Patent Publication Number: US-9844105-B2

Title: Lighting device having a shunt circuit in parallel with a light source circuit therein

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the benefit and priority of Japanese Patent Application No. 2016-027165, filed on Feb. 16, 2016, the entire contents of which is incorporated herein by reference. 
     TECHNICAL FIELD 
     The disclosure relates generally to lighting devices and lighting equipment and, more particularly, to a lighting device configured to apply respective voltage components contained in a pulsating voltage from an AC power supply every period of the pulsating voltage across part and all of solid light sources, and lighting equipment with the lighting device. 
     BACKGROUND ART 
     As a related device, there has been provided a lighting device that is configured to supply solid light sources with a pulsating voltage derived from an AC (alternating-current) voltage supplied from an AC power supply, thereby lighting the solid light sources (see, e.g., an LED driver circuit described in JP 2013-55168A (hereinafter referred to as “Document  1 ”)). The lighting device (LED driver circuit) described in Document  1  includes a full-wave rectifier circuit composed of diodes, a first bypass circuit, a first LED array, a second bypass circuit, a second LED array and a constant current circuit. Each of the first and second LED arrays is formed of a series circuit of LEDs. 
     Two input terminals of the first bypass circuit are electrically connected one-to-one with two pulsating output terminals of the full-wave rectifier circuit. A positive end (anode) of the first LED array is electrically connected to a high potential side output terminal of the first bypass circuit. A negative end (cathode) of the first LED array is electrically connected to a high potential side input terminal of the second bypass circuit. A low potential side output terminal of the first bypass circuit is electrically connected to a low potential side input terminal of the second bypass circuit. A positive end (anode) of the second LED array is electrically connected to a high potential side input terminal of the second bypass circuit. A negative end (cathode) of the second LED array is electrically connected to an input terminal of the constant current circuit. A low potential side output terminal of the second bypass circuit is electrically connected to an output terminal of the constant current circuit. Each of the first and second bypass circuits is composed of transistors, resistors and the like. 
     The lighting device described in Document  1  is configured so that the first bypass circuit allows a first bypass current to flow through during a period of time while no current flows through the first LED array, thereby reducing harmonic distortion of comparatively lower harmonics that may occur in an input current. 
     Incidentally, in the first bypass circuit in the related device described in Document  1 , the two input terminals are electrically connected one-to-one with the two pulsating output terminals of the full-wave rectifier circuit. The first bypass circuit accordingly needs, as a component thereof, a transistor having a blocking voltage higher than a peak voltage of the pulsating voltage, which causes a rise in production cost. 
     SUMMARY OF THE INVENTION 
     It is an object of the disclosure to provide a lighting device and lighting equipment, capable of reducing harmonic distortion of an input current and suppressing a rise in production cost. 
     A lighting device according to one aspect of the disclosure includes a rectifier circuit, a driver circuit and a shunt circuit. The rectifier circuit includes a first polarity output terminal and a second polarity output terminal, and is configured to output a pulsating voltage obtained by rectifying an AC voltage from the first polarity and second polarity output terminals. The driver circuit is configured to apply respective voltage components contained in the pulsating voltage every period of the pulsating voltage across part and all of solid light sources in response to the pulsating voltage and respective ON voltages of light source circuits including the part and all of the solid light sources. The shunt circuit is electrically connected in parallel with a light source circuit having a lowest ON voltage of the light source circuits. The shunt circuit is configured to set a value of an output current from the rectifier circuit to a value proportional to a value of the pulsating voltage while the pulsating voltage is less than the lowest ON voltage. 
     Lighting equipment according to one aspect of the disclosure includes the lighting device, and a body that holds the lighting device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The figures depict one or more implementations in accordance with the present teaching, by way of example only, not by way of limitation. In the figures, like reference numerals refer to the same or similar elements where: 
         FIG. 1  is a block diagram of a lighting device in accordance with Embodiment 1; 
         FIG. 2  is a waveform chart depicting a pulsating voltage and a current to be output from a rectifier circuit in the lighting device; 
         FIGS. 3A to 3D  show current paths in the lighting device in which  FIG. 3A  is a circuit diagram showing a current path in a first mode,  FIG. 3B  is a circuit diagram showing a current path in a second mode,  FIG. 3C  is a circuit diagram showing a current path in a third mode, and  FIG. 3D  is a circuit diagram showing a current path in a fourth mode; 
         FIG. 4  is a circuit diagram of the lighting device; 
         FIG. 5  shows waveforms illustrating operations of the lighting device; 
         FIG. 6  shows waveforms illustrating operations of a shunt circuit in the lighting device; 
         FIG. 7  is a circuit diagram showing another configuration example of the shunt circuit in the lighting device; 
         FIG. 8  is a circuit diagram of a lighting device in accordance with Embodiment 2; 
         FIG. 9  is a circuit diagram of a modified example of the lighting device; and 
         FIGS. 10A, 10B and 10C  show lighting equipment in accordance with Embodiment 3 in which  FIG. 10A  is a perspective view of the lighting equipment,  FIG. 10B  is a perspective view of Modified example 1 of the lighting equipment, and  FIG. 10C  is a perspective view of Modified example 2 of the lighting equipment. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, lighting devices and respective lighting equipment in embodiments will be explained. 
     Embodiment 1 
     The present embodiment is explained with reference to  FIG. 1 . Note that in the example of  FIG. 1 , a lighting device  1 X includes three solid light sources  20 , but a lighting device of the present embodiment is not limited to this. For example, the lighting device of the embodiment may include two solid light sources  20 , or four or more solid light sources  20 . In short, the lighting device of the embodiment includes solid light sources  20 . Each of the solid light sources  20  may be a solid light source array composed of LEDs (light emitting diodes). Each of the solid light sources  20  may be also electrically connected in parallel with a capacitor. 
     The lighting device of the embodiment includes a rectifier circuit  11 , a driver circuit  12  and a shunt circuit  13 . The rectifier circuit  11  includes a first polarity output terminal  113  and a second polarity output terminal  114  and that is configured to output, from the first polarity and second polarity output terminals  113  and  114 , a pulsating voltage V 2  obtained by rectifying an AC voltage V 1 . Desirably, the rectifier circuit  11  is a full-wave rectifier circuit. The driver circuit  12  is configured to apply respective voltage components contained in the pulsating voltage V 2  every period of the pulsating voltage V 2  across part and all of the solid light sources  20  in response to the pulsating voltage V 2  and respective ON voltages of light source circuits including the part and all of the solid light sources  20 . In an example, the driver circuit  12  is electrically connected in series with the solid light sources  20  between the first polarity and second polarity output terminals  113  and  114 , and functions as a constant current source that allows respective currents from the light source circuits to flow through as a constant current. In another example, each of the light source circuits may further include a diode connected in series to its own one or more solid light sources  20 . The shunt circuit  13  is electrically connected in parallel with a light source circuit having a lowest ON voltage of the light source circuits. For example, the shunt circuit  13  may be configured to set a value of an output current I 1  from the rectifier circuit  11  to a value proportional to a value of the pulsating voltage V 2  while the pulsating voltage V 2  is less than the lowest ON voltage V 21 . In the example of  FIG. 1 , the first polarity is positive polarity, and the second polarity is negative polarity. 
     In a first specific example of the embodiment, the solid light sources  20  includes at least two adjoining solid light sources between the first polarity and second polarity output terminals  113  and  114 . The adjoining solid light sources are connected in series. The adjoining solid light sources include first polarity side solid light source  21  or  22  and second polarity side solid light source  22  or  23 . Note that an element other than such a solid light source (e.g., a diode) may intervene between the two adjoining first polarity side solid light source and second polarity side solid light source. A first light source circuit of the light source circuits has a first voltage as an ON voltage. The first light source circuit includes every solid light source, a circuit route of which is nearer to the first polarity output terminal  113  than a circuit route of the second polarity side solid light source, of the solid light sources  20 . A second light source circuit of the light source circuits has a second voltage as an ON voltage. The second light source circuit includes every solid light source, on a side of the first polarity output terminal  113  from the second polarity side solid light source, of the solid light sources  20 . 
     The first specific example can be applied to a configuration as a modified example of  FIG. 1 , in which a lighting device includes two solid light sources  21  and  22  but does not include a solid light source  23  (hereinafter referred to as a “two-light source configuration”). In the two-light source configuration, a first light source circuit (hereinafter referred to as a “first light source circuit  2 A”) includes every solid light source  21 , a circuit route of which is nearer to the first polarity output terminal  113  than a circuit route of the second polarity side solid light source  22 , of the solid light sources  21  and  22 . In an example, the first light source circuit  2 A includes the first polarity side solid light source  21 , and a diode D 1  connected in series thereto, and has an ON voltage V 21  shown in the example of  FIG. 2  as a first voltage (hereinafter referred to as a “first voltage V 21 ”). However, the ON voltage of the diode D 1  is not shown in the example of  FIG. 2 . On the other hand, a second light source circuit (hereinafter referred to as a “second light source circuit  2 B”) includes every solid light source  21 - 22 , on the side of the first polarity output terminal  113  from the second polarity side solid light source  22 , of the solid light sources  21  and  22 . In an example, the second light source circuit  2 B includes the solid light sources  21  and  22 , and a diode D 2  connected in series thereto, and has an ON voltage V 21 +V 22  shown in the example of  FIG. 2  as a second voltage (hereinafter referred to as a “second voltage V 21 −V 22 ”). However, the ON voltage of the diode D 2  is not shown in the example of  FIG. 2 . 
     The first specific example can be also applied to the configuration of  FIG. 1  in which the lighting device includes three solid light sources  21  to  23  (hereinafter referred to as a “three-light source configuration”). In the three-light source configuration, the lighting device includes a first light source circuit  2 A and a second light source circuit  2 B, like the two-light source configuration. In addition, the lighting device includes another first light source circuit (hereinafter referred to as a “first light source circuit  2 C”) and another second light source circuit (hereinafter referred to as a “second light source circuit  2 D”). The first light source circuit  2 C includes every solid light source  21 - 22 , a circuit route of which is nearer to the first polarity output terminal  113  than a circuit route of the second polarity side solid light source  23 , of the solid light sources  21  to  23 . In short, such a circuit route means a route on an electrical circuit (e.g., the circuit as shown in  FIG. 1 ). For example, in the circuit of  FIG. 1  (three-light source configuration), the circuit route of the solid light sources  21 - 22  contained in the first light source circuit  2 C is nearer to the first polarity output terminal  113  than a circuit route of the second polarity side solid light source  23 , of solid light source  21 - 23 . Therefore, even if the second polarity side solid light source  23  is physically nearer to the first polarity output terminal  113  than the solid light sources  21 - 22 , the second polarity side solid light source  23  is not contained in the first light source circuit  2 C. In an example, the first light source circuit  2 C includes the solid light sources  21  and  22 , and a diode D 2  connected in series thereto, and has an ON voltage V 21 +V 22  shown in the example of  FIG. 2  as another first voltage (hereinafter referred to as a “first voltage V 21 -V 22 ”). On the other hand, the second light source circuit  2 D includes every solid light source  21 - 23 , on the side of the first polarity output terminal  113  from the second polarity side solid light source  23 , of the solid light sources  21  to  23 . In an example, the second light source circuit  2 D includes the solid light sources  21  to  23 , and a diode D 3  connected in series thereto, and has an ON voltage V 21 +V 22 +V 23  shown in the example of  FIG. 2  as another second voltage (hereinafter referred to as a “second voltage V 21 -V 23 ”). However, the ON voltage of the diode D 3  is not shown in the example of  FIG. 2 . 
     In a second specific example of the embodiment, the driver circuit  12  is configured to allow a current (only) from the first light source circuit to flow through during (only) a period of time while the pulsating voltage V 2  is greater than or equal to the first voltage and less than the second voltage. 
     The second specific example can be applied to the two-light source configuration. In the two-light source configuration, the driver circuit  12  is configured to allow a current from (only) the first light source circuit  2 A ( 21 , D 1 ) to flow through during (only) a period of time T 2 , T 6  in which the pulsating voltage V 2  is greater than or equal to the first voltage V 21  and less than the second voltage V 21 -V 22 . 
     The second specific example can be applied to the three-light source configuration. In the three-light source configuration, the driver circuit  12  is configured to allow a current from (only) the first light source circuit  2 A to flow through, like the two-light source configuration The driver circuit  12  is further configured to allow a current from (only) the first light source circuit  2 C ( 21 - 22 , D 2 ) to flow through during (only) a period of time T 3 , T 5  in which the pulsating voltage V 2  is greater than or equal to the first voltage V 21 -V 22  and less than the second voltage V 21 -V 23 . 
     As a third specific example of the embodiment, in a configuration in which the second polarity side solid light source is a solid light source, a circuit route of which is nearest to the second polarity output terminal  114 , the driver circuit  12  is configured to allow a current from (only) the second light source circuit to flow through during (only) a period of time while the pulsating voltage V 2  is greater than or equal to the second voltage. In a configuration in which the second polarity side solid light source is a solid light source other than the solid light source, a circuit route of which is nearest to the second polarity output terminal  114 , the driver circuit  12  is configured to allow a current from (only) the second light source circuit to flow through during (only) a period of time while the pulsating voltage V 2  is greater than or equal to the first voltage and less than the second voltage. 
     The third specific example can be applied to the two-light source configuration. In the two-light source configuration, the second polarity side solid light source  22  is a solid light source, a circuit route of which is nearest to the second polarity output terminal  114 . In this configuration, the driver circuit  12  is configured to allow a current from (only) the second light source circuit  2 B ( 21 - 22 , D 2 ) to flow through during (only) a period of time T 3 -T 5  in which the pulsating voltage V 2  is greater than or equal to the second voltage V 21 -V 22 . 
     The third specific example can be applied to the three-light source configuration. In the three-light source configuration, the lighting device includes the second light source circuit  2 B ( 21 - 22 , D 2 ) and the second light source circuit  2 D ( 21 - 23 , D 3 ). The second light source circuit  2 B ( 21 - 22 , D 2 ) does not include the solid light source  23 , a circuit route of which is nearest to the second polarity output terminal  114 . The driver circuit  12  is therefore configured to allow a current from (only) the second light source circuit  2 B to flow through during (only) a period of time T 3 , T 5  in which the pulsating voltage V 2  is greater than or equal to the first voltage V 21 -V 22  and less than the second voltage V 21 -V 23 . The second light source circuit  2 D ( 21 - 23 , D 3 ) includes the solid light source  23 , a circuit route of which is nearest to the second polarity output terminal  114 . The driver circuit  12  is therefore configured to allow a current from (only) the second light source circuit  2 D to flow through during (only) a period of time T 4  in which the pulsating voltage V 2  is greater than or equal to the second voltage V 21 -V 23 . 
     The driver circuit  12  is configured to electrically connect the shunt circuit  13  between the first polarity and second polarity output terminals  113  and  114  while the pulsating voltage V 2  is less than the lowest ON voltage V 21 . The lowest ON voltage V 21  is an ON voltage of the light source circuit including the solid light source  21 , a circuit route of which is nearest to the first polarity output terminal  113 , of the solid light sources  20 . In the example of  FIG. 1 , the lowest ON voltage V 21  is the ON voltage of the light source circuit including only the solid light source  21  and the diode D 1 . 
     In the embodiment, the shunt circuit  13  includes a bleeder resistor  130 . 
     As a fourth specific example of the embodiment, the lighting device includes a reference power supply ( 124  in the examples of  FIGS. 4, 8 and 9 ) and a current sensor (R 1  in the examples). The reference power supply is configured to generate a reference voltage Vx. The current sensor R 1  intervenes between the driver circuit  12  and a side, a circuit route of which is nearer to one of the first polarity and second polarity output terminals  113  and  114  than a circuit route of the driver circuit  12  (a 114 side in the examples). In addition, the driver circuit  12  includes at least first and second circuits ( 121  or  122  and  122  or  123  in the examples). The first and second circuits are electrically connected in series to the aforementioned at least two adjoining first polarity side solid light source  21  or  22  and second polarity side solid light source  22  or  23 , respectively between the first polarity and second polarity output terminals  113  and  114 . Each of the first and second circuits is, for example a constant current circuit configured to cause a value of a current detected through the current sensor to accord with a current value corresponding to the reference voltage Vx. In an example, the reference power supply is configured to: generate a voltage proportional to the pulsating voltage V 2  while a value of the pulsating voltage V 2  is less than the reference voltage Vx; and generate the reference voltage Vx while the value of the pulsating voltage V 2  is greater than or equal to the reference voltage Vx 
     In the fourth specific example, the first circuit  121  electrically connected in series to only the first polarity side solid light source  21 , a circuit route of which is nearest to the first polarity output terminal  113  includes an operational amplifier (U 1  in the examples) and a transistor (Q 1  in the examples). The operational amplifier U 1  has a non-inverting input terminal which the reference voltage Vx is applied to, an inverting input terminal which a voltage derived from the current sensor R 1  is applied to, and an output terminal. The transistor Q 1  has a control terminal (a gate) electrically connected to the output terminal of the operational amplifier U 1 , a first end (a drain) electrically connected to the first polarity side solid light source  21 , and a second end (a source) electrically connected to the current sensor R 1 . In this example, because the first polarity side solid light source  21  conducts while the pulsating voltage V 2  is greater than or equal to the first voltage V 21 , a current is to flow from the first polarity side solid light source  21  to the first circuit  121  (transistor Q 1 ). The first circuit  121  is set to be non-conductive while the pulsating voltage V 2  is greater than or equal to the second voltage V 21 -V 22 . As shown in the example of  FIG. 5 , the first circuit  121  allows a current from only the first polarity side solid light source  21  to flow through during only a period of time while the pulsating voltage V 2  is greater than or equal to the first voltage V 21  and less than the second voltage V 21 -V 22 . The second circuit may be also configured like the first circuit. 
     In the fourth specific example, the shunt circuit  13  includes a series circuit, a resistor R 4  and a switch device Q 6 . The series circuit is, for example a bleeder resistor  130  and a switch device Q 4  that are electrically connected between the first polarity and second polarity output terminals  113  and  114 . The resistor R 4  is electrically connected in series to the solid light source  21 , a circuit route of which is nearest to the first polarity output terminals  113 , of the solid light sources  20 . The switch device Q 6  is configured to turn on in response to a voltage across the resistor R 4 , thereby turning off the switch device Q 4  of the series circuit. 
     Hereinafter, the embodiment is explained with reference to the example of  FIG. 1 . As shown in  FIG. 1 , a lighting device  1 X according to Embodiment 1 includes a rectifier circuit  11 , a driver circuit  12  and a shunt circuit  13 . The rectifier circuit  11  includes a first input terminal  111 , a second input terminal  112 , a first polarity output terminal  113  and a second polarity output terminal  114 . The first input terminal  111  is configured to be electrically connected to one end (e.g., a live conductor) of an AC power supply  4 . The second input terminal  112  is configured to be electrically connected to another end (e.g., a neutral conductor) of the AC power supply  4 . The first polarity output terminal  113  is configured to be electrically connected with a positive electrode of a first solid light source  21 . The second polarity output terminal  114  is electrically connected to an output end of the driver circuit  12 . For example, the rectifier circuit  11  may be a diode bridge. The rectifier circuit  11  is configured to generate a pulsating voltage V 2  by full-wave rectifying an AC voltage V 1  from the first and second input terminals  111  and  112  to output the pulsating voltage V 2  from the first polarity and second polarity output terminals  113  and  114 . Note that each of the “input terminals” and “output terminals” may include a component (a screw terminal or the like) that allows an electric wire or the like to be electrically and mechanically connected to, but may be, for example a lead of an electronic component or part of conductive pattern of a printed circuit board. 
     Preferably, each of the first solid light source  21 , a second solid light source  22  and a third solid light source  23  is composed of a series circuit of light emitting devices. The first solid light source  21  is also electrically connected in parallel with a first capacitor C 1 . The second solid light source  22  is electrically connected in parallel with a second capacitor C 2 . The third solid light source  23  is electrically connected in parallel with a third capacitor C 3 . A negative electrode of the first solid light source  21  is electrically connected to an anode of a first diode D 1 . A negative electrode of the second solid light source  22  is electrically connected to an anode of a second diode D 2 . A negative electrode of the third solid light source  23  is electrically connected to an anode of a third diode D 3 . The first, second and third solid light sources  21 ,  22  and  23  conduct and emit respective light (are lit) while respective voltages applied across their own positive and negative electrodes is greater than or equal to their respective ON voltages (first, second and third ON voltages V 21 , V 22  and V 23 ). 
     The driver circuit  12  has a first constant current circuit  121 , a second constant current circuit  122  and a third constant current circuit  123 . An input terminal of the first constant current circuit  121  is electrically connected to a cathode of the first diode D 1  via the shunt circuit  13 . An input terminal of the second constant current circuit  122  is electrically connected to a cathode of the second diode D 2 . An input terminal of the third constant current circuit  123  is electrically connected to a cathode of the third diode D 3 . Output terminals of the first, second and third constant current circuits  121 ,  122  and  123  are electrically connected to the second polarity output terminal  114  of the rectifier circuit  11 . Each of the first, second and third constant current circuits  121 ,  122  and  123  is configured to convert a current entering its own input terminal into a constant current to output the constant current from its own output terminal. Note that the first, second and third constant current circuits  121 ,  122  and  123  are configured to operate alone and two or more of them do not operate at the same time. 
     The shunt circuit  13  has a bleeder resistor  130  and a control circuit  131 . The shunt circuit  13  is electrically connected in parallel with a series circuit of the first solid light source  21  and the first diode D 1 . A first end of the bleeder resistor  130  is electrically connected to the first polarity output terminal  113  of the rectifier circuit  11  and the positive electrode of the first solid light source  21 . The control circuit  131  is configured to allow a current (a bleeder current) to flow through the bleeder resistor  130  while the first solid light source  21  is non-conductive (it is unlit) and prohibit the bleeder current from flowing while the first solid light source  21  is conductive (it is lit). 
     The first, second and third solid light sources  21 ,  22  and  23  are non-conductive and all of them are unlit while a value of the pulsating voltage V 2  from the rectifier circuit  11  is less than the first ON voltage V 21  (a period of time T 1 , T 7  in  FIG. 2 ). In this case, the second and third constant current circuits  122  and  123  stop operating. On the other hand, the control circuit  131  of the shunt circuit  13  operates to allow a current I 1  from the rectifier circuit  11  to flow through the bleeder resistor  130 . The current flowing through the bleeder resistor  130  flows into the input terminal of the first constant current circuit  121  via the control circuit  131 . The first constant current circuit  121  operates accordingly. A current I 20  (current I 1 ) consequently flows through a path RT 1  shown by a dotted line of  FIG. 3A  that starts from the first polarity output terminal  113  of the rectifier circuit  11  and returns to the second polarity output terminal  114  of the rectifier circuit  11  via the shunt circuit  13  and the first constant current circuit  121 . Hereinafter, an operation mode when the current I 1  flows through the path RT 1  is referred to as a first mode. Here, the period of time while the value of the pulsating voltage V 2  is less than the first ON voltage V 21  is a first period of time while the current  120  flows through the shunt circuit  13 . 
     The first solid light source  21  and the first diode D 1  conduct during a period of time (a period of time T 2 , T 6  in  FIG. 2 ) while the value of the pulsating voltage V 2  is greater than or equal to the first ON voltage V 21  and less than a total value of the first and second ON voltages V 21  and V 22  (hereinafter referred to as a “a first total voltage value”). If the first solid light source  21  and the first diode D 1  conduct, the first constant current circuit  121  operates and then converts a current  121  (the current I 1 ) flowing through the first solid light source  21  into a constant current. The first solid light source  21  is lit by the current I 21  flowing therethrough. Note that the control circuit  131  of the shunt circuit  13  is configured to prohibit the current I 1  from flowing through the bleeder resistor  130  after the current I 21  begins to flow through the first solid light source  21 . Consequently, during a period of time T 2  or T 6 , the current I 1  flows through a path RT 2  shown by a dotted line of  FIG. 3B  that starts from the first polarity output terminal  113  of the rectifier circuit  11  and returns to the second polarity output terminal  114  of the rectifier circuit  11  via the first solid light source  21 , the first diode D 1 , a resistor R 4  of the shunt circuit  13  and the first constant current circuit  121 . Note that the first constant current circuit  121  is configured to convert the current I 21  flowing through the first solid light source  21  into a prescribed constant current value Ist 1  (see  FIG. 2 ). On the other hand, the second and third solid light sources  22  and  23  are non-conductive and remain unlit. Hereinafter, an operation mode when the current I 1  (I 21 ) flows through the path RT 2  is referred to as a second mode. Here, the period of time while the value of the pulsating voltage V 2  is greater than or equal to the first ON voltage V 21  and less than the first total voltage value is a second period of time while the current I 21  flows through only the first solid light source  21  of the solid light sources  20 . 
     During a period of time T 3  or T 5  in  FIG. 2 , the value of the pulsating voltage V 2  is greater than or equal to the first total voltage value (V 21 +V 22 ) and less than a total value of the first total voltage value and the third ON voltage V 23  (hereinafter referred to as a second total voltage value). The first and second solid light sources  21  and  22  and the second diode D 2  conduct during a period of time T 3  or T 5 . If the first and second solid light sources  21  and  22  and the second diode D 2  conduct, the second constant current circuit  122  operates and then converts the currents I 21 , I 22  (the current I 1 ) flowing through the first and second solid light sources  21  and  22  into a constant current. The first and second solid light sources  21  and  22  are lit by the current I 21 , I 22  flowing therethrough. Note that the first constant current circuit  121  stops operating. Consequently, the current I 1  flows through a path RT 3  shown by a dotted line of  FIG. 3C  that starts from the first polarity output terminal  113  of the rectifier circuit  11  and returns to the second polarity output terminal  114  of the rectifier circuit  11  via the first and second solid light sources  21  and  22 , the second diode D 2  and the second constant current circuit  122 . Note that the second constant current circuit  122  is configured to convert the current  121  flowing through the first solid light source  21  and the current I 22  flowing through the second solid light source  22  into the prescribed constant current Ist 1  (see  FIG. 2 ). On the other hand, the third solid light source  23  is non-conductive and remains unlit. Hereinafter, an operation mode when the current I 1  (I 21  and I 22 ) flows through the path RT 3  is referred to as a third mode. 
     During a period of time T 4  in  FIG. 2 , the value of the pulsating voltage V 2  is more than the second total voltage value (V 21 +V 22 +V 23 ). The first, second and third solid light sources  21 ,  22  and  23  and the third diode D 3  conduct during the period of time T 4 . If the first, second and third solid light sources  21 ,  22  and  23  and the third diode D 3  conduct, the third constant current circuit  123  operates and then converts the current I 21 , I 22 , I 23  flowing through the first, second and third solid light sources  21 ,  22  and  23  into the constant current. The first, second and third solid light sources  21 ,  22  and  23  are lit by the currents I 21 , I 22 , I 23  flowing therethrough. Note that the first and second constant current circuits  121  and  122  stop operating. That is, the current I 1  flows through a path RT 4  shown by a dotted line of  FIG. 3D . The path RT 4  starts from the first polarity output terminal  113  of the rectifier circuit  11  and returns to the second polarity output terminal  114  of the rectifier circuit  11  via the first, second and third solid light sources  21 ,  22  and  23 , the third diode D 3  and the third constant current circuit  123 . Note that the third constant current circuit  123  is configured to convert the current flowing through the first solid light source  21 , the current I 22  flowing through the second solid light source  22  and the current I 23  flowing through the third solid light source  23  into the prescribed constant current Ist 1  (see  FIG. 2 ). Hereinafter, an operation mode when the current I 1  (I 21 , I 22  and I 23 ) flows through the path RT 4  is referred to as a fourth mode. Here, the period of time while the value of the pulsating voltage V 2  is greater than or equal to the second total voltage value is a third period of time while every solid light source (the first, second and third solid light sources  21 ,  22  and  23 ) is lit. 
     A circuit configuration of the lighting device  1 X is now explained in further detail with reference to  FIG. 4 . Note that the circuit configuration shown in  FIG. 4  is just a circuit configuration example of the lighting device  1 X. That is, the circuit configuration of the lighting device  1 X is not limited to the circuit configuration shown in  FIG. 4 , but may be modified appropriately. 
     Each of the first, second and third solid light sources  21 ,  22  and  23  includes a solid light source device composed of a surface-mounted light emitting diode (first, second or third solid light source device  210 ,  220  or  230 ). Preferably, each of the first, second and third solid light sources  21 ,  22  and  23  is composed of a series circuit of solid light source devices (first, second or third solid light source devices  210 ,  220  or  230 ). Note that each of the first, second and third solid light source devices  210 ,  220  and  230  may be a solid light source device other than a light emitting diode, such as an organic electroluminescence element or a laser diode. 
     In the example, the first ON voltage V 21  of the first solid light source  21  has a value obtained by multiplying a forward voltage of the first solid light source device  210  and the number of the first solid light source devices  210  connected in series. The second ON voltage V 22  of the second solid light source  22  has a value obtained by multiplying a forward voltage of the second solid light source device  220  and the number of the second solid light source devices  220  connected in series. The third ON voltage V 23  of the third solid light source  23  has a value obtained by multiplying a forward voltage of the third solid light source device  230  and the number of the third solid light source devices  230  connected in series. In an example in which every forward voltage of the first, second and third solid light source devices  210 ,  220  and  230  is 3.1[V], if the number of the first solid light source devices  210  constituting the first solid light source  21  is  14 , the first ON voltage V 21  is given by  43 . 4 [V] (=3.1×14). If the number of the second solid light source devices  220  constituting the second solid light source  22  is  13 , the second ON voltage V 22  is given by 40.3[V] (=3.1×13). If the number of the third solid light source devices  230  constituting the third solid light source  23  is  12 , the third ON voltage V 23  is given by 37.2[V] (=3.1×12). 
     Each of the first, second and third capacitors C 1 , C 2  and C 3  connected one-to-one in parallel with the first, second and third solid light source devices  210 ,  220  and  230  is, for example an aluminum electrolytic capacitor. The first, second and third capacitors C 1 , C 2  and C 3  are configured to smooth their respective currents I 21 , I 22  and I 23 , thereby reducing ripples (fluctuation) of each light output of the first, second and third solid light sources  21 ,  22  and  23 . It is accordingly preferable that the capacitance of the first capacitor C 1  be set so that a time constant determined by the equivalent resistance of the first solid light source  21  and the capacitance of the first capacitor C 1  is larger than the period of the pulsating voltage V 2 . Similarly, the capacitance of the second capacitor C 2  is preferably set so that a time constant determined by the equivalent resistance of the second solid light source  22  and the capacitance of the second capacitor C 2  is larger than the period of the pulsating voltage V 2 . The capacitance of the third capacitor C 3  is preferably set so that a time constant determined by the equivalent resistance of the third solid light source  23  and the capacitance of the third capacitor C 3  is larger than the period of the pulsating voltage V 2 . However, the capacitors C 1  to C 3  are optional components of the lighting device  1 X, and may be omitted appropriately. 
     The driver circuit  12  has a current control circuit  124  in addition to the first to third constant current circuits  121  to  123 . Preferably, the current control circuit  124  is composed of a Zener diode  1240 , a first voltage division resistor R 101 , a second voltage division resistor R 102 , a third voltage division resistor R 103  and a capacitor C 101 . One end of the first voltage division resistor R 101  is electrically connected to the first polarity output terminal  113  of the rectifier circuit  11 . Another end of the first voltage division resistor R 101  is electrically connected to one end of the second voltage division resistor R 102  and a cathode of the Zener diode  1240 . Another end of the second voltage division resistor R 102  is electrically connected to one end of the third voltage division resistor R 103 . Another end of the third voltage division resistor R 103  is electrically connected to an anode of the Zener diode  1240 , the second polarity output terminal  114  of the rectifier circuit  11 , and a first end of the resistor R 1 . The capacitor C 101  is electrically connected in parallel with the third voltage division resistor R 103 . 
     In this example, a voltage divider circuit composed of the first, second and third voltage division resistors R 101 , R 102  and R 103  is configured to divide the pulsating voltage V 2  through the first, second and third voltage division resistors R 101 , R 102  and R 103 , thereby generating a reference voltage Vx. Note that the reference voltage Vx is limited (clamped) to a voltage obtained by dividing a Zener voltage of the Zener diode  1240  by the second and third voltage division resistors R 102  and R 103  during a period time while the pulsating voltage V 2  is greater than or equal to the first ON voltage V 21  (the period of time T 2  to the period of time T 6  in  FIG. 2 ). On the other hand, the reference voltage Vx varies in proportion to the pulsating voltage V 2  during a period of time while the pulsating voltage V 2  is less than the first ON voltage V 21  (a period of time T 1  or T 7  in  FIG. 2 ). Note that the three voltage division resistors R 101  to R 103  and the capacitor C 101  constitute a filter circuit. The filter circuit is configured to reduce noise (harmonic noise) from the AC power supply  4 , thereby preventing the malfunction of the constant current circuits  121  to  123  due to the noise. It is however preferable that the time constant of the filter circuit be less than or equal to one millisecond in order to cause the reference voltage Vx to vary in proportion to the pulsating voltage V 2  during a period of time T 1  or T 7  in the case where the power frequency of the AC power supply  4  is 50 [Hz] or 60 [Hz]. 
     The first constant current circuit  121  may include a transistor Q 1 , an operational amplifier U 1 , a capacitor C 11  and a resistor R 12 . The transistor Q 1  is, for example an enhancement-mode N-channel MOSFET (Metal-Oxide-Semiconductor Field Effect Transistor). A drain of the transistor Q 1  is electrically connected to the cathode of the first diode D 1  via the resistor R 4 . A source of the transistor Q 1  is electrically connected to a second end of the resistor R 1 . A gate of the transistor Q 1  is electrically connected to an output terminal of the operational amplifier U 1 . A non-inverting input terminal of the operational amplifier U 1  is electrically connected to a junction of the voltage division resistors R 102  and R 103 . The non-inverting input terminal of the operational amplifier U 1  is electrically connected to an output terminal of the current control circuit  124  (the junction of the second and third voltage division resistors R 102  and R 103 ). That is, the non-inverting input terminal of the operational amplifier U 1  is supplied with the reference voltage Vx. An inverting input terminal of the operational amplifier U 1  is electrically connected to the output terminal of the operational amplifier U 1  via the capacitor C 11 . The inverting input terminal of the operational amplifier U 1  is also electrically connected to the source of the transistor Q 1  via the resistor R 12 . That is, the inverting input terminal of the operational amplifier U 1  is supplied with a detection voltage Vy proportional to a current flowing through the resistor R 1  (the current I 1 ). The operational amplifier U 1  is to supply the gate of the transistor Q 1  with a voltage (an output voltage) proportional to a difference between the reference voltage Vx and the detection voltage Vy. The operational amplifier U 1  is configured to decrease the output voltage if a value of the current I 1  flowing through the resistor R 1  is greater than a target value corresponding to a value of the reference voltage Vx, thereby decreasing a gate-source voltage of the transistor Q 1  to decrease the current I 1 . The operational amplifier U 1  is also configured to increase the output voltage if the value of the current I 1  is less than the target value, thereby increasing the gate-source voltage of the transistor Q 1  to increase the current  11 . Thus, the operational amplifier U 1  controls the transistor Q 1  so that the current I 1  flowing through the resistor R 1  accords with the target value corresponding to the value of the reference voltage Vx. In the example, the capacitor C 11  and the resistor R 12  constitute a phase compensation circuit that prevents the oscillation of the operational amplifier U 1 . 
     Each of the second and third constant current circuits  122  and  123  has the same circuit configuration as the first constant current circuit  121 . That is, a transistor Q 2 , an operational amplifier U 2 , a capacitor C 21  and a resistor R 22  of the second constant current circuit  122  correspond to the transistor Q 1 , the operational amplifier U 1 , the capacitor C 11  and the resistor R 12  of the first constant current circuit  121 , respectively. Similarly, a transistor Q 3 , an operational amplifier U 3 , a capacitor C 31  and a resistor R 32  of the third constant current circuit  123  correspond to the transistor Q 1 , the operational amplifier U 1 , the capacitor C 11  and the resistor R 12  of the first constant current circuit  121 , respectively. Each of the second and third constant current circuits  122  and  123  is to operate so that the current I 1  flowing through the resistor R 1  accords with a target value corresponding to a value of the reference voltage Vx, like the first constant current circuit  121 . Note that if the second and third solid light sources  22  and  23  do not conduct, the second and third constant current circuits  122  and  123  are prohibited from operating, respectively. It is preferable that the first constant current circuit  121  cut off or decrease a drain current of the transistor Q 1  while the second constant current circuit  122  is operating. It is also preferable that the second constant current circuit  122  cut off or decrease a drain current of the transistor Q 2  while the third constant current circuit  123  is operating. 
     A circuit configuration of the shunt circuit  13  is now explained. As stated above, the shunt circuit  13  includes the bleeder resistor  130  and the control circuit  131 . The first end of the bleeder resistor  130  is electrically connected to the first polarity output terminal  113  of the rectifier circuit  11 . The control circuit  131  includes three switching (switch) devices Q 4 , Q 5  and Q 6  and three resistors R 2 , R 3  and R 4 . Each of the three switching devices Q 4 , Q 5  and Q 6  may be an NPN bipolar transistor. A collector of the switching device Q 4  is electrically connected to a second end of the bleeder resistor  130 . An emitter of the switching device Q 4  is electrically connected to one end of the resistor R 2  and a base of the switching device Q 5 . Another end of the resistor R 2  is electrically connected to an emitter of the switching device Q 5  and an emitter of the switching device Q 6 . A collector of the switching device Q 5  is electrically connected to the first end of the bleeder resistor  130  and the first polarity output terminal  113  of the rectifier circuit  11 , via the resistor R 3 . A collector of the switching device Q 6  is electrically connected to a base of the switching device Q 4  and the collector of the switching device Q 5 . A base of the switching device Q 6  is electrically connected to the cathode of the first diode D 1  and one end of the resistor R 4 . The emitter of the switching device Q 6  is electrically connected to another end of the resistor R 4  and the drain of the transistor Q 1  in the first constant current circuit  121 . The control circuit  131  is configured to turn the switching device Q 4  on, thereby allowing a current to flow through the bleeder resistor  130 . The control circuit  131  is also configured to turn the switching device Q 6  on while the current I 1  flows through the resistor R 4  with the first solid light source  21  and the first diode D 1  conducting, thereby turning the switching device Q 4  off to prohibit the current from flowing through the bleeder resistor  130 . The control circuit  131  is further configured to turn the switching device Q 5  on when the current flowing through the bleeder resistor  130  increases excessively, thereby turning the switching device Q 4  off. In short, the control circuit  131  is configured to: allow a current to flow through the bleeder resistor  130  during a period of time while the value of the pulsating voltage V 2  is less than the first ON voltage V 21 ; and prohibit the current from flowing through the bleeder resistor  130  other than during the period of time. 
     The operations of the lighting device  1 X are explained with reference to  FIGS. 5 and 6 .  FIG. 5  shows waveforms illustrating operations of the lighting device  1 X.  FIG. 5  shows respective waveforms of the pulsating voltage V 2 , the current I 1  the current I 20 , the current I 21 , the current I 22  and the current I 23  from the top.  FIG. 6  shows waveforms illustrating operations of the shunt circuit  13 .  FIG. 6  shows a waveform of the current I 21 , an ON/OFF(conductive/non-conductive) state of the first diode D 1 , an ON/OFF state of the switching device Q 6 , an ON/OFF state of the switching device Q 4  and a waveform of the current I 20  from the top. In  FIGS. 5 and 6 , each horizontal axis represents time “t”, and a time t=t 0 , t 7  corresponds to a zero cross of the pulsating voltage V 2 . 
     During a period of time t=t 0  to t 1 , the value of the pulsating voltage V 2  is less than the first ON voltage V 21 , and therefore all of the first, second and third solid light sources  21 ,  22  and  23  are unlit. While the value of the pulsating voltage V 2  is less than the first ON voltage V 21 , the first solid light source  21  and the first diode D 1  do not conduct (turn on). The switching device Q 6  accordingly turns off because no current therefore flows through the resistor R 4 . In this case, the switching device Q 4  turns on, and therefore the current  120  (current I 1 ) flows through a path of the bleeder resistor  130 , the switching device Q 4 , the resistor R 2  and the first constant current circuit  121 , from the first polarity output terminal  113  of the rectifier circuit  11 . The first constant current circuit  121  causes the current  120  (current I 1 ) flowing through the shunt circuit  13  to accord with the target value corresponding to the value of the reference voltage Vx. Note that during the period of time t=t 0  to t 1 , since the reference voltage Vx from the current control circuit  124  increases in proportion to the pulsating voltage V 2 , the current I 20  (current I 1 ) also increases gradually. 
     During a period of time t=t 1  to t 2 , since the value of the pulsating voltage V 2  is greater than or equal to the first ON voltage V 21  and less than the first total voltage value, the first solid light source  21  and the first diode D 1  conduct (turn on). The current  121  (current I 1 ) accordingly flows through the resistor R 4 . When the current flows through the resistor R 4 , the switching device Q 6  turns on. When the switching device Q 6  turns on, the switching device Q 4  turns off and the current I 20  is therefore prohibited from flowing through the bleeder resistor  130 . The first constant current circuit  121  causes the current I 21  (current I 1 ) flowing through the first solid light source  21  and the first diode D 1  to accord with the target value corresponding to the value of the reference voltage Vx. Note that during a period of time t=t 1  to t 6 , the reference voltage Vx from the current control circuit  124  is limited (clamped) to a voltage obtained by dividing the Zener voltage of the Zener diode  1240  by the second and third voltage division resistor R 102  and R 103 . Therefore, the current I 21  (current I 1 ) is converted into the prescribed current value Ist 1 . 
     During a period of time t=t 2  to t 3 , since the value of the pulsating voltage V 2  is greater than or equal to the first total voltage value and less than the second total voltage value, the first and second solid light source  21  and  22  and the second diode D 2  conduct (turn on) and the first diode D 1  is non-conductive (turns off). When the first diode D 1  turns off, the switching device Q 6  turns off because the current I 21  (current I 1 ) stops flowing through the resistor R 4 . Note that even when the switching device Q 6  turns off, the switching device Q 4  remains to be turned off because no current (current I 20 ) flows towards the shunt circuit  13  while the first solid light source  21  is lit. In this moment, the first constant current circuit  121  stops operating. The second constant current circuit  122  also converts the current I 22  (current I 1 ) flowing through the first and second solid light sources  21  and  22  and the second diode D 2  into the prescribed constant current Ist 1 . 
     During a period of time t=t 3  to t 4 , since the value of the pulsating voltage V 2  is greater than the second total voltage value, the first, second and third solid light sources  21 ,  22  and  23  and the third diode D 3  conduct (turn on). The first and second diodes D 1  and D 2  become also non-conductive (turn off). Although the first diode turns off, the shunt circuit  13  remains to be stopped. The first and second constant current circuits  121  and  122  stop operating. The third constant current circuit  123  converts the current I 23  (current I 1 ) flowing through the first, second and third solid light sources  21 ,  22  and  23  and the third diode D 3  into the prescribed constant current Ist 1 . Note that as shown in  FIG. 3D  the current flowing through the third solid light source  23  is assigned  123  in order to be distinguished from the current I 21  shown in  FIGS. 3B and 5  and the current I 22 (I 21 ) shown in  FIGS. 3C and 5 . That is, as can been seen from Ist 1  of  FIG. 5 , the current flowing through first solid light source  21  as the current I 21  shown in  FIG. 3D  is equal to each of the current I 21  shown in  FIG. 3B  and the current I 21  shown in  FIG. 3C . Similarly, the current flowing through second solid light source  22  as the current I 22  shown in  FIG. 3D  is equal to the current I 22  shown in  FIG. 3C . 
     During a period of time t=t 4  to t 5 , since the value of the pulsating voltage V 2  is greater than or equal to the first total voltage value and less than the second total voltage value, the third solid light source  23  and the third diode D 3  become non-conductive (turn off). The first and second solid light sources  21  and  22  and the second diode D 2  conduct (turn on), while the first diode D 1  remains to be non-conductive (turned off). Although the first diode D 1  is in an OFF state, the shunt circuit  13  remains to be stopped. The third constant current circuit  123  stops operating. The second constant current circuit  122  also converts the current I 22  (current I 1 ) flowing through the first and second solid light sources  21  and  22  and the second diode D 2  into the prescribed constant current Ist 1 . 
     During a period of time t=t 5  to t 6 , since the value of the pulsating voltage V 2  is greater than or equal to the first ON voltage V 21  and less than the first total voltage value, the second and third solid light sources  22  and  23  and the second and third diodes D 2  and D 3  become non-conduct (turn off). The first solid light source  21  and the first diode D 1  also conduct (turn on). When the diode D 1  turns on, the switching device Q 4  turns off. The shunt circuit  13  therefore remains to be stopped. The second constant current circuit  122  also stops operating. The first constant current circuit  121  converts the current I 21  (current I 1 ) flowing through the first solid light source  21  and the first diode D 1  into the prescribed constant current Ist 1 . 
     During a period of time t=t 6  to t 7 , since the value of the pulsating voltage V 2  is less than the first ON voltage V 21 , the first, second and third solid light sources  21 ,  22  and  23  and the first, second and third diodes D 1 , D 2  and D 3  become non-conduct (turn off). Since the first diode D 1  turns off, the switching device Q 4  turns on and the control circuit  131  operates to allow the current I 20  to flow through the bleeder resistor  130 . The second and third constant current circuits  122  and  123  remain to be stopped. The first constant current circuit  121  causes the current I 20  (current I 1 ) flowing the shunt circuit  13  to accord with the target value corresponding to the reference voltage Vx. Note that during the period of time t=t 6  to t 7 , the current I 20  (current I 1 ) gradually decreases because the reference voltage Vx from the current control circuit  124  decreases in proportion to the pulsating voltage V 2 . 
     Subsequently, the lighting device  1 X repeats the operations from time t 0  to time t 7  every half period of the AC voltage V 1  (one period of the pulsating voltage V 2 ). 
     As stated above, the lighting device  1 X causes the current I 20  to flow through the shunt circuit  13  during a period of time (a first period of time) while all the first, second and third solid light sources  21 ,  22  and  23  are unlit, thereby removing a period of time in which no input current (current I 1 ) flows into the lighting device  1 X from the AC power supply  4 . The lighting device  1 X can consequently reduce the harmonic distortion of the input current (current I 1 ). 
     The advantage of the configuration in which the shunt circuit  13  is electrically connected in parallel with the first solid light source  21  is now explained. The pulsating voltage V 2  across the first polarity and second polarity output terminals  113  and  114  reaches a peak value of AC voltage V 1  as a maximum value (about 141 [V] when the effective value is 100 [V]). Therefore, the parallel electrical connection of the shunt circuit  13  with the first polarity and second polarity output terminals  113  and  114  causes the switching device Q 4  of the control circuit  131  requiring a withstand voltage greater than the maximum value of the pulsating voltage V 2  (about 141 [V]). 
     On the other hand, the shunt circuit  13  is electrically connected in parallel with the first solid light source  21  (the first solid light source  21  and the first diode D 1  in the example of  FIG. 1 ). The switching device Q 4  of the control circuit  131  is therefore to be supplied with a forward voltage (the first ON voltage V 21 ) of the first solid light source  21  as a maximum voltage (e.g., about 43 [V]). Therefore, enough withstand voltage for the switching device Q 4  is about 80 [V] at most. A semiconductor switching (switch) device with enough lower withstand voltage than the maximum voltage of the pulsating voltage V 2  (about 141 [V]) can be accordingly employed as the switching device Q 4 , thereby suppressing a rise in production cost. 
     As stated above, the lighting device  1 X includes the rectifier circuit  11 , the driver circuit  12  and the shunt circuit  13 . The rectifier circuit  11  includes the first polarity and second polarity output terminals  113  and  114 . The rectifier circuit  11  is configured to output, from the first polarity and second polarity output terminals  113  and  114 , the pulsating voltage V 2  obtained by rectifying the AC voltage V 1 . The driver circuit  12  is configured to, in response to a value of the pulsating voltage V 2  within one period of the pulsating voltage V 2 , switch sequentially in time between a first period of time, a second period of time, a third period of time, the second period of time and the first period of time. The first period of time is a period of time while the shunt circuit  13  is supplied with the output current I 1  from the first polarity output terminal  113 . The second period of time is a period of time while the first solid light source  21  is supplied with the output current I 1 . The third period of time is a period of time while the solid light sources including the first solid light source  21  (the first, second and third solid light sources  21 ,  22  and  23 ) are supplied with the output current IL The shunt circuit  13  is electrically connected in parallel with the first solid light source  21 . The shunt circuit  13  is configured to allow the output current I 1  proportional to a value of the pulsating voltage V 2  to flow through during the first period of time. 
     With the aforementioned configuration of the lighting device  1 X, it is possible to relatively reduce the withstand voltage of a circuit component of the shunt circuit  13  because the maximum voltage of the pulsating voltage V 2  to be supplied across the shunt circuit  13  is about the forward voltage of the first solid light source  21 . The lighting device  1 X causes a current to flow through the shunt circuit  13 , thereby enabling reduction in harmonic distortion of the input current I 1 . Employing the circuit component with a low withstand voltage enables the suppression of production cost. 
     Preferably, the lighting device  1 X includes capacitors (the first, second and third capacitors C 1 , C 2  and C 3 ) corresponding one-to-one to the solid light sources (the first, second and third solid light sources  21 ,  22  and  23 ). Each of the capacitors (the first, second and third capacitors C 1 , C 2  and C 3 ) is electrically connected in parallel with a corresponding solid light source of the solid light sources (the first, second and third solid light sources  21 ,  22  and  23 ). 
     With the aforementioned configuration of the lighting device  1 X, it is possible to smooth the voltage applied across the solid light sources according to variation of the pulsating voltage V 2  to suppress fluctuation (ripples) of a light output of the solid light sources. 
     In the lighting device  1 X, preferably the shunt circuit  13  is configured to limit the value of the output current I 1  flowing during the first period of time to a prescribed upper limit or less. 
     With the aforementioned configuration of the lighting device  1 X, it is possible to prevent an over-current from flowing through a circuit component (the switching device Q 4 ) of the shunt circuit  13 . 
     Incidentally, the shunt circuit  13  may include a control circuit  131  configured as shown in  FIG. 7 . The control circuit  131  shown in  FIG. 7  includes two switching devices Q 4  and Q 6  and two resistors R 3  and R 4 . A first end of a bleeder resistor  130  and one end of the resistor R 3  are electrically connected to a positive electrode of a first solid light source  21 . A second end of the bleeder resistor  130  is electrically connected to a collector of the switching device Q 4 . Another end of the resistor R 3  is electrically connected to a base of the switching device Q 4  and a collector of the switching device Q 6 . An emitter of the switching device Q 4  and a base of the switching device Q 6  are electrically connected to one end of the resistor R 4  and a cathode of a first diode D 1 . An emitter of the switching device Q 6  is electrically connected to another end of the resistor R 4  and a drain of a transistor Q 1 . 
     The control circuit  131  is configured to turn the switching device Q 4  on, thereby allowing a current  120  to flow through the bleeder resistor  130 . The control circuit  131  is configured to turn the switching device Q 6  on when a current I 21  flows through the resistor R 4  as a result of conduction of the first solid light source  21  and the first diode D 1  and then a voltage across the resistor R 4  exceeds a threshold of a base-emitter voltage of the switching device Q 6 . The control circuit  131  turns the switching device Q 6  on, thereby turning the switching device Q 4  off to prohibit a current from flowing through the bleeder resistor  130 . The control circuit  131  is configured to turn the switching device Q 6  on when the current flowing through the bleeder resistor  130  increases excessively, thereby turning the switching device Q 4  off. That is, the control circuit  131  is configured to allow a current to flow through the bleeder resistor  130  during a period of time while a value of a pulsating voltage V 2  is less than a first ON voltage V 21 , and prohibit the current from flowing through the bleeder resistor  130  other than during the period of time. 
     With the aforementioned configuration of the control circuit  131 , it is possible to omit the switching device Q 5  and the resistor R 5  and also allow the current  120  to flow through the bleeder resistor  130  only during the first period of time. 
     Embodiment 2 
       FIG. 8  shows a circuit configuration of a lighting device  1 Y according to Embodiment 2. Note that since the circuit configuration of the lighting device  1 Y is mostly common to the circuit configuration of the lighting device  1 X shown in  FIG. 4 , identical constituent elements to those of the lighting device  1 X have been allocated identical reference numerals, and description thereof has been omitted as appropriate. 
     The lighting device  1 Y differs from the lighting device  1 X in that it includes an integrated circuit (a first integrated circuit  30 ) as second and third constant current circuits, and a circuit (a shut-down circuit) configured to forcibly deactivate a first constant current circuit  121 . The lighting device  1 Y also differs from the lighting device  1 X in that a shunt circuit  13  includes a control circuit  131  as shown in  FIG. 7 . 
     The first integrated circuit  30  includes transistors Q 2  and Q 3 , a controller  300  configured to control the transistors Q 2  and Q 3 , first and second current sensors  301  and  302 , a control power supply  303  and a thermal sensor  304 . 
     The first current sensor  301  is configured to detect (measure) a value of a current I 22  flowing through the transistor Q 2 . The second current sensor  302  is configured to detect (measure) a value of a current I 23  flowing through the transistor Q 3 . The controller  300  is configured to control a source-gate voltage of the transistor Q 2  so that a current value detected through the first current sensor  301  accords with a target value (e.g., a prescribed current value Ist 1 ). The controller  300  is also configured to control a gate-source voltage of the transistor Q 3  so that a current value detected through the second current sensor  302  accords with the target value (e.g., the prescribed current value Ist 1 ). The thermal sensor  304  is configured to detect (measure) an internal temperature of the first integrated circuit  30 . The control power supply  303  is configured to step-down and convert a pulsating voltage V 2  from first polarity and second polarity output terminals  113  and  114  of a rectifier circuit  11  into a constant voltage to generate a control voltage. The control power supply  303  is also configured to supply the control voltage to the controller  300 , the first and second current sensors  301  and  302 , and the like. The control power supply  303  is configured to compare the internal temperature detected through the thermal sensor  304  with a first threshold and stop supplying the control voltage when the internal temperature exceeds the first threshold. Therefore, when supplying the control voltage is stopped, the controller  300  stops operating. The transistors Q 2  and Q 3  accordingly turn off because each gate-source voltage of the transistors Q 2  and Q 3  becomes zero. It is consequently possible to suppress the increase in the internal temperature of the first integrated circuit  30 . Note that the control power supply  303  is configured to resume supplying the control voltage when the internal temperature detected through the thermal sensor  304  is below a second threshold lower than the first threshold. 
     The shut-down circuit is composed of a switching (switch) device Q 301  and resistors R 333  and R 334 . The switching device Q 301  is, for example an NPN bipolar transistor. A collector of the switching device Q 301  is electrically connected to a non-inverting input terminal of an operational amplifier U 1 . An emitter of the switching device Q 301  is electrically connected to the second polarity output terminal  114  of the rectifier circuit  11 . A base of the switching device Q 301  is electrically connected to one end of the resistor R 333  and one end of the resistor R 334 . Another end of the resistor R 333  is electrically connected to a cathode of a second diode D 2 . Another end of the resistor R 334  is electrically connected to the second polarity output terminal  114  of the rectifier circuit  11  and the emitter of the switching device Q 301 . When the second diode D 2  conducts (turns on) and a current then flows through the resistors R 333  and R 334 , a base-emitter voltage of the switching device Q 301  increases and the switching device Q 301  then turns on. When the switching device Q 301  turns on, the transistor Q 1  turns off because a reference voltage Vx to the non-inverting input terminal of the operational amplifier U 1  becomes almost zero. The first constant current circuit  121  consequently stops operating. On the other hand, when the second diode D 2  is non-conductive (turns off), the base-emitter voltage of the switching device Q 301  decreases and the switching device Q 301  then turns off. 
     As stated above, the lighting device  1 Y is configured to forcibly deactivate the first constant current circuit  121  when the first integrated circuit  30  stops operating due to an abnormal rise in temperature of the first integrated circuit  30  or when the first integrated circuit  30  malfunctions. The lighting device  1 Y can accordingly suppress the occurrence of malfunction caused by a continuous operation of the first constant current circuit  121 . 
       FIG. 9  shows a circuit configuration of a lighting device  1 Z as a modified example of the lighting device  1 Y. The lighting device  1 Z differs from the lighting device  1 Y in that it includes a second integrated circuit  31  in addition to a first integrated circuit  30 . 
     The second integrated circuit  31  includes transistors Q 21  and Q 31 , a controller  310  configured to control the transistors Q 21  and Q 31 , first and second current sensors  311  and  312 , a control power supply  313  and a thermal sensor  314 . In short, the second integrated circuit  31  has a circuit configuration that is the same as that of the first integrated circuit  30 . 
     The first current sensor  311  is configured to detect (measure) a value of a current  122  flowing through the transistor Q 21 . A series circuit of the transistor Q 21  and the first current sensor  311  is electrically connected in parallel with a series circuit of a transistor Q 2  and a first current sensor  301  in the first integrated circuit  30 . The second current sensor  312  is configured to detect (measure) a value of a current I 23  flowing through the transistor Q 31 . A series circuit of the transistor Q 31  and the second current sensor  312  is electrically connected in parallel with a series circuit of a transistor Q 3  and a second current sensor  302  in the first integrated circuit  30 . The controller  310  is configured to control a gate-source voltage of the transistor Q 21  so that a current value detected through the first current sensor  311  accords with a target value (e.g., a prescribed current value Ist 1 ). The controller  310  is also configured to control a gate-source voltage of the transistor Q 31  so that a current value detected through the second current sensor  312  accords with the target value (e.g., the prescribed current value Ist 1 ). The thermal sensor  314  is configured to detect (measure) an internal temperature of the second integrated circuit  31 . The control power supply  313  is configured to step-down and convert a pulsating voltage V 2  from first polarity and second polarity output terminals  113  and  114  of a rectifier circuit  11  into a constant voltage to generate a control voltage. The control power supply  313  is also configured to supply the control voltage to the controller  310 , the first and second current sensors  311  and  312 , and the like. The control power supply  313  is configured to compare the internal temperature detected through the thermal sensor  314  with a first threshold and stop supplying the control voltage when the internal temperature exceeds the first threshold. Therefore, when supplying the control voltage is stopped, the controller  310  stops operating. The transistors Q 21  and Q 31  accordingly turn off because each gate-source voltage of the transistors Q 21  and Q 31  becomes zero. It is consequently possible to suppress the increase in the internal temperature of the second integrated circuit  31 . Note that the control power supply  313  is configured to resume supplying the control voltage when the internal temperature detected through the thermal sensor  314  is below a second threshold lower than the first threshold. 
     With the lighting device  1 Z, respective control of the currents  122  and  123  flowing through the second and third solid light sources  22  and  23  can be shared between the two integrated circuits  30  and  31 . It is accordingly possible to suppress the increase in respective temperatures of the first and second integrated circuits  30  and  31 . In the lighting device  1 Z, the respective control of the currents are shared between the two integrated circuits  30  and  31 , thereby enabling an increase in output and the suppression of cost rise in comparison with a circuit configuration in which one integrated circuit (first integrated circuit  30 ) performs current flow control. 
     Embodiment 3 
     Hereinafter, lighting equipment according to Embodiment 3 will be explained in detail. 
       FIG. 10A  is a perspective view of lighting equipment  5 A according to the embodiment. 
     The lighting equipment  5 A includes a lighting device of the aforementioned lighting devices  1 X,  1 Y and  1 Z, and a body  50 A that houses the lighting device. 
     The lighting equipment  5 A is, for example a down light configured to be recessed into a ceiling. The lighting equipment  5 A includes: the body  50  A that houses first, second and third solid light sources  21 ,  22  and  23  and the lighting device; and a reflector  61 . The body  50  A includes a heat sink  62  with radiation fins in an upper part thereof. The lighting equipment  5 A further includes a power cord  63  fixed from the body  50 A. The power cord  63  is used to electrically connect the lighting device in the body  50 A and an AC power supply  4 . 
     The lighting equipment is not limited to the down light, but may be another type of lighting equipment such as a spot light. 
       FIGS. 10B and 10C  show two pieces of lighting equipment  5 B and  5 C as spot lights configured to be attached to wire ducts  7 . 
     That is,  FIG. 10B  shows the lighting equipment  5 B as Modified Example 1, and  FIG. 10C  shows the lighting equipment  5 C as Modified Example 2. 
     As shown in  FIG. 10B , the lighting equipment  5 B of Modified Example 1 includes a body  50 B, a reflector  64 , a connector  65  and an arm  66 . The body  50 B houses first, second and third solid light sources  21 ,  22  and  23 , and a lighting device. The connector  65  is configured to be attached to the wire duct  7 . The arm  66  is connected the connector  65  and the body  50 B. The lighting device in the body  50 B and the connector  65  are connected via a power cord  67 . 
     As shown in  FIG. 10C , the lighting equipment  5 C of Modified Example 2 includes a body  50 C, a box  68 , a linkage  70  and a power cord  71 . The body  50 C houses first, second and third solid light sources  21 ,  22  and  23 . The box  68  houses a lighting device. The linkage  70  links the body  50 C with the box  68 . The power cord  71  electrically connects the first, second and third solid light sources  21 ,  22  and  23  in the body  50 C and the lighting device in the box  68 . Note that a connector  69  is provided on an upper surface of the box  68  and configured to be detachably attached to and electrically and mechanically connected to the wire duct  7 . 
     As stated above, lighting equipment (lighting equipment  5 A,  5 B or  5 C) includes a lighting device (a lighting device  1 X, by or  1 Z) and a body (a body  50 A,  50 B or  50 C) that holds the lighting device. 
     Since the aforementioned lighting equipment includes a lighting device (a lighting device  1 X, by or  1 Z), it is possible to reduce harmonic distortion of an input current I 1  and suppress a rise in production cost. 
     While the foregoing has described what are considered to be the best mode and/or other examples, it is understood that various modifications may be made therein and that the subject matter disclosed herein may be implemented in various forms and examples, and that they may be applied in numerous applications, only some of which have been described herein. It is intended by the following claims to claim any and all modifications and variations that fall within the true scope of the present teachings.