JP2014072065A - Lighting device and display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lighting device capable of preventing problems such as deterioration of an S/N ratio, and preventing variation of light amount detection results due to a factor such as an individual difference, and a display device.SOLUTION: A current and voltage conversion part 13 converts an output current of an optical sensor S into a voltage and outputs it, and a light source control part 11 controls a light amount of the light source 2 according to brightness setting received by a setting reception part 15 and an output voltage of the current and voltage conversion part 13. Also, a conversion control part 14 controls efficiency for converting a current into a voltage with the current and voltage conversion part 13, so that the output voltage of the current and voltage conversion part 13 when the light source 2 emits light at a predetermined driving amount reaches a predetermined target voltage value. The conversion control part 14 outputs the PWM signals to the current and voltage conversion part 13, and the current and voltage conversion part 13 converts the current into the voltage at conversion efficiency according to a duty ratio of the PWM signals.

Description

  The present invention relates to an illumination device that controls the amount of light using an optical sensor, and a display device that performs display on a liquid crystal display panel using the illumination device.

  A display device that displays an image using a liquid crystal display panel includes an illumination device that irradiates light to the back surface of the liquid crystal display panel. In conventional display devices, the user can often change the setting of the brightness (brightness, brightness, brightness, etc.) of the displayed image according to his / her preference. When the brightness setting is changed, the display device controls the light amount of the light source by the illumination device according to the setting. In order to perform light amount control of a light source with high accuracy, there is an illumination device equipped with an optical sensor that detects the light amount.

  FIG. 11 is a circuit diagram showing a configuration of a conventional light quantity detection circuit. In the figure, S is an optical sensor, and the optical sensor S outputs a current I corresponding to the detected light amount. A resistor Rd is connected in series to the optical sensor S, and a voltage Va = Rd × I applied to the resistor Rd by the current I output from the optical sensor S is input to the non-inverting input terminal (+) of the amplifier Amp. . The illustrated circuit is a non-inverting amplifier circuit, and the output terminal of the amplifier Amp is connected to the inverting amplifier terminal (−) via the resistor Rf, and four resistors Rs1 to Rs4 are connected in parallel to the inverting amplifier terminal. The resistors Rs1 to Rs4 are connected to the ground potential via the switches SW1 to SW4. By controlling the opening and closing of the switches SW1 to SW4, the amplification factor of the non-inverting amplifier circuit can be switched in 16 stages. The light amount detection circuit supplies the output voltage Vb of the amplifier Amp to a control circuit of the illumination device, and the illumination device controls the light amount of the light source according to this.

  Patent Document 1 proposes a gain adjustment type amplifying apparatus that can adjust an optimum bias level with respect to a DC level of an input signal and can accurately control the gain of the input signal. The gain adjusting type amplifying apparatus includes a differential amplifying means in which an input signal is input to one of input terminals and a bias level adjusting means is connected to the other, and an adjusting means for adjusting a current amount of the differential amplifying means. And an analog signal according to the user's specification is provided to the adjusting means.

Japanese Patent Laid-Open No. 06-204766

  There are individual differences in the optical sensor S used for light quantity detection, and even if the light quantity of the light source is the same, the current value output by the optical sensor S may be different. The conventional light quantity detection circuit shown in FIG. 11 is configured to absorb individual differences of the optical sensor S by enabling the amplification factors to be switched by the switches SW1 to SW4. In addition to the individual differences of the optical sensors S, there are various factors that cause variations in the output voltage Vb of the light amount detection circuit, such as individual differences of other circuit elements constituting the circuit.

  However, in this light quantity detection circuit, for example, when the current value output from the optical sensor S is small, the amplification factor of the amplifier circuit is increased, but this causes a problem that the S / N ratio is deteriorated. The gain adjustment type amplifying device described in Patent Document 1 has the same problem. Further, the light quantity detection circuit of FIG. 11 has a problem that it is necessary to connect four control signal lines from a control circuit or the like in order to individually control the opening and closing of the four switches SW1 to SW4.

  The present invention has been made in view of such circumstances, and the object of the present invention is to obtain a light amount detection result due to factors such as individual differences of optical sensors without causing problems such as deterioration of the S / N ratio. It is an object of the present invention to provide an illumination device and a display device that do not cause variations.

  An illumination device according to the present invention includes a receiving unit that receives a set value related to the light amount of a light source, an optical sensor that outputs a current corresponding to the light amount of the light source, and one or a plurality of resistors. A conversion resistor unit that converts the output current into a voltage corresponding to the resistance value of the resistor and outputs the voltage, a smoothing unit that smoothes and outputs the voltage output from the conversion resistor unit, and a pulse signal with a variable duty ratio To the conversion resistance unit, and according to the conversion control unit for controlling the resistance value of the conversion resistance unit, the set value relating to the light quantity received by the reception unit and the output voltage value of the smoothing unit. A light source control unit that controls the amount of light, wherein the conversion resistance unit is configured to switch between two types of resistance values according to a pulse signal output from the conversion control unit, and the conversion control unit includes a predetermined set value Output power of the smoothing unit in So that the value becomes a predetermined target voltage value, characterized in that you have to control the resistance value of the converting resistor unit.

  The lighting device according to the present invention compares the output voltage value of the smoothing unit and the predetermined target voltage value by changing a duty ratio of the pulse signal, and the output voltage value becomes the predetermined target voltage value. Duty ratio determining means for determining the duty ratio of the pulse signal is further provided, and the conversion control section outputs the pulse signal to the conversion resistance section in accordance with the duty ratio determined by the duty ratio determining means. It is characterized by being.

  In the illumination device according to the present invention, the conversion control unit outputs a pulse signal having a duty ratio determined by the duty ratio determination unit to the conversion resistance unit, and the light amount received by the reception unit is set. The apparatus further comprises target voltage value calculation means for calculating a target voltage value corresponding to the set value based on the set value, the predetermined set value, and the predetermined target voltage value, and the light source control unit outputs the output of the smoothing unit The light amount of the light source is controlled so that the voltage value becomes the target voltage value calculated by the target voltage value calculation means.

  In addition, the lighting device according to the present invention is configured such that when the light amount related to the setting value received by the receiving unit is smaller than a predetermined light amount, the second light source is based on the duty ratio determined by the duty ratio determining unit and the predetermined light amount. A duty ratio calculating means for calculating a duty ratio, wherein the conversion control section outputs a pulse signal having a second duty ratio calculated by the duty ratio calculating means to the conversion resistance section; The voltage calculation means further calculates a target voltage value corresponding to the set value based on the duty ratio determined by the duty ratio determination means and the second duty ratio calculated by the duty ratio calculation means. It is characterized by that.

  The lighting device according to the present invention may be configured such that the output voltage value of the smoothing unit is set as the predetermined target voltage value based on a set value related to the amount of light received by the receiving unit and a duty ratio determined by the duty ratio determining unit. A duty ratio calculating means for calculating a duty ratio to be calculated, wherein the conversion control section outputs a pulse signal of the duty ratio calculated by the duty ratio calculating means to the conversion resistance section, and the light source control section Is characterized in that the light quantity of the light source is controlled so that the voltage value output by the smoothing unit becomes the predetermined target voltage value.

  Further, the lighting device according to the present invention includes a predetermined target voltage value determining unit that determines an output voltage value of the smoothing unit when the duty ratio of the pulse signal is a predetermined duty ratio, as the predetermined target voltage value, Duty ratio calculation for calculating a duty ratio based on the set value relating to the light quantity received by the receiving unit and the predetermined duty ratio, wherein the output voltage value of the smoothing unit is the predetermined target voltage value determined by the predetermined target voltage determining unit And the conversion control unit outputs a pulse signal having the duty ratio calculated by the duty ratio calculation unit to the conversion resistance unit, and the light source control unit outputs an output voltage of the smoothing unit. The light quantity of the light source is controlled so that the value becomes the predetermined target voltage value.

  Further, in the lighting device according to the present invention, the conversion resistance unit includes a resistor and a switching element connected in series in a path of a current output from the optical sensor, and the conversion control unit includes the switching element. The resistance value is controlled by controlling opening and closing.

  Moreover, the display apparatus which concerns on this invention is equipped with a liquid crystal display panel and the illuminating device as described in any one of Claim 1 thru | or 7 which irradiates light to the back surface of this liquid crystal display panel. And

In the present invention, the conversion resistance unit configured with one or a plurality of resistors converts the current output from the optical sensor into a voltage and outputs the voltage, and the smoothing unit smoothes the output voltage. The light source control unit receives a set value related to the light amount, and controls the light amount of the light source according to the received set value and the output voltage value of the smoothing unit. The conversion resistance unit is configured to switch between two types of resistance values according to the input pulse signal, and the conversion control unit outputs a pulse signal having a variable duty ratio to the conversion resistance unit to control the resistance value. When the resistance value of the conversion resistance unit is switched by the pulse signal from the conversion control unit, the output voltage of the conversion resistance unit is switched to a pulse shape, and the pulse voltage is smoothed and output by the smoothing unit.
The conversion control unit controls the resistance value of the conversion control unit so that the output voltage value of the smoothing unit at a predetermined setting value related to the light amount becomes a predetermined target voltage value. Thereby, according to factors, such as individual difference of an optical sensor, the conversion efficiency from the electric current by a conversion resistance part to a voltage can be adjusted, and the variation in the output voltage of a smoothing part can be reduced.
The conversion control unit performs so-called PWM (Pulse Width Modulation) control. Thereby, since the conversion control part can control the resistance value of a conversion resistance part with one pulse signal, the control signal line from a conversion control part to a conversion resistance part can be reduced.

  In the present invention, for example, when initial setting or calibration of the lighting device is performed, the output voltage value of the smoothing unit is obtained by changing the duty ratio of the pulse signal, and the output voltage value and the predetermined target voltage value are obtained. And the duty ratio determining means determines the duty ratio at which the output voltage value becomes the predetermined target voltage value. The conversion control unit controls the resistance value of the conversion resistor unit according to the determined duty ratio, and there are the following several methods.

  The conversion control unit outputs the pulse signal having the duty ratio determined by the duty ratio determining unit to the conversion resistance unit. In this case, a target voltage value corresponding to the received set value is calculated based on the set value relating to the received light quantity, the predetermined set value, and the predetermined target voltage value. The light source control unit controls the light amount of the light source so that the output voltage value of the smoothing unit becomes the target voltage value. This makes it possible to control the light quantity of the light source by absorbing individual differences of the optical sensors.

  Furthermore, the duty ratio may be changed when the light amount related to the received set value is smaller than the predetermined light amount. In this case, the duty ratio determining means calculates the second duty ratio according to the duty ratio determined by the predetermined light amount, and the conversion control unit outputs a pulse signal having the second duty ratio to the conversion resistance unit. The target voltage value is calculated by further taking into consideration the previous duty ratio and the second duty ratio (that is, change in the duty ratio). The light source control unit controls the light amount of the light source so that the output voltage value of the smoothing unit becomes the target voltage value. Thereby, it is possible to increase the resolution of light amount detection when the light amount related to the set value is small, and it is possible to improve the light amount control accuracy of the light source when the light amount is small.

  Alternatively, the light source control unit may fix the target voltage value of the output voltage value of the smoothing unit and change the duty ratio. In this case, the duty ratio determined by the duty ratio determining means is changed according to the set value relating to the received light quantity. The light source control unit controls the light amount of the light source so that the output voltage value of the smoothing unit becomes a predetermined target voltage value. Thereby, the resolution of light quantity detection can be increased in the entire range of setting values related to the light quantity, and the accuracy of light quantity control of the light source can be improved.

  In the present invention, for example, when initial setting or calibration of the lighting device is performed, the output voltage value of the smoothing unit when the duty ratio of the pulse signal is set to the predetermined duty ratio is determined as the predetermined target voltage value. The conversion control unit controls the duty ratio of the pulse signal according to the set value related to the light amount so that the output voltage value of the smoothing unit becomes a predetermined target voltage value. Thereby, the time required for initial setting or calibration can be shortened.

Further, in the present invention, the conversion resistance unit is configured such that a resistor and a switching element are connected in series in the output current path of the optical sensor. By controlling the opening and closing of the switching element, the resistance value of the conversion resistance unit can be switched to two types of resistance values. For example, the resistance value of the conversion resistance unit can be switched between a resistance value of a resistor in the current path and an infinite resistance value. Further, for example, by connecting a second resistor in parallel to a resistor and a switching element connected in series, the resistance value of the conversion resistor unit is the resistance value of the second resistor and two types of resistors. It is possible to switch to the combined resistance value.
By switching the resistance value of the conversion resistance unit, the output voltage of the conversion resistance unit with respect to the output current of the optical sensor changes in a pulse shape, but this output voltage is smoothed by the smoothing unit to become a substantially constant voltage. The output voltage value of the smoothing unit is determined according to the duty ratio of the pulse signal input to the conversion resistance unit. Therefore, the conversion control unit can control the conversion efficiency from the current output by the optical sensor to the voltage by controlling the duty ratio of the pulse signal.

  Moreover, in this invention, it is set as the structure which mounts the above illuminating devices in a display apparatus, and an illuminating device irradiates light to the back surface of a liquid crystal panel. As a result, the display device can appropriately adjust the brightness of the display screen in accordance with the user setting.

  In the case of the present invention, the resistance value of the conversion resistor unit is controlled so that the output voltage value of the smoothing unit at the predetermined setting value related to the light amount becomes the predetermined target voltage value, and the output of the smoothing unit according to the detected light amount of the optical sensor By controlling the light amount of the light source based on the voltage value, the resistance value of the conversion resistance unit can be adjusted according to factors such as individual differences of the optical sensors, and variation in the light amount detection result can be reduced. In addition, since it is not configured to adjust the amplification factor of the amplifier, problems such as deterioration of the S / N ratio do not occur. Therefore, the lighting device can perform light amount control with high accuracy, and the display device can adjust the brightness of the screen display with high accuracy.

It is a block diagram which shows the structure of the liquid crystal display device which concerns on this Embodiment. It is a circuit diagram which shows the structure of a current-voltage conversion part. It is a flowchart which shows the procedure of the conversion efficiency determination process of a current-voltage conversion part. It is a flowchart which shows the procedure of the brightness setting change process of a light source. 6 is a schematic diagram for comparing light source control methods of the liquid crystal display devices according to Embodiments 1 and 2. FIG. 10 is a flowchart illustrating a procedure of light source brightness setting change processing of the liquid crystal display device according to the second embodiment. 6 is a schematic diagram for explaining a method of controlling a light source of a liquid crystal display device according to Embodiment 3. FIG. 14 is a flowchart illustrating a procedure of light source brightness setting change processing of the liquid crystal display device according to the third embodiment. It is a schematic diagram for demonstrating the control method of the light source of the liquid crystal display device which concerns on a modification. 14 is a flowchart illustrating a procedure of target voltage value determination processing performed by the liquid crystal display device according to the fourth embodiment. It is a circuit diagram which shows the structure of the conventional light quantity detection circuit.

(Embodiment 1)
Hereinafter, the present invention will be specifically described with reference to the drawings showing embodiments thereof. FIG. 1 is a block diagram showing a configuration of a liquid crystal display device according to the present embodiment. In the figure, reference numeral 1 denotes a liquid crystal display panel. The liquid crystal display panel 1 has liquid crystal pixels arranged in a matrix, and the liquid crystal display device controls the transmittance of light emitted from the light source 2 to the back surface of the liquid crystal display panel 1 for each pixel, thereby producing a monochrome image. Alternatively, color image display is performed.

  In the liquid crystal display device, for example, an image signal from an external device such as a PC (Personal Computer) or a video reproduction device is input to the image input unit 16. The image signal input to the image input unit 16 is given to the image processing unit 17, and the image processing unit 17 performs various image processing on the input image signal according to the control of the main control unit 10. The image signal subjected to the image processing is supplied from the image processing unit 17 to the liquid crystal driving unit 18, and the liquid crystal driving unit 18 outputs a driving signal for driving each pixel of the liquid crystal display panel 1 in accordance with the supplied image signal. Generate and output.

  The liquid crystal display device includes a setting receiving unit 15 for receiving various setting operations related to display. The setting accepting unit 15 has one or a plurality of switches provided on, for example, the lower front portion of the casing of the liquid crystal display device, and accepts a setting operation by a user or the like using these switches. The setting accepting unit 15 accepts an operation related to the change of the setting value for setting of brightness (brightness, brightness or luminance), contrast, color temperature, and / or color balance, for example, and the accepted setting value is sent to the main control unit 10. To notify.

  The main control unit 10 is configured by using an arithmetic processing device such as a CPU (Central Processing Unit) or an MPU (Micro Processing Unit), and controls various operations in the liquid crystal display device and various arithmetic processes related to image display. I do. The main control unit 10 stores the setting value received by the setting receiving unit 15, and controls operations of the light source control unit 11, the conversion control unit 14, the image processing unit 17, the liquid crystal driving unit 18, and the like according to the setting value. Therefore, a control signal is output.

  In addition, the liquid crystal display device includes a light source control unit 11, a light source driving unit 12, a current-voltage conversion unit 13, a conversion control unit 14, an optical sensor S, and the like for controlling the light source 2. The optical sensor S is a sensor that is disposed in the vicinity of the liquid crystal display panel 1 or the light source 2 in the liquid crystal display device and detects the amount of light emitted from the light source 2. The optical sensor S outputs a current corresponding to the detected amount of light, and the current-voltage conversion unit 13 converts this output current into a voltage and outputs it to the light source control unit 11. The light source control unit 11 determines the light emission amount of the light source 2 according to the output voltage of the current-voltage conversion unit 13 and the control signal from the main control unit 10, and the light source 2 emits light with the determined light emission amount. A control signal is output to the drive unit 12. The light source driving unit 12 generates a driving voltage or driving current according to a control signal from the light source control unit 11 and outputs the driving voltage or driving current to the light source 2 to cause the light source 2 to emit light.

  For example, the main control unit 10 outputs a control signal to the light source control unit 11 and controls its operation so that the brightness according to the brightness setting value received by the setting reception unit 15 is obtained. The light source control unit 11 controls the light amount of the light source 2 so that the brightness according to the set value is obtained by a control signal from the main control unit 10. At this time, the light source control unit 11 acquires the detection result of the light amount by the optical sensor S as feedback information, and increases or decreases the light amount of the light source 2 according to the detection result of the light amount, so that the light source is closer to the set brightness. 2 light quantity is controlled. Further, at the time of initial setting or calibration of the liquid crystal display device, the light source control unit 11 gives the detection result of the optical sensor S to the main control unit 10 as necessary.

  Further, in the liquid crystal display device according to the present embodiment, the conversion control unit 14 controls the conversion efficiency of the current-voltage conversion unit 13 in order to improve the accuracy of the amount of light detected by the optical sensor S. The conversion control unit 14 generates a PWM (Pulse Width Modulation) signal for controlling the conversion efficiency of the current-voltage conversion unit 13 according to the control signal from the main control unit 10, and outputs it to the current-voltage conversion unit 13. .

  FIG. 2 is a circuit diagram showing a configuration of the current-voltage converter 13. As described above, the optical sensor S is a sensor that outputs a current I corresponding to the detected light amount, and is configured using, for example, a photodiode (in FIG. 2, the optical sensor S is illustrated as a photodiode). ). The output current I of the optical sensor S is input to a conversion resistance unit 131 configured using resistors Rd and Rp and a transistor T. The conversion resistor 131 converts the output current I of the optical sensor S into a voltage corresponding to the resistance values of the resistors Rd and Rp and outputs the converted voltage. The voltage output from the conversion resistor 131 is smoothed by the capacitor C and output as a substantially constant voltage value Va. In the present embodiment, the voltage output from the conversion resistor 131 is smoothed by the capacitor C. However, the smoothing of the voltage is not limited to the method using the capacitor C. For example, the voltage obtained by performing digital processing such as sampling the output voltage of the conversion resistance unit 131 to obtain a voltage value as a digital value and calculating an average value of the plurality of sampled voltage values. Smoothing may be performed by outputting a value signal.

  Specifically, the resistor Rd of the conversion resistor 131 and the transistor T are connected in series to the anode terminal of the optical sensor S, and the resistor Rp and the capacitor C are connected in parallel to the resistor Rd and the transistor T, respectively. . The voltage value of the anode terminal of the optical sensor S is converted and output as a smoothed voltage value Va.

  When the transistor T is in the open state (the current path from the resistor Rd to the ground potential is non-conductive), the output current I of the optical sensor S flows to the ground potential through the resistor Rp. The value is Rp × I. When the transistor T is in the closed state (the current path from the resistor Rd to the ground potential is conductive), the output current I of the optical sensor S flows to the resistors Rd and Rp, so that the combined resistance of the resistors Rd and Rp is Rdp. The output voltage value of the conversion resistor 131 is Rdp × I (<Rp × I).

  The opening and closing of the transistor T is controlled by a PWM signal output from the conversion control unit 14. This PWM signal is a pulse signal that is repeated so that the high level and the low level have a predetermined duty ratio. When the PWM signal is at a high level, the transistor T is closed, and when the PWM signal is at a low level. The transistor T is opened. By repeating the opening and closing of the transistor T by the PWM signal, the output voltage of the conversion resistance unit 131 repeatedly increases and decreases, but is smoothed by the capacitor C to become a substantially constant voltage value Va. The smoothed voltage value Va is determined by the output current I of the optical sensor S and the duty ratio of the PWM signal. That is, the illustrated circuit is a circuit that can control the conversion efficiency from the current I to the voltage Va by artificially adjusting the combined resistance Rpd of the conversion resistor 131 by controlling the duty ratio of the PWM signal. is there.

  The output voltage Va is input to an amplifier circuit using an amplifier Amp and resistors Rf and Rs. In this amplifier circuit, the voltage Va is input to the non-inverting input terminal (+) of the amplifier Amp, the output terminal of the amplifier Amp is input to the inverting amplifier terminal (−) via the resistor Rf, and the inverting amplifier terminal receives the resistor Rs. And connected to the ground potential via As a result, the output voltage Vb of the amplifier circuit becomes (Rf + Rs) / Rs × Va. This output voltage Vb is given to the light source controller 11.

  The duty ratio of the PWM signal output from the conversion control unit 14 is determined, for example, when a liquid crystal display device manufacturing process or a user who purchases the liquid crystal display device performs initial settings. At this time, the main control unit 10 outputs a control signal to the light source control unit 11 to cause the light source 2 to emit light to have a predetermined light amount (for example, a maximum light amount). Further, the main control unit 10 notifies the conversion control unit 14 of a predetermined duty ratio (for example, 50%) and outputs a PWM signal, and the output voltage of the current-voltage conversion unit 13 which is a result of detecting the light amount by the optical sensor S. Vb is acquired from the light source control unit 11. The main control unit 10 increases or decreases the duty ratio so that the acquired output voltage Vb becomes the predetermined target voltage value, stores the duty ratio when the output voltage Vb becomes the predetermined target voltage value, and uses it for the subsequent control. . The predetermined target voltage value is determined according to the characteristics of the light source 2, the optical sensor S, and the like in the design stage of the liquid crystal display device.

  FIG. 3 is a flowchart showing the procedure of the conversion efficiency determination process of the current-voltage converter 13. The main control unit 10 of the liquid crystal display device outputs a control signal to the light source control unit 11 to cause the light source 2 to emit light with a predetermined driving amount corresponding to a predetermined light amount such as a maximum light amount (step S1). Further, the main control unit 10 sets, for example, a predetermined initial duty ratio such as 50% in the conversion control unit 14 (step S2), and sets the conversion efficiency according to the initial duty ratio in the current-voltage conversion unit 13. .

  Next, the main control unit 10 acquires the value of the output voltage Vb of the current-voltage conversion unit 13 corresponding to the amount of light detected by the optical sensor S from the light source control unit 11 (step S3), and the acquired output voltage Vb is the predetermined target voltage. It is determined whether it is a value (step S4). At this time, the main control unit 10 does not completely match the output voltage Vb with the predetermined target voltage value, but if the output voltage Vb is within the predetermined target voltage value ± α (α is, for example, 5%). The output voltage Vb may be determined to be the target voltage value.

  When it is determined that the output voltage Vb is not the predetermined target voltage value (S4: NO), the main control unit 10 changes the setting of the duty ratio of the PWM signal output from the conversion control unit 14 (step S5), and step S3. The process is returned to and the acquisition and determination of the output voltage Vb are repeated. When it is determined that the output voltage Vb is the predetermined target voltage value (S4: YES), the main control unit 10 stores the duty ratio at this time in a nonvolatile memory or the like (step S6), and ends the process.

  In the normal operation in which the liquid crystal display device according to the present embodiment displays an input image from an external device on the liquid crystal display panel 1, the duty ratio stored in the above process is used in a fixed manner (that is, current). The light quantity is detected by the optical sensor S (with the conversion efficiency of the voltage conversion unit 13 fixed), and the light source 2 is controlled by the light source control unit 11. When a change in a setting value related to brightness setting (hereinafter simply referred to as brightness setting) is received by a user's operation on the setting reception unit 15, the liquid crystal display device receives the light source control unit 11 from the main control unit 10. The change of the set value is notified, and the light source control unit 11 changes the light amount of the light source 2 according to the set value.

  FIG. 4 is a flowchart showing the procedure of the brightness setting change process of the light source 2. The light source control unit 11 of the liquid crystal display device acquires the brightness setting from the main control unit 10 (step S11), and calculates the driving amount of the light source 2 corresponding to the brightness setting (step S12). The driving amount of the light source 2 corresponding to the brightness setting is calculated using a predetermined arithmetic expression. However, a table in which the brightness setting and the drive amount are associated with each other may be stored, and the drive amount may be acquired from this table. Further, the drive amount calculated in step S12 is given as an initial value of the drive amount that is updated in the subsequent processing, and a fixed value unrelated to the brightness setting is calculated and an initial value of the drive amount is not calculated. The driving amount at the previous brightness setting may be used as the initial value.

  Next, the light source control unit 11 calculates a target voltage value of the output voltage Vb of the current-voltage conversion unit 13 corresponding to the brightness setting (step S13). The calculation of the target voltage value corresponding to the brightness setting is performed using a predetermined arithmetic expression. This calculation formula is based on the brightness setting corresponding to the predetermined drive amount for causing the light source 2 to emit light in the process of determining the duty ratio shown in FIG. 3, and the predetermined target detection value used for the determination in step S4. The target voltage value can be calculated by substituting the new brightness setting (or the driving amount of the light source 2 according to the brightness setting) into the arithmetic expression. However, a table in which the brightness setting and the target voltage value are associated with each other may be stored, and the target voltage value may be acquired from this table.

  In the duty ratio determination process of the PWM signal, for example, it is assumed that the duty ratio at which the predetermined target voltage value is V1 is determined to be 60% at a brightness setting of 100% (predetermined drive amount = 100%). Thereafter, the control process of the light source 2 is performed with the duty ratio of the PWM signal fixed at 60%. Here, when the brightness setting is 70%, the target voltage value for the output voltage Vb of the current-voltage converter 13 is V1 × 70/100. That is, the calculation of the target voltage value can be realized by calculating the value of Y using the arithmetic expression Y = V1 / 100 × X when the brightness setting is X%.

  The light source control unit 11 performs the driving with the driving amount calculated in step S12 to cause the light source 2 to emit light (step S14). Next, the light source control unit 11 acquires the output voltage Vb of the current-voltage conversion unit 13 corresponding to the detection value of the optical sensor S (step S15), and the acquired output voltage Vb is the target voltage value calculated in step S13. Is determined (step S16). At this time, the light source control unit 11 does not completely match the output voltage Vb with the target voltage value. If the output voltage Vb is within the target voltage value ± α (α is, for example, 5%), the light source control unit 11 outputs The configuration may be such that the voltage Vb is determined to be the target voltage value.

  When it is determined that the output voltage Vb is not the target voltage value (S16: NO), the light source control unit 11 calculates the driving amount of the light source 2 again to bring the output voltage value Vb closer to the target voltage value (step S17). The process returns to step S14 and the above-described process is repeated. When it determines with the output voltage Vb being a target voltage value (S16: YES), the light source control part 11 complete | finishes a process.

  In the liquid crystal display device according to the first embodiment having the above configuration, the current I output from the optical sensor S is converted into the voltage Vb by the current-voltage conversion unit 13 and output, and the brightness setting received by the setting reception unit 15 The light source controller 11 controls the amount of light from the light source 2 in accordance with the voltage Vb output from the current-voltage converter 13. The liquid crystal display device also converts the conversion efficiency from the current I to the voltage Vb by the current / voltage changing unit 13 so that the output voltage Vb of the current-voltage converting unit 13 when the light source 2 emits light with a predetermined driving amount is Thus, the conversion control unit 14 controls. Thereby, it is possible to prevent variation in the output voltage Vb of the current-voltage conversion unit 13 according to factors such as individual differences of the optical sensors S, and it is possible to perform light amount control of the light source 2 with high accuracy.

  Moreover, the conversion control part 14 outputs a PWM signal to the current voltage conversion part 13, and the current voltage conversion part 13 performs conversion from the current I to the voltage Vb with the conversion efficiency according to the duty ratio of the PWM signal. The current-voltage conversion unit 13 includes a conversion resistance unit 131 whose resistance value changes according to the PWM signal, and a capacitor C that smoothes the voltage obtained by converting the output current I of the optical sensor S by the conversion resistance unit 131. In this configuration, the output voltage Vb changes with a change in resistance value. Thereby, since the conversion efficiency can be controlled by connecting one control signal line from the conversion control unit 14 to the current-voltage conversion unit 13, the number of signal lines can be reduced.

  Further, when initial setting or calibration of the liquid crystal display device is performed, the voltage Vb output from the current-voltage conversion unit 13 is acquired by changing the duty ratio of the PWM signal output from the conversion control unit 14, and the acquired voltage Vb is compared with a predetermined target voltage value to determine a duty ratio at which the output voltage Vb becomes the target voltage value. The conversion control unit 14 outputs a PWM signal having the determined duty ratio. The light source control unit 11 sets the brightness setting received by the setting receiving unit 15, the brightness setting corresponding to the driving amount of the light source 2 at the time of determining the duty ratio (predetermined setting value related to the light amount), and the predetermined target voltage value. Based on the received brightness setting, a target voltage value is calculated. The light source controller 11 controls the light amount of the light source 2 so that the output voltage Vb of the current-voltage converter 13 becomes the calculated target voltage value. Thus, it is possible to control the light quantity of the light source 2 by absorbing individual differences of the optical sensors S.

  The current-voltage converter 13 has a configuration in which a resistor Rd and a transistor T are connected in series to the optical sensor S, and the opening and closing of the transistor T is controlled by a PWM signal. With this configuration, the conversion control of the current-voltage converter 13 can be easily controlled by the conversion controller 14 controlling the duty ratio of the PWM signal. In addition, the light source control unit 11 performs processing with the amplified voltage Vb by converting the output current I of the optical sensor S into the voltage Va, amplifying the voltage Vb with an amplifier circuit, and outputting the voltage Vb. Therefore, processing can be performed with high resolution.

  In this embodiment, the liquid crystal display device has been described as an example. However, the present invention is not limited to this, and the same configuration is applied to other illumination devices that control the light amount of the light source 2 using the optical sensor S. can do. Further, although the conversion efficiency is controlled by controlling the opening and closing of the transistor T of the current-voltage conversion unit 13 by the PWM signal output from the conversion control unit 14, the present invention is not limited to this. For example, the conversion control unit 14 may output a control signal that is linearly converted, and may linearly control the opening and closing of the transistor T of the current-voltage conversion unit 13 according to the control signal. Good. In addition, the circuit configuration of the current-voltage conversion unit 13 illustrated in FIG. 2 is an example, and is not limited thereto. In addition, the current-voltage conversion unit 13 is configured to amplify and output the voltage by the amplifier circuit, but is not limited thereto, and may be configured to not perform amplification. In FIG. 1, the liquid crystal display device includes the main control unit 10, the light source control unit 11, and the conversion control unit 14 as separate blocks. However, the present invention is not limited to this, and two or three of them are included. One may be realized as one block.

(Embodiment 2)
In the liquid crystal display device according to the first embodiment described above, the duty ratio of the previously determined PWM signal is fixedly used, and the duty ratio changes in the control process of the light source 2 according to the subsequent brightness setting. Absent. In the liquid crystal display device according to the second embodiment, when the brightness setting exceeds a predetermined brightness (for example, 50% brightness when the maximum brightness is 100%, etc.), The same light source 2 control process is performed (that is, the previously determined duty ratio is used). When the brightness setting is equal to or lower than the predetermined brightness, the duty ratio is changed and the light source 2 control process is performed. . The liquid crystal display device according to the second embodiment has a configuration in which the duty ratio of the PWM signal is changed in two steps (or more than that) according to the brightness setting received by the setting receiving unit 15.

  FIG. 5 is a schematic diagram for comparing the control method of the light source 2 of the liquid crystal display device according to the first and second embodiments, where the horizontal axis is the brightness setting and the vertical axis is the duty ratio of the PWM signal or the target voltage. A graph with values is shown for each embodiment. As shown in FIG. 5A, in the liquid crystal display device according to Embodiment 1, the duty ratio of the PWM signal is fixed with respect to the change of the brightness setting, and the target voltage value changes according to the brightness setting. As shown in FIG. 5B, the liquid crystal display device according to the second embodiment changes the duty ratio of the PWM signal stepwise depending on whether the brightness setting exceeds 50%, for example, The voltage value also changes discontinuously at a location where the brightness setting is 50%.

  When the brightness setting is 50% or less, the liquid crystal display device according to the second embodiment has a period lower than the previously determined duty ratio of the PWM signal (first duty ratio) (that is, a high level period) The light source 2 is controlled using a duty ratio (second duty ratio). When the duty ratio of the PWM signal decreases, the open time of the transistor T of the current-voltage conversion unit 13 shown in FIG. 2 decreases, and the combined resistance value of the resistors Rd and Rp connected in parallel increases in a pseudo manner. The output voltage Vb increases. Therefore, the target voltage value of the light source controller 11 also increases as shown in FIG. 5B. Thereby, since the resolution of the detection result of the optical sensor S can be increased in a pseudo manner, the control accuracy of the light source 2 when the brightness setting is 50% or less can be improved.

  FIG. 6 is a flowchart showing the procedure of the brightness setting change process of the light source 2 of the liquid crystal display device according to the second embodiment. The main control unit 10 of the liquid crystal display device acquires the brightness setting from the setting receiving unit 15 (step S21), and determines whether or not the brightness setting is 50% or less (step S22). When the brightness setting exceeds 50% (S22: NO), the main control unit 10 causes the light source control unit 11 to perform the same processing as the liquid crystal display device according to the first embodiment. That is, the light source control unit 11 calculates a target voltage value according to the brightness setting using a predetermined arithmetic expression or the like (step S23), and advances the process to step S27.

  When the brightness setting is 50% or less (S22: YES), the main control unit 10 calculates the duty ratio (second duty ratio) of the PWM signal output from the conversion control unit 14 (step S24). The calculation of the second duty ratio in step S24 is performed by multiplying the first duty ratio determined by the processing shown in FIG. 3 by a predetermined coefficient α (where 0 <α <1). The predetermined coefficient α is determined based on the resistance values of the resistors Rd and Rp of the current-voltage conversion unit 13 and the characteristics of the optical sensor S in the design stage of the liquid crystal display device. Next, the main control unit 10 notifies the conversion control unit 14 of the calculated second duty ratio and changes the duty ratio of the PWM signal (step S25). The main control unit 10 notifies the light source control unit 11 of the calculated second duty ratio.

  Next, the light source control unit 11 calculates the target voltage value of the optical sensor S corresponding to the brightness setting in consideration of the duty ratio change by the main control unit 10 (step S26). The change in the output voltage Vb of the current-voltage conversion unit 13 with respect to the change in the duty ratio can be calculated in advance according to the circuit configuration of the current-voltage conversion unit 13 (or obtained by simulation or actual measurement). The light source control unit 11 stores the change in the output voltage Vb with respect to the change in the duty ratio as information such as an arithmetic expression or a table. The light source control unit 11 calculates a target voltage value corresponding to the brightness setting by the same method as in step S23 (or step S13), and further, based on information related to the change in the output voltage Vb with respect to the change in the duty ratio. By correcting the calculated target voltage value, the target voltage value for the changed second duty ratio is calculated. The light source controller 11 advances the process to step S27 after calculating the target voltage value.

  Next, the light source control unit 11 calculates the driving amount of the light source 2 corresponding to the brightness setting (step S27). The driving amount of the light source 2 corresponding to the brightness setting is calculated using a predetermined arithmetic expression. The light source controller 11 performs driving with the calculated driving amount to cause the light source 2 to emit light (step S28). Next, the light source control unit 11 acquires the output voltage Vb of the current-voltage conversion unit 13 corresponding to the detection value of the optical sensor S (step S29), and the acquired output voltage Vb is the target voltage value calculated in step S23 or S26. It is determined whether or not (step S30). When it is determined that the output voltage Vb is not the target voltage value (S30: NO), the light source control unit 11 calculates the driving amount of the light source 2 again to bring the output voltage value Vb closer to the target voltage value (step S31). The process returns to step S28 and the above-described process is repeated. When it determines with the output voltage Vb being a target voltage value (S30: YES), the light source control part 11 complete | finishes a process.

  In the liquid crystal display device according to the second embodiment having the above configuration, when the brightness setting is 50% or less, the duty ratio of the PWM signal output from the conversion control unit 14 is changed from the first duty ratio to the second duty ratio. And the conversion efficiency of the current-voltage conversion unit 13 is changed stepwise. The light source control unit 11 of the liquid crystal display device calculates a target voltage value in consideration of a change in the duty ratio of the PWM signal (that is, the difference between the first and second duty ratios), and outputs the output voltage Vb of the current-voltage conversion unit 13. The light quantity of the light source is controlled so that becomes the target voltage value. Thereby, the resolution of the light quantity detection when the brightness setting is 50% or less can be increased, and the control accuracy of the light source 2 can be improved.

  In the present embodiment, the duty ratio is changed depending on whether the brightness setting exceeds 50%. However, this brightness setting is an example, and the present invention is not limited to this. Further, the second duty ratio may be calculated when the first duty ratio is determined and stored in the main control unit 10 or the light source control unit 11 of the liquid crystal display device. The duty ratio is changed to two types. However, the present invention is not limited to this, and the duty ratio is changed at a plurality of brightness setting points, and control is performed by combining three or more types of duty ratios. Also good.

  The other configuration of the liquid crystal display device according to the second embodiment is the same as the configuration of the liquid crystal display device according to the first embodiment, and therefore, the same components are denoted by the same reference numerals and detailed description thereof is omitted. .

(Embodiment 3)
FIG. 7 is a schematic diagram for explaining a method of controlling the light source 2 of the liquid crystal display device according to the third embodiment. The liquid crystal display device according to Embodiment 3 has a configuration in which the target voltage value is set to a constant value regardless of the brightness setting, and the duty ratio is changed so that the output voltage Vb of the current-voltage conversion unit 13 becomes the target voltage value. It is. Thereby, the resolution of the detection result (that is, the output voltage Vb) of the optical sensor S can be maintained regardless of the change in the light amount of the light source 2 according to the brightness setting.

  FIG. 8 is a flowchart showing the procedure of the brightness setting change process of the light source 2 of the liquid crystal display device according to the third embodiment. The main control unit 10 of the liquid crystal display device acquires the brightness setting from the setting reception unit 15 (step S41), and calculates the duty ratio of the PWM signal according to the acquired brightness setting (step S42). The duty ratio according to the brightness setting is calculated using a predetermined arithmetic expression.

  For example, it is assumed that the duty ratio which becomes the predetermined target voltage value is determined as A at the brightness setting of 100% in the duty ratio determination processing of the PWM signal shown in FIG. Thereafter, when the brightness setting is changed, the duty ratio of the PWM signal is reduced by an amount corresponding to the decrease in the brightness setting. For example, the calculation of the duty ratio can be realized by calculating the value of Y using the arithmetic expression Y = A × β × X when the brightness setting is X%. In this arithmetic expression, β is a coefficient determined at the design stage of the liquid crystal display device.

  The main control unit 10 notifies the conversion control unit 14 of the calculated duty ratio and changes the duty ratio of the PWM signal (step S43). Next, the light source control unit 11 calculates the driving amount of the light source 2 corresponding to the brightness setting (step S44). The driving amount of the light source 2 corresponding to the brightness setting is calculated using a predetermined arithmetic expression. The light source controller 11 performs driving with the calculated driving amount to cause the light source 2 to emit light (step S45). Next, the light source control unit 11 acquires the output voltage Vb of the current-voltage conversion unit 13 corresponding to the detection value of the optical sensor S (step S46), and the acquired output voltage Vb is a predetermined target voltage value (step S4 in FIG. 3). It is the same as that used for the determination) (step S47). When it is determined that the output voltage Vb is not the predetermined target voltage value (S47: NO), the light source control unit 11 calculates the driving amount of the light source 2 again so that the output voltage value Vb approaches the predetermined target voltage value (step S48). ), The process is returned to step S45, and the above process is repeated. When it determines with the output voltage Vb being a predetermined target voltage value (S47: YES), the light source control part 11 complete | finishes a process.

  The liquid crystal display device according to Embodiment 3 having the above configuration is configured to fix the target voltage value to a predetermined target voltage value and change the duty ratio of the PWM signal in accordance with the change in brightness setting. The light source controller 11 controls the driving of the light source 2 so that the output voltage Vb of the current-voltage converter 13 becomes a predetermined target voltage value. Thereby, the resolution of the output voltage Vb can be increased in the entire range of brightness setting, and the accuracy of the light amount control of the light source 2 can be improved.

  Since the other configuration of the liquid crystal display device according to the third embodiment is the same as that of the liquid crystal display device according to the first embodiment, the same portions are denoted by the same reference numerals and detailed description thereof is omitted. .

(Modification)
FIG. 9 is a schematic diagram for explaining a method of controlling the light source 2 of the liquid crystal display device according to the modification. The liquid crystal display device according to the modification performs control combining the control method of the liquid crystal display device according to the first embodiment and the control method of the liquid crystal display device according to the third embodiment. That is, when the brightness setting exceeds a predetermined value, the duty ratio is fixed and the liquid crystal display device according to the first embodiment is controlled to change the target voltage value. When the brightness setting does not exceed the predetermined value, the liquid crystal display device according to the third embodiment is controlled by fixing the target voltage value and changing the duty ratio. Accordingly, it is possible to prevent a decrease in the resolution of the output voltage Vb when the brightness setting does not exceed a predetermined value.

(Embodiment 4)
In the liquid crystal display device according to the fourth embodiment, the light source control unit 11 controls the brightness setting change by fixing the target voltage value and changing the duty ratio in the same manner as the liquid crystal display device according to the third embodiment. Do. However, the liquid crystal display device according to the fourth embodiment differs from the liquid crystal display device according to the third embodiment in the method of determining the initial value of the duty ratio and the target voltage value. The target voltage value used for control by the light source control unit 11 is determined, for example, when the liquid crystal display device manufacturing process or the user who purchased the liquid crystal display device performs initial setting. At this time, the main control unit 10 outputs a control signal to the light source control unit 11 to cause the light source 2 to emit light to have a predetermined light amount (for example, a maximum light amount). Further, the main control unit 10 notifies the conversion control unit 14 of a predetermined duty ratio (for example, 50%) and outputs a PWM signal, and the output voltage of the current-voltage conversion unit 13 which is a result of detecting the light amount by the optical sensor S. Vb is acquired from the light source control unit 11. The main control unit 10 stores the acquired output voltage Vb as a target voltage value and uses it for subsequent control.

  FIG. 10 is a flowchart illustrating a procedure of target voltage value determination processing performed by the liquid crystal display device according to the fourth embodiment. The main control unit 10 of the liquid crystal display device outputs a control signal to the light source control unit 11 to cause the light source 2 to emit light with a predetermined driving amount corresponding to a predetermined light amount such as a maximum light amount (step S51). Further, the main control unit 10 sets a predetermined duty ratio such as a predetermined 50% in the conversion control unit 14 (step S52), and sets the conversion efficiency corresponding to the predetermined duty ratio in the current-voltage conversion unit 13. . Next, the main control unit 10 acquires the value of the output voltage Vb of the current-voltage conversion unit 13 according to the light amount detected by the optical sensor S from the light source control unit 11 (step S53), and uses the acquired output voltage Vb as the target voltage value. Is stored in a non-volatile memory or the like (step S54), and the process is terminated.

  Further, the liquid crystal display device according to the fourth embodiment performs the light amount control of the light source 2 in response to the brightness setting change according to the procedure shown in the flowchart of FIG. However, the initial value of the duty ratio used for the calculation in step S42 is the predetermined duty ratio set in step S52 of FIG. In step S47, the output voltage Vb of the current-voltage converter 13 is compared with the target voltage value stored in step S54 of FIG.

  In the liquid crystal display device according to the fourth embodiment having the above configuration, the current-voltage conversion unit 13 when the conversion control unit 14 outputs a PWM signal having a predetermined duty ratio at the time of initial setting or calibration of the liquid crystal display device. Is stored as a target voltage value. Thereafter, the conversion control unit 14 controls the duty ratio of the PWM signal so that the output voltage Vb of the current-voltage conversion unit 13 becomes the target voltage. Thereby, the time required for the initial setting or calibration of the liquid crystal display device can be shortened.

  Since the other configuration of the liquid crystal display device according to the fourth embodiment is the same as that of the liquid crystal display device according to the third embodiment, the same portions are denoted by the same reference numerals and detailed description thereof is omitted. .

DESCRIPTION OF SYMBOLS 1 Liquid crystal display panel 2 Light source 10 Main control part 11 Light source control part (Duty ratio determination means, target voltage value calculation means, duty ratio calculation means, predetermined target voltage value determination means)
12 light source drive unit 13 current voltage conversion unit 14 conversion control unit 15 setting reception unit (reception unit)
131 Conversion resistance unit Amp amplifier (voltage amplifier)
C capacitor (smoothing part)
Rd, Rf, Rp, Rs Resistance (resistor)
S Optical sensor T Transistor (switching element)

Claims (8)

A reception unit that receives a setting value related to the light amount of the light source;
An optical sensor that outputs a current corresponding to the light amount of the light source;
A conversion resistor unit that includes one or a plurality of resistors, converts the current output from the optical sensor into a voltage corresponding to the resistance value of the resistor, and outputs the voltage;
A smoothing unit that smoothes and outputs the voltage output by the conversion resistor unit;
A conversion control unit that outputs a pulse signal having a variable duty ratio to the conversion resistor unit and controls a resistance value of the conversion resistor unit;
A light source control unit that controls the light amount of the light source according to a set value related to the light amount received by the reception unit and an output voltage value of the smoothing unit, and
The conversion resistance unit is configured to switch between two types of resistance values according to a pulse signal output from the conversion control unit,
The illumination device according to claim 1, wherein the conversion control unit controls a resistance value of the conversion resistance unit so that an output voltage value of the smoothing unit at a predetermined set value becomes a predetermined target voltage value. Duty for changing the duty ratio of the pulse signal, comparing the output voltage value of the smoothing unit and the predetermined target voltage value, and determining the duty ratio of the pulse signal at which the output voltage value becomes the predetermined target voltage value Further comprising a ratio determining means;
The lighting device according to claim 1, wherein the conversion control unit is configured to output the pulse signal to the conversion resistance unit according to the duty ratio determined by the duty ratio determination unit. The conversion control unit is configured to output a pulse signal having a duty ratio determined by the duty ratio determining unit to the conversion resistance unit.
Further comprising target voltage value calculating means for calculating a target voltage value corresponding to the set value based on the set value relating to the amount of light received by the receiving unit, the predetermined set value and the predetermined target voltage value;
The light source control unit controls the light amount of the light source so that an output voltage value of the smoothing unit becomes a target voltage value calculated by the target voltage value calculation unit. 2. The illumination device according to 2. When the light quantity related to the setting value received by the receiving unit is smaller than a predetermined light quantity,
A duty ratio calculating means for calculating a second duty ratio based on the duty ratio determined by the duty ratio determining means and the predetermined light amount;
The conversion control unit is configured to output a pulse signal having a second duty ratio calculated by the duty ratio calculation unit to the conversion resistance unit,
The target voltage calculation means further calculates a target voltage value corresponding to the set value based on the duty ratio determined by the duty ratio determination means and the second duty ratio calculated by the duty ratio calculation means. The lighting device according to claim 3, wherein Duty ratio calculation means for calculating a duty ratio using the output voltage value of the smoothing section as the predetermined target voltage value based on the set value relating to the light quantity received by the reception section and the duty ratio determined by the duty ratio determination means Further comprising
The conversion control unit is configured to output a pulse signal having a duty ratio calculated by the duty ratio calculation unit to the conversion resistance unit,
The lighting device according to claim 2, wherein the light source control unit controls the light amount of the light source so that a voltage value output from the smoothing unit becomes the predetermined target voltage value. . A predetermined target voltage value determining means for determining an output voltage value of the smoothing unit when the duty ratio of the pulse signal is a predetermined duty ratio, as the predetermined target voltage value;
A duty ratio for calculating a duty ratio based on the set value relating to the light quantity received by the receiving unit and the predetermined duty ratio, wherein the output voltage value of the smoothing unit is the predetermined target voltage value determined by the predetermined target voltage determining unit. And a calculating means,
The conversion control unit is configured to output a pulse signal having a duty ratio calculated by the duty ratio calculation unit to the conversion resistance unit,
The lighting device according to claim 1, wherein the light source control unit controls the light amount of the light source so that an output voltage value of the smoothing unit becomes the predetermined target voltage value. The conversion resistance unit includes a resistor and a switching element connected in series in a path of a current output from the optical sensor,
The illumination device according to any one of claims 1 to 6, wherein the conversion control unit controls the resistance value by controlling opening and closing of the switching element. A liquid crystal display panel;
A display device comprising: the illumination device according to any one of claims 1 to 7 irradiating light on a back surface of the liquid crystal display panel.

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