Lighting device and lighting system

Abstract

To provide a lighting device and a lighting system capable of easily and appropriately adjusting a light quantity.SOLUTION: A lighting device 10 includes a plurality of light source units 2 and a bypass circuit 3. The plurality of light source units 2 each are composed of at least one light emitting element 200, and are electrically connected in series. The bypass circuit 3 intermittently bypasses between both ends of part of the light source units 2 among the plurality of light source units 2.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present disclosure relates to a lighting device and a lighting system including a plurality of light-emitting elements.

Background Art

[0002] As related art, for example, a lighting device for a railroad crossing, which includes a light-emitting element such as a light-emitting diode (LED) in a light source unit (light-emitting unit), is known (see, for example, Patent Document 1). The lighting device according to the related art includes a light source unit, a control circuit that controls a current supplied to the light source unit, and a case that houses the light source unit and the control circuit. The lighting fixture is attached to, for example, a support column and supported at an appropriate height for illuminating the railroad crossing.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the configuration of the related art described above, if the current supplied to the light source unit is constant, when the performance (light-emitting efficiency) of the light-emitting element improves, the amount of light emitted from the lighting device may become excessive.

[0005] An object of the present disclosure is to provide a lighting device and a lighting system that can easily adjust the amount of light appropriately.

Means for Solving the Problems

[0006] A lighting device according to an aspect of the present disclosure includes a plurality of light source units and a bypass circuit. Each of the plurality of light source units includes at least one light-emitting element and is electrically connected in series. The bypass circuit intermittently bypasses both ends of some of the plurality of light source units.

[0007] The lighting system according to one aspect of the present disclosure includes the lighting device and a power supply device that supplies power to the plurality of light source units.

Advantages of the Invention

[0008] According to the present disclosure, it is possible to provide a lighting device and a lighting system that can easily adjust the amount of light appropriately.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Modes for Carrying Out the Invention

[0010] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. The following embodiments are an example of embodying the present disclosure and are not intended to limit the technical scope of the present disclosure.

[0011] (Embodiment 1) [1] Overall Configuration First, the overall configuration of the lighting system 100 according to the present embodiment will be described with reference to FIGS. 1 and 2.

[0012] The lighting system 100 includes a lighting device 10 and a power supply device 20. The lighting device 10 includes a plurality of light source units 2 that are electrically connected in series. The power supply device 20 supplies power to the plurality of light source units 2. In the present embodiment, the power supply device 20 receives power supply from the AC power supply AC1 and lights the lighting device 10. The AC power supply AC1 is, for example, a commercial power supply of single-phase 100V, 60Hz.

[0013] In the present embodiment, the lighting system 100 integrally has the lighting device 10 and the power supply device 20 in one housing. That is, the lighting system 100 is a lighting system on the lighting circuit integrated side that can light a plurality of light source units 2 of the lighting device 10 provided in the housing by receiving power supply from the AC power supply AC1.

[0014] This type of lighting system 100 is used in various facilities such as houses, offices, stores, or public facilities (including outdoor facilities), and can illuminate the lighting space by irradiating light from the light source unit 2 to the desired lighting space. In the present embodiment, as an example, it is assumed that the lighting system 100 is a level crossing lighting system installed at a railway level crossing and illuminating the periphery of the level crossing as a lighting space. This lighting system 100 is, for example, a blue projector that outputs blue light having an effect of calming people's minds.

[0015] Here, the plurality of light source units 2 of the lighting device 10 include a light emitting element 200 (see FIG. 2) whose light amount changes according to the magnitude of the supplied current. This light emitting element 200 is, for example, a semiconductor light emitting element such as a light emitting diode (LED: Light Emitting Diode) or an organic EL (Electroluminescence) element. In the present embodiment, as an example, the light emitting element 200 is a blue light emitting diode that outputs blue light.

[0016] Furthermore, each of the plurality of light source units 2 has at least one light emitting element 200. In this embodiment, as an example, the lighting device 10 includes two light source units 2, namely, a first light source unit 21 and a second light source unit 22, as the plurality of light source units 2.

[0017] The first light source unit 21 and the second light source unit 22 each have 12 light emitting elements 200. Specifically, as shown in FIG. 2, the first light source unit 21 has 12 light emitting elements 200 from the first light emitting element 201 to the twelfth light emitting element 212, and the second light source unit 22 has 12 light emitting elements 200 from the thirteenth light emitting element 213 to the twenty-fourth light emitting element 224. Therefore, the lighting device 10 as a whole includes a total of 24 light emitting elements 200 from the first light emitting element 201 to the twenty-fourth light emitting element 224.

[0018] The lighting device 10 according to this embodiment outputs light from these plurality (here, 24) of light emitting elements 200 toward the lighting space. The plurality (here, 24) of light emitting elements 200 are mounted on, for example, a single light source substrate and are modularized. Furthermore, in this embodiment, the plurality (here, 24) of modularized light emitting elements 200 are electrically connected in series.

[0019] The lighting device 10 has a lens in front of the plurality of light emitting elements 200. The plurality of light emitting elements 200 are arranged in a predetermined array on one surface of the light source substrate. As a result, the light output from the plurality of light emitting elements 200 arranged on one surface of the light source substrate is emitted through the lens. The light distribution of the lighting device 10 is determined by the array of the plurality of light emitting elements 200 on the light source substrate and the lens.

[0020] The power supply device 20 supplies power to the plurality of light source units 2 in the lighting device 10 to turn on the plurality of light emitting elements 200 included in the plurality of light source units 2. Specifically, the power supply device 20 converts the alternating current power (alternating current voltage) supplied from the alternating current power supply AC1 into direct current power (direct current voltage) and applies it to the lighting device 10, thereby passing a direct current through the plurality of light source units 2 to turn on the lighting device 10.

[0021] Here, the light output from the plurality of light source units 2 changes according to the magnitude of the direct current supplied from the power supply device 20 to the plurality of light source units 2. The smaller the current supplied to the plurality of light source units 2, the smaller (darker) the light output from the plurality of light source units 2. Conversely, the larger the current supplied to the plurality of light source units 2, the larger (brighter) the light output from the plurality of light source units 2. In the present embodiment, the power supply device 20 is a power supply device of a constant current drive method, and basically, by supplying a constant current to the plurality of light source units 2, the plurality of light source units 2 are lit (emit light) at a substantially constant brightness.

[0022] More specifically, the power supply device 20 is electrically connected to the AC power supply AC1, converts the AC power from the AC power supply AC1 into DC power, and outputs it to the lighting device 10. In the present embodiment, as an example, the power supply device 20 includes an AC-DC converter that converts an AC voltage into a DC voltage, and a DC-DC converter that converts (steps up and down) the DC voltage into a DC voltage of a desired magnitude.

[0023] By the way, as a related art, for example, a lighting device for a railroad crossing, which includes a light emitting element such as a light emitting diode (LED) in a light emitting unit, is known. The lighting device according to the related art includes a light emitting unit, a control circuit that controls the current supplied to the light emitting unit, and a case that houses the light emitting unit and the control circuit. The lighting fixture is attached to a support column, for example, and supported at an appropriate height for illuminating the railroad crossing.

[0024] However, in the configuration of the above related art, if the current supplied to the light source unit is constant, when the performance (light emitting efficiency) of the light emitting element is improved, the amount of light emitted from the lighting device may become excessive.

[0025] In the present embodiment, a lighting device 10 and a lighting system 100 that are easy to appropriately adjust the light amount are realized by the configuration described below.

[0026] [2] Specific Configuration of Lighting Device Next, with reference to FIGS. 1 and 2, the specific configuration of the lighting device 10 according to the present embodiment will be described.

[0027] As described above, the lighting device 10 according to the present embodiment includes a plurality of light source units 2 that are electrically connected in series. Each of the plurality of light source units 2 includes at least one light emitting element 200.

[0028] In the present embodiment, the first light source unit 21 and the second light source unit 22 as the plurality of light source units 2 are electrically connected in series between the output terminals of the power supply device 20 (between the output of the power supply device 20 and the circuit ground). Here, the first light source unit 21 is connected to the high potential side (the positive electrode side of the power supply device 20), and the second light source unit 22 is connected to the low potential side (the circuit ground side).

[0029] Also, the first light emitting element 201 to the twelfth light emitting element 212 that constitute the first light source unit 21 are electrically connected in series in the order of the first light emitting element 201, the second light emitting element 202,..., the twelfth light emitting element 212 from the high potential side (the positive electrode side of the power supply device 20). The thirteenth light emitting element 213 to the twenty-fourth light emitting element 224 that constitute the second light source unit 22 are electrically connected in series in the order of the thirteenth light emitting element 213, the fourteenth light emitting element 214,..., the twenty-fourth light emitting element 224 from the high potential side (the positive electrode side of the power supply device 20).

[0030] In other words, a total of 24 light-emitting elements 200, namely the first light-emitting element 201 to the 24th light-emitting element 224, are electrically connected in series between the output terminals of the power supply device 20 (between the output of the power supply device 20 and the circuit ground) such that the first light-emitting element 201 is on the high potential side (the positive electrode side of the power supply device 20) and the 24th light-emitting element 224 is on the low potential side (the circuit ground side). On top of that, the first light-emitting element 201 to the 12th light-emitting element 212 constitute the first light source unit 21, and the 13th light-emitting element 213 to the 24th light-emitting element 224 constitute the second light source unit 22. The first light-emitting element 201 to the 24th light-emitting element 224 are all (blue) light-emitting diodes, and are each connected with the anode on the high potential side (the positive electrode side of the power supply device 20) and the cathode on the low potential side (the circuit ground side).

[0031] By the way, in the present embodiment, the lighting device 10 further includes a bypass circuit 3 in addition to the plurality of light source units 2. The bypass circuit 3 intermittently bypasses both ends of some of the plurality of light source units 2.

[0032] Furthermore, the lighting device 10 further includes a control unit 4 and a power extraction circuit 5. The control unit 4 controls the switch circuit 31 of the bypass circuit 3. The power extraction circuit 5 generates the power supply for the control unit 4. In the present embodiment, the bypass circuit 3, the control unit 4, and the power extraction circuit 5 are mounted on the same light source substrate as the plurality of light source units 2.

[0033] The bypass circuit 3 is electrically connected between both ends of the first light source unit 21 among the plurality of light source units 2. The bypass circuit 3 has a switch circuit 31 that can switch between two states: an on (conductive) state and an off (cut-off) state. The switch circuit 31 switches between the on state and the off state according to the control signal Si1 from the control unit 4. The control signal Si1 is a signal that periodically repeats an on period for setting the switch circuit 31 to the on state. That is, the bypass circuit 3 intermittently shorts both ends of the first light source unit 21 by periodically setting the switch circuit 31 to the on state according to the control signal Si1.

[0034] That is, the bypass circuit 3 is configured such that the anode of the first light-emitting element 201 and the cathode of the twelfth light-emitting element 212 can be short-circuited by the switch circuit 31. If the switch circuit 31 is in the on state, the connection between the anode of the first light-emitting element 201 and the cathode of the twelfth light-emitting element 212 is bypassed by the bypass circuit 3, and the supply current from the power supply device 20 flows through the bypass circuit 3 instead of the first light source unit 21. As a result, the bypass circuit 3 intermittently bypasses both ends of the first light source unit 21.

[0035] Specifically, the switch circuit 31 includes a semiconductor element, more specifically, a switching element composed of an active element such as a transistor. In this embodiment, as an example, the switching element is an enhancement-type MOSFET (Metal-Oxide-Semiconductor Field Effect Transistor). This switching element changes the conduction state between the drain and the source according to the gate voltage applied to the control terminal (gate terminal). A control signal Si1 is input to the control terminal of the switching element. As an example, the switch circuit 31 is configured such that the switching element turns on when the control signal Si1 is at the H (High) level.

[0036] The control unit 4 mainly includes, for example, a microcontroller or the like. The control unit 4 generates a control signal Si1 and outputs the control signal Si1 to the switch circuit 31 of the bypass circuit 3. The power supply extraction circuit 5 generates a driving voltage for the control unit 4 and outputs the driving voltage to the control unit 4.

[0037] Here, the power extraction circuit 5 extracts power from between both ends of one or more light-emitting elements 200. In the present embodiment, as an example, the power extraction circuit 5 extracts power from between both ends of the 24th light-emitting element 224 included in the second light source unit 22 as shown in FIG. 2 and applies it to the control unit 4. Specifically, the power extraction circuit 5 has a smoothing capacitor C1 connected between both ends of the 24th light-emitting element 224. The power extraction circuit 5 charges the smoothing capacitor C1 with the forward voltage of the 24th light-emitting element 224 and applies the voltage across both ends of the smoothing capacitor C1 to the control unit 4, thereby outputting a driving voltage to the control unit 4. According to this configuration, inside the lighting device 10, the power for driving the control unit 4 can be extracted, and the output of the power supply device 20 can be effectively utilized.

[0038] As described above, the lighting device 10 according to the present embodiment includes a plurality of light source units 2 and a bypass circuit. The plurality of light source units 2 each include at least one light-emitting element 200 and are electrically connected in series. The bypass circuit 3 intermittently bypasses between both ends of some of the plurality of light source units 2.

[0039] In short, during the period when the bypass circuit 3 does not bypass between both ends of some of the plurality of light source units 2, all of the plurality of light source units 2 light up. On the other hand, during the period when the bypass circuit 3 bypasses between both ends of some of the light source units 2, since the said some light source units 2 do not light up, only the remaining light source units 2 among the plurality of light source units 2 light up, and the amount of light emitted from the lighting device 10 is suppressed to be small. By the bypass circuit 3 intermittently bypassing between both ends of some of the light source units 2, the amount of light emitted from the lighting device 10 is intermittently suppressed to be small, and it is possible to suppress the amount of light from the lighting device 10. As a result, even when the performance (light-emitting efficiency) of the light-emitting element 200 is improved, according to the performance of the light-emitting element 200, by adjusting the length of the period during which the bypass circuit 3 bypasses between both ends of some of the light source units 2, it is possible to suppress the amount of light from the lighting device 10 and realize a lighting device 10 and a lighting system 100 in which the amount of light is easily adjusted appropriately.

[0040] FIG. 3 shows the lighting device 10X according to the first comparative example, and FIG. 4 shows the lighting device 10Y according to the second comparative example.

[0041] The lighting device 10X according to the first comparative example does not have the bypass circuit 3 as in the lighting device 10 according to the present embodiment. In this lighting device 10X, the current supplied from the power supply device 20 always flows through all of the plurality of light source units 2, and all of the plurality of light emitting elements 200 included in the plurality of light source units 2 are lit. Therefore, when the performance (light emission efficiency) of the light emitting element 200 is improved, the amount of light emitted from the lighting device 10X may become excessive.

[0042] On the other hand, the lighting device 10Y according to the second comparative example further includes a shunt resistor R1 in addition to the configuration of the lighting device 10X according to the first comparative example. The shunt resistor R1 is electrically connected in parallel to the series circuit of the plurality of light source units 2. In this lighting device 10Y, the current supplied from the power supply device 20 always flows through the plurality of light source units 2 and the shunt resistor R1. That is, the current flowing through the plurality of light source units 2 is smaller than that in the lighting device 10X according to the first comparative example, so the amount of light emitted from the lighting device 10 is suppressed to be small. Therefore, even when the performance (light emission efficiency) of the light emitting element 200 is improved, it is possible to suppress the amount of light from the lighting device 10Y to be small and appropriately adjust the amount of light by adjusting the resistance value of the shunt resistor R1 according to the performance of the light emitting element 200. However, since the current supplied to the shunt resistor R1 becomes heat loss, there is a problem that the amount of heat generated by the lighting device 10Y increases.

[0043] In contrast, according to the lighting device 10 according to the present embodiment, a bypass circuit 3 is provided in parallel to some of the plurality of light-emitting elements 200 electrically connected in series. By intermittently bypassing (short-circuiting) the some of the light-emitting elements 200 with the bypass circuit 3, the some of the light-emitting elements 200 are intermittently turned off to suppress the brightness of the entire lighting device 10. Therefore, according to the lighting device 10, without changing the output current of the power supply device 20 and while reducing the heat generation amount of the lighting device 10 compared to the lighting device 10Y according to the second comparative example, the light amount can be appropriately adjusted compared to the lighting device 10X according to the first comparative example.

[0044] [3] Operation of Lighting Device Next, the operation of the lighting device 10 according to the present embodiment will be described with reference to FIG. 5. FIG. 5 is a timing chart showing an example of the control signal Si1 and the light output of the lighting device 10 with the horizontal axis being the time axis. The light output of the lighting device 10 represents the light output (brightness) when all of the plurality (24) of light-emitting elements 200 of the lighting device 10X according to the first comparative example are lit as 100%, and the light output when the lighting device 10 is turned off as 0%.

[0045] The control unit 4 generates a control signal Si1 that periodically repeats a short-circuit period T1 (denoted as "ON" in the figure) for turning on the switch circuit 31 at a period T0. That is, the switch circuit 31 of the bypass circuit 3 is in the on state only during the short-circuit period T1 (T1 < T0) of the period T0, and bypasses both ends of the first light source unit 21. During the off period T2 (denoted as "OFF" in the figure) of the control signal Si1, the switch circuit 31 of the bypass circuit 3 is in the off state, and both ends of the first light source unit 21 are not bypassed.

[0046] As a result, during the off period T2, the current supplied from the power supply device 20 passes through both the first light source unit 21 and the second light source unit 22, and both the first light source unit 21 and the second light source unit 22 are lit. Therefore, during the off period T2, the light output of the lighting device 10 becomes 100%.

[0047] On the one hand, during the short - circuit period T1, the current supplied from the power supply device 20 passes through the bypass circuit 3 and the second light source unit 22, and only the second light source unit 22 among the first light source unit 21 and the second light source unit 22 lights up. Therefore, during the short - circuit period T1, the light output of the lighting device 10 becomes approximately 50%.

[0048] Therefore, as shown in FIG. 5, the light output of the lighting device 10 changes periodically so as to alternately repeat 100% and approximately 50%. And the ratio of the period during which the light output in unit time becomes approximately 50% is determined by the ratio of the short - circuit period T1 to the period T0. Thereby, it becomes possible to adjust the average value of the light output of the lighting device 10 in unit time according to the ratio (duty ratio) of the short - circuit period T1 in the control signal Si1 generated by the control unit 4.

[0049] Here, the length of the short - circuit period T1 in the period T0 is set according to the dimming rate. As an example, when the period T0 is 10 ms (that is, 100 Hz), the short - circuit period T1 is set to 3 ms and the off - period T2 is set to 7 ms. Thereby, the light output of the lighting device 10 becomes approximately 50% during 30% of the period in unit time, and the light output of the lighting device 10 becomes 100% during 70% of the period in unit time. As a result, the average value of the light output in unit time becomes approximately 85%.

[0050] In short, the bypass circuit 3 bypasses between both ends of some of the light source units 2 during the short-circuit period T1 that is periodically set according to the dimming rate. That is, the bypass circuit 3 shorts between both ends of the first light source unit 21 during the short-circuit period T1 set according to the dimming rate, thereby turning off the first light source unit 21 and suppressing the light output of the lighting device 10 to a small level. As a result, the amount of light emitted from the lighting device 10 is adjusted according to the dimming rate. Consequently, it is only necessary to preset the ratio (duty ratio) of the short-circuit period T1 in the control signal Si1 so that the lighting device 10 is lit at a desired dimming rate according to the characteristics (luminous efficiency) of the known light-emitting element 200, and complex control such as feedback control becomes unnecessary. Therefore, unintentional flickering of the lighting device 10 due to runaway of the control unit 4 caused by disturbances such as response delay or noise in the control system is less likely to occur, and a highly reliable lighting device 10 can be realized.

[0051] [4] Modification Example Hereinafter, modification examples of Embodiment 1 will be listed. The modification examples described below can be applied in appropriate combinations.

[0052] The power extraction circuit 5 is not an essential component of the lighting device 10 and can be omitted as appropriate.

[0053] Further, the lighting device 10 only needs to include a plurality of light source units 2 electrically connected in series, and may include three or more light source units 2.

[0054] Further, the light source unit 2 is not limited to a configuration in which a plurality of light-emitting elements 200 are electrically connected in series, and a plurality of light-emitting elements 200 may be electrically connected in parallel, or electrically connected in parallel and in series.

[0055] Further, the number of light emitting elements 200 constituting the light source unit 2 is not limited to 12 and can be appropriately changed. For example, the number of light emitting elements 200 constituting the first light source unit 21 may be "10", and the number of light emitting elements 200 constituting the second light source unit 22 may be "20". The number of light emitting elements 200 may be different between the plurality of light source units 2. Each light source unit 2 only needs to include at least one light emitting element 200, and it is not essential for each light source unit 2 to include a plurality of light emitting elements 200.

[0056] Further, the light emitting element 200 included in the light source unit 2 is not limited to a light emitting diode, and may be, for example, an organic EL element or other semiconductor light emitting element.

[0057] (Embodiment 2) As shown in FIG. 6, the lighting device 10A according to the present embodiment is different from that of the first embodiment in the configuration of the bypass circuit 3. Hereinafter, the same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof will be omitted as appropriate.

[0058] In the present embodiment, it is assumed that a power supply device designed to have a slow response speed to a sudden change in the load voltage is adopted as the power supply device 20.

[0059] In the present embodiment, the bypass circuit 3 includes limiting loads R11 and R12 having impedance. The bypass circuit 3 bypasses both ends of a part of the light source unit 2 (the first light source unit 21) by electrically connecting the limiting loads R11 and R12 in parallel to a part of the light source unit 2 (the first light source unit 21). According to this configuration, even if a current suddenly increases due to a voltage difference and an inrush current occurs at the moment when the bypass circuit 3 bypasses both ends of a part of the light source unit 2, the current flowing through the bypass circuit 3 can be limited by the limiting loads R11 and R12. As a result, it becomes easier to suppress an overcurrent from flowing through the light source unit 2 (the second light source unit 22) electrically connected in series with the bypass circuit 3.

[0060] Specifically, the bypass circuit 3 has a first switch circuit 31, a second switch circuit 32, a first limiting load R11, and a second limiting load R12. The first limiting load R11 and the second limiting load R12 each consist of a resistor having a predetermined impedance (resistance value). As an example, the resistance values of the first limiting load R11 and the second limiting load R12 are both on the order of a dozen or so ohms.

[0061] The first switch circuit 31 and the second switch circuit 32 are each configured to be switchable between two states: an on (conductive) state and an off (non-conductive) state. The first switch circuit 31 switches between the on state and the off state in response to a control signal Si1 from the control unit 4, and the second switch circuit 32 switches between the on state and the off state in response to a control signal Si2 from the control unit 4.

[0062] The first switch circuit 31 has a semiconductor element, more specifically, a switching element composed of an active element such as a transistor. In this embodiment, as an example, the switching element is an enhancement-type MOSFET. This switching element changes the conductive state between the drain and the source according to the gate voltage applied to the control terminal (gate terminal). The control signal Si1 is input to the control terminal of the switching element. As an example, the first switch circuit 31 is configured such that the switching element turns on when the control signal Si1 is at the H (High) level.

[0063] Similar to the first switch circuit 31, the second switch circuit 32 has a semiconductor element, more specifically, a switching element composed of an active element such as a transistor. In this embodiment, as an example, the switching element is an enhancement-type MOSFET. This switching element changes the conductive state between the drain and the source according to the gate voltage applied to the control terminal (gate terminal). The control signal Si2 is input to the control terminal of the switching element. As an example, the second switch circuit 32 is configured such that the switching element turns on when the control signal Si2 is at the H (High) level.

[0064] The first switch circuit 31, the first limiting load R11, and the second limiting load R12 are electrically connected in series between both ends of the first light source unit 21. The first limiting load R11 is connected to the anode of the first light emitting element 201 via the first switch circuit 31, and is connected to the cathode of the twelfth light emitting element 212 via the second limiting load R12. The second switch circuit 32 is electrically connected between both ends of the first limiting load R11.

[0065] Accordingly, if the first switch circuit 31 is in the off state, the first light source unit 21 is not bypassed, and if the first switch circuit 31 is in the on state, the first light source unit 21 will be bypassed. And when the first switch circuit 31 is in the on state, if the second switch circuit 32 is in the off state, the first limiting load R11 and the second limiting load R12 are electrically connected in series between both ends of the first light source unit 21, and if the second switch circuit 32 is in the on state, the second limiting load R12 is electrically connected between both ends of the first light source unit 21. That is, when the second switch circuit 32 is in the on state, the impedance of the bypass circuit 3 is reduced.

[0066] The first switch circuit 31 and the second switch circuit 32 are controlled by control signals Si1 and Si2 such that the second switch circuit 32 is turned on after a predetermined time from when the first switch circuit 31 is turned on. Thereby, the impedance of the limiting loads R11 and R12 becomes smaller as time elapses after the bypass circuit 3 starts bypassing between both ends of a part of the light source units 2.

[0067] According to this configuration, immediately after the bypass circuit 3 starts bypassing, while limiting the current flowing through the bypass circuit 3 with the limiting loads R11 and R12, it is possible to suppress heat loss in the limiting loads R11 and R12 by reducing the impedance of the limiting loads R11 and R12.

[0068] In addition, the lighting device 10A according to the present embodiment further includes a surge absorption circuit 6. The surge absorption circuit 6 is electrically connected in series with the bypass circuit 3. According to this configuration, even if a current instantaneously increases due to a voltage difference and an inrush current occurs at the moment when the bypass circuit 3 bypasses between both ends of a part of the light source units 2, the inrush current can be made to flow through the surge absorption circuit 6, thereby restricting the current flowing through the light source unit 2. As a result, it becomes easier to suppress an overcurrent from flowing through the light source unit 2 (the second light source unit 22) that is electrically connected in series with the bypass circuit 3.

[0069] Specifically, the surge absorption circuit 6 is inserted between the bypass circuit 3 and the circuit ground. In other words, the surge absorption circuit 6 is electrically connected in parallel with the second light source unit 22.

[0070] The surge absorption circuit 6 includes a third switch circuit 61, a surge absorption capacitor C2, and a discharge resistor R2. The surge absorption capacitor C2 and the discharge resistor R2 are electrically connected in parallel, and are connected between the third switch circuit 61 and the circuit ground. As an example, the capacitance value of the surge absorption capacitor C2 is several tens of μF, and the resistance value of the discharge resistor R2 is about 1 kΩ.

[0071] The third switch circuit 61 is configured to be switchable between two states: an on (conductive) state and an off (cut-off) state. The third switch circuit 61 switches between the on state and the off state according to a control signal Si1 from the control unit 4.

[0072] The third switch circuit 61 includes a semiconductor element, more specifically, a switching element formed of an active element such as a transistor. In the present embodiment, as an example, the switching element is an enhancement-type MOSFET. This switching element changes the conductive state between the drain and the source according to the gate voltage applied to the control terminal (gate terminal). The control signal Si1 is input to the control terminal of the switching element. As an example, the third switch circuit 61 is configured such that the switching element turns on when the control signal Si1 is at the H (High) level.

[0073] Accordingly, if the third switch circuit 61 is in the off state, the surge absorption capacitor C2 is electrically disconnected from the bypass circuit 3, and if the third switch circuit 61 is in the on state, the surge absorption capacitor C2 is electrically connected in series with the bypass circuit 3. Then, when the first switch circuit 31 is in the on state, if the third switch circuit 61 is in the on state, the inrush current passing through the bypass circuit 3 flows to the surge absorption capacitor C2 instead of the second light source unit 22 and is absorbed by the surge absorption capacitor C2. After that, when the third switch circuit 61 becomes off, the charge charged in the surge absorption capacitor C2 is discharged by the discharge resistor R2.

[0074] Next, the operation of the lighting device 10A according to the present embodiment will be described with reference to FIG. 7. FIG. 7 is a timing chart showing an example of the control signal Si1, the control signal Si2, and the light output of the lighting device 10A with the horizontal axis being the time axis. The light output of the lighting device 10A represents the light output (brightness) when all of the plurality (24) of light emitting elements 200 of the lighting device 10X according to the first comparative example are lit as 100%, and the light output when the lighting device 10A is turned off as 0%.

[0075] The control unit 4 generates a control signal Si1 that periodically repeats a short circuit period T1 (denoted as "ON" in the figure) for turning on the first switch circuit 31 at a period T0. That is, the first switch circuit 31 of the bypass circuit 3 is in the on state only during the short circuit period T1 (T1 < T0) of the period T0 and bypasses both ends of the first light source unit 21. During the off period T2 (denoted as "OFF" in the figure) of the control signal Si1, the first switch circuit 31 of the bypass circuit 3 is in the off state, and both ends of the first light source unit 21 are not bypassed.

[0076] Further, the control unit 4 generates a control signal Si2 such that the second switch circuit 32 is turned on after a delay time T11 has elapsed since the first switch circuit 31 became on. That is, the control unit 4 generates a control signal Si2 that periodically repeats an on period T12 (denoted as "ON" in the figure) during which the second switch circuit 32 is turned on, with a period T0.

[0077] Furthermore, in the present embodiment, the on / off state of the third switch circuit 61 is also switched by the control signal Si1, and the third switch circuit 61 is turned on during the short-circuit period T1 of the control signal Si1.

[0078] Therefore, the light output of the lighting device 10A changes at any time within the period T0, for example, as shown in FIG. 7. In the example of FIG. 7, when the first switch circuit 31 and the third switch circuit 61 are turned on during the short-circuit period T1, the current supplied from the power supply device 20 is absorbed by the surge absorption capacitor C2, so the light output of the lighting device 10A drops to approximately 0%. Then, when the surge absorption capacitor C2 is fully charged, current flows through the limiting loads R11 and R12 of the bypass circuit 3 to the second light source unit 22, causing the light output of the lighting device 10A to increase. At this time, since the power supply device 20 has a slow response speed to sudden changes in the load voltage, the current value does not settle at a constant value, and the light output of the lighting device 10A fluctuates around 100%.

[0079] Thereafter, during the on period T12, when the second switch circuit 32 is turned on, the impedance of the bypass circuit 3 decreases, so the heat loss in the bypass circuit 3 is suppressed. At this time, since the power supply device 20 has a slow response speed to sudden changes in the load voltage, the current value does not settle at a constant value, and the light output of the lighting device 10A fluctuates around 100%.

[0080] Thereafter, during the off period T2, since the first switch circuit 31 and the third switch circuit 61 are in the off state, the current supplied from the power supply device 20 will flow to the first light source unit 21 and the second light source unit 22. Therefore, the light output of the lighting device 10A increases. However, due to a sudden change in the load voltage of the power supply device 20, the protection function of the power supply device 20 is activated, and the light output of the lighting device 10A gradually decreases. After once dropping to 0%, it returns to 100%.

[0081] Therefore, as shown in FIG. 7, the light output of the lighting device 10A periodically changes between 100% and 0%. Thus, it becomes possible to adjust the average value of the light output of the lighting device 10A per unit time according to the ratio (duty ratio) of the short-circuit period T1 in the control signal Si1 generated by the control unit 4.

[0082] Here, the length of the short-circuit period T1 in the period T0 is set according to the dimming rate. As an example, when the period T0 is 10 ms (i.e., 100 Hz), the short-circuit period T1 is set to 3 ms, the off period T2 is set to 7 ms, the delay time T11 is set to 2 ms, and the on period T12 is set to 1 ms. In this case, the average value of the light output per unit time is approximately 80%.

[0083] As a modification of Embodiment 2, the surge absorption circuit 6 is not an essential configuration and can be omitted as appropriate. Also, the impedance of the limiting loads R11, R12 being switchable is not an essential configuration, and the second switch circuit 32 can be omitted as appropriate.

[0084] The configuration of Embodiment 2 (including the modifications) can be adopted in appropriate combination with various configurations (including the modifications) described in Embodiment 1.

[0085] [Supplementary Note of the Invention] Hereinafter, the outline of the invention extracted from the above-described embodiments will be appended. Note that each configuration and each processing function described in the following supplementary note can be arbitrarily selected and combined as appropriate.

[0086] <Supplementary Note 1> Each comprising at least one light-emitting element, a plurality of light source units electrically connected in series, A bypass circuit that intermittently bypasses both ends of some of the plurality of light source units, A lighting device.

[0087] <Appendix 2> The bypass circuit bypasses both ends of the some of the light source units during a short-circuit period that is periodically set according to the dimming rate. The lighting device according to Appendix 1.

[0088] <Appendix 3> The bypass circuit includes a limiting load having an impedance, and bypasses both ends of the some of the light source units by electrically connecting the limiting load in parallel with the some of the light source units. The lighting device according to Appendix 1 or 2.

[0089] <Appendix 4> The impedance of the limiting load decreases with the passage of time since the bypass circuit starts bypassing both ends of the some of the light source units. The lighting device according to Appendix 3.

[0090] <Appendix 5> Further comprising a surge absorption circuit electrically connected in series with the bypass circuit. The lighting device according to any one of Appendices 1 to 4.

[0091] <Appendix 6> Further comprising a power extraction circuit that extracts power from between both ends of one or more of the light-emitting elements. The lighting device according to any one of Appendices 1 to 5.

[0092] <Appendix 7> The lighting device according to any one of Appendices 1 to 6, And a power supply device that supplies power to the plurality of light source units. A lighting system.

[0093] <Appendix 8> The power supply device is of a constant current drive type. The lighting system according to Supplementary Note 7.

Explanation of Signs

[0094] 2 Light source unit 3 Bypass circuit 5 Power extraction circuit 6 Surge absorption circuit 10, 10A, 10X, 10Y Lighting device 100 Lighting system 200 Light emitting element R11, R12 Limiting load

Claims

1. A plurality of light source units each comprising at least one light emitting element and electrically connected in series, and a bypass circuit that intermittently bypasses both ends of some of the plurality of light source units. An illumination device.

2. The bypass circuit bypasses both ends of some of the light source units during a short circuit period that is periodically set according to a dimming rate. The illumination device according to Claim 1.

3. The bypass circuit includes a limiting load having an impedance, and bypasses both ends of some of the light source units by electrically connecting the limiting load in parallel with some of the light source units. The illumination device according to Claim 1 or 2.

4. The impedance of the limiting load decreases as time elapses after the bypass circuit starts bypassing both ends of some of the light source units. The illumination device according to Claim 3.

5. Further comprising a surge absorption circuit electrically connected in series with the bypass circuit. The illumination device according to Claim 1 or 2.

6. Further comprising a power extraction circuit that extracts power from between both ends of one or more of the light emitting elements. The illumination device according to Claim 1 or 2.

7. An illumination system comprising the illumination device according to Claim 1 or 2, and a power supply device that supplies power to the plurality of light source units. An illumination system.

8. The power supply device is a constant current drive type. The illumination system according to Claim 7.

Images