JP2004311461A - Device and method for setting driving voltage of led - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a device and a method for setting the driving voltage of an LED in which current consumption can be reduced effectively while absorbing variation in the characteristics of respective LEDs. <P>SOLUTION: The device for setting the driving voltage of an LED comprises a voltage applying section (a microcomputer 32, an applying voltage level setting section 33, a voltage varying circuit 18) for applying a variable voltage to red, green and blue color LEDs, respectively, a detecting section (a luminance/chromaticity meter 31) for detecting the luminance of each color LED when the variable voltage is applied, and a data writing section (a microcomputer 32) for writing the minimum applying voltage level to each color LED in a memory (applying voltage storage registers 11-13) as the driving voltage level of each color LED when a luminance not lower than a desired level is detected in each color LED. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an LED driving voltage setting apparatus and method, and is applied to, for example, a case where an LED (Light Emitting Diode) of three primary colors of R, G, and B emits light to set an LED driving voltage of a liquid crystal display device that performs color display. I can do it.
[0002]
[Prior art]
Conventionally, as a liquid crystal display device using LEDs of three primary colors of R (red), G (green), and B (blue), a liquid crystal display device of a field sequential system (hereinafter, referred to as an FS system) has been realized. (See Patent Document 1 etc.). In the FS type liquid crystal display device, three-color LEDs are provided on the back of the liquid crystal shutter, and each color LED is sequentially turned on at a high speed, and the liquid crystal shutter at each pixel position is opened and closed so as to synchronize with the LED. Can display a desired color.
[0003]
For example, when displaying red, the liquid crystal shutter is opened during the period when the red LED is emitting light, and then the liquid crystal shutter is closed during the period when the green LED is emitting and the period when the blue LED is emitting. Let it work. The same applies to the case where green and blue are displayed. The liquid crystal shutter is opened only during the period when the LED of that color is emitting light, and the liquid crystal shutter is closed during the period when the other LEDs are emitting light.
[0004]
If the liquid crystal shutter is opened while the red and green LEDs are emitting light, Y (yellow) can be displayed. If the liquid crystal shutter is opened while the red and blue LEDs are emitting light, M (magenta) can be displayed. If the liquid crystal shutter is opened while the green and blue LEDs are emitting light, C (cyan) can be displayed, and the liquid crystal shutter is opened during all the periods when the red, green and blue LEDs are emitting light. W (white) can be displayed.
[0005]
As described above, in the FS system, color display is realized based on the principle of the additive method by sequentially emitting the three-color LEDs at a speed higher than the human visual reaction speed. By employing the FS method, a color filter is not required, and clear color display can be performed.
[0006]
[Patent Document 1]
JP 2000-241811 A
[Problems to be solved by the invention]
By the way, with the spread of mobile devices such as mobile phones in recent years, it is desired to realize a display device that can be mounted on the mobile device and that can perform high-definition color display. Here, as described above, the liquid crystal display device using the three-color LED does not require a color filter, so that high-luminance display can be performed.
[0008]
However, in a liquid crystal display device using three-color LEDs, generally, a large number of LED chips constituting each color LED are provided, and a voltage is applied to the large number of LED chips to cause each color LED to emit light. Therefore, power is consumed by many LED chips.
[0009]
On the other hand, since the capacity of a battery is limited in a portable device, the smaller the current consumption of the display device, the better. Needless to say, reduction in current consumption is required not only for portable devices but also for all electric devices.
[0010]
In addition, since LEDs have variations in characteristics, it is necessary to absorb the variations and to perform uniform display. Conventionally, a method such as fine adjustment of the resistance value corresponding to each LED has been adopted to absorb the variation, but there has been a problem that this operation requires extremely complicated work.
[0011]
The present invention has been made in view of the above, and an object of the present invention is to provide an LED drive voltage setting device and a method thereof that can effectively reduce current consumption and absorb variations in characteristics of each LED. I do.
[0012]
[Means for Solving the Problems]
In order to solve such a problem, an LED driving voltage setting device of the present invention is a driving voltage setting device that sets a driving voltage of an LED of an LCD display device that performs color display using each of red, green, and blue LEDs. , A voltage applying means for applying a variable voltage to each of the red, green, and blue LEDs, a detecting means for detecting the luminance of each color LED when the voltage is applied by the voltage applying means, and a detecting means for each color LED. Data writing means for writing the minimum applied voltage value to each color LED when the luminance equal to or greater than the value is detected to the memory as the drive voltage value of each color LED is adopted.
[0013]
An LED driving voltage setting method according to the present invention is a driving voltage setting method for setting a driving voltage of an LED of an LCD display device that performs color display using red, green, and blue LEDs. To a variable voltage applying step of applying a variable voltage to each of the color LEDs, a luminance detecting step of detecting the luminance of each color LED when the variable voltage is applied, and to each of the color LEDs when a luminance equal to or higher than a desired value is detected. And a data writing step of writing the minimum applied voltage value into the memory as the driving voltage value of each color LED.
[0014]
According to this configuration and method, the minimum drive voltage for each color LED can be set independently for each color so that each color LED can emit light with a luminance higher than a desired value. As a result, when each color LED is driven using the memory in which the drive voltage for each color LED is stored independently, it is possible to reduce current consumption while maintaining desired luminance.
[0015]
The LED driving voltage setting device of the present invention further includes PWM control means for controlling each of the red, green, and blue LEDs with a PWM signal having a different duty ratio. In this configuration, the duty ratio of each color LED when a desired luminance is detected is written in the memory.
[0016]
According to the LED drive voltage setting method of the present invention, the variable voltage application step, the luminance detection step, and the data writing step are performed while performing PWM control with a PWM signal having an on-duty ratio equal to or greater than a predetermined value, and the LED drive voltage value for each color is stored in a memory. After writing, the on-duty ratio of the PWM signal is sequentially reduced to finely adjust the luminance of each color LED, and the on-duty ratio of the PWM signal when the desired luminance is obtained is stored in the memory.
[0017]
According to this configuration and method, the duty ratio of the PWM signal to each color LED can be set independently for each color so that each color LED can emit light with a desired luminance. As a result, if each color LED is driven using the memory in which the duty ratio independent of each color LED is stored, the luminance of each color LED can be more minutely brought closer to a desired value.
[0018]
In the LED drive voltage setting device according to the present invention, the voltage applying means independently applies a variable voltage to the same color LED, and the detecting means independently detects the brightness of the same color LED, and writes the data. The means adopts a configuration in which the minimum applied voltage value when the luminance equal to or higher than the desired value is detected for each LED of the same color is independently written into the memory as the drive voltage value.
[0019]
In the driving voltage setting device for an LED of the present invention, the PWM control means controls the same color LED by a PWM signal having a different duty ratio, and the data writing means has a desired luminance for the same color LED. A configuration is adopted in which the duty ratio at the time of detection is independently written in the memory.
[0020]
According to these configurations, even when there is a variation in the driving voltage required to obtain a desired luminance between LEDs of the same color, the minimum driving voltage and the duty ratio according to the variation are set for each LED. In addition, current consumption can be further reduced, and fine brightness adjustment can be performed.
[0021]
BEST MODE FOR CARRYING OUT THE INVENTION
The inventor of the present invention pays attention to the fact that the applied voltage required to cause each of the R, G, and B color LEDs to emit light at a desired luminance is not the same for all the LEDs, but is different for each color LED. The present invention has been reached.
[0022]
The gist of the present invention is to apply a variable voltage to each of the red, green and blue LEDs, detect the brightness of each color LED when the variable voltage is applied, and detect each color LED when a brightness equal to or higher than a desired value is detected. That is, the minimum applied voltage value to each of them is independently set as the driving voltage value of each color LED.
[0023]
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0024]
(Embodiment 1)
In FIG. 1, reference numeral 10 denotes the LED driving device according to the first embodiment as a whole. The LED drive device 10 is provided in a liquid crystal display device, and drives R, G, and B three-color LEDs disposed on the back surface of the liquid crystal panel. In this embodiment, an LED driving device 10 that drives each color LED by a field sequential method will be described.
[0025]
The LED driving device 10 includes an applied voltage storage register 11 for R (red), an applied voltage storage register 12 for G (green), and an applied voltage storage register 13 for B (blue). The registers 11, 12, and 13 store voltage values to be applied to the R, G, and B LEDs, respectively. A bus 14 for setting a stored value is connected to each of the registers 11, 12, and 13, and each of the registers 11, 12, and 13 is connected to each of the registers 11, 12, and 13 via the bus 14 for setting a stored value when the LED driving device 10 is shipped from a product. Are respectively stored.
[0026]
The applied voltage value for each color LED output from each of the registers 11, 12, and 13 is input to the register selection circuit 15. The red LED light emission timing signal TR, the green LED light emission timing signal TG, and the blue LED light emission timing signal TB are input to the register selection circuit 15, and based on the light emission timing signals, the R, G, and B applied voltage values Select one and output.
[0027]
For example, when the red LED light emission timing signal TR has a logical value “1” and the green and blue LED light emission timing signals TG and TB have a logical value “0”, the applied voltage value stored in the R applied voltage storage register 11 is Select output. In the case of this embodiment, since the display of the field sequential system is performed, for example, if the field frequency is 65 Hz, each color LED is caused to emit light sequentially at a frequency of 195 Hz, which is three times that of the field frequency. That is, the register selection circuit 15 sequentially selects and outputs the voltage values stored in the R applied voltage storage register 11, the G applied voltage storage register 12, and the B applied voltage storage register 13 at an interval of about 5 ms.
[0028]
The applied voltage value selected by the register selection circuit 15 is converted into an analog value by a digital-to-analog (DA) conversion circuit 17 of the applied voltage forming unit 16, and then sent to a voltage variable circuit 18. The voltage variable circuit 18 converts the voltage generated by the power supply voltage generation circuit 19 into a voltage corresponding to the analog value input from the digital-to-analog conversion circuit 17, and supplies the voltage to the LED unit 20.
[0029]
As described above, the LED driving device 10 includes the registers 11, 12, and 13 in which the voltage values to be applied to the respective LEDs are stored, and the voltage generated by the power supply voltage generation circuit 19 is stored in the registers 11, 12, and 13. 13 is supplied to the LED after being converted into the value stored in the LED. Thereby, power consumption can be reduced as compared with the case where the same voltage is applied to each color LED.
[0030]
FIG. 2 shows a minimum applied voltage value (hereinafter, referred to as a minimum emission voltage) necessary to obtain a desired luminance in each color LED. As can be seen from this figure, the minimum emission voltages of the green LED and the blue LED are almost the same, but the minimum emission voltage of the red LED is lower than their minimum emission voltages.
[0031]
The applied voltage storage registers 11, 12, and 13 of the LED driving device 10 store the minimum emission voltage value of each color LED. In practice, the stored minimum emission voltage value of the red LED is lower than the values of the green LED and the blue LED. That is, since a minimum necessary voltage can be applied to each color LED, current consumption can be reduced.
[0032]
Also, as can be seen from FIG. 2, the minimum emission voltage also varies for each color LED. For example, a red LED varies between 1.75V and 2.45V, and a green and blue LED varies between 2.9V and 3.9V. This variation in the minimum emission voltage is due to variation in individual products due to LED manufacturing.
[0033]
In this embodiment, not only the applied voltage to the red LED is made smaller than the applied voltage to the green and blue LEDs, but also the applied voltage in consideration of the variation of the minimum emission voltage among the individual products, , 12, and 13 are stored. As a result, it is possible to obtain desired luminance with each color LED while reducing power consumption. The application of the applied voltage values to the color registers 11, 12, and 13 is performed via the stored value setting bus 14, which will be described later.
[0034]
Referring back to FIG. 1, the configuration of the LED driving device 10 will be described. The LED driving device 10 includes an R duty ratio storage register 21, a G duty ratio storage register 22, and a B duty ratio storage register 23. Each of the registers 21, 22, and 23 stores duty ratio data of a PWM signal for performing PWM control of each of the R, G, and B color LEDs. The stored value setting bus 14 is connected to each of the registers 21, 22, and 23, and each of the registers 21, 22, and 23 is connected to each of the registers 21, 22, and 23 via the stored value setting bus 14 when the LED driving device 10 is shipped from a product. Are stored respectively.
[0035]
The duty ratio data for each color LED output from each of the registers 21, 22, and 23 is sent to the PWM waveform forming circuits 24, 25, and 26, respectively. Each of the PWM waveform forming circuits 24, 25, and 26 forms a PWM waveform according to the duty data in synchronization with the clock signal CLK.
[0036]
The PWM waveform forming circuits 24, 25, 26 output a PWM waveform to the bases of the transistors 27, 28, 29 based on the red LED light emission timing signal TR, the green LED light emission timing signal TG, and the blue LED light emission timing signal TB. The output terminals of the R, G, and B LEDs are connected to the collectors of the transistors 27, 28, and 29, respectively, and the emitters are grounded.
[0037]
As a result, during the red LED emission period, only the red LED emission timing signal TR has a logical value of “1”, and only the PWM waveform forming circuit 24 corresponding to the red LED outputs a PWM signal. Current flows through the red LED, and the red LED emits light. Similarly, during the emission period of the green LED, only the green LED emission timing signal TG has a logical value “1”, and a PWM signal is output only from the PWM waveform forming circuit 25 corresponding to the green LED, and the PWM signal is output in response to the PWM signal. Current flows through the green LED, and the green LED emits light. During the emission period of the blue LED, only the blue LED emission timing signal TB has a logical value “1”, and a PWM signal is output only from the PWM waveform forming circuit 26 corresponding to the blue LED, and a current corresponding to the PWM signal is output. It flows to the blue LED, and the blue LED emits light.
[0038]
FIG. 3 shows the configuration of the drive voltage setting device 30 that sets the voltage values to be stored in the applied voltage storage registers 11, 12, and 13 for each color. The drive voltage setting device 30 also stores the duty ratio data for each color LED stored in the duty ratio storage registers 21, 22, and 23 in addition to the voltage values for each color LED stored in the applied voltage storage registers 11, 12, and 13. It has a configuration that can be obtained.
[0039]
The drive voltage setting device 30 has a luminance / chromaticity meter 31 for measuring the luminance and chromaticity of light transmitted from the LCD panel. Incidentally, the light emitted from the LED unit 20 is incident on the luminance / chromaticity meter 31 via the light guide plate (not shown) and the LCD panel 40. The LCD panel 40 is driven to open and close by applying a predetermined voltage from an LCD drive circuit (not shown) at a predetermined timing to the liquid crystal at each pixel position, so that the light emitted from the LED passes or blocks. ing. It is assumed that the LED unit 20, the light guide plate, and the LCD panel 40 are assembled in the same manner as when the product is shipped.
[0040]
The luminance and chromaticity data obtained by the luminance / chromaticity meter 31 are sent to a microcomputer (microcomputer) 32. The drive voltage setting device 30 has an applied voltage value setting unit 33 and a duty ratio setting unit 34, and the voltage value set by the applied voltage value setting unit 33 is sent to the DA conversion circuit 17 of the LED driving device 10. At the same time, the duty ratio data set by the duty ratio setting unit 34 is sent to the PWM waveform forming circuits 24, 25, 26. The set voltage value and the set duty ratio are specified by the microcomputer 32. That is, the microcomputer recognizes the set voltage value and duty ratio.
[0041]
The microcomputer 32 determines whether or not the luminance and chromaticity satisfy predetermined preset values, and when the desired values are satisfied, the voltage value and the duty ratio applied at that time are stored in a storage value setting bus. The data is written into the applied voltage storage registers 11, 12, and 13 and the duty ratio storage registers 21, 22, and 23 through the memory 14. That is, the microcomputer 32 has a function as means for writing stored data to the applied voltage storage registers 11, 12, and 13 and the duty ratio storage registers 21, 22, and 23.
[0042]
4, the recording of the applied voltage value (minimum emission voltage) to the applied voltage storage registers 11, 12 and 13 for each color by the drive voltage setting device 30 and the duty ratio to the duty ratio storage registers 21, 22 and 23 will be described. The data recording process will be described in detail.
[0043]
After starting the process in step ST10, the drive voltage setting device 30 sets the duty ratio in the duty ratio setting unit 34 in the following step ST11. In the case of FIG. 4, since the process is to set the voltage applied to the red LED, the on-duty ratio of the red LED is set to the maximum, and the on-duty ratios of the green and blue LEDs are set to zero. That is, data having the maximum on-duty ratio is given to the PWM waveform forming circuit 24, and data having the on-duty ratio of 0 is given to the PWM waveform forming circuits 25 and 26. In step ST12, the microcomputer 32 sets a target luminance.
[0044]
In step ST13, the applied voltage value setting unit 33 sets the minimum applied voltage value Vmin (for example, 1.5 V), and the voltage variable circuit 18 converts the voltage generated by the power supply voltage generating circuit 19 into this set voltage. Apply to the LED unit 20. At this time, since the PWM signal having the maximum on-duty ratio is output only from the PWM waveform forming circuit 24 for red, only the red LED can emit light.
[0045]
In step ST14, the microcomputer 32 determines whether or not the measured luminance obtained by the luminance / chromaticity meter 31 is larger than the target luminance. If the measured luminance is lower than the target luminance, the process proceeds to step ST15 to set the applied voltage value. The applied voltage set by the unit 33 is increased by k (for example, 0.1 V), and the determination in step ST14 is performed again.
[0046]
If a positive result is obtained in step ST14, this means that the minimum necessary voltage for obtaining the desired luminance is currently applied to the red LED. The voltage value currently set by the applied voltage value setting unit 33 is written in the applied voltage storage register 11. In this manner, the minimum light emission voltage value for the red LED to obtain a desired luminance is stored in the R applied voltage storage register 11.
[0047]
In the following step ST17, the microcomputer 32 determines whether or not the measured brightness matches the target brightness. If not, the process proceeds to step ST18, in which the on-duty ratio set by the duty ratio setting unit 32 is reduced by r. The process returns to step ST17 again.
[0048]
If an affirmative result is obtained in step ST17, this means that the red LED can be made to emit light at the desired luminance by the PWM signal of the duty ratio currently set by the duty ratio setting unit 34, so that the process proceeds to step ST19. Then, the microcomputer 32 writes the voltage value currently set by the duty ratio setting unit 34 in the R applied voltage storage register 11. Thus, the duty ratio data for the red LED to obtain a desired luminance is stored in the R duty ratio storage register 11.
[0049]
In other words, in the processing in steps ST17 to ST19, in other words, after setting the minimum applied voltage capable of obtaining the target luminance in steps ST14 to ST16, the detailed luminance control is performed by the PWM signal to set the target luminance. It can be said that the duty ratio is set so as to approach. The drive voltage setting device 30 ends the data write processing to the R applied voltage storage register 11 and the R duty ratio storage register 21 in the subsequent step ST20.
[0050]
Although the data writing process to the R applied voltage storage register 11 and the R duty ratio storage register 21 has been described here, the G and B applied voltage storage registers 12 and 13 and the G and B duty ratio storage registers are used. The process of writing data to 22 and 23 is performed in the same procedure.
[0051]
Next, a procedure for storing the duty ratio of each color in the registers 21, 22, and 23 to obtain a desired white balance will be described with reference to FIG.
[0052]
When the drive voltage setting device 30 starts the white balance adjustment processing in step ST30, in the following step ST31, the drive voltage setting device 30 stores the applied voltages stored in the applied voltage storage registers 11, 12, 13 and the duty ratio storage registers 21, 22, 23. The LEDs of the respective colors are sequentially illuminated by the PWM signal having the determined on-duty ratio, and the LCD panel 40 is driven by an LCD driving circuit (not shown).
[0053]
Actually, the LED driving device 10 sequentially applies the voltage for each color LED stored in the applied voltage storage registers 11, 12, and 13 to the LED unit 20, and synchronizes with the LED unit 20, so that the PWM waveform forming circuit 24, A PWM signal for each color LED according to the duty ratio stored in the duty ratio storage registers 21, 22, and 23 is formed by 25 and 26.
[0054]
That is, in step ST31, actual LED driving and LCD driving of the field sequential system are performed. Here, it is assumed that the data stored in the applied voltage registers 11, 12, 13 and the duty ratio storage registers 21, 22, 23 are the data set as shown in FIG.
[0055]
In step ST32, the chromaticity of the display color is measured by the luminance / chromaticity meter 31. When this measured chromaticity is plotted in the chromaticity space, it becomes as shown in FIG. Subsequently, the microcomputer 32 calculates the difference between the measured chromaticity and the target value of the white balance, and changes the duty ratio set by the duty ratio setting unit 34 according to the difference, thereby changing the PWM waveform forming circuit 24 for each color. 25 and 26. Here, the microcomputer 32 can read the duty ratio for each color stored in the duty ratio storage registers 21, 22, and 23, and reads the read duty ratio for each color, and the measured chromaticity and white balance. Based on the difference between the target values, the duty ratio for each color to be set next by the duty ratio setting unit 34 is designated. As a result, the duty ratio for each color is set to a value at which a target white balance can be obtained.
[0056]
Specifically, first, in step ST33, it is determined whether or not the Y coordinate of the measured chromaticity is within the white allowable range shown in FIG. 6, and in step ST34, the X coordinate of the measured chromaticity is set in the white allowable range shown in FIG. It is determined whether it is within. If a negative result is obtained in either step ST33 or step ST34, the process proceeds to step ST35, and the duty ratio setting unit 34 changes the duty ratio.
[0057]
The change of the duty ratio is performed in consideration of which direction and how much the measured value deviates from the target point of the white balance. In the case of this embodiment, the microcomputer 32 sets the duty ratio for each color to be given to the LED drive device 10 next by proportionally distributing the shift direction and the shift amount with the chromaticity of R, G, and B.
[0058]
For example, as shown in FIG. 6, consider a case where the Y coordinate of the measured value is shifted in a larger direction with respect to the target point, and the X coordinate of the measured value is shifted in a smaller direction with respect to the target point. Here, the distribution range of the R, G, and B LEDs in the chromaticity space is generally as shown in FIG. 6, so that the Y component of the white balance is reduced and the X component is increased to approach the target point. For this purpose, for example, the on-duty ratio for red is increased, and the on-duty ratio for green is reduced.
[0059]
By setting the next on-duty ratio by proportional distribution in this manner, it is possible to find a duty ratio for each color that can obtain a target white balance with a small number of set times.
[0060]
If a positive result is obtained in both step ST33 and step ST34, which means that the white balance has entered the white allowable range, the driving voltage measuring device 30 proceeds to step ST36 and sets the current duty ratio setting unit. The duty ratios for red, green, and blue set in step 34 are stored in the corresponding duty ratio storage registers 21, 22, and 23, and in step ST37, the white balance adjustment processing ends.
[0061]
As described above, the drive voltage setting device 30 measures the white balance of the actual display color starting from the duty ratio that can obtain the desired luminance independently for each of the R, G, and B color LEDs, and measures the measurement result. A duty ratio storage register for searching for a duty ratio that can obtain a desired white balance while changing the duty ratio for each color according to the duty ratio for each color when the desired white balance is obtained. 21, 22, and 23 are stored.
[0062]
As described above, in the drive voltage setting device 30, since the white balance is adjusted by changing the duty ratio for each color, the white balance can be finely and easily adjusted. Also, by storing the duty ratio for adjusting the white balance in the rewritable registers 21, 22, and 23, the duty ratio unique to each product can be written while measuring the chromaticity of the actual product. Therefore, even when the LED, the light guide plate, and the LCD panel are varied for each product, a desired white balance can be obtained for each product.
[0063]
Next, the operation of the LED driving device 10 will be described with reference to FIG. In the LED driving device 10, first, in the red LED emission period LR, the register selection circuit 15 selects the output of the R applied voltage storage register 11 from the outputs of the applied voltage storage registers 11, 12, and 13, A voltage of 2.2 V corresponding to the output of the R applied voltage storage register is formed, and this 2.2 V voltage is supplied to the LED unit 20 as shown in FIG.
[0064]
When the red LED light emission timing signal TR rises at time t2 in the red LED light emission period LR, the PWM signal of the duty ratio stored in the R duty ratio storage register 21 is output from the PWM waveform forming circuit 24 to the transistor 27. Accordingly, the red LED emits light at a luminance corresponding to the PWM signal. When the red LED light emission timing signal TR falls at a time t3, the output from the PWM waveform forming circuit 24 is stopped, and the register selection circuit 15 replaces the output of the R applied voltage storage register 11 with the G signal. The output of the applied voltage storage register 12 is selectively output.
[0065]
Accordingly, the LED driving device 10 forms a voltage of 3.3 V according to the data of the G applied voltage storage register 12 by the voltage variable circuit 18 during the green LED light emission period LG, and converts the 3.3 V voltage to the LED. It is supplied to the unit 20. When the green LED light emission timing signal TG rises at time t4 in the green LED light emission period LG, the PWM signal of the duty ratio stored in the G duty ratio storage register 22 is output from the PWM waveform forming circuit 25 to the transistor 28. Thus, the green LED emits light at a luminance corresponding to the PWM signal. Eventually, at time t5, when the green LED light emission timing signal TG falls, the output from the PWM waveform forming circuit 25 is stopped, and the register selecting circuit 15 replaces the output of the G applied voltage storage register 12 with the signal for B. The output of the applied voltage storage register 13 is selectively output.
[0066]
As a result, in the blue LED light emission period LB, the LED driving device 10 forms a voltage of 3.4 V according to the data of the B applied voltage storage register 13 by the voltage variable circuit 18, and converts the voltage of 3.4 V to the LED. Supply to the unit 20. When the blue LED light emission timing signal TB rises at time t6 in the blue LED light emission period LB, the PWM signal of the duty ratio stored in the B duty ratio storage register 23 is output from the PWM waveform forming circuit 26 to the transistor 29. Thus, the blue LED emits light with a luminance corresponding to the PWM signal. Eventually, at time t7, when the blue LED emission timing signal TB falls, the output from the PWM waveform forming circuit 26 is stopped, and the register selection circuit 15 replaces the output of the B applied voltage storage register 13 with the R The output of the applied voltage storage register 11 is selectively output.
[0067]
Thereafter, similarly, the red LED light emitting period LR, the green LED light emitting period LG, and the blue LED light emitting period LB are repeated, thereby performing the field sequential color display.
[0068]
Incidentally, in the case of this embodiment, the LED light emission periods LR, LG, LB of each color are selected to be about 5 ms, and the PWM signal output period for each color is selected to be about 2000 μS. The PWM signal waveform has a duty cycle of 50 μS as a unit cycle, and the duty ratio within this unit cycle is stored in the duty ratio storage registers 21 to 23. Incidentally, in the case of the present embodiment, the duty ratio of 8 bits (= 256 patterns) is stored in each of the duty ratio storage registers 21 to 23.
[0069]
Thus, according to the present embodiment, a voltage application unit (microcomputer 32, applied voltage value setting unit 33, voltage variable circuit 18) that applies a variable voltage to each of the red, green, and blue LEDs, and a variable voltage is applied. A detecting unit (brightness / chromaticity meter 31) for detecting the luminance of each color LED at the time, and driving a minimum applied voltage value to each color LED when the luminance of each color LED is higher than a desired value. By providing a data writing unit (microcomputer 32) for writing the voltage value to the memory (the applied voltage storage registers 11 to 13), the current consumption in the LED driving device 10 can be reduced and the characteristics of each LED can be reduced. A drive voltage setting device 30 that can set a drive voltage that can absorb variations can be realized.
[0070]
In addition, since the data of the applied voltage storage registers 11, 12, and 13 can be rewritten via the stored value setting bus 14, the minimum emission voltage (that is, a desired luminance) due to an individual difference is obtained for the LED actually mounted. Therefore, even if there is a variation in the minimum applied voltage necessary for this, the voltage stored in the applied voltage storage registers 11, 12, 13 is appropriately changed in accordance with the variation, so that the variation can be dealt with. Become. As a result, for example, after the product is completed, it is possible to easily set the drive voltage for each color LED independently so that the luminance required for the product can be obtained and the current consumption can be suppressed.
[0071]
Further, by controlling each color LED by PWM, and storing the duty ratio for PWM control in the duty ratio storage registers 21, 22, and 23 independently of each color LED, the luminance of each color LED is set to the duty ratio independent of each color. Since the control can be performed independently by the PWM signal, the brightness of each color LED can be more finely adjusted.
[0072]
Further, a voltage variable circuit 18 is provided, and a voltage generated by one power supply voltage generation circuit 19 is converted into a drive voltage for each color LED, so that a plurality of power supply voltage generation circuits for generating a drive voltage for each color LED are provided. The configuration can be simplified as compared with the case.
[0073]
(Embodiment 2)
FIG. 8, in which parts corresponding to those in FIG. 1 are assigned the same reference numerals, shows a configuration of an LED driving device 50 according to Embodiment 2 of the present invention. The LED driving device 50 has the same configuration as the LED driving device 10 of the first embodiment, except for the way of connecting the LEDs in the LED unit 51.
[0074]
In this embodiment, among the red, green, and blue LEDs, the red LEDs are connected in series. As a result, the number of power supply systems for the red LED is reduced, so that the current consumption required for emitting the red LED can be reduced.
[0075]
That is, in the present embodiment, attention has been paid to the fact that the driving voltage required to cause the red LED to emit light at the desired luminance is substantially half the driving voltage required to cause the green and blue LEDs to emit light at the desired luminance.
[0076]
Thus, it was considered that two cascaded red LEDs can emit light at a voltage substantially equal to the voltage applied to the green and blue LEDs. In short, if the red LEDs are connected in cascade as in this embodiment, the current consumption can be effectively reduced without generating a particularly large voltage in the power supply voltage generation circuit 19.
[0077]
FIG. 9 shows the operation of the LED driving device 50 of this embodiment. The difference from FIG. 7 described above is that, as shown in FIG. 9A, the voltage supplied to the LED unit 51 in the red LED light emission period LR is 2 in order to cause the cascade-connected red LED to emit light at the desired luminance. The only change is from .2V to 4.4V. This voltage of 4.4 V is a voltage within a range of a battery voltage in a normal portable electronic device.
[0078]
Thus, according to the configuration of the present embodiment, the red LEDs of the red, green, and blue LEDs are connected in series, so that the current consumption can be further reduced in addition to the effect of the first embodiment. The LED driving device 50 can be realized.
[0079]
(Other embodiments)
In the above-described embodiment, the LED units 20 and 51 are configured by two red LEDs, blue LEDs, and one green LED, respectively, in order to simplify the drawings and the description. The number is not limited to this.
[0080]
The number of the LED units 20 and 51 may be any number, and the driving voltage and the duty ratio of each color LED may be set independently for each LED unit.
[0081]
Further, a variable voltage is also applied independently to the same color LED, the brightness is also detected independently for the same color LED, and the minimum applied voltage value when the brightness equal to or more than a desired value is detected for each of the same color LEDs is also determined. You may make it set independently as a drive voltage value. In this way, even if there is a variation in the drive voltage required to obtain the desired luminance between the LEDs of the same color, the minimum drive voltage according to the variation can be set for each of the LEDs of the same color. The current can be reduced.
[0082]
Similarly, the LEDs of the same color may be controlled by PWM signals having different duty ratios, and the duty ratio of each LED of the same color when the desired luminance is detected may be independently written in the memory. By doing so, even if there is a variation in the duty ratio required to obtain the desired brightness between the LEDs of the same color, the duty ratio according to the variation can be set for each LED, so that a finer brightness Be able to make adjustments.
[0083]
Further, the present invention can be applied to a case where each white LED of a liquid crystal display device configured to perform color display by combining a plurality of white LEDs and a color filter is driven. That is, by providing a plurality of memories corresponding to the respective white LEDs and storing the minimum emission voltage and the duty ratio according to the variation in the characteristics, the same effects as those of the above-described embodiment can be obtained.
[0084]
Further, in the present invention, the values stored in the applied voltage storage registers 11 to 13 and / or the duty ratio storage registers 21 to 23 may be set according to the arrangement of the LEDs. This makes it possible to easily adjust the brightness according to the arrangement position of the LEDs. For example, in a color filter type liquid crystal display device using a plurality of white LEDs as a backlight, if there is a request to make the luminance near the periphery of the screen higher than the luminance near the center of the screen, it corresponds to the periphery of the screen. If the applied voltage value and the on-duty ratio of the white LED are larger than the applied voltage and the on-duty ratio of the white LED corresponding to the center of the screen, the brightness can be easily adjusted in accordance with the arrangement position of the LED. become.
[0085]
Further, in the above-described embodiment, the driving voltage setting apparatus and method of the present invention have been described by taking as an example the case of setting the driving voltage of the field sequential type LED driving apparatus. However, the driving voltage setting apparatus and method of the present invention are described. The present invention is not limited to this, and can be widely applied to a display device that performs color display using LEDs of three colors of R, G, and B.
[0086]
【The invention's effect】
As described above, according to the present invention, a variable voltage is applied to each of the red, green, and blue LEDs, and the brightness of each of the color LEDs when the variable voltage is applied is detected. When the color display is performed by driving the red, green, and blue LEDs by independently setting the minimum applied voltage value to each of the color LEDs as the drive voltage value of each color LED In addition, it is possible to realize an LED driving voltage setting device and method capable of effectively reducing current consumption.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a configuration of an LED driving device according to a first embodiment. FIG. 2 is a diagram illustrating a minimum voltage value required to obtain a desired luminance in each color LED. FIG. 4 is a block diagram illustrating a configuration of a drive voltage setting device. FIG. 4 is a flowchart illustrating a process of setting an applied voltage and a duty ratio by the drive voltage setting device. FIG. 5 is a diagram illustrating a process of setting a duty ratio for obtaining a desired white balance. FIG. 6 is a chromaticity space diagram for explaining a setting process of a duty ratio for obtaining a desired white balance. FIG. 7 is a waveform diagram for explaining an operation of the LED driving device. FIG. 9 is a block diagram showing a configuration of an LED driving device according to a second embodiment. FIG. 9 is a waveform diagram for explaining the operation of the LED driving device according to the second embodiment.
10, 50 LED driving devices 11 to 13 applied voltage storage register 14 stored value setting bus 15 register selection circuit 16 applied voltage forming unit 17 digital / analog conversion circuit 18 voltage variable circuit 19 power supply voltage generation circuit 20, 51 LED units 21 to 23 Duty ratio storage registers 24 to 26 PWM waveform forming circuit 30 Drive voltage setting device 31 Luminance / chromaticity meter 32 Microcomputer (microcomputer)
33 applied voltage value setting unit 34 duty ratio setting unit TR, TG, TB LED light emission timing signal

Claims (6)

A drive voltage setting device that sets a drive voltage of an LED of an LCD display device that performs color display using each of red, green, and blue LEDs,
Voltage applying means for applying a variable voltage to each of the red, green, and blue LEDs;
Detecting means for detecting the luminance of each color LED when a voltage is applied by the voltage applying means;
Data writing means for writing a minimum applied voltage value to each color LED as a drive voltage value of each color LED to a memory when the detection means detects a luminance equal to or more than a desired value in each color LED, to a memory. LED driving voltage setting device. Further, a PWM control unit for controlling each of the red, green, and blue LEDs with a PWM signal having a different duty ratio is provided.
2. The LED driving voltage setting according to claim 1, wherein the data writing unit writes the duty ratio of each color LED when a desired luminance is detected by each color LED by the detection unit into a memory. apparatus. The voltage applying means independently applies a variable voltage to the same color LED, the detecting means independently detects the luminance of the same color LED, and the data writing means preferably outputs the same color LED. 2. The LED driving voltage setting device according to claim 1, wherein a minimum applied voltage value when a luminance equal to or higher than the value is detected is independently written into a memory as a driving voltage value. The PWM control means controls the LEDs of the same color by PWM signals having different duty ratios, respectively.
3. The LED driving voltage setting device according to claim 2, wherein the data writing unit independently writes the duty ratio when a desired luminance is detected for the same color LED into a memory. A drive voltage setting method for setting a drive voltage of an LED of an LCD display device that performs color display using each of red, green, and blue LEDs,
A variable voltage application step of applying a variable voltage to each of the red, green, and blue LEDs;
A luminance detection step of detecting the luminance of each color LED when a variable voltage is applied;
A data writing step of writing a minimum applied voltage value to each color LED when a luminance equal to or higher than a desired value is detected to a memory as a drive voltage value of each color LED. After performing the variable voltage application step, the luminance detection step, and the data writing step while performing PWM control with a PWM signal having an on-duty ratio equal to or more than a predetermined value, and writing the LED driving voltage value for each color into the memory, the on-duty ratio of the PWM signal 6. The LED drive voltage setting according to claim 5, wherein the luminance of each color LED is gradually adjusted to be finely adjusted, and the on-duty ratio of the PWM signal when a desired luminance is obtained is stored in a memory. Method.

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