LED group abnormality detection device

Abstract

To provide an LED group abnormality detection device with which it is possible to determine abnormality correctly even when there is variation in identification of each LED or when operation from the outside is applied.SOLUTION: An abnormality detection device 10 detects occurrence of abnormality in an LED 104 on the basis of a change of the current value flowing in one or more LED groups 100 constituted by a plurality of LEDs 104 and the applied voltage value. The abnormality detection device 10 includes one or more ampere meters 12 for measuring the current value flowing in each individual LED group 100, and a detection device 16 for detecting abnormality on the basis of the current values measured multiple times. The detection device 16 determines that abnormality has occurred to the LED 104 when a temporal change of the measured value of the current flowing in each LED group 100 exceeds a threshold determined from a predicated variation of measured values due to measurement errors and a variation of characteristics of the LEDs 104.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an abnormality detection device that detects an abnormality in any one of a plurality of LEDs constituting an LED group.

Background Art

[0002] When an LED group is operated in a steady state by a constant current power supply, and no operation is performed from the outside, and each LED is not broken or has no change in characteristics, the current value to each LED does not change. In other words, when the current value to an LED changes even though no operation is performed from the outside and there is no change in the characteristics of each LED, it means that one of the LEDs is broken. Therefore, it is possible to detect that an abnormality has occurred in the LED by observing the time change of the current value to the LED.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, if each LED continues to maintain an ideal state, the abnormality determination of the LED may be made by observing the change in the current value to each LED group. However, in reality, there are measurement errors in the current value and variations in the characteristics of each LED, and furthermore, external operations may be applied. For this reason, it is not possible to perform abnormality detection simply by observing the change in the current value to each LED group, and it is necessary to be able to correctly perform abnormality determination even when these variations and external operations are applied.

[0005] A method of determining whether an abnormality has occurred by comparing the data of the voltage and current of an LED that has been measured and memorized in advance with the measurement results of the current and voltage is widely known. However, since the voltage and current characteristics of a new LED are significantly different from those of an LED after being used for a certain period of time, there has been a problem that this method has a high possibility of not being able to correctly determine an abnormality in an LED after being used for a certain period of time. In addition, since the voltage of an LED changes depending on its own temperature, there is a problem that when the temperature change is large, there is a high possibility of not being able to correctly determine an abnormality in the LED.

[0006] The present invention has been made in view of such problems, and an object thereof is to provide an abnormality detection device for an LED group that can correctly determine an abnormality even when there are variations in the characteristics of each LED, external operations are applied, the LED deteriorates, or the temperature of the LED changes.

Means for Solving the Problems

[0007] According to one aspect of the present invention, An abnormality detection device that detects that an abnormality has occurred in an LED belonging to any one of the LED groups based on a change in the current value flowing through one or a plurality of LED groups composed of a plurality of LEDs, One or a plurality of ammeters that measure the current value flowing through each of the LED groups And a detection device that performs abnormality detection based on the current values measured multiple times, The detection device determines that an abnormality has occurred in the LED when the time change in the actually measured value of the current flowing through each LED group exceeds a threshold value determined from the variation in the measured value expected due to measurement error and variations in the characteristics of the LED. An abnormality detection device is provided.

[0008] According to another aspect of the present invention, An abnormality detection device that detects that an abnormality has occurred in the LED belonging to any of the one or more LED groups composed of a plurality of LEDs based on changes in the current value flowing through the one or more LED groups and the voltage value applied thereto. One or more ammeters that measure the current value flowing through each of the LED groups. A voltmeter that measures the voltage value applied to each of the LED groups. And a detection device that performs abnormality detection based on the current values and voltage values measured multiple times. When the change over time of the actually measured value of the current flowing through each of the LED groups exceeds a threshold value determined from the variation in the measured values expected due to measurement error and the variation in the characteristics of the LEDs, or when the change over time of the actually measured value of the voltage applied to each of the LED groups exceeds a threshold value determined from the variation in the measured values expected due to measurement error and the variation in the characteristics of the LEDs, the detection device determines that an abnormality has occurred in the LED. An abnormality detection device is provided.

[0009] Preferably, Using the change over time of the average value of the actually measured values of the current flowing through each of the LED groups and the change over time of the actually measured values of the current flowing through each of the LED groups, correction is applied so that the change over time of the current of each LED group in which no abnormality occurs becomes zero when the total current flowing through each of the LED groups is changed.

[0010] Preferably, Using the average value and the change over time thereof of the actually measured values of the current flowing through each of the LED groups, the difference between the change over time of the actually measured value of the voltage applied to each of the LED groups, and the data on the current-voltage characteristics of the LED groups prepared in advance, correction is applied so that the change over time of the voltage applied to each of the LED groups in which no abnormality occurs becomes zero when the total current flowing through each of the LED groups is changed.

[0011] Preferably, Based on the pre-prepared data of the current-voltage characteristics of the LED groups, the time variation of the actually measured values of the voltages applied to the respective LED groups, and the average value of the actually measured values of the currents flowing through the respective LED groups, when an abnormality occurs in any of the LEDs, correction is applied so that the time variation of the actually measured values of the currents flowing through the LED groups without the occurrence of an abnormality becomes zero.

[0012] Preferably, Multiply the time variation of the actually measured values of the currents flowing through the respective LED groups by the reciprocal of the average of the actually measured values of the currents flowing through the respective LED groups, and then determine whether there is an abnormality.

[0013] Preferably, Multiply the time variation of the actually measured values of the currents flowing through the respective LED groups by the reciprocal of the average of the actually measured values of the currents flowing through the LED groups that have not been determined to have had an abnormality in the previous abnormality detection among the respective LED groups, and then determine whether there is an abnormality.

[0014] Preferably, Calculate the time variation of the actually measured values of the currents flowing through the respective LED groups from the difference between the actually measured values of the currents flowing through the respective LED groups measured most recently and the actually measured values of the currents flowing through the respective LED groups measured at least two or more times previously.

[0015] Preferably, Calculate the time variation of the actually measured values of the voltages applied to the respective LED groups from the difference between the actually measured values of the voltages applied to the respective LED groups measured most recently and the actually measured values of the voltages applied to the respective LED groups measured at least two or more times previously.

Advantages of the Invention

[0016] According to the abnormality detection device and the abnormality detection method according to the present invention, even if there are variations in the specification of each LED or external operations are applied, corrections corresponding to these elements are applied, so that an accurate abnormality determination can be made.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0018] (Configuration of the abnormality detection device 10) As shown in FIG. 1, the abnormality detection device 10 according to the present embodiment generally includes an ammeter 12, a voltmeter 14, and a detection device 16.

[0019] This abnormality detection device 10 is used for a light emitting device 102 in which six LED groups 100 are connected in parallel to each other. In one LED group 100, two sets in which five LEDs 104 are connected in series are connected in parallel to each other. Of course, the light emitting device 102 to which the abnormality detection device 10 is applied is not limited to this, the number of LED groups 100 may be one or a plurality, and the number of LEDs 104 constituting one LED group 100 and the connection mode are not particularly limited.

[0020] The ammeter 12 measures the current value flowing through one LED group 100, and one ammeter 12 is arranged for one LED group 100. In the present embodiment, since six LED groups 100 are connected in parallel to each other, six ammeters 12 are used.

[0021] The voltmeter 14 measures the voltage value applied to each LED group 100. In the present embodiment, since six LED groups 100 are connected in parallel to each other, one voltmeter 14 is used.

[0022] The detection device 16 is a device that performs abnormality detection based on current values and voltage values measured multiple times, and includes an input device that receives current values and voltage values, an output device for outputting detection results to an external monitor or the like, calculation formulas to be described later, initial setting values, a storage device for storing "V-I characteristic graphs", etc., and an execution device that executes calculations and the like.

[0023] (Method of Abnormality Detection by Abnormality Detection Device 10) [Setting of Threshold Value] When operating under steady state without external operation, ideally, the time change of the current should be 0. However, in the real world, due to measurement errors and temperature characteristics of LEDs, etc., it is necessary to give the threshold a certain width. It is desirable that the method of determining the width of the threshold is larger than the expected measurement error and the change in the measured value due to temperature characteristics.

[0024] For example, when operating under steady state without external operation, if the measured value of the time change of the current varies by about ±50 mA for each measurement due to measurement errors and variations in characteristics, the threshold values are set to +60 mA and -60 mA with a margin.

[0025] Note that so far, the "time change of the current" has been described, but the same applies to the "time change of the actually measured value of the voltage", and the width of the threshold is determined based on the variation in the actually measured value of the voltage expected due to measurement errors and variations in the characteristics of the LEDs.

[0026] [Correction When Changing the Total Current Flowing Through the LED Group] When the total current is changed by operating the power supply of the LED from the outside, the time change of the current and voltage may exceed the threshold. To avoid this, a correction is added to make the time change of the current and voltage generated by the operation of the power supply zero. For specific examples, refer to paragraph

[0060] and paragraph

[0066] .

[0027] [Correction to Make the Time Change of the Actually Measured Value of the Current Flowing Through the LED Group Where No Abnormality Has Occurred Zero] Consider the case where the LEDs are connected in parallel in each LED group. Since the current changes in the LED group where a failure has occurred, an abnormality can be detected, but the current in the LED groups where no abnormality has occurred also changes. Therefore, there is a possibility of false detection of the LED groups where no abnormality has occurred. To avoid this, false detection is prevented by applying a correction such that the time change in the current of the LED groups where no abnormality has occurred becomes zero from the time change in the voltage. For a specific example, refer to paragraph

[0060] .

[0028] Note that in this correction, since the time change in the current of the LED group where an abnormality has occurred becomes larger, there is also an advantage that oversights are reduced. Instead of applying a correction so that the time change becomes zero, a method of changing the threshold value so as not to cause false detection may be used.

[0029] Next, consider the case where the LEDs are not connected in parallel. Even if a short circuit occurs in the LED, the time change in the current remains zero. For this reason, an abnormality in the LED is overlooked. In this case, since the voltage has a time change, a short circuit is detected by observing the time change in the voltage at the same time.

[0030] [Correction such that the same abnormality causes the same time change whether the current in the LED is small or large] Depending on the magnitude of the current in each LED, the magnitude of the time change in the current when an abnormality occurs is different. Also, variations due to measurement errors and LED characteristics change. For example, when the current is small, the time change when an abnormality occurs in the LED becomes small, so oversights are likely to occur. Conversely, when the current is large, the time change when an abnormality occurs in the LED becomes large, so oversights are less likely to occur, but variations due to measurement errors and temperature characteristics also become large, so the possibility of false detection increases. To solve such problems, a correction is applied such that the same abnormality causes the same time change whether the current in the LED is small or large. For a specific example, refer to paragraph

[0077] .

[0031] In the above description, the reciprocal of the current was multiplied, but the reciprocal of the voltage may be multiplied instead. Further, correction may be applied based on a previously prepared table. Furthermore, a method of changing the threshold value may be used. Also, instead of applying correction, by observing the transition of the change over time over a long period, it may be determined whether an abnormality has occurred, or whether it is simply a measurement error or variation due to temperature characteristics.

[0032] [Correction for continuing operation in a state where at least one LED has already failed in one or more places and detecting further abnormalities] Consider a case where, in a state where at least one LED has already failed in one or more places and operation is continued, and a state where the failed LED group and the non-failed LED group are connected in parallel. From this state, consider the case where an abnormality occurs in the LEDs of the LED group where no abnormality has occurred.

[0033] In this case, after multiplying the time change of the actually measured value of the current flowing through each LED group by the reciprocal of the average of the actually measured values of the current flowing through the LED groups that have not been determined to have had an abnormality in any previous abnormality detection among each LED group, it is determined whether there is an abnormality. For a specific example, refer to paragraph

[0080] .

[0034] In the above description, the reciprocal of the average of the actually measured values of the current was multiplied, but the reciprocal of the average of the actually measured values of the voltage may be multiplied instead. Further, correction may be applied based on a previously prepared table. Furthermore, a method of changing the threshold value may be used.

[0035] [Correction when current / voltage sampling and occurrence of LED abnormality occur in the same period] If the sampling period and the timing when an abnormality occurs in some LED and the current changes overlap, the change in current over time will appear small. As a result, the change in current over time when an abnormality occurs in the LED becomes smaller than the width of the threshold value set in advance, and the possibility of overlooking the occurrence of the abnormality increases.

[0036] Therefore, instead of calculating the difference from the previous value, comparison is made with data from two or more steps back. For specific examples, refer to paragraph

[0059] , paragraph

[0060] , and paragraph

[0066] .

[0037] (Method for detecting anomalies using more specific examples) For detecting anomalies in one LED group 100, "Id_n" (where n is the number of the LED group 100) obtained by the following formula (1) is used. For example, when detecting anomalies for each of six LED groups, "Id_1", "Id_2",... "Id_6" are obtained respectively. Id_n = (ΔIf_n - Ikdv) × Ki …(1)

[0038] If the value of "Id_n" obtained by formula (1) is greater than the upper threshold "Ith+", it is determined that a "short circuit failure" has occurred in any one of the LEDs 104 within that LED group 100. If the value is less than the lower threshold "Ith-", it is determined that an "open circuit failure" has occurred in any one of the LEDs 104 within that LED group 100.

[0039] The procedure for obtaining the value of this "Id_n" will be described below.

[0040] (Procedure for calculating "If_n")[[]END] "If_n" is obtained by the following formula (2). If_n = Itest_n - Itest_ave. + I0 …(2)

[0041] "I0" is a standard current value. This standard current value is a pre-determined value. As the standard current value, the most commonly used current value or a value around the middle of the upper and lower limits of the current value can be considered.

[0042] "Itest_n" is the measured value of the current flowing through each LED group 100.

[0043] "Itest_ave." is the average value obtained from the sum of the actually measured values of the current flowing through each LED group 100 (that is, "Itest_n"). For example, when there are six LED groups 100, it is the value obtained by dividing the sum of the actually measured values of the current flowing through each LED group 100 by 6.

[0044] (Calculation procedure of "ΔIf_n") "ΔIf_n" is the change in current over time, and is the difference between "If_n" calculated from the most recently measured "Itest_n" and "If_n" calculated from the "Itest_n" measured two times before. ΔIf_n = (calculated most recently) "If_n" - (calculated two times before) "If_n"

[0045] (Calculation procedure of "Ki") "Ki" is the "correction coefficient by current" and is obtained by the following formula (3). Ki = I0 / Itest_ave....(3)

[0046] "I0" and "Itest_ave." are as described above.

[0047] (Calculation procedure of "Ikdv") "Ikdv" is the "corrected value of voltage change" and is obtained by the following formula (4). Ikdv = Ivt - Itest_ave....(4) The calculation procedure of "Ivt" will be described below.

[0048] (Calculation procedure of "Ivt") First, obtain the value of "Vtest", which is the actually measured value of the voltage applied to each LED group 100. Then, obtain "Vf" (corrected voltage value) by the following formula (5). Vf = Vtest - Kv....(5)

[0049] Here, "Kv" (voltage correction coefficient) is obtained by the following formula (6). Kv = (Voltage value corresponding to Itest_ave. obtained from the V-I characteristic graph) - (Voltage value corresponding to I0 obtained from the V-I characteristic graph) …(6)

[0050] The "V-I characteristic graph" is a graph prepared in advance, for example, like the one shown in Figure 2. In the case of the "V-I characteristic graph" shown in the figure, when "I0" is 600 mA and "Itest_ave." is 800 mA, the voltage corresponding to 600 mA is 12.6 V, and the voltage corresponding to 800 mA is 14.0 V. Thus, "Kv" becomes "14.0 V - 12.6 V" which is "1.4 V". Further, assuming the value of "Vtest" at this time is 14.1 V - I, then "Vf" becomes "14.1 V - 1.4 V" which is "12.7 V".

[0051] Next, "ΔVf" is obtained. "ΔVf" is the change in voltage over time, and it is the difference between "Vf" calculated from the most recently measured "Vtest" and "Vf" calculated from the "Vtest" measured two times before. ΔVf = (Most recently calculated) "Vf" - (Calculated two times before) "Vf"

[0052] Then, the "voltage value corresponding to Itest_ave. obtained from the V-I characteristic graph" is obtained, and "ΔVf" is added to this voltage value to calculate the voltage value "Vt".

[0053] Furthermore, using the V-I characteristic graph, the current value "Ivt" corresponding to the voltage value "Vt" is obtained.

[0054] Thus, the value of "Ikdv" can be calculated.

[0055] (Calculation method of threshold values "Ith+" and "Ith-") The threshold value "Ith+" is obtained by the following formula (7). Ith+ = Ith+0 × I3 / Itest_ave. …(7)

[0056] 「Ith+0」is the standard upper threshold value, which is a predetermined value. Also, "I3" is the average value of the values of "Itest_n" measured two times before, the value of "Itest_n" measured one time before, and the value of "Itest_n" measured most recently in the LED group 100 where no abnormality has occurred so far.

[0057] Also, the threshold value "Ith-" is obtained by the following formula (8). Ith- = Ith-0 × I3 / Itest_ave. …(8)

[0058] 「Ith-0」is the standard lower threshold value, which is a predetermined value. Also, "I3" is the same as that described above.

[0059] (Regarding the measurement interval of current values and voltage values) Previously, for the purpose of reducing the measurement error of current values, a method of measuring the current value several times and taking the average has been widely used. In this case, a finite time is required from the start to the end of the measurement of the current value. On the other hand, when any one of the LEDs 104 in the steady state LED 104 breaks, a finite time is required from the breakdown of the current balance to the transition to a new steady state. If the timing of measuring the current value coincides with the transition period until the steady state is reached, the time change of the current will appear smaller (or larger) compared to the case of measuring the current value in the steady state.

[0060] In contrast, in order to set the measurement interval of the current value to be sufficiently longer than the time period between steady states, rather than comparing with the result measured one time before, comparing with the results measured two or more times before can more accurately grasp the time change of the current value (in the above-described embodiment, it is set two times before). Also, even if the measurement interval is shorter than the transition time of the steady state, it is sufficient if the time interval with the comparison target is large. Note that the transition time of the steady state may be actually measured or predicted from the time constant of the measurement system or the like.

[0061] (Correction example due to voltage change) There are two sets of five LEDs 104 connected in series, and six LED groups 100 in which these two sets are connected in parallel are provided. An example in which these six LED groups 100 are connected in parallel to a single constant current power supply will be described. Also, the threshold values for abnormality determination are such that the upper threshold Ith+ is 100 mA and the lower threshold Ith- is -100 mA.

[0062] A case where one LED 104 in the first LED group 100 and one LED 104 in the second LED group 100 are each open-circuited will be described. Assume that the measured results of the current values flowing through each LED group 100 and the voltage values applied to each LED group 100 are as shown in Table 1.

Table 1

[0063] Focusing on the current values of the first LED group 100 and the second LED group 100, the difference between the first measurement value and the third measurement value is -202 mA, which is smaller than the lower threshold value. Therefore, it can be determined that an abnormality has occurred (since it exceeds the lower threshold value, it is "open-circuit failure").

[0064] On the other hand, focusing on the current values of the remaining third LED group 100 to the sixth LED group 100, the difference between the first measurement value and the third measurement value is +101 mA. Since this value is larger than the upper threshold Ith+, without some correction, the third LED group 100 to the sixth LED group 100, which have no abnormalities, will also be determined to be abnormal.

[0065] From the V-I characteristics in Fig. 2, it can be seen that the current at 11.7V is approximately 500mA and the current at 12.6V is approximately 600mA. Also, since the measured voltage changed from 11.7V to 12.6V, it can be predicted that the current flowing through the normal LED group 100 increased by 600mA - 500mA = 100mA. Therefore, when this 100mA is subtracted from the difference between the first measurement and the third measurement as the correction for the voltage change, the difference between the first measurement and the third measurement of the current of the first LED group 100 and the second LED group 100 becomes -302mA, and the difference between the first measurement and the third measurement of the current of the third LED group 100 to the sixth LED group 100 becomes 1mA. In this way, by performing the correction for the voltage change, misjudgment for the third LED group 100 to the sixth LED group 100 is eliminated. In the above-described embodiment, the correction for the voltage change "Ikdv" is calculated using the calculation of the voltage correction value "Kv" and the corrected voltage "Vf", but the basic concept is the same.

[0066] Also, in the above example, 100mA was subtracted from the change in current over time to correct the change in current over time to 1mA, but the threshold value may be changed instead.

[0067] (Correction for operations on the power supply (change in total current)) In the actual usage environment, the total current may be changed by changing the power supply settings or replacing the power supply itself. It is conceivable to adjust the current of each LED group 100 up or down to achieve the desired illuminance.

[0068] For example, assume that the measured results of the current values flowing through each LED group 100 and the voltage values applied to each LED group 100 are as shown in Table 2.

Table 2

[0069] Focusing on the value of the current flowing through the first LED group 100, the difference between the first measurement and the third measurement is +300 mA. Considering the correction of the voltage change (V-I characteristic), it can be seen that the current at 14 V is approximately 800 mA and the current at 11.7 V is approximately 500 mA. That is, when the correction based on the V-I characteristic is applied, the difference between the first measurement and the third measurement becomes almost 0 mA, and it is possible to avoid misjudging it as an abnormality.

[0070] Similarly, when the V-I characteristic of the LED group 100 changes, it is possible to avoid misjudging it as an abnormality by considering the correction of the voltage change.

[0071] (Regarding the correction of current [Equation (2) "If_n = Itest_n - Itest_ave. + I0"]) Instead of directly using the change in the measured value of the current of each LED group 100 for determination, the change over time of the current after correction based on the power supply setting is used for determination. The power supply setting may be obtained using communication such as RS485, but it is costly because dedicated communication components are required. Therefore, Equation (2) exists to calculate the power supply setting from the sum of the currents of each LED group and apply the correction. Specifically, the average value of the current of each LED group 100 is calculated by dividing the sum of the current values flowing through each LED group 100 by the number of LED groups 100. Then, the difference between the measured value of the current flowing through each LED group 100 and the average value of the current value is taken, and the standard current is added to this to correct the power supply setting.

[0072] For example, when measurement values of current and voltage as shown in Table 3 are obtained and this correction is applied with a standard current I0 = 600 mA, the result is as shown in Table 4, and the difference between the first measurement and the third measurement becomes zero for all LED groups 100, and no abnormal determination is made. When the current value of each LED group 100 does not deviate from the average value, If_n approaches I0, so it is difficult to make a misjudgment even if the total current is changed. Also, since the current used for abnormal determination is changed to the corrected one, the correction for the change in voltage is also changed.

Table 3

Table 4

[0073] (Correction of voltage [for formula (5) "Vf = Vtest - Kv"]) Similarly for voltage, comparison is made using the value obtained by applying correction according to the power supply setting (output current of the power supply). For example, let the voltage value at the standard current I0 be the standard voltage V0. Based on the V-I characteristics, subtract the voltage value corresponding to Itest_ave. from the measured voltage value, and apply a correction of adding the standard voltage V0.

[0074] For example, when measurement values of current and voltage as shown in Table 5 are obtained, if this correction is applied with the standard current I0 = 600 mA and the standard voltage V0 = 12.6 V, the results will be as shown in Table 6. In Table 6, when taking the difference of Vf between the first and third measurements, it becomes 0 V. If the characteristics of each LED group 100 do not deviate from the characteristics used in the calculation (given as parameters), since Vf approaches V0, it is difficult to make a misjudgment even if the power supply setting is changed.

Table 5

Table 6

[0075] (Correction of the voltage change amount using the corrected voltage Vf [for formula (4) "Ikdv = Ivt - Itest_ave."]) When the characteristics of each LED group 100 are almost the same as the characteristics used in the calculation, Vf ≒ V0 regardless of the power supply setting. However, when an abnormality occurs and correcting the change amount of Vf, since the slope of the V-I characteristic varies depending on the magnitude of the voltage, it cannot be obtained from the most recently measured Vf and the Vf measured two times before. Therefore, the correction of the voltage change amount using the corrected voltage Vf (formula (4)) is incorporated.

[0076] For example, assuming a standard current I0 = 800 mA and a standard voltage V0 = 14.0 V, and that one LED 104 in each of the first LED group 100 and the second LED group 100 is open-circuited and damaged between the second and third measurements. Also assume that measurement values of current and voltage as shown in Table 7 are obtained in this case.

Table 7

[0077] Considering the abnormality determination for the third measurement, Itest_ave. = 500 mA, ΔVf = 14.9 V - 14 V = 0.9 V Vt = 11.7 V + 0.9 V = 12.6 V Ikdv = 600 mA - 500 mA = 100 mA As a result, Table 8 is obtained. The difference between the first and third measurements of the current values for the third LED group 100 to the sixth LED group 100 is 901 mA - 800 mA - 100 mA = 1 mA, and the abnormality determination can be avoided. If the Vf values of the first and third measurements are used as they are, from V(800 mA) = 14 V and V(960 mA) = 14.9 V, the correction due to the voltage change would be 160 mA. The difference between the first and third measurements of the current for the third LED group 100 to the sixth LED group 100 is 901 mA - 800 mA - 160 mA = 59 mA, and this alone may result in misjudgment depending on the threshold value. The reason why the determination current for the normal LED group 100 has deviated from 0 mA is that the slope of the V - I characteristic is different near V0 and near Vtest. In order to suppress the influence of the power supply setting, we want to use the time change of Vf instead of the time change of Vtest, but since we want to calculate using the slope near Vtest, the calculation formula is as above.

Table 8

[0078] (When an abnormality occurs when the current value is relatively small, there is a risk of being overlooked because the fluctuation range is small. Correction for avoiding this [regarding formula (3) "Ki = I0 / Itest_ave."]) For example, the upper threshold Ith+ for abnormality determination is set to 100 mA, the lower threshold Ith- is set to -100 mA, the standard current I0 is 600 mA, and the standard voltage V0 is 12.6 V. Assume that one LED 104 in each of the first LED group 100 and the second LED group 100 is open-circuited and damaged between the second and third measurements. Also assume that measurement values of current and voltage as shown in Table 9 are obtained in this case. [Table 9]

[0079] Then, Vt = 11.7 V + (13.5 V - 12.6 V) = 12.6 V The correction Ikdv for the voltage change amount is Ikdv = 600 mA - 500 mA = 100 mA. The difference between the first and third measurements of the first LED group 100 and the second LED group 100 is 398 mA - 600 mA - 100 mA = -302 mA, and the difference between the first and third measurements of the third LED group 100 to the sixth LED group 100 is 701 mA - 600 mA - 100 mA = 1 mA. Then Table 10 is obtained. [Table 10]

[0080] In this way, the determination current of the abnormal LED group 100 is correlated with Itest_ave.. The larger Itest_ave. is, the larger the determination current for abnormality determination is and the easier it is to make a determination. Multiply the coefficient Ki that corrects this difference by the determination current (Equation (3)). And finally, the determination current obtained using Equation (1) is Id = -302 mA * I0 / Itest_ave. = -362.4 mA.

[0081] (Regarding the thresholds "Ith+" and "Ith-" used for abnormality determination [Equation (7) "Ith+ = Ith+0 × I3 / Itest_ave." and Equation (8) "Ith- = Ith-0 × I3 / Itest_ave."]) Assume that when all the LEDs 104 are operating normally, an abnormality occurs in the LED 104 of a certain LED group 100, and the operation continues as it is. Also, assume that the measured values of current and voltage as shown in Table 11 are obtained in this case. Let the standard current I0 = 800 mA and the standard voltage V0 = 14.0 V. Also, let the upper threshold value for abnormality determination be Ith+ = 300 mA and the lower threshold value be Ith- = -300 mA. And assume that two LEDs 104 in the first LED group 100 are short-circuited between the second and third measurements, and one LED 104 in the second LED group 100 is open-circuited between the seventh and eighth measurements.

Table 11

[0082] From the measurement results in Table 11, when each "If_n" and "Vf" are obtained, it becomes as shown in Table 12 (from the sixth to the eighth measurements).

Table 12

[0083] Considering the abnormality determination after the eighth measurement, "Vt = 14.0 V + (13.7 V - 13.3 V) = 14.4 V". Also, the correction Ikdv for the voltage change is "Ikdv = 870 mA - 800 mA = 70 mA". Then, the determination current for the difference between the first and third measurements of the second LED group 100 is "Id = (380 mA - 700 mA - 70 mA) * Ki = -390 mA * 800 mA / 800 mA = -390 mA". Also, the determination current for the difference between the first and third measurements of the third to sixth LED groups 100 is "Id = (760 mA - 700 mA - 70 mA) * Ki = -10 mA * 800 mA / 800 mA = -10 mA".

[0084] The smaller the current “Itest_n” of the LED group 100 without any abnormality is than “Itest_ave.”, the smaller the absolute value of the determination current Id tends to be. If the current Itest_n of the LED group without any abnormality is significantly different from the average current Itest_ave. of the LED group, there may be a possibility that abnormal detection cannot be performed correctly (false detection or detection omission). Therefore, correction of the threshold value for abnormality determination is applied to the currents Itest_n and Itest_ave. of the LED group 100 without any abnormality to prevent false detection and detection omission (Equations (7) and (8)).

[0085] In the above-described measurement example, since “I3 = 700 mA, Itest_ave. = 800 mA”, “Ith- = Ith-0 * 700 mA / 800 mA = 262.5 mA” is obtained, and it can be determined that only the second LED group 100 is abnormal.

[0086] (Others) The above-described Equation (2) “If_n = Itest_n - Itest_ave. + I0” may be simplified to “If_n = Itest_n * I0 / Itest_ave.”.

[0087] Also, Equation (7) “Ith+ = Ith+0 × I3 / Itest_ave.” may be written as “Ith+ = Id * Itest_ave. / I3”.

[0088] Furthermore, although the calculation method of the correction value Ki was “Ki = I0 / Itest_ave.”, it may be changed to a form in which Ki is calculated from the V-I characteristics with detailed conditional branching.

[0089] Also, although the time change of the current is used, the determination may be performed using the time change of the difference in the currents of the LED group 100. For example, when measurement results as shown in Table 13 are obtained, calculating the difference in the currents of adjacent LED groups 100 results in Table 14.

Table 13

Table 14

[0090] In this example, from the difference between the second LED group 100 and the third LED group 100, and the difference between the third LED group 100 and the fourth LED group 100, it can be seen that an abnormality has occurred in the third LED group 100.

[0091] The embodiments disclosed this time should be considered as illustrative in all respects and not restrictive. The scope of the present invention is shown not by the above description but by the claims, and it is intended that all modifications within the meaning and scope equivalent to the claims are included.

Explanation of Reference Numerals

[0092] 10…Abnormality detection device, 12…Ammeter, 14…Voltmeter, 16…Detection device 100…LED group, 102…Light emitting device, 104…LED

Claims

1. An abnormality detection device that detects that an abnormality has occurred in an LED belonging to any of the one or more LED groups composed of a plurality of LEDs based on a change in the current value flowing through the one or more LED groups, comprising: one or more ammeters that measure the current value flowing through each of the LED groups; a detection device that performs abnormality detection based on the current values measured a plurality of times, wherein the detection device determines that an abnormality has occurred in the LED when the change over time in the actually measured value of the current flowing through each LED group exceeds a threshold value determined from the variation in the measured values expected due to measurement error or variations in the characteristics of the LEDs. Abnormality detection device.

2. An abnormality detection device that detects that an abnormality has occurred in an LED belonging to any of the one or more LED groups composed of a plurality of LEDs based on changes in the current value and the applied voltage value flowing through the one or more LED groups, comprising: one or more ammeters that measure the current value flowing through each of the LED groups; a voltmeter that measures the voltage value applied to each LED group; a detection device that performs abnormality detection based on the current values and voltage values measured a plurality of times, wherein the detection device determines that an abnormality has occurred in the LED when the change over time in the actually measured value of the current flowing through each LED group exceeds a threshold value determined from the variation in the measured values expected due to measurement error or variations in the characteristics of the LEDs, or when the change over time in the actually measured value of the voltage applied to each LED group exceeds a threshold value determined from the variation in the measured values expected due to measurement error or variations in the characteristics of the LEDs. Abnormality detection device.

3. Characterized in that correction is applied using the change over time in the average value of the actually measured values of the current flowing through each LED group and the change over time in the actually measured values of the current flowing through each LED group so that the change over time in the current of each LED group where no abnormality occurs becomes zero when the total current flowing through each LED group is changed. The abnormality detection device according to claim 1 or claim 2.

4. Using the average value of the actually measured current flowing through each of the LED groups and its change over time, the difference between the change over time of the actually measured voltage applied to each of the LED groups, and the data of the current-voltage characteristics of the LED groups prepared in advance, correction is applied so that the change over time of the voltage applied to each of the LED groups where no abnormality occurs becomes zero when the sum of the currents flowing through each of the LED groups is changed. The abnormality detection device according to claim 2.

5. From the data of the current-voltage characteristics of the LED groups prepared in advance, the change over time of the actually measured voltage applied to each of the LED groups, and the average value of the actually measured current flowing through each of the LED groups, when an abnormality occurs in any of the LEDs, correction is applied so that the change over time of the actually measured current flowing through each of the LED groups where no abnormality occurs becomes zero. The abnormality inspection device according to claim 2.

6. It is characterized in that after multiplying the change over time of the actually measured current flowing through each of the LED groups by the reciprocal of the average of the actually measured currents flowing through each of the LED groups, it is determined whether there is an abnormality. The abnormality inspection device according to claim 1 or claim 2.

7. It is characterized in that after multiplying the change over time of the actually measured current flowing through each of the LED groups by the reciprocal of the average of the actually measured currents flowing through the LED groups that have not been determined to have an abnormality even once in the previous abnormality detection among each of the LED groups, it is determined whether there is an abnormality. The abnormality inspection device according to claim 1 or claim 2.

8. The calculation of the change over time of the actually measured current flowing through each of the LED groups is performed from the difference between the actually measured current flowing through each of the LED groups measured most recently and the actually measured current flowing through each of the LED groups measured at least two or more times before. The abnormality detection device according to claim 1 or claim 2.

9. The calculation of the change over time of the actually measured voltage applied to each of the LED groups is performed from the difference between the actually measured voltage applied to each of the LED groups measured most recently and the actually measured voltage applied to each of the LED groups measured at least two or more times before. The abnormality detection device according to claim 2.

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