JP4092588B2 - LCD television - Google Patents

Description

  The present invention relates to a liquid crystal television in which a backlight is disposed on the back of a liquid crystal panel, and more particularly to a liquid crystal television that controls lighting of the backlight.

  In a liquid crystal television that displays an image by changing the light transmittance by applying a voltage to the liquid crystal material filled in the pixel and changing the molecular arrangement of the liquid crystal material, a backlight is disposed on the back of the liquid crystal panel, The backlight is turned on to transmit light to the liquid crystal panel.

  A cold cathode fluorescent lamp is used as a fluorescent tube usually used for a backlight. The cold cathode fluorescent lamp is widely used because it can change the shape of the tube according to the purpose of use, and has advantages such as less heat generation. However, the life of the cold cathode fluorescent lamp is shorter than that of the liquid crystal television, and the life of the cold cathode fluorescent lamp is now the life of the liquid crystal television.

As measures for extending the life of the cold cathode fluorescent lamp, there are a method of reducing the tube current flowing through the fluorescent tube and a method of reducing the frequency of use of the cold cathode fluorescent lamp. For example, in order to extend the life of a cold cathode fluorescent lamp, in a backlight composed of a plurality of cold cathode fluorescent lamps, there is known a method of controlling the individual cold cathode fluorescent lamps by a microcomputer based on the accumulated lighting time. (For example, refer to Patent Document 1).
Japanese Patent Laid-Open No. 2001-147481

  The above-described conventional liquid crystal television has the following problems. In other words, the cold cathode fluorescent lamps constituting the backlight are individually controlled by a microcomputer, and the cold cathode fluorescent lamps are individually turned on according to the accumulated usage time. Luminance unevenness occurs at a location where is lit and a location where it is not lit.

  The present invention has been made in view of the above problems, and is a liquid crystal television that can extend the life of a cold cathode fluorescent lamp that constitutes a backlight without causing uneven luminance of an image displayed on a liquid crystal panel. For the purpose of provision.

In order to achieve the above-mentioned object, the invention according to claim 1 receives a television broadcast signal via a liquid crystal panel for displaying video, a speaker for outputting sound, and an antenna, and extracts and outputs the video signal. A tuner circuit, a video display circuit that receives a video signal and displays a video corresponding to the video signal on a screen, a backlight composed of a fluorescent tube that illuminates the liquid crystal panel from the back, a DC voltage, and the DC voltage In a liquid crystal television comprising an inverter circuit for converting to a backlight and supplying the backlight, and a control device for controlling the components,
The control device includes a cumulative time measuring unit that measures a cumulative time during which the AC voltage is supplied to the backlight, and a duty ratio when the cumulative time exceeds a predetermined time with respect to the inverter circuit. A duty ratio control unit that performs control to reduce the duty ratio when it does not exceed, a recording unit that records a correspondence relationship between the cumulative time and the duty ratio, and an operation input of the cumulative time and the duty ratio are received. A duty ratio changing unit that causes the recording means to record the input accumulated time and the duty ratio in association with each other, and the inverter circuit indicates a duty ratio when the DC voltage is converted into an AC voltage. The DC voltage is applied to the AC voltage so that the duty ratio corresponds to the duty ratio instruction signal. The duty ratio control unit converts the duty ratio when the accumulated time exceeds the predetermined time with respect to the duty ratio based on the correspondence relationship recorded in the recording unit. The duty ratio instruction signal for making the duty ratio smaller than when the time is not exceeded is output to the inverter circuit, and the duty ratio is stepwise based on the correspondence relationship recorded in the recording unit. Thus, a plurality of images corresponding to the image controlled by the duty ratio control means can be created by the image display circuit using RGB gradation representation and displayed on the liquid crystal panel.

  That is, in a liquid crystal television including a liquid crystal panel, a speaker, a tuner circuit, a video display circuit, a backlight, an inverter circuit, and a control device, the control device supplies the AC voltage to the backlight. A cumulative time measuring unit that measures the accumulated time, and a duty that controls the inverter circuit so that the duty ratio when the cumulative time exceeds the predetermined time is less than the duty ratio when the predetermined time does not exceed the predetermined time A ratio control unit, a recording unit that records the correspondence between the cumulative time and the duty ratio, and an operation input of the cumulative time and the duty ratio, and the input cumulative time and the duty ratio are associated with each other. A duty ratio changing section for recording in the recording means.

  Further, the inverter circuit receives a duty ratio instruction signal for instructing a duty ratio when the DC voltage is converted into an AC voltage, and the DC voltage is set to a duty ratio corresponding to the duty ratio instruction signal. Is a circuit that converts AC to AC voltage.

  Therefore, the duty ratio control unit does not exceed the predetermined time for the duty ratio when the accumulated time exceeds the predetermined time for the duty ratio based on the correspondence relationship recorded in the recording unit. The duty ratio instruction signal is output to the inverter circuit so that the duty ratio is less than the current duty ratio.

  Further, the duty ratio control unit reduces the voltage supplied to the backlight by decreasing the duty ratio stepwise according to the accumulated time based on the correspondence relationship recorded in the recording unit. Take control.

  In addition, an image corresponding to the image controlled by the duty ratio control unit is created by the image display circuit by RGB gradation expression, and on the liquid crystal panel based on the image controlled by the duty ratio control means. By simultaneously displaying the video created by the video display circuit based on the video created by the video display circuit and the video not controlled by the duty ratio control unit, the user compares the video displayed on the liquid crystal panel. Can be targeted.

According to a second aspect of the present invention, there is provided a liquid crystal comprising: a backlight including a fluorescent tube that illuminates the liquid crystal panel from the back; and an inverter circuit that inputs a DC voltage, converts the DC voltage to the DC voltage, and supplies the DC voltage to the backlight. In television,
A cumulative time measuring means for measuring a cumulative time during which the AC voltage is supplied to the backlight; and a duty ratio when the cumulative time exceeds a predetermined time for the inverter circuit when the duty ratio does not exceed the predetermined time. And a duty ratio control means for performing control to make the ratio less than the ratio.

  That is, in the liquid crystal television having the above-described configuration, the accumulated time measuring means for measuring the accumulated time during which the AC voltage is supplied to the backlight, and the duty when the accumulated time exceeds a predetermined time for the inverter circuit Duty ratio control means for controlling the ratio to be less than the duty ratio when the ratio does not exceed a predetermined time, and the duty ratio control means is configured to control the inverter circuit based on the predetermined time measured by the cumulative time measurement means. Take control.

As described above, according to the first, second, and third aspects, the backlight can be controlled based on the accumulated usage time of the backlight.
Moreover, according to the invention concerning Claim 1 and Claim 4, since a brightness | luminance is reduced in steps, it can control a backlight, without a user feeling uncomfortable about the change of a brightness | luminance.
Moreover, according to the invention concerning Claim 1 and Claim 5, the backlight control according to a user's liking can be performed.
Further, according to the first and sixth aspects of the invention, since the video with control of the backlight and the video without control are displayed, the user can make a judgment on the control of the backlight.

The liquid crystal television which is one embodiment of the present invention will be described according to the following items. (1) Description of liquid crystal television (2) Control method of inverter circuit (3) Embodiment 1
(4) Example 2
(5) Example 3
(6) Summary

(1) Description of Liquid Crystal Television FIG. 1 is a block diagram showing a schematic configuration of a liquid crystal television 1 according to an embodiment of the present invention. As shown in the figure, the liquid crystal television 1 generally includes a tuner circuit 2, a video display circuit 3, a liquid crystal panel 6, a power supply circuit 7, a control device 8, an inverter circuit 14, a backlight 18, and a speaker 19. Consists of. In the above configuration, the control device 8 is connected to each part of the liquid crystal television 1 via the IIC bus 20, and the microcomputer 9 as a component within the control device 8 is also a component within the control device 8. The entire liquid crystal television 1 is controlled in accordance with each program written in the ROM 10 or the like.

  The control device 8 also includes an OSD (On Screen Display) circuit 13. The OSD circuit is connected to the image data generation circuit 4 via the IIC bus 20 and superimposes an OSD signal for generating a selection screen to be displayed on the screen of the liquid crystal panel 6 on the video signal. When the control device 8 inputs a voltage signal from the remote control I / F 12 and detects a corresponding key operation under the control of the microcomputer, the control device 8 receives the operation input from the remote control 21 and generates an OSD signal corresponding to the received operation input. The control device 8 generates an OSD signal for displaying a list of a plurality of operation items on the screen, receives an operation input for selecting one of the operation items displayed on the screen of the liquid crystal panel 6 from the remote controller 21, and A setting process corresponding to the selected operation item is executed.

  The tuner circuit 2 receives a television broadcast signal through an antenna (not shown) under the control of the control device 8. The tuner circuit 2 extracts a video signal and an audio signal as an intermediate frequency signal from the television broadcast signal while performing predetermined signal amplification processing and the like, and outputs them to the video display circuit 3 and the speaker 19.

  The video display circuit 3 includes an image data generation circuit 4 and a panel drive circuit 5. The image data generation circuit 4 converts the input video signal into a digital signal according to the signal level, and performs matrix conversion processing based on the luminance signal and the color difference signal extracted from the video signal, and performs RGB ( Red, green, blue) signal.

  In the panel drive circuit 5, the RGB signal is input and the RGB signal is subjected to scaling processing in accordance with the number of pixels (aspect ratio, m: n) of the liquid crystal panel 6 to be displayed for one screen displayed on the liquid crystal panel 6. Image data is generated. Then, by outputting the image data generated in this way to the liquid crystal panel 6, the liquid crystal panel 6 displays an image based on the image data. As described above, the image data generation circuit 4 and the panel drive circuit 5 constitute a video display circuit that receives a video signal and displays a video corresponding to the video signal on the screen.

  The speaker 19 amplifies the audio signal input from the tuner circuit 2 to a magnitude that is instructed by the user via the remote controller 21 or the like, and outputs the audio by converting the amplified audio signal into air vibration.

  The power supply circuit 7 is supplied with a power supply voltage (AC) from an external commercial power supply or the like, and supplies the supplied power supply voltage to each circuit such as the control device 8 and the inverter circuit 14. The power supply circuit 7 converts the voltage supplied to each circuit from AC to DC as necessary.

  The backlight 18 serves as a light source for irradiating the liquid crystal panel 6 from the back side. In this embodiment, a cold cathode fluorescent tube is used as the backlight.

  The inverter circuit 14 converts the DC voltage supplied from the power supply circuit 7 into an AC voltage, supplies the AC voltage as a drive signal to the backlight 18, and turns on the cold cathode fluorescent tube. The inverter circuit 14 is a switch unit 15 for turning on / off the voltage supplied from the power supply circuit 7, and a main unit that is supplied with the voltage from the switch unit 15 to generate and boost a predetermined AC voltage and apply it to the backlight 18. 16 and a protection unit 17 for protecting the backlight 18.

  The remote controller 21 has a plurality of keys for accepting operations and an infrared transmission circuit for transmitting the infrared signals to the remote control I / F 12, and transmits infrared signals according to the operations of the plurality of keys in a predetermined format. .

  The control device 8 includes a microcomputer 9, an operation panel 11, a ROM 10, a remote control I / F 12, and an OSD circuit 13. Then, the microcomputer 9 executes a predetermined program recorded in the ROM 10 and controls the entire remote controller 21. The remote controller 21 receives an operation input from an operation key, generates control data corresponding to the input content, converts it into an infrared signal, and transmits it.

  The operation panel is attached to the liquid crystal television 1 and includes a plurality of keys for receiving operations. When a plurality of keys on the operation panel 11 are operated, a voltage signal corresponding to each key is sent to the microcomputer 9, and the microcomputer 9 performs an operation associated with the voltage signal.

(2) Control Method of Inverter Circuit Next, the inverter circuit 14 according to the embodiment will be described with reference to FIG. The inverter circuit 14 is a so-called self-excited oscillation circuit and is roughly composed of a switch unit 15 and a main unit 16. The switch unit 15 is supplied with a DC power of 12 V through the connector CN1, and also receives a duty ratio instruction signal from the microcomputer 9.

  When an ON signal is input to the switch unit 15 from the microcomputer 9, a current flows between the base and emitter of the switching transistor Q1, so that a current flows between the emitter and collector of the transistor Q1. When the emitter-collector of the transistor Q1 is energized, a current flows between the base and emitter of the transistor Q9, and a current begins to flow between the emitter and collector of the transistor Q9. As a result, supply of DC power to the main unit 16 is started. When the signal from the microcomputer 9 is turned off, the supply of the DC voltage is stopped. Then, the DC voltage intermittently supplied by repeating this ON / OFF is smoothed by the electrolytic capacitor C1 as a smoothing circuit, and the DC voltage of 12 V is supplied to the main unit 74.

  The main portion 16 of the inverter circuit 14 is a so-called self-excited oscillation circuit, and includes a first field-effect transistor (FET) Q3 and a second FET Q4, and a transformer T1, and self-oscillates. AC power for lighting fluorescent tubes is generated. When an ON signal is input to the switch unit 15, the bias power (DC voltage) supplied from the power circuit 7 is applied to the gate electrodes of the first FET Q3 and the second FET Q4. The first FET Q3 and the second FET Q4 are alternately turned on and off to output an alternating voltage having a predetermined frequency to the primary side of the transformer T1.

  The primary side of the transformer T1 includes a first winding Ta connected at one end to the drain electrode of the first FET Q3, a second winding Tb connected at one end to the drain electrode of the second FET Q4, and a feedback And winding Tc. The secondary side of the transformer T1 is composed of a third winding Td. Further, a positive power supply of about 12 V is supplied to the other end of the first winding Ta and the other end of the second winding Tb. The feedback winding Tc returns a part of the amplified output to the input side of the first FET Q3 and the second FET Q4, and causes a circulation effect of further amplifying it. The main unit 16 is connected with a protection unit 7 for overcurrent protection of the current flowing through the resistor R18.

  In such a configuration, the transformer T1 boosts the alternating voltage input to the primary side, and applies the alternating voltage after the boosting to the backlight 18, thereby turning on the backlight 18.

  Here, the microcomputer 9 performs duty control (PWM control) on the duty ratio instruction signal input to the connector CN1, and controls the backlight 18 by controlling the DC voltage supplied to the main unit 16. At this time, if the time until the electric charge of the capacitor C1 is discharged is t1, and the off time in the duty control of the duty ratio instruction signal performed by the microcomputer 9 is t2, t1> t2. That is, the off time is set shorter than the time required for the electric charge stored in the electrolytic capacitor C1 to become zero.

  FIGS. 3 and 4 show a timing chart of the duty ratio instruction signal output from the microcomputer 9 and the voltage stored in the electrolytic capacitor C1 that changes in accordance with the duty ratio instruction signal. 3 and FIG. 4, the graph shown above is the voltage of the electrolytic capacitor C1, and FIG. 3 is for the case where the backlight is adjusted brighter. Therefore, in FIG. 3, the ON time is longer than that in FIG. 4, and ta1> tb1 and ta2 = tb2.

  Further, since the voltage supplied from the power supply circuit via the connector CN1 in FIG. 2 is 12V, the maximum voltage stored in the electrolytic capacitor C1 is 12V. Shown below is a timing chart of the duty ratio instruction signal input from the microcomputer 9 to the connector CN1, and ON / OFF control is performed depending on whether or not voltage is supplied. That is, a voltage is supplied when on, and no voltage is supplied when off.

  3 and 4, when the power source of the liquid crystal television 1 is turned on and the control of the backlight 18 is started, the input of a duty ratio instruction signal having a preset duty ratio to the connector CN1 is started, and the electrolytic capacitor C1 is started. Repeats storage and discharge. When the amount of voltage stored during the on time and the amount of voltage discharged during the off time are balanced, the average voltage takes a constant value. The average voltage in FIG. 3 is Va, and when the average voltage reaches Va, storage and discharge are repeated in the range of dVa. Similarly, the average voltage in FIG. 4 is Vb, and when the average voltage takes Vb, the storage and discharge are repeated in the range of dVb.

  FIG. 5 shows a correspondence table between the brightness of the backlight, the average voltage stored in the electrolytic capacitor C1 at each brightness, and the ON time of the duty ratio instruction signal input from the microcomputer 9. It is assumed that data indicating this correspondence is recorded in advance in the ROM of the microcomputer 9. It is assumed that “brightness” gradually becomes brighter in the order of 0, 1, 2, 3,. The magnitude relationship between the average voltage and the on-time value is V0 <V1 <V2 <V3 <... <V9, t20 <t21 <t22 <t23 <. Then, ta1 and tb1 in FIGS. 3 and 4 respectively correspond to different values of the on-time in FIG. 5 so that ta1> tb1. In FIG. 5, 10 levels of 0 to 9 are taken as brightness levels, but of course, it may be 5 levels or 20 levels instead of 10 levels, and an arbitrary number of levels can be set. .

(3) Example 1
The liquid crystal television which is one embodiment of the present invention with the above configuration adjusts the backlight, but in the above configuration, the voltage supplied to the control device 8 is reduced according to the cumulative usage time of the cold cathode fluorescent lamp. By performing the control, the tube current flowing through the cold cathode fluorescent lamp is reduced to extend the life.

  FIG. 6 is a block diagram of the control device 8 according to an embodiment of the present invention. The control device 8 is configured to include an accumulated time measuring unit 22, a duty ratio control unit 23, a recording unit 24, and a duty ratio changing unit 25. As shown in the figure, the accumulated time measuring unit 22, the duty ratio control unit 23, the recording unit 24, and the duty ratio changing unit 25 are connected to the microcomputer 9, and constitute a function as the control device 8 by exchanging predetermined data. .

  The accumulated time measuring unit 22 calculates the energization time of the current flowing through the cold cathode fluorescent tube and outputs it to the microcomputer 9. As a method of calculating the energization time, the microcomputer 9 detects the duty ratio instruction signal output to the switch unit 15 of the inverter circuit 14 and calculates the accumulated time of the duty ratio instruction signal based on the clock frequency of the internal clock of the microcomputer 9. By detecting, the energization time of the current flowing through the cold cathode fluorescent tube is calculated.

  The method for calculating the energization time of the current flowing through the cold cathode fluorescent tube is not limited to the above method as long as the energization time is calculated. As another example, the change of the voltage flowing through the cold cathode fluorescent tube may be measured directly, and the voltage may be measured by outputting the voltage to the cumulative time measuring unit 22 as a predetermined energization signal by the conversion circuit.

  The recording unit 24 has a voltage-time correspondence relationship correspondence table which is a correspondence relationship in which the correspondence relationship between the accumulated time of the voltage flowing through the electrolytic capacitor C1 and the duty ratio is recorded. FIG. 7 is a diagram of a voltage / time correspondence table included in the recording unit 24. The voltage-time correspondence table in FIG. 7 displays the brightness level of the backlight 18 in the upper stage in 10 steps, and the maximum accumulated in the electrolytic capacitor C1 in the second row, as in the correspondence table shown in FIG. The ON signal of the duty ratio instruction signal output from the microcomputer 9 to the switch unit 15 at the third stage is recorded.

  From the figure, the 9 levels of brightness are displayed as a voltage value of approximately 95 percent (approximately 12 × 0.95 = 11.5) with respect to the maximum voltage of 12 V input by the power supply circuit 7, which is indicated by the electrolytic capacitor C 1. Means that the maximum voltage stored by is about 11.5V. In order to generate the voltage value of approximately 95%, the microcomputer makes the output time of the duty ratio instruction signal output to the switch unit 15 shorter than when the voltage value of 12 volts is stored in the electrolytic capacitor C1. For this reason, the ON time displayed in the third row is shorter than that in FIG. Apart from this, the recording unit 24 has a plurality of voltage-time correspondence tables in which the maximum voltage stored in the electrolytic capacitor C1 is 95 to 80%.

  The duty ratio control unit 23 controls the duty ratio in the inverter circuit 14 described above. At this time, the duty ratio control unit 23 compares the accumulated time of the voltage supplied to the electrolytic capacitor C1 measured by the accumulated time measuring unit 22 with the accumulated time recorded in advance by the recording unit 24, and based on the above comparison. The duty ratio in the inverter circuit 14 is controlled based on the voltage / time correspondence table.

  The duty ratio changing unit 25 changes the voltage-time correspondence table used by the duty ratio control unit 23 to control the duty ratio of the inverter circuit 14 based on an instruction output by the user using the remote controller 21. The change of the voltage / time correspondence table is arbitrarily accepted by the user via the remote controller 21, and when the user does not select anything, the duty ratio changing unit 25 selects the voltage / time correspondence table selected as the initial setting. .

  From this, the duty ratio control of the inverter circuit 14 which the control apparatus 8 performs is demonstrated. FIG. 8 is a flowchart executed by the microcomputer.

  When the user gives an instruction to display a selection screen on the liquid crystal panel 6 using the remote controller 21, the instruction output from the remote controller 21 is output to the OSD circuit 13 via the remote control I / F 12 and selected by the liquid crystal panel 6. The screen is output. When the user selects the life extension mode of the backlight 18 on the selection screen (not shown), the selection screen shown in FIG. 9 is displayed on the liquid crystal panel 6 (steps S100 and S101).

  From the figure, it is assumed that Table 1, Table 2, and Table 3 are displayed on the selection screen, and the user selects one of the above tables on the selection screen via the remote controller 21 or the like. In each table (1-3), the cumulative energization time of the voltage flowing through the backlight is displayed on the left side in the form of 0-10000, where 0-10000 represents between 0 hours and 10,000 hours. The cumulative energization time increases as it goes down, and shows a maximum of 90000 hours. On the right side, the percentage of the maximum voltage stored in the electrolytic capacitor C1 is shown, and 100 indicates 100 percent.

  When the user selects, for example, the table 1 on the selection screen, the microcomputer 9 reads the cumulative energization time and the percentage of the maximum voltage displayed in the table 1 and instructs the cumulative time measuring unit 22 to output the cumulative time to the microcomputer 9. (Steps S102, S103, S104).

  Next, the microcomputer 9 receives the cumulative energization time calculated by the cumulative time measurement unit 22, and compares the cumulative energization time displayed in the table 1 with the cumulative measurement time calculated by the cumulative time measurement unit 22 (step S105). ). At this time, for example, assuming that the accumulated measurement time calculated by the accumulated time measurement unit 22 is 20000 hours, the microcomputer 9 reads 10001-30000 hours from the accumulated energization time in Table 1, and the maximum voltage corresponding to the accumulated energization time is obtained. Read the percentage.

  Next, the microcomputer 9 instructs the duty ratio changing unit 25 to read from the recording unit 24 the voltage / time correspondence table corresponding to the percentage of the read maximum voltage (step S105). At this time, for example, on the table 1 selected on the selection screen, the percentage of the maximum voltage corresponding to the cumulative energization time calculated by the cumulative time measuring unit 22 is 95%. Therefore, the duty ratio changing unit 25 selects a 95% voltage / time correspondence table from the recording unit 24 and records it in the ROM 10 (step S106).

  Next, the microcomputer 9 instructs the duty ratio control unit 23 to change the duty ratio of the inverter circuit 14, and the duty ratio changing unit 25 is displayed on the time voltage correspondence table selected by the duty ratio changing unit 25. Based on the turned-on time, a duty ratio instruction signal to be output to the switch unit 15 of the inverter circuit 14 is output (step S107). In this way, the microcomputer 9 executes duty ratio control of the inverter circuit 14.

(4) Example 2
In the above configuration, the control device 8 can change each data of the voltage-time correspondence table by an instruction from the user using the remote controller 21 or the like. The instruction sent by the user using the remote control is sent to the duty ratio changing unit 25 via the remote control I / F 12, and the duty ratio changing unit changes the data.

  By making it possible for the user to change the voltage-time correspondence table, it is possible to adjust the backlight according to the user's preference. For example, it is possible to create a voltage-time correspondence table in which the power stored in the electrolytic capacitor C1 is 80% from the beginning so as to maximize the lifetime of the backlight.

  FIG. 10 is a flowchart executed by the microcomputer 9. The flowchart of FIG. 10 is executed when the user selects to change the voltage-time correspondence table on the selection screen displayed on the liquid crystal panel 6 in step S101 of the flowchart of FIG. Therefore, the description of the same flow as the flowchart of FIG. 8 is simplified, and the description will focus on the flow of FIG.

  When the user selects to change the voltage / time correspondence table on the selection screen in step S101 in FIG. 8, the microcomputer 9 reads the voltage / time correspondence table change program recorded in the recording unit 24 and applies the voltage / time correspondence table to the liquid crystal panel 6. A relation table change screen is displayed (step S200). FIG. 11 is a diagram of a voltage / time correspondence table change screen displayed on the liquid crystal panel 6 in step S200. The voltage / time correspondence table change screen is the same as the selection screen displayed in step S101 of FIG.

  From the figure, it is assumed that the user has changed the top row of the percentage of the maximum voltage displayed on the right side from 100 to 95 using the remote controller 21. The microcomputer 9 reads the changed data on the voltage / time correspondence table conversion screen, causes the changed data to be newly recorded in the recording unit 24 as the table A, and enables selection on the selection screen (step S201). At this time, the data that can be changed by the user on the change screen is not limited to the percentage of the maximum voltage, and the cumulative energization time displayed on the left side can be changed. The table number can be arbitrarily selected by the user.

  Next, the microcomputer 9 instructs the duty ratio changing unit 25 to create a new voltage time correspondence table based on the newly created table A, and the duty ratio changing unit 25 receives the above instruction and then creates a new one. A voltage / voltage correspondence table is created and recorded in the recording unit 24 (step S202). When the recording is completed, the microcomputer 9 returns to step S101 in FIG. 8 and executes the following steps.

  The voltage time correspondence table described above is recorded in advance in the ROM 10 at the time of shipment from the factory, but can be replaced later with a new voltage time correspondence table created by the manufacturer. Thus, for example, the cold cathode fluorescent tube is replaced due to some problem, and even if the changed cold cathode fluorescent tube is different from the one used before the change, the characteristics of the changed cold cathode fluorescent tube are different. It is possible to perform appropriate backlight control by changing the voltage-time correspondence table according to the above.

  The voltage / time correspondence table can be changed by connecting the liquid crystal television 1 and the computer to an external input terminal such as a USB and outputting a newly created voltage / time correspondence table from the computer. The change of the voltage / time correspondence table is not limited to the method performed using the above-described computer, and any method may be used as long as the newly created voltage / time correspondence table is recorded in the ROM of the liquid crystal television 1.

(5) Example 3
The liquid crystal television 1 according to the embodiment of the present invention simultaneously displays on the liquid crystal panel 6 an image corresponding to the percentage of the maximum voltage selected by the user on the selection screen and an image corresponding to the maximum voltage of 100%. It is possible to make it.

  This allows the user to compare how much the brightness of the video with the duty ratio control selected on the selection screen changes compared to the brightness of the video without the duty ratio control, and to select a value for the duty ratio control. It can be. For this reason, the control device 8 has the comparison screen generation instruction unit 26 and displays an image corresponding to an image on which a different duty ratio control is performed on the screen of the liquid crystal panel 6.

  FIG. 12 is a block diagram of the control device 8 according to an embodiment of the present invention. As shown in the figure, the control device 8 has a comparison screen generation instruction unit 26. The comparison screen generation instruction unit 26 has a voltage luminance correspondence table of the maximum voltage percentage and luminance displayed in the voltage-time correspondence relationship table, and instructs to process the luminance of the video data based on the voltage luminance correspondence table. The above-described object is achieved.

  FIG. 13 is a diagram showing an image in which the maximum voltage displayed on the liquid crystal panel 6 is 100% and 95% when the user selects 95% as the maximum voltage on the selection screen. The left side of the figure shows the maximum voltage of 100 percent, and the right side shows the maximum voltage of 95 percent. In the displayed figure, an image such as a landscape image is recorded in the ROM 10 in advance, and the difference in luminance based on the difference in the maximum voltage of the image is compared.

  FIG. 14 is a voltage-luminance correspondence table showing the relationship between the maximum voltage stored in the electrolytic capacitor C1 and the luminance of the image displayed on the liquid crystal panel 6 at the maximum voltage. In the upper part, the percentage of the maximum voltage stored in the electrolytic capacitor C1 is displayed, and in the lower part, the luminance corresponding to the maximum voltage in the upper part is displayed. In the luminance display method according to an embodiment of the present invention, the luminance when the maximum voltage is 100% is set to 100, and the value decreases in accordance with the maximum voltage in the upper stage as it goes to the right. The comparison screen generation instruction unit 26 reads the percentage of the maximum voltage in the upper stage and instructs the image data generation circuit 4 so that the luminance of the video displayed on the liquid crystal panel 6 becomes the luminance corresponding to the percentage of the maximum voltage.

The luminance conversion in the image data generation circuit 4 is performed by performing predetermined signal processing on each of the RGB video signals of the video data constituting one frame. If the luminance signal is EY and the RGB video signals are ER, EG, and EB, then EY is

EY = aER + bEG + cEG (a, b, c are constants)

Can be expressed as a linear expression. For example, if the luminance value corresponding to the maximum voltage in the voltage luminance table is 0.95%,

0.95EY = 0.95 × (aER + bEG + cEG)

I can put it. Therefore, when obtaining the luminance from the above equation, the image data generation circuit 4 displays the video of the desired luminance value by multiplying the luminance percentage of the voltage / luminance correspondence table by a predetermined position of each RGB video signal. Can do.

  FIG. 15 is a flowchart executed by the microcomputer 9. The flowchart of FIG. 15 is a flow performed when the user executes a comparison screen display on the selection screen executed in step S101 of FIG. Therefore, the description of the flow performed in FIG. 8 is simplified, and the description of the flowchart of FIG.

  When the user selects the comparison screen display on the selection screen displayed on the liquid crystal panel 6 in step S101 in FIG. 8, the microcomputer 9 instructs the comparison screen generation instruction unit 26 to create a comparison screen (step S300).

  Next, the microcomputer 9 reads the selection screen of FIG. 9 and displays it on the liquid crystal panel 6. If the user selects, for example, the table 2 from the tables displayed on the liquid crystal panel 6, the microcomputer 9 reads the luminance corresponding to the maximum voltage of the table 2 selected by the user from the voltage / luminance correspondence table. An instruction is issued to the comparison screen generation instructing unit 26 so that the luminance of the substantially right half of the image to be displayed becomes the read luminance. In response to the above instruction, the comparison screen generation instruction unit 26 instructs the image data generation circuit 4 to perform signal processing on the video data (step S302).

  Next, the microcomputer instructs the image data generation circuit 4 and the panel drive circuit 5 to display the image subjected to the signal processing on the liquid crystal panel 6, and in response to this, the liquid crystal panel 6 displays the image on the liquid crystal panel. 6 (step S303).

  When the user confirms the image subjected to the signal processing on the liquid crystal panel 6 and determines the table selected on the selection screen, the process returns to step S101 in FIG. 8, otherwise returns to step S301 and the user again sets the table. Is selected again (step S304).

(6) Summary In a liquid crystal television comprising: a backlight composed of a fluorescent tube that illuminates a liquid crystal panel from the back; and an inverter circuit that inputs a DC voltage, converts it to the DC voltage, and supplies the same to the backlight. The cumulative time measuring means for measuring the cumulative time of supplying the AC voltage to the light and the duty ratio when the cumulative time exceeds the predetermined time for the inverter circuit is higher than the duty ratio when the predetermined time does not exceed the predetermined time. By providing a duty ratio control means for performing control to decrease, control for extending the lifetime of the backlight is performed.

A third aspect of the present invention is the liquid crystal television according to the second aspect, wherein the inverter circuit outputs a duty ratio instruction signal for instructing a duty ratio when the DC voltage is converted into an AC voltage. It is a circuit that converts the DC voltage into an AC voltage so that the duty ratio corresponding to the duty ratio instruction signal is input and
The duty ratio control means outputs the duty ratio instruction signal for causing the duty ratio when the cumulative time exceeds the predetermined time to be less than the duty ratio when the cumulative time does not exceed the predetermined time. It is a structure characterized by outputting to a circuit.

  That is, in the liquid crystal television according to claim 2, the inverter circuit inputs a duty ratio instruction signal for instructing a duty ratio when the DC voltage is converted into an AC voltage, and the duty ratio instruction It is a circuit that converts the DC voltage into an AC voltage so as to have a duty ratio corresponding to the signal. Therefore, in order to control the inverter circuit, the duty ratio control means uses a duty ratio when the cumulative time exceeds the predetermined time for the duty ratio than a duty ratio when the cumulative time does not exceed the predetermined time. The duty ratio instruction signal to be reduced is output to the inverter circuit.

  According to a fourth aspect of the present invention, in the liquid crystal television according to the second or third aspect, the duty ratio control means steps the duty ratio in correspondence with the accumulated time. It is the structure which makes it decrease.

  That is, in the liquid crystal television according to any one of claims 2 and 3, the duty ratio control means reduces the duty ratio stepwise corresponding to the accumulated time, thereby reducing the backlight. Increase life.

  According to a fifth aspect of the present invention, in the liquid crystal television according to any one of the second to fourth aspects, recording means for recording a correspondence relationship between the cumulative time and the duty ratio, and the cumulative time And a duty ratio changing means for receiving the operation input of the duty ratio and causing the recording means to record the input accumulated time and the duty ratio in association with each other.

  That is, in the liquid crystal television according to any one of claims 2 to 4, recording means for recording a correspondence relationship between the cumulative time and the duty ratio, and an operation of the cumulative time and the duty ratio Duty ratio changing means for receiving an input and causing the recording means to record the input accumulated time and the duty ratio in association with each other is provided to extend the lifetime of the backlight.

  A sixth aspect of the present invention is the liquid crystal television according to any one of the second to fifth aspects, wherein the control device includes a voltage equivalent value supplied to the backlight by the inverter circuit and the liquid crystal. A voltage-luminance correspondence table having a correspondence relationship with the luminance of the video displayed on the panel, and the video corresponding to the video controlled by the duty ratio control means is based on the voltage-luminance correspondence table. The image display circuit is created by RGB gradation expression, and a plurality of images can be displayed on the liquid crystal panel.

  That is, in the liquid crystal television according to any one of claims 2 to 5, an image corresponding to an image controlled by the duty ratio control means is created by RGB gradation expression of the image display circuit. A plurality of images can be displayed on the liquid crystal panel.

Needless to say, the present invention is not limited to the above embodiments. It goes without saying for those skilled in the art,
・ Apply by changing the combination of the mutually replaceable members and configurations disclosed in the above embodiments as appropriate.
・ Although not disclosed in the above-described embodiments, members and configurations that are known techniques and can be mutually replaced with the members and configurations disclosed in the above-described embodiments are appropriately replaced, and combinations thereof are changed. And apply
・ Although not disclosed in the above-described embodiments, those skilled in the art may appropriately substitute members and configurations that can be assumed as substitutes for the members and configurations disclosed in the above-described embodiments based on known techniques, Change and apply that combination
Is disclosed as an embodiment of the present invention.

It is a block block diagram of a liquid crystal television. It is a circuit diagram of an inverter circuit. It is a timing chart of a duty ratio instruction signal, and a figure of a voltage stored in electrolytic capacitor C1. It is a timing chart of a duty ratio instruction signal, and a figure of a voltage stored in electrolytic capacitor C1. 6 is a correspondence table between an average voltage stored in the electrolytic capacitor C1 and an on-time of a duty ratio instruction signal. It is a block block diagram of a control apparatus. It is a figure of a voltage time correspondence relationship correspondence table. It is a flowchart which a microcomputer performs. It is a figure of the selection screen displayed on a liquid crystal panel. It is a flowchart which a microcomputer performs. It is a figure of a voltage time correspondence table change screen. It is a block block diagram of a control apparatus. It is a figure of the contrast screen which shows the difference in a brightness | luminance. It is a figure of a voltage brightness correspondence table. It is a figure of the flowchart which a microcomputer performs.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Liquid crystal television 2 ... Tuner circuit 3 ... Video display circuit 4 ... Image data generation circuit 5 ... Panel drive circuit 6 ... Liquid crystal panel 7 ... Power supply circuit 8 ... Control apparatus 9 ... Microcomputer 10 ... ROM
11 ... Operation panel 12 ... Remote control I / F
DESCRIPTION OF SYMBOLS 13 ... OSD circuit 14 ... Inverter circuit 15 ... Switch part 16 ... Main part 17 ... Protection part 18 ... Backlight 19 ... Speaker 20 ... IIC bus 21 ... Remote control 22 ... Accumulated time measurement part 23 ... Duty ratio control part 24 ... Recording part 25 ... Duty ratio changing unit 26 ... Comparison screen generation instruction unit

Claims (6)

A liquid crystal panel for displaying images;
A speaker that outputs sound;
A tuner circuit that receives a television broadcast signal via an antenna and extracts and outputs a video signal and an audio signal; a video display circuit that receives the video signal and displays a video corresponding to the video signal;
A backlight consisting of fluorescent tubes that illuminate the LCD panel from the back,
An inverter circuit that inputs a DC voltage, converts the DC voltage, and supplies it to the backlight;
In a liquid crystal television including the liquid crystal panel, the speaker, the tuner circuit, the video display circuit, and a control device that controls the inverter circuit,
The control device
An accumulated time measuring unit that measures the accumulated time of supplying the AC voltage to the backlight;
A duty ratio control unit for controlling the inverter circuit so that the duty ratio when the cumulative time exceeds a predetermined time is less than the duty ratio when the cumulative time does not exceed the predetermined time;
A recording unit that records the correspondence between the cumulative time and the duty ratio;
A duty ratio changing unit that receives an operation input of the cumulative time and the duty ratio, and causes the recording unit to record the input cumulative time and the duty ratio in association with each other;
The inverter circuit inputs a duty ratio instruction signal for instructing a duty ratio when converting the DC voltage to an AC voltage, and converts the DC voltage to an AC voltage so that the duty ratio corresponds to the duty ratio instruction signal. It is a circuit that converts to voltage,
The duty ratio control unit, based on the correspondence relationship recorded in the recording unit, the duty ratio when the cumulative time exceeds the predetermined time for the duty ratio when the predetermined time is not exceeded Outputting the duty ratio instruction signal, which is less than the duty ratio, to the inverter circuit; and
Based on the correspondence recorded in the recording unit, the duty ratio is decreased stepwise,
The control device includes a voltage-luminance correspondence relationship table having a correspondence relationship between a voltage equivalent value supplied to the backlight by the inverter circuit and a luminance of an image displayed on the liquid crystal panel, and the duty ratio. A video corresponding to the video controlled by the control unit is created by the video display circuit by RGB gradation expression, and the video display circuit based on the video controlled by the duty ratio control unit on the liquid crystal panel. A liquid crystal television characterized by simultaneously displaying a created video and a video created by the video display circuit based on a video not controlled by the duty ratio control unit. A backlight consisting of fluorescent tubes that illuminate the LCD panel from the back,
In a liquid crystal television comprising an inverter circuit that inputs a DC voltage, converts the DC voltage, and supplies the converted backlight voltage to the backlight.
A cumulative time measuring means for measuring the cumulative time during which the AC voltage is supplied to the backlight; and a duty ratio when the cumulative time exceeds a predetermined time with respect to the inverter circuit. A liquid crystal television, comprising: duty ratio control means for performing control to reduce the amount of the liquid crystal television. The inverter circuit inputs a duty ratio instruction signal for instructing a duty ratio when converting the DC voltage to an AC voltage, and converts the DC voltage to an AC voltage so that the duty ratio corresponds to the duty ratio instruction signal. It is a circuit that converts to voltage,
The duty ratio control means outputs the duty ratio instruction signal for causing the duty ratio when the cumulative time exceeds the predetermined time to be less than the duty ratio when the cumulative time does not exceed the predetermined time. The liquid crystal television according to claim 2, wherein the liquid crystal television is output to a circuit.   4. The liquid crystal television according to claim 2, wherein the duty ratio control means reduces the duty ratio in a stepwise manner corresponding to the accumulated time. Recording means for recording a correspondence relationship between the accumulated time and the duty ratio;
The apparatus further comprises duty ratio changing means for receiving an operation input of the cumulative time and the duty ratio and causing the recording means to record the input cumulative time and the duty ratio in association with each other. The liquid crystal television according to claim 4. The control device includes a voltage-luminance correspondence table having a correspondence relationship between a voltage equivalent value supplied to the backlight by the inverter circuit and a luminance of an image displayed on the liquid crystal panel, and the duty ratio control unit A plurality of images corresponding to the image controlled by the image display circuit can be created based on the voltage / luminance correspondence table using RGB gradation representation of the image display circuit and displayed on the liquid crystal panel. The liquid crystal television according to any one of claims 2 to 5.

Images