Vehicle-mounted lighting control device and vehicle-mounted lighting control system

Abstract

An objective of the present invention is to provide technology with which it is possible to improve the resolution of a supply voltage in a control unit. This vehicle-mounted lighting control device includes a control unit that controls an output current from a voltage converting unit to a semiconductor light source to a predetermined current, wherein: when a vehicle-mounted lamp fitting is connected to the vehicle-mounted lighting control device, a voltage division circuit that inputs a divided voltage of a supply voltage to the control unit is formed through cooperation between a resistance of the vehicle-mounted lamp fitting and the vehicle-mounted lighting control device; and the divided voltage relating to the supply voltage, which is the total voltage of the forward voltage drops of the semiconductor light sources, corresponds to the maximum input value of the control unit for failure determination of the semiconductor light sources.

Description

In-vehicle lighting control device and in-vehicle lighting control system

[0001] The present disclosure relates to an in-vehicle lighting control device and an in-vehicle lighting control system.

[0002] The number of LEDs (Light Emitting Diodes) in in-vehicle lamps varies depending on the specifications of the in-vehicle lamps. Since the total voltage of the forward voltage drop of the LEDs changes when a constant current flows through each LED depending on the number of LEDs, the in-vehicle lighting control device is configured to supply a voltage corresponding to the number of LEDs to the in-vehicle lamps as a supply voltage.

[0003] Also, as such an in-vehicle lighting control device, a configuration including a control unit and a voltage dividing circuit that divides the supply voltage to the in-vehicle lamps and inputs it to the control unit has been proposed (for example, Patent Document 1). According to such a configuration, even if the supply voltage is large, the control unit can monitor the supply voltage.

[0004] Japanese Patent Application Laid-Open No. 2008-230544

[0005] As described above, the number of LEDs in in-vehicle lamps varies, and as the range of the supply voltage from the in-vehicle lighting control device to the in-vehicle lamps, a wide range from several volts to several tens of volts is assumed. Therefore, in the conventional in-vehicle lighting control device, the resistance value of the voltage dividing circuit is set according to the large supply voltage so that the control unit can monitor a wide range of supply voltages.

[0006] However, when the resistance value of the voltage dividing circuit is set according to the large supply voltage, the resolution of the supply voltage in the control unit becomes low. Also, since the voltage dividing circuit is incorporated in the in-vehicle lighting control device, the resistance value of the voltage dividing circuit is fixed. As a result, there is a problem that the resolution of the supply voltage in the control unit is fixed at a low resolution.

[0007] Therefore, the present disclosure has been made in view of the above problems, and an object thereof is to provide a technology capable of increasing the resolution of the supply voltage in the control unit.

[0008] The in-vehicle lighting control device according to this disclosure is an in-vehicle lighting control device that controls the lighting of a semiconductor light source by being connected to an in-vehicle lighting fixture equipped with a semiconductor light source and a resistor, and comprises a voltage conversion unit that converts the battery voltage into a supply voltage by performing at least one of boosting and stepping down the voltage and supplies the supply voltage to the semiconductor light source, and a control unit that controls the output current from the voltage conversion unit to the semiconductor light source to a predetermined current, and when the in-vehicle lighting fixture is connected to the in-vehicle lighting control device, a voltage divider circuit is formed by the cooperation of the resistor of the in-vehicle lighting fixture and the in-vehicle lighting control device to input a divided voltage of the supply voltage to the control unit, and the divided voltage of the supply voltage, which is the sum of the forward drop voltages of the semiconductor light source, corresponds to the maximum input value of the control unit for fault detection of the semiconductor light source.

[0009] According to this disclosure, when an in-vehicle lighting device is connected to an in-vehicle lighting control device, the resistance of the in-vehicle lighting device and the in-vehicle lighting control device work together to form a voltage divider circuit that inputs a divided supply voltage to the control unit. The divided supply voltage, which is the sum of the forward voltage drops of the semiconductor light source, corresponds to the maximum input value to the control unit for fault detection of the semiconductor light source. With such a configuration, the resolution of the supply voltage in the control unit can be increased.

[0010] The purpose, features, aspects, and advantages of this disclosure will become clearer from the following detailed description and accompanying drawings.

[0011] Figure 1 is a block diagram showing the configuration of an in-vehicle lighting control system according to Embodiment 1. Figure 2 is a block diagram showing the hardware configuration of the control unit according to Embodiment 1. Figure 3 is a block diagram showing the hardware configuration of the control unit according to Embodiment 1. Figure 4 is a diagram showing the relationship between the supply voltage of the voltage conversion unit and the divided voltage input to the control unit. Figure 5 is a diagram showing the relationship between the supply voltage corresponding to the number of LEDs and the divided voltage input to the control unit for each LED. Figure 6 is a block diagram showing the configuration of an in-vehicle lighting control system according to Modification 2. Figure 7 is a block diagram showing the configuration of an in-vehicle lighting control system according to Modification 2. Figure 8 is a diagram showing the relationship between the temperature of the LEDs and the divided voltage input to the control unit.

[0012] <Embodiment 1> Figure 1 is a block diagram showing the configuration of an in-vehicle lighting control system according to this embodiment 1. The in-vehicle lighting control system in Figure 1 comprises an in-vehicle lighting fixture 10 and an in-vehicle lighting control device 20.

[0013] <Vehicle-mounted lighting fixture 10> The vehicle-mounted lighting fixture 10 comprises LEDs 3-1 to 3-n, which are semiconductor light sources, a lower resistor 5-2, which is a resistor, and a thermistor 7-2 for detecting the temperature of LEDs 3-1 to 3-n. In the following description, LEDs 3-1 to 3-n may be abbreviated as LED3 when not distinguished.

[0014] LEDs 3-1 to 3-n, that is, n LEDs 3, are connected in series, and each LED 3 is used as a light source for the low beam and high beam of a vehicle, for example. Each of LEDs 3-1 to 3-n may be a single LED or a group of LEDs called a segment. When the vehicle lighting fixture 10 is attached to the vehicle lighting control device 20, the LEDs 3, lower resistor 5-2, and thermistor 7-2 of the vehicle lighting fixture 10 are electrically connected to the wiring of the vehicle lighting control device 20. Through this connection, LEDs 3 are connected between the voltage conversion unit 1 and ground, the lower resistor 5-2 is connected between the upper resistor 5-1 and the control unit 6 and ground, and thermistor 7-2 is connected between the upper resistor 7-1 and the control unit 6 and ground.

[0015] <In-vehicle lighting control device 20> The in-vehicle lighting control device 20 controls the lighting of the LED 3 of the in-vehicle lighting fixture 10 by being connected to the in-vehicle lighting fixture 10. The in-vehicle lighting control device 20 comprises a boost unit 1a, a step-down unit 1b, semiconductor switching elements FETs (Field Effect Transistors) 4-1 to 4-n, and upper resistors 5-1 and 7-1.

[0016] The boost unit 1a boosts the battery voltage (for example, 12V) from the vehicle battery. The buck unit 1b reduces the output voltage of the boost unit 1a to the supply voltage used to light the LED 3. The voltage conversion unit 1, including the boost unit 1a and the buck unit 1b, converts the battery voltage into a supply voltage by boosting and bucking, and supplies this supply voltage to the LED 3.

[0017] The following explanation will use the example where the forward voltage drop Vf when a predetermined current (e.g., rated current) is passed through one LED 3 is 3V. In this example, if n = 30, that is, if 30 LEDs 3 are connected in series, the total voltage ΣVf of the forward voltage drop Vf required to pass a predetermined current (e.g., rated current) through each LED 3 will be 90V. In such a case, for example, the boost unit 1a is configured to boost the 12V battery voltage to 100V, and the buck unit 1b is configured to step down 100V to a supply voltage of 90V and supply that voltage to the 30 LEDs 3.

[0018] This makes it possible to supply a predetermined current to the 30 LEDs 3, thereby enabling all 30 LEDs 3 to light up. Furthermore, the voltage supplied from the voltage conversion unit 1 to the LEDs 3 is substantially the same as the sum of the forward voltage drops of the LEDs 3.

[0019] As described above, the voltage conversion unit 1, which performs both voltage boosting by the boosting unit 1a and voltage reduction by the bucking unit 1b, allows for a margin in the boosted voltage relative to the supply voltage, and the supply voltage can be easily generated by reducing the boosted voltage. However, depending on the design specifications, the voltage conversion unit 1 may perform either voltage boosting or voltage reduction to convert the battery voltage to the supply voltage, and in such a case, either the boosting unit 1a or the bucking unit 1b may be removed from the voltage conversion unit 1.

[0020] FETs 4-1 to 4-n are provided in correspondence with LEDs 3-1 to 30n, respectively. For example, if the control unit 6 receives an instruction from the higher-level ECU (Electronic Control Unit) to turn off LED 3-1, it turns on (conducts) FET 4-1 to prevent current from flowing to LED 3-1, thereby turning off LED 3-1. For example, if the control unit 6 receives an instruction from the higher-level ECU to turn on LED 3-1, it turns off (does not conduct) FET 4-1 to allow current to flow to LED 3-1, thereby turning on LED 3-1. For example, if LED 3-1 and LED 3-2 are the light sources for the low beam and high beam, respectively, and there is an oncoming vehicle of the vehicle equipped with the vehicle lighting fixture 10, the control unit 6 controls FETs 4-1 and 4-2 according to the instruction from the higher-level ECU to turn on LED 3-1 and turn off LED 3-2.

[0021] The upper resistor 5-1 is connected between the voltage conversion unit 1 and the control unit 6. When the vehicle-mounted lighting fixture 10 is connected to the vehicle-mounted lighting control device 20, a voltage divider circuit is formed through the cooperation of the lower resistor 5-2 and wiring of the vehicle-mounted lighting fixture 10 and the upper resistor 5-1 and wiring of the vehicle-mounted lighting control device 20. This voltage divider circuit generates a voltage divider of the supply voltage from the voltage conversion unit 1 to the LED 3 and inputs it to the control unit 6.

[0022] For example, if the voltage value of the supply voltage from the voltage conversion unit 1 is Vs, the resistance values ​​of the upper resistor 5-1 and the lower resistor 5-2 are R1 and R2, and the voltage division generated by the voltage divider circuit is Vd, then Vd can be expressed as follows.

[0023] Vd = R2 × Vs / (R1 + R2) ... (1) In this embodiment 1, the resistance value (R2) of the lower resistor 5-2 of the vehicle lighting fixture 10 is set so that the voltage division (Vd) of the supply voltage, which is the sum of the forward voltage drops of the LEDs 3 when all are lit, corresponds to the maximum input value (e.g., rated voltage) of the control unit 6 for fault detection of the LEDs 3. In the following, as an example of the voltage division corresponding to the maximum input value of the control unit 6 for fault detection of the LEDs 3, a configuration in which the voltage division matches the maximum input value of the control unit 6 for fault detection of the LEDs 3 will be mainly described.

[0024] The control unit 6 controls the output current from the voltage conversion unit 1 to the LED 3 to a predetermined current. In this embodiment 1, the control unit 6 detects the output current from the voltage conversion unit 1 to the LED 3 from the voltage of a shunt resistor (not shown) connected to the voltage conversion unit 1. The control unit 6 then controls at least one of the boosting of the boost unit 1a and the step-down of the step-down unit 1b so that the output current when the LED 3 is lit becomes a predetermined current (for example, the rated current).

[0025] Furthermore, as described above, the control unit 6 controls the on / off state of FETs 4-1 to 4-n based on instructions from the higher-level ECU, thereby changing the lighting state of LEDs 3-1 to 3-n.

[0026] Furthermore, the control unit 6 monitors the divided voltage of the supply voltage input from the voltage divider circuit in order to monitor the supply voltage, and performs various operations based on the monitoring results. In this embodiment 1, the divided voltage from the voltage divider circuit is periodically input to the control unit 6, and the control unit 6 outputs a short-circuit fault message when the divided voltage input this time becomes smaller than the voltage obtained by lowering the previously input divided voltage by a predetermined short-circuit fault detection voltage. The output of the short-circuit fault message includes, for example, a display of the short-circuit fault message, an audio output, and wireless communication, at least one of these.

[0027] The control unit 6 also detects the resistance value of the thermistor 7-2 and measures the temperature of LEDs 3-1 to 3-n based on that resistance value. When the measured temperature reaches a predetermined derating start temperature, the control unit 6 performs derating control on the voltage conversion unit 1 to reduce the output current of LEDs 3. This makes it possible to suppress thermal damage to LEDs 3 due to heat generated when they are lit.

[0028] The control unit 6 described above is implemented, for example, by the processing circuit 81 shown in Figure 2. The processing circuit 81 may be made of dedicated hardware, or it may be made of a processor that executes a program stored in memory. Examples of processors include central processing units, processing units, arithmetic units, microprocessors, microcomputers, and DSPs (Digital Signal Processors).

[0029] If the processing circuit 81 is dedicated hardware, it may be, for example, a single circuit, a composite circuit, a programmed processor, a parallel programmed processor, an ASIC (Application Specific Integrated Circuit), an FPGA (Field Programmable Gate Array), or a combination thereof. The functions of the control unit 6 may be realized by a circuit with distributed processing circuits, or the functions of each part may be realized by a single processing circuit.

[0030] When the processing circuit 81 is a processor, the functions of the control unit 6 are realized in combination with software, etc. Software, etc. may include, for example, software, firmware, or both. The software, etc. is written as a program and stored in memory. As shown in Figure 3, the processor 82 applied to the processing circuit 81 realizes its functions by reading and executing the program stored in memory 83. This program can also be said to cause the computer to execute the procedures and methods of the control unit 6. Here, memory may be, for example, non-volatile or volatile semiconductor memory such as RAM (Random Access Memory), ROM (Read Only Memory), flash memory, EPROM (Erasable Programmable Read Only Memory), EEPROM (Electrically Erasable Programmable Read Only Memory), HDD (Hard Disk Drive), magnetic disk, flexible disk, optical disk, compact disk, minidisc, DVD (Digital Versatile Disc), their drive devices, or any storage medium used in the future. The processing circuit 81 can realize the functions of the control unit 6 through hardware, software, or a combination thereof.

[0031] Figure 4 shows the relationship between the voltage supplied from the voltage conversion unit 1 to the LED 3 and the divided voltage input from the voltage divider circuit to the control unit 6. The supply voltage is substantially the same as the sum of the forward voltage drops Vf of the LEDs 3, ΣVf, and corresponds to the number of LEDs 3. In the following explanation, we will use as an example a case in which a microcomputer with a maximum input value (e.g., rated voltage) of 5V for fault detection of the LEDs 3 is used in the control unit 6.

[0032] When 30 LEDs 3 are lit and the sum of the forward voltage drops Vf ΣVf is 90V, the voltage divider circuit needs to divide the supply voltage of 90V, which is the sum of the forward voltage drops Vf, into 5V, which matches the maximum input voltage of the control unit 6. The resistance values ​​(R1, R2) of the upper resistor 5-1 and the lower resistor 5-2 in equation (1) above are set so that such voltage division is performed.

[0033] After this setting, if one LED3 is short-circuited, that is, if the supply voltage, which is the sum of the forward drop voltages Vf, changes by 3V, the voltage divider input to the control unit 6 changes by about 0.17V (= 5V ÷ 30 LEDs). However, this change in voltage divider is small, and because the resolution of the supply voltage in the control unit 6 is low, the control unit 6 cannot easily determine whether or not one LED3 is short-circuited.

[0034] On the other hand, when 20 LEDs 3 are lit and the sum of the forward voltage drops Vf ΣVf is 60V, the resistance values ​​(R1, R2) in equation (1) above are set so that the voltage divider circuit divides the 60V supply voltage into 5V. From equation (1) above, it can be seen that the resistance value (R2) when converting a 60V supply voltage (Vs) into a 5V voltage divider is greater than the resistance value (R2) when converting a 90V supply voltage (Vs) into a 5V voltage divider.

[0035] After this setting, if one LED 3 is short-circuited, that is, if the supply voltage, which is the sum of the forward drop voltages Vf, changes by 3V, the voltage divider input to the control unit 6 will change by 0.25V (= 5V ÷ 20 LEDs), which is greater than approximately 0.17V.

[0036] From the above, the resolution of the supply voltage in the control unit 6 when resistance values ​​are set for a small number of 20 LEDs 3 is higher than the resolution of the supply voltage in the control unit 6 when resistance values ​​are set for a large number of 30 LEDs 3.

[0037] In conventional technology, the resistance value of the voltage divider circuit is set to match the number of LEDs 3 (30 LEDs 3 in the example above) so that the control unit 6 can monitor a wide range of supply voltages. Furthermore, because the voltage divider circuit is built into the in-vehicle lighting control device, the resistance value of the voltage divider circuit is fixed. As a result, in conventional technology, even when the number of LEDs 3 is small, the resolution of the supply voltage in the control unit 6 is fixed to the low resolution used when there are many LEDs 3. This problem was particularly evident because the number of LEDs 3 in the in-vehicle lighting fixture 10, and consequently the total voltage of the forward voltage drop, is often unknown until the in-vehicle lighting fixture is installed in the in-vehicle lighting control device.

[0038] In contrast, in this embodiment 1, when the vehicle-mounted lighting fixture 10 is attached to the vehicle-mounted lighting control device 20, the resistance value of the lower resistor 5-2 can be changed to match the number of LEDs 3 in the vehicle-mounted lighting fixture 10, and consequently, the total voltage of the forward voltage drop. Therefore, when the number of LEDs 3 in the vehicle-mounted lighting fixture 10 is small, the resolution of the supply voltage in the control unit 6 can be increased by lowering the resistance value of the lower resistor 5-2.

[0039] Figure 5 shows the relationship between the voltage supplied from the voltage conversion unit 1 to the LED 3 and the voltage division input to the control unit 6 for each LED 3. In Figure 5, the voltage division is shown when the resistance value of the lower resistor 5-2 is set according to the number of LEDs 3 in the vehicle lighting fixture 10, and the value on the vertical axis corresponds to the resolution of the supply voltage in the control unit 6.

[0040] For example, in a configuration with one LED3, if one LED3 is short-circuited, the forward voltage drop of that one LED3 (3V) is less than 5V (= 5V ÷ 1), so the change in the divided voltage input to the control unit 6 is 3V. In a configuration with n LED3s (n≧2), if one LED3 is short-circuited, 5 / n[V] is less than the forward voltage drop of one LED3 (3V), so the change in the divided voltage input to the control unit 6 is 5 / n[V]. Thus, in this embodiment 1, when the number of LED3s in the vehicle lighting fixture 10 is small, the resolution of the supply voltage in the control unit 6 can be increased.

[0041] <Summary of Embodiment 1> According to Embodiment 1 described above, when the in-vehicle lighting fixture 10 is connected to the in-vehicle lighting control device 20, the lower resistor 5-2 of the in-vehicle lighting fixture 10 and the in-vehicle lighting control device 20 work together to form a voltage divider circuit that inputs a divided supply voltage to the control unit 6. The divided supply voltage, which is the sum of the forward voltage drops of the LEDs 3, corresponds to the maximum input value of the control unit 6. With this configuration, when the number of LEDs 3 in the in-vehicle lighting fixture 10 is small, the resolution of the supply voltage in the control unit 6 can be increased, and as a result, it is possible to easily determine whether or not one LED 3 is short-circuited.

[0042] <Modification 1> In Embodiment 1, as an example of the voltage division corresponding to the maximum input value of the control unit 6, a configuration in which the voltage division matches the maximum input value of the control unit 6 (5V in the above example) was described, but it is not limited to this. For example, if only discrete resistance values ​​can be set as the resistance value of the lower resistor 5-2, the voltage division may not match the maximum input value of the control unit 6. In such a case, the voltage division corresponding to the maximum input value of the control unit 6 may, for example, be such that the resistance value of the lower resistor 5-2 is brought as close as possible to the ideal resistance value, and the voltage division is brought as close as possible to the maximum input value of the control unit 6. Alternatively, the voltage division corresponding to the maximum input value of the control unit 6 may be, for example, brought closer to the maximum input value of the control unit 6 than the conventional voltage division.

[0043] <Modification Example 2> In Embodiment 1, the resistor included in the vehicle-mounted lamp 10 was the lower resistor 5-2, but it is not limited to this. For example, as shown in FIG. 6, the resistors included in the vehicle-mounted lamp 10 may be the upper resistor 5-1 and the lower resistor 5-2. Also, for example, as shown in FIG. 7, the resistor included in the vehicle-mounted lamp 10 may be the upper resistor 5-1. Even with these configurations, similar to Embodiment 1, when the number of LEDs 3 in the vehicle-mounted lamp 10 is small, the resolution of the supply voltage in the control unit 6 can be increased.

[0044] <Modification Example 3> FIG. 8 is a diagram showing the relationship between the temperature of the LED 3 and the divided voltage input from the voltage dividing circuit to the control unit 6. In Embodiment 1, the thermistor 7-2 for detecting the temperature of the LED 3 is provided in the vehicle-mounted lamp 10, and the control unit 6 performs delaying control on the voltage conversion unit 1 to suppress thermal breakdown of the LED 3 due to heat generation during lighting based on the temperature detected by the thermistor 7-2.

[0045] Here, since the forward voltage drop of the LED 3 depends on the temperature of the LED 3, as shown in FIG. 8, the divided voltage input from the voltage dividing circuit to the control unit 6 also depends on the temperature of the LED 3. Specifically, there is a dependency such that the higher the temperature of the LED 3, the lower the divided voltage.

[0046] Therefore, when the input divided voltage is smaller than a predetermined delaying start voltage, the control unit 6 may perform delaying control on the voltage conversion unit 1 to reduce the output current. According to such a configuration, it becomes possible to remove the thermistor 7-2 from the vehicle-mounted lamp 10, and thus it becomes possible to remove the input port of the control unit 6 of the vehicle-mounted lighting control device 20.

[0047] <Modification Example 4> In Embodiment 1, when the currently input divided voltage becomes smaller than the voltage obtained by reducing the previously input divided voltage by a predetermined short-circuit fault detection voltage, the control unit 6 outputs a notice of the short-circuit fault, but it is not limited to this. For example, the control unit 6 may output a notice of a fault when the input divided voltage itself, rather than the difference in the input divided voltage, becomes less than or equal to a predetermined threshold value.

[0048] Note that the control unit 6 may obtain a threshold value by communicating with the outside of the in-vehicle lighting control device 20 (for example, a host ECU or the in-vehicle lamp 10), and set the threshold value to a predetermined threshold value for failure determination.

[0049] Further, the control unit 6 may store a table in which the number of LEDs 3 of the in-vehicle lamp 10 and a threshold value suitable for the number are associated in advance. Then, the control unit 6 obtains the number of LEDs 3 of the in-vehicle lamp 10 by communicating with the outside of the in-vehicle lighting control device 20, reads out the threshold value corresponding to the obtained number from the table, and sets the threshold value to a predetermined threshold value for failure determination.

[0050] Also, a plurality of threshold values corresponding to the number of LEDs 3 of the in-vehicle lamp 10 may be set as predetermined threshold values for failure determination. Specifically, in the first embodiment, when one LED 3 is short-circuited in a configuration where the number of LEDs 3 is n (n≧2), the change in the divided voltage input to the control unit 6 is 5 / n [V]. In such a configuration, for example, when the number of LEDs 3 is 5, the change in the divided voltage input to the control unit 6 is 1 V. In this case, for example, 4.5 V, 3.5 V,..., 0.5 V, etc. may be set as the predetermined threshold values for failure determination.

[0051] According to such a configuration, when the input divided voltage is smaller than 4.5 V, 3.5 V,..., 0.5 V, the control unit 6 can determine that one, two,..., five LEDs 3 are short-circuited. Also, similar to the setting of the predetermined threshold value described in the fourth modification example, the predetermined short-circuit failure detection voltage described in the first embodiment may be set.

[0052] In the English disclosure of the present disclosure, the articles 'a' and 'an' mean one or more. Therefore, 'a', 'an', 'one or more', and 'at least one' can be used with the same meaning.

[0053] Note that each embodiment and each modification example can be freely combined, or each embodiment and each modification example can be appropriately modified or omitted.

[0054] The above explanation is illustrative and not limiting in all respects. It should be understood that countless variations not illustrated are conceivable.

[0055] 1 Voltage conversion unit, 3-1 to 3-n LEDs, 4-1 to 4-n FETs, 5-1 Upper resistor, 5-2 Lower resistor, 6 Control unit, 10 In-vehicle lighting fixture, 20 In-vehicle lighting control device.

Claims

1. An in-vehicle lighting control device that controls the illumination of a semiconductor light source by being connected to an in-vehicle lighting device comprising a semiconductor light source and a resistor, comprising: a voltage conversion unit that converts the battery voltage into a supply voltage by performing at least one of boosting and stepping down the voltage and supplies the supply voltage to the semiconductor light source; and a control unit that controls the output current from the voltage conversion unit to the semiconductor light source to a predetermined current, wherein when the in-vehicle lighting device is connected to the in-vehicle lighting control device, a voltage divider circuit is formed by the cooperation of the resistor of the in-vehicle lighting device and the in-vehicle lighting control device to input a divided voltage of the supply voltage to the control unit, and the divided voltage of the supply voltage, which is the sum of the forward drop voltages of the semiconductor light source, corresponds to the maximum input value of the control unit for fault detection of the semiconductor light source.

2. An in-vehicle lighting control device according to claim 1, wherein the control unit performs derating control on the voltage conversion unit to reduce the output current when the input voltage division is smaller than a predetermined derating start voltage.

3. An in-vehicle lighting control device according to claim 1, wherein the control unit outputs a message indicating a short-circuit fault when the voltage divided in the current input becomes smaller than the voltage divided in the previous input by a predetermined short-circuit fault detection voltage.

4. An in-vehicle lighting control device according to claim 1, wherein the control unit outputs a message indicating a short-circuit fault when the input voltage divider falls below a predetermined threshold.

5. An in-vehicle lighting control system comprising: an in-vehicle lighting fixture comprising a semiconductor light source and a resistor; an in-vehicle lighting control device connected to the in-vehicle lighting fixture to control the lighting of the semiconductor light source, wherein the in-vehicle lighting control device comprises: a voltage conversion unit that converts the battery voltage into a supply voltage by performing at least one of boosting and stepping down the voltage and supplies the supply voltage to the semiconductor light source; and a control unit that controls the output current from the voltage conversion unit to the semiconductor light source to a predetermined current, wherein when the in-vehicle lighting fixture is connected to the in-vehicle lighting control device, a voltage divider circuit is formed by the cooperation of the resistor of the in-vehicle lighting fixture and the in-vehicle lighting control device to input a divided voltage of the supply voltage to the control unit, and the divided voltage of the supply voltage, which is the sum of the forward drop voltages of the semiconductor light source, corresponds to the maximum input value of the control unit for fault detection of the semiconductor light source.

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