JP3229792B2 - Liquid crystal display - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a liquid crystal display device, and more particularly to a liquid crystal display device capable of maintaining a good contrast even when the ambient temperature changes.

[0002]

2. Description of the Related Art In a liquid crystal display device, for example, an STN type liquid crystal display device, a contrast adjustment knob is provided because the contrast changes according to the temperature due to the temperature dependence of the liquid crystal. The adjustment voltage V _CON is, for example, 1 V up and down around 1.8 V
The liquid crystal driving voltage VEE can be adjusted in the range of, for example, about 20 to 40 V by the adjustment voltage V _CON so that the contrast can be optimized.

[0003]

SUMMARY OF THE INVENTION It is a main object of the present invention to provide a structure capable of automatically changing a liquid crystal driving voltage in response to a change in ambient temperature and maintaining a constant contrast. I do. In relation to this, it is an object to provide a configuration capable of accurately detecting an ambient temperature without being affected by heat generated by a circuit element. Another object is to provide a configuration capable of coping with a fluctuation in power supply voltage even when the power supply voltage fluctuates, such as when the power supply voltage is mounted on a battery-driven device. Another object is to provide a configuration capable of performing fine adjustment by supplying a contrast adjustment voltage V _CON from the outside in order to be able to cope with a difference in driving conditions such as a frame frequency.

[0004]

According to the present invention, there is provided a liquid crystal display comprising: a liquid crystal panel; and a circuit unit having a power supply circuit for generating a voltage for driving the liquid crystal, the circuit unit being arranged along a vertical direction beside the liquid crystal panel. In the display device, the circuit unit is provided with a circuit for maintaining and outputting a liquid crystal driving voltage at an appropriate voltage according to an ambient temperature by an output of a temperature detection element, and the heat generation amount of the circuit unit is controlled by the temperature detection element. It is characterized by being arranged in a region below many circuit elements.

Further, the present invention provides a liquid crystal panel, a circuit unit having a power supply circuit for generating a liquid crystal driving voltage, and disposed along the vertical direction on the side of the liquid crystal panel, and a frame covering the circuit unit. In the liquid crystal display device having a body, the circuit unit is provided with a circuit for maintaining and outputting a liquid crystal driving voltage at an appropriate voltage according to an ambient temperature by an output of a temperature detecting element, and in a region above the circuit unit. A circuit element generating a large amount of heat is disposed, the temperature detecting element is disposed in a lower region, and an opening corresponding to the temperature detecting element is formed in the frame.

The circuit element generating a large amount of heat can be arranged on the back side of the circuit unit, and the temperature detecting element can be arranged on the front side of the circuit unit.

[0007] Further, a variable resistor connected to a circuit in association with the temperature detecting element can be arranged close to the temperature detecting element so that the variable resistor can be operated from the opening.

[0008]

[0009]

Embodiments of the present invention will be described below with reference to the drawings. 1 and 2, reference numeral 1 denotes a liquid crystal display device (generally called a liquid crystal module), and a liquid crystal panel 2.
A plurality of circuit units 3 including a circuit unit 3a mainly for a power supply system arranged around the panel 2; and a metal frame 4 covering the periphery of the liquid crystal panel 2 and the circuit unit. It is composed. As the liquid crystal panel 2, for example, a TN or STN type in which liquid crystal is sealed between glass substrates and liquid crystal molecules are twisted and held by about 90 to 260 degrees can be used. The circuit unit 3a of the power supply system is configured by incorporating a part of a circuit element constituting a circuit described later on a vertically long printed board 31, and is arranged on the side of the panel 2 along the vertical direction of the panel 2. Circuit unit 3
On the back surface of the unit 3a, circuit elements 61 and 63 that generate a large amount of heat, such as a DC-DC converter and an operational amplifier, are placed in the unit 3a.
And a circuit element such as a temperature detecting element TM or a variable resistor VR, which will be described later, is not affected by the heat generated by the circuit elements 61 and 63 that generate a large amount of heat. As described above, it is arranged in a lower region of the unit 3a, which is a position lower than the circuit element generating a large amount of heat.
In addition, the liquid crystal display device 1 is generally incorporated in a device such as a personal computer or a word processor, and is used so that the upper part of FIG.

In order to make it easier for the temperature detecting element TM to detect the ambient temperature and to facilitate the setting operation of the variable resistor VR disposed close to the temperature detecting element TM, the temperature detecting element TM is provided on the frame 4. An opening 41 is formed corresponding to the positions of TM and the variable resistor VR.

Next, the circuit configuration will be described. As shown in FIG. 3, the liquid crystal display device 1 includes a liquid crystal panel 2, a driving circuit 5 for scanning and signals connected thereto, and a power supply circuit section 6 for supplying a plurality of bias voltages to the driving circuit 5.
And a receiving circuit 7 for receiving an image signal or a display control signal supplied from the outside and selectively supplying the received signal to the drive circuit 5 and the power supply circuit section 6, and a connector 8 for connection to an external device. The main part of the power supply circuit 6 and the connector 8 are
It is arranged in the circuit unit 3a of the power supply system.

As shown in FIGS. 3 and 4, the power supply circuit section 6 supplies a DC power supply [VDD (5V) -GN] from an external device via a connector.
D (0V)], which is applied to a DC-DC converter 61 constituting a liquid crystal driving voltage generating circuit, and the output voltage V
The voltage is converted so as to obtain EE, the voltage is applied to the resistance dividing circuit 62, a plurality of bias voltages are taken out from the resistance dividing point, and these are supplied to the driving circuit 5 via the buffer circuit 63 composed of a plurality of operational amplifiers. Configuration. The DC-DC converter 61 is controlled to start and stop its operation by an ON / OFF signal supplied to the ON / OFF terminal from the receiving circuit 7 and responds to a voltage V _{CON supplied} to the V _CON terminal from the voltage adjusting circuit 9. Thus, the output voltage VEE can be changed. It should be noted that the DC-DC converter 61 may be configured to generate not only the output voltage VEE but also another output voltage having a different voltage range.

The voltage adjustment circuit 9 adjusts the voltage V to be applied to the DC-DC converter 61 so that the contrast of the liquid crystal panel 2 is maintained in an appropriate state even when the ambient temperature changes.
_It has a circuit configuration that corrects _{CON according} to the ambient temperature,
As shown in FIG. 5, the upper limit voltage generating means 91 and the lower limit voltage generating means 92 for determining the fluctuation range of the voltage V _{CO N,}
It has a first resistance circuit 93 and a second resistance circuit 94 whose resistance value changes according to the temperature. The upper limit voltage generating means 91 outputs a constant output voltage while the power supply voltage VDD is, for example, 3 V or more so that the power supply voltage VDD supplied from the outside can be supplied even from a power supply having a large voltage fluctuation such as a battery. It consists of a voltage regulator element that guarantees 2.5V. The lower-limit voltage generating means 92 converts the external adjustment voltage ExV _CON to a predetermined value by the resistors R1 and R2 in order to accept a fine adjustment by the external signal ExV _CON in response to a difference in driving conditions such as a frame frequency. The voltage is divided at a ratio of, for example, 1: 1 and the voltage at the division point is output via the voltage transmission element A. The voltage transmitting element A is provided with an operational amplifier (buffer) using a voltage follower in order to prevent a change in resistance value of the first and second resistance circuits 93 and 94 due to temperature from affecting the voltage dividing ratio of the resistors R1 and R2. ), Etc., to prevent the lower limit voltage from fluctuating. The external adjustment voltage ExV _CON is normally 0.8V ~
When the ratio between the resistors R1 and R2 is set to 1: 1, the output fluctuation range of the lower limit voltage generating means 92 becomes 0.4V to 1.4V. .

The first resistor circuit 93 is constituted by connecting a resistor R4 and a variable resistor VR in series, and the second resistor circuit 94 is constituted by a temperature detecting element TM such as a thermistor whose resistance changes with temperature and a resistor R3. Are connected in parallel.
The series circuit of the first resistance circuit 93 and the second resistance circuit 94 is connected between the output terminals of the upper limit voltage generating means 91 and the lower limit voltage generating means 92. Then, the first resistance circuit 93
And the voltage at the connection point between the second resistor circuit 94 and the second resistor circuit 94 is the adjustment voltage V
It is supplied to the V _CON terminal of the DC-DC converter 61 as _CON. Since the resistance value of the temperature detecting element TM changes as the ambient temperature changes, the voltage value of the adjusting voltage V _CON changes according to the ambient temperature. The adjustment voltage V _CON
Can be finely adjusted up and down by changing the resistance value of the variable resistor VR, or finely adjusted by changing the external adjustment voltage ExV _CON supplied from the outside.

The contrast of the liquid crystal panel 2 changes depending on the temperature. The relationship between the temperature for keeping the contrast constant and the liquid crystal driving voltage VEE can be experimentally obtained, for example, as shown in FIG. . The adjustment voltage V _CON according to the ambient temperature for generating the liquid crystal driving voltage V _EE can also be obtained experimentally as shown in FIG. Therefore, the first resistance circuit 93 and the second resistance circuit 94 are adjusted so that the adjustment voltage V _CON output from the voltage adjustment circuit 9 draws a characteristic as shown in FIG. It is possible to provide the liquid crystal display device 1 that can maintain the contrast of the liquid crystal panel 2 in a favorable and almost constant state irrespective of a temperature change by experimentally obtaining and setting the types and resistance values of the constituent resistors. it can.

In this manner, the liquid crystal driving voltage VEE becomes high when the ambient temperature is low,
When the ambient temperature increases, the voltage is automatically changed to a low voltage, so that the allowable loss of the circuit element at a high temperature can be set small. Therefore, the circuit elements constituting the power supply circuit section 6, the drive circuit 5, and the like can be constituted by components having low allowable loss, suitable for miniaturization and thinning, and the entire apparatus can be miniaturized.
It can be thin and light.

If the temperature detecting element TM is heated by the heat of the heat-generating components of the circuit unit 3a, accurate detection of the ambient temperature may not be possible. The circuit element (DC-DC converter 6) in which the heat generation amount of the circuit unit 3a is ranked higher.
1 and an operational amplifier constituting the buffer circuit 63), the unnecessary heating by the heating circuit element can be prevented, and accurate temperature detection can be performed. Also,
The circuit element that generates a large amount of heat is arranged on the back side of the circuit unit 3a, and the temperature detection element TM is connected to the circuit unit 3a.
Since it is arranged on the front side of a, unnecessary heating by the heating circuit element can be further prevented. Further, since the opening 41 corresponding to the temperature detecting element TM is formed in the frame body 4, the opening 41 promotes the inflow and outflow of air around the temperature detecting element TM, and enables accurate detection of the ambient temperature. be able to. Also, as desired in the opening 41, the temperature detecting element TM
, The variable resistor VR can be adjusted by using the heat dissipation opening 41 in common. It should be noted that the opening 41 is provided in the liquid crystal display device 1.
Is usually provided at a position hidden by the case of the other device, so that the appearance of the other device is not damaged.

[0018]

As described above, according to the present invention, it is possible to provide a configuration capable of automatically changing the liquid crystal driving voltage in response to a change in the ambient temperature and maintaining a constant contrast. . Further, the detection of the ambient temperature can be accurately performed with little influence from the heat generated by the circuit element.
In addition, even when the power supply voltage fluctuates, such as when the power supply voltage is mounted on a battery-driven device, the configuration can be made to be less affected by the fluctuation. In addition, a configuration is possible in which fine adjustment can be performed by supplying a contrast adjusting voltage from the outside, and it is possible to cope with a difference in driving conditions such as a frame frequency. Further, circuit elements constituting a power supply circuit portion, a drive circuit, and the like can be configured by components having small allowable loss, suitable for miniaturization and thinning, and the entire device can be miniaturized, thinned, and lightened.

[Brief description of the drawings]

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

FIG. 2 is a sectional view taken along line II of FIG.

FIG. 3 is a block diagram showing a schematic circuit of the liquid crystal display device according to the embodiment of the present invention.

FIG. 4 is a circuit block diagram of a power supply circuit unit of the embodiment.

FIG. 5 is a circuit diagram of a voltage adjustment circuit according to the embodiment.

[6] temperature and the liquid crystal drive voltage VEE, a characteristic diagram showing the relationship between temperature and adjusting the voltage V _CON.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Liquid crystal display device 2 Liquid crystal panel 3a Circuit unit 4 Frame 5 Drive circuit 6 Power supply circuit part 61 DC-DC converter 9 Voltage adjustment circuit 91 Lower limit voltage generating means 92 Upper limit voltage generating means 93 First resistance circuit 94 Second resistance circuit TM Temperature detection element VR Variable resistor

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) G02F 1/133 580 G02F 1/1333

Claims (4)

(57) [Claims] 1. A liquid crystal display device comprising: a liquid crystal panel; and a circuit unit having a power supply circuit for generating a liquid crystal driving voltage and disposed along a vertical direction beside the liquid crystal panel. Is provided with a circuit for maintaining and outputting the liquid crystal driving voltage at an appropriate voltage according to the ambient temperature by the output of the temperature detecting element, and providing the temperature detecting element in an area below a circuit element having a large heat generation amount of the circuit unit. A liquid crystal display device, comprising: 2. A liquid crystal panel, comprising: a circuit unit having a power supply circuit for generating a liquid crystal driving voltage and arranged along a vertical direction on a side of the liquid crystal panel; and a frame covering the circuit unit. In the liquid crystal display device, the circuit unit is provided with a circuit for maintaining and outputting a liquid crystal driving voltage at an appropriate voltage corresponding to an ambient temperature by an output of a temperature detecting element, and a large amount of heat is generated in a region above the circuit unit. A liquid crystal display device comprising: a circuit element; a temperature detection element disposed in a lower region; and an opening corresponding to the temperature detection element formed in the frame. 3. The liquid crystal according to claim 1, wherein the circuit element generating a large amount of heat is arranged on the back side of the circuit unit, and the temperature detecting element is arranged on the front side of the circuit unit. Display device. 4. A variable resistor according to claim 2, wherein a variable resistor connected to a circuit in association with said temperature detecting element is disposed close to said temperature detecting element so as to be operated from said opening. Liquid crystal display.