Lighting device

Abstract

A lighting device (10) is provided with: a DC-DC converter (12) as a DC power source for supplying current to an LED light source (3); a high-potential-side current detection circuit (13) that detects a current flowing from the DCDC converter (12) to a high-potential-side terminal (3a) of the LED light source (3); a low-potential-side current detection circuit (14) that detects a current flowing from a low-potential-side terminal (3b) of the LED light source (3) to the DC-DC converter (12); and a control circuit (15) that performs a first control in which the control circuit (15) controls the DCDC converter (12) so that the current detected by the high-potential-side current detection circuit (13) becomes constant, and a second control in which the control circuit (15) controls the DCDC converter (12) so that the current detected by the low-potential-side current detection circuit (14) becomes constant when the current detected by the low-potential-side current detection circuit (14) becomes less than a predetermined value. In this way, the output current supplied from the DCDC converter (12) to the LED light source (3) is suppressed.

Description

Technical Field

[0001] This disclosure relates to a lighting device, and more particularly to a lighting device for supplying current to an LED (light-emitting diode) light source. Background Technology

[0002] Previously, a lighting device for supplying current to an LED light source was proposed, which could detect an anomaly 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, leakage of current to the outside of the current loop is detected by detecting the current returning to the DC power supply from the low-potential side terminal of the LED light source.

[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 current leakage to the outside of the current loop occurs, although it is detected as an anomaly, the DC power supply will output a combined current of the supply current to the target LED light source and the current leaking to the outside of the current loop. Therefore, there is a problem that the output current from the DC power supply becomes over-output.

[0009] Therefore, the purpose of this disclosure is to provide a lighting device that can detect the abnormality and suppress the output current from becoming over-output when current leakage occurs outside the current loop.

[0010] Solution for solving the problem

[0011] To achieve the above objectives, one aspect of the present disclosure relates to a lighting device comprising: a DC power supply that supplies current to an LED light source; a high-potential-side current detection circuit that detects the current flowing from the DC power supply to the high-potential-side terminal of the LED light source; a low-potential-side current detection circuit that detects the current flowing from the low-potential-side terminal of the LED light source to the DC power supply; and a control circuit that performs a first control and a second control, wherein in the first control, the control circuit controls the DC power supply to keep the current detected by the high-potential-side current detection circuit constant, and in the second control, if the current detected by the low-potential-side current detection circuit is less than a predetermined value, the control circuit controls the DC power supply to suppress the current supplied from the DC power supply to the LED light source.

[0012] Invention Effects

[0013] According to this disclosure, a lighting device is provided that can detect the abnormality and suppress the output current from becoming over-output in the event of current leakage to the outside of the current loop. Attached Figure Description

[0014] Figure 1 This is a block diagram showing the circuit structure of the lighting device involved in the first reference example.

[0015] Figure 2 It is shown in Figure 1 The diagram shows the current values ​​in the lighting device in the case of an abnormality in which current leaks out of the current loop, as illustrated in the first reference example.

[0016] Figure 3 This is a block diagram showing the circuit structure of the lighting device involved in the second reference example.

[0017] Figure 4 It is shown in Figure 3 The diagram shows the current values ​​in the lighting device in the second reference example, under the condition that an abnormality of current leakage to the outside of the current loop occurs.

[0018] Figure 5 This is a block diagram illustrating the circuit structure of the lighting device according to the embodiment.

[0019] Figure 6 It is shown in Figure 5 The diagram shows the current values ​​in the lighting device under the condition that an abnormality of current leakage to the outside of the current loop occurs in the lighting device according to the embodiment shown.

[0020] Figure 7 It is shown Figure 5 A diagram showing the detailed circuit structure of the lighting device involved in the illustrated embodiment.

[0021] Figure 8 This is a flowchart illustrating the control algorithm of the lighting device according to the embodiment, which suppresses the output current supplied from the DC-DC converter to the LED light source based on the difference between the low potential side current too small threshold and the value of the low potential side current.

[0022] Figure 9 This is a flowchart illustrating a control algorithm of the lighting device according to the embodiment, which suppresses the output current supplied from the DC-DC converter to the LED light source based on the ratio of the low-potential side current being too small to the value of the low-potential side current.

[0023] Figure 10This is a block diagram illustrating the circuit structure of the lighting device according to a first variation of the embodiment.

[0024] Figure 11 This is a block diagram illustrating the circuit structure of the lighting device according to a second variation of the embodiment.

[0025] Figure 12A This is a block diagram illustrating the circuit structure of the lighting device according to the third variation of the embodiment.

[0026] Figure 12B This is a diagram illustrating an application example of the lighting device according to a third variation of the implementation method for vehicle application. Detailed Implementation

[0027] The embodiments of this disclosure 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 and connection methods of constituent elements, steps, and order of steps shown in the following embodiments are examples and are not intended to limit this 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 20a according to the first reference example. The lighting device 20a includes: an input filter 11 that smooths the DC voltage input via input terminals 2a and 2b (i.e., a DC voltage with input terminal 2b as a reference potential and input terminal 2a as a positive potential) to remove noise; a DC-DC converter 12 as a DC power supply that boosts the DC voltage output from the input filter 11; an output filter 16 that smooths the DC voltage output from the DC-DC converter 12 to remove noise and outputs it to the LED light source 3 having a high-potential side terminal 3a and a low-potential side terminal 3b; a low-potential side current detection circuit 14 that detects the current returning from the low-potential side terminal 3b of the LED light source 3 to the DC-DC converter 12 via the output filter 16 and notifies the control circuit 15a; and a control circuit 15a that drives the DC-DC converter 12 based on the notification from the low-potential side current detection circuit 14 to set the current detected by the low-potential side current detection circuit 14 to a constant value as a target. Furthermore, in this example, the LED light source 3 is a light source composed of multiple LEDs connected in series. The light source including the LED light source 3 and the lighting device 20a that supplies current to the light source together constitute a lighting device.

[0029] In such a lighting device 20a, now as Figure 1 As shown, an abnormality occurs where a ground fault occurs at any connection point among the multiple LEDs constituting the LED light source 3, resulting in current (i.e., ground current) leaking out of the current loop. Therefore, the control circuit 15a drives the DC-DC converter 12 based on a notification from the low-potential side current detection circuit 14, so that the current detected by the low-potential side current detection circuit 14 (hereinafter, this current is also referred to as "low-potential side current") becomes a target constant value. Thus, the output current flowing from the DC-DC converter 12 to the high-potential side terminal 3a of the LED light source 3 (hereinafter, this output current is also referred to as "high-potential side current") becomes the sum of the target current value (i.e., low-potential side current) and the ground current.

[0030] Figure 2 It is shown in Figure 1 The diagram illustrates the current values ​​in the lighting device 20a in the first reference example, assuming an abnormality of current leakage to the outside of the current loop. Here, it shows how the output current (i.e., the high-potential side current) flowing from the DC-DC converter 12 to the high-potential side terminal 3a of the LED light source 3 becomes as the grounding current increases. Figure 2 In the diagram, solid lines represent the magnitude of the grounding current, dashed lines represent the magnitude of the current on the low-potential side, and dotted lines represent the magnitude of the current on the high-potential side. Additionally, the single-dotted line represents the "device failure threshold," which serves as the threshold for a high current that could potentially damage the 20A lighting device.

[0031] like Figure 2 As shown, the low-potential side current (dashed line) is maintained at a constant value as a target, but the high-potential side current (dotted line) becomes the sum of the low-potential side current and the grounding current, and therefore increases with the increase of the grounding current (solid line). Therefore, with the increase of the grounding current, the high-potential side current may reach the device failure threshold and become an over-output, thus causing the lighting device 20a to fail. Thus, the lighting device 20a involved in the first reference example has the following problem: in the event of an abnormality such as current leakage outside the current loop due to grounding, the output current supplied by the lighting device 20a to the LED light source 3 becomes an over-output.

[0032] Figure 3This is a block diagram showing the circuit structure of the lighting device 20b according to the second reference example. The lighting device 20b includes: an input filter 11 that smooths the DC voltage input via input terminals 2a and 2b to remove noise; a DC-DC converter 12 as a DC power supply that boosts the DC voltage output from the input filter 11; a high-potential-side current detection circuit 13 that detects the high-potential-side current supplied from the DC-DC converter 12 to the high-potential-side terminal 3a of the LED light source 3 and notifies a control circuit 15b; an output filter 16 that smooths the DC voltage output from the DC-DC converter 12 via the high-potential-side current detection circuit 13 to remove noise and outputs it to the LED light source 3; and a control circuit 15b that drives the DC-DC converter 12 based on the notification from the high-potential-side current detection circuit 13 to make the current detected by the high-potential-side current detection circuit 13 a constant value as a target. Furthermore, the light source including the LED light source 3 and the lighting device 20b supplying current to the light source together constitute a lighting device.

[0033] In such a lighting device 20b, now as Figure 3 As shown, an anomaly occurs due to grounding at any point among the multiple LEDs constituting the LED light source 3, causing current (i.e., grounding current) to leak out of the current loop. Therefore, the control circuit 15b drives the DC-DC converter 12 based on a notification from the high-potential side current detection circuit 13, so that the current detected by the high-potential side current detection circuit 13 (i.e., high-potential side current) becomes a constant value as a target. Thus, in LEDs located on a lower potential side than the point where grounding occurred, only the current remaining after subtracting the grounding current leaking out of the current loop from the high-potential side current supplied to the LED light source 3 flows.

[0034] Figure 4 It is shown in Figure 3 The diagram shows the current values ​​in lighting device 20b under the condition that an abnormality of current leakage to the outside of the current loop occurs in lighting device 20a according to the second reference example. Here, it shows how the current flowing in the LED on the lower potential side than the grounding point (i.e., the low potential side current) becomes as the grounding current increases. Furthermore, Figure 4 The line type shown in the figure is the same as Figure 2 same.

[0035] like Figure 4As shown, the high-potential side current (dotted line) is maintained at the target constant value, but the low-potential side current (dashed line) becomes the current remaining after subtracting the grounding current from the high-potential side current, and therefore decreases as the grounding current (solid line) increases. Therefore, as the grounding current increases, the current flowing in the LED on the lower potential side than where the grounding occurred (i.e., the low-potential side current) decreases, and the brightness of the LED light source 3 further decreases relative to the target brightness. Thus, in the lighting device 20b according to the second reference example, the following problem exists: in the event of an abnormality such as current leakage to the outside of the current loop due to grounding, the brightness of the LED light source 3 in the lighting device 20b decreases.

[0036] Figure 5 This is a block diagram illustrating the circuit structure of the lighting device 10 according to the embodiment. The lighting device 10 includes: an input filter 11 that smooths the DC voltage input via input terminals 2a and 2b to remove noise; a DC-DC converter 12 as a DC power supply that boosts the DC voltage output from the input filter 11; a high-potential-side current detection circuit 13 that detects the high-potential-side current supplied from the DC-DC converter 12 to the high-potential-side terminal 3a of the LED light source 3 and notifies the control circuit 15; an output filter 16 that smooths the DC voltage output from the DC-DC converter 12 via the high-potential-side current detection circuit 13 to remove noise and outputs it to the LED light source 3; and a low-potential-side current detection circuit 14 that detects the current returning from the low-potential-side terminal 3b of the LED light source 3 via the output filter 16. The DCDC converter 12 detects the low-potential-side current and notifies the control circuit 15. The control circuit 15 performs first control and second control. In the first control, the control circuit 15 drives the DCDC converter 12 based on the notification from the high-potential-side current detection circuit 13 to make the high-potential-side current detected by the high-potential-side current detection circuit 13 a constant value as a target. In the second control, if the low-potential-side current detected by the low-potential-side current detection circuit 14 is less than a predetermined value (hereinafter referred to as the "low-potential-side current too low threshold") based on the notification from the low-potential-side current detection circuit 14, the control circuit 15 suppresses the output current supplied from the DCDC converter 12 to the LED light source 3. Furthermore, the control circuit 15 is a microcomputer or the like that that executes a built-in control program. In addition, the light source including the LED light source 3 and the lighting device 10 that supplies current to the light source together constitute a lighting device.

[0037] In such a lighting device 10, now as Figure 5As shown, an anomaly occurs due to grounding at any connection point of the plurality of LEDs constituting the LED light source 3, resulting in current (i.e., grounding current) leaking out of the current loop. Therefore, if the low-potential side current detected by the low-potential side current detection circuit 14 is less than the low-potential side current threshold, the control circuit 15, receiving this notification from the low-potential side current detection circuit 14, performs a second control to suppress the output current supplied from the DC-DC converter 12 to the LED light source 3. Furthermore, the control circuit 15 performs a first control, namely constant current control, to maintain the output current supplied from the DC-DC converter 12 to the LED light source 3 (i.e., the high-potential side current detected by the high-potential side current detection circuit 13) at the suppressed current value.

[0038] Figure 6 It is shown in Figure 5 The diagram illustrates the current values ​​in the lighting device 10 under the condition that an abnormality occurs in the current leakage to the outside of the current loop in the lighting device 10 according to the illustrated embodiment. Here, it shows how the high-potential side current flowing from the DC-DC converter 12 to the high-potential side terminal 3a of the LED light source 3 becomes as the grounding current increases. Furthermore, Figure 6 The line type shown in the figure is the same as Figure 2 Same. Furthermore, a double-dotted line indicates "low-potential side current is below the threshold".

[0039] like Figure 6 As shown, when the low-potential side current (dashed line) exceeds the low-potential side current threshold and decreases as the grounding current (solid line) increases, an anomaly is detected by the control circuit 15. A second control is then used to gradually reduce the high-potential side current (dotted line), which was previously maintained at a constant target value. Furthermore, regarding the degree of suppression of the high-potential side current after an anomaly is detected (i.e., the degree of reduction in the brightness of the LED light source 3), as described later, it can be set to a desired value according to the control algorithm in the control circuit 15.

[0040] Thus, in the case of an abnormality such as current leakage to the outside of the current loop due to grounding, the lighting device 10 according to the embodiment detects the abnormality and, through the second control, suppresses the output current (i.e., the high-potential side current) supplied to the LED light source 3 from becoming an over-output, and through the first control, maintains the suppressed output current at a desired constant value. Therefore, the problems of the lighting device 20a according to the first reference example and the lighting device 20b according to the second reference example are solved.

[0041] The detailed circuit structure and operation of the lighting device 10 according to the embodiment will be described below.

[0042] Figure 7 It is shown Figure 5The diagram shows a detailed circuit structure of the lighting device 10 according to the embodiment shown. The lighting device 10 is a circuit that takes the DC voltage input via input terminals 2a and 2b as input and supplies a constant current to the LED light source 3, which serves as the light source. It includes an input filter 11, a DC-DC converter 12, an output filter 16, a high-potential-side current detection circuit 13, a smoothing capacitor C2, a low-potential-side current detection circuit 14, and a control circuit 15.

[0043] The input filter 11 is a noise filter, such as a smoothing filter composed of coils and capacitors. In addition, a reverse connection protection circuit can be provided for the input filter 11. This reverse connection protection circuit is a protection circuit when DC voltages of opposite polarities (i.e., DC voltages with input terminal 2a as the reference potential and input terminal 2b as the positive potential) are connected to the input terminals 2a and 2b.

[0044] The DC-DC converter 12 is an example of a DC power supply that supplies current to the LED light source 3. It is a buck-boost converter composed of capacitor C1, transistors Tr1 and Tr2, diodes D1 and D2, coil L1, and driver circuit Dr. The output from the DC-DC converter 12 is smoothed by smoothing capacitor C2. The driver circuit Dr is a circuit that, according to the instruction from the control circuit 15, outputs a PWM (Pulse Width Modulation) signal or a logic signal to transistors Tr1 and Tr2 to control the on / off state of transistors Tr1 and Tr2, thereby controlling the output current (i.e., the high-potential side current) from the DC-DC converter 12. The driver circuit Dr is, for example, a microcomputer.

[0045] The high-potential side current detection circuit 13 consists of resistors R1~R4, a differential amplifier Amp1, and a transistor Tr3. The high-potential side current flowing through resistor R1 is converted into a voltage and input to the control circuit 15.

[0046] Output filter 16 is a noise filter, such as a smoothing filter composed of coils and capacitors.

[0047] The LED light source 3 is a light source composed of multiple LEDs connected in series. However, the LED light source 3 is not limited to this structure; it can be composed of a single LED or more LEDs connected in series in parallel. Alternatively, the LED light source 3 can also be composed of multiple LEDs connected in series and a switching element connected in parallel with each of these multiple LEDs.

[0048] The low-potential-side current detection circuit 14 consists of resistors R5~R8, a differential amplifier Amp2, and a transistor Tr4. The low-potential-side current flowing through resistor R5 is converted into a voltage and input to the control circuit 15.

[0049] The control circuit 15 is the circuit that performs the first and second controls described above, and is composed of, for example, a comparator, logic gates, an A / D converter, or a microcomputer. In the first control, the control circuit 15 outputs a control signal to the drive circuit Dr of the DC-DC converter 12 to make a voltage corresponding to the detected current notified by the high-potential-side current detection circuit 13 a constant value, thereby supplying a constant output current from the DC-DC converter 12 to the LED light source 3. Furthermore, in the second control, if the control circuit 15 detects that the low-potential-side current detected by the low-potential-side current detection circuit 14 is less than the low-potential-side current over-limit threshold by comparing the voltage corresponding to the detected current notified by the low-potential-side current detection circuit 14 with a reference voltage corresponding to an internally maintained low-potential-side current over-limit threshold, it outputs a control signal to the drive circuit Dr of the DC-DC converter 12 to suppress the output current supplied from the DC-DC converter 12 to the LED light source 3.

[0050] Furthermore, the low-potential-side current threshold can be a fixed value (e.g., the minimum current value that should be supplied to the LED light source 3) or a variable value determined based on the high-potential-side current detected by the high-potential-side current detection circuit 13 (e.g., the value of the high-potential-side current itself, or a value obtained by adding or subtracting a certain correction value to the value of the high-potential-side current). For example, if the control circuit 15 detects that the low-potential-side current detected by the low-potential-side current detection circuit 14 is less than the high-potential-side current detected by the high-potential-side current detection circuit 13, it can suppress the output current supplied from the DC-DC converter 12 to the LED light source 3. As the low-potential-side current threshold, for example, it can be determined whether to use a fixed value or a variable value based on a preset setting in the control circuit 15.

[0051] Furthermore, as a method for suppressing the output current supplied from the DC-DC converter 12 to the LED light source 3 when the low-potential side current is detected to be less than the low-potential side current threshold, the control circuit 15 employs any of the following control algorithms: (1) suppressing the output current supplied from the DC-DC converter 12 to the LED light source 3 based on the difference between the low-potential side current threshold and the value of the low-potential side current; (2) suppressing the output current supplied from the DC-DC converter 12 to the LED light source 3 based on the ratio of the low-potential side current threshold to the value of the low-potential side current; and (3) cutting off the output current supplied from the DC-DC converter 12 to the LED light source 3. For example, the choice of which control algorithm to use can also be determined based on a preset setting in the control circuit 15.

[0052] Figure 8 This is a flowchart illustrating the control algorithm of the lighting device 10 according to the embodiment, which suppresses the output current supplied from the DC-DC converter 12 to the LED light source 3 based on the difference between the low-potential-side current too small threshold and the value of the low-potential-side current. Here, the operation is shown when the high-potential-side current detected by the high-potential-side current detection circuit 13 is used as the low-potential-side current too small threshold.

[0053] First, the control circuit 15 determines, based on the notification from the low-potential side current detection circuit 14, whether an abnormality has occurred where the low-potential side current detected by the low-potential side current detection circuit 14 is less than the low-potential side current too small threshold (here, the high-potential side current detected by the high-potential side current detection circuit 13) (S10).

[0054] As a result, when an anomaly is detected where the low-potential side current is less than the high-potential side current ("Yes" in S10), the control circuit 15 calculates the difference between these currents (i.e., high-potential side current - low-potential side current) (S11). The larger the calculated current difference, the more significantly the drive circuit Dr of the DC-DC converter 12 is instructed to suppress the output current supplied from the DC-DC converter 12 to the LED light source 3 (S12). Specifically, in step S12, the control circuit 15 performs constant current control (i.e., first control) to maintain the high-potential side current detected by the high-potential side current detection circuit 13 at the suppressed current value. Furthermore, the relationship between the current difference and the degree of suppression of the output current supplied to the LED light source 3 is defined in advance by a function or table.

[0055] With this control algorithm, in the event of an anomaly such as current leakage to the outside of the current loop due to grounding, the output current supplied to the LED light source 3 is suppressed to the desired degree according to the degree of the anomaly, thereby avoiding damage to the lighting device 10 and maintaining the desired brightness.

[0056] Figure 9 This is a flowchart illustrating the control algorithm of the lighting device 10 according to the embodiment, which suppresses the output current supplied from the DC-DC converter 12 to the LED light source 3 based on the ratio of the low-potential-side current too small threshold to the value of the low-potential-side current. Here, the operation is shown when the high-potential-side current detected by the high-potential-side current detection circuit 13 is used as the low-potential-side current too small threshold.

[0057] First, the control circuit 15 determines whether an abnormality has occurred where the low-potential side current detected by the low-potential side current detection circuit 14 is less than the low-potential side current too small threshold (here, the high-potential side current detected by the high-potential side current detection circuit 13) (S20).

[0058] As a result, when an anomaly is detected where the low-potential side current is less than the high-potential side current ("Yes" in S20), the control circuit 15 calculates the ratio of these currents (i.e., low-potential side current / high-potential side current) (S21). The smaller the calculated current ratio, the more significantly the drive circuit Dr of the DC-DC converter 12 is instructed to suppress the output current supplied from the DC-DC converter 12 to the LED light source 3 (S22). In step S22, specifically, the control circuit 15 performs constant current control (i.e., first control) to maintain the high-potential side current detected by the high-potential side current detection circuit 13 at the suppressed current value. Furthermore, the relationship between the current ratio and the degree of suppression of the output current supplied to the LED light source 3 is defined in advance by a function or table.

[0059] With this control algorithm, in the event of an anomaly such as current leakage to the outside of the current loop due to grounding, the output current supplied to the LED light source 3 is suppressed to the desired degree according to the degree of the anomaly, thereby avoiding damage to the lighting device 10 and maintaining the desired brightness.

[0060] Figure 10 This is a block diagram showing the circuit structure of the lighting device 10a according to the first modification of the embodiment. The lighting device 10a according to this modification is a circuit that takes the AC voltage from the AC power supply 5 input via the input terminals 2c and 2d as input and supplies a constant current to the LED light source 3, which is the light source. It includes an input filter 17, an AC-DC converter 18, a DC-DC converter 12, an output filter 16, a high-potential side current detection circuit 13, a low-potential side current detection circuit 14, and a control circuit 15.

[0061] In the lighting device 10a involved in this modified example, compared to Figure 5 The lighting device 10 according to the embodiment shown differs in that: an input filter 17 for AC voltage and an AC-DC converter 18 are provided in the stage before the DC-DC converter 12; and a high-potential side current detection circuit 13, a low-potential side current detection circuit 14, and a control circuit 15 are provided in the stage after the LED light source 3, which is closer to the output filter 16.

[0062] The input filter 17 is a common-mode noise filter, or a common-mode and constant-mode noise filter, for example, composed of a choke coil and a capacitor.

[0063] The AC-DC converter 18 is a circuit that converts AC voltage to DC voltage, such as a diode bridge.

[0064] The output filter 16, the high-potential side current detection circuit 13, the low-potential side current detection circuit 14, and the control circuit 15 have the same circuit structure and function as the lighting device 10 according to the embodiment.

[0065] The lighting device 10a of this first modification includes the same high-potential-side current detection circuit 13, low-potential-side current detection circuit 14, and control circuit 15 as the lighting device 10 of the embodiment, and therefore has the same function as the lighting device 10 of the embodiment. That is, according to the lighting device 10a of the first modification, in the event of an abnormality such as current leakage to the outside of the current loop due to grounding, the abnormality is detected, and the output current (i.e., high-potential-side current) supplied to the LED light source 3 is suppressed from becoming an over-output by the second control, and the suppressed output current is maintained at a desired constant value by the first control. Therefore, the problems of the lighting device 20a of the first reference example and the lighting device 20b of the second reference example are solved.

[0066] Figure 11 This is a block diagram illustrating the circuit structure of the lighting device 10b according to the second modification of the embodiment. The lighting device 10b according to this modification is a circuit that takes the DC voltage input via input terminals 2a and 2b as input and supplies a constant current to LED light sources 3 and 4, which are multiple light sources connected in parallel. It includes an input filter 11, a DC-DC converter 12, output filters 16a and 16b, a high-potential side current detection circuit 13, a low-potential side current detection circuit 14a and 14b, and a control circuit 15.

[0067] In the lighting device 10b involved in this modified example, compared to Figure 5 The lighting device 10 according to the illustrated embodiment differs in that: it is provided with an output filter 16a and an LED light source 3, and an output filter 16b and an LED light source 4, which are multiple light source loads connected in parallel; a high-potential side current detection circuit 13 detects the total current flowing from the DC-DC converter 12 to the high-potential side terminals of the multiple light source loads (i.e., the high-potential side terminals 3a and 4a of the LED light source 3 and 4); and multiple low-potential side current detection circuits 14a and 14b are provided to detect the current flowing from the low-potential side terminals of the multiple light source loads (i.e., the low-potential side terminals 3b of the LED light source 3 and 4b of the LED light source 4) to the DC-DC converter 12 respectively.

[0068] In this modified example, the control circuit 15 performs a first control and a second control. In the first control, the control circuit 15 drives the DC-DC converter 12 based on a notification from the high-potential side current detection circuit 13 to make the high-potential side current detected by the high-potential side current detection circuit 13 a constant value as a target. In the second control, if the low-potential side current detected by at least one of the multiple low-potential side current detection circuits 14a and 14b is less than a predetermined value (i.e., the low-potential side current is too small threshold) based on a notification from the multiple low-potential side current detection circuits 14a and 14b, the control circuit 15 suppresses the output current supplied from the DC-DC converter 12 to the LED light source 3.

[0069] According to the lighting device 10b of this modified example, in the event of an abnormality such as current leakage to the outside of the current loop due to grounding, the abnormality is detected independently for each of the multiple light source loads, and the total current supplied to the multiple light source loads (i.e., LED light sources 3 and 4) (i.e., high-potential side current) is prevented from reaching the device failure threshold and causing the lighting device to fail. Furthermore, the suppressed output current is maintained at a desired constant value through the first control. Therefore, the problems of the lighting device 20a according to the first reference example and the lighting device 20b according to the second reference example are solved.

[0070] Furthermore, in this modified example, the multiple light source loads connected in parallel are groups of output filters and LEDs, but the structure is not limited to this. Alternatively, only one common output filter can be provided for the multiple light source loads, and each of the multiple light source loads is only an LED.

[0071] Figure 12A This is a block diagram showing the circuit structure of the lighting device 10c according to the third modification of the embodiment. The lighting device 10c according to this modification has basically the same structure as the lighting device 10 according to the embodiment, but the difference is that it also has switching elements 19a to 19f connected in parallel with the LEDs 3c to 3h constituting the LED light source 3.

[0072] Here, LEDs 3c to 3h are LED blocks consisting of one or more LEDs connected in series or in parallel, and are respectively assigned to, for example, vehicle headlights, headlights, side lights, etc.

[0073] In addition to the functions described in the embodiment, the control circuit 15 also has the following function: when it is determined that a grounding has occurred, it controls the selective switching elements 19a to 19f to be turned on. For example, it turns on only the switching element corresponding to the LED block that has been grounded to short-circuit only that LED block, thereby allowing the use of other LED blocks.

[0074] Figure 12B This diagram illustrates an application example of the lighting device 10c according to a third variation of the implementation method for vehicle 22. In this application example, LED blocks (LEDs 3c to 3h) constituting the LED light source 3 are distributed and installed in the headlights, side lights, etc. of vehicle 22, and the lighting device 10c is installed in vehicle 22. Vehicle 22 has a body control module 20 as the central control unit for vehicle 22. The lighting device 10c (more specifically, the control circuit 15 of the lighting device 10c when the current detected by the low-potential side current detection circuit 14 is less than a predetermined value) not only controls the operation in the embodiment, but also communicates with the body control module 20 to notify that an abnormality has occurred in the current supply to the LED light source 3.

[0075] According to such an application example, in the event of a ground fault, the body control module 20 of the vehicle 22 is notified of the abnormality, and only the switching element corresponding to the LED block that has been grounded is turned on to short-circuit only that LED block, thereby allowing the use of other LED blocks.

[0076] As described above, the lighting device 10 according to the embodiment includes: a DC-DC converter 12 as a DC power supply that supplies current to the LED light source 3; a high-potential side current detection circuit 13 that detects the current flowing from the DC-DC converter 12 to the high-potential side terminal 3a of the LED light source 3; a low-potential side current detection circuit 14 that detects the current flowing from the low-potential side terminal 3b of the LED light source 3 to the DC-DC converter 12; and a control circuit 15 that performs a first control and a second control. In the first control, the control circuit 15 controls the DC-DC converter 12 to keep the current detected by the high-potential side current detection circuit 13 constant. In the second control, if the current detected by the low-potential side current detection circuit 14 is less than a predetermined value, the control circuit 15 controls the DC-DC converter 12 to suppress the output current supplied from the DC-DC converter 12 to the LED light source 3.

[0077] Therefore, since the first and second controls are performed by the control circuit 15, in the event of an abnormality such as current leakage to the outside of the current loop due to grounding, the abnormality is detected, and the output current supplied to the LED light source 3 (i.e., the high potential side current) is suppressed from becoming an over-output, and the suppressed output current is maintained at the desired constant value.

[0078] Here, the specified value can be either a fixed value or a variable value determined based on the current detected by the high-potential side current detection circuit 13. Thus, by comparing the current detected by the low-potential side current detection circuit 14 with the fixed or variable value, abnormal leakage of current out of the current loop can be monitored.

[0079] Alternatively, in the second control, the control circuit 15 can determine whether the current detected by the low-potential side current detection circuit 14 is less than the specified value based on the difference between the current detected by the low-potential side current detection circuit 14 and the specified value. Or, in the second control, the control circuit 15 can determine whether the current detected by the low-potential side current detection circuit 14 is less than the specified value based on the ratio of the current detected by the low-potential side current detection circuit 14 to the specified value. Thus, abnormal current leakage to the outside of the current loop can be monitored based on either the difference between the current detected by the low-potential side current detection circuit 14 and the specified value or the ratio of the current detected by the low-potential side current detection circuit 14 to the specified value.

[0080] Alternatively, in the second control, the smaller the current detected by the low-potential side current detection circuit 14 is compared to a predetermined value, the more significantly the control circuit 15 suppresses the output current supplied from the DC-DC converter 12 to the LED light source 3. This suppresses the undesirable situation where the output current supplied to the LED light source 3 continuously increases with the increase of current leaking out of the current loop, and maintains the output current at a constant level.

[0081] For example, in the second control, the greater the difference between the current detected by the low-potential side current detection circuit 14 and the specified value, the more the control circuit 15 suppresses the output current supplied from the DC-DC converter 12 to the LED light source 3. Alternatively, in the second control, the smaller the ratio of the current detected by the low-potential side current detection circuit 14 to the specified value, the more the control circuit 15 suppresses the output current supplied from the DC-DC converter 12 to the LED light source 3. Thus, based on the difference between the current detected by the low-potential side current detection circuit 14 and the specified value, or the ratio of the current detected by the low-potential side current detection circuit 14 to the specified value, it is possible to suppress the undesirable situation where the output current supplied to the LED light source 3 continuously increases with the increase of current leaking out of the current loop, and to maintain a constant output current.

[0082] Furthermore, the lighting device 10b of the second modification includes: a DC-DC converter 12 that supplies current to a plurality of LED light sources 3 and 4 connected in parallel; a high-potential side current detection circuit 13 that detects the total current flowing from the DC-DC converter 12 to the high-potential side terminals 3a and 4a of the plurality of LED light sources 3 and 4; a plurality of low-potential side current detection circuits 14a and 14b that detect the current flowing from the respective low-potential side terminals 3b and 4b of the plurality of LED light sources 3 and 4 to the DC-DC converter 12; and a control circuit 15 that performs a first control and a second control. In the first control, the control circuit 15 controls the DC-DC converter 12 to keep the total current detected by the high-potential side current detection circuit 13 constant. In the second control, if the current detected by at least one of the multiple low-potential side current detection circuits 14a and 14b is less than a predetermined value, the control circuit 15 controls the DC-DC converter 12 to suppress the current supplied from the DC-DC converter 12 to the plurality of LED light sources 3 and 4.

[0083] Therefore, in the event of an anomaly such as current leakage to the outside of the current loop due to grounding, the anomaly is detected independently for each of the multiple light source loads, and the total current supplied to the multiple light source loads (i.e., LED light sources 3 and 4) (i.e., the high potential side current) is suppressed from becoming an over-output, and the suppressed output current is maintained at the desired constant value.

[0084] Furthermore, in the third modification, the LED light source 3 and the lighting device 10c are installed in the vehicle 22. The vehicle 22 has a body control module 20 that controls the vehicle 22. If the current detected by the low-potential side current detection circuit 14 is lower than a specified value, the control circuit 15 also communicates with the body control module 20 to notify that the current supply to the LED light source 3 has been abnormal. Thus, if an abnormality such as grounding occurs in the LED light source 3 in the vehicle 22, the body control module 20 of the vehicle 22 can be aware of the situation.

[0085] The lighting device involved in this disclosure has been described above based on the embodiments and modifications, but this disclosure is not limited to these embodiments and modifications. As long as it does not depart from the spirit of this disclosure, various modifications that can be conceived by those skilled in the art to the embodiments and modifications, as well as other ways of constructing by combining some of the constituent elements of the embodiments and modifications, are also included within the scope of this disclosure.

[0086] For example, in the above embodiments and variations, a DC-DC converter 12 is shown as an example of a DC power supply that supplies current to the LED light source 3, etc. However, such a DC power supply is not limited to the DC-DC converter 12. It can be any DC power supply that can adjust the supplied current, or other types of DC voltage sources, DC current sources, etc.

[0087] Furthermore, in the above embodiments and variations, LED light source 3 and the like are examples of light sources, and can also be replaced with other light sources such as organic EL (OLED).

[0088] Furthermore, the predetermined value used in the second control performed by the control circuit 15 (i.e., the threshold value for low-potential-side current being too small) can also be a variable value that can be set by the user through communication with the lighting device 10. Similarly, the target value of the current supplied to the LED light source 3 and the like can also be a variable value that can be set by the user through communication with the lighting device 10.

[0089] 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 recording medium such as a computer-readable DVD containing the program.

[0090] Explanation of reference numerals in the attached figures

[0091] 3, 4: LED light source; 3a, 4a: High-potential side terminals; 3b, 4b: Low-potential side terminals; 10, 10a, 10b, 10c: Lighting device; 12: DC-DC converter (DC power supply); 13: High-potential side current detection circuit; 14, 14a, 14b: Low-potential side current detection circuit; 15: Control circuit; 20: Body control module; 22: Vehicle.

Claims

1. A lighting device, comprising: A DC power supply that supplies current to the LED light source; A high-potential side current detection circuit detects the current flowing from the DC power supply to the high-potential side terminal of the LED light source; A low-potential-side current detection circuit detects the current flowing from the low-potential-side terminal of the light-emitting diode (LED) light source to the DC power supply; and A control circuit performs a first control and a second control. In the first control, the control circuit controls the DC power supply to keep the current detected by the high-potential side current detection circuit constant. In the second control, if the current detected by the low-potential side current detection circuit is less than a predetermined value, the control circuit controls the DC power supply to suppress the current supplied from the DC power supply to the light-emitting diode light source.

2. The lighting device according to claim 1, wherein, The specified value is a fixed value.

3. The lighting device according to claim 1, wherein, The specified value is determined based on the current detected by the high-potential side current detection circuit.

4. The lighting device according to any one of claims 1 to 3, wherein, In the second control, the control circuit determines whether the current detected by the low-potential side current detection circuit is less than the predetermined value based on the difference between the current detected by the low-potential side current detection circuit and the predetermined value.

5. The lighting device according to any one of claims 1 to 3, wherein, In the second control, the control circuit determines whether the current detected by the low-potential side current detection circuit is less than the predetermined value based on the ratio of the current detected by the low-potential side current detection circuit to the predetermined value.

6. The lighting device according to any one of claims 1 to 3, wherein, In the second control, the smaller the current detected by the low-potential side current detection circuit is compared to the predetermined value, the more the control circuit suppresses the current supplied from the DC power supply to the LED light source.

7. The lighting device according to claim 6, wherein, In the second control, the greater the difference between the current detected by the low-potential side current detection circuit and the specified value, the more the control circuit suppresses the current supplied from the DC power supply to the LED light source.

8. The lighting device according to claim 6, wherein, In the second control, the smaller the ratio of the current detected by the low-potential side current detection circuit to the specified value, the more the control circuit suppresses the current supplied from the DC power supply to the light-emitting diode light source.

9. A lighting device, comprising: A DC power supply that supplies current to multiple LED light sources connected in parallel. A high-potential side current detection circuit detects the total current flowing from the DC power supply to the high-potential side terminals of the plurality of light-emitting diode light sources; Multiple low-potential-side current detection circuits detect currents flowing from the low-potential-side terminals of each of the multiple light-emitting diode (LED) light sources to the DC power supply; and A control circuit performs a first control and a second control. In the first control, the control circuit controls the DC power supply to keep the total current detected by the high-potential side current detection circuit constant. In the second control, if the current detected by at least one of the plurality of low-potential side current detection circuits is less than a predetermined value, the control circuit controls the DC power supply to suppress the current supplied from the DC power supply to the plurality of light-emitting diode light sources.

10. The lighting device according to claim 1 or 9, wherein, The light-emitting diode light source and the lighting device are installed in the vehicle. The vehicle is equipped with a body control module for controlling the vehicle. If the current detected by the low-potential side current detection circuit is less than a specified value, the control circuit also notifies the vehicle body control module that an abnormality has occurred in the current supply to the light-emitting diode light source.

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