JP2012124345A - Drive control method of light-emitting diode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a drive control method of an LED.SOLUTION: In the drive control method of an LED, a drive control means 6 predicts the expected temperature to reach of a light-emitting diode 1 according to the temperature near the drive start time detected by a temperature sensor 4 and the drive conditions, and does not change the drive conditions if the expected temperature to reach is below the upper limit value of a set temperature range. If the expected temperature to reach is higher than the upper limit value of a set temperature range, the drive control means 6 changes the drive conditions from the difference of the expected temperature to reach and the upper limit value, and reduces the magnitude of the driving current so that the expected temperature to reach under the drive conditions thus changed falls within the set temperature range.

Description

  The present invention relates to a light emitting diode drive control method, and more particularly to a light emitting diode control method for controlling light emission luminance of a light emitting diode in consideration of a junction temperature of the light emitting diode.

Light-emitting diodes (LEDs) rise in temperature due to their own heat generation during driving and their surrounding components, so the junction temperature, that is, the temperature of the PN junction, for example, 120 ° C to 150 ° C, etc. ) If the temperature rises above, the LED will be damaged, so it must be driven without exceeding the maximum junction temperature, which is the limit.
For this reason, when driving an LED, it is necessary to detect the junction temperature at that time, but since an LED is generally covered with a protective member such as resin, the temperature of the LED is directly attached to detect the junction temperature. Difficult to do.

Therefore, in the conventional LED driving method, the junction temperature is indirectly detected by the following method, and the LED driving current is controlled according to the detected temperature.
That is, in general, in the diode, the forward voltage (Vf) varies in accordance with the temperature. For example, when the constant current is applied, the voltage (Vf) tends to decrease as the temperature increases. Therefore, utilizing this property, the forward voltage of the LED (Vf) is detected, the junction temperature of the LED is estimated from this voltage (Vf), and the estimated temperature is within a temperature range where the LED does not break down. There is known a method of controlling a drive current supplied to an LED so that a constant temperature close to the maximum temperature is obtained (see, for example, Patent Document 1).

  Another method is that there is a correlation between the temperature near the backlight (using the LED) detected using a temperature sensor located in the vicinity of the LED and the junction temperature of the LED. , Detected near temperature (less than 50 ° C, more than 50 ° C and less than 100 ° C, three temperature ranges of 100 ° C and more) and its temperature change (nearly over 50 ° C and less than 100 ° C, 0.5 ° C The brightness of the backlight is controlled by changing the magnitude of the drive current supplied to the LED in accordance with the temperature change of the backlight, and the backlight brightness is reduced when the neighborhood temperature is higher than the set temperature. It is known (see, for example, Patent Document 2).

JP 2004-214519 A JP 2007-219008

  However, the conventional LED drive control method has the following problems.

  In other words, in the conventional LED drive control method by the former, the junction temperature estimated based on the detected forward voltage (Vf) of the forward direction of the LED is a constant temperature close to the maximum temperature within the temperature range where the LED does not break down. Since the drive current is constantly reduced, held, and increased during drive control, the brightness of the LED, which is determined by the magnitude of the drive current, increases and decreases. Large fluctuations in brightness occur. As a result, there are problems that it is difficult for the user to see the display and that the reliability is uneasy.

  On the other hand, in the conventional LED drive control method according to the latter, the LED is driven at the maximum drive current when the near temperature is 50 ° C. or less, and when the near temperature exceeds 50 ° C. and less than 100 ° C. When the temperature rises by 0.5 ° C, the duty ratio is decreased to reduce the drive current, thereby increasing the drive current within this range, and at 100 ° C or higher, the duty ratio is set to zero and the LED drive is stopped. Therefore, when driving is started from a power-off state for a long time and the driving current becomes maximum, and during normal driving in which the driving current can be changed in the range of more than 50 ° C. and less than 100 ° C., A big change occurs in the brightness of the LED. As a result, there are problems that it is difficult for the user to see the display and that the reliability is uneasy.

As described above, in any of the above conventional LED driving methods, the driving current increases or decreases within a certain setting range, so that a large change in the luminance of the LED cannot be avoided. There is a point.
This problem will be described more specifically with reference to FIG. FIG. 6 shows a change in the drive current I supplied to the LED (shown in FIGS. 6A and 6C) and a change in the junction temperature T _J (corresponding to the ambient temperature) at that time (shown in FIG. 6B). ) And (shown in (d)). Here, in the figure, (a) and (b) are cases where the ambient temperature at the start of driving is relatively low, and (c) and (d) are cases where the ambient temperature at the start of driving is relatively high.

First, the case where the ambient temperature at the start of driving is relatively low will be described. In this case, FIG. (A), (b), the junction temperature T _J of the LED drive start (time t ₀₎ is equal to ambient temperature.
Drive current I is first example results that are driven at a duty rate of 100%, the junction temperature T _J of the correlation LED and vicinity temperature not shown is gradually risen sharply. If at time t ₁ the junction temperature T _J reaches the limit temperature T _L, the driving current I is reduced duty ratio is lowered to about 40%. As a result, the brightness of the LED decreases, but the junction temperature _TJ decreases, so that the LED can be prevented from being damaged. When the junction temperature T _J at time t ₂ is the return temperature T _{R (<T L),} since the duty ratio of the drive current I is increased to about 80%, the junction temperature T _J is gradually increased again. When at time t ₃ the junction temperature T _J reaches the limit temperature T _L, then the duty ratio decreases the driving current I is again about 40%. When the junction temperature T _J is the return temperature T _R at time t _4, thereby increasing the drive current I and the duty ratio to about 60%. Junction temperature T _J is at least while gently rises This setting remains within the set temperature range and the return temperature T _R with the limit temperature T _L.

On the other hand, when the ambient temperature at the start of driving is higher than the cases shown in FIGS. 9A and 9B, the drive is performed with a duty ratio of 100%, for example, as shown in FIGS. that the driving current I by the junction temperature T _J went rises rapidly until time t _5, wherein the drive current I is reduced to the duty ratio of about 40% can be allowed to decrease. Junction temperature T _J at time t ₆ the return temperature T becomes _R the duty ratio is increased up to about 80% drive current I is increased. When the junction temperature T _J reaches the limit temperature T _L at time t _7, the duty ratio is reduced to 40% to reduce the driving current I. When the junction temperature T _J is the return temperature T _R at time t _8, when although increasing the duty ratio, this time the ambient temperature at the time of temperature rise is the start of driving of the higher junction temperature T _J ambient temperature at the start of driving is low Because it is faster, the junction temperature T _J is gradually increased by setting it to about 50% lower than the 60% used when the ambient temperature is low, and at least for a while, the limit temperature T _L and the return temperature T _R And try to stay within range.

As described above, the magnitudes of the drive currents greatly differ according to the duty ratio between the times t ₁ and t ₅ immediately after the start of the drive and the drive current control in which the drive current is controlled so as to reduce the drive current thereafter. As a result, the brightness of the LED, which is determined by the magnitude of the applied drive current, also changes greatly.
In this case, as can be seen from the above description, the difference is particularly large when the ambient temperature at the start of driving is high. Such a large change in the luminance of the LED is not preferable for the user from the viewpoint of easy viewing and reliability of the device.
The present invention has been made paying attention to the above-mentioned problems, and the object of the present invention is to control the driving of a light emitting diode that can suppress a large change in the luminance of the LED from the start of driving to during driving. It is to provide a method.

For this purpose, the driving control method of the light emitting diode according to the present invention is:
A light emitting diode that emits light when a drive current is applied;
A temperature sensor capable of detecting the temperature near the light emitting diode;
Drive control means capable of variably controlling the magnitude of the drive current according to the vicinity temperature detected by the temperature sensor;
A drive control method for a light emitting diode drive device comprising:
The drive control means predicts the expected temperature reached by the light emitting diode according to the vicinity temperature at the start of driving detected by the temperature sensor and the driving condition for controlling the driving current,
If this expected temperature is below the upper limit of the set temperature range, the drive current is controlled without changing the drive conditions.
When the predicted temperature is higher than the upper limit of the set temperature range, the drive condition is changed based on the difference between the predicted temperature and the upper limit of the set temperature range, and the expected temperature reached under this changed drive condition is within the set temperature range. The size of the drive current was reduced to fit.
It is characterized by that.

  In the light emitting diode drive control method of the present invention, the predicted temperature reached is predicted from the vicinity temperature at the start of driving and the drive conditions for controlling the drive current, and this predicted temperature is less than or equal to the upper limit value of the set temperature range. In this case, the drive current is controlled without changing the drive conditions, and when the expected temperature reaches higher than the upper limit value of the set temperature range, the drive condition is changed based on the difference between the expected temperature and the upper limit value of the set temperature range. The drive current was reduced so that the expected temperature reached under the set drive conditions was within the set temperature range, so that the drive current did not change substantially from the start of drive to during the drive. It is possible to suppress a large change during the period. Therefore, it is possible to prevent the display or the like from being difficult to see due to a large change in the luminance of the light emitting diode or the user from being uneasy about the reliability of the light emitting diode.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram illustrating a configuration of an LED driving device for realizing a light emitting diode driving control method according to a first embodiment of the present invention. 3 is a control flowchart for executing the LED drive control method according to the first embodiment, which is executed by the LED drive device of FIG. 1. 2 is a control flowchart executed by the LED drive device of FIG. 1 and implementing the LED drive control method of Embodiment 1 when power is turned on again. The LED driving state of the LED driving device in Example 1 is shown, (a), (b) is a case where the ambient temperature is relatively low, (a) is the magnitude of the drive current applied to the LED at that time (B) is a diagram showing the junction temperature of the LED at that time. (C) and (d) are cases where the ambient temperature is relatively high, (c) shows the magnitude of the drive current applied to the LED at that time, and (d) shows the junction temperature of the LED at that time. FIG. The state at the time of LED redrive of the LED drive device in Example 1 is shown, (a), (b) is a case where ambient temperature is comparatively low, Comprising: (a) is the magnitude | size of the drive current applied to LED at that time FIG. 5B is a diagram showing the junction temperature of the LED at that time. (C) and (d) are cases where the ambient temperature is relatively high, (c) shows the magnitude of the drive current applied to the LED at that time, and (d) shows the junction temperature of the LED at that time. FIG. A conventional LED drive control method is shown, in which (a) and (b) are cases where the ambient temperature is relatively low, (a) shows the magnitude of the drive current applied to the LED at that time, and (b) It is a figure which shows the junction temperature of LED at that time, respectively. (C) and (d) are cases where the ambient temperature is relatively high, (c) shows the magnitude of the drive current applied to the LED at that time, and (d) shows the junction temperature of the LED at that time. FIG.

  Hereinafter, embodiments of the present invention will be described in detail based on examples shown in the drawings.

First, the overall configuration of the first embodiment will be described.
As shown in FIG. 1, an LED drive device that implements the light emitting diode (LED) drive control method of Embodiment 1 includes an LED array 1, an LED drive circuit 2, a brightness setting unit 3, a temperature sensor 4, and the like. , A temperature detection unit 5, a drive control unit 6, a prediction calculation unit 7, and a storage unit 8.

  The LED array 1 includes a plurality of LEDs 1a connected in series, emits light when a drive current is applied, and is used for a backlight of a display unit (not shown). This LED array 1 corresponds to a light emitting diode of the present invention.

  The LED drive circuit 2 generates a drive current having a pulse width modulation magnitude according to the duty ratio determined by the drive control unit 6, and applies this drive current to the LED array 1. As a result, the LED 1a emits light with a desired luminance.

  The brightness setting unit 3 is used to select and set the desired brightness of the LED array 1 by a button or switch (not shown), and the brightness setting signal corresponding to the selected brightness setting value is input to the drive control unit 6. To do.

  The temperature sensor 4 is disposed in the vicinity of the LED array 1, continuously generates an analog temperature signal current corresponding to the detected vicinity temperature, and inputs the analog temperature signal current to the temperature detection unit 5.

  The temperature detection unit 5 changes the temperature signal current detected by the temperature sensor 4 into a neighboring temperature signal as a corresponding digital value, and inputs it to the drive control unit 6 and the prediction calculation unit 7. In addition, this neighborhood temperature is used as a temperature corresponding to the junction temperature of the LED 1a, and when the difference between them is large, it is corrected based on a relationship obtained in advance through experiments and simulations, and this correction value is used. You may do it.

The drive control unit 6 uses the drive condition table stored in the storage unit 8 according to the brightness set value set by the brightness setting unit 3 and the neighborhood temperature obtained from the temperature detection unit 5 when the power is turned on. Set the drive conditions. Here, the drive condition is a condition for driving the LED array 1 based on the magnitude of the drive current, the duty ratio, and the like, and the optimum drive condition is set according to the magnitude of the brightness setting value. Then, in the driving condition, at least the magnitude of the drive current period from the start of driving to the junction temperature T _J of the LED array 1 settles stable, set to maintain a substantially constant value It is. These relationships are measured in advance through experiments or the like, and the drive condition table is constructed by finding the optimum values. In addition, it is determined whether to use or change the drive condition as it is according to the magnitude relationship between the predicted arrival temperature predicted by the prediction calculation unit 7 to be described later and the upper limit value of the set temperature range, and a drive that matches the drive condition. A command signal is input to the LED drive circuit 2.

  Based on the vicinity temperature obtained by the temperature detection unit 5 and the drive condition obtained by the drive control unit 7, the prediction calculation unit 7 generates heat and gradually settles and stabilizes when driven under this drive condition. The predicted arrival temperature is predicted, and the predicted arrival temperature signal obtained here is input to the drive control unit 6.

  The storage unit 8 stores the above driving condition table, the predicted near temperature calculated when driving of the LED driving device is stopped, and the driving conditions immediately before the stop, and can supply these data to the driving control unit 6 It is.

  The drive control unit 6 determines the drive conditions as described above. Further, the drive controller 6 further determines the vicinity temperature detected by the temperature detection unit 5 when restarting the startup, and the expected vicinity temperature stored in the storage unit 8 at the end of the previous drive. Depending on the magnitude of the difference, the drive condition stored at the end of the previous drive in the storage unit 8 is decided to be used as it is without change, or the drive command signal is sent to the LED drive circuit 2 There is also input.

When power is supplied to the LED driving device configured as described above, in the LED driving device, the temperature sensor 4 starts to send the detected temperature signal current of the LED array 1 to the temperature detecting unit 5, where the temperature T _C And is input to the drive control object 6 and the prediction calculator 7 as a detected proximity temperature signal. Then, LED drive control is executed according to the flowchart shown in FIG.

That is, in step S1, the drive control unit 6 and the prediction calculation unit 7 read from the temperature detection unit 5 the neighborhood temperature T _C at the time of power-on. The neighborhood temperature T _C (corresponding to the LED junction temperature T _J ) when the power is turned on is the same as the ambient temperature of the LED array 1.

In step S2, the drive control unit 6, Reads a luminance setting value B _R set by the user in the brightness setting portion 3.

In step S3, the drive controller 6, depending on the brightness setting value is set in the vicinity temperature T _C and the brightness setting portion 3 which is input from the temperature detecting section 5 B _R, driving conditions of the LED array 1 (driving Set the current magnitude and duty ratio.

In the subsequent step S4, the prediction calculation unit 7 predicts the predicted arrival temperature T _AP based on the neighborhood temperature T _C input from the temperature detection unit 5 and the drive conditions set by the drive control unit 6.

In subsequent step S5, the drive control unit 6 determines whether or not the expected temperature _TAP exceeds the upper limit temperature (upper limit value) T _L of the set temperature range under the above drive conditions. If the expected temperature T _AP does not exceed the upper limit value _TL of the set temperature range (when the determination is NO), the process proceeds to step S6, and if the expected temperature T _AP exceeds the upper limit value _TL of the set temperature range In the case of YES (YES), the process proceeds to step S9. Here, the upper limit value T _L is the maximum temperature at which the neighborhood temperature T _C does not destroy the LED 1a or a value slightly below it, and the set temperature range is the temperature near the LED array 1 after long-term driving. T _C as a reference to increase the duty ratio when the drops restoration temperature (lower limit) at a temperature range between T _R.

In step S6, the drive control unit 6 does not change the drive condition set in step S3, and the drive condition remains unchanged (at least a period of time from the start of the drive until the junction temperature T _J settles down is substantially constant) A drive current is generated in the LED drive circuit 2 by the current I), and the LED array 1 is driven.

  In the subsequent step S7, the drive control unit 6 determines whether or not the drive is finished. When the driving is not finished (in the case of NO), the process returns to step S6 to drive the LED array 1 under the same driving conditions as before and emit light. On the other hand, if the driving is completed (YES), the process proceeds to step S8.

In step S8, the drive control unit 6 measures the transition of the neighborhood temperature T _{C for} a certain time from the end of driving, and finally the neighborhood temperature T _C is determined from the change state of the neighborhood temperature T _C during this certain time. It predicts a stably settled expected near the temperature T _CP, stores it in the storage unit 8, and respectively stored using the driving conditions at step S6 and terminates the LED drive control. The expected near temperature T _CP corresponds to the ambient temperature when the LED array 1 and its peripheral components are sufficiently cooled and stabilized when the power is turned off.

On the other hand, in step S5, when the drive control unit 6 determines that the predicted temperature T _Ap exceeds the upper limit value _TL of the set temperature range (in the case of YES), the predicted target temperature T _AP is determined in step S9. set temperature range size and the duty ratio of the difference [Delta] T _S in basis the driving conditions the drive current of the upper limit value T _L is changed in the direction to decrease the upper limit value T _L of the set temperature range estimated arrival temperature T _AP Set new drive conditions that will not exceed.

In the subsequent step S10, the drive control unit 6 reduces the drive conditions newly set in step S9 (the period until the junction temperature T _J stabilizes at least from the start of the drive, while reducing the drive current magnitude and duty ratio) Generates a drive current in the LED drive circuit 2 at a substantially constant drive current I), drives the LEF array 1 to emit light.

In the subsequent step S11, the drive control unit 6 determines whether or not the drive is finished. When the driving is not finished (in the case of NO), the process returns to step S10, and the LED array 1 is driven to emit light without changing the driving condition newly set in step S9. On the other hand, in the case of the end of driving (in the case of YES), after proceeding to step S8, the predicted neighborhood temperature T _CP and the driving conditions used in step S10 are stored, and the LED driving control is ended.

  Next, FIG. 3 shows a flowchart executed when it is determined that the driving is finished in step S7 of FIG. In this case, as described below, after the restart is finished, it is determined whether or not the LED array 1 has sufficiently cooled down to the ambient temperature to optimize the drive conditions after the restart.

When power returns after the drive-end is turned on again, the temperature sensor 4 begins to send the detected temperature signal current of the LED array 1 continuously to the temperature detector 5, so that the vicinity of the temperature T _C is obtained here, LED The LED driving control is executed by the driving device along the flowchart shown in FIG.

First, in step S21, the drive control unit 6 reads the temperature near T _C at restart of the LED driving apparatus from the temperature detection unit 5.

In the subsequent step S22, the predicted ambient temperature _TCP stored at the end of the previous drive in step S8 of FIG. 2 is read.

Subsequent step S23, the temperature difference between the predetermined value [Delta] T _C between the ambient predicted temperature T _CP of the previous drive termination read out from the detected temperature signal T _C and the storage unit 8 at Restart read from the temperature detector 5 Judge whether there is. In the case the temperature difference is larger than the predetermined value [Delta] T _C (case of YES), determines that the LED array 1 is not fully down to yet sufficiently its ambient temperature, the previous drive end just before the driving conditions, i.e. storage unit 8 Then, the LED array 1 is driven under the same driving conditions without changing the driving conditions stored in step S8. That is, the process proceeds to step S6 in FIG. 2, and the LED array 1 is driven under the same driving conditions as before.
In contrast, if there is no temperature difference between the predetermined value [Delta] T _C between the neighboring temperature signal T _C and ambient predicted temperature T _CP last detected upon reboot (if NO), LED array 1 is sufficiently cooled Therefore, it is determined that the detected temperature T _C is substantially equal to the ambient temperature, the process proceeds to Step S2 in FIG. 2, the driving conditions stored in the storage unit 8 are read, and the expected temperature T _CP is predicted from these. Then, the process proceeds from the expected temperature T _CP and the upper limit value T _L to whether or not the drive condition is changed according to the flowchart of FIG.

An example of LED drive control executed according to the flowchart of FIG. 2 is shown in FIG. FIGS. 4A and 4B show the case where the ambient temperature is low when the power is turned on after the power is turned off for a long time, and FIGS. 4C and 4D show the surroundings when the power is turned on. Each case shows a high temperature. FIGS. 9A and 9C show the time transition of the magnitude of the LED driving current I, and FIGS. 9B and 9D show the vicinity temperature T _C (corresponding to the junction temperature T _{J of the} LED 1a). Each time transition is shown.

First, if the ambient temperature is low when the power is turned on, the expected temperature _TAP under the driving condition in which the duty factor is about 70% in step S3 does not exceed the upper limit (limit temperature) T _L of the set temperature range. Therefore, as shown in FIG. 5A, the drive current I is raised without changing the drive condition in which the duty ratio is 70% in step S3, and this value is maintained thereafter. As a result, as shown in FIG. (B), the drive starting time t ₀ the vicinity temperature was equal to (the same temperature as the temperature near T _C when the power supply ON after prolonged power OFF) ambient temperature is T _C ( Therefore, the element temperature T _J of the LED array 1) is rises risen sharply, the rate of increase gradually decreases gradually exceed the recovery temperature T _R which is the lower limit of the set range at time t _a After that, the temperature gradually approaches the limit temperature _TL which is the upper limit value of the set temperature range. However, since the driving conditions set duty ratio as described above, the temperature near T _C went close to the limit temperature T _L without exceeding the limit temperature T _L, approximately equal at time t _b, which thereafter the The value is kept stable. Therefore, the junction temperature of the LED 1a is kept at a value lower than the temperature at which the LED 1a is destroyed. In addition, since the drive current is not changed from the start of driving to the time of drive control, fluctuations in luminance of the LED array 1 are suppressed.

On the other hand, when the ambient temperature at the time of power-on is higher than that in FIG. 6A, as shown in FIG. 5C, the driving is performed under the new driving condition in which the duty ratio is reduced to, for example, 55% in step S9. Raise current I and keep this value thereafter. As a result, as shown in FIG. 4D, the neighborhood temperature T _{C which} is equal to the ambient temperature at the drive start time t ₀ rises rapidly and rises, but the rate of increase decreases the duty factor. Therefore, the ambient temperature is kept smaller than in the case of FIG. Moreover, rate of increase gradually decreases gradually, beyond the return temperature T _R of the set range at time t _c, approaches gradually to the limit temperature T _L which is the upper limit value of the set temperature range. However, since the driving condition in which a smaller duty ratio is set as described above is used, the near temperature T _C approaches the limit temperature T _L without exceeding the limit temperature T _L and becomes substantially equal at the time t _d , and thereafter, the value is stable. And kept. Therefore, the junction temperature of the LED 1a is kept at a value lower than the temperature at which the LED 1a is destroyed. In addition, since the drive current is not changed from the start of driving to the time of drive control, fluctuations in luminance of the LED array 1 are suppressed.

Next, FIG. 5 shows an example of LED drive control executed when the LED drive device is restarted, which is executed according to the flowchart of FIG. FIGS. 4A and 4B show the case where the difference between the near temperature T _C detected at the time of restart and the predicted ambient temperature T _CP obtained in step S8 and stored in the storage unit 8 is larger than a predetermined value ΔT _C. FIGS. 7C and 7D respectively show cases where the difference between the near temperature T _C detected at the time of restart and the expected ambient temperature T _C is equal to or less than a predetermined value ΔT _C. Further, FIG. (A), (c) shows a time transition of the magnitude of the LED drive current I, also FIG. (B), (d) is a time transition of the temperature near T _C respectively.

As shown in FIG. 6B, the temperature near the temperature T _C (shown as the drive resumption temperature T _{S in the} figure) detected at the time t _f after the driving is finished at the time t _e , and at step S8 when obtained the expected ambient temperature T _CP which has been stored in the storage unit 8, the temperature difference [Delta] T of greater than a predetermined value [Delta] T _C is, LED array 1 is not fully down yet to its ambient temperature, i.e. at the drive-end Therefore, it is estimated that the ambient temperature has hardly changed since it was restarted in a short time. Therefore, in this case, without changing the driving condition immediately before the end of driving stored in the storage unit 8, the driving condition is maintained as it is (for example, the driving current I with the same duty ratio of 70% as shown in FIG. To drive the LED array 1 to emit light. Therefore, the junction temperature of the LED 1a is kept at a value lower than the temperature at which the LED 1a is destroyed. In addition, since the magnitude of the drive current I is not changed from the start of driving to the time of drive control, fluctuations in luminance of the LED array 1 are suppressed.

On the other hand, as shown in FIG. 4D, the temperature near the temperature T _C detected at the time t _g (> t _f ) at which the driving ends at the time t _e and then restarts (in the figure, as the driving resumption temperature T _S and shown), the expected ambient temperature T _CP which has been stored in the storage unit 8 are obtained in the step S8, when the temperature difference [Delta] T of greater than a predetermined value [Delta] T _C is passed since sufficient time from the time of the drive-end, LED array Since the temperature of 1 has sufficiently decreased to or near that ambient temperature, the ambient temperature may have changed significantly. Therefore, as shown in FIG. 6C, for example, the drive current I is driven under a new drive condition in which the duty ratio at the end of the previous time is increased from 70% to a duty ratio of 80%. Therefore, the junction temperature of the LED 1a is kept at a value lower than the temperature at which the LED 1a is destroyed. In addition, since the magnitude of the drive current I is not changed from the start of driving to the time of drive control, fluctuations in luminance of the LED array 1 are suppressed.

Thus, in the LED driving device of the present embodiment, the expected arrival temperature T _AP of the LED array 1 is predicted according to the vicinity temperature T _C at the start of driving detected by the temperature sensor 4 and the driving conditions, If the expected temperature T _AP is less than the upper limit value T _L of the set temperature range, the driving conditions are not changed.If the expected temperature T _AP is higher than the upper limit value T _L of the set temperature range, the expected temperature T _AP is Since the drive condition was changed from the difference ΔT with the upper limit value T _L and the expected current temperature T _{AP under} this changed drive condition was reduced within the set temperature range, the magnitude of the drive current was reduced. It is possible to keep the drive current substantially constant during the drive control period from the start until at least the junction temperature TJ of the LED array 1 stabilizes, and as a result, a large change in the brightness of the LED array 1 can be achieved during this period. It can be suppressed and is easy for the user to see It is possible to improve the reliability of the display and LED.

  Further, since the driving condition can be set in consideration of the luminance of the LED array 1 set by the user in the luminance setting unit 3, a display that is easy for the user to see is possible.

Further, when the driving of the LED array 1 is finished, a change in the neighborhood temperature T _C after a predetermined time from the end of the driving is detected, and the expected neighborhood temperature T _AP where the temperature of the LED array 1 decreases and stabilizes stably by the end of the driving. in anticipation of storing the driving condition at the end immediately before this predicted temperature near T _AP, upon restart of the LED driving device, the expected temperature near that stores the temperature near T _C detected by the temperature sensor 4 to the restart T _AP and difference drives the LED array 1 by the driving current I of the driving conditions at the end just before is greater than a predetermined value [Delta] T _C, upon restart of the LED driving device, detected by the temperature sensor 4 to the restart The LED array 1 is driven by the driving current I obtained by changing the driving condition immediately before the end when the difference between the measured neighboring temperature T _C and the stored predicted neighboring temperature T _AP is equal to or smaller than the predetermined value ΔT _C. As a result, the temperature of the LED array 1 drops to the ambient temperature in a short time after the restart is completed. Or state of no, or a temperature of the LED array 1 can determine whether sufficient lowered state until ambient temperature, it is possible to determine the optimum driving conditions according to the determination result.

  The present invention has been described based on the above embodiments. However, the present invention is not limited to these embodiments, and is included in the present invention even when there is a design change or the like without departing from the gist of the present invention. .

  For example, in the LED array 1 of the present embodiment, the light emitting diode of the present invention has a plurality of LEDs arranged in one column, but the LEDs may be arranged in a plurality of columns or may be composed of only one LED.

  Further, the LED drive control method of the present invention may be set to take a value different from the duty ratio of the above embodiment.

DESCRIPTION OF SYMBOLS 1 LED array 2 LED drive circuit 3 Brightness setting part 4 Temperature sensor 5 Temperature detection part 6 Drive control part 7 Prediction calculation part 8 Memory | storage part

Claims (3)

A light emitting diode that emits light when a drive current is applied;
A temperature sensor capable of detecting the temperature in the vicinity of the light emitting diode;
Drive control means capable of variably controlling the magnitude of the drive current according to the vicinity temperature detected by the temperature sensor;
A drive control method for a light emitting diode drive device comprising:
The drive control means predicts an expected arrival temperature of the light emitting diode according to a temperature near the start of driving detected by the temperature sensor and a driving condition for controlling the driving current,
If the expected temperature is below the upper limit value of the set temperature range, the drive current is controlled without changing the drive condition,
When the predicted temperature reached is higher than the upper limit value of the set temperature range, the drive condition is changed from the difference between the predicted temperature reached and the upper limit value of the set temperature range, and the predicted temperature reached under the changed drive condition is The magnitude of the drive current is reduced so as to be within the set temperature range.
A drive control method for a light-emitting diode. The light emitting diode drive control method according to claim 1,
The driving condition is set according to the brightness setting value of the light emitting diode in addition to the vicinity temperature,
A drive control method for a light-emitting diode. In the drive control method of the light emitting diode according to claim 1 or 2,
When the driving of the light emitting diode is completed, a change in the vicinity temperature after a predetermined time from the end of the driving is detected, and an expected near temperature at which the temperature of the light emitting diode decreases and stabilizes stably is predicted. Memorize the expected near temperature and the driving conditions just before the end,
When the light emitting diode driving device is restarted, if the difference between the vicinity temperature detected by the temperature sensor at the time of restarting and the stored predicted vicinity temperature is larger than a predetermined value, the driving current under the driving condition immediately before the end To drive the light emitting diode,
When the light emitting diode device is restarted, if the difference between the vicinity temperature detected by the temperature sensor at the time of restart and the stored predicted vicinity temperature is equal to or less than the predetermined value, the driving condition immediately before the end time is changed. The light emitting diode was driven with the obtained drive current.
A drive control method for a light-emitting diode.

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