JP2010113897A - Illumination device - Google Patents

Abstract

To provide a lighting device capable of notifying a user that an LED becomes inconspicuous if used continuously.
In a lighting device having light-emitting diodes D1, D2, D3, and D4 that are driven at a constant current by constant-current circuits 86a, 86b, 86c, and 86d as light sources, a control unit 100 includes light-emitting diodes D1, D2, and D3. , It is determined whether or not the forward voltage of each light emitting diode during the lighting of D4 is greater than or equal to a predetermined magnitude from the initial forward voltage. A certain light emitting diode 110 is turned on.
[Selection] Figure 3

Description

  The present invention relates to a lighting device, and more particularly to a lighting device having an LED (light emitting diode) as a light source.

LEDs have higher efficiency and longer life than halogen bulbs and the like, and in particular, as LED efficiency increases in recent years, lighting devices using LEDs as light sources have been commercialized. For example, a headlight device for an automobile.
Conventionally, the life of a halogen bulb that is generally used as a light source for an automotive headlamp is 1500 to 2000 hours. Therefore, a situation such as a sudden run out of the ball while the vehicle is running can be avoided by taking measures such as a replacement before reaching the end of the service life, such as during periodic inspections.

On the other hand, the LED is generally recognized as a light source that does not cause the ball to break, and the current situation is that almost no countermeasures have been taken.
JP 2000-233679 A

However, recent studies have shown that even LEDs may suddenly become inconspicuous as the cumulative lighting time increases. For this reason, there is a need to take measures such as notifying the user and replacing the headlamp with a new one in advance before becoming inconspicuous.
This problem is not limited to the headlamp device, but is common to lighting devices that cause trouble when suddenly inconspicuous, such as lighting devices used in surgery.

  In view of the above problems, an object of the present invention is to provide an illuminating device capable of informing in advance that an LED will be in a stale state if the LED continues to be used even though the LED has some abnormality.

  In order to solve the above problems, an illumination device according to the present invention is an illumination device having a light-emitting diode driven at a constant current as a light source, and a forward voltage of the light-emitting diode during lighting of the light-emitting diode is in an initial order. A determination unit that determines whether or not the voltage is greater than or equal to a predetermined magnitude; and an output unit that outputs a determination result when it is determined that the voltage is greater than or equal to the predetermined magnitude. To do.

The initial forward voltage has a temperature characteristic, and the initial forward voltage used for the determination is corrected based on an ambient temperature of the light emitting diode at the time of determination by the determination means; To do.
Furthermore, it has an ambient temperature measuring means for measuring the ambient temperature, and an initial forward voltage correcting means for performing the correction based on the ambient temperature measured by the ambient temperature measuring means when making the judgment by the judging means. It is characterized by.

In this case, the initial forward voltage correction unit has a storage unit that stores the relationship between the ambient temperature of the light emitting diode and the forward voltage, and the storage unit stores the storage unit based on the ambient temperature measured by the ambient temperature measurement unit. The correction can be performed based on the relationship stored in the means.
Further, the forward voltage that the light-emitting diode shows during the lighting has temperature characteristics, and the forward voltage used for the determination is corrected based on the ambient temperature of the light-emitting diode at the time of determination by the determination means. It is characterized by being.

  In this case, the forward voltage measuring means for measuring the forward voltage of the light emitting diode during lighting of the light emitting diode, the ambient temperature measuring means for measuring the ambient temperature in the determination by the determining means, and the ambient temperature measuring means Measurement forward voltage correction means for performing the correction on the forward voltage measured by the forward voltage measurement means based on the ambient temperature measured by the step (1).

In the above case, the predetermined magnitude can be 10% of the initial forward voltage used in the determination.
In addition, the output unit may be a notification unit that notifies the user of the determination result.
Furthermore, a switch for turning on and off the light emitting diode may be provided, and each time the switch is turned on, the respective units may function as necessary.

  According to the lighting device having the above-described configuration, when it is determined that the forward voltage during lighting of the light-emitting diode driven by constant current is greater than or equal to a predetermined magnitude from the initial forward voltage, the determination result is output. Therefore, by referring to the output result, it is possible to know that the light emitting diode is in a dotted state if it is used as it is. That is, when the forward voltage of the light emitting diode constituting the lighting device rises in proportion to the cumulative lighting time and eventually becomes inconspicuous, the predetermined voltage is set to the forward voltage in which it becomes inconspicuous. By setting the difference smaller than the difference between the initial voltage and the initial voltage, it becomes possible to know that the light-emitting diode is in a dotted state if it is used as it is.

An embodiment of an illumination device according to the present invention will be described with reference to the drawings, taking as an example the case of application to a headlight device for an automobile.
<Embodiment 1>
(Headlamp unit)
FIG. 1 is a cross-sectional view showing a schematic configuration of a headlamp unit 12 included in an automotive headlamp apparatus (hereinafter simply referred to as “headlamp apparatus”) according to Embodiment 1.

The headlamp unit 12 includes a base 14 to which a light emitting diode (hereinafter referred to as “LED”) module 18 with a heat sink 16, a reflecting mirror 20, a light shielding plate 22, and a lens 24 are attached. It has a configuration.
The reflecting mirror 20 has, for example, a reflecting surface 20A having a spheroidal shape. The reflecting mirror 20 reflects the light emitted from the LED module 18 provided corresponding to the first focal point by the reflecting surface 20A, converges it to the second focal point, and guides it to the lens 24 provided in front thereof. . The light incident on the lens 24 is refracted here and emitted forward with a predetermined spread. The light shielding plate 22 reduces scattered light components from the LED module 18 and direct light to the oncoming vehicle.

(LED module)
FIG. 2 shows a plan view of the LED module 18.
The LED module 18 has a configuration in which a plurality (four in this example) of LED chips D1 to D4 are mounted on the printed wiring board 26.
The LED chips D1 to D4 are all blue light emitting diodes having the same specifications. A phosphor 28 that seals the LED chips D1 to D4 is provided in a region on the printed wiring board 26 surrounded by a one-dot chain line in FIG. The phosphor 28 is made of any resin selected from epoxy, silicone, and fluororesin, and phosphor particles (any one selected from YAG, nitridosilicate, silicate, zion, sialon, and CASN) System phosphor particles) are mixed, and blue light from the LED chips D1 to D4 is converted into yellow light. White light is emitted from the LED module 18 by the color mixture of the yellow light and the blue light that has not been converted into yellow light. Therefore, the LED module 18 can be said to be a module composed of white LEDs.

  FIG. 2B shows a sectional view of the LED chip D1 and its vicinity in the mounted state. The LED chip D1 is a known InGaN-based LED chip, and has a configuration in which an n-type nitride semiconductor layer 32, a light emitting layer 34, and a p-type nitride semiconductor layer 36 are stacked in this order on a sapphire substrate 30. . An ohmic-connected n-side electrode pad 38 is formed on the upper surface of the n-type nitride semiconductor layer 32 that appears after the light emitting layer 34 and the p-type nitride semiconductor layer 36 are partially removed. On the other hand, an ohmic-connected transparent electrode 40 is formed over substantially the entire upper surface of the p-type nitride semiconductor layer 36, and a p-side electrode pad 50 is formed in a partial region of the upper surface of the transparent electrode 40. The LED chip D1 is bonded to the pad 52 of the printed wiring board 26.

  Returning to FIG. 2A, the p-side electrode pads of the LED chips D1 to D4 are connected to the lands 62a, 62b, 62c, and 62d of the wiring pattern 62 by bonding wires 54, 56, 58, and 60, respectively. . On the other hand, the n-side electrode pads of the LED chips D1 to D4 are respectively connected to the lands 64a, 66a, 68a, and 70a of the wiring patterns 64, 66, 68, and 70 provided individually by bonding wires 72, 74, 76, and 78, respectively. It is connected. With the above connection, the LED chips D1 to D4 are electrically connected in parallel on the printed wiring board 26.

  In the vicinity of the LED chips D1 to D4 of the printed wiring board 26, a thermistor 80 (a lead wire extending from the thermistor 80 main body is not shown) is attached as an example of a temperature sensor that is a temperature measuring means. The thermistor 80 is provided to measure the ambient temperature of the LED chips D1 to D4. By providing it in the vicinity of the LED chips D1 to D4, it is possible to measure a temperature that can be substantially equated with the temperatures of the LED chips D1 to D4.

(Overall headlight device)
In FIG. 3, the functional block diagram of the headlamp apparatus 10 is shown.
Each of the p-side electrode pads (not shown in FIG. 3) of the LED chips D1, D2, D3, and D4 is electrically connected to the electrode terminal (not shown) of the anode of the 12 [V] storage battery 82 mounted on the automobile. It is connected to the. On the other hand, each of the n-side electrode pads (not shown in FIG. 3) of the LED chips D1, D2, D3, D4 is connected to the constant current circuits 86a, 86b, 86c, 86d via the resistors 84a, 84b, 84c, 84d. Each is electrically connected.

A switch 88 for turning on / off the LED chips D1, D2, D3, D4 is connected to each of the constant current circuits 86a, 86b, 86c, 86d.
The control unit 100 is configured by, for example, a microcomputer, and has a configuration in which an input / output interface 104, a storage unit 106, an internal timer 108, and the like are connected with a CPU 102 as a center.

  Connected to the input / output interface 104 are lead wires for measuring voltages at point P0, point P1, point P2, point P3, and point P4 shown in FIG. The input / output interface 104 is connected to a display light emitting diode 110 that is turned on at a later-described timing and is used as a warning lamp. The light emitting diode 110 is disposed on an instrument panel (both not shown) provided on the dashboard of the automobile.

The contents stored in the storage unit 106 and how to use the internal timer 108 will be described later.
When the switch 88 is turned on in the headlamp device 10 having the above-described configuration, the LED chips D1, D2, D3, and D4 are respectively connected to the constant current circuits 86a, 86b, 86c, and 86d that are provided correspondingly. , Currents of the same magnitude (for example, 300 [mA]) flow. The CPU 102 of the control unit 100 determines each of the LED chips D1, D2, D3, and D4 during lighting from the voltages at the points P0, P1, P2, P3, and P4 inputted through the input / output interface 104. The forward voltage is calculated. When the voltage value at the point P0 is V0 and the voltage value at the point P1 is V1, the measurement forward voltage Vf1 of the LED chip D1 is
Vf1 = V0−V1
It becomes. Similarly, if the voltage values at points P2, P3, and P4 are V2, V3, and V4, respectively, the measurement forward voltages Vf2, Vf3, and Vf4 of the LED chips D2, D3, and D4 are:
Vf2 = V0−V2
Vf3 = V0−V3
Vf4 = V0−V4
It becomes.

Here, since a constant current of a constant magnitude flows through the LED chips D1, D2, D3, and D4, the measurement forward voltages Vf1, Vf2, Vf3, and Vf4 should always be the same.
However, it has been found that some LED chips change the forward voltage depending on the cumulative lighting time.
(Change in forward voltage due to cumulative lighting time)
As shown in FIG. 2B, the n-type nitride semiconductor layer 32 and the n-side electrode pad 38, and the p-type nitride semiconductor layer 36 and the transparent electrode 40 are ohmically connected to each other. When the connection is good, the forward voltage does not change depending on the cumulative lighting time and shows a constant value. However, if not done well, it has been found that the forward voltage increases with increasing cumulative lighting time. This is considered to be due to an increase in contact resistance due to the progress of deterioration of the connection portion.

FIG. 4 is a graph showing the relationship between the cumulative lighting time and the forward voltage change rate in such an LED chip.
FIG. 4 is a graph with the cumulative lighting time on the horizontal axis and the forward voltage change rate on the vertical axis. The cumulative lighting time is a time obtained by accumulating the time during lighting of the LED chip that is repeatedly turned on and off. The change rate of the forward voltage is the ratio (percentage) of the difference between the forward voltage (hereinafter referred to as “measurement forward voltage”) of the forward voltage measured from time to time after being incorporated as a lighting device with respect to the initial forward voltage. ).

  Here, the “initial forward voltage” refers to a forward voltage measured when the LED chip (light emitting diode) is lit for the first time after manufacture, or from the measured forward voltage in consideration of temperature characteristics as described later. Says corrected forward voltage. In addition, “first time” means not only lighting for the first time after manufacturing, but also lighting for a short period after the second lighting and before the cumulative lighting time before being incorporated as a component of the lighting device after manufacturing. It is a purpose to include.

From FIG. 4, it can be seen that the forward voltage gradually increases until the cumulative lighting time slightly exceeds 30000 hours and the forward voltage change rate reaches 10%, and then rapidly increases. Then, when the rate of change slightly before 40,000 hours slightly exceeds 30 [%], the LED chip becomes non-conductive immediately after falling into a short state inside and does not light up.
Therefore, in this embodiment, the forward voltage of each of the LED chips D1, D2, D3, and D4 is monitored. For example, when the rate of change becomes 10% or more, a warning is displayed as described later, and the LED is displayed. The user is prompted to replace the module 18.

Here, the forward voltage of the LED chip also changes depending on the ambient temperature. That is, it has temperature characteristics. Therefore, it is preferable to correct the initial forward voltage to be compared with the measurement forward voltage to a value corresponding to the ambient temperature. Needless to say, the measurement forward voltage indicates a forward voltage corresponding to the ambient temperature at the time of measurement.
(Change in forward voltage due to ambient temperature)
FIG. 5 is a graph showing how the initial forward voltage changes with respect to the ambient temperature. As shown by the solid line L1 in FIG. 5, it can be seen that the forward voltage gradually decreases as the ambient temperature increases. Therefore, in an illumination device such as a headlamp used in an environment where the ambient temperature changes, the initial forward voltage to be compared with the measurement forward voltage is preferably an initial forward voltage corrected based on the ambient temperature.

Moreover, since the forward voltage of the LED chip has individual differences even when manufactured with the same specifications, it is preferable to consider this point in setting the initial forward voltage to be compared with the measurement forward voltage.
(Difference in forward voltage due to individual differences)
In the case of the LED chip shown in FIG. 5, the value of the initial forward voltage at an ambient temperature of, for example, 25 [° C.] varies in the range of 3.5 [V] to 3.9 [V] due to individual differences. However, in any LED chip, the shape is the same just by moving the graph up and down.

That is, when the initial forward voltage VF is expressed as a function of the ambient temperature Ta (hereinafter referred to as “characteristic function”), the curves (characteristic functions) of L1, L2, and L3 are respectively
VF1 = f (Ta) + C1
VF2 = f (Ta) + C2
VF3 = f (Ta) + C3
It is represented by Here, C1, C2, and C3 are constants.

  Therefore, if the function VF = f (Ta) is obtained in advance from actual measurement data of several LED chips, for example, by measuring the magnitude of the initial forward voltage at an ambient temperature of 25 [° C.] Can be obtained. Using this characteristic function, the initial forward voltage at an arbitrary ambient temperature can be estimated. That is, the initial forward voltage corrected based on the ambient temperature is obtained.

(Storage unit 106 in control unit 100)
FIG. 6 shows a part of the storage area provided in the storage unit 106 (FIG. 3).
The storage unit 106 has a characteristic function storage area 112. The characteristic function storage area 112 stores the characteristic functions of the LED chips D1, D2, D3, and D4. Before the LED chip is mounted on the printed wiring board 26 (FIG. 2), the initial forward voltage when 300 [mA] is energized in a constant temperature bath of 25 [° C.] is measured and based on the measured value. Thus, the characteristic function is determined. The determined characteristic function is stored in the characteristic function storage area 112 in association with the LED chip subjected to (mounted on) the measurement. The characteristic function can be written into the characteristic function storage area 112 using, for example, a personal computer and a PIC writer.

The storage unit 106 also has a measurement forward voltage storage area 114. The measurement forward voltage storage area 114 is composed of storage areas for four measurement forward voltages provided for each of the LED chips D1, D2, D3, and D4.
(Processing content by control unit 100)
Based on the flowchart shown in FIG. 7, the processing content performed by CPU102 (FIG. 3) of the control part 100 is demonstrated.

  First, when the head lamps (LED chips D1 to D4) are turned on by turning on the switch 88 (FIG. 3) (YES in step S1), the CPU 102 stores the measurement forward voltage storage area 114 in the storage unit 106 shown in FIG. Is initialized, and the count value of an internal counter (not shown) is set to an initial value (step S2). Here, the internal counter “m” is a counter for specifying the LED chip to be determined. When m = 1, 2, 3, 4, the determination targets are LED chips D1, D2, D3, respectively. , D4. The internal counter “n” indicates the number of times the measurement forward voltage is stored in the measurement forward voltage storage area 114 in one LED chip.

Subsequently, the ambient temperature is measured by the thermistor 80 (FIG. 3) (step S3). Based on the measured temperature, first, using the characteristic function of the LED chip D1 stored in the characteristic function storage area 112 (FIG. 6), The corrected initial forward voltage is calculated. Then, the reference voltage Vr is calculated by multiplying the calculation result by 1.1 (step S4).
Next, the internal timer 108 (FIG. 3) is reset (step S5), and the forward voltage Vf of the LED chip D1 is measured (step S6).

It is determined whether or not the measured forward voltage Vf is greater than or equal to twice the reference voltage Vr (step S7). If it is less than twice (NO in step S7), the measured forward voltage is stored in the measured forward voltage storage area 114 ( In the first storage area of the LED chip D1 in FIG. 6) (step S8), the internal counter “n” is incremented by one.
On the other hand, when it is determined that the measured forward voltage Vf is twice or more the reference voltage Vr (YES in step S7), steps S8 and S9 are skipped and the measured forward voltage Vf is not adopted. This is because if the measured forward voltage Vf is more than twice the reference voltage Vr, there is a high possibility that noise is superimposed on the measured voltage, and it is considered that an accurate forward voltage could not be measured. is there. In particular, in the case of a headlight device for an automobile as in this example, igniter noise used for ignition of the spark plug of the engine is likely to be superimposed when it is lit during travel. Further, when the engine is started during lighting, noise from the starter motor is particularly easily superimposed.

  Then, for the LED chip D1, the measurement of the forward voltage Vf of the LED chip D1 is repeated until the writing of the measured forward voltage Vf to the measured forward voltage storage area 114 is completed four times (YES in step S10) (steps S5 to S5). S11). At this time, the measurement interval is set to 5 [ms] (step S11). That is, after resetting the internal timer in step S5, it waits for 5 [ms] to elapse (YES in step S11), and executes the next measurement (step S6). This is because when noise is added to the measured forward voltage Vf, if the measurement interval is too short, there is a high possibility that noise will be continuously added. This is to avoid the problem.

When writing of the measured forward voltage Vf to the measured forward voltage storage area 114 is completed four times for the LED chip D1 (YES in step S10), the average of the measured values for the four times is calculated (step S12), It is determined whether or not the forward voltage Vf is equal to or higher than the reference voltage Vr (step S13).
If the average forward voltage Vf is equal to or higher than the reference voltage Vr (YES in step S13), the light emitting diode 110 (FIG. 3) that is a warning lamp is turned on, and the series of processes is terminated. As a result, the user knows that if the headlamp is used as it is, the user will know that it will become inconsequential in the near future, and can take measures such as replacing the LED module 18 with a new one.

On the other hand, when the average forward voltage Vf is lower than the reference voltage Vr (NO in step S13), the remaining LED chips D2 to D4 are sequentially (steps S16 and S17) in the same manner as in the case of the LED chip D1 described above. Then, it is determined whether the current forward voltage is not equal to or higher than the reference voltage Vr. If there is an LED chip whose current forward voltage (average forward voltage of four times) is equal to or higher than the reference voltage Vr (YES in step S13), the light emitting diode 110 (FIG. 3) is turned on at that time. (Step S14), and the series of processes is terminated. A series of processes is also ended when all the forward voltages (average forward voltage of four times) of the LED chips D1 to D4 are less than the reference voltage Vr.
<Embodiment 2>
In the headlamp device 10 (FIG. 3) according to the first embodiment, the LED module 18 is configured by connecting the LED chips D1, D2, D3, and D4 in parallel. On the other hand, in the headlamp device 120 (FIG. 8) according to the second embodiment, the LED module 122 is configured by connecting the LED chips D1, D2, D3, and D4 in series. Except for this point, the headlamp device 120 according to the second embodiment has basically the same configuration as the headlamp device of the first embodiment. Therefore, the description of the common part is omitted, and different parts will be mainly described below.

(Overall headlight device)
In FIG. 8, the functional block diagram of the headlamp apparatus 120 which concerns on Embodiment 2 is shown. As described above, in the headlamp device 120, the LED module 122 is configured by connecting a plurality of LED chips (in this example, four LED chips D1, D2, D3, and D4) in series. The LED module 122 is connected to a constant current circuit 126 through a resistor 126. In FIG. 8, components that are basically the same as those of the headlamp device 10 according to the first embodiment shown in FIG.

Here, when the voltage value at the point P0 is V0, the voltage value at the point P5 is V5, and the forward voltages of the LED chips D1, D2, D3, and D4 are Vf1, Vf2, Vf3, and Vf4, respectively,
V0−V5 = Vf1 + Vf2 + Vf3 + Vf4
Thus, the forward voltage measured by the control unit 100 is a total value of the four LED chips D1, D2, D3, and D4. “Vf1 + Vf2 + Vf3 + Vf4” is referred to as a total measurement forward voltage Vft of all LED chips D1, D2, D3, D4.

(Storage unit 134 in control unit 132)
A part of the storage area provided in the storage unit 134 (FIG. 8) is shown in FIG.
The storage unit 134 has the characteristic function storage area 112 as in the case of the first embodiment, and the characteristic functions storage area 112 stores the characteristic functions of the LED chips D1, D2, D3, and D4 in advance. Yes.

In addition, the storage unit 134 adds (corrects) the initial forward voltage calculated (corrected) using the characteristic function for each of the LED chips D1, D2, D3, and D4 (hereinafter referred to as “total initial forward voltage”). Is stored in the total initial forward voltage storage area 138 (FIG. 9).
The storage unit 134 also has a total measurement forward voltage storage area 140. The total measurement forward voltage storage area 140 includes a storage area for the total measurement forward voltage for four times.

(Processing content by control unit 132)
Based on the flowchart shown in FIG. 10, processing contents executed by the CPU 136 (FIG. 8) of the control unit 132 will be described. Note that processing portions similar to those described with reference to the flowchart of FIG. 7 are omitted or simply mentioned.
First, when the headlamps (LED chips D1 to D4) are turned on (YES in step S21), the CPU 136 executes processing corresponding to steps S2 and S3 in FIG. 7 as preprocessing (step S22). That is, following the initial setting such as clearing the total initial forward voltage storage area 138 and the total measurement forward voltage storage area 140 in the storage unit 134, or setting the count value of an internal counter (not shown) to an initial value, The ambient temperature is measured by the thermistor 80.

Subsequently, each initial forward voltage is calculated from the measured temperature using the characteristic functions of the LED chips D1, D2, D3, and D4 stored in the characteristic function storage area 112, and then the total initial forward voltage is calculated. This is stored in the total initial forward voltage storage area 138 (step S23).
Then, the reference voltage Vr is calculated by multiplying the total initial forward voltage by 1.025 (step S24). The reference voltage Vr is increased by 2.5 [%] of the total initial forward voltage (VF1 + VF2 + VF3 + VF4) in the four LED chips D1, D2, D3, D4. This is because a warning display is possible even when one LED chip having the characteristics shown in FIG.

The subsequent measurement of the forward voltage Vft and the storage process in the storage unit (step S25) are basically the same as the processes in steps S7 to S9 in FIG.
The subsequent comparison processing of the average value of the measurement forward voltage Vft and the reference voltage Vr (step S26) is basically the same as steps S10 to S14 in FIG.

As described above, the present invention has been described based on the embodiment. However, the present invention is not limited to the above-described form, and for example, the following form is also possible.
(1) In the above embodiment, when comparing the measured quasi-voltage and the initial forward voltage, the initial forward voltage is corrected based on the ambient temperature of the LED chips D1 to D4. It is also possible to correct this.

A case where the measurement forward voltage is corrected will be described according to the first embodiment (that is, when the LED chips D1 to D4 are connected in parallel).
For example, the initial forward voltage 3.6 [V] at an ambient temperature of 25 [° C.] is stored in the storage unit 106 (FIG. 3) (in this case, the reference voltage Vr is 3.96 (= 3.6). X 1.1) It is [V].) Then, it is assumed that the measured ambient temperature is 5 [° C.] and the measurement forward voltage is 4.0 [V]. In this case, in order to obtain a forward voltage (corrected measurement forward voltage) that would be measured if the ambient temperature was 25 [° C.], Ta = 5 [° C.] and Ta = Substituting 25 [° C.], a corrected measurement forward voltage is obtained based on the difference. If f (5) -f (25) = 0.1 [V], 3.9 [V] (= 4.0-0.1) is the corrected measurement forward voltage.

Then, the reference voltage and the corrected measurement forward voltage are compared, and it is determined that there is no problem in this case because the reference voltage 3.96> the corrected measurement forward voltage 3.9.
The above specific example is generalized as follows.
(I) A reference voltage Vr corresponding to the initial forward voltage when the ambient temperature is Xr [° C.] is stored in advance.

(Ii) Assume that the measured ambient temperature is Xa [° C.] and the measurement forward voltage is Va [V].
(Iii) Since the graph descends to the right as shown in FIG. 5, the corrected measurement forward voltage Vc is obtained according to the following case.
When Xa> Xr: Vc = Va + | f (Xa) −f (Xr) |
When Xa = Xr: Vc = Va
When Xa <Xr: Vc = Va− | f (Xa) −f (Xr) |
(Iv) The determination is made by comparing Vc with Vr.

In the above example, the reference voltage is stored. However, the present invention is not limited to this, and the initial forward voltage may be stored and the reference voltage may be calculated for each determination.
(2) In the above embodiment, the determination is made based on whether or not the measurement forward voltage is equal to or higher than the reference voltage Vr (a value obtained by increasing the initial forward voltage by a predetermined ratio). Compared with the forward voltage, it may be determined whether the measured forward voltage is larger than the initial forward voltage by a predetermined ratio.
(3) In the above embodiment, when it is determined that the forward voltage of the light-emitting diode during lighting is a predetermined magnitude or more than the initial forward voltage, as an output means for outputting the fact (determination result), The light emitting diode 110 is used as a notification means for notifying the user by light, but the notification means is not limited to this, and a buzzer for notification by sound or a means for notification by sound may be used. Further, means such as a display panel or error information memory storage may be used by data communication.
(4) The output means is not limited to the one that can be immediately recognized by the user, such as the light emitting diode 110. For example, the CPU 102 of the control unit 100 (FIG. 3) outputs that fact (determination result) to the storage unit 106. However, the storage unit 106 may hold (store) information to that effect, that is, that “the forward voltage of the light emitting diode during lighting is determined to be greater than or equal to a predetermined magnitude from the initial forward voltage”. I do not care. By doing so, it becomes possible for the inspector to know “that (determination result)” by checking the storage contents of the storage unit 106 at the time of periodic inspection.
(5) In the above embodiment, the relationship between the ambient temperature and the forward voltage that specifically represents the temperature characteristic of the LED chip is stored in the storage unit in the form of a characteristic function. For example, it may be stored in the storage unit in the form of a table.
(6) In the above embodiment, the thermistor is used as the temperature sensor as the ambient temperature measuring means. However, the present invention is not limited to this. For example, a thermocouple may be used.
(7) In the above embodiment, it is determined whether or not the forward voltage of the light emitting diode is greater than or equal to a predetermined magnitude from the initial forward voltage each time the switch 88 is turned on (steps S1 and S21). 7 and 10), the present invention is not limited to this, and it may be performed periodically while the light emitting diode is lit. In this case, while the cumulative lighting time is recorded, the determination time interval may be shortened as the cumulative lighting time becomes longer.
(8) In the above embodiment, a single-sided electrode is used for the LED chip, but the present invention is not limited to this, and a double-sided electrode may be used. When a single-sided electrode is used, face-down mounting (flip chip mounting) may be performed instead of face-up bonding as in the above embodiment.
(9) In the above embodiment, an InGaN-based white LED is used, but other materials may be used. For example, a ZnSe-based white LED may be used. Moreover, although the sapphire substrate is used as a substrate constituting the LED, other substrates may be used. For example, the substrate may be GaN, SiC, Si, glass, ZnO, AlN, MgO, GaP, GaAs, ZrB2, NGO, LGO, LAO, or the like.
(10) When at least one electrode of the LED chip is connected to the printed wiring board by wire bonding by using a double-sided LED chip or face-up bonding, the following phenomenon occurs.

  That is, when the LED chip is sealed together with the bonding wire and the resin mixed with the phosphor, the resin repeatedly expands and contracts due to the heat from the LED chip by repeatedly turning on and off. As a result, the bonding wire is repeatedly pulled by the resin, and its base gradually becomes thinner. Then, it eventually breaks, and the LED chip suddenly becomes inconspicuous. In this case, since the resistance value increases as the bonding wire becomes thinner, the forward voltage of the LED chip measured on the circuit also gradually increases.

Therefore, the forward voltage may be measured, and a warning to that effect may be output when the measured forward voltage reaches a voltage set lower than the forward voltage when the bonding wire breaks. The “forward voltage” referred to here is, of course, a forward voltage measured via a bonding wire.
(11) In the above embodiment, an example in which the lighting device according to the present invention is applied to an automotive headlamp has been shown. However, the present invention is not limited thereto, and examples thereof include a surgical lighting device and other general lighting devices. It is applicable to.

  The illuminating device according to the present invention can be suitably used for, for example, an illuminating device that particularly disturbs when suddenly inconspicuous, for example, a headlight device for an automobile.

It is sectional drawing which shows schematic structure of the headlamp unit with which a motor vehicle headlamp apparatus is provided. (A) is a top view of the LED module with which a headlamp unit is provided, (b) is one LED chip in an LED module, and an expanded sectional view of the vicinity. 1 is a functional block diagram of an entire automobile headlamp device according to Embodiment 1. FIG. It is a graph which shows the relationship between the cumulative lighting time in LED, and the change rate of a forward voltage. It is a graph showing the change of the forward voltage of LED with respect to ambient temperature. It is a figure which shows the memory area in the memory | storage part which the control part of the motor vehicle headlamp apparatus which concerns on Embodiment 1 has. It is a flowchart which shows the processing content of the said control part. It is a functional block diagram of the whole vehicle headlamp apparatus concerning Embodiment 2. FIG. It is a figure which shows the memory area in the memory | storage part which the control part of the motor vehicle headlamp apparatus which concerns on Embodiment 2 has. It is a flowchart which shows the processing content of the said control part.

Explanation of symbols

10,120 headlamp device 80 thermistor 100,132 control unit 110 light emitting diode D1, D2, D3, D4 LED chip

Claims (9)

A lighting device having a light-emitting diode driven by a constant current as a light source,
Determination means for determining whether or not the forward voltage of the light emitting diode during lighting of the light emitting diode is greater than or equal to a predetermined magnitude from the initial forward voltage;
An output means for outputting the determination result when it is determined that the size is not less than a predetermined size;
A lighting device comprising:   The initial forward voltage has a temperature characteristic, and the initial forward voltage used for the determination is corrected based on an ambient temperature of the light emitting diode at the time of determination by the determination means. Item 2. The lighting device according to Item 1. Ambient temperature measuring means for measuring the ambient temperature upon determination by the determining means;
Initial forward voltage correction means for performing the correction based on the ambient temperature measured by the ambient temperature measurement means;
The lighting device according to claim 2, wherein:   The initial forward voltage correction unit has a storage unit that stores the relationship between the ambient temperature of the light emitting diode and the forward voltage, and is stored in the storage unit from the ambient temperature measured by the ambient temperature measurement unit. The lighting device according to claim 3, wherein the correction is performed based on the relationship.   The forward voltage that the light emitting diode shows during the lighting has temperature characteristics, and the forward voltage used for the determination is corrected based on the ambient temperature of the light emitting diode at the time of determination by the determination means The lighting device according to claim 1, wherein: Forward voltage measuring means for measuring the forward voltage of the light emitting diode during lighting of the light emitting diode;
Ambient temperature measuring means for measuring the ambient temperature upon determination by the determining means;
Measurement forward voltage correction means for correcting the forward voltage measured by the forward voltage measurement means based on the ambient temperature measured by the ambient temperature measurement means;
The lighting device according to claim 5, comprising:   The lighting device according to claim 1, wherein the predetermined magnitude is 10% of an initial forward voltage used in the determination.   The lighting device according to claim 1, wherein the output unit is a notification unit that notifies the user of the determination result. A switch for turning on and off the light emitting diode;
The lighting device according to any one of claims 1 to 8, wherein each unit is made to function as necessary every time the switch is turned on.

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