JPH063648A - Protection circuit against abnormal temperature - Google Patents

Abstract

PURPOSE:To detect temperature with a microcomputer and interrupt power supply after the indication of a temperature abnormality for protecting a liquid crystal panel in a liquid crystal display device using the liquid crystal panel. CONSTITUTION:A comparator circuit 17 constituted of transistors 11 and 12 makes a comparison between the first voltage V1 divided with a thermister 6 and a resistor 7 and the second voltage V2 divided with resistors 8 and 9, on the basis of the temperature characteristic of the thermister 6. An output signal from the circuit 17 is sent to a microcomputer 15. This microcomputer 15 indicates a warning on a liquid crystal display device 2, when temperature becomes equal to or above a certain level, and turns off a semiconductor switch 5. Power supply to the device 2 is thereby interrupted, and the damage of a liquid crystal panel at high temperature is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a temperature abnormality protection circuit used in a liquid crystal display device using a liquid crystal panel.

[0002]

2. Description of the Related Art In recent years, liquid crystal display devices using a liquid crystal panel have been remarkably popularized. In particular, liquid crystal display devices are thin, lightweight, and power-saving for in-vehicle television receivers and other information displays. Taking advantage of the advantage, it has become widely used. Liquid crystal display devices have the advantages of thinness, light weight, and power saving, but have the drawback of being weak in temperature.
In particular, there is a fatal defect that the composition of the liquid crystal is broken at high temperature and cannot be used even if the temperature is returned to room temperature. Considering its use for automobiles, the temperature inside the vehicle becomes extremely high in hot summer in the summer, and the above drawbacks are fatal.Therefore, the conventional method is to detect the temperature of the liquid crystal panel and stop the power supply. Was taken.

An example of a conventional temperature abnormality protection circuit will be described below with reference to FIG. In FIG. 3, 1 is a thermal fuse, 2 is a liquid crystal display device, 3 is a power supply terminal +
Side 4 is a power supply terminal-side. The liquid crystal display device 2 includes a liquid crystal panel, a liquid crystal panel backlight, an image processing circuit,
It shall consist of a liquid crystal panel, a backlight, and a power supply for video processing circuits.

The operation will be described below. Power is supplied to the liquid crystal display device 2 from the power supply terminals 3 and 4. When the ambient temperature rises and reaches the limit temperature of the liquid crystal panel, the temperature fuse 1 is blown and the power supply to the liquid crystal display device 2 is stopped to protect the liquid crystal panel.

[0005]

However, in the above-mentioned structure, the liquid crystal display device suddenly stops its operation at a certain temperature without any notice. Therefore, the liquid crystal display device stops due to the temperature or other troubles. There is a problem that it is impossible to judge whether it is a stop.

In view of the above problems, the present invention first displays a warning on the screen of the liquid crystal display device when a temperature abnormality is detected,
It is intended to provide a temperature abnormality protection circuit capable of stopping energization thereafter.

[0007]

In order to achieve the above object, a temperature abnormality protection circuit of the present invention comprises a temperature-dependent resistor (hereinafter referred to as a thermistor) and a first voltage obtained by dividing the voltage of the first resistor. , A temperature detection circuit for comparing a second voltage obtained by voltage division of the second resistance and a third resistance, and an output of the temperature detection circuit to display a temperature abnormality of the liquid crystal display device on the liquid crystal display device. And a microcomputer (hereinafter, referred to as a microcomputer) that controls the energization of the liquid crystal display device.

[0008]

According to the present invention, since the microcomputer monitors the temperature abnormality in a time series with the above-mentioned configuration, the liquid crystal is judged to be the temperature abnormality only when the temperature abnormality signal is continuously input for a certain time. It is possible to stop energization after displaying a warning on the display device. Further, since it is determined that the temperature is abnormal only when the temperature abnormality signal is continuously input for a certain period of time, it is possible to prevent malfunction due to randomly generated noise.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A temperature abnormality protection circuit according to an embodiment of the present invention will be described below with reference to FIGS.

In FIG. 1, reference numeral 2 is a liquid crystal display device, and 3, 4
Are semiconductor switches, 6 is a thermistor, 7, 8, 9, 10, 14 are resistors, 15 is a microcomputer, 17 is a transistor 11, 12 and a resistor 10 Reference numeral 13 is a circuit, 13 is a transistor for driving the microcomputer 15 by the output of the comparison circuit 17, and 16 is a noise removing capacitor. The operation will be described below.

First, FIG. 2 shows the thermistor 6 and the first resistor 7.
The first voltage V ₁ divided by and the second resistance 8 and the third voltage
The second voltage V ₂ divided by the resistor 9 of FIG.
7 is a graph showing the characteristics of the output voltage V ₃ from 7 with respect to temperature. The voltage V ₂ generated by dividing by the resistors 8 and 9 is constant irrespective of the temperature, but the thermistor 6 has the property that its resistance value decreases as the temperature rises, and thus the thermistor 6 does not.
The voltage V ₁ generated by dividing the voltage with the resistor 7 rises with temperature.

Comparison composed of transistors 11 and 12
The voltage divided by the thermistor 6 and the resistor 7 is applied to the circuit 17.
V₁And the voltage V divided by the resistors 8 and 9₂Added
Has been. While the temperature is low, the voltage V₁Voltage V compared to₂Is high
Since the transistor 12 is on,
Star 11 is off and transistor 13 is off
Output voltage V of the comparison circuit 17₃Becomes 0V. temperature
Higher voltage V₂More voltage V₁Becomes larger, the transition
Transistor 12 turns off, transistor 11 turns on, and resistor 1
A current flows through the transistor 4, the transistor 13 is turned on, and the microcomputer 1
Output voltage V to 5 ₃Is supplied.

The microcomputer 15 constantly outputs the output voltage V of the comparison circuit.
₃ is monitored, and when a temperature abnormality occurs, a warning is displayed on the liquid crystal display device 2, and then a signal is sent to the semiconductor switch 5 to stop the energization of the liquid crystal display device 2.

As described above, according to this embodiment, the first voltage V obtained by dividing the thermistor 6 and the resistor 7 is used.
₁ , a second voltage V ₂ obtained by dividing the resistors 8 and 9, and a comparison circuit 17 including transistors 11 and 12 for comparing the first voltage V ₁ and the second voltage V ₂ . By providing the microcomputer 15 that controls the display and energization of the liquid crystal display device 2 by receiving the output of the comparison circuit 17, the liquid crystal display device does not suddenly stop due to a temperature abnormality, and whether the cause of the stop is due to the temperature abnormality, It is possible to easily determine whether it is another cause.

In the present embodiment, the semiconductor switch 5
May be used as a relay. Further, the thermistor 6 may be an ordinary resistor and the resistor 7 may be a resistor having a positive temperature coefficient. Further, the microcomputer 15 can share the same microcomputer used for television channel selection, remote control, and the like.

[0016]

As described above, according to the present invention, the first voltage obtained by dividing the thermistor and the first resistor and the second voltage obtained by dividing the second resistor and the third resistor. By providing a comparison circuit that compares the output of the comparison circuit and a microcomputer that controls the display and energization of the liquid crystal display device by receiving the output of the comparison circuit, the liquid crystal display device does not stop suddenly due to temperature abnormality, and the cause of the stop is the temperature. It is possible to easily determine whether it is due to an abnormality or another cause, and its practical effect is great.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a temperature abnormality protection circuit according to an embodiment of the present invention.

FIG. 2 is a diagram showing characteristics of voltage of each part with respect to temperature.

FIG. 3 is a circuit diagram of a conventional temperature abnormality protection circuit.

[Explanation of symbols]

2 liquid crystal display device 6 temperature dependent resistance 7 first resistance 8 second resistance 9 third resistance 15 microcomputer 17 comparison circuit (temperature detection circuit) V ₁ first voltage V ₂ second voltage

Claims (1)

[Claims] 1. A temperature for comparing a first voltage obtained by dividing the temperature-dependent resistance and the first resistor with a second voltage obtained by dividing the second resistor and the third resistor. A temperature abnormality including a detection circuit and a microcomputer which receives an output of the temperature detection circuit and causes the liquid crystal display device to display a temperature abnormality of the liquid crystal display device as a warning sentence and controls energization to the liquid crystal display device. Protection circuit.