JP2002062522A - Liquid crystal display device and its voltage for drive adjusting circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide constitution capable of maintaining the contrast of the display panel of a display device at a constant state by changing a liquid crystal driving voltage automatically in accordance with the change of ambient temperature. SOLUTION: A liquid crystal driving voltage generating circuit is provided with an upper limit voltage generating means 91 which converts a power source voltage to be supplied from the outside into a fixed voltage lower than the power source voltage and outputs it as an upper limit voltage, a lower limit voltage generating means 92 which generates a lower limit voltage lower than the upper limit voltage in accordance with the voltage of a voltage for adjustment to be supplied from the outside, a first resistance circuit 93 and a second resistance circuit 94 whose resistance value is changed in accordance with temperature and this display device is made to have constitution in which the first resistance circuit 93 and the second resistance circuit 94 are connected in series and they are connected between terminals performing the supplying of the upper limit voltage and the lower limit voltage and also a voltage at the connection point between the first resistance circuit 93 and the second resistance circuit 94 is supplied as the voltage for adjustment with respect to the liquid crystal driving voltage generating circuit.

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, and a driving voltage adjusting circuit therefor.

[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 VCON is, for example, 1 V up and down around 1.8 V
The liquid crystal drive voltage VEE can be adjusted in the range of, for example, about 20 to 40 V by the adjustment voltage VCON, 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 VCON from the outside so as 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 device having a liquid crystal panel and a power supply circuit for generating a liquid crystal driving voltage. A liquid crystal driving voltage generating circuit for generating a corresponding liquid crystal driving voltage; and a liquid crystal driving voltage adjusting circuit for supplying the adjusting voltage to the liquid crystal driving voltage generating circuit. Is an upper limit voltage generating means for converting a supplied power supply voltage into a constant voltage lower than the voltage and outputting the same as an upper limit voltage, and an upper limit voltage corresponding to a voltage of an externally supplied adjustment voltage. Lower limit voltage generating means for generating a lower limit voltage,
A first resistor circuit, and a second resistor circuit having a resistance value that changes according to temperature.
And the first resistor circuit and the second resistor circuit are connected in series and connected between terminals for supplying the upper limit voltage and the lower limit voltage, and the first resistor circuit and the second resistor circuit are connected to each other. A voltage at a connection point of the second resistance circuit is supplied as an adjustment voltage to the liquid crystal drive voltage generation circuit. Note that an opening can be formed corresponding to the second resistance circuit.

A liquid crystal driving voltage adjusting circuit according to the present invention provides a liquid crystal driving voltage for supplying the adjusting voltage to a liquid crystal driving voltage generating circuit for generating a liquid crystal driving voltage according to the supplied adjusting voltage. An adjusting circuit configured to convert a supplied power supply voltage into a constant voltage lower than the supplied voltage and output the same as an upper limit voltage; and an upper limit voltage corresponding to a voltage of an externally supplied adjusting voltage. A lower-limit voltage generating means for generating a lower-limit voltage lower than the first resistance circuit, a second resistance circuit having a resistance value that changes according to a temperature, and the first resistance circuit and the second resistance circuit. A resistor circuit is connected in series and connected between terminals for supplying the upper limit voltage and the lower limit voltage, and the first resistor circuit and the second resistor circuit are connected to each other.
The voltage at the connection point of the resistor circuit is supplied as an adjustment voltage to the liquid crystal drive voltage generation circuit.

[0006]

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 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 DC power [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 operation of the DC-DC converter 61 is controlled by an ON / OFF signal supplied to the ON / OFF terminal from the receiving circuit 7 and the operation thereof is controlled. In addition, the DC-DC converter 61 responds to the voltage VCON supplied from the voltage adjusting circuit 9 to the VCON terminal. 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.

A voltage adjusting circuit 9 adjusts a voltage V supplied to a DC-DC converter 61 so as to maintain the contrast of the liquid crystal panel 2 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, upper limit voltage generating means 91 and lower limit voltage generating means 92 for determining a fluctuation range of voltage VCON,
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 adjusts the external adjustment voltage ExVCON to a predetermined ratio, for example, by the resistors R1 and R2 in order to accept a fine adjustment by the external signal ExVCON in response to a difference in driving conditions such as a frame frequency. The voltage is divided into 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) by a voltage follower in order to prevent a change in the resistance value of the first and second resistance circuits 93 and 94 due to the temperature from affecting the voltage dividing ratio of the resistors R1 and R2. ), The input resistance is very high to prevent the lower limit voltage from fluctuating. The external adjustment voltage ExVCON is usually 0.8V ~
Since it is set to change between 2.8V, if the ratio of the resistors R1 and R2 is set to 1: 1, the output fluctuation range of the lower limit voltage generating means 92 will be 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 value 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 of the second resistance circuit 94 is the adjustment voltage VCO
N is supplied to the VCON terminal of the DC-DC converter 61. Since the resistance value of the temperature detecting element TM changes as the ambient temperature changes, the voltage value of the adjusting voltage VCON changes according to the ambient temperature. In addition, the adjustment voltage VCON
Can be finely adjusted up and down by changing the resistance value of the variable resistor VR, or can be finely adjusted by changing the external adjustment voltage ExVCON supplied from the outside.

The contrast of the liquid crystal panel 2 changes with the temperature. The relationship between the temperature for maintaining the contrast and the liquid crystal driving voltage VEE can be experimentally obtained, for example, as shown in FIG. . The adjustment voltage VCON according to the ambient temperature for generating the liquid crystal drive voltage VEE can also be obtained experimentally as shown in FIG. Therefore, the first resistance circuit 93 and the second resistance circuit 94 are configured such that the adjustment voltage VCON output from the voltage adjustment circuit 9 draws a characteristic as shown in FIG. By empirically obtaining and setting the type and resistance value of the resistor to be provided, it is possible to provide the liquid crystal display device 1 that can keep the contrast of the liquid crystal panel 2 in a favorable substantially constant state regardless of the temperature change. .

In this way, 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, it may not be possible to detect the ambient temperature accurately. However, as shown in FIGS. 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.

[0015]

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.

FIG. 6 is a characteristic diagram showing a relationship between a temperature and a liquid crystal driving voltage VEE, and a relationship between a temperature and an adjustment voltage VCON.

[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 Upper limit voltage generating means 92 Lower limit voltage generating means 93 First resistance circuit 94 Second resistance circuit TM Temperature detection element VR Variable resistor

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) G09G 3/36 G09G 3/36 F term (Reference) 2H093 NC01 NC47 NC57 ND03 ND37 ND42 NE01 NF13 5C006 AA16 AF46 AF51 AF52 AF53 AF84 BF38 BF42 BF46 FA19 FA21 5C080 AA10 BB05 DD03 EE28 JJ02 JJ03 JJ05

Claims (3)

[Claims] 1. A liquid crystal display device having a liquid crystal panel and a power supply circuit for generating a liquid crystal drive voltage, wherein the power supply circuit is configured to generate a liquid crystal drive voltage according to a supplied adjustment voltage. A voltage generating circuit, and a liquid crystal driving voltage adjusting circuit for supplying the adjusting voltage to the liquid crystal driving voltage generating circuit, wherein the liquid crystal driving voltage generating circuit sets the supplied power supply voltage to be lower than the voltage. Upper limit voltage generating means for converting to a low constant voltage and outputting as an upper limit voltage, and lower limit voltage generating means for generating a lower limit voltage lower than the upper limit voltage in accordance with the voltage of the adjustment voltage supplied from the outside, A first resistance circuit, and a second resistance circuit having a resistance value that changes in accordance with a temperature, wherein the first resistance circuit and the second resistance circuit are connected in series and the upper limit voltage and the lower limit voltage are changed. Feeding end And the first
A voltage at a connection point between the resistor circuit and the second resistor circuit is supplied as an adjustment voltage to the liquid crystal drive voltage generation circuit. 2. The liquid crystal display device according to claim 1, wherein an opening is formed corresponding to the second resistance circuit. 3. A power supply voltage supplied to a liquid crystal driving voltage adjusting circuit for supplying the adjusting voltage to a liquid crystal driving voltage generating circuit for generating a liquid crystal driving voltage according to the supplied adjusting voltage. And a lower limit for generating a lower limit voltage lower than the upper limit voltage corresponding to the voltage of the adjustment voltage supplied from the outside. A voltage generating means, a first resistance circuit, and a second resistance circuit having a resistance value that changes according to temperature, wherein the first resistance circuit and the second resistance circuit are connected in series and the upper limit is set. A configuration for connecting between a terminal for supplying a voltage and a lower limit voltage, and supplying a voltage at a connection point between the first resistance circuit and the second resistance circuit as an adjustment voltage to the liquid crystal drive voltage generation circuit; What you did Characteristic voltage adjustment circuit for driving liquid crystal.