JPS61162029A - Liquid crystal driving circuit - Google Patents

Abstract

PURPOSE:To prevent a liquid crystal display element from the impression of an abnormal voltage at the OFF of a power supply by forming a circuit for deleting the voltage impressed upon the liquid crystal display element before the voltage of a power supply line is dropped at the OFF of the power supply. CONSTITUTION:A DC power supply DC is connected to a power supply terminal A of a liquid crystal driver DR through a diode D and a power supply switch SW and a capacitor C is connected between the power supply terminal A and the earth. A signal terminal A' of the driver DC is connected to the power supply DC through the switch SW. When the switch SW is opened, the terminal A is delayed at its voltage drop due to the discharge of the capacitor C and the driver DC continues the operation. At that time, current from the capacitor C is interrupted by a diode D and can not flow into the terminal A' and the voltage of the terminal A' is dropped prior to the voltage drop of the terminal A. Then, the driver DR deletes the driving voltage wave applied to the liquid crystal display element LCD in a accordance with the voltage drop of the terminal A'.

Description

[Detailed description of the invention] Technical fields> The present invention relates to a liquid crystal drive circuit.

<Prior Art> FIG. 3 shows a conventional liquid crystal drive circuit, and FIG. 4 shows operating waveforms of this liquid crystal drive circuit. When the switch SW is opened to turn off the power at time t when the liquid crystal display element LCD is in the driving state, the voltage applied to the power terminal A and the signal terminal A' of the liquid crystal driver DR decreases, and accordingly, the liquid crystal display The voltage wave applied between terminals B and C of the element LCD gradually decreases. Then, due to the abnormal voltage that gradually decreases after this time, if the liquid crystal display element LCD is a phase transition type, the phase transition mode changes, and the hysteresis caused by this causes disturbance of the liquid crystal phase when the power is turned off. . This disorder of the liquid crystal phase becomes dotted domains that cause display abnormalities, and if used for a long period of time,
Deteriorates the liquid crystal display element.

<Objective of the Invention> The present invention has been made in view of the above circumstances, and its object is to provide a liquid crystal drive circuit that prevents abnormal voltage from being applied to a liquid crystal display element when the power is turned off.

<Configuration of the Invention> The present invention is characterized in that it includes a circuit that eliminates the voltage applied to the liquid crystal display element before the voltage of the power supply line drops when the power is turned off.

<Example> An embodiment of the present invention will be described below.

FIG. 1 shows the configuration of a liquid crystal drive circuit. LCD driver DR
A DC power supply DC is connected to the power supply terminal A of the LCD driver D via a diode D and a power switch SW.
A capacitor +C is connected between the power terminal A of R and the ground. A signal terminal A' of the liquid crystal driver DR is connected to a DC power supply DC via a power switch SW.

FIG. 2 shows operating waveforms of this liquid crystal drive circuit.

When driving the liquid crystal display element LCD, the power switch SW is closed and the terminal A of the liquid crystal driver DR is closed.

A voltage is applied from the DC power supply DC to A', and the oscillator oSC
A voltage wave corresponding to the signal waveform from the liquid crystal display element LCD is applied between terminals B and C of the liquid crystal display element LCD.

Now, at time t, when the power switch SW is opened, the voltage at terminals A and A' of the liquid crystal driver DR drops, but the voltage drop at the power supply terminal A is delayed due to the discharge of the capacitor C, and the liquid crystal driver DR stops operating. continue. On the other hand, at this time, the current from the capacitor C does not flow to the signal terminal A' because it is blocked by the diode D, and the voltage at the signal terminal A' drops before the voltage at the power supply terminal. Then, the liquid crystal driver DR eliminates the drive voltage wave to the liquid crystal display element LCD in accordance with the drop in the voltage of the signal terminal A'.

That is, before the voltage of the power line connected to the power supply terminal A of the liquid crystal driver DR drops, the liquid crystal display element LC
The voltage wave applied to D is extinguished. Therefore, no abnormal voltage is applied to the liquid crystal display element LCD after that time.

Thereafter, when a predetermined time period corresponding to the discharge of the capacitor C has elapsed, the liquid crystal driver DR stops operating.

<Effects of the Invention> As explained above, in the present invention, when the power is turned off, the voltage applied to the liquid crystal display element disappears before the voltage drop in the power supply line occurs, so that no abnormal voltage is applied to the liquid crystal display element. Therefore, display abnormalities of the liquid crystal display element can be prevented, and deterioration of the liquid crystal display element can be prevented.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of an embodiment of the present invention, FIG. 2 is an operating waveform diagram of an embodiment of the invention, FIG. 3 is a circuit diagram of a conventional example, and FIG. 4 is an operating waveform diagram of a conventional example.

Claims (1)

[Claims] A liquid crystal drive circuit comprising a circuit that eliminates the voltage applied to a liquid crystal display element before the voltage of a power supply line drops when the power is turned off.