circuits are interlocked through control terminals and current detection means for detecting the flowing current value is inserted in this circuit. 
     According to the above described configuration, in the LED lighting circuit to be used for an illuminating apparatus and the like, when a current is caused to flow from a DC power supply to an LED module made up of LED load circuits arranged parallel to each other, each LED load circuit being made up of one or a plurality of serially connected LEDs, a value of the current flowing from the DC power supply to the LED module is detected and the DC power supply is controlled through feedback based on the detection result so that the flowing current value is kept to a predetermined value, control elements configuring a current mirror circuit are arranged in series to the LED load circuits, a circuit with the highest voltage drop by LED currents including the sum of LED ON voltages in the LED load circuits is used as a reference, the control element in the circuit is to have a diode structure, and the flowing current values of the control elements of the remaining circuits are interlocked through the control terminals, the LED load circuits are thereby balanced and current detecting means for detecting the flowing current values such as a current/voltage conversion resistor is inserted in this circuit. To be more specific, when the control elements are transistors, the base and the collector, which are control terminals, are short-circuited and the bases are commonly connected. On the other hand, when the control elements are MOS type transistors, the gate and drain, which are control terminals, are short-circuited and the gates are commonly connected. 
     Therefore, since the currents flowing through the LED load circuits are controlled to be constant through the constant current control and current balance control, light outputs from many LEDs can be uniformized. Furthermore, since an LED load circuit with the highest sum of the ON voltages Vf is used for the circuit to create a reference current of the current mirror circuit, such a configuration does not require the circuit that creates only a reference current and can eliminate circuit loss accordingly. Furthermore, even when wire breakage occurs in the LEDs other than the circuit to be a reference, the remaining circuits can continue lighting with the current values remaining constant. 
     Furthermore, in the LED lighting circuit based on the second viewpoint of the present invention, the DC power supply is a DC-DC converter and is preferably configured by including a reference voltage source and a comparator to compare the detection results from the current detection means and control means for controlling the DC power supply so that the flowing current values to the LED module become the predetermined value according to the output from the comparator. 
     According to the above described configuration, since constant current control is performed to control the DC power supply through feedback, losses at the control elements are small compared to constant voltage control and losses can be reduced. 
     Furthermore, the illuminating apparatus based on the second viewpoint of the present invention is preferably designed to use the above described LED lighting circuit. The above described configuration can uniformize light outputs from many LEDs and realize a low-loss illuminating apparatus. 
     Embodiment 1 Based on Third Viewpoint 
       FIG. 11  is a block diagram showing a configuration an LED lighting circuit  231  according to Embodiment 1 based on a third viewpoint of the present invention. This LED lighting circuit  231  is similar to the LED lighting circuit  31  shown in aforementioned  FIG. 1  and corresponding parts will be shown assigned the same reference numerals. Also in this LED lighting circuit  231 , an LED module  32  is configured with three LED load circuits U 1  to U 3  connected in parallel, each LED load circuit being made up of many serially connected LEDs D 1 . The number of series LED loads in each LED load circuit U 1  to U 3  is arbitrary and each LED load circuit may also be constructed of a single LED. 
     Each LED load circuit U 1  to U 3  is configured such that the LEDs D 1  are mounted on and bonded to a common heat sink and a fluorescent substance for wavelength conversion and a light diffusion lens and the like are also attached. The LED module  32  and the LED lighting circuit  231  are used as an illuminating apparatus, and emit blue or ultraviolet light as the LED load, convert, in wavelength, the light from the LED load using the fluorescent substance and emit the light as white light. The number of parallel circuits of the LED load circuits U 1  to U 3  is also arbitrary and a technique for obtaining white light by combining light emitted in three primary colors RGB, for example, is also arbitrary. 
     A DC voltage VDC resulting from converting a voltage Vac from a commercial power supply  33  to DC through a noise cut capacitor C 1  and a rectification bridge  34  and converting the DC to a voltage via a DC-DC converter  35  is added to the LED module  32 . The DC-DC converter  35  is constructed of a voltage boosting chopper circuit configured by including a switching element Q 0  that switches the DC output voltage of the rectification bridge  34 , a choke coil L that stores/discharges excitation energy through the switching, a diode D and a smoothing capacitor C 2  that rectify and smooth the output current from the choke coil L, a resistor R 1  that converts a current flowing through the switching element Q 0  to a voltage for detection and a control circuit  36  that controls the switching of the switching element Q 0 . 
     The current that flows from the DC-DC converter  35 , which is a DC power supply, to the LED module  32  is converted to a voltage value by a current detection resistor R 2 , compared with a reference voltage Vref from a reference voltage source  38  by a comparison circuit  37  and the comparison result is fed back to the control circuit  36 . The control circuit  36  controls the switching frequency and duty of the switching element Q 0  in response to the detection results of the resistors R 1  and R 2 . Constant voltage control over the voltage VDC and constant current control over the current that flows to the LED module  32  are performed in this way. 
     What should be noted is that according to the present embodiment, in the LED load circuits U 1  to U 3 , the control elements Q 1  to Q 3  configuring a current mirror circuit are arranged in series to equalize values of currents flowing through the LED load circuits U 1  to U 3 , one of the control elements Q 1  to Q 3  (Q 1  in the example of  FIG. 11 ) is to have a diode structure so as to become a reference current circuit of the current mirror, the flowing current values of the remaining control circuits (U 2  and U 3  in the example of  FIG. 11 ) are interlocked through control terminals and the LED load circuits U 1  to U 3  are thereby balanced. 
     To be more specific, when the control elements Q 1  to Q 3  are transistors as shown in  FIG. 11 , the base and collector, which are the control terminals in the control element Q 1 , are short-circuited and the bases of the control elements Q 1  to Q 3  are commonly connected. On the other hand, when the control terminals are MOS type transistors, the gate and drain, which are the control terminals in the control element Q 1 , are short-circuited and the gates of the control elements Q 1  to Q 3  are commonly connected. 
     What should be further noted is that an impedance element A is inserted in series in the LED load circuit U 1  of the control element Q 1  been to have the diode structure and the impedance element A is made to produce a voltage drop Va equal to or greater than Vf×n×σ at a rated current, where Vf is the ON voltage of the LED D 1 , σ is a variance thereof and n is the number of serially connected diodes. 
     The impedance element A can be realized from, for example, one or a plurality of diodes as shown in  FIG. 12A , a Zener diode as shown in  FIG. 12B , a resistor as shown in  FIG. 12C , and the like. When the diodes shown in  FIG. 12A  are used, for example, a small variation of 0.7 V can be handled by a single diode, and when the Zener diode shown in  FIG. 12B  is used, a large variation equal to or greater than 2 V as the sum of the ON voltages Vf can be handled and when such a resistor as shown in  FIG. 12C  is used, loss is produced all the time but the resistor can handle a smaller variation than by the diode and is suitable for when the variations in the ON voltages Vf are small or when the number of LEDs D 1  is small. 
     Configured as shown above, even when there are variations in the ON voltages Vf of the LEDs D 1 , the circuit that creates a reference current of the current mirror circuit is a circuit with the highest voltage drop by LED currents including the sum of the ON voltages Vf of the LEDs D 1 , and it is thereby possible to uniformly control the current values in the LED load circuits U 1  to U 3  and uniformize light outputs from many LEDs D 1 . Furthermore, such a configuration does not require the circuit that creates only a reference current and can eliminate circuit loss accordingly. Furthermore, one of the control elements Q 1  to Q 3  of transistors and the like is to have a diode structure and simply configured into a mirror circuit, and therefore the circuit can be realized in a low-cost configuration. 
     Although the DC power supply of this LED lighting circuit  231  is the DC-DC converter  35  having the choke coil L as in the case of the LED lighting circuit  1  in the aforementioned conventional example shown in  FIG. 29 , the DC power supply may also be an insulation type DC-DC converter having the transformer t in the conventional example shown in  FIG. 30 , and the DC power supply to the LED module  32  in particular is arbitrary. However, when constant current control through current mirror operation using the control elements Q 1  to Q 3  is performed, use of constant current control is preferable to use of constant voltage control for the DC power supply. 
     In the above described explanations, the emitter area ratios of the control elements (transistors) Q 1  to Q 3 , that is, the rated currents of LEDs D 1  of the LED load circuits U 1  to U 3  are the same, but the rated currents may also be configured to be different from each other, and in that case, the control elements Q 1  to Q 3  perform control so as to maintain the different set current ratios. Furthermore, organic EL (organic LED) may also be applicable to the LEDs D 1  of the present invention. 
     Furthermore, the impedance element A can also be realized using an LED, and in that case, as shown with an LED lighting circuit  231   a  in  FIG. 13 , in an LED load circuit U 1   a  of an LED module  32   a , it is only necessary to provide an extra LED D 10  to set a greater number of series LEDs of the LED load circuit U 1   a  than the remaining LED load circuits U 2  and U 3 . For example, assuming the accuracy variation of the ON voltages Vf of the LEDs D 1  is σ and the number of serially connected diodes is n, when σ is on the order of 10%, a setting can be made such that the sum of ON voltages Vf of the LED load circuit U 1   a  is always the highest, for example, the number of additional LEDs D 10  is 1 up to the order of n=10 and 2 up to the order of n=20. By adopting such a configuration, it is possible to easily adopt a configuration in which the sum of the ON voltages Vf is the highest and effectively use power consumption by the impedance element A. 
     Embodiment 2 Based on Third Viewpoint 
       FIG. 14  is a block diagram showing a configuration of an LED lighting circuit  251  according to Embodiment 2 based on the third viewpoint of the present invention. In this LED lighting circuit  251 , parts similar and corresponding to those of the aforementioned LED lighting circuit  231  are assigned the same reference numerals and explanations thereof will be omitted. What should be noted is that in this LED lighting circuit  251 , a short-circuit switch SW is provided between terminals of the impedance element A and in a condition in which the short-circuit switch SW is opened and the control elements Q 1  to Q 3  are performing current mirror operation, a Vf detection circuit  252  detects the sum of LED ON voltages Vf in the LED load circuits U 1  to U 3 , and based on the detection result, the switching control circuit  253  closes the short-circuit switch SW when the sum of the ON voltages Vf of the LED load circuit U 1  where the control element Q 1  has the diode structure is the highest, and opens the short-circuit switch SW otherwise. 
       FIG. 15  is a block diagram showing a configuration example of the Vf detection circuit  252  and the switching control circuit  253 . The Vf detection circuit  252  is configured by including two comparators CP 1  and CP 2  and an AND gate G that adds up those outputs. The terminal voltage of the LED load circuit U 1  for which the impedance element A is commonly provided is given to the non-inverted input ends of the comparators CP 1  and CP 2 , and the terminal voltages of the LED load circuits U 2  and U 3  for which the impedance element A is not provided are given to the non-inverted input ends. Therefore, when the terminal voltage of the LED load circuit U 1  is lower, that is, when the amount of voltage drop from the output voltage VDC of the DC-DC converter  35  is higher, high level is outputted from the comparators CP 1  and CP 2 , and when the amount of voltage drop from the LED load circuit U 1  is highest, high level is outputted from the AND gate G. 
     The switching control circuit  253  is configured by including a transistor TR 1 , to the base of which the output of the AND gate G is given, a base resistor R 11  and a collector resistor R 12  thereof and a photocoupler PC which is driven by the transistor TR 1  via the collector resistor R 12 . Therefore, when high level is outputted from the AND gate G, the transistor TR 1  turns ON, a photodiode D 11  of the photocoupler PC lights up, a phototransistor TR 2  configuring the short-circuit switch SW turns ON, which causes the impedance element A to be bypassed. 
     Configured as shown above, when an attempt is made to perform current uniformizing operation using a current mirror as described above, the circuit with the highest sum of the ON voltages Vf of the LEDs D 1  must become the reference current circuit, and since when the Vf detection circuit  252  actually measures the sum of the LED ON voltage Vf in the LED load circuits U 1  to U 3 , the switching control circuit  253  inserts the impedance element A only when the impedance element A is necessary, it is possible to cause the impedance element A to function only when required and reduce losses at the impedance element A. 
     Embodiment 3 Based on Third Viewpoint 
       FIG. 16  is a block diagram showing a configuration of an LED lighting circuit  261  according to Embodiment 3 based on the third viewpoint of the present invention. In this LED lighting circuit  261 , parts similar and corresponding to those of the aforementioned LED lighting circuit  231  are shown assigned the same reference numerals, and explanations thereof will be omitted. What should be noted is that in this LED lighting circuit  261 , an LED module  32   b  is provided with impedance elements A 2  and A 3  in parallel between the terminals of LED load circuits U 2  and U 3  where control elements Q 2  and Q 3  do not form the diode structure. These impedance elements A 2  and A 3  are intended to reduce the impedance of the corresponding LED load circuits U 2  and U 3  and clamp the inter-terminal voltage so as to be lower than the inter-terminal voltage of the LED load circuit U 1  and are made up of, for example, a Zener diode shown in  FIG. 16 , or a configuration with a resistor element further connected in series to the Zener diode may also be used. 
     Configured in this way, the LED load circuit U 1  that creates a reference current of the current mirror circuit is a circuit with the highest voltage drop by LED currents including the sum of the ON voltages Vf of the LEDs D 1  even if there are variations in the ON voltages Vf of the LEDs D 1 , and can still uniformly control current values in the LED load circuits U 1  to U 3  and uniformize light outputs from many LEDs D 1 . Furthermore, such a configuration does not require the circuit that creates only a reference current and can eliminate circuit loss accordingly. 
     Embodiment 4 Based on Third Viewpoint 
       FIG. 17  is a block diagram showing a configuration of an LED lighting circuit  271  according to Embodiment 4 based on the third viewpoint of the present invention. In this LED lighting circuit  271 , parts similar and corresponding to those of the aforementioned LED lighting circuit  231  are shown assigned the same reference numerals, and explanations thereof will be omitted. What should be noted is that when performing feedback control over constant currents of the DC-DC converter  35 , in this LED lighting circuit  271 , a current detection resistor R 2  is inserted in one of the LED load circuits U 1  to U 3  (U 1  in the example of  FIG. 17 ). In this case, loss by the resistor R 2  can be reduced (in the example of  FIG. 17 , approximately ⅓ of that in the example of  FIG. 11 ). Furthermore, even if wire breakage occurs in LEDs D 1  of any LED load circuit other than the LED load circuit which becomes a reference, the remaining circuits can continue lighting with the constant current values. 
     Here, Japanese Patent Laid-Open No. 2006-203044 describes that when currents of the parallel LEDs having different ON voltages Vf are adjusted, transistors are connected in series, their gates are commonly driven, and further dummy diodes are connected in series to LEDs with the small ON voltages Vf so as to reduce differences in the ON voltages Vf. However, this prior art separately creates a reference current of the current mirror and inserts a diode to reduce the difference in the ON voltages Vf, whereas the present embodiment inserts a diode so as to increase the difference in the ON voltages Vf so that a reference current of the current mirror can be created. Therefore, when white light is produced through RGB light emission as in the case of this prior art, a diode is inserted in the element of R having a small ON voltage Vf (on the order of 2 V) according to this prior art, whereas in the present embodiment, a diode is inserted in the system of the element of B with a higher ON voltage Vf (on the order of 3 to 3.5 V), which is totally different. 
     Summary of Third Viewpoint 
     As described above, the LED lighting circuit based on the third viewpoint of the present invention is an LED lighting circuit that causes a current to flow from a DC power supply to an LED module made up of a plurality of LED load circuits arranged parallel to each other, each LED load circuit being made up of one or a plurality of serially arranged LEDs, preferably including control elements arranged in series to the LED load circuits, configuring a current mirror circuit so as to interlock flowing current values in the LED load circuits, one of which is to have a diode structure so as to be a reference current circuit of the current mirror, and an impedance element inserted in series in the circuit of the control element having the diode structure producing a voltage drop of equal to or higher than Vf×n×σ at a rated current, where Vf is an LED ON voltage, σ is a variation thereof and n is the number of serially connected diodes. 
     According to the above described configuration, in the LED lighting circuit to be used for an illuminating apparatus and the like, when a DC power supply drives lighting of an LED module made up of a plurality of LED load circuits arranged parallel to each other, each LED load circuit being made up of one or a plurality of serially arranged LEDs, control elements configuring a current mirror circuit are arranged in series to the LED load circuits, one of the control elements is to have a diode structure so as to be a reference current circuit of the current mirror, flowing current values of the control elements of the remaining circuits are interlocked through the control terminals and the LED load circuits are thereby balanced. To be more specific, when the control elements are transistors, the base and collector, which are the control terminals, are short-circuited and the bases are commonly connected. On the other hand, when the control terminals are MOS type transistors, the gate and drain, which are the control terminals, are short-circuited and the gates are commonly connected. Furthermore, an impedance element which can be realized with a diode and the like is inserted in series to the circuit of the control element which is to have the diode structure producing a voltage drop of equal to or higher than Vf×n×σ at a rated current, where Vf is an LED ON voltage, σ is a variation thereof and n is the number of serially connected diodes. 
     Therefore, even if there is a variation in the LED ON voltages Vf, the circuit that creates a reference current of the current mirror circuit is a circuit with the highest voltage drop by LED currents including the sum of LED ON voltages Vf, and can thereby uniformly control current values in the LED load circuits and uniformize light outputs from many LEDs. Furthermore, such a configuration does not require the circuit that creates only a reference current and can eliminate circuit loss accordingly. 
     Furthermore, in the LED lighting circuit based on the third viewpoint of the present invention, the impedance elements are preferably LEDs. According to the above described configuration, by only setting a greater number of series LEDs of the LED load circuit which becomes a reference current circuit of the current mirror, it is possible to make such a setting that the sum of the ON voltages Vf becomes the highest, easily configure the apparatus and effectively use power consumption by the impedance element. 
     Furthermore, the LED lighting circuit based on the third viewpoint of the present invention preferably includes a short-circuit switch that can short-circuit between terminals of the impedance element, detection means for detecting the sum of the LED ON voltages Vf in the LED load circuits when the short-circuit switch is opened and the control element is performing current mirror operation and switching control means for responding to the detection result of the detection means, closing the short-circuit switch when the sum of the ON voltages Vf of the LED load circuit whose control element has the diode structure is the highest and closing the short-circuit switch otherwise. 
     According to the above described configuration, when an attempt is made to perform current uniformizing operation using the current mirror as described above, the circuit with the highest sum of the ON voltages Vf of the LEDs D 1  must become the reference current circuit, and a short-circuit switch that short-circuits between the terminals of the impedance element is provided beforehand, the detection means actually measures the sum of the LED ON voltages Vf in the LED load circuits, the switching control means closes the short-circuit switch so as not to allow the impedance element to function when the sum of the ON voltages Vf of the LED load circuit whose control element has a diode structure is the highest, and opens the short-circuit switch otherwise to allow the impedance element to function. Therefore, it is possible to allow the impedance element to function for aging and the like only when required, and suppress losses at the impedance element. 
     Furthermore, the LED lighting circuit based on the third viewpoint of the present invention is an LED lighting circuit that causes a current to flow from a DC power supply to an LED module made up of a plurality of LED load circuits arranged parallel to each other, each LED load circuit being made up of one or a plurality of serially connected LEDs, preferably including control elements arranged in series to the LED load circuits configuring a current mirror circuit and interlocks flowing current values in the LED load circuits, one of which is to have a diode structure so as to be a reference current circuit of the current mirror, and an impedance element inserted parallel to circuits other than the circuit of the control element having the diode structure that reduces the impedance of the LED load circuit. 
     According to the above described configuration, in the LED lighting circuit to be used for an illuminating apparatus and the like, when a DC power supply drives lighting of an LED module made up of a plurality of LED load circuits arranged parallel to each other, each LED load circuit being made up of one or a plurality of serially connected LEDs, control elements configuring a current mirror circuit are arranged in series to the LED load circuits, one of the control elements is to have a diode structure so as to be a reference current circuit of the current mirror, flowing current values of the control elements of the remaining circuits are interlocked through control terminals and the LED load circuits are thereby balanced. To be more specific, when the control elements are transistors, the base and collector, which are the control terminals, are short-circuited and the bases are commonly connected. On the other hand, when the control terminals are MOS type transistors, the gate and drain, which are the control terminals, are short-circuited and the gates are commonly connected. Furthermore, an impedance element for reducing the impedance of the LED load circuit is inserted parallel to circuits other than the circuit of the control element having the diode structure. 
     Therefore, even if there is a variation in the LED ON voltages Vf, the circuit to create a reference current of the current mirror circuit is designed to be a circuit with the highest voltage drop by LED currents including the sum of the LED ON voltages Vf, and can uniformly control the current value in the LED load circuits and uniformize light outputs from many LEDs. Furthermore, such a configuration does not require the circuit that creates only a reference current and can eliminate circuit loss accordingly. 
     Furthermore, in the LED lighting circuit based on the third viewpoint of the present invention, the DC power supply is a DC-DC converter and is preferably configured by including the current detection means for detecting a total value of currents flowing through the LED load circuits or a value of current flowing through the LED load circuit corresponding to the diode-connected control element, a reference voltage source and a comparator for comparing the detection results from the current detection means and control means for controlling the DC power supply through feedback so that the sum of values of currents flowing to the LED module becomes a predetermined value according to the output from the comparator. 
     According to the above described configuration, the values of currents flowing from the DC power supply to the LED load circuits are detected, the DC power supply is subjected to constant current control through feedback so that the sum of the flowing current values becomes a predetermined value based on the detection results, and therefore losses at the control elements are small compared to constant voltage control and losses can be reduced. 
     The illuminating apparatus based on the third viewpoint of the present invention preferably uses the above described LED lighting circuit. The above described configuration can uniformize light outputs from many LEDs even if the LED ON voltages (Vf) vary to an extreme degree and realize a low-loss illuminating apparatus. 
     Embodiment 1 Based on Fourth Viewpoint 
       FIG. 18  is a block diagram showing a configuration of an LED lighting circuit  331  according to Embodiment 1 based on a fourth viewpoint of the present invention. In this LED lighting circuit  331 , three LED load circuits U 1   a  to U 3   a  are connected parallel to each other, each LED load circuit being made up of many serially connected LEDs D 1  to configure an LED module  332 . The number of series LED loads in each LED load circuit U 1   a  to U 3   a  is arbitrary and each LED load circuit may also be constructed of a single LED. 
     In the LED load circuits U 1   a  to U 3   a , LEDs D 1  are mounted on and bonded to a common heat sink, and configured with a fluorescent substance for wavelength conversion and a light diffusion lens and the like attached. The LED module  332  and LED lighting circuit  331  are used as an illuminating apparatus, emit blue or ultraviolet light as the LED load, convert, in wavelength, the light from the LED load using the fluorescent substance and emit the light as white light. The number of parallel LED load circuits U 1   a  to U 3   a  is also arbitrary and a technique for obtaining white light by combining light emitted in three primary colors RGB, for example, is also arbitrary. 
     A DC voltage VDC resulting from converting a voltage Vac from a commercial power supply  33  to DC through a noise cut capacitor C 1  and a rectification bridge  34  and converting the DC to a voltage via a DC-DC converter  35  is added to the LED module  332 . The DC-DC converter  35  is constructed of a voltage boosting chopper circuit configured by including a switching element Q 0  that switches the DC output voltage of the rectification bridge  34 , a choke coil L that stores/discharges excitation energy through the switching, a diode D and a smoothing capacitor C 2  that rectify and smooth the output current from the choke coil L, a resistor R 1  that converts a current flowing through the switching element Q 0  to a voltage for detection and a control circuit  36  that controls the switching of the switching element Q 0 . 
     The current that flows from the DC-DC converter  35 , which is a DC power supply, to the LED module  332  is converted to a voltage value by the current detection resistor R 2 , compared with a reference voltage Vref from a reference voltage source  38  by a comparison circuit  37  and the comparison result is fed back to the control circuit  36 . In response to the detection results of the resistors R 1  and R 2 , the control circuit  36  controls the switching frequency and duty of the switching element Q 0 . Constant voltage control over the voltage VDC and collective constant current control over the current that flows to the LED module  332  are performed in this way. 
     In the LED load circuits U 1   a  to U 3   a , control elements Q 1 ′ to Q 3 ′ configuring a current mirror circuit are arranged in series to equalize values of currents flowing through the LED load circuits U 1   a  to U 3   a , a circuit (U 1   a  in the example of  FIG. 18 ) of the circuit with the highest voltage drop by LED currents including the sum of the LED ON voltages Vf in the corresponding LED load circuits U 1   a  to U 3   a  in the control elements Q 1 ′ to Q 3 ′ is used as a reference, the control element (Q 1 ′ in the example of  FIG. 18 ) is to have a diode structure and the flowing current values of the control elements (Q 2 ′ and Q 3 ′ in the example of  FIG. 18 ) of the remaining circuits are interlocked through control terminals and the LED load circuits U 1   a  to U 3   a  are thereby balanced. 
     To be more specific, when the control elements Q 1 ′ to Q 3 ′ are transistors as shown in  FIG. 18 , the base and collector, which are the control terminals, are short-circuited and the bases are commonly connected. On the other hand, when the control terminals are MOS type transistors, the gate and drain, which are the control terminals, are short-circuited and the gates are commonly connected. 
     What should be noted is that in the present embodiment, splitting circuits A are arranged parallel to the LEDs D 1  and each splitting circuit A allows a current at a level predefined for the LED D 1  in the event of wire breakage of the corresponding LEDs (D 1  in the example of  FIG. 18 ) to pass by bypassing the LEDs as shown by reference character F 1  in  FIG. 18 . 
     To be more specific, the splitting circuit A is constructed of elements or a circuit capable of generating a constant current such as a Zener diode ZD as a single unit as shown in  FIG. 19A  and a series circuit of a Zener diode ZD and a resistor R as shown in  FIG. 19B  and the flowing current value thereof is a value preset in the respective LED load circuits U 1   a  to U 3   a . A Zener diode provided for anti-static measures can also be used for the Zener diode ZD provided parallel to the LEDs D 1 . 
     Configured as shown above, the sum of values of currents flowing from the DC-DC converter  35  to the LED load circuits U 1   a  to U 3   a  is controlled to be constant through collective constant current control based on the detection result of the resistor R 2  and the current balance among the LED load circuits U 1   a  to U 3   a  is uniformly controlled by the current mirror circuit, and so light outputs from many LEDs D 1  can be uniformized. Furthermore, since the LED load circuit (U 1   a  in the example of  FIG. 18 ) with the highest sum of the ON voltages Vf of the LEDs D 1  is used for the circuit that creates a reference current of the current mirror circuit, such a configuration does not require the circuit that creates only a reference current and can eliminate circuit loss accordingly. Furthermore, since one of the control elements Q 1 ′ to Q 3 ′ such as transistors is to have a diode structure and simply configured into a mirror circuit, currents can be uniformized in a low-cost configuration. 
     The DC power supply of this LED lighting circuit  331  is a DC-DC converter  35  having the choke coil L, but the DC power supply may also be an insulation-type DC-DC converter having the transformer t shown in the aforementioned conventional example in  FIG. 30  and the DC power supply corresponding to the LED module  332  in particular is arbitrary. However, when constant current control through current mirror operation using the control elements Q 1 ′ to Q 3 ′ is performed, use of constant current control is preferable to use of constant voltage control for the DC power supply. 
     In the above described explanations, the emitter area ratios of the control elements (transistors) Q 1 ′ to Q 3 ′, that is, the rated currents of LEDs D 1  of the LED load circuits U 1 ′ to U 3 ′ are the same, but the rated currents may also be configured to be different from each other and in such a case, the control elements Q 1 ′ to Q 3 ′ perform control so as to maintain the different set current ratios. Furthermore, organic EL (organic LED) may also be applicable to the LEDs D 1  of the present invention. 
     Furthermore, configured as in the present embodiment, the DC-DC converter  35  collectively drives lighting of the LED module  332  made up of a plurality of LEDs D 1  with a constant current, and even if wire breakage occurs in an arbitrary LED D 10 , the current that should flow to the LED D 10  is made to bypass the wire breakage location and flow at the same level as before the wire breakage through the splitting circuit A, and it is thereby possible to prevent an overcurrent from flowing to the remaining LED load circuits U 2   a  and U 3   a  causing lighting up in an overloaded condition and prevent malfunction from escalating into a chain reaction. 
     Furthermore, the splitting circuit A is constructed of a Zener diode ZD or a series circuit of a Zener diode ZD and a resistor R arranged parallel to the LED D 1  and is especially suitable as a splitting circuit provided for every one or a small number of LEDs, eliminates continuous loss and allows a bypass of the current upon detection of wire breakage. 
     Embodiment 2 Based on Fourth Viewpoint 
       FIG. 20  is a block diagram showing a configuration of an LED lighting circuit  351  according to Embodiment 2 based on a fourth viewpoint of the present invention. In this LED lighting circuit  351 , parts similar and corresponding to those of the aforementioned LED lighting circuit  331  are shown assigned the same reference numerals, and explanations thereof will be omitted. What should be noted is that in this LED lighting circuit  351 , splitting circuits A 1  to A 3  are provided for respective LED load circuits U 1  to U 3  each made up of a plurality of serially connected LEDs D 1 . 
     For this purpose, the splitting circuits A 1  to A 3  are configured by including series circuits of impedance elements Z 1  to Z 3  and switch elements SW 1  to SW 3  arranged parallel to the respective LED load circuits U 1  to U 3  and wire breakage detection circuits S 1  to S 3  that detect the presence/absence of wire breakage of LEDs D 1  in the respective LED load circuits U 1  to U 3 , open the switch elements SW 1  to SW 3  in a normal condition and close the switch elements SW 1  to SW 3  when wire breakage is detected. 
     The wire breakage detection circuits S 1  to S 3  are configured by including current/voltage conversion resistors R 11  to R 31  arranged in series to the LED load circuits U 1  to U 3 , comparators CP 1  to CP 3  that compare the inter-terminal voltage of the current/voltage conversion resistors R 11  to R 31  with a predetermined reference voltage Vref 1 , reference voltage sources E 1  to E 3  and base resistors R 12  to R 32  that connect the bases of the switch elements SW 1  to SW 3  made up of transistors and the output ends of the comparators CP 1  to CP 3 . 
     Therefore, when there is no wire breakage in the LEDs D 1  in the LED load circuit U 1  to U 3 , a terminal voltage at a predetermined level is outputted from the current/voltage conversion resistor R 11  to R 31 , which surpasses the reference voltage Vref 1 , causing the comparator CP 1  to CP 3  to output low level, whereby the switch element SW 1  to SW 3  is turned OFF and the impedance element Z 1  to Z 3  is separated from the LED load circuit U 1  to U 3 . On the other hand, when wire breakage occurs, the terminal voltage of the current/voltage conversion resistor R 11  to R 31  becomes ground level, which is lower than the reference voltage Vref 1 , the comparator CP 1  to CP 3  outputs high level, causing the switch element SW 1  to SW 3  to turn ON and the impedance element Z 1  to Z 3  is connected between the output ends of the DC-DC converter  35  in series to the control elements Q 1  to Q 3  instead of the LED load circuits U 1  to U 3 . 
     Such a configuration is especially suitably provided for each LED load circuit U 1  to U 3  made up of a plurality of series LEDs D 1 , making it possible to realize the splitting circuits A 1  to A 3  with small continuous loss and capable of bypassing currents upon detection of wire breakage. 
     Embodiment 3 Based on Fourth Viewpoint 
       FIG. 21  is a block diagram showing a configuration of an LED lighting circuit  361  according to Embodiment 3 based on the fourth viewpoint of the present invention. In this LED lighting circuit  361 , parts similar and corresponding to those in the aforementioned LED lighting circuit  351  are shown assigned the same reference numerals, and explanations thereof will be omitted. What should be noted is that in this LED lighting circuit  361 , the LED load circuit U 1  that creates a reference current of the current mirror circuit is provided with only the current/voltage conversion resistor R 11  and not the splitting circuit A 1 , while in splitting circuits A 2 ′ and A 3 ′ of the remaining LED load circuits U 2  and U 3 , the comparators CP 2  and CP 3  of wire breakage detection circuits S 2 ′ and S 3 ′ compare the inter-terminal voltage of the current/voltage conversion resistor R 11  with the inter-terminal voltage of the current/voltage conversion resistors R 21  and R 31 . 
     As described above, the LED load circuit U 1  that creates a reference current of the current mirror circuit is a circuit with the highest sum of the ON voltages Vf of the LEDs D 1 , and therefore when wire breakage has not occurred in any LED, the terminal voltage of the current/voltage conversion resistor R 11  inserted on the grounding side is lower than the terminal voltage of the remaining current/voltage conversion resistors R 21  and R 31  and the switch elements SW 2  and SW 3  remain OFF. On the contrary, when wire breakage occurs in the LED load circuit U 2  or U 3 , the terminal voltage of the current/voltage conversion resistor R 21  or R 31  is lower than the terminal voltage of the current/voltage conversion resistor R 11  and therefore the switch element SW 2  or SW 3  turns ON. Thus, it is possible to eliminate the reference voltage sources E 2  and E 3  for creating the reference voltage Vref 1  and eliminate complicated adjustment of the reference voltage Vref 1 . When a short-circuit occurs in the LED load circuit U 1  that creates a reference current of the current mirror circuit, all LEDs are turned OFF for the sake of safety. 
     Summary of Fourth Viewpoint 
     As described above, the LED lighting circuit based on the fourth viewpoint of the present invention is an LED lighting circuit that causes a DC power supply to drive lighting of an LED module made up of a plurality of LED load circuits arranged parallel to each other, each LED load circuit being made up of one or a plurality of serially connected LEDs with a constant current, preferably including splitting circuits inserted parallel to one or a plurality of series LEDs between terminals thereof, which allow, in the event of wire breakage of an LED, a current at a level predefined for the LED to bypass the LED. 
     According to the above described configuration, in an LED lighting circuit to be used for an illuminating apparatus and the like, when a DC power supply drives lighting of an LED module made up of a plurality of LED load circuits arranged parallel to each other, each LED load circuit being made up of one or a plurality of serially connected LEDs with a constant current, splitting circuits are provided parallel to terminals of each LED or an arbitrary number of LEDs of an LED load circuit made up of a plurality of serially connected LEDs, each splitting circuit allows, in the event of wire breakage of the corresponding LED, a current at a level predefined for the LED to pass therethrough instead of the LED. 
     Therefore, the DC power supply collectively drives lighting of the LED module made up of a plurality of LEDs with a constant current and even if wire breakage occurs in an arbitrary LED, the current that should flow to the LED bypasses the wire breakage location and flows at the same level as before the wire breakage, makes it possible to prevent an overcurrent from flowing to the remaining LED load circuits, causing lighting up in an overloaded condition and prevent malfunctions from escalating into a chain reaction. 
     Furthermore, in the LED lighting circuit based on the fourth viewpoint of the present invention, the splitting circuit preferably includes a Zener diode. 
     According to the above described configuration, connecting a Zener diode or a series circuit of a Zener diode and a resistor parallel to the LEDs is especially suitable as a splitting circuit arranged for every one or a small number of LEDs, eliminates continuous loss and can bypass the current upon detection of wire breakage. 
     Furthermore, in the LED lighting circuit based on the fourth viewpoint of the present invention, the splitting circuit is preferably configured by including a series circuit of an impedance element and a switch element arranged parallel to the one or a plurality of series LEDs, and a wire breakage detection circuit that detects the presence/absence of wire breakage in the one or plurality of series LEDs, opens the switch element in a normal condition and closes the switch element when wire breakage is detected. 
     The above described configuration is especially suitable as a splitting circuit provided for each LED load circuit made up of a plurality of series LEDs, produces less continuous loss and can bypass currents upon detection of wire breakage. 
     Furthermore, in the LED lighting circuit based on the fourth viewpoint of the present invention, control elements are preferably arranged in series to the LED load circuits, the control elements configure a current mirror circuit and interlock flowing current value of each of the LED load circuits and one of the control elements corresponding to an LED load circuit with the highest voltage drop by LED currents including the sum of LED ON voltages in the corresponding LED load circuit is diode-connected so as to constitute a reference current circuit of the current mirror. 
     According to the above described configuration, control elements configuring a current mirror circuit are arranged in series to the LED load circuits to which constant currents are collectively flown from the DC power supply, a circuit with the highest voltage drop by LED currents including the sum of LED ON voltages Vf in the LED load circuits is used as a reference in the control elements, the control element corresponding to the LED load circuit is to have a diode structure and the flowing current values of the control elements of the remaining circuits are interlocked through control terminals and the LED load circuits are thereby balanced. To be more specific, when the control elements are transistors, the base and collector, which are control terminals, are short-circuited and the bases are connected commonly. On the other hand, when the control elements are MOS type transistors, the gate and drain, which are control terminals, are short-circuited and the gates are connected commonly. 
     Therefore, the current balance between the LED load circuits is uniformly controlled by the current mirror circuit, and so light outputs from many LEDs can be uniformized. Furthermore, since an LED load circuit with the highest sum of ON voltages Vf is used for the circuit that creates a reference current of the current mirror circuit, such a configuration does not require the circuit that creates only a reference current and can eliminate circuit loss accordingly. 
     Furthermore, in the LED lighting circuit based on the fourth viewpoint of the present invention, the DC power supply is a DC-DC converter and is preferably configured by including the current detection means for detecting a total value of currents flowing through the LED load circuits, a reference voltage source and a comparator that compare the detection results from the current detection means, and control means for controlling the DC power supply through feedback so that the sum of values of currents flowing to the LED module becomes a predetermined value according to the output from the comparator. 
     According to the above described configuration, the values of currents flowing from the DC power supply to the respective LED load circuits are detected and the DC power supply is subjected to constant current control through feedback based on the detection results so that the sum of the flowing current values becomes a predetermined value, and therefore losses at the control elements are smaller compared to constant voltage control and losses can be reduced. 
     Furthermore, the illuminating apparatus based on the fourth viewpoint of the present invention preferably uses the above described LED lighting circuit. According to the above described configuration, when the DC power supply collectively drives the LED module made up of a plurality of LEDs with a constant current, it is possible to realize an illuminating apparatus capable of preventing malfunctions from expanding in the event of wire breakage in the LEDs. 
     Embodiment 1 Based on Fifth Viewpoint 
       FIG. 22  is a block diagram showing a configuration of an LED lighting circuit  431  according to Embodiment 1 based on a fifth viewpoint of the present invention. In this LED lighting circuit  431 , an LED module  32  is configured by connecting three LED load circuits U 1  to U 3  in parallel, each LED load circuit being made up of many serially connected LEDs D 1 . The number of series LED loads in each LED load circuit U 1  to U 3  is arbitrary and each LED load circuit may also be constructed of a single LED. 
     Each LED load circuit U 1  to U 3  is configured such that the LEDs D 1  are mounted on and bonded to a common heat sink and a fluorescent substance for wavelength conversion and a light diffusion lens and the like are also attached. The LED module  32  and LED lighting circuit  431  are used as an illuminating apparatus, and emit blue or ultraviolet light as the LED load, convert, in wavelength, the light from the LED load using the fluorescent substance and emit the light as white light. The number of parallel circuits of the LED load circuits U 1  to U 3  is also arbitrary and a technique for obtaining white light by combining light emitted in three primary colors RGB, for example, is also arbitrary. 
     A DC voltage VDC resulting from converting a voltage Vac from a commercial power supply  33  to DC through a noise cut capacitor C 1  and a rectification bridge  34  and converting the DC to a voltage via a DC-DC converter  35  is given to the LED module  32 . The DC-DC converter  35  is constructed of a voltage boosting chopper circuit configured by including a switching element Q 0  that switches the DC output voltage of the rectification bridge  34 , a choke coil L that stores/discharges excitation energy through the switching, a diode D and a smoothing capacitor C 2  that rectify and smooth the output current from the choke coil L, a resistor R 1  that converts a current flowing through the switching element Q 0  to a voltage for detection and a control circuit  36  that controls the switching of the switching element Q 0 . 
     The current that flows from the DC-DC converter  35 , which is a DC power supply, to the LED module  32  is converted to a voltage value by a current detection resistor R 2 , compared with a reference voltage Vref from a reference voltage source  38  by a comparison circuit  37  and the comparison result is fed back to the control circuit  36 . The control circuit  36  controls the switching frequency and duty of the switching element Q 0  in response to the detection results of the resistors R 1  and R 2 . Constant voltage control over the voltage VDC and constant current control over the current that flows to the LED module  32  are performed in this way. 
     What should be noted is that according to the present embodiment, in the respective LED load circuits U 1  to U 3 , control elements Q 1 ′ to Q 3 ′ configuring a current mirror circuit are arranged in series to the LED load circuits U 1  to U 3  to equalize values of currents flowing through the LED load circuits U 1  to U 3 , a circuit (U 1  in the example of  FIG. 22 ) with the highest voltage drop by LED currents including the sum of LED ON voltages Vf in the corresponding LED load circuits U 1  to U 3  in the control elements Q 1 ′ to Q 3 ′ is used as a reference and the control element (Q 1 ′ in the example of  FIG. 22 ) in the circuit is to have a diode structure, the flowing current values of the control elements (Q 2 ′ and Q 3 ′ in the example of  FIG. 22 ) of the remaining circuits are interlocked through the control terminals and the LED load circuits U 1  to U 3  are thereby balanced. 
     To be more specific, when the control elements Q 1 ′ to Q 3 ′ are transistors as shown in  FIG. 22 , the base and collector, which are the control terminals, are short-circuited and the bases are commonly connected. On the other hand, when the control terminals are MOS type transistors, the gate and drain, which are the control terminals, are short-circuited and the gates are commonly connected. 
     What should be further noted is that an impedance circuit  441  is inserted parallel to the LED load circuit (U 1  in the example of  FIG. 22 ) which is the reference current circuit and the impedance circuit  441  bypasses the current that should flow through the LED load circuit U 1  when wire breakage occurs in an LED D 10  in the corresponding LED load circuit U 1  and maintains the reference current of the current mirror circuit. 
     To be more specific, the impedance circuit  441  is constructed of elements or a circuit capable of generating a constant current such as a resistor, a constant current circuit, a Zener diode and a series circuit of a Zener diode and a resistor, and the like, with a switch element Q 4  connected in series, and arranged parallel to the LED load circuit U 1 . Furthermore, a wire breakage detection circuit  442  is provided in connection with the LED load circuit U 1  to detect wire breakage of the LEDs D 10  in the circuit and cause the switch element Q 4  to turn ON. 
     The wire breakage detection circuit  442  which is wire breakage detection means is intended to detect a terminal voltage of the LED load circuit U 1 , that is, a collector voltage of the control element Q 1 ′, configured by including a series circuit of a Zener diode ZD 1  and voltage dividing resistors R 41  and R 42  arranged parallel to the LED load circuit U 1  and a capacitor C 11  arranged parallel to the resistor R 42 , and the connection point among the voltage dividing resistor R 41 , voltage dividing resistor R 42 , and capacitor C 11  is connected to the base of the switch element Q 4  which is made up of a transistor. Due to wire breakage of some LED D 10 , when the terminal voltage of the LED load circuit U 1 , that is, the collector voltage of the control element Q 1 ′ increases to a predetermined voltage which is higher than the sum of the LED ON voltages Vf, the Zener diode ZD 1  turns ON and the switch element Q 4  also turns ON and a current flows through the impedance circuit  441  instead of the LED load circuit U 1  where the wire breakage has occurred. Therefore, the voltage dividing resistors R 41  and R 42  and capacitor C 11  configure control means for controlling the switch element Q 4  in response to the detection result of the Zener diode ZD 1 . 
     Configured as shown above, the sum of values of currents flowing from the DC-DC converter  35  to the LED load circuits U 1  to U 3  is controlled to be constant through collective constant current control based on the detection result of the resistor R 2 , and the current balance among the LED load circuits U 1  to U 3  is uniformly controlled through the current mirror circuit, and it is thereby possible to uniformize light outputs from many LEDs D 1 . Furthermore, since an LED load circuit with the highest sum of the ON voltages Vf of the LEDs D 1  (U 1  in the example of  FIG. 22 ) is used for the circuit (Q 1 ′ in the example of  FIG. 22 ) that creates a reference current of the current mirror circuit, such a configuration does not require the circuit that creates only a reference current and can eliminate circuit loss accordingly. One of the control elements Q 1 ′ to Q 3 ′ made up of transistors and the like is to have a diode structure and only configured into a mirror circuit, and can thereby be realized in a low-cost configuration. 
     As in the case of the LED lighting circuit shown in the aforementioned conventional example in  FIG. 29 , the DC power supply of this LED lighting circuit  431  is a DC-DC converter  35  having the choke coil L, but may also be the insulation-type DC-DC converter having the transformer t shown in the conventional example in  FIG. 30  and the DC power supply for the LED module  32  in particular is arbitrary. However, when constant current control through current mirror operation using the control elements Q 1 ′ to Q 3 ′ is performed, use of constant current control is preferable to use of constant voltage control for the DC power supply. 
     Furthermore, according to the present embodiment, even if wire breakage occurs in the LEDs D 10  of the LED load circuit U 1  which constitutes the reference current circuit, a reference current continues to flow through the impedance circuit  441 , thus making it possible to prevent lighting out from extending to the other LED load circuits U 2  and U 3 . Furthermore, with the switch element Q 4  connected in series thereto, the impedance circuit  441  is arranged parallel to the LED load circuit U 1  which constitutes a reference current circuit of the current mirror, and when wire breakage of some LED D 10  is detected by the wire breakage detection circuit  442 , the switch element Q 4  turns ON, and the impedance circuit  441  is inserted, and it is thereby possible to suppress continuous loss by the impedance circuit  441 , reduce power consumption and guard against wire breakage. 
     As other means of wire breakage detection by the wire breakage detection circuit  442 , the Zener diode ZD 1  may be replaced by a current/voltage conversion resistor R 43  arranged in series to the LED load circuit U 1  which constitutes the reference current circuit in an LED lighting circuit  431   a  shown in  FIG. 23  or a light-emitting diode D 11  in an LED lighting circuit  431   b  shown in  FIG. 24  and so on. 
     To be more specific, in the wire breakage detection circuit  442   a  in  FIG. 23 , a resistor R 44  and a control transistor Q 5  are connected in series between the power supply lines, a voltage obtained from the current/voltage conversion resistor R 43  is given to the base of the transistor Q 5  and the output from the collector is given to the base of the switch element Q 4 . Therefore, while a current is flowing to the LED load circuit U 1 , the transistor Q 5  is ON, the switch element Q 4  is OFF and the impedance circuit  441  is separated. On the contrary, when a current no longer flows to the LED load circuit U 1  due to wire breakage, the transistor Q 5  turns OFF, the switch element Q 4  turns ON and the impedance circuit  441  is inserted. 
     Likewise, in the wire breakage detection circuit  442   b  in  FIG. 24 , the resistor R 44  and a control phototransistor Q 6  are connected in series between the power supply lines and the phototransistor Q 6  together with the light-emitting diode D 11  constitutes a photocoupler PC and the output from the collector is given to the base of the switch element Q 4 . Therefore, while a current is flowing to the LED load circuit U 1 , the phototransistor Q 6  is ON and the switch element Q 4  is QFF and the impedance circuit  441  is separated. On the contrary, when a current no longer flows to the LED load circuit U 1  due to wire breakage, the phototransistor Q 6  turns OFF, the switch element Q 4  turns ON and the impedance circuit  441  is inserted. 
     Embodiment 2 Based on Fifth Viewpoint 
       FIG. 25  is a block diagram showing a configuration of an LED lighting circuit  451  according to Embodiment 2 based on a fifth viewpoint of the present invention. In this LED lighting circuit  451 , parts similar and corresponding to those of the aforementioned LED lighting circuit  431  are shown assigned the same reference numerals, and explanations thereof will be omitted. What should be noted is that in this LED lighting circuit  451 , when a DC-DC converter  35  is subjected to constant current feedback control, a current detection resistor R 2  thereof is inserted in the LED load circuit U 1 , which is the reference current creation circuit. In this case, loss at the resistor R 2  can be reduced (in the example of  FIG. 25 , approximately ⅓ of loss in the example of  FIG. 22 ). Furthermore, even if wire breakage occurs in LEDs D 1  of any circuit other than the LED load circuit which becomes a reference, the remaining circuits can continue lighting with a constant current value. 
     Embodiment 3 Based on Fifth Viewpoint 
       FIG. 26  is a block diagram showing a configuration of an LED lighting circuit  461  according to Embodiment 3 based on the fifth viewpoint of the present invention. In this LED lighting circuit  461 , parts similar and corresponding to those in the aforementioned LED lighting circuit  431  are shown assigned the same reference numerals, and explanations thereof will be omitted. What should be noted is that in this LED lighting circuit  461 , control elements Q 2 ′ and Q 3 ′ corresponding to the LED load circuits U 2  and U 3  other than the LED load circuit U 1 , which is the reference current creation circuit, are provided with switches SW 42  and SW 43  whereby, when the wire breakage detection circuit  442  detects wire breakage of the LED load circuit U 1 , which is the reference current creation circuit, the switch switching control circuit  462  can switch the corresponding control elements QT and Q 3 ′ to a diode connection. 
     Therefore, in response to the occurrence of wire breakage, when the wire breakage detection circuit  442  turns ON one (SW 42  in the example of  FIG. 26 ) of the switches SW 42  and SW 43  which are short-circuit means, constant current operation continues to be performed by the LED load circuit (U 2  in the example of  FIG. 26 ) which has been turned ON and current balance with the remaining LED load circuit (U 3  in the example of  FIG. 26 ) is maintained. Thus, while lighting out is prevented from extending to other LED load circuits (U 2  and U 3  in the example of  FIG. 26 ), the remaining LED load circuits continue lighting with uniform current values. 
     Embodiment 4 Based on Fifth Viewpoint 
       FIG. 27  and  FIG. 28  are block diagrams showing configurations of LED lighting circuits  471  and  481  according to Embodiment 4 based on the fifth viewpoint of the present invention. In these LED lighting circuits  471  and  481 , parts similar and corresponding to those of the aforementioned LED lighting circuit  431  are shown assigned the same reference numerals, and explanations thereof will be omitted. What should be noted is that in the LED lighting circuit  471  first, a wire breakage detection circuit  442   c  detects wire breakage of the LEDs D 10  based on a reduction of the output current of a DC-DC converter  35 . To be more specific, a thyristor Q 7  is connected in series to the impedance element  441 , the cathode of a Zener diode ZD 1  is connected to the high side terminal of the current detection resistor R 2  and the anode of the Zener diode ZD 1  is connected to the base of a switch element Q 4  from a resistor R 45 , the emitter of the switch element Q 4  is connected to the low side terminal of the current detection resistor R 2 . Furthermore, the collector of the control element Q 4  is connected to the gate of the thyristor Q 7  via a bias resistor R 20 . 
     Therefore, when there is no wire breakage in the LEDs D 10 , the inter-terminal voltage of the current detection resistor R 2  is high, the Zener diode ZD 1  and switch element Q 4  turn ON, the gate of the thyristor Q 7  is driven low, the thyristor Q 7  turns OFF, and the impedance circuit  441  is not inserted, and when wire breakage occurs in the LEDs D 10 , the terminal voltage of the current detection resistor R 2  drops, the Zener diode ZD 1  and the control element Q 4  turn OFF, the gate of the thyristor Q 7  is driven high, the thyristor Q 7  turns ON and the impedance circuit  441  is inserted. Once the thyristor Q 7  turns ON, the state thereof is maintained until the power supply is stopped. Therefore, the thyristor Q 7  functions as latch means. The resistor R 45  is provided so as to prevent the Zener diode ZD 1  and the switch terminal Q 4  from absorbing the voltage drop at the current detection resistor R 2  for constant current feedback control. 
     On the other hand, in the LED lighting circuit  481 , a wire breakage detection circuit  482  detects wire breakage of the LEDs D 10  from an increase of the output voltage VDC of the DC-DC converter  35 . To be more specific, the wire breakage detection circuit  482  is configured by including voltage dividing resistors R 21  and R 22  inserted between the output terminals of the DC-DC converter  35  and a comparator  483  and a reference voltage source  484  that compare a voltage at the connection point with a predetermined reference voltage Wref 1 , and the output of the comparator  483  is given to the gate of a thyristor Q 7 . 
     Therefore, when there is no wire breakage in the LEDs D 10 , the output voltage VDC becomes a defined voltage, the comparator  483  outputs low level, the thyristor Q 7  turns OFF, the impedance circuit  441  is not inserted, and when wire breakage occurs in the LEDs D 10 , the output voltage VDC exceeds the defined voltage, the comparator  483  outputs high level, the thyristor Q 7  turns ON and the impedance circuit  441  is inserted. Once the thyristor Q 7  turns ON, the state is maintained until the power supply is stopped as in the case of  FIG. 27 . 
     Adopting such a configuration can also prevent full lighting out while suppressing continuous loss by the impedance circuit  441  even if wire breakage occurs in the LEDs D 10  of the LED load circuit U 1  which becomes a reference. 
     Summary of Fifth Viewpoint 
     As described above, the LED lighting circuit based on the fifth viewpoint of the present invention is an LED lighting circuit that causes a current to flow from a DC power supply to an LED module made up of a plurality of LED load circuits arranged parallel to each other, each LED load circuit being made up of one or a plurality of serially connected LEDs, preferably including control elements arranged in series to the LED load circuits to configure a current mirror circuit and interlock flowing current values in the LED load circuits, one of which being to have a diode structure so that an LED load circuit with the highest voltage drop by LED currents including the sum of LED ON voltages in the LED load circuits becomes a reference current circuit of the current mirror and an impedance circuit arranged parallel to the LED load circuit which constitutes a reference current circuit of the current mirror that keeps a flowing current value to a reference current in the event of wire breakage of some LED in the LED load circuits. 
     According to the above described configuration, in an LED lighting circuit to be used for an illuminating apparatus, when a current is caused to flow from a DC power supply to an LED module made up of a plurality of LED load circuits arranged parallel to each other, each LED load circuit being made up of one or a plurality of serially connected LEDs, control elements configuring a current mirror circuit are arranged in series to the LED load circuits and a circuit with the highest voltage drop by LED currents including the sum of LED ON voltages Vf in the LED load circuits is used as a reference, the control element corresponding to the LED load circuit is to have a diode structure and flowing current values of the control elements of the remaining circuits are interlocked through control terminals and the LED load circuits are thereby balanced. To be more specific, when the control elements are transistors, the base and collector, which are control terminals, are short-circuited and the bases are connected commonly. On the other hand, when the control elements are MOS type transistors, the gate and drain, which are control terminals, are short-circuited and the gates are connected commonly. Furthermore, an impedance circuit is arranged parallel to the LED load circuit that constitutes the reference current circuit and when wire breakage occurs in LEDs in the corresponding LED load circuit, the impedance circuit bypasses the current that should flow through the LED load circuit and maintains the reference current of the current mirror circuit. 
     Therefore, since current balance between the LED load circuits is uniformly controlled by the current mirror circuit, light outputs from many LEDs can be uniformized. Furthermore, since the LED load circuit with the highest sum of the ON voltages Vf is used for the circuit that creates a reference current of the current mirror circuit, such a configuration does not require the circuit that creates only a reference current and can eliminate circuit loss accordingly. Furthermore, even if wire breakage occurs in the LEDs of the LED load circuit that constitutes the reference current circuit, the reference current continues to flow, thus preventing lighting out from extending to the other LED load circuits. 
     Furthermore, in the LED lighting circuit based on the fifth viewpoint of the present invention, the impedance circuit is preferably provided with a switch element connected in series thereto, is arranged parallel to the LED load circuit which constitutes the reference current circuit of the current mirror and further includes wire breakage detection means that detects wire breakage of the LEDs in connection with the LED load circuit which constitutes the reference current circuit of the current mirror and turns ON the switch element. 
     According to the above described configuration, wire breakage detection means is provided and the switch element is also arranged in series to the impedance circuit, and when wire breakage is detected, the switch element is turned ON and the impedance circuit is inserted. 
     The wire breakage detection means can be constructed of, for example, a Zener diode and control means for turning ON the switch element when an increase of the inter-terminal voltage of the LED load circuit due to wire breakage of the LED is equal to or greater than a Zener voltage of the Zener diode or constructed of current detection means such as a current detection resistor or light-emitting diode arranged in series to the LED load circuit that constitutes a reference current circuit of the current mirror, and control means such as a control transistor or phototransistor for turning ON the switch element when the current detection means detects interruption of current due to wire breakage of the LED. 
     Therefore, it is possible to suppress continuous loss by the impedance circuit, reduce power consumption and guard against wire breakage. 
     Furthermore, in the LED lighting circuit based on the fifth viewpoint of the present invention, the impedance circuit is preferably provided with a switch element connected in series thereto, arranged parallel to the LED load circuit that constitutes a reference current circuit of the current mirror and further includes wire breakage detection means for detecting wire breakage of the LED from an increase of the output voltage of the DC power supply or a decrease of the output current and latch means for keeping the switch element ON when wire breakage is detected by the wire breakage detection means. 
     According to the above described configuration, the wire breakage detection means and latch means are provided, the switch element is arranged in series to the impedance circuit, and once wire breakage is detected from an increase of the output voltage of the DC power supply or a decrease of the output current, the switch element is turned ON and the impedance circuit is inserted. 
     Therefore, it is possible to suppress continuous loss by the impedance circuit, reduce power consumption and guard against breakage. 
     Furthermore, the LED lighting circuit based on the fifth viewpoint of the present invention is an LED lighting circuit that causes a current to flow from a DC power supply to an LED module made up of a plurality of LED load circuits arranged parallel to each other, each LED load circuit being made up of one or a plurality of serially connected LEDs, preferably including control elements arranged in series to the LED load circuits to configure a current mirror circuit and interlock flowing current values in the LED load circuits, one of which is to have a diode structure so that an LED load circuit with the highest voltage drop by LED currents including the sum of LED ON voltages in the LED load circuits becomes a reference current circuit of the current mirror, wire breakage detection means arranged in connection with the LED load circuit which constitutes a reference current circuit of the current mirror for detecting wire breakage of LEDs in the LED load circuits and short-circuit means arranged in connection with the control elements corresponding to the LED load circuits other than the LED load circuit that constitutes the reference current circuit of the current mirror, that can switch one of the control elements to a diode connection when the wire breakage detection means detects wire breakage. 
     According to the above described configuration, in an LED lighting circuit to be used for an illuminating apparatus, when a current is caused to flow from a DC power supply to an LED module made up of a plurality of LED load circuits arranged parallel to each other, each LED load circuit being made up of one or a plurality of serially connected LEDs, control elements configuring a current mirror circuit are arranged in series to the LED load circuits and a circuit with the highest voltage drop by LED currents including the sum of LED ON voltages Vf in the LED load circuits is used as a reference, the control element in the circuit out of the control elements is to have a diode structure and flowing current values of the control elements of the remaining circuits are interlocked through control terminals and the LED load circuits are thereby balanced. To be more specific, when the control elements are transistors, the base and collector, which are control terminals, are short-circuited and the bases are connected commonly. On the other hand, when the control elements are MOS type transistors, the gate and drain, which are control terminals, are short-circuited and the gates are connected commonly. Furthermore, wire breakage detection means for detecting wire breakage of LEDs in the LED load circuit in connection with the LED load circuit which constitutes the reference current circuit is provided, short-circuit means that can short-circuit between the base and collector or between the gate and drain in connection with the control elements corresponding to the LED load circuits other than the LED load circuit that constitutes the reference current circuit of the current mirror is provided, and when the wire breakage detection means detects wire breakage, the short-circuit means switches one of the control elements to a diode connection. 
     Therefore, since current balance between the LED load circuits is uniformly controlled by the current mirror circuit, light outputs from many LEDs can be uniformized. Furthermore, since the LED load circuit with the highest sum of the ON voltages Vf is used for the circuit that creates a reference current of the current mirror circuit, such a configuration does not require the circuit that creates only a reference current and can eliminate circuit loss accordingly. Furthermore, when wire breakage occurs in some LED of the LED load circuit that constitutes the reference current circuit, one of the control elements corresponding to the other LED load circuits is diode-connected and continues to perform constant current operation, thus preventing lighting out from extending to the other LED load circuits. 
     Furthermore, in the LED lighting circuit based on the fifth viewpoint of the present invention, the DC power supply is a DC-DC converter and preferably includes current detection means for detecting a total value of currents flowing through the LED load circuits or a value of current flowing through the LED load circuit corresponding to the diode-connected control element, a reference voltage source and a comparator for comparing the detection results from the current detection means and control means for controlling the DC power supply through feedback according to the output from the comparator so that the sum of values of currents flowing to the LED module becomes a predetermined value. 
     According to the above described configuration, value of currents flowing from the DC power supply to the respective LED load circuits is detected and the DC power supply is subjected to constant current control through feedback based on the detection result so that the sum of the flowing current values becomes a predetermined value, and therefore loss at the control elements is smaller compared to constant voltage control and loss can be reduced. 
     Furthermore, the illuminating apparatus based on the fifth viewpoint of the present invention preferably uses the above described LED lighting circuit. 
     According to the above described configuration, it is possible to uniformize light outputs from many LEDs and realize a low-loss illuminating apparatus. 
     Parts in the present description described as means for realizing certain functions are not limited to the configurations described in the description for realizing those functions, and units and parts and the like for realizing those functions are also included therein. 
     INDUSTRIAL APPLICABILITY 
     The present invention can provide an LED lighting circuit capable of uniformizing light outputs from many LEDs.