Lighting device

Abstract

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

Description

Technical Field

[0001] This disclosure relates to a lighting device, and more particularly to a lighting device that supplies current to a light source composed of LEDs (light-emitting diodes). Background Technology

[0002] Previously, a lighting device that supplies current to a light source composed of LEDs has been proposed, which can detect abnormalities such as current leakage to the outside of the current loop due to grounding at any part of the current loop (for example, see Patent Document 1).

[0003] In the technology of Patent Document 1, when an anomaly of current leakage outside the current loop is detected by detecting the current returning to the DC power supply from the low-potential side terminal of the LED, control is performed to reduce the voltage applied to the light source. This suppresses the current leakage outside the current loop.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2004-134147 Summary of the Invention

[0007] The problem the invention aims to solve

[0008] However, in the technology of Patent Document 1, when leakage of current to the outside of the current loop is detected, the control to reduce the output voltage of the switching regulator that applies voltage to the light source has the problem of control complexity.

[0009] Therefore, the purpose of this disclosure is to provide a lighting device that, in the event of abnormal power such as leakage of current out of the current loop, can reduce the voltage applied to the light source through simple control.

[0010] Solution for solving the problem

[0011] To achieve the above objectives, one aspect of the lighting device disclosed herein includes: a constant current source that supplies a constant current to a light source consisting of one or more LEDs connected in series; a switching element 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, when it is determined that the abnormal power detection unit has detected abnormal power, controls at least one of the switching elements to turn on.

[0012] Invention Effects

[0013] According to this disclosure, a lighting device is provided that can reduce the voltage applied to a light source through simple control in the event of abnormal power such as leakage of current to the outside of the current loop. Attached Figure Description

[0014] Figure 1 This is a block diagram illustrating the circuit structure of the lighting device according to the embodiment.

[0015] Figure 2 It is shown Figure 1 The diagram shows a specific circuit structure example of the constant current source and low-potential side current detection circuit.

[0016] Figure 3A This is a flowchart illustrating the basic operation of the lighting device involved in the embodiment.

[0017] Figure 3B This is a diagram illustrating an example of grounding that occurs in the lighting device according to the embodiment.

[0018] Figure 3C This diagram illustrates the state in which the switching element is turned on when a grounding occurs in the lighting device according to the embodiment.

[0019] Figure 4 It is shown that in the process Figure 3A The flowchart shows the timing diagram of the operation of the lighting device under controlled conditions.

[0020] Figure 5 This is a flowchart illustrating the operation of the lighting device according to the embodiment to control the repeated switching on and off of at least one switching element.

[0021] Figure 6 It is shown that in the process Figure 5 The flowchart shows the timing diagram of the operation of the lighting device under controlled conditions.

[0022] Figure 7 This is a flowchart illustrating the operation of the lighting device according to the embodiment in controlling the circuit breaker.

[0023] Figure 8 This diagram illustrates various connection examples between the LED, the light source, and the switching element in the lighting device according to the embodiment.

[0024] Figure 9 This is a diagram illustrating an example of the circuit structure of a lighting device according to a variation of the embodiment.

[0025] Figure 10 This is a flowchart illustrating an example of a method for switching on (the number of switching elements to be switched on) in the event of an abnormal power detection in the embodiments and their variations.

[0026] Figure 11 This is a flowchart illustrating an example of a method for switching on a switching element (the order in which the switching elements are switched on) when an abnormal power is detected in an embodiment and its variations. Detailed Implementation

[0027] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings. Furthermore, the embodiments described below represent specific examples of this disclosure. The numerical values, quantities, constituent elements, arrangement positions of constituent elements, connection methods, steps, and order of steps shown in the following embodiments are examples and are not intended to limit the present disclosure. Additionally, the figures are not necessarily strictly illustrative. In the figures, substantially identical structures are labeled with the same reference numerals, and repeated descriptions are omitted or simplified. Furthermore, "A and B connected" refers to an electrical connection between A and B, including not only the case of a direct connection between A and B, but also the case of an indirect connection between A and B where other circuit elements exist between them.

[0028] Figure 1 This is a block diagram showing the circuit structure of the lighting device 10 according to the embodiment. The lighting device 10 is a device that takes a DC voltage input via input terminals 2a and 2b as input and supplies a constant current to the light source 3, which is composed of LEDs 4a to 4f connected in series, as the target. The lighting device 10 includes a circuit breaker 11, an input filter 12, a constant current source 13, an output filter 14, a low-potential side current detection circuit 15, a control circuit 16, and switching elements 17a to 17f. Furthermore, each of the LEDs 4a to 4f is configured by connecting one or more LEDs in series or in parallel. In addition, the light source 3 and the lighting device 10 that supplies current to the light source 3 together constitute a lighting device.

[0029] Circuit breaker 11 is a switching circuit that connects and disconnects the power supply from the external source to the constant current source 13 under the control of control circuit 16. In this embodiment, it is provided between input terminal 2a and input filter 12, and is, for example, a normally open semiconductor switch or electromagnetic relay. Furthermore, under normal conditions where no abnormalities such as grounding occur, circuit breaker 11 is closed.

[0030] The input filter 12 is a filter that removes noise contained in the DC voltage input from the input terminals 2a and 2b to the lighting device 10. For example, it is a low-pass filter composed of a coil and a capacitor.

[0031] Constant current source 13 is a circuit that supplies a constant target current (i.e., constant current) to light source 3. It will be used later. Figure 2The specific structure will now be described. The constant current source 13 operates such that even with fluctuations in load resistance caused by the switching elements 17a-17f turning on and off, a constant target current is supplied to the light source 3. Therefore, the constant current source 13 has the property of reducing the output voltage when the load resistance decreases due to the switching elements 17a-17f turning on. Furthermore, the constant target current can be either a fixed value or a variable value indicated by the user via infrared communication, etc.

[0032] The output filter 14 is a filter that smooths the voltage and current applied between the high-potential side terminal 3a and the low-potential side terminal 3b of the light source 3 from the constant current source 13. For example, it is a low-pass filter composed of a coil and a capacitor.

[0033] The low-potential-side current detection circuit 15 is an example of an abnormal power detection unit used to detect abnormal power such as leakage of current to the outside of the current loop. In this embodiment, it is a circuit that detects the current returning from the low-potential-side terminal 3b 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. This will be used later. Figure 2 The specific structure will be described below. Furthermore, the low-potential-side current detection circuit 15 is one example of an abnormal power detection unit used to detect abnormal current such as leakage to the outside of the current loop. Other examples of abnormal power detection units will be discussed later. Figure 9 To describe.

[0034] Switching elements 17a-17f are connected in parallel with LEDs 4a-4f, and are switched on and off under the control of control circuit 16. Examples of such elements are FETs (Field Effect Transistors). Furthermore, under normal conditions, all switching elements 17a-17f are off.

[0035] The control circuit 16 is a circuit that determines an abnormality such as grounding has occurred when the low-potential side current detected by the low-potential side current detection circuit 15 is less than a predetermined value, and controls at least one of the switching elements 17a-17f to turn on. For example, it is a microcomputer that executes a built-in control program. By controlling at least one of the switching elements 17a-17f to turn on, the load resistance of the light source 3 decreases, thus reducing the output voltage of the constant current source 13 that continuously supplies constant current. This suppresses current leakage outside the current loop due to grounding or other reasons. Here, the predetermined value can be a pre-set fixed value, or a constant target current output by the constant current source 13, or a value obtained by correcting for the target current (e.g., 0.9 times the target current).

[0036] Here, as described above, the control circuit 16 can also control at least one of the switching elements 17a-17f to be repeatedly switched on and off. Alternatively, the control circuit 16 can control the repeated switching on and off by making the duty cycle smaller as the low-potential side current detected by the low-potential side current detection circuit 15 is smaller than a predetermined value. Furthermore, the control circuit 16 can also control the switching on of more of the multiple switching elements 17a-17f by making more of them switch on as the low-potential side current detected by the low-potential side current detection circuit 15 is smaller than a predetermined value. The control method or both methods can be determined by pre-setting the control circuit 16.

[0037] Furthermore, if the low-potential side current detected by the low-potential side current detection circuit 15 is less than a predetermined value for a predetermined time or longer, the control circuit 16 also controls the circuit breaker 11 to open. Here, the predetermined time can also be determined by pre-setting the control circuit 16.

[0038] Figure 2 It is shown Figure 1 The diagram shows a specific circuit structure example of the constant current source 13 and the low-potential side current detection circuit 15.

[0039] like Figure 2 As shown, the constant current source 13 consists of a DC-DC converter 13a, a high-potential side current detection circuit 13b, and a smoothing capacitor C2. The DC-DC converter 13a is a buck-boost converter consisting 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.

[0040] The high-potential-side current detection circuit 13b consists of resistors R1~R4, a differential amplifier Amp1, and transistor Tr3. It detects the current supplied by the constant current source 13 to the high-potential-side terminal 3a of the light source 3 (hereinafter, this current will also be referred to as the "high-potential-side current"). The high-potential-side current detection circuit 13b converts the current flowing through 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 PWM (Pulse Width Modulation) signals or logic signals to transistors Tr1 and Tr2 to control the switching on and off of 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 (i.e., constant current).

[0041] On the other hand, such as Figure 2As shown, the low-potential-side current detection circuit 15 consists of resistors R5~R8, a differential amplifier Amp2, and a transistor Tr4. It 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 resistor R5 into a voltage and notifies the control circuit 16.

[0042] Next, the operation of the lighting device 10 according to this embodiment, configured as described above, will be explained.

[0043] Figure 3A This is a flowchart illustrating the basic operation of the lighting device 10 according to the embodiment. Now, assume that the lighting device 10 is in a normal state where no grounding or other issues occur. In the normal state, under the control of the control circuit 16, the circuit breaker 11 is turned on, all switching elements 17a to 17f are turned off, and the constant current source 13 supplies a constant target current to the light source 3.

[0044] First, the control circuit 16 determines, based on the notification from the low potential side current detection circuit 15, whether an abnormality has occurred where the low potential side current detected by the low potential side current detection circuit 15 is less than a specified value (e.g., 0.9 times the target current) (S10).

[0045] Now, let's assume it happened. Figure 3B The grounding shown. Figure 3B This diagram illustrates an example of grounding occurring in the lighting device 10 according to the embodiment. In this example, current (i.e., ground current) leaks from the connection point of LED 4c and LED 4d to the outside of the current loop (i.e., ground). In this state, the low-potential-side current detected by the low-potential-side current detection circuit 15 becomes the remaining current (e.g., 0.7 times the target current) obtained by subtracting the ground current leaking to the outside of the current loop from the current detected under normal conditions (i.e., the constant target current).

[0046] Therefore, control circuit 16 determines that an anomaly has occurred, as detected by low-potential side current detection circuit 15, where the low-potential side current is less than a specified value (in S10, this is "yes"). Thus, as... Figure 3C As shown, control (S11) is performed to turn on a specified switching element (e.g., switching element 17a) among the switching elements 17a to 17f. Figure 3C This diagram shows the state in which the switching element 17a is turned on when a grounding occurs in the lighting device 10 according to the embodiment.

[0047] Furthermore, in step S11, when the control circuit 16 turns on the specified switching element, it can also calculate the difference between the specified value and the low-potential side current detected by the low-potential side current detection circuit 15. The larger the calculated difference (i.e., the smaller the low-potential side current is compared to the specified value), the more switching elements are turned on. For example, the control can also be performed as follows: when the low-potential side current is less than the specified value but more than 0.7 times the specified value, only the switching element 17a is turned on; when the low-potential side current is less than 0.7 times the specified value, all switching elements 17a to 17f are turned on.

[0048] Figure 4 It is shown that in the process Figure 3A The flowchart shows the timing diagram of the operation of the lighting device 10 under controlled conditions. Here, the low-potential side current detected by the low-potential side current detection circuit 15 is shown. Figure 4 (a) The control signal for the switching element (in this case, switching element 17a) that is controlled to be turned on by control circuit 16 when an abnormality occurs. Figure 4 (b)) Output voltage of constant current source 13 Figure 4 (c) and the output current of constant current source 13 ( Figure 4 The waveform of (d) is shown. Additionally, a triangle is used to represent the point in time when a grounding event occurred.

[0049] like Figure 4 As shown in (a), when a ground fault occurs, the low-potential-side current detected by the low-potential-side current detection circuit 15 decreases by an amount corresponding to the amount of ground fault current leaking out of the current loop. Thus, as Figure 4 As shown in (b), upon receiving this notification, the control circuit 16 only controls the specified switching element (e.g., switching element 17a) to be turned on. As a result, the number of LEDs receiving current decreases from LEDs 4a-4f to LEDs 4b-4f, the load resistance of the light source 3 decreases, and therefore the output voltage of the constant current source 13 is as follows: Figure 4 As shown in (c), the current is reduced by an amount corresponding to the reduction in load resistance. This reduction in the output voltage of the constant current source 13 suppresses current leakage outside the current loop. Furthermore, as... Figure 4 As shown in (d), the output current of the constant current source 13 maintains a constant current supplying a constant target current to the light source 3.

[0050] Thus, in this embodiment, in the event of current leakage to the outside of the current loop, the voltage applied to the light source 3 is reduced by simply turning on at least one of the switching elements 17a-17f connected in parallel with LEDs 4a-4f, thereby suppressing the current leakage to the outside of the current loop.

[0051] Figure 5This is a flowchart illustrating the operation of the lighting device 10 according to the embodiment to control the switching elements 17a to 17f to be repeatedly turned on and off.

[0052] First, the control circuit 16 determines, based on the notification from the low potential side current detection circuit 15, whether an abnormality has occurred where the low potential side current detected by the low potential side current detection circuit 15 is less than a specified value (e.g., 0.9 times the target current) (S20).

[0053] As a result, due to the occurrence Figure 3B If the grounding is determined to be an abnormality where the low potential side current detected by the low potential side current detection circuit 15 is less than a specified value ("Yes" in S20), the control circuit 16 performs control to repeatedly turn on and off the specified switching elements (e.g., switching elements 17a and 17b) among the switching elements 17a to 17f (S21).

[0054] Furthermore, in step S21, when the control circuit 16 repeatedly turns the specified switching elements on and off, it can also calculate the difference between the specified value and the low-potential side current detected by the low-potential side current detection circuit 15. The larger the calculated difference (i.e., the smaller the low-potential side current is compared to the specified value), the smaller the duty cycle in the control of repeatedly turning on and off. For example, when the low-potential side current is less than the specified value but more than 0.7 times the specified value, the switching elements 17a and 17b can be repeatedly turned on and off with a duty cycle of 50%, and when the low-potential side current is less than 0.7 times the specified value, the switching elements 17a and 17b can be repeatedly turned on and off with a duty cycle of 20%.

[0055] Figure 6 It is shown that in the process Figure 5 The flowchart shows the timing diagram of the operation of the lighting device 10 under controlled conditions. Here, the low-potential side current detected by the low-potential side current detection circuit 15 is shown. Figure 6 (a) Control signals for the switching elements (here, switching elements 17a and 17b) that are controlled to be turned on by control circuit 16 when an abnormality occurs. Figure 6 (b)) Output voltage of constant current source 13 Figure 6 (c) and the output current of constant current source 13 ( Figure 6 The waveform of (d) is shown. Additionally, a triangle is used to represent the point in time when a grounding event occurred.

[0056] like Figure 6 As shown in (a), when a ground fault occurs, the low-potential-side current detected by the low-potential-side current detection circuit 15 decreases by an amount corresponding to the amount of ground fault current leaking out of the current loop. Thus, as Figure 6 As shown in (b), the control circuit 16, upon receiving the notification, controls the designated switching elements (e.g., switching elements 17a and 17b) to repeatedly turn on and off. As a result, the LEDs, which are the objects of current supply, alternately switch between LEDs 4a-4f and LEDs 4c-4f, and the load resistance of the light source 3 alternates between a normal value and a low value, as... Figure 6 As shown in (c), the output voltage of constant current source 13 alternates between a normal value and a low value. This reduces the average value of the output voltage of constant current source 13, thus suppressing the average value of the current leaking out of the current loop. Furthermore, as... Figure 6 As shown in (d), the output current of the constant current source 13 maintains a constant current supplying a constant target current to the light source 3.

[0057] In the event of current leakage outside the current loop, the average value of the voltage applied to the light source 3 is reduced by performing simple control such as repeatedly turning on and off at least one of the switching elements 17a-17f connected in parallel with LEDs 4a-4f, thereby suppressing the average value of the current leaking outside the current loop.

[0058] Figure 7 This is a flowchart illustrating the operation of the lighting device 10 according to the embodiment in controlling the circuit breaker 11. Currently, the lighting device 10 is in a normal state, and the circuit breaker 11 is turned on.

[0059] First, the control circuit 16 determines, based on the notification from the low potential side current detection circuit 15, whether the abnormality of the low potential side current detected by the low potential side current detection circuit 15 being less than a specified value (e.g., 0.9 times the target current) has lasted for a specified time (e.g., 3 seconds) (S30).

[0060] The result is that, in the judgment that it has occurred Figure 3B If the grounding fault shown and the low-potential side current detected by the low-potential side current detection circuit 15 is less than a specified value continue for a specified time (e.g., 3 seconds) ("Yes" in S30), the control circuit 16 controls the circuit breaker 11 to open (S31). This prevents the grounding fault and other abnormalities from continuing.

[0061] also, Figure 3A The flowchart shows the control, Figure 5 The flowchart shows the control and Figure 7 The controls shown in the flowchart can be implemented individually or two or more of these controls can be implemented together.

[0062] For example, in the event of an anomaly such as a ground fault, the smaller the detected low-potential side current is compared to a specified value, the more switching elements can be used as the target. Figure 3A The flowchart shows the control that repeatedly turns the device on and off. Figure 5 (Flowchart).

[0063] Alternatively, instead of step S31 (opening the circuit breaker 11), or in addition to step S31 (opening the circuit breaker 11), the output of the constant current source 13 can be stopped by stopping the operation of the drive circuit Dr of the constant current source 13.

[0064] Alternatively, in the event of an anomaly such as a ground fault, the smaller the detected low-potential side current is compared to a specified value, the more switching elements will be considered. Figure 3A The flowchart shows that the duty cycle of the switch-on process decreases during repeated switching on and off. Figure 5 (Flowchart).

[0065] Furthermore, these controls can be performed, and if the abnormality persists for a specified time, control can be applied to disconnect circuit breaker 11. Figure 7 (Flowchart).

[0066] In addition, in this embodiment, such as Figure 1 As shown, all LEDs 4a to 4f are provided with parallel-connected switching elements 17a to 17f, but this structure is not limited to this one and may also include LEDs without parallel-connected switching elements.

[0067] Figure 8 This diagram illustrates various connection examples between the LED of the light source 3 included in the lighting device 10 according to the embodiment and the switching element. In the light source 3 included in the lighting device 10, connections can be made as follows... Figure 8 As shown in (a), the switching element can be connected in parallel for each LED, or as shown in (a). Figure 8 As shown in (b), it can include LEDs that are not connected in parallel with the switching element, or as shown in (b). Figure 8 As shown in (c), the number of LEDs connected in series with the switching element in parallel can be multiple, or it can be as follows: Figure 8 As shown in (d), there are multiple LEDs that are not connected in parallel with the switching element.

[0068] Figure 9This diagram illustrates an example of the circuit structure of a lighting device according to a variation of the embodiment. The lighting device in this variation essentially has the same structure as the lighting device 10 according to the embodiment, but the specific structure of the abnormal power detection unit differs from that of the embodiment. Specifically, in the embodiment, a low-potential-side current detection circuit 15 is used as a specific example of the abnormal power detection unit, but in this variation, the abnormal power detection unit 20 included in the control circuit 16a is used as a specific structure of the abnormal power detection unit.

[0069] In this modified example, the abnormal power detection unit 20 is a part of the function of the control circuit 16a implemented by the program and the processor executing the program, which detects the duty cycle 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).

[0070] In addition to the functions of the control circuit 16 described in the embodiment, the control circuit 16a also has the following function: when the duty cycle detected by the abnormal power detection unit 20 is outside the specified range, it is determined that an abnormal power has been detected, and control is performed to turn on at least one of the switching elements 17a to 17f. For example, when using... Figure 4 As explained, in the event of current leakage to the outside of the current loop, the load resistance of the light source 3 decreases, thus reducing the output voltage of the constant current source 13. However, to reduce the output voltage of the constant current source 13, the duty cycle of the drive signal output from the drive circuit Dr to the switching elements (i.e., transistors Tr1 and Tr2) will be outside the specified 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 an abnormal power is detected when the duty cycle represented by the drive signal is outside the specified range.

[0071] In this way, by replacing the low potential side current detection circuit 15 in the embodiment with 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, an abnormal power detection unit for detecting abnormal power can also be realized.

[0072] Figure 10This is a flowchart illustrating an example of a method for switching elements 17a-17f to be switched on (the number of switching elements to be switched on) when abnormal power is detected in the embodiment and its variations. Here, when abnormal power is detected by the abnormal power detection unit (S40), the control circuit 16 or 16a changes the number of switching elements to be switched on among the multiple switching elements 17a-17f according to the degree of abnormal power detected by the abnormal power detection unit (S41). For example, when abnormal power is detected by the abnormal power detection unit, the greater the degree of abnormal power detected by the abnormal power detection unit (for example, the smaller the current detected by the low potential side current detection circuit 15 is compared to a predetermined value), the more switching elements 17a-17f are switched on by the control circuit 16 or 16a. Thus, for example, in the case of current leakage to the outside of the current loop, the greater the leakage current, the greater the possibility of suppressing more leakage current.

[0073] Figure 11 This is a flowchart illustrating an example of the method for turning on the switching elements 17a-17f (the order in which the switching elements are turned on) when abnormal power is detected in the embodiment and its variations. Here, when abnormal power is detected by the abnormal power detection unit (S50), as an example, the control circuit 16 or 16a turns on the switching elements sequentially from the switching element closest to the low-potential side terminal 3b of the light source 3 among the plurality of switching elements 17a-17f (S51). As a result, a safer approach can be taken compared to a process that is the opposite in potential relationship (a method of turning on the switching elements sequentially from the switching element closest to the high-potential side terminal 3a of the light source 3).

[0074] Alternatively, if the abnormal power detection unit detects an abnormal power (S50), as another example, the control circuit 16 or 16a sequentially turns on the switching elements (S51) from the last switching element to be turned off when the abnormal power detection unit detected the abnormal power among the multiple switching elements 17a to 17f. Thus, by preferentially short-circuiting the LED block with a high probability of grounding, the possibility of current leakage outside the current loop can be suppressed more effectively.

[0075] Furthermore, as a control process, it is possible to determine whether to use one example (turning on the switching elements sequentially starting from the switching element closest to the low potential side terminal 3b) or another example (turning on the switching elements sequentially by tracing back from the last disconnected switching element) by setting the control circuit 16 or 16a in advance.

[0076] As described above, the lighting device 10 according to the embodiment includes: a constant current source 13 that supplies a constant current to a light source 3 composed of one or more LEDs 4a to 4f connected in series; switching 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 (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) for detecting abnormal power; and a control circuit 16 that, when it is determined that the abnormal power detection unit has detected abnormal power (in the embodiment, the current detected by the low-potential side current detection circuit 15 is less than a predetermined value), controls at least one of the switching elements 17a to 17f to be turned on.

[0077] Therefore, in the event of abnormal power such as leakage of current to the outside of the current loop, the voltage applied to the light source 3 is reduced by simply turning on at least one of the switching elements 17a to 17f connected in parallel with LEDs 4a to 4f, thereby suppressing abnormal power (current leakage to the outside of the current loop, etc.).

[0078] In the lighting device described in this 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 duty cycle of the switching elements based on the drive circuit Dr. If the duty cycle detected by the abnormal power detection unit 20 is outside a predetermined range, the control circuit 16a determines that an abnormal power has been detected and controls at least one of the switching elements 17a to 17f to turn on. In this way, by replacing the low-potential side current detection circuit 15 in the embodiment with 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, an abnormal power detection unit for detecting abnormal power can also be implemented. Furthermore, as a lighting device, both the low-potential 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 can be provided.

[0079] Furthermore, in this embodiment, as described above, the control circuit 16 can also control at least one of the switching elements 17a to 17f to be repeatedly switched on and off. Therefore, by adjusting the on-duty cycle in the repeated switching control, the rate of voltage reduction applied to the light source 3 can be adjusted.

[0080] In this implementation, the smaller the current detected by the low-potential side current detection circuit 15 is compared to a predetermined value, the smaller the on-duty cycle of the control circuit 16 in the repeated on and off control. Therefore, the more current leaks out of the current loop, the lower the voltage applied to the light source 3, and the better the current leakage out of the current loop is suppressed.

[0081] Alternatively, the light source 3 can be composed of multiple LEDs 4a-4f connected in series, and the switching elements 17a-17f can be composed of multiple switching elements 17a-17f connected in parallel with different LEDs 4a-4f. When the abnormal power detection unit detects an abnormal power (in this embodiment, the current detected by the low-potential-side current detection circuit 15 is less than a predetermined value), the control circuit 16 controls at least one of the multiple switching elements 17a-17f to turn on. In this embodiment, the abnormal power detection unit is the low-potential-side current detection circuit 15, and the control circuit 16 performs this control when the current detected by the low-potential-side current detection circuit 15 is less than a predetermined value.

[0082] Therefore, for the lighting device 10 which has a light source 3 consisting of multiple LEDs 4a~4f connected in series, abnormal power such as leakage of current to the outside of the current loop can be suppressed through simple control.

[0083] Furthermore, if the abnormal power detection unit detects an abnormal power (S40), the control circuit 16 or 16a can also change the number of switching elements to be turned on among the multiple switching elements 17a to 17f according to the degree of abnormal power detected by the abnormal power detection unit. Thus, for example, in the event of current leakage to the outside of the current loop, the greater the leakage current, the greater the possibility of suppressing more leakage current.

[0084] At this time, the control circuit 16 can also control the switching elements 17a-17f to be turned on as much as the current detected by the low-potential side current detection circuit 15 is smaller than a specified value. As a result, the more current leaks out of the current loop, the more significantly the voltage applied to the light source 3 is reduced, and the more effectively the current leaking out of the current loop is suppressed.

[0085] Here, if the abnormal power detection unit detects an abnormal power (S50), as an example, the control circuit 16 or 16a may sequentially turn on the switching elements from the low-potential side terminal 3b closest to the light source 3 among the multiple switching elements 17a to 17f (S51). This is a safer approach compared to a process that reverses the potential relationship (sequentially turning on the switching elements from the high-potential side terminal 3a closest to the light source 3).

[0086] Alternatively, if the abnormal power detection unit detects an abnormal power (S50), as another example, the control circuit 16 or 16a sequentially turns on the switching elements (S51) from the last switching element to be turned off when the abnormal power detection unit detected the abnormal power among the multiple switching elements 17a to 17f. Thus, by preferentially short-circuiting the LED block with a high probability of grounding, the possibility of current leakage to the outside of the current loop can be suppressed more effectively.

[0087] Alternatively, the lighting device 10 may also include a circuit breaker 11 that switches the power supply to the constant current source 13 on and off. If the current detected by the low-potential side current detection circuit 15 is less than a specified value for a specified period of time or more, the control circuit 16 controls the circuit breaker 11 to open. This prevents abnormalities such as grounding from persisting.

[0088] The lighting device involved in this disclosure has been described above based on the embodiments, but this disclosure is not limited to these embodiments. Various modifications that can be conceived by those skilled in the art to these embodiments, as well as other ways of constructing by combining some of the constituent elements of the embodiments, are also included within the scope of this disclosure, as long as they do not depart from the spirit of this disclosure.

[0089] For example, in the above embodiment, the constant current source 13 has a DC-DC converter 13a, but it is not limited to such a structure. Other types of variable voltage sources can also be used instead of the DC-DC converter 13a.

[0090] In addition, in the above embodiments, LEDs 4a to 4f are examples of light sources, but they can also be replaced with other light sources such as organic EL (OLED).

[0091] Furthermore, this disclosure can be implemented not only as a lighting device, but also as an illumination device including a lighting device and a light source, or as a control method or program describing the operation of a control circuit, or as a computer-readable recording medium such as a DVD containing the program.

[0092] Explanation of reference numerals in the attached figures

[0093] 3: Light source; 3b: Low potential side terminal; 4a~4f: LED; 10: Lighting device; 11: Circuit breaker; 13: Constant current source; 15: Low potential side current detection circuit; 16, 16a: Control circuit; 17a~17f: Switching element; 20: Abnormal power detection unit; Tr1, Tr2: Transistor (switching element); Dr: Drive circuit.

Claims

1. A lightening device comprising: a constant current source that supplies a constant current to a light source constituted by connecting one or more light emitting diodes in series; a switching element connected in parallel to at least one of the one or more light emitting diodes; an abnormal power detection section for detecting abnormal power; and a control circuit that, in a case where it is determined that the abnormal power detection section has detected abnormal power, performs control to turn on at least one of the switching elements.

2. The lightening device according to claim 1, wherein the abnormal power detection section is a low potential side current detection circuit that detects a current flowing from a 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 in a case where the current detected by the low potential side current detection circuit is less than a prescribed value.

3. The lightening device according to claim 1, wherein the constant current source includes a switching element and a drive circuit that drives the switching element, the abnormal power detection section detects an on duty ratio of the switching element based on the drive circuit, and the control circuit determines that abnormal power has been detected and performs the control in a case where the on duty ratio detected by the abnormal power detection section is outside a prescribed range.

4. The lightening device according to claim 1, wherein, as the control, the control circuit performs control to repeatedly turn on and off at least one of the switching elements.

5. The lightening device according to claim 2, wherein the abnormal power detection section is a low potential side current detection circuit that detects a current flowing from a low potential side terminal of the light source to the constant current source, and the smaller the current detected by the low potential side current detection circuit is in comparison to the prescribed value, the smaller the on duty ratio in the control to repeatedly turn on and off is made by the control circuit.

6. The lightening device according to claim 1, wherein the light source is constituted by connecting a plurality of light emitting diodes in series, the switching element is constituted by a plurality of switching elements connected in parallel to different ones of the plurality of light emitting diodes, and the control circuit, in a case where abnormal power is detected by the abnormal power detection section, performs control to turn on at least one of the plurality of switching elements.

7. The lightening device according to claim 6, wherein the control circuit changes the number of switching elements to be turned on among the plurality of switching elements in accordance with the degree of abnormal power detected by the abnormal power detection section.

8. The lightening device according to claim 6, wherein the abnormal power detection section is a low potential side current detection circuit that detects a current flowing from a low potential side terminal of the light source to the constant current source, and the control circuit performs the control in a case where the current detected by the low potential side current detection circuit is less than a prescribed value.

9. The lightening device according to claim 8, wherein ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ The control circuit performs control to turn on more of the plurality of switching elements as the current detected by the low-potential-side current detection circuit is smaller compared to the prescribed value.

10. The lighting device according to claim 6, wherein In a case where the abnormal power detection section detects abnormal power, the control circuit turns on switching elements in order from the switching element of the plurality of switching elements that is closer to the low-potential-side terminal of the light source.

11. The lighting device according to claim 6, wherein In a case where the abnormal power detection section detects abnormal power, the control circuit turns on switching elements in order from the switching element of the plurality of switching elements that is last turned off when the abnormal power detection section detects abnormal power.

12. The lighting device according to claim 1, wherein Further provided is a breaker that turns on and off the supply of power to the constant current source, In a case where the state in which the abnormal power detection section detects abnormal power continues for a prescribed time or more, the control circuit performs control to turn off the breaker.

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