JPH11183869A - Luminance adjusting device for liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display device capable of obtaining suitable luminance independently of an environmental temperature. SOLUTION: An output signal from a pulse width modulator 8 built in a controller 5 is inputted to a comparator 11 through a low pass filter(LPF) 9 as reference voltage. The detection voltage of a thermistor 10 is inputted to the comparator 11 and compared with the reference voltage, and when both the voltage values coincide with each other, an output signal from the comparator 11 is inputted to a CPU 6. The CPU 6 calculates an environmental temperature from the inputted thermistor voltage, refers to a table 7a stored in a storage device 7 and judges the resistance of a luminance adjusting resitor 4 set up correspondingly to the environmental temperature. Then the CPU 6 outputs a control signal to a changeover switch 3 to switch the common terminal 3a of the switch 3 and select the resistance of the resistor 4. Liquid crystal driving voltage Vo set up at the time is inputted to a liquid crystal display driver 2 to drive the liquid crystal display device 1 at prescribed voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a brightness adjusting device for a liquid crystal display having a structure capable of obtaining an appropriate brightness even when the environmental temperature changes.

[0002]

2. Description of the Related Art The brightness of a display screen of a liquid crystal display (hereinafter abbreviated as LCD), which is widely used in consumer equipment and industrial equipment, changes depending on the environmental temperature. That is, when the environmental temperature is high, the luminance tends to be low, and when the environmental temperature is low, the luminance tends to be high. For this reason, there is a problem that an appropriate luminance cannot be obtained depending on the environmental temperature, and the screen becomes difficult to see.

FIG. 5 is a circuit diagram showing an example of luminance adjustment of a conventional LCD. In FIG. 5, the LCD 1 is connected to the LCD driver 2 by a bus line Ba. Rv
Is a variable resistor for brightness adjustment connected between the + 5V power supply and the ground. Rs is a slider provided on the variable resistor Rv, and slides on the resistance Rt of the variable resistor Rv. According to the position of the slider Rs on the resistance Rt of the variable resistor Rv, a voltage obtained by dividing +5 V of the power supply voltage is obtained. This divided voltage is used as a control voltage for the signal line Sa.
Is input to the LCD driver 2. The LCD driver 2 determines a control voltage to be supplied to the LCD 1 based on the input control voltage and adjusts the brightness of the LCD 1.

[0004]

The control signal generated by the variable resistor Rv has a standard temperature, for example, room temperature 25.
The LCD is adjusted to have a predetermined brightness at a temperature of ° C, and the position of the slider Rs on the resistor Rt is fixed when the product is shipped.
However, the LCD may be used in a cold region or a high temperature region, and the environmental temperature in the region is far from the standard temperature. In such an area, there is a problem that an appropriate luminance set at the standard temperature at the time of product shipment cannot be obtained.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and has a luminance adjusting device for a liquid crystal display, which can obtain an appropriate luminance even when an ambient temperature used is different from a standard temperature. The purpose is to provide.

[0006]

SUMMARY OF THE INVENTION The object of the present invention is to provide a liquid crystal display, comprising: a liquid crystal display; a driving means for driving the liquid crystal display; Achieved by a configuration including a temperature detecting unit, a control unit that outputs a control signal based on an output of the temperature detecting unit, a brightness adjustment resistor of the liquid crystal display, and a switching unit that switches the brightness adjustment resistor based on the control signal. Is done.

According to a second aspect of the present invention, the temperature detecting means of the first aspect of the present invention comprises a temperature detecting element, a comparing means for comparing an output of the temperature detecting element with a reference voltage, and And reference voltage generating means for generating a reference voltage.

According to a third aspect of the present invention, the control means of the first or second aspect of the present invention has a configuration including a table of a temperature detected by a temperature detecting means and a luminance adjustment resistor to be selected. I have.

According to the characteristics of the invention according to claim 1,
Since the brightness adjustment resistor is switched based on the detected temperature, an appropriate brightness can be obtained on the liquid crystal display even when the environmental temperature changes.

Further, in the invention according to claim 2, since the reference voltage for sequentially generating a plurality of reference voltages and the output of the temperature detecting element are compared, the control means does not need to have an analog / digital port, or The temperature can be detected without providing an analog / digital converter separately.

Further, in the invention according to claim 3,
The control means has a table of the temperature detected by the temperature detection means and a luminance adjustment resistor to be selected. For this reason, a control signal for selecting the luminance adjustment resistor can be automatically formed by detecting the temperature.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a brightness adjusting device for a liquid crystal display according to the present invention will be described below with reference to the circuit diagram of FIG. The same portions or corresponding portions as those in the conventional example of FIG. 5 are denoted by the same reference numerals, and detailed description thereof will be omitted. In FIG. 1, reference numeral 3 denotes a changeover switch provided with a common terminal 3a and selection terminals 30 to 33. +
A luminance adjusting resistor 4 is connected between the power supply of 5 V and the ground. The brightness adjusting resistor 4 has resistors R0 to R3 connected in series, and a connection point between the resistors is connected to selection terminals 30 to 32 of the changeover switch 3. The connection point between the +5 V power supply and the resistor R3 is connected to the selection terminal 33 of the changeover switch 3.

By connecting the common terminal 3a to the selection terminals 30 to 32, the LCD driver 2 is supplied with a liquid crystal driving voltage Vo obtained by dividing a voltage of + 5V. Further, by connecting the common terminal 3a to the selection terminal 33, LC
The D driver 2 is supplied with a liquid crystal driving voltage Vo of +5 V corresponding to a power supply voltage.

A control unit 5 has a central processing unit (hereinafter abbreviated as CPU) 6 having an input port 6a and an output port 6b, a storage device 7 having a table 7a, and a pulse width modulator (hereinafter abbreviated as PWM). ) 8 is provided.
The CPU 6 is connected to the storage device 7 by a bus line Bb, and is also connected to the PWM 8 by a bus line Bc.

Table 7a provided in the storage device 7
, The connection position between the common terminal 3a of the changeover switch 3 and the selection terminals 30 to 33, that is, the correspondence between the selected brightness adjustment resistor and the environmental temperature is set. Table 1 shows an example of the table 7a. As is clear from Table 1, the lower the ambient temperature is, the larger the selected brightness adjustment resistance is.
The liquid crystal drive voltage Vo supplied to the D driver 2 decreases. Further, as the ambient temperature increases, the selected luminance adjustment resistance is reduced, and the liquid crystal driving voltage Vo supplied to the LCD driver 2 is increased.

[0016]

[Table 1]

5a, 5b and 5c are terminal pins of the control device 5. The terminal pin 5a is connected to the signal line 8 on the output side of the PWM 8.
a and a low-pass filter (hereinafter abbreviated as LPF) 9
Is connected to the input-side signal line 9a. The terminal pin 5b is
It is connected to the signal line 11a on the output side of the comparator 11. The terminal pin 5c is connected to a signal line 3b for sending a control signal to the changeover switch 3.

L consisting of a reactance L and a capacitor C
The output voltage of the PF 9 is input to the non-inverting input terminal of the comparator 11 through the signal line 9b. The temperature detecting thermistor 10 connected between the +5 V power supply and the ground via the voltage dividing resistor ra has a characteristic that the resistance value changes with a change in temperature, and the temperature-resistance characteristic is set in advance. ing. The thermistor 10 is installed near the LCD 1,
The environmental temperature when the CD 1 is used is detected.

A terminal Ta at a connection point between the voltage dividing resistor ra and the thermistor 10 has a resistance value of the voltage dividing resistor ra and the thermistor 10 connected thereto.
, A voltage (thermistor voltage) obtained by dividing the voltage of +5 V is obtained. The thermistor voltage is input to the inverting input terminal of the comparator 11 via the signal line 10a. The comparator 11 is connected to the thermistor voltage and the LPF 9
When the thermistor voltage becomes higher than the output voltage of the LPF 9 as compared with the output voltage of the LPF 9, a signal is output from the signal line 11a.

FIG. 2 is a characteristic diagram for explaining the operation of the comparator 11. 7A shows the time-output voltage characteristic of the LPF 9, and FIG.
FIG. 3C shows the data output from the PWM 8. When 7-bit data is output from the PWM 8 to the LPF 9, the LPF 9 low-pass filters the input data and inputs a reference voltage Va that increases stepwise with time to the non-inverting input terminal of the comparator 11. The comparator 11 compares the step-like reference voltage Va input from the LPF 9 with the thermistor voltage Vt.
At the timing when the comparison result satisfies Vt> Va, the output level of the comparator 11 is changed from L to H.

Returning to FIG. 1, when the output level of the comparator 11 becomes H, the comparator 11 outputs a signal corresponding to the thermistor voltage Vt. This output signal is sent to the CPU through the signal line 11a and the terminal pin 5b of the control device 5.
6 is input to an input port 6a. The CPU 6 calculates the resistance value of the thermistor 10 based on a signal corresponding to the input thermistor voltage Vt. By calculating the resistance value and referring to the temperature-resistance characteristics of the thermistor 10, the environmental temperature at this time can be detected.

When the environmental temperature is obtained in this way,
The CPU 6 refers to the table 7a of the storage device 7 and determines the connection position between the common terminal 3a of the changeover switch 3 and the selection terminals 30 to 33 which are set corresponding to the environmental temperature, that is, the selected brightness adjustment resistor. to decide. For example, if the environmental temperature is 5 ° C., it is determined from the table of Table 1 that the common terminal 3a is connected to the selection terminal 31. CPU6
The control signal formed based on the result of referring to the table of Table 1 is output from the output port 6b through the signal line 3b. With this control signal, the common terminal 3a is connected to the position of the selected terminal for selection.

By connecting the common terminal 3a to the selection terminals 30 to 33 of the changeover switch 3 in accordance with the environmental temperature, the LCD driver 2 provides the liquid crystal driving voltage Vo set by the brightness adjustment resistor 4 to the LCD driver 2. Is entered. By driving the LCD 1 with this liquid crystal driving voltage, the brightness of the LCD 1 is adjusted, so that the brightness of the LCD 1 can be made appropriate even when the ambient temperature is far from the standard temperature.

FIG. 3 is a flowchart showing the processing procedure of the CPU 6. Next, this flowchart will be described.

(1) The processing program is started in step S1, and then it is determined in step S2 whether or not it is a predetermined time for performing the brightness adjustment of the LCD 1. The predetermined time is, for example, one day a day, such as 9:00 am every day.
It is possible to set a fixed number of times or a plurality of times a day, such as hourly every day, so that the time can be set arbitrarily. If the determination in step S2 is YES (hereinafter abbreviated as Y), then step S2 is executed.
The process proceeds to the process 3 and if the determination at this time is NO (hereinafter abbreviated as N), other processes are executed in a step S4.

(2) In step S3, the value of PWM8 is initialized, and then, in step S5, PWM8 is driven. Then, in step S6, the input port 6
Check the level of the signal input to a. If the determination at this time is Y, the process proceeds to step S7. Also,
If this determination is N, PW is performed by the processing in step S8.
The value of M is incremented by one, and the process returns to step S5 to drive the PWM 8. Hereinafter, the processing of step S5, step S6, and step S8 is repeated, and the input port 6
When the signal level of “a” becomes “H”, the process goes to step S7.

In the process of step S7, referring to the table 7a of the storage device 7, the common terminal 3a and the selection terminal 3 of the changeover switch 3 set corresponding to the environmental temperature are set.
The connection position with 0 to 33, that is, the selected brightness adjustment resistor is checked, and a control signal is set to the output port 6b in step S9. After performing the above processing, step S10
Ends the processing program of the CPU 6.

FIG. 4 shows an LCD I according to an embodiment of the present invention.
FIG. 2 is a block diagram illustrating an example of a C (integrated circuit) module 20. In FIG. 4, the LCD 1 is, for example, 240 × 64
It has a pixel number of dots and is driven by 1 to 64 common electrode driving common drivers 1a and 1 to 240 segment electrode driving segment drivers 1b. A plurality of segment drivers 1b are arranged. For example, 80 segment electrodes of LCDI are driven by three segment drivers of the same specification.

The common driver 1a includes a frame signal FLM of 70 Hz, an alternating signal M, and a latch signal CL1.
Is entered. The AC signal M, the latch signal CL1, and the data shift clock signal CL2 are input to the segment driver 1b.

D is serial data, and D0 to D3 are parallel data. P and S indicate switching between parallel data and serial data input to the segment driver 1b. FIG. 4 shows a state where the switching is on the serial S side. In this state, the reference voltage VSS is applied to the parallel input terminal and the parallel / serial input selection terminal of the segment driver 1b by the jumpers J1 to J3 and the jumper J4.

When selecting parallel data input to the segment driver 1b, the switching is set to the P side. At this time, the parallel terminal of the segment driver 1b is connected to the parallel data D0 to D3, and the parallel / serial input selection terminal is connected to the logic circuit power supply voltage VDD.

VEE is a power supply voltage for the LCD driver. L between the power supply voltage VEE and the LCD driver 2
A transistor Tr for adjusting the CD drive voltage is connected. The changeover switch 3 selects a luminance adjusting resistor, and the liquid crystal driving voltage Vo set based on this is set to the transistor Tr.
As a bias voltage. The current flowing to the LCD driver 2 is controlled by changing the magnitude of the base bias voltage of the transistor Tr.

The drive voltages V1 to V5 of the common driver 1a and the segment driver 1b are defined, for example, in the range of 8 to 20 V in accordance with the magnitude of the current of the transistor Tr. In this way, the detection of the environmental temperature allows L
A predetermined driving voltage is selected from the CD driver 2 and supplied to the common driver 1a and the segment driver 1b.

When the ambient temperature is low, the brightness of the LCD is high. In this case, the liquid crystal driving voltage Vo set in accordance with the detection of the environmental temperature decreases, so that the base bias voltage of the transistor Tr decreases. As a result, the current flowing through the LCD driver 2 decreases, and the LCD drive voltages V1 to V5 decrease. Further, as the environmental temperature increases, the base bias voltage of the transistor Tr increases. In this case, the adjustment is made in a direction to increase the luminance of the display screen of the LCD.

It is also possible to provide an A / D input port in the CPU 6 and directly input the detected voltage of the thermistor to the CPU 6 to detect the ambient temperature.

[0036]

As described in detail above, according to the present invention, since the brightness adjustment resistor is switched based on the detected temperature, an appropriate brightness can be obtained in the liquid crystal display even when the environmental temperature changes. Can be

Further, since the reference voltage for sequentially generating a plurality of reference voltages and the output of the temperature detecting element are compared, it is not necessary to provide an analog / digital port in the control means or to provide an analog / digital converter separately. In both cases, the temperature can be detected.

Further, the control means has a table of the temperature detected by the temperature detection means and a luminance adjustment resistor to be selected. For this reason, a control signal for selecting the luminance adjustment resistor can be automatically formed by detecting the temperature.

[Brief description of the drawings]

FIG. 1 is a circuit diagram illustrating an example of a brightness adjustment device for a liquid crystal display according to an embodiment of the present invention.

FIG. 2 is a characteristic diagram illustrating an operation of a comparator.

FIG. 3 is a flowchart showing a processing procedure of luminance adjustment of the liquid crystal display.

FIG. 4 is a block diagram showing an IC module for a liquid crystal display.

FIG. 5 is a circuit diagram of a conventional example.

[Description of Signs] 1 Liquid crystal display (LCD) 2 Liquid crystal display (LCD) driver 3 Changeover switch 4 Brightness adjustment resistor 5 Control device 6 Central processing unit (CPU) 7 Storage device 8 Pulse width modulator (PWM) Reference Signs List 9 Low-pass filter (LPF) 10 Thermistor 11 Comparator 20 IC module for liquid crystal display

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[Procedure amendment]

[Submission date] March 27, 1998

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Name of invention

[Correction method] Change

[Correction contents]

[Title of the Invention A liquid crystal display device of the bright adjustment device

Claims (3)

[Claims] A liquid crystal display; a driving unit for driving the liquid crystal display; a temperature detection unit; a control unit for outputting a control signal based on an output of the temperature detection unit; And a switching means for switching a brightness adjustment resistor based on a control signal. 2. The temperature detecting means includes: a temperature detecting element;
2. The brightness adjusting device for a liquid crystal display according to claim 1, comprising a comparing means for comparing the output of the temperature detecting element with a reference voltage, and a reference voltage generating means for sequentially generating a plurality of reference voltages. 3. The brightness adjusting device for a liquid crystal display according to claim 1, wherein the control means includes a table of the temperature detected by the temperature detecting means and a brightness adjusting resistor to be selected.