Lighting device

Abstract

A lighting device (10) comprises: a DC-DC converter (12) that is a DC electric power supply for supplying electric current to a LED light source (3); a high-potential-side electric current detection circuit (13) that detects an electric current flowing from the DC-DC converter (12) to a high-potential-side terminal (3a) of the LED light source (3); a low-potential-side electric current detection circuit (14) that detects an electric 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 that performs a first control for controlling the DC-DC converter (12) so that the electric current detected by the high-potential-side electric current detection circuit (13) becomes constant, and a second control for controlling the DC-DC converter (12) so as to suppress the output electric current supplied from the DC-DC converter (12) to the LED light source (3) when the electric current detected by the low-potential-side electric current detection circuit (14) is less than a prescribed value.

Description

lighting device

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

[0002] Conventionally, in lighting devices that supply current to LED light sources, lighting devices have been proposed that can detect abnormalities such as current leakage outside the current loop due to a ground fault or the like at any point in the current loop (see, for example, Patent Document 1).

[0003] In the technology of Patent Document 1, current leakage outside the current loop, etc., is detected by detecting the current returning from the low-potential terminal of the LED light source to the DC power supply.

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

[0005] However, in the technology of Patent Document 1, when current leakage outside the current loop occurs, it is detected as an abnormality, but the DC power supply attempts to output a current that is the sum of the target current supplied to the LED light source and the current leaking outside the current loop, which results in the problem of excessive output current from the DC power supply.

[0006] Therefore, an object of the present disclosure is to provide a lighting device that can detect an abnormality when current leakage occurs outside a current loop and prevent the output current from becoming excessive.

[0007] In order to achieve the above object, a lighting device according to one embodiment of the present disclosure includes 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 a 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 first control to control the DC power supply so that the current detected by the high-potential side current detection circuit is constant, and second control to control the DC power supply so as to suppress the current supplied from the DC power supply to the LED light source when the current detected by the low-potential side current detection circuit is smaller than a predetermined value.

[0008] The present disclosure provides a lighting device that can detect an abnormality when current leakage to the outside of a current loop occurs and can prevent the output current from becoming excessive.

[0009] FIG. 1 is a block diagram showing the circuit configuration of a lighting device according to a first reference example. FIG. 2 is a diagram showing current values ​​in the lighting device according to the first reference example shown in FIG. 1 when an abnormality occurs in which current leaks outside the current loop. FIG. 3 is a block diagram showing the circuit configuration of a lighting device according to a second reference example. FIG. 4 is a diagram showing current values ​​in the lighting device according to the second reference example shown in FIG. 3 when an abnormality occurs in which current leaks outside the current loop. FIG. 5 is a block diagram showing the circuit configuration of a lighting device according to an embodiment. FIG. 6 is a diagram showing current values ​​in the lighting device according to the embodiment shown in FIG. 5 when an abnormality occurs in which current leaks outside the current loop. FIG. 7 is a diagram showing the detailed circuit configuration of the lighting device according to the embodiment shown in FIG. 5. FIG. 8 is a flowchart showing a control algorithm in which a lighting device according to an embodiment suppresses an output current supplied from a DCDC converter to an LED light source in accordance with a difference between a low-potential-side current over-threshold and a low-potential-side current value. FIG. 9 is a flowchart showing a control algorithm in which a lighting device according to an embodiment suppresses an output current supplied from a DCDC converter to an LED light source in accordance with a ratio between a low-potential-side current over-threshold and a low-potential-side current value. Fig. 10 is a block diagram showing a circuit configuration of a lighting device according to a first modified example of the embodiment. Fig. 11 is a block diagram showing a circuit configuration of a lighting device according to a second modified example of the embodiment. Fig. 12A is a block diagram showing a circuit configuration of a lighting device according to a third modified example of the embodiment. Fig. 12B is a diagram showing an example of application of the lighting device according to the third modified example of the embodiment to a vehicle.

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

[0011] 1 is a block diagram showing the circuit configuration of a lighting device 20a according to a first embodiment. The lighting device 20a includes an input filter 11 that smooths and removes noise from a 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), 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 and removes noise from the DC voltage output from the DC-DC converter 12 and outputs the smoothed DC voltage to an LED light source 3 having a high-potential terminal 3a and a low-potential terminal 3b, a low-potential-side current detection circuit 14 that detects a current returning from the low-potential-side terminal 3b of the LED light source 3 via the output filter 16 and notifies a 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 maintain the current detected by the low-potential-side current detection circuit 14 at a target constant value. In this example, the LED light source 3 is a light source formed of a plurality of LEDs connected in series. The lighting device is configured by combining a light source including the LED light source 3 and a lighting device 20a that supplies current to the light source.

[0012] 1, in such lighting device 20a, suppose that a ground fault occurs at one of the connection points of the multiple LEDs that make up LED light source 3, causing an abnormality in which current (i.e., ground fault current) leaks outside the current loop. Then, based on a notification from low-potential-side current detection circuit 14, control circuit 15a drives DCDC converter 12 so that the current detected by low-potential-side current detection circuit 14 (hereinafter, this current will also be referred to as the "low-potential-side current") reaches a target constant value, and the output current flowing from DCDC converter 12 to high-potential-side terminal 3a of LED light source 3 (hereinafter, this output current will also be referred to as the "high-potential-side current") becomes the sum of the target current value (i.e., low-potential-side current) and the ground fault current.

[0013] 2 is a diagram showing current values ​​in the lighting device 20a according to the first reference example shown in FIG. 1 when an abnormality occurs in which current leaks outside the current loop. This diagram shows how the output current (i.e., high-potential side current) flowing from the DC-DC converter 12 to the high-potential side terminal 3a of the LED light source 3 changes with an increase in ground-fault current. In FIG. 2, the solid line indicates the magnitude of the ground-fault current, the dashed line indicates the magnitude of the low-potential side current, and the dotted line indicates the magnitude of the high-potential side current. The dash-dotted line indicates the "device damage threshold," which is the threshold of a large current that may damage the lighting device 20a.

[0014] As shown in Figure 2, the low-potential-side current (dashed line) is maintained at a target constant value, but the high-potential-side current (dotted line) is the sum of the low-potential-side current and the ground-fault current, and therefore increases as the ground-fault current (solid line) increases. As a result, as the ground-fault current increases, the high-potential-side current may reach the device damage threshold, resulting in over-output and potentially damaging the lighting device 20a. Thus, the lighting device 20a according to the first reference example has a problem in that the output current supplied by the lighting device 20a to the LED light source 3 may become over-output if an abnormality occurs in which current leaks outside the current loop due to a ground fault or the like.

[0015] 3 is a block diagram showing the circuit configuration of a lighting device 20b according to a second reference example. The lighting device 20b includes an input filter 11 that smooths and removes noise from the DC voltage input via input terminals 2a and 2b, a DCDC converter 12 as a DC power supply that boosts the DC voltage output from the input filter 11, a high-side current detection circuit 13 that detects a high-side current supplied from the DCDC converter 12 to a high-side terminal 3a of the LED light source 3 and notifies a control circuit 15b of the high-side current detection circuit 13, an output filter 16 that smooths and removes noise from the DC voltage output from the DCDC converter 12 via the high-side current detection circuit 13 and outputs the smoothed DC voltage to the LED light source 3, and a control circuit 15b that drives the DCDC converter 12 based on the notification from the high-side current detection circuit 13 to maintain the current detected by the high-side current detection circuit 13 at a target constant value. The lighting device is configured by combining the light source including the LED light source 3 and the lighting device 20b that supplies current to the light source.

[0016] 3, assume that an abnormality occurs in lighting device 20b, in which current (i.e., ground fault current) leaks outside the current loop due to a ground fault at any one of the multiple LEDs constituting LED light source 3. Then, based on a notification from high-potential side current detection circuit 13, control circuit 15b drives DCDC converter 12 to set the current detected by high-potential side current detection circuit 13 (i.e., high-potential side current) to a target constant value, so that only the current remaining after subtracting the ground fault current that leaked outside the current loop due to the ground fault from the high-potential side current supplied to LED light source 3 flows through the LED on the lower potential side than the location where the ground fault occurred.

[0017] Fig. 4 is a diagram showing current values ​​in the lighting device 20b according to the second reference example shown in Fig. 3 when an abnormality occurs in which current leaks outside the current loop in the lighting device 20a. This diagram shows how the current flowing through the LED on the lower potential side of the ground fault (i.e., the low-potential side current) changes as the ground-fault current increases. The line types shown in Fig. 4 are the same as those in Fig. 2.

[0018] 4 , the high-potential-side current (dotted line) is maintained at a target constant value, but the low-potential-side current (dashed line) is the current remaining after subtracting the ground-fault current from the high-potential-side current, and therefore decreases as the ground-fault current (solid line) increases. Therefore, as the ground-fault current increases, the current flowing through the LEDs on the lower potential side of the location where the ground fault occurred (i.e., the low-potential-side current) decreases, causing the brightness of the LED light source 3 to fall below the target brightness. Thus, the lighting device 20b according to the second reference example has a problem in that the brightness of the LED light source 3 of the lighting device 20b decreases when an abnormality occurs in which current leaks outside the current loop due to a ground fault or the like.

[0019] 5 is a block diagram showing the circuit configuration of a lighting device 10 according to an embodiment. The lighting device 10 includes an input filter 11 that smooths and removes noise from a DC voltage input via input terminals 2 a and 2 b, a DCDC 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 a high-potential-side current supplied from the DCDC converter 12 to a high-potential-side terminal 3 a of the LED light source 3 and notifies the control circuit 15 of the high-potential-side current, an output filter 16 that smooths and removes noise from the DC voltage output from the DCDC converter 12 via the high-potential-side current detection circuit 13 and outputs the smoothed DC voltage to the LED light source 3, and a DC voltage output from a low-potential-side terminal 3 b of the LED light source 3 via the output filter 16. The control circuit 15 includes a low-side current detection circuit 14 that detects the low-side current returning to the DC converter 12 and notifies the control circuit 15 of the detected current, and a first control that drives the DC-DC converter 12 so that the high-side current detected by the high-side current detection circuit 13 reaches a target constant value based on the notification from the high-side current detection circuit 13, and a second control that suppresses the output current supplied from the DC-DC converter 12 to the LED light source 3 when the low-side current detected by the low-side current detection circuit 14 is smaller than a predetermined value (hereinafter, this predetermined value is also referred to as the "low-side current under-threshold") based on the notification from the low-side current detection circuit 14. The control circuit 15 is a microcomputer or the like that executes a built-in control program. The lighting device is configured by combining a light source including the LED light source 3 and a lighting device 10 that supplies current to the light source.

[0020] 5 , in such lighting device 10, suppose that an abnormality occurs in which current (i.e., ground fault current) leaks outside the current loop due to a ground fault at one of the connection points of the multiple LEDs constituting the LED light source 3. Then, if the low-side current detected by the low-side current detection circuit 14 is smaller than the low-side current excessive threshold, the control circuit 15, upon receiving a notification from the low-side current detection circuit 14, performs second control to suppress the output current supplied from the DCDC converter 12 to the LED light source 3. Furthermore, the control circuit 15 performs first control, i.e., constant current control, so that the output current supplied from the DCDC converter 12 to the LED light source 3 (i.e., the high-side current detected by the high-side current detection circuit 13) is maintained at the current value after suppression.

[0021] Fig. 6 is a diagram showing current values ​​in the lighting device 10 according to the embodiment shown in Fig. 5 when an abnormality occurs in which current leaks outside the current loop. This diagram shows the value of the high-potential-side current flowing from the DCDC converter 12 to the high-potential-side terminal 3a of the LED light source 3 as the ground-fault current increases. The types of lines shown in Fig. 6 are the same as those in Fig. 2. Additionally, the "low-potential-side current over-threshold" is indicated by a two-dot chain line.

[0022] 6, when the low-potential-side current (dashed line) decreases below the low-potential-side current insufficient threshold as the ground-fault current (solid line) increases, the control circuit 15 detects this as an abnormality, and the high-potential-side current (dotted line), which had been maintained at a target constant value until then, decreases through the second control. Note that the degree to which the high-potential-side current is suppressed after the abnormality is detected (i.e., the degree to which the brightness of the LED light source 3 decreases) can be set to a desired value depending on the control algorithm in the control circuit 15, as will be described later.

[0023] Thus, with the lighting device 10 according to the embodiment, when an abnormality occurs in which current leaks outside the current loop due to a ground fault or the like, the abnormality is detected, the second control prevents the output current (i.e., the high-potential side current) supplied to the LED light source 3 from becoming excessive, and the first control maintains the output current after the suppression at a desired constant value. Thus, the problems with the lighting device 20a according to the first reference example and the lighting device 20b according to the second reference example are solved.

[0024] The detailed circuit configuration and operation of the lighting device 10 according to the embodiment will be described below.

[0025] Fig. 7 is a diagram showing a detailed circuit configuration of the lighting device 10 according to the embodiment shown in Fig. 5. The lighting device 10 is a circuit that receives a DC voltage via input terminals 2a and 2b as an input and supplies a constant current to an LED light source 3 serving as a light source, and includes an input filter 11, a DCDC converter 12, an output filter 16, a high-side current detection circuit 13, a smoothing capacitor C2, a low-side current detection circuit 14, and a control circuit 15.

[0026] The input filter 11 is a noise filter, and is, for example, a smoothing filter constituted by a coil, a capacitor, etc. The input filter 11 may be provided with a reverse connection protection circuit, which is a protection circuit when DC voltages of opposite polarity are connected to the input terminals 2a and 2b (i.e., DC voltages in which the input terminal 2a is at the reference potential and the input terminal 2b is at the positive potential).

[0027] The DCDC converter 12 is an example of a DC power supply that supplies current to the LED light source 3, and is a step-up / step-down converter composed of a capacitor C1, transistors Tr1 and Tr2, diodes D1 and D2, a coil L1, and a drive circuit Dr. The output from the DCDC converter 12 is smoothed by a smoothing capacitor C2. The drive circuit Dr is a circuit, and may be, for example, a microcomputer, that controls the output current from the DCDC converter 12 (i.e., the high-potential side current) by outputting a PWM (Pulse Width Modulation) signal or a logic signal to the transistors Tr1 and Tr2 to control the on / off of the transistors Tr1 and Tr2 under instructions from the control circuit 15.

[0028] The high-potential-side current detection circuit 13 is composed of resistors R1 to R4, a differential amplifier Amp1, and a transistor Tr3. The high-potential-side current flowing through the resistor R1 is converted into a voltage and input to the control circuit 15.

[0029] The output filter 16 is a noise filter, and is, for example, a smoothing filter configured with a coil, a capacitor, and the like.

[0030] The LED light source 3 is a light source composed of a plurality of LEDs connected in series. However, the LED light source 3 as a light source is not limited to this configuration and may be composed of a single LED, or may be composed of one or more LEDs connected in series and connected in parallel. Furthermore, the LED light source 3 may be composed of a plurality of LEDs connected in series and a switch element connected in parallel to each of one or more of the plurality of LEDs.

[0031] The low-potential-side current detection circuit 14 is composed of resistors R5 to R8, a differential amplifier Amp2, and a transistor Tr4. The low-potential-side current flowing through the resistor R5 is converted into a voltage and input to the control circuit 15.

[0032] The control circuit 15 is a circuit that performs the first control and the second control described above and is composed of, for example, a comparator, a logic gate, 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 DCDC converter 12 to set a voltage corresponding to the detected current notified by the high-side current detection circuit 13 to a target constant value, thereby causing the DCDC converter 12 to supply a constant output current to the LED light source 3. In the second control, the control circuit 15 compares the voltage corresponding to the detected current notified by the low-side current detection circuit 14 with a reference voltage corresponding to an internally stored low-side current under-threshold, and when it detects that the low-side current detected by the low-side current detection circuit 14 is smaller than the low-side current under-threshold, the control circuit 15 outputs a control signal to the drive circuit Dr of the DCDC converter 12 to suppress the output current supplied from the DCDC converter 12 to the LED light source 3.

[0033] The low-potential-side current insufficiency threshold may be a fixed value (e.g., the minimum current value to be supplied to the LED light source 3) or a variable value determined depending 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, when the control circuit 15 detects that the low-potential-side current detected by the low-potential-side current detection circuit 14 is smaller than the high-potential-side current detected by the high-potential-side current detection circuit 13, the control circuit 15 may suppress the output current supplied from the DCDC converter 12 to the LED light source 3. Whether to use a fixed value or a variable value as the low-potential-side current insufficiency threshold may be determined, for example, by a setting in advance in the control circuit 15.

[0034] Furthermore, when the control circuit 15 detects that the low-potential-side current is smaller than the low-potential-side current under-threshold, the control circuit 15 employs one of the following methods for suppressing the output current supplied from the DCDC converter 12 to the LED light source 3: (1) suppressing the output current supplied from the DCDC converter 12 to the LED light source 3 in accordance with the difference between the low-potential-side current under-threshold and the value of the low-potential-side current, (2) suppressing the output current supplied from the DCDC converter 12 to the LED light source 3 in accordance with the ratio between the low-potential-side current under-threshold and the value of the low-potential-side current, and (3) cutting off the output current supplied from the DCDC converter 12 to the LED light source 3. Which control algorithm to use may be determined, for example, by prior settings in the control circuit 15.

[0035] 8 is a flowchart showing a control algorithm in which the lighting device 10 according to the embodiment suppresses the output current supplied from the DCDC converter 12 to the LED light source 3 in accordance with the difference between the low-potential-side current excessive threshold and the value of the low-potential-side current. Here, the operation is shown in the case where the high-potential-side current detected by the high-potential-side current detection circuit 13 is used as the low-potential-side current excessive threshold.

[0036] First, based on a notification from the low-potential-side current detection circuit 14, the control circuit 15 determines whether an abnormality has occurred in which the low-potential-side current detected by the low-potential-side current detection circuit 14 is smaller than the low-potential-side current insufficiency threshold value (here, the high-potential-side current detected by the high-potential-side current detection circuit 13) (S10).

[0037] As a result, if it is determined that an abnormality has occurred in which the low-potential-side current is smaller 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), and instructs the drive circuit Dr of the DCDC converter 12 to suppress the output current supplied from the DCDC converter 12 to the LED light source 3 to a greater extent the greater the calculated current difference (S12). Specifically, in step S12, the control circuit 15 performs constant current control (i.e., first control) so that the high-potential-side current detected by the high-potential-side current detection circuit 13 is maintained at the current value after suppression. Note that 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 a table.

[0038] With this control algorithm, if an abnormality occurs in which current leaks outside the current loop due to a ground fault or the like, the output current supplied to the LED light source 3 is suppressed to a desired degree depending on the severity of the abnormality, thereby preventing damage to the lighting device 10 and maintaining the desired brightness.

[0039] 9 is a flowchart showing a control algorithm in which the lighting device 10 according to the embodiment suppresses the output current supplied from the DCDC converter 12 to the LED light source 3 in accordance with the ratio between the low-potential-side current excessive threshold and the value of the low-potential-side current. Here, the operation is shown in the case where the high-potential-side current detected by the high-potential-side current detection circuit 13 is used as the low-potential-side current excessive threshold.

[0040] First, the control circuit 15 determines whether an abnormality has occurred in which the low potential side current detected by the low potential side current detection circuit 14 is smaller than the low potential side current insufficiency threshold value (here, the high potential side current detected by the high potential side current detection circuit 13) (S20).

[0041] As a result, if it is determined that an abnormality has occurred in which the low-potential-side current is smaller 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), and instructs the drive circuit Dr of the DCDC converter 12 to suppress the output current supplied from the DCDC converter 12 to the LED light source 3 to a greater extent as the calculated current ratio becomes smaller (S22). Specifically, in step S22, the control circuit 15 performs constant current control (i.e., first control) so that the high-potential-side current detected by the high-potential-side current detection circuit 13 is maintained at the suppressed current value. Note that 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 a table.

[0042] With this control algorithm, if an abnormality occurs in which current leaks outside the current loop due to a ground fault or the like, the output current supplied to the LED light source 3 is suppressed to a desired degree depending on the severity of the abnormality, thereby preventing damage to the lighting device 10 and maintaining the desired brightness.

[0043] 10 is a block diagram showing the circuit configuration of a lighting device 10a according to a first modified example of the embodiment. The lighting device 10a according to this modified example is a circuit that receives AC voltage from an AC power supply 5 via input terminals 2c and 2d and supplies a constant current to an LED light source 3 serving as a light source, and includes an input filter 17, an AC-DC converter 18, a DC-DC converter 12, an output filter 16, a high-side current detection circuit 13, a low-side current detection circuit 14, and a control circuit 15.

[0044] The lighting device 10a of this modified example differs from the lighting device 10 of the embodiment shown in Figure 5 in that an input filter 17 for AC voltage and an AC-DC converter 18 are provided in the stage preceding the DC-DC converter 12, and that the high-side current detection circuit 13, the low-side current detection circuit 14, and the control circuit 15 are provided in the stage following the output filter 16 and closer to the LED light source 3.

[0045] The input filter 17 is a common mode noise filter or a common mode and normal mode noise filter, and is configured, for example, by a choke coil and a capacitor.

[0046] The AC-DC converter 18 is a circuit that converts AC voltage into DC voltage, and is, for example, a diode bridge.

[0047] 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 configuration and functions as those of the lighting device 10 according to the embodiment.

[0048] The lighting device 10a according to the first modification includes the same high-side current detection circuit 13, low-side current detection circuit 14, and control circuit 15 as the lighting device 10 according to the embodiment, and therefore has the same functions as the lighting device 10 according to the embodiment. In other words, according to the lighting device 10a according to the first modification, when an abnormality occurs in which current leaks outside the current loop due to a ground fault or the like, the abnormality is detected, and the second control prevents the output current (i.e., the high-side current) supplied to the LED light source 3 from becoming excessive, and the first control maintains the output current after the suppression at a desired constant value. Thus, 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.

[0049] 11 is a block diagram showing the circuit configuration of a lighting device 10b according to a second modification of the embodiment. The lighting device 10b according to this modification is a circuit that receives a DC voltage via input terminals 2a and 2b as an input and supplies a constant current to LED light sources 3 and 4 as a plurality of light sources connected in parallel, and includes an input filter 11, a DCDC converter 12, output filters 16a and 16b, a high-side current detection circuit 13, low-side current detection circuits 14a and 14b, and a control circuit 15.

[0050] The lighting device 10b according to this modified example differs from the lighting device 10 according to the embodiment shown in FIG. 5 in that it is provided with a plurality of light source loads, namely, an output filter 16a and an LED light source 3, and an output filter 16b and an LED light source 4, which are connected in parallel; that the high-side current detection circuit 13 detects the total current flowing from the DCDC converter 12 to the high-side terminals of the plurality of light source loads (i.e., the high-side terminal 3a of the LED light source 3 and the high-side terminal 4a of the LED light source 4); and that it is provided with a plurality of low-side current detection circuits 14a and 14b which detect each current flowing from the low-side terminals of the plurality of light source loads (i.e., the low-side terminal 3b of the LED light source 3 and the low-side terminal 4b of the LED light source 4) to the DCDC converter 12, respectively.

[0051] In this modified example, the control circuit 15 performs a first control of driving the DCDC converter 12 so that the high-side current detected by the high-side current detection circuit 13 is set to a target constant value based on a notification from the high-side current detection circuit 13, and a second control of suppressing the output current supplied from the DCDC converter 12 to the LED light source 3 when the low-side current detected by at least one of the plurality of low-side current detection circuits 14a and 14b is smaller than a predetermined value (i.e., a low-side current insufficiency threshold) based on notifications from the plurality of low-side current detection circuits 14a and 14b.

[0052] According to the lighting device 10b of this modification, when an abnormality occurs in which current leaks outside the current loop due to a ground fault or the like, the abnormality is detected independently for each of the plurality of light source loads, the total current (i.e., the high-potential side current) supplied to the plurality of light source loads (i.e., the LED light sources 3 and 4) is prevented from reaching the device damage threshold and damaging the lighting device, and the first control maintains the output current after the suppression at a desired constant value. Thus, the problems of the lighting device 20a of the first reference example and the lighting device 20b of the second reference example are solved.

[0053] In this modification, each of the plurality of light source loads connected in parallel is a set of an output filter and an LED, but the present invention is not limited to this configuration. Only one output filter may be provided that is shared by the plurality of light source loads, and each of the plurality of light source loads may consist of only an LED.

[0054] 12A is a block diagram showing the circuit configuration of a lighting device 10c according to a third modification of the embodiment. The lighting device 10c according to this modification basically has the same configuration as the lighting device 10 according to the embodiment, but differs from the embodiment in that it further includes switch elements 19a to 19f connected in parallel to the LEDs 3c to 3h that make up the LED light source 3, respectively.

[0055] Here, each of the LEDs 3c to 3h is an LED block made up of one or more LEDs connected in series or in parallel, and is assigned to, for example, a headlamp, a headlight, a side lamp, or the like of a vehicle.

[0056] In addition to the functions of the embodiment, when it is determined that a ground fault has occurred, the control circuit 15 selectively turns on the switch elements 19a to 19f. For example, by turning on only the switch element corresponding to the LED block in which a ground fault has occurred and shorting out only that LED block, the other LED blocks can continue to be used.

[0057] 12B is a diagram showing an example of application of a lighting device 10c according to a third modified example of the embodiment to a vehicle 22. In this example, LED blocks (LEDs 3c to 3h) constituting the LED light source 3 are assigned to the headlights, headlights, side lamps, etc. of the vehicle 22, and the lighting device 10c is provided in the vehicle 22. The vehicle 22 includes a body control module 20, which is the brain that controls the vehicle 22. In addition to the control performed in the embodiment, when the current detected by the low-potential-side current detection circuit 14 is smaller than a predetermined value, the lighting device 10c (more specifically, the control circuit 15 of the lighting device 10c) communicates with the body control module 20 to notify that an abnormality has occurred in the current supply to the LED light source 3.

[0058] In this application example, when a ground fault occurs, the body control module 20 of the vehicle 22 is notified of the abnormality, and only the switch element corresponding to the LED block in which the ground fault occurred is turned on, thereby shorting out only that LED block, allowing the other LED blocks to continue to be used.

[0059] As described above, the lighting device 10 etc. according to the embodiment includes the DCDC converter 12 which is a DC power supply that supplies current to the LED light source 3, the high-side current detection circuit 13 which detects the current flowing from the DCDC converter 12 to the high-side terminal 3 a of the LED light source 3, the low-side current detection circuit 14 which detects the current flowing from the low-side terminal 3 b of the LED light source 3 to the DCDC converter 12, and the control circuit 15 which performs first control which controls the DCDC converter 12 so that the current detected by the high-side current detection circuit 13 is constant, and second control which controls the DCDC converter 12 so as to suppress the output current supplied from the DCDC converter 12 to the LED light source 3 when the current detected by the low-side current detection circuit 14 is smaller than a predetermined value.

[0060] As a result, the first control and the second control are performed by the control circuit 15, so that if an abnormality occurs in which current leaks outside the current loop due to a ground fault or the like, the abnormality is detected, the output current (i.e., the high-potential side current) supplied to the LED light source 3 is prevented from becoming an excessive output, and the output current after the suppression is maintained at a desired constant value.

[0061] Here, the predetermined value may be a fixed value or a variable value that is determined depending on the current detected by the high-potential-side current detection circuit 13. By comparing the current detected by the low-potential-side current detection circuit 14 with the fixed value or the variable value, an abnormality in which current leaks outside the current loop can be monitored.

[0062] Furthermore, in the second control, the control circuit 15 may determine whether the current detected by the low potential side current detection circuit 14 is smaller than a predetermined value based on the difference between the current detected by the low potential side current detection circuit 14 and a predetermined value, or may determine whether the current detected by the low potential side current detection circuit 14 is smaller than a predetermined value based on the ratio between the current detected by the low potential side current detection circuit 14 and the predetermined value. This makes it possible to monitor for an abnormality in which current leaks outside the current loop based on the difference or ratio between the current detected by the low potential side current detection circuit 14 and the predetermined value.

[0063] At this time, in the second control, the smaller the current detected by the low-potential-side current detection circuit 14 is than a predetermined value, the more the control circuit 15 may suppress the output current supplied from the DCDC converter 12 to the LED light source 3. This suppresses the problem that the output current supplied to the LED light source 3 continues to increase as the current leaking outside the current loop increases, and enables the output current to be maintained constant.

[0064] For example, in the second control, the control circuit 15 may be configured to reduce the output current supplied from the DCDC converter 12 to the LED light source 3 to a greater extent the greater the difference between the current detected by the low-potential side current detection circuit 14 and a predetermined value, or the control circuit 15 may be configured to reduce the output current supplied from the DCDC converter 12 to the LED light source 3 to a greater extent the smaller the ratio of the current detected by the low-potential side current detection circuit 14 to the predetermined value. This prevents the output current supplied to the LED light source 3 from continuing to increase as the current leaking outside the current loop increases, based on the difference or ratio between the current detected by the low-potential side current detection circuit 14 and the predetermined value, and allows the output current to be maintained constant.

[0065] Furthermore, a lighting device 10b according to a second modified example includes a DCDC converter 12 that supplies current to a plurality of LED light sources 3 and 4 connected in parallel, a high-side current detection circuit 13 that detects the total current flowing from the DCDC converter 12 to the high-side terminals 3 a and 4 a of the plurality of LED light sources 3 and 4, a plurality of low-side current detection circuits 14 a and 14 b that detect each current flowing from the low-side terminals 3 b and 4 b of the plurality of LED light sources 3 and 4 to the DCDC converter 12, and a control circuit 15 that performs first control that controls the DCDC converter 12 so that the total current detected by the high-side current detection circuit 13 is constant, and second control that controls the DCDC converter 12 to suppress the current supplied from the DCDC converter 12 to the plurality of LED light sources 3 and 4 when the current detected by at least one of the plurality of low-side current detection circuits 14 a and 14 b is smaller than a predetermined value.

[0066] As a result, if an abnormality occurs in which current leaks outside the current loop due to a ground fault or the like, the abnormality is detected independently for each of the multiple light source loads, the total current (i.e., high-potential side current) supplied to the multiple light source loads (i.e., LED light sources 3 and 4) is prevented from becoming an over-output, and the output current after the suppression is maintained at a desired constant value.

[0067] Furthermore, in the third modified example, the LED light source 3 and the lighting device 10c are provided in a vehicle 22, the vehicle 22 includes a body control module 20 that controls the vehicle 22, and when the current detected by the low potential side current detection circuit 14 is smaller than a predetermined value, the control circuit 15 further communicates with the body control module 20 to notify that an abnormality has occurred in the current supply to the LED light source 3. As a result, when an abnormality such as a ground fault occurs in the LED light source 3 in the vehicle 22, the body control module 20 of the vehicle 22 can know this.

[0068] While the lighting device according to the present disclosure has been described above based on the embodiments and modifications, the present disclosure is not limited to these embodiments and modifications. As long as they do not deviate from the gist of the present disclosure, various modifications that a person skilled in the art could conceive of to the present embodiments and modifications, and other forms constructed by combining some of the components of the embodiments and modifications, are also included within the scope of the present disclosure.

[0069] For example, in the above embodiment and modified examples, the DCDC converter 12 is given as an example of a DC power supply that supplies current to the LED light source 3, etc., but such a DC power supply is not limited to the DCDC converter 12, and may be any other type of DC voltage source, DC current source, etc., as long as it is a DC power supply that can adjust the current it supplies.

[0070] In the above-described embodiment and modifications, the LED light source 3 and the like are merely examples of light sources, and may be replaced with other light sources such as organic electroluminescence (OLED).

[0071] Furthermore, the predetermined value used in the second control by the control circuit 15 (i.e., the low-potential-side current insufficiency threshold) may 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, etc. may be a variable value that can be set by the user through communication with the lighting device 10.

[0072] Furthermore, the present disclosure can be realized not only as a lighting device, but also as a lighting device including a lighting device and a light source, as a control method or program that describes the operation of a control circuit, or as a computer-readable recording medium such as a DVD on which the program is recorded.

[0073] 3, 4 LED light source 3a, 4a High potential side terminal 3b, 4b Low potential side terminal 10, 10a, 10b, 10c Lighting device 12 DCDC 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 an LED light source; a high potential side current detection circuit that detects current flowing from the DC power supply to a high potential side terminal of the LED light source; a low potential side current detection circuit that detects 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 that controls the DC power supply so that the current detected by the high potential side current detection circuit is constant, and a second control that controls the DC power supply to suppress the current supplied from the DC power supply to the LED light source when the current detected by the low potential side current detection circuit is smaller than a predetermined value.

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

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

4. A lighting device as described in any one of claims 1 to 3, wherein, in the second control, the control circuit determines whether or not the current detected by the low potential side current detection circuit is smaller 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. A lighting device as claimed in any one of claims 1 to 3, wherein, in the second control, the control circuit determines whether or not the current detected by the low potential side current detection circuit is smaller than the predetermined value based on a ratio between the current detected by the low potential side current detection circuit and the predetermined value.

6. The lighting device according to any one of claims 1 to 3, wherein, in the second control, the control circuit significantly suppresses the current supplied from the DC power supply to the LED light source as the current detected by the low potential side current detection circuit becomes smaller than the predetermined value.

7. The lighting device according to claim 6, wherein, in the second control, the control circuit significantly reduces the current supplied from the DC power supply to the LED light source the greater the difference between the current detected by the low potential side current detection circuit and the predetermined value.

8. The lighting device according to claim 6, wherein, in the second control, the control circuit is adapted to greatly suppress the current supplied from the DC power supply to the LED light source as the ratio of the current detected by the low potential side current detection circuit to the predetermined value becomes smaller.

9. A lighting device comprising: a DC power supply that supplies current to a plurality of LED light sources connected in parallel; a high potential side current detection circuit that detects a total current flowing from the DC power supply to a high potential side terminal of the plurality of LED light sources; a plurality of low potential side current detection circuits that detect each current flowing from a low potential side terminal of each of the plurality of LED light sources to the DC power supply; and a control circuit that performs a first control that controls the DC power supply so that the total current detected by the high potential side current detection circuit is constant, and a second control that controls the DC power supply to suppress the current supplied from the DC power supply to the plurality of LED light sources when a current detected by at least one of the plurality of low potential side current detection circuits is smaller than a predetermined value.

10. A lighting device as claimed in claim 1 or 9, wherein the LED light source and the lighting device are provided in a vehicle, the vehicle includes a body control module that controls the vehicle, and when the current detected by the low potential side current detection circuit is smaller than a predetermined value, the control circuit further communicates with the body control module to notify that an abnormality has occurred in the current supply to the LED light source.

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