JP2010205530A - Multicolor light source lighting system, and backlight device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To smooth sensor signals output in pulse waves in order to control driving of the light source based on detection information of the photosensor and carry out comparative treatment of higher accuracy, for a lighting system generating light of desired chromaticity distribution by mixing multicolor light sources such as LEDs. <P>SOLUTION: The system is provided with a comparative signal generating circuit for extracting given detection signals from detection information of the photosensor and generating comparative signals based on the given detection signals extracted and pulse-width modulation signals. The comparative signals obtained are compared with a given reference signal as a target value, and, with the use of the comparison result, a drive current of the LEDs is PWM controlled. Preferably, a peak-holding circuit is adopted for extracting and holding a peak value from pulse waves constituting sensor output signals, and comparative signals are calculated used for comparative treatment from the peak value and the pulse width. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an illumination system using a multicolor light source, and more particularly to an illumination system using a plurality of LEDs (Light Emitting Diodes) having different emission colors as light sources. The present invention also relates to a backlight device using such an illumination system.

  In an illuminating device in which a plurality of LEDs that emit light of different wavelength bands such as RGB (red, green, blue) are juxtaposed, and each emitted light is mixed to perform surface emission, the light emission amount of the LED is measured by a photosensor, Attempts have been made to obtain light emission of the chromaticity distribution of the period (for example, Patent Document 1). This aims at the effect of correcting the change in the amount of output light due to the deterioration of the LED over time and the temperature change, and is controlled by adjusting the peak value and pulse width of the drive current for each LED.

JP 2004-021147 A

  When the LED is driven and controlled by PWM (Pulse Width Modulation), the output of the optical sensor also corresponds to the PWM waveform, so that the detection information of the optical sensor is smoothed in order to use this as a comparison signal. There is a need to. For example, a smoothing circuit can be formed by combining circuit elements such as a capacitor and a resistor, which can be converted into a DC signal (for example, a voltage signal). However, such a smoothing circuit has a problem that the output signal is not stable due to variations caused by each circuit component itself, temperature characteristics, and the like, and as a result, the light emission of the LED is adjusted by feedback control. , The desired chromaticity may not be obtained.

  The present invention has been made in view of the above-described problems of the prior art, and has the following features.

  That is, a plurality of light sources that emit light of different colors, an optical sensor that detects light emitted from the light sources, and a pulse width modulation signal that outputs a pulse width modulation signal to adjust the amount of light from the plurality of light sources The multi-color light source illumination system comprising: an output circuit; and adjusting a light amount of the plurality of light sources based on information detected by an optical sensor. Based on a predetermined detection signal and the pulse width modulation signal, a comparison signal generation circuit that generates a comparison signal, and a comparison signal output by the comparison signal generation circuit and a predetermined reference signal are generated to generate a correction signal. And a correction signal generation circuit that adjusts the amount of light from the plurality of light sources based on the correction signal.

  According to the present invention, even when each light source is subjected to PWM control, a desired chromaticity distribution can be achieved more reliably without causing problems in the prior art such as variations due to signal smoothing. A useful lighting system can be provided.

It is a disassembled perspective view which shows the example of embodiment of the backlight apparatus which concerns on this invention. It is a figure which shows the example of the sensitivity characteristic of a sensor. It is a block diagram which shows the structural example of the backlight apparatus which concerns on this invention, and its control circuit. It is a figure which shows the example of the pulse signal of the drive current of LED. It is a figure which shows the relationship of each signal of a light control signal, a LED drive current signal, a sensor output signal, and a hold signal. It is a flowchart explaining the method of LED drive control of this invention. It is a figure which shows the structural example of a peak hold circuit.

  FIG. 1 illustrates a configuration example of a backlight device 10 according to one embodiment of the present invention.

  The backlight device 10 of this embodiment includes an LED array 4 in which a plurality of LEDs that emit red (R), green (G), and blue (B) light are arranged in parallel at the bottom of the unit case 2. The optical sensor 6 disposed on the side surface of the back frame 2, the control circuit 12 electrically connected to the optical sensor 6 and each LED array 4, and the unit case bottom surface on which the LED array 4 is disposed An optical member 8 disposed at an interval and a window frame-shaped front frame 1 capable of fixing the optical member 8 between the unit case 2 are provided.

  The LED functions as a light source of the backlight device 10. The peak of the emission spectrum of the LED exists in the wavelength range of 610 to 650 nm for the red LED, the wavelength of 515 to 535 nm for the green LED, and the wavelength of 440 to 470 nm for the blue LED. The LED array 4 is obtained by packaging such RGB light emitting chips as single color LEDs and arranging them in an array on a substrate.

  However, a detailed configuration such as how to configure the LED array 4, for example, in which order the RGB LEDs are arranged, how many LEDs are mounted per array, and how many columns of the LED array 4 are provided, is described in the present invention. It is not limited at all in relation to. The LED to be used is not limited to RGB, and any other light emitting color LED such as yellow or cyan can be used in combination. Each LED may be configured by a multi-chip package in which multi-color light emitting chips are enclosed in a single package, or may have a form in which light emitting chips such as RGB are directly mounted on an LED substrate.

  On the bottom and side surfaces of the unit case 2, a reflective surface is formed with a white reflective sheet or the like over substantially the entire area except for the area where the LED array 4 and the optical sensor 6 are arranged. It has a function of guiding the light reflected by the diffuser plate 8d and the like to the light output part side (front frame 1 side).

  In the present invention, the backlight device 10 is not limited to a so-called direct type, which is arranged in a matrix at the bottom of the unit case 2 as shown in the figure. For example, an LED array is arranged on at least one side surface of the unit case 2. A so-called side light type may be used. In this case, a reflector having a predetermined inclination according to the distance from the LED array 4 is arranged on the bottom surface of the unit case 2 to provide a mechanism for guiding the reflected light to the light emitting part side (front frame 1 side). preferable.

  At a position away from the bottom surface of the unit case 2 by a predetermined distance, an optical sheet composed of a diffusion sheet 8a, a lens sheet 8b, a diffusion sheet 8c, and the like, and an optical member 8 in which the diffusion plate 8d is superimposed are disposed. It is fixed at a predetermined position by a window frame-shaped front frame 1 having a large opening. The multicolor light emitted from each LED is mixed with each other in a hollow region in the backlight device 10 and is diffused and emitted from the surface of the optical member 8 as white light. With such a configuration, surface emission with uniform brightness and chromaticity can be obtained throughout. Further, in order to make the luminance and chromaticity sufficiently uniform, optimization is performed by adjusting the distance between the LED and the optical member 8 in the assembled state of the backlight device 10, the light distribution angle of the LED, and the like. desirable. Since FIG. 1 is only a schematic diagram for explaining an example embodying the present invention, the dimensions of each member illustrated, the distance between the members, and the like do not limit the present invention.

  The optical sensor 6 has a function of detecting light emitted from the LED. The optical sensor 6 is a photodiode formed of silicon or the like having a predetermined wavelength-sensitivity characteristic as illustrated in FIG. Here, the horizontal axis of the figure represents the wavelength [nm], and the vertical axis represents the relative light receiving sensitivity. The light receiving unit having high sensitivity corresponding to each wavelength region of RGB is configured to prevent light of other colors from passing by the color filter. For example, a color filter that shields green and blue light is provided in the vicinity of or close to the light receiving unit having high sensitivity in the red wavelength region. The optical sensor 6 is not limited to the photodiode described above, and a light receiving element such as a photomultiplier tube or a CCD (charge coupled device) can be similarly applied to the present invention.

  The manner in which the optical sensors 6 are attached is not limited to the specific form shown in the figure. For example, a plurality of optical sensors 6 may be arranged on the bottom surface of the unit case 2 so as to be positioned between the LED arrays 4. In addition, a window (not shown) may be provided so that direct light (non-reflected light) from the LED is blocked and only primary or higher-order reflected light enters the light receiving portion of the optical sensor 6.

  Next, a configuration example of the control circuit 12 that controls the backlight device 10 according to the present invention will be described with reference to FIG.

  In the case of the backlight device 10, the emitted light of the LED is detected by the optical sensor 6. The optical sensor 6 outputs a signal 40 corresponding to incident light based on the sensitivity characteristic illustrated in FIG. The characteristics of the emitted light of the LED can be controlled by adjusting the drive current for the LED by the LED driver 18.

For example, as shown in FIG. 4, the LED drive current is a duty ratio of the pulse wave 19 (19R, 19G, 19B) (the ratio of the current supply time τ to the time T of one cycle, that is, the pulse width τ is set to the pulse cycle. The value can be increased or decreased by adjusting (the value divided by T). As shown in the figure, the drive current pulse signal 19R for the red LED, the drive current pulse signal 19G for the green LED, and the drive current pulse signal 19B for the blue LED can be controlled independently with different duty ratios. . Further, I _R , I _G , and I _{B that} are the maximum amplitude values of the pulse wave 19 correspond to peak current values.

  When the emitted light quantity of each LED is adjusted by adjusting the duty ratio of the pulse wave in this way, the optical sensor 6 receives this and outputs an electric signal similar to the pulse wave. The output signal 40 is input to the voltage hold circuit 13 as shown in FIG. The voltage hold circuit 13 is configured to extract a peak value from the input pulse wave and hold (hold) it for a predetermined time. Various known voltage hold circuits can be applied. For example, it is possible to employ a configuration in which a peak potential is maintained by amplifying an input signal with an amplifier circuit, and charging by charging a capacitor or the like via a diode. The voltage value held by the voltage hold circuit 13 is converted from an analog signal to a digital signal 60 via the A / D converter 14 and output to the controller 16.

  The operation of the peak hold circuit will be described by taking the peak hold circuit 200 shown in FIG. 7 as an example. First, the hold value at the start, that is, the output OUT and the input IN are compared by the comparator OP1. Here, when the input voltage is higher, an H level signal is output from the comparator OP1, electricity flows through the diode D, and the capacitor C is charged (arrow 208). A buffer OP2 provided as a voltage follower is connected to the capacitor C, and a signal is sent to the output OUT while maintaining the voltage of the capacitor C (arrow 209). When this is repeated and the output OUT becomes equal to the input IN, electricity stops flowing through the capacitor C, and charging of the capacitor C is stopped. After that, since the circuit 200 outputs the voltage charged in the capacitor C (arrow 209), even if the input voltage decreases, the “held” voltage is output.

  When the held voltage is readjusted, a reset signal is sent from the reset means RE, and the electricity stored in the capacitor C is discharged through the transistor TR (arrow 210), so that the hold value can be reset. .

  Although the peak current can be held with the above-described configuration, the electricity stored in the capacitor C may be gradually dissipated with time, and this is prevented by providing a resistor in the illustrated circuit. Such a configuration can also be adopted. Thus, how the peak hold circuit is specifically configured should not be limited in any way in relation to the present invention.

  Referring again to FIG. 3, the controller 16 compares the comparison signal generation circuit that generates a comparison signal to be used as a comparison target described later based on the input signal 60 with the reference value signal 70 read from the memory 15. The circuit includes at least a correction signal generation circuit that outputs a correction signal 80 based on the comparison result. The comparison signal is generated by, for example, multiplying the input signal 60 corresponding to the peak value of the detection signal output by the optical sensor 6 and the pulse width (deity ratio) of the LED drive current.

  According to the present invention, the comparison signal is calculated by the above-described method, but additional correction may be added to the comparison signal. For example, an application of further correcting the comparison signal based on the detection value of a temperature sensor (not shown) attached close to the LED substrate or the like in consideration of the influence of the ambient temperature of the LED is also possible. In addition, it is possible to simplify and downsize the circuit configuration by configuring a part or all of the components constituting the control circuit 12 with a microcomputer or IC, or by combining a plurality of components. .

  In the above-described example, the LED driving current is described as being controlled by PWM. However, a control system combining peak current control and PWM control may be employed. That is, the reference signal peak value corresponding to the desired dimming rate is read from the storage medium, thereby performing primary dimming by increasing or decreasing the LED drive current, and the slight difference deviating from the predetermined range is PWM It is also possible to perform secondary dimming by control.

FIG. 5 shows an example of a timing chart of input / output signals in each block constituting the control circuit 12, and as shown in FIG. 5A, the lighting period T ₁ , the extinguishing period T ₂ , and the lighting period T _3. A case where the dimming signal 20 is input in this order will be described as an example.

  The LED drive current signal 30 output from the LED driver 18 has a pulse waveform 32 corresponding to PWM control (FIG. 5B). Since the LED emits light in response to the input electrical signal, the signal 40 detected by the optical sensor 6 and output to the control circuit 12 also becomes a pulse wave 42 having a similar period (FIG. 5C). )). In the present invention, the voltage hold circuit 13 holds the peak value (maximum amplitude value) of the optical sensor output signal 40 here. In other words, the output signal 50 of the voltage hold circuit 13 is a DC (direct current) signal 52 in which the peak voltage value is held (FIG. 5D). In FIG. 5C, the waveform 42 of the output signal of the optical sensor is shown by a solid line, but the held signal 52 is also shown by a broken line for easy comparison.

  Thus, since the detection signal 40 of the photosensor represented as the pulse waveform 42 is once converted to a DC voltage by the voltage hold circuit 13, the signal detected by the photosensor can be used more accurately for LED drive control. it can. The signal 50 output from the hold circuit 13 is further digitized and treated as a net sensor output value by multiplying the pulse width (duty ratio) of the dimming signal (for example, LED drive current signal 30). Can do.

  FIG. 5E is a comparative example that employs a method of smoothing with a capacitor C and a resistor R as in the prior art. A pulse waveform 90 indicated by a broken line indicates an output signal of the optical sensor, and a signal 92 indicated by a solid line indicates an output signal smoothed by the CR smoothing circuit. As described above, when a signal is smoothed using a conventional smoothing circuit, although there is a difference in degree depending on the circuit configuration, there is a backlash as shown in the figure due to temperature characteristics and variations of each circuit component. Since it becomes a signal with a stickiness, accuracy will be lost when this is used as a comparison signal.

  On the other hand, in the present invention in which the sensor output signal is converted to a DC voltage, the comparison signal can be calculated more accurately by holding the peak value instead of the pseudo linear signal. It can be applied to high-end backlight devices such as equipment.

  Next, a method for controlling driving by the control circuit 12 will be described. FIG. 6 is a flowchart illustrating the control method of the present invention.

  First, an LED driving signal (or dimming signal) is input from the LED driving circuit, and the LED is turned on (or dimmed) (process 101). Next, the light emitted from the LED is detected by an optical sensor, and a detection signal is sent to a control circuit (for example, the control circuit 12 in FIG. 3) (process 102). Among the output signals from the sensor that are pulse waves, the signal value having the largest amplitude is extracted and held by the peak hold circuit (processing 103). The peak-held signal is converted into a digital value by the A / D converter (process 104).

  The digitized peak value is multiplied by a pulse width (duty ratio) value determined based on the dimming signal to calculate a comparison signal used in the next comparison processing 107 (processing 105). A reference value read from the memory or the like is output together with the comparison signal to the comparison circuit that executes the comparison process 107 (process 106). This reference value becomes the target value of the sensor output value corresponding to the input dimming signal. For example, when the LED is dimmed to 60% of the maximum output, the reference value is determined so that the sensor detection value is approximately 60%. At this time, if necessary, the comparison value may be further corrected based on other factors such as temperature characteristics. Alternatively, it goes without saying that the reference value may be corrected, or both may be corrected.

  In the comparison process 107, the comparison value obtained from the sensor detection signal is compared with a predetermined reference value, and a pulse width modulation signal is generated based on the result of the comparison and correction is made by an amount deviating from the target value (reference value). To do. As a comparison condition, the feedback loop may be repeated until the comparison value and the reference value are completely matched, or the condition is relaxed so that it is within a predetermined numerical range (for example, plus or minus 3%). But you can.

  The correction signal based on the comparison result returns to the LED driving circuit again, generates a predetermined pulse width modulation signal, and dims the LED (processing 108). The emitted light of the LED whose drive current is finely adjusted in this way is detected again by the sensor, the same signal processing and comparison with the reference value are performed, and the process is repeated until predetermined luminance and chromaticity are obtained.

Although not particularly mentioned in the above description of the embodiment of the present invention, the control circuit and the control method based on the present invention are each of RGB (the same applies when colors other than red, green, and blue are included). The same thing may be applied every time, or the present invention is applied to only one of the colors (for example, green), and the other colors (for example, red, blue) are calculated from the ratio of the green LED driving current. You can also For example a red LED, a respective _I R drive current of the blue LED, When _{I B,} they may be calculated from the formula, such as _{I R = α G, I B} = β G (I G is the present invention The driving current of the green LED determined in this way, and α and β are arbitrary constants determined to obtain a desired chromaticity distribution.

  The illumination system according to the present invention and the backlight device adopting the system can be applied to various information display devices, for example, a liquid crystal display suitable for medical devices and televisions, or a wide range of uses such as signage illumination. .

10 Backlight device 12 Control circuit 4 LED array 6 Optical sensor

Claims (4)

Multiple light sources that emit light of different colors;
An optical sensor for detecting light emitted from the light source;
A pulse width modulation signal output circuit that outputs a pulse width modulation signal to adjust the amount of light from the plurality of light sources,
In a multicolor light source illumination system that adjusts the light amounts of the plurality of light sources based on information detected by an optical sensor,
A comparison signal generation circuit that extracts a predetermined detection signal from the detection information and generates a comparison signal based on the extracted predetermined detection signal and the pulse width modulation signal;
A correction signal generation circuit that compares the comparison signal output by the comparison signal generation circuit with a predetermined reference signal to generate a correction signal; and
A multicolor light source illumination system, wherein light amounts from the plurality of light sources are adjusted based on the correction signal.   The multicolor light source illumination system according to claim 1, wherein the detection signal to be extracted is a maximum amplitude value in the detection information.   The multicolor light source illumination system according to claim 1, wherein the comparison signal generation circuit includes a peak hold circuit.   The backlight apparatus which comprised the multicolor light source illumination system in any one of Claim 1 to 3.

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