LIGHTING DEVICE, LIGHTING FIXTURE, LIGHTING SYSTEM AND PROGRAM

Abstract

Lighting device (1) comprising: a supply circuit (11) configured to supply a first current (I1) according to a dimming ratio to a solid-state light source (3) to cause the solid-state light source (3) to emit light in an amount according to the dimming ratio; a constant current circuit (12) connected in parallel to the solid-state light source (3); and a control circuit (13) configured to control the supply circuit (11) and the constant current circuit (12) to cause the solid-state light source (3) to emit light in the amount according to the dimming ratio, wherein, the control circuit (13) controls the supply circuit (11) to cause the supply circuit (11) to continuously output an output current (Io) greater than the first current (I1), and controls the constant current circuit (12) to allow a second current (I2), which is a difference between the output current (Io) and the first current (I1), to continuously flow through the constant current circuit (12), wherein the second current (I2) has a constant value regardless of the dimming ratio.

Description

Technical area

[0001] The present invention relates to lighting devices, lighting fixtures, lighting systems and programs, and more particularly to a lighting device configured to illuminate a solid-state light source, a lighting fixture including the lighting device and the solid-state light source, a lighting system including the lighting fixture, and a program used for the lighting device. State of the art

[0002] Various types of lighting devices have been known which are configured to dim and illuminate a solid-state light source, such as a light-emitting diode (LED) element or an organic electroluminescence (EL) element (see, for example, JP 2015-225825 A). The known lighting device is configured to dim and illuminate the solid-state light source to control the output current by a continuous dimming method in a region in which an output current is large (high dimming ratio region) and to control the output current by a burst dimming method in a region in which the output current is small (low dimming ratio region).

[0003] However, in the known lighting device, a current supplied to the solid-state light source (solid-state light-emitting element), a voltage applied to the solid-state light source (solid-state light-emitting element), or an input voltage to a switching circuit may cause a state where the output current cannot be controlled with the resolution of burst dimming when the output current is controlled by the burst dimming method. For example, the output current cannot be controlled during an off period of a MOSFET (switching element) of the circuit.

[0004] In the case described above, the output current does not change to follow the specified value of a dimming signal, even if the specified value of the dimming signal is changed. Performing a fade-in or fade-out operation results in a condition where shimmering (flickering) of light is easily observed during burst dimming. This is a major disadvantage for lighting fixtures used to produce scenic effects.

[0005] US 2014 / 0184076 A1 describes a dimmable lighting device. A driver is connectable to an external power supply and configured to output a variable drive current for one or more loads, such as LEDs. A low-intensity dimming module can divert some or all of the drive current from the LEDs when a user selects a very low light intensity, allowing the driver to maintain a constant minimum load.

[0006] JP 2013-196759 A describes an LED lighting device. It comprises a constant current supply with a switching element and outputs a constant current by switching this switching element. The LED lighting device comprises a light-emitting diode that emits light in response to an output current from the constant current supply. The LED lighting device has a current path connected to the constant current supply in parallel with the light-emitting diode and splitting the output current from the constant current supply. The LED lighting device has a dimming control circuit that dims the light-emitting diode by increasing and decreasing a current flowing in the current path.

[0007] DE 10 2016 208 069 A1 describes an operating device for operating a light-emitting diode array with at least one light-emitting diode, the operating device comprising: an output for electrically connecting the light-emitting diode array with the at least one light-emitting diode to the operating device; at least one converter stage for providing an operating current at the output of the operating device for the at least one light-emitting diode of the light-emitting diode array connectable to the operating device; a bypass circuit connected in parallel to the output of the operating device and configured to receive a current; and a control circuit configured for amplitude dimming of the at least one light-emitting diode of the light-emitting diode array connectable to the output of the operating device, by controlling the at least one converter stage and the bypass circuit to adjust the amplitude of the operating current according to a dimming value to be achieved. Brief description of the invention

[0008] In view of the foregoing, an object of the present invention is to provide a lighting device, a lighting fixture, a lighting system and a program that enable smooth changing of a light emitted from a solid-state light source even with a relatively low dimming ratio.

[0009] The above object is achieved by a lighting device according to claim 1, a lighting fixture according to claim 7, a lighting system according to claim 8 and a program according to claim 9. Claims 2 to 6 relate to particularly advantageous realizations of the lighting device according to claim 1.

[0010] A lighting device according to one aspect of the present invention includes a supply circuit, a constant current circuit, and a control circuit. The supply circuit is configured to supply a first current according to a dimming ratio to a solid-state light source to cause the solid-state light source to emit light in an amount according to the dimming ratio. The constant current circuit is connected in parallel to the solid-state light source. The control circuit is configured to control the supply circuit and the constant current circuit to cause the solid-state light source to emit light in the amount according to the dimming ratio.At least when the dimming ratio is less than a threshold, the control circuit controls the supply circuit to cause the supply circuit to continuously output an output current greater than the first current and controls the constant current circuit to allow a second current, which is a difference between the output current and the first current, to continuously flow through the constant current circuit.

[0011] A lighting fixture according to one aspect of the present invention includes the lighting device and the solid-state light source.

[0012] A lighting system according to one aspect of the present invention includes a plurality of lighting fixtures and a controller. The controller is configured to transmit a dimming signal indicating the dimming ratio to the lighting fixtures.

[0013] A program according to one aspect of the present invention is a program for causing a computer included in the control circuit of the lighting device to realize, at least when the dimming ratio is less than the threshold value, a function of controlling the supply circuit to cause the supply circuit to continuously output the output current greater than the first current and controlling the constant current circuit to allow the second current, which is a difference between the output current and the first current, to continuously flow through the constant current circuit. Short description of the drawings Fig. 1 is a circuit diagram illustrating a lighting device according to a first embodiment of the present invention; Fig. 2 is an exemplary diagram illustrating the operation of the lighting device; Fig. 3 is an exemplary diagram illustrating the operation of a lighting device according to a second embodiment of the present invention; Fig. Fig. 4 is a perspective view illustrating a lighting fixture according to a third embodiment of the present invention; and Fig. 5 is a block diagram illustrating a lighting system according to a fourth embodiment of the present invention.

[0014] The second embodiment does not fall within the wording of the claims, but is considered to facilitate the understanding of the invention. Description of embodiments

[0015] Hereinafter, lighting devices according to first and second embodiments, a lighting fixture according to a third embodiment, and a lighting system according to a fourth embodiment will be described with reference to the drawings. (First embodiment)

[0016] As in Fig. As shown in Figure 1, a lighting device 1 according to a first embodiment is configured to illuminate a solid-state light source 3 by using electric current from a power supply 2. The lighting device 1 is used in a lighting fixture, for example, for illuminating scenic effects.

[0017] The power supply 2 is, for example, an AC power supply whose power supply voltage has a frequency of 60 Hz or 50 Hz. The power supply 2 supplies the power supply voltage to the lighting device 1.

[0018] The solid-state light source 3 includes solid-state light emitting elements 31 (in Fig. 1 three solid-state light-emitting elements 31). The solid-state light-emitting elements 31 form a series circuit. Each solid-state light-emitting element 31 is, for example, a light-emitting diode. The solid-state light-emitting elements 31 are red light-emitting diodes, such as light-emitting diodes that emit red light (visible light with a wavelength of, for example, 615 nm to 635 nm). The solid-state light-emitting elements 31 may be green light-emitting diodes that emit green light (visible light with a wavelength of, for example, 520 nm to 535 nm). The solid-state light-emitting elements 31 may be blue light-emitting diodes that emit blue light (visible light with a wavelength of, for example, 464 nm to 475 nm). Furthermore, each solid-state light-emitting element 31 does not have to be a light-emitting diode, but can be, for example, an organic electroluminescent element.

[0019] The lighting device 1 according to the first embodiment includes a supply circuit 11, a constant current circuit 12, and a control circuit 13. As a method for dimming the solid-state light source 3 by the lighting device 1, a continuous dimming method (DC dimming method) for increasing and decreasing a DC current supplied to the solid-state light source 3 is used. That is, the continuous dimming method is a method of changing the intensity of a first current I1 continuously supplied to the solid-state light source 3.

[0020] The supply circuit 11 is configured to supply the first current I1 to the solid-state light source 3 according to a dimming ratio, so as to cause the solid-state light source 3 to emit light in an amount corresponding to the dimming ratio. The supply circuit 11 includes an input filter 14, a rectifier circuit 15, a step-up chopper circuit 16, and a step-down chopper circuit 17.

[0021] The input filter 14 is configured to remove unnecessary frequency components, such as noise. Specifically, the input filter 14 includes a high-frequency rejection filter and is configured, for example, to allow the passage of frequency components (60 Hz or 50 Hz) of a power supply voltage of the power supply 2 and to reject a harmonic component. Furthermore, the input filter 14 is configured to reject the harmonic component to prevent the harmonic component of the step-up chopper circuit 16 or the like from reaching the power supply 2.

[0022] Rectifier circuit 15 rectifies (performs full-wave rectification or half-wave rectification of) an AC voltage input via input filter 14 to output a rectified voltage from a pair of output terminals. Rectifier circuit 15 includes, for example, a diode bridge.

[0023] The step-up chopper circuit 16 is configured as a power factor correction circuit. The step-up chopper circuit 16 includes a switching element Q1, an inductor (choke coil) L1, a resistor R1, a diode D1, and a smoothing capacitor C1. The switching element Q1 includes, for example, an n-channel enhancement-mode MOSFET (field-effect transistor). The rectifier circuit 15 has a high-potential side connected to a series circuit of the inductor L1 and the diode D1. More specifically, the series circuit of the inductor L1 and the diode D1 is electrically connected to the high-potential side output terminal of the rectifier circuit 15. Furthermore, a series circuit of the switching element Q1 and the resistor R1 is connected between the output terminal of the rectifier circuit 15 via the inductor L1. Furthermore, the smoothing capacitor C1 is connected between the output terminals of the step-up chopper circuit 16.Turning the switching element Q1 on and off generates a boost voltage across the smoothing capacitor C1.

[0024] The step-down chopper circuit 17 includes a switching element Q2, an inductor L2, a diode D2, a smoothing capacitor C2, and a resistor R2. The switching element Q2 is, for example, an n-channel enhancement-mode MOSFET (field-effect transistor). In the step-down chopper circuit 17, the switching element Q2, the inductor L2, the smoothing capacitor C2, and the resistor R2 are electrically connected in series in this order between the output terminals of the step-up chopper circuit 16 (between both ends of the smoothing capacitor C1). A series circuit of the switching element Q2, the diode D2, and the resistor R2 is electrically connected between the output terminals of the step-up chopper circuit 16 (between both ends of the smoothing capacitor C1). Furthermore, a series circuit of the inductor L2 and the smoothing capacitor C2 is electrically connected between the anode and the cathode of the diode D2.The solid-state light source 3 is electrically connected between both ends of the smoothing capacitor C2.

[0025] The smoothing capacitor C2 is electrically connected in parallel to an output, that is, the solid-state light source 3, of the step-down chopper circuit 17. Therefore, the difference between a peak and a bottom value of an output current Io is reduced, and the waveform of the output current Io approaches a DC waveform including a few current ripples. At this time, a voltage across the smoothing capacitor C2 is substantially equal to a forward voltage of the solid-state light source 3. In the present embodiment, the output current Io is equal to the sum of the first current I1, which is a forward current of the solid-state light source 3, and a second current I2 flowing through the constant current circuit 12. The forward voltage of the solid-state light source 3 is determined according to forward current-forward voltage characteristics of the solid-state light source 3 and the dimming ratio.

[0026] The constant current circuit 12 is electrically connected in parallel with the solid-state light source 3. The constant current circuit 12 includes two resistors R3 and R4 and a switching element Q3. Between the two ends of the smoothing capacitor C2 of the step-down chopper circuit 17, the resistor (resistant element) R4, the switching element Q3, and the resistor R3 are electrically connected in series in this order. The resistor R4 is connected to a high-potential side of the step-down chopper circuit 17, and the resistor R3 is connected to a low-potential side of the step-down chopper circuit 17. More specifically, the resistor R4 is electrically connected to an output terminal on the high-potential side of the step-down chopper circuit 17, and the resistor R3 is electrically connected to an output terminal on the low-potential side of the step-down chopper circuit 17.The switching element Q3 is, for example, an n-channel enhancement-mode MOSFET (field-effect transistor). The switching element Q3 operates in a linear region (active region) in response to a constant current control signal S3, which will be described below. In other words, the switching element Q3 increases and decreases a drain current, which is the second current I2 flowing through the constant current circuit 12, in response to the constant current control signal S3. According to the specified value of the constant current control signal S3, the magnitude of the second current I2 flowing through the constant current circuit 12 is adjusted.

[0027] The control circuit 13 is configured to control the supply circuit 11 and the constant current circuit 12 to cause the solid-state light source 3 to emit light in an amount according to the dimming ratio. The control circuit 13 includes a voltage boost control circuit 131, a controller 132, a voltage drop control circuit 133, and a constant current control circuit 134. The control circuit 13 controls the supply circuit 11 and the constant current circuit 12 by the continuous dimming method, regardless of the dimming ratio.

[0028] A dimming signal S1 input to the control circuit 13 from the outside is a pulse width modulation (PWM) signal, which is a duty cycle (ratio of an on-period to a cycle) that varies according to the dimming ratio. The control circuit 13 receives the dimming signal S1 from an external device, such as a controller, called a dimming control panel, for example. The dimming signal S1 can be a signal conforming to a standardized communication protocol, such as DMX512. Alternatively, the dimming signal S1 can be a signal conforming to a wired communication scheme, such as Universal Asynchronous Transmitter (UART).

[0029] The voltage boost control circuit 131 is configured to perform switching control of turning on and off the switching element Q1 to control the voltage boost operation of the step-up chopper circuit 16. Specifically, the voltage boost control circuit 131 is configured to detect a voltage across the resistor R1 and control the duty cycle of the switching element Q1 such that the voltage across the smoothing capacitor C1 is constant. The voltage boost control circuit 131 compares a current, which is detected by a current detector (not shown) and flows through the inductor L1, with a threshold value to determine a turn-on time of the switching element Q1. Further, the voltage boost control circuit 131 compares the voltage across the resistor R1 (a current flowing through the switching element Q1) with the threshold value to determine a turn-off time of the switching element Q1.The voltage boost control circuit 131 sets the turn-on timing and the turn-off timing of the switching element Q1 to control a boost voltage generated across the smoothing capacitor C1 to be a predetermined voltage.

[0030] The controller 132 includes a microcontroller including a processor, such as a central processing unit (CPU), and a memory. The controller 132 is configured such that a program stored in the memory is executed by the processor (CPU) to control the step-down chopper circuit 17 to dim the light emitted by the solid-state light source 3. The controller 132 externally receives the dimming signal S1 and operates to match the brightness of the light emitted by the solid-state light source 3 with the brightness required by the dimming signal S1.

[0031] The controller 132 stores a dimming table in advance. The dimming table shows the relationship between the duty cycle of the dimming signal S1 and the dimming ratio. The dimming ratio decreases as the duty cycle of the dimming signal S1 increases. Specifically, when the dimming signal S1 has a duty cycle of 0% to 5%, the dimming ratio is 100% (full illumination), while when the dimming signal S1 has a duty cycle of 95% to 100%, the dimming ratio is 0% (light off). When the dimming signal S1 has a duty cycle of 5% to 95%, the dimming ratio decreases as the duty cycle of the dimming signal S1 increases. The previously described relationship (the relationship between the duty cycle of the dimming signal S1 and the dimming ratio) stored in the controller 132 is not limited to the dimming table, but may be a function.

[0032] When the dimming signal S1 is received from the outside, the controller 132 refers to the dimming table to determine a dimming ratio according to the duty cycle of the dimming signal S1. The controller 132 generates a voltage-down control signal S2 according to the determined dimming ratio and outputs the voltage-down control signal S2 to the voltage-down control circuit 133. The voltage-down control signal S2 is a signal indicating the dimming ratio.

[0033] The voltage-down control circuit 133 performs switching control of turning on and off the switching element Q2 of the step-down chopper circuit 17 based on the voltage-down control signal S2 to control the voltage-down operation of the step-down chopper circuit 17. Specifically, the voltage-down control circuit 133 compares a current, which is detected by a current detector (not shown) and flows through the inductor L2, with the threshold value to determine a turn-on timing of the switching element Q2. Further, the voltage-down control circuit 133 compares a voltage across the resistor R2 (a current flowing through the switching element Q2) with the threshold value to determine a turn-off timing of the switching element Q2. That is,The voltage-step-down control circuit 133 adjusts the turn-on and turn-off timing of the switching element Q2 according to the dimming ratio specified by the voltage-step-down control signal S2. Thus, the voltage-step-down control circuit 133 controls the step-down chopper circuit 17 such that the current (output current Io) flowing through the solid-state light source 3 has a current value according to the dimming ratio.

[0034] Here, in the control circuit 13, at least when the dimming ratio is less than the threshold, the controller 132 controls the supply circuit 11 to cause the supply circuit 11 to continuously output the output current Io that is greater than the first current I1. Further, at least when the dimming ratio is less than the threshold, the controller 132 controls the constant current circuit 12 to allow the second current I2, which is a difference between the output current Io and the first current I1, to continuously flow through the constant current circuit 12, maintaining the second current I2 to have a prescribed value. Here, "when the dimming ratio is less than the threshold" means the case where the dimming ratio is greater than 0% and less than the threshold.

[0035] In the control circuit 13 of the first embodiment, the controller 132 controls the supply circuit 11 to continuously output the output current Io greater than the first current I1, and controls the constant current circuit 12 to allow the second current I2 to continuously flow through the constant current circuit 12, regardless of the magnitude of the dimming ratio. That is, when the dimming ratio is less than the threshold value, the supply circuit 11 continuously outputs the output current Io having a current value greater than the first current I1, and the second current I2, whose current value is a constant value, continuously flows through the constant current circuit 12.

[0036] At least when the dimming ratio determined according to the dimming signal S1 is less than the threshold value, the controller 132 outputs a constant current control signal S3 to the constant current control circuit 134. In the first embodiment, the controller 132 outputs the constant current control signal S3 to the constant current control circuit 134 regardless of the value of the dimming ratio determined according to the dimming signal S1. In other words, the controller 132 outputs the constant current control signal S3 to the constant current control circuit 134 if the dimming ratio is less than the threshold value or the dimming ratio is greater than or equal to the threshold value. The constant current control signal S3 is a signal indicating the magnitude (current value) of the second current I2 that will flow through the constant current circuit 12.The constant current control signal S3 of the first embodiment is, for example, a PWM signal that has a constant duty cycle regardless of the dimming ratio. That is, the second current I2 flowing through the constant current circuit 12 has a constant value (fixed value) regardless of the dimming ratio.

[0037] The constant current control circuit 134 controls the switching element Q3 of the constant current circuit 12 to operate in the linear region by using the constant current control signal S3 from the controller 132. The constant current control circuit 134 adjusts the gate-source voltage value of the switching element Q3 such that the second current I2, which will flow through the constant current circuit 12, has a constant value.

[0038] In the first embodiment, the control circuit 13 includes a computer including a processor and a memory, and stores a program for causing the computer to realize the above-described function.

[0039] Next, the lighting device 1 according to the first embodiment will be described with respect to Fig. 2 described.

[0040] First, when the controller 132 of the control circuit 13 receives the dimming signal S1 indicating a specific dimming ratio, it refers to the dimming table to determine a dimming ratio according to the duty cycle of the dimming signal S1. Then, the controller 132 adjusts the output current Io output from the step-down chopper circuit 17 such that the first current I1 flowing through the solid-state light source 3 has a current value corresponding to the dimming ratio. That is, as shown in Fig. 2, the controller 132 outputs the voltage reduction control signal S2 to the voltage reduction control circuit 133 such that the output current Io is the sum of the first current I1 flowing through the solid-state light source 3 and the second current I2 flowing through the constant current circuit 12.

[0041] For example, it is assumed that the first current I1 required for full illumination of the solid-state light source 3 is 500 mA (in Fig. 2, Fig. 100%), and the second current I2 flowing through the constant current circuit 12 is 50 mA (in Fig. 2, Fig. 10%). In order to achieve full illumination (dimming ratio 100%) of the solid-state light source 3, the controller 132 outputs the voltage reduction control signal S2 to the voltage reduction control circuit 133 such that the output current Io is 550 mA (in Fig. 2, Fig. 110%). In order to set the first current I1 to the solid-state light source 3 to 50 mA (10% of the current in the case of full illumination), the controller 132 outputs the voltage reduction control signal S2 to the voltage reduction control circuit 133 such that the output current Io is 100 mA (in Fig. 2, Fig. 20%).

[0042] The voltage-step-down control circuit 133 adjusts the turn-on and turn-off timings of the switching element Q2 based on the voltage-step-down control signal S2. Thus, the step-down chopper circuit 17 controls the output current Io to have a current value corresponding to the determined dimming ratio and outputs the output current Io to the solid-state light source 3 and the constant-current circuit 12.

[0043] Further, when the controller 132 receives the dimming signal S1, it outputs the constant current control signal S3 to the constant current control circuit 134 such that the second current I2, which has a constant value, flows through the constant current circuit 12. The constant current control circuit 134 controls the switching element Q3 to operate in the linear region based on the constant current control signal S3. As a result, the second current I2, which has the constant value, flows through the constant current circuit 12.

[0044] As described above, the first current I1 obtained by subtracting the second current I2 flowing through the constant current circuit 12 from the output current Io of the step-down chopper circuit 17 flows through the solid-state light source 3. That is, the first current I1 according to the dimming ratio flows through the solid-state light source 3. Thus, the solid-state light source 3 can be illuminated with a brightness according to the dimming ratio.

[0045] The lighting device 1 according to the first embodiment described above includes the supply circuit 11, the constant current circuit 12, and the control circuit 13. The supply circuit 11 is configured to supply the first current I1 according to the dimming ratio to the solid-state light source 3 to cause the solid-state light source 3 to emit light in an amount according to the dimming ratio. The constant current circuit 12 is electrically connected in parallel to the solid-state light source 3. The control circuit 13 is configured to control the supply circuit 11 and the constant current circuit 12 to cause the solid-state light source 3 to emit light in an amount according to the dimming ratio. At least when the dimming ratio is less than the threshold value, the control circuit 13 controls the supply circuit 11 to cause the supply circuit 11 to continuously output the output current Io that is greater than the first current I1.Furthermore, at least when the dimming ratio is smaller than the threshold value, the control circuit 13 controls the constant current circuit 12 to allow the second current I2, which is a difference between the output current Io and the first current I1, to flow continuously through the constant current circuit 12.

[0046] At least when the dimming ratio is less than the threshold, the lighting device 1 according to the first embodiment controls the supply circuit 11 to cause the supply circuit 11 to output the output current Io that is greater than the first current I1 supplied to the solid-state light source 3. Further, at least when the dimming ratio is less than the threshold, the lighting device 1 controls the constant current circuit 12 to allow the second current I2, which is the difference between the output current Io and the first current I1, to flow through the constant current circuit 12. Thereby, the lighting device 1 according to the first embodiment enables a reduction in the flicker of a light output from the solid-state light source 3 compared to the case of burst dimming, even when the dimming ratio is relatively low, such as in the case of a fade-in or fade-out operation.Consequently, it is possible to smoothly change the light output from the solid-state light source 3. That is, the lighting device 1 according to the first embodiment enables improvement in the fade-in and fade-out performance at the time of the fade-in or fade-out operation.

[0047] Furthermore, when a continuous dimming method is used as a dimming method of the solid-state light source 3 by the lighting device 1, a small-capacity capacitor can be used as the smoothing capacitor C2, unlike a burst dimming method. More specifically, the burst dimming method requires a large-capacity capacitor as a smoothing capacitor as a countermeasure to video flicker. In contrast, the present embodiment uses the continuous dimming method and thus does not require a large-capacity capacitor as the smoothing capacitor C2, but a small-capacity capacitor is sufficient as a countermeasure. Thus, it is possible to reduce the charging time of the smoothing capacitor C2. Consequently, the output current Io and the first current I1 can be adjusted to the current value corresponding to the dimming ratio in a short period of time.Thus, at the time of fading in or out operation, the light output from the solid-state light source 3 can be changed more smoothly.

[0048] In the lighting device 1 according to the first embodiment, the second current I2 preferably has a constant value regardless of the dimming ratio. The control circuit 13 preferably controls the supply circuit 11 to cause the supply circuit 11 to continuously output the output current Io that is greater than the first current I1, and preferably controls the constant current circuit 12 to allow the second current I2 to continuously flow through the constant current circuit 12 regardless of the strength of the dimming ratio.

[0049] In the lighting device 1 according to the first embodiment, the constant current circuit 12 preferably includes the switching element Q3. The switching element Q3 is electrically connected to the output terminal of the supply circuit 11. The control circuit 13 preferably controls the switching element Q3 to change the intensity of the second current I2.

[0050] In the lighting device 1 according to the first embodiment, the constant current circuit 12 preferably includes a resistive element (resistor R4). The resistive element is electrically connected in series with the switching element Q3.

[0051] In the lighting device 1 according to the first embodiment, in the constant current circuit 12, the switching element Q3 and the resistive element (resistor R4) are electrically connected in series. This can reduce the voltage applied to the switching element Q3, and therefore the loss at the switching element Q3 can be reduced.

[0052] In the lighting device 1 according to the first embodiment, the switching element Q3 is preferably electrically connected to the output terminal of the supply circuit 11 to allow the second current I2 to flow through the switching element Q3.

[0053] Further, in the lighting device 1 according to the first embodiment, the control circuit 13 preferably operates the switching element Q3 in the linear region to change the intensity of the second current I2.

[0054] Furthermore, in the lighting device 1 according to the first embodiment, the control circuit 13 preferably controls the supply circuit 11 and the constant current circuit 12 by the continuous dimming method regardless of the dimming ratio. The continuous dimming method is a method of changing the intensity of the first current I1 continuously supplied to the solid-state light source 3.

[0055] The program according to the first embodiment is a program for causing the computer included in the control circuit 13 of the lighting device 1 to realize the following function. The function is a function of, at least when the dimming ratio is less than the threshold value, controlling the supply circuit 11 to continuously output the output current Io greater than the first current I1 and controlling the constant current circuit 12 to continuously allow the second current I2, which is the difference between the output current Io and the first current I1, to flow through the constant current circuit 12. (Second embodiment)

[0056] A lighting device 1 according to a second embodiment differs from the lighting device 1 according to the first embodiment in that a second current I2 flows through a constant current circuit 12 only when a dimming ratio is less than a threshold. The same components as those of the lighting device 1 according to the first embodiment are denoted by the same reference numerals, and the description thereof will be omitted.

[0057] A control circuit 13 of the second embodiment controls the constant current circuit 12 to allow the second current I2 to flow through the constant current circuit 12 only when the dimming ratio is less than the threshold. Descriptions of functions similar to those of the control circuit 13 of the first embodiment will be omitted.

[0058] Specifically, when the dimming ratio is greater than or equal to the threshold value, the control circuit 13 controls a supply circuit 11 such that the magnitude of an output current Io corresponds to the magnitude of a first current I1, and controls the constant current circuit 12 to prevent the second current I2 from flowing through the constant current circuit 12, while when the dimming ratio is less than the threshold value, the control circuit 13 controls the supply circuit 11 such that the output current Io is greater than the first current I1, and controls the constant current circuit 12 to allow the second current I2 to continuously flow through the constant current circuit 12.

[0059] A controller 132 of the second embodiment outputs a constant current control signal S3 to a constant current control circuit 134 only when the dimming ratio is less than the threshold value. The controller 132 of the second embodiment stores a dimming table representing the relationship between the duty cycle of the constant current control signal S3 and the dimming ratio. That is, the dimming table represents the relationship between the second current I2 and the dimming ratio. Specifically, the dimming table defines the relationship between the second current I2 and the dimming ratio such that the second current I2 is 0 when the dimming ratio is greater than or equal to the threshold value, and that the current value of the second current I2 increases as the dimming ratio decreases when the dimming ratio is less than the threshold value.

[0060] The control circuit 13 of the second embodiment controls the constant current circuit 12 by using the dimming table to increase the second current I2 with decreasing dimming ratio when the dimming ratio is smaller than the threshold value.

[0061] Next, the operation of the lighting device 1 according to the second embodiment will be described with respect to Fig. 3. The threshold is defined as a dimming ratio for the case where the first current I1 is 50 mA (10% of the current in the case of full illumination).

[0062] First, when the controller 132 of the control circuit 13 receives a dimming signal S1 indicating a specific dimming ratio, it determines the dimming ratio according to the duty cycle of the dimming signal S1 with reference to the dimming table. Then, the controller 132 adjusts the output current Io output from a step-down chopper circuit 17 such that the first current I1 flowing through a solid-state light source 3 has a current value corresponding to the dimming ratio. That is, as shown in Fig. 3, when the dimming ratio is greater than or equal to the threshold, the controller 132 outputs the voltage-down control signal S2 to a voltage-down control circuit 133 such that the output current Io is the sum of the first current I1 flowing through the solid-state light source 3 and the second current I2 flowing through the constant-current circuit 12. On the other hand, when the dimming ratio is less than the threshold, the second current I2 does not flow through the constant-current circuit 12, and therefore the controller 132 outputs the voltage-down control signal S2 to the voltage-down control circuit 133 such that the output current Io corresponds to the first current I1 flowing through the solid-state light source 3.

[0063] The voltage-step-down control circuit 133 adjusts the turn-on and turn-off timings of a switching element Q2 based on the voltage-step-down control signal S2. Thus, the step-down chopper circuit 17 controls the output current Io to have a current value corresponding to the determined dimming ratio and outputs the output current Io to the solid-state light source 3 and the constant-current circuit 12.

[0064] Furthermore, when the dimming signal S1 is received, as in Fig. 3, the controller 132 outputs the constant current control signal S3 to the constant current control circuit 134 such that the second current I2 flows through the constant current circuit 12 only when the dimming ratio is less than the threshold value. The constant current control circuit 134 controls a switching element Q3 to operate in a linear region based on the constant current control signal S3. Thus, the second current I2, which has a constant value, flows through the constant current circuit 12. On the other hand, when the dimming ratio is greater than or equal to the threshold value, the controller 132 does not output the constant current control signal S3 to the constant current control circuit 134. The switching element Q3 remains in the off state, and the second current I2 does not flow through the constant current circuit 12.

[0065] According to the above, when the dimming ratio is greater than or equal to the threshold value, the output current Io of the step-down chopper circuit 17 flows through the solid-state light source 3 as the first current I1. On the other hand, when the dimming ratio is less than the threshold value, the first current I1, which is obtained by subtracting the second current I2 flowing through the constant current circuit 12 from the output current Io of the step-down chopper circuit 17, flows through the solid-state light source 3. In either case, the first current I1 flows through the solid-state light source 3 according to the dimming ratio. Thus, the solid-state light source 3 can be illuminated at a brightness according to the dimming ratio.

[0066] For example, it is assumed that the first current I1 required to fully illuminate the solid-state light source 3 is 500 mA (in Fig. 3, Fig. 100%), and the second current I2 flowing through the constant current circuit 12 is 50 mA (in Fig. 3, Fig. 10%). In order to achieve full illumination (dimming ratio 100%) of the solid-state light source 3, the controller 132 outputs the voltage reduction control signal S2 to the voltage reduction control circuit 133 such that the output current Io is 500 mA (in Fig. 3, Fig. 100%). In order to set the first current I1 to the solid-state light source 3 to be less than 50 mA (10% of the current in the case of full illumination), the controller 132 outputs the voltage reduction control signal S2 to the voltage reduction control circuit 133 such that the output current Io is 50 mA (in Fig. 3, Fig. 10%), and the controller 132 outputs the constant current control signal S3 to the constant current control circuit 134.

[0067] Also in the second embodiment, similar to the first embodiment, the control circuit 13 includes a computer including a processor and a memory. The control circuit 13 of the second embodiment stores a program for causing the computer to implement the functions described in the first embodiment and the second embodiment.

[0068] In the lighting device 1 according to the second embodiment described above, when the dimming ratio is greater than or equal to the threshold value, the control circuit 13 preferably controls the supply circuit 11 such that the magnitude of the output current Io corresponds to the magnitude of the first current I1. Further, at least when the dimming ratio is greater than or equal to the threshold value, the control circuit 13 preferably controls the constant current circuit 12 to prevent the second current I2 from flowing through the constant current circuit 12. When the dimming ratio is less than the threshold value, the control circuit 13 preferably controls the supply circuit 11 such that the output current Io is greater than the first current I1.Further, when the dimming ratio is smaller than the threshold value, the control circuit 13 preferably controls the constant current circuit 12 to allow the second current I2 to flow continuously through the constant current circuit 12.

[0069] Furthermore, in the lighting device 1 according to the second embodiment, when the dimming ratio is less than the threshold, the control circuit 13 preferably controls the supply circuit 11 such that the value of the output current Io is constant regardless of the dimming ratio. Furthermore, when the dimming ratio is less than the threshold, the control circuit 13 preferably controls the constant current circuit 12 to increase the second current I2 as the dimming ratio decreases. (Third embodiment)

[0070] With reference to Fig. 4, a lighting fixture 4 according to a third embodiment will be described below. The lighting fixture 4 according to the third embodiment is a so-called horizontal light used to illuminate a background wall surface (horizontal surface) of a studio of a television station, a stage, or the like.

[0071] As in Fig. 4, the lighting fixture 4 according to the third embodiment includes a light source unit 5 as a solid-state light source and a power supply unit 6. The lighting fixture 4 according to the third embodiment will be described below, where the forward and backward directions, the right and left directions and the up and down directions as shown in Fig. 4. That is, in the plane of the sheet of Fig. 4 the left side is defined as the front side and the right side is defined as the back side, and in the plane of the sheet of Fig. 4 the upper side is defined as the left side and the lower side is defined as the right side.

[0072] The light source unit 5 includes four light-emitting diode (LED) modules 50, a first body 51, a reflection block 52, and a heat sink block 53. Each LED module 50 includes solid-state light emitting elements mounted on a surface of a rectangular substrate.

[0073] The first body 51 is made of a metal plate to have a rectangular cuboid shape. The first body 51 has a front surface in which a rectangular window hole 510 is open. In the first body 51, the four LED modules 50 are arranged in two rows and two columns, with surfaces of the LED modules 50 facing the window hole 510.

[0074] The reflection block 52 includes reflectors 520 and a shield 521. The reflectors 520 and the shield 521 are arranged between the window hole 510 and the surfaces of the LED modules 50 in the first body 51 and are configured to control the orientation of the light emitted by the LED modules 50.

[0075] The heat sink block 53 includes heat sinks 530. The heat sinks 530 are arranged at regular intervals along a thickness direction of the heat sinks. The heat sink block 53 is arranged on a rear surface of the first body 51. The heat sink block 53 is preferably thermally connected to each (of substrates) of the four LED modules 50 in the first body 51.

[0076] The power supply unit 6 includes: a circuit block (lighting device 1) including an input filter 14, a rectifier circuit 15, a step-up chopper circuit 16, a step-down chopper circuit 17, a constant current circuit 12, and a control circuit 13; a second body 60 that houses the circuit block; and a pair of arms 61. The circuit block is the lighting device 1 of the first or second embodiment.

[0077] The second body 60 is made of a metal plate to have a flat rectangular cuboid shape for accommodating the circuit block. The pair of arms 61 are provided at respective right and left ends of the second body 60 and protrude upward. Each of the pair of arms 61 has a width in the forward and backward directions, with the width successively narrowing toward the tip end (upper end) of the arm. Each arm 61 has an insertion hole formed in its tip portion, and a bolt of a so-called knob bolt 62 is to be inserted into the through hole. That is, the pair of arms 61 rotatably supports the light source unit 5 by screw bolts inserted into the insertion hole in the tip portion of internally threaded screws provided on both the right and left sides of the first body 51.

[0078] Next, a used state of the lighting fixture 4 according to the third embodiment will be described. The lighting fixture 4 according to the third embodiment is installed, for example, on a floor at a distance from the background wall surface, with the window hole 510 of the light source unit 5 facing the background wall surface. The lighting fixture 4 according to the third embodiment enables substantially uniform irradiation of the background wall surface from its lower portion to its upper portion with illumination light.

[0079] The lighting fixture 4 according to the third embodiment described above includes the lighting device 1 and the solid-state light source (light source unit 5).

[0080] Also, in the lighting fixture 4 according to the third embodiment, at least when the dimming ratio is less than the threshold, the control circuit 13 of the lighting device 1 controls the supply circuit 11 to cause the supply circuit 11 to output an output current Io greater than a first current I1 supplied to the solid-state light source (light source unit 5). Further, at least when the dimming ratio is less than the threshold, the control circuit 13 of the lighting device 1 controls the constant current circuit 12 to allow a second current I2, which is a difference between the output current Io and the first current I1, to flow through the constant current circuit 12.As a result, the lighting fixture 4 according to the third embodiment also enables a reduction in the flickering of light emitted from the solid-state light source compared to the case of burst dimming, even when the dimming ratio is relatively low, such as in the case of fade-in or fade-out operation similar to the first embodiment. Consequently, it is possible to smoothly change the light emitted from the solid-state light source.

[0081] The lighting fixture 4 is not limited to the solid-state light source (light source unit 5) of monochromatic light. As a variation of the third embodiment, the lighting fixture 4 may include a solid-state light source (light source unit) that emits colored light. In this case, the lighting fixture 4 includes, as solid-state light-emitting elements of the solid-state light source, for example, a solid-state light-emitting element that emits red light, a solid-state light-emitting element that emits green light, and a solid-state light-emitting element that emits blue light. Furthermore, the lighting fixture 4 may include a solid-state light-emitting element that emits white light.

[0082] Furthermore, the luminaire 4 is not limited to the horizontal light, but may be a luminaire used in another application. (Fourth embodiment)

[0083] With reference to Fig. 5, a lighting system 7 according to a fourth embodiment will be described below. As shown in Fig. As shown in Figure 5, the lighting system 7 according to the fourth embodiment includes lighting fixtures 4 and a dimming control panel 8 as a controller. The lighting fixtures 4 are connected to the dimming control panel 8 through a feedthrough connection via a communication cable 80. The dimming control panel 8 transmits a dimming signal S1 of a standardized communication protocol, such as DMX512, to the lighting fixtures 4 via the communication cable 80. The lighting fixtures 4 receive the dimming signal S1 transmitted from the dimming control panel 8 via control circuits 13, and the control circuits 13 control the step-down chopper circuits 17 and the constant current circuits 12.

[0084] The lighting system 7 according to the fourth embodiment described above includes the lighting fixtures 4 and the controller (the dimming control panel 8). The controller transmits a dimming signal indicating a dimming ratio to the lighting fixtures 4.

[0085] Also, in the lighting system 7 according to the fourth embodiment, at least when the dimming ratio is less than a threshold value, the control circuit 13 of the lighting device 1 controls a supply circuit 11 to cause the supply circuit 11 to output an output current Io greater than a first current I1 supplied to a solid-state light source 3. Further, at least when the dimming ratio is less than a threshold value, the control circuit 13 of the lighting device 1 controls the constant current circuit 12 to allow a second current I2, which is a difference between the output current Io and the first current I1, to flow through the constant current circuit 12.As a result, the lighting system 7 according to the fourth embodiment also enables a reduction in the flicker of light output from the solid-state light source 3 compared to the case of burst dimming, even when the dimming ratio is relatively low, such as in the case of fade-in or fade-out operation similar to the first embodiment. Consequently, it is possible to smoothly change the light output from the solid-state light source 3.

[0086] The lighting device 1 in each embodiment includes a computer. The computer executes a program to realize the function of the lighting device 1 in each embodiment. The computer includes a processor that operates according to the program as a main hardware configuration. As long as the processor can execute the program to realize the function of the lighting device 1, any type of processor can be used. The processor includes one or more electronic circuits, including a semiconductor integrated circuit (IC) or a large-scale integration (LSI). The electronic circuits may be integrated on a chip or may be provided on chips. The chips may be collected on a device or may be provided as devices.The program is stored in a non-volatile storage medium, such as read-only memory (ROM), an optical disk, or a hard disk. The non-volatile storage medium is a computer-readable storage medium and stores the program in a non-volatile manner. The program can be pre-stored in the non-volatile storage medium or can be supplied to the non-volatile storage medium via a wide-area communications network, such as the Internet.

[0087] The aforementioned first, third, and fourth embodiments are some of several embodiments according to the present invention. In addition, the above first, third, and fourth embodiments can be modified in various ways according to the design, etc., as long as they can achieve the object of the present invention. List of reference symbols 1 lighting device 11 Feed circuit 12 Constant current circuit 13 Control circuit 3 Solid-state light source 4 lighting fixtures 7 Lighting system 8 Dimming control panel (control) I1 First current I2 Second current Io output current Q3 switching element R4 resistance (resistant element)

Claims

[1] Lighting device (1) comprising: a supply circuit (11) configured to supply a first current (I1) according to a dimming ratio to a solid-state light source (3) to cause the solid-state light source (3) to emit light in an amount according to the dimming ratio; a constant current circuit (12) connected in parallel to the solid-state light source (3); and a control circuit (13) configured to control the supply circuit (11) and the constant current circuit (12) to cause the solid-state light source (3) to emit light in the amount according to the dimming ratio, wherein, the control circuit (13) controls the supply circuit (11) to cause the supply circuit (11) to continuously output an output current (Io) greater than the first current (I1), and controls the constant current circuit (12) to allow a second current (I2), which is a difference between the output current (Io) and the first current (I1), to continuously flow through the constant current circuit (12), wherein the second current (I2) has a constant value regardless of the dimming ratio. [2] Lighting device (1) according to claim 1, wherein the constant current circuit (12) includes a switching element (Q3) electrically connected to an output terminal of the supply circuit (11), and the control circuit (13) controls the switching element (Q3) to change a strength of the second current (I2). [3] The lighting device (1) according to claim 2, wherein the constant current circuit (12) includes a resistive element connected in series with the switching element (Q3). [4] The lighting device (1) according to claim 2 or 3, wherein the switching element (Q3) is electrically connected to the output terminal of the supply circuit (11) to allow the second current (I2) to flow through the switching element (Q3). [5] Lighting device (1) according to one of claims 2 to 4, wherein the control circuit (13) operates the switching element (Q3) in a linear range to change the strength of the second current (I2). [6] The lighting device (1) according to any one of claims 1 to 5, wherein the control circuit (13) controls the supply circuit (11) and the constant current circuit (12) by a DC dimming method in which an intensity of the first current (11) continuously supplied to the solid-state light source (3) is changed. [7] Lighting fixtures (4) comprising: the lighting device (1) according to one of claims 1 to 6; and the solid-state light source (3). [8] Lighting system (7) comprising: a plurality of lighting fixtures (4) according to claim 7; and a controller configured to transmit a dimming signal indicating the dimming ratio to the lighting fixtures (4). [9] A program that causes a computer included in the control circuit (13) of the lighting device (1) according to any one of claims 1 to 6 to realize a function of controlling the supply circuit (11) to cause the supply circuit (11) to continuously output the output current (Io) which is greater than the first current (I1), and of controlling the constant current circuit (12) to allow the second current (I2), which is a difference between the output current (Io) and the first current (I1), to continuously flow through the constant current circuit (12), wherein the second current (I2) has a constant value regardless of the dimming ratio.

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