JPS6315226A - Light source controller - Google Patents

Abstract

PURPOSE:To set the contrast of a display part and a transmission part to an optimum state, and to easily read the display contents by controlling the luminance of a back light source of a liquid crystal display panel in accordance with brightness of the periphery. CONSTITUTION:A voltage value which has been obtained by a light quantity detecting means 1 is inputted to an input port of a CPU 3. In such a stage, whether an input voltage value Vin exceeds a value of the upper limit or not is decided, and if it is outside the range, a control voltage signal Vout of a back light source is set to VL of a prescribed value, and with regard to the lower limit, as well, the processing is executed in the same way, and if the value is outside the range, said signal is set to VH of a prescribed value. That is to say, when brightness of the periphery is above some prescribed value, and below the prescribed value, the device executes a control so that brightness of the light source is kept constant. On the other hand, if the Vin is within the range, the voltage value is calculated so that brightness of the periphery and brightness of the back light source are in inverse proportion to each other, and the control voltage signal Vout of the back light source is sent out to an output port. Subsequently, the Vout which is outputted from a CPU 3 is converted to an analog value by a D/A converter 4, a base voltage of a transistor 6 is varied by this analog signal, and the quantity of a current flowing to the back light source 5 is controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a light source control device used in a mode display section of a copying machine or the like, and particularly to a light source control device for a back light source of a liquid crystal display panel.

[Summary of the Disclosure] This specification and drawings describe a light source control device used in a mode display section of a copying machine, etc., which improves the visibility of the mode display section by controlling the brightness of the light source according to the surrounding brightness. The present invention discloses a technology for increasing the power consumption of one display panel and reducing the power consumption and aging stress of one display panel.

Conventionally, the brightness of a backlight source used in a mode display section of a copying machine or the like has always been constant regardless of the surrounding brightness.

Particularly in the case of liquid crystal display panels, in order to improve visibility in dark places, it was necessary to always maximize the brightness. For this reason, not only does the power consumption of the liquid egg display panel increase,
There was a problem in that the thermal stress applied to the liquid crystal itself also increased.

The present invention was made in view of the problems of the prior art, and aims to provide a light source control bag that has good visibility, saves power for the display panel, and reduces the effects of heat stress. It is something to do.

[Means for Solving the Problems] A light source control device according to the present invention includes a light amount detection means for detecting the amount of surrounding light and generating an output signal proportional to the amount of light, and a corresponding output signal from the light amount detection means. The invention is characterized by comprising a central processing unit that generates a control signal, and an illumination unit whose brightness is controlled by the control signal from the central processing unit.

[Function] When ambient light enters the light amount detection means, the light amount detection means generates an output signal proportional to the amount of incident light. In response to this output signal, the central processing unit outputs a predetermined control signal to control the brightness of the light source. That is, when the surroundings are bright, the output is set so that the brightness of the display panel is inversely proportional to the brightness, and when the surroundings are dark, the output is set so that the brightness of the display panel becomes high.

[Embodiment] FIG. 1 is a circuit diagram showing an embodiment of a light amount control device according to the present invention. In Figure 1, 1 is a circuit that detects the surrounding brightness, and 2 is a light amount detection means that generates a voltage according to the amount of light using a light sensor such as CDS, and 2 is a circuit that detects the brightness of the surrounding area. A/ that converts voltage values into digital information
D converter, 3 is a central processing unit (hereinafter cP) which serves as a control means.
(referred to as u) processes input/output data and controls each part. 4 is a D/ that converts the current control signal of the liquid crystal display panel sent from the CPU 3 into an analog quantity.
In the A converter, 5 is a backlight source that is illumination means, and 6 is a transistor that controls the amount of current flowing through the backlight source 5.

Next, the operation will be explained. Each operation is controlled mainly by the CPU, and the flowchart of the operation is shown in Fig. 2.
Further, FIG. 3 shows the relationship between the ambient brightness and the brightness of the back light source to be controlled.

In Fig. 1, first is the light amount detection means! The voltage value obtained is input to the input port of the CPU 3 via the A/D converter 2 (see FIG. 2(a)). Here, the input voltage value Vi
It is determined whether or not n exceeds the upper limit value, and if it is outside the range, the control voltage signal vout of the backlight source is set to a constant value Vt (see Figure 2 (b)), and the same applies to the lower limit. processing, and if it is outside the range, set it to a constant value VH (second
In other words, as shown in FIG. 3, the brightness of the light source is controlled to be constant when the brightness of the surrounding area is above a certain value or below a certain value. On the other hand, if Vin is within the range, calculate the voltage value so that the brightness of the surrounding area and the brightness of the backlight source are inversely proportional (see Figure 2 (d)).
The control voltage signal v out of the backlight source is sent to the output boat (see FIG. 2(e)).

Next, the VouL output from the CPU 3 is converted into an analog value by the D/A converter 4, and the base voltage of the transistor 6 is changed using this analog signal to control the amount of current flowing to the backlight source 5.

[Effects of the Invention] As explained above, by controlling the brightness of the back light source of the liquid crystal display panel according to the surrounding brightness, the contrast between the display area and the transparent area can be optimized. Display contents can be easily read. Furthermore, since there is no need to always maintain maximum brightness, the power consumption of the liquid crystal display panel can be reduced, and the effects of heat stress can be alleviated.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the light amount control device, FIG. 2 is a flowchart of the operation, and FIG. 3 is a diagram showing the relationship between ambient brightness and brightness of a backlight source. l...Light amount detection means, 2...A/D converter. 3...CPU (central processing unit), 4...D/A
Converter, 5... Backlight source, 6... Transistor.

Claims (1)

[Claims] (1) A light amount detection means that detects the amount of surrounding light and generates an output signal proportional to the amount of light, a central processing unit that generates a control signal corresponding to the output signal from the light amount detection means, and the central processing unit. 1. A light source control device comprising an illumination unit whose brightness is controlled by a control signal from a lighting device.