JPS6394228A - Display device for character and graphic - Google Patents

Abstract

PURPOSE:To automatically change the luminance of a penetratively illuminating light source and to obtain an always easily observable display state by providing the titled display device with a driving circuit, a control circuit and an optical sensor for detecting peripheral brightness. CONSTITUTION:The display device is constituted of a liquid crystal display panel 1, the penetratively illuminating light source 2 arranged on the back of the panel 1, the optical sensor 6 for detecting the illumination on a device setting position, the driving circuit 3 capable of changing the luminance of the light source 2, and the control circuit 4 for commanding the circuit 3 to change the luminance of the light source 2 on the basis of a detecting output from the sensor 6. Thereby, the control circuit 4 commands the driving circuit 3 to change the luminance of the light source 2 on the basis of the detecting output from the sensor 6 and the circuit 3 generates a voltage with a duty ratio for setting up the luminance of the light source 2 to an optimum value and impressing the voltage to the light source 2. Since the average operating current of a cooled CRT can be controlled by changing the duty ratio, penetrative illumination light corresponding to the environmental condition of the periphery can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a display device for characters and figures, and more particularly to a display device having a light source for transmitted illumination and a liquid crystal display panel.

2. Description of the Related Art Conventionally, this type of character/figure display device excludes the control circuit 4 in FIG. The drive circuit 3 always lights the light source 2 at a constant brightness.

Therefore, when the surroundings are bright, the brightness of the transmitted illumination light source is insufficient and the display on the LCD panel 1 is difficult to read.When the surroundings are dark, the transmitted illumination light source is too bright and causes eye fatigue. was there.

Problems to be Solved by the Invention The purpose of the present invention is to solve the above-mentioned drawbacks, namely, the problem that the brightness of the display cannot be adjusted depending on the surrounding brightness, resulting in insufficient brightness or too much glare. The object of the present invention is to provide a display device for characters and figures that solves the problem.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention provides a night crystal display panel, a light source for transmitted illumination disposed on the back of the liquid crystal display panel, and an installation position of the display device. A device that adopts a configuration consisting of a source sensor that detects the illuminance of the light source, a drive circuit that can change the brightness of the light source, and a control circuit that instructs the drive circuit to change the brightness of the light source based on the detection output of the light sensor. It is.

Operation Since the present invention is configured as described above, the control circuit instructs the drive circuit to change the brightness based on the detection output of the optical sensor, and the drive circuit adjusts the duty ratio so that the light source has the optimum brightness. generates a voltage and applies it to the light source.

Example Next, embodiments of the present invention will be described with reference to the drawings.

Referring to FIG. 1, which shows a block diagram of an embodiment of the present invention, the character/figure display device of the present invention includes a transmission liquid crystal display panel 1, a cold cathode discharge tube illumination light source 2, and a high frequency inverter. The control circuit 4 includes a drive circuit 3 that uses a 3D drive circuit 3, a control circuit 4 that issues an instruction to change brightness, and an optical sensor 6 that detects ambient brightness and sends the result to the control circuit 4. Further, FIG. 2 is a diagram showing the output waveform of the high frequency inverter of the drive circuit 3.

Next, the operation of this embodiment will be explained using FIGS. 1 and 2.

The light source 2 for transmitted illumination is set at such a brightness that the liquid crystal display panel 1 can be easily read based on the brightness in a standard usage environment. At this time, the oscillation waveform of the high frequency inverter of the drive circuit 3 of the light source 2 is set to have a duty ratio of 50% as shown in FIG. 2(a).

Next, the output of the optical sensor 6 decreases in a dark place compared to the standard usage environment. When the control circuit 4 receives this decreased output, it sets a brightness change instruction signal having a value corresponding to the amount of decrease and transmits it to the drive circuit 3.

The drive circuit 3 lowers the duty ratio of the oscillation waveform of the high frequency inverter to, for example, about 30% as shown in FIG. 2(c) in accordance with the value of this instruction signal.

According to experiments with this circuit, it was possible to operate it stably up to a minimum duty ratio of about 10%.

Furthermore, in a bright place compared to the standard usage environment, the output of the original sensor 6 increases. When the control circuit 4 receives this increased output, it similarly increases the data ratio of the oscillation waveform of the high frequency inverter of the drive circuit 3 to, for example, about 80% as shown in FIG. 2(b). In this case, of course the maximum is 100
%.

By changing the duty ratio, the average operating current of the cold cathode tube can be controlled, and the amount of transmitted illumination light can be obtained in accordance with the surrounding environmental conditions.

Effects of the Invention As explained above, according to the present invention, there is provided a drive circuit that can change the brightness of a light source, a control circuit that instructs the brightness change, and a drive circuit that can detect the surrounding brightness. By including the optical sensor, the brightness of the transmitted illumination light source can be automatically changed according to the surrounding brightness, and an easy-to-read display state can be obtained at all times.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 is an output waveform diagram of a drive circuit. DESCRIPTION OF SYMBOLS 1... Transmissive liquid crystal display panel, 2... Light source for transmissive illumination, 3... Drive circuit, 4... Control circuit, 5... Brightness change instruction signal, 6... Original sensor. Chrysanthemum 1 figure (c) Month 6 of circumference TjfJ: Biting from standard form 5 (Te1-Tee top and = 3θZ) Mz figure

Claims (1)

[Claims] In a character/figure display device comprising a liquid crystal display panel with a transmission amount, a light source for transmitted illumination disposed on the back side of the liquid crystal display panel, and a drive circuit for driving this light source, a light source is provided in the drive circuit. A voltage generating circuit with a variable duty ratio is provided to change the brightness, and an optical sensor is provided to detect the illuminance at the installation position of the display device, and the output of this optical sensor instructs the drive circuit to change the brightness. What is claimed is: 1. A display device for characters and figures, characterized in that it is provided with a control circuit for providing