JPH075428A - Liquid crystal image display device - Google Patents

Abstract

PURPOSE:To provide the liquid crystal image display device which can prolong the life of a light irradiation part. CONSTITUTION:The liquid crystal image display device is provided with a video input terminal 1 to which a video signal including a synchronizing signal is inputted, a liquid crystal panel 3 which displays an image corresponding to the video signal inputted to the video input terminal 1, and a light irradiation part 7 which visualizes the image by irradiating the liquid crystal panel 3 with light is provided with a synchronizing signal discriminating circuit 4 which discriminates whether or not the synchronizing signal is included in the input signal to the video input terminal 1 and a dimming circuit 6 which dimes light irradiating the liquid crystal panel 3 from the light irradiation part 7 more when the input signal to the video input terminal 1 does not have the synchronizing signal than when the synchronizing signal is included in the input signal according to the discrimination result of the synchronizing signal discriminating circuit 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal image display device for displaying an image corresponding to a video signal on a liquid crystal panel and visualizing the image with light emitted from a light emitting section (backlight light source). .

[0002]

2. Description of the Related Art In a liquid crystal image display device, since the liquid crystal panel itself does not emit light, it is necessary to provide a light irradiation section called a backlight on the back surface of the liquid crystal panel. A fluorescent lamp is usually used for this light irradiation section, but the fluorescent lamp has a relatively short life, so that it has to be replaced frequently.

In order to solve this problem, the light irradiation section is turned on or off depending on the presence or absence of a video signal,
A device for prolonging the life of the light irradiation part has been proposed (for example, JP-A-2-280587 and JP-A-3-932).
No. 0 publication).

[0004]

However, the above conventional device has the following problems. (1) Due to the current rush at the time of turning on / off, the life of the electrode of the light irradiation part is deteriorated. (2) In the case of the light irradiation unit using the hot cathode fluorescent lamp, once the light is turned off, the lighting is delayed for a moment when the video signal is detected next time (because preheating is necessary). (3) Once the light is turned off, it takes time until the brightness and the power consumption are stabilized when the light is turned on next time.

The present invention has been made based on such a background, and it is an object of the present invention to provide a liquid crystal image display device capable of prolonging the life of the light irradiating section while solving the drawbacks of the conventional device. To aim.

[0006]

In order to achieve the above object, according to the present invention, a signal input section to which a video signal including a sync signal is input, and an image corresponding to the video signal input to the signal input section. In a liquid crystal image display device having a liquid crystal panel for displaying the image and a light irradiation section for irradiating the liquid crystal panel with light to visualize the image, whether or not there is the synchronization signal in the input signal to the signal input section. A sync signal identifying circuit for identifying whether or not the sync signal is present in the input signal to the signal input unit based on the identification result of the sync signal identifying circuit, and the sync signal is present in the input signal. Further, a dimmer circuit for dimming the light emitted from the light emitting unit to the liquid crystal panel is provided.

[0007]

According to the present invention, whether or not a video signal is input to the signal input section is determined by identifying whether or not there is a sync signal in the input signal to the signal input section by the sync signal identification circuit. When it is identified that there is no signal, the dimmer circuit determines that there is no video signal input to the signal input section.
The light emitted from the light emitting unit to the liquid crystal panel is dimmed compared to when the video signal is input to the signal input unit. Therefore, the electrode life of the light irradiation unit does not deteriorate due to the current rush accompanying the blinking of the light irradiation unit, and in the case of the light irradiation unit using the hot cathode fluorescent lamp, preheating becomes unnecessary, The followability when transitioning to the normal lighting state is improved, light can be immediately irradiated, and the time until the brightness and power consumption are stabilized after the transition from the dimmed state to the normal lighting state is shortened, Immediate and stable irradiation is possible.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of a liquid crystal image display device according to an embodiment. The video signal from the video input unit 1 (corresponding to the signal input unit) is passed through the video circuit 2 and the liquid crystal panel 3 on the one hand.
Is input to the liquid crystal panel 3, and an image corresponding to the video signal is displayed on the liquid crystal panel 3.

On the other hand, the video signal is input to the sync signal identifying circuit 4. The sync signal identification circuit 4 identifies (detects) the sync signal of the video signal, and the output of the sync signal identification circuit 4 is turned on when there is a sync signal and turned off when there is no sync signal.

FIG. 2 is a circuit diagram showing an example of the synchronizing signal discriminating circuit 4. In a simple circuit, as shown in this figure, the synchronizing signal discriminating circuit 4 is composed of an integrating circuit composed of a diode D and a capacitor C. There is. A DC voltage output is taken out from this circuit.

FIG. 3 is a block diagram showing another example of the synchronizing signal identifying circuit 4, which utilizes a microcomputer. In the figure, 41 is a sync signal separation circuit for separating a sync signal from a video signal, 42 is an H / V separation circuit for separating H (horizontal sync signal) and V (vertical sync signal) from the sync signal, and 43 is a sync signal. It is a microcomputer having a discrimination program.

FIG. 4 is a flowchart showing the contents of the discrimination program included in the microcomputer 43. First, if the number of horizontal synchronizing signals is a predetermined value (O in S1)
K), it is discriminated whether or not there is a vertical synchronizing signal (S2), and if there is, it is turned on output from the microcomputer 43 (S).
3).

Returning to FIG. 1, the output of the synchronizing signal identifying circuit 4 is input to the dimming circuit 6 via the timer circuit 5 (the function of the timer circuit 5 will be described later). The dimming circuit 6 controlled by the output of the synchronization signal identifying circuit 4 produces a control signal for changing the brightness of the light emitted from the light emitting section 7 to the liquid crystal panel 3.

Next, the operation of this apparatus will be described. When the sync signal identifying circuit 4 identifies the sync signal of the video signal, the sync signal identifying circuit 4 outputs an ON signal.
As shown in, the 100-duty lighting control signal at the time of lighting is output to the light irradiation unit 7. Therefore, the light irradiation unit 7 is fully turned on.

On the other hand, if the synchronizing signal discriminating circuit 4 does not discriminate the synchronizing signal of the video signal, the synchronizing signal discriminating circuit 4 outputs the signal so that the dimming circuit 6 emits the on / off lighting control signal as shown in FIG. It is output to the unit 7. Therefore, in the light irradiator 7, duty lighting is performed with an on / off timing signal. Actually, since this on / off is performed in a quick cycle, it does not appear that the light emitting section 7 is on / off to the eyes, and further, the light emitting section 7 itself has the light holding ability. It looks like it has been dimmed. That is, if the off period is 90% and the on period is 10%, the light is reduced to about 10%.

Here, when the video signal is frequently interrupted, the timer circuit 5 may be used. This timer circuit 5 is turned on / off (controlled) by the synchronization signal identification circuit 4 and, after a short time has passed, the light irradiation section 7 causes the liquid crystal panel 3 to be turned on.
This is a circuit for starting the dimming control of the light radiated to the, and by this, the degree of lighting and dimming can be relaxed.

[0017]

As described above, according to the present invention,
When there is no synchronization signal in the input signal to the signal input unit, the light emitted from the light emitting unit to the liquid crystal panel is dimmed more than when there is a synchronization signal in the input signal. The power consumption can be suppressed more than by turning on the light, and the following effects are further exhibited. (1) Since there is no current rush associated with the flashing of the light irradiation part,
The life of the light irradiation part (sometimes the filament sphere) can be extended. (2) In the case of a light irradiation section using a hot cathode fluorescent lamp, the pre-heating is not necessary, so that the followability when transitioning from the dimmed state to the normal lighting state is improved, and the light is immediately emitted as in the cold cathode type. Irradiation can be performed. (3) The time until the brightness and power consumption are stabilized at the transition from the dimmed state to the normal lighting state is shortened, and stable irradiation can be performed immediately after the transition to the normal lighting state.

[Brief description of drawings]

FIG. 1 is a block diagram of a liquid crystal image display device according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing an example of a synchronization signal identification circuit.

FIG. 3 is a block diagram showing another example of a synchronization signal identification circuit.

FIG. 4 is a flowchart showing the contents of a determination program included in the microcomputer.

FIG. 5 is a waveform diagram of a light irradiation unit control signal at the time of full lighting.

FIG. 6 is a light irradiation unit control signal waveform diagram at the time of dimming.

[Explanation of symbols]

 1 Video input terminal (signal input part) 3 Liquid crystal panel 4 Sync signal identification circuit 6 Light control circuit 7 Light irradiation part

Claims (1)

[Claims] 1. A signal input unit to which a video signal including a synchronization signal is input, a liquid crystal panel that displays an image corresponding to the video signal input to the signal input unit, and the liquid crystal panel is irradiated with light. A liquid crystal image display device comprising: a light irradiation section for visualizing the image; a sync signal identification circuit for identifying whether or not the sync signal is included in an input signal to the signal input section; and the sync signal identification circuit. On the basis of the identification result of, when the synchronizing signal is not included in the input signal to the signal input unit, the light emitted from the light emitting unit to the liquid crystal panel is more than when the synchronizing signal is included in the input signal. A liquid crystal image display device, which is provided with a dimming circuit for dimming the light.