Lighting device and illumination device

Abstract

To provide a lighting device or the like which comprises a constant current circuit and can suppress a failure of the constant current circuit at a time of an abnormality occurence.SOLUTION: A lighting device 10 comprises: a voltage source circuit 20 that supplies a supply voltage to an anode terminal Ta of a light source 12; a constant current circuit 80 that controls a current value of a supply current as a current flowing through the light source 12; a comparison circuit 30 that compares a cathode voltage as a voltage of a cathode terminal Tc of the light source 12 and a reference voltage; and an abnormality voltage detection circuit 40 that detects an abnormality of the cathode voltage by comparing the cathode voltage and a threshold voltage. The voltage source circuit 20 controls a voltage value of the supply voltage so that the cathode voltage coincides with the reference voltage on the basis of a comparison result of the comparison circuit 30. The abnormality voltage detection circuit 40 stops the supply current on the basis of the comparison result of the cathode voltage and the threshold voltage.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a lighting device and a lighting apparatus.

Background Art

[0002] Conventionally, a lighting device that lights a light source having a light-emitting element such as an LED (Light Emitting Diode) is known (for example, Patent Document 1). The lighting device described in Patent Document 1 includes a boost chopper circuit that supplies current to the LED, and a constant current circuit including a transistor, a differential amplifier, etc. connected in series to the LED. The differential amplifier compares the voltage corresponding to the current flowing through the LED with a reference voltage. In the lighting device described in Patent Document 1, in an attempt to supply a constant current to the LED, the on-resistance of the transistor is adjusted according to the output of the operational amplifier.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a lighting device as described in Patent Document 1, for example, when an LED has a short-circuit failure, most of the output voltage from the boost chopper circuit is applied to the transistor connected in series to the LED. Even in such a case, in order to maintain the current flowing through the boost chopper circuit constant by the constant current circuit, the transistor can be maintained in a state where a large voltage is applied. As a result, the transistor may fail due to heat generation or the like in the transistor.

[0005] The present invention has been made to solve such problems, and provides a lighting device etc. that includes a constant current circuit and can suppress the failure of the constant current circuit when an abnormality occurs. [Means for solving the problem]

[0006] To solve the above problems, one embodiment of the lighting device according to the present invention is a lighting device that supplies current to a light source having an anode terminal and a cathode terminal, comprising: a voltage source circuit that supplies a supply voltage to the anode terminal; a constant current circuit that controls the current value of the supply current, which is the current flowing through the light source; a comparison circuit that compares the cathode voltage, which is the voltage at the cathode terminal, with a reference voltage; and an abnormal voltage detection circuit that detects an abnormality in the cathode voltage by comparing the cathode voltage with a threshold voltage, wherein the voltage source circuit controls the voltage value of the supply voltage so that the cathode voltage matches the reference voltage based on the comparison result of the comparison circuit, and the abnormal voltage detection circuit stops the supply current based on the comparison result of the cathode voltage with the threshold voltage.

[0007] To solve the above problems, one embodiment of the lighting device according to the present invention comprises the above-mentioned lighting device and the above-mentioned light source. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a lighting device equipped with a constant current circuit that can suppress failure of the constant current circuit in the event of an abnormality. [Brief explanation of the drawing]

[0009] [Figure 1] Circuit diagram showing the configuration of the lighting device according to the embodiment. [Modes for carrying out the invention]

[0010] The embodiments of the present invention will be described below with reference to the drawings. The embodiments described below are all specific examples of the present invention. Therefore, the numerical values, shapes, materials, components, arrangement and connection configurations of components, processes (steps), and order of processes shown in the following embodiments are examples and are not intended to limit the present invention. Accordingly, among the components in the following embodiments, those not described in the independent claims representing the highest-level concept of the present invention will be described as optional components.

[0011] Please note that each figure is a schematic diagram and not necessarily a strictly accurate representation. Furthermore, the same reference numerals are used for substantially identical components in each figure, and redundant explanations are omitted or simplified.

[0012] (Embodiment) A lighting device and an illumination device according to an embodiment will be described.

[0013] [1. Structure] First, the configuration of the lighting device and illumination device according to this embodiment will be explained using Figure 1. Figure 1 is a circuit diagram showing the configuration of the illumination device 1 according to this embodiment. Figure 1 also shows the AC power supply 2 that supplies power to the illumination device 1, along with the illumination device 1.

[0014] AC power source 2 is, for example, a grid power source such as an external commercial power supply. AC power source 2 supplies a voltage of, for example, AC 100V to the lighting device 1.

[0015] The lighting device 1 is a device that emits illumination light and comprises a lighting device 10 and a light source 12.

[0016] The lighting device 10 is a circuit that lights up the light source 12 by supplying current to the light source 12, and includes a voltage source circuit 20, a comparison circuit 30, an abnormal voltage detection circuit 40, and a constant current circuit 80. In this embodiment, the lighting device 10 further includes a rectifier circuit 14, a control power supply circuit 22, and a voltage conversion circuit 24. Although not shown, the lighting device 10 may further include a filter circuit to suppress high-frequency components between the rectifier circuit 14 and the AC power supply 2.

[0017] The light source 12 is a light-emitting section having an anode terminal Ta and a cathode terminal Tc. In this embodiment, the light source 12 includes one or more light-emitting elements. As light-emitting elements, solid-state light-emitting elements such as LEDs and organic EL (Electro-Luminescence) elements can be used. In this embodiment, the forward voltage of the light source 12 is greater than the output voltage of the AC power supply 2. The forward voltage of the light source 12 is, for example, 141V or higher.

[0018] The rectifier circuit 14 is a circuit that rectifies the AC power output by the AC power supply 2. The rectifier circuit 14 includes, for example, a diode bridge circuit.

[0019] The voltage source circuit 20 is a circuit that supplies a supply voltage to the anode terminal Ta of the light source 12. The voltage source circuit 20 has the function of controlling the voltage value of the supply voltage. The configuration of the voltage source circuit 20 is not particularly limited as long as it is a power supply circuit that can control the voltage value of the supply voltage. In this embodiment, the voltage source circuit 20 is a boost chopper circuit. The voltage source circuit 20 is connected to the output terminal of the rectifier circuit 14 and outputs a DC voltage. The voltage source circuit 20 has a high voltage terminal Th, a ground terminal Tg, and a signal terminal Ts. The high voltage terminal Th is the output terminal on the high potential side. The ground terminal Tg is the output terminal that is maintained at ground potential. The signal terminal Ts is the terminal to which a signal indicating the comparison result is input from the comparator circuit 30.

[0020] The voltage source circuit 20 controls the voltage value of the supply voltage based on the signal input to the signal terminal Ts. For example, a signal corresponding to the difference between the cathode voltage and the reference voltage is input to the signal terminal Ts. The voltage source circuit 20 controls the voltage value of the supply voltage based on this signal so that the difference between the cathode voltage and the reference voltage becomes zero, that is, the cathode voltage matches the reference voltage. Here, the state described as the cathode voltage matching the reference voltage includes not only the state where the cathode voltage and the reference voltage completely match but also the state where they substantially match. For example, the state described as the cathode voltage matching the reference voltage includes the state where the difference between the cathode voltage and the reference voltage is below the comparison accuracy of the comparison circuit 30. For example, the voltage source circuit 20 may control so that the difference between the cathode voltage and the reference voltage becomes 3% or less of the reference voltage.

[0021] The supply voltage until a predetermined time has elapsed since the start of supply may be lower than the supply voltage to be supplied after the predetermined time has elapsed. Thereby, it is possible to suppress an excessive supply voltage from being supplied to the light source 12 in the transient state immediately after the start of supply.

[0022] The control power supply circuit 22 is a power supply circuit that outputs a constant voltage for control. In the present embodiment, the control power supply circuit 22 receives an output voltage of about 300V from the voltage source circuit 20 and outputs a DC voltage of about 16V. As the control power supply circuit 22, for example, an IPD (Intelligent Power Device) or the like can be used. The IPD has a switching element and a control IC that controls the switching element, and is a circuit that converts voltage.

[0023] The voltage conversion circuit 24 is a circuit that converts the output voltage of the control power supply circuit 22. In the present embodiment, the voltage conversion circuit 24 receives an output voltage of about 16V from the control power supply circuit 22 and outputs a DC voltage of about 6V. As the voltage conversion circuit 24, for example, a well-known circuit such as a circuit combining a Zener diode and a bipolar transistor can be used.

[0024] The comparison circuit 30 is a circuit that compares the cathode voltage, which is the voltage at the cathode terminal Tc, with a reference voltage. Note that the comparison circuit 30 may compare the reference voltage with a voltage corresponding to the cathode voltage, rather than the cathode voltage itself. In this specification, the statement that the comparison circuit 30 compares the cathode voltage with a reference voltage means not only comparing the cathode voltage with a reference voltage, but also comparing the reference voltage with a voltage corresponding to the cathode voltage. The same applies to the following descriptions regarding the comparison of other voltages. In this embodiment, the comparison circuit 30 includes resistors 31, 32, 33, and 34, and an operational amplifier 35.

[0025] Resistor elements 31 and 32 generate a reference voltage by dividing the control voltage, which is a constant voltage output from the control power supply circuit 22. One end of resistor element 31 is connected to the output terminal of the control power supply circuit 22, and the other end is connected to one end of resistor element 32. The other end of resistor element 32 is connected to the ground terminal Tg of the voltage source circuit 20. The voltage at the connection point between resistor element 31 and resistor element 32 is the reference voltage. The reference voltage is not particularly limited as long as it is a voltage lower than the control voltage. The reference voltage is determined according to the characteristics of the operational amplifier 35, etc.

[0026] Resistor 33 is connected to the cathode terminal Tc. One end of resistor 33 is connected to the cathode terminal Tc, and the other end is connected to resistor 34. Resistor 34 is connected in series with resistor 33. One end of resistor 34 is connected to resistor 33, and the other end is connected to the signal terminal Ts of the voltage source circuit 20.

[0027] Operational amplifier 35 is a circuit that compares the cathode voltage with a reference voltage. The reference voltage is input to the non-inverting input terminal of operational amplifier 35, and the cathode voltage is input to the inverting input terminal. In other words, the non-inverting input terminal of operational amplifier 35 is connected to the connection point between resistor 31 and resistor 32, and the inverting input terminal is connected to the connection point between resistor 33 and resistor 34. Operational amplifier 35 outputs a signal from its output terminal that corresponds to the difference between the cathode voltage and the reference voltage. The output terminal of operational amplifier 35 is connected to the signal terminal Ts of the voltage source circuit 20. This allows a signal indicating the comparison result between the cathode voltage and the reference voltage to be output to the voltage source circuit 20.

[0028] The abnormal voltage detection circuit 40 is a circuit that detects abnormalities in the cathode voltage by comparing the cathode voltage with a threshold voltage. Based on the comparison result between the cathode voltage and the threshold voltage, the abnormal voltage detection circuit 40 stops the supply current when an abnormality is detected in the cathode voltage. As described above, if the supply voltage is set low during the period from the start of supply to the time elapsed, the abnormal voltage detection circuit 40 does not need to stop the supply current during the period from the start of supply to the time elapsed. In this embodiment, the abnormal voltage detection circuit 40 has a first detection circuit 50, a second detection circuit 60, and a smoothing circuit 70. The threshold voltage also includes a first threshold voltage that is lower than the reference voltage and a second threshold voltage that is higher than the reference voltage.

[0029] The smoothing circuit 70 is a circuit that smooths the cathode voltage. In other words, the smoothing circuit 70 smooths out rapid fluctuations in the cathode voltage. For example, the smoothing circuit 70 smooths out transient fluctuations in the cathode voltage, such as when the supply current to the light source 12 is started. In this embodiment, the smoothing circuit 70 includes a resistor 71 and a capacitor 72.

[0030] The resistor 71 is connected to the cathode terminal Tc. One end of the resistor 71 is connected to the cathode terminal Tc, and the other end is connected to the capacitor 72.

[0031] Capacitor 72 is connected in series with resistor 71. One end of capacitor 72 is connected to resistor 71, and the other end is connected to the ground terminal Tg of voltage source circuit 20. In other words, an RC circuit is formed by resistor 71 and capacitor 72.

[0032] The first detection circuit 50 compares the cathode voltage with a first threshold voltage lower than the reference voltage and detects when the cathode voltage falls below the first threshold voltage. When the cathode voltage falls below the first threshold voltage, the first detection circuit 50 stops supplying current to the light source 12. In this embodiment, the first detection circuit 50 includes resistors 51, 52, 55, 57, and 58, an operational amplifier 53, a diode 54, switch elements 56 and 59, and a control circuit 26.

[0033] Resistor elements 51 and 52 generate a first threshold voltage by dividing the control voltage, which is a constant voltage output from the control power supply circuit 22. One end of resistor element 51 is connected to the output terminal of the control power supply circuit 22, and the other end is connected to resistor element 52. One end of resistor element 52 is connected to the other end of resistor element 51, and the other end is connected to the ground terminal Tg of the voltage source circuit 20. The voltage at the connection point between resistor element 51 and resistor element 52 is the first threshold voltage. The first threshold voltage can be set appropriately by adjusting the resistance values ​​of resistor elements 51 and 52.

[0034] The resistor 55 is connected between the control power supply circuit 22 and the switch elements 56 and 59. One end of the resistor 55 is connected to the output terminal of the control power supply circuit 22, and the other end is connected to the collector terminal of the switch element 56 and the base terminal of the switch element 59. The resistor 55 prevents a short circuit between the output terminal of the control power supply circuit 22 and the ground terminal Tg of the voltage source circuit 20 when the switch element 56 is turned on.

[0035] Operational amplifier 53 is a circuit that compares the cathode voltage with a first threshold voltage. The non-inverting input terminal of operational amplifier 53 is connected to the connection point between resistor 71 and capacitor 72, and the inverting input terminal is connected to the connection point between resistor 51 and resistor 52.

[0036] Diode 54 is a rectifier element that interrupts the current flowing from the operational amplifier 53 to the control circuit 26. The cathode terminal of diode 54 is connected to the output terminal of the operational amplifier 53, and the anode terminal is connected to one end of the resistor 57.

[0037] Switch element 56 is an element used to control the state of switch element 59. A bipolar transistor can be used as switch element 56. A signal is input to the base terminal of the bipolar transistor switch element 56 via a resistor, and a resistor is connected between the base terminal and the emitter terminal. The collector terminal of switch element 56 is connected to the voltage source circuit 20 and also to the output terminal of the control power supply circuit 22 via a resistor 55. The base terminal of switch element 56 is connected to the control signal output terminal of the control circuit 26, and the emitter terminal is connected to the ground terminal Tg of the voltage source circuit 20.

[0038] The resistor element 57 is inserted between the output terminal of the operational amplifier 53 and the output terminal of the voltage conversion circuit 24. In this embodiment, one end of the resistor element 57 is connected to the anode terminal of the diode 54, and the other end is connected to the signal input terminal of the control circuit 26 and one end of the resistor element 58.

[0039] Resistor 58 is an external pull-up resistor for the signal input terminal of the control circuit 26. One end of resistor 58 is connected to the signal input terminal of the control circuit 26 and the other end of resistor 57, and the other end is connected to the output terminal of the voltage conversion circuit 24. Note that if an internal pull-up is used at the signal input terminal of the control circuit 26, resistor 58 is not necessary. In this configuration without resistor 58, when the output terminal of the operational amplifier 53 is at ground potential, resistor 57 functions as a limiting resistor to suppress a short circuit between the voltage conversion circuit 24 and the operational amplifier 53.

[0040] The switch element 59 is an element for switching the conduction state between the gate terminal of transistor 81 and the ground terminal Tg of the voltage source circuit 20. A bipolar transistor can be used as the switch element 59. A signal is input to the base terminal of the bipolar transistor switch element 59 via a resistor, and a resistor is connected between the base terminal and the emitter terminal. The collector terminal of the switch element 59 is connected to the gate terminal of transistor 81, the base terminal is connected to the connection point between resistor 55 and switch element 56, and the emitter terminal is connected to the ground terminal Tg of the voltage source circuit 20.

[0041] The control circuit 26 controls the supply current by controlling the constant current circuit 80 and also controls the switch element 56. The control circuit 26 sets the current value of the supply current by outputting a PWM (Pulse Width Modulation) signal to the gate terminal of transistor 83. This allows the lighting device 1 to be dimmed. The control circuit 26 controls the conduction state of the switch element 56 by outputting a HIGH level or LOW level signal to the base terminal of the switch element 56 based on the comparison result between the cathode voltage and the first threshold voltage. The output voltage from the voltage conversion circuit 24 is supplied as the operating voltage for the control circuit 26.

[0042] The control circuit 26 can be implemented, for example, by a microcontroller. A microcontroller is a single-chip semiconductor integrated circuit having memory such as ROM or RAM where the program is stored, a processor (CPU) that executes the program, a timer, and input / output circuits including A / D converters, D / A converters, etc. However, the control circuit 26 may also be implemented using electrical circuits other than a microcontroller.

[0043] As mentioned above, if the supply voltage is set low during the period from the start of supply to the time elapsed, the control circuit 26 measures the time elapsed from the start of supply using a timer, and does not need to control the switch element 56 during that time.

[0044] The second detection circuit 60 compares the cathode voltage with a second threshold voltage that is higher than the reference voltage and detects when the cathode voltage exceeds the second threshold voltage. When the cathode voltage exceeds the second detection voltage, the second detection circuit 60 stops supplying current to the light source 12. In this embodiment, the second detection circuit 60 includes a Zener diode 61 and a switch element 62.

[0045] The Zener diode 61 has a Zener voltage (i.e., breakdown voltage) corresponding to the second threshold voltage. The cathode terminal of the Zener diode 61 is connected to the connection point between the resistor 71 and the capacitor 72, and the anode terminal is connected to the base terminal of the switch element 62.

[0046] The switch element 62 is an element for switching the conduction state between the gate terminal of transistor 81 and the ground terminal Tg of the voltage source circuit 20. A bipolar transistor can be used as the switch element 62. A signal is input to the base terminal of the bipolar transistor switch element 62 via a resistor, and a resistor is connected between the base terminal and the emitter terminal. The collector terminal of the switch element 62 is connected to the gate terminal of transistor 81, the base terminal is connected to the anode terminal of Zener diode 61, and the emitter terminal is connected to the ground terminal Tg of the voltage source circuit 20.

[0047] The constant current circuit 80 is a circuit that controls the current value of the supply current, which is the current flowing through the light source 12. In this embodiment, the constant current circuit 80 has a transistor 81 connected to the cathode terminal Tc, and controls the current value of the supply current by continuously changing the resistance value of the transistor 81. The constant current circuit 80 further comprises resistors 82, 84, 85, 86, and 89, a transistor 83, a capacitor 87, and an operational amplifier 88.

[0048] Transistor 81 is an element connected in series with the light source 12. Transistor 81 is an element that can be used as a variable resistor and an on / off switch. In other words, transistor 81 is an element that can continuously switch its resistance value from virtually zero to infinity depending on the voltage applied to each terminal. The state in which the resistance value of transistor 81 is virtually zero means that the resistance value of transistor 81 is, for example, 1Ω or less, and this state is also called the on state. The state in which the resistance value of transistor 81 is infinite means that it is a cutoff state in which no current flows even when a voltage is applied to the drain terminal of transistor 81, and this state is also called the off state. In this embodiment, transistor 81 is an n-channel type MOSFET. The drain terminal of transistor 81 is connected to the cathode terminal Tc of the light source 12. The source terminal of transistor 81 is connected to the resistor 82. The gate terminal of transistor 81 is connected to the resistor 89.

[0049] The resistor 82 is connected in series with the light source 12 and the transistor 81. One terminal and the other terminal of the resistor 82 are connected to the source terminal of the transistor 81 and the ground terminal Tg of the voltage source circuit 20, respectively. As a result, the voltage applied to the resistor 82, that is, the voltage at one terminal of the resistor 82 (the terminal connected to the source terminal of the transistor 81), corresponds to the supply current supplied to the light source 12.

[0050] Transistor 83 is an element that switches its conduction state based on a PWM signal from the control circuit 26. For example, an n-channel MOSFET can be used as transistor 83. The PWM signal from the control circuit 26 is input to the gate terminal of transistor 83. The drain terminal of transistor 83 is connected to the connection point of resistors 84, 85, and 86, and the source terminal is connected to the ground terminal Tg of the voltage source circuit 20.

[0051] Resistor elements 84 and 85 are elements that divide the output voltage of the voltage conversion circuit 24. One end of resistor element 84 is connected to the output terminal of the voltage conversion circuit 24, and the other end is connected to one end of resistor element 85. The other end of resistor element 85 is connected to the ground terminal Tg of the voltage source circuit 20.

[0052] The resistor 86 and capacitor 87 form an integrating circuit that integrates the voltage input to the non-inverting input terminal of the operational amplifier 88. One end of the resistor 86 is connected to the connection point between resistors 84 and 85, and the other end is connected to the non-inverting input terminal of the operational amplifier 88 and one end of the capacitor 87. The other end of the capacitor 87 is connected to the ground terminal Tg of the voltage source circuit 20.

[0053] The operational amplifier 88 is a circuit that outputs a signal corresponding to the difference between the voltage corresponding to the supply current supplied to the light source 12 and the voltage corresponding to the PWM signal from the control circuit 26. The source terminal of transistor 81 and one terminal of resistor 82 are connected to the inverting input terminal of operational amplifier 88. As a result, the voltage applied to resistor 82, that is, the voltage corresponding to the supply current supplied to the light source 12, is input to the inverting input terminal of operational amplifier 88. The non-inverting input terminal of operational amplifier 88 is connected to the connection point between resistor 86 and capacitor 87. The output terminal of operational amplifier 88 is connected to resistor 89.

[0054] The resistor 89 is connected between the output terminal of the operational amplifier 88 and the gate terminal of the transistor 81.

[0055] [2. Operation] Next, the operation of the lighting device 10 will be explained.

[0056] First, let's explain the operation of the constant current circuit 80. The PWM signal from the control circuit 26 is input to the gate terminal of transistor 83 of the constant current circuit 80. As a result, during the period when a HIGH level signal is input to the gate terminal of transistor 83, the drain terminal and source terminal of transistor 83 become conductive (on), and the drain terminal is maintained at the same potential as the ground terminal Tg of the voltage source circuit 20, i.e., at ground potential. On the other hand, during the period when a LOW level signal is input to the gate terminal of transistor 83, the drain terminal and source terminal of transistor 83 become non-conductive (off), and the drain terminal is maintained at a voltage obtained by dividing the output voltage of the voltage conversion circuit 24 by resistors 84 and 85. As a result, the voltage corresponding to the PWM signal is integrated by the integrating circuit (resistor 86 and capacitor 87) and input to the non-inverting input terminal of the operational amplifier 88.

[0057] On the other hand, as described above, a voltage corresponding to the supply current to the light source 12 is input to the inverting input terminal of the operational amplifier 88. Therefore, a signal corresponding to the difference between the voltage corresponding to the supply current and the voltage corresponding to the PWM signal is input from the operational amplifier 88 to the gate terminal of transistor 81. This allows the resistance value between the drain terminal and source terminal of transistor 81 to be controlled to a resistance value corresponding to this difference. As a result, the current value of the supply current can be controlled to the current value corresponding to the PWM signal.

[0058] Next, the operation of the comparator circuit 30 and the voltage source circuit 20 will be explained. As described above, the reference voltage is input to the non-inverting input terminal of the operational amplifier 35 of the comparator circuit 30, and the cathode voltage is input to the inverting input terminal. The operational amplifier 35 outputs a signal corresponding to the difference between the cathode voltage and the reference voltage from its output terminal to the signal terminal Ts of the voltage source circuit 20. As a result, the voltage source circuit 20 can feedback control the output voltage based on the comparison result in the comparator circuit 30. Specifically, if the voltage source circuit 20 is a boost chopper circuit, the output voltage of the voltage source circuit 20 can be controlled by controlling the on-period of the switch elements of the boost chopper circuit. Therefore, the voltage source circuit 20 can control the voltage value of the supply voltage so that the cathode voltage matches the reference voltage based on the comparison result in the comparator circuit 30.

[0059] Next, the operation of the abnormal voltage detection circuit 40 will be described. The cathode voltage is controlled as described above, but in the event of an abnormality, the cathode voltage may be maintained in a state that deviates from the reference voltage.

[0060] For example, if there is an abnormality in the AC voltage supplied from the AC power supply 2, the cathode voltage may drop abnormally. The operational amplifier 53 of the first detection circuit 50 of the abnormal voltage detection circuit 40 outputs a HIGH level voltage when the cathode voltage is above the first threshold voltage, so a reverse voltage is applied to the diode 54. Therefore, the output voltage of the voltage conversion circuit 24 is input to the signal input terminal of the control circuit 26 (the terminal connected to the connection point between resistor element 57 and resistor element 58).

[0061] On the other hand, the operational amplifier 53 outputs a voltage at ground potential when the cathode voltage falls below the first threshold voltage. As a result, a forward voltage is applied to the diode 54. Consequently, the signal input terminal of the control circuit 26 receives a voltage obtained by dividing the output voltage of the voltage conversion circuit 24 by the resistors 57 and 58. In other words, the voltage input to the signal input terminal of the control circuit 26 when the cathode voltage falls below the first threshold voltage is lower than when the cathode voltage is above the first threshold voltage.

[0062] When the voltage input to the signal input terminal is the output voltage of the voltage conversion circuit 24 (i.e., the cathode voltage is equal to or greater than the first threshold voltage), the control circuit 26 outputs a HIGH level voltage to the base terminal of the switch element 56. As a result, the collector terminal and emitter terminal of the switch element 56 are in an ON state, and the potential between the collector terminal of the switch element 56 and the base terminal of the switch element 59 connected to it is maintained at ground potential. Consequently, the collector terminal and emitter terminal of the switch element 59 are maintained in an OFF state.

[0063] On the other hand, if the voltage input to the signal input terminal falls below the output voltage of the voltage conversion circuit 24 (i.e., the cathode voltage falls below the first threshold voltage), the control circuit 26 outputs a LOW level voltage to the base terminal of the switch element 56. As a result, the collector terminal and emitter terminal of the switch element 56 are turned off, and the potential of the collector terminal of the switch element 56 and the base terminal of the switch element 59 connected to it rises to the output voltage of the control power supply circuit 22. Consequently, the collector terminal and emitter terminal of the switch element 59 are turned on, and the gate terminal of the transistor 81 is maintained at ground potential. Therefore, the drain terminal and source terminal of the transistor 81 are turned off, and the current supplied to the light source 12 is stopped. Furthermore, when the voltage source circuit 20 detects that the potential of the collector terminal of the switch element 56 has risen, the voltage source circuit 20 stops supplying the supply voltage. As described above, the first detection circuit 50 of the abnormal voltage detection circuit 40 can stop the supply current when the cathode voltage falls below the first threshold voltage.

[0064] Furthermore, for example, if a short-circuit fault occurs in the light source 12, the cathode voltage may rise abnormally. As described above, a voltage corresponding to the cathode voltage of the light source 12 is applied to the cathode terminal of the Zener diode 61 of the second detection circuit 60 of the abnormal voltage detection circuit 40. When the cathode voltage applied to the Zener diode 61 is below the second threshold voltage, the voltage at the base terminal of the switch element 62 is at a LOW level. On the other hand, when the cathode voltage applied to the Zener diode 61 exceeds the second threshold voltage, conduction occurs between the cathode terminal and the anode terminal of the Zener diode 61. Consequently, the voltage at the base terminal of the switch element 62 is input to a voltage corresponding to the cathode voltage. Therefore, the collector terminal and emitter terminal of the switch element 62 are turned ON, and the gate terminal of the transistor 81 is maintained at ground potential. Therefore, the drain terminal and source terminal of the transistor 81 are turned OFF, and the current supplied to the light source 12 is stopped. As described above, the second detection circuit 60 of the abnormal voltage detection circuit 40 can stop the supply current when the cathode voltage exceeds the second threshold voltage.

[0065] [3. Effects] As described above, the lighting device 10 according to this embodiment supplies current to a light source 12 having an anode terminal Ta and a cathode terminal Tc. The lighting device 10 includes a voltage source circuit 20 that supplies a supply voltage to the anode terminal Ta, a constant current circuit 80 that controls the current value of the supply current, which is the current flowing through the light source 12, a comparison circuit 30 that compares the cathode voltage, which is the voltage at the cathode terminal Tc, with a reference voltage, and an abnormal voltage detection circuit 40 that detects an abnormality in the cathode voltage by comparing the cathode voltage with a threshold voltage. The voltage source circuit 20 controls the voltage value of the supply voltage so that the cathode voltage matches the reference voltage based on the comparison result of the comparison circuit 30. The abnormal voltage detection circuit 40 stops the supply current based on the comparison result between the cathode voltage and the threshold voltage.

[0066] As a result, even if an abnormality occurs in the AC power supply 2 or light source 12 that supplies AC voltage to the lighting device 10, the abnormal voltage detection circuit 40 can stop the current supplied to the light source 12. Therefore, it is possible to prevent the supply of current from continuing even when an abnormality occurs in the AC power supply 2 or light source 12. Therefore, it is possible to prevent the constant current circuit 80 from failing due to an abnormality in the AC power supply 2 or light source 12.

[0067] Furthermore, in the lighting device 10, the threshold voltage may include a first threshold voltage that is lower than the reference voltage. The abnormal voltage detection circuit 40 may have a first detection circuit 50 that compares the cathode voltage with the first threshold voltage and detects when the cathode voltage falls below the first threshold voltage. The first detection circuit 50 may stop supplying current when the cathode voltage falls below the first threshold voltage.

[0068] This prevents the cathode voltage from remaining below the reference voltage. Therefore, for example, if an abnormality occurs in the AC power supply 2 and the cathode voltage drops abnormally, the supply current can be stopped.

[0069] Furthermore, in the lighting device 10, the threshold voltage may include a second threshold voltage that is higher than the reference voltage. The abnormal voltage detection circuit 40 may have a second detection circuit 60 that compares the cathode voltage with the second threshold voltage and detects when the cathode voltage exceeds the second threshold voltage. The second detection circuit 60 may stop the supply current when the cathode voltage exceeds the second threshold voltage.

[0070] This prevents the cathode voltage from remaining above the reference voltage. Therefore, for example, if a short-circuit fault occurs in the light source 12, it is possible to prevent the constant current circuit 80 from failing due to an excessive voltage being applied to it.

[0071] Furthermore, in the lighting device 10, the supply voltage during the period from the start of supply until a predetermined time has elapsed may be lower than the supply voltage supplied after the predetermined time has elapsed. During the period from the start of supply of the supply voltage until a predetermined time has elapsed, the abnormal voltage detection circuit 40 does not need to stop the supply current.

[0072] This makes it possible to suppress the supply of an excessive supply voltage to the light source 12 during the transient state immediately after the start of supply voltage.

[0073] Furthermore, in the lighting device 10, the constant current circuit 80 has a transistor 81 connected to the cathode terminal Tc, and the current value of the supplied current may be controlled by continuously changing the resistance value of the transistor 81.

[0074] This allows for continuous and precise control of the supply current. Furthermore, if the constant current circuit 80 includes such a transistor 81, an excessive voltage may be applied to the transistor 81 in the event of an abnormality. However, in this embodiment, the abnormal voltage detection circuit 40 stops the supply current in the event of an abnormality, thereby suppressing failure of the transistor 81.

[0075] Furthermore, the lighting device 10 may also include a smoothing circuit 70 for smoothing the cathode voltage in the abnormal voltage detection circuit 40.

[0076] This makes it possible to smooth out transient cathode voltage fluctuations, such as when the supply current to the light source 12 is started. This prevents the supply current from being interrupted due to normal transient cathode voltage fluctuations.

[0077] Furthermore, the lighting device 1 according to this embodiment comprises a lighting device 10 and a light source 12.

[0078] This makes it possible to obtain the same effect in lighting device 1 as in lighting device 10.

[0079] (Torture, etc.) Although the lighting device and illumination device according to the present invention have been described above based on embodiments, the present invention is not limited to these embodiments.

[0080] For example, in the above embodiment, operational amplifiers were used to compare voltages in the comparison circuit 30, the abnormal voltage detection circuit 40, and the constant current circuit 80, but comparators or the like may be used instead of operational amplifiers. For example, a comparator may be used instead of the operational amplifier 53 in the abnormal voltage detection circuit 40. In this case, the diode 54 connected to the output terminal of the operational amplifier 53 in the above embodiment becomes unnecessary.

[0081] Furthermore, in the above embodiment, a Zener diode 61 and a switching element 62 were used in the second detection circuit 60, but the configuration of the second detection circuit 60 is not limited to this. For example, the second detection circuit 60 may be implemented using an operational amplifier or a comparator, similar to the first detection circuit 50.

[0082] Furthermore, the present invention also includes forms obtained by applying various modifications to each embodiment that a person skilled in the art could conceive, or forms realized by arbitrarily combining the components and functions of each embodiment without departing from the spirit of the present invention. [Explanation of Symbols]

[0083] 1. Lighting device 10 Lighting device 12 light source 20 Voltage source circuit 30 Comparison circuit 40. Abnormal voltage detection circuit 50 First detection circuit 60 Second detection circuit 70 Smoothing circuit 80 constant current circuit 81 Transistors Ta Anode Terminal Tc cathode terminal

Claims

1. A lighting device that supplies current to a light source having an anode terminal and a cathode terminal, A voltage source circuit that supplies a voltage to the anode terminal, A constant current circuit that controls the current value of the supply current, which is the current flowing through the aforementioned light source, A comparison circuit compares the cathode voltage, which is the voltage at the cathode terminal, with a reference voltage. The system includes an abnormal voltage detection circuit that detects an abnormality in the cathode voltage by comparing the cathode voltage with a threshold voltage. The voltage source circuit controls the voltage value of the supply voltage so that the cathode voltage matches the reference voltage, based on the comparison result of the comparison circuit. The aforementioned reference voltage is a constant voltage. The abnormal voltage detection circuit stops the supply current and stops supplying the supply voltage to the voltage source circuit based on the comparison result between the cathode voltage and the threshold voltage. Lighting device.

2. The threshold voltage includes a first threshold voltage that is lower than the reference voltage. The abnormal voltage detection circuit has a first detection circuit that compares the cathode voltage with the first threshold voltage and detects that the cathode voltage has fallen below the first threshold voltage. The first detection circuit stops the supply current when the cathode voltage falls below the first threshold voltage. The lighting device according to claim 1.

3. The supply voltage during the period from the start of supply until a predetermined time has elapsed is lower than the supply voltage supplied after the predetermined time has elapsed. During the period from the start of supplying the aforementioned supply voltage until a predetermined time has elapsed, the abnormal voltage detection circuit will not stop the supply current. The lighting device according to claim 1 or 2.

4. The constant current circuit has a transistor connected to the cathode terminal, and controls the current value of the supplied current by continuously changing the resistance value of the transistor. The lighting device according to claim 1 or 2.

5. The abnormal voltage detection circuit further comprises a smoothing circuit for smoothing the cathode voltage. The lighting device according to claim 1 or 2.

6. A lighting device according to claim 1 or 2, The light source comprises, Lighting device.

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