Lighting circuit and lighting device

Abstract

To provide a lighting circuit and a lighting device that can suppress pulsation of a current flowing through a light-emitting element in a more appropriate manner.SOLUTION: A lighting circuit 1 for a light source 2 including a light emitting element 21 whose light intensity changes depending on the magnitude of a supply current, includes a constant current circuit 12 and a passive element 13. The constant current circuit 12 has a control element Q1 electrically connected in series with the light source 2, and controls the magnitude of a current I1 flowing through the light source 2. The passive element 13 can be electrically connected in parallel with the control element Q1.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a lighting circuit for a light source including a light emitting element whose light quantity changes according to the magnitude of a current supplied thereto, and to a lighting device. [Background technology]

[0002] As a related art, for example, a lighting circuit (lighting device) for lighting a light-emitting element such as a light-emitting diode is known (for example, see Patent Document 1). The lighting circuit according to the related art is a one-converter type lighting circuit that uses a flyback converter or a SEPIC (Single Ended Primary Inductor Converter) or the like to achieve a high power factor and achieves both power factor correction control and light source current control with a single converter.

[0003] In order to improve the power factor, this type of lighting circuit does not smooth the full-wave rectified voltage obtained by the rectifier circuit, but uses a voltage pulsating with twice the commercial frequency as the input voltage for the converter, so that pulsation with twice the commercial frequency components is likely to occur in the current flowing through the light-emitting element. Therefore, the lighting circuit according to the related art makes it possible to suppress the pulsation (ripple) by using a large-capacity output capacitor (smoothing capacitor) in the output stage. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2016-201243 A Summary of the Invention [Problem to be solved by the invention]

[0005] In the configuration of the related art described above, a large-capacity output capacitor is used to suppress pulsation of the current flowing through the light-emitting element, which may cause problems such as, for example, preventing the miniaturization of the lighting circuit and lengthening the time required from when the power is turned on until the light-emitting element begins to light.

[0006] An object of the present invention is to provide a lighting circuit and a lighting device that are capable of suppressing pulsation of a current flowing through a light-emitting element in a more appropriate manner. [Means for solving the problem]

[0007] A lighting circuit according to one aspect of the present invention is a lighting circuit for a light source including a light emitting element whose light quantity changes according to the magnitude of a current supplied thereto, and includes a constant current circuit and a passive element. The constant current circuit has a control element electrically connected in series with the light source and controls the magnitude of the current flowing through the light source. The passive element can be electrically connected in parallel with the control element.

[0008] A lighting device according to one aspect of the present invention includes the lighting circuit and the light source. Effect of the Invention

[0009] According to the present invention, it is possible to provide a lighting circuit and a lighting device that are capable of suppressing pulsation of a current flowing through a light-emitting element in a more appropriate manner. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic block diagram showing the configuration of an illumination device according to a first embodiment. [Diagram 2] FIG. 2 is a schematic circuit diagram showing a specific example of the lighting device according to the first embodiment. [Diagram 3] FIG. 3 is a schematic waveform diagram showing an operation example of the lighting circuit according to the first embodiment. [Figure 4] FIG. 4 is a schematic circuit diagram showing a specific example of the lighting device according to the second embodiment. [Diagram 5] FIG. 5 is a schematic circuit diagram showing a specific example of an illumination device according to a modification of the second embodiment. [Figure 6] FIG. 6 is a schematic circuit diagram showing a specific example of the lighting device according to the third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. The following embodiment is an example of the present invention, and is not intended to limit the technical scope of the present invention.

[0012] (Embodiment 1) [1] Overall structure First, the overall configuration of an illumination device 10 according to this embodiment will be described with reference to FIGS.

[0013] The lighting device 10 includes a lighting circuit 1 and a light source 2. In this embodiment, the lighting circuit 1 receives power supply from an AC power source AC1 to light the light source 2. The AC power source AC1 is, for example, a single-phase 100V, 60Hz commercial power source.

[0014] In this embodiment, the lighting device 10 has the lighting circuit 1 and the light source 2 integrated into one housing. In other words, the lighting device 10 is a lighting device integrated with the lighting circuit 1, which can light the light source 2 provided in the housing by receiving power supply from an AC power source AC1.

[0015] This type of lighting device 10 can be used in various facilities (including outdoor facilities) such as homes, offices, stores, or public facilities, and can illuminate a desired lighting space by irradiating the space with light from the light source 2.

[0016] Here, the light source 2 includes a light emitting element 21 (see FIG. 2) whose light amount changes according to the magnitude of the supply current. The light emitting element 21 is, for example, a semiconductor light emitting element such as a light emitting diode (LED) or an organic EL (Electroluminescence) element. In this embodiment, as an example, the light emitting element 21 is a light emitting diode.

[0017] Furthermore, the light source 2 has a plurality of light-emitting elements 21. That is, the lighting device 10 according to this embodiment outputs light from the plurality of light-emitting elements 21 toward the lighting space. The plurality of light-emitting elements 21 are mounted on, for example, one light source board and modularized. Furthermore, in this embodiment, the modularized plurality of light-emitting elements 21 are electrically connected in series.

[0018] Furthermore, the lighting device 10 according to the present embodiment has a "dimming function" that adjusts the magnitude of the light output from the light source 2 in response to, for example, a dimming signal Si1 (see FIG. 4) from a dimming device. The dimming signal Si1 is a signal that includes information related to a dimming rate, and is, for example, a signal that is generated in response to an operation input by a user. The dimming device that generates the dimming signal may be provided separately from the lighting device 10, or may be integrated with the lighting device 10.

[0019] Specifically, the lighting circuit 1 changes the magnitude of the current passed through the light source 2 in response to the dimming signal, thereby adjusting the magnitude of the light output from the light source 2. Basically, the lower the dimming rate of the dimming signal, the smaller the current passed through the light source 2, thereby decreasing (darking) the light output from the light source 2. Conversely, the higher the dimming rate of the dimming signal, the larger the current passed through the light source 2, thereby increasing (brightening) the light output from the light source 2.

[0020] In this lighting device 10, the lighting circuit 1 lights (emits light) the light source 2 at a constant brightness by supplying a constant current to the light source 2 as long as the dimming rate does not change. In other words, the lighting circuit 1 converts AC power (AC voltage) supplied from an AC power source AC1 into DC power (DC voltage) and applies it to the light source 2, thereby passing a DC current through the light source 2 and lighting the light source 2.

[0021] 1, the lighting circuit 1 includes a driver circuit 11, an output capacitor C1, and a constant current circuit 12. The lighting circuit 1 according to this embodiment further includes a passive element 13.

[0022] The driver circuit 11 is a circuit for supplying power to the light source 2 to drive (light) the light source 2. The driver circuit 11 is electrically connected to an AC power source AC1, converts AC power from the AC power source AC1 into DC power, and outputs the DC power to an output capacitor C1.

[0023] In this embodiment, as an example, the driver circuit 11 includes an AC-DC converter that converts an AC voltage into a DC voltage, and a DC-DC converter that converts (boosts and bucks) the DC voltage into a DC voltage of a desired magnitude. Furthermore, in this embodiment, the driver circuit 11 has a function as a power factor correction circuit (PFC) for bringing the power factor of the power supply closer to "1". In other words, the driver circuit 11 is an example of a power factor correction circuit.

[0024] The output capacitor C1 is electrically connected to the output of the driver circuit 11, and functions as a smoothing capacitor that smoothes the output voltage of the driver circuit 11. In this embodiment, as an example, the output capacitor C1 is an electrolytic capacitor having an appropriate capacitance.

[0025] The lighting circuit 1 supplies DC power to the light source 2 by applying a voltage across the output capacitor C1 to the light source 2. Here, the light source 2 and a control element Q1 (see FIG. 2) of the constant current circuit 12 are electrically connected in series between both ends of the output capacitor C1 (between the positive terminal and the circuit ground).

[0026] As long as the dimming rate does not change, the constant current circuit 12 performs constant current control to keep the current I1 (see FIG. 2) flowing through the light source 2 at a constant value. Specifically, the constant current circuit 12 adjusts the magnitude of the current flowing through the constant current circuit 12 by controlling the control element Q1, and adjusts the magnitude of the current I1 flowing through the light source 2 that is electrically connected in series with the control element Q1.

[0027] The passive element 13 will be explained in the section "[2] Specific configuration of the lighting circuit."

[0028] Incidentally, in the lighting circuit 1 of the lighting device 10, particularly when the driver circuit 11 has a power factor correction function as in the lighting circuit 1 according to this embodiment, the output current of the driver circuit 11 is likely to include pulsation (ripples). The "pulsation" here refers to a pulsation component included in the DC current output from the driver circuit 11, and has a frequency that depends on the power supply frequency of the AC power supply AC1.

[0029] If such pulsation is included in the current supplied to the light source 2, it may cause flickering in the light from the light source 2. Flickering of the light from the light source 2 may also cause flickering when the illuminated space is photographed with a camera, for example.

[0030] As a related technique, it is possible to suppress ripples by using a large-capacity output capacitor (smoothing capacitor) in the output stage. However, in the configuration of the related technique, a large-capacity output capacitor is used to suppress ripples in the current flowing through the light-emitting element 21, which may cause problems such as preventing the downsizing of the lighting circuit and lengthening the time required from power-on until the light-emitting element 21 starts to light.

[0031] On the other hand, as in the lighting circuit 1 according to the present embodiment, it is also possible to suppress ripples by providing a constant current circuit 12 and controlling the current I1 flowing through the light source 2 to a constant current. In this case, the amount of heat generated by the semiconductor element or the like used as the control element Q1 of the constant current circuit 12 may increase. Therefore, measures such as providing a heat sink for dissipating heat from the control element Q1 or using a plurality of semiconductor elements electrically connected in parallel as the control element Q1 are required, which increases the number of components and causes problems such as preventing the miniaturization of the lighting circuit 1 (in terms of mounting area).

[0032] In this embodiment, a lighting circuit 1 and a lighting device 10 are realized that are capable of suppressing pulsation of the current flowing through the light-emitting element 21 in a more appropriate manner while suppressing the amount of heat generated in the control element Q1 through the configuration described below.

[0033] [2] Specific configuration of the lighting circuit Next, a specific configuration of the lighting circuit 1 according to the present embodiment will be described with reference to FIGS.

[0034] As described above, the lighting circuit 1 according to this embodiment includes the constant current circuit 12 having the control element Q1 electrically connected in series with the light source 2. The constant current circuit 12 controls the magnitude of the current I1 flowing through the light source 2 by controlling the control element Q1.

[0035] In this embodiment, as shown in FIG. 2, the constant current circuit 12 includes a control unit 121 and a shunt resistor R2 in addition to the control element Q1.

[0036] The control element Q1 is a semiconductor element, more specifically, an active element such as a transistor, etc. In this embodiment, as an example, the control element Q1 is an enhancement type n-channel Metal-Oxide-Semiconductor Field Effect Transistor (MOSFET).

[0037] This control element Q1 changes the drain-source conduction state according to the gate voltage applied to the control terminal (gate terminal). The control element Q1 has a drain connected to the light source 2 (light-emitting element 21) and a source connected to the circuit ground (through a shunt resistor R2). In other words, the drain-source of the control element Q1 is electrically connected in series with the light source 2 to form a current path. Therefore, the current I1 flowing through the light source 2 is controlled by changing the drain-source conduction state of the control element Q1.

[0038] The control unit 121 controls the control element Q1. That is, the control unit 121 is electrically connected to the gate of the control element Q1 and changes the drain-source conduction state of the control element Q1. In this embodiment, the control unit 121 is configured with an IC (Integrated Circuit) for constant current control. More specifically, the control unit 121 is a ripple remover circuit that can limit the voltage across both ends (drain-source) of the control element Q1 in order to reduce loss in the constant current circuit 12.

[0039] The shunt resistor R2 is provided to detect the magnitude of the current I1 flowing through the light source 2. The shunt resistor R2 is electrically connected in series with the control element Q1 so that a current equal to the current I1 flowing through the light source 2 flows through the shunt resistor R2. The control unit 121 monitors the current I1 flowing through the light source 2 using the voltage across the shunt resistor R2 as an input.

[0040] As described above, the lighting circuit 1 according to this embodiment includes the passive element 13. The passive element 13 is configured to be electrically connectable in parallel with the control element Q1 of the constant current circuit 12. In this embodiment, the passive element 13 is directly connected between the drain and source of the control element Q1, and is always electrically connected in parallel with the control element Q1.

[0041] In this disclosure, a "passive element" is an element, such as a resistor, capacitor, or coil, that consumes, stores, and / or releases supplied power, and does not perform active operations such as amplifying or rectifying power, as does an active element.

[0042] By providing such a passive element 13, it is possible to divert a part of the current flowing through the control element Q1 of the constant current circuit 12 to the passive element 13. In other words, by electrically connecting the passive element 13 in parallel with the control element Q1, it is possible to divert a part of the current that would normally flow through the control element Q1 to flow through the passive element 13.

[0043] 2, the current I1 flowing through the light source 2 can be divided into a current I11 (also called the "first current") flowing through the control element Q1 and a current I12 (also called the "second current") flowing through the passive element 13 (I1=I11+I12). Therefore, if the magnitude of the current I1 flowing through the light source 2 is the same, the current I11 flowing through the control element Q1 is smaller by the amount of the current I12 flowing through the passive element 13. Therefore, it is possible to suppress the amount of heat generated in the control element Q1.

[0044] As described above, the lighting circuit 1 according to this embodiment is a lighting circuit 1 for a light source 2 including a light emitting element 21 whose light intensity changes depending on the magnitude of a supply current, and includes a constant current circuit 12 and a passive element 13. The constant current circuit 12 has a control element Q1 electrically connected in series with the light source 2, and controls the magnitude of a current I1 flowing through the light source 2. The passive element 13 can be electrically connected in parallel with the control element Q1.

[0045] According to this configuration, the constant current circuit 12 controls the magnitude of the current I1 flowing through the light source 2, and the lighting circuit 1 controls the current I1 flowing through the light source 2 to a constant current and can suppress pulsation (ripple). Therefore, the current supplied to the light source 2 is less likely to include such pulsation, and flickering is less likely to occur in the light from the light source 2. Moreover, since the passive element 13 can be electrically connected in parallel with the control element Q1, the amount of heat generated in the semiconductor element or the like used as the control element Q1 of the constant current circuit 12 can be suppressed by passing a part of the current flowing through the control element Q1 through the passive element 13. Therefore, measures such as providing a heat sink for dissipating the heat of the control element Q1 or electrically connecting multiple semiconductor elements in parallel and using them as the control element Q1 are not necessary, and the number of parts is reduced, making it easier to achieve a reduction in the size (mounting area) of the lighting circuit 1.

[0046] As a result, according to the present embodiment, it is possible to realize a lighting circuit 1 and a lighting device 10 that can suppress pulsation of the current flowing through the light emitting element 21 in a more appropriate manner while suppressing the amount of heat generated in the control element Q1.

[0047] In particular, the lighting circuit 1 according to this embodiment further includes a power factor correction circuit. In this embodiment, the driver circuit 11 having the power factor correction function as described above is an example of the "power factor correction circuit." In the lighting circuit 1 including the power factor correction circuit, the output current of the driver circuit 11 is particularly likely to include pulsations (ripples), so the constant current circuit 12 and the passive element 13 are more useful.

[0048] Moreover, in the lighting circuit 1 according to this embodiment, the passive element 13 includes a resistor R1. The passive element 13 only needs to include at least one resistor R1, and may include multiple resistors. In this case, the multiple resistors are electrically connected in series, in parallel, or in series and parallel. By including the resistor R1 in the passive element 13 in this manner, the amount of heat generated in the control element Q1 can be efficiently reduced, even with a relatively simple configuration.

[0049] In this embodiment, as described above, the constant current circuit 12 has the control unit 121. The control unit 121 controls the control element Q1 according to the magnitude of the second current I12 flowing through the passive element 13. This allows the control unit 121 to efficiently control the control element Q1 in real time. Therefore, as shown in FIG. 3, the current I1 flowing through the light source 2 can be a constant current from which the influence of pulsation is removed as a composite current of the second current I12 (flowing through the passive element 13) and the first current I11 flowing through the control element Q1.

[0050] Here, the control unit 121 obtains the magnitude of the second current I12 from a composite current (current I1 flowing through the light source 2) of the second current I12 (flowing through the passive element 13) and the first current I11 flowing through the control element Q1. That is, the control unit 121 monitors the magnitude of the current I1 flowing through the light source 2, for example, using the voltage across the shunt resistor R2. As shown in FIG. 3, the current I1 is the sum (composite current) of the first current I11 and the second current I12 (I1=I11+I12). Since the magnitude of the first current I11 flowing through the control element Q1 is known to the control unit 121 that controls the control element Q1, if the composite current (current I1 flowing through the light source 2) is known, the magnitude of the second current I12 flowing through the passive element 13 can be obtained by calculating the difference (I1-I11).

[0051] Therefore, even with a relatively simple configuration such as using the shunt resistor R2, the control unit 121 can obtain the magnitude of the second current I12 and can efficiently control the control element Q1.

[0052] [3] Variations Below, we will list some modified examples of the embodiment 1. The modified examples explained below can be applied in appropriate combinations.

[0053] The specific configuration of the lighting circuit 1 is not limited to the configuration shown in Fig. 2, and can be appropriately changed as long as the same function can be realized. For example, the control element Q1 is not limited to an enhancement type n-channel MOSFET, and may be, for example, an IGBT (Insulated Gate Bipolar Transistor) or the like. Similarly, the passive element 13 may include a capacitor or a coil (inductance) in addition to or instead of a resistor.

[0054] Furthermore, the light source 2 is not limited to a configuration in which a plurality of light-emitting elements 21 are electrically connected in series, and may be a configuration in which a plurality of light-emitting elements 21 are electrically connected in parallel, or electrically connected in parallel and in series. The light source 2 is required to include at least one light-emitting element 21, and it is not essential that the light source 2 includes a plurality of light-emitting elements 21.

[0055] Furthermore, the light emitting element 21 included in the light source 2 is not limited to a light emitting diode, but may be, for example, an organic EL element or another semiconductor light emitting element.

[0056] (Embodiment 2) 4, an illumination device 10A according to this embodiment differs from embodiment 1 in the configuration around a passive element 13 in a lighting circuit 1. Hereinafter, the same configuration as in embodiment 1 will be denoted by the same reference numerals and the description will be omitted as appropriate.

[0057] In this embodiment, the passive element 13 includes a plurality of resistors R11 and R12 electrically connected in parallel. This makes it possible to allow a sufficient current I12 to flow through the passive element 13 while keeping the capacitance of each of the resistors R11 and R12 small.

[0058] 4, the lighting circuit 1 according to this embodiment further includes a switching circuit 14. The switching circuit 14 switches the connection mode of the passive element 13 to the control element Q1 in response to the magnitude of the current I1 flowing through the light source 2. In other words, in this embodiment, the passive element 13 is not always connected to the control element Q1 in the same connection mode, but the connection mode of the passive element 13 is switched in response to the magnitude of the current I1 flowing through the light source 2.

[0059] For example, when the dimming ratio is low and the current I1 flowing through the light source 2 is relatively small, the loss in the passive element 13 can be kept small by reducing the proportion of the current diverted from the control element Q1 to the passive element 13.

[0060] In this embodiment, the connection modes include a first mode in which the passive element 13 is electrically connected to the control element Q1, and a second mode in which the passive element 13 is electrically disconnected from the control element Q1. That is, the switching circuit 14 can switch between at least two states: a state in which the passive element 13 is electrically connected to the control element Q1 (first mode), and a state in which the passive element 13 is electrically disconnected from the control element Q1 (second mode).

[0061] Specifically, as shown in Fig. 4, the switching circuit 14 includes a switching element Q2 and a switching control unit 141. The switching element Q2 is electrically connected in series with the passive element 13 across the control element Q1. The switching element Q2 is made of a semiconductor element such as an enhancement type n-channel MOSFET. Therefore, when the switching element Q2 is in an on state (a state in which the drain and source are conductive), the passive element 13 is electrically connected in parallel with the control element Q1 (first mode). On the other hand, when the switching element Q2 is in an off state (a state in which the drain and source are disconnected), the passive element 13 is electrically disconnected from the control element Q1 (second mode).

[0062] According to this configuration, for example, when the dimming rate is low and the current I1 flowing through the light source 2 is relatively small, the passive element 13 is electrically separated from the control element Q1 (second mode), thereby making it possible to suppress loss in the passive element 13.

[0063] Moreover, in this embodiment, the switching circuit 14 switches the connection mode based on a dimming ratio corresponding to the magnitude of the current I1 flowing through the light source 2. Specifically, the switching control unit 141 of the switching circuit 14 mainly comprises, for example, a microcontroller or the like, and acquires a dimming signal Si1 (from a dimming device or the like) as shown in Fig. 4. Then, the switching control unit 141 controls the switching element Q2 to switch the connection mode of the passive element 13 based on the dimming ratio included in the dimming signal Si1.

[0064] This configuration makes it possible to switch the connection state of the passive element 13 with a relatively simple configuration. As an example, if the dimming ratio is equal to or greater than a predetermined threshold, the switching control unit 141 turns on the switching element Q2 to set the passive element 13 to a first state in which it is electrically connected in parallel to the control element Q1. On the other hand, if the dimming ratio is less than the predetermined threshold, the switching control unit 141 turns off the switching element Q2 to set the passive element 13 to a second state in which it is electrically disconnected from the control element Q1.

[0065] Furthermore, in the lighting circuit 1 according to this embodiment, as shown in Fig. 5, the switching circuit 14 may have a time constant for switching the connection mode. Specifically, in the example of Fig. 5, the switching circuit 14 has a resistor R3 and a capacitor C2. The capacitor C2 is electrically connected between the source and gate of the switching element Q2. The resistor R3 is inserted between the switching control unit 141 and the gate of the switching element Q2. As a result, a time constant determined by the resistor R3 and the capacitor C2 is applied to the control by the switching control unit 141 to turn on / off the switching element Q2.

[0066] Therefore, when the switching control unit 141 turns on / off the switching element Q2 to switch the connection mode of the passive element 13, the connection mode of the passive element 13 is switched slowly by so-called soft switching control. As a result, flickering of the light source 2 caused by switching the connection mode can be suppressed compared to when the connection mode of the passive element 13 is switched abruptly.

[0067] The configuration of the second embodiment (including the modified examples) can be adopted in appropriate combination with the various configurations (including the modified examples) described in the first embodiment.

[0068] (Embodiment 3) As shown in Fig. 6, the lighting device 10B according to this embodiment differs from the second embodiment (the modified example shown in Fig. 5) in the configuration of the switching circuit 14 in the lighting circuit 1. Hereinafter, the same components as those in the second embodiment will be denoted by the same reference numerals and the description thereof will be omitted as appropriate.

[0069] In this embodiment, the switching control unit 141 of the switching circuit 14 controls the switching element Q2 based on the voltage across the shunt resistor R2. That is, the switching circuit 14 directly monitors (using the shunt resistor R2) the magnitude of the current I1 flowing through the light source 2, rather than the dimming rate, and switches the connection state of the passive element 13 with respect to the control element Q1 according to the magnitude of the current I1.

[0070] As an example, the switching control unit 141 compares the voltage across the shunt resistor R2, which corresponds to the magnitude of the current I1, with a judgment threshold, and if the voltage across the shunt resistor R2 is equal to or greater than the judgment threshold, the switching control unit 141 switches the switching element Q2 to an ON state, and assumes a first mode in which the passive element 13 is electrically connected in parallel to the control element Q1. On the other hand, if the voltage across the shunt resistor R2 is less than the judgment threshold, the switching control unit 141 switches the switching element Q2 to an OFF state, and assumes a second mode in which the passive element 13 is electrically disconnected from the control element Q1.

[0071] According to this configuration, the switching circuit 14 can autonomously switch the connection state, and therefore there is no need to use an external signal such as the dimming signal Si1. However, the switching control unit 141 needs comparators for the number of switching elements Q2.

[0072] In the lighting circuit 1 according to this embodiment, similarly to the configuration of the second embodiment shown in FIG. 4, the resistor R3 and the capacitor C2 for soft switching can be omitted as appropriate.

[0073] The configuration of the third embodiment (including the modified examples) can be adopted in appropriate combination with the various configurations (including the modified examples) described in the first or second embodiment.

[0074] [Appendix to the invention] The following will provide an overview of the invention extracted from the above-described embodiment. Note that the configurations and processing functions described in the following supplementary notes can be selected and combined as desired.

[0075] <Appendix 1> A lighting circuit for a light source including a light emitting element whose light quantity changes according to the magnitude of a supply current, a constant current circuit having a control element electrically connected in series with the light source and controlling a magnitude of a current flowing through the light source; A passive element that can be electrically connected in parallel with the control element. Lighting circuit.

[0076] <Appendix 2> The passive element includes a resistor. 2. The lighting circuit according to claim 1.

[0077] <Appendix 3> a switching circuit that switches a connection state of the passive element with respect to the control element in accordance with a magnitude of a current flowing through the light source; 3. The lighting circuit according to claim 1 or 2.

[0078] <Appendix 4> The connection mode includes a first mode in which the passive element is electrically connected to the control element, and a second mode in which the passive element is electrically disconnected from the control element. 4. The lighting circuit according to claim 3.

[0079] <Appendix 5> The switching circuit has a time constant for switching the connection mode. 5. The lighting circuit according to claim 3 or 4.

[0080] <Appendix 6> The switching circuit switches the connection mode based on a dimming ratio corresponding to a magnitude of a current flowing through the light source. 6. The lighting circuit according to claim 3,

[0081] <Appendix 7> The constant current circuit has a control unit that controls the control element in accordance with the magnitude of the second current flowing through the passive element. 6. The lighting circuit according to claim 1,

[0082] <Appendix 8> The control unit determines a magnitude of the second current from a combined current of the second current and a first current flowing through the control element. 8. The lighting circuit according to claim 7.

[0083] <Appendix 9> Further comprising a power factor correction circuit. A lighting circuit according to any one of claims 1 to 8.

[0084] <Appendix 10> A lighting circuit according to any one of appendix 1 to 9, The light source, Lighting equipment. [Explanation of symbols]

[0085] 1 Lighting circuit 2 light source 10,10A,10B lighting equipment 11 Driver circuit (power factor correction circuit) 12 Constant current circuit 13 Passive elements 14 Switching circuit 21 Light emitting element I1 Current flowing through the light source (composite current) I11 1st current I12 2nd current Q1 control element R1, R11, R12 resistors

Claims

1. A lighting circuit for a light source including a light emitting element whose light quantity changes according to the magnitude of a supply current, a constant current circuit having a control element electrically connected in series with the light source and controlling a magnitude of a current flowing through the light source; A passive element that can be electrically connected in parallel with the control element. Lighting circuit.

2. The passive element includes a resistor. The lighting circuit according to claim 1.

3. a switching circuit that switches a connection state of the passive element with respect to the control element in accordance with a magnitude of a current flowing through the light source; The lighting circuit according to claim 1 or 2.

4. The connection mode includes a first mode in which the passive element is electrically connected to the control element, and a second mode in which the passive element is electrically disconnected from the control element. The lighting circuit according to claim 3.

5. The switching circuit has a time constant for switching the connection mode. The lighting circuit according to claim 3.

6. The switching circuit switches the connection mode based on a dimming ratio corresponding to a magnitude of a current flowing through the light source. The lighting circuit according to claim 3.

7. The constant current circuit has a control unit that controls the control element in accordance with a magnitude of the second current flowing through the passive element. The lighting circuit according to claim 1 or 2.

8. The control unit determines a magnitude of the second current from a combined current of the second current and a first current flowing through the control element. The lighting circuit according to claim 7.

9. Further comprising a power factor correction circuit. The lighting circuit according to claim 1 or 2.

10. A lighting circuit according to claim 1 or 2; The light source, Lighting equipment.

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