Lighting device

Abstract

A lighting device (10) comprises: a constant current source (13) which supplies a constant current to a light source (3) configured such that LEDs (4a-4f) are connected in series; switch elements (17a-17f) which are connected in parallel with at least one of the LEDs (4a-4f); a low-potential-side current detection circuit (15), which is an example of an abnormal power detection unit for detecting abnormal power (low-potential-side current detection circuit (15) which detects a current that flows from a low-potential-side terminal (3b) of the light source (3) to the constant current source (13)); and a control circuit (16) which, when the current detected by the low-potential-side current detection circuit (15) is less than a prescribed value, performs control to turn on at least one of the switch elements (17a-17f).

Description

lighting device

[0001] The present disclosure relates to a lighting device, and more particularly to a lighting device that supplies current to a light source configured with an LED.

[0002] Conventionally, in a lighting device that supplies current to a light source composed of an LED, a lighting device has been proposed that can detect an abnormality when an abnormality occurs such as current leaking outside the current loop due to a ground fault or the like at any point in the current loop (see, for example, Patent Document 1).

[0003] The technology of Patent Document 1 detects the current returning from the low-potential terminal of the LED to the DC power supply, and when an abnormality in which current is leaking outside the current loop is detected, the voltage applied to the light source is reduced, thereby suppressing the current leaking outside the current loop.

[0004] Japanese Patent Application Laid-Open No. 2004-134147

[0005] However, the technology of Patent Document 1 involves controlling the output voltage of the switching regulator that applies voltage to the light source to decrease when current leakage outside the current loop is detected, which poses the problem of complex control.

[0006] Therefore, the present disclosure aims to provide a lighting device that can reduce the voltage applied to a light source through simple control when abnormal power occurs, such as current leakage outside the current loop.

[0007] In order to achieve the above object, a lighting device according to one embodiment of the present disclosure includes a constant current source that supplies a constant current to a light source configured by one or more LEDs connected in series, a switch element that is connected in parallel with at least one of the one or more LEDs, an abnormal power detection unit that detects abnormal power, and a control circuit that controls at least one of the switch elements to be turned on when the abnormal power detection unit determines that abnormal power has been detected.

[0008] The present disclosure provides a lighting device that can reduce the voltage applied to a light source through simple control when abnormal power occurs, such as current leakage outside the current loop.

[0009] FIG. 1 is a block diagram showing a circuit configuration of a lighting device according to an embodiment. FIG. 2 is a diagram showing a specific example of the circuit configuration of the constant current source and the low-side current detection circuit shown in FIG. 1. FIG. 3A is a flowchart showing the basic operation of the lighting device according to an embodiment. FIG. 3B is a diagram showing an example of a ground fault that occurs in the lighting device according to an embodiment. FIG. 3C is a diagram showing a state in which the switch elements are turned on when a ground fault occurs in the lighting device according to an embodiment. FIG. 4 is a timing chart showing the operation of the lighting device when the control shown in the flowchart of FIG. 3A is performed. FIG. 5 is a flowchart showing the operation of the lighting device according to an embodiment to repeatedly control on and off at least one of the switch elements. FIG. 6 is a timing chart showing the operation of the lighting device when the control shown in the flowchart of FIG. 5 is performed. FIG. 7 is a flowchart showing the operation of the lighting device according to an embodiment to control a circuit breaker. FIG. 8 is a diagram showing various examples of connections between LEDs and switch elements that constitute a light source provided in the lighting device according to an embodiment. FIG. 9 is a diagram showing an example of a circuit configuration of a lighting device according to a modification of the embodiment. FIG. 10 is a flowchart showing an example of how to turn on switch elements (the number of switch elements to be turned on) when abnormal power is detected in the embodiment and its modification. FIG. 11 is a flowchart showing an example of how to turn on switch elements (the order in which switch elements are turned on) when abnormal power is detected in the embodiment and its modifications.

[0010] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. Note that each embodiment described below represents a specific example of the present disclosure. The numerical values, numbers, components, arrangement and connection of components, steps, order of steps, etc. shown in the following embodiments are merely examples and are not intended to limit the present disclosure. Furthermore, each figure is not necessarily an exact illustration. In each figure, substantially identical configurations are assigned the same reference numerals, and redundant explanations are omitted or simplified. Furthermore, "A and B are connected" means that A and B are electrically connected, and includes not only the case where A and B are directly connected, but also the case where A and B are indirectly connected with another circuit element interposed between A and B.

[0011] FIG. 1 is a block diagram showing the circuit configuration of a lighting device 10 according to an embodiment. The lighting device 10 receives a DC voltage via input terminals 2a and 2b and supplies a target constant current to a light source 3 composed of LEDs 4a to 4f connected in series. The lighting device 10 includes a circuit breaker 11, an input filter 12, a constant current source 13, an output filter 14, a low-side current detection circuit 15, a control circuit 16, and switch elements 17a to 17f. Each of the LEDs 4a to 4f is composed of one or more LEDs connected in series or in parallel. The light source 3 and the lighting device 10 that supplies current to the light source 3 together constitute a lighting device.

[0012] The circuit breaker 11 is a switch circuit that turns on and off the power supply from the outside to the constant current source 13 under the control of the control circuit 16, and in this embodiment is provided between the input terminal 2a and the input filter 12, and is, for example, a normally-on semiconductor switch or an electromagnetic relay. Note that in a normal state where no abnormality such as a ground fault occurs, the circuit breaker 11 is on.

[0013] The input filter 12 is a filter that removes noise contained in the DC voltage input to the lighting device 10 from the input terminals 2a and 2b, and is, for example, a low-pass filter configured by a coil and a capacitor.

[0014] The constant current source 13 is a circuit that supplies a constant target current (i.e., a constant current) to the light source 3. A specific configuration will be described later with reference to FIG. 2. The constant current source 13 operates to supply a constant target current to the light source 3 even if the load resistance varies due to the on / off of the switch elements 17a to 17f, and therefore has the property of reducing the output voltage when the load resistance decreases due to the on-state of the switch elements 17a to 17f. The constant target current may be a fixed value, or may be a variable value that is specified by the user via infrared communication or the like.

[0015] The output filter 14 is a filter that smoothes the voltage and current applied from the constant current source 13 between the high potential side terminal 3a and the low potential side terminal 3b of the light source 3, and is, for example, a low pass filter composed of a coil and a capacitor.

[0016] The low potential side current detection circuit 15 is an example of an abnormal power detection unit for detecting abnormal power such as current leakage outside the current loop, and in this embodiment, it is a circuit that detects the current returning from the low potential side terminal 3 b of the light source 3 to the constant current source 13 (hereinafter, this current will also be referred to as the "low potential side current") and notifies the control circuit 16 of a signal indicating the detected current, and its specific configuration will be described later with reference to Fig. 2. Note that the low potential side current detection circuit 15 is an example of an abnormal power detection unit for detecting abnormal power such as current leakage outside the current loop, and other examples of abnormal power detection units will be described later with reference to Fig. 9.

[0017] The switch elements 17a to 17f are connected in parallel to the LEDs 4a to 4f, respectively, and are elements that are turned on and off under the control of the control circuit 16, and are, for example, field effect transistors (FETs). Note that, in a normal state, all of the switch elements 17a to 17f are turned off.

[0018] The control circuit 16 is a circuit, such as a microcomputer executing a built-in control program, that determines that an abnormality such as a ground fault has occurred when the low-potential-side current detected by the low-potential-side current detection circuit 15 is smaller than a predetermined value and controls the turning on of at least one of the switch elements 17a to 17f. By controlling the turning on of at least one of the switch elements 17a to 17f, the load resistance of the light source 3 decreases, thereby reducing the output voltage of the constant current source 13, which continuously supplies a constant current. This reduces current leakage outside the current loop due to a ground fault or the like. Here, the predetermined value may be a preset fixed value, a constant target current output by the constant current source 13, or a value obtained by correcting the target current (e.g., 0.9 times the target current).

[0019] Here, the control circuit 16 may perform the above control by repeatedly turning on and off at least one of the switch elements 17a to 17f. In this case, the control circuit 16 may perform control such that the on-duty of the repeatedly turning on and off is reduced as the low potential side current detected by the low potential side current detection circuit 15 becomes smaller than a predetermined value. Furthermore, the control circuit 16 may perform control such that more of the switch elements 17a to 17f are turned on as the low potential side current detected by the low potential side current detection circuit 15 becomes smaller than a predetermined value. Which control method is used, or whether both control methods are used simultaneously, may be determined by prior settings of the control circuit 16, etc.

[0020] Furthermore, the control circuit 16 also performs control to turn off the circuit breaker 11 when the state in which the low potential side current detected by the low potential side current detection circuit 15 is smaller than a predetermined value continues for a predetermined time or more. Here, the predetermined time may be determined by a setting in advance for the control circuit 16, or the like.

[0021] FIG. 2 is a diagram showing a specific example of the circuit configuration of the constant current source 13 and the low potential side current detection circuit 15 in FIG.

[0022] 2, the constant current source 13 is composed of a DC-DC converter 13a, a high-side current detection circuit 13b, and a smoothing capacitor C2. The DC-DC converter 13a is a step-up / step-down converter composed of a capacitor C1, transistors Tr1 and Tr2, diodes D1 and D2, a coil L1, and a drive circuit Dr. The output from the DC-DC converter 13a is smoothed by the smoothing capacitor C2.

[0023] The high-potential-side current detection circuit 13b is composed of resistors R1 to R4, a differential amplifier Amp1, and a transistor Tr3, and detects the current (hereinafter also referred to as the "high-potential-side current") supplied by the constant current source 13 to the high-potential-side terminal 3a of the light source 3. The high-potential-side current detection circuit 13b converts the current flowing through the resistor R1 into a voltage and notifies the drive circuit Dr. Based on the notification from the high-potential-side current detection circuit 13b, the drive circuit Dr outputs drive signals such as PWM (Pulse Width Modulation) signals or logic signals to the transistors Tr1 and Tr2 to control the on / off of the transistors Tr1 and Tr2 so that the high-potential-side current detected by the high-potential-side current detection circuit 13b becomes a constant target current (a constant current).

[0024] 2, the low-potential-side current detection circuit 15 is composed of resistors R5 to R8, a differential amplifier Amp2, and a transistor Tr4, and detects the low-potential-side current returning from the low-potential-side terminal 3b of the light source 3 to the constant current source 13. The low-potential-side current detection circuit 15 converts the low-potential-side current flowing through the resistor R5 into a voltage and notifies the control circuit 16 of the voltage.

[0025] Next, the operation of the lighting device 10 according to the present embodiment configured as above will be described.

[0026] 3A is a flowchart showing the basic operation of lighting device 10 according to the embodiment. It is assumed that lighting device 10 is in a normal state where no ground fault or the like occurs. In the normal state, under the control of control circuit 16, circuit breaker 11 is turned on, all switch elements 17a to 17f are turned off, and constant current source 13 supplies a constant target current to light source 3.

[0027] First, based on a notification from the low-potential side current detection circuit 15, the control circuit 16 determines whether an abnormality has occurred in which the low-potential side current detected by the low-potential side current detection circuit 15 is smaller than a predetermined value (e.g., 0.9 times the target current) (S10).

[0028] Now, assume that a ground fault as shown in Figure 3B has occurred. Figure 3B is a diagram illustrating an example of a ground fault that has occurred in lighting device 10 according to the embodiment. In this example, current (i.e., ground fault current) leaks from the connection point between LED 4c and LED 4d toward the outside of the current loop (i.e., ground). In this state, the low potential side current detected by low potential side current detection circuit 15 is the current (e.g., 0.7 times the target current) remaining after subtracting the ground fault current that has leaked outside the current loop from the current detected in the normal state (i.e., a constant target current).

[0029] Then, control circuit 16 determines that an abnormality has occurred in which the low potential side current detected by low potential side current detection circuit 15 is smaller than a predetermined value (Yes in S10), and performs control to turn on a predetermined switch element (for example, switch element 17a) among switch elements 17a to 17f (S11), as shown in Fig. 3C. Fig. 3C is a diagram showing a state in which switch element 17a is turned on when a ground fault occurs in lighting device 10 according to the embodiment.

[0030] In step S11, when turning on a predetermined switch element, the control circuit 16 calculates the difference between a predetermined value and the low potential side current detected by the low potential side current detection circuit 15, and the larger the calculated difference (i.e., the smaller the low potential side current is than the predetermined value), the more switch elements may be turned on. For example, when the low potential side current is smaller than the predetermined value and is 0.7 times or more the predetermined value, only the switch element 17a may be turned on, and when the low potential side current is smaller than 0.7 times the predetermined value, all the switch elements 17a to 17f may be turned on.

[0031] 4 is a timing chart showing the operation of lighting device 10 when the control shown in the flowchart of FIG. 3A is performed. Shown here are the waveforms of the low-side current detected by low-side current detection circuit 15 ((a) of FIG. 4), the control signal to a switch element (here, switch element 17a) that is controlled to be turned on by control circuit 16 when an abnormality occurs ((b) of FIG. 4), the output voltage of constant current source 13 ((c) of FIG. 4), and the output current of constant current source 13 ((d) of FIG. 4). The time point at which a ground fault occurs is indicated by a triangle.

[0032] As shown in FIG. 4A, when a ground fault occurs, the low-side current detected by the low-side current detection circuit 15 decreases by the amount of the ground-fault current leaking outside the current loop. The control circuit 16 then receives this notification and controls only a specific switch element (e.g., switch element 17a) to be turned on, as shown in FIG. 4B. As a result, the LEDs receiving current are reduced from LEDs 4a-4f to LEDs 4b-4f, and the load resistance of the light source 3 decreases. As shown in FIG. 4C, the output voltage of the constant current source 13 decreases by the amount of the decrease in load resistance. This decrease in the output voltage of the constant current source 13 can suppress current leakage outside the current loop. The output current of the constant current source 13 is maintained at a constant current that supplies a constant target current to the light source 3, as shown in FIG. 4D.

[0033] In this manner, in the present embodiment, when current leakage outside the current loop occurs, the voltage applied to the light source 3 is reduced by simple control of turning on at least one of the switch elements 17a to 17f connected in parallel to the LEDs 4a to 4f, thereby suppressing the current leaking outside the current loop.

[0034] FIG. 5 is a flowchart showing the operation of the lighting device 10 according to the embodiment to repeatedly control on and off at least one of the switch elements 17a to 17f.

[0035] First, based on a notification from the low-potential side current detection circuit 15, the control circuit 16 determines whether an abnormality has occurred in which the low-potential side current detected by the low-potential side current detection circuit 15 is smaller than a predetermined value (for example, 0.9 times the target current) (S20).

[0036] As a result, when it is determined that an abnormality has occurred in which the low potential side current detected by the low potential side current detection circuit 15 is smaller than a predetermined value due to the occurrence of a ground fault as shown in FIG. 3B (Yes in S20), the control circuit 16 controls predetermined switch elements (for example, switch elements 17a and 17b) among the switch elements 17a to 17f to repeatedly turn on and off (S21).

[0037] In step S21, when repeatedly turning on and off a predetermined switch element, the control circuit 16 calculates the difference between a predetermined value and the low potential side current detected by the low potential side current detection circuit 15, and the larger the calculated difference (i.e., the smaller the low potential side current is than the predetermined value), the smaller the on-duty in the control of repeatedly turning on and off. For example, when the low potential side current is smaller than the predetermined value and is 0.7 times or more the predetermined value, the control circuit 16 may repeatedly turn on and off the switch elements 17a and 17b with an on-duty of 50%, and when the low potential side current is smaller than 0.7 times the predetermined value, the control circuit 16 may repeatedly turn on and off the switch elements 17a and 17b with an on-duty of 20%.

[0038] Fig. 6 is a timing chart showing the operation of lighting device 10 when the control shown in the flowchart of Fig. 5 is performed. Shown here are the waveforms of the low-side current detected by low-side current detection circuit 15 (Fig. 6(a)), the control signal to switch elements (here, switch elements 17a and 17b) controlled to be turned on by control circuit 16 when an abnormality occurs (Fig. 6(b)), the output voltage of constant current source 13 (Fig. 6(c)), and the output current of constant current source 13 (Fig. 6(d)). The time point when a ground fault occurs is indicated by a triangle.

[0039] As shown in FIG. 6A, when a ground fault occurs, the low-side current detected by the low-side current detection circuit 15 decreases by the amount of the ground-fault current leaking outside the current loop. Then, upon receiving this notification, the control circuit 16 controls certain switch elements (e.g., switch elements 17a and 17b) to repeatedly turn on and off, as shown in FIG. 6B. As a result, the LEDs to which current is supplied alternately switch between LEDs 4a-4f and LEDs 4c-4f, causing the load resistance of the light source 3 to alternate between a normal value and a low value. As shown in FIG. 6C, the output voltage of the constant current source 13 alternates between a normal value and a low value. This reduces the average output voltage of the constant current source 13, thereby suppressing the average value of current leaking outside the current loop. The output current of the constant current source 13 is maintained at a constant current that supplies a constant target current to the light source 3, as shown in FIG. 6D.

[0040] In this way, when current leakage outside the current loop occurs, the average value of the voltage applied to the light source 3 is reduced by simple control of repeatedly turning on and off at least one of the switch elements 17a to 17f connected in parallel to the LEDs 4a to 4f, thereby suppressing the average value of the current leaking outside the current loop.

[0041] 7 is a flowchart showing the operation of the lighting device 10 according to the embodiment to control the circuit breaker 11. It is now assumed that the lighting device 10 is in a normal state and the circuit breaker 11 is on.

[0042] First, based on a notification from the low-potential-side current detection circuit 15, the control circuit 16 determines whether an abnormality in which the low-potential-side current detected by the low-potential-side current detection circuit 15 is smaller than a predetermined value (e.g., 0.9 times the target current) has continued for a predetermined period of time (e.g., 3 seconds) (S30).

[0043] 3B occurs, and if it is determined that the abnormality in which the low potential side current detected by the low potential side current detection circuit 15 is smaller than a predetermined value continues for a predetermined time (e.g., 3 seconds) (Yes in S30), the control circuit 16 controls to turn off the circuit breaker 11 (S31), thereby preventing the abnormality such as the ground fault from continuing.

[0044] The control shown in the flowchart of FIG. 3A, the control shown in the flowchart of FIG. 5, and the control shown in the flowchart of FIG. 7 may be performed independently, or two or more of these controls may be performed in combination.

[0045] For example, when an abnormality such as a ground fault occurs, the smaller the detected low-potential-side current is than a predetermined value, the more switch elements are targeted (flowchart of FIG. 3A) and control may be performed to repeatedly turn them on and off (flowchart of FIG. 5).

[0046] Instead of or in addition to step S31 (turning off the circuit breaker 11), the output of the constant current source 13 may be stopped by stopping the operation of the drive circuit Dr of the constant current source 13.

[0047] Furthermore, when an abnormality such as a ground fault occurs, the smaller the detected low potential side current is than a predetermined value, the more switching elements are targeted (flowchart in FIG. 3A), and the smaller the on-duty in the control that repeatedly turns on and off may be (flowchart in FIG. 5).

[0048] Furthermore, while these controls are being performed, if the abnormality continues for a predetermined time, control may be performed to turn off the circuit breaker 11 (flowchart in FIG. 7).

[0049] In addition, in this embodiment, as shown in FIG. 1, switch elements 17a to 17f are provided to be connected in parallel to all of the LEDs 4a to 4f, respectively. However, this configuration is not necessarily limited to this, and LEDs that are not provided with switch elements connected in parallel may also be included.

[0050] Fig. 8 is a diagram showing various connection examples between LEDs and switch elements that constitute the light source 3 included in the lighting device 10 according to the embodiment. In the light source 3 included in the lighting device 10, as shown in Fig. 8(a), a switch element may be connected in parallel to each LED, as shown in Fig. 8(b), an LED may be included that is not connected in parallel to a switch element, as shown in Fig. 8(c), a plurality of series-connected LEDs that are connected in parallel to a switch element may be included, or as shown in Fig. 8(d), a plurality of LEDs may be included that are not connected in parallel to a switch element.

[0051] 9 is a diagram showing an example of the circuit configuration of a lighting device according to a modification of the embodiment. The lighting device according to this modification basically has the same configuration as lighting device 10 according to the embodiment, but the specific configuration of the abnormal power detection unit differs from that of the embodiment. That is, while the embodiment uses low-side current detection circuit 15 as a specific example of the configuration of the abnormal power detection unit, this modification uses abnormal power detection unit 20 provided in control circuit 16a as a specific example of the configuration of the abnormal power detection unit.

[0052] In this modified example, the abnormal power detection unit 20 is a function of the control circuit 16a that is realized by a program and a processor that executes the program, and detects the on-duty of the drive signal output from the drive circuit Dr of the constant current source 13 to the switching elements (i.e., transistors Tr1 and Tr2).

[0053] In addition to the functions of the control circuit 16 described in the embodiment, the control circuit 16a has a function of determining that abnormal power has been detected when the on-duty cycle detected by the abnormal power detection unit 20 falls outside a predetermined range and controlling the turning on of at least one of the switch elements 17a to 17f. As described with reference to FIG. 4, when current leakage occurs outside the current loop, the load resistance of the light source 3 decreases, causing the output voltage of the constant current source 13 to decrease. In order to reduce the output voltage of the constant current source 13, the on-duty cycle of the drive signal output from the drive circuit Dr to the switching elements (i.e., transistors Tr1 and Tr2) falls outside a predetermined range. Therefore, the abnormal power detection unit 20 of the control circuit 16a monitors the drive signal output from the drive circuit Dr and determines that abnormal power has been detected when the on-duty cycle indicated by the drive signal falls outside the predetermined range.

[0054] In this way, instead of the low potential side current detection circuit 15 in the embodiment, an abnormal power detection unit for detecting abnormal power can also be realized by the control circuit 16a (strictly speaking, the abnormal power detection unit 20 of the control circuit 16a) that monitors the drive signal output from the drive circuit Dr.

[0055] 10 is a flowchart showing an example of how to turn on the switch elements 17a-17f (the number of switch elements to turn on) when abnormal power is detected in the embodiment and its modified example. Here, when the abnormal power detection unit detects abnormal power (S40), the control circuit 16 or 16a changes the number of switch elements 17a-17f to turn on (S41) depending on the level of abnormal power detected by the abnormal power detection unit. For example, when the abnormal power detection unit detects abnormal power, the control circuit 16 or 16a turns on more switch elements 17a-17f as the level of abnormal power detected by the abnormal power detection unit increases (e.g., as the current detected by the low-potential-side current detection circuit 15 decreases below a predetermined value). As a result, for example, if current leakage occurs outside the current loop, the greater the leakage current, the greater the likelihood of suppressing the leakage current.

[0056] 11 is a flowchart showing an example of how to turn on the switch elements 17a to 17f (the order in which the switch elements are turned on) when abnormal power is detected in the embodiment and its modified examples. Here, when the abnormal power detection unit detects abnormal power (S50), the control circuit 16 or 16a turns on the switch elements 17a to 17f in order, starting with the switch element closest to the low-potential terminal 3b of the light source 3 (S51), as one example. This provides a safer procedure in terms of potential than the reverse procedure (a method in which the switch elements are turned on in order starting with the switch element closest to the high-potential terminal 3a of the light source 3).

[0057] Alternatively, when the abnormal power detection unit detects abnormal power (S50), as another example, the control circuit 16 or 16a turns on the switch elements 17a to 17f in order, starting with the switch element that was last turned off when the abnormal power detection unit detected abnormal power (S51). This prioritizes short-circuiting the LED block that is most likely to have a ground fault, thereby increasing the possibility of suppressing current leakage outside the current loop.

[0058] Whether to adopt the control procedure in the above example (turning on the switch elements in order from the switch element closest to the low potential side terminal 3 b) or in another example (turning on the switch elements in order from the switch element that was last turned off) may be determined by a prior setting of the control circuit 16 or 16 a.

[0059] As described above, the lighting device 10 according to the embodiment includes a constant current source 13 that supplies a constant current to the light source 3 configured by connecting one or more LEDs 4a to 4f in series, switch elements 17a to 17f that are connected in parallel with at least one of the one or more LEDs 4a to 4f, an abnormal power detection unit for detecting abnormal power (in the embodiment, a low potential side current detection circuit 15 that detects the current flowing from the low potential side terminal 3b of the light source 3 to the constant current source 13), and a control circuit 16 that controls to turn on at least one of the switch elements 17a to 17f when the abnormal power detection unit determines that abnormal power has been detected (in the embodiment, the current detected by the low potential side current detection circuit 15 is smaller than a predetermined value).

[0060] As a result, when abnormal power such as current leakage outside the current loop occurs, the voltage applied to the light source 3 is reduced by simple control of turning on at least one of the switch elements 17a to 17f connected in parallel to the LEDs 4a to 4f, thereby suppressing the abnormal power (such as current leaking outside the current loop).

[0061] In the lighting device according to the modified example, the constant current source 13 includes switching elements (i.e., transistors Tr1 and Tr2) and a drive circuit Dr that drives the switching elements. The abnormal power detection unit 20 detects the on-duty of the switching elements driven by the drive circuit Dr. The control circuit 16a determines that abnormal power has been detected when the on-duty detected by the abnormal power detection unit 20 falls outside a predetermined range, and controls the turning on of at least one of the switch elements 17a to 17f. In this way, instead of the low-side current detection circuit 15 in the embodiment, the abnormal power detection unit for detecting abnormal power can also be realized by the abnormal power detection unit 20 of the control circuit 16a that monitors the drive signal from the drive circuit Dr to the switching elements. Note that the lighting device may include both the low-side current detection circuit 15 in the embodiment and the abnormal power detection unit 20 of the control circuit 16a that monitors the drive signal from the drive circuit Dr to the switching elements.

[0062] In the embodiment, the control circuit 16 may perform the above control by repeatedly turning on and off at least one of the switch elements 17a to 17f. This allows the degree of reduction in the voltage applied to the light source 3 to be adjusted by adjusting the on-duty in the control of repeatedly turning on and off.

[0063] In this case, in the embodiment, the control circuit 16 may reduce the on-duty in the control of repeating on and off as the current detected by the low potential side current detection circuit 15 becomes smaller than a predetermined value. As a result, the voltage applied to the light source 3 decreases more significantly as the current leakage outside the current loop increases, and the current leakage outside the current loop is further suppressed.

[0064] Furthermore, the light source 3 may be configured with a plurality of LEDs 4a-4f connected in series, and the switch elements 17a-17f may be configured with a plurality of switch elements 17a-17f connected in parallel to different ones of the plurality of LEDs 4a-4f, respectively, and the control circuit 16 may perform control to turn on at least one of the plurality of switch elements 17a-17f when the abnormal power detection unit detects abnormal power (in the embodiment, when the current detected by the low-potential-side current detection circuit 15 is smaller than a predetermined value). In the embodiment, the abnormal power detection unit is the low-potential-side current detection circuit 15, and the control circuit 16 performs control when the current detected by the low-potential-side current detection circuit 15 is smaller than a predetermined value.

[0065] This allows for simple control to suppress abnormal power such as current leakage outside the current loop in the lighting device 10 having the light source 3 configured with a plurality of LEDs 4a to 4f connected in series.

[0066] Furthermore, when the abnormal power detection unit detects abnormal power (S40), the control circuit 16 or 16a may change the number of switch elements 17a to 17f to turn on depending on the level of abnormal power detected by the abnormal power detection unit. As a result, for example, when current leakage outside the current loop occurs, the greater the leakage current, the more likely it is that the leakage current can be suppressed.

[0067] At this time, the control circuit 16 may perform control to turn on more of the switch elements 17a to 17f among the plurality of switch elements 17a to 17f as the current detected by the low potential side current detection circuit 15 becomes smaller than a predetermined value. As a result, the voltage applied to the light source 3 decreases more significantly as the current leakage outside the current loop increases, and the current leakage outside the current loop is further suppressed.

[0068] Here, when the abnormal power detection unit detects abnormal power (S50), the control circuit 16 or 16a may, as one example, turn on the switch elements 17a to 17f in order starting from the switch element closest to the low potential side terminal 3b of the light source 3 (S51). This provides a safer procedure in terms of potential than the reverse procedure (a method of turning on the switch elements in order starting from the switch element closest to the high potential side terminal 3a of the light source 3).

[0069] Alternatively, when the abnormal power detection unit detects abnormal power (S50), as another example, the control circuit 16 or 16a turns on the switch elements 17a to 17f in order, starting with the switch element that was last turned off when the abnormal power detection unit detected abnormal power (S51). This prioritizes short-circuiting the LED block that is most likely to have a ground fault, thereby increasing the possibility of suppressing current leakage outside the current loop.

[0070] The lighting device 10 may further include a circuit breaker 11 that turns on and off the power supply to the constant current source 13, and the control circuit 16 may perform control to turn off the circuit breaker 11 when the current detected by the low potential side current detection circuit 15 remains smaller than a predetermined value for a predetermined period of time or more. This prevents an abnormality such as a ground fault from continuing.

[0071] While the lighting device according to the present disclosure has been described above based on the embodiment, the present disclosure is not limited to this embodiment. As long as it does not deviate from the gist of the present disclosure, various modifications conceivable by those skilled in the art to the present embodiment and other forms constructed by combining some of the components of the embodiment are also included within the scope of the present disclosure.

[0072] For example, in the above embodiment, the constant current source 13 has the DC-DC converter 13a, but is not limited to this configuration, and may have another type of variable voltage source instead of the DC-DC converter 13a.

[0073] In the above embodiment, the LEDs 4a to 4f are merely examples of light sources, and may be replaced with other light sources such as organic electroluminescence (OLED).

[0074] Furthermore, the present disclosure can be realized not only as a lighting device, but also as a lighting device including a lighting device and a light source, as a control method or program that describes the operation of a control circuit, or as a computer-readable recording medium such as a DVD on which the program is recorded.

[0075] 3 Light source 3b Low potential side terminal 4a to 4f LED 10 Lighting device 11 Circuit breaker 13 Constant current source 15 Low potential side current detection circuit 16, 16a Control circuit 17a to 17f Switch element 20 Abnormal power detection unit Tr1, Tr2 Transistor (switching element) Dr Drive circuit

Claims

1. A lighting device comprising: a constant current source that supplies a constant current to a light source consisting of one or more LEDs connected in series; a switch element that is connected in parallel with at least one of the one or more LEDs; an abnormal power detection unit for detecting abnormal power; and a control circuit that controls at least one of the switch elements to be turned on when the abnormal power detection unit determines that abnormal power has been detected.

2. The lighting device as described in claim 1, wherein the abnormal power detection unit is a low potential side current detection circuit that detects the current flowing from the low potential side terminal of the light source to the constant current source, and the control circuit determines that abnormal power has been detected and performs the control when the current detected by the low potential side current detection circuit is smaller than a predetermined value.

3. The lighting device as described in claim 1, wherein the constant current source includes a switching element and a drive circuit that drives the switching element, the abnormal power detection unit detects the on-duty of the switching element by the drive circuit, and the control circuit determines that abnormal power has been detected when the on-duty detected by the abnormal power detection unit is outside a predetermined range, and performs the control.

4. The lighting device according to claim 1, wherein the control circuit performs the control by repeatedly turning on and off at least one of the switch elements.

5. The lighting device as described in claim 2, wherein the abnormal power detection unit is a low potential side current detection circuit that detects the current flowing from the low potential side terminal of the light source to the constant current source, and the control circuit reduces the on-duty in the control that repeatedly turns on and off the light as the current detected by the low potential side current detection circuit becomes smaller than the predetermined value.

6. The lighting device according to claim 1, wherein the light source is configured with a plurality of LEDs connected in series, the switch element is configured with a plurality of switch elements each connected in parallel to a different LED among the plurality of LEDs, and the control circuit performs control to turn on at least one of the plurality of switch elements when the abnormal power detection unit detects abnormal power.

7. The lighting device according to claim 6, wherein the control circuit changes the number of switch elements to be turned on among the plurality of switch elements according to the level of abnormal power detected by the abnormal power detection unit.

8. The lighting device as described in claim 6, wherein the abnormal power detection unit is a low potential side current detection circuit that detects a current flowing from the low potential side terminal of the light source to the constant current source, and the control circuit performs the control when the current detected by the low potential side current detection circuit is smaller than a predetermined value.

9. The lighting device according to claim 8, wherein the control circuit performs control to turn on a larger number of switch elements out of the plurality of switch elements as the current detected by the low potential side current detection circuit becomes smaller than the predetermined value.

10. The lighting device according to claim 6, wherein, when the abnormal power detection unit detects abnormal power, the control circuit sequentially turns on, among the plurality of switch elements, the switch element closest to the low potential terminal of the light source.

11. The lighting device as described in claim 6, wherein, when the abnormal power detection unit detects abnormal power, the control circuit sequentially turns on of the plurality of switch elements starting with the switch element that was last turned off when the abnormal power detection unit detected abnormal power.

12. The lighting device as claimed in claim 1, further comprising a circuit breaker which switches on and off the power supply to the constant current source, wherein the control circuit performs control to turn off the circuit breaker when the state in which the abnormal power detection unit detects abnormal power continues for a predetermined period of time or longer.

Images