JP2008091301A - Dimming circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a dimming circuit capable of controlling an amount of light emission in analog manner, responsive to variations in the color component of atmospheric light. <P>SOLUTION: The dimming circuit 1 is provided with each of red, green, and blue-color components. An illuminance sensor 3 is formed as current-output mode for outputting current in analog manner, increasing or decreasing, in response to variations in the increase or decrease of illuminance. A detecting resistor 5 is connected in a luminescent element 2 for detecting the current flowing through it. A drive control circuit 4 always keeps at a predetermined level the voltage value obtained by the current, passing through the luminescent element 2, and the current detected by the illuminance sensor 3 passing through the detecting resistor 5; and has a luminescent element driver 7 for outputting the obtained voltage to the luminescent element 2. The luminescent element 2 glows brightly, when the level is low in the detection illuminance and becomes dark, when the level is high. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a dimming circuit, and more particularly to a dimming circuit suitable for adjusting luminance and chromaticity of a lighting device that illuminates a liquid crystal device.

  In general, in a liquid crystal device used as an image display unit such as a mobile phone, an illumination device that illuminates the liquid crystal device is provided and the luminance of the screen is adjusted according to the ambient brightness.

  Various proposals have been made as light control devices for performing such brightness adjustment (see, for example, Patent Document 1).

  A conventional light control device as disclosed in Patent Document 1 is formed as shown in FIG. 3, for example. In FIG. 3, the illuminance level detected by the illuminance sensor 21 composed of a phototransistor or the like is output to the A / D converter 24 in the IC chip 23 as a voltage change through the resistor 22 for current / voltage conversion. The Subsequently, the analog voltage value input in the A / D converter 24 is converted into a digital value and output to the control circuit 25. In the control circuit 25, the illuminance in the lighting device 27 is calculated according to the input voltage value, and the luminance of the light emitting diode 28 to be lit in the lighting device 27 is calculated and converted into a PWM signal or the like to be driven. Output to. A large number of light-emitting diodes 28 (only one is shown in FIG. 3) are connected to the drive circuit 26. Subsequently, the drive circuit 26 outputs a drive signal to the light emitting diode 28 according to the luminance of the light emitting diode 28 to be emitted, which is input from the control circuit 25, thereby causing the light emitting diode 28 to emit light. When the illuminance level detected by the illuminance sensor 21 is changed, each component is operated corresponding to the change, and the light emitting diode 28 is caused to emit light with the luminance corresponding to the illuminance level.

  In addition, in reflective or transflective liquid crystal devices that place importance on reflection, the liquid crystal devices are illuminated using external light. It has also been proposed to adjust the light accordingly (for example, see Patent Document 2).

  In this patent document 2, the color tone and intensity of external light are detected, and when the external light is not white, the color tone emitted by the illumination device is corrected to be white. Specifically, the correction chromaticity / luminance calculation processing unit calculates the correction value according to the chromaticity and luminance detected by the external chromaticity detection unit and the external luminance detection unit, and drives the LED control unit. And illuminate with white light.

JP-A-10-191467 JP-A-2005-181441

  However, the conventional device disclosed in Patent Document 2 is compatible with colorization of liquid crystal equipment, but the specific circuit configuration is unknown, and the correction chromaticity / luminance calculation processing unit is By calculating the correction value, it is assumed that the signal is processed digitally.

  Furthermore, even if a conventional device as disclosed in Patent Document 1 that digitally processes signals is installed for each color component of light, the following disadvantages are involved in dimming and illumination for each color component. there were.

  That is, since the output of the illuminance sensor 21 is digitally read by A / D conversion, as shown in FIG. 4, the change in the luminance of the illumination device is stepwise with respect to the brightness of the ambient light, which is very visible. There was an inconvenience that there was a sense of incongruity.

  Further, in the vicinity of the threshold of the A / D converter 24 as indicated by a in FIG. 4, there is a disadvantage that flickering occurs due to the switching of the luminance of the lighting device. In order to solve this problem, flickering can be reduced by increasing the dimming gradation, but there is a disadvantage in that the scale of the circuit itself is increased and the cost is increased.

  Further, there is a disadvantage that flickering occurs when the PWM on / off cycle output to the lighting device is slow. To solve this problem, flicker is reduced by increasing the PWM period, but the clock period must be increased, and the increase in the current consumption of the control circuit is expected due to the increase in the clock period. Met. Also, if the PWM cycle is made faster, it is difficult to finely control the duty.

  In addition, the ambient brightness is very large in a dark room (several lux) to sunlight (several hundred thousand lux) and has a very large dynamic range. A large dynamic range is required for the reading circuit and the driving circuit of the illuminating device, resulting in a disadvantage that the circuit scale becomes large.

  In the end, there has not been realized a light control device that emits light of a color tone corresponding to colorization of liquid crystal equipment and can perform light control in an analog manner.

  The present invention has been made in view of these points, and when illuminating a reflective or transflective liquid crystal device with an emphasis on reflection, the amount of luminescence is analogized to changes in the illuminance of the color tone of ambient light. The light intensity for each color tone can be controlled very smoothly, and the color tone of the light emission can be adjusted appropriately in response to the change in the color tone of the surrounding light. It is an object of the present invention to provide a dimming circuit in which it is very easy to realize dimming of a desired dynamic range without generation of brightness and without stepwise luminance change.

  Another object of the present invention is to provide a light control circuit that does not require an illuminance sensor reading circuit, such as an A / D converter, and can simplify the circuit configuration.

  In order to achieve the above object, a dimming circuit according to the present invention includes an illuminance sensor that detects illuminance of ambient light, a light emitting element, and an amount of light emitted from the light emitting element according to the illuminance detected by the illuminance sensor. And a drive control circuit that emits light, the light control circuit comprising the light control circuit for each of the red, green, and blue color components, and the illuminance sensor responds to an increase or decrease in illuminance. It is formed in a current output type that outputs a current that increases and decreases in an analog manner, and a detection resistor that detects a current flowing through the light emitting element is connected to the light emitting element, and the drive control circuit is connected to the detection resistor. A light emitting element driver that outputs to the light emitting element a voltage that always holds a voltage obtained by flowing a current flowing through the light emitting element and a current detected by the illuminance sensor at a predetermined value; The light emitting element emits light brightly at dark detecting illuminance, characterized in that the light emitting dark bright place.

  According to the dimming circuit of the present invention, for each color component of ambient light, the illuminance sensor in each dimming circuit increases or decreases in an analog manner corresponding to the increase or decrease in illuminance of the corresponding color component of light. The light emitting element of the drive control circuit outputs a current to the light emitting element so that the voltage obtained by the current flowing through the light emitting element and the current detected by the illuminance sensor flowing through the detection resistor is always kept at a predetermined value. Because it outputs, the amount of light emitted by the light-emitting element can be adjusted in analogy to the change in illuminance of the color component of the surrounding light, and it emits brightly when the detected illuminance is dark and dark when it is bright Can emit light. As described above, according to the present invention, dimming for each color tone can be controlled very smoothly, and the color tone of light emission can be appropriately dimmed in accordance with the change in the color tone of the surrounding light. There is no occurrence of flickering, and the luminance does not change stepwise, so that it is very easy to realize dimming with a desired dynamic range.

  Further, in the light control circuit according to the present invention, a sensitivity increasing resistor for increasing the sensitivity of the output current is connected to the illuminance sensor, and the light emitting element driver has a current flowing through the light emitting element in the detection resistor and the current sensor. A voltage that always holds a voltage obtained by flowing a current detected by the illuminance sensor and a voltage obtained by flowing the current detected by the illuminance sensor through the sensitivity increasing resistor at a predetermined value is always emitted. It is formed so that it may output to an element.

  According to the light control circuit of the present invention, the light control operation can be performed by freely setting the sensitivity of the illuminance sensor by the resistance value of the sensitivity increasing resistor.

  The light control circuit according to the present invention is characterized in that a color filter for a color component to be detected by an illuminance sensor is attached to detect the illuminance of the color component.

  According to the light control circuit of the present invention, each illuminance sensor receives and detects the color component of the light to be detected through the color filter, thereby accurately detecting the illuminance of each color component of the light and The light emission color tone can be adjusted more appropriately in accordance with the change in the color tone.

  As described above, according to the light control circuit according to the present invention, the amount of light emitted by the light emitting element corresponding to each color component of light is appropriately adjusted in an analog manner corresponding to the change in illuminance of the color component of ambient light. More specifically, the excellent operational effects described in the means for solving the problems of the preceding paragraph can be exhibited.

  Hereinafter, an embodiment of a light control circuit according to the present invention will be described with reference to FIGS.

  FIG. 1 shows a circuit configuration of an embodiment of the present invention. The light control circuit of the present embodiment is suitable for light control for a lighting device of a liquid crystal device including a reflective type or a transflective LCD that places importance on reflection.

  The light control circuit of this embodiment is provided with light control circuits 1R, 1G, and 1B having substantially the same configuration for each color component of light, that is, for each of red (R), green (G), and blue (B).

In the light control circuits 1R, 1G, and 1B of the present embodiment, light emitting elements 2R, 2G, and 2B in which a plurality of LEDs 2a that function as light emitters of a lighting device (not shown) are connected in series, and ambient light of the lighting device Illuminance sensors 3R, 3G, and 3B that detect illuminance, and a drive control circuit 4R that emits light by adjusting the amount of light emitted from the light emitting elements 2R, 2G, and 2B according to the illuminance detected by the illuminance sensors 3R, 3G, and 3B, 4G, 4B. The anodes of the LEDs 2a of the light emitting elements 2R, 2G, and 2B are connected to the output terminals 4oR, 4oG, and 4oB of the drive control circuits 4R, 4G, and 4B, and the cathodes are currents i _LED that flow through the light emitting elements 2R, 2G, and 2B. It is connected to detection resistors 5R, 5G, and 5B that detect R, i _LED- G, and i _LED- B. Color filters 10R, 10G, and 10B corresponding to each color tone are arranged on the light receiving surfaces of the illuminance sensors 3R, 3G, and 3B, and the current i _sens that increases or decreases in an analog manner corresponding to the increase or decrease of the illuminance of each color component. R, i _sens- G, i _sens- B are formed with current output type phototransistors, the collector is connected to the power supply Vcc, the emitter is output currents i _sens- R, i _sens- G, It is connected to the detection resistors 5R, 5G, and 5B through the sensitivity increasing resistors 6R, 6G, and 6B that increase the sensitivity of i _sens- B and is connected to the input terminals 4iR, 4iG, and 4iB of the drive control circuits 4R, 4G, and 4B. ing. In this embodiment, the sensitivity increasing resistors 6R, 6G, and 6B are provided. However, the output currents i _sens- R, i _sens- G, and i _sens- B of the illuminance sensors 3R, 3G, and 3B are the light emitting elements 2R, 2G, This is not necessary when the amount of change can be easily obtained as compared to the currents i _LED- R, i _LED- G, and i _LED- B flowing through 2B. In the present embodiment, the currents i _LED- R, i _LED- G, i _LED- B flowing through the light emitting elements 2R, 2G, 2B are 15 to 20 mA, whereas the output current of the illuminance sensors 3R, 3G, 3B. Since isens _- R, isens _- G, and isens _- B are as small as 0.01 mA, the sensitivity increasing resistances 6R, 6G, and 6B are provided. The drive control times 4R, 4G, and 4B are detected by currents _iLED- R, _iLED- G, _iLED- B, and illuminance sensors 3R, 3G, and 3B that flow through the light-emitting elements 2R, 2G, and 2B to the detection resistors 5R, 5G, and 5B. The voltage V _out that always holds the voltages V _FB- R, V _FB- G, and V _FB- B obtained by the flow of the detected currents i _sen- R, i _sens- G, i _sens- B. _{chromatography R, V out over G, V out -} B light emitting elements 2R, 2G, light emitting element driver 7R output to 2B, 7G, has 7B. As the light emitting element drivers 7R, 7G, and 7B, those having a known configuration may be used, and the control drive circuits 4R, 4G, and 4B may be incorporated in the IC chips 8R, 8G, and 8B.

  Next, the operation of this embodiment will be described.

  The red light component will be described for easy understanding.

  First, a case where the sensitivity increasing resistor 6R is not provided will be described.

In a typical light emitting element driver 7R of the constant current drive type, voltage by applying a current _{i LED over} R flowing through the light emitting element 2R sense resistor 5R (R1 _over R) _{(V FB over} R _{= i LED over} R × R1 _{chromatography} R) is input after being converted, and the output voltage _Vout- R of the control drive circuit 4R is adjusted so that the value is always constant.

Therefore, when the illuminance sensor 3R acts by receiving ambient light transmitted through the red color filter 10R and detects the illuminance of the red component of the ambient light of the illumination device, the detection current i _sens- R is output and detected. It flows through the resistor 5R (R1 _- R). Thereby, the input voltage to the light emitting element driver 7R is obtained by the current i _LED- R flowing through the light emitting element 2R and the current i _sens- R detected by the illuminance sensor 3R flowing through the detection resistor 5R (R1 _- R). The total voltage V _FB− R = (i _LED− R + i _sens− R) × R1 ₋ R. Then, the light emitting element driver 7R sets the output voltage V _out- R of the control drive circuit 4R so that the total voltage V _FB− R = (i _LED− R + i _sen− R) × R1 ₋ R is always constant. The light emitting element 2R is caused to emit light by adjusting.

  Next, the case where the sensitivity increasing resistor 6R is provided will be described.

When there is provided a sensitivity increase resistance 6R, the input voltage to the light emitting element driver 7R, a current flows through the light emitting element 2R _{i LED over} R and illuminance sensor current _i detected by the 3R _{sens over} R and the detection resistor 5R (R1 sum voltage _{(i LED over} R _{+ i sens over} R) × R1 _over R of which is obtained by flowing in _over R), the current detected by the illuminance sensor 3R _{i sens over} R sensitivity increases resistance 6R (R2 _over R) The total voltage V _FB− R = (i _LED− R + i _sen− R) × R1 ₋ R + i _sen− R × R2 ₋ R with the voltage i _sen− R × R2 ₋ R obtained by flowing. Then, the light emitting element driver 7R is configured so that the value of the total voltage V _FB− R = (i _LED− R + i _sen− R) × R1 ₋ R + i _sen− R × R2 ₋ R is always constant. The light emitting element 2R is caused to emit light by adjusting the output voltage _Vout- R.

At this time, the detected current i _sens- R of the illuminance sensor 3R increases in a directly proportional and analog manner as the illuminance of the red component of the ambient light increases, as shown in FIG. At the same time, as shown in FIG. 2B, the amount of light emitted by the light emitting element 3R is high when the illuminance of the red component of the ambient light is low, and decreases proportionally and analogly as the illuminance of the red component of the ambient light increases. To do.

  As a result, light adjustment is performed such that the light-emitting element 2R emits light brightly in a place where the detected illuminance is dark with respect to the red light component and emits light darkly in a bright place.

For example, the output of the illuminance sensor 3R corresponding to the color filter 10R of the red light component increases under the reddish external light such as sunset. Accordingly, the current value i _LED- R of the light emitting element 2R of the red light component is reduced, and the color display of the liquid crystal device is always displayed in a constant color tone without following the color tone of the strong external light of the red component. It will be possible.

  The other light color components (green and blue) work in the same manner, and the liquid crystal device is always illuminated with white light.

  In an illuminating device for a liquid crystal device having a reflective or reflective semi-transmissive LCD for applying this embodiment, a light emitting element is generally arranged as a front light in the reflective type, and as a backlight in the semi-transmissive type. A light emitting element is arranged. The light amount of these illumination devices requires a sufficient amount of light in a dark place, but the light amount of the illumination device does not need so much because there is reflected light from outside light in a bright place. The dimming according to the present embodiment satisfies this need, and particularly in bright places, the amount of light emitted by the light emitting elements 2R, 2G, and 2B can be kept low, and the power consumption can be reduced. .

  In addition, according to the light control circuits 1R, 1G, and 1B of the present embodiment, the light emission amounts of the light emitting elements 2R, 2G, and 2B are adjusted in an analog manner corresponding to changes in the illuminance of the color components of the surrounding light. In addition, it can emit light brightly in a dark place where the detected illuminance is dark and emit light darkly in a bright place. According to this, the light control for each color tone can be controlled very smoothly, and the light emission color tone can be appropriately adjusted in accordance with the change in the color tone of the surrounding light. As a result, flickering of light emission does not occur as in the prior art, and the luminance does not change stepwise, and it is very easy to achieve dimming with a desired dynamic range.

  Furthermore, in the present embodiment, a reading circuit for an illuminance sensor, which has been conventionally required, for example, an A / D converter, a CPU for calculation, and the like are unnecessary, and the circuit configuration can be simplified.

  Further, by installing the sensitivity increasing resistors 6R, 6G, and 6B, the light control operation can be performed by freely setting the sensitivity of the illuminance sensors 3R, 3G, and 3B.

  In addition, this invention is not limited to the said embodiment, A various change is possible as needed.

The circuit diagram which shows one Embodiment of the light control circuit of this invention FIG. 1 shows characteristics in the embodiment shown in FIG. 1, (a) is a characteristic diagram showing the relationship between the intensity of ambient light and the output of the illuminance sensor, and (b) shows the relationship between the intensity of ambient light and the output of the light emitting element. Characteristics chart Circuit diagram showing an example of a conventional dimming circuit A characteristic diagram showing the relationship between the intensity of ambient light and the output of a light emitting device in a conventional dimming circuit

Explanation of symbols

1R, 1G, 1B Dimming circuit 2R, 2G, 2B Light emitting element 3R, 3G, 3B Illuminance sensor 4R, 4G, 4B Drive control circuit 5R, 5G, 5B Detection resistance 6R, 6G, 6B Sensitivity increasing resistance 7R, 7G, 7B Light emitting device driver

Claims (3)

  A dimming circuit comprising: an illuminance sensor that detects the illuminance of ambient light; a light emitting element; and a drive control circuit that emits light by adjusting a light emission amount of the light emitting element according to the illuminance detected by the illuminance sensor. The light control circuit is provided for each of the red, green, and blue color components of light, and the illuminance sensor is formed in a current output type that outputs a current that increases or decreases in an analog manner in response to an increase or decrease in illuminance. And a detection resistor for detecting a current flowing through the light emitting element is connected to the light emitting element, and the drive control circuit includes a current flowing through the light emitting element and a current detected by the illuminance sensor. A light-emitting element driver that outputs to the light-emitting element a voltage that always holds a voltage obtained by flowing to a predetermined value, and the light-emitting element emits light brightly in a dark area of detected illuminance; Light control circuit, characterized in that the light-emitting dark Rui plants.   A sensitivity increasing resistor for increasing the sensitivity of the output current is connected to the illuminance sensor, and the light emitting element driver has a current flowing through the light emitting element and a current detected by the illuminance sensor flowing through the detection resistor. And a voltage that always holds the sum of the voltage obtained by the current detected by the illuminance sensor flowing through the sensitivity increasing resistor at a predetermined value is output to the light emitting element. The light control circuit according to claim 1.   The light control circuit according to claim 1, wherein the illuminance sensor is formed so as to detect the illuminance of the color component by attaching a color filter of the color component to be detected.

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