JPWO2012153594A1 - Lighting device - Google Patents

Abstract

The lighting device includes a light emitting element (4), a constant current circuit (2) for supplying a constant current to the light emitting element, a switching element (6) for switching a current flowing through the light emitting element, and switching by the switching element. A drive signal for controlling the drive signal is supplied to the switching element, the duty ratio of the drive signal is changed to change the luminance of the light emitting element, and when the duty ratio is small, the drive signal And a control circuit (100) that changes the frequency of the drive signal so as to increase the frequency.

Description

  The present invention relates to an illuminating device that adjusts a current flowing through a light emitting element to adjust light.

  In recent years, lighting devices using light-emitting elements such as organic electroluminescence elements (hereinafter referred to as organic EL elements) and LEDs (Light Emitting Diodes) are known.

  In using such an illuminating device, dimming is generally performed to change the luminance of the illuminating device from the viewpoints of power saving and lighting performance.

There are two types of dimming methods: an amplitude dimming method and a PWM dimming method.
In the case of the amplitude dimming method, when the luminance is low, the current flowing through the light emitting element is reduced, and the current is increased as the luminance is increased.

  On the other hand, in the case of the PWM dimming method, the luminance is adjusted by changing the duty ratio of the pulse applied to the switching element that controls the current flowing through the light emitting element while keeping the current constant.

  Japanese Patent Application Laid-Open No. 2007-251036 proposes an illumination device that executes the PWM dimming method when the luminance is low and executes the amplitude dimming method when the luminance is high.

JP 2007-251036 A

  However, when the PWM dimming method is employed in the case of low luminance, the duty ratio of the pulse applied to the switching element is small, so that there is a problem that the off period becomes remarkable and flickering due to repeated on / off becomes conspicuous.

  In order to suppress this flicker, it is conceivable to increase the driving frequency of the switching element. However, increasing the driving frequency leads to an increase in loss in the switching element, and there is a problem that power consumption increases.

  The present invention is intended to solve the above-described problems, and an object of the present invention is to provide a lighting device that can suppress flicker at low luminance and can suppress an increase in power consumption. .

  An illumination device according to an aspect of the present invention controls a light emitting element, a constant current circuit for supplying a constant current to the light emitting element, a switching element for switching a current flowing through the light emitting element, and switching by the switching element. The drive signal is supplied to the switching element, the duty ratio of the drive signal is changed to change the luminance of the light emitting element, and when the duty ratio is small, the frequency of the drive signal is higher than when the duty ratio is large. And a control circuit for changing the frequency of the drive signal.

  ADVANTAGE OF THE INVENTION According to this invention, while suppressing the flicker at the time of a low brightness | luminance, the increase in power consumption can be suppressed.

It is a figure explaining the illuminating device 1 which drives the organic EL element according to Embodiment 1 of this invention. It is a figure explaining the voltage-current characteristic of an organic EL element. It is a figure explaining the electric current-luminance characteristic of an organic EL element. It is a figure explaining the structure of the switch signal adjustment circuit 104 according to Embodiment 1 of this invention. FIG. 6 is a diagram for explaining waveforms of signal lines of a switch signal adjustment circuit 104. It is a figure explaining the brightness | luminance and electric current of the organic EL element 4 according to the change of the light control rate in the illuminating device 1 according to Embodiment 1 of this invention. It is a figure explaining the structure of the illuminating device 1 # according to Embodiment 2 of this invention. It is a figure explaining switch signal adjustment circuit 104 # according to the second embodiment of the present invention. It is a figure explaining the relationship between the voltage of the signal wire | line NA according to Embodiment 2 of this invention, and a ramp generator enable signal. It is a figure explaining the brightness | luminance and electric current of the organic EL element 4 according to the change of the light control rate in the illuminating device 1 # according to Embodiment 2 of this invention.

  Embodiments of the present invention will be described below with reference to the drawings. In the following description, the same parts and components are denoted by the same reference numerals. Their names and functions are also the same.

(Embodiment 1)
FIG. 1 is a diagram for explaining an illumination device 1 for driving an organic EL element according to Embodiment 1 of the present invention.

  Referring to FIG. 1, lighting device 1 according to the first embodiment of the present invention includes a constant current source (constant current circuit) 2, an organic EL element 4 as a light emitting element, a dimming FET 6, and a control circuit 100. Including.

The constant current source 2 supplies a constant current to the organic EL element 4. The constant current source 2, the organic EL element 4, and the dimming FET 6 are connected in series. The dimming FET 6 is a switching element and switches a current flowing through the organic EL element 4. The control circuit 100 outputs a pulse signal (drive signal) supplied to the gate of the dimming FET 6 according to the dimming rate (dimming level).
The organic EL element 4 has a structure in which an organic EL material is sandwiched between electrodes. Carriers input from the electrode are recombined in the organic EL material, and organic molecules excited by the energy of the recombination are in a ground state. The light emitted when returning to the center is used. For at least one of the electrodes sandwiching the organic EL material, a transparent material is used to extract light. The organic EL element 4 is advantageous in that a thin and lightweight light emitting element can be formed.

  The control circuit 100 includes a PWM generation circuit 102 and a switch signal adjustment circuit 104 that adjusts a switch signal.

  The PWM generation circuit 102 generates a PWM signal having a duty ratio corresponding to the dimming rate in accordance with the input of data indicating the dimming rate (dimming level). For example, when the dimming rate is 20%, a PWM signal having a duty ratio of 20% is generated.

  The switch signal adjustment circuit 104 receives the PWM signal from the PWM generation circuit 102 and outputs a pulse signal (drive signal) to the gate of the dimming FET 6.

FIG. 2 is a diagram for explaining voltage-current characteristics of the organic EL element.
Referring to FIG. 2, the organic EL element has a voltage-current characteristic that changes non-linearly as shown in the figure, and current flows out at a voltage equal to or higher than a threshold value.

FIG. 3 is a diagram for explaining the current-luminance characteristics of the organic EL element.
Referring to FIG. 3, since the luminance is proportional to the current, it is possible to emit light with a constant luminance by driving the organic EL element with a constant current.

  FIG. 4 is a diagram illustrating a configuration of switch signal adjustment circuit 104 according to the first embodiment of the present invention.

  Referring to FIG. 4, switch signal adjustment circuit 104 includes low-pass filter 10, comparator 30, comparison unit 20 including comparators 20 </ b> A to 20 </ b> C, ramp generator 40, selector 50, and oscillation circuit 60. , 62, 64, 66.

  The low-pass filter 10 receives the PWM signal, generates a DC voltage signal (analog voltage) having a potential level corresponding to the duty ratio obtained by smoothing the PWM signal, and outputs the DC voltage signal to the signal line NA.

  The comparators 20A to 20C constituting the comparison unit 20 compare the voltage of the signal line NA with the voltage input to each of the comparators 20A to 20C, and send a signal based on the comparison result via the signal lines NB1 to NB3. Output to the selector 50.

  Specifically, the comparator 20A compares the voltage of the signal line NA with the voltage V1, and outputs a signal (“H” level or “L” level) based on the comparison result to the signal line NB1.

  The comparator 20B compares the voltage of the signal line NA with the voltage V2, and outputs a signal (“H” level or “L” level) based on the comparison result to the signal line NB2.

  The comparator 20C compares the voltage of the signal line NA with the voltage V3, and outputs a signal (“H” level or “L” level) based on the comparison result to the signal line NB3.

  There is a relationship of voltage V1 <voltage V2 <voltage V3. The selector 50 switches the oscillation frequency signal output to the ramp generator 40 in response to signals from the signal lines NB1 to NB3.

  The oscillation circuit (OSC1) 60 outputs a first oscillation frequency signal to the selector 50 via the signal line NC1. The oscillation circuit (OSC2) 62 outputs a second oscillation frequency signal to the selector 50 via the signal line NC2. The oscillation circuit (OSC3) 64 outputs a third oscillation frequency signal to the selector 50 via the signal line NC3. The oscillation circuit (OSC4) 66 outputs a fourth oscillation frequency signal to the selector 50 via the signal line NC4. In this example, the oscillation circuits (OSC1, OSC2, OSC3, OSC4) 60, 62, 64, 66 output oscillation frequency signals of 1 KHz, 500 Hz, 200 Hz, and 100 Hz, respectively.

  When the signal transmitted to the signal line NB1 is “L” level, the selector 50 outputs the first oscillation frequency signal input from the signal line NC1 to the ramp generator 40.

  When the signal transmitted to the signal line NB1 is at “H” level, the selector 50 outputs the second oscillation frequency signal input from the signal line NC2 to the ramp generator 40.

  The selector 50 outputs the third oscillation frequency signal input from the signal line NC3 to the ramp generator 40 when the signal transmitted to the signal line NB2 is at “H” level.

  The selector 50 outputs the fourth oscillation frequency signal input from the signal line NC4 to the ramp generator 40 when the signal transmitted to the signal line NB3 is at “H” level.

  The ramp generator 40 generates a triangular wave signal according to the frequency of the oscillation frequency signal based on the oscillation frequency signal from the selector 50 and outputs it to the signal line ND.

  The comparator 30 outputs a pulse signal (drive signal) based on the comparison between the signal transmitted to the signal line NA and the triangular wave signal output from the lamp generator 40 to the dimming FET 6 via the signal line NE.

FIG. 5 is a diagram for explaining the waveform of the signal on each signal line of the switch signal adjustment circuit 104.
FIG. 5A is a diagram for explaining the waveform of each signal line when the duty ratio of the PWM signal from the PWM generation circuit 102 is 20%.

  FIG. 5B is a diagram for explaining the waveform of each signal line when the duty ratio of the PWM signal from the PWM generation circuit 102 is 40%.

  First, the case where the duty ratio of the PWM signal from the PWM generation circuit 102 is 20%, that is, the case where the dimming rate is 20% will be described with reference to FIG.

  When a PWM signal with a duty ratio of 20% is input from the PWM generation circuit 102 to the low-pass filter 10, it is converted into a DC analog voltage by the low-pass filter 10 and output to the signal line NA. In this example, the voltage of the signal line NA is lower than the voltage V1.

  The comparators 20A to 20C constituting the comparison unit 20 compare the voltage V1, the voltage V2, and the voltage V3 with the analog voltage of the signal line NA. In this example, since the analog voltage of the signal line NA is lower than any of the voltage V1, the voltage V2, and the voltage V3, the signal lines NB1, NB2, and NB3 that are the outputs of the three comparators 20A to 20C have “L ”Level output signal is transmitted. As described above, the oscillation circuits 60, 62, 64, and 66 output oscillation frequency signals of 1 KHz, 500 Hz, 200 Hz, and 100 Hz, respectively. Since the signal transmitted to the signal line NB1 is an “L” level signal, the selector 50 outputs the oscillation frequency signal (1 KHz) of the signal line NC1 to the lamp generator 40.

  The ramp generator 40 generates a triangular wave of the oscillation frequency signal (1 KHz) and outputs it to the signal line ND.

  The comparator 30 compares the voltage between the signal line NA and the signal line ND. When the voltage of the signal line NA is high, the comparator 30 outputs an “H” level signal to the signal line NE, and the voltage of the signal line ND is high. Outputs an “L” level signal. Thus, a pulse signal (drive signal) with a duty ratio of 20% at 1 KHz is output to the signal line NE.

  With reference to FIG. 5B, the case where the duty ratio of the PWM signal from the PWM generation circuit 102 is 40%, that is, the case where the dimming rate is 40% will be described.

  When a PWM signal with a duty ratio of 40% is input from the PWM generation circuit 102 to the low-pass filter 10, it is converted into a DC analog voltage by the low-pass filter 10 and output to the signal line NA. In this example, the voltage of the signal line NA is higher than the voltage V1 and lower than the voltage V2.

  The comparators 20A to 20C constituting the comparison unit 20 compare the voltage V1, the voltage V2, and the voltage V3 with the analog voltage of the signal line NA. In this example, since it is higher than the voltage V1 and lower than both the voltage V2 and the voltage V3, the signal lines NB1, NB2, and NB3, which are the outputs of the three comparators 20A to 20C, have “H” level, "L" level and "L" level output signals are transmitted. As described above, the oscillation circuits 60, 62, 64, and 66 output oscillation frequency signals of 1 KHz, 500 Hz, 200 Hz, and 100 Hz, respectively. Since the signal transmitted to the signal line NB1 is an “H” level signal and the signal transmitted to the signal lines NB2 and NB3 is an “L” level signal, the selector 50 has an oscillation frequency of the signal line NC2. A signal (500 Hz) is output to the lamp generator 40.

  The lamp generator 40 generates a triangular wave of an oscillation frequency signal (500 Hz) and outputs it to the signal line ND.

  The comparator 30 compares the voltage between the signal line NA and the signal line ND. When the voltage of the signal line NA is high, the comparator 30 outputs an “H” level signal to the signal line NE, and the voltage of the signal line ND is high. Outputs an “L” level signal. Thus, a pulse signal (drive signal) with a duty ratio of 40% at 500 Hz is output to the signal line NE.

  Similarly, when a PWM signal with a duty ratio of 60% is input from the PWM generation circuit 102 to the low-pass filter 10, the voltage of the signal line NA is higher than the voltage V2 and lower than the voltage V3. In this case, since the signal transmitted to the signal line NB2 is the “H” level signal and the signal transmitted to the signal line NB3 is the “L” level signal, the selector 50 detects the signal line NC3. Is output to the lamp generator 40. The lamp generator 40 generates a triangular wave of the oscillation frequency signal (200 Hz) and outputs it to the signal line ND.

  The comparator 30 compares the voltage between the signal line NA and the signal line ND. When the voltage of the signal line NA is high, the comparator 30 outputs an “H” level signal to the signal line NE, and the voltage of the signal line ND is high. Outputs an “L” level signal. Thus, a pulse signal (driving signal) with a duty ratio of 60% at 200 Hz is output to the signal line NE.

  When a PWM signal with a duty ratio of 80% is input to the low-pass filter 10, the voltage of the signal line NA becomes higher than the voltage V3. In this case, since the signal transmitted to the signal line NB3 is the “H” level signal, the selector 50 outputs the transmission frequency signal (100 Hz) of the signal line NC4 to the lamp generator 40. The ramp generator 40 generates a triangular wave of the oscillation frequency signal (100 Hz) and outputs it to the signal line ND.

  The comparator 30 compares the voltage between the signal line NA and the signal line ND. When the voltage of the signal line NA is high, the comparator 30 outputs an “H” level signal to the signal line NE, and the voltage of the signal line ND is high. Outputs an “L” level signal. Thus, a pulse signal (driving signal) with a duty ratio of 80% at 100 Hz is output to the signal line NE.

  Furthermore, when a PWM signal with a duty ratio of 100%, that is, a DC signal is input to the low-pass filter 10, the voltage of the signal line NA compared by the comparator 30 is always higher than the voltage of the signal line ND. The output of the signal line NE is always an “H” level signal. Thus, a DC drive signal with a duty ratio of 100% is given to the dimming FET 6.

  FIG. 6 is a diagram illustrating the luminance and current of the organic EL element 4 according to the change in the dimming rate in the illumination device 1 according to the first embodiment of the present invention.

  As shown in FIG. 6, the lower the luminance, that is, the lower the duty ratio, the higher the frequency of the pulse signal applied to the dimming FET 6, and the higher the luminance, the lower the frequency of the pulse signal, The current flowing through the organic EL element 4 is changed by switching control of the dimming FET 6.

  According to this embodiment, when the dimming rate is low, that is, when the duty ratio of the pulse signal applied to the switching element (dimming FET 6) is small, flickering is prevented by setting the frequency of the pulse signal high. It is possible. Further, when the dimming rate is high, that is, when the luminance is high, it is possible to suppress the switching loss in the switching element and suppress the increase in power consumption by setting the frequency of the pulse signal low. . In the case where an organic EL element is used as the light emitting element, generally, the light emission color changes if the current value is different, and the color change tends to be large particularly when driven at a low current value. Then, since the current value is not changed, it is possible to suppress the change in the emission color.

  In the present embodiment, the method of switching the pulse signal supplied to the switching element according to the dimming level to four stages (five stages including the case of DC with a duty ratio of 100%) has been described. The present invention is not limited to this method, and it is not particularly limited to this example as long as it can be driven at a higher frequency when the dimming rate is low, that is, when the duty ratio of the pulse signal is small.

(Embodiment 2)
FIG. 7 is a diagram illustrating a configuration of lighting apparatus 1 # according to the second embodiment of the present invention.

  Referring to FIG. 7, illumination device 1 # according to the second embodiment of the present invention replaces constant current source 2 with variable current source 2 # as compared with illumination device 1 of FIG. The point of replacement with # is different.

  The variable current source 2 # changes the magnitude of the constant current supplied to the organic EL element 4 in accordance with an instruction from the control circuit 100 #.

  Control circuit 100 # differs from control circuit 100 in that switch signal adjustment circuit 104 is replaced with switch signal adjustment circuit 104 #.

  The switch signal adjustment circuit 104 # receives the PWM signal from the PWM generation circuit 102, outputs a pulse signal (drive signal) to the gate of the dimming FET 6, and adjusts the current of the variable current source 2 #. An instruction signal is output.

  In the second embodiment, the PWM dimming method is used up to the dimming rate of 50%, and the amplitude dimming method is switched when the dimming rate is 50% or more.

  FIG. 8 is a diagram illustrating switch signal adjustment circuit 104 # according to the second embodiment of the present invention.

  Referring to FIG. 8, switch signal adjustment circuit 104 # according to the second embodiment of the present invention further includes constant current setting circuit 70 and comparator 80, compared to switch signal adjustment circuit 104 in FIG. In addition, the comparison unit 20 is replaced with the comparator 20D, and the oscillation circuits 60 and 66 are deleted. That is, the selector 50 receives the oscillation frequency signals of 500 Hz and 200 Hz from the oscillation circuits 60 and 64, respectively, and the oscillation frequency signal output to the ramp generator 40 is switched according to the output signal of the comparator 20D.

  Constant current setting circuit 70 is connected to signal line NA, and outputs an instruction signal for adjusting the current to variable current source 2 # according to the voltage of signal line NA.

  The comparator 80 compares the voltage of the signal line NA with the voltage V2 #, and outputs a lamp generator enable signal (“H” level or “L” level) based on the comparison result to the lamp generator 40.

  The lamp generator 40 operates in accordance with the lamp generator enable signal. When it is at “L” level, it outputs a triangular wave signal to the signal line ND, and when it is at “H” level, it does not operate. That is, when the ramp generator enable signal is at “H” level, the signal line ND is set at “L” level. In this case, the signal output from the comparator 30 is always at “H” level, and the dimming FET 6 is always on.

  The comparator 20D compares the voltage of the signal line NA with the voltage V1 #, and outputs a signal (“H” level or “L” level) based on the comparison result to the selector 50 via the signal line NB4.

  When the signal transmitted to the signal line NB4 is “L” level, the selector 50 outputs the 500 Hz transmission frequency signal input from the signal line NC2 to the lamp generator 40.

  Further, when the signal transmitted to the signal line NB4 is “H” level, the selector 50 outputs a 200 Hz transmission frequency signal input from the signal line NC3 to the lamp generator 40.

  The other configuration is the same as that described with reference to FIG. 4, and therefore detailed description thereof will not be repeated.

  FIG. 9 is a diagram illustrating the relationship between the voltage of the signal line NA, the ramp generator enable signal, and the output of the constant current setting circuit according to the second embodiment of the present invention.

  Referring to FIG. 9, in this example, the case where the dimming rate is increased with the passage of time, that is, the case where the voltage of the signal line NA is increased is shown.

  Here, the ramp generator enable signal is a signal based on the comparison result between the voltage V2 # and the signal line NA by the comparator 80 as described above. When the dimming rate is low, the voltage of the signal line NA is low, so that the lamp generator enable signal that is the output signal of the comparator 80 is set to the “H” level. Therefore, in accordance with the “H” level ramp generator enable signal, ramp generator 40 outputs a triangular wave signal to signal line ND. In this case, as described in Embodiment 1, a pulse signal (drive signal) based on the comparison between the signal line NA and the signal line ND is transmitted to the signal line NE.

  The constant current setting circuit 70 monitors the voltage of the signal line NA, and outputs an instruction signal corresponding to the voltage of the signal line NA to the variable current source 2 # as shown in FIG. Specifically, when the voltage of the signal line NA is smaller than the voltage V2 #, the instruction signal from the constant current setting circuit 70 is at a predetermined constant level. On the other hand, when the voltage of the signal line NA is equal to or higher than the voltage V2 #, the instruction signal changes according to the voltage of the signal line NA.

  The variable current source 2 # supplies a constant current to the organic EL element 4 in accordance with an instruction signal from the constant current setting circuit 70. In this example, when the voltage level of the signal line NA is smaller than the voltage V2 #, a current that is half the current that flows when the dimming rate is 100% according to the instruction signal from the constant current setting circuit 70. Supply.

  When the voltage level of the signal line NA is equal to or higher than the voltage V2 #, the variable current source 2 # adjusts the magnitude of the current according to the level of the instruction signal from the constant current setting circuit 70. Specifically, if the level of the instruction signal is small, the current flowing through the organic EL element 4 is reduced, and the current is increased as the level of the instruction signal increases.

  In the present embodiment, the voltage V2 # input to the comparator 80 is associated with the voltage of the signal line NA when the dimming rate is 50%. Therefore, when the dimming rate is lower than 50%, the lamp generator enable signal is set to the “H” level, and lamp generator 40 is activated. As a result, a pulse signal (drive pulse) having a predetermined duty ratio is output to the dimming FET 6 to execute dimming control according to the PWM dimming method.

  On the other hand, when the dimming rate is 50% or more, the lamp generator enable signal is set to the “L” level, and the lamp generator 40 is deactivated. As a result, a drive signal of “H” level is always output to the dimming FET 6, and dimming control according to the amplitude dimming method by adjusting the current of the variable current source 2 # is executed instead of the PWM dimming method.

  FIG. 10 is a diagram illustrating the luminance and current of organic EL element 4 according to the change in the light control rate in lighting apparatus 1 # according to the second embodiment of the present invention.

  As shown in FIG. 10, when the dimming rate is lower than 50%, when the duty ratio of the pulse signal is low, the frequency is set high, and the higher the duty ratio is, the lower the frequency is set. The current flowing through the EL element 4 is controlled. On the other hand, when the dimming rate is 50% or more, the dimming is executed by switching from the PWM dimming method to the amplitude dimming method and adjusting the magnitude of the current flowing through the organic EL element 4.

  According to this embodiment, when the dimming rate is low, that is, when the duty ratio of the pulse signal applied to the switching element (dimming FET 6) is small, flickering is prevented by setting the frequency of the pulse signal high. It is possible.

  In this embodiment, when the dimming rate is high, that is, when the luminance is high, the switching element is not switched, and the current is adjusted by the variable current source. The switching loss can be suppressed, and the increase in power consumption can be further suppressed than in the first embodiment.

  In the above embodiment, the organic EL element is used as the light emitting element. However, the present invention is not limited to this, and for example, an LED can be used as the light emitting element.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  DESCRIPTION OF SYMBOLS 1 Illuminating device, 2 constant current source, 2 # variable current source, 4 organic EL element, 10 low pass filter, 20 comparison part, 40 lamp generator, 50 selector, 60-66 oscillation circuit, 70 constant current setting circuit, 100 control circuit , 102 PWM generation circuit, 104 switch signal adjustment circuit.

Claims (4)

A light emitting element (4);
A constant current circuit (2) for supplying a constant current to the light emitting element;
A switching element (6) for switching a current flowing through the light emitting element;
A drive signal for controlling switching by the switching element is supplied to the switching element, the duty ratio of the drive signal is changed to change the luminance of the light emitting element, and when the duty ratio is small, And a control circuit (100) for changing the frequency of the drive signal so that the frequency of the drive signal is higher than when the duty ratio is large. The control circuit includes:
A plurality of oscillation circuits (60 to 66) each having a different oscillation frequency;
A selector (50) for selecting an output of any of the plurality of oscillation circuits according to the dimming level;
The lighting device according to claim 1, wherein the driving signal is generated using a signal having an oscillation frequency selected by the selector. The constant current circuit is provided so that the magnitude of the constant current can be changed,
When changing the luminance of the light emitting element in a region lower than a predetermined value, the constant current is set to a specific value, and the luminance of the light emitting element is changed by changing the duty ratio of the drive signal. ,
When the luminance of the light emitting element is changed in the region of the predetermined value or more, the driving signal is maintained at a high level, and the constant current is changed from the specific value to change the luminance of the light emitting element. The lighting device according to claim 1, wherein the lighting device is changed.   The lighting device according to claim 1, wherein the light emitting element is an organic EL element.

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