CN100392878C - LED driver - Google Patents

Abstract

Current consumption is reduced by storing the driving voltage of each LED in the applied voltage storage register (11, 12, 13) and driving each color LED with an independent driving voltage. In addition, the data of the applied voltage storage registers (11, 12, 13) can be rewritten through the stored value setting bus (14). The voltages stored in the applied voltage storage registers (11, 12, 13) are appropriately changed.

Description

LED driver

technical field

The present invention particularly relates to an LED driving device and an LED driving method for making R, G, and B three primary color LEDs (Light Emitting Diodes, light emitting diodes) emit light to display colors.

Background technique

In the past, in liquid crystal display devices using R (red), G (green), and B (blue) LEDs in three primary colors, for example, the field sequential method (abbreviated as FS method) published in JP-A-2000-241811 has been realized. Liquid crystal display device. In the FS type liquid crystal display device, three-color LEDs are arranged on the back of the liquid crystal shutters, and the liquid crystal shutters at each pixel position are simultaneously turned on and off while the LEDs of each color are sequentially lit at high speed, so that desired colors can be displayed at each pixel position.

For example, to display red, the liquid crystal shutter is opened while the red LED is emitting light, and then the liquid crystal shutter is closed while the green LED and the blue LED are emitting light. The same applies to the case of displaying green and blue, and the liquid crystal shutters are opened only while the LEDs of that color are emitting light, and are closed while the other LEDs are emitting light.

In addition, Y (yellow) can be displayed if the liquid crystal shutter is opened while the red and green LEDs are lit, M (magenta) can be displayed if the liquid crystal shutter is opened while the red and blue LEDs are lit, and M (magenta) can be displayed when the green and blue LEDs are lit. C (cyan) can be displayed by opening the liquid crystal shutter during the period, and W (white) can be displayed by opening the liquid crystal shutter during the entire period when the red, green, and blue LEDs are lit.

The above-mentioned FS method is based on the principle of the additive color method, and realizes the display of colors by sequentially lighting up three-color LEDs at a speed faster than the speed of human visual reaction. In addition, with the FS method, vivid colors can be displayed without using color filters.

In recent years, with the popularization of portable electronic products such as mobile phones, it is desired to realize a display device that can be mounted on portable electronic products and display colors with high definition. Here, as described above, since a liquid crystal display device using three-color LEDs does not require color filters, it can display with high brightness.

However, in a liquid crystal display device using LEDs of three colors, a plurality of LED chips constituting LEDs of each color are generally provided, and a voltage is applied to the plurality of LED chips to cause the LEDs of each color to emit light. Therefore, power is consumed in a plurality of LED chips.

In contrast, the battery capacity of portable electronic products is limited, so the consumption current for the display device should be as low as possible. Of course, this is not limited to portable electronic products, and reducing current consumption is desired by all electronic products.

In addition, since there is a difference in LED characteristics, it is required to eliminate the difference to perform display with uniformity. In order to eliminate this difference, methods such as fine-tuning the resistance value corresponding to each LED have been used in the past, but the problem with the above-mentioned operation is that the process is very complicated.

Contents of the invention

The main purpose of the present invention is to provide a light emitting diode driving device capable of effectively reducing current consumption. Another object of the present invention is to provide a light emitting diode drive device capable of eliminating the difference in characteristics of the respective light emitting diodes.

For this reason, the present invention provides such a light emitting diode driving device, which has:

Power supply voltage generation components;

The applied voltage storage unit, for the red, green, and blue color light-emitting diodes arranged in the display device, independently stores the minimum applied voltage value required to obtain a brightness higher than or equal to the desired brightness as a digital value for each color light-emitting diode;

an applied voltage forming section having a D/A converter for digital-to-analog converting a digital value stored in said applied voltage storing section, and for converting a voltage generated by said power supply voltage generating section into The voltage variable part of the voltage of the magnitude of the analog value converted by the /A converter;

The duty cycle storage part independently stores the duty cycle of the pulse width modulation signal for fine-tuning the brightness of the light emitting diodes of each color according to the light emitting diodes of each color; and

The pulse width modulation control part independently forms a pulse width modulation signal based on the duty ratio stored in the duty ratio storage part for each color light emitting diode, and independently performs pulse width modulation control on each color light emitting diode,

The pulse width modulation control unit performs control to bring the light emission luminance of each color light emitting diode close to the desired luminance while the applied voltage forming unit independently applies different applied voltages to the light emitting diodes of each color.

In addition, the above object is achieved by performing PWM control on each color LED with a PWM (Pulse Width Modulation) signal with a different duty ratio for each color LED under the condition that the minimum driving voltage is applied to each color LED.

Description of drawings

Fig. 1 is a block diagram showing the structure of an LED driving device according to Embodiment 1 of the present invention;

Fig. 2 is a diagram representing minimum voltage values required to obtain desired brightness of LEDs of various colors;

Fig. 3 is a block diagram showing the structure of the drive voltage setting device of the embodiment;

4 is a flow chart for explaining the applied voltage and duty ratio setting processing performed by the driving voltage setting device;

FIG. 5 is a flowchart for explaining a duty ratio setting process for obtaining a desired white balance;

FIG. 6 is a chromaticity space diagram for explaining a duty cycle setting process for obtaining a desired white balance;

Fig. 7 is a waveform diagram used to illustrate the action of the LED driving device;

8 is a block diagram showing the structure of the LED driving device of Embodiment 2;

FIG. 9 is a waveform diagram for explaining the operation of the LED driving device according to the second embodiment.

Detailed ways

The inventors of the present invention completed the present invention by focusing on the fact that the applied voltages required to make LEDs of R, G, and B colors emit light with desired luminance are not the same for all LEDs, but differ for each color LED.

The main content of the present invention is to measure in advance the minimum driving voltages for red, green and blue LEDs that can obtain the desired brightness, store the driving voltages of the LEDs of each color in the storage unit, and apply the stored driving voltages to the LEDs of each color.

Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings.

(implementation 1)

In FIG. 1, 10 generally shows an LED driving device according to Embodiment 1 of the present invention. The LED driving device 10 is provided in a liquid crystal display device, and is used to drive three-color LEDs of R, G and B disposed on the back of the liquid crystal panel. And as a specific example, this embodiment will illustrate the application of the present invention to a field sequential liquid crystal display device.

The LED drive device 10 has 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 above store the voltage values applied to the R, G, and B LEDs, respectively. Each register 11, 12, 13 is connected to the bus 14 for setting the stored value, and when the product of the LED drive device 10 goes off the production line, the bus 14 for setting the stored value makes each register 11, 12, 13 store the value for each color LED respectively. Applied voltage value.

The applied voltage values for the LEDs of the respective colors output from the respective registers 11 , 12 , and 13 are input to the register selection circuit 15 . The red LED light emission timing signal TR, green LED light emission timing signal TG and blue LED light emission timing signal TB are input to the register selection circuit 15, and any one of the applied voltage values of R, G, and B is selected and output according to the light emission timing signal.

For example, when the logic value of the red LED light emission timing signal TR is "1" and the logic values of the green and blue LED light emission timing signals TG, TB are "0", the applied voltage stored in the applied voltage storage register 11 for the output R is selected. value. In this embodiment, because it is displayed in a field-sequential manner, if the field frequency is 65Hz, the LEDs of each color will emit light sequentially at the frequency of 195Hz which is three times higher. 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 intervals of about 5 mS.

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 output 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 .

As mentioned above, the LED driving device 10 has the registers 11, 12, 13 which store the voltage values respectively applied to the LEDs of each color, and converts the voltage generated by the power supply voltage generating circuit 19 into the values stored in the registers 11, 12, 13 and supplies them to LED. Thereby, compared with the case where the same voltage value is applied to each color LED, power consumption can be reduced.

Figure 2 shows the minimum applied voltage value (hereinafter referred to as the minimum luminous voltage) required to obtain the desired brightness for each color LED. From this figure, it can be seen that the minimum light emitting voltage of the green LED and the blue LED are almost the same, but the minimum light emitting voltage of the red LED is lower than the minimum light emitting voltage of the above two.

The applied voltage storage registers 11, 12, and 13 of the LED driving device 10 store the minimum light-emitting voltage values of LEDs of each color. In fact, among the stored minimum light-emitting voltage values, the value of the red LED is lower than the values of the green LED and the blue LED. That is, since the minimum required voltage can be applied to each color LED, the current consumption can be reduced.

In addition, it can be seen from Figure 2 that the minimum light-emitting voltage varies among LEDs of different colors. For example, if it is a red LED, it is distributed between 1.75V and 2.45V; and if it is a green and blue LED, it is distributed between 2.9V and 3.9V. On the other hand, the difference in the minimum light emission voltage is caused by the difference between each product when manufacturing LEDs.

In this embodiment, instead of simply making the applied voltage to the red LED smaller than the green and blue applied voltages, the registers 11, 12, and 13 for each color are also used to store the difference between the minimum light-emitting voltages for each product. The applied voltage is taken into account. Accordingly, desired luminance can be obtained for each color LED while reducing power consumption. The above-mentioned color registers 11, 12, 13 store the applied voltage values through the stored value setting bus 14, which will be described later.

Returning now to FIG. 1, the structure of the LED driving device 10 will be described. The LED drive device 10 has an R duty ratio storage register 21 , a G duty ratio storage register 22 , and a B duty ratio storage register 23 . The above-mentioned registers 21, 22 and 23 respectively store PWM signal duty cycle data for performing PWM control on LEDs of R, G and B colors. Each register 21, 22 and 23 is connected to the bus 14 for setting the stored value. duty cycle data.

The duty ratio data for LEDs of each color output from the respective registers 21 , 22 , and 23 are output to PWM waveform forming circuits 24 , 25 , and 26 , respectively. Each PWM waveform forming circuit 24, 25, 26 forms a PWM waveform corresponding to duty data in synchronization with the clock signal CLK.

The PWM waveform forming circuits 24, 25, 26 output PWM waveforms to the bases of the transistors 27, 28, 29 according to the red LED lighting timing signal TR, the green LED lighting timing signal TG and the blue LED lighting timing signal TB. While the collectors of the transistors 27, 28, 29 are respectively connected to the output terminals of the R, G, and B LEDs, the emitters are grounded.

Thus, during the red LED lighting period, only the logic value of the red LED lighting timing signal TR is "1", and only the PWM waveform forming circuit 24 corresponding to the red LED outputs a PWM signal, and the current corresponding to this PWM signal flows to Red LED, make the red LED glow. Similarly, during the green LED light-emitting period, only the logic value of the green LED light-emitting timing signal TG is "1", and only the PWM waveform forming circuit 25 corresponding to the green LED outputs a PWM signal, and the current corresponding to this PWM signal flows to Green LED, makes the green LED glow. During the period of blue LED lighting, only the logic value of the blue LED lighting timing signal TB is "1", and only the PWM waveform forming circuit 26 corresponding to the blue LED outputs a PWM signal, and the current flow corresponding to this PWM signal to the blue LED to make the blue LED glow.

FIG. 3 shows the configuration of a drive voltage setting device 30 that sets voltage values stored in the applied voltage storage registers 11 , 12 , and 13 for each color. However, the structure of the driving voltage setting device 30 is such that not only the voltage values for the LEDs of each color stored in the applied voltage storage registers 11, 12, and 13 can be obtained, but also the voltage values of the respective colors stored in the duty ratio storage registers 21, 22, and 23 can be obtained. Duty cycle data for the LED.

The drive voltage setting device 30 has a luminance/colorimeter 31 for measuring the luminance and chromaticity of light transmitted from the LCD panel. And the light emitted from the LED unit 20 enters the luminance/colorimeter 31 through the light guide plate (not shown in the figure) and the LCD panel 40 . The LCD driving circuit (not shown in the figure) applies a predetermined voltage to the liquid crystals at each pixel position at a predetermined time to drive the switch of the LCD panel 40 so as to transmit or shield the light emitted by the LED. The LED unit 20 , the light guide plate and the LCD panel 40 are assembled when the product goes off the production line.

The brightness and chromaticity data obtained by the brightness/colorimeter 31 are transmitted to a microcomputer (Microcomputer) 32 . The driving voltage setting device 30 has an applied voltage value setting part 33 and a duty ratio setting part 34, and the voltage value set by the applied voltage setting part 33 is transmitted to the DA conversion circuit 17 of the LED driving device 10, and at the same time, The duty ratio data set by the duty ratio setting unit 34 is transmitted to the PWM waveform forming circuits 24 , 25 , and 26 . The set voltage value and set duty ratio are specified by the microcomputer 32 . That is, the microcomputer recognizes the set voltage value and duty ratio.

The microcomputer 32 judges whether the brightness and chromaticity have reached the preset expected value, and when the expected value is reached, the voltage value and duty ratio applied at this time are written into the applied voltage storage registers 11, 12, 13 and duty ratio storage registers 21, 22, 23. That is, microcomputer 32 has a function as storage data writing means for writing data into applied voltage storage registers 11 , 12 , 13 and duty ratio storage registers 21 , 22 , 23 .

Now use FIG. 4 to describe in detail the recording process of the applied voltage value (minimum luminescence voltage) performed by the driving voltage setting device 30 to the applied voltage storage registers 11, 12, and 13 for each color, and the recording process for the duty ratio storage registers 21, 22, 23 The duty cycle data recording process performed.

When the drive voltage device 30 starts the process of step ST10, the duty ratio of the duty ratio setting unit 34 is set in the next step ST11. Since Fig. 4 is a process for setting the applied voltage value given to the red LED, the on-duty ratio of the red LED is set to the maximum, and the on-duty ratio of the green and blue LEDs is set to 0 . That is, the data with the maximum on-duty ratio is supplied to the PWM waveform forming circuit 24 , and the data with the on-duty ratio of 0 is supplied to the PWM waveform forming circuits 25 and 26 . In step ST12, the microcomputer 32 sets the target brightness.

In step ST13, the applied voltage value setting unit 33 sets the minimum applied voltage value Vmin (such as 1.5V), and the voltage variable circuit 18 converts the voltage generated by the power supply voltage generating circuit 19 into the set voltage and applies it to the LED unit 20. . At this time, only the red LED is in a light-emitting state because the PWM signal with the largest on-duty ratio is output from only the red PWM waveform forming circuit 24 .

In step ST14, the microcomputer 32 judges whether the measured luminance obtained by the luminance/colorimeter 31 is greater than the target luminance, and if it is less than or equal to the target luminance, the process moves to step ST15, and the set applied voltage of the applied voltage value setting part 33 is increased. After the k component (for example, 0.1V), the judgment of step ST14 is performed again.

If an affirmative result is obtained in step ST14, then this represents that the minimum voltage required to obtain the desired brightness is being applied to the red LED, so move to step ST16, and the microcomputer 32 applies the voltage set by the voltage value setting part 33 at present. The value is written into the R application voltage value storage register 11 . Thus, the R applied voltage value storage register 11 stores the minimum light emission voltage value for obtaining the desired luminance of the red LED.

In the next step ST17, the microcomputer 32 judges whether the measured brightness is consistent with the target brightness. ST17.

If an affirmative result is obtained in step ST17, then this represents that the PWM signal of the duty ratio set by the current duty ratio setting part 34 can make the red LED emit light with desired brightness, so move to step ST19, and the microcomputer 32 changes the current duty ratio to the desired brightness. The voltage value set by the setting unit 34 is written in the R application voltage storage register 11 . Thus, the R duty ratio storage register 21 stores the duty ratio data for obtaining the desired luminance of the red LED.

In other words, the processing from step ST17 to step ST19 can be said to be that after the minimum applied voltage that can obtain the target brightness is set in step ST14 to step ST16, the PWM signal is used to perform more detailed brightness control. duty cycle close to the target brightness. The drive voltage setting device 30 ends the data writing process to the R applied voltage storage register 11 and the R duty ratio storage register 21 in the next step ST20.

However, 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 use voltage storage registers 12 and 13 have been described. The data writing process of the duty storage registers 22 and 23 is also performed in the same procedure.

Next, the sequence of storing the duty cycle of each color for obtaining the desired white balance in the registers 21 , 22 , 23 will be described with FIG. 5 .

If the drive voltage setting device 30 starts the white balance adjustment process in step ST30, the applied voltage stored in the applied voltage storage registers 11, 12, and 13 and the values stored in the duty ratio storage registers 21, 22, and 23 are used in the next step ST31. Turning on the PWM signal of the duty cycle makes the LEDs of each color emit light sequentially, and at the same time, the LCD panel 40 is driven by an LCD driving circuit (not shown in the figure).

In fact, the LED driving device 10 sequentially applies the voltages for LEDs of various colors stored in the applied voltage storage registers 11, 12, and 13 to the LED unit 20, and the PWM waveform forming circuits 24, 25, and 26 form the corresponding duty cycle storage registers 21, 13, and 20. 22, 23 store duty cycle LEDs of various colors with the PWM signal to synchronize with it.

That is, in step ST31, LED driving and LCD driving of the field sequential method are actually performed. Here, the data stored in the applied voltage storage registers 11 , 12 , 13 and the duty ratio storage registers 21 , 22 , 23 are assumed to be the data set in FIG. 4 .

In step ST32, the chromaticity of the displayed color is measured by the luminance/colorimeter 31 . When this measured chromaticity diagram is displayed in a chromaticity space, it will be as shown in FIG. 6 . Next, the microcomputer 32 calculates the difference between the measured chromaticity and the target value of the white balance, changes the duty ratio set by the duty ratio setting part 34 according to the difference, and supplies it to the PWM waveform forming circuits 24, 25, 26 for each color. . Here, the microcomputer 32 is configured such that it can read the duty ratios for each color stored in the duty ratio storage registers 21, 22, and 23, and measure the chromaticity and white balance based on the read duty ratios for each color and the target of measuring chromaticity and white balance. The duty ratio for each color set in the duty ratio setting unit 34 is specified by the difference between the values. In this way, the duty ratio for each color is set to a value at which the target white balance can be obtained.

Specifically, it is first judged in step ST33 whether the Y coordinate of the measured chromaticity is within the allowable white range shown in FIG. If a negative result is obtained in either step ST33 or step ST34, the process moves to step ST35, and the duty ratio setting unit 34 changes the duty ratio.

This duty ratio is changed in consideration of how much the measurement value deviates in which direction from the target point of the white balance. In this embodiment, the microcomputer 32 sets the duty ratio for each color to be supplied to the LED driving device 10 next by proportionally distributing the direction and amount of deviation in R, G, and B chromaticity.

Taking FIG. 6 as an example, consider a case where the Y-coordinate of the measured value deviates in a large direction from the target point and the X-coordinate of the measured value deviates in a small direction from the target point. Here, the distribution ranges of the chromaticity space of LEDs of R, G, and B colors are generally shown in Figure 6. Therefore, in order to reduce the Y component of the white balance and increase the X component to approach the target point, for example, the red color can be increased. Use the on-duty cycle and reduce the green on-duty cycle.

By performing the setting of the next on-duty ratio with the above-mentioned proportional distribution, it is possible to find a duty ratio for each color that can obtain the target white balance with a small number of times of setting.

If the drive voltage device 30 obtains positive results in both step ST33 and step ST34, then this represents that the white balance has entered the white allowable range, so move to step ST36, and set the current duty ratio setting section 34 for red, green, and green. The duty ratios for blue and blue are stored in the corresponding duty ratio storage registers 21, 22, and 23, and the white balance adjustment process ends in the next step ST37.

As described above, the driving voltage device 30 measures the actual white balance of the displayed color starting from the duty ratio at which the desired luminance can be independently obtained for each color LED of R, G, and B, and changes the duty ratio for each color based on the measurement result. At the same time, the duty cycle that can obtain the desired white balance is searched, and the duty cycle for each color when the desired white balance is obtained is stored in the corresponding duty cycle storage registers 21 , 22 , 23 .

As described above, since the drive voltage device 30 can adjust the white balance by changing the duty ratio for each color, fine adjustment of the white balance can be easily performed. Furthermore, by storing the duty ratio for adjusting the white balance in the rewritable registers 21, 22, 23, it is possible to write the duty ratio unique to each product while measuring the actual chromaticity of the product, so even if Each product has differences in LEDs, light guide plates, and LCD panels, and it is also possible to obtain the desired white balance in each product.

Next, the operation of the LED driving device 10 in this embodiment will be described using FIG. 7 . The LED drive device 10 first selects the output of the applied voltage storage register 11 for R from the outputs of the applied voltage storage registers 11, 12, and 13 by the register selection circuit 15 during the red LED light-emitting period LR, and forms a corresponding R in the voltage variable circuit 18. After storing the 2.2V voltage output from the register with the applied voltage, the 2.2V voltage is supplied to the LED unit 20 as shown in FIG. 7( a ).

In addition, when the red LED lighting timing signal TR rises at time t2 within the red LED lighting period LR, the duty PWM signal stored in the R duty storage register 21 is output from the PWM waveform forming circuit 24 to the transistor 27 , the red LED can emit light with the brightness corresponding to the PWM signal. When the time t3 is approaching, if the red LED lighting timing signal TR falls, the register selection circuit 15 selects the output of the applied voltage storage register 12 for G instead of the output of the applied voltage storage register 11 for R while the output of the PWM waveform forming circuit 24 stops. output.

Thus, the LED driving device 10 forms a 3.3V voltage corresponding to the data of the G application voltage register 12 by the voltage variable circuit 18 during the green LED light emission period LG, and supplies the 3.3V voltage to the LED unit 20 . Also, when the green LED lighting timing signal TG rises at time t4 within the green LED lighting period LG, the duty ratio PWN signal stored in the duty ratio storage register 22 for G is output from the PWM waveform forming circuit 25 to the transistor 28 , the green LED can emit light with the brightness corresponding to the PWM signal. When time t5 is approaching, if the green LED light-emitting timing signal TG falls, the PWM waveform forming circuit 25 stops outputting, and the register selection circuit 15 selects the output of the applied voltage storage register 13 for B instead of the output of the applied voltage storage register 12 for G. .

Thus, the LED driving device 10 forms a 3.4V voltage corresponding to the data of the B application voltage storage register 13 by the voltage variable circuit 18 during the blue LED lighting period LB, and supplies the 3.4V voltage to the LED unit 20 . In addition, if the blue LED lighting timing signal TB rises at time t6 in the blue LED lighting period LB, the duty ratio PWN signal stored in the duty ratio storage register 23 for B is output from the PWM waveform forming circuit 26 to With the transistor 29, the blue LED can emit light with a brightness corresponding to the PWM signal. When the time t7 approaches, if the blue LED lighting timing signal TB falls, the output of the PWM waveform forming circuit 26 stops, and the register selection circuit 15 selects the output of the R applied voltage storage register 11 instead of the B applied voltage storage register 13 Output.

Similarly, by repeating the red LED light emitting period LR, the green LED light emitting period LG, and the blue LED light emitting period LB, colors can be displayed in a field sequential manner.

In addition, in this embodiment, the light emission period of LR, LG and LB of each color LED is selected at about 5 mS, and the PWM signal output period for each color is selected at about 2000 μS. Furthermore, the PWM signal waveform has a unit period of 50 μS, and the duty ratios within the unit period are stored in the duty ratio storage registers 21 to 23 . Also in this embodiment, each of the duty ratio storage registers 21 to 23 can store duty ratios of 8 bits (=256 types).

Therefore, according to this embodiment, the driving voltage of each color LED is stored in the applied voltage storage registers 11, 12, 13, and the LED driving device 10 capable of reducing current consumption is realized by driving each color LED with an independent driving voltage.

Moreover, the data of the applied voltage registers 11, 12, and 13 can be rewritten via the stored value setting bus 14, so that even if there is a minimum light-emitting voltage due to product differences in actually installed LEDs (that is, to obtain desired brightness Even when there is a difference in the required minimum applied voltage), the voltages stored in the applied voltage registers 11, 12, and 13 can also be appropriately changed to correspond to the difference between the products. Therefore, for example, after the product is completed, it is possible to easily set the respective driving voltages of the LEDs of each color, and the driving voltage can obtain the luminance required by the product while suppressing the current consumption.

In addition, by performing PWM control on each color LED, the duty ratio for PWM control is independently stored in the duty ratio storage registers 21, 22, and 23 for each color LED, so that it is possible to have independent duty ratios for each color. The PWM signal independently controls the brightness of each color LED, so it is possible to adjust the brightness of each color LED more finely.

In addition, by providing the voltage variable circuit 18, the voltage generated by one power supply voltage generating circuit 19 is converted into the driving voltage of each color LED, thereby, compared with the case of providing a plurality of power supply voltage generating circuits that generate the driving voltage of each color LED , which can simplify the structure.

(implementation 2)

FIG. 8 shows the structure of an LED driving device 50 according to Embodiment 2 of the present invention, and the parts in FIG. 8 corresponding to those in FIG. 1 are marked with the same reference numerals. The structure of the LED driving device 50 is the same as that of the LED driving device 10 in Embodiment 1 except for the LED connection method in the LED unit 51 .

In this embodiment, the red LEDs among the red, green and blue LEDs are connected in series. Accordingly, the number of power supply systems for the red LED can be reduced, thereby reducing the current consumption required for the red LED to emit light.

That is, the present embodiment focuses on the fact that the driving voltage required to make the red LEDs emit light with the desired luminance is almost half of that required to make the green and blue LEDs emit light with the desired luminance.

From this, it is conceived that two red LEDs connected in series can be made to emit light at almost the same voltage as that applied to the green and blue LEDs. In other words, if the red LEDs are connected in series as in this embodiment, the power supply voltage generating circuit 19 does not need to generate a particularly large voltage, and the current consumption can be effectively reduced.

FIG. 9 shows the operation of the LED driving device 50 of this embodiment. Wherein, the difference from the above-mentioned Fig. 7 is that as shown in Fig. 9(a), in order to make the red LEDs connected in series emit light with desired brightness, the voltage provided by LR to the LED unit 20 during the red LED light-emitting period is changed from 2.2V to 4.4V . The voltage of 4.4V is within the battery voltage range of general portable electronic products.

Therefore, according to the structure of the present embodiment, red LEDs among the red, green, and blue LEDs are connected in series to realize the LED driving device 50 which can further reduce the current consumption in addition to the effect obtained in the first embodiment.

(other implementations)

However, in the above embodiment, to simplify the drawings and descriptions, the LED units 20 and 51 are composed of two red LEDs, two blue LEDs and one green LED respectively, but the number of LEDs of each color is not limited thereto.

Moreover, there is no limit to the number of LED units 20 and 51 , and the driving voltage and duty cycle of LEDs of each color can be independently set in each LED unit and stored in a memory.

In addition, variable voltages can be independently applied to LEDs of the same color, the brightness of LEDs of the same color can be independently measured, and the minimum applied voltage value when the LEDs of the same color detect brightness higher than or equal to the expected value can be independently set as the driving voltage. The value is stored in the applied voltage storage registers 11 to 13, and each LED is driven with the voltage value. In this way, even if there is a difference in driving voltages required to obtain desired luminance among LEDs of the same color, the LEDs of the same color can be driven with the minimum driving voltage corresponding to the difference, thereby further reducing current consumption.

Similarly, the LEDs of the same color can be controlled with PWM signals with different duty ratios, and the duty ratios when the LEDs of the same color detect the desired brightness can be independently stored in the duty ratio storage registers 21-23, and Each LED is PWM-controlled at this duty ratio. In this way, even if there is a difference in the duty ratio required to obtain the desired brightness among LEDs of the same color, each LED can be PWN-controlled with a duty ratio corresponding to the difference, enabling finer brightness adjustment and white balance. Adjustment.

In addition, it can also be applied to drive each white LED of a liquid crystal display device that combines a plurality of white LEDs and color filters to display colors. That is, if a plurality of memories corresponding to the respective white LEDs are provided, and the plurality of memories store the minimum light emission voltage and duty ratio corresponding to the difference in characteristics, the same effect as the above embodiment can be obtained.

In addition, 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. Thereby, brightness adjustment corresponding to the arrangement position of LED can be performed easily. For example, in a color filter liquid crystal display device using a plurality of white LEDs as the backlight, if there is a requirement to make the brightness near the edge of the screen higher than that near the center of the screen, the white LEDs corresponding to the edge of the screen If the applied voltage value and conduction duty ratio of the white LED corresponding to the central part of the screen are larger than the applied voltage value and conduction duty ratio of the white LED in the center of the screen, the brightness adjustment corresponding to the arrangement position of the LED can be easily performed.

In addition, although the above-mentioned embodiment has described the application of the LED driving device of the present invention to a field sequential liquid crystal display device, the LED driving device of the present invention is not limited thereto, and can also be widely used in applications using R , G, B three-color LED display color display device.

The present invention is not limited to the above-described embodiments, and may be implemented with various changes.

An embodiment of the LED driving device of the present invention adopts a structure that includes: a power supply voltage generating part; an applied voltage storage part that stores the independent applied voltage value of each LED of the red, green, and blue LEDs of the display device; The applied voltage forming part converts the voltage generated by the power supply voltage generating part into the applied voltage value stored in the applied voltage storage part and applies it to each color LED.

According to this configuration, since the following driving voltages are applied to the LEDs of each color based on the voltage values stored in the applied voltage storage means, that is, the same driving voltage is applied to the same color, and different driving voltages are applied to different colors. Current consumption can be reduced compared to the case where the same driving voltage is applied to each color LED.

One embodiment of the LED driving device of the present invention adopts a structure in which the applied voltage storage means is constituted by a writable memory, and the memory is connected to a signal line for inputting an applied voltage value to be stored.

According to this structure, since the independent applied voltage value of each color LED stored in the applied voltage storage means can be changed at any time, even if the actually installed LED has a minimum light emission voltage (that is, required for obtaining desired luminance) due to product differences, When there is a difference in the minimum applied voltage), the voltage stored in the applied voltage storage unit can also be appropriately changed to correspond to the difference between the products. Therefore, for example, after the product is completed, it is possible to easily set the respective driving voltages of the LEDs of each color, and the driving voltage can obtain the luminance required by the product while suppressing the current consumption.

An embodiment of the LED driving device of the present invention is that: the applied voltage storage unit adopts a structure that also stores independent applied voltage values for LEDs of the same color.

According to this configuration, even if there is a difference in the driving voltage required to obtain desired luminance among LEDs of the same color, the LED can be driven with the minimum driving voltage corresponding to the difference, so that the current consumption can be further reduced.

The structure adopted in one embodiment of the LED driving device of the present invention is to have: a duty cycle storage unit, which is composed of a writable memory, and each color LED independently stores and fine-tunes the brightness of each LED of each color during the light-emitting period. The duty ratio of the PWM signal; the PWM control part independently forms a PWM signal based on the duty ratio stored in the duty ratio storage part according to each color LED, and independently performs PWM control on each color LED; the signal line and the duty ratio The storage unit is connected for inputting the duty ratio into the duty ratio storage unit.

According to this configuration, since the luminance of the LEDs of each color can be independently controlled by a PWM signal having an independent duty ratio of each color, finer luminance adjustment of the LEDs of each color can be performed. In addition, since the independent duty ratio of each color stored in the duty ratio storage unit can be changed at any time, even if there is a difference in the brightness of the actually installed LED or the light guide plate and the liquid crystal panel, etc., it can also correspond to the above-mentioned difference through the signal line. The duty ratio at which desired display luminance can be obtained is appropriately written in the duty ratio storage section. In addition, since the duty cycle can be changed independently for each LED color, it is possible to easily adjust the white balance.

The structure adopted in one embodiment of the LED drive device of the present invention is: the applied voltage storage part stores the applied voltage value of each color LED, and the applied voltage value can make each color LED emit light with a brightness higher than or equal to the desired brightness, and the duty cycle The ratio storage means stores a duty ratio for making the light emission brightness of each color LED close to the desired brightness.

According to this configuration, the luminance of each color LED can be made to a desired value while reducing current consumption.

An embodiment of the LED driving device of the present invention adopts a structure in which the duty ratio storage unit also stores independent duty ratios for LEDs of the same color.

According to this configuration, even if there is a difference in the duty ratio required to obtain the desired brightness among LEDs of the same color, the duty ratio corresponding to the difference can be stored in each LED, thereby enabling finer brightness adjustment.

One embodiment of the LED driving device of the present invention adopts a structure in which the red LEDs among the red, green and blue LEDs are connected in series.

According to this configuration, since it is possible to efficiently generate a red LED drive voltage with a low minimum light emission voltage, the current consumption required to cause the red LED to emit light can be reduced. Here, the inventors of the present invention focused on the fact that the driving voltage required to make the red LED emit light with the desired luminance is almost half of the driving voltage required to make the green and blue LEDs emit light with the desired luminance. Almost the same voltage as the green and blue LEDs makes two red LEDs in series glow. That is, according to the above configuration, the current consumption can be reduced without causing the power supply voltage generating unit to generate an unnecessary voltage.

One embodiment of the LED driving device of the present invention adopts the structure that: the power supply voltage generating part generates a single voltage value, the applied voltage forming part has a D/A converter and a voltage variable part, and the D/A converter is used to control the applied voltage. The voltage value stored in the storage unit is converted from digital to analog, and the voltage variable unit is used to convert the single voltage value generated by the power supply voltage generating unit into a voltage equivalent to the analog value converted by the D/A converter.

According to this structure, since the voltage generated by the power supply voltage generating part common to each color LED can be used to form the independent applied voltage of each color LED stored in the applied voltage storage part, it can be compared with the case where a power supply voltage generating part corresponding to each color LED is provided. Simplify construction.

The structure adopted in one embodiment of the driving voltage setting device of the present invention is to have: a voltage applying part, which applies a variable voltage to each LED of red, green, and blue colors; The brightness of each color LED; the data writing part, the detection part writes the minimum applied voltage value of each LED applied to each color LED as the driving voltage value of each color LED when each LED of each color LED detects a brightness higher than or equal to the expected value into memory.

According to this configuration, the minimum driving voltage applied to the LEDs of each color can be independently set for each color, and the minimum driving voltage of each color can cause the LEDs of each color to emit light with a luminance higher than or equal to a desired value.

One embodiment of the LED driving method of the present invention is: pre-determining the minimum driving voltage that can obtain the desired brightness in red, green and blue LEDs, and storing the driving voltage of each LED of the various colors in the applied voltage storage unit. The stored voltage values are applied to the LEDs of each color.

According to this method, since independent driving voltages can be applied to the LEDs of each color based on the voltage value stored in the applied voltage storage means, current consumption can be reduced compared to the case of applying the same driving voltage to the LEDs of each color.

An embodiment of the LED driving method of the present invention is: in the state of applying the minimum driving voltage to each LED of each color, PWM control is performed on each color LED with a PWM signal with a different duty ratio for each LED of each color.

According to this method, it is possible to finely adjust the brightness of each color LED.

As mentioned above, according to the present invention, current consumption can be effectively reduced when driving red, green and blue LEDs to display colors. In addition, it is possible to eliminate the difference in the characteristics of each LED and perform color display with uniformity.

This application is based on patent application 2003-98486, patent application 2003-98487, and patent application 2003-98489 filed on April 1, 2003. The content thereof is included in this application.

The industrial applicability of this invention is that this invention is applicable to a liquid crystal display device etc., for example.

Claims (8)

1. A light-emitting diode driving device, comprising: Power supply voltage generation components; The applied voltage storage unit stores, as a digital value, the minimum applied voltage value required to obtain a luminance higher than or equal to a desired luminance independently for each color light-emitting diode of the red, green, and blue colors provided in the display device. ; an applied voltage forming section having a D/A converter for digital-to-analog converting a digital value stored in said applied voltage storing section, and for converting a voltage generated by said power supply voltage generating section into The voltage variable part of the voltage of the magnitude of the analog value converted by the /A converter; The duty cycle storage part independently stores the duty cycle of the pulse width modulation signal for fine-tuning the brightness of the light emitting diodes of each color according to the light emitting diodes of each color; and The pulse width modulation control part independently forms a pulse width modulation signal based on the duty ratio stored in the duty ratio storage part for each color light emitting diode, and independently performs pulse width modulation control on each color light emitting diode, The pulse width modulation control unit performs control to bring the light emission luminance of each color light emitting diode close to the desired luminance while the applied voltage forming unit independently applies different applied voltages to the light emitting diodes of each color. 2. The light emitting diode driving device according to claim 1, wherein the applied voltage storage means stores digital values that are also independent for light emitting diodes of the same color. 3. The light emitting diode driving device according to claim 1, wherein the duty ratio storage part stores duty ratios which are also independent for light emitting diodes of the same color. 4. The light emitting diode driving device according to claim 1, wherein the red light emitting diodes among the red, green and blue light emitting diodes are connected in series. 5. The LED driving device according to claim 1, comprising: A detection component for detecting the brightness of the red, green and blue light-emitting diodes; The data writing part writes the digital values respectively applied to the light emitting diodes of each color into the applied voltage storage part when the detection part respectively detects that the brightness of the light emitting diodes of each color is higher than or equal to the expected brightness. 6. The light-emitting diode drive device as claimed in claim 5, further having a duty ratio writing part, when the detection part detects desired brightness in each color light-emitting diode respectively, the respective duty ratios of each color light-emitting diode Write to the duty cycle storage unit. 7. The light emitting diode driving device as claimed in claim 5, wherein The applied voltage forming part also independently applies a variable voltage to the light emitting diodes of the same color; The detection component also independently detects the brightness of the same-color light-emitting diode; The data writing unit also independently writes the applied voltage value when each LED detects a brightness higher than or equal to a desired brightness as a digital value in the applied voltage storage unit for the LEDs of the same color. 8. The light emitting diode driving device as claimed in claim 6, wherein The pulse width modulation control part also controls the light emitting diodes of the same color with pulse width modulation signals with different duty ratios; The duty ratio writing unit also independently writes the duty ratio when each LED detects a desired brightness in the duty ratio storage unit for the LEDs of the same color.

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