JPH1090647A - Driving method of liquid crystal display device and liquid crystal display device - Google Patents

Abstract

(57) [Summary] [PROBLEMS] A light source constituting a backlight is a long-time OF
Provided is a liquid crystal display device in which lighting delay or non-lighting of a light source that occurs after being left in an F state (dark state) is prevented, and lighting start characteristics of the light source are improved. SOLUTION: In a liquid crystal display device including a liquid crystal display panel, a light source (3) for irradiating the liquid crystal display panel from the back surface, and a lighting circuit (2) for applying a lighting voltage to the light source, the light source is turned on. In this case, first, a power supply voltage is intermittently applied to the lighting circuit, and after detecting that the light source is normally lit, power supply voltage applying means (1) for continuously applying the power supply voltage to the lighting circuit is provided. , 4).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly to a method of driving a liquid crystal display device having improved starting characteristics at the time of starting a cold cathode tube and a liquid crystal display device.

[0002]

2. Description of the Related Art FIG. 9 is an exploded perspective view of a simple matrix type liquid crystal display module (LCM) which is one of the conventional liquid crystal display devices.

As shown in FIG. 9, a liquid crystal display module (LCM) comprises a frame 501 made of a metal plate,
Silicon spacer 502, liquid crystal display panel (LCD) 5
03, a drive circuit board (SEGP / B) 504, a mold 505, a prism sheet 506, a cold cathode fluorescent lamp (cold cathode tube) 507, a rubber bush 508, a light guide plate 509, and a lower frame 510 shown in FIG. Stacked and assembled.

In FIG. 9, a mold 505, a prism sheet 506, a cold cathode fluorescent lamp 507, and a rubber bush 50 are shown.
8. The light guide plate 509 and the lower frame 510 constitute a backlight for irradiating the liquid crystal display element with light.

As a backlight used in a conventional liquid crystal display module (LCM), a cold cathode fluorescent lamp is disposed close to the side of a light guide plate made of a transparent synthetic resin plate for guiding light. There are known two types: a type in which a plurality of cold cathode fluorescent lamps are arranged in parallel directly below a liquid crystal display element.

The backlight shown in FIG. 9 is of a type in which a cold cathode fluorescent lamp 507 is arranged close to the side of a light guide plate 509 made of a transparent synthetic resin plate for guiding light. .

[0007]

In recent years, as the frame of a liquid crystal display panel (LCD) has become narrower, the diameter of the cold cathode fluorescent lamp 507 has tended to be smaller. However, the cold cathode fluorescent lamp 507 having a smaller diameter has a longer length. If left in the OFF state (dark state) for a time, it has a characteristic that it is difficult to start (it is not turned on).

An inverter circuit is generally used as a lighting circuit for lighting the cold cathode fluorescent lamp 507 shown in FIG. 9, and a driving method for lighting the cold cathode fluorescent lamp 507 is a cold cathode fluorescent lamp. An AC voltage (lighting voltage) is continuously applied to the lamp 507 from the inverter.

Therefore, when the cold-cathode fluorescent lamp 507 that has been left in the OFF state (dark state) for a long time is turned on by the above-described driving method, the cold-cathode fluorescent lamp 507 is difficult to start or does not start. Cold cathode fluorescent lamp 50
There was a problem that the lighting delay of 7 or the non-lighting occurred.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and an object of the present invention is to provide a method for driving a liquid crystal display device and a liquid crystal display device, wherein a light source constituting a backlight is: It is an object of the present invention to provide a technique capable of preventing a light source from being delayed for a long time after being left in an OFF state (dark state) or a non-lighting state, and improving the lighting start characteristic of the light source.

The above and other objects and novel features of the present invention will become apparent from the description of the present specification and the accompanying drawings.

[0012]

SUMMARY OF THE INVENTION Among the inventions disclosed in the present application, the outline of a representative one will be briefly described.
It is as follows.

(1) In a method for driving a liquid crystal display device including a liquid crystal display panel and a light source for irradiating the liquid crystal display panel from the back, first, when the light source is turned on, the light is applied to the light source. Applying a lighting voltage of a voltage higher than a normal lighting voltage to the light source intermittently, and after detecting that the light source is normally lit, continuously applying a steady-state lighting voltage to the light source. It is characterized by.

(2) In a method for driving a liquid crystal display device including a liquid crystal display panel and a light source for irradiating the liquid crystal display panel from the back surface, when the light source is turned on, the light is first applied to the light source. A lighting voltage higher than a normal lighting voltage is intermittently applied to the light source, and after a predetermined time, a steady-state lighting voltage is continuously applied to the light source.

(3) In a liquid crystal display device including a liquid crystal display panel, a light source that irradiates the liquid crystal display panel from the back surface, and a lighting circuit that applies a lighting voltage to the light source, when the light source is turned on, And a power supply voltage application unit that intermittently applies a power supply voltage to the lighting circuit, detects that the light source is normally lit, and then continuously applies the power supply voltage to the lighting circuit. I do.

(4) In a liquid crystal display device including a liquid crystal display panel, a light source for illuminating the liquid crystal display panel from the back surface, and a lighting circuit for applying a lighting voltage to the light source, when the light source is turned on, In addition, there is provided a power supply voltage applying means for intermittently applying a power supply voltage to the lighting circuit and continuously applying the power supply voltage to the lighting circuit after a predetermined time has elapsed.

According to the above means, when the light source constituting the backlight is turned on, first, a lighting voltage having a voltage higher than the steady-state lighting voltage applied to the light source is intermittently applied to the light source, After detecting that the light source is normally lit, or after a lapse of a predetermined time, the steady-state lighting voltage is continuously applied to the light source. A large lighting voltage can be applied intermittently and repeatedly, and the lighting of the light source can be promoted.

This makes it possible to improve the starting characteristics when the light source is turned on.

[0019]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of the present invention applied to a simple matrix type liquid crystal display module (LCM).

In all the drawings for describing the embodiments of the present invention, those having the same functions are denoted by the same reference numerals, and their repeated description will be omitted.

FIG. 1 is a block diagram showing a schematic circuit configuration for lighting a cold cathode fluorescent lamp in a simple matrix type liquid crystal display module (LCM) according to an embodiment of the present invention.

In FIG. 1, 1 is a pulse generation circuit, 2 is a lighting circuit, 3 is a cold cathode fluorescent lamp (cold cathode tube), and 4 is a feedback circuit.

In the embodiment of the present invention, the lighting circuit 2
The low-voltage DC voltage input from the pulse generation circuit 1 is converted and boosted into an AC voltage to generate a lighting voltage for lighting the cold cathode fluorescent lamp 3, and this lighting voltage is applied to the cold cathode fluorescent lamp 3. As a result, the cold cathode fluorescent lamp 3 is turned on.

FIG. 2 is a diagram showing a voltage waveform of an output voltage output from pulse generating circuit 1 shown in FIG.
FIG. 4 is a diagram showing a voltage waveform of a lighting voltage applied to the cold cathode fluorescent lamp 3.

As shown in FIG. 2, the pulse generating circuit 1
When the cold cathode fluorescent lamp 3 is turned on, that is, when the backlight is started, a pulse voltage having a period of several ms to several hundred ms is output.

When this pulse voltage is applied as the power supply voltage of the lighting circuit 2, an alternating lighting voltage is intermittently output from the lighting circuit 2 as shown in FIG.

As shown in FIGS. 2 and 3, after the feedback circuit 4 detects that the cold cathode fluorescent lamp 3 is normally lit, the pulse generating circuit 1 outputs a normal continuous DC voltage. As a result, the lighting circuit 2 continuously outputs an AC lighting voltage.

In this case, when the power of the lighting circuit 2 is turned on, the lighting circuit 2 momentarily outputs a lighting voltage (6 in FIG. 3) which is larger than the lighting voltage (6 in FIG. 3) output in a steady state.
Is output.

Therefore, when lighting the cold cathode fluorescent lamp 3, the pulse voltage from the pulse generation circuit 1 is applied to the lighting circuit 2
As a result, the large lighting voltage is intermittently and repeatedly applied from the lighting circuit 2 to the cold cathode fluorescent lamp 3 instantaneously, and the lighting of the cold cathode fluorescent lamp 3 is promoted. It is.

Thus, the starting characteristics of the cold cathode fluorescent lamp 3 when the cold cathode fluorescent lamp 3 is turned on can be improved.

FIG. 4 is a diagram showing an example of a specific circuit configuration of the pulse generation circuit 1 shown in FIG.

The pulse generating circuit 1 shown in FIG. 4 has an astable multivibrator circuit 40. The astable multivibrator circuit 40 has an NMOS transistor (NM).
4) ON, NMOS transistor (NM3) OFF
At this time, a normal oscillation operation is performed, and when the NMOS transistor (NM3) is ON and the NMOS transistor (NM4) is OFF, the oscillation is stopped.

When the oscillation is stopped, the capacitor (C2) is charged to the polarity shown in the figure. When the oscillation starts, the charge of the capacitor (C2) causes the NMOS transistor (NM1) to charge. Is immediately turned off, and a pulse output having a regular pulse width is obtained from the first pulse.

The output of the feedback circuit 4 is compared with a reference potential (Vc) by a comparison circuit 50, and the output (Vr) of the comparison circuit 50 is compared with an NMOS transistor (Nc).
M3) is applied to the gate electrode and the inverter (V
Through 1), the output of the comparison circuit 50 is applied to the gate electrode of the NMOS transistor (NM4).

Therefore, the astable multivibrator circuit 40 performs an oscillating operation until the output (Vr) of the feedback circuit 4 reaches the reference potential (Vc), and the output (Vr) of the feedback circuit 4 changes to the reference potential (Vr). When the voltage reaches Vc), the oscillation stops.

As a result, an output (Vout) having a voltage waveform as shown in FIG. 2 can be obtained from the connection point between the resistor (R4) and the capacitor (C2) of the unstable multivibrator circuit 40.

This output (Vout) is applied to the gate electrode of the NMOS transistor (NM5) and the inverter (V
By applying the output (Vout) to the gate electrode of the NMOS transistor (NM6) via 2), the lighting circuit 2 supplies the power supply voltage (V) having a voltage waveform as shown in FIG.
in) is applied.

FIG. 5 is a diagram showing an example of a specific circuit configuration of the lighting circuit 2 and the feedback circuit 4 shown in FIG.

In FIG. 5, reference numeral 10 denotes a + input terminal of the DC power supply of the lighting circuit 2, and 11 denotes a ground (hereinafter referred to as GN).
Notated as D. ) -Side input terminal.

The feedback circuit 4 indicated by a dotted line detects the amount of current flowing through the cold cathode fluorescent lamp 3.

The lighting circuit 2 includes a primary circuit 13 for converting a low-voltage DC voltage into a low-voltage AC voltage by an oscillation circuit,
And a transformer 14 which uses the AC voltage as a primary input and converts the secondary output into an AC high voltage.

Reference numeral 12 denotes a control signal input terminal for adjusting the luminance of the cold cathode fluorescent lamp 6 by changing the output voltage of the primary circuit 13.

The feedback circuit 4 is configured such that an LED (light emitting diode) 15a in the photocoupler 15 emits light in accordance with the amount of current flowing through the cold cathode fluorescent lamp 3, and the light is received by the phototransistor 15b in the photocoupler 15. A current (emitter current: Ie) corresponding to the amount of received light flows through the phototransistor 15b.

D1 is an AC high-voltage current path generated on the secondary side of the transformer 14
It is a diode that works to secure with 15a.

The current flowing through the phototransistor 15b is smoothed by a smoothing circuit comprising a resistor (R5) and a capacitor (C3), and is converted into a DC voltage proportional to the current flowing through the cold cathode fluorescent lamp 3, and the feedback circuit 4 (Vr).

Output (Vr) of this feedback circuit 4
Is returned to the primary side circuit 13, the low side AC voltage is increased or decreased in the primary side circuit 13, and the amount of current flowing through the cold cathode fluorescent lamp 6 is kept constant, so that the luminance (light emission amount) is kept constant. I keep it.

As described above, the output (Vr) of the feedback circuit 4 is also input to the pulse generation circuit 1.

FIG. 6 is a diagram showing an example of a specific circuit configuration of the primary circuit 13 shown in FIG.

In FIG. 6, reference numeral 21 denotes a control circuit, which outputs a DC voltage proportional to the input voltage of the CONT terminal 12 to the resistor (R6) and the transformer 22, and when the power supply of the lighting circuit 2 is turned on. For a moment, a DC voltage that is higher than the DC voltage output in a steady state is output.

Tr1 and Tr2 are npn transistors, and their base electrodes are connected to the feedback coil 22a of the transformer 22, respectively.

The collector electrodes of the transistors (Tr1, Tr2) are connected to the primary side coils (22b, 2b).
2c) and the transistors (Tr1, T
The emitter electrode of r2) is shared and connected to GND.

Each transistor (Tr1, Tr2)
, A capacitor (C4) is connected between the collector electrodes.

The cold cathode fluorescent lamp 3, the diode (D1) of the feedback circuit 4 and the photodiode 1 are connected to the output terminals 23 and 24 of the secondary coil 22d of the transformer 22.
5a are connected in series.

In the figure, reference numeral 25 denotes an input terminal of a feedback signal (Vr) from the feedback circuit 4.

In the circuit shown in FIG. 6, the transistor (Tr
1, Tr2) are alternately turned on, so that an AC high voltage is generated at the output terminals 23 and 24 of the secondary coil 22d of the transformer 22.

FIG. 7 shows the feedback circuit 4 shown in FIG.
FIG. 9 is a diagram showing another example of the specific circuit configuration of FIG.

The feedback circuit 4 shown in FIG.
This is an embodiment using a coupling transformer 26 instead of the photocoupler 15 shown in FIG.

As shown in FIG. 7, the primary input of the coupling transformer 26 is connected to the current path of the cold cathode fluorescent lamp 3, while the secondary output of the coupling transformer 26 has one end connected to the GND input terminal 11 The other end is connected to a circuit from the diode (D2) to the GND side input terminal 2 via the resistor (R5).

A voltage corresponding to the current flowing through the cold cathode fluorescent lamp 3 is output to the secondary side of the coupling transformer 26, and the voltage output to the secondary side of the coupling transformer 26 is a diode (D
2) and half-wave rectification by the resistor (R5), and further smoothed by a smoothing circuit composed of the resistor (R5) and the capacitor (C3). A proportional DC voltage can be obtained.

FIG. 8 is a diagram showing another example of a specific circuit configuration of the pulse generation circuit 1 shown in FIG.

In the pulse generating circuit 1 shown in FIG. 8, the voltage at the connection point of the series circuit of the resistor (R7) and the capacitor (C5) is input to the non-inverting input terminal of the comparison circuit 50. This is different from the pulse generation circuit 1 shown in FIG.

The potential of the capacitor (C5) is determined by the resistance (R
7) and the time constant determined by the capacitor (C5), the unstable multivibrator circuit 40 performs an oscillating operation until the potential of the capacitor (C5) reaches the reference potential (Vc). When the potential of the capacitor (C5) reaches the reference potential (Vc), the oscillation stops.

That is, in the pulse generation circuit 1 shown in FIG.
When the cold cathode fluorescent lamp 3 is turned on, a pulse voltage having a period of several ms to several hundred ms is output for a predetermined time.

After a lapse of a predetermined time, the pulse generation circuit 1 outputs a normal continuous DC voltage, whereby the lighting circuit 2 continuously outputs an AC lighting voltage.

In the above description, the case where the present invention is applied to a simple matrix type liquid crystal display device has been described. However, the present invention is not limited to this case. Needless to say, the present invention can be applied to a display device.

As described above, the invention made by the present inventor is:
Although specifically described based on the embodiment, the present invention
It is needless to say that the present invention is not limited to the above-described embodiment, but can be variously modified without departing from the scope of the invention.

[0067]

The effects obtained by the representative ones of the inventions disclosed in the present application will be briefly described as follows.

According to the present invention, when the light source constituting the backlight is turned on, a lighting circuit of a large voltage is momentarily intermittently and repeatedly applied from the lighting circuit to the light source to prompt the lighting of the light source. Therefore, it is possible to improve the starting characteristics when the light source is turned on.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic circuit configuration for lighting a cold cathode fluorescent lamp in a simple matrix type liquid crystal display module (LCM) according to an embodiment of the present invention.

FIG. 2 is a diagram showing a voltage waveform of an output voltage output from a pulse generation circuit 1 shown in FIG.

FIG. 3 is a diagram showing a voltage waveform of a lighting voltage applied to the cold cathode fluorescent lamp 3;

4 is a diagram showing an example of a specific circuit configuration of the pulse generation circuit 1 shown in FIG.

FIG. 5 shows a lighting circuit 2 and a feedback circuit 4 shown in FIG.
FIG. 3 is a diagram showing an example of a specific circuit configuration of FIG.

FIG. 6 is a diagram illustrating an example of a specific circuit configuration of a primary circuit 13 illustrated in FIG. 5;

7 is a diagram showing another example of a specific circuit configuration of the feedback circuit 4 shown in FIG.

8 is a diagram showing another example of a specific circuit configuration of the pulse generation circuit 1 shown in FIG.

FIG. 9 is an exploded perspective view of a simple matrix type liquid crystal display module (LCM) which is one of the conventional liquid crystal display devices.

[Explanation of symbols]

R: resistor, C: capacitor, Tr: transistor, V ...
Inverter, D: diode, NM: NMOS transistor, LCM: liquid crystal display module, 1: pulse generation circuit, 2: lighting circuit, 3: cold cathode fluorescent lamp (cold cathode tube), 4
... feedback circuit, 13 ... primary side circuit, 14, 22
... Transformer, 15 ... Photocoupler, 15a ... Light emitting diode, 15b ... Phototransistor, 21 ... Control circuit, 22a ... Feedback coil, 22b, 22c ... Primary side coil, 22d ... Secondary side coil, 26 ... Coupling transformer,
40 ... unstable multivibrator circuit, 50 ... comparator circuit, 501 ... frame-shaped frame made of metal plate, 502 ...
Silicon spacer, 503 ... Liquid crystal display panel (LC
D), 504... Drive circuit board (SEGP / B), 505
... Mold, 506 ... Prism sheet, 507 ... Cold cathode fluorescent lamp (cold cathode tube), 508 ... Rubber bush, 509 ...
Light guide plate, 510: Lower frame.

Claims (4)

[Claims] 1. A method for driving a liquid crystal display device comprising a liquid crystal display panel and a light source for irradiating the liquid crystal display panel from a back surface, when the light source is turned on,
After intermittently applying a lighting voltage higher than the steady-state lighting voltage applied to the light source to the light source and detecting that the light source is normally lit, the steady-state lighting voltage is continuously changed. A method for driving a liquid crystal display device, wherein the method is applied to the light source. 2. A method for driving a liquid crystal display device comprising: a liquid crystal display panel; and a light source that irradiates the liquid crystal display panel from a back surface.
A lighting voltage higher than a steady-state lighting voltage applied to the light source is intermittently applied to the light source, and after a predetermined time, a steady-state lighting voltage is continuously applied to the light source. Driving method for a liquid crystal display device. 3. A liquid crystal display device comprising: a liquid crystal display panel; a light source that irradiates the liquid crystal display panel from the back surface; and a lighting circuit that applies a lighting voltage to the light source. And a power supply voltage applying means for intermittently applying a power supply voltage to the lighting circuit, detecting that the light source is normally lit, and then continuously applying the power supply voltage to the lighting circuit. Liquid crystal display. 4. A liquid crystal display device comprising: a liquid crystal display panel; a light source that irradiates the liquid crystal display panel from the back surface; and a lighting circuit that applies a lighting voltage to the light source. And a power supply voltage applying means for intermittently applying a power supply voltage to the lighting circuit and continuously applying the power supply voltage to the lighting circuit after a predetermined time has elapsed.