Lighting device

Abstract

To provide a lighting device that can detect an abnormality in the event of current leakage outside a current loop and prevent the output current from becoming an excessive output.SOLUTION: A lighting device 10 includes a DCDC converter 12 which is a DC power supply that supplies a current to an LED light source 3, a high-voltage side current detection circuit 13 which detects the current flowing from the DCDC converter 12 to a high-voltage side terminal 3a of the LED light source 3, a low-voltage side current detection circuit 14 which detects the current flowing from a low-voltage side terminal 3b of the LED light source 3 to the DCDC converter 12, and a control circuit 15 which performs first control which controls the DCDC converter 12 such that the current detected by the high-voltage 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-voltage side current detection circuit 14 is smaller than a predetermined value.SELECTED DRAWING: Figure 5

Description

[Technical field]

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

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

[0003] In the technology of Patent Document 1, current leakage to the outside of 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. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2004-134147 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the technology of Patent Document 1, when a current leak occurs outside the current loop, it is detected as an abnormality, but the DC power supply attempts to output a current equal to the total of the target supply current to the LED light source and the current leaking outside the current loop, which causes a problem that the output current from the DC power supply becomes an over-output.

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

[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-side current detection circuit that detects the current flowing from the DC power supply to a high-side terminal of the LED light source, a low-side current detection circuit that detects the current flowing from the low-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-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-side current detection circuit is smaller than a predetermined value. Effect of the Invention

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

[0009] [Figure 1] FIG. 1 is a block diagram showing a circuit configuration of a lighting device according to a first reference example. [Diagram 2] 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. [Diagram 3] FIG. 3 is a block diagram showing a circuit configuration of a lighting device according to a second reference example. [Figure 4] 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. [Diagram 5] FIG. 5 is a block diagram showing a circuit configuration of a lighting device according to an embodiment. [Figure 6] 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. [Figure 7]FIG. 7 is a diagram showing a detailed circuit configuration of the lighting device according to the embodiment shown in FIG. [Figure 8] FIG. 8 is a flowchart showing a control algorithm in which the lighting device according to the embodiment suppresses the output current supplied from the DC-DC converter to the LED light source in accordance with the difference between the low potential side current excessively low threshold and the value of the low potential side current. [Figure 9] FIG. 9 is a flowchart showing a control algorithm for the lighting device according to the embodiment to suppress the output current supplied from the DC-DC converter to the LED light source in accordance with the ratio between the low potential side current excessively low threshold and the value of the low potential side current. [Figure 10] FIG. 10 is a block diagram showing a circuit configuration of a lighting device according to a first modified example of the embodiment. [Figure 11] FIG. 11 is a block diagram showing a circuit configuration of a lighting device according to a second modified example of the embodiment. [Figure 12A] FIG. 12A is a block diagram showing a circuit configuration of a lighting device according to a third modified example of the embodiment. [Figure 12B] FIG. 12B is a diagram showing an example of application of a lighting device according to a third modified example of the embodiment to a vehicle. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, the embodiments of the present disclosure will be described in detail with reference to the drawings. Note that each of the embodiments described below shows one specific example of the present disclosure. The numerical values, numbers, components, arrangement and connection forms of the components, steps, order of steps, etc. shown in the following embodiments are merely examples and are not intended to limit the present disclosure. In addition, each figure is not necessarily a strict illustration. In each figure, the same reference numerals are used for substantially the same configuration, and duplicated explanations are omitted or simplified. In addition, "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 a circuit configuration of a lighting device 20a according to a first reference example. The lighting device 20a includes an input filter 11 that smoothes a DC voltage inputted through input terminals 2a and 2b (i.e., a DC voltage with the input terminal 2b as a reference potential and the input terminal 2a as a positive potential) to remove noise, a DCDC converter 12 as a DC power supply that boosts the DC voltage outputted from the input filter 11, an output filter 16 that smoothes the DC voltage outputted from the DCDC converter 12 to remove noise and outputs it to an 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 a current returning from the low potential side terminal 3b of the LED light source 3 through the output filter 16 to the DCDC converter 12 and notifies the control circuit 15a, and a control circuit 15a that drives the DCDC converter 12 so that the current detected by the low potential side current detection circuit 14 based on the notification from the low potential side current detection circuit 14 becomes a target constant value. In this example, the LED light source 3 is a light source composed of a plurality of LEDs connected in series. A light source including the LED light source 3 and a lighting device 20a that supplies current to the light source constitute an illumination device.

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

[0013] Fig. 2 is a diagram showing each current value 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 shows what value 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 becomes 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. Also, the dashed and 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 Fig. 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 with an increase in the ground fault current (solid line). Therefore, with an increase in the ground fault current, the high potential side current may reach the device damage threshold, resulting in over-output, which may damage the lighting device 20a. Thus, the lighting device 20a according to the first reference example has a problem that the output current supplied by the lighting device 20a to the LED light source 3 becomes over-output when 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 a circuit configuration of a lighting device 20b according to a second reference example. The lighting device 20b includes an input filter 11 that smoothes the DC voltage input through the input terminals 2a and 2b to remove noise, 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 the high-potential side terminal 3a of the LED light source 3 and notifies the control circuit 15b, an output filter 16 that smoothes the DC voltage output from the DCDC converter 12 through the high-potential side current detection circuit 13 to remove noise and output it to the LED light source 3, and a control circuit 15b that drives the DCDC converter 12 so that the current detected by the high-potential side current detection circuit 13 based on the notification from the high-potential side current detection circuit 13 becomes 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, in such lighting device 20b, it is assumed that an abnormality occurs in which a current (i.e., a ground fault current) leaks outside the current loop due to a ground fault at any of the multiple LEDs constituting the LED light source 3. Then, based on the notification from the high potential side current detection circuit 13, the control circuit 15b drives the DCDC converter 12 so that the current (i.e., the high potential side current) detected by the high potential side current detection circuit 13 becomes a target constant value, so that only the current remaining after subtracting the ground fault current leaked outside the current loop due to the ground fault from the high potential side current supplied to the 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 when an abnormality occurs in which current leaks outside the current loop in the lighting device 20a according to the second reference example shown in Fig. 3. This diagram shows the value of the current flowing through the LED on the lower potential side of the point where the ground fault occurred (i.e., the low potential side current) as the ground fault current increases. Note that the types of lines shown in Fig. 4 are the same as those in Fig. 2.

[0018] As shown in Fig. 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 LED on the lower potential side of the point where the ground fault occurred (i.e., the low-potential side current) decreases, and the brightness of the LED light source 3 decreases 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 a circuit configuration of a lighting device 10 according to an embodiment. The lighting device 10 includes an input filter 11 that smoothes the DC voltage input via input terminals 2a and 2b to remove noise, 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 3a of the LED light source 3 and notifies the control circuit 15, an output filter 16 that smoothes the DC voltage output from the DCDC converter 12 via the high-potential side current detection circuit 13, removes noise, and outputs the DC voltage to the LED light source 3, and a DC 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 detection, 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 is set to 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 based on the notification from 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 insufficient threshold value"). The control circuit 15 is a microcomputer or the like that executes a built-in control program. The lighting device is configured by combining the light source including the LED light source 3 and the lighting device 10 that supplies current to the light source.

[0020] In such a lighting device 10, assume that an abnormality occurs in which a current (i.e., a ground fault current) leaks outside the current loop due to a ground fault at any of the connection points of the LEDs constituting the LED light source 3, as shown in Fig. 5. Then, when the low potential side current detected by the low potential side current detection circuit 14 is smaller than the low potential side current excessively low threshold, the control circuit 15, which has received the notification from the low potential side current detection circuit 14, performs a 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 a first control, i.e., a constant current control, so that the output current supplied from the DCDC 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) is maintained at the current value after suppression.

[0021] Fig. 6 is a diagram showing each current value 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 shows what value 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 with an increase in ground fault current. Note that the type of lines shown in Fig. 6 is the same as that in Fig. 2. In addition, the "low potential side current under-threshold value" is shown by a two-dot chain line.

[0022] 6, when the low potential side current (dashed line) decreases beyond the low potential side current under-threshold value with an increase in the ground fault current (solid line), it is detected as an abnormality by the control circuit 15, and the high potential side current (dotted line), which had been maintained at a target constant value until then, is reduced by the second control. Note that the degree of suppression of the high potential side current after the abnormality is detected (i.e., the degree of reduction in the luminance of the LED light source 3) can be set to a desired value depending on the control algorithm in the control circuit 15, as described later.

[0023] In this way, according to the lighting device 10 of 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, and the output current (i.e., the high-potential side current) supplied to the LED light source 3 is prevented from becoming an over-output by the second control, and the output current after the suppression is maintained at a desired constant value by the first control. 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.

[0024] The circuit configuration and operation of the lighting device 10 according to the embodiment will be described in detail 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 input via input terminals 2a and 2b as an input and supplies a constant current to an LED light source 3 as a light source, and includes an input filter 11, a DCDC 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.

[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 (that is, DC voltages in which the input terminal 2a is at a reference potential and the input terminal 2b is at a positive potential) are connected to the input terminals 2a and 2b.

[0027] The DCDC converter 12 is an example of a DC power supply that supplies a current to the LED light source 3, and is a step-up / step-down converter that is 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 that controls the output current (i.e., high-potential side current) from the DCDC converter 12 by outputting a PWM (Pulse Width Modulation) signal or a logic signal to the transistors Tr1 and Tr2 under the instruction of the control circuit 15 to control the on / off of the transistors Tr1 and Tr2, and is, for example, a microcomputer.

[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, for example, a smoothing filter constituted by 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. The LED light source 3 as a light source is not limited to such a 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. The LED light source 3 may also 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 above-mentioned first control and second control, and is composed of, for example, a comparator, a logic gate, and 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 the voltage corresponding to the detected current notified from the high-potential 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 from the low-potential side current detection circuit 14 with a reference voltage corresponding to a low-potential side current under-threshold value held internally, and 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 when it detects that the low-potential side current detected by the low-potential side current detection circuit 14 is smaller than the low-potential side current under-threshold value.

[0033] The low potential side current insufficiency threshold may be a fixed value (for example, the minimum current value to be supplied to the LED light source 3) or may be a variable value determined depending on the high potential side current detected by the high potential side current detection circuit 13 (for example, 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 DC-C 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 prior setting in the control circuit 15.

[0034] In addition, 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 a method of suppressing the output current supplied from the DCDC converter 12 to the LED light source 3, which is one of the following: (1) suppressing the output current supplied from the DCDC converter 12 to the LED light source 3 according to 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 according to 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 a prior setting 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 DC-DC converter 12 to the LED light source 3 according to the difference between the low potential side current under-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 adopted as the low potential side current under-threshold.

[0036] First, based on a notification from the low potential side current detection circuit 14, the control circuit 15 determines whether or not 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 excessively low threshold value (here, the high potential side current detected by the high potential side current detection circuit 13) (S10).

[0037] As a result, when it is determined that an abnormality occurs 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 those 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 as the calculated current difference increases (S12). In step S12, specifically, 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 DC-DC converter 12 to the LED light source 3 according to the ratio between the low potential side current under-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 adopted as the low potential side current under-threshold.

[0040] First, the control circuit 15 determines whether or not 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 excessively low threshold value (here, the high potential side current detected by the high potential side current detection circuit 13) (S20).

[0041] As a result, when it is determined that an abnormality occurs 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 more as the calculated current ratio becomes smaller (S22). In step S22, specifically, 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 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 a 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 an AC voltage from an AC power source 5 via input terminals 2c and 2d and supplies a constant current to an LED light source 3 as a light source, and includes an input filter 17, an ACDC converter 18, a DCDC 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.

[0044] The lighting device 10a of this modified example differs from the lighting device 10 of the embodiment shown in FIG. 5 in that an input filter 17 for AC voltage and an ACDC converter 18 are provided in the stage preceding the DCDC 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 an AC voltage into a 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 function as the lighting device 10 according to the embodiment.

[0048] The lighting device 10a according to the first modification includes the high-side current detection circuit 13, the low-side current detection circuit 14, and the control circuit 15 similar to those of 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 output current (i.e., the high-side current) supplied to the LED light source 3 is prevented from becoming an over-output by the second control, and the output current after the suppression is maintained at a desired constant value by the first control. 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 a circuit configuration of a lighting device 10b according to a second modified example of the embodiment. The lighting device 10b according to this modified example is a circuit that receives a DC voltage input 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-potential side current detection circuit 13, a low-potential side current detection circuit 14a and 14b, and a control circuit 15.

[0050] The lighting device 10b of this modified example differs from the lighting device 10 of the embodiment shown in FIG. 5 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-side current detection circuit 13 detects the total current flowing from the DCDC converter 12 to the high-side terminals of the multiple 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 multiple low-side current detection circuits 14a and 14b are provided to detect each current flowing from the low-side terminals of the multiple 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.

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

[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 multiple light source loads, and 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 reaching the device damage threshold and damaging the lighting device, and the output current after the suppression is maintained at a desired constant value by the first control. 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 multiple 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 to be shared by the multiple light source loads, and each of the multiple light source loads may be only an LED.

[0054] 12A is a block diagram showing a circuit configuration of a lighting device 10c according to a third modified example of the embodiment. The lighting device 10c according to this modified example 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-19f connected in parallel to the LEDs 3c-3h constituting the LED light source 3, respectively.

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

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

[0057] 12B is a diagram showing an example of application of the lighting device 10c according to the third modified example of the embodiment to a vehicle 22. In this application example, the 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 that is a brain that controls the vehicle 22, and the lighting device 10c (more specifically, the control circuit 15 of the lighting device 10c) notifies the body control module 20 that an abnormality has occurred in the current supply to the LED light source 3 by communicating with the body control module 20 in addition to the control in the embodiment when the current detected by the low potential side current detection circuit 14 is smaller than a predetermined value.

[0058] With such an application example, if 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 only that LED block, allowing the other LED blocks to continue being used.

[0059] As described above, the lighting device 10 according to the embodiment includes the DCDC converter 12 which is a DC power supply that supplies a current to the LED light source 3, the high-side current detection circuit 13 which detects a current flowing from the DCDC converter 12 to the high-side terminal 3a of the LED light source 3, the low-side current detection circuit 14 which detects a current flowing from the low-side terminal 3b of the LED light source 3 to the DCDC converter 12, and the control circuit 15 which performs a first control which controls the DCDC converter 12 so that the current detected by the high-side current detection circuit 13 is constant, and a 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 and 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 determined depending on the current detected by the high potential side current detection circuit 13. In this way, by comparing the current detected by the low potential side current detection circuit 14 with the fixed value or the variable value, it is possible to monitor for an abnormality in which current leaks outside the current loop.

[0062] Furthermore, in the second control, the control circuit 15 may determine whether or not 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, and in the second control, the control circuit 15 may determine whether or not 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 the predetermined value, the more the control circuit 15 may suppress the output current supplied from the DC-DC 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 the output current can be maintained constant.

[0064] For example, in the second control, the control circuit 15 may suppress the output current supplied from the DCDC converter 12 to the LED light source 3 more as the difference between the current detected by the low potential side current detection circuit 14 and the predetermined value increases, and the control circuit 15 may suppress the output current supplied from the DCDC converter 12 to the LED light source 3 more as the ratio of the current detected by the low potential side current detection circuit 14 to the predetermined value decreases. This prevents the output current supplied to the LED light source 3 from increasing 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 the output current can be maintained constant.

[0065] The lighting device 10b according to the second modification includes a DCDC converter 12 that supplies current to the multiple 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 3a and 4a of the multiple LED light sources 3 and 4, a plurality of low-side current detection circuits 14a and 14b that detect each current flowing from the low-side terminals 3b and 4b of the multiple LED light sources 3 and 4 to the DCDC converter 12, and a control circuit 15 that performs a 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 a second control that controls the DCDC converter 12 to suppress the current supplied from the DCDC converter 12 to the multiple LED light sources 3 and 4 when the current detected by at least one of the multiple low-side current detection circuits 14a and 14b 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, and 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] In the third modification, 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 the abnormality.

[0068] Although the lighting device according to the present disclosure has been described above based on the embodiment and the modified examples, the present disclosure is not limited to these embodiment and modified examples. As long as it does not deviate from the gist of the present disclosure, various modifications conceived by a person skilled in the art to the present embodiment and modified examples, and other forms constructed by combining some of the components in the embodiment and modified examples are also included within the scope of the present disclosure.

[0069] For example, in the above embodiment and modified example, 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 embodiment and modified examples, the LED light source 3 and the like are merely examples of light sources, and may be replaced with other light sources such as an organic electroluminescence (OLED).

[0071] Furthermore, the predetermined value (i.e., the low potential side current under-threshold value) used in the second control by the control circuit 15 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 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. [Explanation of symbols]

[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 DC / DC converter (DC power supply) 13 High-side current detection circuit 14, 14a, 14b Low-side current detection circuit 15. Control circuit 20 Body Control Module 22 Vehicles

Claims

1. A DC power source that supplies current to the LED light source; a high-potential side current detection circuit that detects a 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 a current flowing from a low potential side terminal of the LED light source to the DC power supply; a control circuit that performs a first control to control the DC power supply so that the current detected by the high potential side current detection circuit is constant, and a 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; Lighting device.

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

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

4. 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 difference between the current detected by the low potential side current detection circuit and the predetermined value. The lighting device according to any one of claims 1 to 3.

5. 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 of the current detected by the low potential side current detection circuit to the predetermined value. The lighting device according to any one of claims 1 to 3.

6. In the second control, the control circuit reduces the current supplied from the DC power source to the LED light source to a greater extent as the current detected by the low potential side current detection circuit becomes smaller than the predetermined value. The lighting device according to any one of claims 1 to 3.

7. In the second control, the control circuit reduces the current supplied from the DC power source to the LED light source to a greater extent as the difference between the current detected by the low potential side current detection circuit and the predetermined value increases. The lighting device according to claim 6.

8. In the second control, the control circuit is configured to suppress the current supplied from the DC power source to the LED light source to a greater extent as the ratio of the current detected by the low potential side current detection circuit to the predetermined value becomes smaller. The lighting device according to claim 6.

9. A DC power source that supplies current to a plurality of LED light sources connected in parallel; a high-potential side current detection circuit for detecting a total current flowing from the DC power source to high-potential side terminals of the plurality of LED light sources; a plurality of low potential side current detection circuits for detecting currents flowing from the low potential side terminals of the plurality of LED light sources to the DC power supply; a control circuit that performs a first control to control the DC power supply so that the total current detected by the high potential side current detection circuit is constant, and a second control to control the DC power supply so as to suppress a 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; Lighting device.

10. The LED light source and the lighting device are provided in a vehicle, The vehicle includes a body control module that controls the vehicle. 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 the body control module that an abnormality has occurred in the current supply to the LED light source.

10. The lighting device according to claim 1 or 9.

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