JP2022168670A - lighting device - Google Patents

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

The present invention relates to lighting devices.

2. Description of the Related Art Conventionally, a dimming 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, etc.). A problem with such a lighting device is that the response time of the light output to the switching of the dimming signal is long when switching from the off state to the lit state with a low dimming level. In the lighting device disclosed in Patent Document 1, when increasing the dimming level, a current corresponding to a dimming level higher than the target dimming level is supplied to the light source for a predetermined time. This attempts to shorten the response time by promoting the increase in the voltage supplied to the light source.

Japanese Patent Application Laid-Open No. 2008-60492

In the lighting device as disclosed in Patent Document 1, the predetermined time is set shorter than the time required for the dimming level of the light source to reach the target dimming level. This prevents the light output from the light source from temporarily overshooting due to an excessive amount of current supplied to the light source. Therefore, if the predetermined time is not properly set, the response time may not be shortened sufficiently. 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 rise to near the lighting start voltage of the light source within the predetermined time. . In this case, the response time cannot be shortened sufficiently.

SUMMARY OF THE INVENTION The present invention has been made to solve such problems, and provides a lighting device capable of shortening the response time.

To solve the above problems, one aspect of the lighting device according to the present invention is a lighting device that supplies a direct current to a light source that includes one or more light emitting elements, and includes a dimming signal that indicates a dimming level of the light source. a converter circuit for supplying the direct current to the light source based on When the voltage magnitude is less than a predetermined voltage threshold, the converter circuit supplies the direct current with a boost current value greater than a dimming current value corresponding to the dimming level to the light source, and the converter circuit reduces the voltage threshold. It has an update mode, which is an operation mode for updating, in the update mode, the DC voltage higher than the lighting start voltage of the light source is supplied to the light source, and the DC voltage supplied to the light source and the DC current Based on the relationship, the voltage threshold is updated.

ADVANTAGE OF THE INVENTION According to this invention, the lighting device which can shorten response time can be provided.

FIG. 1 is a circuit diagram showing the overall configuration of a lighting device according to Embodiment 1. FIG. FIG. 2 is a circuit diagram showing a circuit configuration example of the step-down chopper circuit according to the first embodiment. 3 is a graph showing the relationship between output voltage and time of the lighting device according to Embodiment 1. FIG. FIG. 4 is a flowchart showing the operation flow of the lighting device according to Embodiment 1 in the update mode. FIG. 5 is a graph showing an example of the relationship between the dimming level corresponding to the DC current supplied to the light source from the lighting device according to Embodiment 1 and the voltage value. FIG. 6 is a graph obtained by logarithmically transforming the horizontal and vertical axes of the curved graph shown in FIG. FIG. 7 is a circuit diagram showing the overall configuration of a lighting device according to Embodiment 2. FIG.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the drawings. It should be noted that each of the embodiments described below is a specific example of the present invention. Therefore, numerical values, shapes, materials, constituent elements, arrangement positions and connection forms of constituent elements, processes (steps), order of processes, and the like shown in the following embodiments are examples and are intended to limit the present invention. is not. Therefore, among the constituent elements in the following embodiments, constituent elements that are not described in independent claims representing the highest level concept of the present invention will be described as optional constituent elements.

Each figure is a schematic diagram and is not necessarily strictly illustrated. Moreover, in each figure, the same code|symbol is attached|subjected to the substantially same structure, and the overlapping description is abbreviate|omitted or simplified.

(Embodiment 1)
A lighting device according to Embodiment 1 will be described.

[1-1. overall structure]
First, the overall configuration of the lighting device according to this embodiment will be described with reference to FIG. FIG. 1 is a circuit diagram showing the overall configuration of a lighting device 30 according to this embodiment. FIG. 1 also shows the AC power supply 20 and the light source 80 together with the lighting device 30 .

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.

The light source 80 includes one or more light emitting elements, and emits light by being supplied with direct current from the lighting device 30 . Solid-state light-emitting elements such as LEDs and organic EL (Electro Luminescence) elements can be used as the light-emitting elements included in the light source 80 .

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

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

The converter circuit 40 is a circuit that supplies direct current to the light source 80 based on the dimming signal indicating the dimming level of the light source 80 . The converter circuit 40 converts the voltage output from the rectifier circuit 32 into 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).

Further, when the dimming level indicated by the dimming signal is lower than the predetermined threshold level and the magnitude of the DC voltage supplied to the light source 80 is smaller than the predetermined voltage threshold, the converter circuit 40 is set to the dimming level. A DC current with a boost current value greater than the corresponding dimming current value is supplied to the light source 80 . Details of the operation of the converter circuit 40 will be described later. In the present embodiment, converter circuit 40 has boost chopper circuit 42 , step-down chopper circuit 50 and control circuit 44 .

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 .

The control circuit 44 is a circuit that controls the step-down chopper circuit 50 based on the 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 the dimming signal included in the control signal. Details of the operation of the control circuit 44 will be described later. The control circuit 44 can be implemented by, for example, a microcomputer. A microcomputer includes memory such as ROM and RAM in which programs are stored, a processor (CPU; Central Processing Unit) that executes programs, a timer, an A/D converter, and an input/output circuit that includes a D/A converter. and a one-chip semiconductor integrated circuit. Note that the control circuit 44 may be implemented using an electric circuit or the like other than a microcomputer.

The step-down chopper circuit 50 is a DC-DC conversion circuit that steps down an input DC 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 . A detailed configuration of the step-down chopper circuit 50 will be described below with reference to FIG. FIG. 2 is a circuit diagram showing a circuit configuration example of the step-down chopper circuit 50 according to this embodiment. 2 also shows the control circuit 44 and the light source 80 together with the step-down chopper circuit 50. As shown in FIG.

The step-down chopper circuit 50 has an input capacitor 51, a switching element 52, a diode 53, an inductor 54, resistance elements 55 and 56, and an output capacitor 57, as shown in FIG.

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 . For example, an electrolytic capacitor can be used as the input-side capacitor 51 .

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 MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor). The drain terminal of the switching element 52 is connected to the high potential side input terminal of the step-down chopper circuit 50 , and the 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 .

Diode 53 is connected between switching element 52 and the input terminal of step-down chopper circuit 50 on the low potential side. In this embodiment, the diode 53 has a cathode terminal connected to the source terminal of the switching element 52 and an anode terminal connected to the low-potential input terminal of the step-down chopper circuit 50 . One terminal of the inductor 54 is also connected to the cathode terminal of the diode 53 .

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 .

The resistance elements 55 and 56 are elements that divide the voltage supplied to the light source 80 . Resistive elements 55 and 56 are connected in series. One terminal of the resistance 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 resistance 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 input terminal on the low potential side of the light source 80 may be at the ground potential. A potential at the connection point of the resistance element 55 and the resistance element 56 is input to the control circuit 44 . Each resistance value of the resistance elements 55 and 56 is determined based on the maximum value of the voltage supplied to the light source, the range of voltage values that can be measured by the control circuit 44, and the like.

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. A capacitor with a relatively large capacity is used as the output-side capacitor 57 in order to enhance the flicker suppressing effect of 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 capacitance of the output-side capacitor 57 is not particularly limited. The capacitance of the output-side capacitor 57 may be, for example, 500 μF or less, or may be 300 μF or less. For example, an electrolytic capacitor can be used as the output side capacitor 57 .

[1-2. motion]
Next, the operation of lighting device 30 according to the present embodiment will be described with reference to FIGS. 3 to 6 while comparing it with a comparative example. FIG. 3 is a graph showing the relationship between output voltage and time of lighting device 30 according to the present embodiment. The vertical axis indicates output voltage, and the horizontal axis indicates time.

Consider a case where lighting device 30 according to the present embodiment starts to supply direct current to light source 80 from a state where the output voltage is zero. For example, when a DC current corresponding to a high dimming level is supplied to the light source 80, such as when supplying the rated current to the light source 80, the value of the DC current supplied to the light source 80 is relatively large. The time required to charge the output capacitor 57 of circuit 50 is relatively short. Therefore, the output voltage of the step-down chopper circuit 50 changes from 0 V (the output voltage at the time t0 shown in FIG. 3) to the lighting start forward voltage VF1 (the (corresponding to the output voltage at time t2 shown in ) relatively quickly. Therefore, the light source 80 is quickly turned on after the DC current supply is started.

On the other hand, when a direct current corresponding to a low dimming level is supplied to the light source 80, the value of the direct current is relatively small. Here, as a lighting device of Comparative Example 1, the step-up chopper circuit 42 and the step-down chopper circuit 50 similar to the lighting device 30 according to the present embodiment are provided, and a relatively small DC current corresponding to a low dimming level is supplied. , the operation of the lighting device that supplies DC current from the time t0 when DC current supply is started 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 having a large capacity. Therefore, it takes a relatively long time for the output voltage of the lighting device to rise to the output voltage corresponding to the lighting start forward voltage VF1 of the light source 80, as indicated by the dashed line in FIG.

As a lighting device of Comparative Example 2 that can reduce the time required for the output voltage of the lighting device to rise from that of the lighting device of Comparative Example 1, the operation of the lighting device that performs the same control as the invention described in Patent Document 1 will be described. do. In the lighting device of Comparative Example 2, when the dimming level indicated by the dimming signal is lower than the predetermined threshold level and the magnitude of the DC voltage supplied to the light source 80 is smaller than the predetermined voltage threshold VF3, the dimming is performed. A DC current with a boost current value greater than the dimming current value corresponding to the 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, the boost current value is higher than the DC current corresponding to the low dimming level until time t3 when the output voltage reaches the predetermined voltage threshold VF3. Supply direct current. Although the threshold level, which is the threshold of the dimming level, is not particularly limited, for example, if the dimming level at the rated current is 100%, the dimming level of 50% may be set as the threshold level.

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 the light source 80 reaches the lighting start forward voltage VF1 at time 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.

However, when the light source 80 is replaced, or when the light source 80 deteriorates, the lighting start forward voltage VF1 of the light source 80 may change. Therefore, the difference between the lighting start forward voltage VF1 of the light source 80 and the voltage threshold VF3 can be large. In addition, considering the individual difference of the light source 80, the voltage threshold must be set to a value sufficiently lower than the lighting start forward voltage. The difference cannot be reduced. Therefore, in the lighting device of Comparative Example 2, the time required to reach the lighting start forward voltage VF1 from the voltage threshold VF3 cannot be shortened.

As in the lighting device of Comparative Example 2, the converter circuit 40 of the lighting device 30 according to the present embodiment has a dimming level indicated by the dimming signal lower than a predetermined threshold level, and the direct current supplied to the light source 80 is When the magnitude of the voltage is less than a predetermined voltage threshold VF2, the light source 80 is supplied with a DC current having a boost current value greater than the dimming current value corresponding to the dimming level. Converter circuit 40 according to the present embodiment further has an update mode, which is an operation mode for updating voltage threshold VF2. In the update mode, the converter circuit 40 supplies a DC voltage equal to or higher 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 . The operation of lighting device 30 in the update mode according to the present embodiment will be described below with reference to FIG. FIG. 4 is a flow chart showing the flow of operation in the update mode of lighting device 30 according to the present embodiment.

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 the dimming level corresponding to the current value. The number of current values to be set is not particularly limited. In this embodiment, a plurality of current values are set. The current value to be set is not particularly limited, but the control circuit 44 may set the current value 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 supplied to the light source 80 to a current value corresponding to a dimming level of 10% or less.

Subsequently, as shown in FIG. 4, the converter circuit 40 supplies the light source 80 with the DC current of the current value set in step S10, and the forward voltage (Vf), that is, the DC voltage output by the converter circuit 40. is measured (S12). Specifically, the control circuit 44 sends 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. to output 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 resistive elements 55 and 56 . By performing such measurements for a plurality of current values, the relationship between the DC current value (current value I0) supplied to the light source 80 and the DC voltage value (voltage value V0) can be obtained. Here, this relationship will be described with reference to FIG. FIG. 5 is a graph showing an example of the relationship between the dimming level D corresponding to the DC current supplied to the light source 80 from the lighting device 30 according to the present embodiment and the voltage value V0. In FIG. 5, for example, dimming level 6503 corresponds to a dimming level of 10%, in which case the value of DC current supplied to light source 80 is 0.1644A. Dimming level 66 also corresponds to the minimum dimming level (0.10% dimming level), in which case the value of the DC current supplied to light source 80 is 0.001749A.

Subsequently, based on the measurement result, the lighting start forward voltage of the light source 80 is acquired (S14). In general, since the resolution of the DC current value that can be supplied to the light source 80 by the lighting device 30 is greater than the DC current value at the start of lighting of the light source 80, it is difficult to obtain the lighting start forward voltage by measurement. Therefore, the lighting start forward voltage is obtained based on the relationship between the DC current value and the DC voltage value measured in step S12. Specifically, in order to transform the curved graph shown in FIG. 5 into a linear graph, the horizontal and vertical axes of FIG. Convert to the natural logarithm of the DC voltage value. A graph converted in this way will be described with reference to FIG. FIG. 6 is a graph obtained by logarithmically transforming the horizontal and vertical axes of the curved graph shown in FIG. The horizontal and vertical axes of the graph shown in FIG. 6 indicate the natural logarithm value of the current value I0 and the natural logarithm value of the voltage value V0, respectively.

By linearly approximating the graph shown in FIG. 6 using, for example, the method of least squares, and obtaining the slope and intercept of the straight line, the voltage value V0 for an arbitrary current value I0 can be calculated. Accordingly, the control circuit 44 obtains the lighting start forward voltage by calculating the voltage value V0 with respect to the current value I0 that flows when the light source 80 starts lighting. In this embodiment, the current value I0 that flows when the light source 80 starts lighting is stored in advance in the control circuit 44 based on the characteristics of the light source 80 . A current value I0 at the start of lighting is, for example, about 1 mA.

Subsequently, 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 value is determined by subtracting a predetermined margin voltage value from the lighting start forward voltage. Thus, by setting the voltage threshold to a value lower than the lighting start forward voltage, the DC voltage supplied to the light source 80 does not overshoot when the DC current of the boost current value is supplied to the light source 80. Accordingly, it is possible to prevent the light source 80 from momentarily lighting brighter than the dimming level. In order to suppress the overshoot of the DC voltage supplied to the light source 80 in this manner, the margin voltage value may be, for example, 5 V or more. Also, in order to suppress the time required until the light source 80 is turned on, the margin voltage value may be 15 V or less. In this embodiment, the margin voltage value is 10V.

Subsequently, the control circuit 44 of the converter circuit 40 sets the voltage threshold to the value determined in step S16 (S18). Thereby, the converter circuit 40 can update the voltage threshold to a value suitable for the characteristics of the light source 80 .

In this way, in order to update the voltage threshold based on the relationship between the DC current and the DC voltage supplied to the light source 80 connected to the lighting device 30, the voltage threshold and the lighting start forward voltage of the light source 80 are adjusted. The difference can be reliably reduced. Therefore, until the DC voltage supplied to the light source 80 reaches near the lighting start forward voltage, a DC current having a boost current value larger than the dimming current value corresponding to the dimming level can be supplied to the light source 80. The time required for lighting 80 can be reliably shortened.

Since the converter circuit 40 has such an update mode, for example, when the light source 80 is replaced, when the light source 80 deteriorates and the characteristics change, by operating in the update mode, the voltage threshold can be changed after the replacement. can be updated based on the characteristics of the light source 80 of Therefore, it is possible to suppress an increase in the time required until the light source 80 is turned on. That is, the response time of the lighting device 30 can be shortened.

[1-3. effects, etc.]
As described above, lighting device 30 according to the present embodiment supplies direct current to light source 80 including one or more light emitting elements. The lighting device 30 includes a converter circuit 40 that supplies 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 responds to the dimming level when the dimming level indicated by the dimming signal is lower than the predetermined threshold level and the magnitude of the DC voltage supplied to the light source 80 is less than the predetermined voltage threshold. A DC current with a boost current value greater than the dimming current value is supplied to the light source 80 . The converter circuit 40 has an update mode, which is an operation mode for updating the voltage threshold. Update the voltage threshold based on the relationship with the DC current.

As a result, the voltage threshold can be updated in accordance with the characteristics of the light source 80, so that the difference between the lighting start forward voltage of the light source 80 and the voltage threshold can be reduced. Therefore, since the DC current of the boost current value can be supplied to the light source 80 up to the vicinity of the lighting start forward voltage of the light source 80, the time from the start of the DC current supply to the lighting of the light source 80 can be shortened. . That is, the response time of the lighting device 30 can be shortened.

Further, in lighting device 30 according to the present embodiment, converter circuit 40 may have output-side capacitor 57 connected in parallel with light source 80 .

When the converter circuit 40 has such an output capacitor 57, when the light source 80 is switched from the off state to the low dimming level lighting state, the direct current of the 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 capacitor 57 . However, in the lighting device 30 according to the present embodiment, the DC current with the boost current value larger than the dimming current value is supplied to the light source 80 until the voltage threshold is reached, so the time required for lighting can be shortened. That is, it is possible to realize the lighting device 30 capable of shortening the response time.

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

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

Converter circuit 140 according to the present embodiment has boost chopper circuit 42 , step-down chopper circuit 50 and control circuit 144 .

Control circuit 144 according to the present embodiment controls the magnitude of the DC current supplied from step-down chopper circuit 50 to light source 80 based on the dimming signal included in the control signal. The control circuit 144 according to the present 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, control circuit 144, in update mode, sets the voltage threshold based on the DC voltage supplied to light source 80 when converter circuit 140 supplies the minimum DC current that can be supplied to light source 80. Update. That is, in the update mode, the minimum DC current value that the converter circuit 140 can supply to the light source 80 is set as the current value of the DC current to be supplied 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 measured forward voltage value. Specifically, a value obtained by subtracting a predetermined margin voltage value from the measured forward voltage is determined as the voltage threshold. The margin voltage value may be appropriately set according to the characteristics of the light source 80 and the like. The margin voltage value according to the present embodiment may be, for example, 5V or more and 15V or less like the margin voltage value according to the first embodiment.

As described above, in the present embodiment, the voltage threshold is updated based on the DC voltage supplied to light source 80 when converter circuit 140 supplies the minimum DC current that can be supplied to light source 80. . Since the DC voltage supplied to light source 80 when converter circuit 140 supplies the minimum DC current that can be supplied to light source 80 is a value close to the lighting start forward voltage of light source 80, this embodiment also , the same effects as those of the first embodiment can be obtained. Further, in the present embodiment, in the update mode, there is only one DC current value to be supplied to the light source 80 and one DC voltage value to be measured, so that the operation of the converter circuit 140 in the update mode can be simplified. .

Further, in lighting device 130 according to the present embodiment, the voltage threshold is set to a predetermined value from the value of the DC voltage supplied to light source 80 when converter circuit 140 supplies the minimum DC current that can be supplied to light source 80. It may be updated to a value obtained by subtracting the margin voltage value.

This allows the voltage thresholds to be updated in a simplified manner. In addition, by setting the voltage threshold to a value lower than the forward voltage, when the DC current of the boost current value is supplied to the light source 80, the DC voltage supplied to the light source 80 overshoots. For a moment, it is possible to suppress lighting brighter than the dimming level.

Also, the margin voltage value may be 5V or more and 15V or less. As a result, the overshoot of the DC voltage supplied to the light source 80 can be suppressed, and the time required until the light source 80 is turned on can be suppressed.

(Modified example, 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.

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.

Further, although the light source 80 is not a constituent element of each lighting device in each of the above-described embodiments, the light source 80 may be included as a constituent element of each lighting device.

In addition, forms obtained by applying various modifications to each embodiment that a person skilled in the art can think of, or realized by arbitrarily combining the constituent elements and functions of each embodiment without departing from the spirit of the present invention. Also included in the present invention.

30, 130 lighting device 40, 140 converter circuit 44, 144 control circuit 57 output side capacitor 80 light source

Claims (5)

A lighting device for supplying a direct current to a light source including one or more light emitting elements,
a converter circuit that supplies the direct current to the light source based on a dimming signal indicating a dimming level of the light source;
The converter circuit controls the dimming level 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. supplying the direct current with a boost current value greater than the dimming current value corresponding to the light source,
The converter circuit has an update mode, which is an operation mode for updating the voltage threshold. The lighting device updates the voltage threshold based on the relationship between the DC voltage and the DC current. The lighting device according to claim 1, wherein the converter circuit has a capacitor connected in parallel with the light source. The lighting according to claim 1 or 2, wherein 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. Device. 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. The lighting device according to claim 4, wherein the margin voltage value is 5V or more and 15V or less.

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