Patent Publication Number: US-2013249412-A1

Title: Lighting circuit and luminaire

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2012-068466, filed on Mar. 23, 2012; the entire contents of which are incorporated herein by reference. 
     FIELD 
     Embodiments described herein relate generally to a lighting circuit and a luminaire. 
     BACKGROUND 
     In recent years, in a luminaire, an incandescent lamp and a fluorescent lamp used as an illumination light source are replaced with a light source that consumes less energy and has longer life such as a light-emitting diode (LED). For example, new illumination light sources such as an electro-luminescence (EL) and an organic light-emitting diode (OLED) are also developed. There is known a luminaire in which a capacitive element such as a capacitor is connected to these light-emitting elements to stably light the light-emitting elements without flickering. In such a luminaire, for example, when a lighting load is replaced or when a load is detached and attached, it is likely that an electric current flows backward from the capacitor to a power supply side and causes a malfunction of a power supply circuit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a circuit diagram illustrating a luminaire including a lighting circuit according to a first embodiment; and 
         FIG. 2  is a circuit diagram illustrating a luminaire including a lighting circuit according to a second embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     In general, according to one embodiment, a lighting circuit includes a first power supply circuit, a first detecting circuit, a first control circuit, and a first protecting circuit. The first power supply circuit is supplied with electric power from a first power supply and outputs a direct current flowing in a first direction. The first detecting circuit detects a first detection value of an electric current flowing between the first power supply circuit and an output terminal. The first control circuit compares the first detection value with a reference value and controls the first power supply circuit. The first protecting circuit is connected to the first detecting circuit and configured to reduce an absolute value of the first detection value if an electric current flows in a direction opposite to the first direction. 
     In general, according to another embodiment, a luminaire includes a lighting circuit and a light-emitting module. The light-emitting module is connected as a lighting load of the lighting circuit and includes a light-emitting element and a capacitive element. The lighting circuit includes a first power supply circuit, a first detecting circuit, a first control circuit, and a first protecting circuit. The first power supply circuit is supplied with electric power from a first power supply and outputs a direct current flowing in a first direction. The first detecting circuit detects a first detection value of an electric current flowing between the first power supply circuit and an output terminal. The first control circuit compares the first detection value with a reference value and controls the first power supply circuit. The first protecting circuit is connected to the first detecting circuit and configured to reduce an absolute value of the first detection value detected if an electric current flows in a direction opposite to the first direction. 
     Embodiments are explained in detail below with reference to the accompanying drawings. In this specification and the figures, components same as those explained concerning the figures already referred to are denoted by the same reference numerals and signs and detailed explanation of the components is omitted as appropriate. 
     First Embodiment 
       FIG. 1  is a circuit diagram illustrating a luminaire including a lighting circuit according to a first embodiment. 
     As shown in  FIG. 1 , a luminaire  1  includes a light-emitting module  2  and a lighting circuit  3  that lights the light-emitting module  2 . 
     The light-emitting module  2  includes a light-emitting element  4  and a capacitive element  5  connected in parallel to the light-emitting element  4 . The light-emitting module  2  is formed in, for example, a columnar shape, for example, a bulb shape and detachably connected to output terminals  7  and  8  of the lighting circuit  3 . The light-emitting element  4  includes, for example, an LED. The light-emitting element  4  is supplied with electric power from the lighting circuit  3  and lit. The capacitive element  5  is, for example, a capacitor and provided near the light-emitting element  4 . In other words, the capacitive element  5  is provided closer to the light-emitting element  4  than, for example, the lighting circuit  3 . The capacitive element  5  reduces noise from the lighting circuit  3  and the like and suppresses fluctuation in a voltage to prevent flickering. 
     The lighting circuit  3  includes a first power supply circuit  9 , a first capacitor  10 , a first detecting circuit  11  that detects an electric current flowing between the first power supply circuit  9  and the output terminal  8 , a first control circuit  12 , and a first protecting circuit  13 . 
     The lighting circuit  3  converts electric power supplied from a first power supply  6  and outputs direct-current power to the light-emitting module  2  via the output terminals  7  and  8 . The first power supply  6  is an alternating-current power supply such as a commercial power supply or is a direct-current power supply such as a secondary battery. 
     The first power supply circuit  9  is supplied with electric power from the first power supply  6  and outputs a direct-current voltage VOUT and a direct current IOUT suitable for the light-emitting element  4  flowing in a first direction. The first power supply circuit  9  includes a switching power supply such as a DC-DC converter. 
     The first capacitor  10  is connected in parallel to an output side of the first power supply circuit  9 , smoothes an output voltage of the first power supply circuit  9 , and removes noise. 
     The first detecting circuit  11  detects a first detection value of an electric current flowing between the first power supply circuit  9  and the output terminal  8  and outputs, as a detection value, a voltage proportional to a current value. In the lighting circuit  3 , the first detecting circuit  11  includes a resistor. A first detection value VDT 1  is a voltage at both ends of the resistor. The polarity of the first detection value VDT 1  is positive polarity if the first detecting circuit  11  detects an electric current in the first direction, which is a direction in which the direct current IOUT output from the first power supply circuit  9  flows. Therefore, if an electric current in a direction opposite to the first direction flows to the first detecting circuit  11 , the first detection value VDT 1  has negative polarity. 
     The first control circuit  12  compares the first detection value VDT 1  detected by the first detecting circuit  11  with a reference value and controls the first power supply circuit  9 . For example, if the first detection value VDT 1  detected by the first detecting circuit  11  is lower than the reference value, the first control circuit  12  controls the first power supply circuit  9  to increase the direct current IOUT to be output. If the first detection value VDT 1  detected by the first detecting circuit  11  is higher than the reference value, the first control circuit  12  controls the first power supply circuit  9  to reduce the direct current IOUT to be output. As a result, the direct current IOUT output from the first power supply circuit  9  is controlled to a predetermined value based on the reference value. The predetermined value is, for example, a current value with which a predetermined optical output can be obtained from the light-emitting module  2 . 
     The first protecting circuit  13  is connected to the first detecting circuit  11 . The first protecting circuit  13  reduces an absolute value of the first detection value VDT 1  detected if an electric current flows in a direction opposite to the first direction, which is a direction of the direct current IOUT output from the first power supply circuit  9 , to be relatively smaller than the absolute value of the first detection value VDT 1  detected if an electric current flows in the first direction. In this specific example, the first protecting circuit  13  includes a Schottky barrier diode connected in parallel to the first detecting circuit  11  with the direction opposite to the first direction set as a forward direction. Therefore, since the Schottky barrier diode is reversely biased with respect to the electric current in the first direction, the Schottky barrier diode does not affect the first detection value VDT 1  having positive polarity in the first detecting circuit  11 . Since the Schottky barrier diode is forward-biased with respect to the electric current in the direction opposite to the first direction, the Schottky barrier diode suppresses the first detection value VDT 1  having negative polarity in the first detecting circuit  11  to a forward direction voltage. 
     If electric power is supplied from the first power supply  6  and the first power supply circuit  9  lights the light-emitting module  2 , the capacitive element  5  is charged to a forward direction voltage of the light-emitting element  4 . Therefore, for example, if the light-emitting module  2  is removed from the luminaire  1  and, thereafter, the same light-emitting module  2  is attached to the luminaire  1 , a high voltage is applied from the light-emitting module  2  side to the first power supply circuit  9 . 
     At this point, for example, if the first protecting circuit  13  is absent, an electric current flows from the capacitive element  5  in the direction of the first power supply circuit  9 , i.e., through a path of the capacitive element  5 , the output terminal  7 , the first power supply circuit  9 , the first detecting circuit  11 , the output terminal  8 , and the capacitive element  5  in the direction opposite to the first direction. As a result, the first detecting circuit  11  outputs the first detection value VDT 1  having negative polarity. Therefore, it is likely that the first control circuit  12  malfunctions and is broken. 
     On the other hand, in this embodiment, the first protecting circuit  13  reducees an absolute value of the first detection value VDT 1  detected if an electric current in the direction of the first power supply circuit  9 , i.e., an electric current in the direction opposite to the first direction flows from the capacitive element  5  to be relatively small. As a result, an absolute value of the first detection value VDT 1  having negative polarity input to the first control circuit  12  is reduced to a relatively small value. Therefore, the first control circuit  12  neither malfunctions nor is broken. 
     The first protecting circuit  13  only has to be capable of protecting the first control circuit  12  from the input of a voltage having negative polarity and a large absolute value by reducing an absolute value of the first detection value VDT 1  detected if an electric current flows in the direction opposite to the first direction to be relatively smaller than the absolute value of the first detection value VDT 1  detected if an electric current flows in the first direction. 
     The first protecting circuit  13  may be, for example, a bypass circuit that is connected in parallel to the first detecting circuit  11  and to which an electric current flows in the direction opposite to the first direction. For example, if the electric current in the direction opposite to the first direction flows between the first power supply circuit  9  and the output terminal  8 , a part of the electric current flows to the first protecting circuit  13  functioning as the bypass circuit. Therefore, a current value flowing to the first detecting circuit  11  decreases. The absolute value of the detection value VDT 1  of the first detecting circuit  11  can be reduced. As a result, the first control circuit  12  neither malfunctions nor is broken or burned. 
     The first protecting circuit  13  may be a clamp circuit that keeps the first detection value VDT 1  at a value equal to or higher than a specified value. For example, if an electric current in the direction opposite to the first direction flows between the first power supply circuit  9  and the output terminal  8 , the first protecting circuit  13  functioning as the clamp circuit can keep an absolute value of the detection value VDT 1  of the first detecting circuit  11  at a relatively small value. As a result, the first control circuit  12  neither malfunctions nor is broken or burned. 
     Second Embodiment 
       FIG. 2  is a circuit diagram illustrating a luminaire including a lighting circuit according to a second embodiment. 
     A luminaire  1   a  according to the second embodiment is different from the luminaire  1  according to the first embodiment in the configuration of the lighting circuit  3 . Specifically, the luminaire  1   a  includes a lighting circuit  3   a , which is formed by adding a second lighting circuit  15  and a selecting circuit  16  to the lighting circuit  3 , and the light-emitting module  2 . 
     The lighting circuit  3  is configured the same as the lighting circuit  3  in the luminaire  1  except that the lighting circuit  3  is connected to the output terminals  7  and  8  via the selecting circuit  16  as a first lighting circuit. The lighting circuit (the first lighting circuit)  3  changes electric power supplied from the first power supply  6  and outputs the direct current IOUT to the light-emitting module  2  via the selecting circuit  16  and the output terminals  7  and  8 . 
     The second lighting circuit  15  is connected to the output terminals  7  and  8  via the selecting circuit  16 . The second lighting circuit  15  includes a second power supply circuit  17 , a second capacitor  18 , and a second detecting circuit  19  that detects an electric current flowing between the second power supply circuit  17  and the output terminal  8  connected via the selecting circuit  16 , a second control circuit  20 , and a second protecting circuit  21 . 
     The second lighting circuit  15  converts electric power supplied from the second power supply  14  and outputs direct-current power to the light-emitting module  2  via the selecting circuit  16  and the output terminals  7  and  8 . The second power supply  14  is an alternating-current power supply such as a commercial power supply or a direct-current power supply such as a secondary battery. The first power supply  6  and the second power supply  14  are power supplies of separate systems. For example, one power supply can be used as a power supply for normal operation and the other power supply can be used as a backup power supply for emergency. 
     In the second lighting circuit  15 , the first power supply  9 , the first capacitor  10 , the output terminal  8 , the first detecting circuit  11 , the first control circuit  12 , and the first protecting circuit  13  in the lighting circuit  3  are respectively replaced with the second power supply circuit  17 , the second capacitor  18 , the output terminal  8  connected via the selecting circuit  16 , the second detecting circuit  19 , the second control circuit  20 , and the second protecting circuit  21 . 
     The second power supply circuit  17  is supplied with electric power from the second power supply  14  and outputs the direct-current voltage VOUT and the direct current IOUT suitable for the light-emitting element  4  flowing in a second direction. The second power supply circuit  17  includes a switching power supply such as a DC-DC converter. 
     The second capacitor  18  is connected in parallel to the output side of the second power supply circuit  17 , smoothes an output voltage of the second power supply circuit  17 , and removes noise. 
     The second detecting circuit  19  detects a second detection value of an electric current flowing between the second power supply circuit  17  and the output terminal  8  connected via the selecting circuit  16  and outputs a voltage proportional to a current value as a detection value. In the second lighting circuit  15 , the second detecting circuit  19  includes a resistor. A second detection value VDT 2  is a voltage at both ends of the resistor. The polarity of the second detection value VDT 2  is positive polarity if the second detecting circuit  19  detects an electric current in the second direction, which is a direction in which the direct current IOUT output from the second power supply circuit  17  flows. Therefore, if an electric current in a direction opposite to the second direction flows to the second detecting circuit  19 , the second detection value VDT 2  has negative polarity. 
     The second control circuit  20  compares the second detection value VDT 2  detected by the second detecting circuit  19  with a reference value and controls the second power supply circuit  17 . For example, if the second detection value VDT 2  detected by the second detecting circuit  19  is lower than the reference value, the second control circuit  20  controls the second power supply circuit  17  to increase the direct current IOUT to be output. If the second detection value VDT 2  detected by the second detecting circuit  19  is higher than the reference value, the second control circuit  20  controls the second power supply circuit  17  to reduce the direct current IOUT to be output. As a result, the direct current IOUT output from the second power supply circuit  17  is controlled to a predetermined value based on the reference value. The predetermined value is, for example, a current value with which a predetermined optical output can be obtained from the light-emitting module  2 . 
     The second protecting circuit  21  is connected to the second detecting circuit  19 . The second protecting circuit  21  reduces an absolute value of the second detection value VDT 2  detected if an electric current flows in a direction opposite to the second direction, which is a direction of the direct current IOUT output from the second power supply circuit  17 , to be relatively smaller than the absolute value of the second detection value VDT 2  detected if an electric current flows in the second direction. In this specific example, the second protecting circuit  21  includes a Schottky barrier diode connected in parallel to the second detecting circuit  19  with the direction opposite to the second direction set as a forward direction. Therefore, since the Schottky barrier diode is reversely biased with respect to the electric current in the second direction, the Schottky barrier diode does not affect the second detection value VDT 2  having positive polarity in the second detecting circuit  19 . Since the Schottky barrier diode is forward-biased with respect to the electric current in the direction opposite to the second direction, the Schottky barrier diode suppresses the second detection value VDT 2  having negative polarity in the second detecting circuit  19  to a forward direction voltage. 
     If electric power is supplied from the second power supply  14  and the second power supply circuit  17  lights the light-emitting module  2 , the capacitive element  5  is charged to a forward direction voltage of the light-emitting element  4 . Therefore, for example, if the light-emitting module  2  is removed from the luminaire  1   a  and, thereafter, the same light-emitting module  2  is attached to the luminaire  1   a , a high voltage is applied from the light-emitting module  2  side to the second power supply circuit  17 . 
     At this point, for example, if the second protecting circuit  21  is absent, an electric current flows from the capacitive element  5  in the direction of the second power supply circuit  17 , i.e., through a path of the capacitive element  5 , the output terminal  7 , the selecting circuit  16 , the second power supply circuit  17 , the second detecting circuit  19 , the selecting circuit  16 , the output terminal  8 , and the capacitive element  5  in the direction opposite to the second direction. As a result, the second detecting circuit  19  outputs the second detection value VDT 2  having negative polarity. Therefore, it is likely that the second control circuit  20  malfunctions and is broken. 
     On the other hand, in this embodiment, the second protecting circuit  21  reduces an absolute value of the second detection value VDT 2  detected if an electric current in the direction of the second power supply circuit  17 , i.e., an electric current in the direction opposite to the second direction flows from the capacitive element  5  to be relatively small. As a result, an absolute value of the second detection value VDT 2  having negative polarity input to the second control circuit  20  is suppressed to a relatively small value. Therefore, the second control circuit  20  neither malfunctions nor is broken. 
     The second protecting circuit  21  only has to be capable of protecting the second control circuit  20  from the input of a voltage having negative polarity and a large absolute value by reducing the absolute value of the second detection value VDT 2  detected if an electric current flows in the direction opposite to the second direction to be relatively smaller than the absolute value of the second detection value VDT 2  detected if an electric current flows in the second direction. 
     The second protecting circuit  21  may be, for example, a bypass circuit that is connected in parallel to the second detecting circuit  19  and to which an electric current flows in the direction opposite to the second direction. For example, if the electric current in the direction opposite to the second direction flows between the second power supply circuit  17  and the output terminal  8  connected via the selecting circuit  16 , a part of the electric current flows to the second protecting circuit  21  functioning as the bypass circuit. Therefore, a current value flowing to the second detecting circuit  19  decreases. The absolute value of the detection value VDT 2  of the second detecting circuit  19  can be reduced. As a result, the second control circuit  20  neither malfunctions nor is broken or burned. 
     The second protecting circuit  21  may be a clamp circuit that keeps the second detection value VDT 2  at a value equal to or higher than a specified value. For example, if an electric current in the direction opposite to the second direction flows between the second power supply circuit  17  and the output terminal  8  connected via the selecting circuit  16 , the second protecting circuit  21  functioning as the clamp circuit can keep an absolute value of the detection value VDT 2  of the second detecting circuit  19  at a relatively small value. As a result, the second control circuit  20  neither malfunctions nor is broken or burned. 
     The selecting circuit  16  selects one of the first power supply circuit  9  and the second power supply circuit  17  and lights the light-emitting element  4  via the output terminals  7  and  8 . The selecting circuit  16  is, for example, a relay. If an output of the first power supply circuit  9  is equal to or larger than a specified value, the selecting circuit  16  selects the first power supply circuit  9  and electrically connects the first power supply circuit  9  to the light-emitting module  2  via the output terminals  7  and  8 . If the output of the first power supply circuit  9  falls below the specified value, the selecting circuit  16  selects the second power supply circuit  17  and electrically connects the second power supply circuit  17  to the light-emitting module  2  via the output terminals  7  and  8 . The specified value is a voltage, an electric current, or electric power necessary for lighting the light-emitting element  4 . For example, if the output of the first power supply circuit  9  falls below the specified value because of abnormality of at least one of the first power supply  6  and the first power supply circuit  9 , the selecting circuit  16  selects an output of the second power supply circuit  17  and lights the light-emitting element  4 . 
     In this embodiment, as a power supply to the light-emitting module  2 , the first power supply  6  and the second power supply  14  of the separate systems can be switched. Therefore, for example, if the luminaire  1   a  is used as an emergency lamp, normal lighting and emergency lighting can be performed by one light-emitting module  2 . 
     In this embodiment, in addition to the effects of the first embodiment, as explained below, even if the selecting circuit  16  switches the selection of the first power supply circuit  9  and the second power supply circuit  17 , the first control circuit  12  and the second control circuit  20  neither malfunction nor are broken. 
     In this embodiment, the first power supply circuit  9  or the second power supply circuit  17  selected by the selecting circuit  16  lights the light-emitting module  2  via the first detecting circuit  11  and the second detecting circuit  19  to which the first protecting circuit  13  and the second protecting circuit  21  are respectively connected. As a result, even if an electric current flows from the capacitive element  5  in the first direction, which is the direction of the first power supply circuit  9 , or flows from the capacitive element  5  in the second direction, which is the direction of the second power supply circuit  17 , the first control circuit  12  and the second control circuit  20  are protected. For example, if the selecting circuit  16  switches the selection from the second power supply circuit  17  to the first power supply circuit  9  or if the selecting circuit  16  switches the selection from the first power supply circuit  9  to the second power supply circuit  17 , the first and second detection values VDT 1  and VDT 2  by the electric current from the capacitive element  5  in the first direction, which is the direction of the first power supply circuit  9 , and the electric current from the capacitive element  5  in the second direction, which is the direction of the second power supply circuit  17 , are suppressed. As a result, the first control circuit  12  and the second control circuit  20  neither malfunction nor are broken. 
     The embodiments are explained above with reference to the specific examples. However, the present disclosure is not limited to the embodiments. Various modifications are possible. 
     For example, the light-emitting element  4  is not limited to the LED and may be an OLED or the like. Plural light-emitting elements  4  may be connected to the light-emitting module  2  in series or in parallel according to a desired optical output. If the plural light-emitting elements  4  are used, the capacitive element  5  can be connected in parallel to the respective light-emitting elements  4 . Further, the capacitive element  5  may be connected to both ends of the plural light-emitting elements  4  connected in series. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the present disclosure. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions, and changes in the form of the embodiments described herein may be made without departing from the spirit of the present disclosure. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the present disclosure.