Lighting device, illumination device, lighting control method, and program

Abstract

To provide a lighting device capable of quickly turning off a light source.SOLUTION: A lighting device supplies a direct current to a light source 80 including a solid light-emitting element. The lighting device includes a converter circuit. The converter circuit supplies a direct current to the light source 80 based on a dimming signal indicating a dimming level of the light source 80. The converter circuit includes a capacitor 57, a discharge path 58, and a switching element 59. The capacitor 57 is connected in parallel to the light source 80. The discharge path 58 is connected in parallel to the capacitor 57. The switching element 59 is provided in the discharge path 58 and electrically connects and disconnects the discharge path 58. Switching element 59 makes discharge path 58 conductive in a turn-off mode in which the dimming level of the dimming signal is the turn-off level.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure generally relates to a lighting device, an illumination device, a lighting control method, and a program, and more particularly to a lighting device that supplies direct current to a light source, an illumination device that includes the lighting device, and a lighting control method and a program that control the lighting device. [Background technology]

[0002] The light emitting element driving device (lighting device) described in Patent Document 1 includes a boost circuit (converter circuit) that supplies a direct current to an LED (light source). The boost circuit includes a capacitor connected in parallel to the LED. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-60492 Summary of the Invention [Problem to be solved by the invention]

[0004] In the light-emitting element driving device described in Patent Document 1, the boost circuit includes a capacitor connected in parallel to the LED. Therefore, even if the current supply from the boost circuit to the LED is stopped to turn off the LED, it takes time for the charge in the capacitor to discharge to the light-off level. This makes it difficult to quickly turn off the LED.

[0005] An object of the present disclosure is to provide a lighting device, an illumination device, a lighting control method, and a program that can quickly turn off a light source. [Means for solving the problem]

[0006] A lighting device according to one aspect of the present disclosure supplies DC current to a light source including a solid-state light-emitting element. The lighting device includes a converter circuit. The converter circuit supplies DC current to the light source based on a dimming signal indicating a dimming level of the light source. The converter circuit includes a capacitor, a discharge path, and a switching element. The capacitor is connected in parallel to the light source. The discharge path is connected in parallel to the capacitor. The switching element is provided in the discharge path and conducts and interrupts the discharge path. The switching element conducts the discharge path in an off mode in which the dimming level of the dimming signal is an off level.

[0007] An illumination device according to one aspect of the present disclosure includes the lighting device and the light source.

[0008] A lighting control method according to one aspect of the present disclosure is a lighting control method for controlling a lighting device that supplies DC current to a light source including a solid-state light-emitting element. The lighting device includes a converter circuit. The converter circuit supplies DC current to the light source based on a dimming signal indicating a dimming level of the light source. The converter circuit includes a capacitor, a discharge path, and a switching element. The capacitor is connected in parallel to the light source. The discharge path is connected in parallel to the capacitor. The switching element is provided in the discharge path and conducts and interrupts the discharge path. The lighting control method includes a control step. In the control step, in a light-off mode where the dimming level of the dimming signal is a light-off level, the switching element is controlled to conduct the discharge path.

[0009] A program according to one aspect of the present disclosure is a program for causing one or more processors to execute the lighting control method. [Effects of the Invention]

[0010] The lighting device, illumination device, lighting control method, and program of the present disclosure have the effect of being able to quickly turn off a light source. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a configuration diagram of a lighting device and an illumination device according to the first embodiment. [Figure 2] FIG. 2 is a circuit diagram showing an example of a circuit configuration of a step-down chopper circuit included in the lighting device. [Figure 3] FIG. 3 is a graph showing the relationship between the output voltage and time when the lighting device is lit. [Figure 4] FIG. 4 is a graph showing the relationship between the output voltage and time when the lighting device is turned off. [Figure 5] FIG. 5 is a flowchart illustrating the operation of the lighting device when the lighting device is turned off. [Figure 6] FIG. 6 is a flowchart illustrating the update function of the lighting device. [Figure 7] FIG. 7 is a graph showing an example of the relationship between the dimming level corresponding to the DC current supplied from the lighting device to the light source and the voltage value of the voltage output from the lighting device to the light source. [Figure 8] FIG. 8 is a graph in which the horizontal and vertical axes of the curved graph shown in FIG. 7 are logarithmically transformed. [Figure 9] FIG. 9 is a circuit diagram showing an example of a circuit configuration of a step-down chopper circuit included in the lighting device according to the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0013] (Embodiment 1) A lighting device and an illumination device according to a first embodiment will be described with reference to FIGS.

[0014] (1) Overview As shown in FIG. 1, a lighting device 30 according to the first embodiment supplies a direct current to a light source 80 including a solid-state light-emitting element. The lighting device 30 includes a converter circuit 40. The converter circuit 40 supplies a direct current to the light source 80 based on a dimming signal indicating a dimming level of the light source 80. As shown in FIG. 2, the converter circuit 40 includes a capacitor 57, a discharge path 58, and a switching element 59. The capacitor 57 is connected in parallel to the light source 80. The discharge path 58 is connected in parallel to the capacitor 57. The switching element 59 is provided in the discharge path 58 and turns on and off the discharge path 58. The switching element 59 turns on the discharge path 58 in a light-off mode. The light-off mode is a mode in which the dimming level of the dimming signal is the light-off level.

[0015] According to this configuration, in the extinction mode, the switching element 59 conducts the discharge path 58. Therefore, in the extinction mode, the charge stored in the capacitor 57 flows through the discharge path 58 and is quickly discharged. That is, the voltage of the capacitor 57 quickly drops. As a result, the light source 80 can be quickly turned off.

[0016] (2) Detailed explanation A lighting device 30 and an illumination device 10 according to the first embodiment will be described with reference to Fig. 1. As shown in Fig. 1, the illumination device 10 receives AC power from an AC power supply 20 and emits illumination light. The illumination device 10 includes a light source 80 and a lighting device 30.

[0017] The AC power supply 20 is a power supply that supplies AC power to the lighting device 30. The AC power supply 20 is, for example, a system power supply such as an external commercial power supply.

[0018] The light source 80 is a light source for illumination and includes one or more light-emitting elements. The light-emitting elements are, for example, solid-state light-emitting elements such as LEDs (Light Emitting Diodes). The light source 80 emits light when a direct current is supplied from the lighting device 30. The light source 80 lights up (emits light) when the output voltage of the lighting device 30 becomes equal to or greater than a lighting start forward voltage VF1. Note that, although the light source 80 is a solid-state light-emitting element in the first embodiment, it is not limited to a solid-state light-emitting element and may be an organic EL (Electro Luminescence) element.

[0019] The lighting device 30 is a device that supplies DC current to the light source 80. More specifically, the lighting device 30 converts the output voltage (i.e., AC voltage) of the AC power supply 20 into a DC voltage, transforms (steps up and down) the converted DC voltage, and outputs the transformed DC voltage to the light source 80 as an output voltage Vout (see FIG. 2 ), thereby supplying DC current to the light source 80. The lighting device 30 includes a rectifier circuit 32 and a converter circuit 40.

[0020] The rectifier circuit 32 is a circuit that converts the output voltage (AC voltage) of the AC power supply 20 into a DC voltage. The rectifier circuit 32 includes, for example, a diode bridge circuit.

[0021] The converter circuit 40 supplies DC current to the light source 80 based on a dimming signal indicating the dimming level of the light source 80. Here, the dimming level indicates one of multiple levels (e.g., 0 to 65025 levels) when the brightness of the light emitted from the light source 80 is expressed using digital values ​​with a resolution of multiple levels. More specifically, the converter circuit 40 receives a dimming signal from an external device (e.g., a PC (Personal Computer)). The dimming signal indicates the dimming level of the light source 80. Hereinafter, the dimming level indicated by the dimming signal will be referred to as the "instructed dimming level." The converter circuit 40 transforms the output voltage (DC voltage) of the rectifier circuit 32 to a voltage equal to or higher than the forward voltage of the light source 80, choppers the transformed voltage so that the average voltage of the transformed voltage corresponds to the instructed dimming level, and outputs the chopper-controlled voltage to the light source 80 as an output voltage Vout. The converter circuit 40 outputs the chopper-controlled voltage to the light source 80, thereby supplying the light source 80 with a current (direct current) corresponding to the instructed dimming level.

[0022] The converter circuit 40 includes a step-up chopper circuit 42 , a step-down chopper circuit 50 , and a control circuit 44 .

[0023] The boost chopper circuit 42 is a DC-DC conversion circuit that boosts the DC voltage input from the rectifier circuit 32. The boost chopper circuit 42 boosts the output voltage of the rectifier circuit 32 to a voltage equal to or higher than the forward voltage of the light source 80, and outputs the boosted voltage to the step-down chopper circuit 50.

[0024] The control circuit 44 is a circuit that controls the step-down chopper circuit 50 based on a dimming signal input from an external device. The control circuit 44 controls the DC current supplied from the step-down chopper circuit 50 to the light source 80 based on the dimming signal input from the external device.

[0025] The control circuit 44 is configured by, for example, a microcomputer (processor). 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. Note that the control circuit 44 may also be configured by an electric circuit other than a microcomputer.

[0026] The step-down chopper circuit 50 is a DC-DC conversion circuit that steps down the output voltage (DC voltage) of the step-up chopper circuit 42 based on the control of the control circuit 44. The step-down chopper circuit 50 performs chopper control (e.g., PWM (Pulse Width Modulation) control) of the DC voltage input from the step-up chopper circuit 42 based on the control of the control circuit 44. Through this chopper control, the step-down chopper circuit 50 steps down the output voltage of the step-up chopper circuit 42 to a voltage corresponding to an instructed dimming level. The step-down chopper circuit 50 outputs the stepped-down voltage (i.e., chopper-controlled voltage) to the light source 80. Through this output, the step-down chopper circuit 50 supplies a DC current corresponding to the instructed dimming level to the light source 80.

[0027] (3) Configuration of the Step-Down Chopper Circuit 50 As shown in FIG. 2, the step-down chopper circuit 50 includes a first input terminal T1 and a second input terminal T2, a first output terminal T3 and a second output terminal T4, a capacitor 51, a switching element 52, a diode 53, an inductor 54, a detection circuit 55, a capacitor 57, a discharge path 58, a switching element 59, and a resistor R3.

[0028] The first input terminal T1 is an input terminal maintained at a potential on the high potential side of the output voltage of the boost chopper circuit 42. The second input terminal T2 is an input terminal maintained at a potential on the low potential side of the output voltage of the boost chopper circuit 42. In other words, the output voltage of the boost chopper circuit 42 is applied to the step-down chopper circuit 50 as a potential difference between the first input terminal T1 and the second input terminal T2. The second input terminal T2 is electrically connected to ground.

[0029] The first output terminal T3 is an output terminal maintained at a potential on the high potential side of the output voltage of the step-down chopper circuit 50. The first output terminal T3 is connected to the first input terminal T1 via an electrical path. The second output terminal T4 is an input terminal maintained at a potential on the low potential side of the output voltage of the step-down chopper circuit 50. The second output terminal T4 is connected to the second input terminal T2 via an electrical path. The light source 80 is connected between the first output terminal T3 and the second output terminal T4. The output voltage of the step-down chopper circuit 50 is output as a potential difference between the first output terminal T3 and the second output terminal T4. In the first embodiment, as described above, the second input terminal T2 is connected to ground, and therefore the electrical path connecting the second input terminal T2 and the second output terminal T4 is maintained at ground potential.

[0030] The capacitor 51 is connected between the first input terminal T1 and the second input terminal T2. The capacitor 51 smoothes, for example, the voltage between the first input terminal T1 and the second input terminal T2 (i.e., the output voltage of the boost chopper circuit 42). The capacitor 51 is, for example, an electrolytic capacitor.

[0031] The switching element 52 choppers (e.g., PWM controls) the voltage input between the first input terminal T1 and the second input terminal T2 (i.e., the output voltage of the boost chopper circuit 42) based on a control signal from the control circuit 44, smoothes the chopper-controlled voltage using a capacitor 57, and outputs the smoothed voltage as an output voltage Vout from between the first output terminal T3 and the second output terminal T4 to the light source 80. The switching element 52 is, for example, an N-channel MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor). The switching element 52 has a first main terminal (e.g., a source terminal), a second main terminal (e.g., a drain terminal), and a control terminal (gate terminal). The first main terminal of the switching element 52 is connected to the cathode terminal of the diode 53. The first main terminal of the switching element 52 is also connected to one terminal of the inductor 54. The second main terminal of the switching element 52 is connected to the first input terminal T1. The control terminal of the switching element 52 is connected to the signal output section of the control circuit 44. The control signal is output from the signal output section of the control circuit 44 to the control terminal of the switching element 52.

[0032] The diode 53 is connected between the first main terminal (source terminal) of the switching element 52 and the second input terminal T2. The cathode terminal of the diode 53 is connected to the first main terminal of the switching element 52, and the anode terminal of the diode 53 is connected to the second input terminal T2. The cathode terminal of the diode 53 is also connected to one terminal of the inductor 54.

[0033] The inductor 54 is connected between the first main terminal (source terminal) of the switching element 52 and the first output terminal T3.

[0034] The capacitor 57 is connected between the first output terminal T3 and the second output terminal T4. In other words, the capacitor 57 is connected in parallel to the light source 80. The capacitor 57 is, for example, an electrolytic capacitor. The capacitor 57 is charged by a voltage chopper-controlled by the switching element 52. The voltage Vc of the capacitor 57 generated by this charging is output as the output voltage Vout from between the first output terminal T3 and the second output terminal T4. The capacitor 57 functions as a smoothing capacitor that smoothes the output voltage Vout of the lighting device 30. By smoothing the output voltage Vout of the lighting device 30 using the capacitor 57, flickering of the light emitted from the light source 80 can be suppressed. To enhance the flicker suppression effect of the capacitor 57, a capacitor with a relatively large capacity is used as the capacitor 57. The capacitance of the capacitor 57 is, for example, 50 μF or more. Note that the upper limit of the capacitance of the capacitor 57 is not particularly limited. The capacitance of the capacitor 57 may be, for example, 500 μF or less or 300 μF or less. The capacitor 57 may be, for example, an electrolytic capacitor.

[0035] The detection circuit 55 is a voltage divider circuit connected in parallel to the capacitor 57 for detecting the voltage Vc of the capacitor 57. The detection circuit 55 detects a voltage obtained by dividing the voltage Vc of the capacitor 57 at a predetermined voltage division ratio. The detection circuit 55 is connected between the first output terminal T3 and the second output terminal T4. The detection circuit 55 has an output section 55a that outputs a detected voltage (hereinafter referred to as the "detected voltage"). The output section 55a is connected to the input section of the control circuit 44. That is, the detected voltage of the detection circuit 55 is input to the input section of the control circuit 44. The control circuit 44 detects the voltage Vc of the capacitor 57 based on the detected voltage input to the input section.

[0036] The detection circuit 55 includes resistors R1 and R2. The resistors R1 and R2 are connected in series between the first output terminal T3 and the second output terminal T4. A first end of the resistor R1 is connected to the first output terminal T3, and a second end of the resistor R1 is connected to a first end of the resistor R2. A second end of the resistor R2 is connected to the second output terminal T4. The connection point between the resistors R1 and R2 is connected to the input of the control circuit 44 as the output 55a of the detection circuit 55. The potential at the connection point between the resistors R1 and R2 (i.e., the voltage obtained by dividing the voltage Vc of the capacitor 57 by a predetermined voltage division ratio) is input to the input of the control circuit 44. In this case, the predetermined voltage division ratio is r2 / (r1+r2). r1 and r2 are the resistance values ​​of the resistors R1 and R2. The resistance values ​​of the resistors R1 and R2 are determined based on the maximum value of the voltage supplied to the light source 80, the range of voltage values ​​that can be measured by the control circuit 44, and other factors.

[0037] The discharge path 58 is a path (electrical path) for discharging the charge stored in the capacitor 57. The discharge path 58 is connected in parallel to the capacitor 57. More specifically, a first end of the discharge path 58 is connected to the first output terminal T3, and a second end of the discharge path 58 is connected to the second output terminal T4.

[0038] The switching element 59 is provided in the discharge path 58 and turns on and off the discharge path 58 in response to control from the control circuit 44. The switching element 59 is, for example, a P-channel MOSFET. The switching element 59 has a first main terminal (e.g., a source terminal), a second main terminal (e.g., a drain terminal), and a control terminal (gate terminal). The two main terminals of the switching element 59 are provided in the discharge path 58. That is, the discharge path 58 has a first path 58a and a second path 58b. The first main terminal (source terminal) of the switching element 59 is connected to the second output terminal T4 via the first path 58a, and the second main terminal (drain terminal) of the switching element 59 is connected to the first output terminal T3 via the second path 58b. The control terminal (gate terminal) is connected to the control circuit 44 and receives a control signal from the control circuit 44. The switching element 59 is switched on and off in response to the control signal from the control circuit 44 input to the control terminal. Switching element 59 conducts discharge path 58 when it is turned on, and cuts off discharge path 58 when it is turned off. When switching element 59 is turned on and discharge path 58 is conductive, the charge stored in capacitor 57 flows through discharge path 58 and is discharged. When switching element 59 is turned off and discharge path 58 is cut off, the charge stored in capacitor 57 stops flowing through discharge path 58 and is no longer discharged.

[0039] Resistor R3 is provided in discharge path 58 and connected in series with switching element 59. The resistance value of resistor R3 is smaller than the resistance value of the combined resistance of detection circuit 55 (i.e., the resistance combined of resistors R1 and R2). This prevents the charge stored in capacitor 57 from flowing through detection circuit 55 instead of through discharge path 58 when switching element 59 is turned on and discharge path 58 is made conductive.

[0040] (4) Details of the processing by the control circuit 44 The control circuit 44 receives the detected voltage from the detection circuit 55 and detects the voltage Vc of the capacitor 57 (i.e., the output voltage Vout of the converter circuit 40) based on the detected voltage. The control circuit 44 then controls the switching elements 52 and 59 based on the dimming signal from the external device and the voltage Vc of the capacitor 57.

[0041] More specifically, the control circuit 44 PWM-controls the switching element 52 based on a dimming signal from an external device and the voltage Vc of the capacitor 57. Through this PWM control, the voltage input between the first input terminal T1 and the second input terminal T2 (i.e., the output voltage of the step-up chopper circuit 42) is stepped down to a voltage corresponding to the dimming level (instructed dimming level) indicated by the dimming signal, and is output from between the first output terminal T3 and the second output terminal T4 to the light source 80 as the output voltage Vout of the lighting device 30. As a result, the light source 80 emits light at a brightness corresponding to the instructed dimming level.

[0042] The output voltage Vout of the lighting device 30 is the output voltage of the converter circuit 40 and also the output voltage of the step-down chopper circuit 50 (i.e., the voltage between the first output terminal T3 and the second output terminal T4). The output voltage Vout is the same voltage as the voltage Vc of the capacitor 57 (i.e., Vout=Vc).

[0043] More specifically, the control circuit 44 determines whether the instructed dimming level is a relatively high dimming level or a relatively low dimming level based on whether the instructed dimming level is equal to or greater than a predetermined threshold level. More specifically, if the instructed dimming level is equal to or greater than the predetermined threshold level, the control circuit 44 determines that the instructed dimming level is a relatively high dimming level. On the other hand, if the instructed dimming level is less than the predetermined threshold level, the control circuit 44 determines that the instructed dimming level is a relatively low dimming level.

[0044] Furthermore, when the instructed dimming level is a relatively high dimming level, the control circuit 44 calculates a duty ratio corresponding to the instructed dimming level and PWM-controls the switching element 52 based on the calculated duty ratio. As a result, the voltage input between the first input terminal T1 and the second input terminal T2 is stepped down to a voltage corresponding to the instructed dimming level by PWM control (i.e., chopper control) of the switching element 52. The stepped-down voltage is output as an output voltage Vout from between the first output terminal T3 and the second output terminal T4 to the light source 80. As a result, the light source 80 emits light at a brightness corresponding to the instructed dimming level. The duty ratio is the ratio of on-time to one on-off cycle when the switching element 52 is PWM-controlled.

[0045] Furthermore, when the instructed dimming level is a relatively low dimming level, the control circuit 44 further determines whether the voltage Vc of the capacitor 57 is equal to or greater than a threshold voltage VF2. The threshold voltage VF2 is a predetermined voltage that is lower by a certain voltage than the turn-on forward voltage VF1 of the light source 80. The turn-on forward voltage VF1 of the light source 80 is the forward voltage at which the light source 80 starts to turn on. In other words, the light source 80 turns on (emits light) at a voltage equal to or greater than the turn-on forward voltage VF1, and turns off at a voltage less than the turn-on forward voltage VF1.

[0046] When the instructed dimming level is a relatively low dimming level and the voltage Vc of the capacitor 57 is less than the threshold voltage VF2, the control circuit 44 determines a boost duty ratio that is higher than the duty ratio corresponding to the instructed dimming level. The boost duty ratio is a predetermined duty ratio having a higher proportion of on time than the duty ratio corresponding to the instructed dimming level. The control circuit 44 then PWM-controls the switching element 52 based on the determined boost duty ratio until the voltage Vc of the capacitor 57 reaches the threshold voltage VF2. As a result, a voltage higher than the voltage corresponding to the instructed dimming level is output as the output voltage Vout from between the first output terminal T3 and the second output terminal T4. As a result, the capacitor 57 is charged more quickly than when the switching element 52 is PWM-controlled based on the duty ratio corresponding to the instructed dimming level.

[0047] When the voltage of capacitor 57 reaches threshold voltage VF2, control circuit 44 changes the duty ratio used in the PWM control of switching element 52 from the boost duty ratio to a duty ratio corresponding to the indicated dimming level. When voltage Vc of capacitor 57 is equal to or higher than threshold voltage VF2, control circuit 44 PWM controls switching element 52 based on the duty ratio corresponding to the indicated dimming level. When capacitor 57 is further charged and voltage Vc of capacitor 57 becomes equal to or higher than illumination start forward voltage VF1, light source 80 emits light at a luminance corresponding to the indicated dimming level.

[0048] Furthermore, when the instructed dimming level is not the lights-out level (for example, the instructed current value is zero) (i.e., when the instructed dimming level is an on level higher than the lights-out level), control circuit 44 controls switching element 59 to turn off and cuts off discharge path 58. This prevents the charge stored in capacitor 57 from flowing through discharge path 58 and being discharged.

[0049] In this way, when the instructed dimming level is a relatively low dimming level and the voltage Vc of the capacitor 57 is less than the threshold voltage VF2, the boost duty ratio is used to charge the capacitor 57 more quickly, thereby enabling the light source 80 to be quickly switched from an off state to on, and to emit light at a brightness corresponding to the instructed dimming level.

[0050] In the following description, the state in which the instructed dimming level of the lighting device 30 is the off level may be referred to as the off mode, and the state in which the instructed dimming level of the lighting device 30 is the on level (a level higher than the off level) may be referred to as the on mode.

[0051] Furthermore, when the instructed dimming level is the extinguishing level (e.g., dimming current value is zero), the control circuit 44 calculates a duty ratio (i.e., a duty ratio of zero) corresponding to the instructed dimming level (i.e., the extinguishing level), and PWM-controls the switching element 52 based on the calculated duty ratio. In this case, the control circuit 44 essentially turns off the switching element 52, stopping the DC current supplied from the lighting device 30 to the light source 80.

[0052] Furthermore, when the instructed dimming level is the extinguishing level (e.g., dimming current value is zero), the control circuit 44 determines whether the voltage Vc of the capacitor 57 is greater than a threshold voltage VF3 (first threshold voltage). The threshold voltage VF3 is the same as the lighting start forward voltage VF1 or a predetermined voltage that is lower than the lighting start forward voltage VF1 by a certain voltage. The threshold voltage VF3 may be the same as the threshold voltage VF2.

[0053] When the instructed dimming level is the extinguishing level and the voltage Vc of the capacitor 57 is greater than the threshold voltage VF3, the control circuit 44 switches the switching element 59 from off to on, thereby making the discharge path 58 conductive. This causes the charge stored in the capacitor 57 to start discharging through the discharge path 58. As a result, the voltage Vc of the capacitor 57 drops more quickly until the voltage Vc becomes less than the illumination start forward voltage V1, compared to when the capacitor 57 naturally discharges without passing through the discharge path 58. As a result, the light source 80 is quickly extinguished from its illuminated state.

[0054] When the instructed dimming level is the extinguishing level, the control circuit 44 determines whether the voltage Vc of the capacitor 57 is equal to or lower than the threshold voltage VF3 (first threshold voltage). If the voltage Vc of the capacitor 57 is not equal to or lower than the threshold voltage VF3, the control circuit 44 keeps the switching element 59 on to continue discharging the charge stored in the capacitor 57. If the voltage Vc of the capacitor 57 is equal to or lower than the threshold voltage VF3, the control circuit 44 switches the switching element 59 from on to on to cut off the discharge path 58. This stops the charge stored in the capacitor 57 from being discharged through the discharge path 58.

[0055] In this way, when the instructed dimming level is the extinguishing level and the voltage Vc of the capacitor 57 is greater than the threshold voltage VF3, the charge stored in the capacitor 57 is quickly discharged via the discharge path 58. This allows the light source 80 to be quickly turned off from the lit state.

[0056] The control circuit 44 also has an update function that updates the threshold voltages VF2 and VF3. The threshold voltages VF2 and VF3 are voltages that are set based on the illumination start forward voltage V1 of the light source 80. The illumination start forward voltage V1 is determined by the characteristics of the light source 80. Therefore, the threshold voltages VF2 and VF3 are determined by the characteristics of the light source 80. For this reason, the illumination start forward voltage VF1 may change if the light source 80 is replaced or if the light source 80 deteriorates. For this reason, the control circuit 44 has an update function that updates the threshold voltages VF2 and VF3 in response to changes in the illumination start forward voltage VF1. Details of this update function will be described later in "(5-4) Operation of the Update Function of the Lighting Device 30."

[0057] (5) Operation The operation of the lighting device 30 according to the first embodiment will be described.

[0058] (5-1) Operation of the lighting device 30 when it is turned on First, the operation of lighting device 30 according to the first embodiment during lighting will be described with reference to FIGS. 3 to 8, in comparison with a lighting device of Comparative Example 1. FIG.

[0059] A case will be described in which the lighting device 30 according to the first embodiment starts supplying a DC current to the light source 80 when the output voltage Vout is zero. For example, when a DC current corresponding to a relatively 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, and therefore the time required to charge the capacitor 57 of the step-down chopper circuit 50 is relatively short. Therefore, as shown by graph G1 in FIG. 3, the output voltage Vout rises relatively quickly from the zero state (the output voltage Vout at time t0 in FIG. 3) to the lighting start forward voltage VF1 (the output voltage Vout at time t2 in FIG. 3). Therefore, the light source 80 lights up quickly after the supply of DC current starts.

[0060] On the other hand, when a DC current corresponding to a relatively low dimming level is supplied to light source 80, the value of the DC current is relatively small. Here, first, the operation of the lighting device of Comparative Example 1 will be described. The lighting device of Comparative Example 1 is configured similarly to lighting device 30 according to Embodiment 1, and supplies a DC current corresponding to a relatively low instructed dimming level (e.g., a DC current of zero value) to light source 80 from time t0. In the lighting device of Comparative Example 1, because the value of the DC current supplied to light source 80 is small, it takes a relatively long time to charge capacitor 57, which has a large capacity. Therefore, as shown in graph G2 of FIG. 3, it takes a relatively long time for output voltage Vout to rise to the lighting start forward voltage VF1.

[0061] Next, an operation of the lighting device 30 according to the first embodiment (operation when a DC current corresponding to a relatively low command dimming level (e.g., a DC current of zero value) is supplied to the light source 80 from time t0) will be described. When the command dimming level is lower than a predetermined threshold level (i.e., a relatively low command dimming level) and the DC voltage supplied to the light source 80 is less than the threshold voltage VF2, the lighting device 30 calculates a boost duty ratio that is a duty ratio higher than the duty ratio corresponding to the command dimming level, and performs PWM control on the switching element 52 based on the calculated boost duty ratio. As a result, the lighting device 30 supplies to the light source 80 a DC current having a boost current value (i.e., a current value corresponding to the boost duty ratio) greater than the value of the DC current corresponding to the command dimming level. That is, when lighting device 30 supplies light source 80 with a DC current corresponding to a relatively low instructed dimming level, as shown in graph G3 of FIG. 3 , lighting device 30 supplies light source 80 with a DC current of a boost current value from time t0 to time t4 when output voltage Vout reaches threshold voltage VF2. As a result, lighting device 30 according to embodiment 1 can charge capacitor 57 more quickly from time t0 to time t4 compared to the lighting device of comparative example 1. Note that the predetermined threshold level is not particularly limited, and for example, a dimming level corresponding to a rated current with a dimming rate of 100% may be set as the threshold level with a dimming level corresponding to a dimming rate of 50%.

[0062] After the output voltage Vout reaches the threshold voltage VF2 (after time t4), the lighting device 30 according to the first embodiment calculates a duty ratio corresponding to the instructed dimming level and PWM-controls the switching element 52 based on the calculated duty ratio. As a result, after time t4, the lighting device 30 according to the first embodiment outputs a DC current corresponding to the instructed dimming level as the output voltage Vout to the light source 80. In the example shown in FIG. 3, the DC voltage supplied to the light source 80 reaches the light-on start forward voltage VF1 at time t5. As a result, as shown in graph G3 in FIG. 3, the output voltage Vout of the lighting device 30 according to the first embodiment reduces the time (t4-t0) for it to reach the threshold voltage VF2 and the time (t5-t0) for it to reach the light-on start forward voltage VF1 compared to the output voltage Vout of the lighting device of Comparative Example 1.

[0063] (5-2) Operation of the lighting device 30 when it is turned off Next, the operation of lighting device 30 according to embodiment 1 when turned off will be described with reference to FIG. 4, in comparison with a lighting device of comparative example 2.

[0064] The lighting device of Comparative Example 2 is a lighting device in which the discharge path 58, the switching element 59, and the resistor R3 are omitted from the lighting device 30 of the first embodiment.

[0065] First, a description will be given of the operation when the lighting device of Comparative Example 2 starts to turn off the light source 80 at time t6. At time t6, the output voltage Vout of the lighting device of Comparative Example 2 is a voltage greater than the threshold voltage VF3.

[0066] When the indicated dimming level becomes the extinction level (e.g., the indicated current value is zero) at time t6, the lighting device of Comparative Example 2 calculates a duty ratio (duty ratio of zero) corresponding to the indicated dimming level (light-off level) and PWM-controls switching element 52 based on the calculated duty ratio. In this case, the DC current value corresponding to the indicated dimming level (light-off level) is zero, so the lighting device of Comparative Example 2 does not substantially supply DC current to light source 80. That is, in the lighting device of Comparative Example 2, when the indicated dimming level is the extinction level and output voltage Vout is greater than threshold voltage VF3, as shown in graph G5 of FIG. 4, the charge stored in capacitor 57 is discharged relatively slowly by natural discharge from the discharge start point (time t6). Therefore, voltage Vc of capacitor 57 (i.e., output voltage Vout) decreases relatively slowly. Then, after time t9, output voltage Vout becomes less than the illumination start forward voltage VF1, and light source 80 is turned off. As described above, in the lighting device of Comparative Example 2, the charge stored in capacitor 57 decreases relatively slowly due to natural discharge, and therefore it takes a relatively long time from the time when light source 80 starts to be turned off (time t6) to the time when light source 80 is effectively turned off (time t9).

[0067] Next, an operation of the lighting device 30 according to the first embodiment will be described when the lighting device 30 starts to turn off the light source 80 at time t6. When the instructed dimming level is the light-off level and the output voltage Vout is greater than the threshold voltage V3, the lighting device 30 according to the first embodiment PWM-controls the switching element 52 based on a duty ratio (e.g., a duty ratio of zero) corresponding to the instructed dimming level (i.e., the light-off level). As a result, the lighting device 30 supplies a DC current (e.g., a DC current of zero value) corresponding to the instructed dimming level (light-off level) to the light source 80. In other words, the lighting device 30 does not substantially supply a DC current to the light source 80. Furthermore, the lighting device 30 switches the switching element 59 from off to on, thereby changing the discharge path 58 from a blocked state to a conductive state. That is, in the lighting device 30 according to the first embodiment, when the instructed dimming level is the light-off level and the output voltage Vout is greater than the threshold voltage VF3, as shown in graph G4 of FIG. 4, the charge stored in the capacitor 57 is rapidly discharged through the discharge path 58 from the discharge start time (time t6), through time t7 when the output voltage Vout becomes the lighting start forward voltage VF1, to time t8 when the output voltage Vout becomes the threshold voltage VF3.

[0068] Then, at time t8, lighting device 30 switches switching element 59 from on to off, thereby blocking discharge path 58. As a result, as shown in graph G4 in Fig. 4, after time t8, the charge stored in capacitor 57 cannot be discharged through discharge path 58 and is discharged relatively slowly by natural discharge. Therefore, voltage Vc of capacitor 57 (i.e., output voltage Vout) decreases relatively slowly after time t8.

[0069] In this way, lighting device 30 according to embodiment 1 conducts discharge path 58 from the time when light source 80 starts to be turned off (time t6) and quickly discharges the charge stored in capacitor 57 through discharge path 58, thereby quickly reducing output voltage Vout from a voltage higher than threshold voltage VF3 to threshold voltage VF3. Therefore, in lighting device 30 according to embodiment 1, the time from the time when light source 80 starts to be turned off (time t6) to time t7 when light source 80 is substantially turned off is shorter than in the lighting device of comparative example 2.

[0070] (5-3) Details of operation of lighting device 30 when turned off With reference to FIG. 5, the operation of lighting device 30 when turned off will be described in detail.

[0071] The control circuit 44 determines whether the instructed dimming level is the light-off level (for example, the instructed current value is zero) (S1). If the result of this determination is that the instructed dimming level is not the light-off level (S1: No), the process returns to step S1.

[0072] On the other hand, if the determination result in step S1 indicates that the instructed dimming level is the extinguishing level (S1: Yes), the control circuit 44 detects the voltage Vc of the capacitor 57 based on the detected voltage of the detection circuit 55 (S2). Then, the control circuit 44 determines whether the voltage Vc of the capacitor 57 is greater than the threshold voltage VF3 (S3). If the determination result indicates that the voltage Vc of the capacitor 57 is not greater than the threshold voltage VF3 (S3: No), the control circuit 44 maintains the OFF state of the switching element 59, thereby maintaining the interruption of the discharge path 58 (S9). Then, the process returns to step S1.

[0073] On the other hand, if the result of the determination in step S3 is that the voltage Vc of the capacitor 57 is greater than the threshold voltage VF3 (S3: Yes), the control circuit 44 switches the switching element 59 from off to on, thereby bringing the discharge path 58 into conduction (S4). With this conduction, the charge stored in the capacitor 57 starts to be discharged through the discharge path 58.

[0074] The control circuit 44 then detects the voltage Vc of the capacitor 57 based on the detected voltage of the detection circuit 55 (S5). The control circuit 44 then determines whether the voltage Vc of the capacitor 57 is equal to or lower than the threshold voltage VF3 (S6). If the result of this determination is that the voltage Vc of the capacitor 57 is equal to or lower than the threshold voltage VF3 (S6: Yes), the control circuit 44 switches the switching element 59 from on to off to interrupt the discharge path 58, thereby ending the discharge of the capacitor 57 (S8). The process then ends.

[0075] On the other hand, if the determination result in step S6 indicates that the voltage Vc of capacitor 57 is not equal to or less than the threshold voltage VF3 (S6: No), the control circuit 44 determines whether the instructed dimming level is the lights-out level (S7). If the determination result indicates that the instructed dimming level is the lights-out level (S7: Yes), the process returns to step S6, and the processes from step S6 onward are repeated. On the other hand, if the determination result in step S7 indicates that the instructed dimming level is not the lights-out level (S7: No), that is, if the instructed dimming level changes from the lights-out level to the lights-on level (i.e., the instructed current value is greater than zero) during the discharge of capacitor 57 in step S4, the control circuit 44 switches the switching element 59 from on to off to interrupt the discharge path 58, thereby terminating the discharge of capacitor 57 (S8). In this case, the discharge of capacitor 57 is forcibly terminated before the voltage Vc of capacitor 57 becomes equal to or less than the threshold voltage VF3. Then, the process ends.

[0076] (5-4) Operation of the update function of the lighting device 30 The operation of the update function of the control circuit 44 of the lighting device 30 will be described with reference to FIG.

[0077] As shown in FIG. 6, the control circuit 44 sets the current value of the direct current to be supplied to the light source 80 (S10). Here, the control circuit 44 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. The control circuit 44 sets, for example, a plurality of current values. Furthermore, the magnitude of the set current value 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 (i.e., a current value with a relatively small value). 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.

[0078] Next, the converter circuit 40 supplies a DC current of the current value set in step S10 to the light source 80, and the control circuit 44 measures the value of the forward voltage Vf (i.e., the DC voltage output by the converter circuit 40) when the DC current is supplied (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 55a of the resistors R1 and R2. By performing such measurements for the multiple current values ​​set, a correspondence relationship between the value of the DC current supplied to the light source 80 (current value I0) and the value of the DC voltage (voltage value V0) can be obtained.

[0079] Here, the above-mentioned correspondence relationship will be explained using Fig. 7. Fig. 7 is a graph showing an example of the relationship between the dimming level D corresponding to the DC current (current value I0) supplied from the lighting device 30 to the light source 80 and the voltage value V0. In Fig. 7, for example, the dimming level 6503 corresponding to the voltage value 146.5V corresponds to a dimming rate of 10%, and the value of the DC current (current value I0) supplied to the light source 80 in this case is 0.1644A. Furthermore, the dimming level 66 corresponding to the voltage value 137.3V corresponds to the minimum dimming level (dimming rate of 0.10%), and the value of the DC current (current value I0) supplied to the light source 80 in this case is 0.001749A.

[0080] Next, the control circuit 44 acquires the forward voltage Vf at which the light source 80 starts to light (i.e., the start-of-light forward voltage VF1) based on the measurement results of step S12 of FIG. 6 (S14). Generally, 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, making it difficult to determine the start-of-light forward voltage VF1 by measurement. Therefore, more specifically, in step S14, the start-of-light forward voltage VF1 is acquired based on the correspondence between the value of the DC current measured in step S12 and the value of the DC voltage. Specifically, to convert the curved graph shown in FIG. 7 into a linear graph, the horizontal and vertical axes of FIG. 7 are converted to 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 thus converted will be described with reference to FIG. 8.

[0081] Fig. 8 is a graph obtained by logarithmically converting the horizontal and vertical axes of the curved graph shown in Fig. 7. The horizontal and vertical axes of the graph shown in Fig. 8 represent the natural logarithm of the current value I0 and the natural logarithm of the voltage value V0, respectively.

[0082] The control circuit 44 calculates a voltage value V0 for an arbitrary current value I0 by linearly approximating the graph shown in Fig. 8 using, for example, the least squares method, and determining the slope and intercept of the approximated line. Through this calculation, the control circuit 44 calculates the voltage value V0 for the current value I0 that flows when the light source 80 starts to light, thereby obtaining the light-on start forward voltage VF1. In the first 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 light is, for example, about 1 mA.

[0083] Next, the control circuit 44 determines threshold voltages VF2 and VF3 based on the illumination start forward voltage VF1 acquired in step S14 (S16). Specifically, the control circuit 44 determines the threshold voltage VF2 to be a voltage lower than the illumination start forward voltage VF1 by a certain voltage (e.g., a slightly lower voltage). For example, the control circuit 44 determines the threshold voltage VF2 to be a voltage obtained by subtracting a predetermined margin voltage from the illumination start forward voltage VF1. By setting the threshold voltage VF2 to a value lower than the illumination start forward voltage VF1 in this manner, it is possible to prevent 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 when a DC current of the boost current value is supplied to the light source 80. In this manner, to prevent an overshoot of the DC voltage supplied to the light source 80, the margin voltage value may be, for example, 5 V or more. Furthermore, to reduce the time required for the light source 80 to light up, the margin voltage value may be 15 V or less. In the first embodiment, the margin voltage value is 10 V.

[0084] More specifically, the control circuit 44 determines the threshold voltage VF3 to be the same as the lighting start forward voltage VF1 or to be a voltage lower than the lighting start forward voltage VF1 by a certain voltage (for example, a voltage slightly lower).

[0085] Next, the control circuit 44 sets the threshold voltages VF2 and VF3 to the values ​​determined in step S16 (S18). As a result, the control circuit 44 updates the threshold voltages VF2 and VF3 to values ​​suitable for the characteristics of the light source 80.

[0086] Because the lighting device 30 has such an updating function, for example, when the light source 80 is replaced or when the light source 80 deteriorates and its characteristics change, the updating function can update the threshold voltages VF2 and VF3 based on the characteristics of the replaced light source 80. Therefore, it is possible to prevent an increase in the time required to turn on the light source 80 and the time required to turn off the light source 80. In other words, it is possible to shorten the response time of the lighting device 30.

[0087] In particular, with regard to the threshold voltage VF2, the threshold voltage VF2 is updated based on the correspondence 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 threshold voltage VF2 and the light turn-on forward voltage VF1 of the light source 80 (a difference due to individual differences between the light source 80). Therefore, until the DC voltage supplied to the light source 80 reaches near the light turn-on forward voltage VF1, it is possible to supply to the light source 80 a DC current with a boost current value that is greater than the dimming current value corresponding to the dimming level, so that the time required for the light source 80 to light can be reliably shortened.

[0088] (6) Effects As described above, the lighting device 30 according to the first embodiment supplies a direct current to the light source 80 including a solid-state light-emitting element. The lighting device 30 includes a converter circuit 40. The converter circuit 40 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 includes a capacitor 57, a discharge path 58, and a switching element 59. The capacitor 57 is connected in parallel to the light source 80. The discharge path 58 is connected in parallel to the capacitor 57. The switching element 59 is provided in the discharge path 58 and makes the discharge path 58 conductive and cuts off. The switching element 59 makes the discharge path 58 conductive in an off mode in which the dimming level of the dimming signal is the off level.

[0089] According to this configuration, in the extinction mode, the switching element 59 conducts the discharge path 58. Therefore, in the extinction mode, the charge stored in the capacitor 57 flows through the discharge path 58 and is quickly discharged. That is, the voltage Vc of the capacitor 57 quickly drops. As a result, the light source 80 can be quickly turned off.

[0090] Furthermore, the lighting device 30 according to the first embodiment further includes a detection circuit 55. The detection circuit 55 is connected in parallel to the capacitor 57 and is a circuit for detecting the voltage Vc of the capacitor 57. In the extinction mode, the switching element 59 conducts the discharge path 58 when the voltage Vc of the capacitor 57 is greater than a threshold voltage VF3 (first threshold voltage). The threshold voltage VF3 is a predetermined voltage that is equal to or less than the lighting start forward voltage VF1 (lighting start voltage) of the light source 80.

[0091] According to this configuration, in the lights-out mode, when the voltage Vc of the capacitor 57 exceeds the threshold voltage VF3 (first threshold voltage), the switching element 59 conducts the discharge path 58. Therefore, in the lights-out mode, when the voltage Vc of the capacitor 57 is relatively high, the charge stored in the capacitor 57 can be discharged by the conduction of the discharge path 58. This makes it possible to suppress the discharge of the charge stored in the capacitor 57 (i.e., unnecessary discharge) when the voltage Vc of the capacitor 57 is sufficiently low.

[0092] Furthermore, in the lighting device 30 according to the first embodiment, in the extinction mode, when the voltage Vc of the capacitor 57 becomes equal to or lower than a threshold voltage VF3 (second threshold voltage), the switching element 59 cuts off the discharge path 58. The threshold voltage VF3 is a predetermined voltage lower than the lighting start forward voltage VF1 (lighting start voltage) of the light source 80.

[0093] According to this configuration, when the voltage Vc of the capacitor 57 becomes equal to or lower than the threshold voltage VF3 (second threshold voltage) and the light source 80 is definitely turned off, the discharge path 58 is cut off to stop the discharge of the charge stored in the capacitor 57. This makes it possible to suppress the discharge of the charge stored in the capacitor 57 (i.e., unnecessary discharge) when the light source 80 is already turned off.

[0094] Furthermore, in lighting device 30 according to the first embodiment, when the dimming level of the dimming signal is not the lights-out level, switching element 59 cuts off discharge path 58. With this configuration, when the dimming level of the dimming signal is not the lights-out level (i.e., when light source 80 is on), it is possible to prevent the charge stored in capacitor 57 from being discharged through discharge path 58.

[0095] Moreover, the lighting device 30 according to the first embodiment further includes a resistor R3 (first resistor). The resistor R3 is provided in the discharge path 58 and connected in series with the switching element 59. The detection circuit 55 has a plurality of resistors R1 and R2 (second resistors) for detecting the voltage Vc of the capacitor 57. The resistance value of the resistor R3 is smaller than the resistance value of a combined resistance obtained by combining the plurality of resistors R1 and R2 of the detection circuit 55. This configuration can prevent the charge stored in the capacitor 57 from flowing to the detection circuit 55 and discharging.

[0096] Furthermore, in the lighting device 30 according to the first embodiment, the capacitor 57 includes an electrolytic capacitor. With this configuration, the capacitor 57 can be made of an electrolytic capacitor, which is easily available.

[0097] Moreover, the illumination device 10 according to the first embodiment includes the lighting device 30 according to the first embodiment and a light source 80. According to this configuration, the illumination device 10 including the lighting device 30 can be provided.

[0098] (7) Aspects other than lighting devices The same functions as those of the lighting device 30 according to the first embodiment may be embodied as a lighting control method, a computer program (program), or a non-transitory recording medium on which a computer program is recorded.

[0099] A lighting control method according to one aspect is a method for controlling a lighting device 30 that supplies a direct current to a light source 80 including a solid-state light-emitting element. The lighting device 30 includes a converter circuit 40. The converter circuit 40 supplies a direct current to the light source 80 based on a dimming signal indicating a dimming level of the light source 80. The converter circuit 40 includes a capacitor 57, a discharge path 58, and a switching element 59. The capacitor 57 is connected in parallel to the light source 80. The discharge path 58 is connected in parallel to the capacitor 57. The switching element 59 is provided in the discharge path 58 and conducts and cuts off the discharge path 58. The lighting control method includes a control step. In the control step, in an extinction mode where the dimming level of the dimming signal is the extinction level, the switching element 59 is controlled to conduct the discharge path 58.

[0100] A program according to one aspect causes one or more processors to execute the lighting control method.

[0101] A non-transitory recording medium according to one embodiment temporarily records a program that causes one or more processors to execute the lighting control method.

[0102] (Embodiment 2) (1) Composition A lighting device 30 according to a second embodiment will be described with reference to Fig. 9. As shown in Fig. 9, the lighting device 30 according to the second embodiment has the same configuration as the lighting device 30 according to the first embodiment, except that the capacitor 57 is replaced with a plurality (n pieces) of capacitors C1 to Cn. The following description of the lighting device 30 according to the second embodiment will focus on the differences from the lighting device 30 according to the first embodiment.

[0103] The plurality of capacitors C1 to Cn are connected between the first output terminal T3 and the second output terminal T4. The plurality of capacitors C1 to Cn are connected in parallel with one another. The plurality of capacitors C1 to Cn are, for example, film capacitors. The combined capacitance of the plurality of capacitors C1 to Cn is approximately the same as the capacitance of the capacitor 57 of the first embodiment (see FIG. 2). Therefore, the capacitance of each of the capacitors C1 to Cn is smaller than the capacitance of the capacitor 57 of the first embodiment.

[0104] (2) Effects The lighting device 30 according to the second embodiment further includes a plurality of capacitors C1 to Cn. The plurality of capacitors C1 to Cn are connected in parallel to one another. With this configuration, the use of the plurality of capacitors C1 to Cn connected in parallel can shorten the overall discharge time of the plurality of capacitors C1 to Cn. As a result, compared to the first embodiment, the time from when the plurality of capacitors C1 to Cn start to discharge until the light source 80 is actually turned off can be shortened.

[0105] (Embodiment 3) (1) Composition A lighting device 30 according to embodiment 3 will be described. The lighting device 30 according to embodiment 2 differs from the lighting device 30 according to embodiment 1 in the method of setting the threshold voltages VF2 and VF3. The following describes the lighting device 30 according to embodiment 2, focusing on the differences from the lighting device 30 according to embodiment 1.

[0106] The lighting device 30 according to the third embodiment includes a rectifier circuit 32 and a converter circuit 40, similar to the lighting device 30 according to the first embodiment (see FIG. 1).

[0107] The converter circuit 40 according to the third embodiment includes a step-up chopper circuit 42, a step-down chopper circuit 50, and a control circuit 44, similar to the converter circuit 40 according to the first embodiment (see FIG. 1).

[0108] The control circuit 44 according to the third embodiment 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 from an external device. The control circuit 44 according to the third embodiment differs from the control circuit 44 according to the first embodiment in the method of determining the threshold voltages VF2 and VF3 in the update function. In the third embodiment, the control circuit 44 updates the threshold voltages VF2 and VF3 in the update function based on the DC voltage supplied to the light source 80 when the converter circuit 40 supplies the minimum DC current that the converter circuit 40 can supply to the light source 80. That is, in the update function, the current value of the DC current to be supplied to the light source 80 is set to the minimum DC current that the converter circuit 40 can supply to the light source 80. The control circuit 44 measures the forward voltage (light-on start forward voltage VF1) when this minimum DC current is supplied to the light source 80, and determines the threshold voltage VF2 based on the measured forward voltage. Specifically, the threshold voltage VF2 is determined by subtracting a predetermined margin voltage from the measured forward voltage. The margin voltage value may be set appropriately depending on the characteristics of the light source 80. The margin voltage value according to the third embodiment may be, for example, 5V or more and 15V or less, similar to the margin voltage value according to the first embodiment.

[0109] Similarly, the control circuit 44 also determines the threshold voltage VF3 based on the forward voltage (lighting start forward voltage VF1) measured as described above.

[0110] (2) Effects As described above, in the third embodiment, the threshold voltages VF2 and VF3 are updated based on the DC voltage supplied to the light source 80 when the converter circuit 40 supplies the minimum DC current that it can supply to the light source 80. The DC voltage supplied to the light source 80 when the converter circuit 40 supplies the minimum DC current that it can supply to the light source 80 is close to the light-on start forward voltage VF1 of the light source 80, and therefore the third embodiment also achieves the same effects as the first embodiment. Furthermore, in the third embodiment, the update function requires only one value for the DC current supplied to the light source 80 and one value for the DC voltage to be measured, and therefore the operation of the converter circuit 40 in the update function can be simplified.

[0111] Furthermore, in the lighting device 30 according to the third embodiment, the threshold voltage VF2 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 40 supplies the minimum DC current that can be supplied to the light source 80.

[0112] This allows the threshold voltage to be updated using a simplified method. Also, by setting the threshold voltage VF2 to a value lower than the forward voltage (light-on start forward voltage VF1), it is possible to prevent 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 when a DC current of the boost current value is supplied to the light source 80.

[0113] 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 light up.

[0114] (Variations, etc.) Although the lighting device 30 and the illumination device 10 according to the present disclosure have been described above based on the first to third embodiments, the present disclosure is not limited to these embodiments.

[0115] For example, in the first to third embodiments, the lighting device 30 includes the rectifier circuit 32 and the boost chopper circuit 42, but these circuits are not essential components of the lighting device 30.

[0116] In addition, this disclosure also includes forms obtained by applying various modifications to each embodiment that a person skilled in the art would think of, or forms realized by arbitrarily combining the components and functions of each embodiment within the scope that does not deviate from the intent of this disclosure.

[0117] (Aspect) The present disclosure includes the following aspects.

[0118] A lighting device (30) of a first aspect supplies a direct current to a light source (80) including a solid-state light-emitting element. The lighting device (30) includes a converter circuit (40). The converter circuit (40) supplies a direct current to the light source (80) based on a dimming signal indicating a dimming level of the light source (80). The converter circuit (40) includes a capacitor (57), a discharge path (58), and a switching element (59). The capacitor (57) is connected in parallel to the light source (80). The discharge path (58) is connected in parallel to the capacitor (57). The switching element (59) is provided in the discharge path (58) and conducts and cuts off the discharge path (58). The switching element (59) conducts the discharge path (58) in an off mode in which the dimming level of the dimming signal is the off level.

[0119] According to this configuration, the switching element (59) conducts the discharge path (58) in the extinction mode. Therefore, in the extinction mode, the charge stored in the capacitor (57) flows through the discharge path (58) and is quickly discharged. That is, the voltage (Vc) of the capacitor (57) quickly drops. As a result, the light source (80) can be quickly turned off.

[0120] The lighting device (30) of the second aspect is the same as that of the first aspect, but further includes a detection circuit (55). The detection circuit (55) is connected in parallel to the capacitor (57) and is a circuit for detecting a voltage (Vc) of the capacitor (57). In the extinction mode, the switching element (59) conducts the discharge path (58) when the voltage (Vc) of the capacitor (57) is greater than a first threshold voltage (VF3). The first threshold voltage (VF3) is a predetermined voltage equal to or less than a lighting start voltage (VF1) at which the light source (80) starts to light.

[0121] According to this configuration, in the light-off mode, when the voltage (Vc) of the capacitor (57) exceeds the first threshold voltage (VF3), the switching element (59) renders the discharge path (58) conductive. Therefore, in the light-off mode, when the voltage (Vc) of the capacitor (57) is relatively high, the discharge path (58) is conductive, allowing the charge stored in the capacitor (57) to be discharged. This makes it possible to suppress discharge of the charge stored in the capacitor (57) (i.e., unnecessary discharge) when the voltage (Vc) of the capacitor (57) is sufficiently low.

[0122] In the lighting device (30) of the third aspect, in the second aspect, the switching element (59) cuts off the discharge path (58) in the extinguishment mode when the voltage (Vc) of the capacitor (57) becomes equal to or lower than the first threshold voltage (VF3).

[0123] According to this configuration, when the voltage (Vc) of the capacitor (57) becomes equal to or lower than the first threshold voltage (VF3) and the light source (80) is definitely turned off, the discharge path (58) can be blocked to stop the discharge of the charge stored in the capacitor (57). This makes it possible to prevent the discharge of the charge stored in the capacitor (57) (i.e., unnecessary discharge) when the light source (80) is already turned off.

[0124] In the lighting device (30) of the fourth aspect, in the second or third aspect, the switching element (59) cuts off the discharge path (58) when the dimming level of the dimming signal is not the light-off level.

[0125] According to this configuration, when the dimming level of the dimming signal is not the extinguishing level (i.e., when the light source (80) is on), the charge stored in the capacitor (57) can be prevented from being discharged through the discharge path (58).

[0126] The lighting device (30) of a fifth aspect is any one of the second to fourth aspects, further including a first resistor (R3). The first resistor (R3) is provided in the discharge path (58) and connected in series with the switching element (59). The detection circuit (55) has a plurality of second resistors (R1, R2) for detecting the voltage (Vc) of the capacitor (57). The resistance value of the first resistor (R3) is smaller than the resistance value of a combined resistance of the plurality of second resistors (R1, R2) of the detection circuit (55).

[0127] This configuration can prevent the charge stored in the capacitor (57) from flowing to the detection circuit (55) and discharging.

[0128] In the lighting device (30) of the sixth aspect, in any one of the first to fifth aspects, the capacitor (57) includes an electrolytic capacitor.

[0129] According to this configuration, the capacitor (57) can be an electrolytic capacitor, which is readily available.

[0130] The lighting device (30) of a seventh aspect is any one of the first to fifth aspects, further comprising a plurality of capacitors (C1 to Cn) including a capacitor (57). The plurality of capacitors (C1 to Cn) are connected in parallel with each other.

[0131] According to this configuration, by using a plurality of capacitors (C1 to Cn) connected in parallel, it is possible to reduce the overall discharge time of the plurality of capacitors (C1 to Cn).

[0132] The lighting device (10) of the eighth aspect includes the lighting device (30) of any one of the first to seventh aspects and a light source (80).

[0133] According to this configuration, it is possible to provide a lighting device (10) including the lighting device (30).

[0134] A lighting control method of a ninth aspect is a method for controlling a lighting device (30) that supplies a direct current to a light source (80) including a solid-state light-emitting element. The lighting device (30) includes a converter circuit (40). The converter circuit (40) supplies a direct current to the light source (80) based on a dimming signal indicating a dimming level of the light source (80). The converter circuit (40) includes a capacitor (57), a discharge path (58), and a switching element (59). The capacitor (57) is connected in parallel to the light source (80). The discharge path (58) is connected in parallel to the capacitor (57). The switching element (59) is provided in the discharge path (58) and conducts and cuts off the discharge path (58). The lighting control method includes a control step. In the control step, the switching element (59) is controlled to conduct the discharge path (58) in an off mode in which the dimming level of the dimming signal is an off level.

[0135] According to this configuration, the switching element (59) is controlled to conduct the discharge path (58) in the extinction mode. Therefore, in the extinction mode, the charge stored in the capacitor (57) flows through the discharge path (58) and is quickly discharged. That is, the voltage (Vc) of the capacitor (57) quickly drops. As a result, the light source (80) can be quickly turned off.

[0136] A program according to a tenth aspect is a program for causing one or more processors to execute the lighting control method according to the ninth aspect.

[0137] According to this configuration, it is possible to provide a program for executing the lighting control method. [Explanation of symbols]

[0138] 10. Lighting equipment 30 Lighting Device 40 Converter Circuit 55 Detection circuit 57 Capacitor 58 Discharge path 59 Switching element 80 light source C1~Cn capacitors R1, R2 resistance (second resistance) R3 resistance (1st resistance) Vc Capacitor voltage VF1 Light-on forward voltage (light-on voltage) VF3 threshold voltage (first threshold voltage)

Claims

1. A lighting device that supplies direct current to a light source including a solid-state light emitting element, a converter circuit for supplying a direct current to the light source based on a dimming signal indicating a dimming level of the light source; The converter circuit a capacitor connected in parallel with the light source; a discharge path connected in parallel to the capacitor; a switching element provided in the discharge path to connect and disconnect the discharge path, The switching element conducts the discharge path in a light-off mode in which the dimming level of the dimming signal is a light-off level. Lighting device.

2. a detection circuit connected in parallel to the capacitor for detecting a voltage of the capacitor; the switching element conducts the discharge path when the voltage of the capacitor is greater than a first threshold voltage in the light-off mode; The first threshold voltage is a predetermined voltage equal to or lower than a lighting start voltage at which the light source starts to light. The lighting device according to claim 1 .

3. the switching element cuts off the discharge path when the voltage of the capacitor becomes equal to or lower than a first threshold voltage in the light-off mode; The lighting device according to claim 2 .

4. The switching element cuts off the discharge path when the dimming level of the dimming signal is not a light-off level. The lighting device according to claim 2 or 3.

5. a first resistor provided in the discharge path and connected in series with the switching element; the detection circuit includes a plurality of second resistors for detecting the voltage across the capacitor; a resistance value of the first resistor is smaller than a resistance value of a combined resistor obtained by combining the plurality of second resistors of the detection circuit; The lighting device according to claim 2 or 3.

6. The capacitor includes an electrolytic capacitor. The lighting device according to any one of claims 1 to 3.

7. Further comprising a plurality of capacitors including the capacitor; The plurality of capacitors are connected in parallel with each other. The lighting device according to any one of claims 1 to 3.

8. The lighting device according to any one of claims 1 to 3, The light source, Lighting equipment.

9. A lighting control method for controlling a lighting device that supplies direct current to a light source including a solid-state light emitting element, the lighting device includes a converter circuit that supplies a direct current to the light source based on a dimming signal indicating a dimming level of the light source; The converter circuit a capacitor connected in parallel with the light source; a discharge path connected in parallel to the capacitor; a switching element provided in the discharge path to connect and disconnect the discharge path, The lighting control method includes a control step of controlling the switching element to conduct the discharge path in a light-off mode in which the dimming level of the dimming signal is a light-off level. Lighting control method.

10. A program for causing one or more processors to execute the lighting control method according to claim 9.

Images