Semiconductor-light-source lighting device

Abstract

To provide a semiconductor light-source lighting device with which it is possible to expand the voltage range in which a step-down converter can be used. A semiconductor light-source lighting device includes: a step-down converter that steps down battery voltage or supplied voltage from a step-up converter which steps up the battery voltage to a predetermined voltage, and that then supplies a predetermined current to an LED circuit; a voltage dividing circuit unit that divides the voltage output from the step-down converter; an AC component extraction unit that extracts an AC component from the divided voltage output from the voltage dividing circuit unit; and a microcomputer configured so that when the AC component is compared with a threshold value and the AC component has exceeded the threshold value a predetermined number of times within a unit time, the microcomputer determines that an open failure has occurred in the LED circuit and outputs an open failure signal.

Description

Semiconductor light source lighting device

[0001] The present disclosure relates to a semiconductor light source lighting device.

[0002] In some cases, semiconductor light sources (typically LEDs) used in automotive lighting fixtures are connected in series, for example, 10 or more, depending on the required light output, design, etc. In this case, the forward drop voltage VF may be approximately 30V to 50V.

[0003] A typical LED has a forward voltage drop VF of 2V to 4V (approximately 3V) when lit. In other words, a power supply of approximately 60V is required to light 10 or more LEDs connected in series. For this reason, a boost converter (constant voltage circuit) is typically used to boost the battery voltage of approximately 12V to approximately 60V, which is greater than the forward voltage drop VF, and then a step-down converter (constant current circuit) receives the output and steps it down to the required voltage, supplying the required voltage and current to the LEDs (see, for example, Patent Document 1).

[0004] JP 2014-170880 A

[0005] This section describes a conventional method for detecting an open circuit fault (disconnection fault) in a semiconductor light source lighting device such as the one described above. When an open circuit fault occurs in a series-connected LED, the output voltage of the buck converter rises to a maximum boost voltage (approximately 60 V). Therefore, a conventional detection method has been to monitor the increased voltage to detect an open circuit fault in an LED. Furthermore, when an open circuit fault occurs, the output of the buck converter fluctuates between, for example, 50 V and 60 V in conjunction with the switching operation of the buck converter, with the maximum output voltage of 60 V (boost voltage) as its peak.

[0006] Therefore, the threshold value for open circuit fault detection needs to be 50 V or less (for example, 49 V). In other words, with conventional open circuit fault detection methods, even if the voltage is boosted up to 60 V by a boost converter, the range of forward drop voltage VF that can actually be used by the step-down converter needs to be limited to 50 V or less.

[0007] Therefore, an object of the present disclosure is to provide a semiconductor light source lighting device that can widen the voltage range in which a step-down converter can be used.

[0008] The semiconductor light source lighting device according to the present disclosure is a semiconductor light source lighting device that controls the lighting of a plurality of semiconductor light sources connected in series, and includes a step-down converter that steps down a battery voltage or a supply voltage from a step-up converter that steps up the battery voltage to a predetermined voltage, and supplies a predetermined current to the plurality of semiconductor light sources; a voltage divider circuit unit that divides the voltage output from the step-down converter; an AC component extraction unit that extracts an AC component from the divided voltage output from the voltage divider circuit unit; and a control unit that compares the AC component with a threshold value and, when the AC component exceeds the threshold value a predetermined number of times within a unit time, determines that an open circuit fault has occurred in the plurality of semiconductor light sources and outputs an open circuit fault signal.

[0009] According to the present disclosure, the voltage range that can be used by a step-down converter can be widened.

[0010] The objects, features, aspects, and advantages of the present disclosure will become more apparent from the following detailed description and the accompanying drawings.

[0011] FIG. 1 is a configuration diagram of a semiconductor light source lighting device according to a first embodiment. FIG. 2 is a timing chart showing the operation of voltage A of the semiconductor light source lighting device according to the first embodiment. FIG. 3 is a timing chart showing the operation of AC component C of the semiconductor light source lighting device according to the first embodiment. FIG. 4 is a configuration diagram of a semiconductor light source lighting device according to a second embodiment. FIG. 5 is a timing chart showing the operation of AC component C of the semiconductor light source lighting device according to the second embodiment. FIG. 6 is a timing chart showing the operation of AC component C of the semiconductor light source lighting device according to the third embodiment. FIG. 7 is a configuration diagram of a semiconductor light source lighting device according to a fourth embodiment. FIG. 8 is a timing chart showing the operation of AC component C of the semiconductor light source lighting device according to the fourth embodiment.

[0012] First Embodiment Configuration of Semiconductor Light Source Lighting Device A first embodiment will be described below with reference to the drawings. Fig. 1 is a configuration diagram of a semiconductor light source lighting device 100 according to the first embodiment.

[0013] As shown in Fig. 1, semiconductor light source lighting device 100 includes a step-up converter 2, a step-down converter 3, a coil 4, a capacitor 5, resistors 6 and 7, a capacitor 8, resistors 9 and 10, and a microcomputer 11. A battery 1 and an LED circuit 12 are connected to semiconductor light source lighting device 100. Battery 1 supplies a voltage of approximately 12 V to semiconductor light source lighting device 100. LED circuit 12 is configured by connecting a plurality of LEDs, which are semiconductor light sources, in series. Semiconductor light source lighting device 100 controls the lighting of LED circuit 12 connected in series.

[0014] The boost converter 2 is a component that boosts the voltage of the battery 1 (hereinafter also referred to as "battery voltage") to a predetermined voltage and functions as a constant voltage power supply. The buck converter 3 is a component that steps down the voltage supplied from the boost converter 2 and functions as a constant current power supply.

[0015] The coil 4 and capacitor 5 are a smoothing circuit located downstream of the step-down converter 3, which smoothes the output of the step-down converter 3 and supplies a predetermined current to the LED circuit 12. In other words, the step-down converter 3 supplies a predetermined current to the LED circuit 12 via the coil 4 and capacitor 5. The resistors 6 and 7 divide the voltage A output from the step-down converter 3 and function as a voltage dividing circuit for monitoring the voltage A supplied to the LED circuit 12.

[0016] Capacitor 8 functions as an AC component extractor that extracts AC component C from divided voltage B output from the voltage divider circuit. Resistors 9 and 10 function as a bias circuit that applies a bias voltage to AC component C (specifically, the voltage of AC component C), applying a bias voltage of 2.5 V to AC component C. Note that the bias voltage is not limited to 2.5 V and may be set to any value, such as a positive voltage, 0 V, or negative voltage. Furthermore, if the bias voltage is set to 0 V, the bias circuit may be omitted.

[0017] The microcomputer 11 functions as a control unit that controls the boost converter 2 and the buck converter 3, and also controls the current supplied to the LED circuit 12. The microcomputer 11 determines whether an open circuit fault has occurred in the LED circuit 12 based on the AC component C and a threshold value, which will be described later. When the microcomputer 11 determines that an open circuit fault has occurred in the LED circuit 12, it outputs an open circuit fault signal to stop driving the boost converter 2 or the buck converter 3, thereby stopping the supply of current to the LED circuit 12.

[0018] Here, the open fault signal does not only refer to an analog voltage signal, but also includes a flag (1 or 0) as a result of determining whether or not an open fault has occurred. The open fault signal may be supplied to an external device of the semiconductor light source lighting device 100, for example, to a host computer (not shown).

[0019] In the first embodiment, semiconductor light source lighting device 100 includes boost converter 2, but this is not necessarily required. For example, if the number of series-connected LEDs in LED circuit 12 is small and the LEDs can be driven by the battery voltage, there is no need to boost the battery voltage. In this case, step-down converter 3 directly receives the battery voltage and functions as a constant current power supply that steps down the battery voltage.

[0020] The circuit configured by resistors 6 and 7, capacitor 8, resistors 9 and 10, and microcomputer 11 constitutes open circuit failure detection circuit 101.

[0021] <Operation of Semiconductor Light Source Lighting Device> Next, a description will be given of the operation of the semiconductor light source lighting device 100. Fig. 2 is a timing chart showing the operation of the voltage A of the semiconductor light source lighting device 100 according to the first embodiment. Fig. 3 is a timing chart showing the operation of the AC component C of the semiconductor light source lighting device 100 according to the first embodiment.

[0022] As shown in Figure 2, when the LED circuit 12 is lit normally, the voltage A is stable at approximately the sum of the forward drop voltages VF of the LED circuit 12. For example, when 10 series-connected LEDs are lit, the voltage A is the sum of the forward drop voltages VF of the lit LEDs (approximately 3V x 10 LEDs = 30V). Furthermore, when only one unit (e.g., five LEDs) out of multiple units (e.g., four units each consisting of five LEDs connected in series) is lit, the voltage A is the sum of the forward drop voltages VF of one unit (approximately 3V x 5 LEDs = 15V). The microcomputer 11 decides how to light the LEDs that make up the LED circuit 12.

[0023] On the other hand, as shown in FIG. 3, the AC component C is stable at a bias voltage of approximately 2.5 V applied from the resistors 9 and 10 regardless of the number of driven LEDs.

[0024] Next, when an open circuit fault occurs in the LED circuit 12, as shown in Figure 2, voltage A rises to the maximum output voltage of the step-down converter 3 and fluctuates with a ripple component within a predetermined voltage range with the maximum output voltage as the upper limit. This depends on the characteristics of the step-down converter 3, capacitor 5, and coil 4. When an open circuit fault occurs, when the high-side switch of the step-down converter 3 is operating, voltage A rises to the boost voltage (maximum of approximately 60 V). On the other hand, when the low-side switch is operating, the charge stored in capacitor 5 is discharged to the step-down converter 3 side, and voltage A drops (to approximately 50 V). By repeating the above process, voltage A repeatedly fluctuates with a ripple component.

[0025] 3, AC component C fluctuates with a ripple component around the bias voltage of 2.5 V in synchronization with the fluctuations in voltage A. As described above, the microcomputer 11 has the function of comparing AC component C with a threshold value to detect the occurrence of an open circuit failure in the LED circuit 12.

[0026] When an open circuit fault occurs in the LED circuit 12, the microcomputer 11 utilizes fluctuations in the AC component C to enable detection of the open circuit fault in the LED circuit 12. As a method for detecting the open circuit fault, the microcomputer 11 is set with a first threshold value (L) and a second threshold value (H) that is greater than the first threshold value (L). The microcomputer 11 determines that an open circuit fault has occurred in the LED circuit 12 when the AC component C exceeds the first threshold value (L) and the second threshold value (H) a predetermined number of times within a unit time.

[0027] When the microcomputer 11 determines that an open circuit fault has occurred in the LED circuit 12, it outputs an open circuit fault signal to the boost converter 2 or the buck converter 3, thereby stopping the operation of the boost converter 2 and the buck converter 3 and stopping the supply of current to the LED circuit 12.

[0028] <Effects> Next, the effects of the semiconductor light source lighting device 100 according to the first embodiment will be described in comparison with a conventional method for detecting an LED open failure.

[0029] In conventional methods for detecting LED open circuit failures, the threshold value had to be set to 50 V or less (for example, 49 V). In other words, even if the voltage was boosted to 60 V by the boost converter 2, the range of forward drop voltage VF that the step-down converter 3 could actually use had to be limited to 50 V or less, and the number of LEDs connected in series had to be limited.

[0030] In contrast, the semiconductor light source lighting device 100 according to the first embodiment includes a step-down converter 3 that steps down the battery voltage or a supply voltage from a step-up converter 2 that steps up the battery voltage to a predetermined voltage, and supplies a predetermined current to the LED circuit 12, a voltage divider circuit unit that divides the voltage A output from the step-down converter 3, an AC component extraction unit that extracts an AC component C from the divided voltage B output from the voltage divider circuit unit, and a microcomputer 11 that compares the AC component C with a threshold value, and when the AC component C exceeds the threshold value a predetermined number of times within a unit time, determines that an open circuit fault has occurred in the LED circuit 12, outputs an open circuit fault signal, and controls to turn off the LED circuit 12.

[0031] Therefore, unlike conventional LED open fault detection methods, where a threshold value is set for voltage A, a threshold value is set for AC component C, eliminating the need to limit the range of forward voltage drop VF. This allows the voltage range usable by the step-down converter 3 to be broadened. As a result, the number of LEDs that can be connected in series and used increases. As described above, since the voltage range usable by the step-down converter 3 can be broadened, the semiconductor light source lighting device 100 can be made smaller than conventional devices when the same number of LEDs are connected in series.

[0032] Although a single threshold value may be used, the above-described embodiment includes a first threshold value and a second threshold value greater than the first threshold value, making it possible to detect the amplitude of AC component C. This allows for even greater accuracy in open circuit fault detection than when open circuit faults are detected using only a single threshold value for voltage A.

[0033] <Embodiment 2> Next, a semiconductor light source lighting device 100 according to embodiment 2 will be described. Fig. 4 is a configuration diagram of semiconductor light source lighting device 100 according to embodiment 2. Note that in embodiment 2, the same components as those described in embodiment 1 are given the same reference numerals and descriptions thereof will be omitted.

[0034] In the first embodiment, the threshold value for detecting an open circuit failure in the LED circuit 12 is set in the microcomputer 11. However, since the threshold value set in the microcomputer 11 is determined by the characteristics specific to each microcomputer 11, it may not be possible to change the threshold value in accordance with the circuit configuration.

[0035] Furthermore, there is a concern that the threshold value may be easily changed due to differences in the temperature characteristics inherent to each microcomputer 11.

[0036] Therefore, in the second embodiment, in order to solve the above-mentioned concerns, it is possible to detect an open circuit failure in the LED circuit 12 without using a threshold value specific to the microcomputer 11 .

[0037] As shown in FIG. 4, the semiconductor light source lighting device 100 according to the second embodiment further includes a window comparator 13 in addition to the components of the first embodiment.

[0038] The window comparator 13 is disposed upstream of the microcomputer 11. A first threshold value and a second threshold value are set in the window comparator 13. The circuit configured by the resistors 6 and 7, the capacitor 8, the resistors 9 and 10, the microcomputer 11, and the window comparator 13 constitutes an open circuit fault detection circuit 102.

[0039] Next, a description will be given of the operation of the semiconductor light source lighting device 100 according to embodiment 2. Fig. 5 is a time chart showing the operation of the AC component C of the semiconductor light source lighting device 100 according to embodiment 2.

[0040] As in the first embodiment, when the LED circuit 12 is lighting normally, the voltage A is stable near the total value of the forward drop voltage VF of the LED circuit 12. The AC component C is also stable near the bias voltage of 2.5 V. Next, when an open circuit fault occurs in the LED circuit 12, the AC component C fluctuates in synchronization with the voltage A, with a ripple component, as shown in FIG.

[0041] Next, a method of detecting an open circuit fault in embodiment 2 will be described. As shown in Fig. 5, in the window comparator 13, the first threshold value is set below 2.5 V (for example, 1 V), and the second threshold value is set above 2.5 V (for example, 4 V). In other words, the first threshold value and the second threshold value are set symmetrically above and below the bias voltage of 2.5 V of the AC component C (the median value of the AC component C).

[0042] The window comparator 13 outputs an H signal while the AC component C fluctuates between the first and second thresholds. On the other hand, when the AC component C is below the first threshold (1 V or less) or above the second threshold (4 V or more), that is, when the AC component C exceeds the first or second threshold, the window comparator 13 outputs an L signal. Because the AC component C contains a ripple component when the LED circuit 12 has an open-circuit fault, it is possible to detect the occurrence of an open-circuit fault by counting the number of H and L signals detected per unit time. For example, the specification may be such that an open-circuit fault is determined to have occurred if five H signals and five L signals are detected within a period of ten switching cycles of the step-down converter 3.

[0043] <Effects> As described above, the semiconductor light source lighting device 100 according to the second embodiment includes the step-down converter 3 that steps down the battery voltage or the supply voltage from the step-up converter 2 that steps up the battery voltage to a predetermined voltage, and supplies a predetermined current to the LED circuit 12, a voltage divider circuit unit that divides the voltage A output from the step-down converter 3, an AC component extraction unit that extracts an AC component C from the divided voltage B output from the voltage divider circuit unit, a window comparator 13 that compares the AC component C with a threshold value and outputs a detection signal when the AC component C exceeds the threshold value, and a microcomputer 11 that determines that an open circuit failure has occurred in the LED circuit 12 when the number of detection signals within a unit time exceeds a predetermined number, and controls the LED circuit 12 to turn off.

[0044] Therefore, open circuit failure detection in the LED circuit 12 can be performed regardless of the characteristics specific to each microcomputer 11. This makes it possible to change the threshold value in accordance with the circuit configuration, and there is no fluctuation in the threshold value due to differences in the temperature characteristics specific to each microcomputer 11, improving the reliability of open circuit failure detection.

[0045] Furthermore, since the threshold values ​​include a first threshold value and a second threshold value greater than the first threshold value, it is possible to detect the amplitude of the AC component C. Therefore, the accuracy of open circuit fault detection can be further improved compared to when an open circuit fault is detected using only one threshold value for the voltage A. Here, it is also possible to use one threshold value, in which case a comparator can be used instead of the window comparator 13.

[0046] Third Embodiment Next, a semiconductor light source lighting device 100 according to a third embodiment will be described. Figures 6 and 7 are timing charts showing the operation of AC component C of semiconductor light source lighting device 100 according to the third embodiment. Note that in the third embodiment, the same components as those described in the first and second embodiments are given the same reference numerals, and description thereof will be omitted.

[0047] In the second embodiment, the first threshold value and the second threshold value are set symmetrically above and below the bias voltage of 2.5 V of the AC component C (the zero point of the AC component C). However, depending on the balance between the circuit configuration, the constants and characteristics of the components, the zero point of the AC component C may deviate from the bias voltage of 2.5 V. In contrast, in the third embodiment, an open fault is correctly detected even if the zero point of the AC component C deviates from the bias voltage of 2.5 V. FIG. 6 shows a case where the zero point of the AC component C is higher than the bias voltage of 2.5 V, and FIG. 7 shows a case where the zero point of the AC component C is lower than the bias voltage of 2.5 V. The first threshold value and the second threshold value are set symmetrically about the zero point of the AC component C.

[0048] The first threshold value and the second threshold value are changed in the window comparator 13. As in the second embodiment, an open circuit fault in the LED circuit 12 is detected by counting the number of times H and L are detected per unit time.

[0049] For example, if the step-down converter 3, the coil 4, or the capacitor 5 is replaced with a component having different characteristics, the change in characteristics due to the component change may cause a fluctuation in the ripple width of the voltage A. However, in the third embodiment, the first threshold value and the second threshold value can be changed in the window comparator 13, so there is no need to change the open fault detection circuit 102 itself.

[0050] A method for changing the first threshold and the second threshold will now be described. Although not shown, two comparators are arranged inside the window comparator 13. A first reference voltage and a second reference voltage are set in the two comparators, respectively. The first reference voltage and the second reference voltage are set as the first threshold and the second threshold, respectively, and the two comparators output H or L. When the AC component C, which is the input voltage, is between the first threshold and the second threshold, the window comparator 13 outputs H, and when the AC component C exceeds the first threshold or the second threshold, the window comparator 13 outputs L.

[0051] The first and second reference voltages are changeable as desired. That is, even if the ripple width of voltage A fluctuates, i.e., even if the zero point of AC component C fluctuates from the bias voltage of 2.5 V, the first and second threshold values ​​can be changed by changing the first and second reference voltages.

[0052] In the above example, the first threshold value and the second threshold value are set symmetrically above and below the zero point of the AC component C. However, this is not limiting, and for example, when the AC component C is distorted, the first threshold value and the second threshold value may be set symmetrically about the median of the upper and lower peak values ​​of the AC component C, that is, the peak-to-peak median. In other words, even when the AC component C varies from the bias voltage of 2.5 V or is distorted, the first threshold value and the second threshold value may be set according to the state of the AC component C.

[0053] <Effects> As described above, in semiconductor light source lighting device 100 according to embodiment 3, the first threshold value and the second threshold value are set symmetrically above and below the zero point of AC component C or the peak-to-peak median value of AC component C. Therefore, even if amplitude fluctuations occur in AC component C in synchronization with fluctuations in the ripple width of voltage A or if AC component C is distorted, changing the first threshold value and the second threshold value makes it possible to detect an open circuit failure corresponding to state fluctuations in AC component C. Furthermore, because the first threshold value and the second threshold value can be changed in window comparator 13, there is no need to change open circuit failure detection circuit 102 itself.

[0054] <Fourth Embodiment> Next, a semiconductor light source lighting device 100 according to a fourth embodiment will be described. Fig. 8 is a configuration diagram of the semiconductor light source lighting device 100 according to the fourth embodiment. Fig. 9 is a timing chart showing the operation of the AC component C of the semiconductor light source lighting device 100 according to the fourth embodiment. Note that in the fourth embodiment, the same components as those described in the first to third embodiments are given the same reference numerals, and description thereof will be omitted.

[0055] In the second and third embodiments, open circuit fault detection is performed by counting the number of times H and L are detected for the first threshold value and the second threshold value per unit time. In contrast, in the fourth embodiment, the accuracy of open circuit fault detection is further improved by determining the occurrence of an open circuit fault by taking into account the integral value of the portion exceeding the first threshold value or the second threshold value, in addition to the open circuit fault detection of the second and third embodiments.

[0056] As shown in FIG. 8, the semiconductor light source lighting device 100 according to the fourth embodiment further includes a pulse width counter 14 in addition to the components of the second embodiment.

[0057] The pulse width counter 14 is disposed between the window comparator 13 and the microcomputer 11 to further improve the accuracy of open circuit fault detection. The pulse width counter 14 integrates the detection signal of the window comparator 13 and outputs the integrated value. Here, the pulse width counter 14 corresponds to the integration circuit section. The circuit configured from the resistors 6 and 7, the capacitor 8, the resistors 9 and 10, the microcomputer 11, the window comparator 13, and the pulse width counter 14 constitutes the open circuit fault detection circuit 103.

[0058] There is a concern that AC component C may momentarily exceed the first or second threshold due to noise or other reasons. Therefore, by focusing on the fact that AC component C fluctuates regularly, the accuracy of open circuit fault detection can be improved by calculating the integral value of the portion exceeding the first or second threshold using the pulse width counter 14. This can also serve as a countermeasure against noise caused by AC component C. The integral value can be calculated by calculating the area of ​​the portion exceeding the first or second threshold, as shown in FIG. 9 , or by calculating the total time during which the window comparator 13 outputs an L signal.

[0059] The first threshold value and the second threshold value are not limited to being set symmetrically above and below the bias voltage of 2.5 V of the AC component C (the zero point of the AC component C), but may be set symmetrically above and below the zero point of the AC component C that has fluctuated from the bias voltage of 2.5 V, as in the third embodiment, or may be set symmetrically above and below the median of the upper and lower peak values ​​of the AC component C.

[0060] <Effects> As described above, semiconductor light source lighting device 100 according to embodiment 4 further includes pulse width counter 14 that integrates the detection signals of window comparator 13 and outputs the integrated value. When the number of detection signals within a unit time exceeds a predetermined number and the integrated value within the unit time exceeds a predetermined value, microcomputer 11 determines that an open circuit failure has occurred in LED circuit 12 and controls LED circuit 12 to be turned off.

[0061] Therefore, noise resistance against the AC component C is improved, and the accuracy of open circuit fault detection can be further improved.

[0062] Although this disclosure has been described in detail, the above description is illustrative in all respects and is not restrictive. It is understood that countless variations not illustrated can be envisioned.

[0063] It should be noted that the embodiments can be freely combined, and each embodiment can be modified or omitted as appropriate.

[0064] 2 Boost converter, 3 Buck converter, 11 Microcomputer, 12 LED circuit, 13 Window comparator, 14 Pulse width counter, 100 Semiconductor light source lighting device.

Claims

1. A semiconductor light source lighting device that controls the lighting of a plurality of semiconductor light sources connected in series, comprising: a step-down converter that steps down a battery voltage or a supply voltage from a step-up converter that steps up the battery voltage to a predetermined voltage, and supplies a predetermined current to the plurality of semiconductor light sources; a voltage divider circuit section that divides the voltage output from the step-down converter; an AC component extraction section that extracts an AC component from the divided voltage output from the voltage divider circuit section; and a control section that compares the AC component with a threshold value, and when the AC component exceeds the threshold value a predetermined number of times within a unit time, determines that an open circuit failure has occurred in the plurality of semiconductor light sources and outputs an open circuit failure signal.

2. The semiconductor light source lighting device according to claim 1, wherein the threshold values ​​include a first threshold value and a second threshold value that is greater than the first threshold value.

3. The semiconductor light source lighting device according to claim 2, wherein the first threshold value and the second threshold value are set symmetrically with respect to a zero point of the AC component.

4. The semiconductor light source lighting device according to claim 2, wherein the first threshold value and the second threshold value are set symmetrically with respect to a midpoint between upper and lower peak values ​​of the AC component.

5. The semiconductor light source lighting device according to claim 2, further comprising a window comparator which compares the AC component with a threshold value and outputs a detection signal when the AC component exceeds the threshold value.

6. A semiconductor light source lighting device as described in claim 5, further comprising an integration circuit section which integrates the detection signal of the window comparator and outputs an integrated value, wherein the control section determines that an open circuit failure has occurred in the plurality of semiconductor light sources when the integrated value exceeds a predetermined value within a unit time, and outputs the open circuit failure signal.