JP2012129050A - Light-emitting device, method for driving light-emitting element, and luminaire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light-emitting device which allows low-cost compensation of the deterioration in the brightness of a light-emitting element with a simple structure, which can keep a fixed brightness even with the connected light-emitting element having a different light emission efficiency, and respond at a high speed with the aid of direct control, and to provide a method for driving the light-emitting element, and a luminaire having the light-emitting element.SOLUTION: The light-emitting device comprises: a light-emitting element; pulse width modulation means for producing a rectangular wave pulse signal; a driving unit for producing a driving current for driving the light-emitting element based on the pulse signal; optical detection means for photoelectric conversion of at least part of light emitted by the light-emitting element; and correction coefficient generation means for calculating a correction coefficient for correcting the duty of the pulse signal based on a value of reciprocal output of the optical detection means with the driving current kept ON. The pulse width modulation means changes the duty based on the correction coefficient and a modulation coefficient.

Description

  The present invention relates to a light-emitting device that stably drives a light-emitting element based on the principle of organic electroluminescence, a method for driving such a light-emitting element, and a lighting device equipped with such a light-emitting element.

  The organic EL light-emitting element is expected to spread as a single light-emitting element or a display. As a single light emitting device, replacement of a fluorescent lamp is aimed at by taking advantage of low power consumption, high luminance and the like. Since the display has advantages such as thinness, high brightness, wide viewing angle, and high display response speed, it is expected as a self-luminous thin display that replaces the plasma display.

  However, it is known that the luminous efficiency (brightness-current density characteristics) of the organic EL light emitting element deteriorates as the driving time elapses and the brightness decreases.

  In order to drive an organic EL light emitting element with a constant luminance, development of an organic EL material with little deterioration is one means. However, in order to quickly bring an organic EL light emitting element to the market, the luminous efficiency of the organic EL light emitting element can be improved. It is important to develop technology that compensates for deterioration and obtains constant brightness.

  In a technique for obtaining a constant luminance by compensating for deterioration in luminous efficiency, for example, a correction coefficient corresponding to the accumulated deterioration time is stored in a table memory, and the drive condition is set according to the accumulated deterioration time based on the correction coefficient. A technique for performing correction has been proposed (see Patent Document 1).

  In addition, a technique has been proposed in which a luminance detection sensor is provided and control is performed to achieve target luminance based on the output (see Patent Document 2).

  Furthermore, a technique for PWM control based on the luminance peak value amount has been proposed (see Patent Document 3).

JP 2005-128272 A JP 2007-183397 A JP 2008-262032 A

  The technique described in Patent Document 1 requires a memory for storing a correction coefficient prepared for each light emitting element, which increases the cost, and has a problem that the variation in luminance between the light emitting elements cannot be made uniform.

  Since the technique described in Patent Document 2 is targeted for the average luminance, an integration circuit for averaging the luminance is required, resulting in high cost, and by performing feedback control to the target luminance. There is a problem that the response speed is slow.

  The technique described in Patent Document 3 has a problem that repeated feedback control is required and the response speed is poor, and a problem that the cost is high on the assumption that data memory is used.

  The present invention has been made in view of such a situation, and can compensate for deterioration in luminance of a light-emitting element at a low cost with a simple configuration, and maintains constant luminance even when light-emitting elements having different light-emitting efficiencies are connected. It is another object of the present invention to provide a light emitting device capable of high-speed response by direct control, a driving method of such a light emitting element, and a lighting device equipped with such a light emitting element.

  The above object is achieved by the invention described below.

1. A light emitting element;
Pulse width modulation means for generating a rectangular wave pulse signal;
Based on the pulse signal, a drive unit that generates a drive current in the form of a pulse signal that drives the light emitting element;
A light emitting device comprising:
A light detecting means for photoelectrically converting at least a part of the light emitted by the light emitting element;
Correction coefficient generating means for generating a correction coefficient for correcting the duty of the pulse signal based on the reciprocal value of the output of the light detection means when the drive current is ON;
Modulation coefficient generation means for generating a modulation coefficient used for calculation with the correction coefficient when correcting the duty of the pulse signal,
The light-emitting device, wherein the pulse width modulation means changes the duty based on the correction coefficient and the modulation coefficient.

  2. 2. The light emitting device according to 1 above, further comprising a first external volume for adjusting a peak value of the driving current.

3. A second external volume for adjusting the correction coefficient;
3. The light emitting device according to 1 or 2, wherein the pulse width modulation unit changes the duty based on an output value of the second external volume.

4). A third external volume for adjusting the modulation coefficient;
4. The light emitting device according to claim 1, wherein the pulse width modulation unit changes the duty based on the correction coefficient and a modulation coefficient modulated by the third external volume. 5. .

5. The third external volume can further adjust the peak value of the drive current, and is configured such that the direction in which the peak value of the drive current increases or decreases is opposite to the increase or decrease of the modulation coefficient,
5. The light emitting device according to 4, wherein the correction coefficient is increased or decreased in the same direction with respect to increase or decrease of the modulation coefficient according to an output value of the third external volume.

  6). 6. The light emitting device according to any one of 1 to 5, further comprising bias setting means for setting a value when the driving current is OFF.

  7). The light emitting device according to any one of 1 to 6, further comprising a life detection notification unit that notifies the outside when the duty changed by the pulse width modulation unit reaches a threshold value.

  8). 8. The light emitting device according to any one of 1 to 7, wherein an input to the correction coefficient generation unit is an analog DC voltage.

  9. The light emitting device according to any one of 1 to 8, wherein the correction coefficient is an analog DC voltage.

  10. The light emitting device according to any one of 1 to 9, wherein an initial duty of the pulse signal is 90% or less.

  11. The light emitting device according to any one of 1 to 9, wherein an initial duty of the pulse signal is 70% or less.

  12 The light emitting device according to any one of 1 to 11, wherein the light emitting element is an organic electroluminescence element.

  13. An illumination device comprising the light-emitting device according to any one of 1 to 12 above.

14 Generating a rectangular wave pulse signal;
Generating a driving current for driving the light emitting element based on the pulse signal;
A method for driving a light emitting device having
Photoelectrically converting and outputting at least part of the light emitted by the light emitting element;
Calculating a correction coefficient for correcting the duty of the pulse signal based on the inverse value of the photoelectrically converted output when the drive current is ON;
Changing the duty based on the correction factor;
A method for driving a light emitting element, comprising:

  Light emitting device capable of compensating for luminance degradation of light emitting element at low cost with a simple configuration, maintaining constant luminance even when connecting light emitting elements having different light emitting efficiencies, and capable of high-speed response by direct control, and such light emitting element Driving method, and a lighting device including such a light emitting element can be provided.

It is an example of the graph which shows the relationship between the electric current of a light emitting element and a brightness | luminance which used the degradation condition as a parameter. It is a block diagram which shows the electric constitution of the light-emitting device 100 using the light emitting element in 1st Embodiment. FIG. 5 is an explanatory diagram for explaining the principle that the average luminance of light emitted from the light emitting element 10 can be made constant even when the light emitting element 10 is deteriorated. 1 is a schematic view of a lighting device 200 using a light emitting device 100. FIG. It is a block diagram which shows the electric constitution of the light-emitting device 100 in 2nd Embodiment. FIG. 3 is an explanatory diagram in which the life of the light emitting device 100 is added to FIG. It is a block diagram which shows the electric constitution of the light-emitting device 100 in 3rd Embodiment. It is explanatory drawing explaining the principle which controls the average brightness | luminance which the light emitting element 10 light-emits by controlling the duty of a drive current according to the output from volume vol2. It is a block diagram which shows the electric constitution of the light-emitting device 100 in 4th Embodiment. FIG. 6 is an explanatory diagram illustrating a function of a bias setting unit 31. It is a block diagram which shows the electric constitution of the light-emitting device 100 in 5th Embodiment. It is explanatory drawing explaining the principle which controls the average brightness | luminance which the light emitting element 10 light-emits by controlling the duty of a drive current according to the output from volume vol3. It is a block diagram which shows the electric constitution of the light-emitting device 100 in 6th Embodiment. It is explanatory drawing explaining the principle which controls the average brightness | luminance which the light emitting element 10 light-emits by controlling the duty and magnitude | size of a drive current according to the output from volume vol3. It is an electric block diagram of embodiment containing all the above embodiments.

(First embodiment)
Hereinafter, a light-emitting device, a driving method of a light-emitting element, and a lighting device according to the present invention will be described with reference to the drawings. In addition, the same code | symbol is attached | subjected to the part which is the same in an embodiment, a specific example, or a corresponding part, and duplication description is abbreviate | omitted suitably.

  FIG. 1 is an example of a graph showing the relationship between the current of the light emitting element and the luminance with the degradation state as a parameter. The horizontal axis represents a relative current value, and the vertical axis represents a relative luminance value. The relationship between the current of an organic EL element (hereinafter referred to as a light emitting element) and luminance will be described with reference to FIG.

  As shown in the figure, the current and the luminance are positively correlated. The relationship between the current and the luminance changes depending on the deterioration state of the light emitting element (initial stage, that is, no deterioration, 30% deterioration, 50% deterioration). Specifically, the luminance decreases as the deterioration progresses. Note that although temperature also affects the relationship between current and luminance, in this specification, the relationship between current and luminance due to temperature change is included in the relationship between current and luminance due to deterioration of a light-emitting element.

  As described above, since the current and the luminance have a positive correlation, when the light emitting element is driven with the pulse current, the luminance is also pulsed. When the light emitting element is driven with a pulse current, the average current of the pulse current is obtained by multiplying the current value when the drive current is ON, that is, the current peak value of the pulse train, by the duty when the drive current is ON. Similarly, the average luminance of light emitted from the light emitting element is obtained by multiplying the luminance when the drive current is ON, that is, the luminance peak value by the duty.

  When the light emitting element deteriorates, as shown in the figure, the conversion efficiency for converting from current to light decreases, so when the same pulse current continues to flow, the luminance peak value decreases as the light emitting element deteriorates. As a result, the average brightness decreases.

  Here, the average luminance changes according to the total current for driving the light emitting element. Therefore, the average luminance can be changed by changing the duty of the pulse current or changing the current peak value of the pulse train. Specifically, for example, when the duty is increased, the average luminance increases, and when the current peak value of the pulse train is decreased, the average luminance decreases. Thus, the average luminance is controlled by the duty and the current peak value.

  Table 1 shows the relationship between the current peak value, the luminance peak value, and the duty for maintaining the average luminance at a constant value for each deterioration state of the light emitting element.

  The initial 1 is a case where there is no deterioration, and it is assumed that the luminance peak value becomes the reference value 100% when the current peak value is the reference value 100%. It is assumed that the duty is 100% (that is, direct current) and the average luminance is a reference value of 100%.

  In the initial stage 2, it is assumed that the element is not deteriorated as in the initial stage 1. When the current peak value is 200%, which is twice as large as the initial current peak value, since the device has deteriorated, the photoelectric conversion efficiency does not deteriorate and the luminance peak value becomes 200%. In order to set the average luminance to the reference value of 100% as in the initial stage 1, the duty may be set to 50%.

  When the element degradation is 30%, the photoelectric conversion efficiency is degraded by 30%. Therefore, when the current peak value is 200%, the luminance peak value is 140%. In order to set the average luminance to the reference value of 100% as in the initial stage 1, the duty should be set to 71.4%.

  When the element degradation is 50%, the photoelectric conversion efficiency is degraded by 50%. Therefore, when the current peak value is 200%, the luminance peak value is 100%. In order to set the average luminance to the reference value of 100% as in the initial stage 1, the duty may be set to 100%.

  Thus, it can be seen that the average luminance can be controlled by the current peak value and the duty according to the deterioration state.

  Note that the duty being 100% indicates that the duty cannot be controlled to maintain the average luminance any more. Therefore, the average luminance decreases as the element further deteriorates.

  FIG. 2 is a block diagram illustrating an electrical configuration of a light-emitting device (hereinafter, referred to as a light-emitting device) 100 using the light-emitting element according to the first embodiment.

  The light emitting device 100 includes a light emitting element 10, a constant luminance circuit 20, a constant current pulse driving circuit 40, and an optical sensor 30.

  The light emitting element 10 is an organic EL element as described above.

  The optical sensor 30 is a light detection means, and for example, a photodiode can be adopted. Other than the photodiode, any device that can measure the power of light can be used. For example, a calorimeter based on the principle of a photothermal conversion material may be used. The optical sensor 30 is disposed so as to receive at least part of the light from the light emitting element 10.

  The constant luminance circuit 20 includes an amplifier circuit 21, a sample hold circuit 22, a correction coefficient generation circuit 23, a reference pulse generation circuit 24, a sampling gate generation circuit 25, a comparison signal generation circuit 26, and a PWM circuit 27. The constant luminance circuit 20 may be a digital circuit or a circuit in which an analog circuit and a digital circuit are mixed. Hereinafter, the constant luminance circuit 20 will be described as an analog circuit.

The amplifier circuit 21 is a circuit that amplifies the input voltage. As a circuit, the gain is set so that the output of the optical sensor 30 at the reference luminance (for example, 1000 cd / m ² ) is amplified to a predetermined output (for example, 1 V).

  The reference pulse generation circuit 24 is a circuit that generates a rectangular wave pulse signal having a predetermined period. The reference pulse is used to generate a sampling gate and a comparison signal. The frequency of the reference pulse is the frequency of the PWM output and the drive current pulse. Note that there is a possibility that problems such as flickering occur if the frequency of the drive current pulse for driving the light emitting element is too low, and problems that the light emitting element cannot follow if the frequency is too high. In this embodiment, the reference pulse is a rectangular wave having a frequency of 120 Hz and a duty of 50%.

  Based on the reference pulse input from the reference pulse generation circuit 24, the sampling gate generation circuit 25 samples the timing at which the sample hold circuit 22 samples the value when the drive current is ON from the pulse voltage input from the amplifier circuit 21. It is a circuit that generates a sampling gate. The sampling gate is a signal synchronized with the drive current pulse, and is set to be shorter than the ON period of the drive current so that only the value when the drive current is ON can be held. Here, the sampling gate is generated as a rectangular wave having a frequency of 120 Hz and a duty of 5% in synchronization with the drive current pulse.

  The sample hold circuit 22 is a circuit that holds the peak value of the voltage input from the amplifier circuit 21 and outputs it as an analog DC voltage. That is, based on the sampling gate generated by the sampling gate circuit 25 from the output of the optical sensor 30 amplified by the amplifier circuit 21, the voltage when the drive current is ON is held and output.

  A low pass filter may be added to the amplifier circuit 21 or the sample hold circuit 22 so as not to detect instantaneous noise as a peak value.

  The correction coefficient generation circuit 23 calculates a reciprocal value of the input voltage from the sample hold circuit, that is, a reciprocal value of a value obtained by amplifying the output of the optical sensor 30 when the drive current is ON by the amplifier circuit 21 to obtain a constant voltage as a correction coefficient. It is a circuit as correction coefficient generation means for generating a value.

  The input from the sample hold circuit 22 to the correction coefficient generation circuit 23 is an analog DC voltage, and the correction coefficient generation circuit 23 is an analog circuit that can process this DC voltage.

  The comparison signal generation circuit 26 generates a modulation coefficient that is a triangular wave signal having the same cycle as the rectangular wave input from the reference pulse generation circuit 24 and the same 1 V triangular wave signal as the predetermined output of the amplifier circuit 21 at the time of reference luminance. It is a generation means.

  A PWM (Pulse Width Modulation) circuit is a pulse width modulation unit that generates a rectangular wave pulse signal while correcting the duty based on the correction coefficient.

  Specifically, the PWM circuit compares the correction coefficient, which is a constant voltage value, and the triangular wave signal, which is a modulation coefficient, which is an output from the comparison signal generation circuit 26, and compares them to the same value. A rectangular wave-like pulse signal whose amplitude changes at is output.

  The constant current pulse drive circuit 40 receives a rectangular wave pulse signal input from the constant luminance circuit 20, and generates a pulse signal drive current to drive the light emitting element 10, thereby driving a constant current drive unit 41. And volume vol1 (first external volume).

  The volume vol1 is, for example, a rotary knob, and the peak value of the drive current can be controlled by rotating the rotary knob. Note that the volume described below including the volume vol1 also has a circuit for generating a current as an output.

  FIG. 3 is an explanatory view for explaining the principle that the average luminance of the light emitted from the light emitting element 10 can be made constant even if the light emitting element 10 is deteriorated.

  3A shows a state in which the light emitting element 10 is in an initial state and has not deteriorated, and FIG. 3B shows a state in which the light emitting element 10 has deteriorated 30% compared to the initial state. FIG. 3C shows a state in which the light emitting element 10 is degraded by 50% compared to the initial state.

  In each figure, the horizontal axis is the volume vol1, the current peak value, the luminance peak value, the correction coefficient and the modulation coefficient, the driving current of the light emitting element 10, the luminance of the light emitting element 10, and the average luminance of the light emitting element 10 from the left. Yes.

  The vertical axis shows values when each reference value is 100%.

  The difference in line type in each figure is that, except for the modulation coefficient, the solid line is when the volume vol1 is the reference value (100%), the dotted line is when the volume vol1 is 150%, the one-dot chain line is when the volume vol1 is 200%, A two-dot chain line indicates a case where the volume vol1 is 300%. Since the drive current and the like are also determined by the characteristics of the light emitting element 10 itself, the following will be described only by comparison with each reference value.

  FIG. 3A will be described. When the volume vol1 is changed from the outside in four stages from the reference value 100% to 150%, 200%, and 300%, the current peak for driving the light emitting element 10 changes as shown in the figure at the same rate. Since it is an initial state with no deterioration, the luminance peak value also changes in the same manner. The constant voltage corresponding to the correction coefficient is 100% when the value of the volume vol1 is a reference value, 66.7% when the value of the volume vol1 is 150%, and 200% when the value of the volume vol1 is 200%. When the value of volume vol1 is 300%, the value is 33.3%.

  In the PWM circuit 27, based on the correction coefficient that is a constant voltage value and the triangular wave signal that is the modulation coefficient of the output from the comparison signal generation circuit 26, the amplitude changes when both are compared and become the same value. A rectangular wave pulse signal is generated. This rectangular wave-shaped pulse signal is input to the constant current pulse driving circuit 40 to generate a rectangular wave-shaped pulse driving current whose duty is adjusted. In the figure, the circuit configuration is such that when the correction coefficient is small with respect to the modulation coefficient, the drive current is 0%, and when the correction coefficient is large with respect to the modulation coefficient, the drive current has a current peak value. Accordingly, when the correction coefficient is smaller than the modulation coefficient, a pulse signal-like drive current with a smaller duty is generated.

  The luminance of the light emitting element 10 has the same waveform as the drive current because the light emitting element 10 is not deteriorated.

  As for the average luminance, since there is no deterioration of the light emitting element 10, there is no deterioration in the average luminance when the volume vol1 is the reference value 100%. Even when the value of the volume vol1 is increased, the magnitude of the luminance peak value and the magnitude of the duty cancel each other, so that a constant value is maintained.

  Next, FIGS. 3B and 3C will be described. In FIG. 3B, since the light emitting element 10 is in a state of 30% deterioration, the luminance peak value is deteriorated by 30% with respect to the current peak value. Since the correction coefficient increases, the intersection between the correction coefficient and the modulation coefficient changes. For this reason, the duty of the drive current also changes, but since the magnitude of the luminance peak value and the magnitude of the duty cancel each other as described above, the average luminance is maintained at a constant value.

  However, when the volume vol1 is the reference value of 100%, the correction coefficient and the modulation coefficient do not cross each other, so that the drive current becomes DC, and the decrease in the luminance peak value due to deterioration cannot be offset, and the average luminance decreases. As shown in FIG. 3C, when the deterioration of the light emitting element 10 further progresses to 50%, the volume vol1 is 150%. Since the correction coefficient and the modulation coefficient do not cross each other, the average luminance decreases for the same reason as described above.

  FIG. 4 is a schematic diagram of a lighting device 200 using the light emitting device 100. FIG. 4A is a schematic diagram of the light emitting device 100. FIG. 4B is a schematic view in which the light emitting device 100 is arranged on the ceiling of the room.

  In FIG. 4A, since the light receiving surface of the light sensor 30 is disposed toward the light emitting surface of the light emitting element 10, the light sensor 30 can receive light from the light emitting element 10 efficiently. Since the size of the photosensor 30 is sufficiently smaller than the size of the light emitting element 10, there is no problem in terms of utilization efficiency of light emitted from the light emitting element 10. In addition, it is desirable that more light can be illuminated if the light receiving surface of the optical sensor 30 is arranged so as to receive light emitted from the light emitting element 10 at a large emission angle without facing the light emitting element 10.

  The volume vol1 is used to control the peak value of the drive current. For example, the peak value of the drive current may be adjusted by a different method without using the volume vol1 at the time of factory shipment. In such a case, setting of volume vol1 is unnecessary. Such a different method includes, for example, adding a circuit capable of adjusting a current value by adjusting a resistance value.

  As described above, it is possible to compensate for the deterioration of the luminance of light emitting elements at a low cost with a simple configuration, and to maintain a constant luminance even when connecting light emitting elements with different luminous efficiencies, and to enable high-speed response by direct control It is possible to provide a device, a driving method of such a light emitting element, and a lighting device equipped with such a light emitting element.

(Second Embodiment)
In the second embodiment, the function of notifying that the lifetime has come to the light emitting device 100 is added to the first embodiment, thereby providing an opportunity to prompt the user to replace the light emitting element 10. Therefore, the light emitting device 100 in which the average luminance is always maintained is obtained.

  FIG. 5 is a block diagram illustrating an electrical configuration of the light emitting device 100 according to the second embodiment.

  In FIG. 5, life detection notification means 50 is newly added to the electrical block diagram of FIG.

  The life detection notification means 50 includes a life detection unit 51 and a notification unit 52.

  The life detection unit 51 has a function of sending a command to the notification unit 52 when the duty in the PWM circuit 27 reaches a threshold value.

  Specifically, as described above, when the duty becomes 100% as the light emitting element 10 is deteriorated, the average luminance is decreased due to the deterioration of the light emitting element 10, and therefore the duty is 100%. When it becomes, it judges that the life has come and sends a command to the notification unit 52.

  The notification unit 52 may be, for example, a light emitting unit including an LED (light emitting diode), a sound generation unit including a speaker, or both of them.

  For example, the notification unit 52 having an LED, which has received a command from the life detection unit 51, informs the outside that the life has reached by emitting light. Since the user can recognize that the lifetime of the light emitting element 10 has come, the light emitting element 10 can be replaced at a timing when the average luminance starts to decrease.

  FIG. 6 is an explanatory diagram in which the lifetime of the light emitting device 100 is added to FIG.

  In FIG. 6A, when the value of the volume vol1 is the reference value 100%, the correction coefficient and the modulation coefficient are in contact with each other, and the average luminance starts to decrease due to future deterioration. Can be judged to have arrived.

  In FIG. 6B, when the value of the volume vol1 is the reference value of 100%, the deterioration has progressed and the decrease in the luminance peak value due to the deterioration cannot be offset by the luminance peak value, and the average luminance is decreased. Resulting in. Accordingly, when the value of the volume vol1 is the reference value 100%, it can be determined that the life has come to an end, so that the life detection notification means 50 continues to notify.

  In FIG. 6C, even when the value of the volume vol1 is further the reference value 150% and 200%, the correction current and the modulation coefficient do not cross or are in contact with each other, so that the drive current becomes DC. The decrease in the luminance peak value due to deterioration cannot be offset, and the average luminance decreases. Therefore, when the value of the volume vol1 is 150% or 200% of the reference value, it can be determined that the life has come, so the life detection notification means 50 notifies.

  In order to cancel out that the luminance peak value decreases due to the deterioration of the light emitting element 10, the duty needs to be 100% or less. The smaller the duty is, the larger the margin for canceling the decrease in the luminance peak value is. For example, the initial duty is desirably 90% or less, and more desirably, the initial duty is 70% or less.

  As described above, according to the second embodiment, there is an opportunity to promote replacement of the light emitting element 10 by adding a function of notifying that the lifetime of the light emitting device 100 has been reached to the first embodiment. The light emitting device 100 that is provided and in which the user always maintains the average luminance can be obtained. In addition, it is possible to avoid power loss that occurs when the light emitting element 10 that has reached the end of its life is continuously used.

(Third embodiment)
In the third embodiment, the average luminance of the light-emitting element 10 can be controlled by changing the duty of the current applied to the light-emitting element 10 from the outside using a volume, compared to the first embodiment. To do.

  FIG. 7 is a block diagram illustrating an electrical configuration of the light emitting device 100 according to the third embodiment.

  In FIG. 7, the volume vol2 (second external volume) is newly added to the electrical block diagram of FIG. 2, and the volume vol2 is adjusted to the value output from the sample hold circuit to the correction coefficient generation circuit 23. The value is to be multiplied.

  FIG. 8 is an explanatory diagram for explaining the principle of controlling the average luminance emitted by the light emitting element 10 by controlling the duty of the drive current in accordance with the output from the volume vol2.

  8A shows a state in which the light emitting element 10 is in an initial state and has not deteriorated, and FIG. 8B shows a state in which the light emitting element 10 has deteriorated 30% compared to the initial state. FIG. 8C shows a state in which the light emitting element 10 is degraded by 50% compared to the initial state.

  When the user adjusts the volume vol2, the output from the volume vol2 can be adjusted as shown in each diagram of FIG.

  In the present embodiment, the magnitude of the correction coefficient is set to be 1.5 times the magnitude of the correction coefficient in the first embodiment by adjusting the volume vol2. However, the numerical value of 1.5 is an exemplary value for explaining the present embodiment, and it is needless to say that other numerical values including 1 or less may be used.

  When the output from the volume vol2 is adjusted, the magnitude of the correction coefficient changes, the intersection of the correction coefficient and the modulation coefficient changes, and the duty of the rectangular wave pulse signal output from the PWM circuit 27 is also 1.5. The duty of the drive current for driving the light emitting element 10 also changes to 1.5 times. Therefore, the average luminance of the light emitting element 10 also changes by 1.5 times.

  In FIG. 8A, when the value of the volume vol1 is the reference value 100%, the duty cannot be increased to increase the average luminance. When the value of the volume vol1 is 150%, 200%, or 300%, the duty is widened, and the average luminance is adjusted and maintained at 1.5 times set by the volume vol2.

  In FIG. 8B, when the value of the volume vol1 is the reference value 100%, 150%, 200%, the correction coefficient is equal to or greater than the modulation coefficient over the entire period, so that the drive current becomes direct current, and the luminance peak due to deterioration. The decrease in value cannot be offset, and the average brightness decreases. However, when the value of the volume vol1 is the reference value 300%, the duty is increased and the average luminance is adjusted and maintained at 1.5 times set by the volume vol2.

  In FIG. 8C, when the value of the volume vol1 is further the reference value of 300%, the duty is widened, and the average luminance is adjusted and maintained at 1.5 times set by the volume vol2.

  As described above, the average luminance of the light emitting element 10 can be controlled by changing the duty of the current applied to the light emitting element 10.

(Fourth embodiment)
In the fourth embodiment, in contrast to the first embodiment, the bias component of the current pulse train applied to the light emitting element 10 is controlled to flow a negative current, that is, a current in the reverse direction. The purpose is to improve the lifespan.

  FIG. 9 is a block diagram showing an electrical configuration of the light emitting device 100 according to the fourth embodiment.

  In FIG. 9, a bias setting unit 31 is newly added to the electrical block diagram of FIG. 2 to add a bias component to the OFF value of the pulse signal output from the PWM circuit 27, and the bias component is biased. The setting unit 31 is configured to decrease.

  FIG. 10 is an explanatory diagram for explaining the function of the bias setting unit 31. 2A shows the waveform of the pulse signal output from the PWM circuit 27, and FIG. 2B shows the waveform of the pulse current output from the constant current drive unit 41. FIG. 4C shows a function that the bias setting unit 31 gives to the constant current driving unit 41.

  The bias setting unit 31 functions so that the input voltage x to the constant current drive unit 41 and the output voltage y from the constant current drive unit 41 have a non-linear response, as shown in FIG. .

  Specifically, when the value of the input voltage x is large, the value of the output voltage y is equal to the input voltage x, and when the value of the input voltage x is small, the value of the output voltage y is the value of the input voltage x. It becomes smaller and the value of the output voltage y becomes negative.

  Needless to say, such a circuit showing a non-linear response is a known circuit and can be easily constructed by, for example, an operational amplifier.

  In this way, by controlling the bias component of the current pulse train applied to the light emitting element 10 and causing a negative current, that is, a current having a different flow direction, to flow, the light emitting element 10 emits light according to the peak value of the current pulse train. At the timing when the element 10 does not emit light, the life of the light emitting element 10 can be improved by flowing a current in the reverse direction. Such an embodiment can improve the lifetime particularly effectively when the light emitting element 10 is an organic EL element.

(Fifth embodiment)
In the fifth embodiment, the average luminance of the light emitting element 10 is changed by changing the duty of the current applied to the light emitting element 10 with respect to the first embodiment by a method different from that of the third embodiment. Can be controlled.

  FIG. 11 is a block diagram illustrating an electrical configuration of the light emitting device 100 according to the fifth embodiment.

  In FIG. 11, the value output from the comparison signal generation circuit 26 is multiplied by the reciprocal of the value adjusted by the volume vol3 (third external volume) so that the value is 0.5 times the reference value. Is set to However, the numerical value of 0.5 is an exemplary value for explaining the present embodiment, and it is needless to say that other numerical values including one or more may be used.

  FIG. 12 is an explanatory diagram for explaining the principle of controlling the average luminance emitted by the light emitting element 10 by controlling the duty of the drive current in accordance with the output from the volume vol3.

  12A shows a state in which the light emitting element 10 is in an initial state and has not deteriorated, and FIG. 12B shows a state in which the light emitting element 10 has deteriorated 30% compared to the initial state. FIG. 12C shows a state in which the light emitting element 10 is degraded by 50% compared to the initial state.

  As described above, the user can adjust the volume vol3 (third external volume) so that the output from the volume vol3 can be adjusted. As shown in FIG. 12, when the output from the volume vol3 is set to 0.5 times, the magnitude of the modulation coefficient changes, the intersection of the correction coefficient and the modulation coefficient changes, and the drive current for driving the light emitting element 10 The duty cycle also changes. Therefore, the average luminance of the light emitting element 10 is adjusted and maintained at 0.5 times set by the volume vol3 while the deterioration is compensated.

  Specifically, in the case of FIGS. 12A and 12B, since the modulation coefficient value increases and the modulation coefficient and the correction coefficient have an intersection, the duty of the drive current also changes. Since the magnitude of the peak value and the magnitude of the duty cancel each other, the average luminance keeps a constant value.

  In the case of FIG. 12 (c), the average luminance similarly keeps a constant value. However, when the value of the volume vol1 is the reference value 100%, the modulation coefficient higher than this and the correction coefficient are in contact with each other. In other words, the average luminance starts to decrease due to future deterioration.

  As described above, the average luminance of the light emitting element 10 can be controlled by changing the duty of the current applied to the light emitting element 10.

(Sixth embodiment)
In the sixth embodiment, the average luminance is controlled while maintaining the duty by enabling the volume vol3 to control the amplitude of the drive current.

  FIG. 13 is a block diagram illustrating an electrical configuration of the light emitting device 100 according to the sixth embodiment. FIG. 14 is an explanatory diagram for explaining the principle of controlling the average luminance emitted by the light emitting element 10 by controlling the duty and the magnitude of the drive current in accordance with the output from the volume vol3.

  In the sixth embodiment, the output of the volume vol3 is connected to the constant current driving unit 41, and the value output from the comparison signal generation circuit 26 is set to the volume vol3 according to the control of the volume vol3 from the outside. The reciprocal of the adjusted value is multiplied, and the peak value of the drive current is multiplied by the value adjusted with the volume vol3.

  That is, the volume vol3 is configured so that the direction in which the modulation coefficient increases or decreases and the direction in which the pulse signal current that is the drive current of the light emitting element 10 increases or decreases are reversed.

  Specifically, when the magnitude of the modulation coefficient is increased in accordance with the control of the volume vol3 controlled from the outside, the peak of the current value is decreased to decrease the emission peak, and the constant voltage as the correction coefficient is increased. Further, by increasing the luminance coefficient (that is, by increasing the correction coefficient in the same direction with respect to the increase of the modulation coefficient), even if the luminance peak is decreased, the duty does not change, so that the luminance can be adjusted to be small.

  When decreasing the magnitude of the modulation coefficient, the peak of the current value is increased to increase the emission peak, and the magnitude of the constant voltage that is the correction coefficient is also reduced (that is, the correction coefficient is set in the same direction with respect to the decrease of the modulation coefficient). Since the duty does not change even if the luminance peak is increased, the luminance can be greatly dimmed.

  In this way, the deterioration of the light emitting element 10 can be compensated by controlling only the peak value of the drive current while maintaining the duty of the pulse signal from the PWM circuit 27 that compensates for the deterioration of the light emitting element 10. Adjust the brightness. For example, when dimming to a low luminance, the light emitting element is driven by reducing only the current peak while maintaining the current duty (not reducing it), compared to the case where the duty is extremely reduced, Stable light emission can be obtained. Further, when the average luminance is small by controlling the volume vol3, the average luminance can be maintained even when the element is deteriorated.

  FIG. 15 is an electric block diagram of an embodiment including all the above embodiments. The functions of the respective embodiments are also provided.

  As described above, according to the present embodiment, a light emitting element, pulse width modulation means for generating a rectangular pulse signal, and a pulse signal-like drive current for driving the light emitting element are generated based on the pulse signal. A light-emitting device, and a light-detecting unit that photoelectrically converts at least a part of light emitted from the light-emitting element; and an inverse value of an output of the light-detecting unit when the driving current is ON. And a correction coefficient generating means for calculating a correction coefficient for correcting the duty of the pulse signal, wherein the pulse width modulation means changes the duty based on the correction coefficient and the modulation coefficient. Therefore, it is possible to compensate for the deterioration of the luminance of the light emitting element at a low cost with a simple configuration, maintain a constant luminance even when connecting light emitting elements with different luminous efficiencies, and enable high-speed response by direct control. It is possible to provide an optical device. Even when the luminance peak increases from the initial stage due to temperature change, element characteristic change, etc., the duty is reduced and the luminance is kept constant.

  In addition, according to another embodiment, the peak value of the drive current can be adjusted by having the first external volume, so that the brightness can be adjusted. It can also be used for adjustment.

  According to another embodiment, by providing the second external volume for adjusting the correction coefficient, the pulse width modulation means changes the duty based on the output value of the second external volume. The average luminance of the light emitting element can be controlled by changing the duty of the current applied to the light emitting element.

  According to another embodiment, by providing a third external volume for adjusting the modulation coefficient, the pulse width modulation means is based on the correction coefficient and the modulation coefficient modulated by the third external volume. The duty can be changed.

  According to another embodiment, the third external volume can further adjust the peak value of the drive current, and the direction in which the peak value of the drive current increases or decreases is opposite to the increase or decrease of the modulation coefficient. In accordance with the output value of the third external volume, the correction coefficient is increased or decreased in the same direction with respect to the increase or decrease of the modulation coefficient, so that the duty for compensating for the deterioration of the light emitting element is maintained. Thus, the average luminance of the light emitting element can be controlled. Also, instead of using a pulse with an extremely small duty (for example, 10% or less) during low-intensity dimming, the current peak is reduced while maintaining the duty, thereby achieving stable driving and stable light emission. It is done.

  According to another embodiment, the life of the light emitting element can be improved because the bias setting means for setting the value when the drive current is OFF is provided.

  Further, according to another embodiment, when the duty changed by the pulse width modulation means reaches a threshold value, there is a life detection notification means for notifying the outside, so there is an opportunity to promote replacement of the light emitting element. It is possible to obtain a light emitting device that is provided and in which the user always maintains the average luminance.

  Further, according to another embodiment, since the input to the correction coefficient generating means is an analog DC voltage, the subsequent processing can be performed with a simple analog circuit. A light-emitting device can be provided.

  According to another embodiment, since the correction coefficient is an analog DC voltage, the subsequent processing can be performed with a simple analog circuit, so that a low-cost light emitting device with a simple configuration is provided. be able to.

  Further, according to another embodiment, since the initial duty of the pulse signal is 90% or less, in order to offset the decrease in the luminance peak value due to the deterioration of the light emitting element, You can get a margin.

  Further, according to another embodiment, since the initial duty of the pulse signal is 70% or less, in order to offset the decrease in the luminance peak value due to the deterioration of the light emitting element, A further margin can be obtained.

  According to another embodiment, since the light-emitting element is an organic electroluminescence element, it is possible to provide a light-emitting device having advantages such as low power consumption and high luminance, which is thin, high-intensity, and wide viewing angle. In addition, a display having advantages such as a high display response speed can be provided.

  Further, according to another embodiment, since any one of the light emitting devices described above is included, the luminance deterioration of the light emitting element can be compensated for at low cost with a simple configuration, and when light emitting elements having different light emitting efficiencies are connected. In addition, it is possible to obtain a lighting device including a light emitting device capable of maintaining a constant luminance and capable of high-speed response by direct control.

  According to another embodiment, there is provided a method for driving a light emitting element, comprising: a step of generating a rectangular wave pulse signal; and a step of generating a drive current for driving the light emitting element based on the pulse signal. Then, the duty of the pulse signal is corrected based on the step of photoelectrically converting and outputting at least part of the light emitted from the light emitting element and the inverse value of the photoelectrically converted output when the driving current is ON. And a step of changing the duty based on the correction coefficient, so that the luminance degradation of the light emitting element can be compensated for at a low cost with a simple configuration, and by direct control. A driving method of a light emitting element capable of high-speed response can be provided.

DESCRIPTION OF SYMBOLS 10 Light emitting element 20 Constant luminance circuit 21 Amplifier circuit 22 Sample hold circuit 23 Correction coefficient generation circuit 24 Reference pulse generation circuit 25 Sampling gate generation circuit 26 Comparison signal generation circuit 27 PWM circuit 30 Optical sensor 31 Bias setting part 40 Constant current pulse drive circuit 41 Constant Current Drive Unit 50 Life Detection Notification Unit 51 Life Detection Unit 52 Notification Unit 100 Light Emitting Device 200 Illumination Device

Claims (14)

A light emitting element;
Pulse width modulation means for generating a rectangular wave pulse signal;
Based on the pulse signal, a drive unit that generates a drive current in the form of a pulse signal that drives the light emitting element;
A light emitting device comprising:
A light detecting means for photoelectrically converting at least a part of the light emitted by the light emitting element;
Correction coefficient generating means for generating a correction coefficient for correcting the duty of the pulse signal based on the reciprocal value of the output of the light detection means when the drive current is ON;
Modulation coefficient generation means for generating a modulation coefficient used for calculation with the correction coefficient when correcting the duty of the pulse signal,
The light-emitting device, wherein the pulse width modulation means changes the duty based on the correction coefficient and the modulation coefficient.   The light emitting device according to claim 1, further comprising a first external volume that adjusts a peak value of the driving current. A second external volume for adjusting the correction coefficient;
3. The light emitting device according to claim 1, wherein the pulse width modulation unit changes the duty based on an output value of the second external volume. 4. A third external volume for adjusting the modulation coefficient;
4. The light emission according to claim 1, wherein the pulse width modulation unit changes the duty based on the correction coefficient and a modulation coefficient modulated by the third external volume. 5. apparatus. The third external volume can further adjust the peak value of the drive current, and is configured such that the direction in which the peak value of the drive current increases or decreases is opposite to the increase or decrease of the modulation coefficient,
5. The light emitting device according to claim 4, wherein the correction coefficient is increased or decreased in the same direction as the modulation coefficient is increased or decreased according to an output value of the third external volume.   6. The light emitting device according to claim 1, further comprising a bias setting unit configured to set a value when the driving current is OFF.   7. The light emitting device according to claim 1, further comprising a life detection notification unit that notifies the outside when the duty changed by the pulse width modulation unit reaches a threshold value. 8.   The light-emitting device according to claim 1, wherein an input to the correction coefficient generation unit is an analog DC voltage.   The light-emitting device according to claim 1, wherein the correction coefficient is an analog DC voltage.   The light emitting device according to claim 1, wherein an initial duty of the pulse signal is 90% or less.   The light emitting device according to claim 1, wherein an initial duty of the pulse signal is 70% or less.   The light emitting device according to claim 1, wherein the light emitting element is an organic electroluminescence element.   An illuminating device comprising the light emitting device according to any one of claims 1 to 12. Generating a rectangular wave pulse signal;
Generating a driving current for driving the light emitting element based on the pulse signal;
A method for driving a light emitting device having
Photoelectrically converting and outputting at least part of the light emitted by the light emitting element;
Calculating a correction coefficient for correcting the duty of the pulse signal based on the inverse value of the photoelectrically converted output when the drive current is ON;
Changing the duty based on the correction factor;
A method for driving a light emitting element, comprising:

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