JPH06175589A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To provide a liquid crystal display device which reduces the power consumption without turning off a back light, a side light, or the like by varying the voltage supplied to a driving means. CONSTITUTION:The temperature detected by a thermistor 7 is converted to a voltage by an inverter input voltage control circuit part 10A and is sent to an inverter input voltage varying power supply circuit part 10B. This circuit part 10B varies and controls the supply voltage in accordance with the control signal and outputs it, to an inverter part 4. Then, the voltage driving a back light 5 is varied, and the brightness of the back light 5 is changed in accordance with the temperature, and therefore, an optimum luminance is given to liquid crystal display. Since the voltage applied to an illuminating element like the back light is varied in this manner, the luminance of liquid crystal is finely controlled, and the power consumption is reduced and the life of liquid crystal is extended.

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 device provided with an illuminating element such as a backlight.

[0002]

2. Description of the Related Art As a conventional example of a liquid crystal display device having a backlight, Toshiba Review (1991 Vo)
l. 46 No. Those disclosed in 12) are known. In this device, a heater is provided over the entire area of the backlight tube in order to improve the brightness rising characteristics at low temperature and to secure the optimum brightness, and the temperature sensor controls the heater to energize the heater at low temperature. FIG. 5 shows the configuration of this device. The R, G, B signals from the image display control unit 1 are sent to the liquid crystal display unit 2 to display an image. The DC voltage from the backlight constant voltage / constant current circuit unit 3 is input to the inverter unit 4 and converted into an AC voltage, and then sent to the backlight 5 to turn on the backlight 5. Heater control circuit section 6
Applies a voltage according to the tube surface temperature of the backlight 5 detected by the thermistor 7 to the heater constant voltage / constant current circuit unit 8, and the heater constant voltage / constant current circuit unit 8 applies the voltage of the heater 9 to the heater constant voltage / constant current circuit unit 8. Occur. In addition, 11 is a diffusion plate and 12 is a reflection plate.

[0003]

In this conventional example, since the heater consumes a large amount of power, a heater power supply circuit is required, and the cost of the heater itself is high, resulting in a very expensive device, and the heater has a low impedance. Therefore, there is a problem that it is difficult to control the heater. In addition, a liquid crystal display device described in Japanese Utility Model Publication No. 4-22614 for reducing power consumption is known.
The voltage for the backlight is simply turned on / off, and fine voltage control is not performed. An object of the present invention is to provide a liquid crystal display device capable of reducing power consumption without turning off a backlight, a sidelight or the like. Another object of the present invention is to change the voltage supplied to the backlight or the like according to the temperature change to improve the brightness rising characteristic at low temperature without providing a heater and to optimize even if the temperature changes. An object of the present invention is to provide a liquid crystal display device capable of ensuring brightness.

[0004]

The present invention will be described with reference to FIG. 1 showing an embodiment.
The liquid crystal display unit 2, an illuminating unit 5 for illuminating the liquid crystal display unit 2, and an illuminating unit 5 having a brightness according to an input voltage.
It is applied to a liquid crystal display device including a driving unit 4 for driving the driving unit 4 and an image display control unit 1 for controlling the image display of the liquid crystal display unit 2, and includes a voltage control unit 10 for varying the voltage supplied to the driving unit 4. By doing so, the above object is achieved. According to a second aspect of the present invention, the liquid crystal display device according to the first aspect further includes temperature detecting means 7 for detecting temperature, and the voltage control means 10 supplies the temperature to the driving means 4 according to the detected temperature. The above-mentioned object is achieved by making the applied voltage variable.

[0005]

According to the first aspect of the present invention, the voltage control means 10 makes the voltage supplied to the driving means 4 variable. The brightness of the lighting unit 5 is variable according to the voltage input via the driving unit 4. That is, the brightness of the liquid crystal display unit 2 is variable. In the invention according to claim 2, for example, the temperature of the tube surface of the illuminating means 5 is detected by the temperature detecting means 7, the voltage of the driving means 4 is variable according to the temperature, and the brightness of the liquid crystal display unit 2 is changed according to the temperature. Will change.

Incidentally, in the section of means and action for solving the above problems for explaining the constitution of the present invention, the drawings of the embodiments are used for the purpose of making the present invention easy to understand. It is not limited to.

[0007]

1 is a block diagram of an embodiment of a liquid crystal display device according to the present invention. The same parts as those in the configuration diagram of the conventional example shown in FIG. 5 are designated by the same reference numerals, and the description thereof will be omitted. Reference numeral 10 denotes an inverter input voltage control circuit unit 10A and an inverter input voltage variable power supply circuit 10B.
Is a voltage control circuit having. The temperature detected by the thermistor 7 is converted into a voltage by the inverter input voltage control circuit unit 10A and sent to the inverter input voltage variable power supply circuit unit 10B as a control signal, and the inverter input voltage variable power supply circuit unit 10B responds to the control signal. The power supply voltage is variably controlled and output to the inverter unit 4. As a result, the voltage for driving the backlight 5 becomes variable, and the brightness of the backlight 5 can be changed according to the temperature, so that the liquid crystal display can have the optimum brightness.

FIG. 2 shows an inverter input voltage control circuit section 10
It is a circuit diagram of an example of A and the inverter input voltage variable power supply circuit unit 10B. The temperature detected by the thermistor 7 is converted into a voltage and input to the 8-bit A / D converter 101, where it is converted into a digital signal and input to the CPU 102. The CPU 102 pulse-width modulates the input digital signal and outputs it. This pulse width modulation output (PWM output) is converted into an analog signal by the low pass filter (LPF) 103 and input to the base of the transistor Q1. The magnitude of the current flowing through the resistor R1 changes depending on the magnitude of the base voltage, and the current flowing through the resistor R2 also varies accordingly, so that the output voltage of the inverter input voltage variable power supply circuit section 10B becomes variable.

FIG. 3 shows a flow chart of a program executed by the CPU 102 of FIG. This figure shows an example in which the luminous efficiency and life are optimal when the tube surface temperature of the backlight 5 is 60 ° C. The surface temperature T ° C. of the backlight tube detected by the thermistor 7 is read in step S1, and the process proceeds to step S2. In step S2, T
C.-60.degree. C. is calculated, and the result is assigned to the variable N. In step S3, whether N is positive or negative is determined. If N is zero or more, the backlight tube surface temperature T ° C. is determined to be 60 ° C. or more, and the process proceeds to step 4. If N is negative, the backlight tube surface temperature T is T.
When it is determined that the temperature is lower than 60 ° C, the process proceeds to step S5. In step 4, the larger the N, the higher the frequency of the PWM output, and in step 5, the smaller the N, the lower the frequency. By such processing by the CPU 102, the output voltage of the inverter input voltage variable power supply circuit 10B becomes lower as the temperature T ° C. detected by the thermistor 7 is higher than 60 ° C. and becomes higher as the temperature T ° C. is lower than 60 ° C. The tube surface temperature T ° C is controlled to be constant at about 60 ° C,
The improvement of the brightness rising characteristic of the liquid crystal display and the compensation of the saturation brightness can be realized without using a heater, and the cost can be reduced as compared with the conventional case.

FIG. 4 is a diagram showing the rise time of luminance at low temperature and the change in relative luminance due to temperature change in each of the conventional example in which the heater control is performed with a constant inverter input voltage and the above-described example. As can be seen from this figure, in the present embodiment, the same brightness rising characteristics as in the conventional case can be obtained without using a heater, and the change in the relative brightness with respect to the temperature change is smaller than in the conventional case. Is obtained.

A high pass filter (HPF) may be used instead of the LPF 103. In this case, the higher the tube surface temperature T ° C. is, the lower the frequency is, and the lower the temperature is 60 ° C., the lower the frequency is. It is possible to control the voltage to be higher, so that the lower the frequency, that is, the temperature is higher than 60 ° C., the lower the voltage is, and the higher the frequency, that is, the temperature is lower than 60 ° C., the higher the voltage is. Similar effects can be obtained. Further, the PWM output, which is the output of the CPU 102 shown in FIG. 2, does not change the frequency according to the temperature as in the embodiment but changes the pulse width. . Furthermore, although a liquid crystal display device with a backlight has been described above, the present invention can also be applied to a liquid crystal display device with a sidelight.

Furthermore, the case where the thermistor 7 is installed on the tube surface of the backlight 5 has been described above, but it is not always necessary to provide the thermistor in contact with the tube surface, and the thermistor may be installed near the backlight 5. . In some cases, the ambient temperature of the place where the liquid crystal display device is installed may be detected. In the case of a vehicle-mounted liquid crystal display device, voltage control may be performed according to the engine cooling water temperature or the like.

In the embodiment configured as described above, the backlight 5 serves as illumination means, the inverter portion 4 serves as drive means, and the inverter input voltage control circuit portion 10A and the inverter input voltage variable power supply circuit portion 10B serve as voltage control. By means 10,
The thermistor 7 corresponds to the temperature detecting means.

[0014]

As described in detail above, according to the present invention, the voltage applied to the lighting element such as the backlight is variable, so that the brightness of the liquid crystal can be finely controlled, the power consumption can be reduced and the life of the liquid crystal can be extended. It becomes possible. In particular, by changing the voltage supplied to the lighting element according to the temperature, it is possible to improve the brightness rise characteristics at low temperatures without providing a heater, and to secure the optimum brightness of the liquid crystal display even when the temperature changes. The effect of being able to do is obtained.

[Brief description of drawings]

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

FIG. 2 is a circuit diagram of an inverter input voltage control circuit unit and an inverter input voltage variable power supply circuit unit in the embodiment.

FIG. 3 is a flowchart of an embodiment of a liquid crystal display device according to the present invention.

FIG. 4 is a diagram showing a rise time of luminance at a low temperature and a change in relative luminance due to temperature change in each of a conventional example in which heater control is performed with a constant inverter input voltage and a present example.

FIG. 5 is a configuration diagram of a conventional liquid crystal display device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image display control section (screen display control means) 2 Liquid crystal module (liquid crystal display section) 3 Constant voltage / constant current circuit section for backlight 4 Inverter section (driving means) 5 Backlight (illumination means) 6 Heater control circuit section 7 Thermistor (Temperature detection means) 8 Heater constant voltage / constant current circuit section 9 Heater 10 Voltage control means 10A Inverter input voltage control circuit section 10B Inverter input voltage variable power supply circuit section 101 8-bit A / D converter 102 CPU 103 Low pass filter ( LPF) R1 resistor R1 R2 resistor R2 Q1 transistor Q1

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tsutomu Sekiguchi 1-18-2 Omorikita, Ota-ku, Tokyo Within Xanavie Informatics Co., Ltd.

Claims (2)

[Claims] 1. A liquid crystal display section, an illuminating means for illuminating the liquid crystal display section, a driving means for driving the illuminating means so as to obtain brightness according to an input voltage, and an image display of the liquid crystal display section. A liquid crystal display device comprising an image display control means for controlling the liquid crystal display device, the liquid crystal display device comprising a voltage control means for varying a voltage supplied to the driving means. 2. The liquid crystal display device according to claim 1, further comprising a temperature detecting means for detecting a temperature, wherein the voltage control means makes the voltage supplied to the driving means variable according to the detected temperature. Liquid crystal display device characterized by.