JP2599766Y2 - LCD display with backlight - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display with a backlight for irradiating light from a cold-cathode tube to a light guide plate and irradiating the light from the light guide plate to the back of the liquid crystal display element.

[0002]

2. Description of the Related Art In a liquid crystal display device of transmission interference, light from a cold cathode tube is converted into planar light source light by a light guide plate and a diffusion sheet on the back surface of the liquid crystal display device in order to make the display easier to see. Irradiation. When such a liquid crystal display with a backlight is used as a display of a computer application device such as a word processor or a personal computer, when the computer application device is used, the user temporarily moves away from the device or uses the liquid crystal display device for the computer. In some cases, the user temporarily suspends use of the terminal without turning off the power, such as by temporarily stopping input operation and viewing related books. In such a case, in order to extend the life of the cold cathode tube of the backlight, the cold cathode tube is turned off. Also, depending on the computer application equipment, if the operation on the equipment is not performed for a certain time,
In some cases, the cold cathode tube is turned off automatically.

[0003]

As described above, when the use of computer-based equipment is temporarily stopped and the cold-cathode tube is turned off as described above, when the computer-based equipment or the like is used again, the time immediately before the cold-cathode tube goes out is turned off. The display state of the liquid crystal display is difficult to see, which causes inconvenience in use. Further, when the liquid crystal display is used at night or in a place where the surroundings are dark, the illumination by the backlight of the cold cathode tube may be too bright.

[0004]

According to the invention, when the light-off means detects that the cold-cathode tube is turned off, the light-emitting diode is turned on by the light-off detection, and the light of the light-emitting diode is transmitted to the light guide plate. Incident.

[0005]

An embodiment of the present invention will be described with reference to the drawings. A light guide plate 12 is disposed on a circuit board 11,
Is fixed to the circuit board 11 by the metal fitting 13. The liquid crystal display element 14 is disposed on the light guide plate 12,
Are fixed to the circuit board 11 by metal fittings 15. A cold-cathode tube 16 is disposed facing one end surface of the light guide plate 12, and the cold-cathode tube 16 is attached to the light guide plate 12 by an attachment cover 17, and light from the cold-cathode tube 16 is reflected by the inner surface of the attachment cover 17. The light enters the light guide plate 12 from its end face. The light propagating in the light guide plate 12 is diffused by a diffusion sheet (not shown) on the liquid crystal display element 14 side, and
, Substantially uniform light is incident on the entire surface. A lead wire 18 for the cold cathode tube 16 is led out. Although not shown, a drive circuit for the liquid crystal display element 14 is mounted on the circuit board 11.

In the present invention, a light-off detecting means for detecting that the cold-cathode tube 16 is turned off is provided. In this embodiment, a light detecting element 21 such as a phototransistor is provided opposite to the end face of the light guide plate 12 opposite to the cold cathode tube 16, and the cold cathode tube 1 passing through the light guide plate 12 at the light detection element 21 is provided.
6 to be able to detect the presence or absence of light.

When the light emission of the cold cathode tube 16 is detected, the light emitting diode 22 is turned on, and the light from the light emitting diode 22 is incident on the light guide plate 12. In this example, a plurality of light emitting diodes 22 are arranged close to and along the end face of the light guide plate 12 opposite to the cold cathode tubes 16. In other words, the wiring board 23 facing the end face of the light guide plate 12 opposite to the cold cathode tube 16 is attached to the circuit board 11, and the light detecting element 21 and the plurality of light emitting diodes 22 are attached to the light guide plate 12 side of the wiring board 23. .

As shown in FIG. 2, the emitter of the phototransistor as the photodetector 21 is grounded through a resistor 25, the collector is connected to a power supply terminal 26, and the emitter is connected to a comparator 27 by resistors 28 and 29. The voltage of the power supply terminal 26 is compared with a reference voltage obtained by dividing the voltage, and the comparison output is supplied to the LED drive circuit 31. The output side of the LED drive circuit 31 is connected to the power supply terminal 26 through the light emitting diode 22.

In this configuration, when the cold-cathode tube 16 is turned on, strong light is received by the phototransistor as the photodetecting element 21, the emitter output voltage is higher than the reference voltage, and the output of the comparator 27 is at a high level. Become, LED
The drive circuit 31 is in a non-drive state. When the cold-cathode tube 16 is turned off, light does not enter the light detecting element 21 and its emitter voltage falls to become equal to or lower than the reference voltage.
Becomes low level, the LED drive circuit 31 operates by this low level, a current flows through each light emitting diode 22, the light emitting diode 22 is turned on, and the light is transmitted to the light guide plate 1.
2, the liquid crystal display element 14 is illuminated with weak light from the light guide plate 12. Therefore, the display of the liquid crystal display element 14 can be viewed as needed when the operation of the computer application device is temporarily stopped and the material is examined.

In a dark place or at night, the cold cathode fluorescent lamp 1 may be used.
In case too bright in by that illumination 6 them off the cold cathode tube 16, becomes illuminated by the light emitting diode 22, the LCD display device 14 is easily visible state. In the above description, the turning off of the cold cathode tube 16 is detected by the light detecting element 21. However, the LED driving circuit 31 may be turned on and off in conjunction with a switch operation on the cold cathode tube 16, and similarly there is no input operation for a predetermined time. When the cold cathode tube 16 is automatically turned off, a detection output indicating that the input operation has not been performed for a predetermined time may be used as a light-off detection output. In FIG. 2 , the resistance value of one of the resistance elements 28 and 29, for example, 29 is made adjustable, and the resistance value is adjusted so that the light emitting diode 22
Can change the light amount at which lighting starts.

[0011]

As described above, according to the present invention, the life of the cold cathode tube 16 can be extended by turning off the cold-cathode tubes 16 as much as possible. The display on the display element does not completely disappear and can be recognized lightly. Further, when the illumination by the cold-cathode tube is too bright, the display can be easily viewed as illumination by the light emitting diode.

[Brief description of the drawings]

FIG. 1A is a cross-sectional view showing an embodiment of the present invention, and FIG. 1B is a plan view omitting a metal fitting 15 thereof.

FIG. 2 is an electric circuit for turning on a light emitting diode by detecting the turning off of a cold cathode tube.

Claims (1)

(57) [Scope of request for utility model registration] 1. A light is incident on the light guide plate from the cold cathode tube, in backlit liquid crystal display that irradiates light from a surface of the light guide plate on the back surface of the liquid crystal display device, turns off the CCFL and the cold cathode tube off means, and turns off detecting means for detecting that the cold-cathode tube was turned off, is turned on by turning off detection of the off detection means, the light is provided and a light emitting diode that is incident on the light guide plate, the The light-off detection means detects the presence or absence of light from the cold cathode tube.
Light-detecting element, and based on the output of the light-detecting element,
It is a means for detecting that the light is turned off.
Display on word processors and personal computers
Backlit liquid crystal display used for the display.