JPH0561793U - Liquid crystal display protection circuit - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a protection circuit which detects the presence or absence of an input signal and protects a liquid crystal display element when there is no signal. [Structure] When the detection circuit 1 detects the presence or absence of an input signal and the detection circuit 1 sends a detection signal without an input signal to the oscillation circuit 2, the oscillation circuit 2 generates an alternating voltage generation signal,
After the alternating voltage generation signal is applied to the liquid crystal display 4, the power supply circuit 3 stops the power supply by the oscillation signal from the oscillation circuit 2, so that the liquid crystal display 4 is protected.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a liquid crystal display, and more particularly to a liquid crystal display provided with a protection circuit for a liquid crystal element when there is no input signal.

[0002]

[Prior Art]

 In this type of liquid crystal display, as shown in FIG. 4, two electrodes 38 are arranged at a narrow interval for each liquid crystal element, and a liquid crystal body is injected between these electrodes, so that each liquid crystal element has a capacitor structure. I am taking it.

Therefore, when the liquid crystal element is driven by direct current, the voltage charged in the interelectrode capacitance Cg gradually increases, and a large amount of electric power is required to shift from the display state to the non-display state.

If the voltage charged in the interelectrode capacitance Cg becomes too large, it causes damage to the liquid crystal layer and shortens the life of the liquid crystal body.

Therefore, in the conventional liquid crystal display, an alternating voltage is generated based on a signal input from the outside and applied to the liquid crystal element, but when the power is turned on with no signal input from the outside. , The alternating voltage is not generated and only the DC voltage is applied.

Therefore, in a device using a conventional liquid crystal display, a power supply circuit equipped with sequence control is used, or a power supply is added to a connector for connection with a device that sends out a signal, so that a physical power supply is provided. In some cases, it has a structure that prevents signal disconnection.

[0007]

[Problems to be solved by the device]

 A conventional LCD protection circuit (not shown) for a liquid crystal display without a signal does not have a signal generation function on the liquid crystal display side. Therefore, when only an input signal is lost, DC is not applied to the liquid crystal element. It was inevitable.

Further, in a protection circuit using a power supply circuit equipped with sequence control for protecting a liquid crystal element, the connectable device is limited and lacks versatility, and in addition, when the power of an external signal source is cut off. Since the power supply sequence cannot be guaranteed, the liquid crystal element is burdened.

Further, even if a circuit that does not impose a load on the liquid crystal is realized, if the liquid crystal driving signal is abnormal, the display is disturbed and the user feels uncomfortable.

Therefore, an object of the present invention is to provide a signal generation function in the liquid crystal display, so that the liquid crystal element can be driven by an alternating voltage even when there is no signal supplied from the outside. The present invention provides a liquid crystal display equipped with.

[0011]

[Means for Solving the Problems]

 Therefore, in order to achieve the above-mentioned object, the liquid crystal display protection circuit according to the first aspect of the present invention detects the presence or absence of an input signal, and based on the detection signal from the detection means, the above-mentioned input signal is detected. It is characterized by comprising an oscillator that oscillates at a predetermined frequency only when it is detected that there is no noise, and a power supply unit that stops the power supply by the output signal from this oscillator.

A liquid crystal display protection circuit according to a second aspect of the present invention is characterized in that the detection means is composed of a first time constant circuit and a peak hold circuit.

Further, the liquid crystal display protection circuit according to the third invention is characterized in that the detection means is composed of a second time constant circuit and a one-shot multivibrator.

[0014]

【Example】

 Next, an embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a block diagram of an embodiment of a protection circuit for a liquid crystal display according to the first invention. FIG. 2 is a detection circuit diagram of an embodiment of a protection circuit for a liquid crystal display according to the second invention. FIG. 3 is a detection circuit diagram of an embodiment of a protection circuit for a liquid crystal display according to the third invention.

As shown in FIG. 1, a protection circuit for a liquid crystal display according to a first invention is based on a detection circuit 1 which is a detection means for detecting the presence or absence of an input signal, and a detection signal from the detection circuit 1. The oscillator circuit 2 is an oscillator that oscillates at a predetermined frequency only when it is detected that there is no input signal, the power supply circuit 3 that is a power supply unit that stops the power supply by the oscillation signal from the oscillator circuit 2, and the detection circuit. An image is displayed when there is an input signal by the circuit 1, or a liquid crystal display 4 which is controlled by an oscillating circuit 2 by an alternating voltage generation signal when there is no input signal.

Here, the operation of the protection circuit of the liquid crystal display according to the first invention will be described. First, the detection circuit 1 detects the presence or absence of an input signal, and when the detection circuit 1 sends a detection signal with no input signal to the oscillation circuit 2, the oscillation circuit 2 generates an alternating voltage generation signal, and this alternating voltage generation signal is generated. After the signal is applied to the liquid crystal display 4, the power supply circuit 3 stops the power supply by the oscillation signal from the oscillation circuit 2, so that the liquid crystal display 4 is protected.

As shown in FIG. 2, the protection circuit for the liquid crystal display according to the second invention receives the input signal and the first time constant circuit 15 including the resistors R1 and R2 and the capacitor C1. It is composed of a transistor Q1 for sending an input signal to the first time constant circuit 15 and a peak hold circuit 16 for sending an output signal from the first time constant circuit 15 through a resistor R3 and a resistor R4 and a transistor Q2. The detection circuit 11 is the same as the first invention except for the above.

In the detection circuit 11, if the frequency of the alternating voltage generation signal required by the liquid crystal display 4 is a high frequency of several kHz or more, even if the detection is performed over several cycles, the detection is performed in a time of 1 ms or less. It becomes possible to do.

However, when the required signal has a low frequency like a vertical drive signal, it takes several tens to hundreds of ms to perform detection if it is detected over several periods.

Therefore, by using a one-shot multivibrator for detection, the detection time can be set to 2 cycles or less, and this problem can be solved.

That is, the second device is used when the alternating voltage generation signal of the liquid crystal device is several kHz or more, and the third device is used when the signal is about several tens Hz.

As shown in FIG. 3, a protection circuit for a liquid crystal display according to a third aspect of the invention includes a second time constant circuit 25 including a resistor R5 and a capacitor C3, and a second time constant circuit 25. The detection circuit 21 is composed of a one-shot multivibrator 27 that detects the presence or absence of an input signal at the detection time based on the time constant of, and the other is the same as the first invention.

Next, the operation of the conventional protection circuit for the liquid crystal display will be described.

As shown in FIG. 4, in the conventional liquid crystal display, two electrodes 38 are arranged at a narrow interval for each liquid crystal element, and a liquid crystal body is injected between the electrodes, so that each liquid crystal element is It has a capacitor structure.

Therefore, when the liquid crystal element is driven by direct current, the voltage charged in the interelectrode capacitance Cg gradually increases, and a large amount of electric power is required to shift from the display state to the non-display state.

If the voltage charged in the interelectrode capacitance Cg becomes too large, it causes damage to the liquid crystal layer and shortens the life of the liquid crystal body.

Therefore, in the conventional liquid crystal display, an alternating voltage is generated based on a signal input from the outside and applied to the liquid crystal element, but when the power is turned on with no signal input from the outside. , The alternating voltage is not generated and only the DC voltage is applied.

Therefore, in a device using a conventional liquid crystal display, a power supply circuit equipped with sequence control is used, or a power supply is added to a connector for connection with a device that sends out a signal, so that a physical power supply is provided. In some cases, it has a structure that prevents signal disconnection.

[0029]

[Effect of the device]

 As described above, according to the liquid crystal display protection circuit of the present invention, the presence or absence of the input signal is always detected by the detection means, and when there is no input signal, the alternating voltage generation signal by the oscillator is used to notify the liquid crystal display. Since the application of DC voltage is prevented, it has the effect of protecting the liquid crystal display and preventing the screen display from being disturbed due to power-off.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of a protection circuit for a liquid crystal display according to the first invention.

FIG. 2 is a detection circuit diagram of an embodiment of a protection circuit for a liquid crystal display according to the second invention.

FIG. 3 is a detection circuit diagram of an embodiment of a protection circuit for a liquid crystal display according to the third invention.

FIG. 4 is an equivalent circuit of a conventional liquid crystal element.

[Explanation of symbols]

 1, 11 and 21 Detection means (detection circuit) 2 Oscillator (oscillation circuit) 3 Power supply unit (power supply circuit) 4 Liquid crystal display 15 First time constant circuit 16 Peak hold circuit 25 Second time constant circuit 27 One-shot multi Vibrator 38 Liquid crystal display (electrode) C1 First time constant circuit (capacitor) C3 Second time constant circuit (capacitor) Cg Liquid crystal display (capacitance between electrodes) Q1, Q2 Peak hold circuit (transistor) R1, R2 1 time constant circuit (resistor) R3, R4 Peak hold circuit (resistor) R5 Second time constant circuit (resistor) Rg Liquid crystal display (electrode resistance)

Claims (3)

[Scope of utility model registration request] 1. A detection means for detecting the presence or absence of an input signal,
Based on the detection signal from the detection means, an oscillator that oscillates at a predetermined frequency only when the absence of the input signal is detected, and a power supply unit that stops the power supply by the output signal from the oscillator. Characteristic liquid crystal display protection circuit. 2. The detection means includes a first time constant circuit,
The protection circuit for a liquid crystal display according to claim 1, wherein the protection circuit is formed of a peak hold circuit. 3. The detection means includes a second time constant circuit,
The protection circuit for a liquid crystal display according to claim 1, wherein the protection circuit comprises a one-shot multivibrator.