Lighting device

Abstract

To provide a lighting device capable of shortening a response time.SOLUTION: A lighting device 30 supplies a DC current to a light source including one or more light-emitting elements. The lighting device comprises a converter circuit 40 that supplies the DC current to a light source 80 on the basis of a dimming signal indicating a dimming level of the light source 80. In a case where the dimming level indicated by the dimming signal is lower than a predetermined threshold level and a magnitude of a DC voltage supplied to the light source 80 is smaller than a predetermined voltage threshold, the converter circuit 40 supplies to the light source 80 the DC current having a boost current value larger than a dimming current value corresponding to the dimming level. The converter circuit 40 has an update mode which is an operation mode to update the voltage threshold and, in the update mode, supplies to the light source 80 the DC voltage equal to or more than a lighting start voltage of the light source 80, and updates the voltage threshold on the basis of a relation between the DC voltage and the DC current to be supplied to the light source 80.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a lighting device. [Background technology]

[0002] Conventionally, dimmable lighting devices that light a light source having a light emitting element such as an LED (Light Emitting Diode) are known (for example, Patent Document 1, etc.). Such lighting devices have a problem in that when switching from an off state to a lighting state with a low dimming level, the response time of the light output to switching of the dimming signal is long. In the lighting device described in Patent Document 1, when increasing the dimming level, a current corresponding to a dimming level higher than a target dimming level is supplied to the light source for a predetermined time. In this way, an increase in the voltage supplied to the light source is promoted, thereby shortening the response time. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2008-60492 A Summary of the Invention [Problem to be solved by the invention]

[0004] In a lighting device such as that described in Patent Document 1, the above-mentioned predetermined time is set to be shorter than the time required for the dimming level of the light source to reach the target dimming level. This prevents the amount of current supplied to the light source from becoming excessive, causing the light output of the light source to temporarily overshoot. For this reason, if the above-mentioned predetermined time is not set appropriately, the response time may not be sufficiently shortened. In particular, if the characteristics of the light source change due to replacement of the light source or deterioration of the light source, the voltage supplied to the light source may not be able to increase to near the light-on start voltage within the above-mentioned predetermined time. In this case, the response time may not be sufficiently shortened.

[0005] The present invention has been made to solve such problems, and provides a lighting device capable of shortening the response time. [Means for solving the problem]

[0006] In order to solve the above problems, one aspect of a lighting device according to the present invention is a lighting device that supplies a DC current to a light source including one or more light-emitting elements, and includes a converter circuit that supplies the DC current to the light source based on a dimming signal indicating a dimming level of the light source, and when the dimming level indicated by the dimming signal is lower than a predetermined threshold level and the magnitude of the DC voltage supplied to the light source is smaller than a predetermined voltage threshold, the converter circuit supplies to the light source the DC current having a boost current value greater than a dimming current value corresponding to the dimming level, and has an update mode which is an operating mode for updating the voltage threshold, and in the update mode, the converter circuit supplies to the light source the DC voltage that is equal to or greater than the turn-on voltage of the light source, and updates the voltage threshold based on the relationship between the DC voltage and the DC current supplied to the light source. Effect of the Invention

[0007] According to the present invention, it is possible to provide a lighting device capable of shortening the response time. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a circuit diagram showing an overall configuration of a lighting device according to a first embodiment. [Diagram 2] FIG. 2 is a circuit diagram showing an example of a circuit configuration of the step-down chopper circuit according to the first embodiment. [Diagram 3] FIG. 3 is a graph showing the relationship between the output voltage and time of the lighting device according to the first embodiment. [Figure 4] FIG. 4 is a flowchart showing the flow of operation of the lighting device according to the first embodiment in the update mode. [Diagram 5]FIG. 5 is a graph showing an example of the relationship between the dimming level corresponding to the DC current supplied from the lighting device according to the first embodiment to the light source and the voltage value. [Figure 6] FIG. 6 is a graph in which the horizontal and vertical axes of the curved graph shown in FIG. 5 are logarithmically transformed. [Figure 7] FIG. 7 is a circuit diagram showing an overall configuration of a lighting device according to the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Each of the embodiments described below shows a specific example of the present invention. Therefore, the numerical values, shapes, materials, components, the arrangement and connection of the components, processes (steps), and the order of processes shown in the following embodiments are merely examples and are not intended to limit the present invention. Therefore, among the components in the following embodiments, components that are not described in the independent claims showing the highest concept of the present invention will be described as optional components.

[0010] In addition, each drawing is a schematic diagram and is not necessarily a precise illustration. In each drawing, the same reference numerals are used for substantially the same configurations, and duplicated explanations are omitted or simplified.

[0011] (Embodiment 1) A lighting device according to a first embodiment will be described.

[0012] [1-1. Overall composition] First, the overall configuration of a lighting device according to the present embodiment will be described with reference to Fig. 1. Fig. 1 is a circuit diagram showing the overall configuration of a lighting device 30 according to the present embodiment. In Fig. 1, an AC power source 20 and a light source 80 are also shown together with the lighting device 30.

[0013] The AC power supply 20 is a power supply that supplies AC power to the lighting device 30, and is, for example, a system power supply such as an external commercial power supply.

[0014] The light source 80 includes one or more light-emitting elements, and emits light when a direct current is supplied from the lighting device 30. As the light-emitting element included in the light source 80, for example, a solid-state light-emitting element such as an LED or an organic EL (Electro Luminescence) element can be used.

[0015] The lighting device 30 is a device that supplies a direct current to the light source 80. The lighting device 30 and the light source 80 constitute a lighting fixture. The lighting device 30 includes a converter circuit 40. In the present embodiment, the lighting device 30 further includes a rectifier circuit 32.

[0016] The rectifier circuit 32 is a circuit that rectifies the AC power output by the AC power supply 20. The rectifier circuit 32 includes, for example, a diode bridge circuit.

[0017] The converter circuit 40 is a circuit that supplies a direct current to the light source 80 based on a dimming signal indicating the dimming level of the light source 80. The converter circuit 40 converts the voltage output from the rectifier circuit 32 to a voltage equal to or higher than the forward voltage of the light source 80 and outputs the voltage. A control signal for controlling the lighting device 30 is input to the converter circuit 40. The control signal includes a dimming signal indicating the dimming level of the light source 80. The converter circuit 40 outputs a current corresponding to the dimming level indicated by the dimming signal. The control signal is input from, for example, an external PC (Personal Computer) or the like.

[0018] Moreover, when the dimming level indicated by the dimming signal is lower than a predetermined threshold level and the magnitude of the DC voltage supplied to the light source 80 is smaller than a predetermined voltage threshold, the converter circuit 40 supplies a DC current having a boost current value greater than the dimming current value corresponding to the dimming level to the light source 80. Details of the operation of the converter circuit 40 will be described later. In this embodiment, the converter circuit 40 has a step-up chopper circuit 42, a step-down chopper circuit 50, and a control circuit 44.

[0019] The boost chopper circuit 42 is a DC-DC conversion circuit that boosts the input DC voltage. The boost chopper circuit 42 boosts the output voltage of the rectifier circuit 32 and outputs it to the step-down chopper circuit 50.

[0020] The control circuit 44 is a circuit that controls the step-down chopper circuit 50 based on a control signal. The control circuit 44 controls the magnitude of the DC current supplied from the step-down chopper circuit 50 to the light source 80 based on a dimming signal included in the control signal. The operation of the control circuit 44 will be described in detail later. The control circuit 44 can be realized by, for example, a microcomputer. The microcomputer is a one-chip semiconductor integrated circuit having memories such as ROM and RAM in which programs are stored, a processor (CPU; Central Processing Unit) that executes the programs, a timer, and input / output circuits including an A / D converter, a D / A converter, etc. The control circuit 44 may be realized by using an electric circuit other than a microcomputer.

[0021] The step-down chopper circuit 50 is a DC-DC conversion circuit that steps down the input direct current voltage. The step-down chopper circuit 50 steps down the output voltage of the step-up chopper circuit 42 and outputs it to the light source 80. Hereinafter, a detailed configuration of the step-down chopper circuit 50 will be described with reference to FIG. 2. FIG. 2 is a circuit diagram showing an example of the circuit configuration of the step-down chopper circuit 50 according to this embodiment. In addition to the step-down chopper circuit 50, the control circuit 44 and the light source 80 are also shown in FIG. 2.

[0022] As shown in FIG. 2, the step-down chopper circuit 50 includes an input-side capacitor 51, a switching element 52, a diode 53, an inductor 54, resistive elements 55 and 56, and an output-side capacitor 57.

[0023] The input-side capacitor 51 is connected between the high-potential side input terminal and the low-potential side input terminal of the step-down chopper circuit 50. As the input-side capacitor 51, for example, an electrolytic capacitor can be used.

[0024] The switching element 52 is connected between the high potential side input terminal of the step-down chopper circuit 50 and the cathode of the diode 53. In this embodiment, the switching element 52 is an N-channel type MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor). A drain terminal of the switching element 52 is connected to the high potential side input terminal of the step-down chopper circuit 50, and a source terminal is connected to the cathode terminal of the diode 53. One terminal of the inductor 54 is also connected to the source terminal of the switching element 52. A gate signal is input from the control circuit 44 to the gate terminal of the switching element 52.

[0025] The diode 53 is connected between the switching element 52 and the low-potential side input terminal of the step-down chopper circuit 50. In this embodiment, the cathode terminal of the diode 53 is connected to the source terminal of the switching element 52, and the anode terminal is connected to the low-potential side input terminal of the step-down chopper circuit 50. In addition, one terminal of the inductor 54 is also connected to the cathode terminal of the diode 53.

[0026] The inductor 54 is connected between the connection point of the switching element 52 and the diode 53 and the high potential side input terminal of the light source 80 .

[0027] The resistive elements 55 and 56 are elements that divide the voltage supplied to the light source 80. The resistive elements 55 and 56 are connected in series. One terminal of the resistive element 55 is connected to the high potential side input terminal of the light source 80, and the other terminal is connected to one terminal of the resistive element 56. The other terminal of the resistive element 56 is connected to the low potential side terminal of the light source 80. In this embodiment, the low potential side input terminal of the light source 80 is at the same potential as the low potential side input terminal of the step-down chopper circuit 50. For example, the low potential side input terminal of the light source 80 may be at ground potential. The potential of the connection point of the resistive elements 55 and 56 is input to the control circuit 44. The resistance values ​​of the resistive elements 55 and 56 are determined based on the maximum value of the voltage supplied to the light source and the range of voltage values ​​that can be measured by the control circuit 44.

[0028] The output side capacitor 57 is a capacitor connected in parallel with the light source 80. In other words, the output side capacitor 57 is connected between the high potential side input terminal and the low potential side input terminal of the light source 80. The output side capacitor 57 also functions as a smoothing capacitor that smoothes the output voltage of the lighting device 30. By smoothing the output voltage of the lighting device 30 with the output side capacitor 57, flickering of the light emitted from the light source 80 can be suppressed. In order to enhance the flicker suppression effect of the output side capacitor 57, a capacitor with a relatively large capacity is used as the output side capacitor 57. The capacity of the output side capacitor 57 is, for example, 50 μF or more. Note that the upper limit value of the capacity of the output side capacitor 57 is not particularly limited. The capacity of the output side capacitor 57 may be, for example, 500 μF or less, or 300 μF or less. For example, an electrolytic capacitor can be used as the output side capacitor 57.

[0029] [1-2. Operation] Next, the operation of lighting device 30 according to the present embodiment will be described with reference to Fig. 3 to Fig. 6 in comparison with a comparative example. Fig. 3 is a graph showing the relationship between the output voltage of lighting device 30 according to the present embodiment and time. The vertical axis represents the output voltage, and the horizontal axis represents the time.

[0030] In the lighting device 30 according to the present embodiment, a case where a DC current is started to be supplied to the light source 80 from a state where the output voltage is zero will be considered. For example, when a DC current corresponding to a high dimming level is supplied to the light source 80, such as when a rated current is supplied to the light source 80, the value of the DC current supplied to the light source 80 is relatively large, so that the time required to charge the output side capacitor 57 of the step-down chopper circuit 50 is relatively short. Therefore, as shown by the dashed line graph in FIG. 3, the output voltage of the step-down chopper circuit 50 rises relatively quickly from 0V (the output voltage at time t0 shown in FIG. 3) to the lighting start forward voltage VF1 of the light source 80 (corresponding to the output voltage at time t2 shown in FIG. 3). Therefore, the light source 80 lights up quickly after the supply of the DC current starts.

[0031] On the other hand, when a DC current corresponding to a low dimming level is supplied to the light source 80, the value of the DC current is relatively small. Here, as a lighting device of Comparative Example 1, the operation of a lighting device that includes the step-up chopper circuit 42 and the step-down chopper circuit 50 similar to the lighting device 30 according to the present embodiment and supplies a relatively small value of DC current corresponding to a low dimming level from the DC current supply start time t0 will be described. In the lighting device of Comparative Example 1, since the value of the DC current supplied to the light source 80 is small, it takes a relatively long time to charge the output side capacitor 57, which has a large capacity. Therefore, as shown by the dashed line in FIG. 3, it takes a relatively long time for the output voltage of the lighting device to rise to an output voltage equivalent to the lighting start forward voltage VF1 of the light source 80.

[0032] As a lighting device of Comparative Example 2 that can reduce the time required for the output voltage of the lighting device to rise compared to the lighting device of Comparative Example 1, the operation of a lighting device that performs the same control as the invention described in the above Patent Document 1 will be described. In the lighting device of Comparative Example 2, when the dimming level indicated by the dimming signal is lower than a predetermined threshold level and the magnitude of the DC voltage supplied to the light source 80 is lower than a predetermined voltage threshold VF3, a DC current having a boost current value larger than the dimming current value corresponding to the dimming level is supplied to the light source 80. That is, when a DC current corresponding to a low dimming level is supplied to the light source 80, a DC current having a boost current value larger than the DC current corresponding to the low dimming level is supplied until time t3 when the output voltage reaches the predetermined voltage threshold VF3. The threshold level that is the threshold of the dimming level is not particularly limited, but for example, a dimming level of 50% may be set as the threshold level, with the dimming level at the rated current being 100%.

[0033] After the output voltage reaches the voltage threshold VF3, the lighting device of Comparative Example 2 outputs a DC current corresponding to the dimming level. In the example shown in Fig. 3, the DC voltage supplied to light source 80 reaches the lighting start forward voltage VF1 at time point t3. As a result, as shown by the solid line graph in Fig. 3, the output voltage of the lighting device of Comparative Example 2 takes less time to reach the voltage threshold VF3 than the output voltage of the lighting device of Comparative Example 1.

[0034] However, when the light source 80 is replaced, when the light source 80 is deteriorated, etc., the light source 80 may change its turn-on forward voltage VF1. This may increase the difference between the turn-on forward voltage VF1 of the light source 80 and the voltage threshold VF3. In addition, taking into account individual differences in the light source 80, the voltage threshold needs to be set to a value sufficiently lower than the turn-on forward voltage, so the difference between the turn-on forward voltage VF1 of the light source 80 and the voltage threshold VF3 cannot be reduced. Therefore, in the lighting device of Comparative Example 2, the time required to reach the turn-on forward voltage VF1 from the voltage threshold VF3 cannot be reduced.

[0035] The converter circuit 40 of the lighting device 30 according to the present embodiment, like the lighting device of the comparative example 2, supplies a DC current having a boost current value greater than a dimming current value corresponding to the dimming level to the light source 80 when the dimming level indicated by the dimming signal is lower than a predetermined threshold level and the magnitude of the DC voltage supplied to the light source 80 is smaller than a predetermined voltage threshold VF2. The converter circuit 40 according to the present embodiment further has an update mode, which is an operation mode for updating the voltage threshold VF2. In the update mode, the converter circuit 40 supplies a DC voltage equal to or greater than the lighting start voltage of the light source 80 to the light source 80, and updates the voltage threshold based on the relationship between the DC voltage and the DC current supplied to the light source 80. Hereinafter, the operation of the lighting device 30 according to the present embodiment in the update mode will be described with reference to FIG. 4. FIG. 4 is a flowchart showing the flow of the operation of the lighting device 30 according to the present embodiment in the update mode.

[0036] As shown in FIG. 4, the converter circuit 40 of the lighting device 30 sets the current value of the direct current to be supplied to the light source 80 in the update mode (S10). Here, the control circuit 44 of the converter circuit 40 may set the current value, or may set another value corresponding to the current value. For example, the control circuit 44 may set a dimming level corresponding to the current value. The number of current values ​​to be set is not particularly limited. In the present embodiment, a plurality of current values ​​are set. In addition, the magnitude of the current value to be set is not particularly limited, but the control circuit 44 may set the current value to be supplied to the light source 80 to a current value corresponding to a low dimming level. For example, the control circuit 44 may set the current value to be supplied to the light source 80 to a current value corresponding to a dimming level of 10% or less.

[0037] 4, the converter circuit 40 supplies the light source 80 with a DC current having a current value set in step S10, and measures a forward voltage (Vf), that is, a value of a DC voltage output by the converter circuit 40 (S12). Specifically, the control circuit 44 outputs a gate signal to the gate terminal of the switching element 52 of the step-down chopper circuit 50 so that the value of the DC current supplied from the converter circuit 40 to the light source 80 becomes the value set in step S10. The control circuit 44 measures the value of the DC voltage supplied to the light source 80 at this time based on the voltage value at the connection point of the resistance elements 55 and 56. By performing such measurements for a plurality of current values, a relationship between the value of the DC current (current value I0) supplied to the light source 80 and the value of the DC voltage (voltage value V0) is obtained. Here, this relationship will be described with reference to FIG. 5. FIG. 5 is a graph showing an example of a relationship between a dimming level D corresponding to a DC current supplied from the lighting device 30 to the light source 80 according to the present embodiment and a voltage value V0. 5, for example, dimming level 6503 corresponds to a dimming level of 10%, and in this case, the value of the DC current supplied to light source 80 is 0.1644 A. Also, dimming level 66 corresponds to the minimum dimming level (dimming level of 0.10%), and in this case, the value of the DC current supplied to light source 80 is 0.001749 A.

[0038] Next, the start-of-light forward voltage of the light source 80 is obtained based on the measurement result (S14). In general, the resolution of the value of the DC current that can be supplied to the light source 80 by the lighting device 30 is greater than the value of the DC current at the start of lighting of the light source 80, so it is difficult to obtain the start-of-light forward voltage by measurement. For this reason, the start-of-light forward voltage is obtained based on the relationship between the value of the DC current measured in step S12 and the value of the DC voltage. Specifically, in order to convert the curved graph shown in FIG. 5 into a linear graph, the horizontal and vertical axes of FIG. 5 are converted into the natural logarithms of the value of the DC current and the value of the DC voltage supplied to the light source 80, respectively. The graph converted in this way will be described with reference to FIG. 6. FIG. 6 is a graph in which the horizontal and vertical axes of the curved graph shown in FIG. 5 are logarithmically converted. The horizontal and vertical axes of the graph shown in FIG. 6 indicate the natural logarithm of the current value I0 and the natural logarithm of the voltage value V0, respectively.

[0039] 6 is linearly approximated using, for example, the least squares method, and the slope and intercept of the line are obtained, thereby allowing calculation of the voltage value V0 for any current value I0. Thus, the control circuit 44 obtains the lighting start forward voltage by calculating the voltage value V0 for the current value I0 that flows when the light source 80 starts to light. In this embodiment, the current value I0 that flows when the light source 80 starts to light is stored in advance in the control circuit 44 based on the characteristics of the light source 80. The current value I0 at the start of lighting is, for example, about 1 mA.

[0040] Next, the control circuit 44 of the converter circuit 40 determines a voltage threshold based on the lighting start forward voltage acquired in step S14 (S16). Specifically, the voltage threshold is determined to be a voltage value slightly lower than the lighting start forward voltage. For example, the voltage threshold is determined to be a value obtained by subtracting a predetermined margin voltage value from the lighting start forward voltage. In this way, by setting the voltage threshold to a value lower than the lighting start forward voltage, when a DC current of the boost current value is supplied to the light source 80, it is possible to suppress the light source 80 from momentarily lighting up brighter than the dimming level due to an overshoot of the DC voltage supplied to the light source 80. In this way, in order to suppress the overshoot of the DC voltage supplied to the light source 80, the margin voltage value may be, for example, 5V or more. In addition, in order to suppress the time required for the light source 80 to light up, the margin voltage value may be 15V or less. In this embodiment, the margin voltage value is 10V.

[0041] Next, the control circuit 44 of the converter circuit 40 sets the voltage threshold to the value determined in step S16 (S18). This allows the converter circuit 40 to update the voltage threshold to a value suitable for the characteristics of the light source 80.

[0042] In this way, the voltage threshold is updated based on the relationship between the DC current and DC voltage supplied to the light source 80 connected to the lighting device 30, so it is possible to reliably reduce the difference between the voltage threshold and the light-on start forward voltage of the light source 80. Therefore, until the DC voltage supplied to the light source 80 reaches near the light-on start forward voltage, a DC current with a boost current value larger than the dimming current value corresponding to the dimming level can be supplied to the light source 80, so that the time required for the light source 80 to light can be reliably shortened.

[0043] Since the converter circuit 40 has such an update mode, for example, when the light source 80 is replaced or when the light source 80 deteriorates and its characteristics change, the voltage threshold can be updated based on the characteristics of the replaced light source 80 by operating in the update mode. Therefore, it is possible to prevent an increase in the time required for the light source 80 to light up. In other words, the response time of the lighting device 30 can be shortened.

[0044] [1-3. Effects, etc.] As described above, the lighting device 30 according to the present embodiment supplies a DC current to the light source 80 including one or more light emitting elements. The lighting device 30 includes a converter circuit 40 that supplies a DC current to the light source 80 based on a dimming signal indicating a dimming level of the light source 80. When the dimming level indicated by the dimming signal is lower than a predetermined threshold level and the magnitude of the DC voltage supplied to the light source 80 is smaller than a predetermined voltage threshold, the converter circuit 40 supplies a DC current having a boost current value greater than a dimming current value corresponding to the dimming level to the light source 80. The converter circuit 40 has an update mode, which is an operation mode for updating the voltage threshold, and in the update mode, supplies a DC voltage equal to or greater than the lighting start voltage of the light source 80 to the light source 80, and updates the voltage threshold based on the relationship between the DC voltage and the DC current supplied to the light source 80.

[0045] This allows the voltage threshold to be updated in accordance with the characteristics of the light source 80, making it possible to reduce the difference between the light-on start forward voltage of the light source 80 and the voltage threshold. Therefore, a DC current of the boost current value can be supplied to the light source 80 up to near the light-on start forward voltage of the light source 80, making it possible to shorten the time from the start of the DC current supply to the lighting of the light source 80. In other words, the response time of the lighting device 30 can be shortened.

[0046] Furthermore, in the lighting device 30 according to the present embodiment, the converter circuit 40 may have an output-side capacitor 57 connected in parallel to the light source 80.

[0047] In the case where the converter circuit 40 has such an output-side capacitor 57, when switching the light source 80 from an off state to a light state at a low dimming level, if a DC current with a dimming current value corresponding to the dimming level is supplied to the light source 80, it takes a relatively long time to charge the output-side capacitor 57. However, in the lighting device 30 according to the present embodiment, a DC current with a boost current value larger than the dimming current value is supplied to the light source 80 until the voltage threshold value is reached, so that the time required for lighting can be shortened. In other words, a lighting device 30 with a shortened response time can be realized.

[0048] (Embodiment 2) A lighting device according to a second embodiment will be described. The lighting device according to this embodiment differs from lighting device 30 according to the first embodiment in the method of setting the voltage threshold. The lighting device according to this embodiment will be described below with reference to FIG. 7, focusing on the differences from lighting device 30 according to the first embodiment. FIG. 7 is a circuit diagram showing the overall configuration of lighting device 130 according to this embodiment. In FIG. 7, AC power source 20 and light source 80 are also shown together with lighting device 130.

[0049] As shown in FIG. 7, a lighting device 130 according to the present embodiment includes a rectifier circuit 32 and a converter circuit 140.

[0050] The converter circuit 140 according to the present embodiment includes a step-up chopper circuit 42, a step-down chopper circuit 50, and a control circuit 144.

[0051] The control circuit 144 according to this embodiment controls the magnitude of the DC current supplied from the step-down chopper circuit 50 to the light source 80 based on the dimming signal included in the control signal. The control circuit 144 according to this embodiment differs from the control circuit 44 according to the first embodiment in the method of determining the voltage threshold in the update mode. In this embodiment, the control circuit 144 updates the voltage threshold in the update mode based on the DC voltage supplied to the light source 80 when the converter circuit 140 supplies the minimum DC current that can be supplied to the light source 80. That is, in the update mode, the current value of the DC current supplied to the light source 80 is set to the minimum DC current that the converter circuit 140 can supply to the light source 80. The control circuit 144 measures the forward voltage when this minimum DC current is supplied to the light source 80, and determines the voltage threshold based on the value of the measured forward voltage. Specifically, the control circuit 144 determines the voltage threshold by subtracting a predetermined margin voltage value from the measured forward voltage. The margin voltage value may be set appropriately according to the characteristics of the light source 80. The margin voltage value according to the present embodiment may be, for example, 5V or more and 15V or less, similar to the margin voltage value according to the first embodiment.

[0052] As described above, in the present embodiment, the voltage threshold is updated based on the DC voltage supplied to the light source 80 when the converter circuit 140 supplies the minimum DC current that can be supplied to the light source 80. The DC voltage supplied to the light source 80 when the converter circuit 140 supplies the minimum DC current that can be supplied to the light source 80 is a value close to the illumination start forward voltage of the light source 80, so that the present embodiment also achieves the same effects as the first embodiment. Furthermore, in the present embodiment, in the update mode, there is only one value for the DC current supplied to the light source 80 and one value for the DC voltage to be measured, so that the operation of the converter circuit 140 in the update mode can be simplified.

[0053] Furthermore, in the lighting device 130 according to this embodiment, the voltage threshold value may be updated to a value obtained by subtracting a predetermined margin voltage value from the value of the DC voltage supplied to the light source 80 when the converter circuit 140 supplies the minimum DC current that can be supplied to the light source 80.

[0054] This allows the voltage threshold to be updated in a simplified manner. Also, by setting the voltage threshold to a value lower than the forward voltage, when a DC current of the boost current value is supplied to the light source 80, it is possible to suppress the light source 80 from momentarily lighting up brighter than the dimming level due to an overshoot of the DC voltage supplied to the light source 80.

[0055] The margin voltage value may be equal to or greater than 5 V and equal to or less than 15 V. This makes it possible to suppress overshoot of the DC voltage supplied to the light source 80, and also to reduce the time required for the light source 80 to be turned on.

[0056] (Variations, etc.) Although the lighting device according to the present invention has been described above based on the embodiments, the present invention is not limited to these embodiments.

[0057] For example, in each of the above embodiments, each lighting device includes the rectifier circuit 32 and the boost chopper circuit 42, but these circuits are not essential components of each lighting device.

[0058] Furthermore, in each of the above embodiments, the light source 80 is not a component of each lighting device, but the light source 80 may be included in a component of each lighting device.

[0059] In addition, the present invention also includes forms obtained by applying various modifications to each embodiment that a person skilled in the art may think of, or forms realized by arbitrarily combining the components and functions of each embodiment within the scope that does not deviate from the spirit of the present invention. [Explanation of symbols]

[0060] 30, 130 Lighting device 40, 140 Converter circuit 44, 144 Control circuit 57 Output Capacitor 80 light source

Claims

1. A lighting device that supplies a direct current to a light source including one or more light emitting elements, a converter circuit for supplying the DC current to the light source based on a dimming signal indicating a dimming level of the light source; When the dimming level indicated by the dimming signal is lower than a predetermined threshold level and the magnitude of the DC voltage supplied to the light source is lower than a predetermined voltage threshold, the converter circuit supplies the DC current to the light source with a boost current value that is greater than a dimming current value corresponding to the dimming level; The converter circuit has an update mode which is an operation mode for updating the voltage threshold, and in the update mode, the converter circuit supplies the light source with the DC voltage equal to or higher than a turn-on voltage of the light source, measures a value of the DC voltage and a value of the DC current, and updates the voltage threshold based on a relationship between the measured value of the DC voltage and the value of the DC current. Lighting device.

2. The converter circuit includes a capacitor connected in parallel with the light source. The lighting device according to claim 1 .

3. The voltage threshold is updated based on the DC voltage supplied to the light source when the converter circuit supplies the minimum DC current that can be supplied to the light source.

3. The lighting device according to claim 1 or 2.

4. The voltage threshold is updated to a value obtained by subtracting a predetermined margin voltage value from the value of the DC voltage supplied to the light source when the converter circuit supplies the minimum DC current that can be supplied to the light source. The lighting device according to any one of claims 1 to 3.

5. The margin voltage value is 5 V or more and 15 V or less. The lighting device according to claim 4.

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