JP2000098346A - LCD drive voltage control circuit - Google Patents

Abstract

(57) Abstract: A liquid crystal drive voltage circuit that corrects a liquid crystal drive voltage supplied to an STN liquid crystal display in accordance with an ambient temperature to obtain an optimal screen display is obtained. SOLUTION: A liquid crystal driving voltage V output from a liquid crystal driving voltage generating circuit 104 is provided on a cathode side of a transistor TR1.
_OUT is input, a liquid crystal drive voltage V _OUT is connected to the base side of the transistor TR1 via a resistor R3, and a thermistor element TH1 whose resistance value changes in response to a temperature change is connected between the base of the transistor TR1 and the ground. A connection with the resistor R4 is connected, and an optimum liquid crystal driving voltage _VEE corresponding to a temperature change is output from the emitter side of the transistor TR1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an STN (Sup).
The present invention relates to a liquid crystal drive voltage control circuit that controls a liquid crystal drive voltage for driving a liquid crystal display.

[0002]

2. Description of the Related Art In general, the threshold voltage of a liquid crystal display element,
It is known that electro-optical characteristics such as response speed change according to changes in ambient temperature. On the screen of a conventional STN liquid crystal display, the contrast ratio is about 18 at room temperature (around 25 ° C.), but at a low temperature (around 0 ° C.).
Or, at a high temperature (around 50 ° C., the contrast ratio is about 8, which is less than half that at normal temperature. Therefore, at a low temperature, the display becomes dim and blackish, and at a high temperature, the display becomes bright and white. In both cases, there is a problem that the screen display is harder to see than at room temperature.

FIG. 6 is a diagram showing a block configuration of a conventional STN liquid crystal display device. In the figure, 600 is an STN liquid crystal display device, 601 is an STN liquid crystal display, 602
Is a liquid crystal control card, 603 is a liquid crystal drive voltage generation circuit, 604 is a digital image control circuit, 605
, A power supply circuit; and 606, an external variable resistor.

A power supply circuit 605 converts a voltage V _CC for driving each of the liquid crystal drive voltage generation circuit 603 and the digital image control circuit 604 based on a power supplied from an external power supply into a liquid crystal drive voltage. The signal is supplied to the generation circuit 603 and the digital image control circuit 604. The digital image control circuit 604 includes digital image data Video / DATA and S
CONT which is a TN liquid crystal display control signal
And outputs CONT to the liquid crystal drive voltage generation circuit 603, and outputs the digital image data DATA
Is output to the STN liquid crystal display 601. The liquid crystal drive voltage generation circuit 603 is provided with a CONT or an external variable resistor 6.
06, the liquid crystal driving voltage _VEE for generating an electric field is supplied to the STN liquid crystal display 601.
The operator operates CONT or an external variable resistor 6 in order to display the STN liquid crystal display 601 on an optimal screen.
06, the liquid crystal drive voltage _VEE is adjusted.

FIG. 7 is a diagram showing a configuration of a liquid crystal drive voltage generating circuit in a conventional STN liquid crystal display device, in which (a) adjusts the liquid crystal drive voltage _VEE by an external variable resistor, and (b) shows. The adjustment of the liquid crystal drive voltage V _EE is performed by an analog switch using CONT. In the figure,
606, an external variable resistor; 701, a DC / DC converter; V _CC , a voltage supplied from a power supply circuit 605;
1 is an inductor for storing and boosting the switching energy of the DC / DC converter 701, and V _OUT is D
A voltage output from the C / DC converter 701, D1 is a diode for preventing a reverse current from the _VEE output terminal, and R2 is a resistor (not shown) by an external variable resistor 606 or an analog switch (described later (b)). V in cooperation with
_A voltage _dividing resistor for dividing voltage from _OUT to _VEE , _VEE is STN
The liquid crystal driving voltage supplied to the liquid crystal display 601, B 1
〜Bn are analog switches selected by CONT output from the digital image control circuit 604. Also, each switch terminal of the analog switch has CO
A resistor (not shown) having a resistance value such that a desired voltage division ratio is obtained by NT is connected.

Since the optimum liquid crystal drive voltage for making the STN liquid crystal display 601 an optimum screen display fluctuates due to a temperature change, adjustment of the external variable resistor 606 or CO
NT resistance value is variable by adjustment of the analog switch B1~Bn by, by varying the dividing ratio of the output voltage V _OUT of the DC / DC converter 701, and adjusted to optimize the liquid crystal drive voltage V _EE, STN liquid crystal display 601.

[0007]

As described above, the conventional S
In a TN liquid crystal display device, in an emergency or maintenance, an operator such as an operator first optimally drives a liquid crystal driving voltage _VEE supplied to an STN liquid crystal display before performing a specific process such as an emergency or maintenance. There has been a problem that the resistance value of the CONT or the external variable resistor 606 must be manually adjusted as necessary so as to obtain a voltage, and an optimum screen display is required.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and corrects a liquid crystal driving voltage supplied to an STN liquid crystal display in accordance with an ambient temperature to provide an optimum screen display. It is an object of the present invention to obtain a liquid crystal drive voltage generation circuit of a device.

[0009]

A liquid crystal drive voltage control circuit according to the present invention includes: a liquid crystal drive voltage generation circuit having a DC / DC converter for generating an output voltage corresponding to an input reference voltage; A temperature correction voltage conversion circuit that outputs a liquid crystal drive voltage based on the voltage output from the generation circuit so that the liquid crystal display becomes an optimal screen display in response to a temperature change.

The temperature correction voltage conversion circuit uses an element having a negative resistivity corresponding to a temperature change as a temperature correction element.

Further, a resistor is connected in series and / or in parallel to the temperature compensating element to adjust the temperature characteristic.

Further, the temperature correction voltage conversion circuit has an emitter follower circuit, and the base of the emitter follower circuit is controlled by dividing the output of the liquid crystal drive voltage generation circuit by a voltage division circuit including a temperature correction element. Things.

[0013] Also, a DC / DC converter for generating an output voltage corresponding to the input reference voltage and a voltage dividing circuit including a temperature compensating element are provided, and the output voltage of the DC / DC converter is divided by the voltage dividing circuit. To generate a reference voltage, DC /
The liquid crystal drive voltage corresponding to the temperature change is output by feedback input to the reference voltage input terminal of the DC converter.

Further, the temperature correction element is a thermistor.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 FIG. 1 is a diagram showing a block configuration of an STN liquid crystal display device according to an embodiment of the present invention. In the figure, 100 is an STN liquid crystal display device, 101 is an STN liquid crystal display, 102 is a liquid crystal control card, 103 is a liquid crystal drive voltage control circuit,
104 is a liquid crystal drive voltage generation circuit, 105 is a liquid crystal drive voltage conversion circuit, 106 is a digital image control circuit,
107 is a power supply circuit.

The power supply circuit 107 is a liquid crystal drive voltage generation circuit 1 based on a power supplied from a power supply.
04 and the digital image control circuit 106 for driving the voltage V _CC to the liquid crystal drive voltage control circuit 1
03 and the digital image control circuit 106. In the liquid crystal drive voltage control circuit 103, based on the voltage V _CC supplied from the power supply circuit 107, the liquid crystal drive voltage generation circuit 104 uses the STN liquid crystal display 101 even under the environmental specifications of the STN liquid crystal display device 100 and the actual use temperature. A voltage V _OUT that can generate a sufficient voltage for driving the LCD is output, and a liquid crystal driving voltage conversion circuit 105 drives the STN liquid crystal display 101 based on the voltage V _OUT so that the STN liquid crystal display 101 has an optimal screen display. A voltage _VEE is generated and supplied to the STN liquid crystal display 101. The digital image control circuit 106
Is Video / DATA which is digital image data.
And set the digital image data DATA to ST
N to the liquid crystal display 101.

In this embodiment, the liquid crystal drive voltage supplied to the STN liquid crystal display 101 has a working temperature range of 0 ° C. to 50 ° C. and an output voltage range of 17.0 V to 2 ° C.
Variable between 1.0V (17.0V / 50 ° C ~ 2
1.0V / 0 ° C., which changes in inverse proportion to the temperature).

FIG. 2 shows an embodiment S of the present invention.
FIG. 3 is a diagram illustrating a circuit configuration of a liquid crystal drive voltage control circuit in a TN liquid crystal display device. The liquid crystal drive voltage control circuit 103 includes:
Liquid crystal drive voltage generation circuit 104 and liquid crystal drive voltage conversion circuit 1
05. In the figure, V _CC is a voltage supplied from the power supply circuit 107, and 201a is D
C / DC converter, L1 is DC / DC converter 20
Inductor 1a for storing and boosting the switching energy of 1a, D1 is a diode for blocking and flowing back current from V _OUT side, R1 and R2 are DC /
This is the external mounting resistance of the DC converter 201a. Also,
V _ref is a reference voltage for obtaining V _OUT by a predetermined calculation formula, and V _OUT is an output voltage of a DC / DC converter obtained by a predetermined calculation formula based on the reference voltage V _ref .

_VEE is an STN liquid crystal display 10
1, Z1 is an impedance composed of a thermistor element TH1 and a resistor R4 having a resistance component that varies linearly with temperature, and TR1 is a resistor R
3 is a transistor for obtaining a constant current output at a predetermined output voltage _VEE based on a divided voltage of the impedance 3 and the impedance Z1.

The output voltage V _OUT generated by the liquid crystal drive voltage generation circuit 104 is represented by the following equation: V _OUT = (1+ (R2 / R1)) V _ref (1) The output voltage V _OUT is determined by setting the resistors R1 and R2 so as to keep the reference voltage _{Vref of} 201a constant.

In the liquid crystal drive voltage conversion circuit 105 at the subsequent stage of the liquid crystal drive voltage generation circuit 104, the transistor TR1
Connects the output voltage V _OUT to the cathode side, connects the output voltage V _OUT to the base side via the resistor R3, and outputs the liquid crystal driving voltage V _EE from the emitter side. Further, a thermistor element TH1 is connected between the base of the transistor TR1 and the ground.
By inserting an impedance Z1 including a resistor R4 and a base current IB of the transistor TR1, the liquid crystal driving voltage V _EE supplied to the STN liquid crystal display 101 is controlled. Further, a variation due to the temperature of the STN liquid crystal display 101 itself is generated by the resistor R3 and the impedance Z1 to generate a correction voltage γV necessary for outputting the liquid crystal driving voltage, and the correction voltage γV is supplied to the STN liquid crystal display 101.

FIG. 3 is a diagram showing the relationship between the optimum drive correction voltage γV and the temperature according to an embodiment of the present invention. ST
N: the liquid crystal drive voltage V required by the liquid crystal display 101
_{Even if EE} is the same value as V _{OUT at} normal temperature (25 ° C),
It changes as shown in the figure depending on the temperature. Therefore, ST
N: the liquid crystal drive voltage V required by the liquid crystal display 101
_In order to obtain _EE , it is necessary to correct V _OUT with an optimum drive correction voltage γV as shown in the figure.

FIG. 4 is a diagram showing the relationship between the temperature and the impedance Z1 composed of the thermistor element TH1 and the resistor R4 in the liquid crystal drive voltage control circuit according to one embodiment of the present invention. As shown in the figure, the inclination of the liquid crystal drive voltage _VEE can be determined by using the relationship between the thermistor element TH1 and the temperature. However, when the drive voltage differs depending on the type of liquid crystal, a resistor is connected to the thermistor element TH1. By connecting in series or in parallel, the liquid crystal drive voltage V _EE
Can be varied and adjusted.

Here, the liquid crystal drive voltage conversion circuit 10 shown in FIG.
5 in the configuration of the resistor R3 and the impedance Z1,
Assuming that the resistance value of the thermistor element TH1 is Rt, the voltage division ratio is: Z1 / (R3 + Z1) = (Rt + R4) / (R3 + Rt
+ R4), and by appropriately selecting the value of R4, it is possible to obtain a liquid crystal driving voltage _VEE having a desired inclination with respect to a temperature change. If R4 = 0 (when the impedance Z1 is composed of only the thermistor element TH1), the voltage division ratio becomes Z1 / (R3 + Z1) = Rt / (R3 + Rt). The change is R4 ≠ than when R4 = 0.
In the case of 0, it becomes gentler.

When the resistor R4 is connected in parallel with the thermistor element TH1, if the resistance in parallel connection of the thermistor TH1 and the resistor R4 is expressed as (Rt // R4), the voltage division ratio is Z1 / (R3 + Z1). ) = (Rt // R4) / (R3 + (R
t // R4)), the change in the resistance value connected in parallel, that is, the change in the voltage division ratio becomes large, and the slope of the correction curve with respect to the temperature change becomes steep.

The liquid crystal control card 102 having this configuration
In mounting the device, the thermistor TH1, which is a circuit element of the liquid crystal drive voltage conversion circuit 105, is attached to a position where the temperature of the STN liquid crystal display 101 can be accurately reflected, for example, in close contact with the back side of the operation panel surface. It is important to note the method.

The liquid crystal driving voltage V _EE supplied to the STN liquid crystal display is as follows: V _EE = V _OUT · γV (2) γV = (R3 / (Rt + R3 + R4)) (3) . Here, Rt, R3, and R4 are resistance values of the thermistor element TH1, the resistor R3, and the resistor R4. From the equation (2), the liquid crystal driving voltage V _EE is
Since it is determined by 4 output a voltage V _OUT between the correction voltage .gamma.V, it would be if the output voltage V _OUT does not change.

In the liquid crystal drive voltage conversion circuit 105 composed of the transistor TR1, the resistor R3, and the impedance Z1 (thermistor element TH1 and the resistor R4), STN
By calculating a correction voltage γV of the liquid crystal drive voltage that differs for each characteristic of the liquid crystal display 101, the liquid crystal drive voltage V
_{Since EE} is obtained, it is effective for the STN liquid crystal display device 100 that is often used unattended for a long time.

Embodiment 2 FIG. 5 is a diagram showing a circuit configuration of a liquid crystal drive voltage control circuit in an STN liquid crystal display device according to one embodiment of the present invention. In the figure,
V _CC , L 1, D 1, R 2 V _OUT , V _ref , and V _EE are the same as those in FIG. 2 described above, and a description thereof will be omitted. 201b is a DC / DC converter, and Z2 is an impedance composed of the thermistor element TH1 and a resistor R5.

In the first embodiment, the liquid crystal driving voltage control circuit 103 outputs a constant voltage V _OUT to the liquid crystal driving voltage generating circuit 104, and outputs the voltage V _OUT , the correction voltage γV, and the liquid crystal driving voltage V _EE . Voltage liquid crystal drive voltage conversion circuit 10
5 has been described, but in this embodiment,
The voltage V _OUT itself output from the liquid crystal drive voltage generation circuit is varied.

[0031] The reference voltage V _{re f} input to the feedback terminal of the DC / DC converter 201b, the impedance Z2 having the thermistor element by adjusting to temperature changes, the output voltage V _OUT of the liquid crystal drive voltage control circuit The output voltage V _OUT is used as a liquid crystal drive voltage V _EE to be supplied to the STN liquid crystal display 101. The output voltage V _OUT in this embodiment is as follows: V _OUT = (1+ (R2 / Z2)) V _ref (4) Z2 = R5 + Rt (5) Here, Rt, R2, and R5 are resistance values of the thermistor element TH1, the resistor R2, and the resistor R5.

Optimal liquid crystal driving voltage V corresponding to temperature change
_EE (= V _OUT ) and the characteristics of the thermistor element TH1 are as follows:
This is the same as FIGS. 3 and 4 of the first embodiment, and a description thereof will be omitted.

In the above description, an example has been described in which the thermistor element TH1 is used as the temperature correction element. However, a thermocouple, a thermo label, a bimetal, a temperature-sensitive ferrite, a transistor, or the like may be used. Further, a quantum sensor or a thermal sensor that detects infrared rays emitted from the object may be used.

[0034]

Since the present invention is configured as described above, it has the following effects.

The liquid crystal drive voltage control circuit according to the present invention comprises:
DC that generates an output voltage corresponding to the input reference voltage
And a liquid crystal drive voltage generating circuit having a DC / DC converter, and a liquid crystal drive voltage for outputting an optimal screen display corresponding to a temperature change based on the voltage output from the liquid crystal drive voltage generating circuit. With the provision of the temperature correction voltage conversion circuit, an STN liquid crystal display device that automatically adjusts to an optimum screen display corresponding to a temperature change can be obtained.

Further, since the temperature correction voltage conversion circuit uses an element having a negative resistivity corresponding to a temperature change as the temperature correction element, the temperature of the liquid crystal driving voltage can be easily corrected.

Further, since the resistors are connected to the temperature compensating element in series and / or in parallel, it is easy to adjust the difference in the driving voltage of the liquid crystal used in the STN liquid crystal display.

Further, the temperature correction voltage conversion circuit has an emitter follower circuit, and the base of the emitter follower circuit is controlled by dividing the output of the liquid crystal drive voltage generation circuit by a voltage division circuit including a temperature correction element. Therefore, it is possible to easily adjust the optimum liquid crystal driving voltage corresponding to the temperature change.

The DC / DC converter further includes a DC / DC converter for generating an output voltage corresponding to the input reference voltage, and a voltage dividing circuit including a temperature correction element. The output voltage of the DC / DC converter is divided by the voltage dividing circuit. To generate a reference voltage, DC /
Since the liquid crystal drive voltage corresponding to the temperature change is output by feedback input to the reference voltage input terminal of the DC converter, the circuit scale can be reduced and the circuit configuration can be simplified.

Further, since the temperature compensating element is a thermistor, the temperature characteristics can be easily adjusted.

[Brief description of the drawings]

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

FIG. 2 is a diagram showing a circuit configuration of a liquid crystal drive voltage control circuit in an STN liquid crystal display device according to an embodiment of the present invention.

FIG. 3 is a diagram illustrating a relationship between an optimum drive correction voltage γV and a temperature according to an embodiment of the present invention;

FIG. 4 is a diagram showing a relationship between a thermistor element TH1 constituting a resistor R4 of the liquid crystal drive voltage control circuit according to an embodiment of the present invention and temperature.

FIG. 5 is a diagram showing a circuit configuration of a liquid crystal drive voltage control circuit in an STN liquid crystal display device according to an embodiment of the present invention.

FIG. 6 is a diagram showing a block configuration of a conventional STN liquid crystal display device.

FIG. 7 is a diagram showing a configuration of a liquid crystal drive voltage generation circuit in a conventional STN liquid crystal display device.

[Explanation of symbols]

100 STN liquid crystal display device, 101 STN liquid crystal display, 102 liquid crystal control card, 10
3 liquid crystal drive voltage control circuit, 104 liquid crystal drive voltage generation circuit, 105 liquid crystal drive voltage conversion circuit, 106
Digital image control circuit, 107 power supply circuit, 201a, 201b step-up DC / D
C converter, 600 STN liquid crystal display, 60
1 STN liquid crystal display, 602 liquid crystal control card, 603 liquid crystal drive voltage generation circuit, 60
4 Digital image control circuit, 605 power supply circuit, 606 external variable resistor, 701 step-up DC / DC converter, voltage supplied from Power power supply, Video / DATA, DATA
Digital image data, CONT STN liquid crystal display control signals, voltage supplied from the V _CC power supply circuit, V _ref reference voltage, V _{O UT} step-up DC / DC converter output voltage, V _EE liquid crystal driving voltages, D1 diode, R1 , R2 External mounting resistance of step-up DC / DC converter, R3
Resistance, R4 resistance, R5 resistance, B1 to Bn analog switch, L1 reactor, TR1 transistor, Z1 impedance, Z2 impedance, TH1 thermistor element.

Claims (6)

[Claims] 1. A liquid crystal driving voltage generating circuit having a DC / DC converter for generating an output voltage corresponding to an input reference voltage, and a liquid crystal display is controlled by a temperature based on a voltage output from the liquid crystal driving voltage generating circuit. A liquid crystal drive voltage control circuit comprising: a temperature correction voltage conversion circuit that outputs a liquid crystal drive voltage that provides an optimal screen display in response to a change. 2. The liquid crystal drive voltage control circuit according to claim 1, wherein the temperature correction voltage conversion circuit uses an element having a negative resistivity corresponding to a temperature change as the temperature correction element. 3. The liquid crystal drive voltage control circuit according to claim 2, wherein resistors are connected in series and / or parallel to the temperature correction element to adjust the temperature characteristics. 4. The temperature correction voltage conversion circuit has an emitter follower circuit, and controls the base of the emitter follower circuit by dividing the output of the liquid crystal drive voltage generation circuit by a voltage division circuit including a temperature correction element. The liquid crystal drive voltage control circuit according to claim 2 or 3, wherein: 5. A DC / DC converter for generating an output voltage corresponding to an input reference voltage, and a voltage dividing circuit including a temperature correction element, wherein the output voltage of the DC / DC converter is divided by the voltage dividing circuit. A liquid crystal driving voltage according to a temperature change by outputting a reference voltage by dividing the voltage by a reference voltage and feeding the reference voltage to a reference voltage input terminal of the DC / DC converter. circuit. 6. The liquid crystal drive voltage control circuit according to claim 2, wherein the temperature correction element is a thermistor.