JP4684209B2 - Liquid crystal display - Google Patents

Description

  The present invention relates to a liquid crystal display device having a backlight, and more particularly, to a liquid crystal display device having means for coping at startup when the power supply voltage is low.

  Liquid crystal display devices are characterized by their small size, thinness, and low power consumption. In recent years, liquid crystal display devices are becoming popular as displays that replace conventional CRTs (Cathode Ray Tubes) due to their improved display quality. Unlike a self-luminous device, a liquid crystal display device requires a light source (backlight) and displays an image by controlling the light transmittance determined by the electro-optical characteristics of the liquid crystal layer.

  By the way, the liquid crystal display device has lower power consumption than the CRT type display device. However, in the large-screen liquid crystal display device, the mounted backlight device becomes larger and the power consumption of the liquid crystal panel itself is lower. The power consumption of the light increases. For example, the power consumption of the backlight accounts for 70% or more of the power supplied to the entire liquid crystal display device.

Accordingly, a situation occurs in which the backlight does not turn on due to insufficient power supply (supply voltage) due to poor wiring of the power cord and poor contact with the power outlet.
When the power supply (supply voltage) is insufficient, the power supply circuit functions so that the power supply to the backlight does not change before and after that. As a result, the AC100V supply current increases. At this time, if the amount of increase in current is large, the primary side circuit components of the transformer of the power supply circuit may be destroyed, burned out, ignited, or a fuse is blown. For this reason, an overcurrent prevention circuit (overcurrent protection circuit) for preventing a current exceeding a predetermined amount from flowing on the primary side of the transformer is provided.

If the supply current of AC100V is suppressed by the overcurrent prevention circuit, the supply voltage for lighting the backlight drops as a result, so that the backlight lighting control does not function normally and the backlight does not light up.
Therefore, a small notification lamp such as an LED is provided in the front cabinet of the display device, and when a problem occurs, the notification lamp is turned on / flashing to notify the user of the occurrence of the problem (for example, patents). Reference 1).
JP 11-1112912 A

However, in the technique disclosed in Patent Document 1, the user cannot recognize the cause of the failure unless the contents corresponding to the state are searched from the lighting / flashing state of the notification lamp. Therefore, even if the voltage drop due to the power supply cord extraordinary wiring is the cause of the failure, there is a problem that it is difficult for the user to properly handle the service unless he / she requests a repair from the service provider.
In addition, when the power supplied to the backlight is insufficient, the backlight is not turned on, so that the user feeling that the backlight and thus the liquid crystal display device has failed works. Therefore, there is a problem that the user seriously thinks about the situation even if it is a minor factor such as poor wiring of the power cord and poor contact with the power outlet.

The present invention has been made in view of the above-described circumstances, and an object of the present invention is to provide a liquid crystal display device capable of preventing a situation in which the backlight does not turn on when the power supply voltage supplied to the backlight is insufficient. To do.
It is another object of the present invention to provide a liquid crystal display device capable of notifying a user when a power supply voltage supplied to a backlight is insufficient.

  A liquid crystal display device according to the present invention includes a liquid crystal panel having a display screen on the front side, a backlight disposed on the back side of the liquid crystal panel, and a power supply circuit for supplying predetermined power to the liquid crystal panel and the backlight. And an overcurrent prevention circuit for preventing an overcurrent from flowing through the power supply circuit, and a voltage detection means for detecting a supply voltage to the backlight. Means for determining whether the part is operating, and whether the supply voltage detected by the voltage detecting means is within a predetermined voltage range when the means determines that the part is operating Voltage determining means for determining whether the voltage determining means is not within a predetermined voltage range, and a reducing means for reducing a current for turning on the backlight by a predetermined amount. The features.

  In this liquid crystal display device, the liquid crystal panel has a display screen on the front side, the backlight is disposed on the back side of the liquid crystal panel, and the power supply circuit supplies predetermined power to the liquid crystal panel and the backlight. The overcurrent prevention circuit prevents an overcurrent from flowing through the power supply circuit, and the voltage detection means detects the supply voltage to the backlight. When the determining means determines whether or not the part other than the backlight is operating at the time of start-up, and the determining means determines that the part other than the backlight is operating, the voltage determining means detects the voltage. It is determined whether the supply voltage detected by the means is within a predetermined voltage range. When the voltage determination unit determines that the voltage is not within the predetermined voltage range, the reduction unit reduces the current for turning on the backlight by a predetermined amount.

  In the liquid crystal display device according to the present invention, when the reducing unit reduces the current by a predetermined amount, the voltage determining unit determines whether or not the supply voltage detected by the voltage detecting unit is within the predetermined voltage range. Further, the reduction means is configured to reduce the current by a predetermined amount until the voltage determination means determines that the supply voltage is within a predetermined voltage range. It is characterized by that.

  In this liquid crystal display device, when the reducing unit reduces the current by a predetermined amount, the voltage determining unit further determines whether or not the supply voltage detected by the voltage detecting unit is within a predetermined voltage range. The reduction means reduces the current for turning on the backlight by a predetermined amount until the voltage determination means determines that the supply voltage is within a predetermined voltage range.

  The liquid crystal display device according to the present invention is characterized in that the reduction means is configured to reduce the current by PWM control.

  In the liquid crystal display device according to the present invention, when the reduction means reduces the current by a predetermined amount, the power supply voltage is insufficient when the voltage determination means determines that the supply voltage is within the predetermined voltage range. It is further provided with a means for displaying on the display screen.

  In this liquid crystal display device, when the voltage reducing means determines that the supply voltage is within the predetermined voltage range when the reducing means has reduced the current by a predetermined amount, the display means has insufficient power supply voltage. Is displayed on the display screen.

  In the liquid crystal display device according to the present invention, when the voltage reducing unit determines that the supply voltage is within the predetermined voltage range when the reducing unit reduces the current by a predetermined amount, the current change is performed. It is further characterized by further comprising means for prohibiting.

  In this liquid crystal display device, when the voltage reducing means determines that the supply voltage is within the predetermined voltage range when the reducing means reduces the current by a predetermined amount, the prohibiting means turns on the backlight. The change of the current is prohibited.

  According to the liquid crystal display device of the present invention, it is possible to realize a liquid crystal display device that can prevent a situation in which the backlight is not turned on when the power supply voltage supplied to the backlight is insufficient.

  Further, according to the liquid crystal display device of the present invention, it is possible to realize a liquid crystal display device that can notify the user when the power supply voltage supplied to the backlight is insufficient. Therefore, after the user himself / herself recognizes the cause of the problem, it is possible to take measures for solving the problem. For example, if the voltage drop due to the power supply cord's extra wiring is the cause of the malfunction, it is possible to perform appropriate processing by the user himself without requesting a service provider for repair. That is, it is possible to reduce the number of repair requests to the service provider due to minor problems.

Hereinafter, the present invention will be described with reference to the drawings illustrating embodiments thereof.
FIG. 1 is a block diagram showing a configuration of an embodiment of a liquid crystal display device according to the present invention.
In this liquid crystal display device, the video signal input from the video input terminal VIDEO IN or the color difference signal input terminal YPBPR IN is switched and input by the AV SW circuit 8 (RGB signals can also be input). The video signal switched and input by the AV SW circuit 8 is given to the LCD control circuit 5. The LCD control circuit 5 performs IP (interlace / progressive) conversion on the given video signal, converts it to the number of pixels corresponding to the resolution of an LCD (Liquid Crystal Display) (liquid crystal panel) 6, and displays it on the LCD 6.

  In ROM7, for example, "The power supply voltage may be lower than the reference voltage. There is a possibility of poor contact with the power cord and the power outlet. Check the connection status of the power cord. OSD (On Screen Display) signal of a message such as “is stored. The OSD signal stored in the ROM 7 is switched and input to the LCD control circuit 5 via a microcomputer (hereinafter referred to as a microcomputer) 3.

Commercial AC power is supplied to a power supply circuit (power supply circuit) 4 through a plug 4a inserted into an outlet (not shown). The power supply circuit 4 supplies the commercial AC power to each DC power corresponding to each part in the liquid crystal display device. Convert to and give to each part. Further, the power supply circuit 4 incorporates an overcurrent prevention circuit that prevents an overcurrent from flowing.
The operation unit 10 includes a remote control device, and includes a power switch and switches for setting and operating volume, brightness, brightness, color, and the like. The operation signal of the power switch is given to the power supply circuit 4, and the operation signal of each other switch is given to the microcomputer 3.

The backlight control circuit 2 includes an inverter, supplies power for lighting a plurality of cold cathode fluorescent lamps 9 used in the backlight 1, controls on / off, and controls light and dark. Further, the current flowing through the backlight 1 is increased or decreased by PWM control.
When an abnormality occurs in the liquid crystal display device, the error display unit 14 displays the abnormality using an LED or the like.

The current detector 11 detects the current flowing through the backlight 1 and gives the detected current value to the microcomputer 3.
The voltage detector 12 (the ground terminal is omitted) detects the voltage supplied to the backlight 1 at the input terminal of the backlight control circuit 2 and supplies the detected voltage value to the microcomputer 3.
The voltage detector 13 (the ground terminal is omitted) detects a voltage applied to each part other than that for lighting the backlight 1, and gives the detected voltage value to the microcomputer 3.
The microcomputer 3 controls the above parts based on the given operation signals and detection signals.

Hereinafter, an example of the operation at the start-up of the liquid crystal display device having such a configuration will be described with reference to the flowcharts of FIGS.
When the user operates the power switch of the operation unit 10 to turn on the power, the microcomputer 3 first causes the power supply circuit 4 to turn on the power of each unit other than the backlight 1 lighting (S1). Next, the power supply voltage V1 other than for lighting the backlight 1 detected by the voltage detector 13 is read (S3), and it is determined whether or not the power supply voltage V1 is within the normal range (S5).

If the power supply voltage V1 is not within the normal range (S5), the microcomputer 3 causes the error display unit 14 to display an error if possible (S19).
If the power supply voltage V1 is within the normal range (S5), the microcomputer 3 causes the backlight control circuit 2 to turn on the power supply for lighting the backlight 1 (S7). Next, the backlight 1 lighting voltage (supply voltage) V2 detected by the voltage detector 12 is read (S9), and it is determined whether or not the voltage V2 is within the normal range (S11).

If the voltage V2 is within the normal range (S11), the microcomputer 3 reads the current I1 for lighting the backlight 1 detected by the current detector 11 (S13), and determines whether or not the current I1 is within the normal range. Determine (S15). If the current I1 is within the normal range (S15), the liquid crystal display device is assumed to be operating normally and is in operation (S17).
If the current I1 is not within the normal range (S15), the microcomputer 3 turns off the power other than the error display unit 14 (S21) and causes the error display unit 14 to display an error (S23).

If the voltage V2 for lighting the backlight 1 is not within the normal range (S11), the microcomputer 3 causes the backlight control circuit 2 to reduce the current for lighting the backlight 1 by a predetermined amount by PWM control (S24). 1 is executed (S25).
Here, the predetermined amount by which the backlight control circuit 2 reduces the current for lighting the backlight 1, as shown in FIG. 4, is the lowest luminance that can be visually recognized from the normally set lighting current value. The difference amount up to the lighting current value that secures the current value is defined as a current divided by N (N is a natural number, N = 3 in FIG. 4).
In the present embodiment, the predetermined amount for reducing the current for turning on the backlight 1 is a constant amount, but it may not be a constant amount. For example, every time the current is reduced, the current to be reduced may be reduced.

Next, the microcomputer 3 reads the voltage V2 for lighting the backlight 1 detected by the voltage detector 12 (S27), and determines whether or not the voltage V2 is within the normal range (S29). If the voltage V2 is within the normal range, it is assumed that the backlight 1 is turned on, and the backlight control circuit 2 holds the current value for lighting the backlight 1 at that time (a means for prohibiting). The brightness is fixed without accepting the brightness changing operation (S31).
The microcomputer 3 then sends to the LCD control circuit 5, for example, “The power supply voltage may be lower than the reference voltage. There is a possibility of poor wiring of the power cord and poor contact with the power outlet. An OSD signal with a message such as “Check the connection status of the cord” is displayed on the LCD 6 (S33).

If the voltage V2 for lighting the backlight 1 detected by the voltage detector 12 is not within the normal range (S29), the microcomputer 3 reads the current I1 for lighting the backlight 1 detected by the current detector 11 ( S35). Next, it is determined whether or not the current I1 is equal to or less than a set value set based on a lighting current value that secures the lowest visible luminance (S37).
If the current I1 is equal to or less than the set value (S37), the microcomputer 3 turns off the power other than the error display unit 14 (S21) and displays an error display on the error display unit 14 because there is no possibility that the backlight 1 is turned on. (S23).

If the current I1 for lighting the backlight 1 is not less than the set value (S37), the microcomputer 3 causes the backlight control circuit 2 to reduce the current for lighting the backlight 1 by a predetermined amount by PWM control (S24). 1 is executed (S25).
In the present embodiment, the light source of the backlight 1 is the cold cathode fluorescent lamp 9, but it may be another arc tube, for example, an LED, and the type of the light source is not limited. Absent.

It is a block diagram which shows the structure of embodiment of the liquid crystal display device which concerns on this invention. 3 is a flowchart showing an example of an operation at the time of starting the liquid crystal display device shown in FIG. 3 is a flowchart showing an example of an operation at the time of starting the liquid crystal display device shown in FIG. It is a characteristic view which shows the electric current-luminance characteristic of a backlight.

Explanation of symbols

1 Backlight 2 Backlight control circuit (reduction means)
3 Microcomputer (means for judging, voltage judging means, prohibiting means)
4 Power supply circuit (power supply circuit, overcurrent prevention circuit)
4a plug 5 LCD control circuit 6 LCD (liquid crystal panel)
7 ROM
8 AV SW circuit 9 Cold cathode fluorescent lamp 10 Operation unit 11 Current detector 12 Voltage detector (voltage detection means)
13 Voltage detector 14 Error display

Claims (5)

A liquid crystal panel having a display screen on the front side, a backlight disposed on the back side of the liquid crystal panel, a power supply circuit for supplying predetermined power to the liquid crystal panel and the backlight, and an overcurrent to the power supply circuit In a liquid crystal display device comprising: an overcurrent prevention circuit that prevents a current from flowing; and a voltage detection unit that detects a supply voltage to the backlight.
Means for determining whether or not the portion excluding the backlight is operating at the time of startup, and the supply voltage detected by the voltage detecting means when the means determines that the portion is operating is a predetermined voltage Voltage determining means for determining whether or not the voltage is within a range; and a reducing means for reducing a current for turning on the backlight by a predetermined amount when it is determined that the voltage determining means is not within the predetermined voltage range; A liquid crystal display device comprising:   When the reduction means reduces the current by a predetermined amount, the voltage determination means is further configured to determine whether or not the supply voltage detected by the voltage detection means is within the predetermined voltage range. 2. The liquid crystal display device according to claim 1, wherein the reduction means is configured to reduce the current by a predetermined amount until the voltage determination means determines that the supply voltage is within a predetermined voltage range.   The liquid crystal display device according to claim 1, wherein the reduction means is configured to reduce the current by PWM (Pulse Width Modulation) control.   When the reduction means reduces the current by a predetermined amount, when the voltage determination means determines that the supply voltage is within the predetermined voltage range, the display screen indicates that the power supply voltage is insufficient. The liquid crystal display device according to claim 1, further comprising a display unit.   The apparatus further comprises means for prohibiting the change of the current when the voltage determining means determines that the supply voltage is within the predetermined voltage range when the reducing means reduces the current by a predetermined amount. 5. The liquid crystal display device according to any one of 1 to 4.

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