JPH0980377A - Dimmer for image display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simplify the constitution of a dimmer for LCD. SOLUTION: A vertical synchronous pulse generation circuit 1 extracts a vertical synchronous pulse from an input video signal. A duty revision circuit 15 revises the duty ratio of the vertical synchronous pulse to supply it to a control circuit 9. The control circuit 9 operates an inverter circuit 11 during the width of the input pulse. The inverter circuit 11 generates an AC voltage while operating to supply it to a back light 13, and lights the back light 13 intermittently.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image display device such as an LCD (liquid crystal display device), and more particularly to a light control device for adjusting the brightness of a light source on a screen.

[0002]

2. Description of the Related Art FIG. 3 shows the structure of a conventional LCD light control device. The PWM (pulse width modulation) circuit 101 generates a pulse having a desired frequency and duty ratio and supplies the pulse to the control circuit 105 of the inverter device 103. The control circuit 105 controls the inverter device 103 during the input pulse width.
Inverter circuit 107 is operated. The inverter circuit 107 generates an AC voltage during operation and supplies it to the backlight 109. The backlight 107 intermittently emits light in accordance with the input AC voltage.

[0003]

SUMMARY OF THE INVENTION In a conventional LCD light control device, means for generating a PWM pulse is indispensable,
The system was complicated.

An object of the present invention is to provide a light control device for an image display device having a simple structure.

[0005]

[Means for Solving the Problems]

(First Configuration Example) Pulse generating means for generating a pulse,
The waveform shaping means for inverting the pulse from the pulse generating means or changing the duty ratio, the inverter means, the control means for controlling the operation of the inverter means according to the output pulse of the waveform shaping means, and the inverter means. A light source to which an output is supplied.

(Second configuration example) A pulse generating means for generating a pulse, a duty ratio changing means for changing a duty ratio of the pulse from the pulse generating means in accordance with an external control signal, an inverter means, and the duty. Control means for controlling the operation of the inverter means according to the output pulse of the ratio changing means, and a light source to which the output of the inverter means is supplied.

[0007]

[Action]

(First Configuration Example) The pulse generating means extracts a vertical synchronizing pulse from an input video signal, for example, and generates a vertical synchronizing pulse. The waveform shaping means inverts the vertical synchronizing pulse from the pulse generating means or changes the duty ratio and supplies it to the control means.

The control means operates the inverter means during the input pulse width. The inverter means generates an AC voltage during operation and supplies it to the light source. The light source emits light intermittently.

(Second Configuration Example) The pulse generating means extracts, for example, a vertical synchronizing pulse from the input video signal,
Generates a vertical sync pulse. The duty ratio changing means is
The duty ratio of the vertical synchronizing pulse from the pulse generating means is changed according to an external control signal and supplied to the control means.

The control means operates the inverter means during the input pulse width. The inverter means generates an AC voltage during operation and supplies it to the light source. The light source emits light intermittently.

[0011]

1 shows a first embodiment of a light control device for an LCD (liquid crystal display device) of the present invention. The vertical sync pulse generation circuit 1 extracts the vertical sync pulse from the input video signal and generates the vertical sync pulse. The waveform shaping circuit 3 inverts the vertical synchronizing pulse from the vertical synchronizing pulse generating circuit 1 or changes it into a pulse having a predetermined duty ratio with a time constant, and supplies it to the first input terminal 5a of the switching circuit 5.

A power supply voltage VCC (for example, 5V) is supplied to the second input terminal 5b of the switching circuit 5. The switching circuit 5 supplies one of the two inputs of the both input terminals to the control circuit 9 of the inverter device 7 or does not supply both of the inputs according to the external control signal. The control circuit 9 continuously operates the inverter circuit 11 of the inverter device 7 when the power supply voltage is supplied from the switching circuit 5, and when the pulse is supplied from the switching circuit 5, changes the pulse width The inverter circuit 11 is operated. Further, when there is no output from the control circuit 9, the inverter circuit 11 does not operate.

While the inverter circuit 11 is operating,
An alternating voltage is generated and supplied to the backlight 13, and the backlight 13 is turned on for the entire time or intermittently.

In the present embodiment, since only the vertical synchronizing pulse in the input video signal is extracted and used, a complicated means such as a PWM circuit is not required and the dimmer can be simply constructed.

FIG. 2 shows a second LCD light control device according to the present invention.
The following shows an example. The same components as those in the first embodiment of FIG. 1 are designated by the same reference numerals.

The vertical synchronizing pulse generating circuit 1 extracts the vertical synchronizing pulse from the input video signal, generates the vertical synchronizing pulse, and supplies it to the duty ratio changing circuit 15. The duty ratio changing circuit 15 changes the duty ratio of the vertical synchronizing pulse according to the external control signal, and supplies it to the control circuit 9 of the inverter device 7. The control circuit 9 operates the inverter circuit 11 during the width of the output pulse from the duty ratio changing circuit 15. During operation, the inverter circuit 11 generates an AC voltage and supplies it to the backlight 13 to intermittently turn on the backlight 13.

In the second embodiment, unlike the first embodiment, the duty ratio of the vertical synchronizing pulse can be changed steplessly according to the external control signal.
Stepless dimming can be realized.

Also in the second embodiment, since only the vertical synchronizing pulse in the input video signal is used, the PWM
No complicated means such as a circuit is required, and the dimmer can be simply constructed. Further, in this embodiment, stepless dimming can be realized.

Although an example of an LCD is given as an example of the image display device, it is not limited to this.

[0020]

According to the present invention, the light control device of the image display device can be easily constructed. Furthermore, stepless dimming is also possible.

[Brief description of drawings]

FIG. 1 is a diagram showing a first embodiment of a light control device for an LCD (liquid crystal display device) of the present invention.

FIG. 2 is a diagram showing a second embodiment of the LCD light control device of the present invention.

FIG. 3 is a view showing a conventional LCD light control device.

[Explanation of symbols]

1 ... Vertical sync pulse generation circuit, 3 ... Waveform shaping circuit, 5 ...
Switching circuit, 7 ... Inverter device, 9 ... Control circuit, 11 ...
Inverter circuit, 13 ... Backlight, 15 ... Duty ratio changing circuit.

Claims (4)

[Claims] 1. A pulse generating means for generating a pulse, a waveform shaping means for inverting the pulse from the pulse generating means or changing a duty ratio, an inverter means, and the inverter according to an output pulse of the waveform shaping means. A light control device for an image display device, comprising: a control means for controlling the operation of the means; and a light source to which the output of the inverter means is supplied. 2. An output pulse of the waveform shaping means is input to a first input terminal, and a DC voltage of a predetermined level is input to the second input terminal, which is arranged between the waveform shaping means and the control means. 2. The light control device for an image display apparatus according to claim 1, further comprising a selection unit that supplies one of the two inputs to the control unit or does not supply both inputs. 3. A pulse generating means for generating a pulse, a duty ratio changing means for changing a duty ratio of the pulse from the pulse generating means according to an external control signal, an inverter means, and an output of the duty ratio changing means. A light control device for an image display device, comprising: a control means for controlling the operation of the inverter means in response to a pulse; and a light source to which an output of the inverter means is supplied. 4. The dimming device for a screen display device according to claim 1, wherein the pulse generated by the pulse generating means is a vertical synchronizing pulse extracted from an input video signal.