JPH0561726U - LCD drive circuit - Google Patents

Abstract

(57) [Summary] [Object] A liquid crystal driving circuit for driving a liquid crystal display used in a wide temperature range, and an object thereof is to enable display discrimination of the liquid crystal display in a wide temperature range. [Configuration] detects the ambient temperature of the liquid crystal display 6 by the thermistor R _TH1, R _TH2, controls the liquid crystal drive voltage by controlling the PNP transistor Q ₁ in accordance with the resistance value of the thermistor R _TH1, R _TH2.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a liquid crystal driving circuit, and more particularly to a liquid crystal driving circuit for driving a liquid crystal display used in a wide temperature range.

[0002]

[Prior Art]

 In recent years, there has been a tendency to use a dot matrix type automobile clock capable of displaying more information even with a display device while outputting a larger amount of information.

FIG. 3 shows a block diagram of a conventional example. In the figure, 1 indicates a liquid crystal bias circuit. The conventional liquid crystal bias circuit 1 divides the power supply voltage V _CC by the resistors R _{1 to} R ₅ and supplies it to the liquid crystal drive circuit 2 as a bias voltage.

The liquid crystal drive circuit 2 is supplied with a bias voltage from the liquid crystal bias circuit 1 and is supplied with display data from the CPU 3.

The liquid crystal drive circuit 2 generates a drive signal from the bias voltage based on the display data and supplies it to the liquid crystal display 4.

The liquid crystal display 4 displays according to the drive signal from the liquid crystal drive circuit 2.

Conventionally, in a vehicle-mounted liquid crystal timepiece, even if the ambient temperature changes, a constant bias voltage is always supplied to the liquid crystal drive circuit 2 from the liquid crystal bias circuit 2 as shown in FIG. , The liquid crystal display 4 was being driven.

[0008]

[Problems to be Solved by the Invention] In a dot matrix liquid crystal display, compared with a segment type liquid crystal display, the optical characteristics (contrast, viewing angle, response, etc.) change significantly with ambient temperature changes, and the operating temperature range is For wide vehicle use, the display becomes unreadable at low or high temperatures.

However, the change of the optical characteristic with respect to the change of the ambient temperature can be changed by the driving voltage of the liquid crystal display.

However, in the conventional liquid crystal drive circuit, since the liquid crystal display is driven at a constant voltage level regardless of the ambient temperature, the optical characteristics of the liquid crystal display change due to the change of the ambient temperature, especially at the operating temperature. When the range is wide, there is a problem that the display cannot be distinguished at low temperature and high temperature.

The present invention has been made in view of the above points, and an object of the present invention is to provide a liquid crystal driving device that can perform display discrimination in a wide operating temperature range.

[0012]

[Means for Solving the Problems]

 According to the present invention, in a liquid crystal drive circuit for supplying a drive signal according to display data to a liquid crystal display, temperature control signal generation means for generating a temperature control signal at a level according to the ambient temperature of the liquid crystal display, Drive signal control means for controlling the drive signal level according to the temperature control signal generated by the temperature control signal generating means.

[0013]

[Action]

 When the ambient temperature of the liquid crystal display changes, the temperature control signal changes according to the change of the ambient temperature.

When the temperature control signal changes, the drive signal control means changes the drive signal level according to the change of the temperature control signal, and supplies the liquid crystal display with a drive signal according to the ambient temperature.

Therefore, the liquid crystal display can be driven with an optimum drive signal according to the ambient temperature.

[0016]

【Example】

 FIG. 1 shows a block diagram of an embodiment of the present invention. In the figure, 5 indicates a liquid crystal bias circuit.

The liquid crystal bias circuit 5 includes resistors R _{6 to} R ₁₀ and a temperature guarantee circuit 5a.

The temperature guarantee circuit 5a is composed of resistance circuits R _A and R _B which serve as temperature control signal generation means and a current control PNP transistor Q ₁ which serves as drive signal control means. Resistance circuit R _A is a more becomes a series circuit with the resistor R ₂ and the thermistor R _TH1 to the resistor R ₁ connected in parallel, and is with its combined resistance value changes constituted by the ambient temperature of the thermistors R _TH1.

The resistance circuit R _B has the same configuration as the resistance circuit R _A, and a series circuit composed of the resistance R ₄ and the thermistor R _TH2 is connected in parallel to the resistance R ₃ and its combined resistance value is determined by the ambient temperature of the thermistor R _TH2. Is configured to change.

The resistance circuits R _A and R _B are connected in series to the constant voltage power supply V _CC , and the connection point of the resistance circuits R _A and R _B is connected to the base of the PNP transistor Q ₁ .

The emitter of the PNP transistor Q ₁ is connected to the resistors R _{6 to} R ₁₀ , and the collector is grounded.

Resistance R₆~ R_TenIs a constant voltage power supply V_CCAnd PNP transistor Q₁It is arranged in series between and. Constant voltage power supply V_CCIs directly supplied to the liquid crystal drive control circuit 7 and the resistor R ₆ ~ R_TenThe voltage divided by is supplied.

The thermistors R _TH1 and R _TH2 are both arranged near the liquid crystal display 6, and their resistance values change according to the ambient temperature of the liquid crystal display 6.

At this time, the resistors R _{1 to} R ₄ and the thermistors R _TH1 and R _TH2 increase the potential (temperature control voltage) at the connection point of the resistance circuits R _A and R _B as the ambient temperature of the liquid crystal display 6 increases. It is set to a value that can be set.

Therefore, when the ambient temperature of the liquid crystal display 6 rises, the temperature control voltage rises accordingly as indicated by the alternate long and short dash line in FIG. When the temperature control voltage rises, the emitter potential of the PNP transistor Q ₁ rises, so that the potential (liquid crystal bias voltage) at the connection point between the resistors R _{6 to} R ₁₀ and the PNP transistor Q ₁ falls.

The liquid crystal drive control circuit 7 generates a liquid crystal drive signal whose output level is proportional to the liquid crystal bias voltage supplied from the liquid crystal bias circuit 5 based on the display data supplied from the CPU 8, and causes the liquid crystal display 6 to display the liquid crystal drive signal. Supply.

In general, the liquid crystal display 6 requires a drive signal level higher than the normal drive signal level in order to perform a display similar to the normal display when the temperature is low.

Therefore, the liquid crystal drive signal is supplied to the liquid crystal display 6 at a level corresponding to the ambient temperature.

As shown in the solid line in FIG. 2, the liquid crystal driving voltage has a characteristic of decreasing with the increase of the ambient temperature of the liquid crystal display 6 as in the present invention, so that the display is performed regardless of the ambient temperature. Therefore, the liquid crystal display 6 can be used in a wide temperature range.

Although the two thermistors R _TH1 and R _TH2 are used in this embodiment, one or more thermistors may be used.

Further, the temperature detection is not limited to the thermistor, and may be any element that can change the liquid crystal drive voltage according to the temperature.

[0032]

[Effect of the device]

 As described above, according to the present invention, by varying the drive signal level of the liquid crystal display according to the ambient temperature of the liquid crystal display, the drive signal according to the change of the optical characteristic due to the temperature of the liquid crystal display is transmitted to the liquid crystal display. Since the liquid crystal display can be supplied, the liquid crystal display can perform display regardless of temperature change, and thus has a feature that it can be used in a wide temperature range.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.

FIG. 2 is a temperature / voltage characteristic diagram of a main part of an embodiment of the present invention.

FIG. 3 is a block configuration diagram of a conventional example.

FIG. 4 is a temperature-voltage characteristic diagram of a main part of a conventional example.

[Explanation of symbols]

5 the liquid crystal bias circuit 6 the liquid crystal display 7 a liquid crystal drive control circuit 8 CPU R _A, R _B the resistance circuit R _TH1, R _TH2 thermistor Q ₁ PNP transistor

Claims (1)

[Scope of utility model registration request] 1. A liquid crystal drive circuit for supplying a drive signal according to display data to a liquid crystal display device, comprising: a temperature control signal generation means for generating a temperature control signal at a level according to an ambient temperature of the liquid crystal display device; A liquid crystal drive circuit, comprising: drive signal control means for controlling the drive signal level according to the temperature control signal generated by the temperature control signal generation means.